JP6436248B2 - Separator and power storage device - Google Patents

Description

The present invention relates to a separator for an electricity storage device containing a non-aqueous electrolyte and an electricity storage device.
This application claims priority on July 1, 2016 based on Japanese Patent Application No. 2016-131598 for which it applied to Japan, and uses the content here.

  Conventionally, power storage devices such as lithium secondary batteries have been widely used for power storage in portable electronic devices such as mobile phones and laptop computers, and electric vehicles. In recent years, the use of power storage devices has been expanded, and various functions are required for power storage devices with the widespread use of power storage devices. For example, portable electronic devices and electric vehicles may be used in a wide temperature range such as high temperatures in midsummer and low temperatures in extremely cold. For this reason, electrical storage devices are required to have good electrochemical characteristics over a wide temperature range.

In addition, in order to prevent global warming, there is an urgent need to reduce CO ₂ emissions, and environmentally friendly vehicles equipped with power storage devices are attracting particular attention. Among environmentally friendly vehicles, in particular, hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and battery electric vehicles (BEV) are required to be spread quickly. Power storage devices mounted on these eco-friendly vehicles are required to have high output performance as a power source of the drive system and have a long life, and further performance improvement is required.
On the other hand, power storage devices mounted on environment-friendly vehicles are required to have higher safety, and contrivances such as provision of a CID (Current Interrupt Device) mechanism have been made. In the CID mechanism, for example, when the internal pressure of a lithium ion battery rises, a PTC (Positive Temperature Coefficient) element or a fuse is operated, and thereby, energization control or electrical connection is cut off.

  Among power storage devices, for example, a lithium ion secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Various separators have been proposed. For example, there are separators using a porous film formed from polyolefin as a raw material and those using a nonwoven fabric.

  However, a separator made of a polyolefin microporous film or a nonwoven fabric cannot sufficiently cope with high functionality such as high capacity and high output of a lithium ion secondary battery. For this reason, in recent years, a separator having a function imparted by applying inorganic particles or the like on a polyolefin microporous film or a nonwoven fabric as a base material has been proposed and put into practical use.

  Patent Document 1 discloses a separator having a film thickness of about 25 μm having a heat resistant resin such as aromatic polyamide and an inorganic filler such as alumina. According to the lithium ion secondary battery using the separator described in Patent Document 1, good rate characteristics can be realized.

JP 2008-266593 A

However, conventional power storage device separators provide functions such as suppressing the increase in internal resistance in the power storage device in the long term, maintaining the cycle characteristics of the power storage device in the long term, and improving the safety of the power storage device. It was difficult.
This invention is made | formed in view of the said situation, and aims at providing a separator with higher safety | security, and an electrical storage device using the same.

The inventors of the present invention have made extensive studies to achieve the above object.
As a result, it was found that a separator having a surface layer containing a lithium salt compound that slowly releases a lithium salt in a non-aqueous electrolyte solution may be used as a separator for an electricity storage device on a polyolefin porous film, thereby completing the present invention. .
That is, the separator and the electricity storage device which are one embodiment of the present invention employ the following configurations.

(1) A separator for an electricity storage device,
A base material comprising a polyolefin porous membrane;
A separator having a surface layer including a lithium salt compound that is provided on at least one surface of the base material and that slowly releases a lithium salt in a non-aqueous electrolyte.

(2) The surface layer includes heat-resistant particles,
(1) The separator according to (1), wherein the adhesion strength of the surface layer to the substrate is 0.3 N / cm or more.
The adhesion strength of the surface layer is preferably 0.5 N / cm or more, more preferably 0.7 N / cm or more, and still more preferably 1.0 N / cm.
As the heat resistant particles, organic compounds and inorganic compounds may be used.

(3) Content of the said lithium salt compound contained in the said surface layer is 10 mass% or less with respect to the said heat resistant particle, The separator as described in (2) characterized by the above-mentioned. 9 mass% or less is preferable, as for content of a lithium salt compound, 8 mass% or less is more preferable, and 7 mass% or less is still more preferable.

(4) The separator according to (2) or (3), wherein the heat-resistant particles have a surface layer containing the lithium salt compound.

(5) The dimensional change rate in the MD direction (flow direction; also referred to as the machine direction) when left in a 150 ° C. environment for 1 hour is compared with the TD direction (MD direction) when left in a 150 ° C. environment for 1 hour. The separator according to any one of (1) to (4), wherein a dimensional change rate obtained by multiplying a dimensional change rate in a substantially vertical direction) is 10% or less. The dimensional change rate is preferably 7% or less, more preferably 6% or less, and still more preferably 5% or less.

(6) The dimensional change rate in the MD direction when left at 150 ° C. for 1 hour is 5% or less,
The separator according to (5), wherein a dimensional change rate in the TD direction when left at 150 ° C. for 1 hour is 2% or less.
The dimensional change rate in the MD direction when left in a 150 ° C. environment for 1 hour and the dimensional change rate in a TD direction when left in a 150 ° C. environment for 1 hour may be calculated from the heat shrinkage rate. Since the separator may expand, the absolute value is used as the heat shrinkage rate. The absolute value of the heat shrinkage rate in the MD direction when left at 150 ° C. for 1 hour is preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less.
The absolute value of the thermal contraction rate in the TD direction when left in a 150 ° C. environment for 1 hour is preferably 1.8% or less, more preferably 1.7% or less, and still more preferably 1.6% or less.

(7) For a solution in which the lithium salt compound contains lithium hexafluorophosphate at a concentration of 1 mol / liter in a non-aqueous solvent containing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3: 7. The separator according to any one of (1) to (6), wherein the solubility at 25 ° C. is 0.003% by mass or more and 2% by mass or less.
The solubility is preferably 0.004 mass% or more and 1.8 mass% or less, more preferably 0.004 mass% or more and 1.7 mass% or less, and further 0.005 mass% or more and 1.7 mass% or less. Preferably, 0.005 mass% or more and 1.6 mass% or less are still more preferable.

(8) The separator according to (7), wherein the solubility of the lithium salt compound is 0.003% by mass or more and 0.4% by mass or less.
The solubility is preferably 0.003% by mass or more, more preferably 0.004% by mass or more, and further preferably 0.005% by mass or more.

(9) The separator according to any one of (1) to (8), wherein the lithium salt compound is selected from the group consisting of lithium sulfonates, lithium phosphates, and lithium carboxylates.
The lithium salt compound is lithium methanesulfonate, lithium ethanesulfonate, lithium difluorophosphate (LiPO ₂ F ₂ ), lithium monofluorophosphate (Li ₂ PO ₃ F), 1,1′-biphenylyl-2-sulfone. Lithium acid, lithium 1,1′-biphenylyl-3-sulfonate and lithium 1,1′-biphenylyl-4-sulfonate, lithium 1,1′-biphenylyl-2-carboxylate, 1,1′-biphenylyl-3 -It is preferable that it is 1 type, or 2 or more types of lithium salt compounds selected from lithium carboxylate and lithium 1,1'- biphenylyl 4-carboxylate. Among these, lithium methanesulfonate, lithium fluorophosphate, lithium 1,1′-biphenylyl-2-sulfonate, lithium 1,1′-biphenylyl-3-sulfonate, 1,1′-biphenylyl-4-sulfone Lithium acid, lithium 1,1′-biphenylyl-2-carboxylate, lithium 1,1′-biphenylyl-3-carboxylate and lithium 1,1′-biphenylyl-4-carboxylate are particularly preferred as the lithium salt compound.

(10) The separator according to (1) to (9), wherein the lithium salt compound is a sulfonic acid lithium salt compound represented by the following general formula (I).

（式（Ｉ）中、Ｒは炭素数が１〜５のアルキル基、又は、炭素数が６〜１２のアリール基を表す。）

(In formula (I), R represents an alkyl group having 1 to 5 carbon atoms or an aryl group having 6 to 12 carbon atoms.)

(11) The separator according to any one of (1) to (10), wherein the thickness of the surface layer is 0.1 μm or more and 10 μm or less.
(12) The separator according to any one of (1) to (11), wherein the content (coating amount) of the lithium salt compound in the surface layer is 0.1 g or more and 10 g or less per 1 m ^2. .
(13) The separator according to any one of (1) to (12), wherein the surface layer further includes a heat resistant resin.

(14) The surface layer is formed on one surface of the base material, and a heat shrinkage relaxation layer containing heat-resistant particles and / or heat-resistant resin is formed on the other surface (1) -Separator in any one of (13).
(15) The heat shrinkage relaxation layer containing heat resistant particles and / or heat resistant resin is formed between the base material and the surface layer. The separator described.
(16) The base material contains polyethylene and / or polypropylene, has a compression modulus of 95 MPa to 150 MPa, and has an average surface roughness (Ra) (Ra (ave)) of 0.01 μm to 0 μm. The separator according to any one of (1) to (15), wherein the separator is 30 μm.

(17) An electricity storage device comprising the separator according to any one of (1) to (16) interposed between opposing electrodes, and a nonaqueous electrolytic solution impregnated in at least the separator.
(18) The non-aqueous electrolyte contains LiPF ₆ and further contains one or more selected from the group consisting of LiPO ₂ F ₂ , LiN (SO ₂ F) ₂ , LiSO ₄ CH ₃ and FSO ₃ Li. The electrical storage device as described in (17) characterized by the above-mentioned.

(19) A separator for an electricity storage device,
A base material comprising a polyolefin porous membrane;
And a surface layer that is provided on at least one surface of the substrate and includes a lithium sulfonate compound represented by the following general formula (I).

（式（Ｉ）中、Ｒは炭素数が１〜５のアルキル基、又は、炭素数が６〜１２のアリール基を表す。）

(In formula (I), R represents an alkyl group having 1 to 5 carbon atoms or an aryl group having 6 to 12 carbon atoms.)

  A separator for an electricity storage device of the present invention comprises a base material comprising a polyolefin porous film, and a surface layer containing a lithium salt compound that is provided on at least one surface of the base material and that slowly releases a lithium salt in a non-aqueous electrolyte. Have. Therefore, the power storage device of the present invention in which the separator of the present invention impregnated with a non-aqueous electrolyte is interposed between opposing electrodes suppresses the increase in internal resistance in the power storage device for a long period of time. It is possible to perform any of the functions such as maintaining the power supply for a long period of time and improving the safety of the power storage device.

It is a cross-sectional schematic diagram for demonstrating the separator of this embodiment. It is a cross-sectional schematic diagram for demonstrating the other example of the separator of this embodiment. It is a cross-sectional schematic diagram for demonstrating the other example of the separator of this embodiment. It is a schematic explanatory drawing for producing the other example of the separator of this embodiment.

A separator according to an embodiment of the present invention is a separator for an electricity storage device, and is provided on a base material made of a polyolefin porous film and at least one surface of the base material, and a lithium salt is gradually added to the non-aqueous electrolyte. And a surface layer containing a lithium salt compound to be released.
In the electricity storage device in which the separator according to one embodiment of the present invention impregnated with a non-aqueous electrolyte is interposed between opposing electrodes, the reason why an increase in impedance due to high-temperature storage can be suppressed is not necessarily clear, but the following I think so.

  That is, in such an electricity storage device, the lithium salt compound contained in the surface layer of the separator gradually releases the lithium salt into the nonaqueous electrolytic solution. More specifically, the lithium salt gradually dissolves out from the lithium salt compound into the non-aqueous electrolyte, and the eluted component is deposited on the electrode to form a stable coating film having high lithium ion conductivity. As a result, it is estimated that an increase in impedance due to high-temperature storage is suppressed in the electricity storage device.

  In one embodiment of the present invention, the lithium salt compound that releases lithium salt into the non-aqueous electrolyte is one that can gradually elute the lithium salt into the non-aqueous electrolyte. If the solubility of the lithium salt compound in the non-aqueous electrolyte is too high or too low, the lithium salt cannot be released slowly into the non-aqueous electrolyte.

Examples of the lithium salt compound that releases lithium salt slowly in the non-aqueous electrolyte include 1 mol / liter in a non-aqueous solvent containing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3: 7. solubility at 25 ° C. for a solution containing lithium hexafluorophosphate (LiPF ₆₎ at a concentration include those of 2 mass% or more 0.003 mass%.
The lithium salt compound having a solubility of less than 0.003% by mass has poor solubility in a non-aqueous electrolyte. For this reason, even if it is contained in the surface layer of the separator, the lithium salt eluted in the non-aqueous electrolyte is insufficient, and the effect of forming a film on the electrode of the electricity storage device is small. Therefore, the effect of suppressing an increase in impedance due to high temperature storage may not be sufficiently obtained.

Hereinafter, a separator and an electricity storage device according to an embodiment of the present invention will be described in detail by way of examples.
[Separator]
FIG. 1 is a schematic cross-sectional view for explaining the separator of this embodiment.
A separator 1 shown in FIG. 1 is for an electricity storage device containing a non-aqueous electrolyte. The separator 1 is in the form of a sheet and includes a base material 2 made of a polyolefin microporous film and a surface layer 3 provided on one surface 2 a of the base material 2.

  The separator 1 isolate | separates between electrodes and prevents a short circuit in the electrical storage device using this. Further, in the electricity storage device using the separator 1, the non-aqueous electrolyte is held in the pores of the base material 2 to form a lithium ion conduction path between the electrodes. Further, the separator 1 of the present embodiment is a shutdown that stops the reaction in the electricity storage device by melting and closing the micropores in the substrate 2 in a predetermined temperature range determined according to the melting point of the substrate 2. It has a function. Therefore, the separator 1 of this embodiment can prevent abnormal heat generation of the electricity storage device, and contributes to ensuring the safety of the electricity storage device.

  The substrate 2 preferably has excellent durability in the thickness direction. Specifically, the compressive elastic modulus of the base material 2 is preferably 95 MPa or more and 150 MPa or less, more preferably 100 MPa or more and 145 MPa or less, and further preferably 105 MPa or more and 130 MPa or less. When the compression elastic modulus of the base material 2 is 95 MPa or more, when a restraining member that suppresses expansion / contraction is provided outside the power storage device or when the power storage device is compressed, it exhibits excellent resistance to compression. It becomes separator 1 to do. That is, even when the electricity storage device is compressed, the separator 1 can maintain the characteristics of the electricity storage device. Moreover, since the base material 2 which consists of a polyolefin microporous film whose compression elastic modulus is 150 Mpa or less is easy to manufacture, it is preferable.

  The base material 2 preferably has an average surface roughness (Ra) (Ra (ave)) of 0.01 μm to 0.30 μm, more preferably 0.05 μm to 0.25 μm. More preferably, the thickness is 0.05 to 0.23 μm. The average value (Ra (ave)) of the surface roughness (Ra) on both the front and back surfaces is measured by measuring the surface roughness (Ra) of the surface of the substrate 2 and the surface roughness (Ra) of the back surface, respectively. The value is calculated.

  The base material 2 having a large average surface roughness (Ra (ave)) is easily crushed when the separator 1 is compressed in the thickness direction. When the average value (Ra (ave)) of the surface roughness (Ra) is 0.30 μm or less, the base material 2 is hardly crushed even when the separator 1 is compressed in the thickness direction. In addition, the substrate 2 composed of a polyolefin microporous film having an average surface roughness (Ra) (Ra (ave)) of 0.01 μm or more is preferable because it is easy to produce.

  The thickness of the base material 2 is preferably 2 μm or more, more preferably 3 μm or more, and further preferably 4 μm or more. Moreover, the thickness of the base material 2 is 30 micrometers or less, Preferably it is 28 micrometers or less, More preferably, it is 26 micrometers or less. When the thickness of the base material 2 is in the above range, a short circuit between the electrodes of the power storage device can be prevented, and an increase in resistance due to an excessive increase in the thickness of the base material 2 can be prevented, accounting for the resistance change of the power storage device. The ratio due to the separator can be reduced. For this reason, it is preferable for the thickness of the base material 2 to be in the above range, since the effect of suppressing the increase in impedance due to high-temperature storage in the electricity storage device having the separator 1 of this embodiment is enhanced.

  The porosity of the polyolefin microporous membrane forming the substrate 2 is preferably 30% or more, more preferably 35% or more, and still more preferably 40% or more. Moreover, the porosity of the polyolefin microporous film forming the substrate 2 is 90% or less, preferably 85% or less, more preferably 80% or less. It is preferable that the porosity of the polyolefin microporous film be in the above range because lithium ion conduction between the electrodes in the electricity storage device having the separator 1 of this embodiment is facilitated, and the effect of suppressing an increase in impedance due to high-temperature storage is enhanced.

  The air permeability (Gurley) of the polyolefin microporous membrane forming the substrate 2 is preferably in the range of 10 sec / 100 ml to 600 sec / 100 ml. When the air permeability is 600 sec / 100 ml or less, sufficient air permeability can be secured, so that an increase in impedance due to high temperature storage of the electricity storage device can be effectively suppressed. Moreover, sufficient electrical insulation can be ensured as said air permeability is 10 sec / 100 ml or more, and a minute short circuit can be prevented. The air permeability is preferably 20 sec / 100 ml or more, and more preferably 30 sec / 100 ml or more. The air permeability is preferably 500 sec / 100 ml or less, and more preferably 400 sec / 100 ml or less.

  Examples of the material for the polyolefin microporous film forming the substrate 2 include polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, or a mixture of these polyolefin resins. The material of the substrate 2 preferably includes polyethylene (PE) and / or polypropylene (PP), and particularly preferably includes polypropylene.

As the substrate 2, a polyolefin microporous film composed of PP or PE can be used, but a polyolefin microporous film having a three-layer structure of PP / PE / PP can also be used.
In the microporous film having the above three-layer structure, the PE layer can be melted to block the microporous formed in the PP layer (hereinafter referred to as thermal blockage, also referred to as shutdown), so that the safety of the electricity storage device is improved. Can be increased. The thermal plugging temperature can be controlled by adjusting the PE raw material constituting the PE layer.

  The heat blocking temperature of the polyolefin microporous membrane forming the substrate 2 is preferably 110 to 180 ° C, and more preferably 120 to 140 ° C. If the heat blocking temperature (shutdown temperature) of the polyolefin microporous membrane is too high, the safety when an internal short circuit occurs in the electricity storage device using the separator 1 is lowered. In addition, if the thermal clogging temperature of the polyolefin microporous membrane is too low, the microporous material melts and becomes non-porous in the temperature range in normal use of the electricity storage device using the separator 1, and the reaction in the electricity storage device stops. End up. For this reason, the thermal clogging temperature of the polyolefin microporous film forming the substrate 2 is determined in accordance with the characteristics of the electricity storage device and the usage environment.

  In order to set the heat blocking temperature (shutdown temperature) of the polyolefin microporous membrane forming the substrate 2 to 170 ° C. or higher, it is preferable to use a material having a melting point of 150 ° C. or higher as the polyolefin microporous membrane. Examples of the polyolefin having a melting point of 150 ° C. or higher include polypropylene (PP). Moreover, in order to set the heat blocking temperature to 150 ° C. or lower, it is preferable to use polyethylene (PE) having a melting point in the range of 110 ° C. to 140 ° C. as the polyolefin microporous membrane.

  The polyolefin microporous film forming the substrate 2 may be a single layer film or a multilayer film. The polyolefin microporous membrane forming the substrate 2 is preferably a single layer film.

  When the polyolefin microporous film forming the substrate 2 is a single layer film, it can be produced by, for example, the dry method or wet method shown below. In any production method, the microporous film is preferably stretched in at least one direction, and preferably uniaxially stretched or biaxially stretched. The polyolefin microporous membrane is preferably produced by uniaxial stretching using a dry method from the viewpoint of suppressing deformation of the separator 1 at a high temperature.

  In the dry method, first, a polyolefin resin is melted and extruded into a film to form a film. Next, the obtained film is annealed and stretched at a low temperature to form an initial stage of pores. Thereafter, the film stretched at a low temperature is stretched at a high temperature to form micropores, thereby forming a polyolefin microporous membrane.

  In the wet method, first, a hydrocarbon solvent or other low molecular weight substance and a polyolefin resin are mixed and heated and melted to form a sheet. Next, the obtained sheet is stretched in the machine direction or in the biaxial direction. Thereafter, the hydrocarbon solvent or other low molecular weight substance is extracted from the stretched sheet with a volatile solvent. This forms micropores to form a polyolefin microporous membrane.

When the polyolefin microporous film forming the substrate 2 is a multilayer film, it can be produced, for example, by the following method.
At the time of producing a microporous film by heating and laminating a plurality of polyolefin microporous membranes comprising a single layer film produced by the above method, or by coextrusion using a T-die, a plurality of polyolefin microporous films are produced. Examples include a method of laminating a porous film.

  When the polyolefin microporous film forming the substrate 2 is a multilayer film, the heat resistance of the separator 1 can be adjusted by including a plurality of polyolefin microporous films having different melting points, which are single-layer films. For example, a multilayer including a polypropylene (PP) microporous membrane having a melting point of 150 ° C. or higher made of a single layer film and a polyethylene (PE) microporous membrane having a melting point in the range of 110 ° C. to 140 ° C. made of a single layer film. It can be a film. In this case, the shape of the separator 1 can be maintained by the polypropylene (PP) microporous membrane even when the micropores of the polyethylene (PE) microporous membrane are melted and made nonporous at a temperature of 150 ° C. Preferable examples of the multilayer film comprising a polypropylene (PP) microporous membrane and a polyethylene (PE) microporous membrane include microporous membranes laminated in the order of polypropylene microporous membrane / polyethylene microporous membrane / polypropylene microporous membrane. It is done.

As shown in FIG. 1, the surface layer 3 provided on one surface 2 a of the substrate 2 contains a lithium salt compound that releases lithium salt slowly in the non-aqueous electrolyte.
The lithium salt compound contained in the surface layer 3 is lithium hexafluorophosphate (LiPF) at a concentration of 1 mol / liter in a non-aqueous solvent containing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3: 7. ₆ ) The solubility at 25 ° C. with respect to the solubility measurement solution is preferably 0.003% by mass or more and 2% by mass or less. The solubility at 25 ° C. in the solubility measurement solution is preferably 0.003% by mass or more, more preferably 0.004% by mass or more, and further preferably 0.005% by mass or more. The solubility at 25 ° C. in the solubility measuring solution is preferably 2% by mass or less, more preferably 0.4% by mass or less, and still more preferably 0.1% by mass or less.

The lithium salt compound having a solubility at 25 ° C. in the solubility measuring solution of 0.003% by mass or more and 2% by mass or less in the electricity storage device using the separator 1 releases the lithium salt into the non-aqueous electrolyte. To do. That is, since the solubility is 0.003% by mass or more, the lithium salt compound is sufficiently eluted in the non-aqueous electrolyte. Moreover, since the solubility is 2% by mass or less, the components eluted from the lithium salt compound into the non-aqueous electrolyte are released into the electrolyte over a long period of time. Therefore, since lithium salt is released into the electrolyte over a long period of time, functions such as suppressing an increase in internal resistance of the electricity storage device, maintaining the cycle characteristics of the electricity storage device, and further improving the safety of the electricity storage device are provided. It is possible to play for a long time.
On the other hand, when the solubility of the lithium salt compound is 0.003% by mass or less, the lithium salt is not released or hardly released, and as a result, the increase in internal resistance of the electricity storage device is suppressed for a long time. It is difficult to achieve functions such as maintaining the cycle characteristics for a long period of time and improving the safety of the electricity storage device.

Examples of the lithium salt compound that gradually releases the lithium salt in the non-aqueous electrolyte include a sulfonic acid lithium salt compound, a lithium phosphate salt compound, and a carboxylic acid lithium salt compound represented by the above general formula (I).
In particular, lithium methanesulfonate, lithium ethanesulfonate, lithium 1,1′-biphenylyl-2-sulfonate, lithium 1,1′-biphenylyl-3-sulfonate, 1,1′-biphenylyl- Lithium 4-sulfonate, lithium fluorophosphate (LiPO ₂ F ₂ ), lithium difluorophosphate (Li ₂ PO ₃ F) as lithium phosphate, lithium 1,1′-biphenylyl-2-carboxylate as lithium carboxylate, Lithium 1,1′-biphenylyl-3-carboxylate and lithium 1,1′-biphenylyl-4-carboxylate are preferred.
Among them, lithium methanesulfonate, lithium fluorophosphate, lithium 1,1′-biphenylyl-2-sulfonate, lithium 1,1′-biphenylyl-3-sulfonate, lithium 1,1′-biphenylyl-4-sulfonate Particularly preferred are lithium 1,1′-biphenylyl-2-carboxylate, lithium 1,1′-biphenylyl-3-carboxylate, and lithium 1,1′-biphenylyl-4-carboxylate.
In the sulfonic acid lithium salt compound represented by the general formula (I), R represents an alkyl group having 1 to 5 carbon atoms or an aryl group having 6 to 12 carbon atoms. The alkyl group and aryl group representing R may have a substituent.
R in the general formula (I) is preferably an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 10 carbon atoms, an alkyl group having 1 to 3 carbon atoms, or 6 to 6 carbon atoms. An aryl group of 8 is more preferred. Among these, an alkyl group having 1 to 2 carbon atoms is particularly preferable.

  Specific examples of the lithium sulfonate compound represented by the general formula (I) include lithium methanesulfonate, lithium ethanesulfonate, lithium propane-1-sulfonate, lithium propane-2-sulfonate, and butane-1-. Lithium sulfonate, lithium butane-2-sulfonate, lithium 2-methylpropane-1-sulfonate, lithium 2-methylpropane-2-sulfonate, lithium pentane-1-sulfonate, 3-methylbutane-1-sulfonate Lithium, lithium 2-methylbutane-1-sulfonate, lithium pentane-2-sulfonate, lithium 3-methylbutane-2-sulfonate, lithium pentane-3-sulfonate, lithium benzenesulfonate, lithium 2-methylbenzenesulfonate Lithium 3-methylbenzenesulfonate Lithium 4-methylbenzenesulfonate, lithium 4-ethylbenzenesulfonate, lithium 2,3-dimethylbenzenesulfonate, lithium 2,4-dimethylbenzenesulfonate, lithium 2,5-dimethylbenzenesulfonate, 2,6- Lithium dimethylbenzenesulfonate, lithium 3,4-dimethylbenzenesulfonate, lithium 3,5-dimethylbenzenesulfonate, lithium 2-cyclohexylbenzenesulfonate, lithium 3-cyclohexylbenzenesulfonate, lithium 4-cyclohexylbenzenesulfonate, Lithium 1,1′-biphenylyl-2-sulfonate, lithium 1,1′-biphenylyl-3-sulfonate, lithium 1,1′-biphenylyl-4-sulfonate, lithium 1,2-ethanedisulfonate, etc. Preferably exemplified. Among these, lithium methanesulfonate, lithium ethanesulfonate, lithium propane-1-sulfonate, lithium propane-2-sulfonate, lithium benzenesulfonate, or lithium 4-methylbenzenesulfonate is preferable, and lithium methanesulfonate , Lithium ethanesulfonate, lithium propane-1-sulfonate, or lithium 1,2-ethanedisulfonate is particularly preferred.

  The increase in internal resistance of the electricity storage device can be reduced over a long period of time by the lithium sulfonate compound. In addition, the cycle characteristics of the electricity storage device can be maintained for a long time by the lithium phosphate salt compound. Further, overcharge of the electricity storage device can be prevented by the lithium carboxylate compound, and safety can be improved.

Only one lithium salt compound may be used, or two or more lithium salt compounds may be mixed and used. The lithium salt compound preferably contains at least one of lithium methanesulfonate and lithium fluorophosphate among the above lithium salt compounds.
From the viewpoint of solubility in the electrolytic solution, the lithium salt compound preferably has a valence of lithium ions to be bonded of 2 or less, more preferably monovalent. A lithium salt compound having a valence of lithium ion of 3 or more becomes extremely difficult for the lithium salt compound to dissolve in the electrolyte, and for this reason, an increase in internal resistance of the electricity storage device is suppressed for a long time. Functions such as maintaining cycle characteristics for a long period of time and improving the safety of the electricity storage device cannot be achieved. As a trivalent lithium salt compound, for example, trilithium phosphate is hexafluorophosphorus at a concentration of 1 mol / liter in a non-aqueous solvent containing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3: 7. The solubility with respect to the electrolyte containing lithium acid (temperature condition: 25 ° C.) is 25 ppm or less. For this reason, trilithium phosphate hardly dissolves in the electrolytic solution, and thus does not perform the above function. On the other hand, the solubility of lithium methanesulfonate in the same electrolyte solution is approximately 80 ppm, and the solubility of lithium monofluorophosphate is approximately 90 ppm. The lithium salt compound is gradually released into the electrolyte solution, and the above-described functions are slow. Expression is possible.

The content (coating amount) of the lithium salt compound in the surface layer 3 is preferably 0.1 g or more per 1 m ² . In this case, since the effect which suppresses the raise of the impedance by the high temperature preservation | save in the electrical storage device using the separator 1 increases more, it is preferable. The content of the lithium salt compound in the surface layer 3 is preferably 10 g or less per 1 m ² . In this case, there is no concern that the content of the lithium salt compound in the surface layer 3 is excessively increased and the shape retaining property of the surface layer 3 is lowered, which is preferable. The lower limit of the content of the lithium salt compounds in the surface layer 3 is more preferably more than 1 m ² per 0.5g, more 2g per 1 m ² is more preferable. The upper limit of the content of the lithium salt compounds in the surface layer 3, more preferably not more than 8g per 1 m ^2, 1 m ² per 5g or less is more preferable.

The surface layer 3 preferably further includes a heat resistant resin in order to prevent the separator 1 from being thermally contracted during charge storage at a high temperature.
Examples of the heat-resistant resin include polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyarylate, polyetherimide, polyamideimide, polyimide, polyamide, and fluorine atom-containing resin. Among these, polyamideimide, polyimide, polyamide, and fluorine atom-containing resin are preferable.
Only one kind of heat-resistant resin may be used, or two or more kinds may be mixed and used.

  The polyamide used as the heat resistant resin is preferably a wholly aromatic polyamide (aramid) from the viewpoint of durability, and more preferably para-type or meta-type wholly aromatic polyamide. Specifically, as the para-type aramid, from the viewpoint of versatility and mechanical properties, copolyparaphenylene, 3,4′-oxydiphenylene, terephthalamide is more preferable. As the meta-type aramid, polymetaphenylene isophthalamide is more preferable from the viewpoint of excellent redox resistance.

  Examples of the fluorine atom-containing resin used as the heat-resistant resin include polyvinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of tetrafluoroethylene and hexafluoropropylene, or a fluoride. Examples thereof include a copolymer of vinylidene, hexafluoropropylene, and chlorotrifluoroethylene. Among these, polyvinylidene fluoride, polytetrafluoroethylene, or a copolymer of tetrafluoroethylene and hexafluoropropylene is more preferable.

The surface layer 3 preferably further includes heat-resistant particles in order to prevent the separator 1 from being thermally contracted during charge storage at a high temperature.
Examples of the heat-resistant particles include silica (SiO ₂ ), alumina (Al ₂ O ₃ ), titania (TiO ₂ ), Li ₄ Ti ₅ O ₁₂ , oxides such as zirconia (ZrO ₂ ) or BaTiO ₃ , or boehmite (Al ₂ O ₃ · 3H ₂ O) and the like. Among these, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), Li ₄ Ti ₅ O ₁₂ , zirconia (ZrO ₂ ), BaTiO ₃ , or boehmite (Al ₂ O ₃ .3H ₂ O) is preferable. (SiO ₂ ), alumina (Al ₂ O ₃ ), Li ₄ Ti ₅ O ₁₂ , BaTiO ₃ , or boehmite (Al ₂ O ₃ .3H ₂ O) is more preferable. In particular, alumina (Al ₂ O ₃ ), Li ₄ Ti ₅ O ₁₂ , BaTiO ₃ , or boehmite (Al ₂ O ₃ .3H ₂ O) is preferable, boehmite (Al ₂ O ₃ .3H ₂ O) or Li ₄ Ti. ₅ O ₁₂ is most preferred.
Only one kind of heat-resistant particles may be used, or two or more kinds may be used in combination.

  When the surface layer 3 further contains heat-resistant particles, it is preferable that the heat-resistant particles have a surface layer containing a lithium salt compound. In the case where the surface layer 3 includes heat-resistant particles having a surface layer containing a lithium salt compound, in the electricity storage device having the separator 1, the lithium salt is likely to be eluted in the non-aqueous electrolyte, and the lithium ion conducts on the electrode. A highly reliable and stable film is easily formed, and the thermal contraction of the separator 1 is effectively suppressed. For this reason, an increase in impedance due to high temperature storage is more effectively suppressed.

  The heat-resistant particles having a surface layer containing a lithium salt compound can be produced, for example, by the method shown below. First, a lithium salt compound is dissolved and / or dispersed in water to obtain a lithium salt compound solution. Next, heat-resistant particles are mixed and dispersed in the lithium salt compound solution to obtain a mixed solution. Thereafter, the water in the mixed solution is removed by evaporating the mixed solution to dryness or using a spray drying method. Through the above steps, heat-resistant particles whose surfaces are coated with a lithium salt compound in a thin film form are obtained.

When the surface layer 3 contains a lithium salt compound and heat-resistant particles, the content of the lithium salt compound contained in the surface layer 3 is preferably 10% by mass or less, and 9% by mass or less with respect to the heat-resistant particles. It is more preferable that it is 8 mass% or less, and 7 mass% or less is still more preferable. When the content of the lithium salt compound is too large, it may affect the adhesion strength between the substrate 2 and the surface layer 3 (adhesion strength decreases), so the above content is desirable.
Further, the content of the lithium salt compound contained in the surface layer 3 is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, with respect to the heat-resistant particles, More preferably, it is at least mass%. By having such a content, functions such as suppressing the increase in internal resistance in the electricity storage device in the long term, maintaining the cycle characteristics of the electricity storage device in the long term, and further improving the safety of the electricity storage device are sufficient. Can be expressed. When the content of the lithium salt compound contained in the surface layer 3 is 10% by mass with respect to the heat-resistant particles, the separator 1 having the surface layer 3 sufficiently containing the lithium salt compound and the heat-resistant particles is obtained. In the electricity storage device having the separator 1, the lithium salt compound is sufficiently eluted in the non-aqueous electrolyte, and a stable coating with high lithium ion conductivity is formed on the electrode, and the thermal contraction of the separator 1 is effective. Therefore, an increase in impedance due to high-temperature storage is more effectively suppressed.

  The thickness of the surface layer 3 is preferably 0.1 μm or more, more preferably 0.3 μm or more, and further preferably 0.5 μm or more. Moreover, the thickness of the surface layer 3 is 10 micrometers or less, Preferably it is 8 micrometers or less, More preferably, it is 6 micrometers or less. When the thickness of the surface layer 3 is in the above range, effects such as suppressing the increase in internal resistance in the power storage device in the long term, maintaining the cycle characteristics of the power storage device in the long term, and improving the safety of the power storage device are obtained. Can be expressed. If the surface layer 3 is made too thick, the entire separator becomes thick, so that the capacity of the electricity storage device becomes relatively small. If the surface layer 3 is made too thin, the amount of the lithium salt compound is not sufficient for effect expression. It is not preferable.

  The surface layer 3 may contain a binder in order to maintain the shape of the surface layer 3 as necessary. Specific examples of the binder include ethylene-acrylic acid copolymers such as ethylene-vinyl acetate copolymer (EVA) and ethylene-ethyl acrylate copolymer, polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF). ), Fluorinated rubber, styrene-butadiene copolymer such as styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), poly N-vinylacetamide, cross-linked acrylic resin, polyurethane, or epoxy resin. Among these, ethylene-acrylic acid copolymer such as ethylene-ethyl acrylate copolymer, polyvinylpyrrolidone (PVP), poly N-vinylacetamide, polyvinylidene fluoride (PVDF), copolymer of styrene and butadiene (SBR) ) Or carboxymethylcellulose (CMC) is more preferable.

  The lithium salt compound may be uniformly dispersed in the surface layer 3, but may be locally unevenly distributed. When the lithium salt compound is unevenly distributed, the surface layer 3 may contain heat-resistant particles, and the lithium salt compound may be unevenly distributed around the heat-resistant particles.

  The surface layer 3 preferably has an adhesion strength of the surface layer 3 to the substrate 2 of 0.3 N / cm or more. When the adhesion strength of the surface layer 3 to the substrate 2 is 0.3 N / cm or more, the detachment of the heat-resistant particles can be reduced. For this reason, the higher adhesion strength is basically preferable, but if it is too high, the whole separator becomes too hard and flexibility tends to be lost. The adhesion strength of the surface layer 3 to the substrate 2 is more preferably 0.5 N / cm or more, further preferably 0.7 N / cm or more, and further preferably 1.0 N / cm or more. The adhesion strength of the surface layer 3 to the substrate 2 is preferably 20 N / cm or less, and more preferably 15 N / cm or less.

  The adhesion strength of the surface layer 3 to the substrate 2 can be measured by, for example, a peel test. The peel test will be described in detail later. In the peel test, the adhesion between the substrate and the surface layer can be evaluated, and the adhesion strength can be used as an index of the difficulty of removing the surface layer from the substrate. Since the adhesion strength of the surface layer to the substrate is high, dropout of the heat-resistant particles and the lithium salt compound can be reduced at the time of manufacturing the battery, and a safer power storage device can be manufactured.

Regarding the shape stability of the separator 1 provided with the surface layer 3 on the substrate 2, the dimensional change rate in the MD direction (flow direction) and the dimension in the TD direction (perpendicular direction) when left at 150 ° C. for 1 hour. The dimensional change rate multiplied by the change rate is preferably 10% or less, and more preferably 4% or less. The dimensional change rate of the entire separator is more preferably 3% or less, and further preferably 2% or less.
When the dimensional change rate of the separator 1 is 10% or less, the shape can be stably maintained even at a high temperature of, for example, 150 ° C., so that the risk of a short circuit or the like can be further reduced.

  The dimensional change rate in the MD direction when left at 150 ° C. for 1 hour is preferably 5% or less, more preferably 4% or less, still more preferably 3% or less, and still more preferably 2%. It is as follows. When the dimensional change rate in the MD direction when left in a 150 ° C. environment for 1 hour is in the above range, the shape stability in the MD direction can be increased, and for example, there is a risk that a short circuit occurs due to shrinkage in the MD direction. Can be reduced.

  The dimensional change rate in the TD direction when left standing at 150 ° C. for 1 hour is preferably 2% or less, more preferably 1.5% or less, and further preferably 1.0% or less. More preferably, it is 0.5% or less. When the dimensional change rate in the TD direction when left in a 150 ° C. environment for 1 hour is in the above range, the shape stability in the TD direction can be remarkably increased. For example, a short circuit due to contraction in the TD direction may occur. Can be significantly reduced.

  The dimensional change rate in the MD direction when left in a 150 ° C. environment for 1 hour and the dimensional change rate in a TD direction when left in a 150 ° C. environment for 1 hour may be calculated from the heat shrinkage rate. Since the separator may expand, the absolute value is used as the heat shrinkage rate. For example, the dimensional change rate of the separator 1 is the absolute value of the thermal shrinkage rate in the MD direction when left in a 150 ° C. environment for 1 hour and the thermal shrinkage rate in the TD direction when left in a 150 ° C. environment for 1 hour. May be measured by multiplying by the absolute value of. The absolute value of the heat shrinkage rate in the MD direction when left in a 150 ° C. environment for 1 hour is preferably 4% or less, more preferably 3% or less, and even more preferably 2% or less. The absolute value of the thermal contraction rate in the TD direction at 150 ° C. is preferably 1.5% or less, more preferably 1.0% or less, and still more preferably 0.5% or less.

The surface layer 3 can be formed by the method shown below, for example.
First, the lithium salt compound is dispersed and dissolved in an organic solvent such as 1-methyl-2-pyrrolidone (NMP) or a solvent such as water to obtain a lithium salt compound-containing slurry. The lithium salt compound-containing slurry may contain, in addition to the lithium salt compound and the solvent, one or more selected from a heat-resistant resin, heat-resistant particles, and a binder as necessary.
Next, the lithium salt compound-containing slurry is applied to one surface 2a of the substrate 2 using a known coating device such as a table coater, a gravure coater, a knife coater, a reverse roll coater, and a die coater, dry. The surface layer 3 is formed by the above process.

In the present embodiment, as illustrated in FIG. 1, the separator 1 in which the surface layer 3 is provided on one surface 2 a of the base material 2 has been described as an example. The surface layer 3 may be provided on both sides.
Such a separator is formed in the same manner as in the method of providing the surface layer 3 after forming the separator 1 having the surface layer 3 provided on the one surface 2a of the substrate 2 by the method described above. 2 can be formed by a method of providing the surface layer 3 on the other surface. Also, for example, in the same manner as described above, the above-described lithium salt compound-containing slurry is prepared, and after the base material 2 is immersed in the lithium salt compound-containing slurry, the excess lithium salt compound-containing slurry is removed. It may be formed.

Further, in the present embodiment, as illustrated in FIG. 1, the separator 1 in which the surface layer 3 is provided in contact with one surface 2a of the base material 2 has been described as an example. As shown in FIG. 2, a heat shrinkage relaxation layer 4 may be provided between the substrate 2 and the surface layer 3.
FIG. 2 is a schematic cross-sectional view for explaining another example of the separator of the present embodiment. The heat shrinkage relaxation layer 4 shown in FIG. 2 includes heat resistant particles and / or heat resistant resin. As the heat-resistant particles and the heat-resistant resin, the same particles as those contained in the surface layer 3 described above can be used. In order to maintain the shape, the heat shrinkage relaxation layer 4 may contain the same binder as that contained in the surface layer 3 described above, if necessary.

  In the electricity storage device having the separator 10 shown in FIG. 2, the separator 10 has the surface layer 3, so that a stable coating with high lithium ion conductivity is formed on the electrode, and the separator 10 has the heat shrinkage relaxation layer 4. The heat shrinkage is effectively suppressed, which is preferable.

Further, in the present embodiment, as illustrated in FIG. 1, the separator 1 in which the surface layer 3 is provided in contact with one surface 2a of the base material 2 has been described as an example. As shown in FIG. 3, the other surface 2 b of the substrate 2 may have a heat shrinkage relaxation layer 5.
FIG. 3 is a schematic cross-sectional view for explaining another example of the separator of the present embodiment. The heat shrinkage relaxation layer 5 shown in FIG. 3 includes heat resistant particles and / or heat resistant resin. As the heat-resistant particles and the heat-resistant resin, the same particles as those contained in the surface layer 3 described above can be used. In order to maintain the shape, the heat shrinkage relaxation layer 5 may contain the same binder as that contained in the surface layer 3 described above, if necessary.

  In the electricity storage device having the separator 11 shown in FIG. 3, the separator 11 has the surface layer 3, so that a stable coating with high lithium ion conductivity is formed on the electrode, and the separator 11 has the heat shrinkage relaxation layer 5. The heat shrinkage is effectively suppressed, which is preferable.

  In the present embodiment, the separator 1 in which the surface layer 3 is provided in contact with the one surface 2a of the base material 2 has been described as an example. However, in the separator of the present embodiment, the surface layer 3 has the first coating film 6 and The second coating film 7 may be included. The first coating film 6 is preferably formed on at least one surface 2 a of the substrate 2, and the second coating film 7 is preferably formed on the surface of the first coating film 6. Although the same thing as what is contained in the surface layer 3 mentioned above can be used for a 1st coating film and a 2nd coating film, it is preferable that the lithium salt compound of the 2nd coating film 7 contains a biphenyl group containing lithium salt. . When the second coating film 7 contains a biphenyl group-containing lithium salt, that is, when the biphenyl group-containing lithium salt is segregated to the surface side of the surface layer 3, the biphenyl group-containing lithium salt dissolves earlier in the electrolyte solution and the gas is released. Can be generated. As a result, the CID mechanism provided in the lithium ion battery can be quickly operated, and the safety can be further improved.

FIG. 4 is a schematic explanatory diagram for producing another example of the separator of the present embodiment. In the method for producing the surface layer 3 shown in FIG. 4, the first coating film 6 is formed on at least one surface 2 a of the substrate 2 by the first head 30, and the second coating 31 is formed on the surface of the first coating film 6 by the second head 31. The surface layer 3 having the first coating film 6 and the second coating film 7 is formed by sequential coating for forming the coating film 7. It is preferable that the distance between the first head 30 and the second head 31 is appropriately determined according to the drying process conditions of the first coating film 6 and the second coating film 7. Moreover, you may form the 1st coating film 6 and the 2nd coating film 7 collectively.
In the formation method of the present embodiment, a third coating film that does not contain a lithium salt compound may be formed before the first coating film 6 is formed. In this case, after the third coating film is formed on at least one surface 2 a of the substrate 2 by the third head, the first coating film 6 and the second coating film 7 are formed by the first head 30 and the second head 31. . As a 3rd coating film, the same thing as what is contained in the heat shrink relaxation layer 4 mentioned above can be used.

  The coating mode shown in FIG. 4 is an example, but when a surface layer mixed with a lithium salt compound is provided on a substrate, the lithium salt compound is uniformly dispersed on the surface layer, unevenly distributed around the heat-resistant filler, or the surface layer. By making it unevenly distributed outside the base material side among them, the adhesive strength of the surface layer with respect to the base material can be kept relatively strong, and problems such as powder falling can be avoided. Further, even when a lithium salt compound is added, the adhesive action of the binder (binder) is not hindered, and the dimensional change rate of the separator at 150 ° C. can be suppressed to 10% or less, preferably 7% or less. Become.

  Specific examples of the separator of the present embodiment include the following (A) to (G). In addition, the separator which concerns on one Embodiment of this invention should just have a surface layer in the at least one surface of a base material, and is not limited to the thing of (A)-(G) shown below.

(A) What has the surface layer 3 which consists only of the lithium salt compound which releases lithium salt slowly in a non-aqueous electrolyte in the at least one surface 2a of the base material 2. FIG.
(B) What has the surface layer 3 which consists of a lithium salt compound and binder which release lithium salt slowly in a non-aqueous electrolyte in the at least one surface 2a of the base material 2. FIG.
(C) One having a surface layer 3 composed of a lithium salt compound that slowly releases a lithium salt in a non-aqueous electrolyte, heat-resistant particles, and a binder on at least one surface 2a of the substrate 2.

(D) having at least one surface 2a of the substrate 2 having a surface layer 3 composed of heat-resistant particles having a surface layer containing a lithium salt compound that releases lithium salt in a non-aqueous electrolyte and a binder. .
(E) What has the surface layer 3 which consists of a lithium salt compound which releases lithium salt slowly in a non-aqueous electrolyte, and a heat resistant resin in the at least one surface 2a of the base material 2.

(F) The surface layer 3 of the above (A) to (D) is formed on one surface 2a of the substrate 2, and the heat shrinkage relaxation layer containing heat resistant particles and / or heat resistant resin is formed on the other surface. What
(G) A heat shrinkage relaxation layer containing heat resistant particles and / or heat resistant resin is formed between one surface 2a of the substrate 2 and the surface layer 3 of the above (A) to (D).

Among the above (A) to (G), (C) to (G) are preferable, and (C) or (D) is more preferable.
In the electricity storage device having the separators (C) to (G), the lithium salt is eluted in the non-aqueous electrolyte, and a stable coating with high lithium ion conductivity is formed on the electrode. Since it is effectively suppressed, an increase in impedance due to high-temperature storage is more effectively suppressed. In particular, in the electricity storage device having the (C) or (D) separator, the effect of suppressing an increase in impedance due to high temperature storage is remarkable.

  The separator 1 according to this embodiment is for an electricity storage device, and is provided on a base material 2 made of a polyolefin porous film and at least one surface 2a of the base material 2, and releases lithium salt into the nonaqueous electrolytic solution gradually. And a surface layer 3 containing a lithium salt compound. Therefore, the electrical storage device having the separator 1 of the present embodiment is a device in which an increase in impedance due to high temperature storage is sufficiently suppressed.

[Power storage device]
The electricity storage device of the present embodiment includes any of the separators described above interposed between opposing electrodes, and at least a non-aqueous electrolyte impregnated in the separator. The non-aqueous electrolyte may be in a liquid form or gelled.
As an electrical storage device of this embodiment, the following 1st-4th electrical storage device is mentioned, for example. Among the first to fourth power storage devices, the first power storage device (lithium battery) or the fourth power storage device (lithium ion capacitor) using a lithium salt as the electrolyte salt in the non-aqueous electrolyte is preferable. The electricity storage device is more preferable. More preferably, the first power storage device is for a lithium secondary battery.

[First power storage device (lithium battery)]
The first power storage device is a lithium battery. In this specification, the lithium battery is a general term for a lithium primary battery and a lithium secondary battery. In this specification, the term lithium secondary battery is used as a concept including a so-called lithium ion secondary battery.
The lithium battery of this embodiment has a positive electrode, a negative electrode, any of the separators interposed between the positive electrode and the negative electrode, and at least a nonaqueous electrolytic solution impregnated in the separator.

In this embodiment, any separator of the above-described embodiment is used as a separator. In the case of using a separator provided with a surface layer containing a lithium salt compound only on one surface of the substrate, the surface layer may be disposed to face either the positive electrode or the negative electrode. When using a separator provided with a surface layer only on one side of the substrate, a higher lithium salt compound concentration in the vicinity of the positive electrode contributes to film formation from an earlier stage, and further increases in impedance due to high-temperature storage. Since it becomes what was suppressed, it is preferable that the surface layer is arrange | positioned facing the positive electrode.
The lithium battery separator of the present embodiment is impregnated with a non-aqueous electrolyte described later.

In the lithium battery of this embodiment, members other than the separator, such as the positive electrode, the negative electrode, and the nonaqueous electrolyte, can be used without particular limitation.
[Positive electrode]
The positive electrode includes a current collector and a positive electrode mixture layer formed on the current collector. The positive electrode mixture layer includes a positive electrode active material, a conductive agent, and a binder.
As the positive electrode current collector, for example, an aluminum foil, a stainless lath plate, or the like can be used.

The positive electrode active material preferably contains at least one selected from the group consisting of lithium-containing composite metal oxides and lithium-containing olivine-type phosphates.
As the lithium-containing composite metal oxide, for example, a composite metal oxide of lithium and one or more selected from the group consisting of cobalt, manganese, and nickel is used. Such lithium-containing composite metal oxides can be used singly or in combination of two or more as the positive electrode active material.

Examples of the lithium-containing composite metal oxide include LiCoO ₂ , LiCo _1-x M _x O ₂ (where M is Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and Cu). One or two or more elements selected from the group consisting of 0.001 ≦ x ≦ 0.05, LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <1 LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O ₂ , LiNi _{0. 8} Co _0.15 Al _0.05 O ₂ , a solid solution of Li ₂ MnO ₃ and LiMO ₂ (M is a transition metal such as Co, Ni, Mn, Fe), and LiNi _0.5 Mn _1.5 O ₄ 1 or more types selected from the group consisting of It is. Two or more of the above lithium-containing composite metal oxides may be used such as LiCoO ₂ and LiMn ₂ O ₄ , LiCoO ₂ and LiNiO ₂ , LiMn ₂ O ₄ and LiNiO ₂ .

As a lithium containing olivine type phosphate, what contains 1 type, or 2 or more types chosen from the group which consists of iron, cobalt, nickel, and manganese is preferable. Specific examples include one or more selected from the group consisting of LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , and LiMnPO ₄ . Among these, LiFePO ₄ or LiMnPO ₄ is preferable.

A part of the lithium-containing olivine-type phosphate may be substituted with another element. Specifically, for example, a part of iron, cobalt, nickel, or manganese is changed to Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, And one or more elements selected from the group consisting of Zr and the like may be substituted.
Moreover, as a lithium containing olivine type phosphate, you may use what was coat | covered with the compound and carbon material containing said element which may be substituted.
Moreover, lithium containing olivine type | mold phosphate can also be mixed with said lithium containing composite metal oxide, and can be used, for example.

The conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change. For example, the conductive agent used for the positive electrode is selected from the group consisting of natural graphite (such as flake graphite), graphite such as artificial graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. One type or two or more types of carbon black may be used, and graphite and carbon black may be appropriately mixed and used.
1-10 mass% is preferable and, as for content of the electrically conductive agent in a positive mix layer, 2-5 mass% is especially preferable.

  As binders, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), carboxymethylcellulose (CMC), ethylene And propylene diene terpolymer.

The density of the positive electrode mixture layer (the portion excluding the current collector of the positive electrode) is usually 1.5 g / cm ³ or more. In order to further increase the capacity of the lithium battery, the density of the positive electrode mixture layer is preferably 2 g / cm ³ or more, more preferably 3 g / cm ³ or more, and still more preferably 3.6 g / cm ³ or more. It is. The density of the positive electrode mixture layer is preferably 4 g / cm ³ or less.

The positive electrode can be produced, for example, by the method shown below. That is, a positive electrode active material, a conductive agent, and a binder are mixed, and a high boiling point solvent such as 1-methyl-2-pyrrolidone is added and kneaded to obtain a positive electrode mixture. After that, the positive electrode mixture is applied onto the current collector, dried, pressure-molded, and heated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours under vacuum to form a positive electrode mixture layer. To do.
The positive electrode is obtained by the above steps.

[Negative electrode]
The negative electrode includes a current collector and a negative electrode mixture layer formed on the current collector. The negative electrode mixture layer includes a negative electrode active material, a conductive agent, and a binder.
As the conductive agent and the binder, the same materials as those used for the positive electrode can be used.
As the negative electrode current collector, for example, a copper foil or the like can be used.

Examples of the negative electrode active material include lithium metal and lithium alloy, and carbon materials capable of inserting and extracting lithium [graphitizable carbon, non-graphitizable carbon having a (002) plane spacing of 0.37 nm or more, ( 002) graphite having an interplanar spacing of 0.34 nm or less], tin (elemental), tin compound, silicon (elemental), silicon compound, or lithium titanate compound such as Li ₄ Ti ₅ O ₁₂ Alternatively, two or more kinds can be used in combination.

Among these, it is preferable to use a highly crystalline carbon material such as artificial graphite or natural graphite in terms of the ability to occlude and release lithium ions, and the (002) plane spacing (d002) is 0.340 nm (nanometer). Hereinafter, it is particularly preferable to use a carbon material having a graphite type crystal structure of 0.335 to 0.337 nm.
In particular, artificial graphite particles having a massive structure in which a plurality of flat graphite fine particles are assembled or bonded non-parallel to each other, and mechanical action such as compressive force, frictional force, shearing force, etc. are repeatedly given, and scaly natural graphite is It is preferable to use spheroidized particles.

The negative electrode is obtained from the X-ray diffraction measurement of the negative electrode mixture layer when pressure-molded so that the density of the negative electrode mixture layer (the portion excluding the negative electrode current collector) is 1.5 g / cm ³ or more. The ratio I (110) / I (004) of the peak intensity I (110) of the (110) plane and the peak intensity I (004) of the (004) plane of the graphite crystal is preferably 0.01 or more. The peak intensity ratio I (110) / I (004) is more preferably 0.05 or more, and still more preferably 0.1 or more. Further, when the crystallinity is lowered due to excessive treatment, the discharge capacity of the lithium battery may be lowered. Accordingly, the peak intensity ratio I (110) / I (004) is preferably 0.5 or less, and more preferably 0.3 or less.

  Examples of metal compounds capable of inserting and extracting lithium as the negative electrode active material include Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, and Zn. , Ag, Mg, Sr, or a compound containing at least one metal element such as Ba. These metal compounds may be used in any form such as simple substance, alloy, oxide, nitride, sulfide, boride, or alloy with lithium, but simple substance, alloy, oxide, alloy with lithium Any of these is preferable because the capacity can be increased. Among these, a metal compound containing at least one element selected from the group consisting of Si, Ge, and Sn is preferable, and a metal compound containing at least one element selected from the group consisting of Si and Sn is more preferable. By using these metal compounds, the capacity of the lithium battery can be increased.

The density of the negative electrode mixture layer (portion excluding the negative electrode current collector) is usually 1.1 g / cm ³ or more. The density of the negative electrode mixture layer is preferably 1.5 g / cm ³ or more, and more preferably 1.7 g / cm ³ or more in order to further increase the capacity of the lithium battery. The density of the negative electrode mixture layer is preferably 2 g / cm ³ or less.

  The negative electrode can be produced, for example, by the method shown below. That is, a negative electrode active material, a conductive agent, and a binder are mixed, and a high boiling point solvent such as 1-methyl-2-pyrrolidone is added and kneaded to obtain a negative electrode mixture. Thereafter, the negative electrode mixture is applied onto the current collector, dried and pressure-molded, and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours under vacuum to form a negative electrode mixture layer. A negative electrode is obtained by the above process.

[Non-aqueous electrolyte]
The nonaqueous electrolytic solution is composed of a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolytic solution can be obtained by dissolving an electrolyte salt in a nonaqueous solvent by a conventionally known method.

[Non-aqueous solvent]
Examples of non-aqueous solvents include cyclic carbonates, chain esters, lactones, ethers, or amides. Among these, in order to synergistically improve the electrochemical characteristics in a wide temperature range, it is preferable that the non-aqueous solvent includes a chain ester, more preferably a chain carbonate, and a cyclic carbonate and a chain carbonate. Most preferably, both carbonates are included.
In the present specification, the term “chain ester” is used as a concept including a chain carbonate and a chain carboxylic acid ester.

  Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one (FEC), trans or Cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter collectively referred to as “DFEC”), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), or 4-ethynyl-1 , 3-dioxolan-2-one (EEC) and the like. Among these, ethylene carbonate, propylene carbonate, 4-fluoro-1,3-dioxolan-2-one, vinylene carbonate, or 4-ethynyl-1,3-dioxolan-2-one (EEC) is more preferable.

When a cyclic carbonate having a carbon-carbon multiple bond such as vinylene carbonate (VC) or a cyclic carbonate having a fluorine atom such as 4-fluoro-1,3-dioxolan-2-one (FEC) is used as the non-aqueous solvent. It is preferable because the effect of suppressing an increase in impedance due to high-temperature storage in a lithium battery is further increased.
As the cyclic carbonate having a carbon-carbon multiple bond, VC, VEC, or EEC is preferable, and VC is more preferable.
As the cyclic carbonate having a fluorine atom, FEC or DFEC is preferable.
When the non-aqueous solvent includes both a cyclic carbonate having a carbon-carbon multiple bond and a cyclic carbonate having a fluorine atom, the effect of suppressing an increase in impedance due to high-temperature storage in a lithium battery is further enhanced.

  The content of the cyclic carbonate having a carbon-carbon multiple bond and / or the cyclic carbonate having a fluorine atom is preferably 0.07% by volume or more, more preferably 0.2% by volume, based on the total volume of the nonaqueous solvent. As mentioned above, More preferably, it is 0.7 volume% or more. Moreover, the upper limit is preferably 7% by volume or less, more preferably 4% by volume or less, and still more preferably 2.5% by volume or less with respect to the total volume of the nonaqueous solvent.

  Examples of chain esters include asymmetric chain carbonates such as methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate, dimethyl carbonate (DMC), and diethyl carbonate. (DEC), symmetric chain carbonates such as dipropyl carbonate or dibutyl carbonate, pivalate esters such as methyl pivalate, ethyl pivalate, or propyl pivalate, or methyl propionate, ethyl propionate, propyl propionate, acetic acid A chain carboxylic acid ester such as methyl, ethyl acetate, or propyl acetate is preferred.

  Among these chain esters, chain esters having a methyl group such as dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, methyl propionate, methyl acetate, or ethyl acetate are preferred, particularly A chain carbonate having a methyl group is preferred.

When chain carbonate is used as the non-aqueous solvent, it is preferable to use two or more kinds. Furthermore, it is more preferable that the non-aqueous solvent includes both a symmetric chain carbonate and an asymmetric chain carbonate, and it is even more preferable that the content of the symmetric chain carbonate is greater than that of the asymmetric chain carbonate.
In particular, it is preferable that dimethyl carbonate is contained as the symmetric chain carbonate. The asymmetric chain carbonate preferably includes a methyl group, and particularly preferably includes methyl ethyl carbonate. It is preferable to include both dimethyl carbonate (DMC) and methyl ethyl carbonate (MEC) as the non-aqueous solvent because the effect of suppressing an increase in impedance due to high-temperature storage in a lithium battery is further enhanced.

  The content of the chain ester is not particularly limited, but it is preferably used in the range of 60 to 90% by volume with respect to the total volume of the nonaqueous solvent. When the content is 60% by volume or more, the viscosity of the nonaqueous electrolytic solution does not become too high, which is preferable. Moreover, when the content is 90% by volume or less, the electric conductivity of the nonaqueous electrolytic solution is lowered, and there is little possibility that the effect of suppressing an increase in impedance due to high-temperature storage in a lithium battery is reduced, which is preferable.

  The volume ratio of the symmetric chain carbonate in the chain carbonate is preferably 51% by volume or more, and more preferably 55% by volume or more. The upper limit is more preferably 95% by volume or less, and still more preferably 85% by volume or less. It is preferable that the proportion of the volume occupied by the symmetric chain carbonate in the chain carbonate is 51% by volume or more and 95% by volume or less because the effect of suppressing an increase in impedance due to high-temperature storage in the lithium battery is further enhanced.

  The ratio between the cyclic carbonate and the chain ester is preferably 10:90 to 45:55, more preferably 15:85 to 40:60, and 20:80 to 35:65. Particularly preferred.

  In order to achieve appropriate physical properties, it is preferable to use a mixture of two or more of the above nonaqueous solvents. Examples of combinations of two or more kinds of non-aqueous solvents include a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate and a chain carboxylic acid ester, a combination of a cyclic carbonate and a lactone, and a cyclic carbonate and a chain carbonate. And a combination of a lactone and a cyclic carbonate, a chain carbonate, and a chain carboxylic acid ester.

[Electrolyte salt]
As the electrolyte salt, various lithium salts that are soluble in a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiPO ₂ F ₂ , Li ₂ PO ₃ F, LiBF ₄ , or LiClO _4, an inorganic lithium salt, LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ or Lithium imide salt such as LiN (SO ₂ C ₂ F ₅ ) ₂ , lithium having a cyclic fluorinated alkylene chain such as (CF ₂ ) ₂ (SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ NLi Salt, lithium salt having SO ₃ group or SO ₄ group such as LiSO ₄ CH ₃ , LiSO ₄ C ₂ H ₅ , or FSO ₃ Li, or bis (oxalato) borate (LiBOB), lithium difluoro (oxalato) borate (LiDFOB) Or lithium tetrafluoro (oxalato) phosphate (LiTFOP) Lithium salts to the rate complexes with anions. As lithium salt, these 1 type, or 2 or more types can be mixed and used.

Among these, the group consisting of LiPF ₆ , LiPO ₂ F ₂ , Li ₂ PO ₃ F, LiBF ₄ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiSO ₄ CH ₃ , and FSO ₃ Li. 1 type or 2 types or more selected from LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiN (SO ₂ F) ₂ , LiSO ₄ CH ₃ , and FSO ₃ Li are preferably used. Is more preferred, and LiPF ₆ is most preferred.

When two or more lithium salts are used as the electrolyte salt, suitable combinations of these lithium salts include LiPF ₆ , and further include LiPO ₂ F ₂ , LiN (SO ₂ F) ₂ , LiSO ₄ CH ₃ , and FSO. It is preferable to include one or more selected from the group consisting of ₃ Li. In such a non-aqueous electrolyte containing an electrolyte salt, a lithium ion compound is contained in the separator and a lithium ion on the electrode is caused by a synergistic effect of the lithium salt being contained together with LiPF ₆ as the electrolyte salt. A highly conductive and stable film is formed. For this reason, the effect which suppresses the raise of the impedance by the high temperature storage in a lithium battery increases further, and it is preferable.

  The concentration of the lithium salt is preferably 0.3 mol / liter or more, more preferably 0.7 mol / liter or more, and still more preferably 1.1 mol / liter or more with respect to the nonaqueous solvent. The concentration of the lithium salt is preferably 2.5 mol / liter or less, more preferably 2.0 mol / liter or less, and still more preferably 1.6 mol / liter or less with respect to the nonaqueous solvent.

When a lithium salt other than LiPF ₆ is included as the electrolyte salt, the proportion of the lithium salt other than LiPF _{6 in the} non-aqueous solvent is preferably 0.001 mol / liter or more. In this case, coupled with the effect of the lithium salt compound contained in the separator, the effect of suppressing an increase in impedance due to high temperature storage in the electricity storage device is further enhanced, and is preferably 1.0 mol / liter or less. And there is little concern that the effect of suppressing the increase in impedance due to high temperature storage is reduced, which is preferable.

The proportion of the lithium salt other than LiPF _{6 in the} non-aqueous solvent is more preferably 0.01 mol / liter or more, particularly preferably 0.03 mol / liter or more, and most preferably 0.04 mol / liter or more. . The upper limit is more preferably 0.5 mol / liter or less, and particularly preferably 0.2 mol / liter or less.

In the lithium battery according to the present embodiment, as a countermeasure against an increase in internal pressure in the battery, a method of providing a safety valve on the battery lid or cutting a member such as a battery can or a gasket can be employed. Further, as a safety measure for preventing overcharge, the battery lid may be provided with a current interruption mechanism that senses the internal pressure in the battery and interrupts the current.
In the lithium battery of this embodiment, the battery structure is not particularly limited, and a coin-type battery, a cylindrical battery, a square battery, a laminate battery, or the like can be applied.

  The lithium battery of the present embodiment has a separator having a surface layer containing a lithium salt compound that slowly releases a lithium salt in a non-aqueous electrolyte on at least one surface of a substrate. For this reason, an increase in impedance due to high temperature storage can be sufficiently suppressed. Specifically, the resistance increase rate before and after high-temperature storage at a charge upper limit voltage of 4.2 V for 2 weeks at 60 ° C. is 120% or less. Thus, in the lithium battery of this embodiment, since the resistance change before and behind high temperature storage is small, it can charge / discharge without degrading performance.

  In the lithium battery of the present embodiment, for example, the end-of-discharge voltage can be set to 2.8 V or lower, and can be set to low voltages of 2.5 V and 2.0 V. In addition, in the lithium battery of this embodiment, although it does not specifically limit about the electric current value of charging / discharging, it can be normally used in 0.1-30C. Moreover, the lithium battery of this embodiment can be charged / discharged at -40-100 degreeC, Preferably it is -10-80 degreeC.

[Second power storage device (electric double layer capacitor)]
The second power storage device is an electric double layer capacitor that stores energy by using an electric double layer capacity at the interface between the electrolyte and the electrode. The most typical electrode active material used for this electricity storage device is activated carbon. Double layer capacity increases roughly in proportion to surface area. In this embodiment, any separator of the above-described embodiment is used as a separator.

[Third power storage device]
The third power storage device is a power storage device (capacitor) that stores energy using electrode doping / dedoping reactions. Examples of the electrode active material used in this power storage device include metal oxides such as ruthenium oxide, iridium oxide, tungsten oxide, molybdenum oxide, and copper oxide, and π-conjugated polymers such as polyacene and polythiophene derivatives. Capacitors using these electrode active materials can store energy associated with electrode doping / dedoping reactions. In this embodiment, any separator of the above-described embodiment is used as a separator.

[Fourth storage device (lithium ion capacitor)]
The fourth power storage device is a lithium ion capacitor (LIC). In a lithium ion capacitor, energy is stored by intercalation of lithium ions into a carbon material such as graphite as a negative electrode. Examples of the positive electrode include those using an electric double layer between an activated carbon electrode and an electrolytic solution, those using a π-conjugated polymer electrode doping / dedoping reaction, and the like. The electrolytic solution contains at least a lithium salt such as LiPF ₆ . In this embodiment, any separator of the above-described embodiment is used as a separator.

  Hereinafter, specific examples of the present invention will be described. The present invention is not limited to these examples.

"Manufacture of separators"
<Polyolefin microporous membrane (A-1): PP / PE / PP three-layer membrane: dry type>
[PP film formation]
Using a T die having a discharge width of 1000 mm and a discharge lip opening of 2 mm, a polypropylene resin having a weight average molecular weight of 470,000, a molecular weight distribution of 7.8, and a melting point of 161 ° C. was melt extruded at a T die temperature of 200 ° C. The discharged film was guided to a cooling roll at 90 ° C. and cooled by blowing cold air at 37.2 ° C., and then 40 m / min. I picked it up. The film thickness of the obtained unstretched polypropylene film (unstretched PP original fabric) was 5.2 μm. The coefficient of variation (CV) with respect to the thickness of the unstretched PP original fabric was 0.016.

[PE film formation]
Using a T-die with a discharge width of 1000 mm and a discharge lip opening of 2 mm, a weight average molecular weight of 320,000, a molecular weight distribution of 7.8, a density of 0.961 g / cm ³ , a melting point of 133 ° C., a melt index of 0.31 The high density polyethylene was melt extruded at a T die temperature of 173 ° C.
The discharged film was led to a 115 ° C. cooling roll, cooled by blowing cold air of 39 ° C., and then 20 m / min. I picked it up. The film thickness of the obtained unstretched polyethylene film (unstretched PE original fabric) was 9.4 μm. The coefficient of variation (CV) with respect to the thickness of the unstretched PE original fabric was 0.016.

[Lamination process]
Using the unstretched PP original fabric and the unstretched PE original fabric thus produced, a three-layer laminated film having a sandwich structure in which both sides of the polyethylene film were sandwiched between polypropylene films was produced as follows.
An unstretched PP raw fabric and an unstretched PE raw fabric were each fed at a speed of 6.5 m / min. The film was unwound and led to a heating roll, and after thermocompression bonding with a roll having a roll temperature of 147 ° C., it was led to a cooling roll at 30 ° C. at the same speed and wound. The unwinding tension was 5.0 kg for PP and 3.0 kg for PE. The obtained three-layer laminated film had a film thickness of 19.6 μm, and the peel strength between the PP film and PE film measured by the following method was 54.7 g / 15 mm.

[Peel strength measurement]
TD direction (perpendicular direction): 15 mm, MD direction (flow direction): 200 mm test piece from three layers laminated film, TD direction center, both ends (10 mm inside from the end), each A side (three layers) A total of 6 samples were collected, one side of the laminated film) and B side (the other side of the three-layer laminated film). The delamination strength was measured with a tensile tester (RTC-1210A) manufactured by ORIENTEC. Measurement conditions were as follows: a load cell of 100N was used, the distance between chucks was 50 mm, and the crosshead speed was 50 mm / min. Conditions. Moreover, the measurement sample which peeled off one part of the measurement adhesive surface of a test piece was created previously, and it set to the T state in the tensile tester. After the start of peeling, the peeling strength of the test piece at 120 mm, 140 mm, 160 mm, 180 mm, and 200 mm peeling was measured, and the average value was evaluated as the peeling strength.

[Stretching process]
The three-layer laminated film was subjected to heat treatment in a hot air circulation oven (heat treatment zone: oven 1) heated to 125 ° C. Next, the heat-treated laminated film was stretched at a low temperature of 18% (initial stretching ratio) between nip rolls maintained at 35 ° C. in a cold stretching zone.
The roll speed on the supply side is 2.8 m / min. Met. The laminated film that has been stretched at a low temperature is subsequently heated in a heat stretching zone (oven 2) heated to 130 ° C. until the roller reaches 190% (maximum stretching ratio) using the difference in the peripheral speed of the roll. Stretched. Thereafter, the heat-stretched laminated film was thermally relaxed to 125% (final draw ratio), and heat-set at 133 ° C. in a heat-setting zone (oven 3). 1) was produced.

  The polyolefin microporous membrane (A-1) (sample) thus obtained had a thickness measured by the following method of 20 μm and an air permeability of 310 sec / 100 ml. In addition, the average value (Ra (ave)) of the surface roughness (Ra) of both surfaces of the polyolefin microporous membrane (A-1) (sample) measured by the following method was 0.18 μm, and the compression modulus was 112 MPa. It was.

[Film thickness measurement]
Five tape-like test pieces were prepared from the sample over the entire width of 50 mm in the MD direction. Five test pieces are stacked, and using an electric micrometer (Millitron 1240 stylus 5 mmφ (flat surface, stylus pressure 0.75 N)) manufactured by Finepreuf Co., Ltd. at equal intervals so that the measurement points are 25 points. The average value was taken as the thickness.

[Measurement of air permeability (Gurley value)]
A test piece having a full width of 80 mm in the MD direction was taken from the sample. Air permeability according to JIS P8117, using a B-type Gurley type densometer (manufactured by Toyo Seiki Co., Ltd.) at three points of the center in the TD direction and the left and right ends (inside 50 mm from the end face) of the test piece. Was measured. The average value of 3 points was evaluated as the Gurley value.

[Surface roughness]
Using a white interferometer (Vertscan 3.0) manufactured by Ryoka Systems Co., Ltd., with the objective lens at a magnification of x5, an image in the range of 1270 μm in the MD direction and 960 μm in the TD direction on the sample surface (one surface) Were collected. Line analysis was performed on the MD direction of the collected image and two arbitrary locations, and the surface roughness (Ra) was measured. Moreover, the surface roughness (Ra) was similarly measured about the back surface (the other surface) of the sample, and the average value of the front surface and the back surface of the sample was evaluated as Ra (ave).

[Compressive modulus]
A plurality of 50 mm square samples were collected from the sample and laminated to prepare a laminated sample having a thickness of 5 mm. A metal cylinder having a diameter of 10 mm was pressed against the laminated sample, and ORIENTEC. In RTC-1250A, a 500 N load cell was used, and a chuck loss head speed of 0.5 mm / min. A stress-strain curve in the compression direction was created under the conditions described above. The compressive elastic modulus was calculated from the slope of the portion where the slope of the stress-strain curve became constant.
The stress is compression load (N) per unit area (mm ² ) = compression stress (N / mm ² ), and the unit is MPa. For example, the stress when a load of 100 N is applied to a metal cylinder having a diameter of 10 mm is 100 N / (5 mm × 5 mm × π) ≈1.27 MPa. The strain is a value obtained by dividing the amount of displacement deformed when compressive stress is applied by the initial thickness (5 mm), and there is no unit. For example, when the initial thickness is deformed from 5 mm to 4.8 mm by the test, the displacement amount is 0.2 mm, and the strain amount is 0.2 mm / 5 mm = 0.04.

<Polyolefin microporous membrane (A-2): PP monolayer membrane: dry type>
By subjecting the unstretched PP raw fabric used in producing the polyolefin microporous membrane (A-1) to the same stretching process as in producing the polyolefin microporous membrane (A-1), polyolefin microporous A membrane (A-2) was obtained.
The polyolefin microporous membrane (A-2) had a thickness of 20 μm and an air permeability of 220 sec / 100 ml. Moreover, the average value (Ra (ave)) of the surface roughness (Ra) of both surfaces was 0.13 μm, and the compression elastic modulus was 137 MPa.

<Polyolefin microporous membrane (A-3): PE monolayer membrane: wet>
A polyethylene resin and liquid paraffin as a plasticizer were supplied to a twin screw extruder and melt kneaded to prepare a polyethylene solution. The obtained polyethylene solution was extruded from a T-die at a predetermined temperature, and a gel-like sheet was formed while being wound with a cooling roll. A thin film was obtained by biaxially stretching this gel sheet.

The obtained thin film was washed with hexane, and liquid paraffin remaining from the thin film was extracted and removed, followed by drying and heat treatment to make the thin film microporous. Through the above steps, a polyolefin microporous membrane (A-3) was obtained.
The polyolefin microporous membrane (A-3) had a thickness of 20 μm and an air permeability of 270 sec / 100 ml. Moreover, the average value (Ra (ave)) of the surface roughness (Ra) on both sides was 0.42 μm, and the compression modulus was 68 MPa.

Separators of Examples 1 to 23 and Comparative Examples 1 to 3 were prepared using the polyolefin microporous membranes (A-1) to (A-3) thus obtained.
In Table 1, the cross-sectional schematic diagram of the separator of Examples 1-23 and Comparative Examples 1-3 is shown. In Table 1, 2 is a polyolefin microporous membrane, 21 is a lithium salt compound, 22 is a heat-resistant particle, 23 is a heat-resistant resin, and 24 is a heat-resistant particle having a surface layer containing a lithium salt compound. .
In Examples 20-23, the codes | symbols 21, 22, and 24 in Table 1 were mixed, and the ratio with which the lithium salt compound was unevenly distributed around the heat resistant particle was large. Example 19 was coated on the substrate so as to have the same structure as Examples 5, 16, 20-23.

"Examples 1, 11, and 18"
Lithium methanesulfonate powder as a lithium salt compound and polyvinylidene fluoride (PVDF) as a binder were mixed at a mixing ratio of lithium methanesulfonate: PVDF (mass ratio) = 95: 5 to obtain a mixture. . The obtained mixture was dispersed or dissolved in 1-methyl-2-pyrrolidone as a solvent to obtain a slurry (C-1) for coating.

The obtained slurry (C-1) was coated with a microporous polyolefin membrane (A-) using a desktop coater so that the coating amount of lithium methanesulfonate per 1 m ² shown in Table 2 (Li salt compound coating amount) was obtained. The surface layer was formed by applying to one side of 1) and heat-treating after drying to obtain the separator of Example 1. The separators of Examples 11 and 18 were obtained in the same manner as Example 1.
The separators of Examples 1, 11, and 18 had a surface layer thickness of 2 μm as measured by the film thickness measurement method described above.

[Adhesion strength]
The adhesion strength was measured by a peel test. An adhesive tape (Kokuyo T-225) was attached to the surface layer of a separator sample cut out with a width of 20 mm and a length of 50 mm to prepare a test sample. The peel strength between the substrate and the surface layer was measured with a peel tester (Nidec Sympo Co., Ltd. FGS-100VC, peel rate 300 mm / min, T-type peel), and from the start of measurement to the end of measurement. Measurement was made over time, and the measurement average value (N / cm) was defined as the adhesion strength.

[Heat shrinkage]
A test piece (200 × 200 mm) was taken from the inside 10 mm from both sides of the sample. A gauge point with a distance between the gauge points of 180 mm was entered in the center of each test piece in the width direction (TD) and length direction (MD) of each test piece, and the dimension between the gauge points was measured with a steel scale. A sample in which the distance between the gauge points was recorded was sandwiched between papers, and left for 1 hour in an environment of 150 ° C. in a hot air circulation type model: DK-43 manufactured by Yamato Kagaku. Thereafter, the sample was taken out and allowed to cool at room temperature, and the distance between the gauge points was measured with a steel rule.
The heat shrinkage rate was calculated by the following equation, assuming that the distance between the pre-heating marks was L1 (mm) and the distance between the marks after heating was L2 (mm).
Thermal contraction rate = (L1-L2) / L1 × 100

[Dimensional change rate]
A value obtained by multiplying the absolute value of the thermal shrinkage rate in the MD direction and the absolute value of the thermal shrinkage rate in the TD direction was calculated as the dimensional change rate.

[Measurement of solubility of lithium salt compound]
About the lithium methanesulfonate as a lithium salt compound used when forming the surface layer of the separator of Example 1, the solubility at 25 ° C. in the following solubility measuring solution was measured by the method shown below.
A solution for measuring solubility containing lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 mol / liter in a non-aqueous solvent containing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3: 7 was prepared. .

Then, a lithium salt compound was added to the solution for measuring solubility at 25 ° C., and ultrasonic waves were applied for 30 minutes to dissolve the lithium salt compound until saturated, thereby obtaining a saturated solution. Thereafter, the saturated solution was filtered using a filter, and the lithium salt compound remaining without being dissolved in the saturated solution was removed. The obtained filtrate was appropriately diluted, the concentration of the lithium salt compound in the filtrate was measured using ion chromatography, and the solubility was calculated.
As a result, the solubility at 25 ° C. in the solubility measurement solution of lithium methanesulfonate was 0.0075% by mass.

"Examples 2 and 3"
Except that the slurry (C-1) was applied to one surface of the polyolefin microporous membrane (A-1) so as to be the coating amount of lithium methanesulfonate (Li salt compound coating amount) shown in Table 2. The separators of Examples 2 and 3 were obtained in the same manner as Example 1.
The separator of Example 2 had a surface layer thickness of 0.7 μm.
The separator of Example 3 had a surface layer thickness of 5 μm.

Example 4
Boehmite powder as heat-resistant particles and PVDF as a binder are mixed at a mixing ratio of boehmite: PVDF (mass ratio) = 95: 5 and dispersed or dissolved in 1-methyl-2-pyrrolidone as a solvent. As a result, a slurry (C-2) for coating was obtained.
The slurry (C-2) was applied to the other surface of the polyolefin microporous membrane (A-1) in the separator of Example 1 using a desktop coater and dried to form a heat shrinkage relaxation layer. 4 separators were obtained.
In the separator of Example 4, the thickness of the heat shrinkage relaxation layer was 4 μm.

"Example 5"
Lithium methanesulfonate powder, boehmite powder, and PVDF as a binder were mixed at a mixing ratio of lithium methanesulfonate: boehmite: PVDF (mass ratio) = 40: 55: 5 to obtain a mixture. When mixing, PVDF was mixed after mixing lithium methanesulfonate and boehmite powder first. The obtained mixture was dispersed or dissolved in 1-methyl-2-pyrrolidone as a solvent to obtain a slurry (C-3) for coating.

The obtained slurry (C-3) was coated with a microporous polyolefin membrane (A-) using a desktop coater so that the coating amount of lithium methanesulfonate per 1 m ² shown in Table 2 (Li salt compound coating amount) was obtained. The surface layer was formed by applying on one surface of 1) and drying to obtain the separator of Example 5.
The separator of Example 5 had a surface layer thickness of 5 μm. The adhesion strength was 0.6 N / cm, and the dimensional change rate was 6.1% (MD direction thermal shrinkage 4.0%, TD direction thermal shrinkage 1.5%).

"Example 6"
The slurry (C-2) was applied to one surface of the polyolefin microporous membrane (A-1) using a desktop coater and dried to form a heat shrinkage relaxation layer. Next, the slurry (C-1) was applied on the heat shrinkage relaxation layer using a desktop coater so that the amount of lithium methanesulfonate per 1 m ² shown in Table 2 was applied, and dried to dry the surface layer. The separator of Example 6 was obtained.
In the separator of Example 6, the thickness of the heat shrinkage relaxation layer was 4 μm, and the thickness of the surface layer was 2 μm. The adhesion strength was 1.6 N / cm, and the dimensional change rate was 3.3% (MD direction heat shrinkage rate 2.7%, TD direction heat shrinkage rate 1.2%).

"Example 7"
The slurry (C-2) was applied to the other surface of the polyolefin microporous membrane (A-1) in the separator of Example 5 using a desktop coater, and dried to form a heat shrinkage relaxation layer. 7 separator was obtained.
In the separator of Example 7, the thickness of the heat shrinkage relaxation layer was 4 μm. The adhesion strength was 1.5 N / cm, and the dimensional change rate was 3.2% (MD direction thermal shrinkage rate 2.8%, TD direction thermal shrinkage rate 1.1%).

"Example 8"
Lithium methanesulfonate powder and boehmite powder were mixed at a mixing ratio of lithium methanesulfonate: boehmite (mass ratio) = 40: 60 to obtain a mixture. The mixing procedure was the same as in Example 5. Water was added to the obtained mixture, and lithium methanesulfonate in the mixture was dissolved in water to form a slurry. Water in the resulting slurry was evaporated using a spray drying method. As a result, boehmite whose surface was coated in a uniform thin film with lithium methanesulfonate was obtained.

  The obtained boehmite having a surface layer containing lithium methanesulfonate, and polyvinylidene fluoride (PVDF) as a binder, boehmite having a surface layer containing lithium methanesulfonate: PVDF ( (Mass ratio) = 95: 5 The mixture was mixed to obtain a mixture. The obtained mixture was dispersed or dissolved in 1-methyl-2-pyrrolidone as a solvent to obtain a slurry (C-4) for coating.

The obtained slurry (C-4) was coated with a microporous polyolefin membrane (A-) using a desktop coater so that the coating amount of lithium methanesulfonate per 1 m ² shown in Table 2 (Li salt compound coating amount) was obtained. The surface layer was formed by applying on one side of 1) and drying to obtain the separator of Example 8.
The separator of Example 8 had a surface layer thickness of 5 μm. The adhesion strength was 0.8 N / cm, and the dimensional change rate was 5.3% (MD direction thermal shrinkage rate 3.5%, TD direction thermal shrinkage rate 1.5%).

"Example 9"
A separator of Example 9 was obtained in the same manner as in Example 5 except that the boehmite powder contained in the slurry (C-3) was replaced with an aramid resin powder.
The separator of Example 9 had a surface layer thickness of 5 μm.

"Example 10"
A separator of Example 10 was obtained in the same manner as in Example 6 except that the heat shrinkage relaxation layer was formed using a slurry in which the boehmite powder contained in the slurry (C-2) was replaced with an aramid resin powder.
In the separator of Example 10, the thickness of the heat shrinkage relaxation layer was 4 μm, and the thickness of the surface layer was 2 μm.

"Example 12"
A separator of Example 12 was obtained in the same manner as Example 1 except that the polyolefin microporous film (A-2) was used instead of the polyolefin microporous film (A-1).
"Example 13"
A separator of Example 13 was obtained in the same manner as Example 1 except that the polyolefin microporous film (A-3) was used instead of the polyolefin microporous film (A-1).

"Example 14"
A separator of Example 14 was obtained in the same manner as in Example 4 except that the heat shrinkage relaxation layer was formed using a slurry in which the boehmite powder contained in the slurry (C-2) was replaced with alumina powder.
In the separator of Example 14, the thickness of the heat shrinkage relaxation layer was 5 μm.

"Example 15"
The separator of Example 15 in the same manner as in Example 4 except that the heat shrinkage relaxation layer was formed using a slurry in which the boehmite powder contained in the slurry (C-2) was replaced with Li ₄ Ti ₅ O ₁₂ powder. Got.
In the separator of Example 15, the thickness of the heat shrinkage relaxation layer was 6 μm.

"Example 16"
The separator of Example 16 was obtained in the same manner as in Example 5 except that the surface layer was formed using a slurry in which the boehmite powder contained in the slurry (C-3) was replaced with Li ₄ Ti ₅ O ₁₂ powder. .
The separator of Example 16 had a surface layer thickness of 6 μm.

"Example 17"
Li ₄ Ti ₅ O ₁₂ powder is used instead of boehmite powder, and the surface is coated with lithium methanesulfonate in a uniform thin film in the same manner as boehmite whose surface is coated with lithium methanesulfonate. Li ₄ Ti ₅ O ₁₂ was obtained.

Then, a boehmite having a surface layer containing methane lithium sulfonic acid contained in the slurry (C-4), was replaced with Li ₄ Ti ₅ O ₁₂ having a surface layer comprising lithium methanesulfonate slurries Was used in the same manner as in Example 8 to form a surface layer, whereby a separator of Example 17 was obtained.
The separator of Example 17 had a surface layer thickness of 5 μm.

"Example 19"
Lithium 1,1′-biphenylyl-4-carboxylate, boehmite powder, and PVDF as a binder are lithium 1,1′-biphenylyl-4-carboxylate: boehmite: PVDF (mass ratio) = 4: 91: The mixture was mixed at a mixing ratio of 5 to obtain a mixture. The obtained mixture was dispersed or dissolved in 1-methyl-2-pyrrolidone as a solvent to obtain a slurry (D-3) for coating. The slurry (D-3) was coated with the polyolefin microporous membrane (A-1) using a desktop coater so that the coating amount of lithium 1,1′-biphenylyl-4-carboxylate was 0.4 g / m ² . The separator was applied to one surface and dried / heat treated to form a surface layer, whereby a separator of Example 19 was obtained.
The separator of Example 19 had a surface layer thickness of 5 μm. The adhesion strength was 1.4 N / cm, and the dimensional change rate was 3.4% (MD direction thermal shrinkage 2.8%, TD direction thermal shrinkage 1.2%).
By incorporating the separator of Example 19 into the lithium ion battery, the lithium carboxylate dissolves earlier in the electrolytic solution and gas can be generated. As a result, the CID mechanism provided in the lithium ion battery can be quickly operated, and the safety can be further improved.

"Example 20"
Lithium methanesulfonate powder, boehmite powder, and PVDF as a binder were mixed at a mixing ratio of lithium methanesulfonate: boehmite: PVDF (mass ratio) = 4: 91: 5 to obtain a mixture. The mixing procedure was the same as in Example 5. The obtained mixture was dispersed or dissolved in 1-methyl-2-pyrrolidone as a solvent to obtain a slurry (D-1) for coating.
The resulting slurry (D-1) was coated with a microporous polyolefin membrane (A-) using a desktop coater so that the coating amount of lithium methanesulfonate per 1 m ² shown in Table 3 (Li salt compound coating amount) was obtained. The separator was applied to one surface of 1) and dried to form a surface layer, whereby a separator of Example 20 was obtained.
The separator of Example 20 had a surface layer thickness of 5 μm. The adhesion strength was 0.7 N / cm, and the dimensional change rate was 5.8% (MD direction thermal contraction rate was 3.6%; TD direction thermal contraction rate was 1.6%).

"Example 21"
Lithium methanesulfonate powder, lithium monofluorophosphate powder, boehmite powder, and PVDF as a binder, lithium methanesulfonate: lithium monofluorophosphate: boehmite: PVDF (mass ratio) = 3: 1: 91: The mixture was mixed at a mixing ratio of 5 to obtain a mixture. As a mixing procedure, lithium methanesulfonate powder, lithium monofluorophosphate powder, and boehmite powder were first mixed, and then PVDF was mixed. The obtained mixture was dispersed or dissolved in 1-methyl-2-pyrrolidone as a solvent to obtain a slurry (D-2) for coating.
The obtained slurry (D-2) was applied to one surface of the polyolefin microporous membrane (A-1) using a tabletop coater so that the Li salt compound application amount per 1 m ² shown in Table 3 was obtained. The surface layer was formed by drying / heat treatment, and the separator of Example 21 was obtained.
The separator of Example 21 had a surface layer thickness of 5 μm. The adhesion strength was 0.7 N / cm, and the dimensional change rate was 6.2% (MD direction thermal shrinkage rate: 3.6%; TD direction thermal shrinkage rate: 1.7%).

"Example 22"
Except that the surface layer was formed using a slurry in which the ratio of the mixture was changed to lithium methanesulfonate: lithium monofluorophosphate: boehmite: PVDF (mass ratio) = 2: 2: 91: 5, the same as in Example 21 Thus, a separator of Example 22 was obtained. The adhesion strength was 0.8 N / cm, and the dimensional change rate was 5.6% (MD direction thermal shrinkage was 3.7%; TD direction thermal shrinkage was 1.5%). The cycle characteristics of the lithium ion secondary battery produced using the separator of Example 22 were also good.

"Example 23"
Except that the surface layer was formed using a slurry in which the ratio of the mixture was changed to lithium methanesulfonate: lithium monofluorophosphate: boehmite: PVDF (mass ratio) = 1: 3: 91: 5, the same as in Example 21 Thus, a separator of Example 23 was obtained. The adhesion strength was 0.7 N / cm, and the dimensional change rate was 6.8% (MD direction thermal shrinkage was 3.8%; TD direction thermal shrinkage was 1.8%). The cycle characteristics of the lithium ion secondary battery produced using the separator of Example 23 were also good.
By incorporating the separators of Examples 21 to 23 into the lithium ion battery, lithium fluorophosphate can be gradually released into the electrolytic solution over a long period of time. This makes it possible to maintain the cycle characteristics of the lithium ion battery for a long period of time.

"Comparative Examples 1 and 2"
A polyolefin microporous membrane (A-1) was used as a separator.

“Comparative Example 3”
A separator of Comparative Example 3 was obtained in the same manner as in Example 1 except that the surface layer was formed using a slurry in which the lithium methanesulfonate powder contained in the slurry (C-1) was replaced with lithium sulfate powder.
The separator of Comparative Example 3 had a surface layer thickness of 2 μm.

[Measurement of solubility of lithium salt compound]
Regarding the lithium monofluorophosphate of Examples 20 to 23 used in forming the surface layer of the separator and the lithium sulfate of Comparative Example 3, the solubility at 25 ° C. with respect to the above-mentioned solution for measuring the solubility was determined by the above-described lithium methanesulfonate. The solubility was determined in the same manner as the solubility at 25 ° C. in the solubility measurement solution.
As a result, the solubility at 25 ° C. in the solution for measuring the solubility of lithium monofluorophosphate was 0.009% by mass. The solubility at 25 ° C. in the solution for measuring the solubility of lithium sulfate was less than 0.0010% by mass.

"Manufacture of lithium ion secondary batteries"
Using the separators of Examples 1 to 23 and Comparative Examples 1 to 3 thus obtained, lithium ion secondary batteries were produced by the method shown below.

[Examples 1 to 10, 12 to 17, Comparative Examples 1 and 3, Examples 19 to 23]
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ; 94% by mass and acetylene black (conductive agent); 3% by mass are mixed, and polyvinylidene fluoride (binder); A positive electrode mixture paste was prepared by adding to and mixing with the solution dissolved in methyl-2-pyrrolidone. This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried and pressurized, and cut into a predetermined size to produce a strip-like positive electrode. The density of the portion (positive electrode mixture layer) excluding the current collector of the positive electrode was 3.6 g / cm ³ .

Further, artificial graphite (d002 = 0.335 nm, negative electrode active material); 95% by mass in a solution in which polyvinylidene fluoride (binder); 5% by mass was previously dissolved in 1-methyl-2-pyrrolidone. In addition, the mixture was mixed to prepare a negative electrode mixture paste. This negative electrode mixture paste was applied to one side of a copper foil (current collector), dried and pressurized, and cut into a predetermined size to produce a negative electrode. The density of the portion (negative electrode mixture layer) excluding the current collector of the negative electrode was 1.5 g / cm ³ . Further, as a result of X-ray diffraction measurement of the negative electrode mixture layer, the ratio of the peak intensity I (110) of the (110) plane of the graphite crystal to the peak intensity I (004) of the (004) plane [I (110) / I (004)] was 0.1.

Ethylene carbonate (EC), 4-fluoro-1,3-dioxolan-2-one (FEC), vinylene carbonate (VC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC) in a volume ratio of 25: 3: 2 In a non-aqueous solvent mixed at 30:40, LiPF ₆ as an electrolyte salt was dissolved to 1.1 mol / L to obtain a non-aqueous electrolyte.

  Then, a separator was placed between the positive electrode and the negative electrode with the surface layer facing the positive electrode (no surface layer in Comparative Example 1), and the separator was laminated and accommodated in an exterior material made of a laminate film. Then, the nonaqueous electrolyte solution was added to the exterior material and sealed, and the laminated lithium ion secondary batteries of Examples 1 to 10, 12 to 17, 19 to 23, and Comparative Examples 1 and 3 were produced.

Example 11
The laminated lithium ion secondary of Example 11 is the same as Example 1 except that the separator is disposed and laminated with the surface layer facing the negative electrode between the positive electrode and the negative electrode. A battery was produced.

Example 18
As the non-aqueous electrolyte, the LiPF _{6 of the} non-aqueous electrolyte used in Example 1 was changed from 1.1 mol / L to LiPF ₆ ; 1.1 mol / L + LiPO ₂ F ₂ ; 0.1 mol / L. A laminated lithium ion secondary battery of Example 18 was made in the same manner as Example 1 except that.
[Comparative Example 2]
As the non-aqueous electrolyte, the LiPF _{6 of the} non-aqueous electrolyte used in Example 1 was changed from 1.1 mol / L to LiPF ₆ ; 1.1 mol / L + LiPO ₂ F ₂ ; 0.1 mol / L. A laminated lithium ion secondary battery of Comparative Example 2 was produced in the same manner as in Comparative Example 1 except that this was done.

  The high temperature storage characteristics of the lithium ion secondary batteries of Examples 1 to 23 and Comparative Examples 1 to 3 thus prepared were evaluated by the following method. The results are shown in Table 2. Table 2 shows the Li compound, Li compound coating amount, polyolefin microporous film, electrode facing the surface layer, heat resistant particles or heat resistant resin, and electrolyte salt in the surface layer of the separator for each lithium ion secondary battery. . Table 3 further shows Li chloride A in the surface layer, Li chloride B in the surface layer, and Li chloride rate (A: B).

[Evaluation of high-temperature storage characteristics]
<Initial impedance measurement>
In a constant temperature bath at 25 ° C., the battery was charged with a constant current and a constant voltage of 0.2 C for 3 hours to a charge end voltage of 3.72 V, and the impedance was measured at 1 kHz in the charged state.
<Impedance measurement after high temperature storage>
After measuring the initial impedance, the battery was charged in a constant temperature bath at 60 ° C. with a constant current and a constant voltage of 0.2 C for 3 hours to a charge end voltage of 4.2 V, and stored in the charged state for 2 weeks. After storage, the battery was discharged to a final discharge voltage of 2.7 V under a constant current of 0.2C. Thereafter, the battery was charged with a constant current and a constant voltage of 0.2 C for 3 hours to a charge end voltage of 3.72 V, and the impedance was measured at 1 kHz in the charged state.

The impedance increase rate (%) due to high-temperature storage was determined by the following equation using the results of the impedance measurement at the initial stage and after high-temperature storage thus measured. The results are shown in Table 2.
Impedance increase rate (%) = [(impedance after high temperature storage−initial impedance) ÷ impedance after high temperature storage] × 100

As shown in Table 2, in the lithium ion secondary batteries of Examples 1 to 18, 20 to 23, the rate of increase in impedance due to high temperature storage was small as compared with the lithium ion secondary batteries of Comparative Examples 1 to 3. .
In Examples 1-18 and 20-23, the solubility at 25 ° C. with respect to the solution for measuring the solubility of lithium methanesulfonate used when forming the surface layer of the separator is 0.0075% by mass. The solubility at 25 ° C. with respect to the solution for measuring the solubility of lithium monofluorophosphate used when forming the surface layers of the separators of Examples 21 to 23 is 0.009% by mass. Therefore, in Examples 1 to 23, the solubility at 25 ° C. with respect to the solution for measuring the solubility of the lithium salt compound used in forming the surface layer of the separator is in the range of 0.005% by mass to 0.1% by mass. It is. Further, the solubility at 25 ° C. with respect to the solution for measuring the solubility of lithium sulfate used when forming the surface layer of the separator of Comparative Example 3 is less than 0.0010% by mass. From this, the effect that the increase rate of the impedance by the high temperature storage in the lithium ion secondary batteries of Examples 1 to 23 is low is that lithium salt (lithium methanesulfonate) is gradually released from the surface layer of the separator in the non-aqueous electrolyte. It is estimated that this is because

From the results of Example 1 and Examples 4, 6, 7, and 10, it was found that the rate of increase in impedance due to high-temperature storage was further reduced when the separator had a heat shrinkage relaxation layer.
From the results of Example 1 and Examples 5, 8, and 9, it was found that when the surface layer of the separator contains a heat-resistant resin or heat-resistant particles, the rate of increase in impedance due to high-temperature storage is further reduced.

From the results of Example 1 and Example 11, it is found that the rate of increase in impedance due to high-temperature storage is further reduced by placing a separator between the positive electrode and the negative electrode with the surface layer facing the positive electrode. It was.
From the results of Example 1 and Example 18, it was found that the addition rate of LiPO ₂ F ₂ to the non-aqueous electrolyte containing LiPF ₆ further reduced the increase rate of impedance due to high-temperature storage.

  From the results of Example 20 and Examples 21 to 23, the surface layer of the separator used two types of lithium powder, but the increase in impedance due to high-temperature storage was greater than when one type of lithium powder was used. It was found that the increase in impedance was reduced to almost the same level as in Example 20 by changing the Li salt ratio in the surface layer.

  The electricity storage device having the separator of the present invention is excellent in the effect of suppressing resistance change before and after high-temperature charge storage. In particular, by using the separator of the present invention as a separator for an electricity storage device such as a lithium secondary battery mounted in a hybrid electric vehicle, a plug-in hybrid electric vehicle, a battery electric vehicle, etc., resistance change before and after storage at high temperature charge is suppressed. it can.

DESCRIPTION OF SYMBOLS 1, 10, 11 Separator 2 Base material 2a One side 2b The other side 3 Surface layer 4, 5 Thermal contraction alleviation layer 6 1st coating film 7 2nd coating film 30 1st head 31 2nd head

Claims (7)

A separator for an electricity storage device,
A base material comprising a polyolefin porous membrane;
A surface layer that is provided on at least one surface of the base material and includes a lithium salt compound that slowly releases a lithium salt in a non-aqueous electrolyte and heat-resistant particles;
The lithium salt compound is unevenly distributed on the outer side of the surface layer opposite to the substrate, or covers the heat-resistant particles, and ethylene carbonate and methyl ethyl carbonate are in a volume ratio of 3: 7. in a non-aqueous solvent containing at the rate of solubility at 25 ° C. at a concentration of 1 mole / liter for a solution containing lithium hexafluorophosphate state, and are 2 wt% or less than 0.003 wt%, said base material A separator characterized by having an adhesion strength of the surface layer to 0.7 N / cm or more . The separator according to claim 1 , wherein the content of the lithium salt compound contained in the surface layer is 10% by mass or less with respect to the heat-resistant particles. The dimensional change rate obtained by multiplying the dimensional change rate in the MD direction when left in a 150 ° C. environment for 1 hour by the dimensional change rate in the TD direction when left in a 150 ° C. environment for 1 hour is 10% or less. The separator according to claim 1 or 2 , characterized by the above. The dimensional change rate in the MD direction is 5% or less,
The separator according to claim 3 , wherein a dimensional change rate in the TD direction is 2% or less.   The separator according to claim 1, wherein the solubility of the lithium salt compound is 0.003% by mass or more and 0.4% by mass or less. An electrical storage device comprising: the separator according to any one of claims 1 to 5 interposed between opposing electrodes; and a nonaqueous electrolytic solution impregnated in at least the separator. The non-aqueous electrolyte contains LiPF ₆ and further contains one or more selected from the group consisting of LiPO ₂ F ₂ , LiN (SO ₂ F) ₂ , LiSO ₄ CH ₃ and FSO ₃ Li. The power storage device according to claim 6 .

Images