JP2002231209A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a temperature rise in an overcharge process of a non-aqueous electrolyte secondary battery using a particularly thin separator made of a polymer microporous membrane, thereby improving safety during overcharge. Improve. SOLUTION: 100 to 170 ° C, 30 to 6 in the longitudinal direction.
100 kg / cm ^{2 with} a tensile load of 100 kg / cm ²
120 ° C, or 120-1 with the width fixed
A non-aqueous electrolyte secondary battery using a separator having a gas permeability resistance of 50 to 700 seconds / 100 ml after heat treatment at 40 ° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having an improved separator.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery using lithium as a negative electrode active material (lithium secondary battery) has a high energy density and contains flammable substances. A high degree of safety is also required in use. To cope with this, many safety measures have been devised.These measures include the method of incorporating safety devices in the battery container, power pack, or equipment, and the overcharging resistance of the power generation element itself of the battery. It is roughly divided into the method of giving.

[0003] As an example of a method for providing the power generating element itself with overcharge resistance, many improvements have been made on the separator. The separator has a basic role of preventing a short circuit between the positive electrode and the negative electrode during storage or normal use of the battery and preventing self-discharge. As a function unique to the separator of a non-aqueous electrolyte secondary battery, when the battery temperature rises significantly due to an external short circuit or overcharging with an excessive current, etc., the porous separator made of a polyolefin resin or the like is substantially softened. Cut off the current by changing to non-porous
There is a so-called shutdown function.

However, if the temperature of the battery further rises after the shutdown, the separator melts to form a large hole, and a large short-circuit current flows between the positive and negative electrodes, causing the battery to generate heat, that is, a so-called meltdown occurs. It can be said that the higher the temperature when the meltdown occurs, the higher the safety. However, in reality, if the thermal fusibility is increased in order to enhance the shutdown function of the separator, the temperature at which meltdown occurs is lowered, resulting in reduced safety.

[0005] In order to solve the above-mentioned problem, a separator mainly combining a porous body of a polyolefin resin and a heat-resistant porous body has been studied. For example, JP-A-8-87995 proposes a separator having a laminated structure of a porous body of a polyolefin resin and a porous body of polyphenylene sulfide. Also, Japanese Patent Application Laid-Open
Japanese Patent No. 161775 discloses a battery structure in which each of a positive electrode plate and a negative electrode plate is covered with a polyolefin resin separator, and a porous film of a heat-resistant resin is disposed between the separators. Japanese Patent Application Laid-Open No. 9-27311 proposes using a nonwoven fabric made of fibrillated organic fibers having a fiber diameter of 1 μm or less as a separator. However, it is technically difficult to obtain a thin separator by these methods.
If it is less than m, there is a problem that a homogeneous product cannot be obtained.

[0006] In recent years, competition for higher capacity of non-aqueous electrolyte secondary batteries has increased more and more.
Improvements in battery structures have been made to reduce the occupied volume of battery components other than the active material and increase the amount of active material that can be accommodated in the battery. Therefore, thinner separators are increasingly required. However, thinner separators tend to cause internal short circuits. When the amount of the active material is further increased, the amount of energy contained in the battery increases. For these reasons, when the thickness of the separator is reduced, it becomes more difficult to ensure safety. Also, with the rapid spread of devices in recent years, demands for short-time charging (rapid charging) have been increasing in order to improve user convenience. In order to meet this demand, it is necessary to secure the safety by reliably suppressing the temperature rise of the battery even when the battery is overcharged with an excessive current due to the failure of the charger.

However, it is difficult to secure safety when a battery using a thin separator is overcharged with a large current only by the conventional method of increasing the internal resistance of the battery by shutting down the separator and cutting off the overcharge current. It is. That is,
When the separator is thin, even if it can be shut down by a conventional method, an extremely large hole is likely to be generated due to the subsequent meltdown. This allows
As a result, a large internal short-circuit current flows into the battery to further increase the battery temperature, which makes it difficult to ensure the safety of the battery during overcharge.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems relating to the safety of a non-aqueous electrolyte secondary battery particularly using a thin separator, and suppresses an excessive rise in battery temperature during overcharge. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery having a high capacity.

[0009]

A first non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte containing a lithium salt, and a separator comprising a polymer microporous membrane.
After the polymer microporous membrane has been subjected to a heat treatment in the atmosphere at a temperature of 100 to 170 ° C. for 15 to 20 minutes,
It has an air resistance of 0 to 700 seconds / 100 ml.

A second non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte containing a lithium salt, and a rectangular separator comprising a microporous polymer membrane. The film is subjected to a tensile load of 30 to 60 kg / cm < ² >
After a heat treatment for 15 to 20 minutes in the above temperature range, it has an air resistance of 50 to 700 seconds / 100 ml.

The third non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte containing a lithium salt, and a rectangular separator comprising a microporous polymer membrane. The film is fixed in the width direction, and is
After being subjected to a heat treatment in a temperature range of 40 ° C. for 15 to 20 minutes, it has an air resistance of 50 to 700 seconds / 100 ml.

A fourth non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte containing a lithium salt, and a rectangular separator comprising a microporous polymer membrane. The film is subjected to a tensile load of 30 to 60 kg / cm < ² >
After a heat treatment for 15 to 20 minutes in a temperature range of 90 to 90% pore diameter (D ₉₀ ) of 0.05 to 0.5 μm.

A fifth non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte containing a lithium salt, and a rectangular separator comprising a microporous polymer membrane. The film is fixed in the width direction, and is
After a heat treatment in a temperature range of 40 ° C. for 15 to 20 minutes, a 90% pore size (D ₉₀ ) has a pore size distribution of 0.05 to 0.5 μm.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a substantial overshoot when a battery is overcharged with excessive current by generating a moderate amount of internal short-circuit current at a relatively early stage of overcharge. This is to reduce the charging current. As a result, it is possible to suppress the excessive temperature rise of the battery at the time of overcharging, and to provide a non-aqueous electrolyte secondary battery excellent in safety. The first non-aqueous electrolyte secondary battery of the present invention has a physical property of having an air permeability resistance of 50 to 700 seconds / 100 ml after being subjected to a heat treatment in the temperature range of 100 to 170 ° C. for 15 to 20 minutes. Is used as a separator material.

When the non-aqueous electrolyte secondary battery is overcharged, it is considered that the electrolyte or the like decomposes or reacts with the active material, and some conductive material is formed on the positive electrode or the negative electrode. As the overcharge state progresses, the conductive substance grows inside the pores of the separator and eventually penetrates through the separator to cause an internal short circuit. Although the mechanism of suppressing the temperature rise of the battery during overcharging in the present invention has not been sufficiently elucidated, the magnitude of the internal short-circuit current is appropriately controlled by appropriately managing the state of the pores of the separator. However, by preventing the depth of charge of the positive electrode and the negative electrode from reaching an unnecessarily excessive state from a relatively early stage of the overcharge process, the temperature rise during overcharge was suppressed, and the danger due to overheating of the battery was suppressed. It is considered something.

If the separator has too many pores, that is, if the air permeability is too small, the internal short-circuit current generated during the above-mentioned overcharging tends to be large, and the heat generated by the internal short-circuit current rather causes the battery The temperature rises to a dangerous situation. Conversely, when the separator has few pores, that is, when the air resistance is large, the internal short-circuit current decreases,
The overcharge state progresses further. In this case, if the separator is thin and the shutdown function does not work enough,
The overcharge state progresses to a dangerous situation. Therefore, in order to generate an appropriate amount of internal short-circuit current due to overcharging and to suppress a rise in battery temperature, it is necessary to control the air permeability resistance of the separator to an appropriate range.

[0017] The separator material generally shrinks when exposed to high temperatures, reducing its porosity. It is important that the above-mentioned appropriate air resistance is controlled by the air resistance at the temperature to which the separator in the battery is exposed at the time of overcharge, and this air resistance is generally the air resistance at room temperature. Less than air resistance. The present inventors diligently studied the relationship between the air resistance of the separator material after heat treatment at 100 to 170 ° C. and the temperature rise of the battery at the time of overcharging, and found that the air permeability after heat treatment at 100 to 170 ° C. It has been found that it is preferable to use a polymer microporous membrane having a resistance of 50 to 700 seconds / 100 ml as a separator material of a nonaqueous electrolyte secondary battery.

That is, the air resistance after the heat treatment is 50 seconds /
When a separator material having a value of less than 100 ml is used, excessive internal short-circuit current occurs due to excessively large pores of the separator at the time of overcharge, and a rapid temperature rise of the battery occurs at the time of overcharge. On the other hand, the above air resistance is 700 seconds / 1.
When a separator material having a value larger than 00 ml is used, the internal short-circuit current at the time of overcharge is small, and the overcharge current does not sufficiently decrease due to the internal short-circuit, but the battery temperature rises rapidly. Furthermore, when a separator material having an air resistance after the above treatment of 50 to 700 seconds / 100 ml is used, an appropriate internal short-circuit current occurs at the time of overcharging, and an excessive temperature rise of the battery can be prevented.

The air resistance referred to in the present invention is determined by the Japanese Industrial Standards (JIS P8117-1998, hereinafter referred to as JIS).
Air resistance measured in accordance with a measuring device and a measuring method specified in the above.
When a pressure difference of 1.23 kPa is applied to the front and back of a polymer microporous membrane of 42 mm ² or a separator made of a polymer microporous membrane, the time required for 100 ml of air to pass (sec / sec)
100 ml). This value is also called the Gurley number,
The smaller the value, the easier the layer is to allow air to pass.

Further, in the second and third non-aqueous electrolyte secondary batteries of the present invention, the separator used in the second and third non-aqueous electrolyte secondary batteries is obtained by processing a polymer microporous membrane into a rectangular shape, and has three
After a heat treatment for 15 to 20 minutes in a temperature range of 100 to 120 ° C. in a state where a tensile load of 0 to 60 kg / cm ² is applied, or 120 to 140 ° C. in a state of being fixed in the width direction in the air After the heat treatment for 15 to 20 minutes in the above temperature range, the air permeability resistance measured by the method according to the JIS is 50 to 700 seconds / 100 ml. Further, the air resistance is 300 to 600 seconds /
Preferably it is 100 ml.

Even when exposed to the same high environmental temperature,
The stress applied to the separator changes the state of the heat shrinkage, and also changes the air resistance. It is difficult to accurately simulate the state of the stress applied to the separator in the electrode group when the battery is overcharged. Therefore, the present inventors set the separator as 30 to 6 in the length direction as a heating condition under which the air resistance can be measured with good reproducibility after the heating.
In a state where a tensile load of 0 kg / cm ² is applied, the temperature is maintained in the temperature range of 100 to 120 ° C. for 15 to 20 minutes, or 12 seconds with the separator fixed in the width direction.
It has been found experimentally that it is preferable to hold the solution in a temperature range of 0 to 140 ° C. for 15 to 20 minutes.

Further, as a result of examining the relationship between the air resistance of the separator after the heat treatment under the above preferable conditions and the battery temperature at the time of overcharging, the air resistance was found to be 50 to 700 seconds / 100 m.
In the case of using a separator of l, the rise in battery temperature during overcharge is suppressed, and in the case of using a separator out of the range of air permeability, the battery temperature suddenly rises during overcharge. I found it.

According to the fourth and fifth nonaqueous electrolyte secondary batteries of the present invention, the separator used is a polymer microporous membrane processed into a rectangular shape, and has a length of 30 to 60 in the longitudinal direction.
1 kg / cm ² in air with a tensile load applied
After performing a heat treatment at a temperature of 00 to 120 ° C. for 15 to 20 minutes, or in a state of being fixed in the width direction,
In the pore size distribution after a heat treatment at a temperature of 140 ° C. for 15 to 20 minutes, the 90% pore size (D ₉₀ ) is 0.05%.
A separator having a thickness of about 0.5 μm is used.

In a battery using a separator having a D ₉₀ of less than 0.05 μm after the above heat treatment, an internal short circuit is unlikely to occur at the time of overcharging, and the overcharging state further progresses, and the temperature rises excessively. Becomes The D ₉₀ of 0.5μ
In a battery using a separator larger than m, the internal short-circuit current increases at the time of overcharging, resulting in a dangerous situation. D above
_In a battery using a separator whose ₉₀ is 0.05 to 0.5 μm, an appropriate short-circuit current occurs at the time of overcharging, and the temperature rise of the battery can be effectively suppressed. Further, when D ₉₀ is 0.08 to 0.3 μm, a more excellent effect is obtained. The pore size distribution referred to here is measured by the mercury porosimeter method, and D ₉₀ is an integrated value of the area from the small pore size side to the large pore size side of the pore size distribution diagram,
The hole diameter when the integrated area becomes 90% of the total area.

In this pore size distribution, in the case of a battery using a separator having an average pore size (D ₅₀ ) of more than 0.1 μm, the internal short-circuit current at the time of overcharge increases, and conversely, the D ₅₀ becomes 0. If it is less than 01 μm, the internal short-circuit current is small, so that the overcharge state further progresses, and in any case, the battery temperature rises to a dangerous state. When the above D ₅₀ is 0.1μm 0.01 is moderate internal short circuit current is generated during overcharging of the battery, it can be effectively suppressed excessive temperature rise of the battery. The term D ₅₀ integrates the area subjected large pore diameter from a small diameter side of the pore size distribution diagram, a pore diameter at which the accumulated area reaches 50% of the total area.

As a separator material in the non-aqueous electrolyte secondary battery of the present invention, it is preferable to use an electronically insulating polymer microporous membrane having high ion permeability and appropriate mechanical strength. Specifically, such as polypropylene resin, polyethylene resin alone, or a laminate or composite of these, such as a polymer microporous membrane excellent in organic solvent resistance and affinity with the organic solvent, furthermore From the viewpoint of heat resistance, it is preferable to use a microporous film or nonwoven fabric made of an aramid resin or the like. The thickness of the separator can be usually 5 to 100 μm. Particularly, when a thin separator having a thickness of 5 to 20 μm is used, the remarkable effects of the present invention are obtained, and a high-capacity high-capacity capacitor is obtained. Can be provided. The porosity of the separator material is determined according to physical properties such as ion permeability and viscosity of the electrolyte, or mechanical properties such as the strength and elongation of the separator itself. ~
Desirably, it is 80%.

As the positive electrode material in the non-aqueous electrolyte secondary battery of the present invention, a lithium-containing transition metal oxide, for example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , L _{x
i x Co y Ni 1-y} O 2, Li x Co y M 1-y O z, Li x Ni
_{1-y M y O z,} Li x Mn 2 O 4, Li x Mn 2-y M y O 4 , etc. (M is Na, Mg, Sc, Y, Mn, Fe, Co, N
at least one selected from the group consisting of i, Cu, Zn, Al, Cr, Pb, Sb, and B, 0 ≦ x ≦ 1.2, 0 ≦ y ≦
0.9, 2.0 ≦ z ≦ 2.3) can be used.
Here, the above-mentioned x value is a value before the start of charge / discharge, and decreases by charging and increases by discharging. It is also possible to use a mixture of a plurality of different positive electrode materials. Usually, the above-mentioned positive electrode material is used in the form of a powder, and its particle size is not particularly limited, but preferably has an average particle size of 1 to 30 μm.

As the conductive agent for the positive electrode in the non-aqueous electrolyte secondary battery of the present invention, an electron conductive material which does not cause a chemical change in the charge / discharge potential of the positive electrode material, for example, natural graphite such as flake graphite, artificial graphite Such as graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc., conductive fibers such as carbon fiber and metal fiber, carbon fluoride, aluminum etc. Metal powders, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic conductive materials such as polyphenylene derivatives can be used alone or in combination. Among these conductive agents, artificial graphite and acetylene black are particularly preferred. The amount of the conductive agent is not particularly limited, but is preferably 1 to 30% by weight based on the positive electrode material.

The positive electrode binder in the non-aqueous electrolyte secondary battery of the present invention may be any of a thermoplastic resin and a thermosetting resin, for example, polyethylene (PE), polypropylene (PP), and polypropylene. Tetrafluoroethylene (P
TFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), fluorine Vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoro Propylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or its Na ion crosslinked product, ethylene-methacrylic acid copolymer or its Na ion Materials such as a cross-linked product, an ethylene-methyl acrylate copolymer or its Na ion cross-linked product, an ethylene-methyl methacrylate copolymer or its Na ion cross-linked material can be used alone or as a mixture. Among these materials, more preferred materials are PVDF and PTFE.

The material of the current collector for the positive electrode in the nonaqueous electrolyte secondary battery of the present invention may be an electronic conductor that does not cause a chemical change in the charge / discharge potential of the positive electrode material. In addition to titanium, carbon, conductive resin, and the like, aluminum or stainless steel surface-treated with carbon or titanium can be used, and aluminum or an aluminum alloy is particularly preferable. In addition, a material obtained by oxidizing the surface of each of the above materials or a material having a surface with irregularities by surface treatment can be used. As the shape of the current collector, in addition to a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foam, a fiber group, a molded article of a nonwoven fabric, or the like can be used. Is not particularly limited, but usually a particle having a thickness of 1 to 500 μm can be used.

As the material of the negative electrode in the nonaqueous electrolyte secondary battery of the present invention, in addition to a carbon material capable of reversibly storing and releasing cations such as lithium ions by charge and discharge,
Aluminum, various alloys mainly composed of aluminum, metal lithium, and various metal oxides such as SnO ₂ can be used. Further, the binder for the negative electrode may be any of a thermoplastic resin and a thermosetting resin, for example, PE, PP, PTFE, PVDF, styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, FEP, PFA, vinylidene fluoride
Hexafluoropropylene copolymer, ETFE resin, P
CTFE, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ECTFE, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoro Ethylene copolymer, ethylene-acrylic acid copolymer or its Na ion crosslinked product, ethylene-methacrylic acid copolymer or its Na ion crosslinked product, ethylene-
Materials such as a methyl acrylate copolymer or a cross-linked Na ion thereof, an ethylene-methyl methacrylate copolymer or a cross-linked Na ion material can be used alone or in combination. Among these, more preferred materials are styrene butadiene rubber, polyvinylidene fluoride, ethylene-acrylic acid copolymer or a cross-linked Na ion thereof,
An ethylene-methacrylic acid copolymer or its Na ion crosslinked product, an ethylene-methyl acrylate copolymer or its Na ion crosslinked product, an ethylene-methyl methacrylate copolymer or its Na ion crosslinked product.

The material of the current collector for the negative electrode in the nonaqueous electrolyte secondary battery of the present invention may be an electron conductive material which does not cause a chemical change in the charge / discharge potential of the negative electrode material.
For example, stainless steel, nickel, copper, titanium, carbon,
In addition to conductive resin, copper and stainless steel are converted to carbon,
Those surface-treated with nickel or titanium, those oxidized on the surface, and the like can be used. In particular, copper or a copper alloy is preferably used. In addition, it is preferable to provide an uneven portion on the surface of the current collector by surface treatment. As the shape of the current collector, other than a foil, a film, a sheet, a net, a punched one, a lath body, a porous body, a foamed body, a molded body of a fiber group, and the like are used.
Although it is not particularly limited, a material having a thickness of 1 to 500 μm is usually used.

The non-aqueous electrolyte in the non-aqueous electrolyte secondary battery of the present invention comprises a non-aqueous solvent and a lithium salt dissolved therein. As the non-aqueous solvent, for example,
Ethylene carbonate (EC), propylene carbonate
(PC), cyclic carbonates such as butylene carbonate (BC) and vinylene carbonate (VC), chains such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dipropyl carbonate (DPC) Carbonates, methyl formate, methyl acetate, methyl propionate,
Aliphatic carboxylic acid esters such as ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2
Chain ethers such as dimethoxyethane (DME), 1,2-diethoxyethane (DEE) and ethoxymethoxyethane (EME); cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; dimethyl sulfoxide; Dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone , 3-
An aprotic organic solvent such as methyl-2-oxazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, ethyl ether, 1,3-propanesultone, anisole, dimethylsulfoxide, N-methylpyrrolidone, and the like can be used. A single or a mixture of two or more of these non-aqueous solvents is used as a solvent for dissolving the lithium salt. Among them, it is preferable to use a mixed solvent of a cyclic carbonate and a chain carbonate, or a mixed solvent of a cyclic carbonate, a chain carbonate and an aliphatic carboxylic acid ester.

As the electrolyte to be dissolved in these non-aqueous solvents, for example, LiClO ⁴ , LiBF ⁴ , LiPF ⁶ , LPF
iAlCl ⁴ , LiSbF ⁶ , LiSCN, LiCl, L
iCF ³ SO ³ , LiCF ³ CO ² , Li (CF ³ SO ² )
² , LiAsF ⁶ , LiN (CF ³ SO ² ) ² , LiB ¹⁰ C
l ¹⁰ , lithium lower aliphatic carboxylate, LiCl, Li
Lithium salts such as Br, LiI, lithium chloroborane, lithium tetraphenylborate, and imides can be used alone or in combination of two or more.
It is more preferable to include iPF ^6.

A particularly preferred non-aqueous electrolyte in the present invention contains at least EC and contains LiPF as a lithium salt.
⁶ is an electrolytic solution. The amount of the nonaqueous electrolyte added to the battery is not particularly limited, but a required amount can be used depending on the amounts of the positive electrode material and the negative electrode material and the size of the battery. The amount of the lithium salt dissolved in the nonaqueous solvent is not particularly limited, but is usually 0.2 to 2 mol / l, and particularly preferably 0.5 to 1.5 mol / l.

Further, for the purpose of improving the charge / discharge characteristics, for example, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme,
It is also effective to add additives such as pyridine, hexaphosphoric acid triamide, nitrobenzene derivatives, crown ethers, quaternary ammonium salts, ethylene glycol dialkyl ether, and phosphate esters to the electrolytic solution.

As additives to the positive and negative electrode mixture, fillers, dispersants, ion conductors, pressure enhancers and the like can be used. The filler is a constituent battery
Any material that does not cause a chemical change may be used, and usually, olefin-based polymers such as polypropylene and polyethylene,
Fibers such as glass and carbon are used. The addition amount of the filler is not particularly limited, but is 0 to 30% by weight based on the electrode mixture.
It is preferred that

The present invention provides a coin type, a button type, a sheet type,
The present invention can be applied to any non-aqueous electrolyte secondary battery such as a battery of a stacked type, a cylindrical type, a flat type, a square type, and the like, and a large battery used for an electric vehicle and the like. The non-aqueous electrolyte secondary battery of the present invention is a portable information terminal, a portable electronic device, a small household power storage device,
It can be used for a motorcycle, an electric vehicle, a hybrid electric vehicle, and the like, but is not particularly limited thereto.

[0039]

EXAMPLES The present invention will be described in more detail with reference to Examples. In each of the following examples, various separators having different physical properties such as air resistance and pore size distribution after heat treatment, or different thicknesses are produced, and these separators are used to form a cylindrical separator having a structure shown in FIG. A non-aqueous electrolyte secondary battery was manufactured. The temperature change during overcharging of the produced nonaqueous electrolyte secondary batteries was measured, and the relationship between the maximum temperature reached on the battery surface and the physical properties and thickness of the separator after the heat treatment was clarified.

In FIG. 1, a positive electrode 11 and a negative electrode 12 are spirally wound via a rectangular separator 13 to form an electrode plate group. The electrode plate group is wound in a direction coinciding with the longitudinal direction of the separator 13. This electrode group is housed in a stainless steel case 14 together with a non-aqueous electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent,
The opening of the case 14 is closed via the gasket 17 to the sealing plate 1.
Sealed at 8. The sealing plate 18 is configured by stacking a stainless steel positive electrode terminal plate 19 and a stainless steel back cover 16, and the back cover 16 and the positive electrode 11 are connected by spot welding via a lead piece 20. The electrode plate group and the inner bottom surface of the case 14 are insulated by an insulating plate 15 made of polypropylene. The outermost peripheral portion of the electrode plate group is a negative electrode 12.
Is connected to the case 14. In the case of a commercially available cylindrical nonaqueous electrolyte secondary battery, a safety element such as a safety valve or a PTC element is incorporated between the positive electrode terminal plate of the sealing plate and the back plate. For the purpose of sex evaluation,
These safety elements are not incorporated in the sealing plate 18.

The positive electrode 11 is made of lithium cobalt oxide powder 85
% By weight, 10% by weight of carbon powder of conductive agent and P of binder
5% by weight of VDF resin was mixed and these were dehydrated N-
A slurry was prepared by dispersing in 2-methylpyrrolidone (dehydrated NMP), applied to a positive electrode current collector made of aluminum foil, dried, and then rolled. Negative electrode 12
Mixes 95% by weight of artificial graphite powder as a negative electrode material and 5% by weight of a PVDF resin as a binder and dehydrates them by NMP.
To prepare a slurry, which was coated on a negative electrode current collector made of a copper foil, dried, and then rolled.

The non-aqueous electrolyte has a volume ratio of EC: PC: D
1 mol of LiPF ₆ was added to a solvent mixed at EC = 5: 1: 4.
1 / l was used. The produced cylindrical battery has a diameter of 18 mm and a height of 65 mm. While the design capacity of a normal commercial battery of this size is 1800 mAh,
In each of the batteries of the examples, the design capacity was set to 2000 mAh in order to increase the capacity compared to a commercially available battery. As a result, in the batteries of the examples, the occupied allowable volume of the separator is smaller than that of the commercially available battery.
For 5 to 27 μm, a thin separator having a thickness of less than 25 μm was used. The amount of the electrolyte of the battery in each example was 3.8 ml.
And Hereinafter, each embodiment will be specifically described.

Example 1 In this example, various microporous films of polyethylene (PE) having different physical properties were prepared, and cut into predetermined dimensions to prepare various separators. P
The microporous membrane of E was manufactured by the method described below. First, a PE resin having a weight average molecular weight of 500,000 and a PE resin having a weight average molecular weight of 50,000 were prepared, and the respective mixing ratios were 38:
Various mixed resin raw materials were produced by mixing and changing the ratio between 2: 2 and 2:38. 60 parts by weight of liquid paraffin is mixed with 40 parts by weight of the mixed resin raw material, and the mixture is melt-kneaded in a twin-screw extruder, and is extruded and cast from a coat hanger die onto a cooling roll to have a thickness of 0.9 m.
m of various polymer gel sheets were prepared. Further, the polymer gel sheet is stretched so as to have an area of 7 × 7 times using a simultaneous biaxial stretching machine, and the stretched polymer gel sheet is immersed in methylene chloride to extract and remove liquid paraffin. Change the thickness to 5-20 μm,
Nine types of microporous membranes having different mixing ratios of E resin were produced.
This is cut into dimensions of 50 mm in width and 120 mm in length, and 9
Various kinds of rectangular separators were produced. In this case, the separator was processed such that the stretching direction in the process of producing the microporous membrane coincided with the longitudinal direction of the separator.

Next, samples for evaluating physical properties were collected for each type of separator, and after heat treatment was performed on these samples, the air resistance was measured. The heat treatment was performed under any one of the following three conditions. (A) Heat the sample in air at 100 ° C. or 170 ° C. for 15 minutes. (B) The sample was placed in the longitudinal direction at 30 kg / cm ² or 60 kg / cm ^2.
Heating is performed at 100 ° C. or 120 ° C. in the atmosphere for 15 minutes while applying a tensile load of kg / cm ² . (C) The sample is heated at 120 ° C. or 140 ° C. for 15 minutes in the air, fixing both ends in the width direction so strongly that shrinkage deformation due to heating is prevented.

The air resistance was measured after the heat treatment.
The measurement was performed using a type A measuring device in a laboratory controlled at 23 ° C. in accordance with JIS. Next, the cylindrical batteries of FIG. 1 were prepared using the nine types of separators whose air permeability was not measured, and an overcharge test was performed on these nine types of batteries by the method described below. .

The battery was charged at a constant current of 1100 mA to a charging voltage of 4.2 V, and then charged at a constant current of 1100 mA.
A charge / discharge cycle of discharging to 0 V was repeated 10 times. The discharge capacity at the tenth cycle is defined as the initial capacity of the battery. Thereafter, the battery was charged to a charging voltage of 4.2 V by 1100.
The battery was charged at a constant current of mA and further overcharged for 3 hours at a constant current of 1800 mA. The surface temperature of the battery during the overcharge process was measured, and the maximum temperature was measured.
Charging and discharging were performed in a constant temperature bath at 20 ° C. Tables 1 to 3 show these results. Table 1 shows test results when the above three types of heating test conditions (a) were applied.

[0047]

[Table 1]

As can be seen from Table 1, in the batteries using the separators of types 1 to 6, the maximum temperature reached on the battery surface during overcharge was suppressed to a relatively low temperature of 140 to 152 ° C. 100 ℃ or 170 ℃
Air resistance after heating at 50 to 700 seconds / 100m
It can be seen that the battery uses a separator having a physical property of 1. At the same time, if they have this property,
It can be seen that a battery with high safety can be obtained even with a separator as thin as 20 μm. On the other hand, in the batteries using the separators of types 7 to 9, the maximum attainable temperature of the battery surface was abnormally high at 200 ° C. or higher, and the air permeability resistance after the heat treatment was 50 seconds / 100 ml. Or a separator using a separator exceeding 700 seconds / 100 ml. Table 2 shows test results when the above-mentioned heating test condition (b) was applied.

[0049]

[Table 2]

From Table 2, it can be seen that in the batteries using the separators of types 1 to 6, the maximum attainable temperature of the battery surface during overcharge was suppressed to a relatively low temperature of 140 to 151 ° C. , In each case, 30kg /
A battery using a separator having physical properties of 50 to 700 seconds / 100 ml after being heated at 100 ° C. or 120 ° C. in the air under a tensile load of cm ² or 60 kg / cm ^2. You can see that there is. At the same time, it can be seen that a battery with high safety can be obtained even if a separator as thin as 5 to 20 μm is used if it has these properties. On the other hand, in the batteries using separators of types 7 to 9, the maximum temperature reached on the battery surface was 200
° C or more, which are abnormally high, and all of them have an air resistance after heat treatment of less than 50 seconds / 100 ml or 700
It is a battery using a separator exceeding 100 seconds / 100 ml. Table 3 shows test results when (c) among the above-mentioned heating test conditions was applied.

[0051]

[Table 3]

As shown in Table 3, in the batteries using the separators of types 1 to 6, the maximum temperature reached on the battery surface during overcharge was suppressed to a relatively low temperature of 140 to 153 ° C. , Fixed in the width direction
It can be seen that the battery uses a separator having physical properties such that the air resistance after heating at 0 ° C. or 140 ° C. for 15 minutes is 50 to 700 seconds / 100 ml. At the same time,
It can be seen that a battery with high safety can be obtained even if a separator as thin as 5 to 20 μm is used if it has these properties. On the other hand, in batteries using separators of types 7 to 9,
In any case, the maximum temperature reached on the battery surface was abnormally high at 200 ° C. or higher, and all of them had air permeability resistance after heat treatment of less than 50 seconds / 100 ml or 700 seconds / 100 ml.
This is a battery using a separator having a capacity of more than 100 ml.

Example 2 In this example, nine types of separators were produced in the same manner as in Example 1. Samples collected from each type of separator were subjected to the heat treatment under the above-mentioned heat treatment conditions (2) or (3), and the pore size distribution was measured by a mercury porosimeter method, and the 90% pore size (D
₉₀ ) asked. Thereafter, using the respective types of separators, batteries similar to those in Example 1 were manufactured, and these batteries were subjected to an overcharge test in exactly the same manner as in Example 1.
Table 4 shows the test results when (b) among the above-mentioned heating test conditions is applied, and Table 5 shows the test results when (c) is applied.

[0054]

[Table 4]

[0055]

[Table 5]

As shown in Tables 4 and 5, for the batteries of types 1 to 6, the maximum temperature reached on the battery surface during overcharge was 1
The temperature is controlled to a relatively low temperature of 52 ° C. or less, and these are all 30 kg / cm ² or 6 kg in the longitudinal direction.
100 ° C. under a tensile load of 0 kg / cm ²
Or after heating at 120 ° C., or after heating at 120 ° C. or 140 ° C. for 15 minutes with fixing in the width direction.
₉₀ indicates that the battery uses a separator having physical properties of 0.05 to 0.5 μm. At the same time, it can be seen that a battery with high safety can be obtained even if a separator as thin as 5 to 20 μm is used if it has the above physical properties.
On the other hand, in all of the batteries of types 7 to 9, the maximum attained temperature of the battery surface is abnormally high at 200 ° C. or higher, and all of them have a D ₉₀ after the heat treatment of less than 0.05 μm, or
This is a battery using a separator exceeding 0.5 μm.

Example 3 In this example, 13 types of separators and batteries using these were produced and evaluated in the same manner as in Example 1. On the other hand, the samples collected from each type of separator were subjected to heat treatment under two types of heat treatment conditions in the same manner as in Example 2, and the pore size distribution was measured.
To obtain an average pore diameter (D _50). Table 6 shows the test results when (b) among the above-mentioned heating test conditions, and Table 7 shows the test results when (c) was applied.

[0058]

[Table 6]

[0059]

[Table 7]

As shown in Tables 6 and 7, in the batteries using the types 10 to 13 separators, the maximum temperature reached on the battery surface during overcharge was suppressed to a relatively low temperature of about 150 ° C. Is 30k in the length direction
After heating at 100 ° C. or 120 ° C. while applying a tensile load of g / cm ² or 60 kg / cm ² , or after heating at 120 ° C. or 140 ° C. for 15 minutes while fixing in the width direction, the D ₅₀ is It can be seen that the battery uses a separator having physical properties of 0.01 to 0.1 μm.
At the same time, it can be seen that a battery with high safety can be obtained even if a separator as thin as 5 to 20 μm is used if it has the above physical properties. On the other hand, in the case of batteries using separators of types 7 to 9, the maximum temperature reached 20
Abnormally high at 0 ° C. or higher, all of these are batteries using a separator having a D ₅₀ after heat treatment of less than 0.01 μm or more than 0.1 μm. In Examples 1 to 3,
In each case, the heat treatment time was set to 15 minutes. Even when the heat treatment time was set to 20 minutes, it was confirmed that the air permeability resistance of the same sample after the heat treatment showed the same value. The processing time is preferably 15 to 20 minutes.

[0061]

According to the present invention, a high-capacity non-aqueous electrolyte secondary battery excellent in safety which can effectively suppress a rise in temperature during overcharge even when a thin separator is used. Can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a cylindrical nonaqueous electrolyte secondary battery manufactured in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Positive electrode 12 Negative electrode 13 Separator 14 Case 15 Insulating plate 16 Back cover 17 Gasket 18 Sealing plate 19 Positive electrode terminal plate 20 Lead piece

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 6, 2001 (2001.3.6)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0002

[Correction method] Change

[Correction contents]

[0002]

BACKGROUND ART Nonaqueous electrolyte secondary battery using lithium as the negative electrode active material (lithium secondary battery), the high energy density, to a built-in combustibles, for example, abnormality such as overcharge or external short circuit A high degree of safety is required even in various usage situations. To cope with this, many safety measures have been devised.These measures include the method of incorporating safety devices in the battery container, power pack, or equipment, and the overcharging resistance of the power generation element itself of the battery. It is roughly divided into the method of giving.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction contents]

As the electrolyte to be dissolved in these non-aqueous solvents, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LPF
iAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, L
iCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ S
O ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB
₁₀ Cl ₁₀ , lithium lower aliphatic carboxylate, LiCl,
LiBr, LiI, lithium salts such as lithium chloroborane, lithium tetraphenylborate, imides, and the like can be used alone or in combination of two or more. In particular, it is more preferable to include LiPF ₆ .

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction contents]

A particularly preferred non-aqueous electrolyte in the present invention contains at least EC and contains LiPF as a lithium salt.
₆ is an electrolytic solution. The amount of the nonaqueous electrolyte added to the battery is not particularly limited, but a required amount can be used depending on the amounts of the positive electrode material and the negative electrode material and the size of the battery. The amount of the lithium salt dissolved in the nonaqueous solvent is not particularly limited, but is usually 0.2 to 2 mol / l, and particularly preferably 0.5 to 1.5 mol / l.

Continued on the front page (72) Inventor Yoshiaki Nitta 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Inventor Shozo Takahashi 1006 Kazuma, Kazuma, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. EE02 EE04 HH00 HH03 HH06 5H029 AJ12 AK03 AK18 AL02 AL11 AL12 AM02 AM03 AM04 AM05 AM07 CJ01 CJ02 CJ28 DJ04 DJ13 EJ12 HJ00 HJ04 HJ06 HJ14

Claims (9)

[Claims] 1. A separator comprising a positive electrode, a negative electrode, a non-aqueous electrolyte containing a lithium salt, and a microporous polymer membrane,
After the polymer microporous membrane has been subjected to a heat treatment in the atmosphere at a temperature of 100 to 170 ° C. for 15 to 20 minutes,
A nonaqueous electrolyte secondary battery having an air resistance of 0 to 700 sec / 100 ml. 2. A positive electrode, a negative electrode, a nonaqueous electrolyte containing a lithium salt, and a rectangular separator composed of a microporous polymer membrane, wherein the microporous polymer membrane has a length of 30 to 60 in the longitudinal direction.
After being subjected to a heat treatment in a temperature range of 100 to 120 ° C. for 15 to 20 minutes in a state where a tensile load of kg / cm ² is applied, it has an air resistance of 50 to 700 seconds / 100 ml. Non-aqueous electrolyte secondary battery characterized by the above-mentioned. 3. A positive electrode, a negative electrode, a non-aqueous electrolyte containing a lithium salt, and a rectangular separator composed of a polymer microporous membrane, wherein the polymer microporous membrane is fixed in the width direction, and After being subjected to a heat treatment for 15 to 20 minutes in a temperature range of １４０140 ° C., 50 to 700 seconds / 100 ml
A non-aqueous electrolyte secondary battery characterized by having a degree of air resistance. 4. A rectangular separator comprising a positive electrode, a negative electrode, a non-aqueous electrolyte containing a lithium salt, and a microporous polymer membrane, wherein the microporous polymer membrane has a length of 30 to 60 in the longitudinal direction.
After applying a heat treatment for 15 to 20 minutes in a temperature range of 100 to 120 ° C. in the atmosphere under a tensile load of kg / cm ² , the 90% pore diameter (D ₉₀ ) is 0.05 to 0.05%.
A non-aqueous electrolyte secondary battery having a pore size distribution of 0.5 μm. 5. A positive electrode, a negative electrode, a nonaqueous electrolyte containing a lithium salt, and a rectangular separator composed of a polymer microporous membrane, wherein the polymer microporous membrane is fixed in the width direction and has a thickness of 120 μm in air. after having been subjected to heat treatment in 15 to 20 minutes at a temperature range of to 140 ° C., 90% pore diameter (D ₉₀₎ is 0.0
A non-aqueous electrolyte secondary battery having a pore size distribution of 5 to 0.5 μm. 6. The non-aqueous electrolyte secondary battery according to claim 4, wherein an average pore size (D ₅₀ ) in the pore size distribution is 0.01 to 0.1 μm. 7. The non-aqueous electrolyte solution according to claim 1, wherein the polymer microporous membrane is made of at least one selected from the group consisting of a polypropylene resin, a polyethylene resin, and an aramid resin. Next battery. 8. The polymer microporous membrane according to claim 1, wherein the polymer microporous membrane is formed by laminating two or more resin layers selected from the group consisting of a polypropylene resin, a polyethylene resin, and an aramid resin. 3. The non-aqueous electrolyte secondary battery according to 1. 9. The non-aqueous electrolyte secondary battery according to claim 1, wherein said separator has a thickness of 5 to 20 μm.