JP2003223933A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery, which is prevented from thermal runaway at the time of overcharging, and is improved in safety. <P>SOLUTION: A power generation element 2 is created by winding a positive- electrode plate and a negative-electrode plate through a separator with a shutdown function which consists of fine porous membrane of a thermoplastic resin. The power generation element 2 is stored in a thermally shrinkable tube 11 which thermally shrinks at the temperature lower than a shutdown temperature of the separator, and is sealed together with the electrolyte in the metal-laminate resin-film case 6. By this, even if gas is generated inside the power generation element 2 at the time of overcharging, shutdown of the separator occurs quickly and uniformly and the safety of the battery can be improved by preventing the gas from being accumulated in the power generation element 2 to form air bubbles, by preventing electric current concentration and by making the electrode plate, a heating element, and the separator closely adhered. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In a non-aqueous electrolyte secondary battery such as a lithium-ion battery, its power generating element is generally laminated with a positive electrode plate and a negative electrode plate via a separator, and the power generating element is bound by an adhesive tape or the like. It is enclosed in a battery case together with a non-aqueous electrolyte. In order to prevent the internal temperature of the battery from rising due to overcharging or short-circuiting, and the non-aqueous electrolyte in the battery may gush out, the separator is equipped with a shutdown function. Has been.
The separator having this shutdown function is, for example, one in which a thermoplastic resin film is provided with a large number of fine pores, and by closing the fine pores at a predetermined temperature, the ions passing through the separator are blocked, and thus non-aqueous. The current of the electrolyte secondary battery is cut off.

[0003]

However, the adhesive tape or the like for binding the power generating elements is to prevent the electrode plate and the separator from coming apart, so that the space between the adjacent electrode plates does not become wide. It does not compress. Therefore, during overcharging or the like, when gas is generated inside the power generation element as the charging progresses, the gap between the electrode plates may partially widen and bubbles may accumulate. In this case, since the current does not flow in the portion where the bubbles are accumulated, the charging current is concentrated in the portion where the bubbles are not accumulated, and the partial temperature rise becomes large. As described above, when the temperature rise is large, there is a case where the temperature keeps rising even after the separator is shut down and the positive electrode plate and the negative electrode plate are short-circuited, and further heat generation occurs, which results in thermal escape. .

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery which prevents heat escape and is excellent in safety.

[0005]

As means for achieving the above object, the invention of claim 1 is a power generating element constructed by laminating a positive electrode plate and a negative electrode plate with a thermoplastic resin separator interposed therebetween. And a non-aqueous electrolyte secondary battery in which a non-aqueous electrolyte is housed in a battery case. It is characterized by being compressed.

According to a second aspect of the present invention, in the first aspect, the heat-responsive body is a heat-shrinkable tube made of a heat-shrinkable resin film that shrinks by heat, and the power generating element is inside the heat-shrinkable tube. It is characterized in that it is housed in the battery case in a state of being housed in.

According to a third aspect of the present invention, in the second aspect, the power generating element is formed by winding the positive electrode plate and the negative electrode plate with the separator interposed therebetween, and
A non-aqueous electrolyte secondary battery in which the power-generating element is housed in the heat-shrinkable tube along a direction parallel to the winding surface of the power-generating element, wherein the heat-shrinkable tube has a through hole. However, it has a feature.

According to a fourth aspect of the present invention, in the first aspect, the battery case is made of a flexible resin film, and the heat-responsive body shrinks by heat. And is characterized in that the battery case is housed in the heat shrink tube with the power generating element housed therein.

[0009]

<Invention of Claim 1><Invention of Claim 1> According to the invention of Claim 1, the heat responsive body is deformed by receiving heat, and the power generating element provided with the positive electrode plate and the negative electrode plate is arranged in the stacking direction. It is designed to be compressed. Therefore, when the temperature rises, by compressing the power generation element in the stacking direction, it is possible to prevent gas from forming bubbles as gas between the positive electrode plate and the negative electrode plate forming the power generation element. Thereby, current concentration due to bubbles between the positive electrode plate and the negative electrode plate is prevented and a partial temperature rise is not caused, so that the safety of the battery can be improved.

<Invention of Claim 2> Furthermore, in the invention of Claim 2, the heat-responsive body is composed of a heat-shrinkable tube made of a heat-shrinkable resin film, and the power-generating element is housed therein. Thus, the non-aqueous electrolyte secondary battery according to the present invention can be manufactured with a simple structure. Further, since the heat-shrinkable tube has a tubular shape, the power generating element can be compressed over the entire circumference thereof, and bubbles can be prevented from accumulating between the electrode plates over the entire circumference of the power generating element.

<Invention of Claim 3> In particular, according to the invention of Claim 3, the heat-shrinkable tube is provided with a through hole.
Thus, the power generating element is wound and configured, and is housed in the heat-shrinkable tube along a direction parallel to the winding surface, so that the winding surface of the power-generating element is covered with the heat-shrinkable tube. Even in the secondary battery, the electrolytic solution can easily penetrate into the power generating element through the through hole.

<Invention of Claim 4> According to the invention of Claim 4, the power-generating element housed in the heat-shrinkable tube is housed in the battery case made of a flexible resin film. Therefore, it suffices to provide the heat-shrinkable tube on the outside of the battery case made of the conventional resin film, which facilitates the design and manufacture.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment> FIG. 1 shows a laminated non-aqueous electrolyte secondary battery 1 according to a first embodiment of the present invention as claimed in claim 2 (hereinafter, referred to as a laminated battery 1).
Is omitted). This laminated battery 1
Is configured by accommodating the elliptical vortex-shaped power generating element 2 together with an electrolytic solution (not shown) as a non-aqueous electrolyte in a metal laminated resin film case 6 as a battery case.

The power generating element 2 includes a positive electrode plate, a separator, a negative electrode plate, and a separator (not shown) wound in this order, and the tape 1
It is configured to be wound at 0. Both the positive electrode plate and the negative electrode plate are made of a metal collector having a mixture layer formed thereon, the collector at the winding start end of the positive electrode plate is exposed and the positive electrode terminal 7 is welded, and the winding start end of the negative electrode plate is formed. The current collector of the part is exposed and the negative electrode terminal 8 is welded. The tape 10 is made by coating an adhesive on one side of a resin film such as polypropylene, and the metal-laminated resin film case 6 is made by laminating a flexible resin film such as polypropylene on a metal foil such as aluminum. It is sealed to form a bag.

Further, the power generating element 2 is housed in a heat shrinkable tube 11 which is a heat responding body, and the outer peripheral surface thereof is covered with the heat shrinkable tube 11. The heat-shrinkable tube 11 receives heat to shrink and compress the power generating element 2 from the outer peripheral surface thereof toward the center of the winding axis, that is, along the stacking direction of the power generating element 2.

The power generating element 2 is a heat shrinkable tube 11
The metal laminated resin film case 6 is accommodated in the metal laminated resin film case 6 so that its opening surface and the winding axis center of the power generating element 2 are substantially vertical, and the opening of the metal laminated resin film case 6 is welded to the positive electrode. And the negative electrode terminals 7 and 8
Is fixed and the laminated battery 1 is sealed.

Here, the separator is a microporous film of a thermoplastic resin, and the micropores are closed at the shutdown temperature. The thermoplastic resin used as the separator may be polyethylene, polypropylene, or the like, and polyethylene is preferably used because of its shutdown temperature and stability with respect to the electrolytic solution.

The heat-shrinkable tube 11 is made of a heat-shrinkable resin film. The heat-shrinkable resin film is made of a thermoplastic resin such as a polyolefin resin obtained by polymerizing ethylene or propylene, or a copolymer of ethylene and acrylic acid or methacrylic acid. Ionomer resin crosslinked with metal ions,
Polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, polystyrene, and fluororesins such as tetrafluoroethylene and vinylidene fluoride can be used alone or in admixture.

The heat-shrinkable tube 11 is formed by forming the above-mentioned thermoplastic resin into a tube shape and then cross-linking it with an electron beam or the like.
It can be formed by expanding the tube diameter. The temperature at which the gas is generated has a certain range depending on conditions such as the type of the separator and the charging current, but it is considered that the temperature is at least lower than the shutdown temperature of the separator. Therefore, the heat shrinkable tube 11 starts shrinking due to heat. In order to prevent heat escape, the temperature is preferably at or below the temperature at which the electrolytic solution decomposes to generate gas, and at least below the shutdown temperature of the separator. As a result, before the shutdown of the separator begins, the heat-shrinkable tube 11 can surely shrink to compress the power-generating element 2, prevent air bubbles from accumulating in the power-generating element 2, and serve as a heat-generating electrode plate. Adhering the separators to each other promotes uniform shutdown of the separators, thereby preventing heat escape. Ethylene propylene rubber, which is a polyolefin-based resin, is preferably used for the heat-shrinkable tube 11 in terms of the temperature at which the heat-shrinkage starts and the stability with respect to the electrolytic solution.

The heat shrinkage rate of the heat shrinkable tube 11 in the circumferential direction is preferably 40% or more. This is because if the heat shrinkage rate is less than 40%, the tension for compressing the power generation element 2 is insufficient and it is impossible to prevent bubbles from accumulating inside the power generation element 2. The heat shrinkage is represented by K in the following equation, where L _{0 is} the length of the film before heating and L ₁ is the length of the film after heating. K [%] = (L ₀ −L ₁ ) / L ₀ × 100

The thickness of the heat shrinkable tube 11 is 10
It is desirable that the thickness is 0 μm or more and 500 μm or less. Its thickness is 10
This is because when it is 0 μm or less, the force for compressing the power generation element 2 becomes small as in the case where the heat shrinkage rate is low. Also,
If the thickness is 500 μm or more, it is not preferable because the heat shrinkable tube 11 is difficult to handle during manufacturing and the volume energy density of the battery is lowered.

The Young's modulus of the heat-shrinkable tube 11 is
In the heating state (shutdown temperature of the separator), 5 MPa or more and 40 MPa or less is desirable. This is because when the Young's modulus in the heated state is 5 MPa or less, the tension of the heat-shrinkable tube 11 becomes small even if the heat-shrinkage rate is large. On the other hand, when the Young's modulus is 40 MPa or more, the heat-shrinkable tube 11 is hard, so the compression of the power generation element 2 is not uniform, and bubbles may accumulate in a portion where the pressure is low, which is not desirable.

<Second Embodiment> FIG. 2 is an exploded view of a prismatic nonaqueous electrolyte secondary battery 21 (hereinafter abbreviated as prismatic battery 21) according to a second embodiment of the present invention as claimed in claim 3. It is a perspective view. This prismatic battery 21 is different from the laminated battery 1 according to the first embodiment in a battery case 26. With respect to the same configuration as that of the above-described embodiment, duplicated description of the structure, operation and effect will be omitted.

The prismatic battery 21 is an elliptical spiral power generating element 22.
Is housed in a rectangular parallelepiped battery case 26 made of aluminum or the like together with the electrolytic solution, and the battery case 26 is also sealed by caulking or the like with a case lid 29 also made of aluminum or the like.

The power generating element 22 is housed in a heat shrink tube 31 which is a heat responsive body along the longitudinal direction of the winding surface thereof, and the heat shrink tube 31 is provided with a number of through holes 34. The electrolytic solution penetrates the power generation element 22 through the through holes 34.

A positive electrode lead 27 is welded to the end of winding of the positive electrode plate 23, and one end of the positive electrode lead 27 is
It is welded to a positive electrode terminal 32 provided on the case lid 29. Thereby, the positive electrode plate 23 is electrically connected to the positive electrode terminal 32. Similarly, one end of the negative electrode lead 28 is welded to the case lid 29 so that the negative electrode plate 24 is attached to the case lid 2.
9 is electrically connected. The positive electrode terminal 32 is insulated from the case lid 29 by a gasket (not shown).

Further, a safety valve 30 is provided on the case lid 29, and when the battery temperature rises and the internal pressure rises,
The electrolytic solution inside and the gas generated by its decomposition are discharged to the outside. Further, the battery case 26 is provided with a liquid injection port 33 on its side surface, and the power generation element 2 is housed in the battery case 26 and a case lid 29 is attached, and then an electrolytic solution is injected into the battery case 26. It can then be sealed.

[0028]

[Example] 1. Preparation of Sample Battery <Example 1> The laminated battery 1 according to the first embodiment was prepared. The positive electrode plate was produced by forming a positive electrode material mixture layer on both surfaces of a current collector made of aluminum foil by a known method using lithium cobalt oxide as a positive electrode active material. Further, the positive electrode plate had a positive electrode current collector at one end exposed, and the positive electrode terminal 7 made of aluminum pieces was welded to the positive electrode current collector. The negative electrode plate is
A negative electrode mixture layer was formed on both surfaces of a collector made of copper foil by a known method using graphite as a negative electrode active material. A negative electrode terminal 8 made of a copper piece was welded to one end of the negative electrode plate in the same manner as the positive electrode plate. As the separator, a microporous membrane obtained by subjecting polyethylene to microporation was used. The shutdown temperature of the separator used was 120 ° C. As the non-aqueous electrolyte, a mixed solution containing 1 mol / l of LiPF ₆ and ethylene carbonate and diethyl carbonate = 1: 1 was used.

The heat-shrinkable tube 11 was made of ethylene propylene rubber, had a heat-shrinkage start temperature of 50 ° C. lower than the shutdown temperature of the separator, and had a Young's modulus of 10 MPa at that temperature. The heat shrinkage rate of the heat shrinkable tube 11 is 50% in the circumferential direction, and the thickness is 5
The one having a diameter of 00 μm was used.

The laminated battery 1 was assembled as follows. After the power generating element 2 was housed in the heat shrinkable tube 11, the power generating element 2 was housed in the metal laminated resin film case 6. After that, the power generation element was sufficiently wetted, and an amount of electrolyte that was not excessive was poured. The laminated battery 1 into which the electrolytic solution was injected was precharged at a constant current of 400 mA for 30 minutes, and then sealed and welded to produce a laminated battery 1 having a nominal capacity of 1000 mAh.

Comparative Example 1 A laminate type battery 1 was produced in the same manner as in Example 1 except that the heat shrinkable tube 11 covering the power generating element 2 was not provided.

Example 2 In Example 2, the prismatic battery 21 according to the second embodiment shown in FIG. 2 was manufactured. Positive plate 2
3, the negative electrode plate 24 and the separator 25 were manufactured in the same manner as in Example 1.

As the heat-shrinkable tube 31, the same one made of ethylene propylene rubber as in Example 1 was used. Further, the heat-shrinkable tube 31 was provided with a circular through hole 34 having a diameter of 3 mm. The ratio of the total area of all the through holes 34 to the total area of the heat shrinkable tube 31 was 30%.

The power generating element 22 is attached to the heat shrinkable tube 3
Then, it was housed in the battery case 26, and the rectangular battery 21 was assembled by a known method in the same manner as in Example 1.

<Comparative Example 2> A prismatic battery 21 was produced in the same manner as in Example 2 except that the heat shrinkable tube 31 covering the power generating element 22 was not provided.

2. Test method Three laminated batteries 1 each of Example 1 and Comparative Example 1, and three prismatic batteries 21 of Example 2 and Comparative Example 2
Each battery was manufactured individually and subjected to an overcharge test in a constant temperature bath at 25 ° C. Overcharge test is 10V at a constant current of 1A
Was charged, the temperature inside the power generation element 2 was measured, and the presence or absence of heat escape was observed.

3. Results and Discussion <Laminated battery> The results of performing the overcharge test on the laminated battery 1 of Example 1 and Comparative Example 1 are shown below. The graphs of FIG. 3 and FIG. 4 are graphs showing changes in internal temperature with respect to the charging current amount of the laminated battery 1. FIG. 3 shows changes in the internal temperature of the laminated battery 1 in Example 1 provided with the heat-shrinkable tube, and FIG. 4 shows changes in the internal temperature of the laminated battery 1 in Comparative Example 1 not provided with the heat-shrinkable tube. Both FIG. 3 and FIG. 4 show the measured values of one battery. Table 1 shows the number of batteries that did not cause heat escape and the number of batteries that did not cause heat escape among the laminated batteries 1 of Example 1 and Comparative Example 1.

[0038]

[Table 1]

Approximately 4000 mA in both Example 1 and Comparative Example 1.
At the time of charging for h, the voltage between terminals reached 10 V and heat was generated. At that time, as shown in FIG. 1, the temperature inside the battery of Example 1 rises to about 100 ° C., while the temperature inside the battery of Comparative Example 1 rises to about 400 ° C. as shown in FIG. I arrived. In addition, all three of the batteries of Example 1 did not reach heat escape, whereas all three of the batteries of Comparative Example 1 reached heat escape.

As described above, by accommodating the power generating element 2 in the heat shrinkable tube 11, it is possible to prevent heat escape and improve the safety of the battery at the time of overcharging. This is to prevent the gas from accumulating in the power generating element 2 and forming bubbles even if the gas is generated in the power generating element 2 during overcharging, preventing current concentration and also being a heat generating electrode plate. It is thought that this is because the separators were brought into close contact with each other and the separators were shut down quickly and uniformly.

Also, when the temperature of the battery rises due to a cause other than overcharging, the heat-shrinkable tube 11 keeps the power generating element 2
It is considered that the deformation of the power generation element 2 can be prevented by compressing As a result, even when gas is generated due to decomposition of the electrolytic solution due to temperature rise, etc., it is possible to prevent short circuit between the positive electrode and the negative electrode due to deformation, and prevent thermal escape. Conceivable.

<Square Batteries> The results of the overcharge test of the prismatic batteries 21 of Example 2 and Comparative Example 2 are shown below. The number of batteries that did not lead to heat escape and the number of batteries that led to heat escape among the rectangular batteries 21 of Example 2 provided with the heat shrink tube 31 and Comparative example 2 not provided with the heat shrink tube 31 are shown. 2 shows.

[0043]

[Table 2]

The prismatic batteries 21 provided with the heat-shrinkable tube 31 in Example 2 did not all escape heat, whereas the prismatic batteries 21 not provided with the heat-shrinkable tube 31 in Comparative Example 2 were three batteries. Of these, two batteries had heat escape.

Therefore, the power generation element 2 is the same as in the first embodiment.
Since the heat-shrinkable tube 31 was housed in the heat-shrinkable tube 31, it was possible to prevent heat escape and improve the safety of the battery.

<Other Embodiments> The present invention is not limited to the embodiments described above and the drawings. For example, the following embodiments are also included in the technical scope of the present invention. In addition to the above, various modifications can be made without departing from the scope of the invention.

(1) In the first embodiment, the power generating element 2 is used.
Is housed in the heat-shrinkable tube 11 and then housed in the metal laminated resin film case 6.
The position of is not limited to this. The metal-laminated resin film case 6 accommodating the power generation element 2 can be accommodated in the heat-shrinkable tube 11 to form a laminated non-aqueous electrolyte secondary battery. This embodiment corresponds to the invention of claim 4. Further, the film case itself can be configured by a heat responsive body such as a heat shrink film.

(2) In the second embodiment, the negative electrode plate 24
Although the negative electrode lead 28 connected to the case is welded to the case lid 29 to electrically connect the negative electrode plate 24 to the outside, the method of connecting the negative electrode plate 24 is not limited to this. For example, the negative electrode plate 24 and the battery case 26 can be brought into contact with each other through the through hole 34 provided in the heat shrinkable tube 31, and the negative electrode plate 24 can be electrically connected to the outside.

In this case, when the battery temperature rises, the heat shrinkable tube 31 shrinks, and the power generating element 22 is compressed and becomes smaller. Therefore, the power generation element 22 separates from the battery case 26, and the connection between the external circuit and the power generation element 22 is cut off.
As a result, charging / discharging of the non-aqueous electrolyte secondary battery is stopped, and the safety of the battery can be improved. The positive electrode plate 2
It is also possible to connect 3 to the outside by contact.

(3) In the above embodiment, the shape of the heat responsive body is a tube, but the shape of the heat responsive body is not limited to this. For example, a method of accommodating the power generation elements 2 and 22 in a bag-shaped heat-shrinkable resin film, a method of winding using a strip-shaped heat-shrinkable resin film having the same width as that of the power generation elements 2 and 22, and a thin tape-shaped heat The shrinkable resin film may be spirally wound around the power generating elements 2 and 22. Alternatively, a mesh-shaped or string-shaped material can be used.

(4) In the above embodiment, the heat-shrinkable tubes 11 and 3 made of a heat-shrinkable resin film are used as the heat responders.
However, the material of the heat responsive body is not limited to this. For example, it is possible to compress the power generating elements 2 and 22 by using a spiral shape memory alloy, a bimetal, or the like, the diameter of which becomes smaller as the temperature rises. The heat shrinkage start temperature in this case is the temperature at which the spiral thermal responsive body made of a shape memory alloy, a bimetal, or the like begins to tighten the power generating element.

(5) In the above embodiment, an example in which a non-aqueous electrolytic solution in which an electrolyte salt is dissolved in a non-aqueous solvent is used as the non-aqueous electrolyte is shown, but the form of the non-aqueous electrolyte is not limited to this. For example, the present invention can be applied to a non-aqueous electrolyte secondary battery in which a solid electrolyte and an electrolytic solution are used together, a solid electrolyte is used between electrode plates, and an active material layer is impregnated with the electrolytic solution. In that case, the solid electrolyte can be used in combination with the separator 25. A known solid electrolyte can be used as the solid electrolyte, and an inorganic solid electrolyte or a polymer solid electrolyte can be used. In particular, a porous polymer solid electrolyte can be preferably applied.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a laminated non-aqueous electrolyte secondary battery according to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view of a prismatic non-aqueous electrolyte secondary battery according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a change in battery temperature with respect to a charging current amount of the laminated battery of Example 1 in an overcharge test.

FIG. 4 is a diagram showing a change in battery temperature with respect to a charging current amount of a laminated battery of Comparative Example 1 in an overcharge test.

[Explanation of symbols]

2 ... Power generation element 6 ... Metal laminated resin film case 11 ... Heat shrink tube

Claims (4)

[Claims] 1. A non-aqueous electrolyte secondary battery in which a power generating element formed by laminating a positive electrode plate and a negative electrode plate via a thermoplastic resin separator and a non-aqueous electrolyte are housed in a battery case. A non-aqueous electrolyte secondary battery, wherein the power generating element is compressed along the stacking direction thereof by a heat responsive body that receives heat and deforms when the temperature of the power generating element is increased. 2. The heat-responsive body is a heat-shrinkable tube made of a heat-shrinkable resin film that shrinks due to heat, and the power generation element is housed in the battery case while being housed in the heat-shrinkable tube. Claim 1 characterized by the above.
The non-aqueous electrolyte secondary battery described. 3. The power generating element is configured by winding the positive electrode plate and the negative electrode plate with the separator interposed therebetween, and the power generating element is arranged in a direction parallel to a winding surface of the power generating element. The non-aqueous electrolyte secondary battery housed in a heat-shrinkable tube, wherein the heat-shrinkable tube is provided with a through hole. 4. The battery case is made of a flexible resin film, and the heat-responsive body is a heat-shrinkable tube made of a heat-shrinkable resin film that shrinks by heat. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is housed in the heat-shrinkable tube in a state of housing the power generation element.