JP2014211994A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device which is capable of improving the effect of preventing leakage of a nonaqueous electrolyte inside the power storage device with a simple configuration when discharging a gas generated inside the power storage device, exhibits less reduction in capacitance, and is excellent in long-term reliability.SOLUTION: The power storage device includes exterior film materials 2 which enclose an electrode body 1 and airtightly seal it by a heat-welded part 20. The heat-welded part 20 is formed by superposing the exterior film materials 2 on each other and performing heat welding. The power storage device also includes: a porous film 3 which is interposed between the exterior film materials 2 in a part of the heat-welded part 20 and whose one end is exposed from the heat-welded part 20 toward the electrode body 1; and a hole 4 provided in the exterior film materials 2 so as to face to the porous film 3. The gas generated inside the power storage device enters the porous film 3 from the exposed one end of the porous film 3, reaches the hole 4 provided in the exterior film materials 2, and is discharged from the hole 4 to the outside of the power storage device.

Description

  The present invention relates to an electric storage device such as an electric double layer capacitor, a hybrid capacitor typified by a lithium ion capacitor, and a lithium ion battery used for various electric devices, particularly those that are externally covered with an exterior film material.

  As a conventional power storage device, for example, an electric double layer capacitor is simply configured by laminating a polarizable electrode on the positive electrode side and a polarizable electrode on the negative electrode side with a separator interposed therebetween, And it is comprised by impregnating this electrode body with a non-aqueous electrolyte. In such an electric double layer capacitor, when energization is performed for a long time at a certain voltage, gas is generated therein, and the pressure in the electric double layer capacitor is increased by the generated gas. Then, it is known that the internal stress of the generated gas causes deformation of the electrode body and the capacitance or cycle life of the electric double layer capacitor.

  Therefore, in such an electricity storage device, measures are taken to prevent the above problem by attaching a gas release valve and releasing the internal gas when the internal pressure of the electricity storage device exceeds a certain level (for example, Patent Documents). 1 (see FIG. 3).

  Patent Document 1 discloses a configuration in which an outer side of a gas release valve welded to an inner surface of an exterior film material of an electric double layer capacitor is covered with a permeable film capable of transmitting gas. In general, a porous film is used as the transmission film. Since this porous film does not permeate the non-aqueous electrolyte in the electric double layer capacitor, the non-aqueous electrolyte is prevented from leaking out together with the gas from the gas release valve. Further, the problem that the electrolyte contained in the non-aqueous electrolyte precipitates as a salt in the gas release valve, which occurs as a result of this leakage, and prevents the gas release valve from operating normally is prevented.

JP 2003-37028 A

  However, since the above porous film is generally thin, it may permeate the non-aqueous electrolyte.

  Therefore, the present invention has been made to solve the above-described problems, and its purpose is to prevent the leakage of the non-aqueous electrolyte inside the electricity storage device when releasing the gas generated inside the electricity storage device. It is an object of the present invention to provide an electricity storage device that can be improved with a simple configuration and that is excellent in long-term reliability with little decrease in capacitance.

  In order to solve the above-described problem, an electricity storage device of the present invention includes an electrode body and an exterior film material that encloses the electrode body and hermetically seals the electrode body with a heat welding portion, and the heat welding portion includes: It is an electrical storage device formed by superposing the exterior film materials on each other by thermal welding, and is interposed between the exterior film materials in a part of the thermal welding portion and has one end toward the electrode body. It is characterized by comprising a porous film exposed from the heat-welded portion and holes provided in the exterior film material so as to face the porous film.

  Moreover, it is preferable that the said porous film has an opening part larger than the said hole, and the clearance gap between the said hole and an opening part is sealed by the said heat welding part.

  Moreover, it is preferable to further provide a gas release valve that covers the hole in an airtight manner.

  Moreover, it is preferable that the said porous film consists of polytetrafluoroethylene.

  According to the present invention, the gas generated inside the electricity storage device passes through the inside of the porous film interposed between the exterior film materials along the surface direction of the porous film. And the gas which passed the inside of a porous film is discharge | released from the hole provided in an exterior film material. Therefore, this invention can lengthen the distance of a gas passage path compared with the case where gas has passed in the thickness direction in the conventional porous film with thin thickness.

  Then, when the non-aqueous electrolyte tries to pass through the porous film together with the gas, the distance of the gas passage route is long, so that the non-aqueous electrolyte cannot pass through the porous film. Therefore, this invention can improve the leakage prevention effect of the electrolyte solution which a porous film has. As a result, it is possible to provide a power storage device that eliminates the volume expansion of the power storage device and has excellent long-term reliability with little decrease in capacitance.

It is a top view of the electrical storage device which shows an example of embodiment of this invention. It is a side view of an electrical storage device showing an example of an embodiment of the present invention. It is sectional drawing which shows the XX view in FIG. FIG. 4 is a plan view around the porous film according to the embodiment of the present invention shown in FIG. 3. It is sectional drawing which shows another example of embodiment of this invention in FIG. FIG. 6 is a cross-sectional view taken along the line XX in FIG. 1 and showing another example of the embodiment of the present invention. It is a top view of embodiment of this invention shown in FIG. 6, and is a top view around a porous film. It is a top view of embodiment of this invention shown in FIG. 6, and is a top view around a porous film. 10 is a plan view showing a half of an aluminum laminate film used in the electricity storage device of Comparative Example 3. FIG. The gas discharge valve periphery used for the electrical storage device of the comparative example 3 is shown, (A) is sectional drawing, (B) is a bottom view.

  An example of the embodiment of the present invention will be described below. With reference to FIGS. 1-5, the electrical storage device in Embodiment 1 of this invention is comprised by the electrode body 1, the exterior film material 2, the porous film 3, the hole 4, and the lead terminal 5. As shown in FIG. Yes. Further, the exterior film material 2 is obtained by integrating two outer film material halves 2a and 2b and integrating them with a heat weld portion 20 formed by thermally welding the outer edge portions thereof. And the electrode body 1 and the nonaqueous electrolyte are enclosed in the exterior film material 2.

  The electrode body 1 is obtained by laminating or winding a laminate in which a positive electrode and a negative electrode are sequentially stacked via a separator. The positive electrode and the negative electrode are obtained by forming an active material layer containing a carbon material or a metal compound powder on one or both sides of a current collector made of a metal foil. This active material layer is manufactured by a known method using an electricity storage device such as a lithium ion battery or an electric double layer capacitor. For example, in the case of an active material layer for an electric double layer capacitor, polytetrafluoroethylene is added to and mixed with a mixture of activated carbon and carbon black, and then manufactured by press molding or roll molding. Moreover, you may manufacture by the method of making it the thin coating film by apply | coating after making the said mixture into a slurry form.

  A protruding exposed portion is formed at one end of the positive and negative electrode current collectors constituting the electrode body 1. The exposed portion is assembled for each of the positive electrode and the negative electrode, and the plate-like lead terminal 5 is attached to the aggregate of the exposed portion by ultrasonic welding, spot welding, or the like.

  The electrode body 1 is airtightly accommodated by the exterior film material 2 together with the non-aqueous electrolyte in a state where the lead terminal 5 is drawn out. In this embodiment, the exterior film material 2 is formed by integrating two halves 2a and 2b of the exterior film material on each outer edge portion. Moreover, in the half bodies 2a and 2b of the exterior film material, a concave portion for accommodating the electrode body 1 is press-molded in a region excluding the outer edge portion. In addition, the exterior film material 2 may be made to be overlap | superposed by bend | folding the integral object of the magnitude | size for two half bodies.

  As the exterior film material 2, an aluminum laminate film that is light and thin and excellent in gas barrier properties is suitably used. In the aluminum laminated film, a resin layer such as a polypropylene layer or a nylon layer is laminated on both sides of the aluminum layer. And the resin layer mutually integrates by heat welding by heating the outer edge part of the exterior film material 2 in the state which mutually overlap | superposed. Thus, since the inside of the electricity storage device is hermetically sealed by the heat welding part 20, the non-aqueous electrolyte and gas inside the electricity storage device will not leak to the outside.

  The porous film 3 is interposed between the halves 2a and 2b of the exterior film material in a part of the heat-welded portion 20 at the outer edge of the exterior film material 2. At this time, each interface between the half bodies 2a and 2b of the exterior film material and the porous film 3 is sealed by thermal welding. And the one end 3e of the porous film 3 is exposed from the heat welding part 20 toward the electrode body 1 inside an electrical storage device. That is, one end 3e of the porous film 3 is in a state in which it can come into contact with the nonaqueous electrolyte solution or gas inside the electricity storage device. On the other hand, the other end 3s of the porous film 3 is sealed by a heat-sealed portion having a width w1, as shown in FIG. The width w1 is, for example, 3 to 10 mm, and is not particularly limited as long as it is a width capable of hermetically sealing the electricity storage device. In addition, the position of the heat welding part 20 which provides the porous film 3 is not specifically limited.

  The exterior film material 2 is provided with one or more holes 4 at positions facing the porous film 3, and the holes 4 penetrate the exterior film material. The holes 4 are provided at a certain distance l from one end 3e of the porous film 3 toward the other end 3s. The distance l is a gas passage route and a non-aqueous electrolyte passage inhibition length, and is set to a distance at least where the nonaqueous electrolyte solution in the electricity storage device does not reach the hole 4. The shape of the hole 4 is not particularly limited, and may be circular or polygonal. Moreover, the hole 4 should just be provided in either half body 2a, 2b of an exterior film material.

  As the porous film 3, a non-woven fabric made of polytetrafluoroethylene (PTFE) can be suitably used. Specifically, an oleovent filter Htype manufactured by Japan Gore Co., Ltd. can be exemplified. Since such a porous film 3 has a large contact angle with the non-aqueous electrolyte and has air permeability, it is possible to suppress the passage of the non-aqueous electrolyte and allow only gas to pass therethrough.

  Next, the operation of the invention in Embodiment 1 of the present invention will be described. With reference to FIG. 3 and FIG. 4, the gas generated inside the electricity storage device by the charge / discharge cycle of the electricity storage device enters the porous film 3 from the exposed end 3 e of the porous film 3. And the gas which penetrate | invaded in the porous film 3 reaches | attains the hole 4 provided in the exterior film material 2, and is discharge | released from the hole 4 to the exterior of an electrical storage device. At this time, the non-aqueous electrolyte in the electricity storage device tries to enter the porous film 3 due to the internal pressure of the electricity storage device, but the distance l from the one end 3e to the hole 4 is long, so that it does not reach the hole 4 Can not. Therefore, in the conventional electricity storage device, the passage inhibition length of the non-aqueous electrolyte with respect to the porous film was restricted to several tens of μm to several hundreds of μm, which is the thickness of the porous film. A long passage inhibition length of several mm or more in the surface direction of the porous film 3 can be freely set. Therefore, the porous film 3 and the holes 4 can improve the leakage prevention effect of the non-aqueous electrolyte inside the electricity storage device with a simple configuration while releasing the gas inside the electricity storage device.

  Moreover, in Embodiment 1 of this invention, as shown in FIG. 5, it is preferable to provide the gas discharge valve 40 which airtightly covers the hole 4. The gas release valve 40 includes a valve body 46, a valve hole 47, and an elastic member 48. The valve body 46 has a cavity inside, and valve holes 47 are respectively provided on the upper and lower surfaces of the valve body 46 so as to communicate with the cavity. The elastic member housed in the cavity of the valve body 46 seals the valve hole 47 on one surface of the valve body 46. The valve body 46 is welded to the exterior film material 2a around the hole 4 by ultrasonic welding or the like. Further, the valve hole 47 sealed by the elastic member 47 communicates with the hole 4.

  In the gas release valve 40, the valve hole 47 communicating with the hole 4 is sealed with the elastic member 48, so that outside air does not enter the power storage device through the hole 4. Further, when the gas in the electricity storage device is released from the hole 4, the elastic member blocking the valve hole 47 is lifted by the gas pressure and passes through the valve hole 47. Then, the gas inside the electricity storage device is released from the gas release valve 40. As described above, the gas release valve 40 functions as a check valve. However, the gas release valve 40 is not limited to the above-described gas release valve 40 as long as it functions as a check valve. May be adopted.

  Next, Embodiment 2 of the present invention will be described with reference to FIGS. The same description as in the first embodiment will not be repeated. With reference to FIG. 6 and FIG. 7, in the electricity storage device according to the second embodiment, the porous film 3 has an opening 30 larger than the holes 4 as compared with the electricity storage device of the first embodiment. And inside the opening part 30, the heat welding part 21 by the half bodies 2a and 2b of the exterior film material is formed along the opening part 30, and the gap between the hole 4 and the opening part 30 is formed by the heat welding part 21. It is sealed. Thereby, outside air does not enter through the hole 4 from the outside of the electricity storage device.

  Referring to FIG. 7, the width w2 of the heat welding part 21 is, for example, 0.5 to 3 mm. The width W2 and the strength of thermal welding are set so that a part of the thermal welding part 21 peels when the pressure inside the electric storage device reaches a certain threshold value.

  Referring to FIG. 8, when gas is generated inside the electricity storage device and the internal pressure of the electricity storage device increases, the gas that has passed through porous film 3 peels off heat-welded portion 21. Then, the gas passes through the peeling portion of the heat welding portion 21 and is released from the hole 4 to the outside of the electricity storage device. At this time, as in the first embodiment, the porous film 3 and the holes 4 can improve the leakage prevention effect of the nonaqueous electrolytic solution inside the electricity storage device with a simple configuration while releasing the gas inside the electricity storage device. it can.

  Further, in the second embodiment, as described in the first embodiment, by providing the gas release valve 40, the outside air can enter the inside of the electricity storage device through the holes 4 even after the heat welding portion 21 is peeled off. Can be prevented.

  Next, an embodiment of the present invention will be described using an electric double layer capacitor as an electricity storage device.

1. Preparation of electrode body

1.0 g of activated carbon having a specific surface area of 1800 m ² / g, 0.1 g of ketjen black, and 0.1 g of polyvinylidene fluoride are mixed and kneaded in a mortar, and an appropriate amount of N-methyl-2-pyrrolidone is added to the mixture. An adjusted slurry was obtained. This slurry is applied to both sides or one side of a 0.05 mm thick current collector, and then dried at 120 ° C. for 2 hours to obtain 0.08 mm thick (single side coated) and 0.10 mm thick (double side coated) electrodes. A sheet was produced. And the obtained electrode sheet was shape | molded by rectangle with the defined magnitude | size, and the protrusion-shaped exposed part was provided in the end of each electrode sheet.

  Subsequently, two electrodes coated on both sides were laminated, and one side coated electrode was further laminated one by one on both ends. Then, a cellulose separator having a thickness of 0.05 mm was interposed between the electrodes to obtain an electrode body. For each of the positive electrode and the negative electrode, the protruding exposed portions of the current collector were assembled, and lead terminals made of aluminum were attached to each by ultrasonic welding. Thus, an electrode body was prepared.

2. Production of electricity storage device [Example 1]

  Two halves were prepared by pressing the recesses while leaving the outer edge portion of the rectangular aluminum laminate film, and a hole was provided in a part of the outer edge portion of one half body. Then, these two halves were overlapped, and a PTFE nonwoven fabric (Orevent filter Htype manufactured by Gore Japan) was interposed as a porous film between the halves at positions facing the holes. Moreover, the electrode body was accommodated in the internal space of the aluminum laminate film formed by abutting the concave portions of the half body, and the lead terminals were drawn out of the aluminum laminate film.

Next, 1M-triethylmethylammonium BF ₄ / propylene carbonate as a nonaqueous electrolyte was vacuum impregnated into the electrode body. And the electrode body was airtightly sealed by heat-sealing the outer edge part of the half body of the laminated | stacked aluminum laminate film, and forming a heat welding part. At this time, one end of the porous film is exposed from the heat welded portion toward the electrode body, and is in a state where it can contact the non-aqueous electrolyte. Thus, an electricity storage device of Example 1 was obtained.
[Example 2]

In the porous film, an opening larger than the hole is provided at a position opposite to the hole, and the gap between the hole and the opening is sealed with a heat welded portion. An electricity storage device was obtained.
Example 3

The electricity storage in Example 3 was performed in the same manner as in Example 1 except that a gas release valve constituted by a valve body, a valve hole, and an elastic member was attached to the aluminum laminate film by ultrasonic welding so as to cover the hole in an airtight manner. Got a device.
[Comparative Example 1]

An electricity storage device of Comparative Example 1 was obtained in the same manner as in Example 1 except that neither a hole nor a porous film was provided.
[Comparative Example 2]

An electricity storage device of Comparative Example 2 was obtained in the same manner as in Example 3 except that a polyimide nonwoven fabric was used instead of the PTFE nonwoven fabric, which was a porous film.
[Comparative Example 3]

  Referring to FIG. 9 and FIG. 10, two halves obtained by press-molding the recesses while leaving the outer edge portion on the rectangular aluminum laminate film are prepared, and no contact is made with the electrode body in the recesses of one half 2c. A hole 14 was provided at the position. Then, a PTFE nonwoven fabric 13 (Oleovent filter Htype manufactured by Japan Gore) was attached to the periphery of the hole 14 by ultrasonic welding so as to close the hole 14 from the recessed side 2r of the half 2c. Further, the same gas release valve 50 as in Example 3 was attached to the aluminum laminate film by ultrasonic welding so that the hole 14 was airtightly covered from the convex side 2f of the half body 2c. Thereafter, the half body 2c is overlapped with another half body, the electrode body is accommodated in the internal space of the aluminum laminate film formed by abutting the concave portion of the half body, and the lead terminals are drawn out of the aluminum laminate film. . And the subsequent process was carried out similarly to Example 1, and obtained the electrical storage device of the comparative example 3.

3. Evaluation test

  The electricity storage devices of Examples 1 to 3 and Comparative Examples 1 to 3 prepared as described above were placed in a thermostat set to 60 ° C., and a voltage of 2.7 V was applied to each electricity storage device.

  Table 1 shows the changes in capacitance after 100 hours and 300 hours of voltage application to the electricity storage devices of Examples 1 to 3 and Comparative Examples 1 to 3. The change in capacitance was evaluated with the initial value of capacitance before voltage application being 100.

  Referring to Table 1, when comparing the electricity storage device of Example 1 and the electricity storage device of Comparative Example 1, in the electricity storage device of Example 1, a hole was provided in the heat-welded portion of the aluminum laminate film and opposed to the hole. Thus, it turns out that an electrical storage device with little fall of an electrostatic capacitance can be obtained by providing the porous film of a PTFE nonwoven fabric.

  Note that after 300 hours of voltage application, in the electricity storage device of Comparative Example 1, the pressure in the electricity storage device was increased by the gas generated inside, and the heat-welded portion of the aluminum laminate film was peeled off. For this reason, it is considered that the outside air flows into the electricity storage device and the capacitance is greatly reduced.

  Further, comparing the electricity storage device of Example 2 and the electricity storage device of Comparative Example 1, in the electricity storage device of Example 2, the gap between the opening of the porous film and the hole of the aluminum laminate film was sealed with a heat welding part. By doing so, it can be seen that an electricity storage device with a smaller decrease in capacitance than in Example 1 can be obtained.

  Moreover, when comparing the electricity storage device of Example 3 and the electricity storage device of Comparative Example 2, in the electricity storage device of Example 3, a hole was formed in the heat-welded portion of the aluminum laminate film, and the PTFE nonwoven fabric was opposed to the hole. It can be seen that by providing a porous film and covering the pores of the aluminum laminate film with a gas release valve in an air-tight manner, an electricity storage device with a lower capacitance than that of Example 2 can be obtained.

  In addition, in the electricity storage device of Comparative Example 2 after 300 hours of voltage application, the electrolyte solution passed through the polyimide nonwoven fabric and leaked from the hole to the gas release valve, and the electrolyte was deposited as crystals on the gas release valve. . This indicates that a porous film that is not a PTFE nonwoven fabric is not suitable.

  Furthermore, comparing the electricity storage device of Example 3 and the electricity storage device of Comparative Example 3, in the electricity storage device of Example 3, electricity storage with little decrease in capacitance was achieved by interposing a porous film between the aluminum laminate films. You can see that you get a device.

  In addition, after 300 hours of voltage application, in the electricity storage device of Comparative Example 3, the electrolyte was deposited as crystals on the gas release valve, but such a phenomenon was not seen in the electricity storage device of Example 3. . If this pays attention to the passage inhibition length of the nonaqueous electrolyte in the porous film, the electricity storage device of Example 3 can secure the passage inhibition length along the surface direction of the porous film. It shows that the passage of the non-aqueous electrolyte can be suppressed.

  As described above, the electricity storage device of the present invention according to Examples 1 to 3 has little decrease in capacitance and is excellent in long-term reliability. In addition, in the Example disclosed this time, the electric double layer capacitor was used as the electricity storage device, but it is clear that the present invention can be widely applied to all electricity storage devices including the exterior film material.

DESCRIPTION OF SYMBOLS 1 Electrode body 2 Exterior film material 2a, 2b Exterior film material half 3 Porous film 4 Hole 5 Lead terminal 20, 21 Thermal welding part 30 Opening part 40 Gas release valve

Claims (4)

An electrode body, and an exterior film material that encloses the electrode body and hermetically seals the electrode body by a heat welding portion, and the heat welding portion is formed by heat welding by overlapping the exterior film materials. An electricity storage device comprising:
A porous film that is interposed between the exterior film materials in a part of the heat-welded portion and has one end exposed from the heat-welded portion toward the electrode body,
An electricity storage device comprising: a hole provided in the exterior film material so as to face the porous film.   The power storage device according to claim 1, wherein the porous film has an opening larger than the hole, and a gap between the hole and the opening is sealed by the heat welding part.   The electricity storage device according to claim 1, further comprising a gas release valve that covers the hole in an airtight manner.   The electricity storage device according to claim 1, wherein the porous film is made of polytetrafluoroethylene.

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