JP2018147849A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery that prevents moisture infiltration from the outside to the inside of a battery case and leakage of a nonaqueous electrolytic solution from the inside of the case to the outside, and realizes a current interruption mechanism and an erroneous operation prevention of a gas discharge valve due to an increase in internal pressure of a battery case.SOLUTION: The nonaqueous electrolyte secondary battery includes a gasket (50) made of a synthetic resin for sealing between a lid and a current collector terminal. The gasket has irregularities (53, 54) on a surface (51) exposed inside a battery case.SELECTED DRAWING: Figure 3

Description

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

  Lithium ion secondary batteries and other non-aqueous electrolyte secondary batteries are becoming increasingly important as on-vehicle power supplies or personal computers and portable terminals. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source mounted on a vehicle.

  A non-aqueous electrolyte secondary battery used as a vehicle-mounted high-output power source includes, for example, a battery case in which a battery case body and a lid are welded, an electrode body accommodated in the battery case, and the electrode body Electrically connected current collecting terminals (positive current collecting terminal and negative current collecting terminal) and external connection terminals provided on the outer surface of the lid (referred to as the outer surface of the battery case; the same shall apply hereinafter). (A positive electrode terminal and a negative electrode terminal), and the positive and negative current collector terminals and the positive and negative electrode terminals are electrically connected through a through hole formed through the lid. Further, in the through hole, an insulating gasket is interposed between the lid and the current collecting terminal, so that the battery case and the current collecting terminal are insulated together with sealing (sealing).

  As said gasket, the thing of patent document 1 is known, for example. The gasket described in Patent Document 1 (FIG. 2 of Patent Document 1) has an insulating interposition portion that is held between the positive electrode terminal member (FIG. 1 of Patent Document 1) and the lower surface of the battery case lid. The insulating intervening portion is made of a synthetic resin, and has a crystallinity higher than that of the portion other than the insulating intervening portion (insertion portion and insulating side wall portion). For this reason, since the density of the insulating interposition part is high, the molecules constituting the electrolytic solution are difficult to permeate the insulating interposition part, so that there is no possibility that the electrolytic solution leaks out of the battery through the inside of the gasket.

JP 2014-029839 A

By the way, in non-aqueous electrolyte secondary batteries in which the electrolyte is composed of a non-aqueous solvent, gas such as carbon dioxide (CO ₂ ) is generated inside the battery case due to charge / discharge, overcharge, or storage at high temperatures. There is a case. In addition, moisture may enter the battery, resulting in deterioration of battery characteristics and generation of the gas described above.
Therefore, in the nonaqueous electrolyte secondary battery, a gas discharge valve for discharging the gas generated inside the battery case to the outside of the battery case is provided on the lid. In addition, the nonaqueous electrolyte secondary battery is provided with a pressure-operated current interrupt device (CID: Current Interrupt Device) that interrupts the current path of the battery when the battery is overcharged. In addition, there is a lithium ion secondary battery that includes a gas generating agent that can decompose into a nonaqueous electrolyte solution to generate gas (for example, CO ₂ gas) when a predetermined battery voltage is exceeded. The gas generating agent is decomposed to generate a predetermined type of gas when the battery is overcharged. And the internal pressure in a battery case rises with the gas pressure, and it is comprised so that the electric current interruption mechanism which detected the pressure rise may act | operate.

However, if the density of the gasket interposed between the lid and the current collecting terminal is excessively high, the permeation of gases such as carbon monoxide (CO) and carbon dioxide (CO ₂ ) to the outside of the battery is suppressed, Since the battery internal pressure is likely to rise, a malfunction such as the current cutoff mechanism and / or the gas discharge valve operating unexpectedly early may occur. On the other hand, if the gasket density is too low, the amount of moisture entering the inside of the battery case from the outside of the battery case and leakage of the non-aqueous electrolyte to the outside of the battery case may be undesirable.

  Therefore, the present invention has been created to solve the above-described problems, and suppresses intrusion of moisture from the outside of the battery case to the inside of the case and leakage of the electrolyte from the inside of the battery case to the outside, and the battery. An object of the present invention is to provide a non-aqueous electrolyte secondary battery that can achieve both a current interruption mechanism due to an increase in internal pressure of a case and a malfunction prevention of a gas discharge valve.

In order to achieve the above object, the present invention provides:
A battery case comprising: a battery case body having an opening; a lid that closes the opening; and a connection terminal for external connection provided on the outer surface side of the lid;
An electrode body housed inside the battery case;
One end is electrically connected to the electrode body inside the battery case, and the other end is a current collecting terminal electrically connected to the connection terminal through a through-hole provided in the lid,
A synthetic resin gasket that seals between the lid and the current collector terminal;
A non-aqueous electrolyte secondary battery is provided.
And in the non-aqueous electrolyte secondary battery disclosed here, the said gasket has an uneven | corrugated | grooved part in the surface exposed inside the said battery case, It is characterized by the above-mentioned.

Since the molecules of carbon dioxide gas and other gas species generated inside the battery are small, they easily pass through the polymer chain gap of the synthetic resin forming the gasket. That is, gas such as carbon dioxide gas has a faster diffusion rate in the gasket than the rate at which it dissolves in the gasket. In other words, when considering the rate at which a gas such as carbon dioxide gas permeates through the gasket, the rate at which the gas contacts the gasket surface and dissolves in the gasket is the rate-determining process.
However, in the non-aqueous electrolyte secondary battery disclosed herein, the surface of the gasket that is exposed to the internal space inside the battery case (that is, the inside of the case where the gas generated in the battery case can be in direct contact). The exposed surface has an uneven portion. For this reason, since the area exposed to the inside of the battery case in the gasket can be increased, the permeation amount of gas such as carbon dioxide gas to the gasket can be increased accordingly.
Therefore, according to the non-aqueous electrolyte secondary battery disclosed herein, it is possible to prevent malfunction of the current interrupt mechanism and the gas discharge valve due to the increase in the internal pressure of the battery case.

Further, when the area exposed to the inside of the battery case in the gasket increases, the contact amount of the non-aqueous electrolyte to the gasket may also increase, but the molecules of the non-aqueous electrolyte components (typically non-aqueous solvents) are large. Therefore, it cannot substantially pass through the polymer chain gap of the synthetic resin forming the gasket. That is, when considering the speed at which the non-aqueous electrolyte passes through the gasket, the diffusion speed of the non-aqueous electrolyte in the gasket is diffusion-controlled.
Therefore, even if the area exposed to the inside of the battery case in the gasket is increased, leakage of the nonaqueous electrolyte solution to the outside of the battery case can be prevented.
Furthermore, when considering the amount of moisture that permeates through the gasket from the outside of the battery and enters the inside of the battery, dissolution of the gasket into the portion exposed to the outside of the battery is the rate-limiting process.
Therefore, even if the area exposed to the inside of the battery case in the gasket is increased, an increase in the amount of moisture entering the battery from the outside of the battery can be suppressed.
That is, according to the non-aqueous electrolyte secondary battery disclosed herein, it is possible to suppress both the ingress of moisture from the outside to the inside of the battery case and the leakage of the non-aqueous electrolyte from the inside to the outside of the battery case.

It is a fragmentary sectional view which shows typically the external shape of the lithium ion secondary battery which is one Embodiment of the nonaqueous electrolyte secondary battery disclosed here. It is a disassembled perspective view which shows the cover body and current collection terminal with which the lithium ion secondary battery shown in FIG. 1 was equipped. It is a perspective view of the gasket before an assembly | attachment. (A) is sectional drawing which shows typically the insulation structure by the side of the positive electrode of the lithium ion secondary battery shown in FIG. 1, (b) is a cross section of the state which removed the battery case main body from sectional drawing shown to (a) FIG. (A) is a chart showing the contents of levels 1 to 3 of the gasket used in the experiment, and (b) is a chart showing a list of experimental results. 6 is a graph showing a list of experimental results in FIG.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a general configuration and manufacturing process of a battery that does not characterize the present invention) It can be grasped as a design matter of those skilled in the art based on the prior art. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in each drawing, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

In this specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a so-called storage battery such as a lithium ion secondary battery and a power storage element such as an electric double layer capacitor. The “non-aqueous electrolyte secondary battery” refers to a secondary battery provided with a non-aqueous electrolyte (that is, an electrolyte containing a supporting electrolyte in a non-aqueous solvent). The “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as a charge carrier and is charged and discharged by the movement of lithium ions between the positive and negative electrodes.
Hereinafter, the present invention will be described in detail by taking a flat rectangular lithium ion secondary battery as an example. The embodiments described below are not intended to limit the present invention to those described in the embodiments.

FIG. 1 is a partial cross-sectional view schematically showing the outer shape of the lithium ion secondary battery according to the present embodiment. FIG. 2 shows a lid and a current collecting terminal provided in the lithium ion secondary battery shown in FIG. FIG. In the following description, the lithium ion secondary battery may be simply referred to as a battery.
The lithium ion secondary battery 10 according to the present embodiment has a configuration in which a wound electrode body 30 including a predetermined battery constituent material is accommodated in a battery case 20 together with a suitable nonaqueous electrolyte. In the present embodiment, the lithium ion secondary battery 10 is a square battery, but the shape of the battery is not limited to a square shape, and may be a cylindrical shape or the like.

  The battery case 20 is a so-called rectangular battery case body 21 formed in a flat and bottomed rectangular parallelepiped shape, an opening portion 21A formed in the upper part of the battery case body 21, and the opening portion 21A. And a lid 22. Specifically, the lid 22 is fitted into the opening 21A of the battery case body 21, and the lid 22 is welded by laser welding a joint 25 between the outer edge of the lid 22 and the battery case body 21 around the opening 21A. It is fixed to the battery case body 21 and seals the inside of the battery case.

  The material of the battery case 20 may be the same as that used in the conventional nonaqueous electrolyte secondary battery, and is not particularly limited. A battery case 20 mainly composed of a lightweight and highly heat conductive metal material is preferable, and examples of such a metal material include aluminum, stainless steel, and nickel-plated steel. The battery case 20 (specifically, the battery case main body 21 and the lid body 22) used in the present embodiment is made of aluminum or an alloy mainly composed of aluminum.

  The outer shape of the lid 22 is a substantially rectangular shape that matches the shape of the opening 21A (the opening shape of the battery case body 21). A gas discharge valve 27 is provided at the center of the lid body 22 to allow the inside and outside of the case to communicate with each other to release the internal pressure when the internal pressure of the battery case 20 rises. Next to the gas discharge valve 27, there is provided an inlet 28 for injecting an electrolyte when manufacturing the battery. The injection port 28 is covered with a liquid injection plug 29 and fixed by welding. As a result, the inlet 28 is sealed (sealed).

  The wound electrode body 30 is accommodated in the battery case main body 21 in a posture such that the wound shaft is laid down so that the winding shaft is substantially parallel to the lid body 22. The wound electrode body 30 includes a sheet-like separator (separator sheet) 36 between a sheet-like positive electrode (positive electrode sheet) 32 and a negative electrode (negative electrode sheet) 34 in the same manner as the wound electrode body of a normal lithium ion secondary battery. It can be produced by laminating while interposing, winding in the longitudinal direction and dragging.

  The material and the member itself constituting the wound electrode body 30 may be the same as the electrode body provided in the conventional lithium ion secondary battery, and there is no particular limitation. The wound electrode body 30 of the present embodiment includes a positive electrode sheet 32 having a positive electrode active material layer on a long positive electrode current collector (eg, aluminum foil), and a long negative electrode current collector (eg, copper foil). A negative electrode sheet 34 having a negative electrode active material layer thereon and a separator sheet 36 are included.

As the positive electrode active material, an oxide-based active material having a layered structure or an oxide-based active material having a spinel structure used for a positive electrode of a general lithium ion secondary battery can be preferably used. Typical examples of such active materials include lithium transition metal oxides such as lithium cobalt oxides, lithium nickel oxides, and lithium manganese oxides. Examples of the negative electrode active material include carbon materials such as graphite (graphite), non-graphitizable carbon (hard carbon), and graphitizable carbon (soft carbon).
As the separator sheet 36, for example, a porous sheet made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, or a non-woven fabric can be used.

The non-aqueous electrolyte interposed between the positive electrode sheet 32 and the negative electrode sheet 34 contains a supporting salt in a suitable non-aqueous solvent, and is conventionally known as non-aqueous electrolysis for use in lithium ion secondary batteries. The liquid can be employed without any particular limitation. For example, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or the like can be used as the non-aqueous solvent. As the supporting salt, for example, a lithium salt such as LiPF ₆ can be suitably used.

The positive electrode current collector terminal 40 is welded to the positive electrode sheet 32, and the negative electrode current collector terminal 80 is welded to the negative electrode sheet 34. These current collecting terminals 40 and 80 have positive and negative terminal lead-out holes (through holes) 242 and 244 provided in the vicinity of one end in the longitudinal direction of the lid 22 and in the vicinity of the other end, respectively. Each penetrates and is pulled out from the inside of the battery case 20. As shown in FIGS. 1 and 2, the positive electrode current collecting terminal 40 is electrically composed of a positive electrode internal terminal 420 mainly located inside the battery case 20 and a positive electrode external terminal 460 mainly located outside the battery case 20. It has a connected configuration. The negative electrode current collecting terminal 80 also has a configuration in which a negative electrode internal terminal 820 and a negative electrode external terminal 860 formed in substantially the same shape as the positive electrode side are electrically connected.
Hereinafter, the terminal structure according to the present embodiment will be described in detail mainly on the positive electrode side, and the description of the negative electrode side having a terminal structure having substantially the same shape will be simplified or omitted.

  As shown in FIG. 2, the lower end 422A of the positive electrode internal terminal 420 is joined and electrically connected to the positive electrode sheet 32 by, for example, ultrasonic welding. The positive electrode internal terminal 420 is formed following a plate-like (strip-like) first lead portion 422 extending substantially perpendicularly from the lower end 422A to the lid body 22 and the upper end of the first lead portion, and substantially perpendicular to the upper end ( In FIG. 2, a plate-like second lead portion 424 that bends from the back side to the front side of the drawing and extends substantially parallel to the inner surface of the lid 22 (referred to as the inner surface of the battery case; hereinafter the same), and the second lead. And a protrusion 426 extending substantially perpendicularly from the center of the plate surface to the outside of the battery. The protruding portion 426 is configured as a rivet portion, and the positive internal terminal 420 and the positive external terminal are formed by caulking the rivet portion through the terminal lead hole 242 and the through hole (rivet hole) 462A of the positive external terminal 460. 460 is connected (fastened). As a constituent material of the positive electrode internal terminal 420 and the positive electrode external terminal 460, a metal material having good conductivity is preferable, and aluminum is typically used.

  As shown in FIG. 2, the positive external terminal 460 includes a first connection portion 462 having a through hole 462A through which the protrusion 426 can be inserted before the caulking, and a center side in the longitudinal direction of the lid body 22 from the first connection portion 462. The second connection portion (outer end portion) 464 is formed to be raised in a stepped manner outside the battery case 20. As shown in FIG. 2, the second connection portion 464 is formed with a bolt insertion hole 464A through which the shaft portion 674 of the terminal bolt 670 corresponding to the connection terminal for external connection according to the present embodiment can be inserted. The shaft portion 674 of the terminal bolt 670 is passed through the bolt insertion hole 464A from below, and the shaft portion 674 protrudes upward from the second connection portion 464. The terminal bolt 670 can be connected (fixed) to the positive external terminal 460 by tightening a fixing nut (not shown).

  In the caulking, the gasket 50 according to the present embodiment is sandwiched between the inner surface of the lid body 22 surrounding the terminal lead hole 242 and the second lead portion 424, and the outer surface of the lid body 22 surrounding the terminal lead hole 242 and the positive electrode. The insulator 60 is sandwiched between the first connection portion 462 of the external terminal 460. By such caulking, the positive electrode current collector terminal 40 is fixed to the lid body 22, and the gasket 50 is compressed between the lid body 22 and the second lead portion 424 of the positive electrode current collector terminal 40 to thereby surround the terminal lead-out hole 242. Is sealed (sealed). Further, the gasket 50 insulates the battery case 20 (inner surface of the lid body 22) from the positive electrode current collector terminal 40 (second lead portion 424), and the insulator 60 allows the battery case 20 (outer surface of the lid body 22). And the positive external terminal 460 (first connection portion 462) are insulated. The insulating structure near the terminal lead hole 242 will be described later.

  The insulator 60 includes an attachment portion 620 sandwiched between the upper surface (front surface) of the lid body 22 surrounding the terminal lead hole 242 and the first connection portion 462 of the positive electrode external terminal 460, and the second connection portion 464 of the positive electrode external terminal 460. And an extension 640 extending between the lid 22 and the lid 22. The attachment portion 620 has a dish portion that extends along the outer surface of the lid body 22. The first connection part 462 of the positive electrode external terminal 460 is arranged in accordance with the depression of the dish part.

  The extension portion 640 has a rectangular opening shape having a long side in the longitudinal direction of the insulator 60 (which coincides with the longitudinal direction of the lid body 22), and is a bolt receiver that can receive the head 672 of the terminal bolt 670. A hole 642 is formed. The head 672 is formed so that the cross section perpendicular to the axis of the terminal bolt 670 has a rectangular shape that is slightly smaller than the opening shape of the bolt receiving hole 642. The terminal bolt 670 has its head 672 inserted into the bolt receiving hole 642 so that its rotation is restricted (co-rotation is prevented), and the shaft portion 674 protrudes through the bolt insertion hole 464A of the positive external terminal 460. Arranged (mounted).

Next, the structure of the gasket will be described with reference to FIGS. FIG. 3 is a perspective view of the gasket 50 before assembly.
The gasket 50 is formed in a substantially disk shape, and a through hole 55 for inserting the protruding portion 426 (FIG. 2) of the positive electrode current collecting terminal 40 is formed at the center thereof. In addition, in the gasket 50, a surface (outer peripheral surface) 51 exposed inside the battery case 20 is formed with a plurality of concave portions 53 that are recessed toward the through hole 55 along the circumferential direction. Convex portions 54 are formed between 53. Each recess 53 is formed in a shape in which the outer peripheral surface 51 is cut out in a substantially rectangular parallelepiped shape, and a side wall 53b formed between the bottom wall 53a and both ends of the bottom wall 53a and the outer peripheral surface 51, respectively. 53c. Further, a flat seal surface portion 52 that can come into contact with the inner surface of the lid 22 is formed on the upper surface (and the lower surface) of the gasket 50.

  As described above, by forming the concave portion 53 and the convex portion 54 on the outer peripheral surface 51 exposed inside the battery case 20 of the gasket 50, the exposed area of the outer peripheral surface 51 increases. The area where the generated carbon dioxide gas or the like comes into contact with the outer peripheral surface 51 can be increased. The shape of each recess 53 may be a shape obtained by cutting out the outer peripheral surface 51 into a hemispherical shape, a cylindrical shape, or a triangular pyramid shape, and is not limited. Further, the exposed area of the outer peripheral surface 51 can be increased by forming a plurality of groove-shaped concave portions on the outer peripheral surface 51 to form the concaves and convexes. In the present embodiment, only the outer peripheral surface 51 of the gasket 50 is exposed inside the battery. However, if there is a portion exposed inside the battery other than the outer peripheral surface 51, the portion and the outer periphery are exposed. Unevenness can be formed on the surface to increase the exposed area. In the present embodiment, six concave portions 53 and six convex portions 54 are formed, but the number is not limited. In the present embodiment, the gasket 50 has a substantially disc shape, but the shape of the gasket is not limited to a polygon or the like.

Next, the insulating structure of the lid body 22 and the positive electrode current collector terminal 40 by the gasket 50 will be described with reference to FIGS.
4A is a cross-sectional view schematically showing an insulating structure on the positive electrode side of the lithium ion secondary battery shown in FIG. 1, and is a cross-sectional view when cut in a direction perpendicular to the wide surface of the battery case 20. FIG. FIG. 5 is a cross-sectional view including the axis of the terminal lead hole 242 (the axis passing through the center of the terminal lead hole 242 and perpendicular to the radial direction of the through hole). FIG. 4B is a cross-sectional view in a state where the battery case main body 21 is removed from the cross-sectional view shown in FIG.

  As shown in FIG. 4A, the gasket 50 is held between the lid body 22 and the positive electrode current collecting terminal 40 (second lead portion 424). The gasket 50 is made of a synthetic resin having gas permeability. The inner surface 243 of the lid body 22 is prevented from coming into contact with the positive electrode current collector terminal 40 by the seal surface portion 52 of the gasket 50, whereby the lid body 22 (battery case 20) and the positive electrode current collector terminal 40 are insulated. ing. Further, the insulator 60 is sandwiched between the positive electrode external terminal 460 and the outer surface 245 of the lid body 22 to prevent the positive electrode external terminal 460 and the lid body 22 (battery case 20) from coming into contact with each other. The body 22 (battery case 20) and the positive electrode external terminal 460 are insulated. A gap 22B is formed between the outer peripheral surface 51 of the gasket 50 and the flange portion 22A formed on the peripheral edge of the inner surface of the lid 22, and the outer peripheral surface 51 is brought into the battery case 20 by the gap 22B. It is in an exposed state. The concave portion 53 and the convex portion 54 correspond to the concave and convex portion according to claim 1 of the present application.

  The gasket 50 having the concave portion 53 and the convex portion 54 is obtained by molding a synthetic resin material by, for example, injection molding or hot press molding using a mold having a shape corresponding to the concave portion 53 and the convex portion 54 in advance. Can be produced. Alternatively, a gasket without the concave portion 53 and the convex portion 54 can be first produced by molding, and the concave portion 53 and the convex portion 54 can be provided by cutting.

  The constituent material of the gasket 50 is not particularly limited, but preferred examples include hydrophobic polyolefin resins (eg, polypropylene (PP), polyethylene (PE)), fluorine resins (eg, perfluoroalkoxyalkanes). And synthetic resin materials such as (PFA) and polytetrafluoroethylene (PTFE)). These materials are formed by polymer chains and aggregates thereof, and a gas such as carbon dioxide gas easily passes through the polymer chain gap.

  The structure on the negative electrode side in the lithium ion secondary battery 10 of the present embodiment is substantially the same as that on the positive electrode side except for the material of the negative electrode current collector terminal 80. That is, one end of the negative electrode current collecting terminal 80 is electrically connected to the negative electrode sheet 34 by, for example, resistance welding. The negative electrode current collecting terminal 80 includes a negative electrode internal terminal 820 and a negative electrode external terminal 860 that are formed in substantially the same shape as the positive electrode internal terminal 420. The negative internal terminal 820 and the negative external terminal 860 are electrically connected by caulking to the first connection portion. The caulking is performed by sandwiching the gasket 50, the lid body 22 and the insulator 60 between the terminals 820 and 860, as in the positive electrode side. The gasket 50 has the above-described concave portion 53 and convex portion 54 on the outer peripheral surface 51 as in the positive electrode side. The negative external terminal 860 is formed in a staircase shape having a first connection portion and a second connection portion. A terminal bolt 670 is inserted from below into the bolt insertion hole provided in the second connection portion so that a connecting member for external connection can be coupled (fixed) to the shaft portion 674 (FIG. 2). It is configured. The constituent material of the negative electrode internal terminal 820 and the negative electrode external terminal 860 is preferably a metal material having good conductivity, for example, copper. The material and shape of the gasket 50 and the insulator 60 may be the same as those on the positive electrode side.

  Hereinafter, although the test example regarding this invention is demonstrated, it is not intending to limit this invention to what is shown to this specific example.

In this test example, the permeation amount of carbon dioxide gas that permeated through the gasket 50 from the inside of the battery and leaked to the outside of the battery, and the permeation amount of moisture that permeated the gasket 50 from the outside of the battery and entered the inside of the battery were measured. Moreover, in this test example, the relationship between the area of the outer peripheral surface 51 of the gasket 50, that is, the exposed area of the gasket 50 exposed inside the battery, and each transmission amount was obtained.
In FIG. 3, symbol L1 indicates the length from the center of the gasket 50 to the convex portion 54, that is, the maximum diameter of the gasket 50, and symbol L2 indicates the length from the center of the gasket 50 to the bottom wall 53a of the concave portion 53, That is, the minimum diameter of the gasket 50 is indicated, and the symbol t indicates the thickness of the gasket 50. In this test example, the gasket 50 having a maximum diameter L1 of 5.0 mm and a thickness t of 0.6 mm was used as a base. The exposed area of the outer peripheral surface 51 of the gasket 50 was changed by making the maximum diameter L1 and the thickness t constant and changing the minimum diameter L2. When the minimum diameter L2 is shortened, the depth of each recess 53 is increased, and the areas of the side walls 53b and 53c of each recess 53 are increased, so that the exposed area of the outer peripheral surface 51 is increased.

Fig.5 (a) is a table | surface which shows the content of the levels 1-3 of the gasket used by this test example. Level 1 is a gasket having the same maximum diameter L1 and minimum diameter L2 of 5.0 mm, that is, a base gasket in which the concave portion 53 and the convex portion 54 are not formed on the outer peripheral surface 51, and the exposed area of the outer peripheral surface 51 is 18 .9 mm ² . Level 2 is a gasket having a minimum diameter L2 of 4.5 mm, that is, a gasket having a concave portion 53 and a convex portion 54 formed on the outer peripheral surface 51 and a depth of the concave portion 53 of 0.5 mm. Is 21.5 mm ² . Level 3 is a gasket having a minimum diameter L2 of 4.0 mm, that is, a gasket having a concave portion 53 and a convex portion 54 formed on the outer peripheral surface 51 and a depth of the concave portion 53 of 1.0 mm. Is 24.2 mm ² .

Then, a flat rectangular lithium ion secondary battery in which the gaskets of levels 1 to 3 are mounted at predetermined positions as shown in FIG. 4A is stored for one month in an environment of 60 ° C. The permeation amount [μg] of carbon dioxide gas (CO ₂ ) leaking to the outside was measured. This measurement was performed twice under the same environment. In addition, a flat rectangular lithium ion secondary battery with each level 1 to 3 gasket attached in place is stored for one month in an environment of 60 ° C. and 98% RH. The permeation amount [μg] was measured. This measurement was also performed twice under the same environment. The measurement result is shown in FIG. FIG. 6 is a graph showing a list of experimental results in FIG.

As shown in the table of FIG. 5B and the graph of FIG. 6, when the exposed area of the outer peripheral surface 51 of the gasket 50 increased, the water permeation amount hardly changed, but the carbon dioxide gas (CO2) permeation amount. Increased with increasing exposed area.
That is, according to this test example, by increasing the exposed area of the outer peripheral surface 51 of the gasket 50 inside the battery, it is possible to increase the amount of permeation of gas such as carbon dioxide gas generated inside the battery to the outside of the battery. And it was shown that the increase in the permeation | transmission amount of the water | moisture content which permeates into the inside of a battery from the battery exterior can be suppressed.
Since the carbon dioxide gas molecules generated inside the battery are small, they easily pass through the polymer chain gap of the synthetic resin forming the gasket 50. That is, the diffusion rate in the gasket 50 is faster than the rate at which a gas such as carbon dioxide gas dissolves in the gasket 50. In other words, when the speed at which a gas such as carbon dioxide gas permeates through the gasket 50 is considered, the speed at which the gas dissolves into the gasket 50 is considered to be the rate-determining process. For this reason, it was determined that the permeation amount of gas such as carbon dioxide gas to the gasket 50 increased by increasing the exposed area of the outer peripheral surface 51 of the gasket 50 inside the battery.
Further, when considering the amount of moisture that permeates through the gasket 50 from the outside of the battery and enters the inside of the battery, it is considered that dissolution of the gasket 50 to the outer peripheral surface 51 exposed to the outside of the battery is a rate-limiting process. . For this reason, even if the exposed area of the outer peripheral surface 51 of the gasket 50 to the inside of the battery is increased, an increase in the amount of moisture that enters the battery from the outside of the battery can be suppressed.
Furthermore, when the exposed area of the outer peripheral surface 51 of the gasket 50 to the inside of the battery increases, the amount of the non-aqueous electrolyte dissolved in the gasket 50 also increases. However, the molecules of the components (non-aqueous solvent) constituting the non-aqueous electrolyte are Since it is large, it is difficult to pass through the polymer chain gap of the synthetic resin forming the gasket 50. That is, when considering the speed at which the non-aqueous electrolyte permeates through the gasket, it is considered that the diffusion speed of the non-aqueous electrolyte in the gasket 50 is diffusion-controlled. For this reason, even if the exposed area of the outer peripheral surface 51 of the gasket 50 to the inside of the battery is increased, leakage of the nonaqueous electrolytic solution to the outside of the battery case can be suppressed.
As is clear from this test example, according to the lithium ion secondary battery 10 including the gasket 50 of the above-described embodiment, the amount of moisture that enters the inside of the battery case 20 from the outside of the battery case 20 and the nonaqueous electrolyte solution It is possible to achieve both the suppression of leakage and the prevention of malfunction of the current cut-off mechanism and the gas discharge valve (gas discharge valve) due to the increase in the internal pressure of the battery case 20.

  The lithium ion secondary battery 10 of this embodiment is suitable for a power source for driving a vehicle such as a hybrid vehicle or an electric vehicle. The power source for driving the vehicle may be an assembled battery in which a plurality of secondary batteries are combined.

10 Lithium ion secondary battery (non-aqueous electrolyte secondary battery)
20 Battery Case 21 Battery Case Main Body 22 Lid 30 Winding Electrode Body 32 Positive Electrode Sheet 34 Negative Electrode Sheet 36 Separator Sheet 40 Positive Electrode Current Collection Terminal 50 Gasket 51 Outer Surface 52 Seal Surface 53 Recess 53a Bottom Wall 53b, 53c Side Wall 54 Protrusion 55 Through hole 60 Insulator 80 Negative electrode current collector terminal 242 Terminal lead hole 420 Positive electrode internal terminal 426 Projection portion 460 Positive electrode external terminal 670 Terminal bolt (connection terminal)
820 Negative electrode internal terminal 860 Negative electrode external terminal

Claims (1)

A battery case comprising: a battery case body having an opening; a lid that closes the opening; and a connection terminal for external connection provided on the outer surface side of the lid;
An electrode body housed inside the battery case;
One end is electrically connected to the electrode body inside the battery case, and the other end is a current collecting terminal electrically connected to the connection terminal through a through-hole provided in the lid,
A synthetic resin gasket that seals between the lid and the current collector terminal;
A non-aqueous electrolyte secondary battery comprising:
The non-aqueous electrolyte secondary battery, wherein the gasket has an uneven portion on a surface exposed inside the battery case.

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