Flat type battery

A flat type battery includes an exterior member housing an electrolytic solution and a power generating element. The power generating element contains electrodes alternating layered between electrolyte layers, and expands with use in a layering direction of the electrodes. The exterior member forms a tightly sealed space in which the power generating element is housed, and in which an extra space is formed between the exterior member and a side surface extending along the layering direction of the power generating element. The exterior member includes a volume adjustment portion allowing for an increase in the volume of the extra space by expanding in response to a pressure rise inside the tightly sealed space while the exterior member is being pressed against the surfaces intersecting the layering direction of the power generating element due to a pressure difference between the exterior and the interior.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of International Application No. PCT/JP2015/069027, filed Jul. 1, 2015.

BACKGROUND

Field of the Invention

The present invention relates to a flat type battery. The flat type battery of the present invention is used, for example, as a driving power source or an auxiliary power source for a motor, or the like, of vehicles, such as fuel cell vehicles and hybrid electric vehicles.

Background Information

Conventionally, as a battery corresponding to one form of a flat type battery, there is a lithium ion secondary battery that is configured by sealing a laminate type power generating element, which carries out charging/discharging, and an electrolytic solution, with an exterior member (see, Japanese Laid-Open Patent Application No. 2001-297748 referred to herein as Patent Document 1).

The power generating element is configured by laminating an electrolyte layer, which holds an electrolyte, and an electrode. The power generating element expands in the layering direction with use.

The exterior member forms a tightly sealed space that contains a space in which the power generating element is housed, and an extra space. The exterior member is pressed against a surface, which intersects the layering direction of the power generating element, due to a pressure difference between the pressure of the tightly sealed space and the pressure of the exterior space.

SUMMARY

Inside the power generating element, while charging and discharging are repeated, the active material in the electrode reacts with the electrolytic solution to generate gas. Part of the gas that is generated inside the power generating element moves to the extra space.

At this time, if the volume of the extra space is small, the pressure inside the tightly sealed space formed by the exterior member easily rises due to the movement of the gas. As a result, the movement of the gas to the extra space is not carried out smoothly. Therefore, there is the problem that the amount of electrolytic solution in the power generating element is relatively reduced due to gas remaining in the power generating element, which results in the occurrence of partial liquid depletion.

On the other hand, if the volume of the extra space is large, the shape of the extra space tends to change greatly, as the pressure inside the tightly sealed space formed by the exterior member rises. If the shape of the extra space changes greatly, a force acts on the exterior member to separate the exterior member from a surface intersecting the layering direction of the power generating element. Thus, part of the gas that has moved to the space easily enters between the exterior member and the surface intersecting the layering direction of the power generating element. As a result, there is the problem that pressure from the exterior member is not uniformly applied to the surface intersecting the layering direction of a power generating element, so that the performance of the battery deteriorates.

Therefore, in order to solve the problem described above, an object of the present invention is to provide a flat type battery capable of preventing liquid depletion while maintaining a state in which pressure from an exterior member acts uniformly onto a surface intersecting the layering direction of a power generating element.

The flat type battery according to the present invention, which realizes the object described above, comprises an electrolytic solution, and a power generating element that contains electrolyte layers and a plurality of electrodes layered with each of the electrolyte layers therebetween, and that expands with use in the layering direction of the electrodes. The flat type battery according to the present invention further comprises an exterior member that forms a tightly sealed space that contains a space in which the power generating element is housed and an extra space. The extra space is formed between the exterior member and a side surface along the layering direction of the power generating element. The exterior member includes a volume adjustment portion that allows for an increase in the volume of the extra space by expanding in accordance with a pressure rise inside the tightly sealed space while the exterior member is being pressed against the surfaces intersecting the layering direction of the power generating element due to a pressure difference between the exterior and the interior. The volume adjustment portion allows for an increase in the volume of the extra space while maintaining the state in which the exterior member is pressed against the surfaces intersecting the layering direction of the power generating element.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The first embodiment, the second embodiment, and the third embodiment according to the present invention will be described below, with reference to the appended drawings.

In the explanations of the drawings, the same elements are assigned the same reference symbols, and redundant explanations are omitted.

In all of the figures fromFIGS. 1 to 19, the directions are shown using arrows indicated by X, Y, and Z. The direction of the arrow indicated by X indicates the length direction of the flat type battery (corresponding to the direction intersecting the layering direction of the power generating element). The direction of the arrow indicated by Y indicates the width direction of the flat type battery that intersects the length direction X (corresponding to the direction intersecting the layering direction of the power generating element). The direction of the arrow indicated by Z indicates the layering direction of the power generating element.

The sizes and ratios of the members in the drawing may be exaggerated for the sake of explanation, and may be different from the actual sizes and ratios. For example, the thicknesses of the members along the layering direction (Z direction) are exaggerated inFIGS. 4-6, and the like.

First Embodiment

The flat type battery will be described with reference toFIGS. 1-9.

First, the configuration of the flat type battery will be described with reference toFIGS. 1-6, based on a lithium ion secondary battery100comprising a laminated type power generating element as an example.

FIG. 1is a perspective view illustrating a lithium ion secondary battery100according to the present embodiment.FIG. 2is a plan view illustrating the lithium ion secondary battery100.FIG. 3is an exploded perspective view illustrating the lithium ion secondary battery100disassembled into constituent parts.FIG. 4is a partial end surface view illustrating the lithium ion secondary battery100along line4-4shown inFIG. 1.FIGS. 5(A)and (B) are schematic cross-sectional views illustrating the lithium ion secondary battery100along line5-5shown inFIG. 2, with the electrolytic solution10and the power generating element50omitted.FIG. 6is a cross-sectional view of the lithium ion secondary battery100along line5-5shown inFIG. 2.

Overall Structure of the Battery

As illustrated inFIGS. 4 and 5, the lithium ion secondary battery100according to the present embodiment comprises an electrolytic solution10, and a power generating element50that contains electrolyte layers20and a plurality of positive electrodes30and negative electrodes40layered with each of the electrolyte layers20therebetween, and that expands with use in the layering direction Z of the positive electrodes30and the negative electrodes40. The lithium ion secondary battery100further comprises an exterior member110forming a tightly sealed space80that in turn contains a space60in which the power generating element50is housed and an extra space70. The extra space70is formed between the exterior member110and a side surface SS along the layering direction Z of the power generating element50. The exterior member110is pressed against surfaces SU, SB, which intersect the layering direction Z of the power generating element50, due to a pressure difference between the exterior and the interior. The exterior member110includes a volume adjustment portion140that allows for an increase in the volume of the extra space70by expanding in accordance with a pressure rise inside the tightly sealed space80. The volume adjustment portion140allows for an increase in the volume of the extra space70while maintaining the state in which the exterior member110is pressed against the surfaces SU, SB intersecting the layering direction Z of the power generating element50. Each of the component elements will be described in detail below.

Power Generating Element

The power generating element50is a laminated power generating element that includes electrolyte layers20, and a plurality of positive electrodes30and negative electrodes40that are layered with each of the electrolyte layer20therebetween, as illustrated inFIG. 3. When the number of laminations of the positive electrodes30is d and the capacity of the battery is Q, it is preferable that 0.7≤Q/d≤5.0 be satisfied. In the present embodiment, since a negative electrode40is disposed on the outermost layer of the power generating element50, when the number of laminations of the positive electrodes30is d, the number of laminations of the negative electrodes40is d+1. In addition, in the case that a positive electrode30is disposed on the outermost layer of the power generating element50, the number of laminations of the negative electrodes40may be set to d to satisfy 0.7≤Q/d≤5.0.

The power generating element50comprises one surface SU intersecting the layering direction Z, another surface SB intersecting the layering direction Z, and a side surface SS along the layering direction Z, as illustrated inFIG. 4. The side surface SS along the layering direction Z is configured from the sequence of side surfaces of the electrolyte layers20, the positive electrodes30, and the negative electrodes40, along the layering direction Z of the power generating element50.

Positive Electrode

A positive electrode30is formed by positive electrode active material layers32being provided to a positive electrode current collector31, as illustrated inFIG. 4.

The positive electrode current collector31is made of, for example, aluminum, and is formed into a thin film shape.

The positive electrode active material layer32is formed by applying and drying a positive electrode slurry, prepared by mixing the materials described below in a predetermined ratio, on both surfaces of the positive electrode current collector31such that a portion of the positive electrode current collector31is exposed. Furthermore, the dried positive electrode active material layers32are pressed from both sides of the positive electrode current collector31, in a state of being bonded to both surfaces of the positive electrode current collector31. A positive electrode tab31ais joined to a portion of the positive electrode current collector31where the positive electrode active material layer32is not formed.

The positive electrode slurry contains a positive electrode active material, a conductive assistant, a binder, and a viscosity adjusting solvent. LiNiCoAlO2is used in a ratio of 90 wt % as the positive electrode active material. Acetylene black is used in a ratio of 5 wt % as the conductive assistant. PVDF is used in a ratio of 5 wt % as the binder.

Negative Electrode

A negative electrode40is formed by negative electrode active material layers42being provided to a negative electrode current collector41.

The negative electrode current collector41is made of, for example, copper, and is formed into a thin film shape.

The negative electrode active material layer42is formed by applying and drying a negative electrode slurry, prepared by mixing the materials described below in a predetermined ratio, on both surfaces of the negative electrode current collector41such that a portion of the negative electrode current collector41is exposed. Furthermore, the dried negative electrode active material layers42are pressed from both sides of the negative electrode current collector41, in a state of being bonded to both surfaces of the negative electrode current collector41. A negative electrode tab41a(refer toFIG. 1andFIG. 2) is joined to a portion of the negative electrode current collector41where the negative electrode active material layer42is not formed.

The negative electrode slurry contains a negative electrode active material, a conductive assistant, a binder, and a viscosity adjusting solvent. A coated natural graphite is used in a ratio of 94 wt % as the negative electrode active material. Acetylene black is used in a ratio of 1 wt % as the conductive assistant. PVDF is used in a ratio of 5 wt % as the binder. NMP is used as a solvent for adjusting the viscosity of the slurry.

Electrolyte Layer

The electrolyte layer20comprises a separator impregnated with the electrolytic solution10. The electrolyte layer20comprising the separator functions as a spatial partition (spacer) between the positive electrode30and the negative electrode40. In addition, together with the above, the electrolyte layer also functions to hold the electrolyte, which is the transfer medium for lithium ions between the positive and negative electrodes at the time of charging and discharging.

The separator is not particularly limited, and a conventionally well-known separator may be appropriately used. Examples include nonwoven fabric separators and porous sheet separators made of polymers or fibers that absorb and hold the electrolyte.

Electrolytic Solution

A conventionally well-known electrolytic solution may be appropriately used as the electrolytic solution10. In the present embodiment, the electrolytic solution is configured using a liquid electrolyte, but the electrolytic solution may be configured using a gel electrolyte.

A liquid electrolyte is obtained by lithium salt, which is a supporting salt, being dissolved in a solvent. Examples of the solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propionate (MP), methyl acetate (MA), methyl formate (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and γ-butyrolactone (GBL). One of these solvents may be used alone, or two or more may be used in combination. While not particularly limited, examples of the supporting salt (lithium salt) include inorganic acid anionic salts such as LiPF6, LiBF4, LiCIO4, LiAsF6, LiTaF6, LiSbF6, LiAICI4, Li2B10Cl10, LiI, LiBr, LiCI, LiAICI, LiHF2, and LiSCN, and organic acid anionic salts such as LiCF3SO3, Li (CF3SO2)2N, LiBOB (lithium bis oxide borate), LiBETl (lithium bis (perfluoroethanesulfonyl)imide; also written as Li (C2F5SO2)2N, and the like. These electrolyte salts may be used alone or in the form of a mixture of two or more.

Exterior Member

The exterior member110includes a first exterior member120and a second exterior member130, which are joined to each other, as illustrated inFIG. 5(A). The exterior member110forms a tightly sealed space80inside the exterior member110.

The first exterior member120and the second exterior member130are joined to each other by an end portion120E of the first exterior member120being joined to an end portion130E of the second exterior member130. The tightly sealed space80is formed by the first exterior member120and the second exterior member130being joined to each other.

The tightly sealed space80is in a reduced pressure state. That is, the pressure inside the tightly sealed space80is lower than the pressure outside the tightly sealed space80. The tightly sealed space80includes a space60in which the power generating element50is housed, and an extra space70, as illustrated inFIG. 5(B).

The first exterior member120and the second exterior member130are joined in a state of sandwiching the power generating element50in the layering direction Z of the power generating element50, as illustrated inFIG. 6.

The first exterior member120comprises an abutting portion121that abuts the surface SU intersecting the layering direction Z of the power generating element50, a joint portion122that is joined to the second exterior member130, and a connecting portion123that connects the abutting portion121and the joint portion122.

The second exterior member130comprises an abutting portion131that abuts the surface SB intersecting the layering direction Z of the power generating element50, a joint portion132that is joined to the first exterior member120, and a connecting portion133that connects the abutting portion131and the joint portion132.

The abutting portion121is pressed against the surface SU intersecting the layering direction Z of the power generating element50, due to a pressure difference between the outside pressure and the inside pressure of the tightly sealed space80described above. The abutting portion131is similarly pressed against the surface SB intersecting the layering direction Z of the power generating element50, due to said pressure difference.

An end portion121E of the abutting portion121abuts an end portion E1of the surface SU intersecting the layering direction Z of the power generating element50. An end portion131E of the abutting portion131abuts an end portion E2of the surface SB intersecting the layering direction Z of the power generating element50.

The joint portion122and the joint portion132are joined and have a predetermined width.

The connecting portion123connects the end portion121E of the abutting portion121and the joint portion122. The connecting portion133connects the end portion131E of the abutting portion131and the joint portion132.

The extra space70is formed between the connecting portion123and the connecting portion133of the exterior member110and the side surface SS along the layering direction of the power generating element50. The extra space70is disposed surrounding the power generating element50.

The first exterior member120and the second exterior member130include a volume adjustment portion140that allows for an increase in the volume of the extra space70by expanding in accordance with a pressure rise inside the tightly sealed space80. The volume adjustment portion140allows for an increase in the volume of the extra space70while maintaining the state in which the exterior member110is pressed against the surfaces SU, SB intersecting the layering direction Z of the power generating element50. In the present embodiment, the volume adjustment portion140is configured by forming a loose portion in parts of the connecting portion123and the connecting portion133.

In the present embodiment, the ratio Vl/Va of the volume of the power generating element50(volume of the space60in which the power generating element50is housed) VI relative to the volume Va of the tightly sealed space80is set within a predetermined range. Specifically, the ratio of the volume Vl of the power generating element50relative to the volume Va of the tightly sealed space80is set to 0.800≤Vl/Va≤0.995. The volume Va of the tightly sealed space80can be measured using Archimedes's method. In addition, in the present embodiment, the volume Vl of the power generating element50is obtained by multiplying the area of the negative electrode40by the thickness of the power generating element50.

In the present embodiment, the first exterior member120and the second exterior member130are each configured by a laminated sheet with a three-layer structure. The first layer corresponds to a thermal adhesive resin and is formed using, for example, polyethylene (PE), ionomer, or ethylene vinyl acetate (EVA). The material of the first layer is placed adjacent to the negative electrode40. The second layer corresponds to a metal formed into a foil; for example, an Al foil or a Ni foil is used. The third layer corresponds to a resin film; for example, rigid polyethylene terephthalate (PET) or nylon is used. The material of the third layer is placed adjacent to the positive electrode30.

In the lithium ion secondary battery100according to the present embodiment, the sealing of the electrolytic solution10and the power generating element50by the first exterior member120and the second exterior member130is carried out with the following procedure.

First, a portion of the perimeter of the first exterior member120and the second exterior member130is opened, and the rest of the perimeter is sealed by thermal welding, or the like. At this time, the joint portion122and the joint portion132are joined to each other.

Next, an electrolytic solution is injected from the opened portion of the first exterior member120and the second exterior member130to impregnate the electrolyte layer20with the electrolytic solution.

Then, the interior of the first exterior member120and the second exterior member130is decompressed from the opened portion to release the air, and the opened portion is also thermally fused and completely sealed.

With the procedure described above, the electrolytic solution10and the power generating element50are sealed in a depressurized state by the first exterior member120and the second exterior member130.

Next, the operation of the lithium ion secondary battery100according to the present embodiment will be described with reference toFIGS. 7-9.

FIG. 7is an enlarged view for explaining the operation of the volume adjustment portion140of the lithium ion secondary battery100, corresponding to the portion surrounded by the broken line portion M1ofFIG. 6, showing the volume adjustment portion140before the volume of the extra space70is increased.FIG. 8is an enlarged view for explaining the operation of the volume adjustment portion140of the lithium ion secondary battery100, corresponding to the portion surrounded by the broken line portion M1ofFIG. 6, showing the volume adjustment portion140while the volume of the extra space70is being increased.FIG. 9is an enlarged view for explaining the operation of the volume adjustment portion140of the lithium ion secondary battery100, corresponding to the portion surrounded by the broken line portion M2ofFIG. 8.

The lithium ion secondary battery100according to the present embodiment is repeatedly charged and discharged as a driving power source or an auxiliary power source of a motor, or the like, of vehicles, such as fuel cell vehicles and hybrid electric vehicles.

As charging and discharging are repeatedly carried out, the positive electrode30or the negative electrode40reacts with the electrolytic solution10to generate gas11inside the power generating element50.

The gas11is moved to the extra space70formed between the exterior member110and the side surface SS along the layering direction Z of the power generating element50, as illustrated inFIG. 7.

At this time, in the present embodiment, the ratio Vl/Va of the volume Vl of the power generating element relative to the volume Va of the tightly sealed space80before use is less than or equal to 0.995. Thus, the volume of the extra space70is larger than a predetermined value before use. As a result, even if the gas11is moved to the extra space70, the pressure inside the tightly sealed space80will not immediately rise.

The volume adjustment portion140is in a relaxed state while the amount of gas11that has moved to the extra space70is small. Thereafter, when the amount of gas11that has moved to the extra space70increases, the volume adjustment portion140changes to a stretched state, as illustrated inFIG. 8. A rise in the pressure inside the tightly sealed space80, which occurs due to the gas11moving to the extra space70, is thereby suppressed. Thus, the movement of the gas11that is generated inside the power generating element50is prevented from being obstructed by an increase in the pressure of the tightly sealed space80. As a result, the movement of the gas11that is generated inside the power generating element50is promoted, and an occurrence of liquid depletion due to the gas11remaining inside the power generating element50is prevented. In addition, the power generating element50can expand in the layering direction Z with use. When the power generating element50expands in the layering direction Z, the volume adjustment portion140changes to a stretched state, in the same manner as the case in which the gas11moves, as described above with reference toFIG. 8. A rise in the pressure inside the tightly sealed space80, which occurs due to the power generating element50expanding in the layering direction Z, is thereby suppressed. As a result, the occurrence of liquid depletion is also prevented even when the power generating element50expands.

Additionally, the exterior member110is pressed against surfaces SU, SB intersecting the layering direction Z of the power generating element50, due to a pressure difference between the outside space and the tightly sealed space80. As a result, pressures P1, P2from the exterior member110are uniformly applied to the surfaces SU, SB intersecting the layering direction Z of the power generating element50(refer toFIG. 7).

Then, the volume adjustment portion140allows for an increase in the volume of the extra space70while maintaining the state in which the exterior member110is pressed against the surfaces SU, SB intersecting the layering direction Z of the power generating element50. As a result, a gap is prevented from being formed between the exterior member110and the surfaces SU, SB intersecting the layering direction Z of the power generating element50. Thus, gas11is prevented from entering between the exterior member110and the surface SU intersecting the layering direction Z of the power generating element50, as illustrated inFIG. 9. In addition, while not shown, gas11is similarly prevented from entering between the exterior member110and the surface SB intersecting the layering direction Z of the power generating element50. As a result, a state in which pressures P1, P2from the exterior member110are uniformly applied to the surfaces SU, SB intersecting the layering direction Z of the power generating element50is maintained.

Action and Effects

The lithium ion secondary battery100according to the present embodiment comprises an electrolytic solution10, and a power generating element50that contains electrolyte layers20and a plurality of positive electrodes30and negative electrodes40layered with each of the electrolyte layers20therebetween, and that expands with use in the layering direction Z of the positive electrodes30and the negative electrodes40. In addition, the lithium ion secondary battery100comprises an exterior member110forming a tightly sealed space80containing a space60in which the power generating element50is housed, and an extra space70. The extra space70is formed between the exterior member110and a side surface SS along the layering direction Z of the power generating element50. The exterior member110includes a volume adjustment portion140allowing for an increase in the volume of the extra space70by expanding in response to a pressure rise inside the tightly sealed space80while the exterior member is being pressed against the surfaces SU, SB intersecting the layering direction Z of the power generating element50due to a pressure difference between the exterior and the interior. The volume adjustment portion140allows for an increase in the volume of the extra space70while maintaining the state in which the exterior member110is pressed against the surfaces SU, SB intersecting the layering direction Z of the power generating element50.

According to such a configuration, an increase in the volume of the extra space70corresponding to a pressure rise inside the tightly sealed space80is permitted by the volume adjustment portion140. A rise in the pressure inside the tightly sealed space80, which occurs due to gas11generated in the power generating element50moving to the extra space70, is thereby suppressed. Thus, it becomes possible to smoothly move the gas11generated inside the power generating element50to the extra space70. In addition, the volume adjustment portion140allows for an increase in the volume of the extra space70while maintaining the state in which the exterior member110is pressed against the surfaces SU, SB intersecting the layering direction Z of the power generating element50. As a result, a gap is prevented from forming between the exterior member110and the surfaces SU, SB intersecting the layering direction Z of the power generating element50. Thus, it becomes difficult for a part of the gas11that has moved to the extra space70to enter between the exterior member110and the surfaces SU, SB intersecting the layering direction Z of the power generating element50. Therefore, it is possible to provide a lithium ion secondary battery100that is capable of preventing liquid depletion while maintaining a state in which pressure from the exterior member110acts uniformly on surfaces SU, SB intersecting the layering direction Z of the power generating element50.

In addition, in the lithium ion secondary battery100according to the present embodiment, the ratio of the volume Vl of the power generating element relative to the volume Va of the tightly sealed space80before use satisfies 0.800≤Vl/Va≤0.995.

According to such a configuration, since Vl/Va is less than or equal to 0.995 before use, the volume of the extra space70is larger than a predetermined value. As a result, a rise in the pressure inside the tightly sealed space80, which occurs due to the gas11generated in the power generating element50moving to the extra space70, is further alleviated. Thus, it becomes possible to more reliably carry out a smooth movement of the gas11generated inside the power generating element50to the extra space70.

Additionally, since Vl/Va is greater than or equal to 0.800 before use, the volume of the extra space70is smaller than a predetermined value. As a result, it becomes possible more reliably to prevent a gap from forming between the exterior member110and the surfaces SU, SB intersecting the layering direction Z of the power generating element50, caused by a significant change in the shape of the extra space70. Thus, it becomes possible more reliably to prevent a part of the gas11that has moved to the extra space70from entering between the exterior member110and the surfaces SU, SB intersecting the layering direction Z of the power generating element50.

Additionally, in the lithium ion secondary battery100according to the present embodiment, the extra space70is disposed surrounding the power generating element50.

According to such a configuration, the average movement distance of the gas11generated inside the power generating element50with respect to the extra space70becomes small. As a result, it becomes possible to even more reliably carry out a smooth movement of the gas11generated inside the power generating element50to the extra space70.

In addition, in the lithium ion secondary battery100according to the present embodiment, the positive electrodes30and the negative electrodes40are electrode plates having a rectangular shape. The aspect ratio of the electrode plates that constitute the positive electrodes30and the negative electrodes40is 1 to 3.

According to such a configuration, the aspect ratio of the lithium ion secondary battery100can be adjusted in accordance with the space in which the lithium ion secondary battery100is mounted. As a result, the utilization efficiency of the space in which the lithium ion secondary battery100is mounted is improved.

Modified Example of the First Embodiment

In the lithium ion secondary battery100according to the first embodiment, the volume adjustment portion140allows for an increase in the volume of the extra space70by the connecting portion123and the connecting portion133changing from a loose state to a stretched state. However, the configuration of the volume adjustment portion140may be changed as long as the configuration can allow for an increase in the volume of the extra space70while maintaining the state in which the exterior member110is pressed against the surfaces SU, SB intersecting the layering direction Z of the power generating element50.

For example, as the volume adjustment portion140, an expandable portion may be formed in the connecting portion123and the connecting portion133.

FIG. 10is an enlarged view illustrating the volume adjustment portion140of a lithium ion secondary battery200according to the present modified example, corresponding to the portion surrounded by the broken line portion M1ofFIG. 6.FIG. 11is an enlarged view illustrating the volume adjustment portion140of the lithium ion secondary battery200according to the present modified example, corresponding to the portion surrounded by the broken line portion M1ofFIG. 6, showing the volume adjustment portion140while the volume is being adjusted.

In the lithium ion secondary battery200according to the present modified example, an expandable portion125is formed in the connecting portion123as the volume adjustment portion140, as illustrated inFIG. 10. Additionally, an expandable portion135is formed in the connecting portion133as the volume adjustment portion140.

The expandable portions125,135expand as the amount of gas11that has moved to the extra space70increases, as illustrated inFIG. 11. A rise in the pressure inside the tightly sealed space80, which occurs due to gas11generated in the power generating element50moving to the extra space70, is thereby more reliably suppressed. As a result, it becomes possible to even more reliably carry out a smooth movement of the gas11generated inside the power generating element50to the extra space70.

Second Embodiment

The lithium ion secondary battery300according to the second embodiment is different from the lithium ion secondary battery100according to the first embodiment in the following feature.

That is, in the lithium ion secondary battery100according to the first embodiment, the ratio of the volume Vl of the power generating element50relative to the volume Va of the tightly sealed space80is regulated within a predetermined range.

On the other hand, the lithium ion secondary battery300according to the second embodiment is different from the lithium ion secondary battery100according to the first embodiment in that the angle formed between the connecting portion of the exterior member and a direction Y that intersects the layering direction Z of the power generating element50is regulated.

The configuration according to the above-described difference will be described below. However, configurations that are the same as the configuration of the lithium ion secondary battery100according to the first embodiment will be given the same reference symbols and descriptions thereof will be omitted.

FIGS. 12(A)and (B) are schematic cross-sectional views corresponding toFIGS. 5(A)and (B).FIG. 13is a cross-sectional view corresponding toFIG. 6, illustrating the lithium ion secondary battery300according to the present embodiment.FIG. 14is an enlarged view illustrating the volume adjustment portion340of the lithium ion secondary battery300according to the present embodiment, corresponding to the portion surrounded by the broken line portion M3ofFIG. 13.

As illustrated inFIGS. 12 and 13, the lithium ion secondary battery300according to the present embodiment comprises an electrolytic solution10(not shown), and a power generating element50that contains electrolyte layers20and a plurality of positive electrodes30and negative electrodes40layered with each of the electrolyte layers20therebetween, and that expands with use in the layering direction Z of the positive electrodes30and the negative electrodes40. The lithium ion secondary battery300further comprises an exterior member310forming a tightly sealed space380containing a space360in which the power generating element50is housed, and an extra space370. The extra space370is formed between the exterior member310and a side surface SS along the layering direction Z of the power generating element50. The exterior member310is pressed against surfaces SU, SB intersecting the layering direction Z of the power generating element50, due to a pressure difference between the exterior and the interior. The exterior member310includes a volume adjustment portion340that allows for an increase in the volume of the extra space370by expanding in accordance with a pressure rise inside the tightly sealed space380. The volume adjustment portion340allows for an increase in the volume of the extra space370while maintaining the state in which the exterior member310is pressed against the surfaces SU, SB intersecting the layering direction Z of the power generating element50.

The configuration of the lithium ion secondary battery300according to the present embodiment is the same as the configuration of the lithium ion secondary battery100according to the first embodiment, except that the configuration of the exterior member310is different from the configuration of the exterior member110of the lithium ion secondary battery100according to the first embodiment. Thus, descriptions of the configurations other than the exterior member310are omitted.

Exterior Member

The exterior member310includes a first exterior member320and a second exterior member330, which are joined to each other, as illustrated inFIG. 12(A). The exterior member310forms a tightly sealed space380inside the exterior member310.

The first exterior member320and the second exterior member330are joined to each other by an end portion320E of the first exterior member320being joined to an end portion330E of the second exterior member330. The tightly sealed space380is formed by the first exterior member320and the second exterior member330being joined to each other.

The tightly sealed space380is in a reduced pressure state. That is, the pressure inside the tightly sealed space380is lower than the pressure outside the tightly sealed space380. The tightly sealed space380includes a space360in which the power generating element50is housed, and an extra space370, as illustrated inFIG. 12(B).

The first exterior member320and the second exterior member330are joined in a state of sandwiching the power generating element50in the layering direction Z of the power generating element50, as illustrated inFIG. 13.

The first exterior member320comprises an abutting portion321that abuts the surface SU intersecting the layering direction Z of the power generating element50, a joint portion322that is joined to the second exterior member330, and a connecting portion323that connects the abutting portion321and the joint portion322.

The second exterior member330comprises an abutting portion331that abuts the surface SB intersecting the layering direction Z of the power generating element50, a joint portion332that is joined to the first exterior member320, and a connecting portion333that connects the abutting portion331and the joint portion332.

The abutting portion321is pressed against the surface SU intersecting the layering direction Z of the power generating element50, due to a pressure difference between the outside pressure and the inside pressure of the tightly sealed space380described above. The abutting portion331is similarly pressed against the surface SB intersecting the layering direction Z of the power generating element50, due to said pressure difference.

The end portion321E of the abutting portion321abuts an end portion E1of the surface SU intersecting the layering direction Z of the power generating element50. The end portion331E of the abutting portion331abuts an end portion E2of the surface SB intersecting the layering direction Z of the power generating element50.

The joint portion322and the joint portion332are joined, provided with a predetermined width.

The joint portion322comprises a first end portion322a, which is disposed at a boundary between a portion of the first exterior member320that is joined to the second exterior member330and a portion that is not joined to the second exterior member330, and a second end portion322bthat is different from the first end portion322a.

The joint portion332comprises a first end portion332a, which is disposed at a boundary between a portion of the second exterior member330that is joined to the first exterior member320and a portion that is not joined to the first exterior member320, and a second end portion332bthat is different from the first end portion332a.

In the exterior member110, at locations where the positive electrode tab31a(negative electrode tab41a) is taken out from the inside to the outside of the lithium ion secondary battery300, the first exterior member320and the second exterior member330are joined via the positive electrode current collector31(negative electrode current collector41) and the positive electrode tab31a(negative electrode tab41a) (refer toFIG. 4). In these locations, the boundary between the portion joined to the positive electrode current collector31(negative electrode current collector41) or the positive electrode tab31a(negative electrode tab41a) and the portion not joined to the positive electrode current collector31(negative electrode current collector41) or the positive electrode tab31a(negative electrode tab41a) corresponds to the first end portion322a,332a.

The connecting portion323connects the end portion321E of the abutting portion321and the first end portion322aof the joint portion322. The connecting portion333connects the end portion331E of the abutting portion331and the first end portion332aof the joint portion332.

The extra space370is formed between the connecting portion323and the connecting portion333and the side surface SS along the layering direction of the power generating element50. The extra space370is disposed surrounding the power generating element50.

The first exterior member320and the second exterior member330include a volume adjustment portion340that allows for an increase in the volume of the extra space370by expanding in accordance with a pressure rise inside the tightly sealed space380. The volume adjustment portion340allows for an increase in the volume of the extra space370while maintaining the state in which the exterior member310is pressed against the surface SU intersecting the layering direction Z of the power generating element50. In the present embodiment, the volume adjustment portion340is configured by forming a loose portion in parts of the connecting portion323and the connecting portion333.

In the present embodiment, the angle formed by the connecting portions323,333and the direction Y intersecting the layering direction Z of the power generating element50is regulated within a predetermined range. Specifically, the angle θ1(θ2) formed by the straight line H1(H2) that connects the end portion E1(E2) of the surface SU (SB) intersecting the layering direction Z of the power generating element50and the first end portion322a(332a) of the joint portion322(332), and the straight line G intersecting the layering direction Z of the power generating element50, satisfies 15°≤θ1(θ2)≤62°, as illustrated inFIG. 14. InFIG. 14, the straight line G extends along the direction Y, which intersects the layering direction Z of the power generating element50. θ1and θ2can be measured by a geometric method using, for example, a cross-sectional image of the lithium ion secondary battery300acquired using an X-ray CT device. The average value θa of θ1and θ2=(θ1+θ2)/2 may be set in a range of 15°≤θa≤62°, giving consideration to measurement errors of θ1and θ2.

Next, the operation of the lithium ion secondary battery300according to the present embodiment will be described, with reference toFIG. 15.

FIG. 15is an enlarged view illustrating the volume adjustment portion340of the lithium ion secondary battery300, corresponding to the portion surrounded by the broken line portion M3ofFIG. 13, showing the volume adjustment portion340while the volume of the extra space370is being increased. InFIG. 15, the electrolytic solution10and the gas11are omitted.

As described above in the first embodiment, gas11is generated inside the power generating element50by repeated charging and discharging of the lithium ion secondary battery300. Then, the gas11that is generated inside the power generating element50moves to the extra space370.

If the amount of gas11that has moved to the extra space370increases, pressure P3(P4) acts on the connecting portion323(333) from the electrolytic solution10that is housed in the extra space370. As a result, the connecting portion323(333) is stretched, and tensile force T1(T2) is generated in the connecting portion323(333).

Then, due to the tensile force T1(T2) generated in the connecting portion323(333), a force F1(F2) acts to press the end portion321E (331E) of the abutting portion321(331) against the end portion E1(E2) of the surface SU (SB) intersecting the layering direction Z of the power generating element50.

The force F1(F2) becomes weaker as the angle θ1(θ2), which is formed by the straight line H1(H2) that connects the end portion E1(E2) of the surface SU (SB) and the joint portion322(332) of the first exterior member320and the second exterior member330and by the direction Y that intersects the layering direction Z of the power generating element50, becomes smaller.

Here, in the lithium ion secondary battery300according to the present embodiment, θ1(θ2) is less than or equal to 62°. Thus, by the end portion321E (331E) of the abutting portion321(331) being strongly pressed against the end portion E1(E2) of the surface SU (SB) intersecting the layering direction Z of the power generating element50, the shape of the power generating element50is prevented from changing.

Action and Effects

According to the lithium ion secondary battery300of the present embodiment, the exterior member310includes a first exterior member320and a second exterior member330, which are joined to each other. In the first exterior member320and the second exterior member330, an end portion320E of the first exterior member320is joined to an end portion330E of the second exterior member330, in a state of sandwiching the power generating element50in the layering direction Z of the power generating element50. The angle θ1(θ2), which is formed by the straight line H1(H2) that connects the end portion E1(E2) of the surface SU (SB) intersecting the layering direction Z of the power generating element50and the joint portion322(332) of the first exterior member320and the second exterior member330and by the direction Y that intersects the layering direction Z of the power generating element50before use, satisfies 15°≤θ1(θ2)≤62°.

According to such a configuration, since θ1(θ2) is less than or equal to 62°, of the force that acts on the abutting portion321(331) from the connecting portion323(333), the force in the layering direction Z of the power generating element50becomes weaker. As a result, it is possible to prevent the shape of the power generating element50from being changed, due to a force in the layering direction Z acting on the power generating element50from the exterior member310. As a result, a state in which pressures P1, P2from the exterior member110are uniformly applied to the surfaces SU, SB intersecting the layering direction Z of the power generating element50is more reliably maintained.

In addition, the volume of the extra space70decreases as θ1(θ2) increases. Then, the utilization efficiency of the space for mounting the lithium ion secondary battery300according to the present embodiment becomes higher as the volume of the extra space70becomes smaller. In the present embodiment, since θ1(θ2) is greater than or equal to 15°, the utilization efficiency of the space for mounting the lithium ion secondary battery300according to the present embodiment is high.

Third Embodiment

The lithium ion secondary battery400according to the third embodiment is different from the lithium ion secondary battery300according to the second embodiment in the following feature.

That is, in the lithium ion secondary battery300according to the second embodiment, the portions where the first exterior member320and the second exterior member330are joined (joint portion322,332) are disposed between one outermost surface (surface SU inFIG. 13) and the other outermost surface (surface SB inFIG. 13) of the power generating element50in the layering direction Z.

On the other hand, the lithium ion secondary battery400according to the third embodiment is different from the lithium ion secondary battery300according to the second embodiment in that the portions where the first exterior member and the second exterior member are joined are disposed on the same outermost surface of the power generating element50in the layering direction Z.

The configuration according to the above-described difference will be described below. However, configurations that are the same as the configuration of the lithium ion secondary battery300according to the second embodiment will be given the same reference symbols and descriptions thereof will be omitted.

FIG. 16is a cross-sectional view corresponding toFIG. 4, illustrating the lithium ion secondary battery400according to the present embodiment.FIGS. 17(A)and (B) are schematic cross-sectional views corresponding toFIGS. 5(A)and (B).FIG. 18is a cross-sectional view corresponding toFIG. 6, illustrating the lithium ion secondary battery400according to the present embodiment.FIG. 19is an enlarged view illustrating the volume adjustment portion440of the lithium ion secondary battery400according to the present modified example, corresponding to the portion surrounded by the broken line portion M4ofFIG. 18.

As illustrated inFIGS. 16 and 17, the lithium ion secondary battery400according to the present embodiment comprises an electrolytic solution10(not shown), and a power generating element450that contains electrolyte layers20and a plurality of positive electrodes30and negative electrodes40layered with each of the electrolyte layers20therebetween, and that expands with use in the layering direction Z of the positive electrodes30and the negative electrodes40. The lithium ion secondary battery400further comprises an exterior member410forming a tightly sealed space480containing a space460in which the power generating element450is housed, and an extra space470. The extra space470is formed between the exterior member410and a side surface SS along the layering direction Z of the power generating element450. The exterior member410is pressed against surfaces SU, SB intersecting the layering direction Z of the power generating element450, due to a pressure difference between the exterior and the interior. The exterior member410includes a volume adjustment portion440that allows for an increase in the volume of the extra space470in accordance with a pressure rise inside the tightly sealed space480. The volume adjustment portion440allows for an increase in the volume of the extra space470while maintaining the state in which the exterior member410is pressed against the surfaces SU, SB intersecting the layering direction Z of the power generating element450.

The configuration of the lithium ion secondary battery400according to the present embodiment is the same as the configuration of the lithium ion secondary battery300according to the second embodiment, except that the configurations of the power generating element450and the exterior member410are different from the configurations of the power generating element50and the exterior member310of the lithium ion secondary battery300according to the second embodiment. Thus, descriptions of the configurations other than the power generating element450and the exterior member410are omitted.

Power Generating Element

The configuration of the power generating element450is the same as the configuration of the power generating element50of the lithium ion secondary battery300according to the second embodiment, except that the thickness of the power generating element450in the layering direction Z is half the thickness of the power generating element50in the layering direction Z. The thickness of the power generating element450in the layering direction Z can be adjusted by changing the number of laminations of the electrolyte layers20, the positive electrodes30, and the negative electrodes40. If the number of laminations of the positive electrodes30is d and the capacity of the battery is Q, it is preferable that 0.7≤Q/d≤5.0 be satisfied. Since a negative electrode40is disposed on the outermost layer of the power generating element450, if the number of laminations of the positive electrodes30is d, the number of laminations of the negative electrodes40is d+1. In addition, in the case that a positive electrode30is disposed on the outermost layer of the power generating element450, the number of laminations of the negative electrodes40may be set to d, to satisfy 0.7≤Q/d≤5.0.

Exterior Member

The exterior member410includes a first exterior member420and a second exterior member430, which are joined to each other, as illustrated inFIG. 17(A). The exterior member410forms a tightly sealed space480inside the exterior member410.

The first exterior member420and the second exterior member430are joined to each other by an end portion420E of the first exterior member420being joined to an end portion430E of the second exterior member430. The tightly sealed space480is formed by the first exterior member420and the second exterior member430being joined to each other.

The tightly sealed space480is in a reduced pressure state. That is, the pressure inside the tightly sealed space480is lower than the pressure outside the tightly sealed space480. The tightly sealed space480includes a space460in which the power generating element450is housed, and an extra space470, as illustrated inFIG. 17(B).

The first exterior member420and the second exterior member430are joined in a state of sandwiching the power generating element450in the layering direction Z of the power generating element450, as illustrated inFIG. 18.

The first exterior member420comprises an abutting portion421that abuts the surface SU intersecting the layering direction Z of the power generating element450, a joint portion422that is joined to the second exterior member430, and a connecting portion423that connects the abutting portion421and the joint portion422.

The second exterior member430extends in the direction of the surface intersecting the layering direction of the power generating element450. The second exterior member430comprises an abutting portion431that abuts the surface SB intersecting the layering direction Z of the power generating element450, a joint portion432that is joined to the first exterior member420, and a connecting portion433that connects the abutting portion431and the joint portion432.

The abutting portion421is pressed against the surface SU intersecting the layering direction Z of the power generating element450, due to the difference between the external and the internal pressure of the tightly sealed space480described above. The abutting portion431is similarly pressed against the surface SB intersecting the layering direction Z of the power generating element450, due to said pressure difference.

The end portion421E of the abutting portion421abuts an end portion E1of the surface SU intersecting the layering direction Z of the power generating element450.

The joint portion422and the joint portion432are joined, provided with a predetermined width.

The joint portion422comprises a first end portion422a, which is disposed at a boundary between a portion of the first exterior member420that is joined to the second exterior member430and a portion that is not joined to the second exterior member430, and a second end portion422bthat is different from the first end portion422a.

The joint portion432comprises a first end portion432a, which is disposed at a boundary between a portion of the second exterior member430that is joined to the first exterior member420and a portion that is not joined to the first exterior member420, and a second end portion432bthat is different from the first end portion432a.

In the exterior member410, at locations in which the positive electrode tab31a(negative electrode tab41a) is taken out from the inside to the outside of the lithium ion secondary battery400, the first exterior member420and the second exterior member430are joined via the positive electrode current collector31(negative electrode current collector41) and the positive electrode tab31a(negative electrode tab41a) (refer toFIG. 16). In these locations, the boundary between the portion joined to the positive electrode current collector31(negative electrode current collector41) or the positive electrode tab31a(negative electrode tab41a) and the portion not joined to the positive electrode current collector31(negative electrode current collector41) or the positive electrode tab31a(negative electrode tab41a) corresponds to the first end portion422a,432a.

The connecting portion423connects the end portion421E of the abutting portion421and the first end portion422aof the joint portion422. The connecting portion433connects the end portion431E of the abutting portion431and the first end portion432aof the joint portion432.

The extra space470is formed between the connecting portion423and the connecting portion433and the side surface SS along the layering direction of the power generating element450. The extra space470is disposed surrounding the power generating element450.

The first exterior member420includes a volume adjustment portion440that allows for an increase in the volume of the extra space470by expanding in accordance with a pressure rise inside the tightly sealed space480. The volume adjustment portion440allows for an increase in the volume of the extra space470while maintaining the state in which the exterior member410is pressed against the surface SU intersecting the layering direction Z of the power generating element450. In the present embodiment, the volume adjustment portion440is configured by forming a loose portion in a part of the connecting portion423.

In the present embodiment, the angle formed by the connecting portion423and the direction Y intersecting the layering direction Z of the power generating element450is regulated within a predetermined range. Specifically, the angle θ3, which is formed by the straight line H3that connects the end portion421E of the surface SU intersecting the layering direction Z of the power generating element450and the first end portion422aof the joint portion422and by the planar direction of the second exterior member430, satisfies 15°≤θ3≤62°, as illustrated inFIG. 19. As described above, the planar direction of the second exterior member430is a direction intersecting the layering direction Z of the power generating element450.

The lithium ion secondary battery400according to the present modified example comprising the configuration described above also exerts the same effects as the lithium ion secondary battery according to the second embodiment.

EXAMPLES

The present invention is described in further detail, using the following Examples A1-A19, B1-B16, and Comparative Examples A1-A3, and B1-B3. However, the technical scope of the present invention is not limited to the following examples.

Examples A1-A19 and Comparative Examples A1-A3 were mainly used in order to investigate the relationship between the capacity retention rate and the value of the ratio Vl/Va of the volume Vl of the power generating element relative to the volume Va of the tightly sealed space80. In addition, Examples B1-B16 and Comparative Examples B1-B3 were mainly used in order to investigate the relationship between the capacity retention rate and the angle θ (corresponding to the average value θa=(θ1+θ2)/2 of θ1and θ2, described above in the second embodiment) formed by a straight line that connects the sealing point of the laminate external casing and an end portion of the surface intersecting the layering direction of the power generating element and by the direction intersecting the layering direction of the power generating element.

The test method and the manufacturing method of the lithium ion secondary battery are common to Examples A1-A19, and B1-B16, as well as Comparative Examples A1-A3, and B1-B3. The lithium ion secondary batteries according to Examples A1-A19 and Comparative Examples A1-A3 are distinguished by the value of the ratio Vl/Va of the volume Vl of the power generating element relative to the volume Va of the tightly sealed space80, or by the material of the negative electrode. Additionally, Examples B1-B16 and Comparative Examples B1-B3 are distinguished by the value of the angle θ. The test method and the manufacturing method of the lithium ion secondary battery according to Examples A1-A19, and B1-B16, as well as Comparative Examples A1-A3, and B1-B3 will be described below.

Preparation of the Positive Electrodes

90 wt % of NMC complex oxide LiNi0.5Mn0.3Co0.2O2, 5 wt % of Ketjen black as conductive assistant, 5 wt % of polyvinylidene fluoride (PVdF) as binder, and an appropriate amount of NMP as slurry viscosity adjusting solvent were mixed to prepare a positive electrode active material slurry.

Next, the obtained positive electrode active material slurry was applied to an aluminum foil (thickness of 20 μm) as a current collector.

Next, compression-molding was carried out with a roll press machine after drying at 120° C. to prepare a positive electrode active material layer positive electrode.

A positive electrode active material layer was also formed on the rear surface with the same method as the method described above, to prepare a positive electrode made by positive electrode active material layers being formed on both surfaces of a positive electrode current collector.

Preparation of the Negative Electrodes

96.5 wt % of artificial graphite or silicon as negative electrode active material, 1.5 wt % of ammonium salt of carboxymethyl cellulose as binder, and 2.0 wt % of styrene butadiene copolymer latex were dispersed in purified water to prepare a negative electrode active material slurry.

Next, the negative electrode active material slurry was applied to a copper foil (thickness of 10 am), which becomes a negative electrode current collector.

Next, compression-molding was carried out with a roll press machine after drying at 120° C. to prepare a negative electrode active material layer negative electrode.

A negative electrode active material layer was also formed on the rear surface by the same method as the method described above to prepare a negative electrode made by negative electrode active material layers being formed on both surfaces of a negative electrode current collector.

Preparation of Cells

Power generating elements were prepared by alternately laminating the positive electrodes and the negative electrodes prepared by the above-described method with separators interposed therebetween.

Then, the prepared power generating elements were placed in an aluminum laminate sheet bag, and an electrolytic solution was injected.

A solution obtained by dissolving 1.0 M of LiPF6 in a mixed solvent of ethylene carbonate (EC):diethyl carbonate (DEC):ethyl methyl carbonate (EMC) (volume ratio 1:1:1) was used as the electrolytic solution.

Next, under vacuum conditions, the opening of the aluminum laminate bag was sealed such that the current extraction tabs connected to both electrodes are led out, to complete a laminate type lithium ion secondary battery.

In Examples B1-B16 and Comparative Examples B1-B3, angle θ, which is formed by a straight line that connects the sealing point of the laminate external casing and an end portion of the surface intersecting the layering direction of the power generating element and by the direction intersecting the layering direction of the power generating element, on the cross section of the completed lithium ion secondary battery, was confirmed with an X-ray CT device (SMX-225 CT, manufactured by Shimadzu Corporation, X-ray tube voltage: 170 kV, X-ray tube current: 40 μA).

Durability Test

Initial performance check—The completed batteries were subjected to 0.2C_CCCV charging (upper limit voltage 4.15V, 8 hours), and then subjected to 0.2C_CC discharging (lower limit voltage 2.5V cut), in a thermostatic chamber set to 25° C., to check the initial charge/discharge capacity. In addition, the volumes and thicknesses of the completed batteries were measured. The volumes of the batteries were measured by Archimedes' method. In addition, the thickness of the battery was multiplied by the area of the negative electrode to obtain the volume of the power generating element.

Durability Test

The completed batteries were subjected to 1,000 cycles of 1C_CCCV charging (upper limit voltage 4.15V, 2 hours) and 1C_CC discharging (lower limit voltage 2.5V cut), in a thermostatic chamber set to 45° C. It is possible to check the performance during the durability test at 25° C. during the durability test (for example, every 250 cycles).

Performance Check During the Durability Test

The batteries after the durability test were subjected to 0.2C_CCCV charging (upper limit voltage 4.15V, 8 hours), and then subjected to 0.2C_CC discharging (lower limit voltage 2.5V), in a thermostatic chamber set to 25° C., to check the charge/discharge capacity after the durability test. In addition, the volumes and thicknesses of the batteries after the durability test were measured. The volumes of the batteries were measured by Archimedes' method. In addition, the thickness of the battery was multiplied by the area of the negative electrode to obtain the volume of the power generating element.

Next, the test results of the capacity retention rate and the volume increase rate of the lithium ion secondary batteries according to Examples A1-A19 and B1-B16 as well as Comparative Examples A1-A3 and B1-B3 are considered.

First, the test results of Examples A1-A19 and Comparative Examples A1-A3 are considered, with reference to Table 1 andFIG. 20.

Table 1 below is a table showing the test results of the capacity retention rate and the volume increase rate of the lithium ion secondary batteries according to Examples A1-A19 and Comparative Examples A1-A3.

Table 1 shows the ratio Vl/Va of the volume Vl of the power generating element relative to the volume Va of the tightly sealed space80, as well as the material used for the positive electrode and the negative electrode of the lithium ion secondary batteries according to Examples A1-A19 and Comparative Examples A1-A3. Additionally, the values of the capacity retention rate and the volume increase rate are indicated by “-” in Table 1 for lithium ion secondary batteries in which liquid depletion occurred during the test.

FIG. 20is a view illustrating the relationship between the volume increase rate V % and the capacity retention rate C % of the lithium ion secondary battery according to Examples A1-A19 and Comparative Examples A1-A3.

Regarding Examples A1-A19, the ratio of the volume Vl of the power generating element relative to the volume Va of the tightly sealed space satisfied Vl/Va≤0.995, as shown in Table 1. Then, as shown in Table 1 andFIG. 20, Examples A1-A19 all comprise high capacity retention rates exceeding 80%.

On the other hand, regarding Comparative Example A1-A3, the ratio of the volume Vl of the power generating element relative to the volume Va of the tightly sealed space was Vl/Va>0.995, as shown in Table 1. Then, as shown in Table 1 andFIG. 20, Comparative Examples A1-A3 all comprise low capacity retention rates below 80%.

Therefore, it can be seen that the capacity retention rate is higher when Vl/Va≤0.995 compared to when Vl/Va>0.995. That is, it can be seen that liquid depletion is less likely to occur by setting Vl/Va≤0.995.

On the other hand, as shown in Table 1, it can be seen that the volume increase rate approaches 0% as Vl/Va approaches 0.8. It is thought that, since the ratio of the volume of the extra space relative to the volume Va of the tightly sealed space increases as Vl/Va approaches 0.8, the volume expansion of the power generating element in the layering direction is absorbed by the change in the shape of the extra space, and the volume increase rate approaches 0%. When Vl/Va becomes smaller than 0.8 and the ratio of the volume of the extra space increases further, the shape of the extra space tends to change significantly, as the pressure inside the tightly sealed space rises. When the shape of the extra space changes significantly, part of the gas that has moved to the extra space enters between the exterior member and the surface intersecting the layering direction of the power generating element, and it becomes difficult for the pressure from the exterior member to be uniformly applied to the surface intersecting the layering direction of the power generating element. Therefore, from the point of view of making the pressure that is applied from the exterior member to the surface intersecting the layering direction of the power generating element uniform to prevent a deterioration of the battery performance, it is advantageous to set Vl/Va≥0.8.

Next, the test results of Examples B1-B16 and Comparative Examples B1-B3 are considered, with reference to Table 2 andFIG. 21.

Table 2 below shows the test results of the capacity retention rate and the volume increase rate of the lithium ion secondary batteries according to Examples B1-B16 and Comparative Examples B1-B3.

Table 2 shows the angle θ, which is formed by a straight line that connects the sealing point of the laminate external casing and an end portion of the surface intersecting the layering direction of the power generating element and by the direction intersecting the layering direction of the power generating element, as well as the material used for the positive electrode and the negative electrode of the lithium ion secondary batteries according to Examples B1-B16 and Comparative Examples B1-B3.

FIG. 21is a view illustrating the relationship between the volume increase rate V % and the capacity retention rate C % of the lithium ion secondary battery according to Examples B1-B16 and Comparative Examples B1-B3.

As shown in Table 2, regarding Examples B1-B16, the angle θ satisfied θ≤62°. Then, as shown in Table 2 andFIG. 21, Examples B1-B16 all comprise high capacity retention rates exceeding 80%.

On the other hand, regarding comparative examples B1-B3, the angle θ was θ>62°. Then, as shown in Table 2 andFIG. 21, Comparative Examples B1-B3 all comprise low capacity retention rates below 80%.

Therefore, it can be seen that the capacity retention rate is higher when the angle θ, which is formed by a straight line that connects the sealing point of the laminate external casing and an end portion of the surface intersecting the layering direction of the power generating element and by the direction intersecting the layering direction of the power generating element, satisfies θ≤62°, compared to when θ>62°. That is, it can be seen that by setting θ≤62°, it becomes possible to more reliably maintain a state in which pressure from the exterior member acts uniformly on a surface intersecting the layering direction of a power generating element.

On the other hand, as shown in Table 2, it can be seen that the volume increase rate approaches 0% as θ approaches 15°. It is thought that, since the ratio of the volume of the extra space relative to the volume Va of the tightly sealed space increases as θ approaches 15°, the volume expansion of the power generating element in the layering direction is absorbed by the change in the shape of the extra space, and the volume increase rate approaches 0%. When θ becomes smaller than 15° and the ratio of the volume of the extra space increases further, the shape of the extra space tends to change significantly, as the pressure inside the tightly sealed space rises. When the shape of the extra space changes significantly, part of the gas that has moved to the extra space enters between the exterior member and the surface intersecting the layering direction of the power generating element, and it becomes difficult for the pressure from the exterior member to be uniformly applied to the surface intersecting the layering direction of the power generating element. Therefore, from the point of view of making the pressure that is applied from the exterior member onto the surface intersecting the layering direction of the power generating element uniform to prevent a deterioration of the battery performance, it is advantageous to set θ≥15°.

The present invention is not limited to the embodiment described above, and various modifications are possible within the scope of the claims.

For example, in the second embodiment and the third embodiment, the ratio of the volume Vl of the power generating element relative to the volume Va of the tightly sealed space80may also be regulated within a predetermined range, in the same manner as in the first embodiment.

In addition, in the second embodiment and the third embodiment, an expandable portion may be formed in the exterior member as the volume adjustment portion, in the same manner as in the modified example of the first embodiment.

Furthermore, in the first embodiment, the second embodiment, and the third embodiment, the exterior member is configured by joining a first exterior member and a second exterior member, which are configured as separate bodies. However, a form of the exterior member that is, for example, integrally configured in the form of a bag, is also included in the technical scope of the present invent.