Electric storage device and electric storage apparatus

An electric storage device includes: an electrode assembly in which electrodes are wound such that paired curved portions and a straight portion connecting the paired curved portions are formed; a case which houses the electrode assembly, the case comprising a convex part protruding toward the straight portion of the electrode assembly to support the straight portion; and a support portion which supports the curved portion toward an inside of the electrode assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese patent applications No. 2013-206086, filed on Oct. 1, 2013, and No. 2014-173813, filed on Aug. 28, 2014, which are incorporated by reference.

FIELD

The present invention relates to an electric storage device which can be charged and discharged.

BACKGROUND

Conventionally, there is a known electric storage device such as a secondary battery which can be charged and discharged. The electric storage device includes an electrode assembly formed by layering positive electrodes and negative electrodes with separators interposed therebetween and a case housing the electrode assembly. Among electric storage devices of this type, as shown inFIG. 8, there is one in which a case101has a substantially rectangular parallelepiped external shape capable of housing an electrode assembly102inside itself and paired side walls101a,101aforming the case101have a plurality of convex parts104,104, . . . protruding toward an inside of the case101(JP-A-62-126566).

In such an electric storage device100, the convex parts104press substantially the entire electrode assembly102toward an inner side in a layered direction at predetermined pressure to narrow intervals between the adjacent electrodes103in substantially the entire electrode assembly102. As a result, charge-discharge efficiency of the electric storage device100is enhanced.

SUMMARY

An object of the present invention to provide an electric storage device including an electrode assembly which is formed by winding electrodes and in which partial clearances are less liable to be formed between the adjacent electrodes.

An electric storage device according to an aspect of the invention includes: an electrode assembly in which electrodes are wound such that paired curved portions and a straight portion connecting the paired curved portions are formed; a case which houses the electrode assembly, the case comprising a convex part protruding toward the straight portion of the electrode assembly to support the straight portion; and a support portion which supports the curved portion toward an inside of the electrode assembly.

DESCRIPTION OF EMBODIMENTS

An electric storage device200shown inFIG. 9includes an electrode assembly202formed by winding band-shaped electrodes201, the electrode assembly202being housed in a case203. The band-shaped electrodes201are wound such that a section orthogonal to a winding axis has an elliptic shape. The case203has paired side walls205,205which are parallel to a major axis direction (a vertical direction inFIG. 9) of the electrode assembly202and which respectively have convex parts204protruding toward the electrode assembly202. The convex parts204pinch the electrode assembly202in a minor axis direction (a left-right direction inFIG. 9) so as to narrow intervals between the adjacent electrodes201in the wound electrode assembly202.

In this electric storage device200, if expansion and contraction of the electrode assembly202is repeated due to repetition of charge-discharge or the like, displacements of the electrodes201gather in curved portions (which are end portions of the electrode assembly202in the major axis direction and also are curved portions of the electrodes201)202A not pressed by the convex parts204. Then, partial clearances and the like are formed between the electrodes201layered in the curved portions202A. If the partial clearances are formed between the electrodes201forming the electrode assembly202in this manner, charge-discharge efficiency is reduced.

An electric storage device according to an aspect of the invention includes: an electrode assembly in which electrodes are wound such that paired curved portions and a straight portion connecting the paired curved portions are formed; a case which houses the electrode assembly, the case comprising a convex part protruding toward the straight portion of the electrode assembly to support the straight portion; and a support portion which supports the curved portion toward an inside of the electrode assembly.

With this structure, in the case, the straight portion is supported by the convex part and also the curved portion is supported by the support portion toward the inside of the electrode assembly. Therefore, it is possible to suppress gathering of displacement of the electrodes in the curved portion, the gathering caused by repetition of expansion and contraction of the electrode assembly during charge-discharge, or the like. In this way, it is possible to prevent forming of partial clearances between the electrodes layered at the curved portions of the electrode assembly. Here, the curved portions of the electrode assembly refer to portions of which peripheral faces are curved, and the straight portion of the electrode assembly refers to a portion of which peripheral face is substantially straight.

The support portion may support at least one of the paired curved portions of the electrode assembly.

With this structure, it is possible to prevent forming of the partial clearances between the electrodes layered at least at one of the paired curved portions. In this way, as compared with a structure in which only a straight portion of an electrode assembly is supported, the intervals between the electrodes forming the electrode assembly become narrow, which increases charge-discharge efficiency.

The case may have a substantially rectangular frame-shaped section and house the electrode assembly such that a side of the substantially rectangular frame-shaped section extends along the straight portion, the support portion may be disposed in a corner portion of the substantially rectangular frame-shaped section in the case.

In this manner, because the support portion is disposed in the corner portion of the substantially rectangular frame-shaped section in the case, the support portion is supported by the case from two directions. In this way, the support portion can effectively support the curved portion of the electrode assembly toward inside. As a result, it is possible to more reliably prevent forming of the partial clearances between the electrodes layered in the curved portion.

The support portion may be disposed while being elastically deformed between the case and the curved portion of the electrode assembly.

In this manner, the curved portion of the electrode assembly is supported by utilizing resilience generated by the elastic deformation of the support portion. Therefore, even if the electrode assembly expands and contracts due to the charge-discharge or the like, i.e., changes in size (winding diameter), the support portion can follow the change in size and continue to support the curved portion.

The electric storage device may include an insulating member disposed between the case and the electrode assembly to insulate the case and the electrode assembly from each other, wherein the support portion may be a part of the insulating member.

With this structure, the support portion is formed by using the part of the insulating member for insulating the case and the electrode assembly from each other, and therefore it is possible to reduce the number of parts forming the electric storage device as compared with a case in which a member forming the support portion is disposed separately.

The insulating member may have a portion curved to bulge toward the electrode assembly, and the curved portion of the insulating member may support the curved portion of the electrode assembly.

In this manner, with the simple structure in which the part of the insulating member is curved to bulge toward the electrode assembly, it is possible to form the support portion for supporting the curved portion toward the inside of the electrode assembly.

A dimension of the support portion in a direction orthogonal to a winding direction of the electrodes is preferably substantially equal to or greater than a dimension of the electrode assembly in the direction orthogonal to the winding direction.

With this structure, substantially the entire curved portion in the direction orthogonal to the winding direction of the electrodes is supported at the curved portion, and therefore it is possible to effectively prevent forming of the partial clearances between the layered electrodes at substantially the entire curved portion in the direction orthogonal to the winding direction.

Preferably, the case may have a plurality of the convex parts.

With this structure, because the straight portion of the straight portion is supported by plural convex parts, it is possible to effectively prevent forming of the partial clearances between the layered electrodes at the straight portion due to the charge-discharge.

The case may have a wall portion having a wave-shaped inner surface and a wave-shaped outer surface and having a substantially constant thickness, and the wave-shaped inner surface forms a plurality of the convex parts, and the plurality of convex parts support the straight portion of the electrode assembly at intervals.

With this structure, the straight portion of the electrode assembly is supported by the plurality of convex parts, and therefore it is possible to more effectively suppress forming of the clearances between the electrodes in the straight portion due to the charge-discharge. Furthermore, by providing the plurality of convex parts, rigidity of the case increases.

In the above-described structure, preferably, the case has a substantially-rectangular bottom wall portion when viewed in a direction of a normal, the wall portion has paired wall portions extending substantially vertically from paired long sides of the bottom wall portion, and a maximum clearance between the paired wall portions is greater than a dimension in a short-side direction of the bottom wall portion.

With this structure, when the plurality of electric storage devices are arranged with the straight portions being opposed and bound by a restraining member, the convex parts are pressed by the adjacent battery or the restraining member, and therefore the convex parts can reliably support the straight portion.

According to another aspect of the invention, there is provided an electric storage apparatus including the electric storage device and a restraining member.

According to the aspects of the invention, it is possible to provide the electric storage device including the electrode assembly which is formed by winding the electrodes and in which partial clearances are less liable to be formed between the adjacent electrodes, and the electric storage apparatus including the electric storage device.

An embodiment of the invention will be described below with reference toFIGS. 1 to 3. An electric storage device according to the embodiment is a nonaqueous electrolyte secondary battery (hereafter, merely referred to as “battery”) such as a lithium ion secondary battery.

As shown inFIGS. 1 to 3, a battery10includes a case20, an electrode assembly12, paired current collectors14,14, an insulating member30, support members (support portions)32, and paired terminal portions16,16. In the battery10, the winding-type electrode assembly12is housed in the case20, a section of the electrode assembly12orthogonal to a winding axis having an elliptic shape.

The case20includes a case main body22and a lid body24. The case20houses, in an inner space S surrounded with the case main body22and the lid body24, the electrode assembly12, the paired current collectors14,14, electrolyte solution, and the like. The case main body22and the lid body24are made of aluminum or aluminum-based metal material such as an aluminum alloy, for example. By welding end portions of the case main body22and the lid body24to each other, the case20is formed.

The case main body22has a flat rectangular cylindrical shape having a bottom. Specifically, the case main body22has a bottom wall portion220and a rectangular cylindrical peripheral wall221rising from a peripheral edge of the bottom wall portion220in a direction of a normal to the bottom wall portion220. The bottom wall portion220is in a rectangular shape long in one direction and having four arc-shaped corners when viewed in the direction of the normal to the bottom wall portion220. The peripheral wall221has paired long wall portions222,222rising from long side positions of the peripheral edge of the bottom wall portion220and paired short wall portions223,223rising from short-side positions of the peripheral edge of the bottom wall portion220. In the following description, a long-side direction of the bottom wall portion220will be referred to as an X-axis direction, a short-side direction of the bottom wall portion220will be referred to as a Y-axis direction, and the direction of the normal to the bottom wall portion220will be referred to as a Z-axis direction (seeFIG. 1).

Each of the long wall portions222has the plurality of convex parts225,225, . . . protruding toward an inner side of the case20. To put it concretely, the long wall portion222has a triangular wave-shaped portion222A which repeatedly bends alternately toward an inside and an outside of the case20at a position corresponding to a straight portion12B of the electrode assembly12in a section along the Y-Z plane. At the triangular wave-shaped portion222A, angle portions protruding from portions224positioned on an outermost side of the case20toward the inner side (toward the electrode assembly) form the convex parts225.

As shown inFIG. 3, in the embodiment, the portions224of the triangular wave-shaped portions222A positioned on the outermost sides of the case20are positioned on outer sides in the Y-axis direction than end portions in the Y-axis direction of the bottom wall portion220. In other words, a longest interval between the paired long wall portions222is longer than a dimension in a short-side direction of the bottom wall portion220. Therefore, if a plurality of batteries are arranged with the long wall portions222being opposed and bound by a restraining member (if the plurality of batteries are pressed in a direction orthogonal to the long wall portions222(seeFIG. 10)), the portions224are pressed by the adjacent batteries or the restraining member and, as a result, the convex parts225reliably support (or press) the straight portion12B of the electrode assembly12.

In the embodiment, dimensions in the Z-axis direction of the triangular wave-shaped portions222A are substantially equal to a dimension in the Z-axis direction of the straight portion of the electrode assembly12.

In the paired long wall portions222,222arranged parallel to each other, the respective convex parts225are arranged to protrude in a direction approaching each other at opposed positions in the Z-axis direction. In this way, the respective convex parts225protrude toward the straight portion12B of the electrode assembly12to support the straight portion12B inward in a minor axis direction of the electrode assembly12. In other words, the opposing paired convex parts225,225make up a set, the plurality of sets of convex parts225are arranged in the Z-axis direction, and each of the sets pinches the straight portion12B (electrode assembly12) in the minor axis direction of the electrode assembly12.

In the specification, the sentence, “the convex parts225support the straight portion12B of the electrode assembly12” includes a case in which the convex parts225are directly or indirectly in contact with the straight portion12B of the electrode assembly12when the section of the single battery shown inFIG. 3is observed with a CT scan using X-rays. The sentence, “the convex parts225support the straight portion12B of the electrode assembly12” includes a case in which the convex parts225are directly or indirectly in contact with the straight portion12B of the electrode assembly12when the sections of the batteries are observed with the CT scan using X-rays in a state in which the plurality of batteries are arranged with the long wall portions222being opposed and bound by the restraining member (the state in which the plurality of batteries are pressed in the direction orthogonal to the long wall portions222).

The convex parts225of the singe battery may be away from the straight portion12B of the electrode assembly12when the long wall portions222are not pressed. Such a battery is preferable, because it is relatively easy to form the convex parts225on the case main assembly22.

Each of the convex parts225extends continuously substantially throughout the entire X-axis direction of the long wall portion222. In other words, a dimension in the X-axis direction of the convex part225is substantially the same as a dimension in the X-axis direction of the electrode assembly12housed in the case20.

The short wall portions223connect the end portions of the paired long wall portions222,222arranged parallel to each other at an interval in the Y-axis direction. In this way, the paired long wall portions222,222and the paired short wall portions223,223form the rectangular cylindrical peripheral wall221.

The lid body24is placed on an opening peripheral edge portion of the case main body22to close an opening of the case main body22. The lid body24has a shape conforming to an outer peripheral edge (outline) of the case main body22in a plan view. In other words, the lid body24is a rectangular plate material long in the X-axis direction and having four arc-shaped corners in the plan view.

Moreover, the lid body24is provided with paired terminal through holes240,240, a gas release vent242, and a filling portion244(seeFIG. 2). The paired terminal through holes240,240are formed at an interval in the X-axis direction in the lid body24. The gas release vent242has a thin-walled portion and is formed at a center of the lid body24. The thin-walled portion in the embodiment is in a Y shape. The gas release vent242releases gas in the case20by tearing the thin-walled portion to connect the inside and the outside of the case20when internal pressure (gas pressure) in the case20exceeds a predetermined value. In this way, the gas release vent242reduces the increased internal pressure of the case20. The filling portion244has an electrolyte solution filling hole245formed in the lid body24and a plug body246for closing the electrolyte solution filling hole245. The electrolyte solution filling hole245is an opening through which the electrolyte solution is filled into the case20. The plug body246is fitted into the electrolyte solution filling hole245after the filling to thereby close the electrolyte solution filling hole245.

The electrode assembly12has a band-shaped positive electrode (electrode as a positive electrode)120, a band-shaped negative electrode (electrode as a negative electrode)122, and band-shaped separators124. The positive electrode120and the negative electrode122are wound into an elliptic cylindrical shape with separators124interposed therebetween and while displaced from each other in a width direction (a direction orthogonal to a longitudinal direction of the band-shaped electrodes, i.e., the X-axis direction inFIG. 1) to thereby form the electrode assembly12(seeFIG. 2). The elliptic cylindrical shaped electrode assembly12has an elliptic sectional shape (an outline of the section) along the Y-Z plane.

In the following description, the end portions in the Z-axis of the electrode assembly12(the elliptic shaped section) which are curved portions on the peripheral face of the electrode assembly12(i.e., the portions where the positive electrode120and the negative electrode122are alternately layered while being curved with the separators interposed therebetween) will be referred to as curved portions12A. The portion of the electrode assembly12positioned between the curved portions12A, which is a substantially straight portion on a peripheral face of the electrode assembly12(i.e., the portion where the positive electrode120and the negative electrode122are alternately layered in substantially straight states with the separators interposed therebetween), will be referred to as the straight portion12B. The diameter in the Z-axis direction of the elliptic shape will be referred to as the major axis and the diameter in the Y-axis direction of the elliptic shape will be referred to as the minor axis.

The positive electrode120is formed by a band-shaped sheet of aluminum film supporting a positive active material on its surface, for example. The negative electrode122is formed by a band-shaped sheet of copper film supporting a negative active material on its surface, for example. Each of the positive electrode120and the negative electrode122has a portion not coated with the active material at an end edge portion in the width direction (X-axis direction). As a result, at end portions in the width direction (X-axis direction) of the electrode assembly12, aluminum film and copper film not coated with the active materials are exposed. In this manner, the electrode assembly12has a positive-side protruding part (a positive electrode of the electrode assembly)126formed by only the positive electrode120(the portion not coated with the positive active material) protruding at one end portion in the width direction (X-axis direction) of the electrode assembly12and a negative-side protruding part (a negative electrode of the electrode assembly)126formed by only the negative electrode122(the portion not coated with the negative active material) protruding at the other end portion in the width direction (X-axis direction).

The electrode assembly12formed as described above is housed into a bag-shaped insulating member30(described later) and then housed into the case20so that one side of a substantially rectangular frame-shaped section of the case20(e.g., a section of the long wall portion222extending in the substantially vertical direction inFIG. 3) and the straight portion12B of the electrode assembly12are positioned along each other. Specifically, the electrode assembly12is housed in the case20in such an attitude that a direction of the winding axis corresponds to the longitudinal direction (X-axis direction) of the case20and that the major axis direction corresponds to the direction of the normal to the bottom wall portion (Z-axis direction).

The insulating member30is formed into the bag shape having an open upper portion (upper end in the Z-axis direction) by bending a sheet-shaped member cut into a predetermined shape and having an insulation property. The insulating member30is disposed between the case20(specifically, the case main body22) and the electrode assembly12. In other words, the electrode assembly12is put into the insulating member30and then housed into the case20. The insulating member30insulates the case20and the electrode assembly12from each other. The insulating member30in the embodiment is made of polypropylene, polyphenylene sulfide, or the like, for example.

The support members32are disposed in corner portions of the section along the Y-Z plane of the case20(the substantially rectangular frame-shaped section (seeFIG. 3)) to support (or press) the curved portions12A toward the inside of the electrode assembly (radially inwardly). In this manner, because the support members32are disposed in the corner portions of the section in the case20, the support members32are supported by the case20from two directions (e.g., the lower left support member32inFIG. 3is supported by the bottom wall portion220and the long wall portion222). In this way, the support members32can effectively support the curved portions12A of the electrode assembly12toward inside. The support members32are disposed in the respective four corner portions in the case20. Each of the support members32in the embodiment is a cylindrical member made of resin such as polypropylene and has substantially the same length as a length of the electrode assembly12in the X-axis direction. The support members32are disposed while being elastically deformed (concretely, while being pressed by the curved portions12A toward inner peripheral faces of the corner portions of the case20) between the insulating member30disposed along an inner peripheral face of the case20and the curved portions12A of the electrode assembly12and support the curved portions12A with resilience generated by the elastic deformation.

In the specification, the sentence, “the support members32(support portions) support the curved portions12A of the electrode assembly12” includes a case in which the support members32are directly or indirectly in contact with the curved portions12A of the electrode assembly12when the section of the single battery shown inFIG. 3is observed with a CT scan using X-rays. The sentence, “the support members32(support portions) support the curved portions12A of the electrode assembly12” includes a case in which the support members32are directly or indirectly in contact with the curved portions12A of the electrode assembly12when the sections of the batteries are observed with the CT scan using X-rays in a state in which the plurality of batteries are arranged with the long wall portions222being opposed and bound by the restraining member (the state in which the plurality of batteries are pressed in the direction orthogonal to the long wall portions222(SeeFIG. 10)).

It is preferable that the support members32are elastically deformed due to contact between the support members32and the curved portions12A. In this way, by utilizing the resilience due to the elastic deformation of the support members32, it is possible to support the curved portions12A.

The current collectors14are disposed along the electrode assembly12in the case20and provide conductivity between the protruding parts126of the electrode assembly12and the terminal portions16. The battery10in the embodiment includes the current collector14for the positive electrode and the current collector for the negative electrode. The current collector14for the positive electrode provides conductivity between the protruding part126on the positive electrode side and the terminal portion16for the positive electrode. The current collector14for the negative electrode provides conductivity between the protruding part126on the negative electrode side and the terminal portion16for the negative electrode. In the embodiment, the current collector14for the positive electrode is made of aluminum, an aluminum alloy, or the like, for example. The current collector14for the negative electrode is made of copper, a copper alloy, or the like, for example.

Each of the current collectors14has a terminal-side connection portion140to be directly or indirectly connected to the terminal portion16and an electrode assembly-side connection portion141to be directly or indirectly connected to the protruding part126of the electrode assembly12. The current collector14is formed into a shape (substantially L shape) bent at a boundary portion between the terminal-side connection portion140and the electrode assembly-side connection portion141to conform to the electrode assembly12in a front view by bending a plate-shaped metal material cut into a predetermined shape.

Each of the terminal portions16is mounted to the lid assembly24while passing through the terminal through hole240in the lid assembly24. Specifically, the terminal portion16has an external terminal160, a rivet161, and a conductive portion162. The external terminal160extends upward outside the case20. The rivet161passes through the terminal through hole240in the lid assembly24to fix the current collector14(the terminal-side connection portion140) and the conductive portion162to the lid assembly24while providing conductivity between the current collector14and the conductive portion162. The conductive portion162connects the external terminal160to the current collector14to be able to provide conductivity between the external terminal160and the current collector14via the rivet161.

In the battery10formed as described above, in the case20, the straight portion12B is supported (or pressed) toward inside in the layered direction of the electrodes (the positive electrode120and the negative electrode122) by the convex parts225, and also the curved portions12A are supported toward inside in the layered direction of the electrodes120and122by the support members32. Therefore, it is possible to suitably suppress gathering of displacement of the electrodes120and122in the curved portions12A, the gathering caused by repetition of expansion and contraction of the electrode assembly12during charge-discharge. In this way, it is possible to prevent forming of partial clearances between the electrodes120and122layered at the curved portions12A of the electrode assembly12. Each of the protruding part126on the positive electrode side and the protruding part126on the negative electrode side that are connected to the current collectors14is not pressed by the convex parts225, because the protruding parts126have smaller thicknesses than the straight portion12B of the electrode assembly12pressed by the convex parts225.

The battery10in the embodiment has the structure for supporting the curved portions12A of the electrode assembly12by utilizing the resilience generated by the elastic deformation of the support members32. Therefore, even if the electrode assembly12expands and contracts due to the charge-discharge or the like, i.e., the electrode assembly12changes in size (winding diameter), the support members32follow the change in size and can suitably continue to support the curved portions12A.

Because the lengths in the X-axis direction of the support members32in the embodiment are substantially the same as the length in the X-axis direction of the electrode assembly12, substantially the entire curved portions12A in the X-axis direction are supported by the support members32. Therefore, substantially throughout the X-axis direction of the curved portions12A, it is possible to prevent forming of the partial clearances between the layered electrodes120and122.

An electric storage device and an electric storage apparatus are not limited to those in the above-described embodiment but can be changed in various ways without departing from the gist of the invention.

Specific structures of the support portions (support members)32are not limited. Although the support members32in the embodiment are separate from the insulating member30, the case20, and the like, the support portions may be formed as parts of the insulating member30, parts of the case20, or the like.

For example, as show inFIG. 4, as support portions32A, an insulating member30may be curved to bulge toward curved portions12A, and curved portions of the insulating member30may support the curved portions12A in corner portions in the case20. Alternatively, as support portions, corner portions of the case20may bulge inward similarly to the insulating member30shown inFIG. 4and parts of the bulging case20may support the curved portions12A.

In this structure, the support portions32A are formed by using the parts of the case20or the insulating member30and therefore, it is possible to reduce the number of parts forming the battery10as compared with a case in which the members forming the support portions are disposed separately.

Although the support members (support portions)32in the embodiment support the curved portions12A by using the resilience generated by the elastic deformation, the invention is not limited to it. Support portions (support members) may be formed by members such as rigid bodies which are not elastically deformed or which are hardly elastically deformed as in the above case in which the support portions are formed by using the parts of the case20, for example. Even with such hard support portions (support members), it is possible to prevent forming of the partial clearances between the layered electrodes120and122in the curved portions12A, if the curved portions12A are supported toward the inside of the electrode assembly12.

Although the support members32are respectively disposed in the four corner portions in the case20in the battery10in the above embodiment, the invention is not limited to it. The support portions (support members) may be disposed only either in the opposite corner portions on a side of the bottom wall portion220or the opposite corner portions on a side of the lid assembly24. With this structure, it is possible to prevent forming of the partial clearances between the layered electrodes120and122in the curved portion12A at least on one side in the major axis direction (Z-axis direction). In this way, as compared with the structure in which only the straight portion12B of the electrode assembly12is supported toward the inside in the layered direction of the electrodes120and122, intervals between the electrodes120and122forming the electrode assembly12become narrow, which increases the charge-discharge efficiency.

Moreover, the number of electrode assemblies12housed in the case20is not limited. Although the one electrode assembly12is housed in the case20in the above embodiment, two electrode assemblies12,12may be housed in one case20A, for example, as shown inFIG. 5. Alternatively, three or more electrode assemblies12,12, . . . may be housed in one case. In this case, support members (support portions)32are preferably disposed at positions between the curved portions12A,12A in a Y-axis direction in addition to corner portions as shown inFIG. 5.

Although the insulating member30in the above embodiment is formed by folding the sheet-shaped member having insulation property into the bag shape, i.e., the insulating member30in the above embodiment can be returned into the sheet shape when unfolded, the invention is not limited to it. The insulating member30may be formed into a bag shape (i.e., formed into the bag shape by gluing, welding, or the like).

Although the support members (support portions)32in the embodiment have substantially the same lengths as the length of the electrode assembly12in the X-axis direction, the invention is not limited to this structure. The support members may have greater lengths than the length of the electrode assembly12in the X-axis direction.

Although the convex parts225in the above embodiment continuously extend in the X-axis direction, the invention is not limited to it. The convex parts may extend intermittently in the Z-axis direction. Although the plurality of convex parts225,225, . . . are continuously arranged in the Z-axis direction on each of the long wall portions222, the invention is not limited to this structure. On each of the long wall portions222, the plurality of convex parts225,225, . . . may be arranged at intervals in the Z-axis direction. Sectional shapes of the convex parts225along the Y-axis direction and the Z-axis direction are not limited to the triangular angle shapes. For example, as shown inFIG. 6, convex parts225A may be formed to have arc-shaped sections. As shown inFIG. 7, convex parts225B may be formed to have portions (tip end portions in a protruding direction) which come in contact with an electrode assembly12and are flat faces along the straight portion12B of the electrode assembly12. Convex parts225may be formed by partially increasing thicknesses of long wall portions222. Although the insulating member30is not shown inFIG. 6andFIG. 7, the insulating member30is disposed between the case20, and the electrode assembly12and the support members32in the actual battery10. Although the plurality of convex parts225,225, . . . extend to boundaries between the long wall portions222and the short wall portions223on each of the long wall portions222, the invention is not limited to this structure. For example, a plurality of convex parts225,225, . . . may be formed only at positions near a center in an X-axis direction of each long wall portion222.

Although the secondary battery (lithium ion secondary battery) which can be charged and discharged has been described in the above embodiment, the battery may be of any type and size (capacity). Although the lithium-ion secondary battery has been described as an example of the electric storage device in the above embodiment, the invention is not limited to it. For example, the invention can be applied to various secondary batteries, a primary battery, and an electric storage device of a capacitor such as an electric double layer capacitor.