Secondary battery

Abstract

To provide a secondary battery having a flat shaped winding electrode body in which the generation of the center cut is suppressed.SOLUTION: A secondary battery 100 that is disclosed in here, comprises a flat shaped winding electrode body 20 formed by winding a first separator 26, a negative electrode 24, a second separator 27, and a positive electrode 22. The positive electrode 22 comprises a first adhesive layer 22b on both surfaces. By the first adhesive layer 22b, one surface of the positive electrode 22 and the first separator 26 are adhered. The other surface of the positive electrode 22 and the second separator 27 are adhered. At least one of the first separator 26 and the second separator 27, comprises second adhesive layers 26c and 27c to a winding start end region As positioned on a winding start end side from a winding start end 22s of the positive electrode 22, and the first separator 26 and the second separator 27 are adhered by the second adhesive layers 26c and 27c.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a secondary battery.

Background Art

[0002] Conventionally, a wound electrode body in which a strip-shaped first separator, a strip-shaped negative electrode, a strip-shaped second separator, and a strip-shaped positive electrode are laminated and wound around a winding shaft, and a battery case for housing the wound electrode body are known. For example, Patent Document 1 discloses a flat wound electrode body composed of a flat portion having a pair of flat outer surfaces and a pair of curved portions (R portions) provided at both ends of the flat portion and having curved outer surfaces.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A flat wound electrode body is formed, for example, by press-molding a cylindrical electrode body. In this case, a force (so-called springback) to restore to a cylindrical shape is generated in the wound electrode body after press-molding until it is inserted into the battery case. As a result, the thickness of the wound electrode body may increase, and the insertability into the battery case may decrease. Also, in the flat portion of the wound electrode body, the inter-pole distance between the positive and negative electrodes may locally increase, and an increase in resistance and precipitation of charge carriers (for example, Li) may easily occur.

[0005] As a result of repeated studies by the present inventors, it has been newly found that when the electrode body is press-molded, the pressing pressure is not sufficiently transmitted to the flat portion, so that a large gap is opened by springback in the vicinity of the winding shaft where the first separator and the second separator directly face each other (the central portion of the wound electrode body). In addition, concomitantly with this, it has been newly found that the first separator and / or the second separator is bent, the local interelectrode distance opening at the flat portion becomes large, and the interelectrode distance varies. Hereinafter, the phenomenon of a large gap opening at the central portion of the wound electrode body and the phenomenon of the local interelectrode distance opening at the flat portion are collectively referred to as "mid-split".

[0006] The present invention has been made in view of the above circumstances, and its main object is to provide a secondary battery including a flat wound electrode body in which the occurrence of mid-split is suppressed.

Means for Solving the Problems

[0007] According to the present invention, there is provided a secondary battery including a flat wound electrode body in which a strip-shaped first separator, a strip-shaped negative electrode, a strip-shaped second separator, and a strip-shaped positive electrode are laminated and wound around a winding axis, and a battery case that houses the wound electrode body. The positive electrode includes a first adhesive layer on both surfaces, and the first adhesive layer adheres one surface of the positive electrode to the first separator and the other surface of the positive electrode to the second separator. At least one of the first separator and the second separator includes a second adhesive layer in a winding start region located on the winding start side with respect to the winding start end of the positive electrode, and the second adhesive layer adheres the first separator and the second separator.

[0008] By the second adhesive layer, the first separator and the second separator are adhered in the winding start-end region, thereby suppressing the opening of a large gap at the center of the wound electrode body. Further, by the first adhesive layer, the positive electrode is adhered to the first separator and the second separator respectively, thereby suppressing the local opening of the inter-pole distance at the flat portion. Therefore, according to the technology disclosed herein, the occurrence of middle cracks can be suppressed, and the increase in the thickness of the wound electrode body after press forming can be suppressed. As a result, a decrease in the insertability into the battery case, an increase in resistance, the precipitation of charge carriers (e.g., Li), etc. can be suppressed.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0010] Hereinafter, with reference to the drawings, some preferred embodiments of the technology disclosed herein will be described. Note that matters other than those specifically mentioned in this specification and necessary for the implementation of the technology disclosed herein (for example, general configurations and manufacturing processes of secondary batteries that do not characterize the technology disclosed herein) can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common general knowledge in the relevant field. Note that the notation "A to B" indicating a range in this specification includes the meaning of "A or more and B or less" as well as the meaning of "exceeding A" and "less than B".

[0011] Note that in this specification, the term "secondary battery" generally refers to all rechargeable power storage devices in which charge carriers move between a positive electrode and a negative electrode through an electrolyte. The electrolyte may be any of a liquid electrolyte (electrolyte solution), a gel electrolyte, or a solid electrolyte. Secondary batteries include, in addition to so-called storage batteries (chemical batteries) such as lithium-ion secondary batteries and nickel-metal hydride batteries, capacitors (physical batteries) such as lithium-ion capacitors and electric double layer capacitors.

[0012] FIG. 1 is a perspective view schematically showing a secondary battery 100. FIG. 2 is a schematic longitudinal sectional view taken along line II-II of FIG. 1. FIG. 3 is a schematic cross-sectional view taken along line III-III of FIG. 1. FIG. 4 is a schematic longitudinal sectional view taken along line IV-IV of FIG. 2. In the following description, the reference signs L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, respectively. Also, the reference sign X in the drawings indicates the short side direction (thickness direction) of the secondary battery 100, the reference sign Y indicates the long side direction of the secondary battery 100 orthogonal to the short side direction, and the reference sign Z indicates the vertical direction of the secondary battery 100. However, these are merely directions for convenience of explanation and do not limit the installation form of the secondary battery 100 in any way.

[0013] As shown in FIG. 2, the secondary battery 100 includes a battery case 10, a plurality of wound electrode bodies 20 (see also FIGS. 3 and 4), a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collecting member 50, and a negative electrode current collecting member 60. Although not shown, the secondary battery 100 further includes an electrolytic solution here. The secondary battery 100 is a non-aqueous electrolytic solution secondary battery here. The secondary battery 100 is preferably a lithium-ion secondary battery.

[0014] As the electrolytic solution, those used in general secondary batteries (for example, lithium-ion secondary batteries) can be used without particular limitation. As an example, a non-aqueous electrolytic solution in which a supporting salt is dissolved in a non-aqueous solvent can be mentioned. As an example of the non-aqueous solvent, carbonate solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate can be mentioned. As an example of the supporting salt, lithium salts containing fluorine such as LiPF 6 etc. can be mentioned. The electrolytic solution may contain additives as necessary. However, the electrolytic solution may be in a solid state (solid electrolyte) and integrated with the wound electrode body 20.

[0015] The battery case 10 is a housing that houses the wound electrode body 20 and the electrolytic solution. As shown in FIG. 1, the battery case 10 has a flat and bottomed rectangular parallelepiped shape (rectangular) outer shape here. The secondary battery 100 is preferably a rectangular battery having a rectangular battery case 10. The material of the battery case 10 may be the same as those conventionally used and is not particularly limited. The battery case 10 is preferably made of metal, and more preferably made of, for example, aluminum, aluminum alloy, iron, iron alloy, etc. However, the battery case 10 may be in the form of a laminated film bag.

[0016] As shown in FIG. 2, the battery case 10 includes an outer package 12 having an opening 12h and a sealing plate (lid) 14 that seals the opening 12h. The battery case 10 preferably includes the outer package 12 and the sealing plate 14. The outer package 12 and the sealing plate 14 have sizes corresponding to the size of the wound electrode body 20, the number of accommodated (one or more. Here, a plurality.), etc.

[0017] The outer package 12 is a bottomed and rectangular container having an opening 12h on the upper surface. As shown in FIG. 1, the outer package 12 includes a substantially rectangular bottom wall 12a, a pair of long side walls 12b extending from the long sides of the bottom wall 12a and facing each other, and a pair of short side walls 12c extending from the short sides of the bottom wall 12a and facing each other. The bottom wall 12a faces the opening 12h (see FIG. 2). The long side wall 12b has a larger area than the short side wall 12c. The long side wall 12b is an example of the "first side wall", and the short side wall 12c is an example of the "second side wall".

[0018] The sealing plate 14 is a plate-like member attached to the outer package 12 so as to close the opening 12h of the outer package 12. The sealing plate 14 faces the bottom wall 12a of the outer package 12. The sealing plate 14 is substantially rectangular. The battery case 10 is integrated by joining (for example, welding) the sealing plate 14 to the periphery of the opening 12h of the outer package 12. Thereby, the battery case 10 is hermetically sealed (closed).

[0019] As shown in FIG. 2, the sealing plate 14 is provided with a liquid injection hole 15, a gas discharge valve 17, and terminal lead-out holes 18 and 19. The liquid injection hole 15 is a through hole for injecting an electrolytic solution into the battery case 10 after assembling the sealing plate 14 to the outer package 12. The liquid injection hole 15 is sealed by a sealing member 16 after the injection of the electrolytic solution. The gas discharge valve 17 is a thin-walled portion configured to break when the pressure in the battery case 10 becomes equal to or higher than a predetermined value and discharge the gas in the battery case 10 to the outside. The terminal lead-out holes 18 and 19 are respectively formed at both ends in the long side direction Y of the sealing plate 14. The terminal lead-out holes 18 and 19 are through holes penetrating the sealing plate 14 in the vertical direction Z.

[0020] The positive terminal 30 is attached to one end of the sealing plate 14 in the long side direction Y (the left end in FIGS. 1 and 2). The negative terminal 40 is attached to the other end of the sealing plate 14 in the long side direction Y (the right end in FIGS. 1 and 2). The positive terminal 30 and the negative terminal 40 are preferably attached to the sealing plate 14. The positive terminal 30 and the negative terminal 40 are inserted through the terminal lead-out holes 18 and 19, and a part thereof is exposed on the surface of the sealing plate 14. The positive terminal 30 and the negative terminal 40 are connected to other secondary batteries or external devices via an external connection member such as a bus bar.

[0021] As shown in FIG. 2, the positive terminal 30 is electrically connected to the positive electrode 22 (see FIG. 5) of the wound electrode body 20 inside the battery case 10 via the positive electrode current collecting member 50 and the positive electrode tab group 22g (that is, a plurality of laminated positive electrode tabs 22t) described later. The positive terminal 30 is preferably made of metal, and more preferably made of, for example, aluminum or an aluminum alloy. The negative terminal 40 is electrically connected to the negative electrode 24 (see FIG. 5) of the wound electrode body 20 inside the battery case 10 via the negative electrode current collecting member 60 and the negative electrode tab group 24g (that is, a plurality of laminated negative electrode tabs 24t) described later. The negative terminal 40 is preferably made of metal, and more preferably made of, for example, copper or a copper alloy. The positive terminal 30 and the negative terminal 40 are insulated from the sealing plate 14 by a gasket 92. The gasket 92 is preferably made of resin.

[0022] The positive electrode current collector member 50 is a conductive member, and here it is attached to the sealing plate 14. As shown in FIG. 2, the positive electrode current collector member 50 is insulated from the inner surface of the sealing plate 14 by a resin-made internal insulating member 94. The positive electrode current collector member 50 electrically connects the positive electrode tab group 22g of the wound electrode body 20 and the positive electrode terminal 30. The positive electrode current collector member 50 has a plate-shaped first region extending in the long side direction Y along the inner surface of the sealing plate 14. One end (the right side in FIG. 2) of the positive electrode current collector member 50 (specifically, the first region) in the long side direction Y is electrically connected to the positive electrode tab group 22g. The other end (the left side in FIG. 2) of the positive electrode current collector member 50 (specifically, the first region) in the long side direction Y is electrically connected to the lower end portion 30c of the positive electrode terminal 30. The positive electrode current collector member 50 is preferably made of a metal with excellent conductivity, for example, it is made of aluminum or an aluminum alloy. The positive electrode current collector member 50 may be made of the same kind of metal as the positive electrode tab 22t and / or the positive electrode terminal 30.

[0023] The negative electrode current collector member 60 is a conductive member, and here it is attached to the sealing plate 14. The negative electrode current collector member 60 is insulated from the inner surface of the sealing plate 14 by a resin-made internal insulating member 94. The negative electrode current collector member 60 electrically connects the negative electrode tab group 24g of the wound electrode body 20 and the negative electrode terminal 40. As shown in FIG. 2, the negative electrode current collector member 60 has a plate-shaped first region extending in the long side direction Y along the inner surface of the sealing plate 14. One end (the left side in FIG. 2) of the negative electrode current collector member 60 (specifically, the first region) in the long side direction Y is electrically connected to the negative electrode tab group 24g. The other end (the right side in FIG. 2) of the negative electrode current collector member 60 (specifically, the first region) in the long side direction Y is electrically connected to the lower end portion 40c of the negative electrode terminal 40. The negative electrode current collector member 60 is preferably made of a metal with excellent conductivity, for example, it is made of copper or a copper alloy. The negative electrode current collector member 60 may be made of the same kind of metal as the negative electrode tab 24t and / or the negative electrode terminal 40.

[0024] As shown in FIGS. 3 and 4, in the secondary battery 100 of the present embodiment, a plurality (specifically, two) of wound electrode bodies 20 are accommodated in the battery case 10. However, the number of wound electrode bodies 20 arranged in one battery case 10 is not particularly limited, and it may be one, or three or more. The plurality of wound electrode bodies 20 are arranged inside the battery case 10 in a state covered with an electrode body holder 29 made of a resin sheet. Thereby, the wound electrode body 20 is prevented from directly contacting the exterior body 12.

[0025] FIG. 5 is a perspective view schematically showing the configuration of the wound electrode body 20. FIG. 6 is a cross-sectional view schematically showing the cross-sectional structure of the wound electrode body 20 in a direction orthogonal to the winding axis WL. FIG. 7 is an exploded view schematically showing the winding start end portion of the wound electrode body 20. In FIGS. 5 and 7, the reference sign LD indicates the longitudinal direction (i.e., the conveyance direction) of the wound electrode body 20 manufactured in a strip shape. Among the longitudinal direction LD, the winding start end side is indicated as S, and the winding end side is indicated as E. Further, the reference sign WD in FIG. 5 is a direction orthogonal to the longitudinal direction LD, and indicates the winding axis direction of the wound electrode body 20. The winding axis direction WD is substantially parallel to the vertical direction Z of the secondary battery 100 here.

[0026] As shown in FIGS. 3 and 6, the wound electrode body 20 has a flat outer shape. The flat wound electrode body 20 has a pair of curved portions 20r with a curved outer surface and a flat portion 20f with a flat outer surface connecting the pair of curved portions 20r. As shown in FIG. 2, the wound electrode body 20 is accommodated inside the battery case 10 in a direction in which the winding axis direction WD substantially coincides with the vertical direction Z, in other words, in a direction in which the winding axis direction WD is substantially orthogonal to the sealing plate 14 and the bottom wall 12a. As shown in FIG. 3, the pair of curved portions 20r face the pair of short side walls 12c of the exterior body 12, and the flat portion 20f faces the long side wall 12b of the exterior body 12.

[0027] As shown in FIG. 5, the wound electrode body 20 is configured by laminating a strip-shaped first separator 26, a strip-shaped negative electrode 24, a strip-shaped second separator 27, and a strip-shaped positive electrode 22, and winding them around a winding axis WL. As shown in FIG. 2, the end faces of the wound electrode body 20 (that is, the laminated surfaces where the positive electrode 22 and the negative electrode 24 are laminated, both ends in the winding axis direction WD of FIG. 5) face the bottom wall 12a and the sealing plate 14. On the upper part of the wound electrode body 20, a positive electrode tab group 22g and a negative electrode tab group 24g, which will be described later, protrude.

[0028] The secondary battery 100 has a so-called upper tab structure in which a positive electrode tab group 22g and a negative electrode tab group 24g are provided at the end portion (upper side in FIG. 2) on the sealing plate 14 side of the wound electrode body 20. When the secondary battery 100 has an upper tab structure, for example, when a force is applied from the vertical direction Z of the wound electrode body 20, it is likely to cause a mid-split, so it is particularly effective to apply the technology disclosed herein. However, the secondary battery 100 may have a so-called side tab structure in which a positive electrode tab group 22g and a negative electrode tab group 24g are provided at both end portions (left and right in FIG. 2) on the side of the pair of short side walls 12c of the wound electrode body 20.

[0029] As shown in FIG. 5, in the present embodiment, when the length in the direction along the winding axis WL of the wound electrode body 20 (that is, the winding axis direction WD) is L1, and the length in the direction perpendicular to the winding axis WL and perpendicular to the thickness direction of the wound electrode body 20 (that is, the longitudinal direction LD) is L2, L2 is twice or more of L1. The length L1 is the same as the length of the widths of the first separator 26 and the second separator 27. According to the inventor, since the pressing pressure is difficult to be transmitted to the flat portion 20f, when the length L2 is long, the formability of the wound electrode body 20 deteriorates and springback or mid-split is likely to occur. Therefore, it is effective to apply the technology disclosed herein. Among them, when the length Lf of the flat portion 20f of the wound electrode body 20 in the longitudinal direction L D is 15 cm or more, it is particularly effective to apply the technology disclosed herein.

[0030] As shown in FIG. 6, in the wound electrode body 20, the first separator 26 and the second separator 27 are wound prior to the negative electrode 24 to the positive electrode 22. The winding start ends 26s of the first separator 26 and the winding start ends 27s of the second separator 27 are located in the flat portion 20f. Neither the positive electrode 22 nor the negative electrode 24 is disposed at the central portion (near the winding axis WL) of the wound electrode body 20. The central portion of the wound electrode body 20 is composed of the first separator 26 and the second separator 27. Therefore, at the central portion of the wound electrode body 20, the first separator 26 and the second separator 27 are directly opposed (abutted). Hereinafter, the first bending point from the winding start ends 26s and 27s is defined as the first bending point P1, the second bending point is defined as the second bending point P2, and the third bending point is defined as the third bending point P3.

[0031] After being folded back at the first bending point P1, the first separator 26 and the second separator 27 are folded back at the second bending point P2. Here, the negative electrode 24 is wound prior to the positive electrode 22. The winding start end 24s of the negative electrode 24 is located in the flat portion 20f. The winding start end 24s of the negative electrode 24 is sandwiched between the outer peripheral side of the second separator 27 and the inner peripheral side of the first separator 26 folded back at the second bending point P2 on the winding start end side with respect to the third bending point P3, and is wound together with the first separator 26 and the second separator 27. The winding start end 22s of the positive electrode 22 is located in the flat portion 20f. The winding start end 22s of the positive electrode 22 is sandwiched between the outer peripheral side of the first separator 26 folded back at the third bending point P3 and the inner peripheral side of the second separator 27 at a position on the winding end side (a position beyond the third bending point P3) with respect to the third bending point P3, and is wound on the outer peripheral side of the first separator 26. The second separator 27 is wound on the outer peripheral side of the positive electrode 22. The negative electrode 24 is wound on the outer peripheral side of the second separator 27.

[0032] The winding end 22e of the positive electrode 22 is located in the curved portion 20r. Here, the winding end 22e of the positive electrode 22 is arranged on the winding start side rather than the winding end side of the winding end 24e of the negative electrode 24. The winding end 24e of the negative electrode 24 is located in the curved portion 20r. Here, the winding end 24e of the negative electrode 24 is arranged on the winding end side rather than the winding start side of the winding end 22e of the positive electrode 22. The winding end 24e of the negative electrode 24 is covered from the outer peripheral side by a pair of separators formed by the first separator 26 and the second separator 27. The winding end 26e of the first separator 26 and the winding end 27e of the second separator 27 are located in the curved portion 20r. The winding end portion (the outermost peripheral portion) of the second separator 27 forms the outer peripheral surface of the wound electrode body 20. A winding tape 28 is attached to the winding end 26e of the first separator 26 and the winding end 27e of the second separator 27.

[0033] As shown in FIG. 5, the positive electrode 22 is a strip-shaped member. The positive electrode 22 includes a strip-shaped positive electrode current collector 22c, a positive electrode active material layer 22a fixed to at least one surface of the positive electrode current collector 22c, and a first adhesive layer 22b provided on both surfaces of the positive electrode 22. For each member constituting the positive electrode 22, conventionally known materials that can be used in a general secondary battery (for example, a lithium ion secondary battery) can be used without particular limitation. For example, the positive electrode current collector 22c is preferably made of a metal foil, and an aluminum foil or an aluminum alloy foil is particularly preferred.

[0034] As shown in FIG. 5, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction LD of the positive electrode current collector 22c. As shown in FIG. 7, the positive electrode active material layer 22a is formed on both surfaces (the first surface and the second surface, the upper surface and the lower surface in FIG. 7) of the positive electrode current collector 22c here. The positive electrode active material layer 22a contains a positive electrode active material capable of reversibly occluding and releasing charge carriers. As the positive electrode active material, a lithium transition metal composite oxide is preferable, and it is more preferable to contain Ni. As an example of the lithium transition metal composite oxide containing Ni, lithium nickel cobalt manganese composite oxide can be mentioned. The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, for example, a conductive material, a positive electrode binder, various additive components, etc. As the conductive material, for example, a carbon material such as acetylene black (AB) is preferable. As the positive electrode binder, for example, polyvinylidene fluoride (PVdF) is preferable.

[0035] The porosity of the positive electrode active material layer 22a can be generally 10 to 40%, for example, 20 to 30%. The porosity of the positive electrode active material layer 22a is typically smaller than the porosity of the first separator 26 and the second separator 27 (specifically, the porosity of the base material layer 26a or the heat-resistant layer 26b described later). In this specification, the "porosity" refers to the value obtained by dividing the total pore volume (cm 3 ) obtained by measurement with a mercury porosimeter by the apparent volume (cm 3 ) of the active material layer and multiplying by 100.

[0036] As shown in FIG. 5, the first adhesive layer 22b is provided in a strip shape along the longitudinal direction LD of the positive electrode current collector 22c. As shown in FIG. 7, the first adhesive layer 22b is provided uniformly from the winding start end 22s to the winding end 22e of the positive electrode 22. Since it is difficult to form the first adhesive layer 22b at the end of the positive electrode active material layer 22a, it is provided here with an area smaller than that of the positive electrode active material layer 22a in a plan view. The positive electrode active material layer 22a is exposed on a part of the surface of the positive electrode 22. However, in other embodiments, it may be provided so as to cover the entire positive electrode active material layer 22a (with substantially the same size as the positive electrode active material layer 22a).

[0037] The first adhesive layer 22b is provided so as to be in contact with the first separator 26 and the second separator 27. That is, as shown in FIG. 7, the first adhesive layer 22b is provided on both surfaces of the positive electrode 22 (the first surface and the second surface, the upper surface and the lower surface in FIG. 7), respectively. Specifically, it is provided on the positive electrode active material layers 22a provided on the first surface and the second surface of the positive electrode current collector 22c, respectively. The first adhesive layer 22b is formed on the surface facing the first separator 26 and the surface facing the second separator 27, respectively. The first adhesive layer 22b constitutes the outermost surface of the positive electrode 22 on the first surface and the second surface. The first adhesive layers 22b provided on the first surface and the second surface are adhered to the first separator 26 and the second separator 27, respectively, by, for example, press molding at room temperature or hot press molding. Thereby, it is possible to suppress the local opening of the interelectrode distance at the flat portion 20f and effectively suppress the occurrence of mid-cracks.

[0038] The first adhesive layer 22b is a layer containing a first adhesive layer binder (adhesive). The configuration of the first adhesive layer 22b is not particularly limited and may be the same as those conventionally known. As the first adhesive layer binder, a conventionally known resin material having a certain viscosity with respect to the first separator 26 and the second separator 27 can be used without particular limitation. Specific examples include resins such as acrylic resins, fluorine-based resins, epoxy resins, urethane resins, and ethylene vinyl acetate resins. Among them, acrylic resins and fluorine-based resins are preferred because they have high flexibility and can preferably exhibit adhesiveness to the first separator 26 and the second separator 27. Examples of the fluorine-based resin include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). The first adhesive layer 22b may contain other materials (for example, inorganic fillers such as alumina) in addition to the first adhesive layer binder. Since the first adhesive layer 22b contains a first adhesive layer binder having high affinity with the electrolytic solution, it can be a layer that absorbs the electrolytic solution and swells.

[0039] The first adhesive layer 22b can be produced, for example, by applying an adhesive layer forming slurry obtained by mixing or dispersing the above-described materials (such as the first adhesive layer binder) in an appropriate solvent onto the surface of the positive electrode active material layer 22a and drying it.

[0040] In the wound electrode body 20, as shown in FIG. 5, a plurality of positive electrode tabs 22t protrude outward (to the left side in FIG. 5) from the base connected to one end side in the winding axis direction WD. The plurality of positive electrode tabs 22t are provided at predetermined intervals (intermittently) along the longitudinal direction LD. The number of positive electrode tabs 22t attached to one wound electrode body 20 (specifically, the positive electrode 22) can be generally several tens or more, for example, about 40 to 60. The plurality of positive electrode tabs 22t may have different sizes and shapes from each other. Here, the positive electrode tab 22t is a part of the positive electrode 22. Here, the positive electrode tab 22t is a region where the positive electrode active material layer 22a is not formed and the positive electrode current collector 22c is exposed. However, the positive electrode tab 22t may be a member different from the positive electrode 22. By providing the plurality of positive electrode tabs 22t, unevenness in resistance and potential within the positive electrode 22 can be reduced.

[0041] The plurality of positive electrode tabs 22t are laminated at one end in the winding axis direction WD of the wound electrode body 20 to form a positive electrode tab group 22g (see FIGS. 2 and 4). As shown in FIG. 4, the plurality of positive electrode tabs 22t are bent and curved. The tip portions of the plurality of positive electrode tabs 22t are joined to the positive electrode current collecting member 50. The plurality of positive electrode tabs 22t (positive electrode tab group 22g) are electrically connected to the positive electrode terminal 30 via the positive electrode current collecting member 50. The plurality of positive electrode tabs 22t are preferably joined to the positive electrode current collecting member 50 in a bent and curved state.

[0042] As shown in FIG. 5, the negative electrode 24 is a strip-shaped member. The negative electrode 24 includes a strip-shaped negative electrode current collector 24c and a negative electrode active material layer 24a fixed to at least one surface of the negative electrode current collector 24c. Here, the negative electrode 24 does not include an adhesive layer. However, it may have an adhesive layer on its surface and be adhered to the first separator 26 and the second separator 27, respectively. For each member constituting the negative electrode 24, conventionally known materials that can be used in a general secondary battery (for example, a lithium-ion secondary battery) can be used without particular limitation. For example, the negative electrode current collector 24c is preferably made of a metal foil, and a copper foil or a copper alloy foil is particularly preferred.

[0043] As shown in FIG. 5, the negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction LD of the negative electrode current collector 24c. As shown in FIG. 7, here, the negative electrode active material layer 24a is formed on both surfaces (the first surface and the second surface, the upper surface and the lower surface in FIG. 7) of the negative electrode current collector 24c, respectively. The negative electrode active material layer 24a contains a negative electrode active material capable of reversibly occluding and releasing charge carriers. As the negative electrode active material, for example, a carbon material such as graphite or a Si-containing material is preferable. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as a negative electrode binder, a conductive material, and various additive components. As the negative electrode binder, for example, rubbers such as styrene-butadiene rubber (SBR) and celluloses such as carboxymethyl cellulose (CMC) are preferable. As the conductive material, a carbon material is preferable.

[0044] In the wound electrode body 20, as shown in FIG. 5, a plurality of negative electrode tabs 24t project outward (to the left side in FIG. 5) from the base connected to one end side in the winding axis direction WD. The plurality of negative electrode tabs 24t are provided at predetermined intervals (intermittently) along the longitudinal direction LD. In the winding axis direction WD, the negative electrode tabs 24t are provided at the end on the same side (the left side in FIG. 5) as the positive electrode tabs 22t. The number of negative electrode tabs 24t attached to one wound electrode body 20 (specifically, the negative electrode 24) is substantially equivalent to the number of positive electrode tabs 22t, and can generally be several tens or more, for example, about 40 to 60. The plurality of negative electrode tabs 24t may have different sizes and shapes from each other. Here, the negative electrode tabs 24t are part of the negative electrode 24. The negative electrode tabs 24t are regions where the negative electrode current collector 24c is exposed without the formation of the negative electrode active material layer 24a. However, the negative electrode tabs 24t may be separate members from the negative electrode 24. By providing the plurality of negative electrode tabs 24t, unevenness in resistance and potential within the negative electrode 24 can be reduced.

[0045] The plurality of negative electrode tabs 24t are laminated at one end in the winding axis direction WD of the wound electrode body 20 to form a negative electrode tab group 24g (see FIG. 2). Although not shown, the plurality of negative electrode tabs 24t are bent and curved in the same manner as the plurality of positive electrode tabs 22t described above. The tip portions of the plurality of negative electrode tabs 24t are joined to the negative electrode current collecting member 60. The plurality of negative electrode tabs 24t (negative electrode tab group 24g) are negative pole terminal 4 electrically connected to 0. It is preferable that the plurality of negative electrode tabs 24t are joined to the negative electrode current collecting member 60 in a bent and curved state.

[0046] As shown in FIG. 5, the first separator 26 and the second separator 27 are each strip-shaped members. The first separator 26 and the second separator 27 are members that insulate the positive electrode active material layer 22a of the positive electrode 22 and the negative electrode active material layer 24a of the negative electrode 24. In the present embodiment, as shown in FIG. 7, the first separator 26 and the second separator 27 each include a resin base material layer 26a, 27a, a heat resistance layer (HRL) 26b, 27b provided on one surface of the base material layers 26a, 27a, and a second adhesive layer 26c, 27c provided on the surfaces of the heat resistance layers 26b, 27b. The first separator 26 and the second separator 27 preferably each include the base material layer 26a, 27a and the heat resistance layer 26b, 27b.

[0047] The first separator 26 and the second separator 27 have the same configuration here. However, in other embodiments, they may have different configurations. For example, the first separator 26 or the second separator 27 may not include the second adhesive layers 26c, 27c. That is, in the technology disclosed herein, it is sufficient that at least one of the first separator 26 and the second separator 27 is provided with the second adhesive layers 26c, 27c. Also, the heat resistance layers 26b, 27b and the second adhesive layers 26c, 27c are provided here only on one surface of the base material layers 26a, 27a. However, in other embodiments, in the first separator 26 and / or the second separator 27, the second adhesive layers 26c, 27c may be provided on both surfaces respectively. Thereby, a large gap opening at the center of the wound electrode body 20 can be suppressed at a high level.

[0048] As the base material layers 26a and 27a, a porous sheet conventionally known and used for separators of secondary batteries can be used without particular limitation. Among them, from the viewpoint of sufficiently ensuring flexibility, a porous sheet made of polyolefin, that is, a porous sheet made of a polyolefin resin is preferable. As the polyolefin resin, polyethylene (PE), polypropylene (PP), or a mixture thereof is preferable, and it is more preferable to be made of PE. The base material layers 26a and 27a may have a single-layer structure or a multilayer structure of two or more layers (for example, a three-layer structure such as PP / PE / PP). The porosity of the base material layers 26a and 27a is typically higher than the porosity of the positive electrode active material layer 22a, and can generally be 20% or more, for example, 30 to 50%.

[0049] As shown in FIG. 7, the heat-resistant layers 26b and 27b are provided on the surfaces of the base material layers 26a and 27a. The heat-resistant layers 26b and 27b are provided in a strip shape along the longitudinal direction LD of the base material layers 26a and 27a. By providing the first separator 26 and the second separator 27 with the heat-resistant layers 26b and 27b, respectively, the heat shrinkage of the first separator 26 and the second separator 27 can be suppressed, contributing to an improvement in the safety of the secondary battery 100. The heat-resistant layers 26b and 27b are preferably provided on at least the surfaces facing the positive electrode 22. It is preferable that at least one (preferably both) of the first separator 26 and the second separator 27 is provided with the heat-resistant layers 26b and 27b on the surfaces facing the positive electrode 22. According to the study by the present inventor, when the heat-resistant layers 26b and 27b are provided on the surfaces facing the positive electrode 22, the adhesiveness with the positive electrode 22 becomes particularly poor, and the moldability of the wound electrode body 20 tends to deteriorate. Therefore, it is particularly effective to apply the technology disclosed herein. However, the heat-resistant layers 26b and 27b are not essential and can be omitted in other embodiments.

[0050] The heat-resistant layers 26b and 27b are layers containing an inorganic filler. As the inorganic filler, those conventionally known and used in this kind of application can be used without particular limitation. The inorganic filler preferably contains insulating ceramic particles such as alumina, boehmite, aluminum hydroxide, and titania. The heat-resistant layers 26b and 27b may further contain a heat-resistant layer binder. The heat-resistant layers 26b and 27b preferably contain an inorganic filler and a heat-resistant layer binder. As the heat-resistant layer binder, those conventionally known and used in this kind of application can be used without particular limitation. The porosity of the heat-resistant layers 26b and 27b is typically higher than that of the positive electrode active material layer 22a, and further higher than that of the base material layers 26a and 27a, and can generally be 50% or more, for example, 50 to 80%, 60 to 70%.

[0051] As shown in FIG. 7, the second adhesive layers 26c and 27c are respectively provided on the surfaces of the heat-resistant layers 26b and 27b. The second adhesive layers 26c and 27c are provided in at least the region (winding start-end region As) located on the winding start-end side of the winding start-end 22s of the positive electrode 22. As described above, since the pressing pressure is difficult to be transmitted to the flat portion 20f, the second adhesive layers 26c and 27c are preferably provided at least in the flat portion 20f of the winding start-end region As. The winding start-end region As includes a region where the second adhesive layer 26c of the first separator 26 abuts against the opposing second separator 27, and the second adhesive layer 27c of the second separator 27 abuts against the first separator 26.

[0052] The second adhesive layers 26c and 27c are provided only in the winding start-end region As here. In other words, the second adhesive layers 26c and 27c are not provided outside the winding start-end region As here. Since the second adhesive layers 26c and 27c have high resistance, by minimizing (reducing) the second adhesive layers 26c and 27c to the minimum necessary, an increase in battery resistance can be suppressed. However, the region where the second adhesive layers 26c and 27c are formed can be arbitrarily changed according to, for example, the design of the wound electrode body 20. In other embodiments, for example, the second adhesive layers 26c and 27c may be provided on the entire surfaces of the first separator 26 and / or the second separator 27. In that case, it is preferable that the mass per unit area of the second adhesive layers 26c and 27c is less outside the winding start-end region As than in the winding start-end region As.

[0053] The second adhesive layers 26c and 27c are provided here in a direct facing region Af where the first separator 26 and the second separator 27 directly face each other (in other words, the region where only the first separator 26 and the second separator 27 are wound). More specifically, they are provided in a region Ac from a position at a predetermined interval from the winding start-ends 26s and 27s, passing through the first bending point P1 and the second bending point P2, and up to before the winding start-end 24s of the negative electrode 24. In the region Ac, the first separator 26 and the second separator 27 are adhered by the second adhesive layers 26c and 27c. The second adhesive layer 26c is adhered to the opposing second separator 27, for example, by press molding at room temperature or heat press molding, and the second adhesive layer 27c is adhered to the first separator 26, for example, by press molding at room temperature or heat press molding. Thereby, it is possible to suppress the opening of a large gap at the center of the wound electrode body 20 where it is difficult for press pressure to be applied, and effectively suppress the occurrence of internal cracks.

[0054] In the rewinding start region As, when the entire area of the directly facing region Af is taken as 100%, it is preferable that the area of the region Ac (the region where the first separator 26 and the second separator 27 are adhered by the second adhesive layers 26c and 27c) is 30% or more. Thereby, while reducing the second adhesive layers 26c and 27c (typically, the amount of the second adhesive layer binder), the opening of a large gap at the center of the wound electrode body 20 and the increase in the thickness of the wound electrode body 20 can be more effectively suppressed. The ratio of the area of the region Ac in the directly facing region Af is more preferably 50% or more, and even more preferably 70% or more. The ratio of the area of the region Ac in the directly facing region Af may be 95% or less or 90% or less.

[0055] The second adhesive layers 26c and 27c are layers containing a second adhesive layer binder (adhesive). The configuration of the second adhesive layers 26c and 27c is not particularly limited and may be the same as those conventionally known. As the second adhesive layer binder, a conventionally known resin material having a certain viscosity with respect to the first separator 26 and the second separator 27 can be used without particular limitation. Specific examples include resins such as acrylic resins, fluorine-based resins, epoxy resins, urethane resins, and ethylene vinyl acetate resins. Among them, acrylic resins and fluorine-based resins are preferable because they have high flexibility and can preferably exhibit adhesiveness to the first separator 26 and the second separator 27. Examples of the fluorine-based resin include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). The second adhesive layers 26c and 27c may contain other materials (for example, inorganic fillers such as alumina) in addition to the second adhesive layer binder. The second adhesive layers 26c and 27c can be layers that have a relatively high affinity with the electrolytic solution and absorb and swell with the electrolytic solution, for example, as compared with the heat-resistant layers 26b and 27b.

[0056] Note that the second adhesive layers 26c and 27c can be produced, for example, by applying an adhesive layer forming slurry obtained by mixing or dispersing the above-described materials (such as the second adhesive layer binder) in an appropriate solvent onto the surfaces of the heat-resistant layers 26b and 27b (or the base material layers 26a and 27a) and drying them.

[0057] The second adhesive layers 26c and 27c may be made of a material different from that of the first adhesive layer 22b. The second adhesive layers 26c and 27c may contain an adhesive layer binder different from that of the first adhesive layer 22b. For example, either one of the first adhesive layer 22b and the second adhesive layers 26c and 27c may contain an acrylic resin, and the other may contain a fluororesin. Thereby, the adhesiveness can be improved. Alternatively, the second adhesive layers 26c and 27c may be made of the same material as the first adhesive layer 22b. The second adhesive layers 26c and 27c may contain the same adhesive layer binder as the first adhesive layer 22b. For example, both the first adhesive layer 22b and the second adhesive layers 26c and 27c may contain an acrylic resin. For example, both the first adhesive layer 22b and the second adhesive layers 26c and 27c may contain a fluororesin. Thereby, when forming the second adhesive layers 26c and 27c, the labor of preparing the slurry can be reduced.

[0058] The mass per unit area of the second adhesive layers 26c and 27c is preferably larger than the mass per unit area of the first adhesive layer 22b. That is, the heat-resistant layers 26b and 27b (or the base material layers 26a and 27a) on which the second adhesive layers 26c and 27c are provided have a higher porosity than the positive electrode active material layer 22a. For this reason, when trying to form the second adhesive layers 26c and 27c on the surfaces of the heat-resistant layers 26b and 27b (or the base material layers 26a and 27a), the constituent material of the second adhesive layers 26c and 27c (mainly the second adhesive layer binder) is likely to penetrate into the heat-resistant layers 26b and 27b (or the base material layers 26a and 27a). The second adhesive layer binder that has penetrated into the heat-resistant layers 26b and 27b (or the base material layers 26a and 27a) does not contribute to the adhesive force. Therefore, in the second adhesive layers 26c and 27c, it is preferable to relatively increase the mass per unit area (typically, the mass of the adhesive layer binder) compared to the case of forming the first adhesive layer 22b on the surface of the positive electrode active material layer 22a. In other words, the mass per unit area of the first adhesive layer 22b is preferably smaller than the mass per unit area of the second adhesive layers 26c and 27c. Thereby, in the region where the positive electrode 22 and the negative electrode 24 face each other, the amount of the high-resistance adhesive layer binder can be reduced, and an increase in battery resistance can also be suppressed.

[0059] In a region where the first separator 26 and the second separator 27 directly face each other (for example, the direct facing region Af), it is preferable that there is a region where the second adhesive layers 26c and 27c do not intervene between the first separator 26 and the second separator 27. In the present embodiment, as shown in FIG. 6, in the winding end region located on the winding end side with respect to the winding end 24e of the negative electrode 24, the second adhesive layers 26c and 27c do not intervene between the first separator 26 and the second separator 27. Further, as shown in FIG. 7, in the direct facing region Af of the winding start region As, the second adhesive layers 26c and 27c are not provided in the vicinity of the winding starts 26s and 27s. Thereby, the second adhesive layers 26c and 27c (typically, the amount of the second adhesive layer binder) can be reduced, and an increase in battery resistance can be suppressed. Also, it is possible to prevent the electrolyte from being absorbed by the second adhesive layers 26c and 27c in a portion that does not contribute to the battery reaction and the electrolyte from being depleted. Therefore, the amount of the electrolyte can be reduced and the cost of manufacturing the battery can be reduced.

[0060] As described above, by providing the second adhesive layers 26c and 27c in the winding start region As and bonding the first separator 26 and the second separator 27, it is possible to suppress the formation of a large gap at the center of the wound electrode body 20. Further, by providing the first adhesive layer 22b on both surfaces of the positive electrode 22 and bonding the positive electrode 22 to the first separator 26 and the second separator 27, respectively, it is possible to suppress a local increase in the distance between the positive electrode 22 and the negative electrode 24 in the flat portion 20f. Therefore, according to the technology disclosed herein, it is possible to suppress the occurrence of mid-splitting while reducing the amount of the adhesive layer binder. Preferably, a wound electrode body 20 without mid-splitting can be realized. Thereby, an increase in the thickness of the wound electrode body 20 after press molding can be suppressed, and as a result, a decrease in the insertability into the battery case 10, an increase in resistance, precipitation of charge carriers (for example, Li), etc. can be suppressed. Further, by providing the first adhesive layer 22b on the positive electrode 22, the amount of the adhesive layer binder used can be relatively reduced compared to the case where the adhesive layer is provided over the entire first separator 26 and / or the second separator 27, and an increase in battery resistance can be suppressed.

[0061] On the other hand, according to the study by the present inventors, in the configuration where the adhesive layer is not provided on the separator and the adhesive layer is provided on the entire positive electrode, since the boundaries between the separators are not adhered at the center of the wound electrode body as described above, a relatively large gap is generated at the center of the wound electrode body compared to the technology disclosed herein. Conversely, in the configuration where the adhesive layer is not provided on the positive electrode and the adhesive layer is provided on the entire separator, since the adhesive layer binder penetrates into the separator as described above, when attempting to achieve the desired adhesive force, the amount of the adhesive layer binder used is relatively larger compared to the case where the adhesive layer is provided on the positive electrode. As a result, compared to the technology disclosed herein, the battery resistance relatively increases and the battery characteristics (e.g., output characteristics) deteriorate. These facts support the significance of the technology disclosed herein.

[0062] The secondary battery 100 can be used for various applications, but it can be preferably used as a power source (driving power source) for a motor mounted on applications that require high capacity, such as a mobile body (typically, vehicles such as passenger cars and trucks). The type of the vehicle is not particularly limited, and examples include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), and a battery electric vehicle (BEV).

[0063] As described above, some embodiments of the present invention have been described, but the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the content disclosed herein and the common general knowledge in the art. The technology described in the claims includes various modifications and changes of the above-exemplified embodiments. For example, it is possible to replace a part of the above-described embodiments with other modified forms, and it is also possible to add other modified forms to the above-described embodiments. Further, if the technical feature is not described as essential, it can be appropriately deleted.

[0064] As described above, specific embodiments of the technology disclosed herein include those described in the following sections. Item 1: A secondary battery comprising a flat wound electrode body in which a strip-shaped first separator, a strip-shaped negative electrode, a strip-shaped second separator, and a strip-shaped positive electrode are laminated and wound around a winding axis, and a battery case for housing the wound electrode body, wherein the positive electrode has first adhesive layers on both surfaces, and the first adhesive layer adheres one surface of the positive electrode to the first separator and the other surface of the positive electrode to the second separator, and at least one of the first separator and the second separator has a second adhesive layer in a winding start region located on the winding start side of the winding start end of the positive electrode, and the second adhesive layer adheres the first separator and the second separator. Item 2: The secondary battery according to Item 1, wherein when the length of the wound electrode body in the direction along the winding axis of the wound electrode body is L1 and the length in a direction perpendicular to the winding axis and perpendicular to the thickness direction of the wound electrode body is L2, L2 is not less than twice L1. Item 3: A positive electrode tab group including a plurality of positive electrode tabs provided at one end of the wound electrode body in the winding axis direction and electrically connected to the positive electrode, and a negative electrode tab group including a plurality of negative electrode tabs provided at one end of the wound electrode body in the winding axis direction and electrically connected to the negative electrode, the battery case including an exterior body including an opening, a bottom wall facing the opening, a pair of first side walls extending from the bottom wall and facing each other, and second side walls extending from the bottom wall and facing each other, and a sealing plate for sealing the opening, wherein the positive electrode tab group and the negative electrode tab group are provided at the end of the wound electrode body on the sealing plate side. Item 4: The secondary battery according to any one of Items 1 to 3, wherein at least one of the first separator and the second separator includes a base material layer made of polyolefin and a heat-resistant layer formed on the surface of the base material layer facing the positive electrode and including an inorganic filler and a heat-resistant layer binder. Item 5: In the winding start-end region, when the total area of the direct facing region where the first separator and the second separator directly face each other is taken as 100%, the area of the region where the first separator and the second separator are adhered by the second adhesive layer is 30% or more. The secondary battery according to any one of Items 1 to 4. Item 6: In the region where the first separator and the second separator directly face each other, there is a region where the second adhesive layer does not intervene between the first separator and the second separator. The secondary battery according to any one of Items 1 to 5. Item 7: The first adhesive layer and the second adhesive layer are made of different materials. The secondary battery according to any one of Items 1 to 6. Item 8: The first adhesive layer and the second adhesive layer are made of the same material. The secondary battery according to any one of Items 1 to 7. Item 9: The mass per unit area of the second adhesive layer is greater than the mass per unit area of the first adhesive layer. The secondary battery according to any one of Items 1 to 8.

Explanation of Signs

[0065] 10 Battery case 12 Outer package 14 Sealing plate 20 Wound electrode body 20f Flat part 20r Curved part 22 Positive electrode 22e Winding end 22s Winding start 22t Positive electrode tab 24 Negative electrode 24e Winding end 24s Winding start 24t Negative electrode tab 26 First separator 26a Base material layer 26b Heat-resistant layer 26c Second adhesive layer 27 Second separator 27a Base material layer 26b Heat-resistant layer 27c Second adhesive layer 100 Secondary battery

Claims

1. A flat wound electrode body in which a strip-shaped first separator, a strip-shaped negative electrode, a strip-shaped second separator, and a strip-shaped positive electrode are laminated and wound around a winding axis, A secondary battery comprising: a battery case for housing the wound electrode body, The positive electrode includes a first adhesive layer on both surfaces, The first adhesive layer adheres one surface of the positive electrode to the first separator and the other surface of the positive electrode to the second separator, At least one of the first separator and the second separator includes a second adhesive layer in a winding start region located on the winding start side of the winding start end of the positive electrode, The second adhesive layer adheres the first separator and the second separator, In the winding start region, when the total area of the direct facing region where the first separator and the second separator directly face each other is 100%, the area of the region where the first separator and the second separator are adhered by the second adhesive layer is 30% or more. Secondary battery.

2. The wound electrode body, When the length in the direction along the winding axis of the wound electrode body is L1, When the length in a direction perpendicular to the winding axis and perpendicular to the thickness direction of the wound electrode body is L2, L2 is 2 times or more of L1, The secondary battery according to claim 1.

3. A positive electrode tab group including a plurality of positive electrode tabs provided at one end of the wound electrode body in the winding axis direction and electrically connected to the positive electrode, A negative electrode tab group including a plurality of negative electrode tabs provided at one end of the wound electrode body in the winding axis direction and electrically connected to the negative electrode, The battery case, An exterior body including an opening, a bottom wall facing the opening, a pair of first side walls extending from the bottom wall and facing each other, and a second side wall extending from the bottom wall and facing each other, A sealing plate for sealing the opening, The positive electrode tab group and the negative electrode tab group are provided at the end of the wound electrode body on the sealing plate side. The secondary battery according to claim 1 or 2.

4. At least one of the first separator and the second separator, A base material layer made of polyolefin, A heat-resistant layer formed on the surface of the base material layer facing the positive electrode and including an inorganic filler and a heat-resistant layer binder. The secondary battery according to claim 1 or 2.

5. In a region where the first separator and the second separator directly face each other, there is a region where the second adhesive layer does not intervene between the first separator and the second separator. The secondary battery according to claim 1 or 2.

6. The first adhesive layer and the second adhesive layer are made of different materials. The secondary battery according to claim 1 or 2.

7. The first adhesive layer and the second adhesive layer are made of the same material. The secondary battery according to claim 1 or 2.

8. The mass per unit area of the second adhesive layer is greater than the mass per unit area of the first adhesive layer. The secondary battery according to claim 1 or 2.

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