Secondary battery and method for manufacturing the same

Abstract

The present invention provides a secondary battery and a method for manufacturing the secondary battery. In a secondary battery in which a wound electrode body in a bent electrode tab group is housed in a battery case, an increase in the local inter-electrode distance at a flat portion near the electrode tab group is suppressed. The secondary battery comprises a flat wound electrode body and a battery case for housing the wound electrode body. The wound electrode body of the secondary battery comprises a positive electrode tab group formed by stacking positive electrode tabs and a negative electrode tab group formed by stacking negative electrode tabs, and the positive electrode tab group and the negative electrode tab group are respectively bent. The separator (30) of the secondary battery comprises a strip-shaped base material layer (32) and a surface layer (34) containing inorganic particles and a binder. At least one of the positive electrode plate (10) and the negative electrode plate (20) is bonded to the surface layer (34) of the separator (30). As a result, the inter-electrode distance between the positive electrode plate and the negative electrode plate can be appropriately maintained via the separator, thereby suppressing the increase in the local inter-electrode distance near the electrode tab group.

Description

Technical Field

[0001] The present invention relates to a secondary battery and a method for manufacturing the secondary battery. Background Art

[0002] Secondary batteries, such as lithium-ion secondary batteries, typically include: an electrode body having a pair of electrode plates (a positive plate and a negative plate); a battery case that houses the electrode body; and electrode terminals (a positive terminal and a negative terminal) exposed to the outside of the battery case. Furthermore, each electrode plate constituting the electrode body includes, for example, an electrode core (a positive electrode core and a negative electrode core) that is a foil-like metal member, and electrode active material layers (a positive electrode active material layer and a negative electrode active material layer) formed on the surface of the electrode core.

[0003] As an example of the electrode body of the secondary battery, a wound electrode body formed by winding a positive electrode plate and a negative electrode plate with a separator can be cited. As a separator for such a wound electrode body, a porous strip film having a substrate layer composed of a resin material such as polyethylene (PE) can generally be used. In addition, from the viewpoint of improving the safety of the secondary battery, a separator having a heat-resistant layer formed on the surface of the substrate layer is sometimes used. For example, in Patent Document 1, a separator having a porous resin layer (substrate layer) and a porous heat-resistant layer laminated on at least one side of the resin layer is disclosed. Moreover, the heat-resistant layer contains a filler and a binder composed of an inorganic material. The separator having such a heat-resistant layer suppresses thermal contraction when the temperature rises, and therefore can prevent the occurrence of internal short circuits and improve the safety of the secondary battery.

[0004] In addition, a plurality of electrode tabs, each stacked together to expose the electrode core, are sometimes formed at both ends of the wound electrode body along the winding axis (winding axis direction). This electrode tab group is connected to a conductive member such as an electrode current collector. Furthermore, by connecting this current collector to the electrode terminal, electrical conduction can be established between the wound electrode body inside the battery case and the electrode terminal outside the battery case.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2012 / 124093 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] As an example of the shape of the above-mentioned wound electrode body, a flat shape can be cited. The flat-shaped wound electrode body is made by stamping a cylindrical wound electrode body (cylindrical body) made by winding the positive electrode plate and the negative electrode plate through a separator. A pair of curved portions with curved outer surfaces and a flat portion with a flat outer surface connecting the pair of curved portions are formed in the wound electrode body. In the flat portion of the flat-shaped wound electrode body, the distance between the positive electrode plate and the negative electrode plate (inter-electrode distance) is small, thereby promoting the movement of charge carriers between the electrodes.

[0010] In addition, in the field of secondary batteries in recent years, a structure has been proposed in which the wound electrode body is housed inside the battery case while the electrode tab group is bent. As a result, it is possible to save space in the electrode tab group and increase the width of the wound electrode body to a position close to the inner wall of the battery case. As a result, the volume of the wound electrode body relative to the content of the battery case increases, which can greatly contribute to the improvement of battery performance. However, in a secondary battery with this structure, stress is applied to the flat portion close to the electrode tab group when the electrode tab group is bent, which may cause a local increase in the inter-electrode distance. If this local increase in the inter-electrode distance occurs, the charge and discharge reaction may become uneven, resulting in the precipitation of charge carriers, etc.

[0011] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a secondary battery in which a wound electrode assembly with a bent electrode tab group is housed in a battery case, wherein an increase in the local inter-electrode distance in a flat portion near the electrode tab group is suppressed.

[0012] Means for solving problems

[0013] In order to achieve the above-mentioned object, according to the technology disclosed herein, a secondary battery having the following structure is provided.

[0014] The secondary battery disclosed herein comprises a flat-shaped wound electrode body formed by winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween, and a battery case for housing the wound electrode body. The flat-shaped wound electrode body comprises a pair of curved portions with curved outer surfaces and a flat portion connecting the pair of curved portions with a flat outer surface. The positive electrode plate comprises a strip-shaped positive electrode core and a positive electrode active material layer formed on at least one surface of the positive electrode core. The negative electrode plate comprises a strip-shaped negative electrode core and a negative electrode active material layer formed on at least one surface of the negative electrode core. In addition, a positive electrode tab group is formed at one end in the winding axis direction of the wound electrode body, wherein the positive electrode tabs are stacked to expose the positive electrode core. A negative electrode tab group is formed at the other end in the winding axis direction of the wound electrode body, wherein the negative electrode tabs are stacked to expose the negative electrode core. The positive electrode tab assembly is bent while being bonded to a positive electrode current collector, which is a plate-shaped conductive member. The negative electrode tab assembly is bent while being bonded to a negative electrode current collector, which is a plate-shaped conductive member. Furthermore, the secondary battery separator disclosed herein comprises a strip-shaped substrate layer and a surface layer formed on at least one surface of the substrate layer and containing inorganic particles and a binder. At least one of the flat portions of the positive electrode plate and the negative electrode plate is bonded to the surface layer of the separator.

[0015] The inventors have conducted various studies and found that if a diaphragm with a heat-resistant layer is used to improve safety, the local increase in the inter-electrode distance is likely to occur in the flat part near the electrode tab group. In this regard, the inventors conducted an investigation in the following manner. Conventional diaphragms are pressed and deformed along the concave and convex surfaces of the electrode plates (positive plates and negative plates) by stamping, and are interlocked with the electrode plates. If the diaphragm and the electrode plates are bonded in this way, it is easy to maintain the inter-electrode distance between the positive plate and the negative plate. On the other hand, the strength of the diaphragm with a heat-resistant layer is relatively high, and it is difficult to deform such that it is interlocked with the electrode plates. That is, the diaphragm with a heat-resistant layer loses the inter-electrode distance maintenance function of the conventional diaphragm. The secondary battery disclosed herein is completed based on this understanding. Specifically, the diaphragm of the secondary battery of the above structure has a surface layer containing inorganic particles and a binder to prevent internal short circuits caused by thermal shrinkage. However, the surface layer in the technology disclosed herein is different from the heat-resistant layer in the prior art, and has adhesion to the extent that it is interlocked and bonded with the electrode plates by stamping. This allows the inter-electrode distance-maintaining function of the separator and electrode plate to be appropriately utilized. Therefore, even when a wound electrode assembly with a bent electrode tab assembly is housed within the battery case, the local increase in inter-electrode distance in the flat portion near the electrode tab assembly can be suppressed without compromising safety. As a result, a secondary battery with stable quality near the junction between the electrode current collector and the electrode tab assembly can be obtained.

[0016] In a preferred embodiment of the secondary battery disclosed herein, the content of inorganic particles relative to the total mass of the surface layer is 70% to 80% by mass. As the content of inorganic particles in the surface layer is reduced, it becomes easier to exert the inter-electrode distance maintenance effect brought about by the adhesion between the electrode plate and the surface layer. On the other hand, if the content of inorganic particles in the surface layer is excessively reduced, it is possible to produce adhesion in the surface layer, and the production of the wound electrode body becomes difficult. In addition, by adding a certain amount of inorganic particles to the surface layer, the thermal shrinkage of the diaphragm can be appropriately prevented. From these viewpoints, the content of inorganic particles in the surface layer is preferably in the range of 70% to 80% by mass.

[0017] In one embodiment of the secondary battery disclosed herein, the surface layer contains at least one of alumina particles and boehmite particles as inorganic particles. This can appropriately prevent thermal shrinkage of the separator.

[0018] In one embodiment of the secondary battery disclosed herein, the surface layer contains polyvinylidene fluoride as a binder, thereby more effectively maintaining the inter-electrode distance due to the adhesion between the electrode plate and the surface layer.

[0019] In one embodiment of the secondary battery disclosed herein, the surface layer has a mesh structure containing a plurality of voids. This provides high flexibility, thereby making the thickness of the flat portion of the wound electrode body uniform and helping to reduce variations in the inter-electrode distance.

[0020] In the method of forming the surface layer of the above-mentioned reticular structure, the porosity of the surface layer of the separator disposed in the area not facing the positive and negative plates is preferably 50% or greater. This can impart appropriate flexibility to the surface layer and more appropriately suppress variations in the inter-electrode distance. Furthermore, in this specification, "the porosity of the surface layer of the separator disposed in the area not facing the positive and negative plates" refers to the porosity of the surface layer of the separator before stamping.

[0021] In one embodiment of a secondary battery disclosed herein, multiple wound electrode bodies are housed within a battery case. In such a secondary battery, local increases in the inter-electrode distance may occur near the electrode tab groups of the multiple wound electrode bodies. In contrast, the disclosed technique can suppress local increases in the inter-electrode distance within each of the multiple wound electrode bodies and is therefore preferably applicable to secondary batteries equipped with multiple wound electrode bodies.

[0022] In the embodiment comprising multiple wound electrode bodies, a separator is preferably disposed at the outermost periphery of the wound electrode bodies, with adjacent wound electrode bodies bonded to each other via the surface layer of the separator. This restricts movement of the wound electrode bodies within the battery case, thereby preventing damage to the wound electrode bodies due to external impact or vibration.

[0023] In one embodiment of the secondary battery disclosed herein, a separator is disposed at the outermost periphery of a wound electrode body. The end of the separator is adhered to the outermost surface of the wound electrode body via a winding tape. The winding tape is disposed along a straight line connecting the positive and negative electrode tab groups. This prevents the wound electrode body from unwinding, thereby further effectively suppressing an increase in the inter-electrode distance in the vicinity of the electrode tab group, and achieving a stable bond between the electrode tab group and the electrode current collectors (positive and negative).

[0024] In one embodiment of the secondary battery disclosed herein, a separator is disposed at the outermost periphery of a wound electrode assembly. The end of the separator is adhered to the outermost surface of the wound electrode assembly via a winding tape. The ratio of the thickness of the separator surface layer between the positive and negative electrode plates to the thickness of the separator surface layer disposed in an area not facing the positive and negative electrode plates is 0.9 or less. This prevents the formation of height differences in the flat portion due to the thickness of the winding tape, thereby preventing degradation of battery performance due to variations in surface pressure relative to the flat portion.

[0025] In one embodiment of the secondary battery disclosed herein, one longitudinal end of the positive electrode plate is positioned inside the flat portion of the wound electrode body as the positive electrode starting end, while the other longitudinal end is positioned outside the flat portion of the wound electrode body as the positive electrode terminal end. Furthermore, one longitudinal end of the negative electrode plate is positioned inside the flat portion of the wound electrode body as the negative electrode starting end, while the other longitudinal end is positioned outside the flat portion of the wound electrode body as the negative electrode terminal end. With this configuration, in a flat wound electrode body, the starting ends of the positive and negative electrode plates can be positioned inside the flat portion, while the terminal ends can be positioned outside the flat portion.

[0026] In the aforementioned arrangement of the positive electrode leading end and the positive electrode trailing end on the flat portion, the bonding strength between the positive electrode leading end and the surface layer is preferably greater than the bonding strength between the positive electrode trailing end and the surface layer. This increases the bonding strength within the wound electrode body, thereby more effectively maintaining the inter-electrode distance.

[0027] In the embodiment where the positive electrode starting end and the negative electrode terminal are arranged on the flat portion, the bonding strength between the positive electrode terminal and the surface layer is preferably greater than that between the negative electrode terminal and the surface layer. This can improve the permeability of the electrolyte into the wound electrode body.

[0028] In the aforementioned embodiment in which the positive electrode leading end and the negative electrode trailing end are disposed within the flat portion, when a plurality of wound electrode bodies are housed within the battery case, and a separator is disposed at the outermost periphery of the wound electrode bodies, and adjacent wound electrode bodies are bonded via the surface layer of the separator, the bonding strength between adjacent wound electrode bodies is preferably greater than the bonding strength between the positive electrode trailing end and the surface layer. This more reliably restricts movement of the wound electrode bodies within the battery case, and more appropriately prevents damage to the wound electrode bodies.

[0029] In addition, as another aspect of the technology disclosed herein, a method for manufacturing a secondary battery is provided. This manufacturing method comprises: a step of winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween to form a cylindrical body; a step of punching the cylindrical body to form a flat wound electrode body; and a step of housing the wound electrode body inside a battery case. Moreover, in the manufacturing method disclosed herein, the wound electrode body is a wound electrode body in any of the above-mentioned embodiments. According to this manufacturing method, a secondary battery can be manufactured in which the increase in the local inter-electrode distance at the flat portion near the electrode tab group is suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a perspective view schematically showing a secondary battery according to one embodiment.

[0031] Figure 2 It is along Figure 1 Schematic longitudinal sectional view along line II-II.

[0032] Figure 3 It is along Figure 1 Schematic longitudinal cross-sectional view along line III-III.

[0033] Figure 4 It is along Figure 1 Schematic cross-sectional view along line IV-IV.

[0034] Figure 5 It is a perspective view schematically showing the electrode assembly attached to the sealing plate.

[0035] Figure 6 It is a perspective view schematically showing an electrode assembly to which a positive electrode second current collector and a negative electrode second current collector are attached.

[0036] Figure 7 It is a schematic diagram showing the structure of a wound electrode body of a secondary battery according to one embodiment.

[0037] Figure 8 It is schematically represented Figure 7 Front view of the wound electrode body.

[0038] Figure 9 It is along Figure 8 Schematic longitudinal sectional view along line IX-IX.

[0039] Figure 10 This is an enlarged view schematically showing the interface between the positive electrode plate, the negative electrode plate, and the separator of the wound electrode assembly of the secondary battery according to one embodiment. DETAILED DESCRIPTION

[0040] Hereinafter, embodiments of the technology disclosed herein will be described with reference to the accompanying drawings. In addition, matters other than those specifically mentioned in this specification and required for the implementation of the technology disclosed herein (for example, the general structure and manufacturing process of the battery) can be understood as design matters made by those skilled in the art based on the existing technology in this field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in this field. In addition, the expression "A to B" indicating a range in this specification includes the meaning of "above A and below B", and includes the meaning of "preferably greater than A" and "preferably less than B".

[0041] In addition, in this specification, "secondary battery" refers to a general storage device in which a charge and discharge reaction occurs by the movement of charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. In addition to so-called storage batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, the secondary battery also includes capacitors such as double-layer capacitors. The following describes an embodiment of the invention in the case of a lithium-ion secondary battery among the above-mentioned secondary batteries.

[0042] In addition, in the various figures referenced in this specification, the reference symbol X represents the "depth direction," the reference symbol Y represents the "width direction," and the reference symbol Z represents the "height direction." Furthermore, F in the depth direction X represents "front," and Rr represents "rear." L in the width direction Y represents "left," and R represents "right." Furthermore, U in the height direction Z represents "up," and D represents "down." However, these directions are defined for ease of explanation and are not intended to limit the configuration of the secondary battery disclosed herein.

[0043] <First embodiment>

[0044] 1. Structure of secondary batteries

[0045] Below, refer to Figures 1 to 10 One embodiment of the secondary battery disclosed herein will be described. Figure 1 It is a perspective view schematically showing the secondary battery according to this embodiment. Figure 2 It is along Figure 1 Schematic longitudinal sectional view along line II-II. Figure 3 It is along Figure 1 Schematic longitudinal cross-sectional view along line III-III. Figure 4 It is along Figure 1 Schematic cross-sectional view along line IV-IV. Figure 5 It is a perspective view schematically showing the electrode assembly attached to the sealing plate. Figure 6 It is a perspective view schematically showing an electrode assembly to which a positive electrode second current collector and a negative electrode second current collector are attached. Figure 7 It is a schematic diagram showing the structure of a wound electrode body of the secondary battery according to this embodiment. Figure 8 It is schematically represented Figure 7 Front view of the wound electrode body. Figure 9 It is along Figure 8 Schematic longitudinal sectional view along line IX-IX. Figure 10 This is an enlarged view schematically showing the interface between the positive electrode plate, the negative electrode plate, and the separator of the wound electrode assembly of the secondary battery according to this embodiment.

[0046] like Figure 2 As shown, the secondary battery 100 of this embodiment includes a wound electrode body 40 and a battery case 50 that houses the wound electrode body 40. The specific structure of the secondary battery 100 will be described below.

[0047] (1) Battery housing

[0048] The battery case 50 is a frame that houses the wound electrode body 40. Although not shown in the figure, a non-aqueous electrolyte is also housed inside the battery case 50. Figure 1 As shown, the battery case 50 in this embodiment has a flat, bottomed rectangular parallelepiped (square) shape. Furthermore, any conventionally known material can be used as the battery case 50 without particular limitation. For example, the battery case 50 can be made of metal. Examples of materials for the battery case 50 include aluminum, aluminum alloys, iron, and iron alloys.

[0049] like Figure 1 and Figure 2As shown, the battery case 50 includes an outer body 52 and a sealing plate 54. The outer body 52 is a flat, square container with an opening 52h on its upper surface. The outer body 52 includes a bottom wall 52a that is roughly rectangular when viewed from above, a pair of long side walls 52b extending from the long sides of the bottom wall 52a to the upper side in the height direction Z, and a pair of short side walls 52c extending from the short sides of the bottom wall 52a to the upper side in the height direction Z. On the other hand, the sealing plate 54 is a plate-shaped member that is roughly rectangular when viewed from above and blocks the opening 52h of the outer body 52. Moreover, the outer peripheral edge of the sealing plate 54 is joined (e.g., welded) to the outer peripheral edge of the opening 52h of the outer body 52. Thus, a battery case 50 with an airtight interior is produced. In addition, a liquid injection hole 55 and a gas discharge valve 57 are provided on the sealing plate 54. The liquid injection hole 55 is a through hole provided for injecting non-aqueous electrolyte into the interior of the sealed battery case 50. The injection hole 55 is sealed by a sealing member 56 after the nonaqueous electrolyte is injected. The gas discharge valve 57 is a thin-walled portion designed to rupture (open) when a large amount of gas is generated in the battery case 50 to discharge the gas.

[0050] (2) Electrolyte

[0051] As described above, in addition to the wound electrode body 40, an electrolyte (not shown) is also housed inside the battery case 50. As the electrolyte, the electrolyte used in the conventionally known secondary battery can be used without particular limitation. For example, as the electrolyte, a non-aqueous electrolyte in which a supporting salt is dissolved in a non-aqueous solvent can be used. As an example of the non-aqueous solvent, carbonate solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate can be listed. As an example of the supporting salt, fluorine-containing lithium salts such as LiPF6 can be listed.

[0052] (3) Electrode terminals

[0053] In addition, on one side in the width direction Y of the sealing plate 54 ( Figure 1 、 Figure 2 A positive electrode terminal 60 is attached to the end portion (left side in FIG. 1 ). The positive electrode terminal 60 is connected to a plate-shaped positive electrode external conductive member 62 on the outside of the battery case 50. On the other hand, on the other side ( Figure 1 、 Figure 2 A negative terminal 65 is attached to the end (on the right side in the figure). A plate-shaped negative external conductive member 67 is attached to the negative terminal 65. These external conductive members (positive external conductive member 62 and negative external conductive member 67) are connected to other secondary batteries and external devices via external connecting members (such as busbars). In addition, the external conductive members are preferably made of a metal with excellent conductivity (such as aluminum, aluminum alloy, copper, or copper alloy).

[0054] (4) Electrode collector

[0055] like Figures 3 to 5 As shown, in the secondary battery 100 of this embodiment, a plurality (three) of wound electrode bodies 40 are housed in a battery case 50. The detailed structure will be described later, but each wound electrode body 40 is provided with a positive electrode tab group 42 and a negative electrode tab group 44 (see Figure 7 and Figure 8 ).like Figure 4 As shown, these electrode tab groups (positive electrode tab group 42 and negative electrode tab group 44 ) are bent in a state where they are joined to electrode current collectors (positive electrode current collector 70 and negative electrode current collector 75 ).

[0056] Specifically, the positive electrode tab group 42 of each of the plurality of wound electrode bodies 40 is connected to the positive electrode terminal 60 via the positive electrode current collector 70. The positive electrode current collector 70 is housed inside the battery case 50. Figure 2 and Figure 5 As shown, the positive electrode current collector 70 includes a first positive electrode current collector 71 and a plurality of second positive electrode current collectors 72. The first positive electrode current collector 71 is a plate-shaped conductive member extending in the width direction Y along the inner side surface of the sealing plate 54, and the second positive electrode current collector 72 is a plate-shaped conductive member extending in the height direction Z. In addition, the lower end portion 60c of the positive terminal 60 is inserted into the interior of the battery case 50 through the terminal insertion hole 58 of the sealing plate 54 and connected to the first positive electrode current collector 71 (see Figure 2 ). On the other hand, Figures 4 to 6 As shown in FIG. 1 , in the secondary battery 100, there are provided positive electrode second current collectors 72 in a number corresponding to the number of wound electrode bodies 40. Each positive electrode second current collector 72 is connected to the positive electrode tab group 42 of the wound electrode body 40. Figure 4 and Figure 5 As shown, the positive electrode tab group 42 of the wound electrode body 40 is bent so that the positive electrode second current collector 72 faces one side surface 40a of the wound electrode body 40. As a result, the upper end of the positive electrode second current collector 72 is electrically connected to the positive electrode first current collector 71.

[0057] On the other hand, the negative electrode tab group 44 of each of the plurality of wound electrode bodies 40 is connected to the negative terminal 65 via the negative electrode collector 75. The connection structure on the negative electrode side is substantially the same as the connection structure on the positive electrode side described above. Specifically, the negative electrode collector 75 includes a negative electrode first collector 76 and a plurality of negative electrode second collectors 77. The negative electrode first collector 76 is a plate-shaped conductive member extending in the width direction Y along the inner side surface of the sealing plate 54, and the negative electrode second collector 77 is a plate-shaped conductive member extending in the height direction Z (see Figure 2 and Figure 5 ). The lower end portion 65c of the negative electrode terminal 65 is inserted into the interior of the battery case 50 through the terminal insertion hole 59 and connected to the negative electrode first current collector 76 (see Figure 2 ). On the other hand, the plurality of negative electrode second current collectors 77 are connected to the negative electrode tab group 44 of the wound electrode body 40 (see Figures 4 to 6 ). Furthermore, the negative electrode tab assembly 44 is bent so that the negative electrode second current collector 77 faces the other side surface 40b of the wound electrode body 40. Thus, the upper end of the negative electrode second current collector 77 is electrically connected to the negative electrode first current collector 76. Furthermore, metals with excellent electrical conductivity (such as aluminum, aluminum alloys, copper, and copper alloys) can also be preferably used as the electrode current collectors (positive electrode current collector 70 and negative electrode current collector 75).

[0058] (5) Insulation components

[0059] In addition, in the secondary battery 100, various insulating members are installed to prevent electrical conduction between the wound electrode body 40 and the battery case 50. Specifically, an external insulating member 92 (see FIG. 1 ) is interposed between the positive electrode external conductive member 62 (negative electrode external conductive member 67) and the outer side surface of the sealing plate 54. Figure 1 ). This prevents the positive electrode external conductive member 62, the negative electrode external conductive member 67 from being electrically connected to the sealing plate 54. In addition, gaskets 90 are respectively installed in the terminal insertion holes 58 and 59 of the sealing plate 54 (see Figure 2 ). Thus, the positive terminal 60 (or the negative terminal 65) inserted into the terminal insertion holes 58 and 59 can be prevented from being electrically connected to the sealing plate 54. In addition, an internal insulating member 94 is arranged between the positive first current collector 71 (or the negative first current collector 76) and the inner side surface of the sealing plate 54. The internal insulating member 94 has a plate-shaped base 94a between the positive first current collector 71 (or the negative first current collector 76) and the inner side surface of the sealing plate 54. Thus, the positive first current collector 71, the negative first current collector 76 and the sealing plate 54 can be prevented from being electrically connected. In addition, the internal insulating member 94 has a protrusion 94b (refer to Figure 2 and Figure 3 ). Thus, the movement of the wound electrode body 40 in the height direction Z can be restricted, and the wound electrode body 40 can be prevented from directly contacting the sealing plate 54. In addition, the plurality of wound electrode bodies 40 are supported by an electrode body holder 98 (see FIG. 1 ) made of an insulating resin sheet. Figure 3 ) is contained inside the battery case 50 in a covered state. This prevents the wound electrode body 40 from directly contacting the outer casing 52. In addition, the materials of the above-mentioned insulating members are not particularly limited as long as they have the specified insulation properties. As an example, synthetic resin materials such as polyolefin resins (for example, polypropylene (PP), polyethylene (PE)), fluorine-based resins (for example, perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE)) can be used.

[0060] (6) Winding electrode body

[0061] like Figure 7 As shown, the electrode body used in the secondary battery 100 of this embodiment is a flat wound electrode body 40 formed by winding a positive electrode plate 10 and a negative electrode plate 20 with a separator 30 interposed therebetween. The flat wound electrode body 40 has a pair of curved portions 40r with curved outer surfaces and a flat portion 40f with a flat outer surface connecting the pair of curved portions 40r (see FIG. Figure 3 and Figure 9 ). In addition, in the secondary battery 100, the wound electrode body 40 is housed in the battery case 50 in such a manner that the winding axis WL of the wound electrode body 40 is substantially aligned with the width direction Y of the secondary battery 100 (see Figure 2 ). That is, the "winding axis direction" in the following description is substantially the same direction as the width direction Y in the drawings.

[0062] As described above, the wound electrode body 40 in this embodiment is housed inside the battery case 50 in a state where the positive electrode tab group 42 and the negative electrode tab group 44 are bent. This allows the width of the wound electrode body 40 to be increased to a position close to the inner wall of the battery case 50, thereby significantly contributing to improved battery performance. However, when the positive electrode tab group 42 (negative electrode tab group 44) is bent, stress is applied to the flat portion 40f located near the positive electrode tab group 42 (negative electrode tab group 44), and therefore, there is a possibility of a local increase in the inter-electrode distance. In contrast, the secondary battery 100 in this embodiment has a structure that can appropriately suppress the increase in the inter-electrode distance even when the positive electrode tab group 42 (negative electrode tab group 44) of the wound electrode body 40 is bent. The specific structure of the wound electrode body 40 in this embodiment is described below.

[0063] (a) Positive plate

[0064] like Figure 7 and Figure 10 As shown in FIG. 1 , the positive electrode plate 10 is a long strip-shaped member. The positive electrode plate 10 includes a positive electrode core 12 that is a strip-shaped metal foil and a positive electrode active material layer 14 applied to the surface of the positive electrode core 12. In addition, from the perspective of battery performance, the positive electrode active material layer 14 is preferably applied to both sides of the positive electrode core 12. In addition, in the positive electrode plate 10, the positive electrode tab 12t extends from one end side in the winding axis direction (width direction Y) toward the outside ( Figure 7 The positive electrode tab 12t protrudes from the left side of the positive electrode plate 10. Furthermore, a plurality of positive electrode tabs 12t are formed at predetermined intervals along the longitudinal direction L of the long, strip-shaped positive electrode plate 10. The positive electrode tab 12t is an area where the positive electrode active material layer 14 is not applied, exposing the positive electrode core 12. Furthermore, a protective layer 16 extending along the longitudinal direction L of the positive electrode plate 10 is formed in an area adjacent to the end edge of the positive electrode tab 12t.

[0065] As the components constituting the positive electrode plate 10, conventionally known materials used in general secondary batteries (e.g., lithium-ion secondary batteries) can be used without particular limitation. For example, a metal material having a predetermined conductivity can be preferably used as the positive electrode core 12. The positive electrode core 12 is preferably made of, for example, aluminum or an aluminum alloy.

[0066] In addition, the positive electrode active material layer 14 is a layer containing a positive electrode active material. The positive electrode active material is a granular material that can reversibly absorb and release charge carriers. From the perspective of stably producing a high-performance positive electrode plate 10, the positive electrode active material is preferably a lithium transition metal composite oxide. Among the above-mentioned lithium transition metal composite oxides, as a transition metal, a lithium transition metal composite oxide containing at least one of the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn) is particularly preferred. As specific examples, lithium nickel cobalt manganese composite oxides (NCM), lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, lithium nickel manganese composite oxides, lithium nickel cobalt aluminum composite oxides (NCA), lithium iron nickel manganese composite oxides, etc. can be listed. In addition, as a preferred example of a lithium transition metal composite oxide that does not contain Ni, Co and Mn, lithium iron phosphate composite oxides (LFP) can be listed. In addition, the term "lithium nickel cobalt manganese composite oxide" in this specification is a term that includes oxides containing added elements in addition to the main constituent elements (Li, Ni, Co, Mn, O). Examples of such added elements include transition metal elements such as Mg, Ca, Al, Ti, V, Cr, Si, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, Sn, and typical metal elements. In addition, the added elements may also be semi-metal elements such as B, C, Si, P, and non-metal elements such as S, F, Cl, Br, and I. Although detailed description is omitted, this point is also the same for other lithium transition metal composite oxides described as "lithium nickel cobalt manganese composite oxides". In addition, the positive electrode active material layer 14 may also contain additives other than the positive electrode active material. As an example of such additives, conductive materials, binders, etc. may be listed. As a specific example of a conductive material, carbon materials such as acetylene black (AB) may be listed. As a specific example of a binder, resin binders such as polyvinylidene fluoride (PVdF) may be listed. Furthermore, the content of the positive electrode active material when the total solid content of the positive electrode active material layer 14 is 100 mass % is generally 80 mass % or more, typically 90 mass % or more.

[0067] On the other hand, the protective layer 16 is a layer having lower conductivity than the positive electrode active material layer 14. By arranging the protective layer 16 in an area adjacent to the end edge of the positive electrode plate 10, it is possible to prevent internal short circuits caused by direct contact between the positive electrode core 12 and the negative electrode active material layer 24 when the separator 30 is damaged. For example, as the protective layer 16, it is preferred to form a layer containing insulating ceramic particles. Examples of the ceramic particles include inorganic oxides such as aluminum oxide (Al2O3), magnesium oxide (MgO), silicon dioxide (SiO2), and titanium dioxide (TiO2), nitrides such as aluminum nitride and silicon nitride, metal hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide, clay minerals such as mica, talc, boehmite, zeolite, apatite, and kaolin, and glass fibers. Considering insulation and heat resistance, aluminum oxide, boehmite, aluminum hydroxide, silicon dioxide, and titanium dioxide are preferred among the above materials. In addition, the protective layer 16 may also contain a binder for fixing the ceramic particles to the surface of the positive electrode core 12. Examples of such binders include resin binders such as polyvinylidene fluoride (PVdF). Furthermore, the protective layer is not an essential component of the positive electrode plate. In other words, in the secondary battery disclosed herein, a positive electrode plate without a protective layer can also be used.

[0068] In addition, the thickness t2 of the positive electrode plate 10 (see Figure 10 ) is preferably 80 μm or more, more preferably 100 μm or more, and further preferably 120 μm or more. The positive electrode plate 10 having such a sufficient thickness has a large elastic effect after stamping, so it is possible that the elastic effect remaining in the bent portion 40r causes the flat portion 40f to expand and rebound, and the inter-electrode distance is likely to increase. The details will be described later, but according to the technology disclosed herein, not only the increase in the inter-electrode distance caused by the bending of the electrode tab group can be appropriately suppressed, but also the increase in the inter-electrode distance caused by rebound can be appropriately suppressed. In addition, from the viewpoint of easily preventing rebound, the thickness of the positive electrode plate 10 is preferably 200 μm or less, more preferably 180 μm or less, and further preferably 160 μm or less. In addition, the "thickness of the positive electrode plate" in this specification is the total thickness of the positive electrode core and the positive electrode active material layer.

[0069] Furthermore, the surface roughness of the positive electrode plate 10 (typically the surface roughness of the positive electrode active material layer 14) is preferably 0.01 μm or more, more preferably 0.02 μm or more. The specific situation will be described later, but in the present embodiment, the surface layer 34 of the separator 30 is deformed and fitted to match the concave and convex surface of the positive electrode plate 10, so that the separator 30 is bonded to the positive electrode plate 10 to exert the function of maintaining the inter-electrode distance. From the viewpoint of properly achieving the bonding between the separator 30 and the positive electrode plate 10, the positive electrode plate 10 preferably has a surface roughness of a certain value or more. On the other hand, the upper limit of the surface roughness of the positive electrode plate 10 is not particularly limited, and may also be 3 μm or less. In addition, the "surface roughness" in this specification is the arithmetic mean roughness Ra.

[0070] In addition, the positive electrode active material layer 14 preferably contains large positive electrode active material particles with a peak particle size in the range of 10 μm to 20 μm and small positive electrode active material particles with a peak particle size in the range of 2 μm to 6 μm in the particle size distribution analyzed by laser diffraction / scattering. In this way, by mixing two types of positive electrode active material particles with different particle sizes, fine irregularities are formed on the surface of the positive electrode active material layer 14, thereby achieving more appropriate adhesion between the positive electrode plate 10 and the separator 30. In addition, the large particles and small particles mentioned above can be the same type of lithium transition metal composite oxide or different types of lithium transition metal composite oxide.

[0071] In addition, in recent years, from the perspective of increasing battery capacity, attempts have been made to form a positive electrode active material layer with a filling density of 2 g / cc or more. However, since such a high-density positive electrode active material layer has a large reaction force relative to stamping, it may become the main reason for promoting the increase in the inter-electrode distance caused by the above-mentioned rebound. However, according to the technology disclosed herein, even in the case of forming a high-density positive electrode active material layer of 2 g / cc or more (preferably 2.5 g / cc or more), the rebound of the wound electrode body can be appropriately suppressed. In other words, according to the technology disclosed herein, a high-density positive electrode active material layer that was difficult to use in the previous technology can be easily used, which can contribute to the improvement of the battery capacity. In addition, from the perspective of appropriately preventing rebound, the filling density of the positive electrode active material layer 14 is preferably 4 g / cc or less.

[0072] (b) Negative plate

[0073] like Figure 7 and Figure 10As shown in FIG. 1 , the negative electrode plate 20 is a long strip-shaped member. The negative electrode plate 20 includes a negative electrode core 22 that is a strip-shaped metal foil and a negative electrode active material layer 24 applied to the surface of the negative electrode core 22. In addition, from the perspective of battery performance, the negative electrode active material layer 24 is preferably applied to both sides of the negative electrode core 22. In addition, the negative electrode plate 20 is provided with a side extending from one end side in the winding axis direction (width direction Y) toward the outside ( Figure 7 A protruding negative electrode tab 22t is shown (on the right side of the figure). A plurality of negative electrode tabs 22t are provided at predetermined intervals in the longitudinal direction L of the negative electrode plate 20. The negative electrode tabs 22t are areas where the negative electrode core 22 is exposed without applying the negative electrode active material layer 24.

[0074] As the various components constituting the negative electrode plate 20, conventionally known materials used in general secondary batteries (e.g., lithium-ion secondary batteries) can be used without particular limitation. For example, a metal material having a predetermined conductivity can be preferably used as the negative electrode core 22. The negative electrode core 22 is preferably made of, for example, copper or a copper alloy.

[0075] In addition, the negative electrode active material layer 24 is a layer containing a negative electrode active material. As the negative electrode active material, there is no particular limitation as long as it can reversibly occlude and release charge carriers in the relationship with the above-mentioned positive electrode active material, and materials that can be used in general secondary batteries in the past can be used without particular restrictions. Examples of the negative electrode active material include carbon materials, silicon-based materials, and the like. As carbon materials, for example, graphite, hard carbon, soft carbon, amorphous carbon, and the like can be used. In addition, amorphous carbon-coated graphite in which the surface of graphite is coated with amorphous carbon can also be used. On the other hand, examples of silicon-based materials include silicon, silicon oxide (silicon dioxide), and the like. In addition, silicon-based materials can also contain other metal elements (such as alkaline earth metals) and their oxides. In addition, the negative electrode active material layer 24 can also contain additives other than the negative electrode active material. As an example of the additive, a binder, a thickener, and the like can be mentioned. As a specific example of the binder, a rubber-based binder such as styrene-butadiene rubber (SBR) can be mentioned. Specific examples of thickeners include carboxymethyl cellulose (CMC). The negative electrode active material content, when the total solid content of the negative electrode active material layer 24 is 100% by mass, is approximately 30% by mass or greater, and typically 50% by mass or greater. The negative electrode active material may comprise 80% by mass or greater, or 90% by mass or greater, of the negative electrode active material layer 24. The width w2 of the negative electrode active material layer 24 is preferably 200 mm to 450 mm, more preferably 250 mm to 350 mm, and even more preferably 270 mm to 320 mm.

[0076] In addition, the thickness t3 of the negative electrode plate 20 (see Figure 10) is preferably 100 μm or more, more preferably 130 μm or more, and further preferably 160 μm or more. Similar to the above-mentioned positive electrode plate 10, if the negative electrode plate 20 becomes thicker, it is possible to promote the increase in the inter-electrode distance caused by rebound. However, according to the technology disclosed herein, even when a negative electrode plate 20 of such a thickness is used, the occurrence of rebound can be appropriately suppressed. On the other hand, from the viewpoint of easily preventing rebound, the thickness of the negative electrode plate 20 is preferably 250 μm or less, more preferably 220 μm or less, and further preferably 190 μm or less. In addition, the "thickness of the negative electrode plate" in this specification is the total thickness of the negative electrode core and the negative electrode active material layer.

[0077] In addition, similar to the surface roughness of the positive electrode plate 10 described above, the surface roughness of the negative electrode plate 20 (typically the surface roughness of the negative electrode active material layer 24) is preferably adjusted from the perspective of appropriately achieving adhesion between the separator 30 and the negative electrode plate 20. For example, the surface roughness of the negative electrode plate 20 is preferably 0.05 μm or more, more preferably 0.1 μm or more. As a result, the separator 30 and the negative electrode plate 20 can be appropriately bonded, and the inter-electrode distance maintenance effect brought about by the technology disclosed herein can be more appropriately exerted. In addition, the upper limit of the surface roughness of the negative electrode plate 20 is not particularly limited, and can also be 5 μm or less.

[0078] (c) Diaphragm

[0079] like Figure 7 and Figure 9 As shown, the wound electrode body 40 in this embodiment includes two separators 30. Each separator 30 is an insulating sheet formed with a plurality of tiny through-holes through which charge carriers can pass. By placing the separator 30 between the positive electrode plate 10 and the negative electrode plate 20, contact between the positive electrode plate 10 and the negative electrode plate 20 is prevented while allowing charge carriers (e.g., lithium ions) to move between the positive electrode plate 10 and the negative electrode plate 20.

[0080] like Figure 10 As shown, the separator 30 in this embodiment has a strip-shaped base layer 32 and a surface layer 34 formed on the surface (both sides) of the base layer 32. The detailed function will be described later, but in this embodiment, the surface layer 34 on one side of the separator 30 of the above structure is bonded to the positive electrode plate 10, and the surface layer 34 on the other side is bonded to the negative electrode plate 20. As a result, the inter-electrode distance maintenance function brought by the separator 30 is fully utilized, thereby preventing the local increase in the inter-electrode distance near the bent electrode tab group. In addition, the flat portion 40f of the wound electrode body 40 (see Figure 9 ) expands in the thickness direction (depth direction X), and thus, it is possible to suppress the increase in the inter-electrode distance caused by rebound. The diaphragm 30 having this structure will be described below.

[0081] First, the substrate layer 32 can use the substrate layer used in the separator of the conventionally known secondary battery without any particular limitation. For example, the substrate layer 32 is preferably a porous sheet-like member containing a polyolefin resin or the like. In this way, the flexibility of the separator 30 can be fully ensured, and the production (winding and stamping) of the wound electrode body 40 can be easily implemented. In addition, as the polyolefin resin, polyethylene (PE), polypropylene (PP) or the like or a mixture thereof can be used. In addition, the porosity of the substrate layer 32 is preferably 20% to 70%, more preferably 30% to 60%, and further preferably 40% to 50%. In this way, the charge carriers can be appropriately moved between the positive electrode plate 10 and the negative electrode plate 20. In addition, the "porosity" in this specification means the porosity before stamping unless otherwise mentioned. In addition, the "porosity before stamping" can be obtained by measuring the separator arranged in an area that is not facing the positive electrode plate and the negative electrode plate. Examples of the "area that is not facing the positive electrode plate and the negative electrode plate" include Figure 7 The “region 30 a where only the separator 30 extends” formed on both side edges of the wound electrode body 40 , etc.

[0082] like Figure 10 As shown, the surface layer 34 in this embodiment is a layer formed on both sides of the substrate layer 32. The surface layer 34 contains inorganic particles and a binder. As inorganic particles, there can be listed ceramic particles containing ceramics such as aluminum oxide, silicon dioxide, titanium dioxide, boehmite, aluminum hydroxide, magnesium carbonate, magnesium oxide, zirconium oxide, zinc oxide, iron oxide, cerium dioxide, and yttrium oxide as main components. The surface layer 34 containing such inorganic particles has excellent heat resistance. As a result, the thermal shrinkage of the diaphragm 30 when the temperature rises can be suppressed, which helps to improve the safety of the secondary battery 100. In addition, among the above-mentioned ceramic particles, aluminum oxide particles and boehmite particles are particularly preferred from the viewpoint of suppressing the thermal shrinkage of the diaphragm 30. In addition, the average particle size of the inorganic particles is preferably, for example, 0.15μm to 2μm, more preferably 0.3μm to 0.7μm, and further preferably 0.3μm to 0.5μm. In addition, the specific surface area of the inorganic particles is preferably, for example, 2m 2 / g~13m 2 In addition, the "average particle size" in this specification refers to the particle size (D 50 particle size).

[0083] Then, as the binder of the surface layer 34, any resin material known in the art with a certain degree of viscosity can be used without particular limitation. For example, the binder of the surface layer 34 is preferably a resin material such as an acrylic resin, a polyolefin resin, a cellulose resin, or a fluorine resin. As the acrylic resin, a resin having an acrylate polymer as the main component can be used. In addition, as the polyolefin resin, polyethylene (PE), polypropylene (PP), etc. can be used. In addition, as the cellulose resin, carboxymethyl cellulose (CMC), etc. can be used. In addition, as the fluorine resin, polyvinylidene fluoride (PVdF), etc. can be used. In addition, the surface layer 34 can also contain two or more of these binder resins. In addition, among the above-mentioned binder resins, PVdF can more appropriately exert adhesion to the electrode plate. In addition, the surface layer 34 preferably contains the same binder as the binder of the electrode active material layer of the opposing electrode plate. As an example, when the positive electrode active material layer 14 contains PVdF, it is preferred to use PVdF as the binder of the surface layer 34 facing the positive electrode active material layer 14. This can further improve the bonding strength between the surface layer 34 and the positive electrode plate 10 .

[0084] In addition, the surface layer 34 preferably adjusts the content of inorganic particles so as to exert a prescribed adhesiveness relative to the positive electrode plate 10 (or negative electrode plate 20). For example, the content of inorganic particles in the surface layer 34 is preferably less than 90% by mass, more preferably 85% by mass or less, and particularly preferably 80% by mass or less. If the content of inorganic particles in the surface layer 34 is set to a certain amount or less, the surface layer 34 is easily deformed during stamping, and therefore, the inter-electrode distance maintaining effect brought about by the intercalation (bonding) of the positive electrode plate 10 (or negative electrode plate 20) and the surface layer 34 can be properly exerted. On the other hand, if the content of inorganic particles in the surface layer 34 is excessively reduced, the content of resin materials such as binders becomes relatively more, and therefore, it is possible to produce adhesiveness in the surface layer 34 before stamping. In such a case, it may become difficult to wind the positive electrode plate 10 and the negative electrode plate 20 across the separator 30. From this viewpoint, the content of inorganic particles in the surface layer 34 is preferably 60% by mass or more, more preferably 65% by mass or more, and particularly preferably 70% by mass or more. In addition, by forming the surface layer 34 containing a certain amount of inorganic particles, internal short circuits caused by thermal shrinkage of the diaphragm 30 can also be appropriately prevented. In addition, the "content of inorganic particles" in this specification refers to the mass ratio of the inorganic particles relative to the total mass of the surface layer.

[0085] In addition, the surface layer 34 preferably has a mesh structure containing a plurality of voids. In the surface layer 34, inorganic particles are dispersed inside the binder resin solidified into a mesh shape. The surface layer 34 with the mesh structure has high flexibility and is therefore deformed in a flattened manner during stamping. As a result, the separator 30 can absorb the deviation in the thickness t1 of the wound electrode body 40, thereby suppressing the precipitation of charge carriers caused by the deviation in the inter-electrode distance. In addition, the porosity of the surface layer 34 with the mesh structure is preferably 50% or more, more preferably 60% or more, and particularly preferably 70% or more. As a result, appropriate flexibility can be imparted to the surface layer 34, suppressing the deviation in the thickness t1 of the wound electrode body 40. On the other hand, considering the strength of the separator 30, the porosity of the surface layer 34 is preferably 90% or less, more preferably 80% or less.

[0086] Furthermore, the mesh-structured surface layer 34 is preferably formed so that the packing density on the electrode plate side (outside the separator 30) is higher than the packing density on the substrate layer 32 side (inside the separator 30). As a result, the surface layer 34 on the substrate layer 32 side is preferentially pressed and deformed during press forming, thereby preventing the voids in the surface layer 34 on the electrode plate side from collapsing. This can suppress the reduction in the permeability of the electrolyte near the electrode plate, helping to prevent drying out.

[0087] In addition, the thickness t4 of the diaphragm 30 (see Figure 10 ) is preferably 4 μm or more, more preferably 8 μm or more, and further preferably 12 μm or more. Similar to the above-mentioned positive electrode plate 10 and negative electrode plate 20, if the thickness t4 of the separator 30 increases, there is a tendency to promote the increase in the inter-electrode distance caused by rebound. However, according to the technology disclosed herein, even when a separator 30 of sufficient thickness as described above is used, the occurrence of rebound can be appropriately suppressed. On the other hand, from the viewpoint of easily preventing the occurrence of rebound, the thickness of the separator 30 is preferably 28 μm or less, more preferably 24 μm or less, and further preferably 20 μm or less. In addition, the "thickness t4 of the separator 30" in this specification is the total thickness of the substrate layer 32 and the surface layer 34.

[0088] 2. Secondary Battery Manufacturing Method

[0089] The structure of the secondary battery 100 of this embodiment has been described above. Next, the manufacturing steps of the secondary battery 100 will be described, along with a detailed description of the inter-electrode distance maintenance effect achieved by the disclosed technology. Furthermore, the manufacturing method of the secondary battery 100 of this embodiment includes (1) a winding step, (2) a stamping step, and (3) a storage step.

[0090] (1) Winding process

[0091] In this process, first, a laminated body is prepared in which the separator 30, the negative electrode plate 20, the separator 30, and the positive electrode plate 10 are laminated in this order (see Figure 7 At this time, the stacking positions of the respective sheet members in the width direction Y are adjusted so that only the positive electrode tab 12t of the positive electrode plate 10 is stacked from one side in the width direction Y ( Figure 7 The side edge of the negative electrode plate 20 protrudes from the other side (the left side) and only the negative electrode tab 22t of the negative electrode plate 20 protrudes from the other side ( Figure 7 The side edge of the electrode tab group (on the right side in the figure) protrudes. Then, a cylindrical wound body (cylindrical body) is produced by winding the produced stacked body. The number of windings at this time is preferably adjusted appropriately in consideration of the performance of the secondary battery 100 as the target, manufacturing efficiency, etc. In addition, the technology disclosed herein can be particularly preferably applied to a wound electrode body 40 with a winding number of 20 turns or more. Specifically, as the winding number of the wound electrode body 40 increases, the number of electrode tabs constituting the electrode tab group increases. In order to properly bend an electrode tab group with a large number of stacked electrode tabs, a large external force is required, and therefore, a large stress is easily applied to the flat portion 40f near the electrode tab group. However, according to the technology disclosed herein, the inter-electrode distance maintaining function brought about by the separator 40 is appropriately exerted, and therefore, even in a wound electrode body 40 with a winding number of 20 turns or more, the local increase in the inter-electrode distance near the electrode tab group can be sufficiently suppressed. In addition, for the sake of convenience of explanation, Figure 9 The wound electrode body 40 shown shows a structure with a significantly reduced number of windings. Figure 9 The number of windings of the wound electrode body 40 shown does not limit the number of windings of the wound electrode body disclosed herein.

[0092] (2) Stamping process

[0093] In this step, the wound cylindrical body is punched to produce a flat wound electrode body 40 (see Figure 9 ).like Figure 9 As shown in FIG. 1 , the flat wound electrode body 40 after stamping has a pair of curved portions 40r with curved outer surfaces and a flat portion 40f connecting the pair of curved portions 40r with a flat outer surface. Figure 7 and Figure 8 As shown, a positive electrode tab group 42 composed of stacked positive electrode tabs 12t is formed at one end of a flat, stamped wound electrode body 40 in the width direction Y, and a negative electrode tab group 44 composed of stacked negative electrode tabs 22t is formed at the other end. Furthermore, a core portion 46 is formed in the center of the wound electrode body 40 in the width direction Y, where the positive electrode active material layer 14 and the negative electrode active material layer 24 face each other.

[0094] Here, in this embodiment, during stamping, the surface layer 34 of the separator 30 is bonded to the positive electrode plate 10 (negative electrode plate 20). Specifically, the wound body is flattened during stamping, and as a result, a large pressure is applied to each of the sheet-like components (positive electrode plate 10, negative electrode plate 20, and separator 30) located on the flat portion 40f. At this time, in this embodiment, by adjusting the content of inorganic particles in the surface layer 34, the pressure during stamping, etc., the surface layer 34 is deformed to match the concave and convex surfaces of the positive electrode active material layer 14 (or negative electrode active material layer 24). As a result, at the interface between the separator 30 and the positive electrode plate 10 (or negative electrode plate 20) on the flat portion 40f of the wound electrode body 40, the separator 30 and the positive electrode plate 10 (negative electrode plate 20) are embedded and bonded, so that the inter-electrode distance between the positive electrode plate 10 and the negative electrode plate 20 is maintained by the separator 30.

[0095] In addition, the bonding strength between the surface layer 34 arranged on the flat portion 40f of the wound electrode body 40 before being housed in the battery case 50 and the electrode plate (typically the positive electrode plate 10) is preferably 0.5 N / m or more, more preferably 0.75 N / m or more, and further preferably 1.0 N / m or more. It is preferred to adjust the content of inorganic particles in the surface layer 34 and the pressure during stamping so as to ensure appropriate bonding strength between the surface layer 34 and the electrode plate. Thereby, the increase in the local inter-electrode distance caused by the bending of the electrode tab group and the increase in the inter-electrode distance caused by rebound can be more appropriately suppressed, respectively. In addition, the "bonding strength" in this specification is the 90° peel strength based on JIS Z0237.

[0096] Then, if Figure 8 and Figure 9 As shown, in this embodiment, the separator 30 is arranged on the outermost surface of the wound electrode body 40 after stamping. The shape of the wound electrode body 40 is maintained by attaching a winding fixing tape 38 to the terminal end 30e of the separator 30. In addition, the winding fixing tape 38 is preferably arranged on a straight line connecting the positive electrode tab group 42 and the negative electrode tab group 44. As a result, the winding of the wound electrode body 40 can be prevented from loosening, and therefore, the local increase in the inter-electrode distance in the flat portion 40f near the electrode tab group (positive electrode tab group 42, negative electrode tab group 44) can be more appropriately suppressed.

[0097] In addition, when the winding fixing tape 38 is attached to the terminal portion 30e of the diaphragm 30, it is preferred to adjust the flexibility of the surface layer 34 and the pressure of stamping so that the ratio of the thickness of the surface layer 34 before stamping to the thickness of the surface layer 34 after stamping is reduced to less than 0.9 (more preferably less than 0.8, further preferably less than 0.7, and particularly preferably less than 0.6). As a result, the thickness of the winding fixing tape 38 can be absorbed by the pressing deformation of the surface layer 34, thereby preventing a large height difference from being generated in the flat portion 40f. As a result, the reduction in battery performance caused by the deviation of the surface pressure relative to the flat portion 40f can be suppressed. In addition, this effect can be particularly appropriately exerted in a secondary battery 100 having a plurality of wound electrode bodies 40 such as the present embodiment. In addition, the above-mentioned "thickness of the surface layer before stamping" can be similarly adjusted to the above-mentioned "porosity before stamping" by using an area that is not facing the negative electrode plate and the positive electrode plate (for example, Figure 7 On the other hand, the "thickness of the surface layer after stamping" can be measured based on the thickness of the surface layer 34 of the separator 30 between the positive electrode plate 10 and the negative electrode plate 20 (for example, near the center of the flat portion 40f).

[0098] In addition, if Figure 9 As shown, in the wound electrode body 40 after stamping, one end of the strip-shaped positive electrode plate 10 in the longitudinal direction is arranged inside the wound electrode body 40 as the positive electrode starting end portion 10s. In addition, the other end of the positive electrode plate 10 is arranged outside the wound electrode body 40 as the positive electrode terminal portion 10e. Similarly, one end of the strip-shaped negative electrode plate 20 is arranged inside the wound electrode body 40 as the negative electrode starting end portion 20s. In addition, the other end of the negative electrode plate 20 is arranged outside the wound electrode body 40 as the negative electrode terminal portion 20e. In addition, in this wound electrode body 40, the positive electrode starting end portion 10s, the positive electrode terminal portion 10e, the negative electrode starting end portion 20s, and the negative electrode terminal portion 20e are all arranged on the flat portion 40f of the wound electrode body 40.

[0099] Moreover, in Figure 9 In the wound electrode body 40 of the structure shown, it is preferable that the positive electrode leading end portion 10s and the surface layer 34 (see Figure 10 ) is greater than the bonding strength between the positive electrode terminal end 10e and the surface layer 34. This strengthens the bonding strength within the wound electrode body 40, allowing the inter-electrode distance maintenance effect provided by the disclosed technology to be more effectively exerted. Furthermore, when the wound electrode body 40 is manufactured to enhance the bonding strength within the body, the thickness of the surface layer 34 bonded to the positive electrode leading end 10s within the electrode body is thinner than the thickness of the surface layer 34 bonded to the positive electrode terminal end 10e.

[0100] In addition, Figure 9 In the wound electrode body 40 shown, the bonding strength between the positive electrode terminal portion 10e and the surface layer 34 is preferably greater than the bonding strength between the negative electrode terminal portion 20e and the surface layer 34. This facilitates the penetration of the electrolyte near the surface of the negative electrode plate 20, which is preferable from the perspective of preventing dry-up. Furthermore, when the wound electrode body 40 is manufactured so that the bonding strength between the negative electrode terminal portion 20e and the surface layer 34 is relatively low, the thickness of the surface layer 34 bonded to the positive electrode terminal portion 10e is thinner than the thickness of the surface layer 34 bonded to the negative electrode terminal portion 20e.

[0101] Furthermore, during press forming, no significant pressure is applied to the curved portion 40r of the wound electrode body 40. Therefore, the surface layer 34 of the separator 30 located at the curved portion 40r tends to be thicker than the surface layer 34 of the separator 30 located at the flat portion 40f. Specifically, the thickness of the surface layer 34 of the curved portion 40r can be 1.5 to 3 times the thickness of the surface layer 34 of the flat portion 40f. More specifically, the thickness of the surface layer 34 of the curved portion 40r tends to be approximately 1 μm thicker than the thickness of the surface layer 34 of the flat portion 40f.

[0102] (3) Storage process

[0103] In this process, the wound electrode body 40 formed in the press forming process is housed in the battery case 50. Specifically, Figure 6 As shown, the positive electrode second current collector 72 is joined to the positive electrode tab group 42 of the wound electrode body 40, and the negative electrode second current collector 77 is joined to the negative electrode tab group 44. Figure 5 As shown, a plurality of (3 in the figure) wound electrode bodies 40 are arranged in a manner that the flat portions 40f face each other. Then, a sealing plate 54 is arranged above the plurality of wound electrode bodies 40, and the positive electrode tab group 42 of each wound electrode body 40 is bent so that the positive electrode second current collector 72 faces the side surface 40a of one side of the wound electrode body 40. Thus, the positive electrode first current collector 71 is connected to the positive electrode second current collector 72. Similarly, the negative electrode tab group 44 of each wound electrode body 40 is bent so that the negative electrode second current collector 77 faces the side surface 40b of the other side of the wound electrode body 40. Thus, the negative electrode first current collector 76 is connected to the negative electrode second current collector 77. As a result, the wound electrode body 40 is mounted on the sealing plate 54 via the positive electrode collector 70 and the negative electrode collector 75.

[0104] In the connection between the sealing plate 54 and the wound electrode body 40, stress from bending the electrode tab assembly is applied to the flat portion 40f adjacent to the electrode tab assembly (positive electrode tab assembly 42 and negative electrode tab assembly 44). As a result, the inter-electrode distance increases in the flat portion 40f near the electrode tab assembly, potentially causing charge carrier precipitation. However, in this embodiment, the electrode plate is bonded to the separator 30, preventing the inter-electrode distance from increasing even when stress from bending the electrode tab assembly is applied.

[0105] Then, in this step, the wound electrode body 40 mounted on the sealing plate 54 is held by the electrode body holder 98 (see Figure 3 ) is covered and then housed inside the outer body 52. As a result, the flat portion 40f of the wound electrode body 40 faces the long side wall 52b of the outer body 52 (that is, the flat surface of the battery case 50). In addition, the upper curved portion 40r faces the sealing plate 54, and the lower curved portion 40r faces the bottom wall 52a of the outer body 52. Then, after the opening 52h on the upper surface of the outer body 52 is blocked with the sealing plate 54, the outer body 52 and the sealing plate 54 are joined (welded) to construct the battery case 50. Thereafter, the electrolyte is injected into the interior of the battery case 50 from the injection hole 55 of the sealing plate 54, and the injection hole 55 is blocked by the sealing member 56. Through the above process, the secondary battery 100 of this embodiment is manufactured. As described above, the secondary battery 100 bonds the separator 30 to the electrode plate via the surface layer 34, thereby suppressing the increase in the local inter-electrode distance caused by the stress when the electrode tab group (positive tab group 42 and negative tab group 44) is bent. As a result, the precipitation of charge carriers caused by the increase in the local inter-electrode distance can be suppressed. In addition, according to this embodiment, the occurrence of rebound of the wound electrode body 40 after stamping can also be suppressed. Therefore, the increase in battery resistance and the precipitation of charge carriers caused by rebound can also be appropriately suppressed. In addition, the wound electrode body 40 with suppressed rebound can maintain the thickness dimension t1, so it can be easily accommodated in the outer body 52, which can also contribute to the improvement of manufacturing efficiency.

[0106] <Other Implementation Methods>

[0107] The above describes one embodiment of the technology disclosed herein. Furthermore, the above embodiment is an example of applying the technology disclosed herein and does not limit the technology disclosed herein. Other embodiments of the technology disclosed herein will be described below.

[0108] (1) Surface layer formation surface

[0109] In the above-mentioned embodiment, a surface layer 34 is formed on both sides of the substrate layer 32. However, the surface layer does not need to be formed on both sides of the substrate layer, as long as it is formed on at least one side of the surface of the substrate layer. However, if the adhesion between the separator and the electrode body, the suppression of the thermal shrinkage of the separator, etc. are taken into account, the surface layer is preferably formed on both sides of the substrate layer. In addition, as described above, the surface layer has a better inclination than the negative plate in adhesion to the positive plate. If this is taken into account, when the surface layer is formed only on one side of the surface of the substrate layer, it is preferably formed on the surface of the side in contact with the positive plate.

[0110] (2) Number of wound electrode bodies

[0111] The secondary battery 100 of the above embodiment houses three wound electrode bodies 40 inside the battery case 50. However, the number of electrode bodies housed in one battery case is not particularly limited and may be two or more (a plurality) or one. Figure 3 In the secondary battery 100 shown, which includes multiple wound electrode assemblies 40, there is a risk of localized increases in the inter-electrode distance near the electrode tab group of each wound electrode assembly 40. In contrast, the technology disclosed herein enables a structure that suppresses this local increase in the inter-electrode distance for each of the multiple wound electrode assemblies 40. Therefore, the technology disclosed herein is particularly suitable for use in secondary batteries 100 that include multiple wound electrode assemblies 40.

[0112] In addition, in the secondary battery 100 having a plurality of wound electrode bodies 40 as in the above-mentioned embodiment, it is preferable to arrange a separator 30 having a surface layer 34 on the outermost periphery of the wound electrode body 40. Thus, the adjacent wound electrode bodies 40 are bonded to each other via the outermost separator 30, thereby limiting the movement of the wound electrode bodies 40 inside the battery case 50. As a result, it is possible to prevent the wound electrode bodies 40 from being damaged by external impacts and vibrations (external forces). For example, Figure 6 As shown, when the wound electrode body 40 and the electrode collector (positive electrode second collector 72, negative electrode second collector 77) are connected via the electrode tab group (positive electrode tab group 42, negative electrode tab group 44), the electrode tab group may be broken due to the movement of the wound electrode body 40 under the action of external force. In contrast, by bonding a plurality of wound electrode bodies 40 via a separator 30, the movement of each wound electrode body 40 can be restricted, thereby preventing damage to the electrode tab group. In addition, when bonding a plurality of wound electrode bodies 40 via a separator 30, it is preferred that the bonding strength between adjacent wound electrode bodies 40 is stronger than that of the positive terminal portion 10e (refer to FIG. Figure 9 ) has a high bonding strength with the surface layer 34. This can more reliably restrict the movement of the wound electrode body 40 and more appropriately prevent the wound electrode body 40 (eg, the electrode tab group) from being damaged.

[0113] Furthermore, when a separator 30 is disposed on the outermost periphery of the wound electrode body 40, the wound electrode body 40 on both outer sides in the depth direction X can be bonded to the electrode body holder 98 via the surface layer 34 of the separator 30. This can more reliably restrict the movement of the wound electrode body 40 within the battery case 50, thereby further appropriately preventing damage to the wound electrode body 40.

[0114] (3) Dimensions of the wound electrode body

[0115] As described above, the technology disclosed herein can not only suppress the increase in the local inter-electrode distance near the electrode tab group, but also suppress the expansion (rebound) of the flat portion of the wound electrode body. Here, the rebound of the wound electrode body is particularly prone to occur in a wound electrode body having the following external dimensions. However, according to the technology disclosed herein, the rebound can be appropriately suppressed even when a wound electrode body having the following external dimensions is used. That is, the technology disclosed herein can be particularly preferably applied to a secondary battery having a wound electrode body having the following external dimensions.

[0116] First, the width dimension w1 of the positive electrode active material layer 14 (see Figure 7 ) is preferably 200 mm or more. As the width dimension w1 of the positive electrode active material layer 14 becomes longer, the wound electrode body 40 becomes larger, and therefore, there is a tendency for the elastic effect generated by the bent portion 40r after stamping to become larger. In addition, the width dimension w1 of the positive electrode active material layer 14 is more preferably 200 mm to 400 mm, further preferably 250 mm to 350 mm, and particularly preferably 260 mm to 300 mm, for example, about 280 mm. In addition, the above-mentioned "width dimension of the positive electrode active material layer" refers to the length of the positive electrode active material layer in the direction in which the winding axis of the wound electrode body extends (winding axis direction).

[0117] Second, the thickness dimension t1 of the wound electrode body 40 (see Figure 9 ) is preferably 8 mm or greater. When the thickness dimension t1 of the wound electrode body 40 increases, the elastic effect of the bent portion 40r after stamping also increases. The thickness dimension t1 of the wound electrode body 40 is more preferably 8 mm to 25 mm, further preferably 8 mm to 20 mm, and particularly preferably 10 mm to 15 mm, for example, approximately 12 mm. The "thickness dimension of the wound electrode body" refers to the length of the flat portion in a direction perpendicular to the flat portion.

[0118] Third, the height dimension h1 of the wound electrode body 40 (see Figure 8) is preferably 120 mm or less. When the height dimension h1 of the wound electrode body 40 is shortened, the pair of curved portions 40r are brought closer together, so the elastic force generated by each curved portion 40r easily acts on the entire flat portion 40f. The height dimension h1 of the wound electrode body 40 is more preferably 60 mm to 120 mm, further preferably 80 mm to 110 mm, and particularly preferably 90 mm to 100 mm, for example, approximately 94 mm. The "height dimension of the wound electrode body" refers to the length from the upper end of one curved portion to the lower end of the other curved portion.

[0119] Furthermore, in a secondary battery having multiple wound electrode bodies, the aforementioned external dimensions may be common to or different between the wound electrode bodies. Furthermore, it is not necessary for all of the wound electrode bodies to have the aforementioned external dimensions; at least one wound electrode body may have the aforementioned external dimensions. However, if all of the wound electrode bodies have the aforementioned external dimensions, springback is more likely to occur in each of the wound electrode bodies. Therefore, the springback suppression effect provided by the disclosed technology is more effectively utilized.

[0120] While the present invention has been described in detail above, the above description is for illustrative purposes only. That is, the technology disclosed herein includes various modifications and alterations of the above-described specific examples.

[0121] Description of Reference Numerals

[0122] 10 positive plate

[0123] 12 positive electrode core

[0124] 14 Positive electrode active material layer

[0125] 16 protective layer

[0126] 20 negative plate

[0127] 22 Negative electrode core

[0128] 24 Negative electrode active material layer

[0129] 30 diaphragm

[0130] 32 base material layer

[0131] 34 Surface layer

[0132] 38 Winding fixing belt

[0133] 40 wound electrode body

[0134] 40f flat part

[0135] 40r bend

[0136] 42 positive electrode tab assembly

[0137] 44 negative electrode tab assembly

[0138] 50 battery housing

[0139] 60 Positive terminal

[0140] 65 Negative terminal

[0141] 70 positive electrode collector

[0142] 75 negative electrode collector

[0143] 100 Secondary batteries.

Claims

1. A secondary battery comprising a flat wound electrode body formed by winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween, and a battery case housing the wound electrode body, wherein: The flat wound electrode body includes a pair of curved portions whose outer surfaces are curved and a flat portion connecting the pair of curved portions whose outer surfaces are flat. The positive electrode plate includes a strip-shaped positive electrode core and a positive electrode active material layer formed on at least one surface of the positive electrode core. The negative electrode plate includes a strip-shaped negative electrode core and a negative electrode active material layer formed on at least one surface of the negative electrode core. A positive electrode tab group formed by stacking positive electrode tabs with the positive electrode core exposed is formed at one end portion of the wound electrode body in the winding axis direction, and a negative electrode tab group formed by stacking negative electrode tabs with the negative electrode core exposed is formed at the other end portion of the wound electrode body in the winding axis direction. The positive electrode tab group is bent while being joined to the positive electrode current collector as a conductive member, and the negative electrode tab group is bent while being joined to the negative electrode current collector as a conductive member. The separator comprises a strip-shaped base layer and a surface layer formed on at least one surface of the base layer and containing inorganic particles and a binder. At least one of the positive electrode plate and the negative electrode plate of the flat portion is bonded to the surface layer of the separator. One end of the positive electrode plate in the longitudinal direction is arranged inside the flat portion of the wound electrode body as a positive electrode starting end, and the other end is arranged outside the flat portion of the wound electrode body as a positive electrode terminal end, and One end of the negative electrode plate in the longitudinal direction is arranged as a negative electrode starting end inside the flat portion of the wound electrode body, and the other end is arranged as a negative electrode terminal end outside the flat portion of the wound electrode body. The bonding strength between the positive electrode starting portion and the surface layer is greater than the bonding strength between the positive electrode terminal portion and the surface layer, and the bonding strength between the positive electrode terminal portion and the surface layer is greater than the bonding strength between the negative electrode terminal portion and the surface layer.

2. The secondary battery according to claim 1, wherein The content of the inorganic particles relative to the total mass of the surface layer is 70% by mass to 80% by mass.

3. The secondary battery according to claim 1 or 2, wherein The surface layer contains at least one of alumina particles and boehmite particles as the inorganic particles.

4. The secondary battery according to claim 1 or 2, wherein The surface layer contains polyvinylidene fluoride as the binder.

5. The secondary battery according to claim 1 or 2, wherein The surface layer has a network structure including a plurality of voids.

6. The secondary battery according to claim 5, wherein The porosity of the surface layer of the separator disposed in a region not facing the positive electrode plate and the negative electrode plate is 50% or more.

7. The secondary battery according to claim 1 or 2, wherein A plurality of the wound electrode bodies are housed in the battery case.

8. The secondary battery according to claim 7, wherein The separator is disposed on the outermost periphery of the wound electrode body, and adjacent wound electrode bodies are bonded to each other via the surface layer of the separator.

9. The secondary battery according to claim 1 or 2, wherein The separator is arranged on the outermost periphery of the wound electrode body, and the end portion of the separator is adhered to the outermost surface of the wound electrode body by a winding fixing tape. The winding and fixing tape is arranged on a straight line connecting the positive electrode tab group and the negative electrode tab group.

10. The secondary battery according to claim 1 or 2, wherein The separator is arranged on the outermost periphery of the wound electrode body, and the end portion of the separator is adhered to the outermost surface of the wound electrode body by a winding fixing tape. A ratio of the thickness of the surface layer of the separator interposed between the positive electrode plate and the negative electrode plate to the thickness of the surface layer of the separator disposed in a region not facing the positive electrode plate and the negative electrode plate is 0.9 or less.

11. The secondary battery according to claim 1 or 2, wherein A plurality of the wound electrode bodies are housed in the battery case, and the separator is disposed on the outermost periphery of the wound electrode bodies. Adjacent wound electrode bodies are bonded to each other via the surface layer of the separator. The bonding strength between the adjacent wound electrode bodies is greater than the bonding strength between the positive electrode terminal portion and the surface layer.

12. A method for manufacturing a secondary battery, wherein: The method for manufacturing a secondary battery comprises: The process of winding the positive electrode plate and the negative electrode plate with a separator interposed therebetween to form a cylindrical body; a step of punching the cylindrical body to produce a flat wound electrode body; and a step of housing the wound electrode assembly in a battery case, The wound electrode body is a wound electrode body included in the secondary battery according to any one of claims 1 to 11.

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