Secondary battery and method for manufacturing secondary battery

Abstract

To provide a secondary battery and a method for manufacturing the secondary battery with which it is possible to suppress the occurrence of minute short-circuiting caused by implementation of hot aging.SOLUTION: An electrode body of the secondary battery is composed of a cathode sheet having a cathode active material layer on both sides of a cathode collector and electrically connected to a cathode-side external terminal at one end in a width direction and an anode sheet having an anode active material layer on both sides of an anode collector and electrically connected to an anode-side external terminal at the other end in the width direction, the cathode sheet and the anode sheet being alternately laminated via a separator sheet. In a region constituting the outermost layer of the electrode body, the separator sheet constitutes an outer surface of the electrode body, and an opening region is formed in at least a section of one end of the separator sheet in the width direction. In the opening region, a side face of the anode sheet disposed on the inner layer side of the separator sheet is exposed in such a manner that the side face does not touch the separator sheet.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a secondary battery and a method for manufacturing a secondary battery. [Background technology]

[0002] 2. Description of the Related Art Secondary batteries using a non-aqueous electrolyte and an electrode assembly in which a positive electrode sheet including a positive electrode active material layer and a negative electrode sheet are laminated with a separator sheet interposed therebetween are known (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 50-106627 [Patent Document 2] JP 2014-238990 A Summary of the Invention [Problem to be solved by the invention]

[0004] After the initial charge, secondary batteries may be subjected to high-temperature aging treatment to dissolve or precipitate metallic foreign matter that may have been mixed into the secondary battery during the manufacturing process. "High-temperature aging treatment" refers to keeping a secondary battery in a high SOC (State of Charge) state (e.g., 3.97 V) at high temperatures (e.g., 60°C or higher) for a long period of time (e.g., 24 hours or more).

[0005] When a secondary battery is subjected to high-temperature aging treatment, there is a risk of a micro-short circuit occurring in the outermost layer region of the electrode assembly. The "micro-short circuit" refers to a phenomenon in which a metal component contained in the positive electrode active material layer is dissolved into the non-aqueous electrolyte, and the metal component is locally deposited on the surface of the negative electrode facing the part of the positive electrode where the metal component has dissolved, resulting in an electrical connection between the positive electrode and the negative electrode.

[0006] For example, in a lithium ion secondary battery, when a negative electrode sheet is disposed in the region constituting the outermost layer of the electrode body, at the end of the electrode body to which the external terminal on the positive electrode side is connected, lithium ions that have moved from the positive electrode to the negative electrode during high-temperature aging treatment may move to the negative electrode active material layer on the outermost layer side via the nonaqueous electrolyte. In this state, oxygen contained in the space inside the case further permeates the separator sheet of the outermost layer and reacts with the lithium ions that have moved to the negative electrode active material layer on the outermost layer side, thereby inducing the elution of metal components from the positive electrode active material layer of the positive electrode. For this reason, a "micro-short circuit" is likely to occur during high-temperature aging treatment. When a micro-short circuit occurs, the self-discharge amount of the secondary battery increases.

[0007] The inventors of the present application also noticed that the above-mentioned movement of lithium ions is likely to occur in the contact area between the outermost separator sheet and the side surface of the negative electrode sheet. This is believed to be because the separator sheet arranged along the side surface of the negative electrode sheet is likely to form a flow path for lithium ions via the nonaqueous electrolyte held in the separator sheet.

[0008] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a secondary battery that can suppress the occurrence of micro-short circuits caused by high-temperature aging treatment, and a method for manufacturing the secondary battery. [Means for solving the problem]

[0009] A secondary battery according to a first aspect of the present disclosure comprises an electrode body, a non-aqueous electrolyte, and a case that accommodates the electrode body and the non-aqueous electrolyte. The electrode body is configured by stacking a positive electrode sheet having positive electrode active material layers on both sides of a positive electrode collector and electrically connecting to a positive electrode external terminal at one end in the width direction, and a negative electrode sheet having negative electrode active material layers on both sides of a negative electrode collector and electrically connecting to a negative electrode external terminal at the other end in the width direction, with a separator sheet interposed between them. In a region that constitutes the outermost layer of the electrode body, the separator sheet constitutes the outer surface of the electrode body, and an opening region is formed in at least a part of one end in the width direction of the separator sheet. In the opening region, a side surface of the negative electrode sheet arranged on the inner layer side of the separator sheet is exposed, and the side surface is configured not to come into contact with the separator sheet.

[0010] In the secondary battery according to the first aspect of the present disclosure, a positive electrode sheet having a positive electrode active material layer on both sides of a positive electrode current collector and a negative electrode sheet having a negative electrode active material layer on both sides of a negative electrode current collector are laminated with a separator sheet interposed therebetween to form an electrode body. In addition, the electrode body is electrically connected to an external terminal on the positive electrode side at one end in the width direction of the positive electrode sheet. Therefore, ions move from one end in the width direction of the positive electrode sheet to the end on the negative electrode sheet side. These ions may move from the negative electrode active material layer formed on the inner layer side of the negative electrode current collector to the negative electrode active material layer formed on the outer layer side of the negative electrode current collector by using a nonaqueous electrolyte as a medium on the side of the negative electrode sheet. In the region constituting the outermost layer of the electrode body, if the reaction between the ions that have moved to the negative electrode active material layer on the outermost layer side and oxygen contained in the space inside the case is promoted, the elution of metal components from the positive electrode active material layer of the positive electrode sheet is induced, and micro-short circuiting is likely to occur. In addition, the above-mentioned ion movement is likely to occur in the contact region between the separator sheet of the outermost layer and the side of the negative electrode sheet. This is believed to be because the separator sheet disposed along the side surface of the negative electrode sheet is likely to form flow paths for ions via the nonaqueous electrolyte held in the separator sheet.

[0011] Therefore, in the secondary battery according to the first aspect of the present disclosure, an opening region is formed in at least a part of one end in the width direction of the separator sheet in the region constituting the outermost layer of the electrode body. In this opening region, the side surface of the negative electrode sheet arranged on the inner layer side of the separator sheet is exposed, and the side surface is configured not to come into contact with the separator sheet. This suppresses the movement of ions via the nonaqueous electrolyte held in the separator sheet on the side of the negative electrode sheet. As a result, the occurrence of micro-short circuits caused by the implementation of high-temperature aging treatment is suppressed.

[0012] A secondary battery according to a second aspect of the present disclosure has the configuration described in the first aspect, and the opening region is formed by folding back at least a portion of one end of the separator sheet in the width direction toward the outer layer and overlapping it on the outer surface.

[0013] In the secondary battery according to the second aspect of the present disclosure, an opening region can be formed by folding back one end of the separator sheet in the width direction toward the outer layer side. In addition, since the folded portion of the separator sheet is overlapped on the outer surface of the electrode body, the thickness of the separator sheet is increased in the portion of the electrode body where micro-short circuits are likely to occur. This prevents ions that have migrated to the negative electrode active material layer on the outermost layer side from reacting with oxygen contained in the space inside the case. As a result, the occurrence of micro-short circuits caused by the implementation of high-temperature aging treatment is simply and effectively prevented.

[0014] A secondary battery according to a third aspect of the present disclosure has the configuration according to the first aspect, wherein the open region is formed by removing at least a portion of one end in the width direction of the separator sheet.

[0015] In the secondary battery according to the third aspect of the present disclosure, an opening region can be formed by removing one end of the separator sheet in the width direction. This prevents ions that have migrated to the outermost negative electrode active material layer from reacting with oxygen contained in the space inside the case. As a result, the occurrence of micro-short circuits caused by the high-temperature aging treatment can be easily prevented.

[0016] A secondary battery according to a fourth aspect of the present disclosure has a configuration according to any one of the first to third aspects, wherein the electrode body is composed of a wound electrode body in which the positive electrode sheet and the negative electrode sheet are stacked together with the separator sheet interposed therebetween and wound around a winding axis, and in a cross-sectional view perpendicular to the winding axis, the wound electrode body has a pair of curved portions in which the outer surface is curved, and a pair of flat portions that connect the pair of curved portions and have flat outer surfaces, one end of which in the winding axis direction is connected to an external terminal on the positive electrode side, and the opening region is formed in at least one region of the pair of curved portions.

[0017] When a secondary battery composed of a flat wound electrode body having a pair of curved parts and a pair of flat parts is subjected to high-temperature aging, a micro-short circuit is likely to occur at the curved part with the largest curvature in the cross section of the wound electrode body. This is thought to be due to the fact that gaps are likely to occur between the positive electrode sheet and the negative electrode sheet and the separator sheet at the curved part with the largest curvature in the cross section of the wound electrode body, and therefore ions are likely to move through the non-aqueous electrolyte in the separator sheet as well as the non-aqueous electrolyte that has penetrated into the gap between the sheets. In this state, when the metal component contained in the outermost positive electrode active material layer is dissolved into the non-aqueous electrolyte, the density of the metal component increases on the surface of the negative electrode active material layer facing the positive electrode active material layer, making it easier for the metal component to precipitate, thereby inducing a micro-short circuit.

[0018] In the secondary battery according to the fourth aspect of the present disclosure, the separator sheet has an opening in at least one of the curved portions. Therefore, in the area where micro-short circuits are likely to occur during high-temperature aging, the movement of ions through the non-aqueous electrolyte held in the separator sheet is suppressed on the side of the negative electrode sheet. As a result, the occurrence of micro-short circuits caused by the high-temperature aging is effectively suppressed.

[0019] A secondary battery according to a fifth aspect of the present disclosure has a configuration according to any one of the first to third aspects, wherein the opening region is formed in a region constituting the outermost layer of the electrode body, the region being located at the upper part within the case.

[0020] When a secondary battery having an electrode body and a nonaqueous electrolyte contained in a case is subjected to high-temperature aging, a micro-short circuit is likely to occur in the region constituting the outermost layer of the electrode body, which is located in the upper part of the case. One of the reasons for this is thought to be that the electrode body is more likely to come into contact with oxygen contained in the space within the case in the upper part of the case than in the lower part of the case.

[0021] In the secondary battery according to the fifth aspect of the present disclosure, the opening region of the separator sheet is formed in a region that is located at the upper part of the case among the regions that constitute the outermost layer of the electrode assembly. Therefore, in the region where micro-short circuits are likely to occur during high-temperature aging treatment, the movement of ions via the nonaqueous electrolyte held in the separator sheet on the side of the negative electrode sheet is suppressed. As a result, the occurrence of micro-short circuits due to high-temperature aging treatment is effectively suppressed.

[0022] A manufacturing method for a secondary battery according to a sixth aspect of the present disclosure is a manufacturing method for a secondary battery according to any one of the first to third aspects, comprising the steps of: setting a protruding region at one end in the width direction of the separator sheet, the protruding region protruding in the width direction from one end in the width direction of the negative electrode sheet in a state in which the electrode body is constructed; and forming the opening region in at least a part of the set protruding region that constitutes the outermost layer of the electrode body.

[0023] In the method for producing a secondary battery according to the sixth aspect of the present disclosure, a protruding region is set at one end in the width direction of the separator sheet, protruding in the width direction from one end in the width direction of the negative electrode sheet in a state in which the electrode body is constructed. Then, an opening region is formed in at least a part of the region constituting the outermost layer of the electrode body among the set protruding regions. Therefore, the electrode body obtained by this is configured such that, in the region constituting the outermost layer, the side of the negative electrode sheet arranged on the inner layer side of the separator sheet is exposed through the opening region, and the side does not come into contact with the separator sheet. As a result, a secondary battery in which the occurrence of micro-short circuit due to the implementation of high-temperature aging treatment is suppressed can be obtained. In addition, the protruding region can utilize the protruding region at the end of the separator sheet provided in the conventional design to prevent physical short circuit due to direct contact between the positive electrode sheet and the negative electrode sheet, and no additional member is required. Therefore, a secondary battery with excellent productivity can be obtained. Effect of the Invention

[0024] According to the present disclosure, a secondary battery capable of suppressing the occurrence of micro-short circuits caused by the implementation of high-temperature aging treatment and a method for manufacturing the secondary battery are provided. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a perspective view showing the appearance of a secondary battery according to an embodiment. [Diagram 2] FIG. 2 is an exploded perspective view of the secondary battery according to the embodiment. [Diagram 3] FIG. 3 is a cross-sectional view of the electrode body shown in FIG. 2 taken along line C3-C3. [Figure 4] 4 is a partially enlarged cross-sectional view showing a cross-section of the electrode body shown in FIG. 2 taken along line C4-C4. [Diagram 5] FIG. 5 is a flow diagram showing a method for producing a secondary battery. [Figure 6] FIG. 6 is a diagram for explaining the manufacturing process of a secondary battery, and is a perspective view showing a flat wound electrode body in a partially developed state. [Figure 7] FIG. 7 is a diagram for explaining the mechanism of a micro-short circuit that occurs in a region that constitutes the outermost layer of an electrode assembly in a secondary battery in which no protruding region is formed on the outermost negative electrode current collector. [Figure 8] FIG. 8 is a graph showing the occurrence or absence of a micro-short circuit versus the amount of electrolyte in a secondary battery in which an electrode assembly and a non-aqueous electrolyte are housed in a case. [Figure 9] 9(A) and 9(B) are cross-sectional views that diagrammatically show modified examples of the electrode body according to the embodiment. [Figure 10] 10(A) and 10(B) are schematic diagrams of separator sheets showing modified examples of the open area according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] In the present disclosure, a numerical range indicated using "~" means a range including the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0027] Hereinafter, an embodiment of a secondary battery according to the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and description thereof will not be repeated.

[0028] (Overview) FIG. 1 is a perspective view showing the appearance of a secondary battery 1A according to an embodiment. As shown in FIG. 1, the secondary battery 1A includes a flat wound electrode body 10A, a non-aqueous electrolyte (not shown), and a case 20. The wound electrode body 10A and the non-aqueous electrolyte are housed in the case 20. The case 20 has a long plate-shaped sealing plate 21. Note that an arrow X shown appropriately in each drawing indicates the width direction of the secondary battery 1A. An arrow Y indicates the depth direction of the secondary battery 1A. An arrow Z indicates the up-down direction (height direction) of the secondary battery 1A, and coincides with the direction of gravity. Note that these directions do not limit the directions of the secondary battery of the present disclosure during use.

[0029] The secondary battery 1A is, for example, a rectangular lithium secondary battery. The size of the secondary battery 1A is not particularly limited. The length L1 of the secondary battery 1A in the up-down direction Z is, for example, 5.0 cm to 8.0 cm. The length L2 of the secondary battery 1A in the width direction X is, for example, 10.0 cm to 15.0 cm. The length L3 of the secondary battery 1A in the depth direction Y is, for example, 1.0 cm to 3.0 cm. Applications of the secondary battery 1A include, for example, in-vehicle use, information and communication technology (for example, personal computers, smartphones, etc.), power storage, etc.

[0030] (Non-aqueous electrolyte) The non-aqueous electrolyte contains an electrolyte and a non-aqueous solvent. Examples of the electrolyte include lithium salts containing fluorine (e.g., lithium hexafluorophosphate, lithium tetrafluoroborate, etc.), and lithium salts not containing fluorine (e.g., lithium perchlorate, lithium tetrachloroaluminate, etc.). Examples of the non-aqueous solvent include cyclic carbonates (e.g., ethylene carbonate, etc.), and chain carbonates (e.g., dimethyl carbonate, ethyl methyl carbonate, etc.). The non-aqueous electrolyte may further contain an additive (e.g., lithium bis(oxalate) borate, etc.).

[0031] (case) 2 is an exploded perspective view of the secondary battery 1A. As shown in FIG. 2, the case 20 has a sealing plate 21, a bottomed rectangular cylindrical exterior can 22, a pair of external terminals 23, a pair of insulators 24, and an insulating bag 25. The exterior can 22 has an opening 220. The sealing plate 21 is fixed to the opening 220 by welding. The pair of external terminals 23 are electrically connected to the wound electrode body 10A and fixed to the sealing plate 21 via the pair of insulators 24. Hereinafter, the pair of external terminals 23 may be referred to separately as a positive electrode side external terminal 23A and a negative electrode side external terminal 23B.

[0032] (Outer can) The exterior can 22 contains the wound electrode body 10A and a nonaqueous electrolyte. The exterior can 22 has an opening 220 that is open on the upper side. The shape from the upper side of the opening 220 is approximately rectangular. The material of the exterior can 22 is a metal (e.g., aluminum, copper, iron, an alloy of these, etc.).

[0033] (Sealing board) The sealing plate 21 seals the opening 220 of the outer can 22. The shape of the sealing plate 21 is a long plate, as shown in Fig. 2. The entire periphery of a peripheral edge P21 of the sealing plate 21 is welded to the opening 220 of the outer can 22 by an energy beam. The energy beam includes a laser beam and an electron beam. The material of the sealing plate 21 is a metal (e.g., aluminum, copper, iron, an alloy of these, etc.).

[0034] (External terminal) The pair of external terminals 23 electrically connect the wound electrode body 10A and an external device (not shown). One of the pair of external terminals 23 is a positive electrode side external terminal 23A, and the other is a negative electrode side external terminal 23B. Each of the pair of external terminals 23 has a current collector terminal 231, a terminal plate 232, and a bolt 233. The current collector terminal 231, the terminal plate 232, and the bolt 233 are integrally fixed to the sealing plate 21 so as to sandwich the sealing plate 21. In the positive electrode side external terminal 23A, the current collector terminal 231 is electrically connected to a positive electrode current collector 111 (see FIG. 4) described later. In the negative electrode side external terminal 23B, the current collector terminal 231 is electrically connected to a negative electrode current collector 121 (see FIG. 4) described later. The current collecting terminal 231, the terminal plate 232, and the bolt 233 are each made of a metal (for example, aluminum, copper, iron, an alloy thereof, or the like).

[0035] (Insulator) The pair of insulators 24 electrically insulate the sealing plate 21 from the pair of external terminals 23. Each of the pair of insulators 24 is sandwiched and fixed between the sealing plate 21 and each of the pair of external terminals 23. The insulators 24 are resin molded bodies.

[0036] (Insulating packaging) The insulating bag 25 electrically insulates the wound electrode body 10A from the sealing plate 21 and the outer can 22. The insulating bag 25 houses the wound electrode body 10A. A portion of the insulating bag 25 may be welded to the wound electrode body 10A. The material of the insulating bag 25 is a resin (e.g., polyethylene, polypropylene, etc.).

[0037] (Wound electrode body) FIG. 3 is a cross-sectional view of the wound electrode body 10A shown in FIG. 2 cut along the line C3-C3. As shown in FIG. 3, the wound electrode body 10A stores electrical energy by a battery reaction. As shown in FIG. 3, the wound electrode body 10A has a positive electrode sheet 11, a negative electrode sheet 12, a first separator sheet 13, and a second separator sheet 14. The first separator sheet 13, the positive electrode sheet 11, the second separator sheet 14, and the negative electrode sheet 12 are laminated in this order and wound around a winding axis (not shown) along the width direction X of the secondary battery 1A. In FIG. 2, the winding axis direction is indicated by an arrow 10DA. In FIG. 3, the winding direction of the wound electrode body 10A is indicated by an arrow D10B.

[0038] In the above-described wound electrode body 10A, the first separator sheet 13, the positive electrode sheet 11, the second separator sheet 14, and the negative electrode sheet 12 are laminated in this order along the radial direction of the wound electrode body 10A. In other words, the region that constitutes the outermost layer of the wound electrode body 10A is the region that constitutes the outermost periphery of the wound electrode body 10A.

[0039] A region R13 (hereinafter also referred to as the "outermost region R13") that constitutes the outermost periphery of the first separator sheet 13 is disposed in a region that constitutes the outermost layer of the wound electrode body 10A. This outermost region R13 constitutes the outer surface S10 of the wound electrode body 10A.

[0040] Furthermore, a region R12 (hereinafter also referred to as "outermost region R12") that constitutes the outermost periphery of the negative electrode sheet 12 is disposed on the inner layer side of the outermost region R13 of the first separator sheet 13. This outermost region R12 is located on the outer layer side of the wound electrode body 10A with respect to a region R11 (hereinafter also referred to as "outermost region R11") that constitutes the outermost periphery of the positive electrode sheet 11.

[0041] Furthermore, between the outermost region R11 of the positive electrode sheet 11 and the outermost region R12 of the negative electrode sheet 12, a region R14 that forms the outermost periphery of the second separator sheet 14 (hereinafter also referred to as "outermost region R14") is disposed.

[0042] The wound electrode body 10A has a pair of curved portions 10A1 in which the outer surface S10 of the wound electrode body 10A is curved, and a pair of flat portions 10A2 in which the outer surface S10 of the wound electrode body 10A connecting the pair of curved portions 10A1 is flat. Hereinafter, the upper curved portion 10A1 of the pair of curved portions 10A1 is also referred to as the "first curved portion 10A1a." The lower curved portion 10A1 of the pair of curved portions 10A1 is also referred to as the "second curved portion 10A1b." In the first embodiment, the first curved portion 10A1a is the curved portion 10A1 of the pair of curved portions 10A1 in which the outermost periphery of the first separator sheet 13 and the second separator sheet 14 is wound last.

[0043] When housed in the case 20, the wound electrode body 10A has a first curved portion 10A1a housed in an area located in the upper part of the case 20. Also, a second curved portion 10A1b is housed in an area located in the lower part of the case 20. In the areas located in the upper and lower parts of the case 20, the stacking direction (radial direction) of the wound electrode body 10A is approximately the direction of gravity.

[0044] The wound electrode body 10A has a positive electrode side external terminal 23A electrically connected to one end 10A3 in the winding axis direction D10A (width direction X), and a negative electrode side external terminal 23B electrically connected to the other end 10A4 in the winding axis direction D10A (see Figure 2).

[0045] (Positive electrode sheet) Fig. 4 is a partially enlarged cross-sectional view showing a cross section of the wound electrode body 10A shown in Fig. 2 taken along line C4-C4. Fig. 4 shows an enlarged view of the region constituting the outermost layer at one end 10A3 and the other end 10A4 in the winding axis direction D10A of the wound electrode body 10A. In Fig. 4, the outer layer side of the wound electrode body 10A is indicated by an arrow OUT, and the inner layer side is indicated by an arrow IN.

[0046] As shown in Fig. 4, the positive electrode sheet 11 has a positive electrode current collector 111 and a positive electrode active material layer 112 supported on both sides of the positive electrode current collector 111. The positive electrode sheet 11 has an uncoated region R11A and a coated region R11B. The uncoated region R11A indicates a region of the positive electrode sheet 11 where the positive electrode active material layer 112 is not formed on both sides of the positive electrode current collector 111. The uncoated region R11A is included in one end portion 10A3 of the winding axis direction D10A of the wound electrode body 10A. The length of the uncoated region R11A in the winding axis direction D10A is, for example, 0.5 cm to 2.0 cm. The coated region R11B is a region of the positive electrode sheet 11 where the positive electrode active material layer 112 is formed on both sides of the positive electrode current collector 111, and indicates a region excluding the uncoated region R11A. An end of the coated region R11B is a non-facing region R11BN that does not face the negative electrode active material layer 122 of the negative electrode sheet 12 located on the outer layer side of the positive electrode sheet 11. This non-facing region R11BN is included in the other end 10A4 in the winding axis direction D10A of the wound electrode body 10A.

[0047] The positive electrode current collector 111 is a metal foil (for example, aluminum foil or the like). The positive electrode active material layer 112 contains a positive electrode active material and a positive electrode binder. The positive electrode active material is a substance capable of occluding and releasing lithium ions. Examples of the positive electrode active material include lithium nickel-based oxides, lithium cobalt-based oxides (for example, LiCoO2, etc.), and lithium manganese-based oxides (for example, LiMn2O4). Examples of the lithium nickel-based oxides include LiCoO2, ternary lithium transition metal oxides, and solid solution-type lithium-excess transition metal oxides. The ternary lithium transition metal oxide is represented by the general formula (A): Li(LiaMnxCoyNiz)O2 (where a, x, y, z in the formula (A) satisfy a + x + y + z ≒ 1 and xyz ≠ 0). The solid solution-type lithium-excess transition metal oxide is represented by the general formula (B): xLi[Li1 / 3Mn2 / 3]O2·(1 - x)LiMeO2 (where Me is one or more transition metals and x satisfies 0 < x ≦ 1). Examples of the positive electrode binder include fluororesins (for example, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, etc.), polyvinyl acetate, and the like. The positive electrode active material layer may contain a conductive auxiliary agent (for example, acetylene black, etc.), a thickening agent, a surfactant, a dispersant, a wetting agent, an antifoaming agent, etc., as necessary.

[0048] (Negative electrode sheet) The negative electrode sheet 12 has a negative electrode current collector 121 and a negative electrode active material layer 122 supported on both sides of the negative electrode current collector 121. The negative electrode sheet 12 has an uncoated region R12A and a coated region R12B. The uncoated region R12A indicates a region of the negative electrode sheet 12 where the negative electrode active material layer 122 is not formed on both sides of the negative electrode current collector 121. The uncoated region R12A is included in the other end 10A4 in the winding axis direction D10A of the wound electrode body 10A. The length of the uncoated region R12A in the winding axis direction D10A is, for example, 0.5 cm to 2.0 cm. The coated region R12B is a region of the negative electrode sheet 12 where the negative electrode active material layer 122 is formed on both sides of the negative electrode current collector 121, and indicates the region excluding the uncoated region R12A. An end of the coated region R12B is a non-facing region R12BN that does not face the positive electrode active material layer 112 of the positive electrode sheet 11 located on the inner layer side with respect to the negative electrode sheet 12. This non-facing region R12BN is included in one end 10A3 in the winding axis direction D10A of the wound electrode body 10A.

[0049] The negative electrode current collector 121 may be a copper foil or the like. The negative electrode active material layer 122 contains a negative electrode active material and a negative electrode binder. The negative electrode active material is a material capable of absorbing and releasing lithium ions (for example, a carbon material (for example, natural graphite, artificial graphite, etc.)). Examples of the negative electrode active material include a fluororesin (for example, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, etc.), polyvinyl acetate, etc. The positive electrode active material layer may contain a conductive assistant (for example, acetylene black, etc.), a thickener, a surfactant, a dispersant, a wetting agent, an antifoaming agent, etc., as necessary.

[0050] (separator sheet) Each of the first separator sheet 13 and the second separator sheet 14 maintains a gap between the positive electrode sheet 11 and the negative electrode sheet 12 to prevent contact short circuit, and also maintains a non-aqueous electrolyte. Each of the first separator sheet 13 and the second separator sheet 14 may be, for example, a porous resin flat plate. Examples of the material for the resin flat plate include resin (e.g., polyethylene, polypropylene, etc.). The configuration (size, material, pore size, etc.) of the first separator sheet 13 and the configuration of the second separator sheet 14 may be the same or different.

[0051] The first separator sheet 13 and the second separator sheet 14 have regions constituting their ends in the width direction X that form protruding regions XP (see FIGS. 4 and 6). The protruding regions XP are regions that protrude in the width direction X beyond the ends in the width direction X of the positive electrode active material layer 112 of the positive electrode sheet 11 and the negative electrode active material layer 122 of the negative electrode sheet 12 when the first separator sheet 13, the positive electrode sheet 11, the second separator sheet 14, and the negative electrode sheet 12 are laminated in this order. The protruding regions XP are provided to reliably prevent contact short-circuiting between the positive electrode sheet 11 and the negative electrode sheet 12.

[0052] In the wound electrode body 10A, one end 10A3 in the winding axis direction D10A (width direction X) and the other end 10A4 in the winding axis direction D10A are assembled for connection to the corresponding external terminal 23. For this reason, at one end D10A3 of the wound electrode body 10A, the side of one end in the width direction X constituting the coating region R12B of the negative electrode sheet 12 is surrounded by the protruding region XP of the first separator sheet 13 and the protruding region XP of the second separator sheet 14. On the other hand, at the other end D10B of the wound electrode body 10A, the side of the other end in the width direction X constituting the coating region R11B of the positive electrode sheet 11 is surrounded by the protruding region XP of the first separator sheet 13 and the protruding region XP of the second separator sheet 14.

[0053] 4, in the region constituting the outermost layer of the wound electrode body 10A, the outermost peripheral region R13 of the first separator sheet constituting the outer surface S10 of the wound electrode body 10A is disposed. The protruding region XP of this outermost peripheral region R13 surrounds the side of the negative electrode sheet 12 while contacting the side surface 12S of one end of the negative electrode sheet 12 in the width direction X.

[0054] Here, an opening region R13A is formed in at least a part of one end (projecting region XP) in the width direction X in the outermost peripheral region R13 of the first separator sheet. The opening region R13A is a region configured to expose the side surface 12S of one end in the width direction X in the outermost peripheral region R12 of the negative electrode sheet 12 and not to contact the side surface 12S with the outermost peripheral region R13 of the first separator sheet. In addition, in the opening region R13A, the outermost peripheral region R13 of the first separator sheet does not contact the outermost peripheral region R14 of the second separator sheet 14.

[0055] In this embodiment, the opening region R13A is formed by folding back one end in the width direction X of the first separator sheet 13 toward the outer layer side. The folded-back portion 131 formed in the first separator sheet 13 is overlapped on the outer surface S10 of the wound electrode body 10A. The opening region R13A is configured to have an open end that is open on one side in the width direction X.

[0056] As an example, the open region R13A is formed in a region that constitutes the first curved portion 10A1a of the pair of curved portions 10A1 of the wound electrode body 10A that is disposed at the upper portion inside the case 20 (see FIG. 3). The width L4 (see FIG. 6) of the open region R13A is preferably equal to or greater than the sum of the thicknesses of the negative electrode active material layers 122 on both sides of the negative electrode current collector 121, and is, for example, 0.02 mm to 4.5 mm.

[0057] [Secondary battery manufacturing method] Next, a method for manufacturing the secondary battery 1A according to the embodiment will be described. As shown in Fig. 5, the secondary battery 1A is manufactured through a source step, an opening region forming step, a winding step, a pressing step, a terminal welding step, a cell drying step, a liquid injection and sealing step, an activation step, and an evaluation step.

[0058] (source process) In the forming process, the positive electrode sheet 11, the negative electrode sheet 12, the first separator sheet 13 and the second separator sheet 14 that constitute the battery element are formed (step S1). In the forming process, an opening region forming process is performed on the first separator sheet 13. In the opening region forming process, a protruding region XP is set at one end in the width direction X of the first separator sheet 13. This protruding region can utilize a protruding region at the end of a separator sheet that is provided in a conventional design (for example, the secondary battery 1B shown in FIG. 7) to prevent a physical short circuit due to direct contact between the positive electrode sheet 11 and the negative electrode sheet 12. Then, in the open region forming step, an open region R13A is formed in at least a part of the region that constitutes the outermost layer of the wound electrode body 10A, out of the set protruding region XP.

[0059] The opening region R13A can be formed, for example, by providing a pair of cut portions extending in the width direction X and spaced apart in the winding direction D10B at one end of the first separator sheet 13 in the width direction X, and folding back the inner region of the pair of cut portions toward the outer layer side.

[0060] The opening region forming step may be performed after the winding step or after the pressing step. Also, in the winding step, the opening region forming step may be configured such that the step of forming the pair of cut portions is performed in the winding step from the viewpoint of making the thickness of the separator sheet uniform, and the step of forming the folded portion 131 is performed after the winding step or after the pressing step.

[0061] (winding process) In the winding step, the positive electrode sheet 11, the negative electrode sheet 12, the first separator sheet 13, and the second separator sheet 14 are wound in a stacked state into a substantially cylindrical shape to form a wound body (step S2).

[0062] (Pressing process) In the pressing step, the wound body formed into a substantially cylindrical shape is pressed to form a flat wound electrode body 10A (step S3). Fig. 6 is a perspective view showing a part of the wound electrode body 10A formed in the pressing step in a developed state. As shown in Fig. 6, in the region of one end 10A3 in the winding axis direction D10A of the wound electrode body 10A, an opening region R13A provided in the first separator sheet 13 exposes a side surface 12S of one end in the width direction X of the negative electrode sheet 12.

[0063] (Terminal welding process) In the terminal welding process, the positive electrode external terminal 23A is joined to one end 10A3 of the wound electrode body 10A in the winding axis direction D10A by, for example, resistance welding (step S4). Also, the negative electrode external terminal 23B is joined to the other end 10A4 of the wound electrode body 10A in the winding axis direction D10A by, for example, ultrasonic welding. Then, these are inserted into the case 20, and the sealing plate 21 is attached to close the opening of the case 20 by, for example, laser welding.

[0064] (Cell drying process) In the cell drying step, the secondary battery 1A is vacuum-dried to remove moisture contained in the wound electrode body 10A (step S5).

[0065] (Liquid injection / sealing process) In the liquid injection and sealing step, non-aqueous electrolyte is injected from an injection port (reference number omitted) formed in sealing plate 21, and a cap (reference number omitted) is attached to the injection port by, for example, laser welding to seal it (step S6).

[0066] (activation process) In the activation process, the secondary battery 1A is initially charged and then stored at high temperature for a certain period of time to perform high-temperature aging treatment to dissolve metallic foreign matter and stabilize the SEI (Solid Electrolyte Interphase) coating (Step S7).

[0067] (Evaluation process) In the evaluation process, cell voltage, battery resistance, and the like are inspected, and lithium ion secondary batteries 10 that exhibit predetermined performance are selected (step S8).

[0068] (Action and Effects) The operation and effects of this embodiment will be described below.

[0069] However, when a high-temperature aging process is performed on a secondary battery having a structure in which oxygen contained in the space inside the case 20 is likely to come into contact with the outermost negative electrode active material layer, a micro-short circuit may occur at the end of the electrode body electrically connected to the external terminal on the positive electrode side. The mechanism by which such a micro-short circuit occurs will be described with reference to FIG.

[0070] FIG. 7 shows a region constituting the outermost layer of the wound electrode body 10A in a secondary battery 1B according to a comparative example. This FIG. 7 is a cross-sectional view corresponding to FIG. 4 according to the above embodiment, and shows an enlarged view of one end 10A3 in the winding axis direction D10A of the wound electrode body 10A. The secondary battery 1B according to the comparative example is similar to the secondary battery 1A of the above embodiment, except that the outermost peripheral region R13 of the first separator sheet 13 does not have an open region R13A. Therefore, the same components as those of the secondary battery 1A are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0071] In the secondary battery 1B, the outermost region R13 of the first separator sheet 13 constitutes the outer surface of the wound electrode body 10A, and the outermost region R12 of the negative electrode sheet 12 is disposed on the inner layer side of the outermost region R13. Therefore, the region constituting the outermost periphery of the positive electrode sheet 11 contributes to the battery reaction of the secondary battery 1B, so that the energy density can be increased. On the other hand, when oxygen contained in the space within the case 20 permeates the first separator sheet 13, it is easily brought into contact with the negative electrode active material layer 122 on the outermost layer side.

[0072] In the high-temperature aging treatment, a secondary battery 1B with a high SOC (for example, 3.97 V) is used. In the secondary battery 1B with a high SOC, many lithium ions are present in a region (reference numerals omitted) facing the positive electrode active material layer 112 in the inner negative electrode active material layer 122 constituting the outermost peripheral region R12 of the negative electrode sheet 12. On the other hand, it is considered that almost no lithium ions are present in the non-facing region R12BN not facing the positive electrode active material layer 112. It is also considered that almost no lithium ions are present in the outer negative electrode active material layer 122 (i.e., the outermost negative electrode active material layer 122) constituting the outermost peripheral region R12.

[0073] As shown in FIG. 7, when a high-temperature aging treatment is performed on a secondary battery 1B with a high SOC, lithium ions 40 migrate from the positive electrode active material layer 112 constituting the outermost region R11 of the positive electrode sheet 11 to the outermost region R12 of the negative electrode sheet 12.

[0074] In the outermost region R12, in the negative electrode active material layer 122 on the inner layer side, due to the difference in concentration of lithium ions 40, the lithium ions 40 present in the region facing the positive electrode active material layer 112 move to the non-facing region R12BN that does not face the positive electrode active material layer 112 (in the direction of arrow D1).

[0075] The lithium ions 40 that have migrated to the non-facing region R12BN of the inner negative electrode active material layer 122 migrate (in the direction of arrow D2) through the non-aqueous electrolyte (not shown) to the side of the negative electrode current collector 111 and to the outermost negative electrode active material layer 122 due to the difference in concentration of lithium ions.

[0076] When oxygen contained in the case 20 permeates through the first separator sheet 13, the outermost negative electrode active material layer 122 comes into contact with oxygen in the case 20. As a result, the lithium ions that have migrated to the outermost negative electrode active material layer 122 react with oxygen to form a coating 42 on the surface of the negative electrode active material layer 122. In other words, the lithium ions that have migrated to the outermost negative electrode active material layer 122 react with oxygen and are consumed. As a result, in the inner negative electrode active material layer 122, the migration of lithium ions to the non-facing region R12BN is accelerated due to the consumption of lithium ions caused by the formation of the coating 42.

[0077] With such movement of lithium ions, the potential of the end portion adjacent to the non-facing region R12BN in the facing region of the inner negative electrode active material layer 122 rises locally. Furthermore, due to the local potential leveling, the potential of the end portion adjacent to the non-facing region R12BN of the negative electrode active material layer 122 also rises in the facing region of the outermost positive electrode active material layer 112. In other words, the outermost peripheral region R11 of the positive electrode sheet 11 locally becomes an overvoltage (for example, 4.3 V or more).

[0078] When an overvoltage occurs in the positive electrode sheet 11, the crystal structure of the positive electrode active material layer 112 collapses, and the metal component 44 contained in the positive electrode active material layer 112 becomes more likely to dissolve into the non-aqueous electrolyte. The metal component 44 dissolved into the non-aqueous electrolyte becomes more likely to deposit on the surface of the opposing portion of the negative electrode active material layer 122 on the inner layer side. As a result, a metal deposit 46 that electrically connects the positive electrode sheet 11 and the negative electrode sheet 12 is formed on the surface of the negative electrode active material layer 122 on the inner layer side. As a result, a micro-short circuit occurs.

[0079] In order to verify the mechanism of such micro-short circuit occurrence, the correlation between the presence or absence of a micro-short circuit at end 10A3 connected to positive external terminal 23A in the region constituting the outermost layer of wound electrode body 10A in secondary battery 2B of the comparative example and the amount of nonaqueous electrolyte in case 20 was verified.

[0080] In FIG. 8, the horizontal axis indicates the amount of nonaqueous electrolyte, and the vertical axis indicates the presence or absence of a micro-short circuit. The amount of nonaqueous electrolyte on the horizontal axis is based on Comparative Example 1, in which a micro-short circuit occurred at the end 10A3 connected to the positive external terminal 23A in the region constituting the outermost layer of the wound electrode body 10A, and the amount of electrolyte in Comparative Example 1 is set to 100[%], and the electrolyte amount is indexed and shown for each comparative example. As shown in FIG. 8, in Comparative Example 1, in which the amount of nonaqueous electrolyte is set to 100[%], a micro-short circuit occurs at the end 10A3 connected to the positive external terminal 23A in the region constituting the outermost layer of the wound electrode body 10A.

[0081] On the other hand, in Example 2 where the amount of non-aqueous electrolyte was set to 74[%], no micro-short circuit occurred. This is believed to be because in Comparative Example 2 where the amount of non-aqueous electrolyte in the case 20 was less than that in Example 1, the movement of lithium ions 40 (arrow D2 in FIG. 7) mediated by the non-aqueous electrolyte was suppressed in the outermost peripheral region R12 of the negative electrode sheet 12. That is, in Example 2, the amount of lithium ions that move to the outermost negative electrode active material layer 122 is small, so that consumption of lithium ions 40 by oxygen in the case 20 is suppressed and no micro-short circuit occurs.

[0082] Furthermore, even in Comparative Example 3, in which the amount of nonaqueous electrolyte was set to 140%, no micro-short circuit occurred. This is believed to be because, in Comparative Example 3, in which the amount of nonaqueous electrolyte in case 20 is greater than in Example 1, the nonaqueous electrolyte is injected up to the upper region of case 20, so that the region constituting the outermost layer of wound electrode body 10A is prevented from coming into contact with the air contained in the space within the case. That is, in Example 3, the amount of oxygen that permeates through the outermost region R13 of first separator sheet 13 is small, so consumption of lithium ions 40 by oxygen in case 20 is prevented, and no micro-short circuit occurs.

[0083] As shown in FIG. 8, the verification results according to Comparative Examples 1 to 3 all demonstrate the effectiveness of the mechanism of occurrence of the micro-short circuit shown in FIG.

[0084] From the above, firstly, when a high-temperature aging process is performed on a secondary battery configured so that oxygen contained in the space inside the case is likely to come into contact with the outermost negative electrode active material layer, it is considered that a micro-short circuit is likely to occur at the end of the electrode body electrically connected to the external terminal on the positive electrode side. This is believed to be caused by the reaction of lithium ions with oxygen on the surface of the negative electrode active material layer.

[0085] Secondly, when a high-temperature aging process is performed on a secondary battery having a configuration in which the non-aqueous electrolyte in the case is likely to come into contact with the outermost negative electrode active material layer, it is considered that a micro-short circuit is likely to occur at the end of the electrode body electrically connected to the external terminal on the positive electrode side. This is believed to be caused by the migration of lithium ions 40 to the outermost negative electrode active material layer via the non-aqueous electrolyte.

[0086] The inventors of the present application also noticed that the movement of the lithium ions 40 described above is likely to occur in the contact region between the outermost peripheral region R13 of the first separator sheet 13 and the side surface 12S of the negative electrode sheet 12. This is believed to be because the protruding region XP of the first separator sheet 13 arranged along the side surface 12S of the negative electrode sheet 12 is likely to form a flow path for the lithium ions 40 via the nonaqueous electrolyte held in the first separator sheet 13.

[0087] In contrast, in the secondary battery 1A according to this embodiment, an opening region R13A is formed in at least a part of one end in the width direction X of the first separator sheet 13 in the region constituting the outermost layer of the wound electrode body 10A. In this opening region R13A, the side surface 12S of the negative electrode sheet 12 arranged on the inner layer side of the first separator sheet 13 is exposed, and the side surface 12S is configured not to come into contact with the first separator sheet 13. This suppresses the movement of lithium ions 40 via the nonaqueous electrolyte held in the first separator sheet 13 on the side of the negative electrode sheet 12. As a result, the occurrence of micro-short circuits caused by the implementation of high-temperature aging treatment is suppressed.

[0088] In this embodiment, an opening region R13A can be formed by folding back one end of the first separator sheet 13 in the width direction X toward the outer layer side. In addition, since the folded portion 131 of the first separator sheet 13 is overlapped with the outer surface S10 of the wound electrode body 10A, the thickness of the first separator sheet 13 is increased in the part of the wound electrode body 10A where micro-short circuits are likely to occur. This prevents the lithium ions 40 that have moved to the negative electrode active material layer 122 on the outermost layer side from reacting with oxygen contained in the space inside the case. As a result, the occurrence of micro-short circuits caused by the implementation of the high-temperature aging treatment is simply and effectively prevented.

[0089] However, when a secondary battery composed of a flat wound electrode body having a pair of curved parts and a pair of flat parts is subjected to high-temperature aging, a micro-short circuit is likely to occur at the curved part with the largest curvature in the cross section of the wound electrode body. This is thought to be due to the fact that gaps are likely to occur between the positive electrode sheet and the negative electrode sheet and the separator sheet at the curved part with the largest curvature in the cross section of the wound electrode body, and therefore ions are likely to move through the non-aqueous electrolyte in the separator sheet as well as the non-aqueous electrolyte that has entered the gap between the sheets. In this state, when the metal component contained in the outermost positive electrode active material layer is dissolved into the non-aqueous electrolyte, the density of the metal component increases on the surface of the negative electrode active material layer facing the positive electrode active material layer, making it easier for the metal component to precipitate, thereby inducing a micro-short circuit.

[0090] In contrast, in this embodiment, the opening region R13A of the first separator sheet 13 is formed in one of the pair of curved portions 10A1, the first curved portion 10A1a. Therefore, in the portion where micro-short circuits are likely to occur during the high-temperature aging treatment, the movement of lithium ions 40 via the nonaqueous electrolyte held in the first separator sheet 13 on the side of the negative electrode sheet 12 is suppressed. As a result, the occurrence of micro-short circuits due to the high-temperature aging treatment is effectively suppressed.

[0091] Furthermore, it is known that when a high-temperature aging treatment is performed on a secondary battery in which an electrode body and a nonaqueous electrolyte are housed in a case, micro-short circuits are likely to occur in the region constituting the outermost layer of the electrode body, which is located in the upper part of the case. One of the reasons for this is thought to be that the electrode body is more likely to come into contact with oxygen contained in the space within the case in the upper part of the case than in the lower part of the case.

[0092] In contrast, in this embodiment, the first curved portion 10A1a where the open region R13A is formed is disposed in a region that is located at the upper part of the case 20, among the regions that constitute the outermost layer of the wound electrode body 10A. This makes it possible to suppress the movement of lithium ions 40 toward the outermost layer side of the negative electrode sheet 12 in a region where micro-short circuits are likely to occur during the high-temperature aging treatment. As a result, the occurrence of micro-short circuits due to the high-temperature aging treatment is effectively suppressed.

[0093] As shown in FIG. 6, in the method for manufacturing the secondary battery 1A according to this embodiment, a protruding region XP is set at one end in the width direction X of the first separator sheet 13, protruding in the width direction X from one end in the width direction X of the negative electrode sheet 12 in a state in which the wound electrode body 10A is constructed. Then, of the set protruding region XP, an opening region R13A is formed in at least a part of the region constituting the outermost layer of the wound electrode body 10A. Therefore, in the wound electrode body 10A obtained in this way, in the region constituting the outermost layer, the side surface 12S of the negative electrode sheet 12 arranged on the inner layer side of the first separator sheet 13 is exposed through the opening region R13A, and the side surface 12S is configured not to come into contact with the first separator sheet 13. As a result, a secondary battery 1A in which the occurrence of micro-short circuit due to the implementation of high-temperature aging treatment is suppressed can be obtained. In addition, the protruding region XP can utilize the protruding region at the end of the separator sheet, which is provided in the conventional design to prevent a physical short circuit caused by direct contact between the positive electrode sheet and the negative electrode sheet, and does not require any additional members, so that the secondary battery 1A can be obtained with excellent productivity.

[0094] (Modifications of the electrode body) In the above embodiment, the opening region R13A is formed in the first curved portion 10A1a of the wound electrode body 10A, but this is not limited to this. A wound electrode body 10B of a first modified example shown in Fig. 9(A) or a wound electrode body 10C of a second modified example shown in Fig. 9(B) may be used in place of the wound electrode body 10A.

[0095] In the wound electrode body 10B according to the first modification, an open region R13A is formed in the first curved portion 10A1a and the second curved portion 10A1b in the outermost layer region of the wound electrode body 10B (FIG. 9(A)).

[0096] In a wound electrode body 10C according to the second modification, an open region R13A is formed around the entire periphery of the outermost layer region of the wound electrode body 10B (FIG. 9(B)).

[0097] In the above embodiment and each modified example, the opening region R13A is not formed in the pair of flat portions 10A2, but may be formed in at least a part of the pair of flat portions 10A2.

[0098] Furthermore, when a second separator sheet 14 is disposed on the outer layer side of the negative electrode sheet 12, an opening region similar to the opening region R13A may be formed in the second separator sheet.

[0099] (Modification of the opening area) In the above embodiment and each modified example, the opening region R13A is configured to include the folded portion 131, but this is not limited to this. For example, as shown in Fig. 10(A), the folded portion 131 may be omitted. The opening region R13B shown in Fig. 10(A) is configured by forming a rectangular groove-shaped cutout portion 132 in the protruding region XP at one end of the first separator sheet 13 in the width direction X. Alternatively, as shown in FIG. 10(B), a rectangular opening 133 may be formed in a protruding region XP at one end in the width direction X of the first separator sheet 13 to form an opening region R13C.

[0100] The opening regions R13B, R13C shown in Figures 10(A) and 10(B) are formed by partially removing one end of the first separator sheet in the width direction X, and therefore can be formed in a single process during the source process. Moreover, similarly to the opening region R13A of the above embodiment, the lithium ions 40 that have migrated to the outermost negative electrode active material layer 122 are prevented from reacting with oxygen contained in the space inside the case, thereby preventing the occurrence of micro-short circuits caused by the high-temperature aging treatment.

[0101] In the above embodiment and each modified example, the electrode body of the secondary battery is configured to be composed of wound electrode bodies 10A to 10C in which the positive electrode sheet 11 and the negative electrode sheet 12 are stacked on each other with the separator sheets 13 and 14 interposed therebetween and wound around the winding axis, but this is not limited thereto. As the electrode body of the secondary battery according to the present disclosure, for example, an electrode body configured by stacking a positive electrode sheet and a negative electrode sheet on each other in one direction with the separator sheet interposed therebetween may be applied. In this case, the electrode body may be configured such that an external terminal on the positive electrode side is connected to one end in a direction perpendicular to the stacking direction, and an external terminal on the negative electrode side is connected to the other end in a direction perpendicular to the stacking direction.

[0102] In the above embodiment and each modified example, the first separator sheet 13 and the second separator sheet 14 are used, but only one of the first separator sheet 13 and the second separator sheet 14 may be used. [Explanation of symbols]

[0103] 1A secondary battery 10A wound electrode body 10B wound electrode body 10C wound electrode body 10A1 Curved section 10A1 Flat part 10A3 end 11 Positive electrode sheet 111 Positive electrode current collector 112 Cathode active material layer 12 Negative electrode sheet 121 Negative electrode current collector 122 Negative electrode active material layer 13 First separator sheet (separator sheet) R13A opening area R13B opening area R13C opening area 14 Second separator sheet (separator sheet) 20 cases S10 outer surface 23A Positive external terminal 23B Negative external terminal XP salient area

Claims

1. An electrode assembly, a non-aqueous electrolyte, and a case that accommodates the electrode assembly and the non-aqueous electrolyte, The electrode body is configured by laminating a positive electrode sheet having a positive electrode active material layer on both sides of a positive electrode current collector and electrically connecting to a positive electrode side external terminal at one end in the width direction, and a negative electrode sheet having a negative electrode active material layer on both sides of a negative electrode current collector and electrically connecting to a negative electrode side external terminal at the other end in the width direction, with a separator sheet interposed between them; In a region constituting the outermost layer of the electrode body, the separator sheet constitutes an outer surface of the electrode body, and an opening region is formed in at least a part of one end of the separator sheet in the width direction, In the opening region, a side surface of the negative electrode sheet disposed on the inner layer side of the separator sheet is exposed, and the side surface is configured not to come into contact with the separator sheet. Secondary battery.

2. The opening region is formed by folding back at least a part of one end portion in the width direction of the separator sheet toward the outer layer side and overlapping it on the outer surface. The secondary battery according to claim 1 .

3. The opening region is formed by removing at least a part of one end portion in the width direction of the separator sheet. The secondary battery according to claim 1 .

4. the electrode body is constituted by a wound electrode body in which the positive electrode sheet and the negative electrode sheet are laminated with each other via the separator sheet and wound around a winding axis, and in a cross-sectional view in a direction perpendicular to the winding axis, the wound electrode body has a pair of curved portions in which the outer surface is curved, and a pair of flat portions that connect the pair of curved portions and have flat outer surfaces, and one end in the winding axis direction is connected to an external terminal on the positive electrode side, The opening region is formed in at least one region of the pair of curved portions. The secondary battery according to any one of claims 1 to 3.

5. The opening region is formed in a region constituting the outermost layer of the electrode body, the region being located at an upper portion within the case. The secondary battery according to any one of claims 1 to 3.

6. A method for producing a secondary battery according to any one of claims 1 to 3, comprising the steps of: a protruding region is set at one end in the width direction of the separator sheet, the protruding region protruding in the width direction from one end in the width direction of the negative electrode sheet in a state in which the electrode body is constructed; The method includes forming the opening region in at least a part of the region constituting the outermost layer of the electrode body among the set protruding regions. A method for manufacturing a secondary battery.

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