Secondary battery

Abstract

To provide a secondary battery with high energy density, in which the occurrence of microscopic short-circuiting due to a high-temperature aging process is suppressed.SOLUTION: A secondary battery includes an electrode body, a nonaqueous electrolyte solution, and a case that accommodates the electrode body and the nonaqueous electrolyte solution. In the electrode body, a positive electrode sheet including a positive electrode active material layer on both surfaces of a positive electrode current collector and a negative electrode sheet including a negative electrode active material layer on both surfaces of a negative electrode current collector are stacked on each other through a separator sheet. In a region forming an outermost layer of the electrode body, an outer surface of the electrode body is formed by the separator sheet and the negative electrode sheet is disposed on an inner layer side of the separator sheet. In at least a part of an end part electrically connected to an external terminal on a positive electrode side, a gas barrier layer that does not transmit oxygen is provided between the negative electrode active material layer and the separator sheet that forms the outer surface.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to secondary batteries. [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.

[0003] 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).

[0004] 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.

[0005] For example, in a lithium ion secondary battery, when a negative electrode sheet is disposed on the inner layer side of a separator sheet constituting the outer surface 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 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, inducing the elution of metal components from the metal active material layer of the positive electrode. Therefore, in a secondary battery configured so that oxygen contained in the space inside the case is likely to come into contact with the negative electrode active material layer on the outermost layer side, 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.

[0006] Patent Document 1 discloses a method for manufacturing a secondary battery that prevents the occurrence of micro-short circuits caused by high-temperature aging treatment. The manufacturing method disclosed in Patent Document 1 includes preparing a wound electrode body in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and wound, constructing a secondary battery by housing the wound electrode body together with a non-aqueous electrolyte in a battery case, and performing an aging treatment on the secondary battery.

[0007] In the wound electrode body obtained by the manufacturing method disclosed in Patent Document 1, the outermost positive electrode portion constituting the outermost periphery of the positive electrode is disposed in the region constituting the outermost periphery (outermost layer) of the wound electrode body, and in the outermost positive electrode portion, no positive electrode active material layer is formed on either side of the positive electrode current collector. Therefore, it is considered that the oxygen that has permeated the separator is prevented from reaching the negative electrode active material layer by the outermost positive electrode portion, thereby preventing the occurrence of the above-mentioned "micro-short circuit". [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2014-35877 A Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the secondary battery obtained by the manufacturing method disclosed in Patent Document 1, the positive electrode located at the outermost periphery of the positive electrode does not contribute to the battery reaction of the secondary battery. The "battery reaction" refers to a reaction in which ions enter and leave (intercalate) the positive electrode active material layer and the negative electrode active material layer. Therefore, a secondary battery with a higher energy density is required.

[0010] The present disclosure has been made in consideration of the above circumstances, and aims to provide a secondary battery in which the occurrence of micro-short circuits caused by high-temperature aging treatment is suppressed and the energy density of the secondary battery is high. [Means for solving the problem]

[0011] A secondary battery according to a first aspect of the present disclosure comprises an electrode body, a non-aqueous electrolyte, and a case housing the electrode body 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 a negative electrode sheet having a negative electrode active material layer on both sides of a negative electrode current collector 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 the negative electrode sheet is disposed on the inner layer side of the separator sheet. At least a part of an end that is electrically connected to an external terminal on the positive electrode side has a gas barrier layer that does not allow oxygen to pass between the separator sheet that constitutes the outer surface and the negative electrode active material layer.

[0012] In the secondary battery according to the first aspect of the present disclosure, in the region constituting the outermost layer of the electrode assembly having a laminated structure, a separator sheet constitutes the outer surface of the electrode assembly, and a negative electrode sheet is disposed on the inner layer side of the separator sheet. In other words, the region constituting the outermost periphery of the positive electrode sheet contributes to the battery reaction of the secondary battery. As a result, in the first aspect, the energy density of the secondary battery is higher than that of conventional batteries.

[0013] When a high-temperature aging treatment is performed on a secondary battery having a structure in which oxygen contained in the space inside the case is likely to come into contact with the negative electrode active material layer on the outermost layer side, 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. In the first embodiment, the electrode body has a gas barrier layer that does not allow oxygen to pass between the separator sheet constituting the outer surface and the negative electrode active material layer at at least a part of the end electrically connected to the external terminal on the positive electrode side. Therefore, when oxygen in the case passes through the separator sheet, it is suppressed from coming into contact with the negative electrode active material layer on the outermost layer side. As a result, the occurrence of a micro-short circuit caused by the high-temperature aging treatment is suppressed.

[0014] In a secondary battery according to a second aspect of the present disclosure, in the configuration described in the first aspect, a portion of the gas barrier layer is formed along the stacking direction from an end of the negative electrode active material layer toward the inner layer side, and covers a side of an end of the negative electrode current collector on the outermost layer side.

[0015] In addition, when a high-temperature aging treatment 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 negative electrode active material layer on the outermost layer side, 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. In the secondary battery according to the second aspect, a part of the gas barrier layer is formed along the stacking direction from the end of the negative electrode active material layer to the inner layer side, and is configured to cover the side of the end of the negative electrode current collector on the outermost layer side. Therefore, the gas barrier layer can sufficiently cover the side of the negative electrode active material layer on the outermost layer side. As a result, in the region constituting the outermost layer of the electrode body, the non-aqueous electrolyte in the case is prevented from coming into contact with the negative electrode active material layer on the outermost layer side. This effectively prevents the occurrence of a micro-short circuit caused by the high-temperature aging treatment.

[0016] A secondary battery according to a third aspect of the present disclosure has the configuration according to the first or second aspect, 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 in a direction perpendicular to the winding axis, the electrode body has a pair of curved portions whose outer surfaces are 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 gas barrier layer is formed in at least one region of the pair of curved portions.

[0017] When a high-temperature aging treatment is performed on a secondary battery composed of a flat wound electrode body having a pair of curved parts and a pair of flat parts, it is considered that a micro-short circuit is likely to occur in the curved part with the largest curvature in the cross section of the wound electrode body. In the curved part with the largest curvature in the cross section of the wound electrode body, when a metal component contained in the positive electrode active material layer on the outermost layer side is dissolved into a 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, and the metal component is likely to precipitate. In the secondary battery according to the third aspect, the gas barrier layer is formed in at least one region of the pair of curved parts. Therefore, during the high-temperature aging treatment, at least a part of at least one of the pair of curved parts, the oxygen contained in the space inside the case is prevented from contacting the negative electrode active material layer on the outermost layer side. This effectively suppresses the occurrence of a micro-short circuit caused by the high-temperature aging treatment.

[0018] A secondary battery according to a fourth aspect of the present disclosure has the configuration described in the first aspect, in which the gas barrier layer is formed in a region constituting the outermost layer of the electrode body, the region being located at the upper part within the case.

[0019] When a high-temperature aging treatment is performed on a secondary battery having a configuration in which an electrode body and a nonaqueous electrolyte are accommodated in a case, it is considered that a micro-short circuit is likely to occur in a region located at the upper part of the case among the regions constituting the outermost layer of the electrode body. One of the reasons is that the electrode body tends to come into contact with oxygen contained in the space in the case more easily in the region located at the upper part of the case than in the region located at the lower part of the case. In the secondary battery according to the fourth aspect, a gas barrier layer is formed in a region located at the upper part of the case among the regions constituting the outermost layer of the electrode body. Therefore, the oxygen in the case is prevented from coming into contact with the negative electrode active material layer on the outermost layer side in the region that is likely to come into contact with oxygen in the case. This effectively prevents the occurrence of a micro-short circuit caused by the high-temperature aging treatment.

[0020] A secondary battery according to a fifth aspect of the present disclosure has the configuration according to the first aspect, wherein the gas barrier layer does not have ion conductivity.

[0021] In the secondary battery according to the fifth aspect of the present disclosure, the gas barrier layer is configured to be impermeable to oxygen contained in the space inside the case and to have no ion conductivity. Therefore, in a secondary battery configured to obtain a battery reaction by the movement of ions, the movement of ions to the region constituting the outermost layer of the electrode body through the gas barrier layer is suppressed. As a result, the occurrence of micro-short circuits caused by the implementation of high-temperature aging treatment is effectively suppressed. Effect of the Invention

[0022] According to the present disclosure, a secondary battery is provided in which the occurrence of micro-short circuits caused by the implementation of high-temperature aging treatment is suppressed and the energy density of the secondary battery is high. [Brief description of the drawings]

[0023] [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 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 that does not have a gas barrier layer. [Figure 6] FIG. 6 is a graph showing the occurrence or absence of a micro-short circuit with respect to the amount of electrolyte in a secondary battery having a configuration in which an electrode assembly and a non-aqueous electrolyte are housed in a case. [Figure 7] 7(A) and 7(B) are cross-sectional views that diagrammatically show modified examples of the electrode body according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] 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.

[0025] 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.

[0026] (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.

[0027] 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.

[0028] (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.).

[0029] (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.

[0030] (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.).

[0031] (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.).

[0032] (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).

[0033] (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.

[0034] (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.).

[0035] (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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] Furthermore, on the outer layer side of the outermost peripheral region R11 of the positive electrode sheet 11, a region R14 that constitutes the outermost periphery of the second separator sheet 14 (hereinafter also referred to as the "outermost peripheral region R14") is disposed.

[0040] 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.

[0041] 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.

[0042] 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).

[0043] (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.

[0044] 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.

[0045] 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 oxide 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 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 in formula (B), 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, if necessary, a conductive auxiliary agent (for example, acetylene black, etc.), a thickening agent, a surfactant, a dispersant, a wetting agent, an antifoaming agent, and the like.

[0046] (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 of the winding electrode body 10A in the winding axis direction D10A. The length L5 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. The end of the negative electrode sheet 12 on the first direction side (negative X-axis direction) in the winding axis direction D10A is the coated region R12B. 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.

[0047] 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.

[0048] (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.

[0049] (Gas barrier layer) Here, in the region constituting the outermost layer (outermost periphery) of the wound electrode body 10A, a gas barrier layer 30 is formed between the outermost peripheral region R13 of the first separator sheet 13 constituting the outer surface S10 and the negative electrode active material layer 122 in the outermost peripheral region R12 of the negative electrode sheet 12. The gas barrier layer 30 has excellent gas barrier properties that prevent oxygen from passing through, and prevents oxygen present in the space within the case 20 from contacting the outermost negative electrode active material layer 122. In addition, the gas barrier layer 30 preferably does not have ion conductivity for ions such as lithium ions.

[0050] In this embodiment, the gas barrier layer 30 is formed in a first curved portion 10A1a that is housed in an upper region of the case 20 in a region that constitutes the outermost layer of the wound electrode body 10A (see FIG. 3). The gas barrier layer 30 is also formed in at least an end portion 10A3 that is electrically connected to the positive electrode external terminal 23A in a region that constitutes the outermost layer of the wound electrode body 10A.

[0051] The gas barrier layer 30 has a first gas barrier layer 31 and a second gas barrier layer 32 (see FIG. 4). The first gas barrier layer 31 is formed in the end 10A3 of the wound electrode body 10A from the end (outer end) of the outermost negative electrode active material layer 122 along the width direction X. The second gas barrier layer 32 is formed in the stacking direction from the end (outer end) of the outermost negative electrode active material 122 to the inner layer side, and is configured to cover the side of the outermost peripheral region R12 of the negative electrode sheet 12. It is preferable that the length L4 of the first gas barrier layer 31 in the width direction X covers the outermost negative electrode active material 122.

[0052] In addition, at the end 10A3 of the wound electrode body 10A, the length L5 in the stacking direction of the second gas barrier layer 32 is greater than the thickness of the negative electrode active material layer 122. Therefore, the end of the second gas barrier layer 32 in the stacking direction is located on the inner layer side of the negative electrode current collector 121. In other words, the second gas barrier layer 32 covers the negative electrode active material layer 122 on the outermost layer side and the side of the end (outer end) of the negative electrode current collector 121. The length L5 in the stacking direction of the second gas barrier layer 32 is preferably equal to or greater than the length that reaches the negative electrode current collector 121 and covers the negative electrode current collector, and is, for example, 20 mm to 40 mm. The second gas barrier layer does not have to extend in the stacking direction.

[0053] The gas barrier layer 30 is formed, for example, in a sheet or thin film shape, and is bonded to the contact surface with the outermost peripheral region R12 of the negative electrode sheet 12 using an adhesive (not shown) in the manufacturing process of the wound electrode body 10A. The gas barrier layer 30 can be formed, for example, by coating the surface of a metal foil (aluminum foil, etc.) with a resin (polyethylene, polypropylene, etc.) having excellent solvent resistance. The gas barrier layer 30 can also be formed, for example, from a thin film of polypropylene resin.

[0054] The adhesive used to bond the gas barrier layer 30 to the outermost peripheral region R12 of the negative electrode sheet 12 is not particularly limited, but is preferably a material that is not required for non-aqueous electrolytes and is electrochemically stable. For example, polypropylene (PP), polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc. can be used. The gas barrier layer 30 does not shift relative to the outermost peripheral region R12 of the negative electrode sheet 12 to which it is bonded and fixed, due to the adhesive function generated by the application of pressure and heat. The adhesive makes it easy to fix the gas barrier layer 30 to the negative electrode sheet 12.

[0055] (Action and Effects) In the secondary battery 1A according to the embodiment described above, in the region constituting the outermost layer of the wound electrode body 10A, the outer surface S10 of the wound electrode body 10A is constituted by the outermost region R13 of the first separator sheet 13, and the outermost region R12 of the negative electrode sheet 12 is disposed on the inner layer side of the outermost region R13. In other words, the region R11 constituting the outermost periphery of the positive electrode sheet 11 contributes to the battery reaction of the secondary battery 1A. As a result, the energy density of the secondary battery 1A is higher than that of the conventional battery.

[0056] 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.

[0057] Fig. 5 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. 5 is a cross-sectional view corresponding to Fig. 4 according to the above embodiment, and shows an enlarged view of one end 10A3 (see Fig. 2) 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 it does not have a gas barrier layer 30. Therefore, the same reference numerals are used for the same configurations as the secondary battery 1A, and detailed description thereof will be omitted.

[0058] 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. For this reason, 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.

[0059] 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. 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.

[0060] As shown in FIG. 5, 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.

[0061] 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).

[0062] 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.

[0063] 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.

[0064] 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).

[0065] 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.

[0066] 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.

[0067] In FIG. 6, 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. 6, 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.

[0068] 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. 5) 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 moving 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.

[0069] 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.

[0070] As shown in FIG. 6, 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.

[0071] 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.

[0072] 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.

[0073] In contrast, in the secondary battery 1A according to this embodiment, the wound electrode body 10A has a first gas barrier layer 31 that is impermeable to oxygen between the first separator sheet 13 constituting the outer surface S10 and the negative electrode active material layer 122 in at least a part of the end portion 10A3 electrically connected to the positive electrode external terminal 23A. Therefore, when oxygen in the case 20 permeates the first separator sheet 13, it is prevented from coming into contact with the negative electrode active material layer 122 on the outermost layer side. As a result, the occurrence of micro-short circuits due to the implementation of the high-temperature aging treatment is suppressed.

[0074] In the secondary battery 1A according to this embodiment, the second gas barrier layer 32 is formed along the stacking direction from the end of the negative electrode active material layer 122 to the inner layer side, and is configured to cover the side of the end (outer end) of the negative electrode current collector 121 on the outermost layer side. Therefore, the second gas barrier layer 32 can sufficiently cover the side of the negative electrode active material layer 122 on the outermost layer side. As a result, in the region constituting the outermost layer of the wound electrode body 10A, the nonaqueous electrolyte in the case 20 is prevented from contacting the negative electrode active material layer 122 on the outermost layer side. This effectively prevents the occurrence of micro-short circuits caused by the implementation of high-temperature aging treatment.

[0075] Thirdly, when a high-temperature aging treatment is performed on a secondary battery composed of a flat wound electrode body having a pair of curved portions and a pair of flat portions, it is considered that a micro-short circuit is likely to occur in the curved portion with the largest curvature in the cross section of the wound electrode body. One of the reasons is considered to be that in the curved portion with the largest curvature in the cross section of the wound electrode body, when a metal component contained in the positive electrode active material layer on the outermost layer side dissolves 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 more likely to precipitate.

[0076] In contrast, in the secondary battery 1A according to this embodiment, the gas barrier layer 30 is formed in the region of the first curved portion 10A1a, which is the upper one of the pair of curved portions 10A1. Therefore, during the high-temperature aging treatment, the oxygen contained in the space inside the case 20 is prevented from contacting the outermost negative electrode active material layer 122 at the first curved portion 10A1a. This effectively prevents the occurrence of micro-short circuits caused by the high-temperature aging treatment.

[0077] Fourthly, 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, it is considered that 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 considered 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.

[0078] In contrast, in the secondary battery 1A according to this embodiment, the gas barrier layer 30 is formed in a region that constitutes the outermost layer of the wound electrode body 10A and is located at the upper part of the case 20, i.e., in the first curved portion 10A1a. This prevents oxygen in the case 20 from coming into contact with the outermost negative electrode active material layer 122 in a region that is likely to come into contact with oxygen in the case 20. This effectively prevents the occurrence of micro-short circuits caused by the implementation of high-temperature aging treatment.

[0079] Furthermore, in this embodiment, the gas barrier layer 30 is configured to be impermeable to oxygen contained in the space within the case 20 and to have no ion conductivity. Therefore, in the region constituting the outermost layer of the wound electrode body 10A, migration of lithium ions to the outermost negative electrode active material layer 122 is suppressed via the gas barrier layer 30. This effectively suppresses the occurrence of micro-short circuits caused by the implementation of high-temperature aging treatment.

[0080] (Modifications of the electrode body) In the above embodiment, the gas barrier layer 30 is formed on 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. 7(A) or a wound electrode body 10C of a second modified example shown in Fig. 7(B) may be applied in place of the wound electrode body 10A.

[0081] In the wound electrode body 10B according to the first modification, a gas barrier layer 30 is formed on the first curved portion 10A1a and the second curved portion 10A1b in the outermost layer region of the wound electrode body 10B (FIG. 7(A)).

[0082] In a wound electrode body 10C according to the second modification, a gas barrier layer 30 is formed around the entire periphery of the outermost layer region of the wound electrode body 10B.

[0083] In the above embodiment and each modified example, the gas barrier layer 30 is not formed on the pair of flat portions 10A2, but may be formed on at least a part of the pair of flat portions 10A2.

[0084] 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.

[0085] In the above embodiment and each of the modified examples, the gas barrier layer 30 may be configured by omitting one of the first gas barrier layer 31 and the second gas barrier layer 32.

[0086] 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]

[0087] 1A secondary battery 10A wound electrode body 10A1 Curved section 10A1 Flat part 10A3 end 10B wound electrode body 10C wound electrode body 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) 14 Second separator sheet (separator sheet) 30 Gas barrier layer 20 cases S10 outer surface 23A Positive external terminal

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 a negative electrode sheet having a negative electrode active material layer on both sides of a negative electrode current collector with a separator sheet interposed therebetween, In a region constituting the outermost layer of the electrode body, the separator sheet constitutes the outer surface of the electrode body, the negative electrode sheet is disposed on the inner layer side of the separator sheet, and a gas barrier layer that does not allow oxygen to pass therethrough is provided between the separator sheet constituting the outer surface and the negative electrode active material layer in at least a part of an end portion electrically connected to an external terminal on a positive electrode side. Secondary battery.

2. a portion of the gas barrier layer is formed along a stacking direction from an end of the negative electrode active material layer toward an inner layer side, and covers a side of an end of the negative electrode current collector on an outermost layer side; The secondary battery according to claim 1 .

3. 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 electrode body has a pair of curved portions whose outer surfaces are 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 gas barrier layer is formed in at least one region of the pair of curved portions. The secondary battery according to claim 1 or 2.

4. The gas barrier layer is formed in a region that constitutes the outermost layer of the electrode body and is located in an upper portion within the case. The secondary battery according to claim 1 or 2.

5. The gas barrier layer does not have ion conductivity. The secondary battery according to claim 1 or 2.

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