Secondary battery

Abstract

This secondary battery comprises: an electrode group in which a positive electrode, a negative electrode provided with a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode are wound; an electrolyte; an exterior body that accommodates the electrode group and the electrolyte and that has a cylindrical lateral part and a bottom part; and a negative electrode lead that connects the negative electrode to the inner surface of the bottom part of the exterior body. The inner surface of the lateral part of the exterior body has a first region and a second region. The first region is covered with an insulating layer. The negative electrode has an outermost circumferential portion disposed on the outermost circumference of the electrode group. The negative electrode current collector at the outermost circumferential portion is in contact with the second region. The proportion of the area of the first region with respect to the total area of the first region and the second region is 35-60%.

Description

secondary battery CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-062967, filed on April 9, 2024, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a secondary battery including a wound electrode group.

[0003] The secondary battery includes an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, an electrolyte, and an exterior body that houses the electrode group and the electrolyte.

[0004] Patent Document 1 proposes a lithium secondary battery comprising: "a metal lid provided gas-and-liquid-tight at the opening of a metal case containing an electrode plate group and a non-aqueous electrolyte; a positive electrode terminal and a negative electrode terminal connected to lead wires extending from the positive electrode plate and the negative electrode plate of the electrode plate group projecting through the metal lid in an electrically insulating and gas-and-liquid-tight manner; and a synthetic resin layer integrally provided on the entire inner surface of the metal case."

[0005] Japanese Patent Application Publication No. 9-63549

[0006] Secondary batteries are required to have reduced internal resistance and improved safety in the event of an external short circuit.

[0007] One aspect of the present disclosure relates to a secondary battery comprising: an electrode group formed by winding a positive electrode, a negative electrode including a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; an exterior body that accommodates the electrode group and the electrolyte and has a cylindrical side portion and a bottom portion; and a negative electrode lead that connects the negative electrode to an inner surface of the bottom portion, wherein the inner surface of the cylindrical side portion has a first region and a second region, and the first region is covered with an insulating layer; the negative electrode has an outermost portion that is disposed at the outermost periphery of the electrode group, and the negative electrode current collector of the outermost portion is in contact with the second region, and a ratio of an area of ​​the first region to a total area of ​​the first region and the second region is 35% or more and 60% or less.

[0008] According to the present disclosure, in a secondary battery, it is possible to reduce the internal resistance and improve safety in the event of an external short circuit.

[0009] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0010] Fig. 3 is a cross-sectional view schematically showing an example of a secondary battery according to an embodiment of the present disclosure; Fig. 4 is a front view schematically showing a main part of an outer can (a portion in which an electrode group is housed); Fig. 5 is a cross-sectional view cut in half schematically showing a main part of an outer can in which an electrode group is housed; Fig. 6 is a cross-sectional view taken along line IV-IV in Fig. 3; Fig. 7 is a cross-sectional view taken along line V-V in Fig. 3;

[0011] Below, embodiments according to the present disclosure will be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when numerical values ​​for specific physical properties or conditions are exemplified as lower and upper limits, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit.

[0012] A secondary battery according to an embodiment of the present disclosure includes an electrode assembly formed by winding a positive electrode, a negative electrode including a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; an exterior housing containing the electrode assembly and the electrolyte and having a cylindrical side portion and a bottom portion; and a negative electrode lead connecting the negative electrode to the inner surface of the bottom portion of the exterior housing. The inner surface of the side portion of the exterior housing has a first region and a second region, and the first region is covered with an insulating layer. The negative electrode has an outermost portion disposed at the outermost periphery of the electrode assembly, and the negative electrode current collector at the outermost periphery is in contact with the second region. The ratio of the area S1 of the first region to the combined area S0 of the first region and the second region (hereinafter also referred to as the "S1 / S0 ratio") is 35% or more and 60% or less. In this case, the internal resistance (cell resistance) of the battery is reduced and the safety of the battery in the event of an external short circuit is improved. Since the first region is covered with an insulating layer, the insulating layer is interposed between the outermost negative electrode current collector and the first region of the side of the exterior body. The total area S0 of the first region and the second region is the area of ​​the region where the outermost negative electrode current collector faces the inner surface of the cylindrical side of the exterior body.

[0013] The negative electrode of the secondary battery of the present disclosure is connected to the bottom of the exterior body via a negative electrode lead and to the side of the exterior body via the outermost negative electrode current collector. This reduces cell resistance. In the secondary battery of the present disclosure, two paths for current flow are formed between the negative electrode and the exterior body. That is, a side path through the contact region (second region) between the outermost negative electrode current collector and the side of the exterior body, and a bottom path through the negative electrode lead are formed. The existence of these two paths reduces cell resistance. By adjusting the resistance between the outermost negative electrode current collector and the side of the exterior body using the S1 / S0 ratio, it is possible to adjust the cell resistance and the balance of the current flowing through the two paths.

[0014] When an insulating layer is appropriately interposed between the outermost negative electrode current collector and the inner side surface of the exterior body with the S1 / S0 ratio being within a range of 60% or less, the resistance between the outermost negative electrode current collector and the side surface of the exterior body is reduced, thereby reducing cell resistance. Furthermore, when an insulating layer is appropriately interposed between the outermost negative electrode current collector and the inner side surface of the exterior body with the S1 / S0 ratio being within a range of 35% to 60%, the short-circuit current in the event of an external short circuit can be appropriately distributed between the side path and the bottom path, thereby preventing a large short-circuit current from flowing through the side path and causing a temperature rise at the side of the exterior body. Furthermore, a large short-circuit current from flowing through the bottom path and causing a temperature rise at the bottom of the exterior body can be prevented.

[0015] If the S1 / S0 ratio is less than 35%, the proportion of insulating layers interposed between the outermost negative electrode current collector and the side of the outer casing is small, and the resistance between the outermost negative electrode current collector and the side of the outer casing is low. However, the short-circuit current flowing through the side path increases, generating large amounts of Joule heat, which can cause a temperature rise on the side of the outer casing. If the temperature rises on the side of the battery (side of the outer casing) during an external short circuit, it can damage the battery or, when multiple batteries are used in a module, affect adjacent batteries.

[0016] If the S1 / S0 ratio is greater than 60%, the proportion of an insulating layer interposed between the outermost negative electrode current collector and the side portion of the exterior body increases, increasing the resistance between the outermost negative electrode current collector and the side portion of the exterior body, which may result in increased cell resistance. If the S1 / S0 ratio is even greater, such as 80% or greater, the short-circuit current flowing through the bottom path during an external short circuit may increase, generating significant Joule heat and causing a temperature rise at the bottom of the exterior body. In particular, if the outermost negative electrode current collector and the side portion of the exterior body are not in contact (i.e., if almost the entire area facing the outermost negative electrode current collector on the inner surface of the side portion of the exterior body is covered with an insulating layer), short-circuit current may concentrate on the negative electrode lead, causing an abnormal temperature rise at the bottom of the exterior body, which may easily damage the battery.

[0017] (Insulating Layer) One or more insulating layers may be formed. The insulating layers may be formed of the same material or different materials. The insulating layer may contain a resin. From the viewpoint of chemical stability, thermal stability, etc., the insulating layer may contain at least one selected from the group consisting of polypropylene (PP), polyethylene, polyimide, polyvinyl chloride, Kapton, fluororesin, silicone, rubber, polyester, epoxy resin, melamine, phenolic resin, and polyurethane. Among these, PP, polyethylene, and polyimide are preferred.

[0018] The insulating layer may be a resin layer. For example, the bottom inner surface of the exterior body and portions of the side inner surface other than the second region may be covered with a mask, and the resin layer may be selectively formed in the first region of the side inner surface of the exterior body by vapor deposition. Alternatively, a ring-shaped resin member may be prepared in advance and placed between the ring-shaped first region of the exterior body and the negative electrode current collector at the outermost periphery of the electrode group, thereby forming a ring-shaped insulating layer in the first region of the side inner surface of the exterior body.

[0019] Furthermore, from the viewpoint of chemical stability, thermal stability, etc., the insulating layer may contain a metal oxide. From the same viewpoint, the metal oxide may contain at least one selected from the group consisting of Al, Zr, Mg, Ti, Ce, Zn, Sn, Ba, Y, Si, Ni, Mn, Nb, Fe, Ca, Ge, and Bi.

[0020] The insulating layer may be a metal oxide layer. For example, the bottom inner surface of the exterior body and the portions of the side inner surface other than the second region may be covered with a mask, and the metal oxide layer may be selectively formed in the first region of the side inner surface of the exterior body by vapor deposition.

[0021] From the viewpoint of easily ensuring uniformity of the surface pressure of the electrode group, the thickness of the insulating layer may be 60 μm or less, 40 μm or less, or 30 μm or less. From the viewpoint of easily ensuring insulation between the outermost negative electrode current collector and the first region, the thickness of the insulating layer may be 3 μm or more, or 10 μm or more. The thickness of the insulating layer may be, for example, 3 μm or more and 60 μm or less (or 40 μm or less). In the case of a resin layer, it may be, for example, 10 μm or more and 60 μm or less (or 40 μm or less). In the case of a metal oxide layer, it may be, for example, 3 μm or more and 30 μm or less (or 15 μm or less). When multiple insulating layers are formed, it is preferable that each insulating layer has a thickness within the above range and is approximately the same as each other. By using a vapor deposition method, it is possible to form a layer (particularly a metal oxide layer) with excellent insulation properties and a small thickness within the above range, which makes it easy to ensure uniformity of the surface pressure of the electrode group.

[0022] (Exterior Body) One or more first regions may be arranged on the inner surface of the side portion of the exterior body. When multiple first regions are arranged, the area S1 is the total area of ​​the multiple first regions. The multiple first regions may be arranged in a predetermined pattern. The multiple first regions may be arranged in a ring shape along the circumferential direction of the inner surface of the cylindrical side portion. For example, two to four first regions may be arranged in a ring shape. In this case, from the viewpoint of facilitating the formation of an insulating layer and ensuring insulation between the outermost negative electrode current collector and the first region, the width of one first region may be 1 mm or more, 3 mm or more, or 8 mm or more. From the viewpoint of facilitating the provision of a second region, the width of one first region may be 35 mm or less, 20 mm or less, or 15 mm or less. It is preferable that the widths of the multiple first regions each be within the above range. For example, the widths of the multiple first regions each may be 1 mm or more and 35 mm or less, or 8 mm or more and 20 mm or less.

[0023] Alternatively, the plurality of first regions may be arranged in a dot pattern on the inner surface of the cylindrical side portion. The dot shape may be circular or polygonal, such as rectangular. In this case, the maximum diameter of one first region may be, for example, 1 mm or more and 35 mm or less (or 20 mm or less), or 1 mm or more and 15 mm or less. In this case, it is preferable that the maximum diameters of the plurality of first regions are each within the above range.

[0024] The exterior body functions as a negative electrode terminal. The cylindrical side and bottom of the exterior body are electrically connected. The exterior body may be a single piece. The exterior body may be, for example, a metal can (exterior can) obtained by a predetermined can manufacturing process (DI: Drawing and Ironing process) using a stainless steel plate or the like. The surface of the stainless steel plate or the like may be nickel-plated. Alternatively, the exterior body may be composed of a cylindrical metal can and a negative electrode terminal plate covering one opening of the cylindrical metal can.

[0025] (Other) The negative electrode may include a negative electrode composite layer supported on a negative electrode current collector. In this case, it is preferable that the negative electrode does not have a negative electrode composite layer supported in the region facing the second region of the outermost periphery (the negative electrode current collector is exposed). Because it is easy to perform the above-mentioned adjustment using the S1 / S0 ratio and to fabricate the negative electrode, it is preferable that the negative electrode does not have a negative electrode composite layer supported in the entire region facing the inner side surface of the outer periphery's exterior body. The negative electrode composite layer only needs to be formed on the surface of the negative electrode current collector facing the positive electrode (positive electrode composite layer). The region facing the first region of the outermost periphery may not have a negative electrode composite layer supported thereon, or may have a negative electrode composite layer supported thereon. For example, the negative electrode composite layer may be supported in the end of the region facing the inner side surface of the outer periphery's exterior body, opposite the winding end of the negative electrode (for example, an end occupying 20% ​​or less or 10% or less of the area of ​​the outermost periphery).

[0026] From the viewpoint of easily suppressing a temperature rise at the side of the exterior body, the negative electrode lead is preferably attached to a predetermined location other than the outermost periphery of the negative electrode. Examples of the material for the negative electrode lead include nickel and nickel alloys.

[0027] The secondary battery may include a sealing body (sealing plate) that seals the opening of the exterior body. The sealing body is electrically connected to the positive electrode and functions as a positive electrode terminal. A gasket may be interposed between the sealing body and the open end of the exterior body to electrically insulate the sealing plate from the exterior body. The positive electrode and the sealing body are electrically connected via, for example, a positive electrode lead. Examples of materials for the positive electrode lead include aluminum and aluminum alloys.

[0028] The winding end of the electrode group may be fixed with tape. The tape may be attached to the negative electrode current collector along the outer periphery of the outermost periphery. From the viewpoint of easily adjusting the resistance between the negative electrode current collector at the outermost periphery and the side part of the outer casing by the S1 / S0 ratio, it is preferable that the tape be attached at a position overlapping with the insulating layer (first region) when the electrode group is housed in the outer casing.

[0029] Examples of secondary batteries include nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries and lithium metal secondary batteries. The negative electrode of a lithium ion secondary battery includes a negative electrode composite layer supported on a negative electrode current collector. The negative electrode composite layer includes a negative electrode active material that occludes lithium ions during charging and releases lithium ions during discharging. The negative electrode of a lithium metal secondary battery is a negative electrode in which lithium metal precipitates during charging and dissolves in an electrolyte during discharging. The negative electrode may be composed of only a negative electrode current collector, or lithium metal may precipitate on the surface of the negative electrode current collector during charging. The negative electrode of a lithium metal secondary battery may have a thin negative electrode composite layer supported on the surface of the negative electrode current collector.

[0030] The diameter of the secondary battery (cylindrical battery) of the present disclosure may be, for example, 15 mm or more, 20 mm or more, or 40 mm or more. The height of the secondary battery may be, for example, 65 mm or more, 70 mm or more, or 80 mm or more. The rated capacity of the secondary battery may be, for example, 2000 mAh or more, 3000 mAh or more, or 10000 mAh or more.

[0031] Examples of components of a nonaqueous electrolyte secondary battery are described below, although the secondary battery is not limited to the examples described below.

[0032] (Negative Electrode) The negative electrode includes, for example, a negative electrode current collector and a negative electrode mixture layer supported on the surface of the negative electrode current collector. The negative electrode mixture layer includes, for example, a negative electrode active material, a binder, and a thickener. The negative electrode is obtained, for example, by applying a negative electrode slurry to both sides of the negative electrode current collector, drying the coating, and then rolling to form a negative electrode mixture layer. The negative electrode slurry includes a negative electrode mixture and a dispersion medium (e.g., water). The negative electrode mixture layer may be formed on only one side or both sides of the negative electrode current collector. In this case, the negative electrode current collector may be exposed in a predetermined region of the surface (the surface region facing the outer casing) without being coated with the negative electrode slurry. Alternatively, the negative electrode current collector may be exposed in the predetermined region by, for example, scraping off the negative electrode mixture layer. In the case of a lithium metal secondary battery, the negative electrode may be formed only with the negative electrode current collector.

[0033] The negative electrode mixture contains at least a negative electrode active material and may contain other components as needed, such as a binder, a thickener, and a conductive material.

[0034] The negative electrode active material may be a material that reversibly absorbs and releases lithium ions. Examples of the negative electrode active material include carbonaceous materials, Si-containing materials, and Sn-containing materials. The negative electrode may contain one type of negative electrode active material or a combination of two or more types. Examples of the carbonaceous material include graphite, easily graphitized carbon (soft carbon), and hardly graphitized carbon (hard carbon).

[0035] Examples of the negative electrode active material include a carbonaceous material, a Si-containing material, and a Sn-containing material. The negative electrode may contain one or more negative electrode active materials. Examples of the carbonaceous material include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon).

[0036] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0037] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, rubber polymers, etc. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride, etc. Examples of thickeners include carboxymethyl cellulose (CMC), sodium salt of CMC, etc.

[0038] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0039] Examples of materials for the negative electrode current collector (conductive sheet) include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys, which have high electrical conductivity, are preferred.

[0040] The thickness of the negative electrode current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0041] (Positive Electrode) The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode is obtained, for example, by applying a positive electrode slurry including the positive electrode active material, the conductive material, and the binder to both sides of the positive electrode current collector, drying the coating, and then rolling the coating to form a positive electrode mixture layer. The positive electrode slurry includes a positive electrode mixture and a dispersion medium (for example, N-methyl-2-pyrrolidone). The positive electrode mixture layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides.

[0042] The positive electrode mixture contains at least a positive electrode active material and may contain other components as needed, such as a binder and a conductive material.

[0043] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Among these, lithium-containing transition metal oxides are preferred because of their low production cost and high average discharge voltage.

[0044] Examples of transition metal elements contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. The lithium-containing transition metal oxide may contain one or more transition metal elements. The transition metal element may be Ni, Co, and / or Mn. The lithium-containing transition metal oxide may contain one or more typical elements as needed. Examples of typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The typical element may be Al, etc.

[0045] Among the lithium-containing transition metal oxides, composite oxides containing Ni, Co and / or Mn as transition metal elements, which may contain Al as an optional component, and which have a layered rock-salt type crystal structure are preferred in terms of obtaining high capacity.

[0046] As the binder, conductive material, etc., for example, those exemplified for the negative electrode can be used. The shape and thickness of the positive electrode current collector can be selected from the shape and range of the positive electrode current collector.

[0047] Examples of materials for the positive electrode current collector (conductive sheet) include aluminum (Al), titanium (Ti), iron (Fe), and alloys containing these metal elements. The alloy may be an Al alloy, a Ti alloy, an Fe alloy, or the like. The Fe alloy may be stainless steel (SUS).

[0048] The thickness of the positive electrode current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0049] (Separator) A porous sheet having ion permeability and insulating properties is used for the separator. Examples of porous sheets include thin films, woven fabrics, nonwoven fabrics, etc. having micropores. The material of the separator is not particularly limited, and a polymeric material may be used. Examples of polymeric materials include olefin resins, polyamide resins, cellulose, etc. Examples of olefin resins include polyethylene, polypropylene, and ethylene-propylene copolymers, etc. The separator may contain additives (such as inorganic fillers) as necessary. The thickness of the separator is not particularly limited, and is, for example, 5 μm or more and 100 μm or less.

[0050] (Electrolyte) A non-aqueous electrolyte having lithium ion conductivity can be used as the electrolyte. The non-aqueous electrolyte is not particularly limited, and a non-aqueous electrolyte used in a known non-aqueous electrolyte secondary battery can be used. The non-aqueous electrolyte contains, for example, a non-aqueous solvent and lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be in a liquid state or a gel state.

[0051] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0052] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof. The non-aqueous electrolyte may contain only one of these non-aqueous solvents or two or more of them. Examples of halogen-substituted derivatives include fluorides. Examples of lithium salts include LiPF ６ The concentration of the lithium salt in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less.

[0053] FIG. 1 is a cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment of the present disclosure. Note that an insulating layer 61 is formed on the inner side surface of the exterior body, but the insulating layer 61 is omitted in FIG. 1 . The secondary battery according to the present disclosure is not limited to this. FIG. 2 is a front view schematically illustrating a main portion of an exterior can (a portion in which an electrode group is housed). FIG. 3 is a cross-sectional view cut in half schematically illustrating a main portion of an exterior can housing an electrode group. In FIG. 3 , the electrode group and the exterior can are shown, and other components such as a negative electrode lead are omitted. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3 , including a first region in FIG. 3 . FIG. 5 is a cross-sectional view taken along line V-V in FIG. 3 , including a second region in FIG. 3 .

[0054] Cylindrical secondary battery 10 includes a battery case 30, a wound electrode group 14, and an electrolyte (not shown) housed within battery case 30. Battery case 30 includes a cylindrical outer can 38 (outer body) with a bottom made of metal (e.g., SUS), a sealing plate 31 (sealing body) that seals the opening of outer can 38, and a gasket 37 interposed between the open end of outer can 38 and sealing plate 31. Insulating plates 17 and 18 are disposed within outer can 38 at both ends of electrode group 14.

[0055] The sealing plate 31 includes a filter 32, a lower valve body 33, an insulating member 34, an upper valve body 35, and a cap 36. All of the members except for the insulating member 34 are electrically connected to one another.

[0056] The cylindrical electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator 13 so that the separator 13 is disposed between the positive electrode 11 and the negative electrode 12. The positive electrode 11, the negative electrode 12, and the separator 13 are each strip-shaped. The positive electrode 11 includes a positive electrode current collector and positive electrode composite layers formed on both sides of the positive electrode current collector. The negative electrode 12 includes a negative electrode current collector and negative electrode composite layers formed on both sides of the negative electrode current collector.

[0057] One end of the positive electrode lead 19 is connected to the positive electrode 11, and the other end of the positive electrode lead 19 is connected to the sealing plate 31 (filter 32). That is, the positive electrode 11 is electrically connected to a cap 36 that also serves as a positive electrode terminal. One end of the negative electrode lead 20 is connected to the negative electrode 12, and the other end of the negative electrode lead 20 is connected to the inner surface of a bottom 38b of an outer can 38 that also serves as a negative electrode terminal.

[0058] The exterior can 38 accommodates the electrode group 14 and an electrolyte (not shown). The negative electrode 12 has an outermost peripheral portion 12a that is disposed at the outermost periphery 14s of the electrode group 14. In the entire region of the outermost peripheral portion 12a that faces the inner surface of the exterior can side portion 38a (the surface of the negative electrode current collector that faces the inner surface of the exterior can side portion 38a), the negative electrode composite layer is not supported, and the negative electrode current collector is exposed.

[0059] As shown in FIG. 2 , the exterior can 38 has a cylindrical side portion 38a and a bottom portion 38b. The inner surface of the cylindrical side portion 38a has a first region 51 and a second region 52. The first region 51 is covered with an insulating layer 61. The insulating layer 61 is interposed between the negative electrode current collector of the outermost peripheral portion 12a and the first region 51. The negative electrode current collector of the outermost peripheral portion 12a is in contact with the second region 52. The ratio of the area S1 of the first region to the total area S0 of the first and second regions (the area of ​​the region where the inner surface of the exterior can side portion 38a faces the negative electrode current collector of the outermost peripheral portion 12a) is 35% or more and 60% or less. The area S1 of the first region 51 is the total area of ​​the 1A region 51a and the 1B region 51b.

[0060] The first region 51 includes a 1A region 51a facing one end 141 of the electrode group 14 in the winding axis direction, and a 1B region 51b facing the other end 142 of the electrode group 14 in the winding axis direction. The insulating layer 61 includes a 1A insulating layer 61a covering the 1A region 51a, and a 1B insulating layer 61b covering the 1B region 51b. The second region 52 includes a region 52a facing a central portion of the electrode group 14 in the winding axis direction. By ensuring region 52a, the central portion of the negative electrode current collector in the outermost peripheral portion 12a can stably contact the inner surface of the outer can side portion 38a, making it easier to reduce cell resistance.

[0061] The thickness T1a of the first-A insulating layer 61a and the thickness T1b of the first-B insulating layer 61b are preferably 60 μm or less and 40 μm or less, respectively. Although T1a and T1b may be different, it is preferable that T1a and T1b are approximately the same from the viewpoints of facilitating the formation of the insulating layer and facilitating the uniformity of the surface pressure of the electrode group.

[0062] As shown in FIGS. 2 to 4 , the first A region 51 a (first A insulating layer 61 a) and the first B region 51 b (first B insulating layer 61 b) are provided in a ring shape along the circumferential direction of the inner surface of the cylindrical side portion 38 a. From the viewpoints of facilitating the formation of an insulating layer and ensuring insulation between the outermost negative electrode current collector and the first region, the width W1 a of the first A region 51 a (first A insulating layer 61 a) and the width W1 b of the strip-shaped first B region 51 b (first B insulating layer 61 b) may be 1 mm or more and 35 mm or less, or 8 mm or more and 20 mm or less. W1 a and W1 b may be different, but from the viewpoints of facilitating the formation of an insulating layer and facilitating uniform surface pressure of the electrode group, it is preferable that W1 a and W1 b be approximately the same.

[0063] 3, distance L1 between 1A insulating layer 61a and one end 141 of electrode group 14 in the winding axis direction, and distance L2 between 1B insulating layer 61b and the other end 142 of electrode group 14 in the winding axis direction may each be, for example, 2 to 6 mm. Although L1 and L2 may be different, it is preferable that L1 and L2 are approximately the same from the viewpoints of making it easier to face the two insulating layers to the electrode group, easier to stably face the central portion of the electrode group in the winding axis direction to the inner surface of the side portion of the exterior can, and easier to uniform the surface pressure of the electrode group.

[0064] The winding end of the electrode group 14 may be fixed with insulating tape. In this case, the tape is preferably attached at a position that overlaps the insulating layer 61 when the electrode group 14 is housed in the exterior can 38.

[0065] <<Notes>> The above embodiments disclose the following: (Technology 1) A secondary battery comprising: an electrode group formed by winding a positive electrode, a negative electrode including a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; an exterior body accommodating the electrode group and the electrolyte and having a cylindrical side portion and a bottom portion; and a negative electrode lead connecting the negative electrode to an inner surface of the bottom portion, wherein the inner surface of the cylindrical side portion has a first region and a second region, the first region being covered with an insulating layer, the negative electrode having an outermost peripheral portion disposed at the outermost periphery of the electrode group, the negative electrode current collector at the outermost peripheral portion being in contact with the second region, and a ratio of an area of ​​the first region to a combined area of ​​the first region and the second region being 35% or more and 60% or less. (Technology 2) The secondary battery according to Technology 1, wherein the negative electrode includes a negative electrode composite layer supported on the negative electrode current collector, and the negative electrode composite layer is not supported in a region of the outermost periphery facing the second region. (Technology 3) The secondary battery according to Technology 1 or 2, wherein the insulating layer includes at least one selected from the group consisting of polypropylene, polyethylene, polyimide, polyvinyl chloride, Kapton, fluororesin, silicone, rubber, polyester, epoxy resin, melamine, phenolic resin, and polyurethane. (Technology 4) The secondary battery according to any one of Technology 1 to 3, wherein the insulating layer includes a metal oxide, and the metal oxide includes at least one selected from the group consisting of Al, Zr, Mg, Ti, Ce, Zn, Sn, Ba, Y, Si, Ni, Mn, Nb, Fe, Ca, Ge, and Bi. (Technology 5) The secondary battery according to any one of Technology 1 to 4, wherein the insulating layer has a thickness of 60 μm or less. (Technology 6) The secondary battery according to any one of Technologies 1 to 5, wherein the plurality of first regions are provided in a ring shape along the circumferential direction of the inner surface of the cylindrical side portion. (Technology 7) The secondary battery according to Technology 6, wherein the width of each of the plurality of first regions is 1 mm or more and 35 mm or less. (Technology 8) The secondary battery according to any one of Technologies 1 to 5, wherein the plurality of first regions are arranged in a dot pattern on the inner surface of the cylindrical side portion.(Technology 9) The secondary battery according to any one of Techniques 1 to 8, wherein the first region includes a 1A region facing one end side of the electrode group in the winding axis direction and a 1B region facing the other end side of the electrode group in the winding axis direction, the insulating layer includes a 1A insulating layer covering the 1A region and a 1B insulating layer covering the 1B region, and the second region includes a region facing a center part of the electrode group in the winding axis direction.

[0066] [Examples] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0067] Secondary Batteries E1-E2, R1-R2 (Preparation of Positive Electrodes) Positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone was added and stirred to prepare a positive electrode slurry. A lithium-containing transition metal oxide containing nickel, cobalt, and aluminum was used as the positive electrode active material. The positive electrode slurry was then applied to both sides of aluminum foil serving as a positive electrode current collector. The coating was dried and rolled with a roller to form a positive electrode composite layer. The positive electrode current collector with the positive electrode composite layer formed on both sides was then cut to a predetermined size to prepare a strip-shaped positive electrode.

[0068] (Preparation of Negative Electrode) Graphite (negative electrode active material), styrene-butadiene copolymer rubber (SBR), and carboxymethyl cellulose Na salt (CMC-Na) were mixed in a mass ratio of 98:1:1, and an appropriate amount of water was added and stirred to prepare a negative electrode slurry. The negative electrode slurry was then applied to both sides of copper foil serving as a negative electrode current collector, the coating was dried, and the mixture was rolled with a roller to form a negative electrode composite layer. The negative electrode current collector with the negative electrode composite layer formed on both sides was cut to a predetermined size to prepare a strip-shaped negative electrode. On one surface of the region that would become the outermost periphery of the negative electrode (the entire region facing the inner surface of the exterior can side), the negative electrode current collector was exposed without forming a negative electrode composite layer.

[0069] (Preparation of non-aqueous electrolyte) LiPF 6 was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 3:7). ６was dissolved in a solution at a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[0070] (Preparation of Electrode Assembly) One end of an aluminum positive electrode lead was attached to the positive electrode. One end of a nickel negative electrode lead was attached to the negative electrode (at a predetermined location other than the region that would become the outermost periphery when the electrode assembly was constructed). The positive electrode and negative electrode were spirally wound in an inert gas atmosphere with a polyethylene porous film interposed therebetween as a separator to prepare an electrode assembly. The negative electrode had an outermost periphery that was positioned at the outermost periphery of the electrode assembly, and the negative electrode current collector was exposed over the entire region facing the inner side surface of the outer periphery of the outer can.

[0071] The winding end of the electrode assembly was fixed with polypropylene tape, which was attached at a predetermined location along the outer periphery of the negative electrode current collector so that the tape would overlap with the insulating layer when the electrode assembly was housed in an outer can.

[0072] (Preparation of Outer Can) An outer can made of stainless steel (SUS) and having a cylindrical side and bottom was prepared. Specifically, an outer can 38 was prepared, in which the first regions 51a, 51b of the inner surface of the side were covered with insulating layers 61a, 61b, as shown in Figures 2 and 3 . Polypropylene (PP) layers (30 μm thick) were formed as the insulating layers 61a, 61b covering the first regions 51a, 51b of the inner surface of the side. The PP layers were formed by vacuum deposition, with the inner bottom surface of the outer can and the inner side surface except for the second regions covered with a mask.

[0073] The S1 / S0 ratio was set to the values ​​shown in Table 1 by changing the widths W1a and W1b of the first regions 51a and 51b (insulating layers 61a and 61b). W1a and W1b were set to the same value. The total width of the insulating layer shown in Table 1 is the sum of the widths W1a and W1b of the insulating layers 61a and 61b. In other words, the total width of the insulating layer is equivalent to twice the value of W1a (or W1b). L1 and L2 in FIG. 3 were each set to 5 mm.

[0074] (Assembly of Secondary Battery) The electrode group was housed in an outer can. At this time, the other end of the positive electrode lead was connected to a sealing plate. The other end of the negative electrode lead was connected to the inner bottom surface of the outer can. The outermost negative electrode current collector was brought into contact with the second region on the inner side surface of the outer can. An insulating layer was interposed between the outermost negative electrode current collector and the first region. At this time, the tape attached to the outer periphery of the electrode group was brought into contact with the insulating layer covering the inner side surface (first region) of the outer can. After injecting the nonaqueous electrolyte, the opening of the outer can was sealed by covering it with a sealing plate. At this time, a gasket was interposed between the sealing plate and the open end of the outer can. In this way, a cylindrical nonaqueous electrolyte secondary battery was produced.

[0075] Secondary battery R3: Only the first region was disposed on the inner side surface of the outer can, without disposing the second region. That is, the S1 / S0 ratio was set to 100%. A PP layer was interposed between the outermost negative electrode current collector and the inner side surface of the outer can in the entire area where the outermost negative electrode current collector and the inner side surface of the outer can faced each other. Except for the above, secondary battery R3 was fabricated in the same manner as secondary battery E1.

[0076] [Evaluation] (External Short-Circuit Test) A secondary battery was charged at a constant current of 500 mA until the voltage reached 4.2 V, and the internal resistance (cell resistance) was measured. Next, the fully charged secondary battery was connected to a fixed resistor of 10 mΩ to cause an external short circuit. The temperature near the center of the side surface (exterior body side) of the cylindrical battery during the external short circuit was measured using a thermocouple, and the maximum temperature at this time was measured.

[0077] The evaluation results are shown in Table 1. E1 and E2 are examples, and R1 to R3 are comparative examples.

[0078]

[0079] In the batteries E1 and E2, in which the S1 / S0 ratio was 35 to 60%, the internal resistance was small and the temperature of the side surface of the battery was low during an external short circuit.

[0080] Battery R1, which had an S1 / S0 ratio of less than 35%, had a low internal resistance but a high temperature on the side of the battery during an external short circuit. Battery R2, which had an S1 / S0 ratio of more than 60%, had a low temperature on the side of the battery during an external short circuit but an increased internal resistance.

[0081] In Battery R3, the negative electrode current collector at the outermost periphery of the negative electrode did not come into contact with the outer can, which increased the internal short circuit. In Battery R3, the short circuit current concentrated in the negative electrode lead during an external short circuit, causing a rapid rise in the temperature of the negative electrode lead and an abnormal rise in the temperature of the bottom of the outer can (bottom of the battery) to which the negative electrode lead was connected.

[0082] <Secondary batteries E3-E4, R4-R5> Aluminum oxide (Al) is used instead of the PP layer. ２ O ３ A 4 μm thick aluminum oxide layer was formed in a first region on the inner side surface of the outer can. The aluminum oxide layer was formed by vacuum deposition, with the bottom inner surface of the outer can and the portion of the inner side surface of the side surface other than the second region covered with a mask. Except for the above, secondary batteries E3-E4 and R4-R5 were fabricated and evaluated in the same manner as secondary batteries E1-E2 and R1-R2.

[0083] Secondary battery R6: The second region was not disposed on the inner side surface of the outer can, and only the first region was disposed. That is, the S1 / S0 ratio was set to 100%. In the entire area where the outermost negative electrode current collector and the inner side surface of the outer can face each other, an aluminum oxide layer was interposed between the outermost negative electrode current collector and the inner side surface of the outer can, instead of a PP layer. Except for the above, secondary battery R6 was fabricated and evaluated in the same manner as secondary battery E3.

[0084] The evaluation results are shown in Table 2. E3 and E4 are examples, and R4 to R6 are comparative examples.

[0085]

[0086] In the batteries E3 and E4, in which the S1 / S0 ratio was 35 to 60%, the internal resistance was small and the temperature of the side surface of the battery was low during an external short circuit.

[0087] Battery R4, which had an S1 / S0 ratio of less than 35%, had a low internal resistance but a high temperature on the side of the battery during an external short circuit. Battery R5, which had an S1 / S0 ratio of more than 60%, had a low temperature on the side of the battery during an external short circuit but an increased internal resistance.

[0088] In Battery R6, the negative electrode current collector at the outermost periphery of the negative electrode did not come into contact with the outer can, which increased the internal short circuit. In Battery R6, the short circuit current concentrated in the negative electrode lead during an external short circuit, causing a rapid rise in the temperature of the negative electrode lead and an abnormal rise in the temperature of the bottom of the outer can (bottom of the battery) to which the negative electrode lead was connected.

[0089] The present disclosure can be used in a secondary battery in which a wound electrode group is housed in an exterior body.

[0090] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0091] 10: secondary battery, 11: positive electrode, 12: negative electrode, 12a: outermost periphery of negative electrode, 13: separator, 14: electrode group, 14s: outermost periphery of electrode group, 31: sealing plate, 38: outer can, 51: first region, 52: second region, 61: insulating layer

Claims

1. A secondary battery comprising: an electrode group formed by winding a positive electrode, a negative electrode having a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; an exterior body that houses the electrode group and the electrolyte and has a cylindrical side portion and a bottom portion; and a negative electrode lead that connects the negative electrode to the inner surface of the bottom portion, wherein the inner surface of the cylindrical side portion has a first region and a second region, and the first region is covered with an insulating layer, the negative electrode has an outermost portion that is disposed at the outermost periphery of the electrode group, and the negative electrode current collector at the outermost portion is in contact with the second region, and the ratio of the area of ​​the first region to the combined area of ​​the first region and the second region is 35% or more and 60% or less.

2. The secondary battery according to claim 1, wherein the negative electrode comprises a negative electrode composite layer supported on the negative electrode current collector, and the negative electrode composite layer is not supported in a region of the outermost periphery facing the second region.

3. The secondary battery according to claim 1, wherein the insulating layer contains at least one material selected from the group consisting of polypropylene, polyethylene, polyimide, polyvinyl chloride, Kapton, fluororesin, silicone, rubber, polyester, epoxy resin, melamine, phenolic resin, and polyurethane.

4. The secondary battery according to claim 1, wherein the insulating layer contains a metal oxide, and the metal oxide contains at least one element selected from the group consisting of Al, Zr, Mg, Ti, Ce, Zn, Sn, Ba, Y, Si, Ni, Mn, Nb, Fe, Ca, Ge, and Bi.

5. The secondary battery according to claim 1, wherein the insulating layer has a thickness of 60 μm or less.

6. The secondary battery according to claim 1, wherein a plurality of said first regions are provided in a ring shape along the circumferential direction of the inner surface of said cylindrical side portion.

7. The secondary battery according to claim 6, wherein the width of each of the plurality of first regions is 1 mm or more and 35 mm or less.

8. The secondary battery according to claim 1, wherein a plurality of said first regions are arranged in a dot pattern on the inner surface of said cylindrical side portion.

9. The secondary battery described in claim 1, wherein the first region includes a 1A region facing one end side of the electrode group in the winding axis direction and a 1B region facing the other end side of the electrode group in the winding axis direction, the insulating layer includes a 1A insulating layer covering the 1A region and a 1B insulating layer covering the 1B region, and the second region includes a region facing a center part of the electrode group in the winding axis direction.

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