Secondary battery

Abstract

This secondary battery comprises: an electrode group in which a positive electrode, a negative electrode that is provided with a negative electrode collector, and a separator which is between the positive electrode and the negative electrode are wound; an electrolyte; a metal exterior body that accommodates the electrode group and the electrolyte and that has a cylindrical side part and a bottom part; at least one insulating tape that fixes the winding end part of the electrode group; and a negative electrode lead that connects the negative electrode and an inner surface of the bottom part of the exterior body. The negative electrode has an outermost peripheral part that is disposed at the outermost periphery of the electrode group. The tape is affixed to the negative electrode collector along the outer periphery of the outermost peripheral part. The negative electrode collector of the outermost peripheral part to which the tape is affixed and the inner surface of the cylindrical side part are in contact. The width A of the negative electrode collector of the outermost peripheral part and the total width B of the tape satisfy the relational expression 0.4≤(A-B) / A≤0.65.

Description

secondary battery CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-062968, 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 non-aqueous electrolyte secondary battery comprising: an electrode group in which a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are wound; a tape for fixing at least the winding end of the electrode group; and a non-aqueous electrolyte, wherein, at least in a charged state, the negative electrode contains lithium metal and / or a lithium alloy, and the tape has a tensile strength of 20 N / 10 mm or less when the elongation rate is 200% or more."

[0005] International Publication No. 2019 / 003641

[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 including: 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; a metal exterior body that houses the electrode group and the electrolyte and has a cylindrical side portion and a bottom portion; at least one insulating tape that fixes a winding end end of the electrode group; and a negative electrode lead that connects the negative electrode to an inner surface of the bottom portion, wherein the negative electrode has an outermost peripheral portion that is arranged at the outermost periphery of the electrode group, the tape is attached to the negative electrode current collector along the outer periphery of the outermost peripheral portion, the negative electrode current collector at the outermost peripheral portion to which the tape is attached is in contact with the inner surface of the cylindrical side portion, and a width A of the negative electrode current collector at the outermost peripheral portion and a total width B of the tapes satisfy the relational expression: 0.4≦(A−B) / A≦0.65.

[0008] According to the present disclosure, the internal resistance of a secondary battery can be reduced and safety during an external short circuit can be improved.

[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. 1 is a cross-sectional view schematically showing an example of a secondary battery according to an embodiment of the present disclosure; Fig. 2 is a schematic front view of the side of an example of a wound electrode group when viewed from the winding end side; Fig. 3 is a schematic front view of the side of an example of a wound electrode group when viewed from the opposite side to the winding end; Fig. 4 is a schematic top view of one end face of an example of a wound electrode group when viewed from the winding axis direction.

[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; a metal exterior housing containing the electrode assembly and the electrolyte and having a cylindrical side and a bottom; at least one insulating tape securing the winding end of the electrode assembly; and a negative electrode lead connecting the negative electrode to the inner surface of the bottom of the exterior housing. The negative electrode has an outermost portion disposed at the outermost periphery of the electrode assembly. The tape is attached to the negative electrode current collector along the outer periphery of the outermost portion. The negative electrode current collector at the outermost portion to which the tape is attached is in contact with the inner surface of the side of the exterior housing. The width A of the outermost negative electrode current collector and the total width B of the tape satisfy the relation: 0.4≦(A−B) / A≦0.65. In this case, the internal resistance (cell resistance) of the battery is reduced and the safety of the battery during an external short circuit is improved. The total width B of the tape means the total width of the multiple tapes when the winding end of the electrode group is fixed with multiple tapes.

[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 current paths are formed between the negative electrode and the exterior body. That is, a side path through the contact area 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. By utilizing the insulating properties of the tape, the resistance between the outermost negative electrode current collector and the side of the exterior body can be adjusted by adjusting the degree of coverage of the outermost negative electrode current collector with the tape, i.e., (A-B) / A. This allows the cell resistance to be adjusted and the balance of the current flowing through the two paths to be adjusted.

[0014] When (A-B) / A is within the range of 0.4 or more and tape is appropriately interposed between the outermost negative electrode current collector and the inner side surface of the exterior body, 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 (A-B) / A is within the range of 0.4 or more and 0.6 or less and tape is appropriately interposed between the outermost negative electrode current collector and the inner side surface of the exterior body, 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 (A-B) / A is greater than 0.65, the proportion of tape 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 significant 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, can affect adjacent batteries.

[0016] If (A-B) / A is less than 0.4, the proportion of tape interposed between the outermost negative electrode current collector and the side of the outer casing increases, which may increase the resistance between the outermost negative electrode current collector and the side of the outer casing, resulting in increased cell resistance. If (A-B) / A is even smaller, such as 0.2 or less, 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 outer casing. In particular, if the outermost negative electrode current collector and the side of the outer casing are not in contact (i.e., if almost the entire outermost negative electrode current collector is covered with insulating tape), short-circuit current may concentrate on the negative electrode lead, causing an abnormal temperature rise at the bottom of the outer casing, which may easily damage the battery.

[0017] (Tape) The tape includes an insulating substrate layer. The substrate layer is composed of a sheet-like insulating substrate. The substrate layer may contain one type of insulating material, or may contain two or more types of insulating materials. The substrate layer may be a resin substrate layer. Examples of resin materials contained in the substrate layer include olefin resin, fluororesin, polyester resin, silicone resin, polyimide, polyvinyl chloride, etc. Examples of olefin resins include polyethylene, polypropylene, etc. Examples of fluororesins include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0018] From the viewpoint of high chemical stability, thermal stability, tensile strength, etc., it is particularly preferred that the base layer contains at least one selected from the group consisting of polyethylene, polypropylene, and polyimide.

[0019] From the viewpoint of facilitating fixing the winding end of the electrode group, the tape preferably includes an adhesive layer. The adhesive layer is preferably disposed on one surface (the surface on the outermost periphery side) of the base layer. In this case, the outermost negative electrode current collector and the base layer can be easily adhered to each other via the adhesive layer. The adhesive layer is formed from an adhesive. Examples of adhesives include acrylic adhesives, silicone adhesives, rubber adhesives, etc. Among these, acrylic adhesives are preferred from the viewpoint of heat resistance, etc. The thickness of the adhesive layer is, for example, 5 to 25% of the thickness of the base layer.

[0020] From the viewpoint of easily reducing cell resistance and easily ensuring energy density (battery capacity), the thickness of the tape is preferably 60 μm or less, more preferably 40 μm or less or 30 μm or less. From the viewpoint of ensuring insulation by the tape and preventing the tape from breaking, the thickness of the tape may be, for example, 10 μm or more. The thickness of the tape is the total thickness of the base layer and the adhesive layer.

[0021] When the winding end is fixed with multiple tapes, it is preferable that each of the multiple tapes (e.g., tapes 41 and 42 in Fig. 3) has a thickness within the above-mentioned preferred range. Furthermore, the thicknesses of the multiple tapes may be different from each other as long as the effects of the present disclosure are not impaired, but from the viewpoints of reducing cell resistance and ensuring uniformity of surface pressure on the electrode group, it is preferable that the thicknesses of the multiple tapes are approximately the same.

[0022] The width of one tape is, for example, 8 mm or more and 20 mm or less. In this case, the winding end can be stably fixed by the tape. When the winding end is fixed by multiple tapes, the widths of the multiple tapes may be different from each other, but from the viewpoint of reducing internal resistance and uniformity of surface pressure on the electrode group, it is preferable that the widths of the multiple tapes are approximately the same.

[0023] The tape is preferably wound around the electrode assembly so that both ends do not overlap. When the winding end is fixed with multiple tapes, it is preferable that each of the multiple tapes is wound around the electrode assembly so that both ends do not overlap. The length of the tape (the dimension in the longitudinal direction of the strip-shaped tape) is preferably shorter than the outer periphery of the electrode assembly (the outermost periphery of the negative electrode) by 1 mm or more and 7 mm or less. The tape is preferably wound, for example, 0.8 to 0.99 times around the outer periphery of the electrode assembly. In this case, the effect of fixing the electrode assembly is enhanced, stress associated with expansion and contraction of the electrode assembly is easily alleviated, and damage to the positive and negative electrodes (particularly breakage of the negative electrode current collector) associated with expansion and contraction of the electrode assembly is easily suppressed.

[0024] (Exterior Body) 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) made 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, the negative electrode does not have the negative electrode composite layer supported on at least a portion of the region facing the inner side surface of the outer casing at the outermost periphery (the negative electrode current collector is exposed). The negative electrode composite layer may be formed on the surface of the negative electrode current collector facing the positive electrode (positive electrode composite layer). It is preferable that the negative electrode composite layer is not supported on 70% or more (or 80%) or 90% or more of the area of ​​the region facing the inner side surface of the outer casing at the outermost periphery. It is more preferable that the negative electrode composite layer is not supported on the entire region facing the inner side surface of the outer casing at the outermost periphery. For example, the negative electrode composite layer may be supported on the end of the region facing the inner side surface of the outer casing at the outermost periphery 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] 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.

[0029] 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.

[0030] Examples of components of a nonaqueous electrolyte secondary battery are described below, although the secondary battery is not limited to the examples described below.

[0031] (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.

[0032] 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.

[0033] 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).

[0034] 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).

[0035] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0036] 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.

[0037] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0038] 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.

[0039] 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.

[0040] (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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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).

[0047] 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.

[0048] (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.

[0049] (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.

[0050] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0051] 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.

[0052] FIG. 1 is a cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment of the present disclosure. Although a stop tape 40 is wound around the circumferential surface of the electrode group 14, the stop tape 40 is omitted from FIG. 1. FIGS. 2 to 4 are front views illustrating an example of a wound electrode group in which the winding end is secured with tape. FIGS. 2 and 3 are side views of the electrode group, with FIG. 2 being a view from the X1 direction in FIG. 4 and FIG. 3 being a view from the X2 direction in FIG. 4. FIG. 4 is a view of the electrode group from the direction of the winding axis, and a view from the Y direction in FIGS. 2 and 3. The secondary battery according to the present disclosure is not limited to this.

[0053] 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 an outer can 38 having cylindrical sides and a bottom, a sealing plate 31 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. Outer can 38 is a cylindrical case with a bottom made of metal (e.g., SUS). Insulating plates 17 and 18 are disposed within outer can 38 at both ends of electrode group 14.

[0054] 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.

[0055] 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.

[0056] 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 bottom surface of an outer can 38 that also serves as a negative electrode terminal.

[0057] The exterior can 38 accommodates the electrode group 14 and an electrolyte (not shown). The winding end 14e of the electrode group 14 is fixed with at least one insulating tape 40. 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 side surface of the exterior can 38 (the surface of the negative electrode current collector facing the inner side surface of the exterior can 38), the negative electrode composite material layer is not supported, and the negative electrode current collector is exposed. The tape 40 is attached to the negative electrode current collector along the periphery of the outermost peripheral portion 12a. The negative electrode current collector of the outermost peripheral portion 12a to which the tape 40 is attached is in contact with the inner side surface of the exterior can 38.

[0058] The tape 40 includes a first tape 41 and a second tape 42 attached to the negative electrode current collector of the outermost peripheral portion 12a at one end 141 side and the other end 142 side in the winding axis direction of the electrode group 14, respectively. The width A of the negative electrode current collector of the outermost peripheral portion 12a and the combined width B of the first tape and the second tape satisfy the relationship 0.4≦(A−B) / A≦0.65. The first tape 41 has a width B1, and the second tape 42 has a width B2, satisfying B=B1+B2. It is preferable that B1 and B2 are the same. That is, it is preferable that B1=B2=(½)B.

[0059] 2 , when the tape 40 (first tape 41 and second tape 42) is attached to the negative electrode current collector of the outermost peripheral portion 12a along the outer periphery of the outermost peripheral portion 12a, the negative electrode current collector of the outermost peripheral portion 12a is likely to come into contact with the outer can 38 at the center portion 143 in the winding axis direction of the electrode group 14. This makes it possible to more stably fix the winding end portion 14e of the electrode group 14 and also makes it easier to reduce internal resistance.

[0060] The first tape 41 includes a first base layer. The second tape 42 includes a second base layer. The first base layer and the second base layer may be made of the same material or different materials.

[0061] The first tape 41 includes a first adhesive layer disposed on one surface (the surface on the outermost periphery) of the first base layer. The second tape 42 includes a second adhesive layer disposed on one surface (the surface on the outermost periphery) of the second base layer. The first adhesive layer and the second adhesive layer may each be conductive. The first adhesive layer and the second adhesive layer may be made of the same or different materials.

[0062] The tapes 41, 42 are each wrapped around the electrode group 41 so that both ends do not overlap. That is, in the wrapping direction of the tapes 41, 42, there are portions 41a, 42a on the outer circumferential surface of the electrode group 14 where the tapes 41, 42 are not wrapped. The length of the tapes 41, 42 (the dimension in the length direction of the strip-shaped tapes 41, 42) is preferably shorter than the outer circumferential length of the electrode group 14 by 1 mm or more and 7 mm or less. The tapes 41, 42 are preferably wrapped around the outer circumferential surface of the electrode group 14 by, for example, 0.8 to 0.99 revolutions.

[0063] As shown in FIG. 2 , the distance L1 between the tape 41 and one end 141 of the electrode group 14 in the winding axis direction and the distance L2 between the tape 42 and the other end 142 of the electrode group 14 in the winding axis direction may each be, for example, 2 to 5 mm. While L1 and L2 may be different, from the viewpoint of facilitating stable fixation of the electrode group, it is preferable that L1 and L2 are approximately the same. As shown in FIG. 2 , the distance L3 between the tape 41 and the tape 42 is preferably, for example, 18 to 46 mm. In this case, it is easy to ensure a sufficient area for direct contact between the negative electrode current collector of the outermost peripheral portion 12 a and the outer can 38 at the central portion 143 in the winding axis direction of the electrode group 14.

[0064] <<Appendix>> The above description of the embodiments discloses the following technology: (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; a metal exterior body accommodating the electrode group and the electrolyte and having a cylindrical side portion and a bottom portion; at least one insulating tape for fixing a winding end of the electrode group; and a negative electrode lead for connecting the negative electrode to the inner surface of the bottom portion, wherein the negative electrode has an outermost peripheral portion disposed at the outermost periphery of the electrode group, the tape is attached to the negative electrode current collector along the outer periphery of the outermost peripheral portion, the negative electrode current collector at the outermost peripheral portion to which the tape is attached is in contact with the inner surface of the cylindrical side portion, and a width A of the negative electrode current collector at the outermost peripheral portion and a total width B of the tapes satisfy the relational expression: 0.4≦(A−B) / A≦0.65. (Technology 2) The secondary battery according to Technology 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 at least a part of a region of the outermost peripheral portion facing the inner surface of the cylindrical side portion. (Technology 3) The secondary battery according to Technology 1 or 2, wherein the tape comprises a base material layer, and the base material layer contains at least one material selected from the group consisting of polyethylene, polypropylene, and polyimide. (Technology 4) The secondary battery according to any one of Technology 1 to 3, wherein the thickness of the tape is 60 μm or less. (Technology 5) The secondary battery according to any one of Technology 1 to 4, wherein the length of the tape is shorter than the outer periphery of the outermost peripheral portion of the electrode group by 1 mm or more and 7 mm or less. (Technology 6) The secondary battery according to any one of Techniques 1 to 5, wherein the tape includes a first tape and a second tape attached to the outermost negative electrode current collector at one end side and the other end side in the winding axis direction of the electrode group, respectively, and a width A of the outermost negative electrode current collector and a width B of the total of the first tape and the second tape satisfy the relational expression: 0.4≦(A−B) / A≦0.65.

[0065] [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.

[0066] Secondary Batteries E1-E2, R1-R3 (Preparation of Positive Electrode) 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.

[0067] (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 (64 mm wide). One surface of the region that would become the outermost periphery of the negative electrode (the entire region facing the outer can) was left exposed without forming a negative electrode composite layer.

[0068] (Preparation of non-aqueous electrolyte) LiPF 6 was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 3:7). ６ was dissolved in a solution at a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[0069] (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 excluding the outermost periphery). In an inert gas atmosphere, the positive electrode and negative electrode were spirally wound with a polyethylene porous film as a separator therebetween to prepare an electrode assembly.

[0070] (Securing the winding end of the electrode group) The winding end of the electrode group was secured with tape. Specifically, as shown in Figures 2 to 4, a first tape 41 and a second tape 42 were attached to two locations on the outer periphery of the outermost peripheral portion 12a (one end 141 side of the winding shaft and the other end 142 side).

[0071] The width B1 of the first tape 41 and the width B2 of the second tape 42 were each set to B / 2. The width B1 of the first tape 41 and the thickness of the second tape 42 were each set to 30 μm. The first tape 41 and the second tape 42 each included a base layer (thickness 20 μm) and an adhesive layer formed on one surface of the base layer (the surface on the outermost periphery). The base layer was made of polypropylene (PP). The adhesive layer was made of an acrylic adhesive.

[0072] The distance L1 between the first tape 41 and one end 141 of the electrode group 14 in the winding axis direction and the distance L2 between the second tape 42 and the other end 142 of the electrode group 14 in the winding axis direction were each 5 mm. The lengths of the first tape 41 and the second tape 42 were each 2 mm shorter than the length of the outer periphery 14s of the electrode group 14.

[0073] The width A of the outermost periphery of the negative electrode was 64 mm. The width (B / 2) of the first tape 41 and the width (B / 2) of the second tape 42 were changed to obtain the total width B of the tapes shown in Table 1.

[0074] (Assembly of Secondary Battery) A bottomed, cylindrical stainless steel (SUS) outer can having cylindrical sides and a bottom was prepared. The electrode group was housed in the 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 peripheral surface of the electrode group (the outermost negative electrode current collector) to which tape was attached was brought into contact with the inner side surface of the outer can. After injecting a 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 manner, a cylindrical nonaqueous electrolyte secondary battery was fabricated.

[0075] [Evaluation] (External Short Circuit Test) A constant current of 500 mA was charged until the voltage reached 4.2 V to obtain a fully charged secondary battery, 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 side) of the cylindrical battery during the external short circuit was measured using a thermocouple, and the maximum temperature at this time was measured. The results are shown in Table 1. E1 and E2 are examples, and R1 to R3 are comparative examples.

[0076]

[0077] In the batteries E1 and E2 in which (AB) / A was in the range of 0.4 to 0.65, the internal resistance was small and the temperature of the side surface of the battery was low during an external short circuit.

[0078] In battery R1, where (A-B) / A was greater than 0.65, the internal resistance was small, but the short-circuit current flowing from the outermost negative electrode current collector to the side of the exterior body was large, resulting in a high temperature on the side of the battery during an external short circuit.In battery R2, where (A-B) / A was less than 0.4, the resistance between the outermost negative electrode current collector and the side of the exterior body was large, resulting in an increase in internal resistance.

[0079] In Battery R3, the negative electrode current collector at the outermost periphery was almost entirely covered with tape, which increased the internal resistance. 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 exterior housing to which the negative electrode lead was connected.

[0080] The present disclosure can be used in a secondary battery in which a wound electrode group is housed in an exterior body.

[0081] 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.

[0082] 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, 14e: winding end of electrode group, 31: sealing plate, 38: outer can, 40: tape, 41: first tape, 42: second tape

Claims

1. A secondary battery comprising: an electrode group wound with 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; a metal exterior body accommodating the electrode group and the electrolyte and having a cylindrical side and a bottom; at least one insulating tape fixing the end of the winding of the electrode group; and a negative electrode lead connecting the negative electrode to the inner surface of the bottom, wherein the negative electrode has an outermost portion that is positioned at the outermost periphery of the electrode group, the tape is attached to the negative electrode current collector along the outer periphery of the outermost portion, the negative electrode current collector at the outermost portion to which the tape is attached is in contact with the inner surface of the cylindrical side, and a width A of the negative electrode current collector at the outermost portion and a total width B of the tapes satisfy the relational expression: 0.4≦(A−B) / A≦0.

65.

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 at least a portion of the region of the outermost peripheral portion facing the inner surface of the cylindrical side portion.

3. The secondary battery according to claim 1, wherein the tape comprises a substrate layer, and the substrate layer contains at least one material selected from the group consisting of polyethylene, polypropylene, and polyimide.

4. The secondary battery according to claim 1, wherein the thickness of the tape is 60 μm or less.

5. The secondary battery according to claim 1, wherein the length of the tape is shorter than the outer periphery of the outermost portion of the electrode group by a range of 1 mm to 7 mm.

6. The secondary battery according to claim 1, wherein the tape includes a first tape and a second tape attached to the outermost negative electrode current collector at one end side and the other end side in the winding axis direction of the electrode group, respectively, and a width A of the outermost negative electrode current collector and a width B of the combined width of the first tape and the second tape satisfy the relational expression: 0.4≦(A−B) / A≦0.65.

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