Cylindrical secondary battery

Abstract

A battery (10) comprises a wound electrode body (14), an electrolyte, and an exterior can that accommodates the electrode body and the electrolyte. A negative electrode (12) has a both-side mixture layer disposition part (50) in which a negative electrode mixture layer (42) is disposed on both sides of the negative electrode core body (40) in the thickness direction. The both-side mixture layer disposition part (50) includes a thin portion (51), which has a first thickness, and a thick portion (52), which has a second thickness larger than the first thickness. In the negative electrode (12), the thick portion (52) includes a winding inner-side start end facing portion (53) that radially faces a winding start-side start end (11a) of a positive electrode (11) on a winding inner side.

Description

Cylindrical secondary battery

[0001] The present disclosure relates to a cylindrical secondary battery.

[0002] Conventionally, as a cylindrical secondary battery, there is one described in Patent Document 1. This cylindrical secondary battery has a non-opposing portion where the negative electrode provided with a negative electrode mixture layer does not face the positive electrode on the inner side of the winding of the electrode body, and there are two or more turns of the non-opposing portion. By providing the non-opposing portion on the inner side of the winding, this non-aqueous electrolyte secondary battery suppresses deformation on the inner side of the winding of the electrode body.

[0003] Japanese Unexamined Patent Application Publication No. 2013-137946

[0004] In a cylindrical secondary battery, during charging and discharging, the negative electrode expands and contracts in the radial direction. Also, the electrode body may deform around the starting end of the positive electrode where a step occurs along with the expansion and contraction of the negative electrode. When such deformation occurs, the distance between the positive and negative electrodes changes around the starting end, and there is a risk of variation in the self-discharge amount. Therefore, an object of the present disclosure is to provide a cylindrical secondary battery capable of suppressing deformation around the starting end of the positive electrode in the electrode body.

[0005] To solve the above problems, the cylindrical secondary battery according to the present disclosure includes an electrode body in which a positive electrode including a positive electrode core and a positive electrode mixture layer and a negative electrode including a negative electrode core and a negative electrode mixture layer are wound via a separator, an electrolyte, and an exterior can that houses the electrode body and the electrolyte. The negative electrode has a both-side mixture layer arrangement portion where the negative electrode mixture layers are arranged on both sides in the thickness direction of the negative electrode core. The both-side mixture layer arrangement portion includes a thin portion having a first thickness and a thick portion having a second thickness greater than the first thickness. In the negative electrode, a winding inner-side starting-end opposing portion that radially opposes the starting end on the winding start side of the positive electrode on the inner side of the winding is included in the thick portion.

[0006] According to the cylindrical secondary battery according to the present disclosure, deformation around the starting end of the positive electrode in the electrode body can be suppressed.

[0007] This is an axial cross-sectional view of a cylindrical secondary battery according to one embodiment of the present disclosure. (a) is a schematic radial cross-sectional view of the electrode body at the winding start side, and (b) is a schematic cross-sectional view including the thickness direction and radial direction when the positive electrode and negative electrode are unfolded into elongated lengths, and is a schematic cross-sectional view of the area around the starting end of the positive electrode at the winding start side. (a) is a schematic radial cross-sectional view of the electrode body at the winding start side of a cylindrical battery of a reference example, and (b) is a schematic cross-sectional view including the thickness direction and radial direction when the positive electrode and negative electrode of a cylindrical battery of a reference example are unfolded into elongated lengths, and is a schematic cross-sectional view of the area around the starting end of the positive electrode at the winding start side. This is a schematic cross-sectional view of the area around the starting end of the positive electrode corresponding to Figure 2(b) in the first modified cylindrical secondary battery. This is a schematic cross-sectional view of the area around the starting end of the positive electrode corresponding to Figure 2(b) in the second modified cylindrical secondary battery. This is a schematic cross-sectional view of the area around the starting end of the positive electrode corresponding to Figure 2(b) in the third modified cylindrical secondary battery. This is a schematic cross-sectional view of the area around the starting end of the positive electrode corresponding to Figure 2(b) in the fourth modified cylindrical secondary battery.

[0008] Hereinafter, embodiments of the cylindrical secondary battery according to this disclosure will be described in detail with reference to the drawings. The cylindrical secondary battery of this disclosure may be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. In the following, a cylindrical lithium-ion secondary battery is given as an example of one embodiment of the cylindrical secondary battery 10, but the cylindrical secondary battery of this disclosure is not limited to this.

[0009] It is intended from the outset that new embodiments can be constructed by appropriately combining the characteristic features of the embodiments and modifications described below. In the following embodiments, the same reference numerals are used for the same components in the drawings, and redundant explanations are omitted. In addition, multiple drawings include schematic diagrams, and the dimensional ratios such as length, width, and height of each component do not necessarily match between different drawings. In this specification, the axial (height direction) sealing body 19 side of the cylindrical secondary batteries 10, 110, 210, 310, and 410 is referred to as "upper," and the axial bottom 20A side of the outer casing 20 is referred to as "lower." Also, in the following description, the radial direction is the radial direction of the cylindrical secondary battery 10 and coincides with the radial direction of the outer casing 20. Among the components described below, components that are not described in the independent claim indicating the highest-level concept are optional components and are not essential components.

[0010] Figure 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to one embodiment of the present disclosure. As shown in Figure 1, the cylindrical secondary battery (hereinafter simply referred to as "battery") 10 comprises an electrode body 14, a non-aqueous electrolyte, an outer casing 20 housing the electrode body 14 and the non-aqueous electrolyte, and a sealing body 19 that closes an opening located at the upper end of the outer casing 20 via an annular gasket 24. The gasket 24 is preferably made of an insulating material with excellent compressibility and resistance, such as PP (polypropylene), PPS (polyphenylene sulfide), PFA (perfluoroalkoxyalkane), or PPT (polypropylene terephthalate). In the example shown in Figure 1, the outer casing 20 has a bottomed cylindrical shape, but the outer casing may have openings at both the upper and lower ends, and each opening may be closed by one or more members.

[0011] The electrode body 14 includes a long positive electrode 11, a long negative electrode 12, and two long separators 13 interposed between the positive electrode 11 and the negative electrode 12, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound around the separators 13. The negative electrode 12 is formed to be slightly larger in dimensions than the positive electrode 11. The negative electrode 12 is formed to be longer than the positive electrode 11 in the winding direction and in the axial direction. The two separators 13 are formed to be slightly larger in dimensions than the positive electrode 11 and are arranged to sandwich the positive electrode 11. The separators 13 protrude above and below the positive electrode 11 and the negative electrode 12.

[0012] Non-aqueous electrolytes are ionic conductive (e.g., lithium ion conductive). Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes. Liquid electrolytes (electrolytes) contain a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. Non-aqueous solvents may contain halogen-substituted compounds (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in these solvents are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0013] As solid electrolytes, for example, solid or gel-like polymer electrolytes, inorganic solid electrolytes, etc., are used. Polymer electrolytes include, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As matrix polymers, for example, polymer materials that absorb non-aqueous solvents and gel are used. As polymer materials, for example, fluororesins, acrylic resins, polyether resins, etc., are used. As inorganic solid electrolytes, for example, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0014] The positive electrode 11 has a positive electrode core 30 (see Figure 2) and positive electrode mixture layers 32 (see Figure 3) formed on both sides of the positive electrode core 30. The positive electrode core 30 can be made of a metal foil that is stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The positive electrode mixture layers 32 contain a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 is manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core 30, drying the coating film, and then compressing it to form the positive electrode mixture layers 32 on both sides of the positive electrode core 30.

[0015] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. A preferred example of a lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0016] Examples of conductive agents included in the positive electrode mixture layer 32 include carbon black such as acetylene black and Ketjen black, and carbon materials such as graphite. Examples of binders included in the positive electrode mixture layer 32 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0017] The negative electrode 12 has a negative electrode core 40 (see Figure 2) and negative electrode mixture layers 42 (see Figure 2) formed on both sides of the negative electrode core 40. The negative electrode core 40 can be made of a metal foil that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on its surface. The negative electrode mixture layers 42 contain a negative electrode active material and a binder. The negative electrode 12 is manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layers 42 on both sides of the negative electrode core 40.

[0018] Generally, carbon materials that reversibly intercalate and release lithium ions are used as the negative electrode active material. Preferred carbon materials are graphite such as natural graphite such as flake graphite, lump graphite, and earthy graphite, and artificial graphite such as lump graphite and graphitized mesophase carbon microbeads. The negative electrode mixture layer 42 may contain a silicon (Si) material as the negative electrode active material. In addition, metals other than Si that alloy with lithium, alloys containing such metals, compounds containing such metals, etc., may be used as the negative electrode active material.

[0019] The binder contained in the negative electrode mixture layer 42 may be fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, etc., as in the case of the positive electrode 11, but preferably styrene-butadiene rubber (SBR) or a modified version thereof is used. In addition to SBR, the negative electrode mixture layer 42 may also contain CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, etc.

[0020] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of the separator 13 is preferably polyethylene, polyolefin resins such as polypropylene, or cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0021] An upper insulating plate 15 is positioned above the electrode body 14, and an annular lower insulating plate 16 is positioned below the electrode body 14. In the example shown in Figure 1, a positive electrode lead 17 attached to the radially intermediate portion of the positive electrode 11 extends through a through hole in the upper insulating plate 15 towards the sealing body 19 and is connected to the lower surface of the sealing body 19 by welding or the like. On the other hand, a negative electrode lead 18 attached to the winding start side of the negative electrode 12 extends through a through hole in the lower insulating plate 16 towards the bottom 20A of the outer can 20 and is connected to the inner surface of the bottom 20A by welding or the like. To effectively suppress short circuits, it is preferable that the area around the joint where the positive electrode lead 17 is joined to the positive electrode 11 is covered with insulating tape (not shown), and it is preferable that the area around the joint where the negative electrode lead 18 is joined to the negative electrode 12 is covered with insulating tape 70 (see Figure 2(a)). Here, these insulating tapes are made of insulating materials, for example, a polyimide film may form the base material and silicone may form the adhesive material.

[0022] The negative electrode 12 has a negative electrode core exposed portion 40a at the end of the winding where the negative electrode mixture layer 42 is not provided and the negative electrode core body 40 is exposed. The outer surface of the winding of the negative electrode core exposed portion 40a constitutes the outermost outer surface of the electrode body 14 and contacts the inner surface of the outer casing 20. By electrically connecting the winding start and end ends of the negative electrode 12 in the negative electrode longitudinal direction to the outer casing 20 in this way, the negative electrode current path is shortened and the electrical resistance is reduced. The sealing body 19 to which the positive electrode lead 17 is connected becomes the positive electrode terminal, and the outer casing 20 to which the negative electrode lead 18 and the negative electrode core exposed portion 40a are connected becomes the negative electrode terminal.

[0023] A gasket 24 is provided between the outer casing 20 and the sealing body 19 to ensure airtightness inside the battery and insulation between the outer casing 20 and the sealing body 19. The outer casing 20 has a cylindrical portion 20B and a bottom portion 20A, and the cylindrical portion 20B includes an annular grooved portion 28 and an annular shoulder portion 29. The grooved portion 28 is formed by spinning a part of the cylindrical portion 20B to create a recess radially inward. On the other hand, the shoulder portion 29 is formed when the upper end of the cylindrical portion 20B is bent radially inward and crimped to the flange portion (peripheral edge) 31 of the sealing body 19, and extends radially inward. The sealing body 19 is fixed to the outer casing 20 by being sandwiched between the shoulder portion 29 and the grooved portion 28 via the gasket 24 through crimping.

[0024] The sealing body 19 is equipped with a current interruption mechanism. The sealing body 19 has a structure in which a metal terminal plate 21, an annular insulating plate 23, and a metal rupture plate 22 are stacked in order from the electrode body 14 side. The rupture plate 22 constitutes a valve body and is positioned opposite the terminal plate 21 with the insulating plate 23 in between. The insulating plate 23 has an opening 23A in its radial center and a ventilation hole 23B is provided in the portion that overlaps with the ventilation hole 21C of the terminal plate 21.

[0025] The rupture plate 22 has a valve portion 22A on its radially central side that ruptures as the internal pressure of the battery increases. The terminal plate 21 has an annular portion 21A and a central portion 21B that is connected to the radially inward end of the annular portion 21A and is located in the radially central part. The central portion 21B has a disc shape and is thinner than the annular portion 21A.

[0026] The valve portion 22A is joined to the central portion 21B of the terminal board 21 by welding or the like through an opening 23A in the insulating plate 23. The valve portion 22A includes a projection 33 located in the radial center and projecting downward, and a thin-walled portion 34 located radially outside the projection 33. The thickness of the thin-walled portion 34 decreases as it extends radially outward. Because the thickness of the thin-walled portion 34 decreases as it extends radially outward, an annular space 39 is provided below the thin-walled portion 34. The insulating plate 23 is positioned radially outside the projection 33 so as to surround the projection 33 around its entire circumference. The insulating plate 23 includes a portion located between the rupture plate 22 and the terminal board 21.

[0027] The rupture plate 22 holds the insulating plate 23, and the insulating plate 23 holds the terminal plate 21. Specifically, the rupture plate 22 includes an annular thickened portion 35 connected to the radially outward end of the thinned portion 34, and the thickened portion 35 has an annular projection 37 that protrudes downward. The outer circumferential surface of the insulating plate 23 is fitted and fixed to the inner circumferential surface of the annular projection 37. The insulating plate 23 also has an annular projection 38 that protrudes downward on the outer circumferential side, and the inner circumferential surface of the annular projection 38 is fitted and fixed to the outer circumferential surface of the terminal plate 21. The insulating plate 23 includes a clamping portion that is sandwiched radially between the annular projection 37 and the terminal plate 21. The ventilation hole 21C is provided in the annular portion 21A. The positive lead 17 is joined to the lower surface of the annular portion 21A. The terminal board 21 to which the positive lead 17 is connected and the rupture plate 22 are electrically connected, thereby forming a current path from the electrode body 14 to the rupture plate 22.

[0028] In the above configuration, when the battery 10 overheats and the internal pressure rises, the valve portion 22A inverts so that it becomes convex axially upward, using the radially outward annular end 22B, which has low rigidity in the thin-walled portion 34, as a fulcrum. Simultaneously with this inversion, the central portion 21B is separated from the annular portion 21A or detaches from the valve portion 22A. Since the valve portion 22A is insulated from the annular portion 21A by the insulating plate 23, the current path is interrupted by this inversion. This interruption suppresses the overheating of the battery 10. If the internal pressure of the battery rises further, the annular end 22B of the thin-walled portion 34 breaks, forming a gas outlet. As a result, high-temperature gas and molten material are discharged outside the battery 10, and the battery 10 becomes safe.

[0029] The case described above includes a terminal plate 21, a rupture plate 22, and an insulating plate 23 located between them. However, the sealing body may also have a laminated structure including two rupture plates (lower valve body and upper valve body) and an annular insulating plate sandwiched between the two rupture plates, and may further include a convex terminal cap covering the two rupture plates. Alternatively, the sealing body may consist only of rupture plates. Or, the sealing body may not have rupture plates, and the bottom of the outer casing may have a thin, easily breakable portion that breaks when the battery overheats abnormally.

[0030] In the example shown in Figure 1, the battery 10 has one positive electrode lead 17 extending from an intermediate part, such as the radial center of the electrode body 14, toward the sealing body 19. However, the battery may also have a plurality of positive electrode leads that electrically connect the positive electrode of the electrode body to the sealing body, and one end of each of the plurality of positive electrode leads may be joined to the positive electrode at intervals from each other in the longitudinal direction of the positive electrode.

[0031] In this case, the reduction in electrical resistance is greatly increased by effectively shortening the positive electrode current path, so it is preferable for the battery to have four or more positive electrode leads, and even more preferable for it to have eight or more positive electrode leads. Also, when the battery has three or more positive electrode leads, the reduction in electrical resistance is greatly increased by effectively shortening the positive electrode current path, so it is preferable that the centers of the three or more positive electrode leads in the longitudinal direction of the positive electrode are arranged at approximately equal intervals in the longitudinal direction of the positive electrode. Furthermore, one end of the electrode body in the axial direction may be composed of a strip-shaped positive electrode core exposed portion, and this positive electrode core exposed portion may be joined to the positive electrode current collector plate. The positive electrode may then be electrically connected to the sealing body based on the electrical connection of the positive electrode core exposed portion to the positive electrode current collector plate.

[0032] The battery 10 has one negative electrode lead 18 extending from the radial winding start end of the electrode body 14 toward the bottom 20A, and the exposed negative electrode core 40a is in contact with the outer casing 20. However, regardless of whether the exposed negative electrode core 40a is in contact with the outer casing 20 or not, the battery may have a plurality of negative electrode leads that electrically connect the negative electrode of the electrode body to the bottom of the outer casing, with one end of each of the plurality of negative electrode leads joined to the negative electrode at intervals in the longitudinal direction of the negative electrode, and the other ends of the plurality of negative electrode leads joined to the bottom of the outer casing. Alternatively, regardless of whether the exposed negative electrode core 40a is in contact with the outer casing 20 or not, one axial end of the electrode body may be composed of a strip-shaped exposed negative electrode core, and this exposed negative electrode core may be joined to the upper surface of the negative electrode current collector plate by laser welding or the like. The lower surface of the negative electrode current collector plate may then be electrically connected to the bottom of the outer casing by laser welding or the like, thereby electrically connecting the negative electrode to the outer casing. Furthermore, although the case in which the positive electrode is electrically connected to the sealing body and the negative electrode is electrically connected to the outer can has been described, the negative electrode may also be electrically connected to the sealing body and the positive electrode may be electrically connected to the outer can.

[0033] Figure 2(a) is a schematic radial cross-sectional view of the starting end of the electrode body 14. Figure 2(b) is a schematic cross-sectional view including the thickness direction and radial direction when the positive electrode 11 and negative electrode 12 are unfolded into elongated lengths, and is a schematic cross-sectional view of the area around the starting end of the winding of the positive electrode 11. Note that the separator 13 is not shown in Figure 2(a) and subsequent figures, and the insulating tape 70 is not shown in Figures 1, 2(b), 3(b), and 4 to 7.

[0034] As shown in Figure 2, the negative electrode 12 has a double-sided compound layer arrangement portion 50 in which negative electrode compound layers 42 are arranged on both sides of the negative electrode core body 40. The double-sided compound layer arrangement portion 50 includes a thin-walled portion 51 having a first thickness and a thick-walled portion 52 having a second thickness greater than the first thickness. In the negative electrode 12, the inner-winding start end opposing portion 53, which is radially opposed to the starting end 11a on the winding start side of the positive electrode 11 on the winding start side, is included in the thick-walled portion 52. The thick-walled portion 52 has a non-opposing portion 55 that is located closer to the winding start side than the inner-winding start end opposing portion 53 and does not radially oppose the positive electrode 11.

[0035] Next, the effects of the battery 10 according to this disclosure will be explained. Figure 3(a) is a schematic radial cross-sectional view of the starting side of the winding of the electrode body 514 of a cylindrical battery (hereinafter simply referred to as "battery") 510 of a reference example. Figure 3(b) is a schematic cross-sectional view including the thickness direction and radial direction when the positive electrode 11 and negative electrode 512 of the cylindrical battery 510 are unfolded into an elongated shape, and is a schematic cross-sectional view of the area around the starting end on the winding side of the positive electrode 11. The battery 510 has a double-sided compound layer arrangement portion 550 in which negative electrode compound layers 542 are arranged on both sides in the thickness direction of the negative electrode core body 40, and the thickness of the double-sided compound layer arrangement portion 550 is substantially constant and is substantially the same as the first thickness of the battery 10.

[0036] In cylindrical secondary batteries, the negative electrode expands and contracts radially during charging and discharging. Against this backdrop, if the thickness of the compound layer arrangement portion 550 on both sides is approximately constant, as in battery 510, the negative electrode 512 is subjected to a radial compressive force when it expands. As a result, the area around the inner-winding start end opposing portion 553 of the negative electrode 512, which is radially opposed to the start end 11a on the winding side, tends to bend radially outward towards the space R on the winding start side of the start end 11a, indicated by arrow A, near the inner-winding corner portion 11b of the start end 11a where a step occurs, and deformation can occur around the start end 11a. When such deformation occurs, the distance between the positive and negative electrodes changes around the start end, which may cause variations in the amount of self-discharge.

[0037] In contrast, according to the battery 10 of this disclosure, the inner-winding start end opposing portion 53 of the negative electrode 12, which is radially opposed to the start end 11a on the winding side, is included in the thickened portion 52, resulting in increased rigidity. Therefore, deformation around the start end 11a of the negative electrode 12 due to expansion and contraction of the negative electrode 12 is suppressed, and the high roundness of the electrode body 14 is easily maintained over a long period of time. As a result, the distance between the positive and negative electrodes does not change easily around the start end 11a, so variations in the amount of self-discharge can be reduced.

[0038] Furthermore, the inner starting end opposing portion 53 of the negative electrode 12, located on the winding start side of the electrode body 14, is included in the thickened portion 52, resulting in increased rigidity. Therefore, even if the negative electrode 12 repeatedly expands and contracts, deformation of the winding start side of the electrode body 14 is suppressed. Consequently, deformation of the hollow portion 14A of the electrode body 14 (see Figures 1 and 2(a)), which serves as an exhaust path for high-temperature gases during abnormal overheating of the battery 10, is suppressed. This allows for smooth exhaust of high-temperature gases during abnormal overheating of the battery 10, thereby increasing the safety of the battery 10.

[0039] It is preferable that the thickened portion 52 includes a portion that extends continuously from the inner side starting end opposing portion 53 to a point 5 mm towards the end of the winding, in order to effectively suppress deformation around the starting end 11a of the electrode body 14, and it is even more preferable that the thickened portion 52 includes a portion that extends continuously from the inner side starting end opposing portion 53 to a point 10 mm towards the end of the winding. Furthermore, it is most preferable that the thickened portion 52 includes a portion that extends continuously from the inner side starting end opposing portion 53 to a point 15 mm towards the end of the winding, in order to further effectively suppress deformation around the starting end 11a of the electrode body 14.

[0040] In other words, the dimension indicated by a1 in Figure 2(b) is preferably 5 mm or more, more preferably 10 mm or more, and most preferably 15 mm or more. Furthermore, deformation around the outer end facing portion (indicated by 57 in Figure 2(a)) that is radially opposed to the starting end on the winding side of the positive electrode at the negative electrode can be effectively suppressed, and it is easier to maintain a state of high roundness around the positive electrode starting end of the electrode body 14 for a longer period of time. Therefore, it is preferable that the thickened portion includes a portion that exists continuously from the inner end facing portion (indicated by 53 in Figure 2(a)) to a portion beyond the outer end facing portion, and it is preferable that the outer end facing portion is included in the thickened portion.

[0041] It is preferable that the maximum thickness b1 of the thick-walled portion 52 (maximum value of the second thickness) is 105% or more of the minimum thickness c1 of the thin-walled portion 51 (minimum value of the first thickness), as this effectively suppresses deformation around the starting end 11a of the electrode body 14. Furthermore, it is preferable that the maximum thickness b1 of the thick-walled portion 52 is 130% or less of the minimum thickness c1 of the thin-walled portion 51, as this makes it easier to achieve high roundness of the electrode body 14 and effectively suppresses variations in the amount of self-discharge.

[0042] If there is a stepped portion between the thick portion and the thin portion of the negative electrode, the positive electrode may get caught on the stepped portion and break. Since it becomes difficult for the positive electrode 11 to get caught on the negative electrode 12, it is preferable that the thick portion 52 has a thickness gradient portion 59 (see FIG. 2) whose thickness gradually increases from the winding end side toward the winding start side. In the example shown in FIG. 2, both the negative electrode mixture layer 42a disposed on the inner side of the winding of the negative electrode core 40 and the negative electrode mixture layer 42b disposed on the inner side of the winding of the negative electrode core 40 have thickness gradient portions 59a and 59b that are substantially symmetric in the thickness direction. However, regarding the thick portion, only one of the negative electrode mixture layer disposed on the inner side of the winding and the negative electrode mixture layer disposed on the inner side of the winding of the negative electrode core may have a thickness gradient portion whose thickness gradually increases from the winding end side toward the winding start side.

[0043] If the density of the negative electrode mixture layer 42 in the thick portion 52 is substantially the same as the density of the negative electrode mixture layer 42 in the thin portion 51, the electrode body 14 of the present disclosure can be easily manufactured by simply applying (disposing) a thick negative electrode mixture slurry at the location where the thick portion 52 is provided. In addition, the mass of the negative electrode mixture layer disposed per unit area of the negative electrode core in the thick portion may be substantially the same as the mass of the negative electrode mixture layer disposed per unit area of the negative electrode core in the thin portion. In this case, the material cost of the negative electrode mixture layer can be reduced.

[0044] The present disclosure is not limited to the above-described embodiments and their modified examples, and various improvements and modifications are possible within the scope of the matters described in the claims of the present application and their equivalent scope. For example, in the above-described embodiment, the thick portion 52 had a thickness gradient portion 59 whose thickness gradually increased toward the winding start side. However, as shown in FIG. 4, the negative electrode 112 of the battery 110 has both-side mixture layer disposed portions 150 in which negative electrode mixture layers 142 are disposed on both sides in the thickness direction of the negative electrode core 40, and the both-side mixture layer disposed portions 150 may include a thin portion 151 having a first thickness and a thick portion 152 having a second thickness thicker than the first thickness. And the thickness of the thick portion 152 may be substantially constant, or the thick portion 152 may be continuous with the thin portion 151 via a stepped portion.

[0045] Of the negative electrode 112, the inner-winding start end opposing portion 153 that is radially opposite to the start end 11a of the positive electrode 11 on the winding side is included in the thickened portion 152. The thickened portion 152 has a non-opposing portion 155 located closer to the winding start side than the start end 11a. In this case as well, deformation around the start end 11a of the electrode body 114 can be suppressed even more effectively, so the longitudinal distance of the negative electrode shown as a2 in Figure 4, that is, the length of the portion of the thickened portion 152 that is continuously present from the inner-winding start end opposing portion 153 towards the winding end side, is preferably 5 mm or more, more preferably 10 mm or more, and most preferably 15 mm or more.

[0046] Furthermore, even in this case, it is preferable that the thickened portion 152 includes a portion that is continuously present from the inner starting end opposing portion 153 to the outer starting end opposing portion that radially opposes the starting end 11a of the positive electrode 11 on the outer side, as this makes it easier to maintain a high degree of roundness around the positive electrode starting end of the electrode body 14 over the long term. Also, even in this case, it is preferable that the maximum thickness (maximum value of the second thickness) b2 of the thickened portion 152 is 105% or more of the minimum thickness (minimum value of the first thickness) c2 of the thinned portion 151, as this effectively suppresses deformation around the starting end 11a of the electrode body 114. Furthermore, it is preferable that the maximum thickness b2 of the thickened portion 152 is 130% or less of the minimum thickness c2 of the thinned portion 151, as this makes it easier to maintain a high degree of roundness around the positive electrode starting end of the electrode body 114.

[0047] In the battery 110, at the winding inner side start end facing portion 153, the thickness of the negative electrode mixture layer 152a disposed on the winding outer surface of the negative electrode core 40 was substantially the same as the thickness of the negative electrode mixture layer 152b disposed on the winding inner surface of the negative electrode core 40. However, as shown in FIG. 5, the negative electrode 212 of the battery 210 has a both-side mixture layer arrangement portion 250 in which negative electrode mixture layers 242 are disposed on both sides in the thickness direction of the negative electrode core 40, and the both-side mixture layer arrangement portion 250 may include a thin portion 251 having a first thickness and a thick portion 252 having a second thickness greater than the first thickness. Also, the winding inner side start end facing portion 253 that radially faces the start end 11a of the positive electrode 11 on the winding inner side among the negative electrode 212 may be included in the thick portion 252. And at the winding inner side start end facing portion 253, the thickness of the negative electrode mixture layer 252a disposed on the winding outer surface of the negative electrode core 40 may be different from the thickness of the negative electrode mixture layer 252b disposed on the winding inner surface of the negative electrode core 40, and as shown in FIG. 5, the thickness of the negative electrode mixture layer 252a may be greater than the thickness of the negative electrode mixture layer 252b.

[0048] Alternatively, as shown in FIG. 6, the negative electrode 312 of the battery 310 has a both-side mixture layer arrangement portion 350 in which negative electrode mixture layers 342 are disposed on both sides in the thickness direction of the negative electrode core 40, and the both-side mixture layer arrangement portion 350 may include a thin portion 351 having a first thickness and a thick portion 352 having a second thickness greater than the first thickness. Also, the winding inner side start end facing portion 353 that radially faces the start end 11a of the positive electrode 11 on the winding inner side among the negative electrode 312 may be included in the thick portion 352. And at the winding inner side start end facing portion 353, the thickness of the negative electrode mixture layer 352a disposed on the winding outer surface of the negative electrode core 40 may be smaller than the thickness of the negative electrode mixture layer 252b disposed on the winding inner surface of the negative electrode core 40.

[0049] Alternatively, as shown in FIG. 7, the negative electrode 412 of the battery 410 has a both-side mixture layer arrangement portion 450 in which negative electrode mixture layers 442 are disposed on both sides in the thickness direction of the negative electrode core 40, and the both-side mixture layer arrangement portion 450 may include a thin portion 451 having a first thickness and a thick portion 452 having a second thickness greater than the first thickness. Also, the winding inner side start end facing portion 453 that radially faces the start end 11a of the positive electrode 11 on the winding inner side among the negative electrode 412 may be included in the thick portion 452. And a plurality of thick portions 452 may be provided at intervals in the negative electrode longitudinal direction.

[0050] In this case, as shown in Figure 7, the thickness of the negative electrode mixture layer 452a arranged on the outer surface of the negative electrode core 40 changes at positions in the longitudinal direction of the negative electrode, while the thickness of the negative electrode mixture layer 452b arranged on the inner surface of the negative electrode core 40 may be substantially constant. Alternatively, when multiple thickened sections are provided at intervals in the longitudinal direction of the negative electrode, the thickness of the negative electrode mixture layer arranged on the outer surface of the negative electrode core may be substantially constant at positions in the longitudinal direction of the negative electrode, while the thickness of the negative electrode mixture layer arranged on the inner surface of the negative electrode core may change at positions in the longitudinal direction of the negative electrode. Alternatively, when multiple thickened sections are provided at intervals in the longitudinal direction of the negative electrode, both the thickness of the negative electrode mixture layer arranged on the outer surface of the negative electrode core and the thickness of the negative electrode mixture layer arranged on the inner surface of the negative electrode core may change at positions in the longitudinal direction of the negative electrode. Even in the modified examples shown in Figures 5 to 7, deformation around the starting end 11a of the positive electrode 11 in the electrode bodies 214, 314, and 414 can be suppressed.

[0051] Furthermore, the cylindrical secondary battery of this disclosure may have the following configurations: Configuration 1: A cylindrical secondary battery comprising an electrode body in which a positive electrode including a positive electrode core and a positive electrode mixture layer and a negative electrode including a negative electrode core and a negative electrode mixture layer are wound with a separator, an electrolyte, and an outer casing for housing the electrode body and the electrolyte, wherein the negative electrode has double-sided mixture layer arrangement portions in which the negative electrode mixture layer is arranged on both sides in the thickness direction of the negative electrode core, the double-sided mixture layer arrangement portions include a thin-walled portion having a first thickness and a thick-walled portion having a second thickness greater than the first thickness, and the thick-walled portion includes an inner-winding start end opposing portion that is radially opposed to the starting end on the winding start side of the positive electrode on the winding start side. Configuration 2: The cylindrical secondary battery according to Configuration 1, wherein the thick-walled portion includes a portion that exists continuously from the inner-winding start end opposing portion to a location 5 mm towards the winding end. Configuration 3: The cylindrical secondary battery according to Configuration 2, wherein the thickened portion includes a portion that extends continuously from the inner starting end opposing portion to a point located 10 mm towards the end of the winding. Configuration 4: The cylindrical secondary battery according to any one of Configurations 1 to 3, wherein the thickened portion includes a portion that extends continuously from the inner starting end opposing portion to a point beyond the outer starting end opposing portion that is radially opposite to the starting end on the outer side of the negative electrode. Configuration 5: The cylindrical secondary battery according to any one of Configurations 1 to 4, wherein the maximum value of the second thickness is 105% or more of the minimum value of the first thickness. Configuration 6: The cylindrical secondary battery according to any one of Configurations 1 to 5, wherein at the inner starting end opposing portion, the thickness of the negative electrode mixture layer arranged on the outer surface of the negative electrode core body is different from the thickness of the negative electrode mixture layer arranged on the inner surface of the negative electrode core body. Configuration 7: The cylindrical secondary battery according to any one of Configurations 1 to 6, wherein the thickened portion is provided in multiple locations at intervals in the longitudinal direction of the negative electrode. Configuration 8: A cylindrical secondary battery according to any one of Configurations 1 to 7, wherein the thick-walled portion includes a thickness gradient portion in which the thickness gradually increases from the end of winding to the beginning of winding. Configuration 9: A cylindrical secondary battery according to any one of Configurations 1 to 8, wherein the mass of the negative electrode mixture layer arranged per unit area of ​​the negative electrode core in the thick-walled portion is substantially the same as the mass of the negative electrode mixture layer arranged per unit area of ​​the negative electrode core in the thin-walled portion.Configuration 10: A cylindrical secondary battery according to any one of Configurations 1 to 8, wherein the density of the negative electrode mixture layer in the thick-walled portion is substantially the same as the density of the negative electrode mixture layer in the thin-walled portion.

[0052] 10, 110, 210, 310, 410 Cylindrical secondary battery, 11 Positive electrode, 11a Starting end, 11b Inner corner of winding, 12, 112, 212, 312, 412 Negative electrode, 13 Separator, 14, 114, 214, 314, 414 Electrode body, 14A Hollow section, 15 Upper insulating plate, 16 Lower insulating plate, 17 Positive electrode lead, 18 Negative electrode lead, 19 Sealing body, 20 Outer can, 20A Bottom section, 20B Cylindrical section, 21 Terminal plate, 21A Annular section, 21B Central section, 21C Ventilation hole, 22 Rupture plate, 22A Valve section, 22B Annular end section, 23 Insulating plate, 23A Opening, 23B Ventilation hole, 24 Gasket, 28 Grooved portion, 29 Shoulder portion, 30 Positive electrode core, 32 Positive electrode mixture layer, 33 Protruding portion, 34 Thin-walled portion, 35 Thick-walled portion, 37, 38 Annular protruding portion, 39 Space, 40 Negative electrode core, 40a Negative electrode core exposed portion, 42, 42a, 42b, 142, 242, 252a, 252b, 342, 352a, 352b, 442, Negative electrode mixture layer, 50, 150, 250, 350, 450 Mixture layer arrangement portion on both sides, 51, 151, 251, 351, 451 Thin-walled portion of mixture layer arrangement portion on both sides 52, 152, 152a, 152b, 252, 352, 452 Thickened portion of the compound layer arrangement on both sides, 53, 153, 253, 353, 453 Opposing portion of the starting end on the inside of the winding, 55, 155 Non-opposing portion, 59, 59a, 59b Thickness gradient portion, 70 Insulating tape.

Claims

1. A cylindrical secondary battery comprising: an electrode body in which a positive electrode including a positive electrode core and a positive electrode mixture layer and a negative electrode including a negative electrode core and a negative electrode mixture layer are wound with a separator in between; an electrolyte; and an outer container housing the electrode body and the electrolyte, wherein the negative electrode has double-sided mixture layer arrangement portions in which the negative electrode mixture layer is arranged on both sides in the thickness direction of the negative electrode core, the double-sided mixture layer arrangement portions include a thin-walled portion having a first thickness and a thick-walled portion having a second thickness greater than the first thickness, and in the negative electrode, a winding-side starting end opposing portion that is radially opposed to the starting end on the winding-starting side of the positive electrode is included in the thick-walled portion.

2. The cylindrical secondary battery according to claim 1, wherein the thickened portion includes a portion that is continuously present from the portion opposite the inner starting end of the winding to a portion located 5 mm towards the end of the winding.

3. The cylindrical secondary battery according to claim 2, wherein the thickened portion includes a portion that is continuously present from the portion opposite the inner starting end of the winding to a portion located 10 mm towards the end of the winding.

4. The cylindrical secondary battery according to claim 1, wherein the thickened portion includes a portion that is continuously present from the portion facing the inner starting end on the inside of the winding to a portion that extends beyond the portion facing the outer starting end on the outside of the winding that is radially opposite to the starting end on the outside of the winding at the negative electrode.

5. The cylindrical secondary battery according to any one of claims 1 to 4, wherein the maximum value of the second thickness is 105% or more of the minimum value of the first thickness.

6. The cylindrical secondary battery according to any one of claims 1 to 4, wherein, in the portion facing the inner starting end of the winding, the thickness of the negative electrode mixture layer arranged on the outer surface of the winding of the negative electrode core body is different from the thickness of the negative electrode mixture layer arranged on the inner surface of the winding of the negative electrode core body.

7. The cylindrical secondary battery according to any one of claims 1 to 4, wherein the thickened portions are provided in multiple locations at intervals in the longitudinal direction of the negative electrode.

8. The cylindrical secondary battery according to any one of claims 1 to 4, wherein the thickened portion includes a thickness gradient portion in which the thickness gradually increases from the end of the winding to the beginning of the winding.

9. The cylindrical secondary battery according to any one of claims 1 to 4, wherein the mass of the negative electrode mixture layer disposed per unit area of ​​the negative electrode core in the thick-walled portion is substantially the same as the mass of the negative electrode mixture layer disposed per unit area of ​​the negative electrode core in the thin-walled portion.

10. The cylindrical secondary battery according to any one of claims 1 to 4, wherein the density of the negative electrode mixture layer in the thick-walled portion is substantially the same as the density of the negative electrode mixture layer in the thin-walled portion.

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