Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery includes: an electrode body (14) in which a positive electrode (11) and a negative electrode (12) are wound with a separator (13) therebetween; and an outer can that accommodates the electrode body (14). The negative electrode (12) includes a negative electrode core body (30) and a mixture layer (32) that is provided on at least one surface of the negative electrode core body (30) and that contains an active material. The negative electrode (12) has a negative electrode winding-start-side end portion (12a) that is positioned closer to the winding-start side than a positive electrode start end (B1) serving as a winding-start-side end of the positive electrode (11). The negative electrode winding-start-side end portion (12a) has: two outer surfaces (S1, S2) that are provided on at least one surface, away from each other in the winding direction of the negative electrode (12) and that are formed of the mixture layer; and recesses (50, 51) that are sandwiched between the two outer surfaces (S1, S2) and that are recessed toward the negative electrode core body (30) from the respective outer surfaces (S1, S2).

Description

Nonaqueous Electrolyte Secondary Battery

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

[0002] Conventionally, there is a nonaqueous electrolyte secondary battery described in Patent Document 1. This nonaqueous electrolyte secondary battery includes an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. In this nonaqueous electrolyte secondary battery, of the negative electrode, there is provided a negative electrode winding start side end portion located on the winding start side relative to a positive electrode starting end that is the winding start side end of the positive electrode.

[0003] International Publication No. 2018 / 180748

[0004] On the other hand, as in the configuration described in Patent Document 1, when a negative electrode winding start side end portion located on the winding start side relative to the positive electrode starting end is provided in the negative electrode, expansion of the electrode plate due to charge and discharge causes stress concentration in the vicinity of the positive electrode starting end at the negative electrode winding start side end portion, which may lead to electrode plate deformation such as buckling. As a result, the positive electrode starting end abuts against the portion where the electrode plate deformation has occurred via the separator, and breakage of the separator may cause a voltage drop.

[0005] Accordingly, an object of the nonaqueous electrolyte secondary battery of the present disclosure is to suppress electrode plate deformation of the negative electrode that causes a voltage drop.

[0006] A nonaqueous electrolyte secondary battery according to the present disclosure includes: an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator interposed therebetween; and an outer can that accommodates the electrode body. The negative electrode includes a strip-shaped negative electrode core and a mixture layer provided on at least one surface of the negative electrode core and containing an active material. The negative electrode has a negative electrode winding start side end portion located on the winding start side relative to a positive electrode starting end that is the winding start side end of the positive electrode. The negative electrode winding start side end portion is provided on at least one surface so as to be spaced apart in a winding direction of the negative electrode, and is a nonaqueous electrolyte secondary battery including two outer surfaces formed by the mixture layer, and a recess sandwiched between the two outer surfaces and recessed toward the negative electrode core side from each of the outer surfaces.

[0007] In the non-aqueous electrolyte secondary battery according to this disclosure, by positioning the positive electrode start end of the recess at a portion of the negative electrode winding start end that is away from the positive electrode start end, when the electrode plates expand during charging and discharging of the secondary battery, the negative electrode winding start end becomes more flexible in the less rigid portion that includes the bottom of the recess away from the positive electrode start end. As a result, stress near the positive electrode start end of the negative electrode winding start end is relieved, and electrode plate deformation in that portion can be suppressed. Furthermore, since the positive electrode does not face the portion of the negative electrode winding start end that includes the bottom of the recess via a separator, deformation of the portion including the bottom of the recess does not cause a voltage drop in the secondary voltage. Therefore, electrode plate deformation of the negative electrode, which causes a voltage drop in the secondary battery, can be suppressed.

[0008] This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of this disclosure. This is a schematic diagram showing the arrangement relationship of the positive electrode, negative electrode, and separator at the winding start end portion shown in Figure 1, with the positive electrode, negative electrode, and separator extended in a straight line. This is a schematic diagram showing the winding start end portion of the electrode body shown in Figure 1, with a cross-section perpendicular to the central axis of the outer casing. This is a diagram corresponding to Figure 3, showing a state in which deformation occurs at the winding start end of the negative electrode, away from the positive electrode start end, in the embodiment. This is a diagram showing electrode plate deformation occurring near the positive electrode start end at the winding start end portion of the electrode body constituting a comparative example of a non-aqueous electrolyte secondary battery, when the electrode plate expands, and is a schematic diagram corresponding to a circumferential part of the cross-section perpendicular to the central axis of the outer casing. This is a diagram corresponding to Figure 2 in an electrode body constituting another example of the embodiment of a non-aqueous electrolyte secondary battery. This is a diagram corresponding to Figure 3 in an electrode body constituting another example of the embodiment of a non-aqueous electrolyte secondary battery. This is a diagram corresponding to Figure 2 in an electrode body constituting another example of the embodiment of a non-aqueous electrolyte secondary battery. This figure corresponds to Figure 3, showing an electrode body constituting a non-aqueous electrolyte secondary battery, which is another embodiment of the present invention.

[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. Furthermore, 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. Moreover, this disclosure is not limited to the embodiments and modifications described below, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0010] Figure 1 is an axial cross-sectional view of the non-aqueous electrolyte secondary battery 10 according to the embodiment. Figure 2 is a schematic diagram showing the arrangement of the positive electrode 11, negative electrode 12, and separator 13 at the winding start end, with the positive electrode 11, negative electrode 12, and separator 13 extended in a straight line. Figure 3 is a schematic diagram showing the winding start end of the electrode body 14 in a cross-section perpendicular to the central axis O of the outer casing 15. Figure 4 is a diagram corresponding to Figure 3, showing a state in which deformation has occurred at the end of the negative electrode winding start end, away from the positive electrode start end.

[0011] As shown in Figure 1, the non-aqueous electrolyte secondary battery 10 has a wound electrode body 14 in which the positive electrode 11 and the negative electrode 12 are wound around each other via the separators 13, and a positive electrode 11 and a negative electrode 12 are strip-shaped and have opposite polarities. The non-aqueous electrolyte secondary battery 10 also has a bottomed cylindrical outer casing 15 that houses the electrode body 14 and a sealing body 16 that closes the opening of the outer casing 15. The outer casing 15 contains the electrode body 14 together with the non-aqueous electrolyte.

[0012] The outer container 15 is a bottomed cylindrical metal container having a cylindrical portion 15a and a bottom portion provided at one end of the cylindrical portion 15a in the axial direction α. ​​The outer container 15 has a grooved portion 21, described later, formed on the other end in the axial direction α, which is the open end of the cylindrical portion 15a, and the sealing body 16 is supported by the grooved portion 21 and closes the opening of the outer container 15. For the sake of explanation, in the following, the sealing body 16 side of the non-aqueous electrolyte secondary battery 10 will be considered the top, and the bottom side of the outer container 15 will be considered the bottom.

[0013] The non-aqueous electrolyte has ionic conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte (non-aqueous electrolyte solution), but may also be a solid electrolyte using a gel-like polymer or the like. The non-aqueous electrolyte secondary battery 10 is preferably a lithium-ion battery. The electrolyte salt may be, for example, LiBF ４ LiPF ６ Lithium salts such as the above are used. Non-aqueous solvents include, for example, esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), as well as ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain halogen-substituted products in which at least some of the hydrogen atoms in these solvents are replaced with halogen atoms such as fluorine.

[0014] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated linear carbonates, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP). In terms of suppressing the deterioration of the charge-discharge cycle characteristics of non-aqueous electrolyte secondary batteries or improving the output characteristics, the non-aqueous electrolyte preferably contains 5% by mass or more of FEC relative to the mass of the non-aqueous electrolyte, and more preferably contains 5% to 15% by mass of FEC.

[0015] 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.

[0016] As described above, the electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strips, and are alternately stacked in the radial direction β of the electrode body 14 by being wound in a spiral. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the longitudinal and transverse directions of the electrode plate. The separator 13 is formed to be at least slightly larger than the positive electrode 11, with one separator facing the outer circumference and one facing the inner circumference of the positive electrode 11.

[0017] The separator 13 is placed between the negative electrode 12 and the positive electrode 11. In this example, two separators 13 are placed so as to sandwich the positive electrode 11, but the two separators may also be placed so as to sandwich the negative electrode 12.

[0018] A positive electrode tab 19 and a negative electrode tab 20 are connected to the electrode body 14. The positive electrode tab 19 electrically connects the positive electrode 11 and the sealing body 16. The positive electrode tab 19 is located, for example, in the center of the electrode plate of the positive electrode 11, at a position away from the winding start end and winding end end of the electrode body 14, approximately in the center of the radial direction β of the electrode body 14. The positive electrode tab 19 is a strip-shaped conductive member. The constituent material of the positive electrode tab 19 is not particularly limited, but it is preferable that the positive electrode tab 19 be made of a metal mainly composed of aluminum.

[0019] The negative electrode tab 20 is joined to the core body exposed surface 31a (Figure 2) of the core body exposed portion 31, described later, which is provided at the negative electrode winding start end, which is one end in the longitudinal direction of the negative electrode 12. In the example shown in Figure 1, the positive electrode tab 19 extends towards the sealing body 16 through the opening of the upper insulating plate 17 and is joined to the lower surface of the sealing body 16, so that the sealing body 16 becomes the positive electrode terminal. The negative electrode tab 20 is bent along the inner surface of the bottom of the outer can 15 through the through hole of the annular lower insulating plate 18 and is connected to the inner surface of the bottom of the outer can 15 by welding or the like, so that the outer can 15 becomes the negative electrode terminal. The negative electrode tab 20 is a strip-shaped conductive member. The constituent material of the negative electrode tab 20 is not particularly limited. Preferably, the negative electrode tab 20 is made of a metal mainly composed of nickel or copper, or a metal containing both nickel and copper.

[0020] The outermost surface of the electrode body 14 has an exposed portion of the surface of the negative electrode core that constitutes the negative electrode 12, and the negative electrode core is in contact with the inner surface of the outer casing 15. As a result, both the starting end and ending end of the negative electrode 12 are electrically connected to the outer casing 15, ensuring good current collection.

[0021] Referring to Figure 2, the positive electrode 11 has a strip-shaped positive electrode core 41 and positive electrode mixture layers 42 formed on both sides of the positive electrode core 41. The positive electrode core 41 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. A preferred positive electrode core 41 is a metal foil mainly composed of aluminum or an aluminum alloy. The thickness of the positive electrode core 41 is, for example, 10 μm to 30 μm.

[0022] The positive electrode composite layer 42 preferably contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is formed on both sides of the positive electrode core. The thickness of the positive electrode composite layer 42 is, for example, 40 μm to 100 μm on one side. For the positive electrode active material, for example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, etc. is used. The positive electrode tab 19 is directly joined to the positive electrode core 41 by ultrasonic welding or the like.

[0023] The positive electrode 11 is manufactured by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of the positive electrode core 41, followed by drying and rolling.

[0024] Examples of positive electrode active materials include lithium-containing transition metal oxides containing transition metal elements such as Co, Mn, and Ni. While lithium-containing transition metal oxides are not particularly limited, they generally have the formula Li １＋ｘ MO ２ It is preferable that the composite oxide is represented by the formula (wherein -0.2 < x ≤ 0.2, and M includes at least one of Ni, Co, Mn, and Al).

[0025] Examples of the conductive agents mentioned above include acetylene black (AB), carbon black (CB) such as Ketjenblack, and carbon materials such as graphite. Examples of the binders mentioned above include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins. These resins may also be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc. These may be used individually or in combination of two or more types.

[0026] The positive electrode tab 19 is formed on one side of the positive electrode 11 and is joined, for example, by ultrasonic welding, to the exposed surface of the positive electrode core 41 that is exposed from the positive electrode mixture layer 42. In this state, the positive electrode tab 19 extends from the upper end, which is one end in the width direction of the positive electrode core 41.

[0027] The negative electrode 12 has a strip-shaped negative electrode core 30 and negative electrode mixture layers 32 formed on both sides of the negative electrode core 30. The negative electrode core 30 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 layer 32 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR). The thickness of the negative electrode mixture layer 32 is, for example, 40 μm to 100 μm on one side. For the negative electrode active material, for example, graphite or a Si-containing material can be used. The negative electrode tab 20 is preferably directly joined to the negative electrode core by ultrasonic welding or the like.

[0028] The negative electrode 12 is manufactured by, for example, applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and water to both sides of the negative electrode core 30, followed by drying and rolling.

[0029] The negative electrode active material is not particularly limited as long as it can reversibly intercept and release lithium ions. For example, carbon materials such as natural graphite and artificial graphite, metals that alloy with lithium such as Si and Sn, or alloys and composite oxides containing these can be used. The binder contained in the negative electrode mixture layer is, for example, the same resin as in the case of the positive electrode 11. When preparing the negative electrode mixture slurry with an aqueous solvent, styrene-butadiene rubber (SBR), CMC or its salts, polyacrylic acid or its salts, polyvinyl alcohol, etc. can be used. These may be used individually or in combination of two or more. In particular, it is preferable that the negative electrode active material contains Si.

[0030] Each separator 13 is made of a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of each separator 13 is preferably an olefin resin such as polyethylene or polypropylene. The thickness of each separator 13 is, for example, 10 μm to 50 μm. There is a trend towards thinner separators 13 as batteries become more high-capacity and high-power. Each separator 13 has a melting point of, for example, 130°C to 180°C.

[0031] An annular gasket 27 is interposed between the outer casing 15 and the sealing body 16. The sealing body 16 is crimped and fixed to the upper end, which is the open end of the outer casing 15, via the gasket 27. Specifically, the upper end of the outer casing 15 is crimped to the peripheral edge of the sealing body 16 via the gasket 27. This seals the inside of the battery.

[0032] The outer can 15 has, for example, a grooved portion 21 formed by pressing the side surface from the outside to support the sealing body 16. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the outer can 15, and its upper surface supports the sealing body 16.

[0033] The sealing body 16 has a structure in which an internal terminal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 16 has, for example, a disc shape or a ring shape, and each component except the insulating member 24 is electrically connected to one another. The cap 26 has an annular flange provided on its outer circumference and a hat shape with a cylindrical portion in the center whose upper end is closed. The internal terminal plate 22 has a central hole that penetrates vertically. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central portions, and the insulating member 24 is interposed between their respective peripheral portions. The components constituting the sealing body 16 are stacked axially on the flange portion of the sealing body 16.

[0034] When the internal pressure of the battery rises to a predetermined value, the lower valve body 23 deforms and breaks, pushing the upper valve body 25 upward toward the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further and reaches a predetermined value, the upper valve body 25 breaks, and gas is discharged from the opening 26a of the cap 26.

[0035] The configuration of the negative electrode winding start end 12a, which is located on the winding start side of the positive electrode 11, will be explained in detail below using Figures 2 and 3. The negative electrode winding start end 12a is on the inner circumference side of the positive electrode start end B1 and is located on the winding start side of the positive electrode start end B1. In Figure 2, the portion of the negative electrode 12 indicated by arrow A2 is the negative electrode winding start end 12a, and the portion indicated by arrow A1 is the positive electrode facing portion of the negative electrode 12 that faces the positive electrode 11 via the separator 13. In Figure 3, the separator is not shown.

[0036] The negative electrode 12 has a core body exposed portion 31 at the negative electrode winding start end 12a, where the negative electrode mixture layer 32 is absent on both sides of the negative electrode core body 30. The core body exposed portion 31 is provided in a predetermined range from the negative electrode start end B2, which is the negative electrode winding start end, toward the winding end of the negative electrode 12. Therefore, on both sides of the core body exposed portion 31, there are core body exposed surfaces 31a and 31b where the negative electrode mixture layer 32 is absent, extending from the negative electrode start end B2 toward the winding end. Of the core body exposed surfaces 31a and 31b, the negative electrode tab 20 is joined to the outer core body exposed surface 31a facing the outer circumference by ultrasonic welding or the like. In this state, the negative electrode tab 20 extends from the lower end, which is one end in the width direction of the negative electrode core body 30.

[0037] An insulating tape 34 is applied to the exposed core surface 31a on the outer side of the winding, so as to cover the surface of the exposed core surface 31a and the negative electrode tab 20 that overlaps the exposed core surface 31a. The insulating tape 34 is applied from near the beginning end of the winding towards the end end of the winding on the exposed core surface 31a, but does not reach the negative electrode mixture layer 32 on the outer side of the winding.

[0038] Furthermore, the end of the insulating tape 34 at the winding end may extend further towards the winding end than shown in Figure 2, covering a portion of the outer surface of the negative electrode mixture layer 32 on the outside of the winding.

[0039] Furthermore, in this embodiment, a compound layer forming section 49 is provided on both the outer and inner surfaces of the negative electrode core 30, where the negative electrode compound layer 32 is laminated, at the portion of the negative electrode winding start end 12a located on the winding start side from the positive electrode start end B1, on the winding end side from the exposed core portion 31. Also, on both sides of the compound layer forming section 49, a recess 50 on the outer side and a recess 51 on the inner side are provided in portions that coincide with each other in the winding direction. As a result, both the outer and inner surfaces of the negative electrode winding start end 12a are provided with two outer surfaces S1 and S2 formed by the negative electrode compound layer 32, spaced apart in the winding direction of the negative electrode 12, and recesses 50 and 51 sandwiched between the two outer surfaces S1 and S2, recessed toward the negative electrode core 30 side from each outer surface S1 and S2.

[0040] In this example, the bottom surface S3 of each recess 50, 51 is formed by the negative electrode mixture layer 32. As a result, each recess 50, 51 is formed by two portions of the negative electrode mixture layer 32 on the outer and inner sides of the winding that are separated in the winding direction of the negative electrode 12 (the portions including S1 and S2 in Figure 2), and a portion of the negative electrode mixture layer 32 that is sandwiched between the two portions (the portions including S1 and S2 in Figure 2) and has a smaller thickness than the two portions (the portion including S3 in Figure 2).

[0041] In the method for manufacturing the negative electrode 12, for example, when applying a negative electrode mixture slurry to form a negative electrode mixture layer 32 on both sides of the negative electrode core 30, the amount of negative electrode mixture slurry applied per unit area to the portion where the bottom surface of each recess 50, 51 coincides with the thickness direction of the negative electrode 12 is less than the amount of negative electrode mixture slurry applied per unit area to other portions, thereby forming each recess 50, 51. As a result, the amount of negative electrode mixture applied per unit area to the portion where the bottom surface of each recess 50, 51 coincides with the thickness direction of the negative electrode 12 at the negative electrode winding start end 12a is less than the amount of negative electrode mixture applied per unit area to the portion where the outer surfaces S1, S2 at the negative electrode winding start end 12a coincide with the thickness direction.

[0042] Further, an end B3 of each of the recesses 50 and 51 on the positive electrode starting end B1 side is positioned closer to the winding start side than the positive electrode starting end B1 in the negative electrode winding start side end portion 12a. Accordingly, by positioning the end B3 of each of the recesses 50 and 51 on the positive electrode starting end B1 side at a portion of the negative electrode winding start side end portion 12a away from the positive electrode starting end B1, when the electrode plate expands during charge and discharge of the secondary battery 10, the negative electrode winding start side end portion 12a is likely to bend at portions corresponding to the recesses 50 and 51 having low rigidity. Therefore, stress in the vicinity of the positive electrode starting end B1 of the negative electrode winding start side end portion 12a is relieved, and electrode plate deformation at that portion can be suppressed. Further, since the positive electrode 11 does not face the respective recesses 50 and 51 of the negative electrode winding start side end portion 12a with the separator 13 interposed therebetween, deformation of the portions of the negative electrode winding start side end portion 12a corresponding to the respective recesses 50 and 51 does not cause a voltage drop of the secondary battery 10. Therefore, electrode plate deformation of the negative electrode 12 that causes a voltage drop of the secondary battery 10 can be suppressed.

[0043] As a method for forming the respective recesses 50 and 51, in addition to reducing the coating amount of the negative electrode mixture for forming the negative electrode mixture layer at portions corresponding to the respective recesses 50 and 51 as described above, the respective recesses 50 and 51 can also be formed by scraping off a part of the surface of the negative electrode mixture layer 32 of the negative electrode winding start side end portion 12a by laser irradiation or the like.

[0044] It is preferable that the end B3 of each of the recesses 50 and 51 on the positive electrode starting end side is arranged at a position advanced 0.1 turn or more and 1 turn or less toward the winding start side from the positive electrode starting end B1.

[0045] Further, it is preferable that each of the recesses 50 and 51 has a width of 1 mm or more and 10 mm or less in the winding direction of the negative electrode 12. It is more preferable that each of the recesses 50 and 51 has a width of 1 mm or more and 5 mm or less in the winding direction of the negative electrode 12.

[0046] Further, as shown in FIG. 3, it is preferable that each of the recesses 50 and 51 is arranged at a position that does not overlap the negative electrode tab 20 in a radial direction from the central axis O of the outer can. According to this preferable configuration, since the respective recesses 50 and 51 do not overlap the radially outer side of the highly rigid negative electrode tab 20, deformation of the negative electrode winding start side end portion 12a by the respective recesses 50 and 51 is more likely to occur. Thereby, electrode plate deformation in the vicinity of the positive electrode starting end B1 of the negative electrode winding start side end portion 12a described later can be more significantly suppressed.

[0047] Incidentally, in this example, the winding start-side end of the negative electrode mixture layer 32 on the outer winding side and the winding start-side end of the negative electrode mixture layer 32 on the inner winding side are aligned with the winding direction of the negative electrode 12. On the other hand, a configuration may be adopted in which the winding start-side end of one negative electrode mixture layer 32 among both the negative electrode mixture layer 32 on the outer winding side and the negative electrode mixture layer 32 on the inner winding side is positioned closer to the winding start side than the winding start end of the other negative electrode mixture layer 32. In addition, in this example, the negative electrode mixture layers 32 are provided on both surfaces of the negative electrode core 30, but the negative electrode mixture layer 32 may also be provided only on one surface of the negative electrode core 30.

[0048] As described above, in the present embodiment, by positioning the end B3 on the positive electrode start end B1 side of the recesses 50 and 51 at a portion of the negative electrode winding start side end 12a that is away from the positive electrode start end B1, when the electrode plate expands during charge and discharge of the secondary battery 10, the negative electrode winding start side end 12a is likely to bend at the low-rigidity portion including the bottom surfaces S3 of the recesses 50 and 51 that are away from the positive electrode start end B1. Therefore, the stress in the vicinity of the positive electrode start end B1 of the negative electrode winding start side end 12a is relieved, and electrode plate deformation at that portion can be suppressed. In addition, since the positive electrode 11 does not face the portion including the bottom surfaces S3 of the recesses 50 and 51 of the negative electrode winding start side end 12a via the separator 13, deformation of the portion including the bottom surfaces S3 of the recesses 50 and 51 does not cause a voltage drop in the secondary battery 10. Therefore, deformation of the negative electrode 12 that would cause a voltage drop of the secondary battery 10 can be suppressed.

[0049] The effects of this embodiment will be explained in detail with reference to Figures 3 and 4. As shown in Figure 3, in this example, recesses 50 and 51 are provided at the negative electrode winding start end 12a. The ends B3 of the recesses 50 and 51 on the positive electrode start end B1 side are located closer to the winding start than the positive electrode start end B1. Therefore, when the secondary battery expands due to charging and discharging, the negative electrode winding start end 12a is more likely to bend in the less rigid portion that includes the bottom surface S3 of the recesses 50 and 51, which is away from the positive electrode start end B1. As a result, when the electrode plate expands due to the charging and discharging cycle of the secondary battery, if a compressive stress is generated in the negative electrode 12 in the circumferential direction, the negative electrode winding start end 12a easily deforms in the portion that includes the bottom surface S3 of the recesses 50 and 51, and a bent portion 60 is generated, for example, as shown in Figure 4. Therefore, the stress in the negative electrode 12 in the portion facing the vicinity of the positive electrode start end B1 is relieved, and electrode plate deformation in that portion can be suppressed. Furthermore, the positive electrode 11 does not face the portion of the negative electrode winding start end 12a including the bottom surface S3 of the recesses 50 and 51, even with the separator 13 in between. Therefore, deformation of the portion of the negative electrode winding start end 12a including the bottom surface S3 does not cause a voltage drop in the secondary battery. Consequently, deformation of the negative electrode plate, which causes a voltage drop, can be suppressed.

[0050] On the other hand, Figure 5 shows that in the electrode body 14a constituting the comparative example non-aqueous electrolyte secondary battery, electrode plate deformation occurs near the positive electrode start end B1 at the winding start end of the negative electrode 12 when the electrode plate expands, and is a schematic diagram corresponding to a part of the circumferential direction of the cross section perpendicular to the central axis of the outer casing.

[0051] In the comparative example shown in Figure 5, unlike the embodiments in Figures 1 to 4, no recess is formed at the negative electrode winding start end 12a, and the thickness of the negative electrode mixture layer 32 is constant throughout the winding direction.

[0052] Figure 5 schematically shows the inner circumferential end 14b and outer circumferential portion 14c of the electrode body 14a in the oblique grid section. The separator is not shown. In this comparative example, as shown in Figure 5(a), when the electrode plates expand during charging and discharging, pressure is applied from the inner surface of the outer can, causing the internal pressure of the electrode body 14a to increase radially inward, and slip occurs as the negative electrode winding start end 12a moves to one side in the winding direction, reducing the inner diameter.

[0053] On the other hand, as shown in Figure 5(b), as the internal pressure increases, compressive stress occurs in the circumferential direction in the direction indicated by the black arrow in each electrode plate. At this time, the portion of the inner circumferential side of the negative electrode 12 that is opposite the positive electrode, shown on the right side of Figure 5(b), is compressed by members on both radial sides, increasing the frictional force and thus hindering movement in the sliding direction. On the other hand, the negative electrode winding start end 12a, which is located on the winding start side of the positive electrode start end B1, is prone to circumferential movement toward the positive electrode start end B1, so electrode plate deformation such as buckling occurs in portion G of Figure 5(b). As a result, if the winding start end of the positive electrode 11 abuts against portion G of Figure 5(b) via a separator (not shown), and the separator is damaged, it will cause a voltage drop in the secondary battery.

[0054] According to the embodiments shown in Figures 1 to 4 above, the stress near the positive electrode starting end B1 of the negative electrode winding starting end 12a is relieved as described above, so that deformation of the negative electrode 12 plate, which causes a voltage drop in the secondary battery, can be suppressed.

[0055] Furthermore, in the embodiments shown in Figures 1 to 4, it is preferable that the ends B3 of each recess 50, 51 on the positive electrode starting end B1 side of the negative electrode winding starting end 12a are positioned at a location that is 0.1 turns or more but less than 1 turn toward the winding starting end from the positive electrode starting end B1. This preferred configuration makes it easier to more effectively relieve the stress concentrated in the portion of the negative electrode 12 that faces the vicinity of the positive electrode starting end B1. On the other hand, if the ends B3 of each recess 50, 51 on the positive electrode starting end B1 side are positioned at a location that is less than 0.1 turns toward the winding starting end from the positive electrode starting end B1, the vicinity of the positive electrode starting end B1 in the negative electrode 12 becomes more prone to deformation, and the winding starting end of the positive electrode may abut against that deformed portion. Furthermore, if the end B3 of each recess 50, 51 on the positive electrode starting end B1 side is positioned beyond 1.0 turn from the positive electrode starting end B1 towards the winding start, the distance in the winding direction between the end of each recess 50, 51 and the vicinity of the positive electrode starting end B1 becomes excessive, making it difficult to effectively relieve stress in the portion of the negative electrode facing the vicinity of the positive electrode starting end B1.

[0056] Figure 6 is a diagram of an electrode body 14d constituting a non-aqueous electrolyte secondary battery in another embodiment, corresponding to Figure 2. Figure 7 is a diagram of the electrode body 14d, corresponding to Figure 3. In the configuration of this example, no recess is formed on the winding side of the negative electrode winding start end 12a, and the thickness of the negative electrode mixture layer 32 on the winding side is constant throughout the winding direction.

[0057] On the other hand, a recess 52 is formed on the outer side of the negative electrode winding start end 12a, but the bottom surface S4 of the recess 52 is formed not by the negative electrode mixture layer, but by the outer surface of the negative electrode core 30. Specifically, in this example, the recess 52 on the outer side of the negative electrode winding start end 12a is formed by two parts of the outer negative electrode mixture layer 32 that are separated in the winding direction of the negative electrode 12 (parts including S1 and S2 in Figure 6), and a part of the negative electrode core 30 sandwiched between the two parts (parts including S1 and S2 in Figure 6) where the outer negative electrode mixture layer is not provided (part including S4 in Figure 6). As a result, the outer surface of the winding start end 12a of the negative electrode is provided apart in the winding direction of the negative electrode 12 and includes two outer surfaces S1 and S2 formed by the negative electrode mixture layer 32, and a recess 52 sandwiched between the two outer surfaces S1 and S2, which is recessed toward the negative electrode core 30 side from each of the outer surfaces S1 and S2.

[0058] In this example, the outer surface of the negative electrode winding start end 12a is provided with a recess 52 sandwiched between two outer surfaces S1 and S2, and recessed toward the negative electrode core 30 side of each outer surface S1 and S2. This allows for stress relief in the negative electrode 12 near the positive electrode start end B1, thereby suppressing electrode plate deformation in that area. In this example, the other configurations and functions are the same as those in Figures 1 to 4.

[0059] In this example, the recess 52 is formed only on the outer side of the negative electrode winding start end 12a. However, the recess at the negative electrode winding start end can also be provided only on the inner side instead of the outer side. In this case, the bottom surface of the recess on the inner side is formed by the inner surface of the negative electrode core 30.

[0060] Figure 8 is a diagram of an electrode body 14e constituting a non-aqueous electrolyte secondary battery in another embodiment, corresponding to Figure 2. Figure 9 is a diagram of the electrode body 14e, corresponding to Figure 3. In this example, unlike the configurations shown in Figures 6 and 7, a recess 53 is formed on the inside of the winding of the negative electrode winding start end 12a, similar to the outside of the winding, and the bottom surface S5 of the recess 53 is formed not by the negative electrode mixture layer, but by the inner surface of the winding of the negative electrode core 30. Specifically, in this example, the recess 53 on the inside of the winding of the negative electrode winding start end 12a is formed by two parts of the negative electrode mixture layer 32 on the inside of the winding that are separated in the winding direction of the negative electrode 12 (parts including S1 and S2 in Figure 8), and a part sandwiched between two parts (parts including S1 and S2 in Figure 8) where the negative electrode mixture layer on the inside of the winding of the negative electrode core 30 is not provided (part including S5 in Figure 8). As a result, the inner surface of the negative electrode winding start end 12a is provided apart in the winding direction of the negative electrode 12 and includes two outer surfaces S1 and S2 formed by the negative electrode mixture layer 32, and a recess 53 sandwiched between the two outer surfaces S1 and S2, which is recessed toward the negative electrode core 30 side of each outer surface S1 and S2.

[0061] In this example, since recesses are formed on both the outer and inner sides of the negative electrode winding start end, the portion of the negative electrode winding start end 12a that is further away from the positive electrode start end B1 towards the winding start becomes more easily deformable. As a result, the stress in the negative electrode 12 in the portion facing the vicinity of the positive electrode start end B1 is more easily relieved than in the configurations of Figures 6 and 7, and the deformation of the electrode plate in that portion is further suppressed. In this example, the other configurations and functions are the same as those in Figures 1 to 4, or Figures 6 and 7.

[0062] The inventors performed a charge-discharge cycle test using the secondary batteries of Examples 1 to 3, which have the configurations of the above embodiments, and the comparative secondary battery, which has the configuration of the comparative example shown in Figure 5(a), performing a predetermined number of charge-discharge cycles. After the charge-discharge cycle test, the secondary batteries were disassembled to check for any deformation of the electrode plates at the inner circumference end of the electrode body. Example 1 is a secondary battery that includes an electrode body having the same configuration as the electrode body 14 shown in Figures 1 to 4. Example 2 is a secondary battery that includes an electrode body having the same configuration as the electrode body 14d shown in Figures 6 and 7. Example 3 is a secondary battery that includes an electrode body having the same configuration as the electrode body 14e shown in Figures 8 and 9. In Example 1, the thickness of the portion including the bottom surface of each recess in the negative electrode mixture layer on both sides of the negative electrode winding start end was 5% to 20% of the thickness on both sides in the winding direction, and 10% to 40% for both sides combined.

[0063] After this charge-discharge cycle test, plate deformation was confirmed in the comparative example, but no plate deformation was observed in any of Examples 1 to 3. This confirmed the effectiveness of each embodiment.

[0064] The present disclosure is further illustrated by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery comprising: an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator between them; and an outer can for housing the electrode body, wherein the negative electrode comprises: a strip-shaped negative electrode core; and a composite layer containing an active material provided on at least one surface of the negative electrode core; the negative electrode has a negative electrode winding start end located on the winding start side of the positive electrode start end, which is the winding start end of the positive electrode; and the negative electrode winding start end comprises: two outer surfaces formed by the composite layer, provided at least on one surface apart in the winding direction of the negative electrode; and a recess sandwiched between the two outer surfaces and recessed toward the negative electrode core from each of the outer surfaces. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the amount of composite material forming the composite layer applied to the region including the bottom surface of the recess is less than that applied to the region including each of the outer surfaces. Configuration 3: The non-aqueous electrolyte secondary battery according to claim 1 or configuration 2, wherein the recess is formed by two portions of the composite layer that are separated in the winding direction of the negative electrode, and a portion of the composite layer sandwiched between the two portions and having a smaller thickness than the two portions. Configuration 4: The non-aqueous electrolyte secondary battery according to claim 1 or configuration 2, wherein the recess is formed by two portions of the composite layer that are separated in the winding direction of the negative electrode, and a portion of the negative electrode core body sandwiched between the two portions and not provided with the composite layer. Configuration 5: The non-aqueous electrolyte secondary battery according to any one of configurations 1 to 4, wherein the end of the recess on the positive electrode starting end side is positioned at a location that is 0.1 turns or more but 1 turn or less toward the winding start side from the positive electrode starting end in the winding direction of the negative electrode. Configuration 6: The non-aqueous electrolyte secondary battery according to any one of configurations 1 to 5, wherein the negative electrode contains Si.

[0065] 10 Non-aqueous electrolyte secondary battery (secondary battery), 11 Positive electrode, 12 Negative electrode, 13 Separator, 14, 14a, 14d, 14e Electrode body, 15 Outer can, 15a Cylindrical part, 16 Sealing body, 17 Upper insulating plate, 18 Lower insulating plate, 19 Positive electrode tab, 20 Negative electrode tab, 21 Grooved part, 22 Internal terminal plate, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 27 Gasket, 30 Negative electrode core, 31 Core body exposed part, 31a, 31b Core body exposed surface, 32 Negative electrode mixture layer, 34 Insulating tape, 41 Positive electrode core, 41a, 41b Core body exposed surface, 42 Positive electrode mixture layer, 44, 45, 46 Adhesive layer, 49 Mixture layer forming part, 50, 51 Recessed portion, 60 Bent portion, S1, S2 Outer surface, S3, S4, S5 Bottom surface

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator in between; and an outer casing for housing the electrode body, wherein the negative electrode comprises a strip-shaped negative electrode core and a composite layer containing an active material provided on at least one surface of the negative electrode core, the negative electrode has a negative electrode winding start end located on the winding start side of the positive electrode start end which is the winding start end of the positive electrode, and the negative electrode winding start end comprises two outer surfaces formed by the composite layer and provided at least on one surface apart in the winding direction of the negative electrode, and a recess sandwiched between the two outer surfaces and recessed toward the negative electrode core from each of the outer surfaces.

2. The amount of the mixture applied per unit area of ​​the portion of the negative electrode winding starting end that coincides in the thickness direction with the bottom surface of the recess is less than the amount of the mixture applied per unit area of ​​the portion of the negative electrode winding starting end that coincides in the thickness direction with each of the outer surfaces. The non-aqueous electrolyte secondary battery according to claim 1.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the recess is formed by two portions of the mixture layer that are separated in the winding direction of the negative electrode, and a portion of the mixture layer that is sandwiched between the two portions and has a smaller thickness than the two portions.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the recess is formed by two portions of the mixture layer that are separated in the winding direction of the negative electrode, and a portion of the negative electrode core body sandwiched between the two portions and not provided with the mixture layer.

5. The end of the recess on the positive electrode starting end side is positioned at a location that is 0.1 turns or more but 1 turn or less toward the winding start side from the positive electrode starting end in the winding direction of the negative electrode, as described in claim 1.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode contains Si.

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