Secondary battery

Abstract

This secondary battery is characterized by comprising: an electrode body in which a positive electrode (11) and a negative electrode (12) are wound with a separator (13) interposed therebetween; a negative electrode current collector plate (17) electrically connected to the negative electrode (12); and an electrolyte solution, the negative electrode (12) having a negative electrode core body (40) and negative electrode mixture layers (42) disposed on the negative electrode core body (40), a negative electrode core body exposed part (44) on which the negative electrode mixture layers (42) are not disposed being provided at one end of the negative electrode core body (40) in the winding axis direction of the electrode body, the negative electrode core body exposed part (44) being joined to the negative electrode current collector plate (17), a swellable resin layer (46) being provided on the negative electrode core body exposed part (44).

Description

secondary battery

[0001] The present disclosure relates to secondary battery technology.

[0002] The secondary battery includes, for example, a wound electrode body in which a separator is disposed between a positive electrode having a positive electrode mixture layer disposed on a positive electrode core and a negative electrode having a negative electrode mixture layer disposed on a negative electrode core, and the positive electrode and negative electrode are wound together while being insulated by the separator.

[0003] Among secondary batteries equipped with a wound electrode assembly, there is known a battery that employs an end-face current collection structure from the viewpoint of improving battery output. The end-face current collection structure is, for example, a structure in which exposed portions of an electrode core disposed at both ends of the electrode assembly in the direction of the winding axis are joined to current collector plates.

[0004] Conventionally, in batteries employing an end-face current collection structure, a technique has been known in which, for example, a notch or a through-hole is provided in the exposed portion of the electrode core that is joined to the current collector plate in order to increase the permeability of the electrolyte into the electrode body and improve the rapid charging characteristics of the battery (e.g., Patent Documents 1 and 2).

[0005] JP 2000-77054 A JP 2015-103420 A

[0006] However, in the prior art, the electrolyte permeability into the electrode assembly is insufficient, so there is room for improvement in the rapid charging characteristics of the battery.

[0007] Therefore, an object of the present disclosure is to provide a secondary battery with excellent rapid charging characteristics.

[0008] A secondary battery according to one aspect of the present disclosure comprises an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a first current collector plate electrically connected to one of the positive electrode and the negative electrode, and an electrolyte, wherein the one electrode has a strip-shaped first core and a first mixture layer arranged on the first core, and a first core exposed portion on which the first mixture layer is not arranged is provided at one end of the first core in the winding axis direction of the electrode body, the first core exposed portion is joined to the first current collector plate, and a swellable resin layer is provided on the first core exposed portion.

[0009] According to one aspect of the present disclosure, a secondary battery with excellent rapid charging characteristics can be provided.

[0010] Fig. 1 is a cross-sectional view showing an example of the configuration of a secondary battery according to an embodiment; Fig. 2 is a perspective view showing an example of the configuration of a wound electrode body; Fig. 3 is a partially enlarged cross-sectional view showing the configuration of the vicinity of the lower end of the wound electrode body; Fig. 4 is a partially enlarged cross-sectional view showing another example of the configuration of the vicinity of the lower end of the wound electrode body; Fig. 5 is a partially enlarged cross-sectional view showing the configuration of the vicinity of the upper end of the wound electrode body.

[0011] The drawings referred to in the following description of the embodiments are schematic, and the dimensional ratios of the components depicted in the drawings may differ from those of the actual components.

[0012] Fig. 1 is a cross-sectional view showing an example of the configuration of a secondary battery according to an embodiment. The secondary battery 10 shown in Fig. 1 includes a wound electrode assembly 14, an electrolyte (not shown), an outer can 15 that houses the electrode assembly 14, the electrolyte, etc., and a sealing body 16 that closes the opening of the outer can 15. For ease of explanation, the sealing body 16 side will be referred to as "top" and the bottom side of the outer can 15 will be referred to as "bottom."

[0013] The electrolyte solution has, for example, lithium ion conductivity. The electrolyte solution includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. The electrolyte salt includes, for example, LiPF ６ Lithium salts such as

[0014] Fig. 2 is a perspective view showing an example of the configuration of a wound-type electrode assembly. In Fig. 2, the ends of the members constituting the electrode assembly are shown in a developed state in order to explain the configuration of the wound-type electrode assembly. As shown in Figs. 1 and 2, the electrode assembly 14 is a wound-type electrode assembly having a positive electrode 11, a negative electrode 12, and a separator 13 disposed between the positive electrode 11 and the negative electrode 12, and the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween.

[0015] As shown in FIG. 2 , the positive electrode 11 has a strip-shaped positive electrode core 30 and positive electrode mixture layers 32 disposed on both sides of the positive electrode core 30. Furthermore, at an upper end (one end) of the positive electrode core 30 in the direction of the winding axis of the electrode body 14, the positive electrode mixture layer 32 is not disposed, and a positive electrode core exposed portion 34 where the positive electrode core 30 is exposed is provided. The positive electrode core exposed portion 34 is provided, for example, from one end to the other end in the longitudinal direction of the positive electrode core 30. Furthermore, the negative electrode 12 has a strip-shaped negative electrode core 40 and negative electrode mixture layers 42 disposed on both sides of the negative electrode core 40. Furthermore, at a lower end (the other end) of the negative electrode core 40 in the direction of the winding axis of the electrode body 14, the negative electrode mixture layer 42 is not disposed, and a negative electrode core exposed portion 44 where the negative electrode core 40 is exposed is provided. The negative electrode substrate exposed portion 44 is provided, for example, from one end to the other end in the longitudinal direction of the negative electrode substrate 40. That is, in the electrode body 14 shown in FIG. 2 , the upper end of the electrode body 14 in the winding axis direction is formed by the positive electrode substrate exposed portion 34, and the lower end of the electrode body 14 in the winding axis direction is formed by the negative electrode substrate exposed portion 44. The width of the positive electrode substrate exposed portion 34 (the length of the electrode body 14 in the winding axis direction) is, for example, 2 mm or more and 20 mm or less. Furthermore, the width of the negative electrode substrate exposed portion 44 (the length of the electrode body 14 in the winding axis direction) is, for example, 2 mm or more and 20 mm or less.

[0016] The positive electrode core 30 constituting the positive electrode 11 may be, for example, a metal foil such as aluminum or an aluminum alloy that is stable within the potential range of the positive electrode 11, or a film having such a metal disposed on the surface. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 50 μm or less. The positive electrode mixture layer 32 includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced by applying a positive electrode mixture slurry containing the positive electrode active material and the like onto the positive electrode core 30, drying the coating, and then rolling it to form the positive electrode mixture layer 32 on the positive electrode core 30. The positive electrode mixture layer 32 may be formed on only one side of the positive electrode core 30 or on both sides. The thickness of the positive electrode mixture layer 32 is, for example, 10 μm or more and 150 μm or less on one side of the positive electrode core 30.

[0017] Examples of the positive electrode active material include lithium-containing metal composite oxides. Examples of metal elements contained in the lithium-containing metal composite oxides include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0018] Examples of conductive agents include carbon materials such as carbon black such as acetylene black and ketjen black, graphite, and carbon nanotubes (single-walled carbon nanotubes, multi-walled carbon nanotubes, etc.) Examples of binders include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, styrene-butadiene copolymer (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and polyethylene oxide (PEO).

[0019] The negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 42 formed on both sides of the negative electrode core 40. Examples of the negative electrode core 40 include a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, and a film with such a metal disposed on the surface layer. The thickness of the negative electrode core 40 is, for example, 5 μm or more and 50 μm or less. The negative electrode mixture layer 42 includes, for example, a negative electrode active material, a binder, and the like. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing the negative electrode active material and the like onto the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on the negative electrode core 40. The negative electrode mixture layer 42 may be formed on only one side or both sides of the negative electrode core 40. The thickness of the negative electrode mixture layer 42 is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode substrate 40 .

[0020] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Examples of carbon materials include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. In addition to carbon materials, examples of negative electrode active materials include metals that alloy with lithium, such as Si and Sn, alloys containing such metals, and compounds containing such metals. Examples of binders include the same materials as those used in the positive electrode 11. The negative electrode mixture layer 42 may also contain a conductive agent.

[0021] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and 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.

[0022] The secondary battery 10 shown in FIG. 1 has a negative electrode current collector 17 arranged below the electrode body 14. The negative electrode current collector 17 is a metal plate made of, for example, nickel or a nickel alloy. A negative electrode core exposed portion 44 at the lower end of the electrode body 14 is joined to the negative electrode current collector 17 by welding or the like. The negative electrode current collector 17 is also joined to the inner surface of the bottom plate of the outer can 15 by welding or the like. In other words, the negative electrode core exposed portion 44 is electrically connected to the outer can 15 via the negative electrode current collector 17, and the outer can 15 serves as the negative electrode terminal.

[0023] The outer can 15 is, for example, a cylindrical metal container with a bottom. A gasket 27 is provided between the outer can 15 and the sealing body 16 to ensure airtightness inside the battery. The outer can 15 has, for example, a grooved portion 21 that protrudes inward from a portion of the side surface and supports 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 supports the sealing body 16 on its upper surface.

[0024] The sealing body 16 shown in FIG. 1 has a structure in which, in order from the electrode body 14 side, a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked. Each component constituting the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges. If the internal pressure of the secondary battery 10 increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 23 may deform and rupture, pushing the upper valve body 25 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 further increases, the upper valve body 25 may rupture, and gas may be discharged through the through-hole 26a of the cap 26.

[0025] The secondary battery 10 shown in FIG. 1 also includes a positive electrode current collector 18 disposed above the electrode assembly 14, a circular insulating plate 19 disposed on the positive electrode current collector 18, and a connection lead 20. The positive electrode current collector 18 is a metal plate made of, for example, aluminum or an aluminum alloy. The connection lead 20 is a metal member made of, for example, aluminum or an aluminum alloy. A positive electrode core exposed portion 34 at the upper end of the electrode assembly 14 is joined to the positive electrode current collector 18 by welding or the like. The lower end of the connection lead 20 is joined to the upper surface of the positive electrode current collector 18 by welding or the like. The connection lead 20 extends through a through hole in the insulating plate 19 toward the sealing body 16, and the upper end of the connection lead 20 is joined to the lower surface of the filter 22 of the sealing body 16 by welding or the like. The positive electrode core exposed portion 34 is electrically connected to the filter 22 via the positive electrode current collector 18 and the connection lead 20. In other words, the cap 26 electrically connected to the filter 22 serves as the positive electrode terminal.

[0026] 1 employs an end surface current collecting structure in which exposed portions of the cores located at the ends of the electrode body 14 in the winding axis direction are joined to current collecting plates in both the positive electrode 11 and the negative electrode 12, and current is collected directly from the cores. However, in the secondary battery of this embodiment, one of the positive electrode and the negative electrode may have an end surface current collecting structure, and the other electrode may have a structure in which, instead of the end surface current collecting structure, an electrode lead is connected to the other electrode and current is collected via the electrode lead, for example.

[0027] 3 is a partially enlarged cross-sectional view showing the configuration of the vicinity of the lower end of the wound electrode assembly. The negative electrode substrate exposed portion 44 shown in FIG. 3 extends downward in the direction of the winding axis of the electrode assembly 14 from the end A on the negative electrode mixture layer 42 side. The negative electrode substrate exposed portion 44 has a bending point R, from which the negative electrode substrate exposed portion 44 is bent radially inward of the electrode assembly 14, and the bent negative electrode substrate exposed portion 44 is joined to the negative electrode current collector plate 17. Note that the negative electrode substrate exposed portion 44 may also be bent radially outward of the electrode assembly 14 from the bending point R. It is desirable that the negative electrode substrate exposed portion 44 be bent radially inward or outward of the electrode assembly 14 at an angle of 30° or more and 90° or less with respect to the direction of the winding axis of the electrode assembly 14. The negative electrode substrate exposed portion 44 may extend linearly to the negative electrode current collector plate 17 , and the tip of the negative electrode substrate exposed portion 44 may be joined to the negative electrode current collector plate 17 .

[0028] As shown in FIG. 3 , a swellable resin layer 46 is provided on the negative electrode core exposed portion 44. In the present disclosure, "swellable" means that the resin layer absorbs the electrolyte and swells. The negative electrode core exposed portion 44 has a negative electrode core exposed portion 44a on the inner circumferential surface side of the negative electrode core 40 and a negative electrode core exposed portion 44b on the outer circumferential surface side of the negative electrode core 40. In FIG. 3 , the resin layer 46 is provided on the negative electrode core exposed portion 44a on the inner circumferential surface side of the negative electrode core 40. The inner circumferential surface of the negative electrode core 40 refers to the surface of the negative electrode core 40 that is located radially inward of the wound negative electrode 12 when the negative electrode 12 is wound. The outer circumferential surface of the negative electrode core 40 refers to the surface of the negative electrode core 40 that is located radially outward of the wound negative electrode 12 when the negative electrode 12 is wound. By providing the resin layer 46 on the negative electrode core exposed portion 44 in this manner, the electrolyte is retained in the swellable resin layer 46, making it easier for the electrolyte to be supplied into the electrode assembly 14. Therefore, even when rapid charging is performed, a shortage of electrolyte from the electrode assembly 14 is prevented, resulting in a secondary battery with excellent rapid charging characteristics. Furthermore, because the negative electrode core exposed portion 44 is reinforced by the resin layer 46, deformation (e.g., breaking or bending) or damage (e.g., cutting) of the negative electrode core exposed portion 44 is suppressed even when uneven stress is applied to the negative electrode core exposed portion 44 due to slight movement of the electrode associated with charging and discharging. If the negative electrode core exposed portion 44 is deformed or damaged, for example, the deformed or damaged negative electrode core exposed portion 44 may break through the separator, causing an internal short circuit. In this embodiment, the resin layer 46 suppresses deformation and damage to the negative electrode core exposed portion 44, thereby suppressing the occurrence of an internal short circuit associated with charging and discharging.

[0029] As shown in FIG. 3 , the resin layer 46 may be provided on the negative electrode core exposed portion 44 a on the inner circumferential surface side of the negative electrode core 40. Alternatively, although not shown in the figures, the resin layer 46 may be provided on the negative electrode core exposed portion 44 b on the outer circumferential surface side of the negative electrode core 40. Alternatively, the resin layer 46 may be provided on both the negative electrode core exposed portion 44 a and the negative electrode core exposed portion 44 b. Among these, the resin layer 46 is preferably provided on the negative electrode core exposed portion 44 a on the inner circumferential surface side of the negative electrode core 40. Generally, the negative electrode core exposed portion 44 is bent radially inward from the bending point R of the electrode body 14. Therefore, by providing the resin layer 46 on the negative electrode core exposed portion 44 a on the inner circumferential surface side of the negative electrode core 40, the negative electrode core exposed portion 44 b on the outer circumferential surface side of the negative electrode core 40 can be used as a joint surface with the negative electrode current collector plate 17, and an increase in electrode plate resistance can be suppressed. Furthermore, by bending the negative electrode core exposed portion 44 from the bending point R toward the radially inward direction of the electrode body 14, the electrolyte is also more easily retained in the space between the resin layer 46 on the negative electrode core exposed portion 44 a on the inner circumferential surface side of the negative electrode core 40 and the adjacent negative electrode core exposed portion 44 on the radially inner side of the electrode body 14. As a result, even when rapid charging is performed, a shortage of electrolyte in the electrode body 14 is further suppressed, resulting in a secondary battery with superior rapid charging characteristics.

[0030] 3 , the resin layer 46 may be disposed over the entire area from the end A on the negative electrode mixture layer 42 side to the end B on the negative electrode current collector 17 side in the negative electrode core exposed portion 44a on the inner circumferential surface side of the negative electrode core 40. However, in order to prevent damage to the resin layer 46 at the bending point R and to prevent a decrease in the electrolyte retention ability, the resin layer 46 may be disposed in the area in the negative electrode core exposed portion 44a from the bending point R to the end B on the negative electrode current collector 17 side, and may not be disposed in the area from the end A on the negative electrode mixture layer 42 side to the bending point R.

[0031] 4 is a partially enlarged cross-sectional view showing another example of the configuration of the vicinity of the lower end of a wound-type electrode assembly. As shown in Fig. 4, the resin layer 46 on the negative electrode core exposed portion 44a provided on one negative electrode core 40 may be in contact with the negative electrode core exposed portion 44b (or a resin layer (not shown) provided on the negative electrode core exposed portion 44b) provided on another negative electrode core 40 adjacent to the one negative electrode core 40 on the radially inner side of the electrode assembly 14. This increases the amount of electrolyte held in the space between the resin layer 46 on the negative electrode core exposed portion 44a on the inner circumferential surface side of the negative electrode core 40 and the adjacent negative electrode core exposed portion 44 on the radially inner side of the electrode assembly 14, resulting in a secondary battery with superior rapid charging characteristics.

[0032] The resin layer 46 is not particularly limited as long as it is a layer mainly made of a swellable resin. Here, "mainly made of resin" means that the resin accounts for the largest proportion of the materials constituting the resin layer 46. The resin content in the resin layer 46 is preferably, for example, 80% by mass or more, and more preferably 90% by mass or more. The resin layer 46 is formed, for example, by applying a resin solution to the negative electrode substrate exposed portion 44. Examples of the resin contained in the resin layer 46 (i.e., the resin contained in the resin solution) include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, styrene-butadiene copolymer (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and polyethylene oxide (PEO). Among these, the resin preferably contains at least one selected from the group consisting of carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), and polyethylene oxide (PEO) in terms of flexibility, electrolyte retention, etc.

[0033] The thickness of the resin layer 46 is not limited, but is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 20 μm or less.

[0034] When electronic conductivity is to be imparted to the resin layer 46, the resin layer 46 may contain a conductive agent. Examples of the conductive agent include carbon black such as acetylene black or ketjen black, graphite, and carbon materials such as carbon nanotubes (single-walled carbon nanotubes, multi-walled carbon nanotubes, etc.). The content of the conductive agent in the resin layer 46 is, for example, 1% by mass or more and 20% by mass or less.

[0035] In the present embodiment, the resin layer 46 is preferably disposed on the negative electrode substrate exposed portion 44, but the same effect can be achieved even if the resin layer 46 is disposed on the positive electrode substrate exposed portion 34. Furthermore, the resin layer 46 may be disposed on both the negative electrode substrate exposed portion 44 and the positive electrode substrate exposed portion 34.

[0036] 5 is a partially enlarged cross-sectional view showing the configuration near the upper end of a wound electrode assembly. When the resin layer 46 is applied to the positive electrode 11 side, as with the negative electrode 12 side, the resin layer 46 may be provided on the positive electrode core exposed portion 34a on the inner circumferential surface side of the positive electrode core 30, or on the positive electrode core exposed portion 34b on the outer circumferential surface side of the positive electrode core 30, or on both. Among these, as shown in FIG. 5 , it is preferable to provide the resin layer 46 on the positive electrode core exposed portion 34a on the inner circumferential surface side of the positive electrode core 30. The inner circumferential surface of the positive electrode core 30 refers to the surface of the positive electrode core 30 that is located radially inward of the wound positive electrode 11 when the positive electrode 11 is wound. The outer circumferential surface of the positive electrode core 30 refers to the surface of the positive electrode core 30 that is located radially outward of the wound positive electrode 11 when the positive electrode 11 is wound. 5, the resin layer 46 may be disposed over the entire area from the end of the positive electrode core exposed portion 34a on the inner circumferential surface side of the positive electrode core 30 on the positive electrode mixture layer 32 side to the end on the positive electrode current collector 18 side. However, if the positive electrode core exposed portion 34 has a bending point and is bent from the bending point toward the inside in the radial direction of the electrode body 14, the resin layer 46 may be disposed in the area of ​​the positive electrode core exposed portion 34a from the bending point to the end on the positive electrode current collector 18 side, and the resin layer 46 may not be disposed in the area from the end on the positive electrode mixture layer 32 side to the bending point.

[0037] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0038] Example 1 Preparation of Positive Electrode 100 parts by mass of a positive electrode active material, 1 part by mass of acetylene black (AB), and 0.9 parts by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. ０．８８ Co ０．０９ Al ０．０３ O ２ An aluminum-containing lithium nickel cobalt oxide represented by the formula (1) was used. Next, the positive electrode mixture slurry was applied to both sides of the aluminum foil so as to form the above-mentioned exposed portion of the positive electrode substrate. This coating was dried, rolled, and cut to a predetermined electrode plate size to produce a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode substrate.

[0039] [Preparation of Negative Electrode] 95 parts by mass of graphite, 5 parts by mass of silicon oxide (SiO), 1 part by mass of sodium carboxymethyl cellulose (CMC-Na), and 1 part by mass of styrene butadiene rubber (SBR) were mixed, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of the copper foil so that the aforementioned negative electrode core exposed portion was formed. This coating was dried, rolled, and cut to a predetermined electrode plate size to prepare a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode core.

[0040] A resin solution containing 2% by mass of carboxymethyl cellulose was applied to the entire area of ​​one of the negative electrode substrate exposed portions to form a resin layer. When the negative electrode was wound, this negative electrode substrate exposed portion became the negative electrode substrate exposed portion on the inner peripheral surface side of the negative electrode substrate.

[0041] [Preparation of Electrolyte Solution] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:7, and lithium hexafluorophosphate (LiPF ６ An electrolyte solution was prepared by dissolving 1.5 mol / liter of ammonium hydroxide in water.

[0042] [Test Cell Preparation] A wound electrode assembly was prepared by spirally winding a positive electrode and a negative electrode with a polyethylene microporous membrane separator interposed therebetween. A positive electrode current collector and a negative electrode current collector were placed on the top and bottom of the electrode assembly, respectively. The exposed positive electrode substrate at the top end and the exposed negative electrode substrate at the bottom end of the electrode assembly were bent inward and then welded to the positive electrode current collector and the negative electrode current collector. The electrode assembly was then placed in a bottomed cylindrical outer can, and the negative electrode current collector was welded to the bottom of the bottomed cylindrical outer can. The positive electrode current collector and the seal were connected with a connecting tab. After pouring a nonaqueous electrolyte into the outer can, the opening of the outer can was sealed with a seal via a gasket to prepare a cylindrical test cell.

[0043] Example 2 A test cell was produced in the same manner as in Example 1, except that a resin layer was formed on the region from the bending point to the end on the negative electrode current collector plate side in the negative electrode core exposed portion on the inner circumferential surface side of the negative electrode core.

[0044] Example 3 A test cell was prepared in the same manner as in Example 1, except that in forming the resin layer, the resin in the resin solution was changed from carboxymethyl cellulose to polyvinylidene fluoride.

[0045] Example 4 A test cell was prepared in the same manner as in Example 1, except that in forming the resin layer, the resin in the resin solution was changed from carboxymethyl cellulose to polytetrafluoroethylene.

[0046] Example 5 A test cell was prepared in the same manner as in Example 1, except that in forming the resin layer, the resin in the resin solution was changed from carboxymethyl cellulose to polyacrylonitrile.

[0047] Example 6 A test cell was prepared in the same manner as in Example 1, except that in forming the resin layer, the resin in the resin solution was changed from carboxymethyl cellulose to polyacrylic acid.

[0048] Example 7 A test cell was prepared in the same manner as in Example 1, except that in forming the resin layer, the resin in the resin solution was changed from carboxymethyl cellulose to styrene-butadiene copolymer.

[0049] Example 8 A test cell was prepared in the same manner as in Example 1, except that in forming the resin layer, the resin in the resin solution was changed from carboxymethyl cellulose to nitrile butadiene rubber.

[0050] Example 9 A test cell was prepared in the same manner as in Example 1, except that in forming the resin layer, the resin in the resin solution was changed from carboxymethyl cellulose to a polyimide resin.

[0051] Example 10 A test cell was prepared in the same manner as in Example 1, except that in forming the resin layer, the resin in the resin solution was changed from carboxymethyl cellulose to polyvinyl alcohol.

[0052] Example 11 A test cell was prepared in the same manner as in Example 1, except that in forming the resin layer, the resin in the resin solution was changed from carboxymethyl cellulose to polyethylene oxide.

[0053] Comparative Example 1 A test cell was prepared in the same manner as in Example 1, except that no resin layer was formed on the exposed portion of the negative electrode substrate.

[0054] Comparative Example 2 A test cell was produced in the same manner as in Example 1, except that no resin layer was formed on the negative electrode substrate exposed portion, and multiple linear cut portions (see Patent Document 1) were formed on the negative electrode substrate exposed portion.

[0055] [Direct Current Resistance (DCR)] In an environment of 25°C, the test cells of each Example and Comparative Example were charged at a constant current of 0.1 C until the battery voltage reached 4.2 V, and then at a constant voltage of 4.2 V until the current reached 0.01 C. After a 10-minute rest, the cells were discharged at 0.1 C until the current reached 2.5 V. Then, the cell voltage (V1) immediately before the start of discharge during the constant current discharge process and the cell voltage (V2) 10 seconds after discharge were measured, and the DC resistance was calculated. As a result, no difference was observed between the test cells of each Example and Comparative Example.

[0056] [Evaluation of Internal Short Circuits] In a 25°C environment, test cells of each Example and Comparative Example were charged at a constant current of 0.5 C to a battery voltage of 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 0.01 C. Subsequently, the test cells were discharged at a constant current of 0.5 C to 2.5 V. This charge / discharge cycle was repeated for five cycles. After the sixth cycle of constant current / constant voltage charging, each test cell was placed in a thermostatic chamber at 60°C and left for 12 hours at high temperature for storage. The change in voltage was calculated from the battery voltage of the test cell in the charged state before and after high-temperature storage. Test cells with a change in voltage of 0.1 V or more were considered to have experienced an internal short circuit. The number of test cells with an internal short circuit out of 50 test cells is summarized in Table 1.

[0057] [Rapid Charging Test] In an environment of 45°C, the test cells of each Example and Comparative Example were charged at a constant current of 2 C until the battery voltage reached 4.2 V, and then discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V. This charge / discharge cycle was counted as one cycle, and 100 cycles were performed. The capacity retention rate was calculated using the following formula, and the results are summarized in Table 1. Capacity retention rate = (discharge capacity at 100th cycle / initial discharge capacity) x 100

[0058]

[0059] As shown in Table 1, Examples 1 to 11 had higher capacity retention rates in the rapid charge test than Comparative Examples 1 and 2. From these results, it can be said that in a secondary battery employing an end-face current collecting structure in which the exposed portion of the substrate is joined to the current collecting plate, providing a resin layer on the exposed portion of the substrate can provide excellent rapid charge characteristics. Furthermore, Examples 1 to 11 also suppressed the occurrence of internal short circuits compared to Comparative Examples 1 and 2. This result is thought to be due to the fact that in a secondary battery employing an end-face current collecting structure in which the exposed portion of the substrate is joined to the current collecting plate, providing a resin layer on the exposed portion of the substrate suppresses deformation and damage to the exposed portion of the substrate due to charge and discharge.

[0060] The present disclosure will be further described by the following embodiments. Configuration 1: A secondary battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a first current collector plate electrically connected to one of the positive electrode and the negative electrode, and an electrolyte, wherein the one electrode has a strip-shaped first core and a first mixture layer disposed on the first core, a first core exposed portion on which the first mixture layer is not disposed is provided at one end of the first core in the winding axis direction of the electrode assembly, the first core exposed portion being joined to the first current collector plate, and a swellable resin layer is provided on the first core exposed portion. Configuration 2: The secondary battery according to Configuration 1, further comprising a second current collector plate electrically connected to the other of the positive electrode and the negative electrode, wherein the other electrode has a strip-shaped second core and a second mixture layer disposed on the second core, wherein one end of the second core in the winding axis direction of the electrode body is provided with a second core exposed portion on which the second mixture layer is not disposed, and the second core exposed portion is joined to the second current collector plate, and wherein a resin layer is provided on the second core exposed portion.Configuration 3: The secondary battery according to Configuration 1 or 2, wherein the first core exposed portion has a first core exposed portion on the inner winding surface side of the first core and a first core exposed portion on the outer winding surface side of the first core, and wherein the resin layer is provided on the first core exposed portion on the inner winding surface side of the first core. Configuration 4: The secondary battery according to Configuration 3, wherein the first substrate exposed portion has a bending point and is bent radially inward from the bending point to the electrode body, and the resin layer is provided on a region of the first substrate exposed portion on the inner winding surface side of the first substrate from the bending point to the end portion on the first current collector plate side.Configuration 5: The secondary battery according to Configuration 2, wherein the second substrate exposed portion has a second substrate exposed portion on the inner winding surface side of the second substrate and a second substrate exposed portion on the outer winding surface side of the second substrate, and the resin layer is provided on the second substrate exposed portion on the inner winding surface side of the second substrate.Configuration 6: The secondary battery according to Configuration 5, wherein the second substrate exposed portion has a bending point and is bent radially inward from the bending point of the electrode assembly, and the resin layer is provided on a region of the second substrate exposed portion on the inner circumferential surface side of the second substrate, from the bending point to the end portion on the second current collector plate side. Configuration 7: The secondary battery according to any one of Configurations 1 to 6, wherein the resin layer contains at least one selected from the group consisting of carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), nitrile-butadiene rubber (NBR), polyimide resin, polyvinyl alcohol (PVA), and polyethylene oxide (PEO). Configuration 8: The secondary battery according to any one of Configurations 1 to 7, wherein the resin layer contains a conductive material. Configuration 9: The secondary battery according to any one of Configurations 1 to 8, wherein the one electrode is a negative electrode.

[0061] REFERENCE SIGNS LIST 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 16 sealing body, 17 negative electrode current collector plate, 18 positive electrode current collector plate, 19 insulating plate, 20 connection lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a through hole, 27 gasket, 30 positive electrode core, 32 positive electrode mixture layer, 34, 34a, 34b positive electrode core exposed portion, 40 negative electrode core, 42 negative electrode mixture layer, 44, 44a, 44b negative electrode core exposed portion, 46 resin layer.

Claims

1. A secondary battery comprising: an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a first current collector electrically connected to one of the positive electrode and the negative electrode; and an electrolytic solution, wherein the one electrode has a strip-shaped first core body and a first mixture layer disposed on the first core body, and a first core body exposed portion where the first mixture layer is not disposed is provided at one end of the first core body in the winding axis direction of the electrode body, the first core body exposed portion is joined to the first current collector, and a resin layer having swelling property is provided on the first core body exposed portion.

2. The secondary battery according to claim 1, further comprising a second current collector electrically connected to the other of the positive electrode and the negative electrode, wherein the other electrode has a strip-shaped second core body and a second mixture layer disposed on the second core body, and a second core body exposed portion where the second mixture layer is not disposed is provided at one end of the second core body in the winding axis direction of the electrode body, the second core body exposed portion is joined to the second current collector, and a resin layer is provided on the second core body exposed portion.

3. The secondary battery according to claim 1, wherein the first core body exposed portion has a first core body exposed portion on the inner peripheral surface side of the winding of the first core body and a first core body exposed portion on the outer peripheral surface side of the winding of the first core body, and the resin layer is provided on the first core body exposed portion on the inner peripheral surface side of the winding of the first core body.

4. The secondary battery according to claim 3, wherein the first core body exposed portion has a bending point and is bent from the bending point toward the inner side in the radial direction of the electrode body, and the resin layer is provided in a region from the bending point to the end on the first current collector side in the first core body exposed portion on the inner peripheral surface side of the winding of the first core body.

5. The secondary battery according to claim 2, wherein the second core body exposed portion has a second core body exposed portion on the inner peripheral surface side of the winding of the second core body and a second core body exposed portion on the outer peripheral surface side of the winding of the second core body, and the resin layer is provided on the second core body exposed portion on the inner peripheral surface side of the winding of the second core body.

6. The secondary battery according to claim 5, wherein the second core body exposed portion has a bending point and is bent from the bending point toward the inner side in the radial direction of the electrode body, and the resin layer is provided in a region from the bending point to the end on the second current collector side in the second core body exposed portion on the inner peripheral surface side of the winding of the second core body.

7. The secondary battery according to any one of claims 1 to 6, wherein the resin layer contains at least one selected from the group consisting of carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), nitrile butadiene rubber (NBR), polyimide resin, polyvinyl alcohol (PVA), and polyethylene oxide (PEO).

8. The secondary battery according to any one of claims 1 to 6, wherein the resin layer contains a conductive material.

9. The secondary battery according to any one of claims 1 to 6, wherein the one electrode is a negative electrode.

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