Nonaqueous electrolyte secondary battery

Abstract

Disclosed is a nonaqueous electrolyte secondary battery (10) which is characterized by comprising: an electrode body (14) that is obtained by winding a positive electrode (11) and a negative electrode (12) with a separator (13) being interposed therebetween; a nonaqueous electrolyte; and an outer package can (16) that houses the electrode body (14) and the nonaqueous electrolyte. This nonaqueous electrolyte secondary battery (10) is also characterized in that: the negative electrode (12) has a negative electrode core body (40) and a negative electrode mixture layer (41) that is provided on the negative electrode core body (40); an exposed part (42) in which the surface of the negative electrode core body (40) is exposed is formed on the outer peripheral surface of the electrode body (14); the exposed part (42) is in contact with the inner surface of the outer package can (16); the nonaqueous electrolyte contains a heterocyclic compound that comprises at least one electron-withdrawing group R and a heterocyclic ring; the electron-withdrawing group R contains oxygen and / or nitrogen; and the heterocyclic ring contains nitrogen and sulfur.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to technology for non-aqueous electrolyte secondary batteries.

[0002] BACKGROUND ART Conventionally, non-aqueous electrolyte secondary batteries have been widely known, which include an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a non-aqueous electrolyte, and an outer can that houses the electrode assembly and the non-aqueous electrolyte.

[0003] For example, Patent Documents 1 and 2 disclose nonaqueous electrolyte secondary batteries having a current collecting structure in which, for the purpose of reducing resistance or the like, an exposed portion is formed on the outer peripheral surface of a wound electrode body, where the surface of a negative electrode core is exposed, and the exposed portion is brought into contact with the inner surface of a metal outer can that serves as the negative electrode external terminal.

[0004] International Publication No. WO 2016 / 147564 International Publication No. WO 2012 / 042830

[0005] However, in a nonaqueous electrolyte secondary battery having a current collection structure in which an exposed portion of a negative electrode core formed on the outer peripheral surface of an electrode body is in contact with the inner surface of an outer can, metal may leach out from the positive electrode, the outer can, etc., and deposit on the negative electrode core, which may prevent a sufficient reduction in the initial battery resistance.

[0006] Therefore, an object of the present disclosure is to improve the reduction of initial battery resistance in a nonaqueous electrolyte secondary battery having a current collection structure in which an exposed portion of a negative electrode core formed on the outer peripheral surface of an electrode assembly is brought into contact with the inner surface of an outer can.

[0007] One aspect of the present disclosure is a non-aqueous electrolyte secondary battery including: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a non-aqueous electrolyte; and an outer can that accommodates the electrode assembly and the non-aqueous electrolyte, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer provided on the negative electrode core, an exposed portion in which the surface of the negative electrode core is exposed is formed on the outer peripheral surface of the electrode assembly, and the exposed portion is in contact with the inner surface of the outer can, and the non-aqueous electrolyte includes a heterocyclic compound including at least one electron-withdrawing group R and a heterocycle, the electron-withdrawing group R includes oxygen and / or nitrogen, and the heterocycle includes nitrogen and sulfur.

[0008] According to one aspect of the present disclosure, in a nonaqueous electrolyte secondary battery having a current collection structure in which an exposed portion of a negative electrode core formed on the outer peripheral surface of an electrode assembly is in contact with the inner surface of an outer can, it is possible to improve the reduction in initial battery resistance.

[0009] 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment;

[0010] A non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a non-aqueous electrolyte, and an outer can housing the electrode assembly and the non-aqueous electrolyte, wherein the negative electrode has a negative electrode core and a negative electrode composite layer provided on the negative electrode core, the outer peripheral surface of the electrode assembly has an exposed portion where the surface of the negative electrode core is exposed, and the exposed portion is in contact with the inner surface of the outer can, and the non-aqueous electrolyte includes a heterocyclic compound containing at least one electron-withdrawing group R and a heterocycle, wherein the electron-withdrawing group R contains oxygen and / or nitrogen, and the heterocycle contains nitrogen and sulfur. Furthermore, in the present disclosure, the heterocyclic compound (thiazole compound) contained in the non-aqueous electrolyte suppresses metal elution from the positive electrode, the outer can, and the like, thereby reducing the amount of eluted metal deposited on the negative electrode core. As a result, it is believed that the effect of reducing the initial battery resistance due to the current collection structure in which the exposed portion of the negative electrode core formed on the outer peripheral surface of the electrode assembly comes into contact with the inner surface of the exterior can is sufficiently obtained.

[0011] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described below. The drawings referred to in the following embodiment are schematic, and the dimensional ratios of the components depicted in the drawings may differ from those of the actual battery.

[0012] FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment. The nonaqueous electrolyte secondary battery 10 shown in FIG. 1 includes an electrode assembly 14, a nonaqueous electrolyte, and an outer can 16 that accommodates the electrode assembly 14, the nonaqueous electrolyte, and the like. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The outer can 16 is, for example, a cylindrical metal container with a bottom and an opening on one axial side. The nonaqueous electrolyte secondary battery 10 shown in FIG. 1 includes a sealing body 17, which closes the opening of the outer can 16. The nonaqueous electrolyte secondary battery 10 shown in FIG. 1 also includes insulating plates 18 and 19 disposed above and below the electrode assembly 14, respectively.

[0013] The positive electrode 11 has a positive electrode core 30 and a positive electrode composite layer 31 provided on the positive electrode core 30. Similarly, the negative electrode 12 has a negative electrode core 40 and a negative electrode composite layer 41 provided on the negative electrode core 40. In the nonaqueous electrolyte secondary battery 10, the negative electrode 12 is disposed on the outer peripheral surface of the electrode body 14. That is, the outermost peripheral surface of the electrode body 14 is formed by the negative electrode 12. The electrode body 14 has a positive electrode lead 20 connected to the positive electrode core 30 by welding or the like. In this embodiment, no negative electrode lead is provided, but a negative electrode lead may be provided on the inner peripheral side of the electrode body 14, for example.

[0014] An exposed portion 42, in which the surface of the negative electrode core 40 is exposed, is formed on the outer peripheral surface of the electrode body 14. The exposed portion 42 may be formed on a part of the outer peripheral surface of the electrode body 14, but is preferably formed on the entire outer peripheral surface. The exposed portion 42 may be formed on only one side (outer surface) of the negative electrode core 40 facing outward from the electrode body 14, or may be formed on both sides of the negative electrode core 40. The exposed portion 42 is formed, for example, within a range of a length equivalent to approximately one to two revolutions around the circumference of the electrode body 14 from one longitudinal end of the negative electrode core 40 located on the outer peripheral surface of the electrode body 14.

[0015] In the nonaqueous electrolyte secondary battery 10, the exposed portion 42 of the negative electrode core 40 contacts the inner surface of the outer can 16, electrically connecting the negative electrode 12 and the outer can 16. The exposed portion 42 contacts the inner surface of the outer can 16 over the entire periphery of the electrode body 14, for example. In the nonaqueous electrolyte secondary battery 10, the outer can 16 electrically connected to the negative electrode 12 serves as the negative electrode external terminal.

[0016] As described above, the outer can 16 is a cylindrical metal container with a bottom and an opening on one axial side. A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure sealing of the battery interior and insulation between the outer can 16 and the sealing body 17. The outer can 16 has, for example, a protruding portion 21, which is a portion of the side surface that protrudes inward and supports the sealing body 17. The protruding portion 21 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the outer can 16 by the protruding portion 21 and the open end of the outer can 16 that is crimped to the sealing body 17.

[0017] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulator 25, an upper valve body 26, and a cap 27 are stacked in this order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disk or ring shape, and each component except for the insulator 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulator 25 is interposed between their respective peripheral edges. If an abnormality occurs in the battery and the internal pressure increases, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure further increases, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0018] The above-mentioned positive electrode lead 20 passes through the through-hole of the insulating plate 18 and extends toward the sealing body 17, and is connected by welding or the like to the underside of the filter 23, which is the bottom plate of the sealing body 17. In the nonaqueous electrolyte secondary battery 10, the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, serves as the positive electrode external terminal.

[0019] The non-aqueous electrolyte, the positive electrode 11, the negative electrode 12, and the separator 13 will be described below.

[0020] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent, an electrolyte salt, and a heterocyclic compound containing at least one electron-withdrawing group R and a heterocycle. Hereinafter, the heterocycle and the heterocyclic compound may be referred to as "heterocycle (H)" and "heterocyclic compound (C)," respectively. The electron-withdrawing group R contains oxygen and / or nitrogen. The heterocycle (H) contains nitrogen and sulfur. As described above, the inclusion of the heterocyclic compound (C) in the non-aqueous electrolyte suppresses metal elution from the positive electrode, outer can, etc., which leads to a sufficient reduction in initial battery resistance due to the current collection structure in which the exposed portion of the negative electrode core formed on the outer peripheral surface of the electrode assembly contacts the inner surface of the outer can.

[0021] The non-aqueous electrolyte may contain only one type of compound as the heterocyclic compound (C), or may contain multiple types of compounds.

[0022] The electron-withdrawing group R contained in the heterocyclic compound (C) may contain only one of oxygen and nitrogen, or may contain both. For example, the electron-withdrawing group R may be a carbonyl group (—C(═O)—), a nitrile group (—C≡N), a sulfonyl group (—S(═O)—), or a hydroxyl group (—S(═O)—) in order to further improve the reduction of the initial battery resistance. ２ The hydroxy group, which is the electron-withdrawing group R, may be bonded to a carbon atom constituting a saturated hydrocarbon group (e.g., an alkyl group or an alkylene group). The nitrile group may be contained in a thionitrile group. The sulfonyl group may be a sulfonate ester bond (-S(=O) ２ —O—). The C═O moiety contained in an isocyanate group and an isothiocyanate group is not usually considered to be a carbonyl group. Therefore, in this specification, the C═O moiety contained in an isocyanate group and an isothiocyanate group is not considered to be a carbonyl group.

[0023] The carbonyl group may be contained in at least one selected from the group consisting of an aldehyde group (-CHO), a ketone, an amide bond (C(=O)-N), an ester bond (COO), and a carboxy group (-COOH). That is, the electron-withdrawing group R may be at least one selected from the group consisting of an aldehyde group, a carbonyl group contained in a ketone, an amide bond, an ester bond, and a carboxy group.

[0024] The number of electron-withdrawing groups R contained in the heterocyclic compound (C) may be 1, 2 or more, 5 or more, or 5 or less. The number of heterocycles (H) contained in the heterocyclic compound (C) may be 1, 2, 3 or less, or 3 or more.

[0025] The heterocycle (H) contains nitrogen and sulfur. The heterocycle (H) may or may not have aromaticity. The number of atoms constituting the heterocycle (H) may be in the range of 5 to 8, or in the range of 5 to 7, or may be 5 or 6. That is, the heterocycle (H) may be a five-membered ring, a six-membered ring, a seven-membered ring, or an eight-membered ring.

[0026] The heterocycle (H) may satisfy the following conditions (1) and / or (2), or may satisfy the following conditions (1) and (3): (1) The heterocycle (H) is composed of one nitrogen atom, one sulfur atom, and multiple carbon atoms; (2) The nitrogen atom forms a double bond with one adjacent carbon atom that constitutes the heterocycle (H); and (3) The nitrogen atom forms a single bond with each of the two adjacent carbon atoms that constitute the heterocycle (H).

[0027] The heterocycle (H) may be a thiazole ring represented by the following formula:

[0028]

[0029] The heterocycle (H) may be a thiomorpholine ring represented below.

[0030]

[0031] The heterocycle (H) may be a thiazepine ring represented by the following formula: The thiazepine ring may be a 1,3-thiazepine ring or a 1,4-thiazepine ring.

[0032]

[0033] The heterocycle (H) may contain at least one ring selected from the group consisting of a thiazole ring, a thiomorpholine ring, and a thiazepine ring.

[0034] The structure of the heterocyclic compound (C) other than the heterocycle (H) and the electron-withdrawing group R is not limited as long as the effects of the present disclosure are obtained. The portion other than the heterocycle (H) and the electron-withdrawing group R may be composed only of hydrocarbons. Examples of hydrocarbons include hydrocarbon groups (including hydrocarbon chains). Examples of hydrocarbons include aliphatic hydrocarbons and aromatic hydrocarbons. The heterocyclic compound (C) may contain an ether bond, a thioether bond, nitrogen not included in the electron-withdrawing group R, etc.

[0035] The molecular weight of the heterocyclic compound (C) may be 100 or more, or 130 or more, and may be 400 or less, or 370 or less.

[0036] As the heterocyclic compound (C), a compound that dissolves in the non-aqueous solvent of the non-aqueous electrolyte is preferably used.

[0037] Examples of the heterocyclic compound (C) include 4,5-dimethyl-1,3-thiazole-2-carbaldehyde, 4,5,6,7-tetrahydro-1,3-benzothiazole-2-carbaldehyde, ethyl 2-ethynyl-4-methylthiazole-5-carboxylate, N-benzyl-2-ethynyl-4-methylthiazole-5-carboxamide, 4-methyl-5-(2-thiocyanatoethyl)thiazole, perfluorophenyl 4,5-dimethylthiazole-2-sulfonate, 2-(trimethylsilyl)thiazole-4-carbaldehyde, 4-(((tert-butyl Examples of the thiocyanate include 1-(5-(hydroxymethyl)-4-methylthiazol-2-yl)ethan-1-one, 5-isocyanato-4-methyl-2-phenylthiazole, 5-isocyanato-4-methyl-2-(pyrazin-2-yl)thiazole, 2-ethylthiomorpholine-4-carbaldehyde, 2,3-dimethylthiomorpholine-4-carbaldehyde, 2-methyl-4-thiocyanatobenzo[b][1,4]thiazepine, and 4-methyl-2-thiocyanatobenzo[b][1,4]thiazepine. Among these, it is preferable that the heterocyclic compound (C) contains at least one selected from the group consisting of 4,5-dimethyl-1,3-thiazole-2-carbaldehyde, 4,5,6,7-tetrahydro-1,3-benzothiazole-2-carbaldehyde, 2-ethylthiomorpholine-4-carbaldehyde, and 2,3-dimethylthiomorpholine-4-carbaldehyde, in that it is possible to further improve the reduction in initial battery resistance.

[0038] The heterocyclic compound (C) may be a commercially available compound, or may be synthesized according to a known synthesis method.

[0039] The content of the heterocyclic compound (C) in the non-aqueous electrolyte may be 0.1 mass % or more, 0.5 mass % or more, or 1.0 mass % or more, and may be 10.0 mass % or less, 5.0 mass % or less, or 3.0 mass % or less. By setting the content within the above range, it is possible to further reduce the initial battery resistance.

[0040] The content of the heterocyclic compound (C) in the non-aqueous electrolyte is determined using gas chromatography under the following conditions. Used equipment: GC-2010 Plus, manufactured by Shimadzu Corporation. Column: HP-1 (film thickness 1 μm, inner diameter 0.32 mm, length 60 m), manufactured by J&W. Column temperature: heated from 50°C to 90°C at a heating rate of 5°C / min, maintained at 90°C for 15 minutes, then heated from 90°C to 250°C at a heating rate of 10°C / min, and maintained at 250°C for 15 minutes. Split ratio: 1 / 50. Linear velocity: 30.0 cm / sec. Injection port temperature: 270°C. Injection volume: 1 μL. Detector: FID 290°C (sens. 10 １ )

[0041] Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC) and ethylene carbonate (EC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl formate, ethyl formate, propyl formate, methyl acetate (MA), ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The non-aqueous electrolyte may contain only one non-aqueous solvent, or may contain two or more non-aqueous solvents.

[0042] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０Examples of the lithium salts include lithium carboxylates, lower aliphatic carboxylates, LiCl, LiBr, LiI, borates, and imide salts. Examples of the borates include lithium difluorooxalate borate and lithium bis(oxalate) borate. Examples of the imide salts include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ The non-aqueous electrolyte may contain only one type of electrolyte salt or may contain two or more types of electrolyte salts. The concentration of the electrolyte salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less.

[0043] (Positive Electrode) As described above, the positive electrode 11 includes a positive electrode core 30 and a positive electrode composite layer 31 provided on the positive electrode core 30. Examples of the positive electrode core 30 include a foil of a metal stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, and a film having such a metal disposed on its surface. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 50 μm or less. The positive electrode composite layer 31 includes, for example, a positive electrode active material, a conductive material, a binder, and the like. The positive electrode composite layer 31 may be disposed on only one surface of the positive electrode core 30, or may be disposed on both surfaces of the positive electrode core 30. The positive electrode 11 is obtained, for example, by applying and drying a positive electrode composite slurry containing, for example, a positive electrode active material, onto the positive electrode core 30, thereby forming a positive electrode composite layer 31 on the positive electrode core 30, and then rolling the positive electrode composite layer 31.

[0044] The positive electrode active material may be, for example, a lithium transition metal composite oxide containing transition metal elements such as Ni, Co, or Mn. Metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, and Bi. Among these, it is preferable to contain at least one of Ni, Co, and Mn. Examples of suitable composite oxides include lithium transition metal composite oxides containing Ni, Co, and Mn, and lithium transition metal composite oxides containing Ni, Co, and Al. One type of lithium transition metal composite oxide may be used alone, or multiple types may be used in combination.

[0045] The lithium transition metal composite oxide has, for example, a layered rock salt structure. Examples of the layered rock salt structure include a layered rock salt structure belonging to the space group R-3m and a layered rock salt structure belonging to the space group C2 / m. Among these, a layered rock salt structure belonging to the space group R-3m is preferred from the viewpoints of high capacity and stability of the crystal structure. The content of the positive electrode active material is, for example, 90% by mass or more and 99% by mass or less with respect to the mass of the positive electrode mixture layer.

[0046] Examples of conductive materials include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powder, and conductive whiskers. One type of conductive material may be used alone, or multiple types may be used in combination. The content of the conductive material may be, for example, 0.1% by mass or more and 5% by mass or less with respect to the total mass of the positive electrode mixture layer.

[0047] Examples of binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer, acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer, styrene-butadiene copolymer (SBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), and polyethylene oxide (PEO). One type of binder may be used alone, or multiple types may be used in combination. The content of the binder may be 0.6% by mass or more and 1.5% by mass or less with respect to the total mass of the positive electrode mixture layer.

[0048] (Negative Electrode) As described above, the negative electrode 12 has a negative electrode core 40 and a negative electrode composite layer 41 disposed on the negative electrode core 40. The negative electrode 12 also has an exposed portion 42 in which the surface of the negative electrode core 40 is exposed, in a portion corresponding to the outer peripheral surface of the electrode body 14. Examples of the negative electrode core 40 include a metal foil made of copper, a copper alloy, or the like that is stable within the potential range of the negative electrode 12, and a film having such a metal disposed on its surface. The thickness of the negative electrode core 40 is, for example, 5 μm or more and 50 μm or less. The negative electrode composite layer 41 includes, for example, a negative electrode active material, a binder, and the like. The negative electrode composite layer 41 may be formed on only one surface of the negative electrode core 40, or on both surfaces of the negative electrode core 40. The negative electrode 12 is obtained, for example, by applying and drying a negative electrode composite slurry containing a negative electrode active material and the like onto the negative electrode core 40 to form a negative electrode composite layer 41 on the negative electrode core 40, and then rolling the negative electrode composite layer 41.

[0049] The negative electrode active material is not particularly limited as long as it is a material that reversibly absorbs and releases ions such as lithium ions, but examples thereof include carbon-based materials. Examples of carbon-based materials include natural graphite such as flake graphite, lump graphite, and earthy graphite, and graphite such as lump artificial graphite and artificial graphite such as graphitized mesophase carbon microbeads. The negative electrode active material may also be a metal that alloys with lithium, such as Si or Sn, an alloy containing such a metal, or a compound containing such a metal. For example, in terms of increasing the capacity of the battery, the negative electrode active material preferably contains a compound containing Si (hereinafter referred to as a Si-containing material).

[0050] The Si-containing material includes, for example, a lithium ion conductive phase and a silicon phase (silicon particles in one aspect) dispersed within the lithium ion conductive phase. The lithium ion conductive phase includes, for example, at least one of a silicon oxide phase, a silicate phase, and a carbon phase.

[0051] The silicate phase preferably contains at least one element selected from the group 2 elements of the periodic table, including alkali metal elements such as lithium, sodium, potassium, rubidium, cesium, and francium, and elements of Group 2 of the periodic table, including beryllium, magnesium, calcium, strontium, barium, and radium, in terms of high lithium ion conductivity, etc. Among these, a silicate phase containing lithium (hereinafter sometimes referred to as a lithium silicate phase) is preferred in terms of high lithium ion conductivity, etc.

[0052] The lithium silicate phase can be, for example, a compound of the formula: Li ２ｚ SiO ２＋ｚ (0<z<2). From the viewpoints of stability, ease of preparation, lithium ion conductivity, and the like, z preferably satisfies the relationship 0<z<1, and more preferably z=1 / 2.

[0053] The Si-containing material in which the silicon phase is dispersed in the silicon oxide phase can be, for example, a material having the general formula SiO ｘ (The range of 0<x<2 is preferred, and the range of 0.5≦x≦1.6 is more preferred.) The Si-containing material in which the silicon phase is dispersed in the carbon phase can be represented by, for example, the general formula Si ｘ C ｙ(The ranges of 0<x≦1 and 0<y≦1 are preferred).

[0054] The content ratio of the Si-containing material in the negative electrode active material may be 0.5% by mass or more, 3% by mass or more, or 5% by mass or more, and may be 20% by mass or less, 18% by mass or less, or 15% by mass or less, from the viewpoint of increasing the capacity of the battery, etc.

[0055] Examples of the binder include the same materials as those used in the case of positive electrode 11. Note that negative electrode mixture layer 41 may also contain a conductive material.

[0056] 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.

[0057] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0058] Example 1 Preparation of Positive Electrode A positive electrode composite slurry was prepared by mixing lithium cobalt oxide, acetylene black, and polyvinylidene fluoride, which are positive electrode active materials, in a solids mass ratio of 100:1:1, and using N-methylpyrrolidone (NMP) as a dispersion medium. The slurry was applied to both sides of a positive electrode core made of aluminum foil, and the coating was dried and rolled to obtain a positive electrode having positive electrode composite layers formed on both sides of the positive electrode core.

[0059] [Negative Electrode Fabrication] Graphite, carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a solids mass ratio of 100:1:1, and an appropriate amount of water was added to prepare a negative electrode composite slurry. The slurry was applied to both sides of a copper foil negative electrode core, and the coating was dried and rolled to obtain a negative electrode with a negative electrode composite layer formed on both sides of the negative electrode core. An exposed portion was provided at one longitudinal end of the negative electrode, exposing the surface of the negative electrode core.

[0060] [Preparation of non-aqueous electrolyte] 0.5 mass % of 4,5-dimethyl-1,3-thiazole-2-carbaldehyde, which is a heterocyclic compound (C), was added to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 to prepare a non-aqueous electrolyte solution containing lithium hexafluorophosphate (LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.0 mol / L of ammonium hydroxide in water.

[0061] [Fabrication of Non-Aqueous Electrolyte Secondary Battery] (1) After attaching a positive electrode lead to the positive electrode, a separator made of a polyethylene microporous film was placed between the positive electrode and the negative electrode to form a wound electrode assembly. The electrodes and separator were wound so that the exposed portion of the negative electrode core formed the outer circumferential surface of the electrode assembly. (2) Insulating plates were placed above and below the electrode assembly, and the positive electrode lead was welded to a sealing member, and the electrode assembly was then housed in an outer can. (3) A non-aqueous electrolyte was injected into the outer can using a reduced pressure method, and the opening of the outer can was sealed with a sealing member via a gasket. This resulted in a non-aqueous electrolyte secondary battery. This non-aqueous electrolyte secondary battery has a current collecting structure (so-called JRC structure) in which the exposed portion of the negative electrode core contacts the inner surface of the outer can.

[0062] Example 2 A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that 1 mass % of 4,5-dimethyl-1,3-thiazole-2-carbaldehyde was added to the mixed solvent.

[0063] Example 3 A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that 1 mass % of 2-ethylthiomorpholine-4-carbaldehyde was added to the mixed solvent.

[0064] Comparative Example 1 A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that 4,5-dimethyl-1,3-thiazole-2-carbaldehyde was not added to the mixed solvent.

[0065] Comparative Example 2 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that 4,5-dimethyl-1,3-thiazole-2-carbaldehyde was not added to the mixed solvent, and the current collecting structure on the negative electrode side was a current collecting structure in which the negative electrode lead attached to the negative electrode was welded to the outer can instead of the JRC structure.

[0066] Comparative Example 3 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that 1 mass % of 4,5-dimethyl-1,3-thiazole-2-carbaldehyde was added to the mixed solvent, and the current collecting structure on the negative electrode side was changed from the JRC structure to a current collecting structure in which the negative electrode lead attached to the negative electrode was welded to the outer can.

[0067] Comparative Example 4 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that 1 mass % of thiazole was added to the mixed solvent.

[0068] [Measurement of Initial Battery Resistance] In an environment of 25°C, the nonaqueous electrolyte secondary batteries of each Example and Comparative Example were charged to 50% SOC at a constant current of 0.5 C. The voltage at this time was designated as V0. Next, the batteries were discharged for 10 seconds at a constant current of 0.5 C. The voltage at this time was designated as V1. The direct current resistance (DCR) was then calculated using the following formula. This was designated as the initial battery resistance, and the initial battery resistances of each Example and Comparative Example are summarized in Table 1. However, in Table 1, the initial battery resistance of Comparative Example 1 is set as the reference (100), and the initial battery resistances of the other Examples and Comparative Examples are shown relative to each other. DCR = (V0 - V1) / 0.5 C

[0069]

[0070] As in Examples 1 to 3, the effect of reducing initial battery resistance was sufficient by employing a JRC structure as the current collecting structure of the negative electrode and adding a heterocyclic compound containing an electron-withdrawing group R containing oxygen and / or nitrogen and a heterocyclic ring containing nitrogen and sulfur to the non-aqueous electrolyte. On the other hand, as in Comparative Examples 2 to 4, when the JRC structure was not employed as the current collecting structure of the negative electrode and / or when a heterocyclic compound containing an electron-withdrawing group R containing oxygen and / or nitrogen and a heterocyclic ring containing nitrogen and sulfur was not added to the non-aqueous electrolyte, the effect of reducing battery resistance was not obtained.

[0071] The present disclosure is further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery comprising: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a non-aqueous electrolyte; and an outer can accommodating the electrode assembly and the non-aqueous electrolyte, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer provided on the negative electrode core, wherein an exposed portion where the surface of the negative electrode core is exposed is formed on the outer peripheral surface of the electrode assembly, and the exposed portion is in contact with the inner surface of the outer can, wherein the non-aqueous electrolyte comprises a heterocyclic compound comprising at least one electron-withdrawing group R and a heterocycle, wherein the electron-withdrawing group R comprises oxygen and / or nitrogen, and the heterocycle comprises nitrogen and sulfur. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the electron-withdrawing group R comprises at least one selected from the group consisting of a carbonyl group, a nitrile group, a sulfonyl group, an isocyanate group, an isothiocyanate group, and a hydroxy group, and wherein the hydroxy group is bonded to a carbon constituting a saturated hydrocarbon group. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 3, wherein the carbonyl group is contained in at least one selected from the group consisting of an aldehyde group, a ketone, an amide bond, an ester bond, and a carboxy group.Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the heterocycle includes at least one selected from the group consisting of a thiazole ring, a thiomorpholine ring, and a thiazepine ring.Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the heterocyclic compound includes at least one selected from the group consisting of 4,5-dimethyl-1,3-thiazole-2-carbaldehyde, 4,5,6,7-tetrahydro-1,3-benzothiazole-2-carbaldehyde, 2-ethylthiomorpholine-4-carbaldehyde, and 2,3-dimethylthiomorpholine-4-carbaldehyde. Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the content of the heterocyclic compound in the nonaqueous electrolyte is 0.1% by mass or more and 3% by mass or less.

[0072] REFERENCE SIGNS LIST 10 nonaqueous electrolyte secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 16 outer can, 17 sealing body, 18, 19 insulating plate, 20 positive electrode lead, 21 protruding portion, 23 filter, 24 lower valve body, 25 insulator, 26 upper valve body, 27 cap, 28 gasket, 30 positive electrode core body, 31 positive electrode composite layer, 40 negative electrode core body, 41 negative electrode composite layer, 42 exposed portion.

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a non-aqueous electrolyte; and an outer can accommodating the electrode assembly and the non-aqueous electrolyte, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer provided on the negative electrode core, an exposed portion where the surface of the negative electrode core is exposed is formed on the outer peripheral surface of the electrode assembly, and the exposed portion is in contact with the inner surface of the outer can, wherein the non-aqueous electrolyte comprises a heterocyclic compound comprising at least one electron-withdrawing group R and a heterocycle, the electron-withdrawing group R comprises oxygen and / or nitrogen, and the heterocycle comprises nitrogen and sulfur.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electron-withdrawing group R comprises at least one selected from the group consisting of a carbonyl group, a nitrile group, a sulfonyl group, an isocyanate group, an isothiocyanate group, and a hydroxy group, and the hydroxy group is bonded to a carbon constituting a saturated hydrocarbon group.

3. The nonaqueous electrolyte secondary battery according to claim 2, wherein the carbonyl group is contained in at least one selected from the group consisting of an aldehyde group, a ketone, an amide bond, an ester bond, and a carboxy group.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the heterocycle includes at least one selected from the group consisting of a thiazole ring, a thiomorpholine ring, and a thiazepine ring.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the heterocyclic compound includes at least one selected from the group consisting of 4,5-dimethyl-1,3-thiazole-2-carbaldehyde, 4,5,6,7-tetrahydro-1,3-benzothiazole-2-carbaldehyde, 2-ethylthiomorpholine-4-carbaldehyde, and 2,3-dimethylthiomorpholine-4-carbaldehyde.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the heterocyclic compound in the non-aqueous electrolyte is 0.1% by mass or more and 3% by mass or less.

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