Non-aqueous electrolyte secondary battery and method for manufacturing a non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolytic solution secondary battery (1) has a wound electrode body (2) in which a positive electrode (11) and a negative electrode (12) are wound with a separator interposed therebetween, a non-aqueous electrolytic solution, and a battery case for accommodating the wound electrode body (2) and the non-aqueous electrolytic solution. The relationship between the elemental nitrogen concentration A1 derived from a dinitrile-group-containing compound in an outermost circumferential surface (2a) of the wound electrode body (2), and the elemental nitrogen concentration B derived from a dinitrile-group-containing compound in an inner region located further inward than the outermost circumferential surface (2a) of the wound electrode body (2), satisfies A1>B.

Description

[Technical Field]

[0001] This disclosure relates to a non-aqueous electrolyte secondary battery and a method for manufacturing a non-aqueous electrolyte secondary battery. [Background technology]

[0002] In recent years, non-aqueous electrolyte secondary batteries have been widely used as high-power, high-energy-density secondary batteries. These batteries consist of an electrode body in which a positive electrode and a negative electrode are wound with a separator in between, and a non-aqueous electrolyte, and charge and discharge are performed by moving lithium ions between the positive and negative electrodes.

[0003] For example, Patent Documents 1 to 4 propose a non-aqueous electrolyte secondary battery that uses a non-aqueous electrolyte to which a nitrile compound has been added. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 07-176322 [Patent Document 2] Japanese Patent Publication No. 2004-179146 [Patent Document 3] Japanese Patent Publication No. 2010-073367 [Patent Document 4] Japanese Patent Publication No. 2006-073513 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Incidentally, while adding nitrile compounds to a non-aqueous electrolyte can suppress the leaching of metal components from electrodes and battery cases into the non-aqueous electrolyte, it presents the problem of increasing the initial resistance of non-aqueous electrolyte secondary batteries.

[0006] Therefore, the object of this disclosure is to provide a non-aqueous electrolyte secondary battery and a method for manufacturing the same that can suppress metal elution into the non-aqueous electrolyte and an increase in the initial resistance of the battery.

Means for Solving the Problem

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a wound electrode body in which a positive electrode and a negative electrode are wound via a separator, a non-aqueous electrolyte, and a battery case that houses the wound electrode body and the non-aqueous electrolyte. In the non-aqueous electrolyte secondary battery, a nitrogen element concentration A1 derived from a dinitrile group-containing compound on the outermost peripheral surface of the wound electrode body and a nitrogen element concentration B derived from the dinitrile group-containing compound in an internal region inside the outermost peripheral surface of the wound electrode body satisfy the relationship A1 > B.

[0008] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a wound electrode body in which a positive electrode and a negative electrode are wound via a separator, a non-aqueous electrolyte, and a battery case that houses the wound electrode body and the non-aqueous electrolyte. In the non-aqueous electrolyte secondary battery, a nitrogen element concentration A2 derived from a dinitrile group-containing compound on the inner wall of the battery case and a nitrogen element concentration B derived from the dinitrile group-containing compound in an internal region inside the outermost peripheral surface of the wound electrode body satisfy the relationship A2 > B.

[0009] A method for manufacturing a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a step of applying a dinitrile group-containing compound to the outermost peripheral surface of a wound electrode body in which a positive electrode and a negative electrode are wound via a separator, and a step of housing the wound electrode body to which the dinitrile group-containing compound is applied and the non-aqueous electrolyte in a battery case. The dinitrile group-containing compound is a compound represented by the chemical formula NC-X-CN (where X is an aliphatic hydrocarbon group having 1 to 12 carbon atoms (which may have a heteroatom) or an aromatic hydrocarbon group having 6 to 20 carbon atoms (which may have a heteroatom)).

[0010] Also, a method for manufacturing a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a step of applying a dinitrile group-containing compound to the inner wall of a battery case, and a step of accommodating a wound electrode body in which a positive electrode and a negative electrode are wound via a separator and a non-aqueous electrolyte in the battery case to which the dinitrile group-containing compound is applied. The dinitrile group-containing compound is a compound represented by the chemical formula NC-X-CN (where X is an aliphatic hydrocarbon group having 1 to 12 carbon atoms (which may have heteroatoms) or an aromatic hydrocarbon group having 6 to 20 carbon atoms (which may have heteroatoms)).

Advantages of the Invention

[0011] According to one aspect of the present disclosure, it is possible to provide a non-aqueous electrolyte secondary battery and a method for manufacturing the same that can suppress metal elution into the non-aqueous electrolyte and an increase in the initial resistance of the battery. <(

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a perspective view showing the appearance of a non-aqueous electrolyte secondary battery according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the non-aqueous electrolyte secondary battery taken along line L1-L1 in FIG. 1.

Modes for Carrying Out the Invention

[0013] Hereinafter, an example of a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure will be described. The drawings referred to in the following description of the embodiments are schematically depicted, and dimensional ratios and the like of the components depicted in the drawings may differ from reality.

[0014] FIG. 1 is a perspective view showing the appearance of a non-aqueous electrolyte secondary battery according to an embodiment. FIG. 2 is a cross-sectional view of the non-aqueous electrolyte secondary battery taken along line L1-L1 in FIG. 1.

[0015] The non-aqueous electrolyte secondary battery 1 according to the present embodiment includes an electrode body 2, a non-aqueous electrolyte (not shown), and a battery case 3.

[0016] The battery case 3 houses the electrode body 2, a non-aqueous electrolyte, etc., and is composed of, for example, a case body 5 having an opening and a sealing body 6 that seals the opening of the case body 5. The case body 5 is, for example, a bottomed cylindrical metal outer casing, and a groove 5c protruding inward along the circumferential direction is formed on the upper part of the case body 5. The sealing body 6 is supported by the groove 5c and seals the opening of the case body 5. To ensure airtightness inside the battery, it is desirable to provide a gasket between the case body 5 and the sealing body 6.

[0017] The electrode body 2 shown in Figure 2 is a wound-type electrode body in which a positive electrode 11 and a negative electrode 12 are wound around a separator (hereinafter referred to as wound-type electrode body 2). However, in Figure 2, the separator placed between the positive electrode 11 and the negative electrode 12 is not shown. The wound-type electrode body 2 shown in Figure 2 is cylindrical, but the shape of the wound-type electrode body 2 is not limited to this, and it may be flattened or the like.

[0018] The negative electrode 12 comprises a negative electrode current collector 14 and a negative electrode active material layer 16 disposed on the negative electrode current collector 14. It is desirable that the negative electrode active material layer 16 be disposed on both sides of the negative electrode current collector 14.

[0019] Furthermore, the negative electrode 12 does not have a negative electrode active material layer 16 on the negative electrode current collector 14, and has exposed negative electrode current collector portions 14a and 14b where the negative electrode current collector 14 is exposed. As shown in Figure 2, the exposed negative electrode current collector portion 14a is located on the innermost circumference side of the electrode body 2, and the exposed negative electrode current collector portion 14b is located on the outermost circumference side of the electrode body 2. In the exposed negative electrode current collector portion 14b shown in Figure 2, the radially outer surface (outer surface) 15 of the electrode body 2 has the negative electrode current collector 14 exposed for a length that encircles the outermost end of the electrode body 2 by more than one turn, forming the outermost surface 2a of the electrode body 2. The elements forming the outermost surface 2a of the electrode body 2 are determined according to the design of the electrode body 2. For example, if the negative electrode active material layer 16 extends to the outermost periphery of the electrode body 2, then the surface of the negative electrode active material layer 16 in the extended portion and the outer surface 15 of the exposed negative electrode current collector portion 14b become the outermost periphery surface 2a of the electrode body 2. Also, if the outermost periphery of the electrode body 2 is designed to be a separator, then the radially outer surface of the electrode body 2 at the outermost periphery of the separator becomes the outermost periphery surface 2a of the electrode body 2. Furthermore, if the outermost periphery of the electrode body 2 is designed to be a positive electrode 11, then the radially outer surface of the electrode body 2 at the outermost periphery of the positive electrode 11 becomes the outermost periphery surface 2a of the electrode body 2.

[0020] In this embodiment, the outer surface 15 of the exposed negative electrode current collector portion 14b is the outermost outer surface 2a of the electrode body 2. In this case, it is desirable that the outer surface 15 of the exposed negative electrode current collector portion 14b is in contact with the inner wall of the case body 5. This allows the case body 5 to be used as the negative electrode terminal. Alternatively, in this embodiment, instead of or in combination with the structure in which the outer surface 15 of the exposed negative electrode current collector portion 14b is in contact with the inner wall of the case body 5, the case body 5 may be used as the negative electrode terminal by connecting one end of the negative electrode tab to the negative electrode 12 (for example, the exposed negative electrode current collector portion 14a) and connecting the other end to the case body 5 (for example, the bottom).

[0021] Incidentally, when manufacturing a non-aqueous electrolyte secondary battery, as will be described later, a dinitrile group-containing compound is applied to the outermost surface 2a of the electrode body 2, or to the inner wall of the battery case 3. Therefore, in the non-aqueous electrolyte secondary battery 1 of this embodiment, the nitrogen element concentration A1 derived from the dinitrile group-containing compound on the outermost surface 2a of the electrode body 2 (outer surface 15 of the exposed negative electrode current collector portion 14b in Figure 2) and the nitrogen element concentration B derived from the dinitrile group-containing compound in the internal region inside the outermost surface 2a of the electrode body 2 satisfy the relationship A1 > B, and / or, the nitrogen element concentration A2 derived from the dinitrile group-containing compound on the inner wall of the battery case 3 and the nitrogen element concentration B derived from the dinitrile group-containing compound in the internal region inside the outermost surface 2a of the electrode body 2 satisfy the relationship A2 > B. The internal region inside the outermost surface 2a of the electrode body 2 means the region radially inward of the electrode body 2 from the outermost surface 2a of the electrode body 2. Furthermore, "derived from dinitrile group-containing compound" refers to the dinitrile group-containing compound itself, or the decomposition products of the dinitrile group-containing compound due to charge-discharge reactions, etc. In other words, in this embodiment, the dinitrile group-containing compound and its decomposition products are more abundant on the outermost surface 2a of the electrode body 2 and / or on the inner wall of the battery case 3 than in the internal region inside the outermost surface 2a of the electrode body 2.

[0022] Conventionally, when a dinitrile group-containing compound is added to a non-aqueous electrolyte, it decomposes during charging and discharging, and a film of the decomposition products of the dinitrile group-containing compound is formed on the outermost surface 2a and internal regions of the electrode body 2, as well as on the inner wall of the battery case 3. This film suppresses the leaching of metal components from the outermost surface 2a of the electrode body 2 and the battery case 3 into the non-aqueous electrolyte. By suppressing such metal leaching into the non-aqueous electrolyte, effects such as suppressing the deterioration of charge-discharge cycle characteristics can be obtained. However, the film formed on the negative electrode active material layer in the internal region of the electrode body 2 becomes a resistive component, thus increasing the initial resistance of the battery.

[0023] On the other hand, in the case of a non-aqueous electrolyte secondary battery of this embodiment, where A1, A2, and B satisfy the relationship A1 > B and / or A2 > B, a large film of decomposition products of the dinitrile group-containing compound is formed on the outermost surface 2a of the electrode body 2 and the inner wall of the battery case 3, while a small film of decomposition products of the dinitrile group-containing compound is formed in the internal region of the electrode body 2. In this state, the elution of metal components from the outermost surface 2a of the electrode body 2 and the battery case 3 into the non-aqueous electrolyte is suppressed, and furthermore, it becomes difficult for a film that acts as a resistive component to form on the negative electrode active material layer and other parts in the internal region of the electrode body 2, thus suppressing the increase in the initial resistance of the battery.

[0024] It is preferable that the ratio (B / A1) of the nitrogen element concentration B derived from the dinitrile group-containing compound in the internal region of the electrode body 2 inside the outermost surface 2a to the nitrogen element concentration A1 derived from the dinitrile group-containing compound at the outermost surface 2a of the electrode body 2 is 0.5 or less. Furthermore, it is preferable that the ratio (B / A2) of the nitrogen element concentration B derived from the dinitrile group-containing compound in the internal region inside the outermost surface 2a of the electrode body 2 to the nitrogen element concentration A2 derived from the dinitrile group-containing compound at the inner wall of the battery case 3 is 0.5 or less. By satisfying the above ranges, metal elution into the non-aqueous electrolyte or an increase in the initial resistance of the battery may be suppressed compared to cases where the above ranges are not satisfied.

[0025] The nitrogen element concentration A1 derived from the dinitrile group-containing compound on the outermost surface 2a of the electrode body 2, or the nitrogen element concentration A2 derived from the dinitrile group-containing compound on the inner wall of the battery case 3, is preferably in the range of 2 to 20 atomic percent, and more preferably in the range of 2 to 10 atomic percent, for example, in terms of suppressing metal elution into the non-aqueous electrolyte. Furthermore, the nitrogen element concentration B derived from the dinitrile group-containing compound in the internal region inside the outermost surface 2a of the electrode body 2 is preferably 1 atomic percent or less, and preferably zero, for example, in terms of suppressing an increase in the initial resistance of the battery. Refer to the Examples section for the method of measuring the nitrogen element concentration derived from the dinitrile group-containing compound.

[0026] The negative electrode current collector 14 can be, for example, a foil of a metal that is stable in the potential range of the negative electrode 12, such as copper, or a film on which the metal is arranged on the surface.

[0027] The negative electrode active material layer 16 includes, for example, a negative electrode active material, a binder, and the like.

[0028] The negative electrode active material is not particularly limited as long as it is a material capable of intercalating and releasing lithium ions. For example, carbon materials such as graphite, non-graphitizable carbon, easily graphitizable carbon, fibrous carbon, coke, and carbon black, metals that alloy with Li such as Si and Sn, metal compounds containing Si and Sn, and lithium titanium composite oxides may be used. In order to increase the capacity of the battery, the negative electrode active material preferably includes, for example, a carbon material and a Si material, and the proportion of the Si compound to the total mass of the negative electrode active material is 5.5% by mass or more. The Si material is, for example, SiO x Examples include (0.5 ≤ x ≤ 1.6).

[0029] Examples of binders include fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0030] The negative electrode 12 can be manufactured, for example, by preparing a negative electrode composite slurry containing a negative electrode active material, a binder, etc., applying this negative electrode composite slurry onto the negative electrode current collector 14, drying it to form a negative electrode active material layer 16, and then rolling this negative electrode active material layer.

[0031] The positive electrode 11 includes a positive electrode current collector 18 and a positive electrode active material layer 20 disposed on the positive electrode current collector 18. As shown in FIG. 2, it is desirable that the positive electrode active material layer 20 be disposed on both surfaces of the positive electrode current collector 18. Although the description in the figure is omitted, the positive electrode 11 has a positive electrode current collector exposed portion where the positive electrode active material layer 20 is not disposed on the positive electrode current collector 18 and the positive electrode current collector is exposed. Then, one end of the positive electrode tab is connected to the positive electrode current collector exposed portion, and the other end is connected to the inner wall of the sealing body 6. Thereby, the sealing body 6 becomes the positive electrode 11 terminal.

[0032] For the positive electrode current collector 18, a foil of a metal stable within the potential range of the positive electrode 11 such as aluminum, a film having the metal disposed on the surface layer, or the like can be used.

[0033] The positive electrode active material layer 20 contains, for example, a positive electrode active material, a binder, a conductive material, and the like.

[0034] Examples of the positive electrode active material include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium transition metal oxide is, for example, Li x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M 1-y O z 、Li x Ni 1-y M y O z 、Li x Mn2O4, Li x Mn 2-y M y O4, LiMPO4, Li2MPO4F (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These may be used alone or in combination of multiple types. In terms of achieving a high capacity of the battery, the positive electrode active material is Li x NiO2, Li x Coy Ni 1-y O2, Li x Ni 1-y M y O z It is preferable to contain a lithium nickel composite oxide such as (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≦ 1.2, 0 < y ≦ 0.9, 2.0 ≦ z ≦ 2.3).

[0035] Examples of the conductive material include carbon-based particles such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. These may be used alone or in combination of two or more.

[0036] Examples of the binder include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, and polyolefin-based resins. These may be used alone or in combination of two or more.

[0037] The positive electrode 11 can be produced, for example, by applying a positive electrode composite material slurry containing a positive electrode active material, a binder, a conductive material, etc. onto the positive electrode current collector 18, drying to form the positive electrode active material layer 20, and then rolling the positive electrode active material layer 20.

[0038] For the separator, for example, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include microporous thin films, woven fabrics, non-woven fabrics, etc. As the material of the separator, olefin-based resins such as polyethylene and polypropylene, and cellulose are suitable. The separator may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. Also, a multilayer separator including a polyethylene layer and a polypropylene layer may be used, or a separator having a material such as an aramid-based resin or ceramic coated on the surface of the separator may be used.

[0039] The non-aqueous electrolyte contains an electrolyte salt and a non-aqueous solvent for dissolving the electrolyte salt. The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, borate salts such as Li2B4O7, Li(B(C2O4)F2), imide salts such as LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2){l, m are integers of 0 or more}, and the like. The lithium salt may be used alone or in combination of two or more. Among these, from the viewpoints of ionic conductivity, electrochemical stability, etc., it is preferable to use LiPF6. The concentration of the lithium salt is preferably 0.8 to 1.8 mol per 1 L of the non-aqueous solvent.

[0040] For the non-aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these can be used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine.

[0041] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone; and linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate.

[0042] Examples of the above ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methylphenyl ether. Examples include chain ethers such as ethylphenyl ether, butylphenyl ether, pentylphenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0043] As the halogen-substituted product, it is preferable to use fluorinated cyclic carbonate esters such as fluoroethylene carbonate (FEC), fluorinated linear carbonate esters, or fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP).

[0044] The manufacturing method for a non-aqueous electrolyte secondary battery according to this embodiment includes the steps of applying a dinitrile group-containing compound to the outermost surface 2a (outer surface 15 of the exposed negative electrode current collector portion 14b in Figure 2) of a wound electrode body 2 in which a positive electrode 11 and a negative electrode 12 are wound via a separator, and housing the wound electrode body 2 coated with the dinitrile group-containing compound and the non-aqueous electrolyte in a battery case 3. In the manufacturing method of this embodiment, the method may also include the step of applying the dinitrile group-containing compound to the inner wall of the battery case 3 before housing the wound electrode body 2 coated with the dinitrile group-containing compound and the non-aqueous electrolyte in the battery case 3. Then, by charging and discharging the non-aqueous electrolyte secondary battery obtained by the manufacturing method of this embodiment, a non-aqueous electrolyte secondary battery is obtained in which the nitrogen element concentration A1 derived from the dinitrile group-containing compound on the outermost surface 2a of the wound electrode body 2 and the nitrogen element concentration B derived from the dinitrile group-containing compound in the internal region inside the outermost surface 2a of the wound electrode body 2 satisfy the relationship A1 > B.

[0045] The method for manufacturing a non-aqueous electrolyte secondary battery according to this embodiment includes the steps of: applying a dinitrile group-containing compound to the inner wall of a battery case 3; and housing a wound electrode body 2, in which a positive electrode 11 and a negative electrode 12 are wound via a separator, and a non-aqueous electrolyte in the battery case 3 coated with the dinitrile group-containing compound. In the manufacturing method of this embodiment, the method may also include the step of applying the dinitrile group-containing compound to the outermost circumferential surface 2a of the wound electrode body 2 (the outer surface 15 of the negative electrode current collector exposed portion 14b in Figure 2) before housing the wound electrode body 2 and the non-aqueous electrolyte in the battery case 3 coated with the dinitrile group-containing compound. By charging and discharging the non-aqueous electrolyte secondary battery obtained by the manufacturing method of this embodiment, a non-aqueous electrolyte secondary battery is obtained in which the nitrogen element concentration A2 derived from the dinitrile group-containing compound on the inner wall of the battery case 3 and the nitrogen element concentration B derived from the dinitrile group-containing compound in the internal region inside the outermost circumferential surface 2a of the wound electrode body 2 satisfy the relationship A2 > B.

[0046] In the above manufacturing method, it is preferable not to apply the dinitrile group-containing compound to the internal region inside the outermost surface 2a of the wound electrode body 2. However, if the dinitrile group-containing compound is applied to the internal region inside the outermost surface 2a of the wound electrode body 2, it is preferable to apply less of the dinitrile group-containing compound to the internal region than to the outermost surface 2a of the wound electrode body 2.

[0047] In the above manufacturing method, when applying the dinitrile group-containing compound to the inner wall of the battery case 3, the dinitrile group-containing compound may be applied to both the inner wall of the case body 5 and the inner wall of the sealing body 6, but it is preferable to apply the dinitrile group-containing compound to at least the inner wall of the case body 5. This is because the metal of the case body 5, which is in contact with the non-aqueous electrolyte, is prone to leaching.

[0048] The dinitrile group-containing compound used in the above manufacturing method is not particularly limited as long as it is a compound having two nitrile groups in one molecule. However, for example, it is preferable to include a compound represented by the chemical formula NC-X-CN (wherein X is a C1-C12 aliphatic hydrocarbon group (which may have a heteroatom) or a C6-C20 aromatic hydrocarbon group (which may have a heteroatom)) in order to effectively suppress metal elution. The aliphatic hydrocarbon group may be linear or cyclic, and the linear aliphatic hydrocarbon group may be linear or branched.

[0049] The number of carbon atoms in the aliphatic hydrocarbon group is preferably in the range of C1 to C12, and more preferably in the range of C2 to C10, in order to effectively suppress metal elution into the non-aqueous electrolyte. Similarly, the number of carbon atoms in the aromatic hydrocarbon group is preferably in the range of C6 to C20, and more preferably in the range of C8 to C18, in order to effectively suppress metal elution into the non-aqueous electrolyte.

[0050] Aliphatic hydrocarbon groups include, for example, alkyl groups, alkenyl groups, and alkynyl groups. Aromatic hydrocarbon groups include, for example, phenyl groups, tolyl groups, benzyl groups, and phenethyl groups.

[0051] Aliphatic hydrocarbon groups and aromatic hydrocarbon groups may have heteroatoms that are substituted with hydrogen or carbon atoms. The heteroatoms are not particularly limited, but examples include boron, silicon, nitrogen, sulfur, fluorine, chlorine, and bromine.

[0052] Examples of dinitrile group-containing compounds include adiponitrile, succinonitrile, glutalonitrile, malononitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile, fumaronitrile, 3-hexenedinitrile, maleonitrile, 1,12-dicyanododecane, tetramethylsuccinonitrile, 2-methylglutalonitrile, 2,4-dimethylglutalonitrile, 2,2,4,4-tetramethylglutalonitrile, 1,4-dicyanopentane, 2,5-dimethyl-2,5-hexanedicarbonitrate, 2,6-dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, t Examples include ert-butylmalonitrile, methyl succinonitrile, 2,2-dimethyl succinonitrile, 2,3-dimethyl succinonitrile, trimethyl succinonitrile, tetramethyl succinonitrile, 3,3'-oxydipropionitrile, 3,3'-thiodipropionitrile, 3,3'-(ethylenedioxy)dipropionitrile, 3,3'-(ethylenedithio)dipropionitrile, 1,2-benzodinitrile, 1,3-benzodinitrile, 1,4-benzodinitrile, 1,2-dicyanocyclobutane, 1,1-dicyanoethyl acetate, 2,3-dicyanohydroquinone, 4,5-dicyanoimidazole, 2,4-dicyano-3-methylglutaamide, 9-dicyanomethylene-2,4,7-trinitrofluorene, and 2,6-dicyanotoluene. These may be used individually or in combination of two or more. [Examples]

[0053] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0054] <Examples> [Fabrication of the positive electrode] As the positive electrode active material, aluminum-containing lithium nickel cobalt oxide (LiNi 0.88 Co 0.09 Al 0.03 O2 was used. A cathode composite slurry was prepared by mixing 100 parts by mass of the above cathode active material, 1 part by mass of acetylene black, and 0.9 parts by mass of polyvinylidene fluoride in an N-methyl-2-pyrrolidone (NMP) solvent. This slurry was applied to both sides of a 15 μm thick aluminum foil, and after the coating film was dried, the coating film was rolled with a rolling roller to produce a cathode in which cathode active material layers were formed on both sides of the cathode current collector. The produced cathode was cut to a width of 57.6 mm and a length of 679 mm for use.

[0055] [Fabrication of the negative electrode] As the negative electrode active material, a mixture of 95 parts by mass of graphite powder and 5 parts by mass of Si oxide was used. A negative electrode slurry was prepared by dispersing 100 parts by mass of the negative electrode active material, 1 part by mass of carboxymethylcellulose (CMC), and 1 part by mass of styrene-butadiene rubber (SBR) in water. This slurry was applied to both sides of an 8 μm thick copper foil, and after the coating film was dried, the coating film was rolled using a rolling roller to produce a negative electrode in which negative electrode active material layers were formed on both sides of the negative electrode current collector. The produced negative electrode was cut to a width of 58.6 mm and a length of 662 mm for use.

[0056] [Preparation of non-aqueous electrolyte] It was prepared by dissolving LiPF6 at a concentration of 1.4 mol / L in a non-aqueous solvent prepared by mixing ethylene carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75, and then adding 3% by mass of vinylene carbonate (VC).

[0057] [Construction of a non-aqueous electrolyte secondary battery] An aluminum positive electrode lead was attached to the positive electrode current collector, and a nickel-copper-nickel negative electrode lead was attached to the negative electrode current collector. A polyethylene separator was then used to wind the electrodes together between the positive and negative electrodes to create a wound electrode body. 0.1% by mass of adiponitrile relative to the mass of the non-aqueous electrolyte to be injected was applied to the outermost surface of the electrode body, which is the exposed portion of the negative electrode current collector, using a brush application method. Insulating plates were placed above and below this wound electrode body, the negative electrode lead was welded to the case body, and the positive electrode lead was welded to the sealing body, thereby housing the electrode body inside the case body. After injecting the non-aqueous electrolyte into the case body using a reduced pressure method, the open end of the case body was crimped with a sealing body with a gasket to create a non-aqueous electrolyte secondary battery. The battery capacity was 3300mAh.

[0058] <Comparative Example 1> A non-aqueous electrolyte secondary battery was prepared in the same manner as in the example, except that adiponitrile was not applied to the outer surface of the wound electrode body.

[0059] <Comparative Example 2> A non-aqueous electrolyte secondary battery was prepared in the same manner as in the example, except that adiponitrile was not applied to the outer surface of the wound electrode body and 0.1% by mass of adiponitrile was added to the non-aqueous electrolyte of the example.

[0060] <Comparative Example 3> A non-aqueous electrolyte secondary battery was prepared in the same manner as in the example, except that adiponitrile was not applied to the outer surface of the wound electrode body and 1% by mass of adiponitrile was added to the non-aqueous electrolyte of the example.

[0061] [Method for measuring eluted Fe concentration] After leaving the non-aqueous electrolyte secondary batteries of the examples and comparative examples at 25°C for 24 hours, holes were made in the battery cases and the non-aqueous electrolyte inside the batteries was extracted using a centrifuge. Nitric acid was added to the extracted non-aqueous electrolyte to dilute it, and this diluted solution was used as the measurement sample. The amount of Fe (μg) in the measurement sample was measured using an inductively coupled plasma (ICP) emission spectrometer, and the amount of Fe per unit mass of the non-aqueous electrolyte (μg / g) was defined as the eluted Fe concentration. A lower value indicates that metal elution into the non-aqueous electrolyte was suppressed.

[0062] [Measurement of initial resistance] Under an ambient temperature of 25°C, the non-aqueous electrolyte secondary batteries of the examples and each comparative example were charged with a constant current of 990mA (0.3It) to 4.2V, and then charged with a constant voltage of 4.2V with a termination current of 66mA to adjust the state of charge (SOC) to 100%. Then, under an ambient temperature of 25°C, the AC impedance was measured, and the resistance value at 1kHz was measured and taken as the initial resistance.

[0063] [Measurement of nitrogen element concentration derived from dinitrile group-containing compounds] Each battery, whose initial resistance was measured, was discharged at a constant current of 1650 mA (0.5 It) to 3.0 V at an ambient temperature of 25°C. After that, each battery was disassembled in an argon gas atmosphere, and the exposed negative electrode current collector portion, which is the outermost surface of the electrode body, was cut out. The negative electrode, which is the innermost surface of the electrode body (center of the electrode body's winding core), was also cut out. Each of these was introduced into an X-ray photoelectron analyzer (ESCA) without being exposed to the atmosphere, and the nitrogen element concentration was measured. The nitrogen element concentration measured at this time is the nitrogen element concentration in the coating of decomposition products such as dinitrile group-containing compounds. The nitrogen element concentration ratio (B / A) was calculated by taking the nitrogen element concentration at the outermost surface of the electrode body as nitrogen element concentration A derived from the dinitrile group-containing compound at the outermost surface of the electrode body, and the nitrogen element concentration of the negative electrode at the innermost surface of the electrode body as nitrogen element concentration B derived from the dinitrile group-containing compound in the internal region of the electrode body. Regarding the measurement of nitrogen element concentration in the internal region of the electrode body, if it is known that the battery does not contain dinitrile group-containing compounds, any one location within the internal region of the electrode body may be used as the measurement site. However, if it is unknown whether or not the battery contains dinitrile group-containing compounds, it is necessary to use multiple locations (preferably 10 to 15 locations) within the internal region of the electrode body as measurement sites. The highest nitrogen element concentration among the various measurement sites within the internal region of the electrode body should then be adopted.

[0064] Table 1 summarizes the results for the eluted Fe concentration, initial resistance, and nitrogen element concentration ratio (B / A) for the examples and each comparative example.

[0065] [Table 1]

[0066] As shown in Table 1, the initial resistance of the example was equivalent to that of Comparative Example 1 and lower than that of Comparative Examples 2 and 3. Furthermore, the eluted Fe concentration in the example was lower than that of Comparative Examples 1 to 3. Therefore, it can be said that the example successfully suppressed metal elution into the non-aqueous electrolyte and also reduced the initial resistance of the battery. [Explanation of Symbols]

[0067] 1 Non-aqueous electrolyte secondary battery, 2 Electrode body (winding type electrode body), 2a Outermost peripheral surface, 3 Battery case, 5 Case body, 5c Groove, 6 Sealing body, 11 Positive electrode, 12 Negative electrode, 14 Negative electrode current collector, 14a, 14b Exposed parts of negative electrode current collector, 15 Outer surface, 16 Negative electrode active material layer, 18 Positive electrode current collector, 20 Positive electrode active material layer.

Claims

1. A non-aqueous electrolyte secondary battery comprising a wound electrode body in which a positive electrode and a negative electrode are wound with a separator in between, a non-aqueous electrolyte, and a battery case that houses the wound electrode body and the non-aqueous electrolyte, A non-aqueous electrolyte secondary battery in which the nitrogen element concentration A1 derived from the dinitrile group-containing compound at the outermost surface of the wound electrode body and the nitrogen element concentration B derived from the dinitrile group-containing compound in the internal region inside the outermost surface of the wound electrode body satisfy the relationship A1 > B.

2. A non-aqueous electrolyte secondary battery comprising a wound electrode body in which a positive electrode and a negative electrode are wound with a separator in between, a non-aqueous electrolyte, and a battery case that houses the wound electrode body and the non-aqueous electrolyte, A non-aqueous electrolyte secondary battery in which the nitrogen element concentration A2 derived from the dinitrile group-containing compound in the inner wall of the battery case and the nitrogen element concentration B derived from the dinitrile group-containing compound in the internal region inside the outermost surface of the wound electrode body satisfy the relationship A2 > B.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the ratio (B / A1) of the nitrogen element concentration B in the internal region of the wound electrode body to the nitrogen element concentration A1 on the outermost surface of the wound electrode body is 0.5 or less.

4. The non-aqueous electrolyte secondary battery according to claim 2, wherein the ratio (B / A2) of the nitrogen element concentration B in the internal region of the wound electrode body to the nitrogen element concentration A2 in the inner wall of the battery case is 0.5 or less.

5. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the dinitrile group-containing compound is a compound represented by the chemical formula NC-X-CN (wherein X is a C1 to C12 aliphatic hydrocarbon group (which may have a heteroatom) or a C6 to C20 aromatic hydrocarbon group (which may have a heteroatom).

6. A step of applying a dinitrile group-containing compound to the outermost surface of a wound electrode body in which a positive electrode and a negative electrode are wound with a separator in between, A method for manufacturing a non-aqueous electrolyte secondary battery, comprising the steps of housing the wound electrode body coated with the dinitrile group-containing compound and the non-aqueous electrolyte in a battery case, A method for producing a non-aqueous electrolyte secondary battery, wherein the dinitrile group-containing compound is a compound represented by the chemical formula NC-X-CN (wherein X is a C1-C12 aliphatic hydrocarbon group (which may have a heteroatom) or a C6-C20 aromatic hydrocarbon group (which may have a heteroatom).

7. A step of applying a dinitrile group-containing compound to the inner wall of the battery case, A method for manufacturing a non-aqueous electrolyte secondary battery, comprising the steps of housing a wound electrode body, in which a positive electrode and a negative electrode are wound with a separator in between, and a non-aqueous electrolyte in a battery case coated with the dinitrile group-containing compound, A method for producing a non-aqueous electrolyte secondary battery, wherein the dinitrile group-containing compound is a compound represented by the chemical formula NC-X-CN (wherein X is a C1-C12 aliphatic hydrocarbon group (which may have a heteroatom) or a C6-C20 aromatic hydrocarbon group (which may have a heteroatom).

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