JP7514150B2 - Nonaqueous electrolyte and nonaqueous secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte and a non-aqueous secondary battery using the same.

The way lithium-ion batteries, which have been used as single cells for mobile and IT applications, is being used is changing dramatically with the global trend of electrifying automobiles. Automotive batteries are required to both reduce the amount of cobalt used and improve energy density, and several technologies have been reported for making full use of chemically unstable nickel (Ni)-based positive electrode active materials.

For example, the following non-patent document 1 reports _that the charge-discharge cycle performance of a lithium ion battery using _{LiNi0.6Co0.2Mn0.2O2} in the positive electrode is improved by adding _{diphenyldimethoxysilane} to the non-aqueous electrolyte. Also, the following patent document ₁ reports that a lithium ion battery can improve cycle characteristics and initial charge-discharge characteristics by including at least one of an alkoxysilane compound and its hydrolysate in the negative electrode active material.

JP 2011-124047 A

Electrochimica Acta 236 (2017) 61-71

However, in Non-Patent Document 1 and Patent Document 1, diffusion is the rate-limiting factor for lithium ion conduction, and in conventional non-aqueous electrolytes to which a resistive component such as a dialkoxysilane compound is added, diffusion within the electrode layer is inhibited, resulting in a loss of performance when operating the non-aqueous secondary battery at high current density.

The present invention was made in consideration of the above circumstances, and aims to provide a nonaqueous electrolyte and a nonaqueous secondary battery that suppresses deterioration of the positive electrode active material with a high nickel (Ni) ratio and can be operated at a high current density.

The inventors conducted extensive research and experimentation to solve the above problems, and discovered that a nonaqueous electrolyte solution containing a specific silane compound and acetonitrile can solve the problems on the positive and negative electrodes of a nonaqueous secondary battery without interfering with each other, enabling the nonaqueous secondary battery to operate stably at a high current density, thus completing the present invention.

That is, the present invention is as follows.
[1] A non-aqueous electrolyte solution containing a non-aqueous solvent and _LiPF6 ,
the non-aqueous solvent contains acetonitrile, vinylene carbonate, and ethylene sulfite, and the volume ratio of the vinylene carbonate is less than the volume ratio of the ethylene sulfite;
Furthermore, a non-aqueous electrolyte solution containing diphenyldialkoxysilane.
[2] The nonaqueous electrolyte solution according to [1], wherein the content of acetonitrile in the nonaqueous solvent is 5 to 97% by volume based on the total amount of the nonaqueous solvent.
[3] The nonaqueous electrolyte solution according to [1] or [2], characterized in that the content of the diphenyldialkoxysilane is 0.01 mass% or more and 10 mass% or less with respect to the total amount of the nonaqueous solvent.
[4] The nonaqueous electrolyte solution according to any one of the above [1] to [3], wherein the diphenyldialkoxysilane is diphenyldimethoxysilane.
[5] A non-aqueous secondary battery comprising a positive electrode having a positive electrode active material layer on one or both sides of a current collector, a negative electrode having a negative electrode active material layer on one or both sides of a current collector, a separator, and the non-aqueous electrolyte solution according to any one of [1] to [4] above,
The positive electrode active material layer is formed of the following general formula (1):
_{LipNiqCoR MnsMtOu ( 1 ) ​}
In the formula, M is at least one metal selected from the group consisting of aluminum (Al), tin (Sn), indium (In), iron (Fe), vanadium (V), copper (Cu), magnesium (Mg), titanium (Ti), zinc (Zn), molybdenum (Mo), zirconium (Zr), strontium (Sr), and barium (Ba), and is in the ranges of 0<p<1.3, 0<q<1.2, 0<r<1.2, 0≦s<0.5, 0≦t<0.3, 0.7≦q+r+s+t≦1.2, 1.8<u<2.2, and p is a value determined by the charge/discharge state of the battery.
A non-aqueous secondary battery comprising at least one selected from the group consisting of lithium-containing metal oxides represented by the following formula:
[6] The nonaqueous secondary battery according to [5], wherein the nickel (Ni) content q of the lithium-containing metal oxide represented by the general formula (1) is 0.5<q<1.2.

According to the present invention, the hydrogen fluoride (HF) trapping effect of diphenyldialkoxysilane suppresses the deterioration of a positive electrode active material having a high nickel (Ni) ratio, and also suppresses the decomposition of the acetonitrile solvent, which reduces the Lewis acid catalytic activity of _PF5 contained in _LiPF6 and contributes to high ionic conductivity. Furthermore, according to the present invention, the formation of a negative electrode SEI (Solid Electrolyte Interface) that is highly durable against acetonitrile and its decomposition products is promoted, thereby providing a nonaqueous electrolyte and a nonaqueous secondary battery that can be stably operated at a high current density.

1 is a plan view illustrating a schematic example of a nonaqueous secondary battery according to an embodiment of the present invention. 2 is a cross-sectional view taken along line AA in FIG. 1.

The following is a detailed description of an embodiment of the present invention (hereinafter, simply referred to as the "present embodiment"). Note that in this specification, a numerical range described using "~" includes the numerical values described before and after it.

<Non-aqueous secondary battery>
The nonaqueous secondary battery of this embodiment is a secondary battery comprising the nonaqueous electrolyte together with a positive electrode and a negative electrode, and may be, for example, a lithium ion battery, more specifically, a lithium ion battery shown in a schematic plan view in FIG. 1 and a schematic cross-sectional view in FIG. 2. The lithium ion battery 100 shown in FIGS. 1 and 2 comprises a separator 170, a positive electrode 150 and a negative electrode 160 sandwiching the separator 170 from both sides, a positive electrode lead body 130 (connected to the positive electrode 150) and a negative electrode lead body 140 (connected to the negative electrode 160) sandwiching a laminate of these (the separator 170, the positive electrode 150, and the negative electrode 160), and a battery exterior 110 that houses them. The laminate of the positive electrode 150, the separator 170, and the negative electrode 160 is impregnated with the nonaqueous electrolyte according to this embodiment.

<1. Non-aqueous electrolyte>
In the present embodiment, the "nonaqueous electrolyte solution" refers to a nonaqueous electrolyte solution in which water is 1 mass % or less relative to the total amount of the nonaqueous electrolyte solution, and which contains a nonaqueous solvent and _LiPF6 . The non-aqueous electrolyte according to the present embodiment preferably contains as little water as possible, but may contain a very small amount of water as long as it does not impede the solution of the problems of the present invention. The amount of the nonaqueous electrolyte is 300 ppm by mass or less, and preferably 200 ppm by mass or less, based on the total amount of the nonaqueous electrolyte. As long as this is the case, the other components can be appropriately selected and applied from the constituent materials in the known non-aqueous electrolyte used in lithium ion batteries.

<1-1. Non-aqueous solvent>
In the present embodiment, the term "non-aqueous solvent" refers to elements in the non-aqueous electrolyte excluding lithium salt and various additives. When the non-aqueous electrolyte contains an additive for protecting an electrode, the term "non-aqueous solvent" refers to elements in the non-aqueous electrolyte excluding lithium salt and additives other than the additive for protecting an electrode. Examples of non-aqueous solvents include alcohols such as methanol and ethanol; aprotic solvents, etc. Among them, aprotic solvents are preferred as non-aqueous solvents. The non-aqueous solvent may contain a solvent other than the aprotic solvent as long as it does not hinder the problem solving of the present invention.

The non-aqueous solvent for the non-aqueous electrolyte of the present invention contains acetonitrile as an aprotic solvent. The non-aqueous solvent contains acetonitrile, which improves the ionic conductivity of the non-aqueous electrolyte, thereby increasing the diffusibility of lithium ions in the battery. Therefore, when the non-aqueous electrolyte contains acetonitrile, lithium ions can be well diffused even to the area near the current collector where lithium ions are difficult to reach during high-load discharge, especially in a positive electrode in which the positive electrode active material layer is thickened to increase the loading amount of the positive electrode active material. As a result, it is possible to extract sufficient capacity even during high-load discharge, and a non-aqueous secondary battery with excellent load characteristics can be obtained.

In addition, by containing acetonitrile in the non-aqueous solvent, the rapid charging characteristics of the non-aqueous secondary battery can be improved. In constant current (CC)-constant voltage (CV) charging of a non-aqueous secondary battery, the capacity per unit time during the CC charging period is greater than the charge capacity per unit time during the CV charging period. When acetonitrile is used as the non-aqueous solvent for the non-aqueous electrolyte, the range in which CC charging can be performed can be expanded (CC charging time can be extended), and the charging current can also be increased, so that the time from the start of charging to fully charging the non-aqueous secondary battery can be significantly shortened.

Acetonitrile is easily decomposed by electrochemical reduction. Therefore, when using acetonitrile, it is preferable to use another solvent (e.g., an aprotic solvent other than acetonitrile) together with acetonitrile as a non-aqueous solvent, and/or to add an additive for protecting electrodes to form a protective film on the electrodes.

The content of acetonitrile in the non-aqueous solvent is preferably 5 to 97% by volume relative to the total amount of the non-aqueous solvent. The lower limit of the content of acetonitrile is more preferably 10% by volume or more, and even more preferably 20% by volume or more, relative to the total amount of the non-aqueous solvent. The upper limit of the content of acetonitrile is more preferably 85% by volume or less, and even more preferably 66% by volume or less, relative to the total amount of the non-aqueous solvent. When the content of acetonitrile is 5% by volume or more relative to the total amount of the non-aqueous solvent, the ionic conductivity of the non-aqueous electrolyte increases, and the non-aqueous secondary battery tends to exhibit high output characteristics, and furthermore, the dissolution of the lithium salt can be promoted. In addition, when the content of acetonitrile in the non-aqueous solvent is within the above range, the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery tend to be further improved while maintaining the excellent performance of acetonitrile.

Examples of aprotic solvents other than acetonitrile include cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds having sulfur atoms, linear fluorinated carbonates, cyclic ethers, mononitriles other than acetonitrile, alkoxy-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, linear ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the aprotic solvents have been replaced with halogen atoms.

Acetonitrile, which is one component of non-aqueous solvents, is easily electrochemically decomposed by reduction, so the non-aqueous electrolyte according to this embodiment is characterized in that the non-aqueous solvent contains, in addition to acetonitrile, vinylene carbonate and ethylene sulfite, and the volume ratio of vinylene carbonate is less than the volume ratio of ethylene sulfite.

When the non-aqueous solvent according to this embodiment contains acetonitrile, vinylene carbonate as a cyclic carbonate, and ethylene sulfite as an organic compound having a sulfur atom, when the non-aqueous electrolyte is used in a non-aqueous secondary battery, deterioration of the positive electrode active material with a high nickel (Ni) ratio is suppressed, and the battery operates at a high current density.

The negative electrode protective coating derived from vinylene carbonate has high resistance, which tends to lead to performance degradation during rapid charging and in low-temperature environments, and to battery swelling due to gas generation during decomposition. Ethylene sulfite has a lower lowest unoccupied molecular orbital (LUMO) level than other oxygen-containing and sulfur-containing compounds, and can be reductively decomposed at a lower potential than vinylene carbonate to form a negative electrode protective coating, making it possible to solve the problems caused by the negative electrode protective coating derived from vinylene carbonate by reducing the amount of vinylene carbonate added. In addition, the negative electrode protective coating derived from ethylene sulfite has low resistance over a wide temperature range, and further promotes the formation of a negative electrode SEI (Solid Electrolyte Interface) that is highly durable against acetonitrile and its decomposition products, thereby providing a nonaqueous electrolyte and a nonaqueous secondary battery that can operate stably at a high current density.

In this embodiment, the total content of vinylene carbonate and ethylene sulfite in the nonaqueous electrolyte is preferably 0.1% by volume or more and less than 10% by volume with respect to the total amount of the nonaqueous solvent, from the viewpoint of suppressing an increase in internal resistance.

Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate;

Fluoroethylene carbonates include, for example, 4-fluoro-1,3-dioxolane-2-one, 4,4-difluoro-1,3-dioxolane-2-one, cis-4,5-difluoro-1,3-dioxolane-2-one, trans-4,5-difluoro-1,3-dioxolane-2-one, 4,4,5-trifluoro-1,3-dioxolane-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolane-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolane-2-one;

Lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;

Examples of organic compounds containing sulfur atoms include ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methyl sulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene 1,3-sultone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite;

Examples of chain carbonates include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and diisobutyl carbonate;

Cyclic ethers include, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

Examples of mononitriles other than acetonitrile include propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;

Alkoxy-substituted nitriles include, for example, methoxyacetonitrile and 3-methoxypropionitrile;

Dinitriles include, for example, malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile;

Cyclic nitriles include, for example, benzonitrile;

Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelate, methyl caproate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, propyl valerate, propyl pivalate, propyl hydroangelate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, isopropyl pivalate propyl, isopropyl hydroangelate, isopropyl caproate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelate, isobutyl caproate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl pivalate, tert-butyl hydroangelate, and tert-butyl caproate;

Examples of chain ethers include dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

Examples of fluorinated ethers include Rf ²⁰ -OR ²¹ (wherein Rf ²⁰ represents an alkyl group containing a fluorine atom, and R ⁷ represents a monovalent organic group which may contain a fluorine atom);

Ketones include, for example, acetone, methyl ethyl ketone, and methyl isobutyl ketone;

Examples of the compound in which some or all of the H atoms of the aprotic solvent are substituted with halogen atoms include compounds in which the halogen atoms are fluorine;
The following can be mentioned.

Examples of the fluorinated chain carbonate include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethylmethyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. The fluorinated chain carbonate is represented by the following general formula:
R ⁷ —O—C(O)O—R ⁸
{In the formula, R ⁷ and R ⁸ are at least one selected from the group consisting of CH ₃ , CH ₂ CH ₃ , CH ₂ CH ₂ CH ₃ , CH(CH ₃ ) ₂ , and CH ₂ Rf ⁹ , Rf ⁹ is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R ⁷ and/or R ⁸ contain at least one fluorine atom.}
It can be expressed as:

Examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters are represented by the following general formula:
R ¹⁰ —C(O)O—R ¹¹
In the formula, R ¹⁰ is at least one selected from the group consisting of CH ₃ , CH ₂ CH ₃ , CH ₂ CH ₂ CH ₃ , CH(CH ₃ ) ₂ , CF ₃ CF ₂ H, CFH ₂ , CF ₂ Rf ¹² , CFHRf ¹² , and CH ₂ Rf ¹³ ; R ¹¹ is at least one selected from the group consisting of CH ₃ , CH ₂ CH ₃ , CH ₂ CH ₂ CH ₃ , CH(CH ₃ ) ₂ , and CH ₂ Rf ¹³ ; Rf ¹² is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom may be substituted with at least one fluorine atom; Rf ¹³ is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom; and R ¹⁰ and/or R ¹¹ contains at least one fluorine atom, and when R ¹⁰ is CF ₂ H, R ¹¹ is not CH ₃ .
It can be expressed as:

In this embodiment, the aprotic solvent other than acetonitrile may be used alone or in combination of two or more.

In the present embodiment, it is preferable to use acetonitrile in combination with one or more of a cyclic carbonate and a chain carbonate as the nonaqueous solvent from the viewpoint of improving the stability of the nonaqueous electrolyte. From this viewpoint, it is more preferable to use acetonitrile in combination with a cyclic carbonate as the nonaqueous solvent in the present embodiment, and it is even more preferable to use acetonitrile in combination with both a cyclic carbonate and a chain carbonate.

When a cyclic carbonate other than vinylene carbonate is used together with acetonitrile, it is particularly preferred that such a cyclic carbonate includes ethylene carbonate and/or fluoroethylene carbonate.

<1-2. Electrolyte salt>
The nonaqueous electrolyte solution of the present embodiment is not particularly limited as long as it contains LiPF _6. For example, in the present embodiment, the lithium salt contains LiPF ₆ and a lithium-containing imide salt.

The lithium-containing imide salt is a lithium salt represented by LiN(SO ₂ C _m F _2m+1 ) ₂ (wherein m is an integer of 0 to 8), and specifically, it is preferable that the lithium-containing imide salt contains at least one of LiN(SO ₂ F) ₂ and LiN(SO ₂ CF ₃ ) _2. Only one or both of these imide salts may be contained. Alternatively, the lithium-containing imide salt may contain an imide salt other than these imide salts.

When acetonitrile is contained in the non-aqueous solvent, since the saturation concentration of the lithium-containing imide salt relative to acetonitrile is higher than that of LiPF ₆ , it is preferable to contain the lithium-containing imide salt at a molar concentration of LiPF ₆ ≦lithium-containing imide salt, since this can suppress the association and precipitation of the lithium salt and acetonitrile at low temperatures. In addition, it is preferable from the viewpoint of the amount of ions supplied that the content of the lithium-containing imide salt is 0.5 mol to 3 mol per 1 L of the non-aqueous solvent. According to an acetonitrile-containing non-aqueous electrolyte solution containing at least one of LiN(SO ₂ F) ₂ and LiN(SO ₂ CF ₃ ) ₂ , the reduction in ion conductivity in a low temperature range such as −10° C. or −30° C. can be effectively suppressed, and excellent low-temperature characteristics can be obtained. In this way, by limiting the content, it is also possible to more effectively suppress the increase in resistance during high-temperature heating.

The lithium salt may further include a fluorine-containing inorganic lithium salt other than LiPF ₆ , for example, LiBF ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiSbF ₆ , Li ₂ B ₁₂ F _b H _12-b (wherein b is an integer of 0 to 3), etc. The term "inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion and is soluble in acetonitrile. The term "fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion, contains a fluorine atom in the anion, and is soluble in acetonitrile. The fluorine-containing inorganic lithium salt is excellent in that it forms a passive film on the surface of the metal foil that is the positive electrode current collector, and inhibits corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts are used alone or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound that is a double salt of LiF and Lewis acid is preferable, and among them, when using a fluorine-containing inorganic lithium salt having a phosphorus atom, it is more preferable because it is easy to release free fluorine atoms. A representative fluorine-containing inorganic lithium salt is _LiPF6 , which dissolves and releases _PF6 anion. When using a fluorine-containing inorganic lithium salt having a boron atom as the fluorine-containing inorganic lithium salt, it is preferable because it is easy to capture excess free acid components that may cause battery deterioration, and from this viewpoint, _LiBF4 is particularly preferable.

The content of the fluorine-containing inorganic lithium salt in the nonaqueous electrolyte of this embodiment is not particularly limited, but is preferably 0.01 mol or more, more preferably 0.02 mol or more, and even more preferably 0.03 mol or more per 1 L of nonaqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above-mentioned range of 0.01 mol or more, the ionic conductivity increases and high output characteristics tend to be exhibited. In addition, the content of the fluorine-containing inorganic lithium salt is preferably less than 1.5 mol, more preferably less than 0.5 mol, and even more preferably less than 0.1 mol per 1 L of nonaqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above-mentioned range of less than 1.5 mol, the ionic conductivity increases and high output characteristics can be exhibited, and the decrease in ionic conductivity associated with an increase in viscosity at low temperatures tends to be suppressed, and the high-temperature cycle characteristics and other battery characteristics of the nonaqueous secondary battery tend to be further improved while maintaining the excellent performance of the nonaqueous electrolyte.

The nonaqueous electrolyte of this embodiment may further contain an organic lithium salt. An "organic lithium salt" refers to a lithium salt that contains a carbon atom in the anion and is soluble in acetonitrile.

The organic lithium salt may be an organic lithium salt having an oxalic acid group. Specific examples of the organic lithium salt having an oxalic acid group include, for example, organic lithium salts represented by LiB(C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiPF ₄ (C ₂ O ₄ ), and LiPF ₂ (C ₂ O ₄ ) ₂ , and the like, among which at least one lithium salt selected from the lithium salts represented by LiB(C ₂ O ₄ ) ₂ and LiBF ₂ (C ₂ O ₄ ) is preferred. It is more preferable to use one or more of these together with a fluorine-containing inorganic lithium salt. The organic lithium salt having an oxalic acid group may be added to a non-aqueous electrolyte solution or may be contained in the negative electrode (negative electrode active material layer).

From the viewpoint of better ensuring the effect of its use, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte is preferably 0.005 mol or more, more preferably 0.02 mol or more, and even more preferably 0.05 mol or more, per 1 L of the non-aqueous solvent of the non-aqueous electrolyte. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte is too large, there is a risk of precipitation. Therefore, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte is preferably less than 1.0 mol, more preferably less than 0.5 mol, and even more preferably less than 0.2 mol, per 1 L of the non-aqueous solvent of the non-aqueous electrolyte.

It is known that organic lithium salts having an oxalic acid group are poorly soluble in organic solvents with low polarity, particularly in chain carbonates. Organic lithium salts having an oxalic acid group may contain a small amount of lithium oxalate, and when mixed to form a non-aqueous electrolyte solution, they may react with a small amount of moisture contained in other raw materials to generate new white precipitates of lithium oxalate. Therefore, the content of lithium oxalate in the non-aqueous electrolyte solution of this embodiment is not particularly limited, but is preferably 0 to 500 ppm.

In addition to the lithium salts listed above, lithium salts generally used for non-aqueous secondary batteries may be added supplementarily as the lithium salt in this embodiment. Specific examples of other lithium salts include inorganic lithium salts that do not contain a fluorine atom in the anion, such as LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiB ₁₀ Cl ₁₀ , and chloroborane Li; organic lithium salts, such as LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , LiC _n F _(2n+1) SO ₃ {wherein n ≥ 2}, lower aliphatic carboxylic acid Li, tetraphenylborate Li, and LiB(C ₃ O ₄ H ₂ ) ₂ ; and LiPF _n (C _p F _2p+1 ) _6-n such as LiPF ₅ (CF ₃ ). organic lithium salts represented by the formula: (wherein n is an integer of 1 to 5, and p is an integer of 1 to 8); organic lithium salts represented by LiBF _q (C _s F _2s+1 ) _4-q , such as LiBF ₃ (CF ₃ ), (wherein q is an integer of 1 to 3, and s is an integer of 1 to 8); lithium salts combined with polyvalent anions;
The following formula (a):
LiC( _SO2RA ⁾ ( _SO2RB ⁾ ( _SO2RC ⁾ (a)
{In the formula, R ^A , R ^B , and R ^C may be the same or different and each represents a perfluoroalkyl group having 1 to 8 carbon atoms.}
The following formula (b):
LiN( _SO2ORD ) ₍ ^SO2ORE ) ( ^b )
{wherein R ^D and R ^E may be the same or different and each represent a perfluoroalkyl group having 1 to 8 carbon atoms.}, and the following formula (c):
LiN( _SO2RF ⁾ ( _SO2ORG ) ( ^c )
{In the formula, R ^F and R ^G may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms.}
One or more of these can be used together with the fluorine-containing inorganic lithium salt.

<1-3. Additives>
The non-aqueous electrolyte according to the present embodiment may contain additives in addition to the non-aqueous solvent and electrolyte salt described above.

<Diphenyldialkoxysilane>
The non-aqueous electrolyte in this embodiment contains diphenyldialkoxysilane. When the non-aqueous electrolyte is used in a non-aqueous secondary battery, the diphenyldialkoxysilane can act as an additive for protecting an electrode. Specific examples of diphenyldialkoxysilane additives for protecting an electrode include, for example, diphenyldimethoxysilane, diphenyldiethoxysilane, diphenyldipropoxysilane, and diphenyldibutoxysilane. These are used alone or in combination of two or more. Among them, it is more preferable to use diphenyldimethoxysilane, which has the smallest molecular weight, because the number of moles per unit weight increases.

The content of diphenyldialkoxysilane in this embodiment is not particularly limited, but is preferably in the range of 0.01% by mass or more and 10% by mass or less with respect to the total amount of the non-aqueous solvent. The lower limit of the diphenyldialkoxysilane content is more preferably 0.02% by mass or more, and even more preferably 0.05% by mass or more, with respect to the total amount of the non-aqueous solvent. The upper limit of the diphenyldialkoxysilane content is more preferably 5% by mass or less, and even more preferably 3% by mass or less, with respect to the total amount of the non-aqueous solvent. By adjusting the content of diphenyldialkoxysilane within the above range, there is a tendency to be able to add even better battery characteristics without impairing the basic functions as a non-aqueous secondary battery.

<Other electrode protection additives>
The other electrode protection additives are not particularly limited as long as they do not impede the solution of the problems by the present invention, and may substantially overlap with the substances that act as a solvent for dissolving lithium salts (i.e., the above-mentioned non-aqueous solvents) (however, acetonitrile, vinylene carbonate, ethylene sulfite, and diphenyldialkoxysilane are excluded). The electrode protection additive is preferably a substance that contributes to improving the performance of the non-aqueous electrolyte and non-aqueous secondary battery in this embodiment, but also includes substances that are not directly involved in electrochemical reactions.

Specific examples of other electrode protection additives include, for example, 4-fluoro-1,3-dioxolane-2-one, 4,4-difluoro-1,3-dioxolane-2-one, cis-4,5-difluoro-1,3-dioxolane-2-one, trans-4,5-difluoro-1,3-dioxolane-2-one, 4,4,5-trifluoro-1,3-dioxolane-2-one, and 4,4,5,5-tetrafluoro-1,3-dioxolane-2-one. Fluoroethylene carbonates such as 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one; unsaturated bond-containing cyclic carbonates such as 4,5-dimethylvinylene carbonate and vinylethylene carbonate; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone. lactones, cyclic ethers, cyclic ethers, cyclic sulfur compounds, cyclic sulfur compounds, cyclic sulfur compounds, cyclic sulfur compounds, cyclic anhydrides ...

The content of the electrode protection additive in the non-aqueous electrolyte in this embodiment is not particularly limited, but the content of the electrode protection additive relative to the total amount of the non-aqueous solvent is preferably 0.1 to 30 volume %, more preferably 0.3 to 15 volume %, and even more preferably 0.5 to 4 volume %.

In this embodiment, the greater the content of the electrode protection additive, the more the deterioration of the nonaqueous electrolyte is suppressed. However, the smaller the content of the electrode protection additive, the more the high-output characteristics of the nonaqueous secondary battery in a low-temperature environment are improved. Therefore, by adjusting the content of the electrode protection additive within the above-mentioned range, it tends to be possible to maximize the excellent performance based on the high ionic conductivity of the nonaqueous electrolyte without impairing the basic functions of the nonaqueous secondary battery. By preparing the nonaqueous electrolyte with such a composition, it tends to be possible to further improve all of the cycle performance of the nonaqueous secondary battery, the high-output performance in a low-temperature environment, and other battery characteristics.

<Other optional additives>
In this embodiment, for the purpose of improving the charge-discharge cycle characteristics, high-temperature storage properties, and safety (e.g., prevention of overcharging) of the nonaqueous secondary battery, a nonaqueous electrolyte solution is used containing, for example, a sulfonic acid ester, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, a phosphoric acid ester [ethyl diethylphosphonoacetate (EDPA): (C ₂ H ₅ O) ₂ (P═O)—CH ₂ (C═O)OC ₂ H ₅ , tris(trifluoroethyl)phosphate (TFEP): (CF ₃ CH ₂ O) ₃ P═O, triphenyl phosphate (TPP): (C ₆ H ₅ O) ₃ P═O: (CH ₂ ═CHCH ₂ O) ₃ It is also possible to appropriately contain an optional additive selected from compounds such as cyclic compounds containing nitrogen with no steric hindrance around the unshared electron pair (e.g., pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole), and derivatives of these compounds. Phosphate esters are particularly effective because they have the effect of suppressing side reactions during storage.

The content of the other optional additives in this embodiment is calculated as a mass percentage relative to the total mass of all components constituting the nonaqueous electrolyte. There are no particular limitations on the content of the other optional additives, but it is preferably in the range of 0.01% by mass to 10% by mass, more preferably 0.02% by mass to 5% by mass, and even more preferably 0.05% by mass to 3% by mass, relative to the total amount of the nonaqueous electrolyte. By adjusting the content of the other optional additives within the above range, it tends to be possible to add even better battery characteristics without impairing the basic functions as a nonaqueous secondary battery.

2. Positive electrode and positive electrode current collector
The positive electrode 150 shown in Figures 1 and 2 is composed of a positive electrode active material layer made of a positive electrode mixture and a positive electrode current collector. The positive electrode 150 is not particularly limited as long as it acts as a positive electrode of a non-aqueous secondary battery, and may be a known one. The positive electrode in the present invention contains a lithium-containing compound containing Fe, and preferably also contains nickel (Ni) at a relatively high ratio.

The positive electrode active material layer preferably contains a positive electrode active material and, if necessary, further contains a conductive additive and a binder.

The positive electrode active material layer preferably contains a material capable of absorbing and releasing lithium ions as the positive electrode active material. When such a material is used, it is preferable because it tends to be possible to obtain a high voltage and a high energy density.

The positive electrode active material may be, for example, a positive electrode active material containing at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and may be represented by the following general formula (a):
_{LipNiqCoR MnsMtOu ( 1 ) ​}
In the formula, M is at least one metal selected from the group consisting of aluminum (Al), tin (Sn), indium (In), iron (Fe), vanadium (V), copper (Cu), magnesium (Mg), titanium (Ti), zinc (Zn), molybdenum (Mo), zirconium (Zr), strontium (Sr), and barium (Ba), and is in the ranges of 0<p<1.3, 0<q<1.2, 0<r<1.2, 0≦s<0.5, 0≦t<0.3, 0.7≦q+r+s+t≦1.2, 1.8<u<2.2, and p is a value determined by the charge/discharge state of the battery.
At least one Li-containing metal oxide selected from the lithium (Li)-containing metal oxides represented by the following formula (1) is preferred.

Specific examples of the positive electrode active material include lithium cobalt oxides such as _LiCoO2 ; lithium manganese oxides such as _LiMnO2 , _LiMn2O4 , and _Li2Mn2O4 ; _lithium nickel oxides such as _LiNiO2 ; _{and LizMO2} such as _{LiNi1 / 3Co1 / 3Mn1 / 3O2 , LiNi0.5Co0.2Mn0.3O2 , and LiNi0.8Co0.2O2 .} (wherein M contains at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and represents two or more metal elements selected from the group consisting of Ni, Mn, Co, Al, and Mg, and z represents a number greater than 0.9 and less than 1.2)

In particular, when the Ni content ratio q of the Li-containing metal oxide represented by the general formula (1) is 0.5<q<1.2, it is preferable because it is possible to reduce the amount of Co used, which is a rare metal, and to achieve a high energy density. _{Examples of such positive} electrode active materials _{include lithium - containing composite metal oxides such as LiNi0.6Co0.2Mn0.2O2 , LiNi0.75Co0.15Mn0.15O2 , LiNi0.8Co0.1Mn0.1O2 , LiNi0.85Co0.075Mn0.075O2 , LiNi0.8Co0.15Al0.05O2 , LiNi0.81Co0.1Al0.09O2 , and LiNi0.85Co0.1Al0.05O2 .}

On the other hand, the higher the Ni content in the positive electrode active material layer, the more degradation tends to progress at low voltages. The positive electrode active material of the Li-containing metal oxide represented by the general formula (1) essentially has active sites that oxidize and deteriorate the non-aqueous electrolyte, but these active sites may unintentionally consume the compound added to protect the negative electrode on the positive electrode side. Among these, acid anhydrides tend to be susceptible to this effect. In particular, when acetonitrile is contained as the non-aqueous solvent, the effect of adding an acid anhydride is enormous, so the consumption of the acid anhydride on the positive electrode side is a fatal problem.

In addition, the decomposition products of these additives that are taken in and deposited on the positive electrode side not only increase the internal resistance of the non-aqueous secondary battery, but also accelerate the deterioration of the lithium salt. Furthermore, the protection of the negative electrode surface, which was the original purpose, becomes insufficient. In order to deactivate the active sites that essentially cause the oxidative deterioration of the non-aqueous electrolyte, it is important to have a component that controls the Jahn-Teller distortion or plays a role as a neutralizer. Therefore, it is preferable that the positive electrode active material contains at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

For the same reason, it is preferable that the surface of the positive electrode active material is coated with a compound containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. It is more preferable that the surface of the positive electrode active material is coated with an oxide containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. Furthermore, it is particularly preferable that the surface of the positive electrode active material is coated with at least one oxide selected from the group consisting of ZrO ₂ , TiO ₂ , Al ₂ O ₃ , NbO ₃ , and LiNbO ₂ , since this does not inhibit the permeation of lithium ions.

The positive electrode active material may be a lithium-containing compound other than the Li-containing metal oxide represented by formula (1), and is not particularly limited as long as it contains lithium. Examples of such lithium-containing compounds include composite oxides containing lithium and transition metal elements, metal chalcogenides containing lithium, metal phosphate compounds containing lithium and transition metal elements, and metal silicate compounds containing lithium and transition metal elements. From the viewpoint of obtaining a higher voltage, the lithium-containing compound is preferably a metal phosphate compound containing lithium and at least one transition metal element selected from the group consisting of Co, Ni, Mn, Fe, Cu, Zn, Cr, V, and Ti.
More specifically, the lithium-containing compound is represented by the following formula (Xa):
_{LivMID2 (} ^Xa )
{In the formula, D represents a chalcogen element, M ^{and I} represent one or more transition metal elements including at least one transition metal element, and the value of v is determined depending on the charge/discharge state of the battery and represents a number from 0.05 to 1.10.}
The following formula (Xb):
_LiwMIIPO4 ( ^Xb ₎
{wherein M ^II represents one or more transition metal elements including at least one transition metal element, and the value of w is determined depending on the charge/discharge state of the battery and represents a number from 0.05 to 1.10.}, and the following formula (Xc):
_{LitMIIIuSiO4 (} ^Xc ₎
In the formula, M ^III represents one or more transition metal elements including at least one transition metal element, the value of t is determined depending on the charge/discharge state of the battery and represents a number from 0.05 to 1.10, and u represents a number from 0 to 2.
Examples of the compounds include those represented by the following formula:

The lithium-containing compound represented by the above formula (Xa) has a layered structure, and the compounds represented by the above formulas (Xb) and (Xc) have an olivine structure. These lithium-containing compounds may be those in which, for the purpose of stabilizing the structure, part of the transition metal element is replaced with Al, Mg, or other transition metal element, those in which these metal elements are contained in the crystal grain boundaries, those in which part of the oxygen atoms is replaced with fluorine atoms, etc., and those in which at least part of the surface of the positive electrode active material is coated with another positive electrode active material, etc.

In this embodiment, the positive electrode active material may be the lithium-containing compound alone, or may be used in combination with other positive electrode active materials.

Examples of such other positive electrode active materials include metal oxides or metal chalcogenides having a tunnel structure and a layered structure, sulfur, conductive polymers, etc. Examples of metal oxides or metal chalcogenides having a tunnel structure and a layered structure include oxides, sulfides, and selenides of metals other than lithium, such as MnO ₂ , FeO ₂ , FeS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS ₂ , MoS ₂ , and NbSe _2. Examples of conductive polymers include conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole.

The above-mentioned other positive electrode active materials may be used alone or in combination of two or more, with no particular restrictions. However, it is preferable that the positive electrode active material layer contains at least one transition metal element selected from Ni, Mn, and Co, since it is possible to reversibly and stably store and release lithium ions and achieve a high energy density.

When a lithium-containing compound and another positive electrode active material are used in combination as the positive electrode active material, the ratio of the lithium-containing compound to the total positive electrode active material is preferably 80% by mass or more, and more preferably 85% by mass or more.

Examples of conductive additives include carbon black, such as graphite, acetylene black, and ketjen black, and carbon fiber. The content of the conductive additive is preferably 10 parts by mass or less, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the positive electrode active material.

Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene butadiene rubber, and fluororubber. The binder content is preferably 6 parts by mass or less, and more preferably 0.5 to 4 parts by mass, per 100 parts by mass of the positive electrode active material.

The positive electrode active material layer is formed by dispersing a positive electrode mixture, which is a mixture of a positive electrode active material and, if necessary, a conductive assistant and a binder, in a solvent to form a positive electrode mixture-containing slurry, which is then applied to a positive electrode current collector, dried (solvent removal), and pressed if necessary. There are no particular limitations on the solvent, and any conventionally known solvent can be used. Examples include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

The positive electrode current collector is composed of a metal foil such as aluminum foil, nickel foil, or stainless steel foil. The positive electrode current collector may have a carbon coating on the surface, or may be processed into a mesh shape. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

<3. Negative electrode and negative electrode current collector>
1 and 2 is composed of a negative electrode active material layer made of a negative electrode mixture and a negative electrode current collector. The negative electrode 160 can function as a negative electrode of a non-aqueous secondary battery.

The negative electrode active material layer preferably contains a negative electrode active material and, if necessary, a conductive additive and a binder.

Examples of negative electrode active materials include amorphous carbon (hard carbon), graphite (e.g., artificial graphite, natural graphite, etc.), pyrolytic carbon, coke, glassy carbon, baked bodies of organic polymer compounds, mesocarbon microbeads, carbon fiber, activated carbon, carbon colloids, and carbon black, as well as metal lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, organic polymer compounds, etc. The negative electrode active materials may be used alone or in combination of two or more.

From the viewpoint of increasing the battery voltage, the negative electrode active material layer preferably contains, as the negative electrode active material, a material capable of absorbing lithium ions at a potential lower than 0.4 V vs. Li/Li ⁺ .

Examples of the conductive additive include carbon black, such as graphite, acetylene black, and ketjen black, and carbon fiber. The content of the conductive additive is preferably 20 parts by mass or less, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the negative electrode active material.

Examples of binders include carboxymethyl cellulose, PVDF, PTFE, polyacrylic acid, and fluororubber. Other examples include diene rubbers such as styrene-butadiene rubber. The binder content is preferably 10 parts by mass or less, and more preferably 0.5 to 6 parts by mass, per 100 parts by mass of the negative electrode active material.

The negative electrode active material layer is formed by dispersing a negative electrode mixture, which is a mixture of a negative electrode active material and, if necessary, a conductive assistant and a binder, in a solvent to form a negative electrode mixture-containing slurry, which is then applied to the negative electrode current collector, dried (solvent removal), and pressed if necessary. There are no particular limitations on the solvent, and any conventionally known solvent can be used. Examples include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

The negative electrode current collector is composed of a metal foil such as copper foil, nickel foil, or stainless steel foil. The surface of the negative electrode current collector may be coated with carbon, or the negative electrode current collector may be processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

<4. Separator>
2, the non-aqueous secondary battery 100 in this embodiment is preferably provided with a separator 170 between the positive electrode 150 and the negative electrode 160 from the viewpoint of preventing short circuits between the positive electrode 150 and the negative electrode 160 and providing safety such as shutdown. The separator 170 is not limited, but may be the same as that provided in known non-aqueous secondary batteries, and is preferably an insulating thin film having high ion permeability and excellent mechanical strength. Examples of the separator 170 include woven fabric, non-woven fabric, and synthetic resin microporous membrane, and among these, synthetic resin microporous membrane is preferable.

As a synthetic resin microporous film, for example, a microporous film containing polyethylene or polypropylene as a main component, or a polyolefin-based microporous film such as a microporous film containing both of these polyolefins is preferably used. As a nonwoven fabric, for example, a porous film made of a heat-resistant resin such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, or aramid can be used.

The separator 170 may be configured as a single layer or multiple layers of one type of microporous film, or may be configured as a stack of two or more types of microporous films. The separator 170 may be configured as a single layer or multiple layers of a mixed resin material formed by melting and kneading two or more types of resin materials.

For the purpose of imparting functionality, inorganic particles may be present on the surface or inside of the separator, and other organic layers may be further coated or laminated. Also, a crosslinked structure may be included. These methods may be combined as necessary to improve the safety performance of the nonaqueous secondary battery.

By using such a separator 170, it is possible to achieve the good input/output characteristics and low self-discharge characteristics required for lithium ion batteries for the high-power applications described above.

The thickness of the microporous membrane usable as a separator is not particularly limited, but is preferably 1 μm or more from the viewpoint of membrane strength, and is preferably 500 μm or less from the viewpoint of permeability. The thickness of the microporous membrane is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 25 μm or less, from the viewpoint of use in high-output applications such as safety tests that have a relatively high heat generation and require self-discharge characteristics better than conventional ones, and from the viewpoint of winding properties in a large battery winding machine. Note that, when emphasis is placed on achieving both short-circuit resistance and output performance, the thickness of the microporous membrane is more preferably 15 μm or more and 25 μm or less, but more preferably 10 μm or more and less than 15 μm, when emphasis is placed on achieving both high energy density and output performance.

From the viewpoint of following the rapid movement of lithium ions during high output, the porosity of the microporous membrane usable as a separator is preferably 30% or more and 90% or less, more preferably 35% or more and 80% or less, and even more preferably 40% or more and 70% or less. If priority is given to improving output performance while ensuring safety, the porosity of the microporous membrane is particularly preferably 50% or more and 70% or less, and if emphasis is placed on achieving both short circuit resistance and output performance, the porosity is particularly preferably 40% or more and less than 50%.

The air permeability of the microporous membrane usable as the separator is preferably 1 sec/100 cm ³ or more and 400 sec/100 cm ³ or less, more preferably 100 sec/100 cm ³ or more and 350/100 cm ³ or less, from the viewpoint of the balance between the membrane thickness and the porosity. In addition, when emphasizing both short circuit resistance and output performance, the air permeability of the microporous membrane is particularly preferably 150 sec/100 cm ³ or more and 350 sec/100 cm ³ or less, and when prioritizing improvement of output performance while ensuring safety, it is particularly preferably 100/100 cm ³ seconds or more and less than 150 sec/100 cm ^3. On the other hand, when a nonaqueous electrolyte solution with low ion conductivity is combined with a separator within the above range, the migration rate of lithium ions is not determined by the structure of the separator, but by the high ion conductivity of the nonaqueous electrolyte solution, and there is a tendency that the expected input/output characteristics cannot be obtained. Therefore, the ionic conductivity of the non-aqueous electrolyte is preferably 10 mS/cm or more, more preferably 15 mS/cm, and even more preferably 20 mS/cm, but the thickness, air permeability, and porosity of the separator, and the ionic conductivity of the non-aqueous electrolyte are not limited to the above examples.

<5. Battery exterior>
The configuration of the battery exterior 110 of the nonaqueous secondary battery 100 shown in Figures 1 and 2 is not particularly limited, and for example, a battery exterior of either a battery can or a laminate film exterior body can be used. As the battery can, for example, a metal can such as a square, rectangular tube, cylindrical, elliptical, flat, coin, or button type made of steel, stainless steel, aluminum, clad material, etc. can be used. As the laminate film exterior body, for example, a laminate film made of a three-layer structure of a heat-melting resin/metal film/resin can be used.

The laminate film exterior body can be used as an exterior body by stacking two sheets with the heat-melting resin side facing inward, or by folding the laminate film exterior body so that the heat-melting resin side faces inward and sealing the ends with heat sealing. When using a laminate film exterior body, the positive electrode lead body 130 (or a lead tab connected to the positive electrode terminal and the positive electrode terminal) may be connected to the positive electrode current collector, and the negative electrode lead body 140 (or a lead tab connected to the negative electrode terminal and the negative electrode terminal) may be connected to the negative electrode current collector. In this case, the laminate film exterior body may be sealed with the ends of the positive electrode lead body 130 and the negative electrode lead body 140 (or the lead tabs connected to the positive electrode terminal and the negative electrode terminal, respectively) pulled out to the outside of the exterior body.

6. How to make a battery
The nonaqueous secondary battery 100 in this embodiment is produced by a known method using the above-mentioned nonaqueous electrolyte, a positive electrode 150 having a positive electrode active material layer on one or both sides of a current collector, a negative electrode 160 having a negative electrode active material layer on one or both sides of a current collector, a battery exterior 110, and, if necessary, a separator 170.

First, a laminate consisting of a positive electrode 150, a negative electrode 160, and optionally a separator 170 is formed. For example:
An embodiment in which a long positive electrode 150 and a long negative electrode 160 are wound in a stacked state with the long separator interposed between the positive electrode 150 and the negative electrode 160 to form a laminate having a wound structure;
An embodiment in which the positive electrode 150 and the negative electrode 160 are cut into a plurality of sheets having a certain area and shape, and the positive electrode sheets and the negative electrode sheets are alternately stacked with a separator sheet interposed therebetween to form a laminate having a laminate structure;
An embodiment in which a laminate having a laminated structure is formed by folding a long separator in a zigzag manner and inserting positive electrode sheets and negative electrode sheets alternately between the zigzag-like separators;
etc. are possible.

Next, the above-mentioned laminate is housed in a battery exterior 110 (battery case), the nonaqueous electrolyte according to this embodiment is poured into the battery case, and the laminate is immersed in the nonaqueous electrolyte and sealed, thereby producing the nonaqueous secondary battery according to this embodiment.

Alternatively, a gel-state electrolyte membrane can be prepared in advance by impregnating a substrate made of a polymer material with a nonaqueous electrolyte solution, and a laminated structure can be formed using a sheet-like positive electrode 150, a negative electrode 160, and the electrolyte membrane, as well as a separator 170 if necessary, and then the laminated structure can be housed in a battery exterior 110 to prepare a nonaqueous secondary battery 100.

If the electrodes are arranged so that there is a portion where the outer edge of the negative electrode active material layer overlaps with the outer edge of the positive electrode active material layer, or there is a portion where the width is too small in the non-facing portion of the negative electrode active material layer, the position of the electrodes may be shifted during battery assembly, which may result in a decrease in the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable to fix the positions of the electrodes in the electrode body used in the non-aqueous secondary battery in advance using tapes such as polyimide tape, polyphenylene sulfide tape, and polypropylene (PP) tape, adhesives, etc.

In this embodiment, when a non-aqueous electrolyte using acetonitrile is used, the lithium ions released from the positive electrode during the initial charge of the non-aqueous secondary battery may diffuse throughout the negative electrode due to its high ionic conductivity. In non-aqueous secondary batteries, the area of the negative electrode active material layer is generally made larger than that of the positive electrode active material layer. However, if lithium ions diffuse and are absorbed to a portion of the negative electrode active material layer that does not face the positive electrode active material layer, these lithium ions will not be released during the initial discharge and will remain in the negative electrode. Therefore, the contribution of the lithium ions that are not released becomes the irreversible capacity. For this reason, the initial charge/discharge efficiency may be low in non-aqueous secondary batteries using a non-aqueous electrolyte containing acetonitrile.

On the other hand, if the area of the positive electrode active material layer is larger than that of the negative electrode active material layer or if the two are the same, current tends to concentrate at the edge of the negative electrode active material layer during charging, making it easier for lithium dendrites to form.

For the above reasons, there is no particular restriction on the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other, but it is preferably greater than 1.0 and less than 1.1, more preferably greater than 1.002 and less than 1.09, even more preferably greater than 1.005 and less than 1.08, and particularly preferably greater than 1.01 and less than 1.08. In a non-aqueous secondary battery using a non-aqueous electrolyte solution containing acetonitrile, the initial charge/discharge efficiency can be improved by reducing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other.

Reducing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other means limiting the ratio of the area of the portion of the negative electrode active material layer that does not face the positive electrode active material layer. This makes it possible to reduce as much as possible the amount of lithium ions absorbed in the portion of the negative electrode active material layer that does not face the positive electrode active material layer among the lithium ions released from the positive electrode during the initial charge (i.e., the amount of lithium ions that are not released from the negative electrode during the initial discharge and become irreversible capacity). Therefore, by designing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other within the above range, it is possible to improve the load characteristics of the battery by using acetonitrile, increase the initial charge/discharge efficiency of the battery, and further suppress the generation of lithium dendrites.

The non-aqueous secondary battery 100 in this embodiment can function as a battery by initial charging, but is stabilized by decomposing a part of the non-aqueous electrolyte during the initial charging. There is no particular restriction on the method of initial charging, but the initial charging is preferably performed at 0.001 to 0.3 C, more preferably at 0.002 to 0.25 C, and even more preferably at 0.003 to 0.2 C. It is also preferable that the initial charging is performed via a constant voltage charge in the middle. The constant current for discharging the design capacity in 1 hour is 1 C. By setting the voltage range in which the lithium salt is involved in the electrochemical reaction to be long, a stable and strong SEI is formed on the surface of the electrode (negative electrode 160), which has the effect of suppressing an increase in internal resistance, and the reaction product is not firmly fixed only to the negative electrode 160, but in some way has a good effect on members other than the negative electrode 160, such as the positive electrode 150 and the separator 170. For this reason, it is very effective to perform the initial charge while taking into account the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte.

The nonaqueous secondary battery 100 in this embodiment can also be used as a battery pack in which multiple nonaqueous secondary batteries 100 are connected in series or in parallel. From the viewpoint of managing the charge/discharge state of the battery pack, the operating voltage range per battery is preferably 2 to 5 V, more preferably 2.5 to 5 V, and particularly preferably 2.75 V to 5 V.

The above describes the form for implementing the present invention, but the present invention is not limited to the above embodiment. The present invention can be modified in various ways without departing from the gist of the invention.

The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples.

(1) Preparation of non-aqueous electrolyte solution Various non-aqueous solvents and various additives were mixed in an inert atmosphere to a predetermined concentration, and various lithium salts were added to a predetermined concentration to prepare non-aqueous electrolyte solutions (S01) to (S04). The abbreviations for non-aqueous solvents, lithium salts, and additives in Table 1 have the following meanings. The mass % of the additive in Table 1 indicates the ratio of mass parts to 100 mass parts of the non-aqueous electrolyte excluding the additive.
(Lithium salt)
_LiPF6 : Lithium hexafluorophosphate LiFSI: Lithium bis(fluorosulfonyl)imide (non-aqueous solvent)
AcN: Acetonitrile EMC: Ethyl methyl carbonate EC: Ethylene carbonate VC: Vinylene carbonate (Additives: Other)
DPDMS: diphenyldimethoxysilane

(2) Preparation of Nonaqueous Secondary Battery (2-1) Preparation of Positive Electrode (A) A composite oxide of lithium, nickel, manganese, and _cobalt ( _{LiNi0.8Mn0.1Co0.1O2} ) as a positive electrode active material, ( _B ) _acetylene black powder as a conductive additive, and (C) polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of 95:3:2 to obtain a positive electrode mixture.

N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture so that the solid content was 68 mass% and further mixed to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one side of an aluminum foil having a thickness of 15 μm and a width of 280 mm, while adjusting the basis weight of the positive electrode mixture-containing slurry, so as to have a coating width of 240 to 250 mm, a coating length of 125 mm, and an uncoated length of 20 mm, using a three-roll transfer coater, and the solvent was dried and removed in a hot air drying oven. The obtained electrode roll was trimmed and cut on both sides, and dried under reduced pressure at 130 ° C. ^for 8 hours. Thereafter, the positive electrode consisting of the positive electrode active material layer and the positive electrode current collector was obtained by rolling with a roll press so that the density of the positive electrode active material layer was 3.3 g / cm 3. The basis weight excluding the positive electrode current collector was 15.5 mg / cm ² .

(2-2) Preparation of Negative Electrode (a) As a negative electrode active material, artificial graphite powder (density 2.23 g/cm ³ ) having a number average particle diameter of 12.7 μm, (b) as a conductive assistant, acetylene black powder (density 1.95 g/cm ³ ) having a number average particle diameter of 48 nm, and (c) as a binder, a carboxymethyl cellulose (density 1.60 g/cm ³ ) solution (solid content concentration 1.83 mass%) and a diene rubber (glass transition temperature: −5° C., number average particle diameter when dried: 120 nm, density 1.00 g/cm ³ , dispersion medium: water, solid content concentration 40 mass%) were mixed in a solid content mass ratio of (a) 95.7:(b) 0.5:(c) 3.8 to obtain a negative electrode mixture.

Water was added as a solvent to the obtained negative electrode mixture so that the solid content was 45% by mass, and further mixed to prepare a negative electrode mixture-containing slurry. The negative electrode mixture-containing slurry was applied to one side of a copper foil having a thickness of 8 μm and a width of 280 mm, while adjusting the basis weight of the negative electrode mixture-containing slurry, so as to have a coating width of 240 to 250 mm, a coating length of 125 mm, and an uncoated length of 20 mm, using a three-roll transfer coater, and the solvent was dried and removed in a hot air drying oven. The obtained electrode roll was trimmed and cut on both sides, and dried under reduced pressure at 80 ° C. for 12 hours. Thereafter, the negative electrode active material layer was rolled with a roll press so that the density of the negative electrode active material layer was 1.5 g / cm ³ , and a negative electrode (N1) consisting of a negative electrode active material layer and a negative electrode current collector was obtained. The basis weight of the negative electrode active material layer was 11.9 mg / cm ² .

(2-3) Assembly of a non-aqueous secondary battery A test cell "PAT-cell" manufactured by EL-Cell was used as the non-aqueous secondary battery. The positive electrode obtained in (2-1) above was punched out into a disk shape with a diameter of 18 mm, and was superimposed on one side of a separator ("FS-5P" manufactured by EL-Cell: two layers of polypropylene (PP)/polyethylene (PE), thickness 220 μm) to obtain a laminate. The laminate was inserted into a cell case, and 120 μl of electrolyte was uniformly dropped onto the separator using a pipette. Next, the negative electrode obtained in (2-2) above was punched out into a disk shape with a diameter of 18 mm, and was superimposed on the separator side of the laminate, an upper plunger was attached, a screw cap was attached to the cell base, and the wing nut was tightened to seal the cell.

(3) Evaluation of non-aqueous secondary batteries For the non-aqueous secondary batteries obtained as described above, first, an initial charge process and an initial charge/discharge capacity measurement were performed according to the procedure in (3-1) below. Next, each coin-type non-aqueous secondary battery was evaluated according to the procedure in (3-2) below. The charge/discharge was performed using a charge/discharge device BCS-805 (product name) manufactured by BioLogic and a programmable thermostatic bath MK115 (product name) manufactured by Binder. A test cell stand "PAT-Stand" manufactured by EL-Cell was used for the connection between the charge/discharge device and PAT-Cell.

Here, 1C means the current value at which a fully charged battery is expected to be discharged completely in 1 hour when discharged at a constant current.

(3-1) Initial charge/discharge treatment of non-aqueous secondary battery The ambient temperature of the non-aqueous secondary battery was set to 25° C., and the battery was charged at a constant current of 0.185 mA equivalent to 0.025 C until it reached 3.1 V, then at a constant current of 0.37 mA equivalent to 0.05 C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current attenuated to 0.025 C. The battery was then discharged to 3.0 V at a constant current of 1.11 mA equivalent to 0.15 C.

Next, the battery was charged at a constant current of 1.48 mA, which corresponds to 0.2 C, until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current decayed to 0.025 C. The battery was then discharged to 3 V at a current value of 1.48 mA, which corresponds to 0.2 C. The battery was then charged and discharged in the same manner as above for one cycle.

(3-2) Cycle Test The non-aqueous secondary battery that had been subjected to the initial charge/discharge treatment according to the method described in (3-1) above was charged at an ambient temperature of 55° C. and a constant current of 11.1 mA, equivalent to 1.5 C, until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current attenuated to 0.025 C. The battery was then discharged to 3 V at a current value of 11.1 mA, equivalent to 1.5 C. Then, 100 cycles of charging and discharging were performed in the same manner as above.

The capacity retention rate was calculated as the discharge capacity at the 100th cycle of the cycle test, when the discharge capacity at the first cycle of the cycle test was taken as 100%.

(3-3) Nonaqueous secondary battery [Example 1 and Comparative Examples 1 to 3]
Non-aqueous secondary batteries were assembled as described above using each of the electrolyte solutions shown in Table 2, and the initial charge/discharge treatment and cycle test were carried out. The interpretation of each test result will now be described.

The capacity retention rate is an index showing the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle. In the above cycle test, charging and discharging are repeated at a higher current density than in a general cycle test, and the larger the value, the less capacity degradation occurs when the battery is repeatedly charged and discharged. The capacity retention rate is preferably 85% or more, more preferably 86% or more, and even more preferably 88% or more.

In Example 1, it was confirmed that there was little decrease in the capacity retention rate when repeatedly charging and discharging at 1.5 C, and that cycle performance was improved. In other words, it was confirmed that stable operation was achieved at a high current density. On the other hand, in Comparative Example 1, which used an electrolyte solution that did not contain ethylene sulfite or DPDMS, and Comparative Examples 2 and 3, which used electrolyte solutions that contained DPDMS but did not contain ethylene sulfite, the capacity retention rate in the cycle test was significantly decreased compared to Example 1.

From the above results, in this embodiment, by preparing a nonaqueous electrolyte solution by containing vinylene carbonate and ethylene sulfite in a nonaqueous solvent and mixing DPDMS as a diphenyl dialkoxysilane in an appropriate ratio, it was confirmed that even when the nonaqueous secondary battery is repeatedly charged and discharged at a high current density, there is little capacity deterioration and stable operation is achieved.

The nonaqueous secondary battery of the present invention is expected to be used, for example, as an automobile storage battery for hybrid vehicles, plug-in hybrid vehicles, electric vehicles, etc., as well as an industrial storage battery for power tools, drones, electric motorcycles, etc., and even as a residential power storage system.

REFERENCE SIGNS LIST 100 non-aqueous secondary battery 110 battery exterior 120 space in battery exterior 130 positive electrode lead body 140 negative electrode lead body 150 positive electrode 160 negative electrode 170 separator

Claims (5)

A non-aqueous electrolyte solution containing a non-aqueous solvent and _LiPF6 ,
the non-aqueous solvent contains acetonitrile, vinylene carbonate, and ethylene sulfite, and the volume ratio of the vinylene carbonate is less than the volume ratio of the ethylene sulfite;
Further, the non-aqueous solvent contains a diphenyldialkoxysilane , and the content of the diphenyldialkoxysilane is 0.01% by mass or more and 10% by mass or less based on the total amount of the non-aqueous solvent.
Non-aqueous electrolyte. The nonaqueous electrolyte solution according to claim 1, wherein the content of acetonitrile in the nonaqueous solvent is 5 to 97% by volume relative to the total amount of the nonaqueous solvent. The nonaqueous electrolyte solution according to claim 1 or 2 , wherein the diphenyldialkoxysilane is diphenyldimethoxysilane. A non-aqueous secondary battery comprising a positive electrode having a positive electrode active material layer on one or both sides of a current collector, a negative electrode having a negative electrode active material layer on one or both sides of a current collector, a separator, and the non-aqueous electrolyte solution according to any one of claims 1 to 3 ,
The positive electrode active material layer is formed of the following general formula (1):
_{LipNiqCoR MnsMtOu ( 1 ) ​}
In the formula, M is at least one metal selected from the group consisting of aluminum (Al), tin (Sn), indium (In), iron (Fe), vanadium (V), copper (Cu), magnesium (Mg), titanium (Ti), zinc (Zn), molybdenum (Mo), zirconium (Zr), strontium (Sr), and barium (Ba), and is in the ranges of 0<p<1.3, 0<q<1.2, 0<r<1.2, 0≦s<0.5, 0≦t<0.3, 0.7≦q+r+s+t≦1.2, 1.8<u<2.2, and p is a value determined by the charge/discharge state of the battery.
A non-aqueous secondary battery comprising at least one selected from the group consisting of lithium-containing metal oxides represented by the following formula: 5. The nonaqueous secondary battery according to claim 4 , wherein the nickel (Ni) content q of the lithium-containing metal oxide represented by the general formula (1) is 0.5<q<1.2.

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