JP7530257B2 - Non-aqueous electrolyte for lithium-ion secondary battery and non-aqueous electrolyte lithium-ion secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte for lithium ion secondary batteries. More specifically, the present invention relates to a non-aqueous electrolyte for lithium ion secondary batteries containing a specific antimony compound, and a non-aqueous electrolyte lithium ion secondary battery.

Non-aqueous electrolyte secondary batteries such as lithium secondary batteries have been put to practical use in a wide range of applications, including power sources for so-called small consumer devices such as mobile phones such as smartphones and laptops, and on-board power sources for driving electric vehicles, and there is an increasing demand for higher battery characteristics.

Various technologies have been proposed to improve the battery characteristics of non-aqueous electrolyte secondary batteries. For example, Patent Document 1 discloses a technology in which a non-aqueous electrolyte contains metal ions such as lead, bismuth, and antimony, which deposit as metals at active sites on the surface of the negative electrode, thereby reducing the reactivity of the non-aqueous electrolyte and improving the cycle characteristics. Patent Document 2 discloses a technology in which a non-aqueous electrolyte contains trichlorides of arsenic, antimony, phosphorus, and the like, which suppress the formation of dendrites on the metallic lithium negative electrode and improve the cycle characteristics.

Among the characteristics required for non-aqueous electrolyte secondary batteries, suppression of internal resistance is one of the battery characteristics that is considered important in obtaining rapid charging characteristics and high output. As a means of suppressing internal resistance, many studies have been conducted in the fields of positive and negative electrode active materials and additives for non-aqueous electrolytes. For example, Patent Document 3 discloses a technology for suppressing resistance by using graphite with azide groups on the surface as the negative electrode. In addition, Patent Document 4 discloses a technology for suppressing internal resistance by including bis(vinylsulfonyl)methane and lithium bis(oxalate)difluorophosphate in a non-aqueous electrolyte.

Japanese Patent Application Publication No. 8-171936 Japanese Unexamined Patent Publication No. 110562/1983 JP 2018-67455 A JP 2011-040333 A

In the above Patent Documents 1 and 2, the internal resistance caused by additives was not fully considered. The present invention has been made in consideration of this background art, and provides a nonaqueous electrolyte for lithium ion secondary batteries that has excellent internal resistance characteristics of nonaqueous electrolyte lithium ion secondary batteries, and a nonaqueous electrolyte lithium ion secondary battery that has excellent internal resistance characteristics.

As a result of intensive research into solving the above problems, the present inventors have found that the above problems can be solved by including a specific antimony compound in the non-aqueous electrolyte for lithium ion secondary batteries used in non-aqueous electrolyte lithium ion secondary batteries. That is, the gist of the present invention is as follows.

[1] A non-aqueous electrolyte for a lithium ion secondary battery, comprising an antimony compound (A) having one or more Sb—F bonds in the molecule.
[2] The nonaqueous electrolyte for a lithium ion secondary battery according to [1], wherein the number of Sb—F bonds in the molecule is 3.
[3] The nonaqueous electrolyte solution for lithium ion secondary batteries according to [1] or [2], wherein the content of the antimony compound (A) is 0.001% by mass or more and 10% by mass or less with respect to the total amount of the nonaqueous electrolyte solution.
[4] The nonaqueous electrolyte solution for a lithium ion secondary battery according to any one of [1] to [3], wherein the nonaqueous electrolyte solution contains at least one selected from the group consisting of a compound having a carbon-carbon unsaturated bond, a compound having an oxalate structure, and a compound having an isocyanate group.
[5] A non-aqueous electrolyte lithium ion secondary battery comprising a negative electrode and a positive electrode capable of absorbing and releasing metal ions, and a non-aqueous electrolyte solution, the non-aqueous electrolyte solution being the non-aqueous electrolyte solution according to any one of [1] to [4].
[6] The nonaqueous electrolyte lithium ion secondary battery according to any one of [1] to [5], wherein the negative electrode contains a carbonaceous material as an active material, and the positive electrode contains a transition metal oxide containing Ni, Co, and Mn as an active material.

By using the nonaqueous electrolyte for lithium ion secondary batteries of the present invention, a nonaqueous electrolyte lithium ion secondary battery with excellent internal resistance characteristics can be obtained.

The present invention will be described in detail below. The following description is an example (representative example) of the present invention, and the present invention is not limited thereto. In addition, the present invention can be modified and carried out as desired without departing from the gist of the present invention.
In this specification, the expression "~" indicates a range including the numbers before and after it.

[1. Non-aqueous electrolyte for lithium ion secondary batteries]
A nonaqueous electrolyte solution for a lithium ion secondary battery (hereinafter also simply referred to as "nonaqueous electrolyte solution") used in a nonaqueous electrolyte lithium ion secondary battery (hereinafter also simply referred to as "nonaqueous electrolyte secondary battery") according to an embodiment of the present invention contains an antimony compound (A).

[1-1. Antimony compound (A)]
The non-aqueous electrolyte according to one embodiment of the present invention contains a specific antimony compound (A) (hereinafter, sometimes referred to as "compound (A)"). Compound (A) is a compound in which a fluorine element and an antimony element in a molecule form a bond (Sb-F). The bond between Sb and F is a covalent bond or an ionic bond. The number of bonds between an antimony element and a fluorine element may be at least one in the molecular structure, but from the viewpoint of high symmetry and excellent ease of synthesis or availability, the number of bonds between an antimony element and a fluorine element is preferably 3, 5, or 6. In addition, in order to enhance the effect of interaction with the positive electrode, the number of bonds between an antimony element and a fluorine element is preferably 3 or 5. When the number of bonds between an antimony element and a fluorine element is 6, compound (A) exists as a hexafluoroantimonate salt. This is because the hexafluoroantimony anion has an action effect on the positive electrode, but in the anionic state, it is considered that the stabilizing effect on the positive electrode is small. In addition, in order to enhance the stability of the electrolyte, it is particularly preferable that the number of bonds between an antimony element and a fluorine element is 3. When the number of bonds is 5, the valence of the antimony element in compound (A) becomes 5, and it is considered that the Lewis acidity increases, resulting in a decrease in the stability of the electrolyte.

Antimony may be bonded to an element (other element) other than fluorine as long as the effects of the present invention can be obtained. For example, the elements of Groups 13 to 16 in the long periodic table can be mentioned. From the viewpoint of easiness in forming a bond with antimony, B, Al, C, Si, N, P, Sb, O or S is particularly preferable, and among these, B, C, Si, N, P, O or S is more preferable, and furthermore, among these, O is preferable from the viewpoint of increasing the ability to interact with the positive electrode surface.
The number of bonds between antimony element and other elements may be 0 or more and 5 or less, but is preferably 0, that is, antimony element is preferably bonded only to fluorine element.

When another element is bonded to antimony, examples of the group bonded to antimony include -OY, -COY, -CO ₂ Y, -OCOY, -OCO ₂ Y, -OSO ₂ Y", -OSO ₃ Y, -OP(O)(OY) ₂ , -OBY ₂ , -SY, -SOY, -SO ₂ Y, -SO ₃ Y, -NY' ₂ , -PY ₂ , -P(O)Y ₂ , -OP(O)Y" ₂ , -SiY ₃ , -OSiY ₃ , -BY ₂ , -NYCOY, -CONY _2. , -CN, -NCO or a hydrocarbon group which may have a substituent; Y represents an arbitrary organic group; Y' each independently represents a hydrogen atom, a halogen atom or an arbitrary organic group; Y" each independently represents a halogen atom or an arbitrary organic group; and A represents an oxygen atom or a sulfur atom. Among these, the hydrocarbon group which may have a substituent, -OY, -COY, -OCOY, _-OSO2Y " or -OP(O)Y" ₂ is preferable, and the hydrocarbon group which may have a substituent, -OCOY or -OY is more preferable.

The optional organic groups represented by Y, Y', and Y" include hydrocarbon groups which may have a substituent. Examples of the hydrocarbon group include linear, branched, or cyclic alkyl groups, alkenyl groups, and aryl groups. Examples of the substituent include alkyl groups such as methyl groups; aryl groups such as phenyl groups; and halogen atoms such as fluorine atoms.

The number of carbon atoms in the linear, branched or cyclic alkyl group which may have a substituent, represented by Y, Y', and Y", is usually 1 or more, and usually 10 or less, preferably 5 or less, and more preferably 3 or less. Specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a 2-ethylhexyl group, an n-nonyl group, an n-decyl group, and a 2,2,2-trifluoroethyl group, and the like. A methyl group is preferred.
The alkenyl group which may have a substituent represented by Y, Y', and Y" is preferably an alkenyl group having 1 to 4 carbon atoms. Specific examples thereof include a vinyl group, a 1-methylethenyl group, and a 2-methyl-1-propenyl group.
The aryl group which may have a substituent represented by Y, Y', and Y" is preferably an aryl group having 6 to 10 carbon atoms. Specific examples thereof include a phenyl group, a tolyl group, a 1-naphthyl group, and a 2-naphthyl group.
When the hydrocarbon groups represented by Y, Y', and Y'' have a substituent, the above number of carbon atoms includes the number of carbon atoms of the substituent.

The halogen atom represented by Y' and Y'' is preferably a fluorine atom.
A is preferably an oxygen atom.

Examples of the hydrocarbon group that may have a substituent include an alkyl group, an alkenyl group, an alkynyl group, an aryl group, and the like, with an aryl group being preferred. Examples of the substituent include an alkyl group such as a methyl group; an aryl group such as a phenyl group; a halogen atom such as a fluorine atom; and the like.

The alkyl group which may have a substituent is preferably an alkyl group having 1 to 10 carbon atoms. Specific examples of the alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, a tert-butyl group, an n-pentyl group, a hexyl group, a benzyl group, and a phenethyl group.
The alkenyl group which may have a substituent is preferably an alkenyl group having 2 to 10 carbon atoms, and specific examples include a vinyl group, an allyl group, a methacryl group, and a 2-butenyl group.
The alkynyl group which may have a substituent is preferably an alkynyl group having 2 to 10 carbon atoms, and specific examples include an ethynyl group, a 2-propynyl group, a 2-butynyl group, and a 3-butynyl group.
The aryl group which may have a substituent is preferably an aryl group having 6 to 10 carbon atoms, specific examples of which include a phenyl group and a tolyl group, with the phenyl group being preferred.

As the -COY (acyl group), an acyl group having 2 to 10 carbon atoms is preferred, and specific examples include an acetyl group, a propionyl group, an acryloyl group, a methacryloyl group, and a benzoyl group.

As -OY, a group having 1 to 10 carbon atoms is preferred, and specific examples include a methoxy group, an ethoxy group, an n-propyl ether group, an n-butyl ether group, and a tert-butyl ether group, with a methoxy group being preferred.

As the -OCOY (acyloxy group), an acyloxy group having 2 to 10 carbon atoms is preferred, and specific examples include an acetyloxy group, a propionyloxy group, an acryloyloxy group, a methacryloyloxy group, and a benzoyloxy group, with an acetyloxy group being preferred.

Specific examples of --OSO ₂ Y" (sulfonyloxy group) include a tosyloxy group, a mesyloxy group, and a fluorosulfonyloxy group.

Specific examples of --OP(O)(OY) ₂ (phosphate ester group) include a dimethyl phosphate ester group, and a bis(2,2,2-trifluoroethyl)phosphate ester group.

Examples of —CO ₂ Y include a methyloxycarbonyl group and a benzyloxycarbonyl group.

Examples of —OCO ₂ Y include a methoxycarbonyloxy group, an ethoxycarbonyloxy group, and the like.

Examples of —OSO ₃ Y include a methoxysulfonyloxy group, an ethoxysulfonyloxy group, and the like.

Examples of —OBY ₂ (borate ester group) include a dimethyl borate ester group and a diethyl borate ester group.

Examples of -SY include a methyl thioether group and an ethyl thioether group.

Examples of -SOY (sulfinyl group) include methyl sulfoxide group, ethyl sulfoxide group, etc.

Examples of —SO ₂ Y (sulfonyl group) include a mesyl group and a tosyl group.

Examples of —SO ₃ Y include a methoxysulfonyl group and an ethoxysulfonyl group.

Examples of _--NY'.sub.2 (amino group) include a dimethylamino group and a diethylamino group.

Examples of --PY ₂ (phosphine group) include a dimethylphosphine group and a diethylphosphine group.

Examples of —P(O)Y ₂ (phosphoryl group) represented by Z ¹ to Z ¹¹ include a dimethylphosphoryl group and a diethylphosphoryl group.

Examples of —OP(O)Y ₂ (phosphate ester group) include a difluorophosphate ester group.

Examples of _--SiY3 include a trimethylsilyl group and a triethylsilyl group.

Examples of _--OSiY3 include a trimethylsiloxy group, a triethylsiloxy group, an isopropylsiloxy group, a t-butyldimethylsiloxy group, and a triphenylsiloxy group.

Examples of --BY ₂ (boron group) include a dimethylborane group and a diethylborane group.

Examples of --NYCOY or --CONY ₂ (amide group) include a dimethylamide group and a methylacetamide group.

In the case where antimony element is bonded only to fluorine element, specific examples of compound (A) include antimony trifluoride, antimony pentafluoride, hexafluoroantimonate, and magic acid (FSO ₃ H.SbF ₅ ) salt. Examples of counter cations of hexafluoroantimonate and magic acid include cations of alkali metal elements such as sodium, potassium, rubidium, and cesium; cations of alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; cations of transition metals such as iron, copper, nickel, cobalt, manganese, titanium, platinum, and silver; and organic cations of elements in Groups 13 to 16 of the long periodic table, such as ammonium cations, organic ammonium substituted with a hydrocarbon group, and heterocyclic aromatic ammonium. As compound (A), from the viewpoint of obtaining excellent internal resistance characteristics, antimony trifluoride and sodium hexafluoroantimonate are preferable, and antimony trifluoride is particularly preferable.

Compound (A) may be used alone or in combination of two or more kinds. Compound (A) may be commercially available or may be obtained by synthesis using a known method. When obtained by synthesis, the target compound can be obtained by, for example, using a Grignard reagent of the target functional group with an antimony compound such as antimony chloride, or by carrying out a cation exchange reaction with commercially available hexafluoroantimonate.

The content of the compound (A) in the non-aqueous electrolyte is not particularly limited as long as it does not significantly impair the effects of the present invention. Specifically, the lower limit of the content of the compound (A) in the non-aqueous electrolyte is preferably 0.001% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more. The upper limit is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and even more preferably 0.5% by mass.
The content of the compound (A) is most preferably 0.3% by mass or less. When the content of the compound (A) is within the above range, the resistance suppression effect is more easily exhibited without impairing other battery performance. When the non-aqueous electrolyte solution contains two or more types of the compound (A), the total amount of the compounds (A) is the content of the compound (A).
The method for identifying the molecular structure of the compound (A) and the method for measuring the content are not particularly limited, and may be appropriately selected from known methods depending on the type of compound. Examples of known methods include a combination of inductively coupled plasma (ICP) emission spectroscopy, nuclear magnetic resonance (NMR), liquid chromatography, and the like.

The inclusion of the antimony compound (A) has the effect of suppressing the internal resistance of a non-aqueous electrolyte secondary battery, particularly the internal resistance after cycling. The reason for this effect is presumed to be due to the following mechanism.
It is believed that the antimony compound (A) contained in the non-aqueous electrolyte stabilizes the positive electrode surface by interacting with the positive electrode surface and forming a bond, and suppresses side reactions occurring at the interface between the positive electrode and the electrolyte. Since the increase in deposits due to the oxidative decomposition of the electrolyte and the structural change of the positive electrode surface are the causes of the increase in internal resistance, it is believed that the antimony compound (A) can provide a resistance suppression effect. In addition, the antimony compound (A) is adsorbed on the positive electrode surface, which physically prevents the salt and solvent molecules of the electrolyte from approaching, and is also expected to have the effect of suppressing oxidation reactions caused by the salt and solvent molecules.
The nature of the antimony compound (A) varies greatly depending on the type of element directly bonded to the antimony element, and it is believed that the antimony compound bonded to the fluorine element with the highest electronegativity has a high ability to interact with the positive electrode surface. In addition, when the bond between the antimony compound (A) and the positive electrode surface is formed, it is expected that the functional group bonded to the antimony element will be released. It is generally proposed that the antimony compound (A) having an Sb-F bond can form a good coating by releasing F anions when reacting with the positive electrode, and LiF is expected to cover the positive electrode surface as a coating and suppress contact with the electrolyte. In other words, it is estimated that the antimony compound having an Sb-F bond has a high effect of reducing the positive electrode resistance due to two effects: the stabilizing effect on the positive electrode by the Sb element and the effect of suppressing contact with the electrolyte by the LiF coating.

[1-2. Electrolytes]
The non-aqueous electrolyte for lithium ion secondary batteries of the present embodiment contains a lithium salt as an electrolyte. The non-aqueous electrolyte may contain other electrolytes as long as the effects of the present invention are obtained. Specific examples of the lithium salt will be described in detail below.

<Lithium salt>
There are no particular limitations on the lithium salt, and any lithium salt may be used as long as it is known to be used for this purpose. Specific examples include the following:

_Examples of lithium salts include lithium fluoroborates such as _LiBF4 ; lithium fluorophosphates such as _LiPF6 , _Li2PO3F , _{and LiPO2F2; lithium tungstates such as Li2WO4, Li4WO5, and Li6W2O9; lithium carboxylates such as CH3COOLi(CH2COOLi)2 ; lithium sulfonates such as LiFSO3 and CH3SO3Li ; LiN} ( _FSO2 ) _{2 ,} LiN _{( FSO2} )( _{CF3SO2 )} , LiN _{( CF3SO2} ) ₂ , _{and LiN} ( _{C2F5SO2 ) 2 .} Examples of the lithium salts include lithium imide salts such as lithium cyclic 1,2-perfluoroethane disulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, etc.; lithium methide salts such as LiC(FSO ₂ ) ₃ , LiC(CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , etc.; lithium oxalate salts such as lithium difluorooxalatoborate, lithium bis(oxalato)borate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, lithium tris(oxalato)phosphate, etc.; and other fluorine-containing organic lithium salts.

Among these, lithium fluoroborates, lithium fluorophosphates, lithium sulfonates, lithium imide salts, lithium methide salts, lithium oxalate salts, etc. are more preferred because they have the effect of improving low-temperature output characteristics, high-rate charge/discharge characteristics, impedance characteristics, high-temperature storage characteristics, cycle characteristics, etc. More preferred are LiPF ₆ , LiN(FSO ₂ ) ₂ , lithium bis(oxalato)borate, or LiFSO ₃ , and particularly preferred is LiPF _6. The above lithium salts may be used alone or in combination of two or more kinds.
The combination of two or more kinds of lithium salts is not particularly limited, but examples thereof include _LiPF6 and LiN( _FSO2 ) ₂ , _LiPF6 and _LiBF4 , _LiPF6 and LiN( _CF3SO2 ) ₂ , _LiBF4 and LiN _{( FSO2} ) ₂ , _LiBF4 , _LiPF6 and LiN( _FSO2 ) ₂ , etc. Among these, the combinations of _LiPF6 and LiN( _FSO2 ) ₂ , _LiPF6 and _LiBF4 , or _LiBF4 , _LiPF6 and LiN( _FSO2 ) ₂ are preferred.

The nonaqueous electrolyte according to this embodiment may be an embodiment that does not contain sodium and sodium salt as electrolytes. "Does not contain sodium and sodium salt" means that sodium and sodium salt are not intentionally added, and sodium and sodium salt that may be contained as impurities may be contained in the nonaqueous electrolyte. Furthermore, the electrolyte may be an embodiment that uses only lithium salt. "Uses only lithium salt" means that the only electrolyte that is intentionally added is lithium salt, and electrolytes other than lithium salt that may be contained as impurities may be contained in the nonaqueous electrolyte.

The total concentration of electrolytes (especially lithium salts) in the non-aqueous electrolyte is not particularly limited, but is usually 8% by mass or more, preferably 8.5% by mass or more, more preferably 9% by mass or more, and is usually 18% by mass or less, preferably 17% by mass or less, more preferably 16% by mass or less, based on the total amount of the non-aqueous electrolyte. If the total concentration of electrolytes is within the above range, the electrical conductivity is appropriate for battery operation, and sufficient output characteristics tend to be obtained.

[1-3. Non-aqueous solvent]
The non-aqueous electrolyte according to the present embodiment contains a non-aqueous solvent that dissolves the electrolyte, similar to a general non-aqueous electrolyte. There is no particular limitation on the non-aqueous solvent used here, and a known organic solvent can be used. Examples of the organic solvent include saturated cyclic carbonates, chain carbonates, chain carboxylic acid esters, cyclic carboxylic acid esters, ether compounds, and sulfone compounds, but are not particularly limited thereto. These can be used alone or in any combination and ratio of two or more.
The combination of two or more non-aqueous solvents is not particularly limited, and examples thereof include saturated cyclic carbonates and chain carboxylates, cyclic carboxylates and chain carbonates, or saturated cyclic carbonates, chain carbonates and chain carboxylates. Among these, the combination of saturated cyclic carbonates and chain carbonates, or saturated cyclic carbonates, chain carbonates and chain carboxylates is preferred.

[1-3-1. Saturated cyclic carbonates]
Examples of saturated cyclic carbonates include those having an alkylene group usually having 2 to 4 carbon atoms, and from the viewpoint of improving the battery characteristics resulting from the improvement of the degree of dissociation of lithium ions, saturated cyclic carbonates having 2 to 3 carbon atoms are preferably used. In this specification, the term "saturated cyclic carbonate" does not include fluorine-containing cyclic carbonates.

Examples of the saturated cyclic carbonate include ethylene carbonate, propylene carbonate, and butylene carbonate. Among them, ethylene carbonate or propylene carbonate is preferred, and ethylene carbonate, which is less susceptible to oxidation and reduction, is more preferred. The saturated cyclic carbonate may be used alone or in any combination and ratio of two or more.

The content of the saturated cyclic carbonate is not particularly limited, and is arbitrary as long as it does not significantly impair the effect of the present invention according to this embodiment, but is usually 3% by volume or more, preferably 5% by volume or more, and is usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less, based on the total amount of the nonaqueous solvent in the nonaqueous electrolyte. By setting it in this range, the decrease in electrical conductivity due to the decrease in the dielectric constant of the nonaqueous electrolyte can be avoided, and the large current discharge characteristics, stability to the negative electrode, and cycle characteristics of the nonaqueous electrolyte secondary battery can be easily set in a good range, and the oxidation/reduction resistance of the nonaqueous electrolyte tends to be improved, and the stability during high-temperature storage tends to be improved.
In the present embodiment, the volume percentage refers to the volume ratio of the non-aqueous electrolyte solution to the total amount of the solvent at 25° C. and 1 atmospheric pressure.

[1-3-2. Chain carbonate]
As the chain carbonate, one having 3 to 7 carbon atoms is usually used, and in order to adjust the viscosity of the electrolyte solution within an appropriate range, a chain carbonate having 3 to 5 carbon atoms is preferably used.

Specific examples of chain carbonates include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, ethyl methyl carbonate, and methyl-n-propyl carbonate. Dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are particularly preferred.

Chain carbonates having fluorine atoms (hereinafter sometimes abbreviated as "fluorinated chain carbonates") can also be suitably used. The number of fluorine atoms in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, and preferably 4 or less. When the fluorinated chain carbonate has multiple fluorine atoms, the multiple fluorine atoms may be bonded to the same carbon or different carbons. Examples of fluorinated chain carbonates include fluorinated dimethyl carbonate derivatives such as fluoromethyl methyl carbonate; fluorinated ethyl methyl carbonate derivatives such as 2-fluoroethyl methyl carbonate; and fluorinated diethyl carbonate derivatives such as ethyl-(2-fluoroethyl) carbonate.

The chain carbonates may be used alone or in any combination of two or more in any ratio.

The amount of the chain carbonate is not particularly limited, but is usually 15% by volume or more, preferably 20% by volume or more, more preferably 25% by volume or more, and usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less, based on the total amount of the nonaqueous solvent in the nonaqueous electrolyte. By setting the amount of the chain carbonate in the above range, the viscosity of the nonaqueous electrolyte can be set in an appropriate range, the decrease in ion conductivity can be suppressed, and the output characteristics of the nonaqueous electrolyte secondary battery can be easily set in a good range.

Furthermore, by combining a specific chain carbonate with a specific amount of ethylene carbonate, battery performance can be significantly improved.

For example, when dimethyl carbonate and ethyl methyl carbonate are selected as specific chain carbonates, the content of ethylene carbonate is not particularly limited and is arbitrary as long as it does not significantly impair the effects of the present invention according to this embodiment, but is usually 15% by volume or more, preferably 20% by volume or more, and usually 45% by volume or less, preferably 40% by volume or less, based on the total amount of non-aqueous solvent in the non-aqueous electrolyte solution, and the content of dimethyl carbonate is usually 20% by volume or more, preferably 30% by volume or more, and usually 50% by volume or less, preferably 45% by volume or less, based on the total amount of non-aqueous solvent in the non-aqueous electrolyte solution, and the content of ethyl methyl carbonate is usually 20% by volume or more, preferably 30% by volume or more, and usually 50% by volume or less, preferably 45% by volume or less. By setting the content within the above range, there is a tendency for excellent high-temperature stability and suppression of gas generation.

[1-3-3. Chain carboxylate ester]
Examples of the chain carboxylate include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, methyl isobutyrate, ethyl isobutyrate, and methyl pivalate. Among them, methyl acetate, ethyl acetate, propyl acetate, and butyl acetate are preferred from the viewpoint of improving battery characteristics. Chain carboxylates in which a part of the hydrogen of the above-mentioned compounds is replaced with fluorine (e.g., methyl trifluoroacetate, ethyl trifluoroacetate, etc.) can also be used suitably. The chain carboxylate may be used alone or in any combination and ratio of two or more.

The amount of the chain carboxylate ester is not particularly limited, but is usually 3% by volume or more, preferably 5% by volume or more, more preferably 10% by volume or more, and usually 30% by volume or less, preferably 20% by volume or less, more preferably 15% by volume or less, based on the total amount of the nonaqueous solvent in the nonaqueous electrolyte. By setting the amount of the chain carboxylate ester in the above range, the viscosity of the nonaqueous electrolyte can be set in an appropriate range, the decrease in ion conductivity can be suppressed, and the output characteristics of the nonaqueous electrolyte secondary battery can be easily set in a good range.

[1-3-4. Cyclic carboxylate esters]
Examples of the cyclic carboxylate include γ-butyrolactone and γ-valerolactone. Among these, γ-butyrolactone is more preferable. Cyclic carboxylates in which some of the hydrogen atoms of the above-mentioned compounds are replaced with fluorine can also be used suitably. The cyclic carboxylates may be used alone or in any combination and ratio of two or more.

The content of the cyclic carboxylate is not particularly limited, but is usually 3 vol.% or more, preferably 5 vol.% or more, more preferably 10 vol.% or more, and usually 30 vol.% or less, preferably 20 vol.% or less, more preferably 15 vol.% or less, based on the total amount of the nonaqueous solvent in the nonaqueous electrolyte. By setting the content of the cyclic carboxylate within the above range, the viscosity of the nonaqueous electrolyte can be set to an appropriate range, the decrease in ion conductivity can be suppressed, and the output characteristics of the nonaqueous electrolyte secondary battery can be easily set to a good range.

[1-3-5. Ether compounds]
Preferred examples of the ether-based compound include chain ethers having 3 to 10 carbon atoms, such as dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether; and cyclic ethers having 3 to 6 carbon atoms, such as tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, and 1,4-dioxane.
Among these, the chain ether having 3 to 10 carbon atoms is preferably dimethoxymethane, diethoxymethane, or ethoxymethoxymethane, since it has a high solvation ability for lithium ions, improves ion dissociation, has a low viscosity, and provides high ionic conductivity. The cyclic ether having 3 to 6 carbon atoms is preferably tetrahydrofuran,
1,3-dioxane or 1,4-dioxane is preferred. The ether-based compounds may be used alone or in any combination of two or more in any ratio.

The content of the ether-based compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention, but is usually 1% by volume or more, preferably 2% by volume or more, more preferably 3% by volume or more, and usually 30% by volume or less, preferably 25% by volume or less, more preferably 20% by volume or less, based on the total amount of the non-aqueous solvent. If the content of the ether-based compound is within the above-mentioned preferred range, it is easy to ensure the effect of improving the degree of lithium ion dissociation of the ether and improving the ion conductivity due to the reduced viscosity. In addition, when the negative electrode active material is a carbonaceous material, the phenomenon in which the chain ether is co-inserted with the lithium ion can be suppressed, so that the input/output characteristics and the charge/discharge rate characteristics can be set to appropriate ranges.

[1-3-6. Sulfone compounds]
The sulfone compound is not particularly limited, and may be a cyclic sulfone or a chain sulfone. When the sulfone compound is a cyclic sulfone, it usually has 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms, and when the sulfone compound is a chain sulfone, it usually has 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. The number of sulfonyl groups in one molecule of the sulfone compound is not particularly limited, but is usually 1 or 2.

Examples of cyclic sulfones include monosulfone compounds such as trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones; and disulfone compounds such as trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones. Among these, from the viewpoint of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolanes) are particularly preferred.

As the sulfolane, sulfolane or a sulfolane derivative is preferred. As the sulfolane derivative, one or more of the hydrogen atoms bonded to the carbon atoms constituting the sulfolane ring are preferably substituted with a fluorine atom or an alkyl group.

Among these, 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,3-difluorosulfolane, 2-trifluoromethylsulfolane, 3-trifluoromethylsulfolane, etc. are preferred because of their high ionic conductivity and high input/output.

Examples of chain sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, and pentafluoroethyl methyl sulfone. Among these, dimethyl sulfone, ethyl methyl sulfone, and monofluoromethyl methyl sulfone are preferred in that they improve the high-temperature storage stability of the electrolyte.

The content of the sulfone-based compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention according to this embodiment, but is usually 0.3 vol.% or more, preferably 0.5 vol.% or more, more preferably 1 vol.% or more, and is usually 40 vol.% or less, preferably 35 vol.% or less, more preferably 30 vol.% or less, based on the total amount of the nonaqueous solvent in the nonaqueous electrolyte. If the content of the sulfone-based compound is within the above range, an electrolyte with excellent high-temperature storage stability tends to be obtained.

[1-4. Auxiliaries]
Various auxiliary agents may be contained within the range that does not significantly impair the effects of the present invention. As the auxiliary agent, any conventionally known agent may be used. In addition, the auxiliary agent may be used alone or in any combination and ratio of two or more types.

Examples of auxiliary agents that may be contained in the non-aqueous electrolyte include compounds having a carbon-carbon unsaturated bond, compounds having an oxalate structure, fluorine-containing cyclic carbonates, compounds having an isocyanato group (isocyanate group), sulfur-containing organic compounds, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, carboxylic anhydrides, borates, compounds having a P-F bond, and compounds having a SO ₂ structure. For example, compounds described in International Publication No. 2015/111676 can be mentioned. These auxiliary agents may be contained in the non-aqueous electrolyte, and include those that are added, as well as those that are generated in the non-aqueous electrolyte or in the non-aqueous electrolyte battery during battery operation.

Among the above compounds, particularly preferred additives that have a particularly high additive effect and exhibit a synergistic effect include (a) a compound having a carbon-carbon unsaturated bond, (b) a compound having an oxalate structure, (c) a compound having an isocyanate group, (d) a compound having a P-F bond, (e) a compound having a SO ₂ structure, and (f) a silicon-containing compound, among which (a) a compound having a carbon-carbon unsaturated bond, (b) a compound having an oxalate structure, and (c) a compound having an isocyanate group are particularly preferred. These are highly effective in suppressing side reactions on the negative electrode, and it is believed that the effect of the antimony compound (A) on the positive electrode is further enhanced by reducing the consumption of the antimony compound (A) at the negative electrode.

<1-4-1. (a) Compounds having carbon-carbon unsaturated bonds>
The compound having a carbon-carbon unsaturated bond is not particularly limited as long as it is a compound having a carbon-carbon unsaturated bond, and any compound can be used as long as it does not significantly impair the effects of the present invention. Among them, carbonates having a carbon-carbon unsaturated bond, isocyanurates having a carbon-carbon unsaturated bond, cyclic sulfonic acid esters having a carbon-carbon unsaturated bond, cyclic sulfones having a carbon-carbon unsaturated bond, and silane compounds having a carbon-carbon unsaturated bond are preferred, and cyclic carbonates having a carbon-carbon unsaturated bond and isocyanurates having a carbon-carbon unsaturated bond are particularly preferred. Specifically, vinylene carbonate, vinyl ethylene carbonate, ethynyl ethylene carbonate, or triallyl isocyanurate is preferred.
The compound having a carbon-carbon unsaturated bond may be used alone or in any combination and ratio of two or more. The content of the compound having a carbon-carbon unsaturated bond is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention, but is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and most preferably 1% by mass or less, based on the total amount of the nonaqueous electrolyte.

<1-4-2. (b) Compounds having an oxalate structure>
The compound having an oxalato structure is not particularly limited as long as it is a compound having an oxalato structure, and any compound can be used as long as it does not significantly impair the effects of the present invention. Among them, lithium salts having an oxalato structure are preferred. Specifically, lithium difluorooxalatoborate, lithium bis(oxalato)borate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, and lithium tris(oxalato)phosphate are preferred, and lithium bis(oxalato)borate is particularly preferred. The compound having an oxalato structure may be used alone or in any combination and ratio of two or more.
The content of the compound having an oxalate structure is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention; however, it is usually 0.001 mass% or more, preferably 0.01 mass% or more, more preferably 0.1 mass% or more, and is usually 10 mass% or less, preferably 5 mass% or less, more preferably 3 mass% or less, even more preferably 2 mass% or less, and most preferably 1 mass% or less, based on the total amount of the nonaqueous electrolyte solution.
However, the lithium salt having an oxalate structure may be used as an electrolyte, and in that case, the content is not limited to the above amount.

<1-4-3. (c) Compound having an isocyanate group>
The compound having an isocyanate group is not particularly limited as long as it is a compound having an isocyanate group, and any compound can be used as long as it does not significantly impair the effects of the present invention. Specific examples include aliphatic hydrocarbon monoisocyanate compounds such as methyl isocyanate, ethyl isocyanate, vinyl isocyanate, and allyl isocyanate;
aliphatic hydrocarbon diisocyanate compounds such as chain aliphatic hydrocarbon diisocyanates, such as butyl diisocyanate or hexamethylene diisocyanate, or alicyclic hydrocarbon diisocyanates, such as 1,3-bis(isocyanatomethyl)cyclohexane or dicyclohexylmethane 4,4'-diisocyanate;
aromatic hydrocarbon monoisocyanate compounds such as aromatic monoisocyanates such as phenyl isocyanate, or aromatic monosulfonyl isocyanates such as (ortho-, meta-, para-)toluenesulfonyl isocyanate;
Aromatic hydrocarbon diisocyanate compounds such as m-xylylene diisocyanate, tolylene-2,4-diisocyanate, and diphenylmethane diisocyanate; and the like.
Preferably, an aliphatic hydrocarbon diisocyanate compound such as a chain aliphatic hydrocarbon diisocyanate or an alicyclic hydrocarbon diisocyanate;
Aromatic hydrocarbon monoisocyanate compounds such as aromatic monoisocyanates or aromatic monosulfonyl isocyanates;
Aromatic hydrocarbon diisocyanate compounds;
More preferred are linear aliphatic hydrocarbon diisocyanates such as hexamethylene diisocyanate, alicyclic hydrocarbon diisocyanates such as 1,3-bis(isocyanatomethyl)cyclohexane, and aromatic hydrocarbon diisocyanates such as diphenylmethane diisocyanate, and compounds thereof.
Particularly preferred is 1,3-bis(isocyanatomethyl)cyclohexane.
The compound having an isocyanate group may be used alone or in any combination of two or more kinds in any ratio.
The content of the compound having an isocyanate group is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present invention; however, it is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and most preferably 1% by mass or less, based on the total amount of the nonaqueous electrolyte solution.

<1-4-4. (d) Compounds having a P—F bond>
The compound having a P-F bond is not particularly limited as long as it is a compound having a P-F bond in the molecule, and any compound can be used as long as it does not significantly impair the effects of the present invention. Among them, a phosphate having a P-F bond is preferred. Specific structures include monofluorophosphate and difluorophosphate. The counter cation of the phosphate having a P-F bond is not particularly limited, but examples include metal cations such as lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, and barium; and ammonium ions represented by [NR ¹³ R ¹⁴ R ¹⁵ R ¹⁶ ] ⁺ (wherein R ¹³ to R ¹⁶ each independently represent a hydrogen atom or an organic group having 1 to 12 carbon atoms). Among them, a lithium ion is particularly preferred. In addition, the number of P-F bonds contained in the molecule is preferably 2 or more. Specifically, lithium difluorophosphate is particularly preferred. The compound having a P-F bond may be used alone or in any combination and ratio of two or more.
The content of the compound having a P-F bond is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention; however, it is usually 0.001 mass% or more, preferably 0.01 mass% or more, more preferably 0.1 mass% or more, and is usually 10 mass% or less, preferably 5 mass% or less, more preferably 3 mass% or less, even more preferably 2 mass% or less, and most preferably 1 mass% or less, based on the total amount of the nonaqueous electrolyte solution.

<1-4-5. (e) Compounds having _SO2 structure>
The compound having the _SO2 structure is not particularly limited as long as it has an _SO2 structure in the molecule, and any compound can be used as long as it does not significantly impair the effects of the present invention. Among them, lithium salts having the _SO2 structure or ester compounds having the _SO2 structure are preferred.
Examples of lithium salts having an _SO2 structure include:
Lithium fluorosulfonate ( _LiFSO3 );
Fluorosulfonylimide lithium salts such as lithium bis(fluorosulfonyl)imide (LiN( _FSO2 ) ₂ ), LiN _{( FSO2} ) _{( CF3SO2} ), LiN( _CF3SO2 ) _{2 ;}
Fluorosulfonylmethide lithium salts such as LiC( _FSO2 ) ₃ ;
Lithium fluorosulfonylborates such as LiBF ₃ (FSO ₃ ) and LiB(FSO ₂ ) ₄ ; and the like.
Among the compounds having an SO ₂ structure, Li salts having an F—S bond are preferred, with LiFSO ₃ and LiN(FSO ₂ ) ₂ being particularly preferred.
Examples of esters having an _SO2 structure include:
Chain sulfonic acid esters such as methyl methanesulfonate and ethyl methanesulfonate;
Cyclic sulfonic acid esters such as 1,3-propane sultone, 1-propene 1,3-sultone, etc.;
Chain sulfate esters such as dimethyl sulfate and diethyl sulfate;
cyclic sulfates such as ethylene sulfate, propylene sulfate, and the like;
The compound having the _SO2 structure may be used alone or in any combination of two or more in any ratio.
The content of the compound having an _SO2 structure is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention. However, the content is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and most preferably 1% by mass or less, based on the total amount of the nonaqueous electrolyte.
However, LiN( _FSO2 ) ₂ may be used as an electrolyte, and in that case, the content is not limited to the above. In addition, for example, a compound having an _SO2 structure, such as a sulfone-based compound, may be used as a non-aqueous solvent, and in that case, the content is not limited to the above.

<1-4-6. (f) Silicon-containing compounds>
The silicon-containing compound is not particularly limited as long as it is a compound containing silicon element, and any compound can be used as long as it does not significantly impair the effects of the present invention. Specific examples include:
Organomonosilane compounds such as trimethylsilane, trimethylvinylsilane, and trimethylallylsilane;
Disilane compounds such as hexamethyldisilane and hexaethyldisilane;
Organosiloxane compounds such as hexamethyldisiloxane and hexaethyldisiloxane; and the like.
Preferred are monosilane compounds having a carbon-carbon unsaturated bond such as a vinyl group, an alkenylene group, or an alkynylene group, such as trimethylvinylsilane or trimethylallylsilane; siloxane compounds having a carbon-carbon unsaturated bond such as a vinyl group, an alkenylene group, or an alkynylene group, such as tetramethyl-1,3-divinyldisiloxane or tetramethyl-1,3-diallyldisiloxane; and disilane compounds such as hexamethyldisilane or hexaethyldisilane.
More preferred are alkenylalkylsilane compounds such as trimethylvinylsilane and trimethylallylsilane; and unsubstituted disilane compounds such as hexamethyldisilane and hexaethyldisilane.
Particularly preferred are trimethylvinylsilane and hexamethyldisilane.
The silicon-containing compounds may be used alone or in any combination of two or more in any ratio.
The content of the silicon-containing compound is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present invention; however, it is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and most preferably 1% by mass or less, based on the total amount of the nonaqueous electrolyte solution.

In this specification, the composition of the nonaqueous electrolyte solution refers to a composition analyzed at any stage, such as when the nonaqueous electrolyte solution is produced, when the nonaqueous electrolyte solution is injected into a battery, or when the nonaqueous electrolyte solution is shipped as a battery.
That is, the nonaqueous electrolyte may be mixed so that the ratio of each component is a predetermined composition when preparing the nonaqueous electrolyte. After preparing the nonaqueous electrolyte, the nonaqueous electrolyte itself can be subjected to analysis to confirm the composition. The nonaqueous electrolyte may be collected from the completed nonaqueous electrolyte secondary battery and subjected to analysis. Examples of a method for collecting the nonaqueous electrolyte include a method of collecting the electrolyte by opening a part or all of the battery container or by providing a hole in the battery container. The electrolyte may be collected by centrifuging the opened battery container, or an extraction solvent (e.g., acetonitrile dehydrated to a water content of 10 ppm or less) may be placed in the opened battery container or the extraction solvent may be brought into contact with the battery element to extract the electrolyte. The nonaqueous electrolyte collected by such a method can be subjected to analysis. The collected nonaqueous electrolyte may be diluted to provide conditions suitable for analysis and subjected to analysis.

The optimal method for analyzing the non-aqueous electrolyte solution varies depending on the composition of the non-aqueous electrolyte solution, the type of antimony compound (A), etc., but specifically, there are inductively coupled plasma (ICP) emission spectroscopy, nuclear magnetic resonance (hereinafter sometimes abbreviated as NMR), gas chromatography, ion chromatography, and other liquid chromatography. Hereinafter, the analysis method using NMR will be described. In an inert atmosphere, the non-aqueous electrolyte solution is dissolved in a deuterated solvent dehydrated to 10 ppm or less, and placed in an NMR tube to perform NMR measurement. In addition, a double tube may be used as the NMR tube, with the non-aqueous electrolyte solution placed in one tube and the deuterated solvent placed in the other tube to perform NMR measurement. Examples of the deuterated solvent include deuterated acetonitrile and deuterated dimethyl sulfoxide. When determining the concentration of the components of the non-aqueous electrolyte solution, a specified amount of a standard substance is dissolved in the deuterated solvent, and the concentration of each component can be calculated from the ratio of the spectra. In addition, the concentration of one or more components constituting the non-aqueous electrolyte may be determined in advance by another analytical method such as gas chromatography, and the concentration may be calculated from the spectrum ratio of the component with known concentration to the other components. The nuclear magnetic resonance analyzer used is preferably an apparatus with a proton resonance frequency of 400 MHz or more. Examples of the nuclides to be measured include ^1H , ^31P , ^19F , and ^121Sb .
These analytical techniques may be used alone or in combination of two or more.

[2. Non-aqueous electrolyte lithium ion secondary battery]
A nonaqueous electrolyte lithium ion secondary battery (nonaqueous electrolyte secondary battery) according to another embodiment of the present invention is a nonaqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions, a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions, and a nonaqueous electrolyte.

[2-1. Nonaqueous electrolyte for lithium ion secondary batteries]
As the non-aqueous electrolyte solution, the above-mentioned non-aqueous electrolyte solution for lithium ion secondary batteries (non-aqueous electrolyte solution) is used. Note that, within the scope of the present invention, it is also possible to mix the above-mentioned non-aqueous electrolyte solution with other non-aqueous electrolyte solutions and use them.

[2-2. Negative electrode]
The negative electrode refers to an electrode having a negative electrode active material on at least a portion of the surface of a current collector.

[2-2-1. Negative electrode active material]
The negative electrode active material used in the negative electrode is not particularly limited as long as it can electrochemically absorb and release metal ions. Specific examples include carbonaceous materials and metals that can be alloyed with Li. Among these, the following are preferred: particles containing lithium, lithium-containing metal composite oxide materials, and mixtures thereof. Among these, the following are preferred: carbonaceous materials, Li-containing alloys, and the like, which have good cycle characteristics and safety, and further have excellent continuous charging characteristics. It is preferable to use particles containing a metal capable of being alloyed with Li or a mixture of particles containing a metal capable of being alloyed with Li and graphite particles. These may be used alone or in combination of two or more kinds. They may be used in any combination.

[2-2-2. Carbonaceous material]
Examples of the carbonaceous material include natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. Of these, natural graphite is preferred. Two or more of them may be used in any combination and in any ratio.
Examples of natural graphite include scaly graphite, flake graphite, and/or graphite particles obtained by subjecting such graphite to treatments such as spheroidization and densification. Among these, graphite particles having excellent particle packing properties and charge/discharge rate characteristics are preferably used. From this viewpoint, spherical or ellipsoidal graphite particles that have been subjected to a spheroidizing treatment are particularly preferred.
The average particle size (d50) of the graphite particles is usually 1 μm or more and 100 μm or less.

[2-2-3. Physical properties of carbonaceous materials]
The carbonaceous material as the negative electrode active material preferably satisfies at least one of the characteristics such as the physical properties and shape shown in the following (1) to (4), and particularly preferably satisfies a plurality of the characteristics simultaneously.
(1) X-ray diffraction parameters The d value (interlayer distance) of the lattice plane (002 plane) of the carbonaceous material determined by X-ray diffraction according to the Gakushin method is usually 0.335 nm or more and 0.360 nm or less. The crystallite size (Lc) of the carbonaceous material determined by X-ray diffraction according to the Gakushin method is 1.0 nm or more.
(2) Volume-Based Average Particle Size The volume-based average particle size of a carbonaceous material is a volume-based average particle size (median diameter) determined by a laser diffraction/scattering method, and is usually 1 μm or more and 100 μm or less.
(3) Raman R value and Raman half width The Raman R value of a carbonaceous material is a value measured by argon ion laser Raman spectroscopy, and is usually 0.01 or more and 1.5 or less.
Further, the Raman half-width of the carbonaceous material around 1580 cm ^-1 is not particularly limited, but is usually 10 cm ^-1 or more and 100 cm ^-1 or less.
(4) BET Specific Surface Area The BET specific surface area of a carbonaceous material is the value of the specific surface area measured by the BET method, and is usually 0.1 m ² ·g ⁻¹ or more and 100 m ² ·g ⁻¹ or less.
The negative electrode active material may contain two or more carbonaceous materials having different properties, where the properties refer to one or more characteristics selected from the group consisting of X-ray diffraction parameters, volume-based average particle size, Raman R value, Raman half-width, and BET specific surface area.
Preferred examples include a case where the volume-based particle size distribution is not symmetrical about the median size, where two or more types of carbonaceous materials having different Raman R values are contained, and where X-ray diffraction parameters are different.

[2-2-4. Particles containing metals capable of being alloyed with Li]
The particles containing a metal capable of being alloyed with Li may be any of those known in the art, but from the viewpoint of capacity and cycle life, it is preferable that the particles are, for example, particles of a metal selected from the group consisting of Sb, Si, Sn, Al, As, and Zn or a compound thereof. In addition, when the particles containing a metal capable of being alloyed with Li contain two or more kinds of metals, the particles may be alloy particles made of an alloy of these metals.
In addition, examples of the compound of the metal capable of being alloyed with Li include metal oxides, metal nitrides, metal carbides, etc. The compound may contain two or more metals capable of being alloyed with Li. Among these, the metal capable of being alloyed with Li or its compound is preferably metal Si (hereinafter, sometimes referred to as Si) or a compound containing Si, from the viewpoint of increasing capacity.

In this specification, Si or Si-containing compounds are collectively referred to as Si compounds. Specific examples of Si compounds include _SiOx , _SiNx , _SiCx , and _SiZxOy (Z=C, N). As the Si compound, Si _oxide ( _SiOx ) is preferred because it has a larger theoretical capacity than graphite, and amorphous Si or nano-sized Si crystals are preferred because they allow easy ingress and egress of alkali ions such as lithium ions and can provide a high capacity.
This general formula, SiO _x , can be obtained by using silicon dioxide (SiO ₂ ) and Si as raw materials, and the value of x is usually 0<x<2.
The average particle size (d50) of the particles containing a metal capable of being alloyed with Li is usually 0.01 μm or more and 10 μm or less from the viewpoint of cycle life.

[2-2-5. Mixture of particles containing a metal capable of alloying with Li and graphite particles]
The mixture of particles containing a metal capable of being alloyed with Li and graphite particles used as the negative electrode active material may be a mixture in which the particles containing a metal capable of being alloyed with Li and the graphite particles are mixed in a state of independent particles, or may be a composite in which the particles containing a metal capable of being alloyed with Li are present on the surface or inside of graphite particles.
The content of the particles containing a metal capable of being alloyed with Li relative to the total content of the particles containing a metal capable of being alloyed with Li and the graphite particles is usually 1 mass % or more and 99 mass % or less.

[2-2-6. Lithium-containing metal composite oxide materials]
The lithium-containing metal composite oxide material used as the negative electrode active material is not particularly limited as long as it is capable of absorbing and releasing lithium ions. From the viewpoint of high current density charge/discharge characteristics, however, a lithium-containing composite metal oxide material containing titanium is preferred, a composite oxide of lithium and titanium (hereinafter sometimes abbreviated as "lithium titanium composite oxide") is more preferred, and a lithium titanium composite oxide having a spinel structure is particularly preferred since it significantly reduces output resistance.

Furthermore, the lithium and/or titanium of the lithium titanium composite oxide may be substituted with another metal element, for example, at least one element selected from the group consisting of Al, Ga, Cu and Zn.
As _the lithium titanium composite oxide, Li4 _{/ 3Ti5/ 3O4} , _Li1Ti2O4 and Li4/ _{5Ti11 / 5O4} are preferred. Also, as the lithium titanium composite oxide in which part of the lithium and/or _titanium is replaced with another element, for example, Li4 _/ 3Ti4 _/ 3Al1 _{/ 3O4} is preferred.

[2-2-7. Configuration and preparation method of negative electrode]
The negative electrode can be manufactured by any known method as long as it does not significantly impair the effects of the present invention. For example, the negative electrode can be formed by adding a binder, a solvent, and, if necessary, a thickener, a conductive material, a filler, etc. to the negative electrode active material to form a slurry, which is applied to a current collector, dried, and then pressed to form a negative electrode active material layer.

[2-2-7-1. Current collector]
Any known current collector can be used to hold the negative electrode active material. Examples of the current collector for the negative electrode include metal materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel, and copper is particularly preferred from the standpoints of ease of processing and cost.
The shape of the current collector may be, for example, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punched metal, a foamed metal, or the like. Among them, a metal thin film or a metal foil is preferable. A copper foil is more preferable, and a rolled copper foil by a rolling method and an electrolytic copper foil by an electrolytic method are even more preferable. The metal thin film and the metal foil may be appropriately formed into a mesh shape. When the negative electrode current collector is in the form of a foil, a plate, a film, or the like, the thickness of the current collector is arbitrary, but is usually 1 μm or more and 1 mm or less.

[2-2-7-2. Binder]
There are no particular limitations on the binder that binds the negative electrode active material, so long as it is a material that is stable to the solvent of the nonaqueous electrolyte solution or the nonaqueous solvent used in the production of the electrode.
Specific examples include rubber-like polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber, and fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers. These may be used alone or in any combination and ratio of two or more.
The ratio of the binder to the negative electrode active material is usually 0.1% by mass or more and 20% by mass or less.
In particular, when the binder contains a rubber-like polymer such as SBR as a main component, the ratio of the binder to the negative electrode active material is usually 0.1% by mass or more and 5% by mass or less. Also, when the binder contains a fluorine-based polymer such as polyvinylidene fluoride as a main component, the ratio of the binder to the negative electrode active material is usually 1% by mass or more and 15% by mass or less.

[2-2-7-3. Thickener]
The thickener is usually used to adjust the viscosity of the slurry. The thickener is not particularly limited, but specific examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, etc. These may be used alone or in any combination and ratio of two or more.
Furthermore, when a thickener is used, the ratio of the thickener to the negative electrode active material is usually 0.1% by mass or more and 5% by mass or less.

There are no particular limitations on the type of solvent used to form the slurry, so long as it is capable of dissolving or dispersing the negative electrode active material, binder, and the thickener, conductive material, filler, etc., which are used as needed, and either an aqueous solvent or an organic solvent may be used.

[2-2-8. Electrode density]
The electrode structure when the negative electrode active material is made into an electrode is not particularly limited, but the density of the negative electrode active material layer present on the current collector is usually 1 g cm ⁻³ or more and 2.2 g cm ⁻³ or less. It is.

[2-2-9. Thickness of negative electrode plate]
The thickness of the negative electrode (also referred to as "negative electrode plate") is designed to match the positive electrode (also referred to as "positive electrode plate") to be used and is not particularly limited, but the thickness of the negative electrode active material layer obtained by subtracting the thickness of the current collector from the thickness of the negative electrode is usually 15 μm or more and 300 μm or less.

[2-2-10. Surface coating of negative electrode plate]
The negative electrode plate may have a surface to which a substance having a different composition from that of the negative electrode plate (a surface-attached substance) is attached. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate.

[2-3. Positive electrode]
The positive electrode refers to a current collector having a positive electrode active material on at least a portion of its surface.

[2-3-1. Positive electrode active material]
The positive electrode active material (lithium transition metal compound) used in the positive electrode will be described below.

[2-3-1-1. Lithium transition metal compounds]
The lithium transition metal compound is a compound having a structure capable of desorbing (releasing) and inserting (absorbing) lithium ions, and examples thereof include sulfides, phosphate compounds, silicate compounds, borate compounds, lithium transition metal composite oxides, etc. Among these, lithium transition metal composite oxides are preferred.
Examples of lithium transition metal composite oxides include those with a spinel structure that allows three-dimensional diffusion and those with a layered structure that allows two-dimensional diffusion of lithium ions. Examples of lithium transition metal composite oxides having a spinel structure include compounds represented by the general formula Li _x M ₂ O ₄ (M is at least one transition metal, and examples of the transition metal include Ni, Co, Mn, etc.), and specific examples include LiMn ₂ O ₄ , LiCoMnO ₄ , LiNi _0.5 Mn _1.5 O ₄ , and LiCoVO ₄ . Examples of lithium transition metal composite oxides having a layered structure include compounds represented by the general formula Li _x MO ₂ (M is at least one transition metal, and examples of the transition metal include Ni, Co, Mn, etc.), and specific examples include LiCoO ₂ , LiNiO ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.80 Co _0.15 Al _{0.05 O 2} , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , Li _1.05 Ni 0.33 Co _0.33 Mn _0.33 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , Li _1.05 Ni _0.5 Examples of such _alloys include _{Co0.2Mn0.3O2 , LiNi0.6Co0.2Mn0.2O2 , and LiNi0.8Co0.1Mn0.1O2} . Of these, it _{is preferable} to contain at least Ni, Co _, and _Mn .
Among these, the positive electrode active material is preferably a lithium transition metal oxide containing Ni, Co, and Mn, and more preferably a lithium transition metal composite oxide containing Ni, Co, and Mn. In addition, in the lithium transition metal oxide or lithium transition metal composite oxide containing Ni, Co, and Mn, from the viewpoint of suppressing the initial internal resistance, it is preferable that 40 mol % or more of the transition metal contained is Ni, more preferably 50 mol % or more is Ni, and even more preferably 60 mol % or more is Ni.

Among these, lithium transition metal composite oxides having a layered structure are preferred, and lithium transition metal composite oxides represented by the following composition formula (I) are more preferred.
Li _a1 Ni _b1 Co _c1 M _d1 O ₂ ...(I)
(In the composition formula (I), the numerical values are 0.9≦a1≦1.1, 0.3≦b1≦0.9, 0.1≦c1≦0.5, and 0.0≦d1≦0.5, and 0.5≦b1+c1 and b1+c1+d1=1 are satisfied. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er.)
In the composition formula (I), it is preferable that d1 has a value of 0.1≦d1≦0.5.

In particular, the lithium transition metal composite oxide represented by the above composition formula (I) is preferably a lithium transition metal composite oxide represented by the following composition formula (II).
Li _a2 Ni _b2 Co _c2 M _d2 O ₂ ...(II)
(In formula (II), the numerical values are 0.90≦a2≦1.10, 0.50≦b2≦0.98, 0.01≦c2<0.50, and 0.01≦d2<0.50, and b2+c2+d2=1 is satisfied. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er.)

_{Specific examples of} suitable lithium transition metal composite _{oxides represented by composition formula ( II ) include LiNi0.85Co0.10Al0.05O2 , LiNi0.80Co0.15Al0.05O2 , LiNi0.5Co0.2Mn0.3O2 , Li1.05Ni0.50Co0.20Mn0.30O2 , LiNi0.6Co0.2Mn0.2O2 , and LiNi0.8Co0.1Mn0.1O2 .}

In each composition formula, M is preferably Mn or Al, since this increases the structural stability of the lithium transition metal composite oxide and suppresses structural deterioration during repeated charging and discharging.

[2-3-1-2. Introduction of different elements]
The lithium transition metal compounds represented by the composition formula (I) or (II) may contain elements other than those defined by the composition formula (I) or (II) as long as they do not impair the effects of the present invention. Elements may be introduced.

[2-3-1-3. Surface coating]
The positive electrode active material may have a surface-attached substance having a different composition from the positive electrode active material. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate. Carbonates are preferred because they improve the affinity between the compounds represented by the composition formulas (I) and (II) and the positive electrode.
These surface-adhering substances can be attached to the surface of the positive electrode active material, for example, by dissolving or suspending them in a non-aqueous solvent, adding them to the positive electrode active material by impregnation, and drying.
The amount of the surface-attaching substance is preferably 1 μmol/g or more, more preferably 10 μmol/g or more, and is usually 1 mmol/g or less, based on the positive electrode active material.
Hereinafter, in this specification, a positive electrode active material having the above-mentioned surface-adhering substance attached to its surface is also referred to as a "positive electrode active material".

[2-3-1-4. Blending]
These positive electrode active materials may be used alone or in any combination of two or more in any ratio.

[2-3-2. Positive electrode configuration and manufacturing method]
The configuration of the positive electrode will be described below. In this embodiment, the positive electrode can be prepared by forming a positive electrode active material layer containing a positive electrode active material, a conductive material, and a binder on a current collector. The positive electrode using the positive electrode active material can be manufactured by a conventional method. That is, the positive electrode active material, the conductive material, the binder, and if necessary, a thickener, etc. are mixed in a dry state to form a sheet, which is then pressed onto the positive electrode current collector, or these materials are dissolved or dispersed in a solvent to form a slurry, which is then applied to the positive electrode current collector and dried to form a positive electrode active material layer on the current collector. In addition, for example, the above-mentioned positive electrode active material may be roll-formed into a sheet electrode, or may be compression-formed into a pellet electrode.
Hereinafter, the case where the slurry is successively applied to the positive electrode current collector and then dried will be described.

[2-3-2-1. Active material content]
The content of the positive electrode active material in the positive electrode active material layer is usually 80% by mass or more and 98% by mass or less.

[2-3-2-2. Density of positive electrode active material layer]
In order to increase the packing density of the positive electrode active material, the positive electrode active material layer obtained by coating and drying is preferably compacted by a hand press, a roller press, etc. The density of the positive electrode active material layer is usually 1.5 g/ ^cm3 or more, preferably 3.0 g/ ^cm3 or more, more preferably 3.3 g/ ^cm3 or more, and is usually 3.8 g/ ^cm3 or less.

[2-3-2-3. Conductive material]
As the conductive material, any known conductive material can be used. Specific examples include metal materials such as copper and nickel; carbonaceous materials such as natural graphite, graphite, and carbon black; and the like. These may be used alone or in any combination and ratio of two or more. The conductive material is used so as to be contained in the positive electrode active material layer in an amount of usually 0.01% by mass or more and 50% by mass or less.

[2-3-2-4. Binder]
The binder used in producing the positive electrode active material layer is not particularly limited. For example, when the positive electrode active material layer is formed by a coating method, the type is not particularly limited as long as it is a material that is dissolved or dispersed in a solvent for the slurry. In view of weather resistance, chemical resistance, heat resistance, flame retardancy, and the like, preferred are fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; and CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide.
In addition, mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, etc. of the above polymers can also be used. The binder may be used alone or in any combination and ratio of two or more kinds.
Furthermore, when a resin is used as a binder, the weight average molecular weight of the resin is optional as long as it does not significantly impair the effects of the present invention, but is usually from 10,000 to 3,000,000. When the molecular weight is in this range, the strength of the electrode is improved, and the electrode can be suitably formed.
The proportion of the binder in the positive electrode active material layer is usually 0.1 mass % or more and 80 mass % or less.

[2-3-2-5. Solvent]
The solvent for forming the slurry is not particularly limited as long as it is capable of dissolving or dispersing the positive electrode active material, the conductive material, the binder, and the thickener used as needed, and either an aqueous solvent or an organic solvent may be used.

[2-3-2-6. Current collector]
The material of the positive electrode current collector is not particularly limited, and any known material can be used. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum. Among them, aluminum is preferable.
The shape of the current collector may be metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punched metal, foamed metal, etc. Among these, metal thin film or metal foil is preferable. The thin film may be appropriately formed into a mesh shape. When the shape of the positive electrode current collector is a foil, plate, or film, the thickness of the current collector is optional, but is usually 1 μm or more and 1 mm or less.

[2-3-2-7. Thickness of positive electrode plate]
The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the positive electrode active material layer obtained by subtracting the thickness of the current collector from the thickness of the positive electrode plate is usually 10 μm or more and 500 μm or less.

[2-3-2-8. Surface coating of positive electrode plate]
The positive electrode plate may have a material of a different composition attached to its surface. The material may be the same as the surface-attached material that may be attached to the surface of the positive electrode active material.

[2-4. Separator]
A separator is usually interposed between the positive electrode and the negative electrode to prevent short circuiting. In this case, the non-aqueous electrolyte is usually impregnated into the separator before use.

[2-4-1. material]
The material for the separator is not particularly limited as long as it is stable against the non-aqueous electrolyte solution. However, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, barium sulfate, Examples of the material include sulfates such as calcium sulfate, inorganic materials such as glass filters made of glass fibers, and resins such as polyolefins, more preferably polyolefins, and particularly preferably polyethylene or polypropylene. Any of the above materials may be used, or two or more of them may be used in any combination and ratio.

[2-4-2. Thickness]
The thickness of the separator is not limited, but is usually 1 μm or more and 50 μm or less.

[2-4-3. form]
The separator is preferably in the form of a thin film such as a nonwoven fabric, a woven fabric, or a microporous film. In the thin film form, a film having a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. Other than the above-mentioned independent thin film shape, a separator may be used in which a composite porous layer containing the above-mentioned inorganic particles is formed on the surface layer of the positive electrode and/or negative electrode using a resin binder. Of these, the separator is preferably in the form of a porous sheet or nonwoven fabric, which has excellent liquid retention properties.

[2-4-4. Porosity]
When a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is not limited, but is usually 20% or more and 90% or less.

[2-4-5. Air permeability]
The air permeability characteristic of a separator in a non-aqueous electrolyte secondary battery can be understood by the Gurley value. The Gurley value indicates the difficulty of air passing through in the thickness direction of the film, and is expressed as the number of seconds required for 100 mL of air to pass through the film. The Gurley value of a separator is arbitrary, but is usually 10 to 1000 seconds/100 mL.

[2-5. Battery design]
[2-5-1. Electrode group]
The electrode group may have a laminated structure in which the positive electrode plate and the negative electrode plate are sandwiched between the separator, or a structure in which the positive electrode plate and the negative electrode plate are spirally wound with the separator between them. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy rate) is usually 40% or more and 90% or less.

[2-5-2. Current collection structure]
In the case where the electrode group has the above-mentioned laminated structure, a structure formed by bundling the metal core parts of the electrode layers and welding them to a terminal is preferably used. It is also preferably used to provide multiple terminals in the electrode to reduce resistance. In the case where the electrode group has the above-mentioned wound structure, the internal resistance can be reduced by providing multiple lead structures on each of the positive electrode and the negative electrode and bundling them to a terminal.

[2-5-3. Protection elements]
As the protective element, a PTC (Positive Temperature Coefficient) element whose resistance increases with heat generation due to an excessive current, etc., a temperature fuse, a thermistor, a valve (current cutoff valve) that cuts off the current flowing in the circuit due to a sudden increase in the internal pressure or temperature of the battery during abnormal heat generation, etc. It is preferable to select the above protective element under conditions that will not operate during normal use at a high current, and it is more preferable to design the battery so that abnormal heat generation or thermal runaway does not occur even without the protective element.

[2-5-4. Exterior Body] A non-aqueous electrolyte secondary battery is usually constructed by housing the above-mentioned non-aqueous electrolyte, negative electrode, positive electrode, separator, etc. in an exterior body (exterior case). There are no limitations on this exterior body, and any known exterior body can be used as long as it does not significantly impair the effects of the present invention.
The material of the exterior case is not particularly limited as long as it is a substance that is stable against the non-aqueous electrolyte solution used. From the viewpoint of weight reduction, metals such as aluminum and aluminum alloys, or laminate films are preferably used.
Examples of exterior cases using the above metals include those in which metals are welded to each other by laser welding, resistance welding, or ultrasonic welding to form a sealed, airtight structure, and those in which the above metals are used with a resin gasket in between to form a crimped structure.

[2-5-5. shape]
The shape of the exterior case is also arbitrary, and may be, for example, cylindrical, rectangular, laminated, coin-shaped, large, or the like.

[2-6. Uses]
The nonaqueous electrolyte according to this embodiment is useful because it can suppress the internal resistance of a nonaqueous electrolyte secondary battery.
The nonaqueous electrolyte according to the present embodiment and the nonaqueous electrolyte secondary battery using the same can be used in various known applications using nonaqueous electrolyte secondary batteries.Specific examples include notebook computers, pen-input personal computers, mobile personal computers, electronic book players, mobile phones, mobile fax machines, mobile copiers, mobile printers, headphone stereos, video movie machines, liquid crystal televisions, handheld cleaners, portable CDs, mini discs, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power sources, motors, motorcycles, motorized bicycles, bicycles, lighting equipment, toys, game equipment, watches, power tools, strobes, cameras, home backup power sources, business backup power sources, load leveling power sources, natural energy storage power sources, etc.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded. Examples 1, 2, 8, and 9 described below are reference examples.

The compounds used in this example and the comparative examples are listed below.

Compound 1: Antimony trifluoride ( _SbF3 )
Compound 2: Sodium hexafluoroantimonate (Na[ _SbF6 ])
Compound 3: Antimony trichloride ( _SbCl3 )

化合物４：ビニレンカーボネート

Compound 4: Vinylene carbonate

化合物５：リチウムビス（オキサラト）ボレート

Compound 5: Lithium bis(oxalato)borate

化合物６：１，３－ビス（イソシアナトメチル）シクロヘキサン

Compound 6: 1,3-bis(isocyanatomethyl)cyclohexane

<Examples 1 to 9 and Comparative Examples 1 to 3>
[Preparation of negative electrode]
To 98 parts by mass of the carbonaceous material, an aqueous dispersion was added so that sodium carboxymethylcellulose was 1 part by mass as a thickener and binder, and further an aqueous dispersion was added so that styrene-butadiene rubber was 1 part by mass, and the mixture was mixed in a disperser to form a slurry. The obtained slurry was applied to one side of a copper foil having a thickness of 10 μm, dried, and pressed to form a negative electrode.

[Preparation of Positive Electrode]
(Examples 1 to 7, Comparative Examples 1 to 2)
85 parts by mass of Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ as a positive electrode active material, 10 parts by mass of carbon black as a conductive material, and 5 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methylpyrrolidone solvent to form a slurry. This was uniformly applied to both sides of an aluminum foil with a thickness of 15 μm, dried, and then pressed to form a positive electrode. In the table, this positive electrode is referred to as NMC111.

(Examples 8 to 9, Comparative Example 3)
90 parts by mass of Li( _{Ni0.5Mn0.3Co0.2} ) _O2 as a positive electrode active material _, 7 parts by mass of carbon black as a conductive material, and 3 parts by mass _of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methylpyrrolidone solvent to form a slurry.
The mixture was uniformly applied to both sides of an aluminum foil with a thickness of 1 μm, dried, and pressed to form a positive electrode. In the table, this positive electrode is referred to as NMC532.

[Preparation of non-aqueous electrolyte]
Under a dry argon atmosphere, LiPF 6, which had been thoroughly dried as an electrolyte, was dissolved in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio EC:DMC:EMC = 3:3: ₄ ) to a concentration of 1.0 mol/L (12% by mass relative to the total amount of the non-aqueous electrolyte solution) (hereinafter, this is referred to as reference electrolyte solution 1). Compounds 1 to 6 were added to reference electrolyte solution 1 so as to have the contents shown in Table 1 below, to prepare non-aqueous electrolyte solutions of Examples 1 to 9 and Comparative Example 1. In addition, in Comparative Examples 2 to 3 in Table 1 below, reference electrolyte solution 1 itself was used as the non-aqueous electrolyte solution. Note that the "content (mass%)" in the table is the content of the compound when the entire non-aqueous electrolyte solution is 100% by mass.

[Manufacture of non-aqueous electrolyte secondary battery]
The above positive electrode, negative electrode, and polyethylene separator were laminated in the order of negative electrode, separator, and positive electrode to prepare a battery element. This battery element was inserted into a bag made of a laminate film of aluminum (thickness 40 μm) coated on both sides with a resin layer so that the positive and negative electrode terminals were protruding, and the above prepared nonaqueous electrolyte solution was then injected into the bag and vacuum sealed to prepare a laminate type nonaqueous electrolyte secondary battery.

<Evaluation of non-aqueous electrolyte secondary batteries>
[Initial conditioning]
In a thermostatic bath at 25 ° C., in Examples 1 to 7 and Comparative Examples 1 and 2, the battery was charged to 3.6 V at a current equivalent to 0.025 C, then charged to 4.2 V at 1/6 C, and discharged to 2.5 V at 1/6 C. After charging to 4.1 V at 1/6 C, aging was performed under the conditions of 60 ° C. and 12 hours. Then, the battery was discharged to 2.5 V at 1/6 C at 25 ° C. to stabilize the laminated battery. Furthermore, the battery was charged to 4.2 V at 1/6 C, then discharged to 2.5 V at 1/6 C, and initial conditioning was performed. In Examples 8 to 9 and Comparative Example 3, the battery was charged to 3.6 V at a current equivalent to 0.0125 C, then charged to 4.3 V at 1/12 C, and discharged to 2.5 V at 1/12 C. After charging to 4.1 V at 1/12 C, aging was performed under the conditions of 60 ° C. and 12 hours. Thereafter, the laminated battery was stabilized by discharging to 2.5 V at 1/12 C at 25° C. Furthermore, the battery was charged to 4.3 V at 1/12 C, and then discharged to 2.5 V at 1/12 C for initial conditioning.

[Measurement of initial resistance]
The resistance of the non-aqueous electrolyte secondary battery that had been initially conditioned in the above-mentioned manner in a thermostatic bath at 25°C was measured as follows. In Examples 1 to 7 and Comparative Examples 1 and 2, the non-aqueous electrolyte secondary battery after the initial conditioning was charged at 1/6C to 3.72V. This was discharged at 0.5C, 1.0C, 1.5C, 2.0C, and 2.5C at 25°C, respectively, and the voltage was measured 2 seconds after the start of each discharge process. In Examples 8 to 9 and Comparative Example 3, the non-aqueous electrolyte secondary battery after the initial conditioning was charged at 1/12C to 3.72V. This was discharged at currents of 0.25C, 0.5C, 0.75C, 1C, and 1.25C, and the voltage was measured 2 seconds after the start of each discharge process. The initial resistance value (Ω) was calculated from the slope of the current-voltage line.

[Charge-discharge cycle test]
The nonaqueous electrolyte secondary batteries whose initial resistance had been measured by the above method were subjected to a charge-discharge cycle test as follows. In Examples 1 to 7 and Comparative Examples 1 and 2, the batteries were discharged to 2.5 V at 1/3 C in a thermostatic chamber at 45° C. Then, the batteries were charged to 4.2 V and discharged to 2.5 V, and this cycle was repeated 101 times. The 1st, 51st, and 101st charge-discharge cycles were performed at 1/3 C, and the remaining charge-discharge cycles were performed at 1 C.
In Examples 8 to 9 and Comparative Example 3, the battery was discharged to 2.5 V at 1/6 C. Then, the battery was charged to 4.3 V and discharged to 2.5 V, and this cycle was repeated 101 times. The 1st, 51st, and 101st charge/discharge cycles were performed at 1/6 C, and the remaining charge/discharge cycles were performed at 1 C.

[Measurement of resistance after charge/discharge cycle test]
The resistance of the non-aqueous electrolyte secondary battery subjected to the charge-discharge cycle test in the above-mentioned manner in a thermostatic bath at 25°C was measured as follows. In Examples 1 to 7 and Comparative Examples 1 and 2, the non-aqueous electrolyte secondary battery after the charge-discharge cycle test was charged at 1/6C to 3.72V. This was discharged at 0.5C, 1.0C, 1.5C, 2.0C, and 2.5C at 25°C, respectively, and the voltage was measured at 2 seconds after the start of each discharge process. In Examples 8 to 9 and Comparative Example 3, the non-aqueous electrolyte secondary battery after the charge-discharge cycle test was charged at 1/12C to 3.72V. This was discharged at currents of 0.25C, 0.5C, 0.75C, 1C, and 1.25C, and the voltage was measured at 2 seconds after the start of each discharge process. The resistance value (Ω) after the cycle was calculated from the slope of the current-voltage line.

[Calculation of internal resistance increase rate]
The resistance increase rate due to the charge-discharge cycle test was calculated by calculating the resistance value after cycling (Ω)/initial resistance value (Ω). The results of the resistivity increase rate evaluated using the nonaqueous electrolyte secondary batteries of Examples 1 to 9 and Comparative Examples 1 to 3 are shown in Table 1.
The smaller the internal resistance increase rate, the more the increase in resistance due to the charge-discharge cycle test is suppressed. Moreover, a value of 1.0 or less indicates that there is no change in internal resistance before and after the charge-discharge cycle test, and the effect of suppressing internal resistance is particularly excellent.

From Table 1 above, as shown in Examples 1 to 9, it can be seen that the nonaqueous electrolyte secondary batteries (Examples 1 to 9) using a nonaqueous electrolyte containing an antimony compound (compound 1 or 2) having one or more Sb—F bonds in the molecule had a lower internal resistance increase rate than the nonaqueous electrolyte secondary battery (Comparative Example 1) using a nonaqueous electrolyte containing an antimony compound (compound 3) different from the antimony compound having one or more Sb—F bonds in the molecule and the reference electrolyte 1 (Comparative Example 2).
Furthermore, from Table 1 above, it can be seen that the effect of suppressing an increase in internal resistance is superior when a compound having a carbon-carbon unsaturated bond (compound 4) is used in combination as an auxiliary (Example 3), when a compound having an oxalate structure (compound 5) is used in combination (Examples 4 to 6), or when a compound having an isocyanate group (compound 6) is used in combination (Example 7) compared to when no auxiliary is used (Example 1).
Moreover, from Table 1 above, it can be seen that the reduction in the rate of increase in internal resistance by the addition of the antimony compound (A) is greater when NMC532 is used as the positive electrode (Examples 8 to 9, Comparative Example 3) than when NMC111 is used as the positive electrode (Examples 1 to 7, Comparative Examples 1 and 2).

The nonaqueous electrolyte according to this embodiment makes it possible to obtain a nonaqueous electrolyte secondary battery with excellent internal resistance characteristics.

Claims (4)

A non-aqueous electrolyte solution for a lithium ion secondary battery containing an antimony compound (A) ,
The antimony compound (A) is at least one selected from the group consisting of antimony trifluoride and sodium hexafluoroantimonate, and
The non-aqueous electrolyte solution for a lithium ion secondary battery contains at least one selected from the group consisting of a compound having a carbon-carbon unsaturated bond, a compound having an oxalate structure, and a compound having an isocyanate group. 2. The non-aqueous electrolyte solution for a lithium ion secondary battery according to claim 1 , wherein the content of the antimony compound (A) is 0.001% by mass or more and 10% by mass or less with respect to the total amount of the non-aqueous electrolyte solution. 3. A non-aqueous electrolyte lithium ion secondary battery comprising a negative electrode and a positive electrode capable of absorbing and releasing metal ions, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution is the non-aqueous electrolyte solution for lithium ion secondary batteries according to claim 1 or 2 . 4. The nonaqueous electrolyte lithium ion secondary battery according to claim 3 , wherein the negative electrode comprises a carbonaceous material as an active material, and the positive electrode comprises a lithium transition metal oxide containing Ni, Co, and Mn as an active material.