JP7168158B2 - Non-aqueous electrolyte for batteries and lithium secondary batteries - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to non-aqueous electrolytes for batteries and lithium secondary batteries.

In order to improve the performance of a battery containing a non-aqueous battery electrolyte (for example, a lithium secondary battery), various additives are added to the non-aqueous battery electrolyte.
For example, in Patent Document 1, as a non-aqueous electrolyte solution that is unlikely to cause battery swelling, in the molecular structure, a vinyl group, an ethynyl group, an ethynylene group, a vinylene group, a vinylidene group, and a A compound consisting of carbon, fluorine and hydrogen, having at least one carbon-carbon unsaturated bond group selected from the group consisting of groups in which hydrogen is substituted with fluorine, wherein at least hydrogen bonded to carbon A non-aqueous electrolyte for a battery is disclosed, which is characterized by comprising a non-aqueous solvent in which an unsaturated hydrocarbon (a) having 6 to 16 carbon atoms, one of which is substituted with fluorine, and a lithium salt.
Further, Patent Document 2 describes (I) (A) a fluorine-containing cyclic carbonate and (B) a fluorine-containing unsaturated hydrocarbon as non-aqueous electrolyte solutions for lithium secondary batteries having excellent high-temperature cycle characteristics and oxidation resistance. A solvent for dissolving an electrolyte salt containing a compound, wherein the solvent for dissolving the electrolyte salt contains 3% by volume or more of the fluorine-containing cyclic carbonate (A), and the fluorine-containing unsaturated hydrocarbon compound (B) is a fluorine-containing cyclic Disclosed is a non-aqueous electrolyte for a lithium secondary battery, which contains a solvent for dissolving an electrolyte salt, which is contained in an amount of 0.1 to 40 parts by volume per 100 parts by volume of a carbonate (A), and (II) an electrolyte salt. there is
Further, in Patent Document 3, a cyclic sulfate ester compound with a specific structure is contained as a non-aqueous electrolytic solution that can significantly suppress the decrease in open-circuit voltage during charging and storage of the battery while improving the capacity maintenance performance of the battery. Non-aqueous electrolytes are disclosed.

Japanese Patent No. 4608197 Japanese Patent No. 5573639 Japanese Patent No. 5524347

However, there are cases where it is required to reduce the battery resistance after storage for conventional non-aqueous battery electrolytes and batteries.
Accordingly, an object of the present disclosure is to provide a non-aqueous electrolyte for batteries capable of reducing battery resistance after storage, and a lithium secondary battery using this non-aqueous electrolyte for batteries.

Means for solving the above problems include the following aspects.
<1> Additive A, which is a compound represented by the following formula (A);
an additive B which is a compound represented by the following formula (B);
A non-aqueous electrolyte for batteries containing

In formula (A), R ^a1 represents a hydrocarbon group having 1 to 12 carbon atoms substituted with at least one fluorine atom.

In formula (B), R ^b1 to R ^b4 are each independently a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, a group represented by formula (1), or a group represented by formula (2) represents In formulas (1) and (2), * represents a bonding position.

<2> A non-aqueous electrolyte for a battery, further comprising an additive C which is a compound represented by the following formula (C).

In formula (C), R ^c1 and R ^c2 each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group.

<3> The non-aqueous electrolyte for batteries according to <2>, wherein the content of the additive C is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte for batteries.
<4> The content of the additive A is 0.001% by mass to 10% by mass with respect to the total amount of the battery non-aqueous electrolyte,
The non-aqueous for battery according to any one of <1> to <3>, wherein the content of the additive B is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte for battery. Electrolyte.

<5> a positive electrode;
Metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped/dedoped with lithium ions, transition metal nitrides that can be doped/dedoped with lithium ions, and lithium a negative electrode containing, as a negative electrode active material, at least one selected from the group consisting of carbon materials capable of ion doping and dedoping;
The non-aqueous electrolyte for batteries according to any one of <1> to <4>,
Lithium secondary battery including.
<6> A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to <5>.

According to the present disclosure, a non-aqueous electrolyte for batteries capable of reducing battery resistance after storage, and a lithium secondary battery using this non-aqueous electrolyte for batteries are provided.

1 is a schematic perspective view showing an example of a laminate type battery, which is an example of a lithium secondary battery of the present disclosure; FIG. FIG. 2 is a schematic cross-sectional view in the thickness direction of a laminated electrode body housed in the laminated battery shown in FIG. 1; FIG. 2 is a schematic cross-sectional view showing an example of a coin-type battery, which is another example of the lithium secondary battery of the present disclosure;

In this specification, a numerical range represented by "to" means a range including the numerical values before and after "to" as lower and upper limits.
As used herein, the amount of each component in the composition refers to the total amount of the multiple substances present in the composition unless otherwise specified when there are multiple substances corresponding to each component in the composition. means

[Non-aqueous electrolyte for batteries]
The non-aqueous electrolyte for a battery of the present disclosure (hereinafter also simply referred to as "non-aqueous electrolyte") includes an additive A which is a compound represented by the following formula (A) and a compound represented by the formula (B) an additive B that is
contains

In formula (A), R ^a1 represents a hydrocarbon group having 1 to 12 carbon atoms substituted with at least one fluorine atom.

In formula (B), R ^b1 to R ^b4 are each independently a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, a group represented by formula (1), or a group represented by formula (2) represents In formulas (1) and (2), * represents a binding position

According to the non-aqueous electrolyte of the present disclosure, battery resistance after storage can be reduced.
Although the reason why such an effect is produced is not clear, it is presumed as follows. However, the non-aqueous electrolytic solution of the present disclosure is not limited for the following presumed reasons.

When the non-aqueous electrolyte solution of the present disclosure is used, the combination of the additive A and the additive B is considered to have the effect of lowering the battery resistance during storage. As a result, it is considered that the effect of low battery resistance after storage is achieved.

Each component of the non-aqueous electrolyte of the present disclosure will be described below.

<Additive A>
Additive A is a compound represented by the following formula (A).
Additive A may be only one compound corresponding to the compound represented by the following formula (A), or may be two or more compounds corresponding to the compound represented by the following formula (A). may

In formula (A), R ^a1 represents a hydrocarbon group having 1 to 12 carbon atoms substituted with at least one fluorine atom.

In the formula (A), the hydrocarbon group represented by R ^a1 may be a linear hydrocarbon group, a branched hydrocarbon group, or a cyclic hydrocarbon group.
In the above hydrocarbon group represented by R ^a1 , the hydrocarbon group having 1 to 12 carbon atoms substituted with at least one fluorine atom (that is, the unsubstituted hydrocarbon group having 1 to 12 carbon atoms) is an alkyl group Or an alkenyl group is preferable, and an alkyl group is more preferable.
The hydrocarbon group represented by R ^a1 may be substituted with at least one fluorine atom, but is preferably a perfluorohydrocarbon group, more preferably a perfluoroalkyl group.
The number of carbon atoms in the above hydrocarbon group represented by R ^a1 is preferably 3 to 10, more preferably 4 to 10, still more preferably 4 or 6, and particularly preferably 6.
In formula (A), the compound in which R ^a1 is a perfluoroalkyl group having 6 carbon atoms is perfluorohexylethylene (abbreviated as PFHE).

In the "hydrocarbon group having 1 to 12 carbon atoms substituted with at least one fluorine atom" represented by R ^a1 , the "hydrocarbon group having 1 to 12 carbon atoms" substituted with at least one fluorine atom (i.e. , an unsubstituted hydrocarbon group having 1 to 12 carbon atoms), for example,
methyl group, ethyl group, n-propyl group, isopropyl group, 1-ethylpropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, 2-methylbutyl group, 3,3-dimethylbutyl group , n-pentyl group, isopentyl group, neopentyl group, 1-methylpentyl group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, n-heptyl group, isoheptyl group, sec-heptyl group, tert - Alkyl groups such as heptyl group, n-octyl group, isooctyl group, sec-octyl group, tert-octyl group;
vinyl group, 1-propenyl group, allyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, pentenyl group, hexenyl group, isopropenyl group, 2-methyl-2-propenyl group, 1-methyl-2 -propenyl group, 2-methyl-1-propenyl group, alkenyl group such as octamethylene group;
etc.

The content of additive A (the total content when additive A is two or more compounds) is preferably 0.001% by mass to 10% by mass, and 0.001% by mass to 10% by mass, relative to the total amount of the non-aqueous electrolyte. 001% by mass to 5% by mass, more preferably 0.001% by mass to 3% by mass, still more preferably 0.01% by mass to 3% by mass, 0.1 to 3% by mass is more preferable, 0.1 to 2% by mass is more preferable, and 0.1 to 1% by mass is particularly preferable.

<Additive B>
Additive B is a compound represented by the following formula (B).
Additive B may be a single compound corresponding to the compound represented by the following formula (B), or two or more compounds corresponding to the compound represented by the following formula (B). may

In formula (B), R ^b1 to R ^b4 are each independently a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, a group represented by formula (1), or a group represented by formula (2) represents In formulas (1) and (2), * represents a binding position

In formula (B), the hydrocarbon group having 1 to 6 carbon atoms represented by R ^b1 to R ^b4 is preferably an alkyl group, an alkenyl group, or an alkynyl group, more preferably an alkyl group or an alkenyl group, and an alkyl group. is particularly preferred.
In formula (B), the number of carbon atoms in the hydrocarbon groups having 1 to 6 carbon atoms represented by R ^b1 to R ^b4 is preferably 1 to 3, more preferably 1 or 2, and particularly preferably 1.

In formula (B), R ^b1 to R ^b4 are each independently preferably a hydrogen atom, a methyl group, an ethyl group, a group represented by formula (1), or a group represented by formula (2), A hydrogen atom, a methyl group, a group represented by the formula (1), or a group represented by the formula (2) is more preferable, and a hydrogen atom, a group represented by the formula (1), or a group represented by the formula (2) are more preferred.

Specific examples of the compound represented by the formula (B) include compounds represented by the following formulas (B-1) to (B-4) (hereinafter referred to as compound (B-1) to compound (B -4)), but the compound represented by formula (B) is not limited to these specific examples.
Among these, compounds (B-1) to (B-3) are particularly preferred.

The content of additive B (the total content when additive B is a compound of two or more kinds) is preferably 0.001% by mass to 10% by mass, and 0.001% by mass to 10% by mass, based on the total amount of the non-aqueous electrolyte. 001% by mass to 5% by mass, more preferably 0.001% by mass to 3% by mass, still more preferably 0.01% by mass to 3% by mass, 0.1 to 3% by mass is more preferable, 0.1 to 2% by mass is more preferable, and 0.1 to 1% by mass is particularly preferable.

In the non-aqueous electrolyte, the content mass ratio of additive B to additive A (hereinafter, content mass ratio [additive B/additive A]) is such that the above-described effects of the non-aqueous electrolyte of the present disclosure are more effective. from the viewpoint of performance, it is preferably 0.1 or more and 5.0 or less, more preferably 0.2 or more and 2.0 or less, and still more preferably 0.5 or more and 2.0 or less.

<Additive C>
The non-aqueous electrolytic solution of the present disclosure preferably further contains additive C, which is a compound represented by formula (C) below.
When the non-aqueous electrolytic solution of the present disclosure contains the additive C, the above-described effects of the non-aqueous electrolytic solution of the present disclosure are exhibited more effectively.

In formula (C), R ^c1 and R ^c2 each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group.

Examples of the compound represented by formula (C) include vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, bropylvinylene carbonate, dimethylvinylene carbonate, diethylvinylene carbonate, dipropylvinylene carbonate, and the like.
Among these, vinylene carbonate (a compound in which R ^c1 and R ^c2 are both hydrogen atoms in formula (C)) is particularly preferred.

When the non-aqueous electrolyte of the present disclosure contains the additive C, the content of the additive C (the total content when the additive C is a compound of two or more types) is relative to the total amount of the non-aqueous electrolyte , preferably 0.001% by mass to 10% by mass, more preferably 0.001% by mass to 5% by mass, even more preferably 0.001% by mass to 3% by mass, 0.01% by mass to 3% by mass %, more preferably 0.1 to 3% by mass, even more preferably 0.1 to 2% by mass, and particularly preferably 0.1 to 1% by mass.

When the non-aqueous electrolyte of the present disclosure contains additive C, the content mass ratio of additive C to additive A in the non-aqueous electrolyte (hereinafter, the content mass ratio [additive C/additive A]) is , preferably 0.1 or more and 5.0 or less, more preferably 0.2 or more and 2.0 or less, from the viewpoint that the above-described effects of the non-aqueous electrolytic solution of the present disclosure are more effectively exhibited, It is more preferably 0.2 or more and less than 1.0, still more preferably 0.4 or more and 0.9 or less, and still more preferably 0.5 or more and 0.9 or less.

When the non-aqueous electrolyte of the present disclosure contains the additive C, the content mass ratio of the additive C to the additive B in the non-aqueous electrolyte (hereinafter, the content mass ratio [additive C / additive B]) is , preferably 0.1 or more and 5.0 or less, more preferably 0.2 or more and 2.0 or less, from the viewpoint that the above-described effects of the non-aqueous electrolytic solution of the present disclosure are more effectively exhibited, It is more preferably 0.2 or more and less than 1.0, still more preferably 0.4 or more and 0.9 or less, and still more preferably 0.5 or more and 0.9 or less.

Next, other components of the non-aqueous electrolyte will be described. A non-aqueous electrolyte generally contains an electrolyte and a non-aqueous solvent.

(Non-aqueous solvent)
A non-aqueous electrolyte generally contains a non-aqueous solvent.
As the non-aqueous solvent, various known solvents can be appropriately selected, but it is preferable to use at least one selected from cyclic aprotic solvents and chain aprotic solvents.

When aiming to improve the flash point of the solvent in order to improve battery safety, it is preferable to use a cyclic aprotic solvent as the non-aqueous solvent.

(Cyclic aprotic solvent)
Cyclic aprotic solvents that can be used include cyclic carbonates, cyclic carboxylic acid esters, cyclic sulfones, and cyclic ethers.

Cyclic aprotic solvents may be used singly or in combination.
The mixing ratio of the cyclic aprotic solvent in the non-aqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass. By setting such a ratio, the conductivity of the electrolytic solution, which is related to the charge/discharge characteristics of the battery, can be increased.

Specific examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate and 2,3-pentylene carbonate. Of these, ethylene carbonate and propylene carbonate, which have high dielectric constants, are preferably used. Ethylene carbonate is more preferable for batteries using graphite as the negative electrode active material. Moreover, these cyclic carbonates may be used in combination of two or more.

Specific examples of cyclic carboxylic acid esters include γ-butyrolactone, δ-valerolactone, and alkyl-substituted compounds such as methyl γ-butyrolactone, ethyl γ-butyrolactone, and ethyl δ-valerolactone.
A cyclic carboxylic acid ester has a low vapor pressure, a low viscosity, and a high dielectric constant, and can lower the viscosity of the electrolyte without lowering the flash point of the electrolyte and the dissociation degree of the electrolyte. For this reason, it has the feature that the conductivity of the electrolyte, which is an index related to the discharge characteristics of the battery, can be increased without increasing the flammability of the electrolyte. It is preferred to use a cyclic carboxylic acid ester as the cyclic aprotic solvent. γ-Butyrolactone is most preferred.

Moreover, the cyclic carboxylic acid ester is preferably used by being mixed with another cyclic aprotic solvent. Examples include mixtures of cyclic carboxylic acid esters with cyclic carbonates and/or chain carbonates.

Specific examples of combinations of cyclic carboxylic acid esters and cyclic carbonates and/or chain carbonates include γ-butyrolactone and ethylene carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate, γ-butyrolactone and ethylene carbonate and methylethyl carbonate, γ-butyrolactone and ethylene carbonate and diethyl carbonate, γ-butyrolactone and propylene carbonate, γ-butyrolactone and propylene carbonate and dimethyl carbonate, γ-butyrolactone and propylene carbonate and methyl ethyl carbonate, γ-butyrolactone and propylene carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and dimethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and methyl ethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and dimethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and sulfolane, γ-butyrolactone and ethylene carbonate and sulfolane, γ-butyrolactone and propylene carbonate Sulfolane, γ-butyrolactone, ethylene carbonate, propylene carbonate, sulfolane, γ-butyrolactone tyrolactone, sulfolane, dimethyl carbonate and the like.

Examples of cyclic sulfones include sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethylsulfone, diethylsulfone, dipropylsulfone, methylethylsulfone, methylpropylsulfone, and the like.
Dioxolane can be mentioned as an example of a cyclic ether.

(chain-like aprotic solvent)
As the chain aprotic solvent, chain carbonates, chain carboxylic acid esters, chain ethers, chain phosphates, and the like can be used.

The mixing ratio of the linear aprotic solvent in the non-aqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass.

Specific examples of chain carbonates include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, dibutyl carbonate, methyl pentyl carbonate, Ethylpentyl carbonate, dipentyl carbonate, methylheptyl carbonate, ethylheptyl carbonate, diheptyl carbonate, methylhexyl carbonate, ethylhexyl carbonate, dihexyl carbonate, methyloctyl carbonate, ethyloctyl carbonate, dioctyl carbonate, methyltrifluoroethyl carbonate and the like. These chain carbonates may be used in combination of two or more.

Specific examples of chain carboxylic acid esters include methyl pivalate.
Specific examples of chain ethers include dimethoxyethane and the like.
Specific examples of chain phosphates include trimethyl phosphate and the like.

(combination of solvents)
The non-aqueous solvent contained in the non-aqueous electrolyte of the present disclosure may be of only one type, or may be of two or more types.
In addition, even if only one or more kinds of cyclic aprotic solvents are used, only one or more kinds of chain aprotic solvents are used, or cyclic aprotic solvents and chain protic solvents are used. A solvent may be mixed and used. When especially intended to improve the load characteristics and low-temperature characteristics of the battery, it is preferable to use a combination of a cyclic aprotic solvent and a chain aprotic solvent as the non-aqueous solvent.

Furthermore, from the electrochemical stability of the electrolytic solution, it is most preferable to apply a cyclic carbonate to the cyclic aprotic solvent and a chain carbonate to the chain aprotic solvent. Also, the combination of the cyclic carboxylic acid ester and the cyclic carbonate and/or the chain carbonate can increase the conductivity of the electrolytic solution, which is related to the charge/discharge characteristics of the battery.

Specific examples of combinations of cyclic carbonate and chain carbonate include ethylene carbonate and dimethyl carbonate, ethylene carbonate and methylethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, propylene carbonate and methylethyl carbonate, propylene carbonate and Diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and methyl ethyl carbonate and diethyl carbonate , ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate and diethyl carbonate Carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, methylethyl carbonate, diethyl carbonate and the like.

The mixing ratio of the cyclic carbonate and the chain carbonate is 5:95 to 80:20, more preferably 10:90 to 70:30, particularly preferably 15:85, in terms of a mass ratio of cyclic carbonate:chain carbonate. ~55:45. By setting such a ratio, it is possible to suppress an increase in the viscosity of the electrolytic solution and increase the degree of dissociation of the electrolyte, so that the conductivity of the electrolytic solution, which is related to the charge/discharge characteristics of the battery, can be increased. Also, the solubility of the electrolyte can be further increased. Therefore, the electrolytic solution having excellent electrical conductivity at room temperature or low temperature can be obtained, and the load characteristics of the battery at room temperature to low temperature can be improved.

(Other solvents)
Examples of non-aqueous solvents include solvents other than those mentioned above.
Specific examples of other solvents include amides such as dimethylformamide, chain carbamates such as methyl-N,N-dimethylcarbamate, cyclic amides such as N-methylpyrrolidone, and N,N-dimethylimidazolidinone. Examples include boron compounds such as cyclic urea, trimethyl borate, triethyl borate, tributyl borate, trioctyl borate, and trimethylsilyl borate, and polyethylene glycol derivatives represented by the following general formula.
HO _{( CH2CH2O} ) _aH
HO[ _{CH2CH ( CH3} )O]bH
_{CH3O ( CH2CH2O} ) _cH
CH3O[ _{CH2CH ( CH3} )O] _{dH
CH3O ( CH2CH2O ) eCH3
CH3O} [ _{CH2CH ( CH3} )O] _{fCH3
C9H19PhO ( CH2CH2O} ) _g [ _{CH ( CH3} )O] _hCH3
(Ph is a phenyl group)
_CH3O [ _CH2CH ( _CH3 )O] _iCO [OCH _{( CH3} ) _CH2 ] _jOCH3
In the above formula, a to f are integers of 5 to 250, g to j are integers of 2 to 249, 5≦g+h≦250, and 5≦i+j≦250.

(Electrolytes)
Various known electrolytes can be used for the non-aqueous electrolyte of the present disclosure, and any of those commonly used as electrolytes for non-aqueous electrolytes can be used.

Specific examples of the electrolyte _{include ( C2H5} ) _4NPF6 , _{( C2H5} ) _4NBF4 , _{( C2H5} ) _4NClO4 , _{( C2H5 ) 4NAsF6 , ( C2} H ₅ ) ₄ N ₂ SiF ₆ , (C ₂ H ₅ ) ₄ NOSO ₂ C _k F _(2k+1) (k=an integer from 1 to 8), (C ₂ H ₅ ) ₄ NPF _n [C _k F _(2k+1) ] _(6-n) Tetraalkylammonium salts such as (n = 1 to 5, k = an integer of 1 to 8), LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO _{2 CkF (2k+1)} (k=an integer of 1 to 8), LiPF _n [C _k F _(2k+1) ] _(6−n) (n=1 to 5, k=an integer of 1 to 8) and the like. . Lithium salts represented by the following general formula can also be used.

^LiC ( _SO2R7 )( ^SO2R8 )( _SO2R9 ), LiN ₍ ^SO2OR10 ) _{( SO2OR11} ), ^LiN ₍ ^SO2R12 ) ₍ ^SO2R13 ) ⁽ where R ⁷ to R ¹³ may be the same or different and each is a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms). These electrolytes may be used alone or in combination of two or more.
Among these, lithium salts are particularly desirable, and LiPF ₆ , LiBF ₄ , LiOSO ₂ C _k F _(2k+1) (k=an integer of 1 to 8), LiClO ₄ , LiAsF ₆ , LiNSO ₂ [C _k F _{( 2k+1)} ] ₂ (k=an integer of 1 to 8) and LiPF _n [C _k F _(2k+1) ] _(6−n) (n=1 to 5, k=an integer of 1 to 8) are preferable.

The electrolyte is usually contained in the non-aqueous electrolyte at a concentration of 0.1 mol/L to 3 mol/L, preferably 0.5 mol/L to 2 mol/L.

In the non-aqueous electrolyte solution of the present disclosure, when a cyclic carboxylic acid ester such as γ-butyrolactone is used together as a non-aqueous solvent, it is particularly desirable to contain LiPF ₆ . Since LiPF ₆ has a high degree of dissociation, it can increase the conductivity of the electrolyte and also has the effect of suppressing the reductive decomposition reaction of the electrolyte on the negative electrode. LiPF ₆ may be used alone, or LiPF ₆ and other electrolytes may be used. As other electrolytes, any of those that are usually used as electrolytes for non-aqueous electrolytes can be used, but among the specific examples of the lithium salts described above, lithium salts other than LiPF ₆ are preferable. .
Specific examples include LiPF ₆ and LiBF ₄ , LiPF ₆ and LiN[SO ₂ C _k F _(2k+1) ] ₂ (k=an integer of 1 to 8), LiPF ₆ and LiBF ₄ and LiN[SO ₂ C _k F _{( 2k+1)} ] (k=an integer from 1 to 8).

The proportion of LiPF ₆ in the lithium salt is preferably 1% to 100% by mass, more preferably 10% to 100% by mass, still more preferably 50% to 100% by mass. Such an electrolyte is preferably contained in the non-aqueous electrolyte at a concentration of 0.1 mol/L to 3 mol/L, preferably 0.5 mol/L to 2 mol/L.

The nonaqueous electrolyte of the present disclosure is not only suitable as a nonaqueous electrolyte for lithium secondary batteries, but also a nonaqueous electrolyte for primary batteries, a nonaqueous electrolyte for electrochemical capacitors, and an electric double layer capacitor. It can also be used as an electrolyte for aluminum electrolytic capacitors.

[Lithium secondary battery]
A lithium secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte of the present disclosure.

(negative electrode)
The negative electrode may include a negative electrode active material and a negative electrode current collector.
The negative electrode active material in the negative electrode includes metal lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped/dedoped with lithium ions, and lithium ions that can be doped/dedoped. At least one selected from the group consisting of transition metal nitrides and carbon materials capable of doping and dedoping lithium ions (may be used alone, or a mixture containing two or more of these may be used. good) can be used.
Examples of metals or alloys that can be alloyed with lithium (or lithium ions) include silicon, silicon alloys, tin, and tin alloys. Lithium titanate may also be used.
Among these, a carbon material capable of doping/dedoping lithium ions is preferable. Examples of such carbon materials include carbon black, activated carbon, graphite materials (artificial graphite, natural graphite), amorphous carbon materials, and the like. The carbon material may be fibrous, spherical, potato-like, or flake-like.

Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500° C. or lower, and mesophase pitch carbon fiber (MCF).
Examples of the graphite material include natural graphite and artificial graphite. Graphitized MCMB, graphitized MCF, and the like are used as artificial graphite. As the graphite material, one containing boron can also be used. As the graphite material, those coated with metals such as gold, platinum, silver, copper, and tin, those coated with amorphous carbon, and those in which amorphous carbon and graphite are mixed can be used.

These carbon materials may be used singly or in combination of two or more.
As the above-mentioned carbon material, a carbon material in which the interplanar spacing d(002) of the (002) plane measured by X-ray analysis is 0.340 nm or less is particularly preferable. As the carbon material, graphite having a true density of 1.70 g/cm ³ or more or a highly crystalline carbon material having properties close thereto is also preferable. The energy density of the battery can be increased by using the above carbon materials.

The material of the negative electrode current collector in the negative electrode is not particularly limited, and any known material can be used.
Specific examples of the negative electrode current collector include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among them, copper is particularly preferable from the viewpoint of ease of processing.

(positive electrode)
The positive electrode may include a positive electrode active material and a positive electrode current collector.
Examples of positive electrode active materials for the positive electrode include transition metal oxides or sulfides such as MoS ₂ , TiS ₂ , MnO ₂ and V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , _{LiNiXCo (1−X)} O ₂ [0<X<1], α-NaFeO Li _1+α Me _1-α O ₂ having a ₂ -type crystal structure (Me is a transition metal element including Mn, Ni and Co, 1.0 ≦(1+α)/(1−α)≦1.6), LiNi _x Co _y Mn _z O ₂ [x+y+z=1, 0<x<1, 0<y<1, 0<z<1] (for example, composite _{oxides composed} of _lithium and a transition _metal such as _{LiNi0.33Co0.33Mn0.33O2} , _{LiNi0.5Co0.2Mn0.3O2 , LiFePO4} , _{LiMnPO4 ;} Examples thereof include conductive polymer materials such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline complexes. Among these, a composite oxide composed of lithium and a transition metal is particularly preferred. Carbon materials can also be used as the positive electrode when the negative electrode is lithium metal or a lithium alloy. A mixture of a composite oxide of lithium and a transition metal and a carbon material can also be used as the positive electrode.
One type of positive electrode active material may be used, or two or more types may be mixed and used. If the positive electrode active material has insufficient conductivity, it can be used together with a conductive aid to form the positive electrode. Examples of conductive aids include carbon materials such as carbon black, amorphous whiskers, and graphite.

The material of the positive electrode current collector in the positive electrode is not particularly limited, and any known material can be used.
Specific examples of the positive electrode current collector include metal materials such as aluminum, aluminum alloys, stainless steel, nickel, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and the like.

(separator)
The lithium secondary battery of the present disclosure preferably includes a separator between the negative electrode and the positive electrode.
The separator is a film that electrically insulates the positive electrode and the negative electrode and allows lithium ions to pass through, and is exemplified by a porous film and a polymer electrolyte.
A microporous polymer film is preferably used as the porous membrane, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, polyester, and the like.
In particular, porous polyolefin is preferable, and specific examples include porous polyethylene film, porous polypropylene film, or multilayer film of porous polyethylene film and polypropylene film. Other resins having excellent thermal stability may be coated on the porous polyolefin film.
Examples of polymer electrolytes include polymers in which lithium salts are dissolved and polymers swollen with an electrolytic solution.
The non-aqueous electrolyte of the present disclosure may be used for the purpose of swelling a polymer to obtain a polymer electrolyte.

(Battery configuration)
The lithium secondary battery of the present disclosure can take various known shapes, such as cylindrical, coin, square, laminate, film, and other arbitrary shapes. However, the basic structure of the battery is the same regardless of the shape, and the design can be changed depending on the purpose.

An example of the lithium secondary battery (non-aqueous electrolyte secondary battery) of the present disclosure is a laminate type battery.
FIG. 1 is a schematic perspective view showing an example of a laminate type battery, which is an example of the lithium secondary battery of the present disclosure, and FIG. 2 shows the thickness of the laminated electrode body housed in the laminate type battery shown in FIG. 1 is a schematic sectional view in a direction; FIG.
The laminated battery shown in FIG. 1 contains a non-aqueous electrolyte (not shown in FIG. 1) and a laminated electrode assembly (not shown in FIG. 1), and the peripheral portion is sealed. It has a laminated exterior body 1 whose inside is sealed by. As the laminated exterior body 1, for example, a laminated exterior body made of aluminum is used.
As shown in FIG. 2, the laminated electrode body housed in the laminated outer package 1 is composed of a laminated body in which a positive electrode plate 5 and a negative electrode plate 6 are alternately laminated with separators 7 interposed therebetween, and this laminated body. a surrounding separator 8; The positive electrode plate 5, the negative electrode plate 6, the separator 7, and the separator 8 are impregnated with the non-aqueous electrolyte of the present disclosure.
Each of the plurality of positive electrode plates 5 in the laminated electrode body is electrically connected to the positive electrode terminal 2 via a positive electrode tab (not shown), and a part of the positive electrode terminal 2 is the laminated outer body 1. It protrudes outward from the peripheral edge (Fig. 1). A portion of the peripheral end portion of the laminate package 1 where the positive electrode terminal 2 protrudes is sealed with an insulating seal 4 .
Similarly, each of the plurality of negative electrode plates 6 in the laminated electrode body is electrically connected to the negative electrode terminal 3 via a negative electrode tab (not shown). It protrudes outward from the peripheral edge of the body 1 (Fig. 1). A portion where the negative terminal 3 protrudes from the peripheral end portion of the laminate outer package 1 is sealed with an insulating seal 4 .
In the laminate type battery according to the above example, the number of positive electrode plates 5 is five and the number of negative electrode plates 6 is six. The outer layers are laminated in such a manner that all of them serve as the negative electrode plate 6 . However, the number of positive plates and the number and arrangement of negative plates in the laminate type battery are not limited to this example, and it goes without saying that various modifications may be made.

Another example of the lithium secondary battery of the present disclosure is a coin-type battery.
FIG. 3 is a schematic perspective view showing an example of a coin-type battery, which is another example of the lithium secondary battery of the present disclosure.
In the coin-type battery shown in FIG. 3, a disk-shaped negative electrode 12, a separator 15 filled with a non-aqueous electrolyte, a disk-shaped positive electrode 11, and optionally spacer plates 17 and 18 made of stainless steel or aluminum are arranged in this order. In a stacked state, they are accommodated between the positive electrode can 13 (hereinafter also referred to as "battery can") and the sealing plate 14 (hereinafter also referred to as "battery can cover"). The positive electrode can 13 and the sealing plate 14 are caulked and sealed with a gasket 16 interposed therebetween.
In this example, the non-aqueous electrolytic solution of the present disclosure is used as the non-aqueous electrolytic solution injected into the separator 15 .

The lithium secondary battery of the present disclosure is obtained by charging and discharging a lithium secondary battery (lithium secondary battery before charging and discharging) containing the negative electrode, the positive electrode, and the non-aqueous electrolyte of the present disclosure. It may be a lithium secondary battery.
That is, in the lithium secondary battery of the present disclosure, first, a lithium secondary battery before charging and discharging including the negative electrode, the positive electrode, and the non-aqueous electrolyte of the present disclosure is produced, and then the lithium secondary battery before charging and discharging is produced. It may be a lithium secondary battery produced by charging and discharging a lithium secondary battery one or more times (charged and discharged lithium secondary battery).

Applications of the lithium secondary battery of the present disclosure are not particularly limited, and can be used for various known applications. For example, notebook computers, mobile computers, mobile phones, headphone stereos, video movies, liquid crystal televisions, handy cleaners, electronic notebooks, calculators, radios, backup power supply applications, motors, automobiles, electric vehicles, motorcycles, electric motorcycles, bicycles, electric It can be widely used in small mobile devices and large devices such as bicycles, lighting equipment, game machines, clocks, power tools, and cameras.

Examples of the present disclosure are shown below, but the present disclosure is not limited to the following examples.
In the following examples, the "addition amount" means the content in the finally obtained non-aqueous electrolyte (that is, the amount relative to the total amount of the finally obtained non-aqueous electrolyte).
Moreover, "wt%" means mass%.

[Example 1]
A coin-type battery (test battery), which is a lithium secondary battery, was produced in the following procedure.
<Production of negative electrode>
Amorphous coated natural graphite (97 parts by mass), carboxymethyl cellulose (1 part by mass) and SBR latex (2 parts by mass) were kneaded with a water solvent to prepare a pasty negative electrode mixture slurry.
Next, this negative electrode mixture slurry is applied to a negative electrode current collector made of strip-shaped copper foil with a thickness of 10 μm, dried, and then compressed by a roll press to form a sheet-like negative electrode composed of a negative electrode current collector and a negative electrode active material layer. got At this time, the negative electrode active material layer had a coating density of 10 mg/cm ² and a filling density of 1.5 g/ml.

<Preparation of positive electrode>
LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (90 parts by mass), acetylene black (5 parts by mass) and polyvinylidene fluoride (5 parts by mass) were kneaded using N-methylpyrrolidinone as a solvent to form a paste. A positive electrode mixture slurry was prepared.
Next, this positive electrode mixture slurry is applied to a positive electrode current collector made of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and then compressed by a roll press to form a sheet-like positive electrode comprising a positive electrode current collector and a positive electrode active material layer. got At this time, the coating density of the positive electrode active material layer was 30 mg/cm ² and the filling density was 2.5 g/ml.

<Preparation of non-aqueous electrolyte>
As non-aqueous solvents, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed at a ratio of 30:30:40 (mass ratio), respectively, to obtain a mixed solvent.
LiPF ₆ as an electrolyte was dissolved in the obtained mixed solvent so that the concentration of LiPF ₆ in the finally obtained non-aqueous electrolytic solution was 1.0 mol/L.
For the solution obtained above,
Perfluorohexylethylene (hereinafter also referred to as "PFHE") as additive A (addition amount 0.5% by mass),
The following compound (B-1) as additive B (in Table 1, simply referred to as "B-1") (addition amount 0.5% by mass), and vinylene carbonate as additive C (hereinafter, "VC" Also called) (addition amount 0.2% by mass)
was added to obtain a non-aqueous electrolyte.

<Production of coin-type battery>
The above-mentioned negative electrode and the above-mentioned positive electrode were punched into discs each having a diameter of 14 mm and a diameter of 13 mm to obtain a coin-shaped negative electrode and a coin-shaped positive electrode, respectively. Also, a microporous polyethylene film with a thickness of 20 μm was punched out into a disk shape with a diameter of 17 mm to obtain a separator.
The obtained coin-shaped negative electrode, separator, and coin-shaped positive electrode were stacked in this order in a battery can made of stainless steel (2032 size), and then 20 μL of the above non-aqueous electrolyte was added to the battery can. It was injected and impregnated into the separator, the positive electrode, and the negative electrode.
Next, an aluminum plate (thickness: 1.2 mm, diameter: 16 mm) and a spring were placed on the positive electrode, and the battery was sealed by crimping the battery can lid via a polypropylene gasket.
As a result, a coin-shaped battery (that is, a coin-shaped lithium secondary battery) having the configuration shown in FIG. 3 and having a diameter of 20 mm and a height of 3.2 mm was obtained.

<Evaluation of battery resistance>
The obtained coin-type battery was conditioned, and the battery resistance of the conditioned coin-type battery was evaluated.
Here, “conditioning” refers to charging and discharging the coin battery three times between 2.75 V and 4.2 V at 25° C. in a constant temperature bath.
Hereinafter, "high-temperature storage" means an operation of storing a coin-type battery at 80°C for 48 hours in a constant temperature bath.
Below, the battery resistance (DCIR) was measured under two temperature conditions of 25°C and -20°C.

(Measurement of battery resistance (DCIR) before high temperature storage)
The SOC (State of Charge) of the coin-shaped battery after conditioning was adjusted to 80%, and then the DCIR (Direct current internal resistance) of the coin-shaped battery before high-temperature storage was measured by the following method.
Using the coin-type battery adjusted to SOC 80% as described above, discharge CC10s at a discharge rate of 0.2C, rest for 300 seconds, discharge CC10s at a discharge rate of 1C, rest for 300 seconds, discharge CC10s at a discharge rate of 2C, A pause of 300 seconds and CC10s discharge at a discharge rate of 5C were performed in this order.
In addition, CC10s discharge means discharging for 10 seconds with a constant current (Constant Current).
The DC resistance is obtained based on the relationship between each discharge rate and the voltage at 10 seconds after the start of discharge at each discharge rate. Ω).
The results are shown in Table 1 (“before storage” column).

(Measurement of battery resistance (DCIR) after high temperature storage)
After conditioning and before adjusting the SOC to 80%, the coin-type battery is CC-CV charged to 4.25 V at a charge rate of 0.2 C at 25 ° C. in a constant temperature chamber, and then subjected to high temperature storage. The battery resistance (Ω) after high-temperature storage was measured in the same manner as the measurement of the battery resistance before high-temperature storage described above, except that the was added.
The results are shown in Table 1 ("After storage" column).
Here, CC-CV charging means constant current-constant voltage.

(Calculation of ratio [after storage/before storage] (-20°C))
The ratio [after storage/before storage] (-20° C.) was obtained from the following formula.
Ratio [after storage/before storage] = Battery resistance after high temperature storage (-20°C) (Ω)/Battery resistance before high temperature storage (-20°C) (Ω)
The smaller the ratio [after storage/before storage], the greater the degree of decrease in battery resistance due to high-temperature storage, which means that the battery characteristics are desirable.
The results are shown in Table 1 (“after storage/before storage” column).

(Discharge capacity (0.2C) before high temperature storage; capacity before storage)
The conditioned coin-type battery was CC-CV charged to 4.25 V at a charge rate of 0.2 C at 25 ° C. in a constant temperature bath, and then at a discharge rate of 0.2 C at 25 ° C., after high temperature storage. Discharge capacity (0.2C) (mAh) was measured.
The results are shown in Table 1 (“before storage” column).

(Discharge capacity after high temperature storage (residual capacity; 0.2C))
Conditioning was applied to the coin-type battery obtained above.
After the conditioning, the coin-type battery was CC-CV charged to 4.25 V at a charge rate of 0.2 C in a constant temperature bath at 25° C., and then stored at a high temperature.
The coin-type battery after high-temperature storage was subjected to CC discharge at a discharge rate of 0.2C at 25°C, and the discharge capacity (remaining capacity: 0.2C) after high-temperature storage was measured.
The results are shown in Table 1 ("Remaining" column).

(Discharge capacity after high temperature storage (recovery capacity; 0.2C))
The above conditioning was applied to the coin-type battery obtained above.
After the conditioned coin-type battery was CC-CV charged to 4.25 V at a charge rate of 0.2 C in a constant temperature bath at 25° C., the coin-type battery was stored at a high temperature.
The coin-type battery after high-temperature storage is CC-discharged at a discharge rate of 0.2 C until the SOC becomes 0% at 25 ° C. in a constant temperature bath, and then CC-CV charged to 4.2 V at a charge rate of 0.2 C. Then, CC discharge was performed at a discharge rate of 0.2 C, and the discharge capacity (recovery capacity; 0.2 C) after high temperature storage was measured.
The results are shown in Table 1 ("Recovery" column).

(Discharge capacity (1C) before high temperature storage; capacity before storage)
The discharge capacity (1C) before high temperature storage was measured in the same manner, except that the charge rate and discharge rate were changed to 1C with respect to the discharge capacity (0.2C) before high temperature storage.
The results are shown in Table 1 (“before storage” column).

(Discharge capacity after high temperature storage (recovery capacity; 1C))
The discharge capacity after high temperature storage (recovery capacity; 1C) was measured in the same manner except that the charge rate and discharge rate were changed to 1C with respect to the discharge capacity (recovery capacity; 0.2C) after high temperature storage. .
The results are shown in Table 1 ("Recovery" column).

(OCV decrease after high temperature storage (mV))
The above conditioning was applied to the coin-type battery obtained above.
After the conditioned coin-type battery was CC-CV charged to 4.25 V at a charge rate of 0.2 C in a constant temperature bath at 25° C., the coin-type battery was stored at a high temperature.
The open circuit voltage (OCV) [V] of the coin-type battery after high-temperature storage was measured at 25° C., and the OCV decrease (mV) was calculated by the following formula.
Table 1 shows the results.
OCV decrease (mV) = 4250 (mV) - open circuit voltage after high temperature storage (mV)

[Comparative Example 1]
The same operation as in Example 1 was performed except that PFHE was not used in the preparation of the non-aqueous electrolyte.
Table 1 shows the results.

As shown in Table 1, in Example 1, in which the non-aqueous electrolyte contains both additive A and additive B, the battery resistance after storage was reduced.
Specifically, in Example 1, the battery resistance before storage was low to some extent, and the degree of decrease in battery resistance due to storage was large (that is, "after storage/before storage" was small). was effectively reduced.
Furthermore, in Example 1, compared with Comparative Example 1, the battery capacity and the open circuit voltage (OCV) decreased at similar levels.

1 Laminated exterior body 2 Positive electrode terminal 3 Negative electrode terminal 4 Insulating seal 5 Positive electrode plate 6 Negative electrode plates 7, 8 Separator 11 Positive electrode 12 Negative electrode 13 Positive electrode can 14 Sealing plate 15 Separator 16 Gaskets 17, 18 Spacer plate

Claims (8)

Additive A, which is a compound represented by the following formula (A);
an additive B that is at least one selected from the group consisting of the following compound (B-1), the following compound (B-2), and the following compound (B-3) ;
A non-aqueous electrolyte for batteries containing

[In formula (A), R ^a1 represents a hydrocarbon group having 1 to 12 carbon atoms substituted with at least one fluorine atom. ]

2. The non-aqueous electrolyte for a battery according to claim 1, wherein said additive B is at least one selected from the group consisting of said compound (B-1) and said compound (B-2). 2. The non-aqueous electrolyte for a battery according to claim 1, wherein said additive B is said compound (B-1). 4. The non-aqueous electrolyte for a battery according to any one of claims 1 to 3, further comprising an additive C which is a compound represented by the following formula (C).

[In formula (C), R ^c1 and R ^c2 each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group. ] 5. The nonaqueous electrolyte for battery according to claim 4 , wherein the content of said additive C is 0.001% by mass to 10% by mass with respect to the total amount of the nonaqueous electrolyte for battery. The content of the additive A is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte for batteries,
The non-aqueous battery according to any one of claims 1 to 5 , wherein the content of the additive B is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte for batteries. Electrolyte. a positive electrode;
Metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped/dedoped with lithium ions, transition metal nitrides that can be doped/dedoped with lithium ions, and lithium a negative electrode containing, as a negative electrode active material, at least one selected from the group consisting of carbon materials capable of ion doping and dedoping;
The non-aqueous electrolyte for batteries according to any one of claims 1 to 6 ,
Lithium secondary battery including. A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to claim 7 .

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