JP7103713B2 - Non-aqueous electrolyte for batteries and lithium secondary battery - Google Patents

Description

The present disclosure relates to a non-aqueous electrolyte solution for a battery and a lithium secondary battery.

In recent years, lithium secondary batteries have been widely used as power sources for electronic devices such as mobile phones and notebook computers, electric vehicles, and power storage. In particular, recently, there has been a rapid increase in demand for batteries with high capacity, high output, and high energy density that can be installed in hybrid vehicles and electric vehicles.
The lithium secondary battery includes, for example, a positive electrode and a negative electrode containing a material capable of storing and releasing lithium, and a non-aqueous electrolyte solution for a battery containing a lithium salt and a non-aqueous solvent.
As the positive electrode active material used for the positive electrode, for example, lithium metal oxides such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , and LiFePO ₄ are used.
The non-aqueous electrolyte solution for batteries includes LiPF ₆ , LiBF ₄ , and LiN (SO ₂ CF ₃ ) in a mixed solvent (non-aqueous solvent) of carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. _2. A solution mixed with a Li electrolyte such as LiN (SO ₂ CF ₂ CF ₃ ) ₂ is used.
On the other hand, as active materials for negative electrodes used for negative electrodes, metallic lithium, metal compounds capable of storing and releasing lithium (single metal, oxides, alloys with lithium, etc.) and carbon materials are known, and lithium is particularly used. Lithium secondary batteries using coke, artificial graphite, and natural graphite that can be stored and released have been put into practical use.

In order to improve the performance of a battery (for example, a lithium secondary battery) containing a non-aqueous electrolyte solution for a battery, various additives are added to the non-aqueous electrolyte solution for a battery.
For example, as a non-aqueous electrolyte solution for a battery that can improve the storage characteristics of a battery after charging, a non-aqueous electrolyte solution for a battery containing at least one of lithium monofluorophosphate and lithium difluorophosphate as an additive is known. (For example, see Patent Document 1 below).
Further, as a non-aqueous electrolyte solution for a battery capable of improving the cycle characteristics and storage characteristics of a battery, a non-aqueous electrolyte solution for a battery containing lithium bis (oxalate) borate as an additive is known (for example, the following patent documents). 2).

Japanese Patent No. 3439085 Japanese Patent No. 3730855

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

Means for solving the above problems include the following aspects.
<1> Additive A, which is at least one selected from the group consisting of compounds represented by the following formula (A), and
Additive B, which is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate, and
Additive C, which is at least one selected from the group consisting of compounds represented by the following formula (C), and
An electrolyte containing lithium hexafluorophosphate and a compound represented by the following formula (1), and
A non-aqueous electrolyte solution for batteries containing.

[In the formula (A), R ¹ is a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, and a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom. Or represents a fluorine atom. ]

[In the formula (C), M represents a boron atom or a phosphorus atom, X represents a halogen atom, R represents an alkylene group having 1 to 10 carbon atoms, an alkylene group having 1 to 10 carbon atoms, and carbon. It represents an arylene group having a number of 6 to 20 or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain a substituent or a hetero atom in the structure), and m represents 1 to 1 to. It represents an atom of 3, n represents an atom of 0 to 4, and q represents 0 or 1. ]

In formula (1), R ¹¹ and R ¹² independently represent a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group, respectively.

<2> The non-aqueous electrolyte solution for a battery according to <1>, wherein the molar ratio of the compound represented by the formula (1) to the lithium hexafluorophosphate in the electrolyte is 0.01 to 1.
<3> The non-water battery non-water according to <1> or <2>, wherein the total concentration of the lithium hexafluorophosphate and the compound represented by the formula (1) is 0.1 mol / L to 3 mol / L. Electrolyte.

<4> The non-water battery non-water according to any one of <1> to <3>, wherein the additive C is at least one selected from the group consisting of compounds represented by the following formula (C2). Electrolyte.

[In the formula (C2), M represents a boron atom or a phosphorus atom, X represents a halogen atom, m represents an integer of 1 to 3, and n represents an integer of 0 to 4. ]

<5> The additive C is described in any one of <1> to <5>, which is at least one selected from the group consisting of lithium bis (oxalate) borate and lithium difluoro (oxalate) borate. Non-aqueous electrolyte for batteries.
<6> 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 electrolytic solution for batteries.
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 solution for batteries.
4. Non-water for batteries according to any one of <1> to <5>, 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 solution for batteries. Electrolyte.

<7> Further, for a battery according to any one of <1> to <6>, which contains at least one additive D selected from the group consisting of compounds represented by the following formula (D). Non-aqueous electrolyte.

[In formula (D), Y ¹ and Y ² each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group. ]

<8> The non-aqueous electrolyte solution for batteries according to <7>, wherein the content of the additive D is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte solution for batteries.
<9> Positive electrode and
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 nitrogen products that can be doped / dedoped with lithium ions, and lithium. A negative electrode containing at least one selected from the group consisting of carbon materials capable of doping and dedoping ions as a negative electrode active material, and a negative electrode.
The non-aqueous electrolyte solution for batteries according to any one of <1> to <8>.
Lithium secondary battery including.
<10> A lithium secondary battery obtained by charging / discharging the lithium secondary battery according to <9>.

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

It is a schematic perspective view which shows an example of the laminated type battery which is an example of the lithium secondary battery of this disclosure. It is schematic cross-sectional view in the thickness direction of the laminated type electrode body housed in the laminated type battery shown in FIG. It is the schematic cross-sectional view which shows the example of the coin type battery which is another example of the lithium secondary battery of this disclosure.

In the present specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.
In the present specification, the amount of each component in the composition is the total amount of the plurality of substances present in the composition unless otherwise specified, when a plurality of substances corresponding to each component are present in the composition. Means.

[Non-aqueous electrolyte for batteries]
The non-aqueous electrolyte solution for batteries (hereinafter, also simply referred to as “non-aqueous electrolyte solution”) of the present disclosure is used.
Additive A, which is at least one selected from the group consisting of compounds represented by the following formula (A), and
Additive B, which is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate, and
Additive C, which is at least one selected from the group consisting of compounds represented by the following formula (C), and
An electrolyte containing lithium hexafluorophosphate and a compound represented by the following formula (1), and
Contains.

In formula (A), R ¹ is a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or Represents a fluorine atom.

In the formula (C), M represents a boron atom or a phosphorus atom, X represents a halogen atom, R represents an alkylene group having 1 to 10 carbon atoms, an alkylene group having 1 to 10 carbon atoms, and a carbon number of carbon atoms. It represents an arylene group of 6 to 20 or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain a substituent or a hetero atom in the structure), and m is 1 to 3 Represents an integer of, n represents an atom of 0 to 4, and q represents 0 or 1.

In formula (1), R ¹¹ and R ¹² independently represent a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group, respectively.

According to the non-aqueous electrolyte solution of the present disclosure, the battery resistance after storage can be reduced.
The reason why such an effect is exhibited is not clear, but it is considered that the combination of Additive A, Additive B, and Additive C forms a high-quality film having low resistance after storage of the battery on the electrode surface. Be done.

Further, in the non-aqueous electrolyte solution of the present disclosure, when lithium hexafluorophosphate and the compound represented by the formula (1) are used in combination as the electrolyte, lithium hexafluorophosphate is used alone as the electrolyte. In comparison, it is believed that the stability of the electrolyte during storage is improved. As a result, it is considered that the battery resistance after storage (for example, after high temperature storage) can be further reduced.

Further, in the non-aqueous electrolyte solution of the present disclosure, by using lithium hexafluorophosphate and the compound represented by the formula (1) in combination, as compared with the case where lithium hexafluorophosphate is used alone as the electrolyte. It is also excellent in storage characteristics other than battery resistance (for example, high temperature storage characteristics).

Hereinafter, each component of the non-aqueous electrolytic solution of the present disclosure will be described.

<Additive A>
Additive A is at least one selected from the group consisting of compounds represented by the following formula (A).

In formula (A), R ¹ is a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, a hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or Represents a fluorine atom.

In the "hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by ^R1 , the unsubstituted hydrocarbon group having 1 to 6 carbon atoms was substituted with at least one fluorine atom. Has a structure.
Examples of the unsubstituted hydrocarbon group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a 1-ethylpropyl group, an n-butyl group, an isobutyl group and a 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- Alkyl group such as hexyl 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 Examples include groups, alkenyl groups such as 1-methyl-2-propenyl group, 2-methyl-1-propenyl group; and the like.

Examples of the "hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by R ¹ include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, and 2,2,2-. Fluoroalkyl groups such as trifluoroethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, perfluorohexyl group, perfluoroisopropyl group, perfluoroisobutyl group; 2-fluoroethenyl Group, 2,2-difluoroethenyl group, 2-fluoro-2-propenyl group, 3,3-difluoro-2-propenyl group, 2,3-difluoro-2-propenyl group, 3,3-difluoro-2- Fluoroalkenyl groups such as methyl-2-propenyl group, 3-fluoro-2-butenyl group, perfluorovinyl group, perfluoropropenyl group, perfluorobutenyl group; and the like can be mentioned.

The "hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by ^R1 is an alkyl group substituted with at least one fluorine atom or substituted with at least one fluorine atom. An alkenyl group is preferred, and an alkyl group substituted with at least one fluorine atom is more preferred.
The "hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by ^R1 may be substituted with at least one fluorine atom, but is a perfluorohydrocarbon group. Is preferable.
The carbon number of the "hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by ^R1 is preferably 1 to 3, more preferably 1 or 2, and particularly preferably 1.

In the "hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by ^R1 , the hydrocarbon oxy group having 1 to 6 carbon atoms substituted is substituted with at least one fluorine atom. Has a structure that has been modified.
The unsubstituted hydrocarbon oxy group having 1 to 6 carbon atoms includes a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, an n-butoxy group, a 2-butoxy group, a tert-butoxy group, a cyclopropyloxy group and a cyclopentyl group. An alkoxy group such as an oxy group; an alkenyloxy group such as an allyloxy group and a vinyloxy group; and the like can be mentioned.

The "hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by ^R1 is substituted with an alkoxy group substituted with at least one fluorine atom or at least one fluorine atom. The alkenyloxy group is preferable, and the alkoxy group substituted with at least one fluorine atom is more preferable.
The "hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by ^R1 may be substituted with at least one fluorine atom, but is a perfluorohydrocarbon oxy group. It is preferable to have.
The carbon number of the "hydrocarbon oxy group having 1 to 6 carbon atoms substituted with at least one fluorine atom" represented by ^R1 is preferably 1 to 3, more preferably 1 or 2, and particularly preferably 1.

As R ¹ , a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom is preferable, and an alkyl group having 1 to 6 carbon atoms substituted with at least one fluorine atom is more preferable, and the number of carbon atoms is 1. A perfluoroalkyl group of ~ 6 is more preferable, a perfluoromethyl group (also known as trifluoromethyl group) or a perfluoroethyl group (also known as pentafluoroethyl group) is more preferable, and a perfluoromethyl group (also known as trifluoromethyl group) is more preferable. Group) is particularly preferable.

As the compound represented by the formula (A), lithium trifluoromethylsulfonate or lithium pentafluoroethylsulfonate is preferable, and lithium trifluoromethylsulfonate is particularly preferable.

The content of the additive A is preferably 0.001% by mass to 10% by mass, more preferably 0.001% by mass to 5% by mass, and 0.001% by mass to 3% by mass with respect to the total amount of the non-aqueous electrolyte solution. %, More preferably 0.01% by mass to 3% by mass, further preferably 0.1 to 3% by mass, further preferably 0.1 to 2% by mass. It is preferably 0.1 to 1% by mass, and particularly preferably 0.1 to 1% by mass.

<Additive B>
Additive B is at least one selected from the group consisting of lithium monofluorophosphate (Li ₂ PO ₃ F) and lithium difluorophosphate (Li PO ₂ F ₂ ).
Additive B preferably contains lithium difluorophosphate.

The content of the additive B is preferably 0.001% by mass to 10% by mass, more preferably 0.001% by mass to 5% by mass, and 0.001% by mass to 3% by mass with respect to the total amount of the non-aqueous electrolyte solution. %, More preferably 0.01% by mass to 3% by mass, further preferably 0.1 to 3% by mass, further preferably 0.1 to 2% by mass. It is preferably 0.1 to 1% by mass, and particularly preferably 0.1 to 1% by mass.

<Additive C>
Additive C is at least one selected from the group consisting of compounds represented by the following formula (C).

In the formula (C), M represents a boron atom or a phosphorus atom, X represents a halogen atom, R represents an alkylene group having 1 to 10 carbon atoms, an alkylene group having 1 to 10 carbon atoms, and a carbon number of carbon atoms. It represents an arylene group of 6 to 20 or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain a substituent or a hetero atom in the structure), and m is 1 to 3 Represents an atom of, n represents an atom of 0 to 4, and q represents 0 or 1.

Specific examples of the halogen atom represented by X in the formula (C) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and the fluorine atom is particularly preferable.

In the formula (C), R is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms. show.
These groups represented by R (that is, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, and a halogenated arylene group having 6 to 20 carbon atoms). The group) may contain a substituent or a heteroatom in the structure.
Specifically, instead of the hydrogen atom of these groups, as a substituent, a halogen atom, a chain or cyclic alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, or a cyano group. , A carbonyl group, an acyl group, an amide group, or a hydroxyl group.
Further, instead of the carbon element of these groups, a structure in which a nitrogen atom, a sulfur atom, or an oxygen atom is introduced as a hetero atom may be used.
Further, when q is 1 and m is 2 to 4, m R may be bonded to each other. Such examples include ligands such as ethylenediaminetetraacetic acid.

The carbon number of the alkylene group having 1 to 10 carbon atoms in R is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1. The alkylene group having 1 carbon atom is a methylene group (that is, -CH _2- group).
In R, the halogenated alkylene group having 1 to 10 carbon atoms means that at least one of the hydrogen atoms contained in the alkylene group having 1 to 10 carbon atoms is a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine). It means a group replaced with an atom, preferably a fluorine atom.
The number of carbon atoms of the halogenated alkylene group having 1 to 10 carbon atoms is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1.
The carbon number of the arylene group having 6 to 20 carbon atoms in R is preferably 6 to 12.
The halogenated arylene group having 6 to 20 carbon atoms in R means that at least one of the hydrogen atoms contained in the arylene group having 6 to 20 carbon atoms is a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine). It means a group replaced with an atom, preferably a fluorine atom.
The halogenated arylene group having 6 to 20 carbon atoms preferably has 6 to 12 carbon atoms.

As R, an alkylene group having 1 to 10 carbon atoms is preferable, an alkylene group having 1 to 6 carbon atoms is more preferable, an alkylene group having 1 to 3 carbon atoms is further preferable, and an alkylene group having 1 carbon atom (that is, a methylene group). ) Is particularly preferable.

In the formula (C), m represents an integer of 1 to 3, n represents an integer of 0 to 4, and q represents 0 or 1.
The compound in which q is 0 in the formula (C) is specifically an oxalate compound represented by the following formula (C2).

In formula (C2), M, X, m, and n are synonymous with M, X, m, and n, respectively, in formula (C).

Specific examples of the compound represented by the formula (C) (including the case where the compound is represented by the formula (C2); the same applies hereinafter) include.
Lithium difluorobis (oxalate) phosphate,
Lithium tetrafluoro (oxalate) phosphate,
Lithium Tris (Oxalato) Phosphate,
Lithium difluoro (oxalate) oxalate,
Oxalate compounds such as bis (oxalate) lithium oxalate (above, compounds in which q is 0);
Difluorobis (malonate) lithium phosphate,
Lithium tetrafluoro (malonate) phosphate,
Tris (malonate) lithium phosphate,
Difluoro (malonate) lithium borate,
A malonate compound such as lithium bis (malonate) borate (above, a compound in which q is 1 and R is a methylene group);
And so on.
The compound represented by the formula (C) is selected from the group consisting of lithium difluorobis (oxalate) phosphate, lithium tetrafluoro (oxalate) phosphate, lithium difluoro (oxalate) borate, and lithium bis (oxalate) borate. It is preferable to contain at least one selected from the group consisting of lithium bis (oxalate) borate and lithium difluoro (oxalate) borate, and more preferably to contain at least one selected from the group consisting of lithium bis (oxalate) borate. (Hereinafter, it may be referred to as "LiBOB") is particularly preferable.

The content of the additive C is preferably 0.001% by mass to 10% by mass, more preferably 0.001% by mass to 5% by mass, and 0.001% by mass to 3% by mass with respect to the total amount of the non-aqueous electrolyte solution. %, More preferably 0.01% by mass to 3% by mass, further preferably 0.1 to 3% by mass, further preferably 0.1 to 2% by mass. It is preferably 0.1 to 1% by mass, and particularly preferably 0.1 to 1% by mass.

The total content of Additive A, Additive B and Additive C is preferably 0.003% by mass to 10% by mass, more preferably 0.003% by mass to 5% by mass, based on the total amount of the non-aqueous electrolyte solution. , 0.003% by mass to 3% by mass, further preferably 0.03% by mass to 3% by mass, and even more preferably 0.3 to 3% by mass.

<Electrolyte>
The non-aqueous electrolyte solution of the present disclosure contains an electrolyte containing both lithium hexafluorophosphate (hereinafter, also referred to as LiPF ₆ ) and a compound represented by the following formula (1).

In formula (1), R ¹¹ and R ¹² independently represent a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group, respectively.

It is preferable that R ¹¹ and R ¹² in the formula (1) are independently fluorine atoms or trifluoromethyl groups, respectively.

Examples of the compound represented by the formula (1) include lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethylsulfonyl) imide, and lithium bis (pentafluoroethylsulfonyl) imide.
Lithium bis (fluorosulfonyl) imide (abbreviated as LiFSI) is a compound in which R ¹¹ and R ¹² are both fluorine atoms in the formula (1).
Lithium bis (trifluoromethylsulfonyl) imide (abbreviated as LiTFSI) is a compound in which both R ¹¹ and R ¹² are trifluoromethyl groups in the formula (1). Lithium bis (trifluoromethylsulfonyl) imide is sometimes referred to as lithium bis (trifluoromethanesulfonyl) imide.
Lithium bis (pentafluoroethylsulfonyl) imide is a compound in which both R ¹¹ and R ¹² are pentafluoroethyl groups in the formula (1).

In the electrolyte, the molar ratio of the compound represented by the formula (1) to LiPF ₆ (hereinafter, also referred to as the molar ratio [compound represented by the formula (1) / LiPF ₆ ]) is not particularly limited.
The molar ratio [compound represented by the formula (1) / LiPF ₆ ] is preferably 0.01 to 1, more preferably 0.05 or more and less than 1 from the viewpoint of further improving the high temperature storage characteristics of the battery. Yes, more preferably 0.05 to 0.8, still more preferably 0.1 to 0.5.

In the non-aqueous electrolytic solution of the present disclosure, the total concentration of lithium hexafluorophosphate and the compound represented by the formula (1) is not particularly limited, but the total concentration is preferably 0.1 mol / L to 3 mol / L. It is more preferably 0.5 mol / L to 2 mol / L.

The electrolyte may contain at least one compound other than lithium hexafluorophosphate and the compound represented by the formula (1).
Other compounds include LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiPF _n [ _Ck F _{(2k + 1)} ] _(6-n) (n = 1 to 5, k = 1 to 8 integers). , LiC (SO ₂ R ²⁷ ) (SO ₂ R ²⁸ ) (SO ₂ R ²⁹ ) (where R ²⁷ to R ²⁹ may be the same or different from each other and are perfluoroalkyl groups having 1 to 8 carbon atoms. ), LiN (SO ₂ OR ³⁰ ) (SO ₂ OR ³¹ ) (where R ³¹ and R ³² may be the same or different from each other and are perfluoroalkyl groups having 1 to 8 carbon atoms), LiN (SO). ₂ R ³² ) (SO ₂ R ³³ ) (where R ³² and R ³³ may be the same or different from each other and are perfluoroalkyl groups with 1 to 8 carbon atoms; where R ³² is 1 carbon atom. Alternatively, in the case of 2 perfluoroalkyl groups, R ³³ is a perfluoroalkyl group having 3 to 8 carbon atoms), and the like.

The ratio of lithium hexafluorophosphate and the compound represented by the formula (1) in the electrolyte is preferably 50% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, and further. It is preferably 90% by mass to 100% by mass.

<Additive D>
The non-aqueous electrolytic solution of the present disclosure may contain the additive D.
Additive D is at least one selected from the group consisting of compounds represented by the following formula (D).
In general, a battery using a non-aqueous electrolytic solution containing the additive D tends to have a high battery resistance.
In this regard, when the non-aqueous electrolyte solution of the present disclosure contains the additive D, the combination of the additives A to C has the effect of lowering the battery resistance after storage as compared with the battery resistance before storage. To.
Therefore, when the non-aqueous electrolytic solution of the present disclosure contains the additive D, the effect that the battery resistance after storage can be reduced is achieved even though the non-aqueous electrolytic solution contains the additive D. ..

In formula (D), Y ¹ and Y ² each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group.
Examples of the compound represented by the formula (D) include vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, bropyrvinylene carbonate, dimethylvinylene carbonate, diethylvinylene carbonate, dipropylvinylene carbonate and the like. Of these, vinylene carbonate is the most preferable.

When the non-aqueous electrolyte solution of the present disclosure contains the additive D, the content of the additive D is preferably 0.001% by mass to 10% by mass, preferably 0.001% by mass, based on the total amount of the non-aqueous electrolyte solution. It is more preferably ~ 5% by mass, further preferably 0.001% by mass to 3% by mass, further preferably 0.01% by mass to 3% by mass, and 0.1 to 3% by mass. Is even more preferable, 0.1 to 2% by mass is further preferable, and 0.1 to 1% by mass is particularly preferable.

<Non-aqueous solvent>
The non-aqueous electrolyte solution generally contains a non-aqueous solvent.
As the non-aqueous solvent, various known ones can be appropriately selected, but it is preferable to use at least one selected from a cyclic aprotic solvent and a chain aprotic solvent.

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

(Cyclic aprotic solvent)
As the cyclic aprotic solvent, cyclic carbonate, cyclic carboxylic acid ester, cyclic sulfone, and cyclic ether can be used.

The cyclic aprotic solvent may be used alone or in combination of two or more.
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 related to the charge / discharge characteristics of the battery can be increased.

Specific examples of the cyclic carbonate 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 having a high dielectric constant are preferably used. In the case of a battery using graphite as the negative electrode active material, ethylene carbonate is more preferable. Moreover, you may use these cyclic carbonates in mixture of 2 or more types.

Specific examples of the cyclic carboxylic acid ester include alkyl substituents such as γ-butyrolactone, δ-valerolactone, methyl γ-butyrolactone, ethyl γ-butyrolactone, and ethyl δ-valerolactone.

The cyclic carboxylic acid ester has a low vapor pressure, a low viscosity, and a high dielectric constant, and can reduce the viscosity of the electrolytic solution without lowering the ignition point of the electrolytic solution and the degree of dissociation of the electrolyte. Therefore, it has a feature that the conductivity of the electrolytic solution, which is an index related to the discharge characteristics of the battery, can be increased without increasing the flammability of the electrolytic solution. It is preferable to use a cyclic carboxylic acid ester as the cyclic aprotic solvent. Among the cyclic carboxylic acid esters, γ-butyrolactone is most preferable.

Further, the cyclic carboxylic acid ester is preferably used by mixing with another cyclic aprotic solvent. For example, a mixture of a cyclic carboxylic acid ester and a cyclic carbonate and / or a chain carbonate can be mentioned.

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

(Chain aprotic solvent)
As the chain aprotic solvent, a chain carbonate, a chain carboxylic acid ester, a chain ether, a chain phosphate ester and the like can be used.

The mixing ratio of the chain 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.

Specifically, as the chain carbonate, 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, Examples thereof include 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. Two or more kinds of these chain carbonates may be mixed and used.

Specific examples of the chain carboxylic acid ester include methyl pivalate.
Specific examples of the chain ether include dimethoxyethane and the like.
Specific examples of the chain phosphate ester include trimethyl phosphate and the like.

(Solvent combination)
The non-aqueous solvent used in the non-aqueous electrolytic solution of the present disclosure may be one type or a mixture of a plurality of types. Further, only one or more kinds of cyclic aprotic solvents may be used, one or more kinds of chain aprotic solvents may be used, or cyclic aprotic solvents and chain protics. Solvents may be mixed and used. When it is particularly 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 aprotic solvent.

Further, from the viewpoint of the electrochemical stability of the electrolytic solution, it is most preferable to apply cyclic carbonate to the cyclic aprotic solvent and to apply chain carbonate to the chain aprotic solvent. Further, the conductivity of the electrolytic solution related to the charge / discharge characteristics of the battery can also be enhanced by the combination of the cyclic carboxylic acid ester and the cyclic carbonate and / or the chain carbonate.

Specific combinations of cyclic carbonate and chain carbonate include ethylene carbonate and dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, propylene carbonate and methyl ethyl carbonate, and propylene carbonate. 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, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate and diethyl Examples thereof include carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate.

The mixing ratio of the cyclic carbonate and the chain carbonate is expressed by mass ratio, and the cyclic carbonate: chain carbonate is 5:95 to 80:20, more preferably 10:90 to 70:30, and particularly preferably 15:85. It is ~ 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 related to the charge / discharge characteristics of the battery can be increased. Moreover, the solubility of the electrolyte can be further increased. Therefore, since the electrolytic solution having excellent electrical conductivity at normal temperature or low temperature can be obtained, the load characteristics of the battery at normal temperature to low temperature can be improved.

Specific examples of combinations of cyclic carboxylic acid ester and cyclic carbonate and / or chain carbonate include γ-butyrolactone and ethylene carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate, and γ-butyrolactone and ethylene carbonate and methyl ethyl. 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, ethylene carbonate and propylene carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate and dimethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate and diethyl carbonate, γ-Butyrolactone, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone, 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-buty Examples thereof include lolactone, sulfolane and dimethyl carbonate.

(Other solvents)
Examples of the non-aqueous solvent include other solvents other than the above.
Specific examples of other solvents include amides such as dimethylformamide, chain carbamates such as methyl-N and N-dimethylcarbamate, cyclic amides such as N-methylpyrrolidone, and N, N-dimethylimidazolidinone. Examples thereof 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 formulas.
HO (CH ₂ CH ₂ O) _a H
HO [CH ₂ CH (CH ₃ ) O] _b H
CH ₃ O (CH ₂ CH ₂ O) _c H
CH ₃ O [CH ₂ CH (CH ₃ ) O] _d H
CH ₃ O (CH ₂ CH ₂ O) _e CH ₃
CH ₃ O [CH ₂ CH (CH ₃ ) O] _f CH ₃
C ₉ H ₁₉ PhO (CH ₂ CH ₂ O) _g [CH (CH ₃ ) O] _h CH ₃
(Ph is a phenyl group)
CH ₃ O [CH ₂ CH (CH ₃ ) O] _i CO [OCH (CH ₃ ) CH ₂ ] _j OCH ₃
In the above formula, a to f are integers of 5 to 250, g to j are integers of 2 to 249, and 5 ≦ g + h ≦ 250, 5 ≦ i + j ≦ 250.

The non-aqueous electrolyte solution of the present disclosure is not only suitable as a non-aqueous electrolyte solution for a lithium secondary battery, but also a non-aqueous electrolyte solution for a primary battery, a non-aqueous electrolyte solution for an electrochemical capacitor, and an electric double layer capacitor. , Can also be used as an electrolytic solution for aluminum electrolytic capacitors.

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

(Negative electrode)
The negative electrode may include a negative electrode active material and a negative electrode current collector.
Examples of the negative electrode active material in the negative electrode include metallic 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 nitridants 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 the metal or alloy that can be alloyed with lithium (or lithium ion) include silicon, a silicon alloy, tin, and a tin alloy. Further, lithium titanate may be used.
Among these, a carbon material capable of doping and 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 form of 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. As the artificial graphite, graphitized MCMB, graphitized MCF and the like are used. Further, as the graphite material, a material containing boron or the like can also be used. Further, as the graphite material, a material coated with a metal such as gold, platinum, silver, copper or tin, a material coated with amorphous carbon, or a mixture of amorphous carbon and graphite can also be used.

These carbon materials may be used alone or in admixture of two or more.
As the carbon material, a carbon material having a surface spacing d (002) of the (002) plane measured by X-ray analysis of 0.340 nm or less is particularly preferable. Further, 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 to the graphite is also preferable. When the carbon material as described above is used, the energy density of the battery can be further increased.

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. Of these, 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 the positive electrode active material in the positive electrode include transition metal oxides or transition metal sulfides such as MoS ₂ , TiS ₂ , MnO ₂ , and V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiNi _X Co. _(1-X) O ₂ [0 <X <1], Li _{1 + α} Me _1-α O ₂ having an α-NaFeO type ₂ crystal structure (Me is a transition metal element containing Mn, Ni and Co, 1.0. ≦ (1 + α) / (1-α) ≦ 1.6), LiNi _x Coy Mn _z O ₂ [x + _y + z = 1, 0 <x <1, 0 <y <1, 0 <z <1] (for example, LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ etc.), LiFePO ₄ , LiMnPO ₄ and other composite oxides composed of lithium and transition metals, Examples thereof include conductive polymer materials such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiaizole, and polyaniline complex. Among these, a composite oxide composed of lithium and a transition metal is particularly preferable. When the negative electrode is a lithium metal or a lithium alloy, a carbon material can also be used as the positive electrode. Further, as the positive electrode, a mixture of a composite oxide of lithium and a transition metal and a carbon material can also be used.
The positive electrode active material may be used alone or in combination of two or more. When the positive electrode active material has insufficient conductivity, it can be used together with a conductive auxiliary agent to form a positive electrode. Examples of the conductive auxiliary agent 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 contains a separator between the negative electrode and the positive electrode.
The separator is a membrane that electrically insulates the positive electrode and the negative electrode and allows lithium ions to pass through, and examples thereof include a porous membrane and a polyelectrolyte.
As the porous film, a microporous polymer film is preferably used, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, polyester and the like.
In particular, porous polyolefin is preferable, and specifically, a porous polyethylene film, a porous polypropylene film, or a multilayer film of a porous polyethylene film and a polypropylene film can be exemplified. The porous polyolefin film may be coated with another resin having excellent thermal stability.
Examples of the polymer electrolyte include a polymer in which a lithium salt is dissolved, a polymer inflated with an electrolytic solution, and the like.
The non-aqueous electrolyte solution 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, and can be formed into a cylindrical type, a coin type, a square type, a laminated type, a film type, or any other shape. However, the basic structure of the battery is the same regardless of the shape, and the design can be changed according to the purpose.

An example of the lithium secondary battery (non-aqueous electrolyte secondary battery) of the present disclosure is a laminated battery.
FIG. 1 is a schematic perspective view showing an example of a laminated battery which is an example of the lithium secondary battery of the present disclosure, and FIG. 2 is a thickness of a laminated electrode body housed in the laminated battery shown in FIG. It is a schematic sectional view of a direction.
The laminated battery shown in FIG. 1 contains a non-aqueous electrolytic solution (not shown in FIG. 1) and a laminated electrode body (not shown in FIG. 1), and the peripheral edge thereof is sealed. A laminated exterior body 1 whose inside is hermetically sealed is provided. 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 exterior body 1 is a laminated body in which a positive electrode plate 5 and a negative electrode plate 6 are alternately laminated via a separator 7, and a laminated body of the laminated body. A separator 8 that surrounds the periphery is provided. The positive electrode plate 5, the negative electrode plate 6, the separator 7, and the separator 8 are impregnated with the non-aqueous electrolytic solution of the present disclosure.
The plurality of positive electrode plates 5 in the laminated electrode body are all electrically connected to the positive electrode terminal 2 via the positive electrode tab (not shown), and a part of the positive electrode terminal 2 is the laminated exterior body 1. It protrudes outward from the peripheral end (Fig. 1). The portion of the peripheral end of the laminated exterior body 1 from which the positive electrode terminal 2 protrudes is sealed with an insulating seal 4.
Similarly, the plurality of negative electrode plates 6 in the laminated electrode body are all electrically connected to the negative electrode terminal 3 via the negative electrode tab (not shown), and a part of the negative electrode terminal 3 is the laminated exterior. It protrudes outward from the peripheral end of the body 1 (FIG. 1). A portion of the laminated exterior body 1 where the negative electrode terminal 3 protrudes is sealed by an insulating seal 4.
In the laminated battery according to the above example, the number of positive electrode plates 5 is 5 and the number of negative electrode plates 6 is 6. The outer layers are all laminated so as to be the negative electrode plate 6. However, it goes without saying that the number of positive electrode plates, the number of negative electrode plates, and the arrangement of the laminated battery are not limited to this example, and various changes 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 injected with a non-aqueous electrolytic solution, a disk-shaped positive electrode 11, and, if necessary, spacer plates 17 and 18 made of stainless steel or aluminum are arranged in this order. In a laminated state, it is stored 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 lid”). The positive electrode can 13 and the sealing plate 14 are caulked and sealed via the gasket 16.
In this example, the non-aqueous electrolytic solution of the present disclosure is used as the non-aqueous electrolytic solution to be injected into the separator 15.

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

The use of the lithium secondary battery of the present disclosure is not particularly limited, and it can be used for various known uses. For example, laptops, mobile computers, mobile phones, headphone stereos, video movies, LCD TVs, handy cleaners, electronic notebooks, calculators, radios, backup power supplies, motors, automobiles, electric cars, bikes, electric bikes, bicycles, electric It can be widely used regardless of whether it is a small portable device or a large device such as a bicycle, a lighting device, a game machine, a clock, a power tool, or a camera.

Hereinafter, examples of the present disclosure will be shown, but the present disclosure is not limited to the following examples.
In the following examples, the "addition amount" represents the content in the finally obtained non-aqueous electrolytic solution (that is, the amount with respect to the total amount of the finally obtained non-aqueous electrolytic solution).
Further, "wt%" means mass%.

[Example 1]
A coin-type battery (test battery), which is a lithium secondary battery, was produced by the following procedure.
<Manufacturing 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 an aqueous solvent to prepare a paste-like negative electrode mixture slurry.
Next, this negative electrode mixture slurry is applied to a negative electrode current collector made of a strip-shaped copper foil having a thickness of 10 μm, dried, and then compressed by a roll press to form a sheet-shaped negative electrode composed of a negative electrode current collector and a negative electrode active material layer. Got At this time, the coating density of the negative electrode active material layer was 10 mg / cm ² , and the packing density was 1.5 g / ml.

<Preparation of positive electrode>
LiNi _0.5 Mn _0.3 Co _0.2 O ₂ (90 parts by mass), acetylene black (5 parts by mass) and polyvinylidene fluoride (5 parts by mass) are kneaded with N-methylpyrrolidinone as a solvent to form a paste. A positive mixture slurry was prepared.
Next, this positive electrode mixture slurry is applied to a positive electrode current collector of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and then compressed by a roll press to form a sheet-shaped positive electrode composed of the positive electrode current collector and the 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 packing density was 2.5 g / ml.

<Preparation of non-aqueous electrolyte solution>
As a non-aqueous solvent, ethylene carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC) were mixed at a ratio of 30:35:35 (mass ratio) to obtain a mixed solvent.
In the obtained mixed solvent, LiPF ₆ and LiFSI (lithium bis (fluorosulfonyl) imide) as electrolytes were added, and the concentration of LiPF ₆ in the finally obtained non-aqueous electrolyte solution was 1.0 mol / L, and the concentration was 1.0 mol / L. , The solution was dissolved so that the concentration of LiFSI in the finally obtained non-aqueous electrolyte solution was 0.2 mol / L. That is, in the finally obtained non-aqueous electrolytic solution, the total concentration of LiPF ₆ and LiFSI is 1.2 mol / L, and the molar content ratio [LiFSI / LiPF ₆ ] is 0.2.
For the solution obtained above
As additive A, lithium trifluoromethylsulfonate (hereinafter, also referred to as "TFMSLi") (addition amount: 0.5% by mass),
Lithium difluorophosphate (hereinafter, also referred to as "LiDFP") (addition amount: 1.0% by mass) as additive B, and lithium bis (oxalate) borate (hereinafter, also referred to as "LiBOB") (addition) as additive C. Amount 0.5% by mass)
Vinylene carbonate (hereinafter, also referred to as "VC") as additive D (addition amount 0.4% by mass)
Was added to obtain a non-aqueous electrolyte solution.

<Making coin-type batteries>
The above-mentioned negative electrode was punched in a disk shape with a diameter of 14 mm and the above-mentioned positive electrode was punched in a disk shape, respectively, to obtain a coin-shaped negative electrode and a coin-shaped positive electrode, respectively. Further, a microporous polyethylene film having a thickness of 20 μm was punched into a disk shape having a diameter of 17 mm to obtain a separator.
The obtained coin-shaped negative electrode, separator, and coin-shaped positive electrode are laminated in a stainless steel battery can (2032 size) in this order, and then 20 μL of the above-mentioned non-aqueous electrolyte solution is placed in the battery can. It was injected and immersed in 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 described above, a coin-type battery (that is, a coin-type lithium secondary battery) having a diameter of 20 mm and a height of 3.2 mm and having the configuration shown in FIG. 3 was obtained.

<Evaluation of battery resistance>
The battery resistance of the obtained coin-type battery was evaluated.
Hereinafter, "conditioning" refers to repeating charging and discharging of a coin-type battery between 2.75V and 4.2V three times at 25 ° C. in a constant temperature bath.
Hereinafter, "high temperature storage" means an operation of storing a coin-type battery in a constant temperature bath at 80 ° C. for 48 hours.

(Measurement of battery resistance (-20 ° C) before high temperature storage)
After conditioning, the SOC (State of Charge) of the coin cell battery is adjusted to 80%, and then DCIR (Direct current internal resistance) before high temperature storage of the coin cell battery is performed at -20 ° C by the following method. ) Was measured.
Using the above-mentioned coin-type battery adjusted to SOC 80%, CC10s discharge at a discharge rate of 0.2C, pause for 300 seconds, CC10s discharge at a discharge rate of 1C, pause for 300 seconds, discharge rate at -20 ° C. CC10s discharge at 2C, pause for 300 seconds, and CC10s discharge at a discharge rate of 5C were performed in this order.
The CC10s discharge means to discharge at a constant current for 10 seconds.
The DC resistance was obtained based on the relationship between each discharge rate and the voltage 10 seconds after the start of discharge at each discharge rate, and the obtained DC resistance (Ω) was used as the battery resistance (Ω) before high-temperature storage of the coin-type battery. Ω) (-20 ° C).
The results are shown in Table 1.

(Measurement of battery resistance (-20 ° C) after high temperature storage)
An operation in which a coin-type battery after conditioning and before adjusting the SOC to 80% is charged with CC-CV to 4.25 V at a charging rate of 0.2 C at 25 ° C in a constant temperature bath, and then stored at a high temperature. The battery resistance (Ω) after high-temperature storage was measured in the same manner as the above-mentioned measurement of battery resistance before high-temperature storage except that.
The results are shown in Table 1.
Here, CC-CV charging means constant current-constant voltage.

(Measurement of increase rate of battery resistance due to high temperature storage)
The rate of increase in battery resistance due to high temperature storage was calculated by the following formula. The results are shown in Table 1.
Increase rate of battery resistance due to high temperature storage (%)
= [(Battery resistance after high temperature storage (Ω) -Battery resistance before high temperature storage (Ω)) / Battery resistance before high temperature storage (Ω)] × 100

[Example 2]
In the preparation of the non-aqueous electrolyte solution, the same operation as in Example 1 was carried out except that LiFSI was changed to the same number of moles of LiTFSI (lithium bis (trifluoromethylsulfonyl) imide).
The results are shown in Table 1.

[Reference Example 1]
In the preparation of the non-aqueous electrolyte solution, LiFSI was not used, and the amount of LiPF ₆ was changed so that the concentration of LiPF ₆ in the finally obtained non-aqueous electrolyte solution was 1.2 mol / L. Performed the same operation as in Example 1.
The results are shown in Table 1.

[Reference example 2]
In the preparation of the non-aqueous electrolyte solution, the same operation as in Example 1 was carried out except that the additive A was not used.
The results are shown in Table 1.

[Reference Example 3]
In the preparation of the non-aqueous electrolyte solution, the same operation as in Example 1 was carried out except that the additive B was not used.
The results are shown in Table 1.

[Reference Example 4]
In the preparation of the non-aqueous electrolyte solution, the same operation as in Example 1 was carried out except that the additive C was not used.
The results are shown in Table 1.

[Reference Example 5]
In the preparation of the non-aqueous electrolyte solution, the same operation as in Example 2 was carried out except that the additive A was not used.
The results are shown in Table 1.

[Reference Example 6]
In the preparation of the non-aqueous electrolyte solution, the same operation as in Example 2 was carried out except that the additive B was not used.
The results are shown in Table 1.

[Reference Example 7]
In the preparation of the non-aqueous electrolyte solution, the same operation as in Example 2 was carried out except that the additive C was not used.
The results are shown in Table 1.

As shown in Table 1, in the batteries of Examples 1 and 2, the battery resistance after high temperature storage was reduced as compared with the battery of Reference Example 1.
Further, in the batteries of Examples 1 and 2, the rate of increase in battery resistance due to high temperature storage was reduced as compared with the battery of Reference Example 1. Specifically, in the batteries of Examples 1 and 2, the rate of increase in battery resistance due to high temperature storage was a negative value, that is, the battery resistance did not increase but rather decreased due to high temperature storage.

Further, from the comparison between Example 1 and Reference Examples 2 to 4 (contrast in the group in which the compound (1) is LiFSI), the example containing all of the additive A, the additive B, and the additive C is included. In No. 1, the battery resistance after high-temperature storage was reduced as compared with Reference Examples 2 to 4 in which any one of Additive A, Additive B, and Additive C was not contained.
Similarly, from the comparison between Example 2 and Reference Examples 5 to 7 (contrast in the group in which compound (1) is LiTFSI), all of Additive A, Additive B, and Additive C are included. In Example 2, the battery resistance after high-temperature storage was reduced as compared with Reference Examples 5 to 7 which did not contain any one of Additive A, Additive B, and Additive C.

[High temperature storage characteristics other than battery resistance]
The high-temperature storage characteristics other than the battery resistance were evaluated for the coin-type batteries in each of Example 1, Example 2, and Reference Example 1.
Details will be shown below.

(Discharge capacity before high temperature storage (0.2C); capacity before storage)
The conditioned coin cell battery is 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 stored at a high temperature at 25 ° C. at a discharge rate of 0.2 C. The discharge capacity (0.2C) was measured.
The results are shown in Table 2 (“Capacity before storage” column in “Discharge capacity (0.2C)” column).

(Recovery discharge capacity after high temperature storage (0.2C); Recovery capacity after storage)
The conditioned coin-type battery was CC-CV charged to 4.25 V at a charging rate of 0.2 C at 25 ° C. in a constant temperature bath, and then stored at a high temperature.
The coin-type battery after high-temperature storage is CC-discharged at 25 ° C. in a constant temperature bath at a discharge rate of 0.2 C until the SOC reaches 0%, and then CC-CV is 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 recovery discharge capacity (0.2 C) after high temperature storage was measured.
The results are shown in Table 2 (“Recovery capacity after storage” column in the “Discharge capacity (0.2C)” column).

(Capacity retention rate during high temperature storage (0.2C); Capacity retention rate)
The capacity retention rate (0.2C) during high-temperature storage was determined by the following formula.
Capacity retention rate during high-temperature storage (0.2C) (%) = [Recovery discharge capacity after high-temperature storage (0.2C) / Discharge capacity before high-temperature storage (0.2C)] x 100
The results are shown in Table 2 (“Capacity retention rate column” column in the “Discharge capacity (0.2C)” column).

(Discharge capacity before high temperature storage (1.0C), recovery discharge capacity after high temperature storage (1.0C), and capacity retention rate during high temperature storage (1.0C))
Except for changing the discharge rate and charge rate to 1.0C, respectively, the discharge capacity before high-temperature storage (0.2C), the recovery discharge capacity after high-temperature storage (0.2C), and the capacity during high-temperature storage. Similar to the maintenance rate (0.2C), the discharge capacity before high temperature storage (1.0C), the recovery discharge capacity after high temperature storage (1.0C), and the capacity maintenance rate during high temperature storage (1.0C). Was asked for each.
The results are shown in Table 2 (in the "Discharge capacity (1.0C)" column, the "Pre-storage capacity" column, the "Post-storage recovery capacity" column, and the "Capacity retention rate" column).

(Open circuit voltage (OCV) before high temperature storage)
The conditioned coin-type battery is CC-CV charged to 4.25V at a charging rate of 0.2C at 25 ° C in a constant temperature bath, and the CC-CV-charged coin-type battery has an open circuit voltage (Open Circuit) at 25 ° C. Voltage; OCV) [mV] was measured, and the obtained value was taken as the open circuit voltage (OCV) before high temperature storage.
The results are shown in Table 2 (“OCV before storage” column).

(Opening voltage (OCV) after high temperature storage)
The coin-type battery whose open circuit voltage was measured before high-temperature storage was CC-CV charged to 4.25 V at a charging rate of 0.2 C at 25 ° C. in a constant temperature bath, and then stored at high temperature.
The open circuit voltage (OCV) [mV] of the coin cell battery after high temperature storage was measured at 25 ° C., and the obtained value was taken as the open circuit voltage (OCV) after high temperature storage.
The results are shown in Table 2 (“OCV after storage” column).

(Opening voltage drop due to high temperature storage; ΔOCV)
The open circuit voltage decrease due to high temperature storage was calculated by the following formula. The smaller the decrease in open circuit voltage due to high-temperature storage, the better the high-temperature storage characteristics.
Opening voltage drop due to high temperature storage = Opening voltage before high temperature storage (OCV) -Opening voltage after high temperature storage (OCV)
The results are shown in Table 2 (“ΔOCV” column).

As shown in Table 2, the batteries of Examples 1 and 2 were also excellent in high temperature storage characteristics other than battery resistance. Specifically, the batteries of Examples 1 and 2 have a large recovery capacity after high-temperature storage (“recovery capacity after storage”), an excellent capacity retention rate during high-temperature storage, and an open-circuit voltage after high-temperature storage (“after storage”). OCV ”) was high, and the decrease in open circuit voltage (“ΔOCV”) due to high temperature storage was suppressed.

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

Claims (10)

Additive A, which is at least one selected from the group consisting of compounds represented by the following formula (A), and
Additive B, which is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate, and
Additive C, which is at least one selected from the group consisting of compounds represented by the following formula (C), and
An electrolyte containing lithium hexafluorophosphate and a compound represented by the following formula (1), and
A non-aqueous electrolyte solution for batteries containing.

[In the formula (A), R ¹ is a hydrocarbon group having 1 to 6 carbon atoms substituted with at least one fluorine atom, or a hydrocarbon oxy having 1 to 6 carbon atoms substituted with at least one fluorine atom. Represents a group . ]

[In the formula (C), M represents a boron atom or a phosphorus atom, X represents a halogen atom, R represents an alkylene group having 1 to 10 carbon atoms, an alkylene group having 1 to 10 carbon atoms, and carbon. It represents an arylene group having a number of 6 to 20 or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain a substituent or a hetero atom in the structure), and m represents 1 to 1 to. It represents an atom of 3, n represents an atom of 0 to 4, and q represents 0 or 1. ]

[In formula (1), R ¹¹ and R ¹² each independently represent a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group. ] The non-aqueous electrolytic solution for a battery according to claim 1, wherein the molar ratio of the compound represented by the formula (1) to lithium hexafluorophosphate is 0.01 to 1. The non-aqueous electrolytic solution for a battery according to claim 1 or 2, wherein the total concentration of the lithium hexafluorophosphate and the compound represented by the formula (1) is 0.1 mol / L to 3 mol / L. The non-aqueous electrolytic solution for a battery according to any one of claims 1 to 3, wherein the additive C is at least one selected from the group consisting of compounds represented by the following formula (C2).

[In the formula (C2), M represents a boron atom or a phosphorus atom, X represents a halogen atom, m represents an integer of 1 to 3, and n represents an integer of 0 to 4. ] The battery according to any one of claims 1 to 4, wherein the additive C is at least one selected from the group consisting of lithium bis (oxalate) borate and lithium difluoro (oxalate) borate. Non-aqueous electrolyte. 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 solution for batteries.
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 solution for batteries.
The non-water for battery according to any one of claims 1 to 5, 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 solution for battery. Electrolyte. The non-aqueous electrolysis for batteries according to any one of claims 1 to 6, further comprising an additive D which is at least one selected from the group consisting of compounds represented by the following formula (D). liquid.

[In formula (D), Y ¹ and Y ² each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group. ] The non-aqueous electrolyte solution for batteries according to claim 7, wherein the content of the additive D is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte solution for batteries. With the 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 nitrogen products that can be doped / dedoped with lithium ions, and lithium. A negative electrode containing at least one selected from the group consisting of carbon materials capable of doping and dedoping ions as a negative electrode active material, and a negative electrode.
The non-aqueous electrolyte solution for a battery according to any one of claims 1 to 8.
Lithium secondary battery including. A lithium secondary battery obtained by charging / discharging the lithium secondary battery according to claim 9.

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