JP7206556B2 - 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 electrolytic solution with excellent safety, high conductivity, and low viscosity, [A] includes a fluorinated carbonate, a cyclic carbonate, and a chain carbonate, and (i) The content of cyclic carbonate is 2 to 63 mol%, (ii) the content of chain carbonate is 2 to 63 mol%, and (iii) the content of fluorinated carbonate is 60 to 96 mol% (however, ( The total of i) to (iii) does not exceed 100 mol %), and is characterized by comprising a non-aqueous solvent in which the fluorinated carbonate is a compound having a specific chemical structure, and [B] an electrolyte. Non-aqueous electrolytes are disclosed.

In addition, in Patent Document 2, in an electrochemical element (especially a high-voltage lithium secondary battery) in which the positive electrode potential in a fully charged state is 4.35 V or more with respect to the potential of metallic lithium, As a non-aqueous electrolytic solution that causes little decrease in battery capacity and generates little gas during high-temperature storage, it is composed of a non-aqueous solvent containing cyclic carbonate and chain carbonate as main components and an electrolyte solute, and 60% by weight of cyclic carbonate. % or more is 4-fluoroethylene carbonate, and 25% or more by weight of the linear carbonate is methyl-2,2,2-trifluoroethyl carbonate, ethyl-2,2,2-trifluoroethyl carbonate and di-2,2,2-trifluoroethyl carbonate. At least one fluorinated chain carbonate selected from the group consisting of 2,2-trifluoroethyl carbonate, and the weight ratio of the cyclic carbonate to the chain carbonate is 3:97 to 35:65. A non-aqueous electrolytic solution for an electrochemical device is disclosed in which the positive electrode potential is 4.35 V or more with respect to the potential of metallic lithium.

Further, Patent Document 3 describes a non-aqueous electrolyte containing a non-aqueous solvent and a lithium electrolyte as a non-aqueous electrolyte having a high energy density and excellent safety when used in a lithium secondary battery. As a solvent, a phosphoric acid compound selected from tris(trimethylsilyl) phosphate, bis(trimethylsilyl) methyl phosphate, dimethyltrimethylsilyl phosphate and diethyltrimethylsilyl phosphate is added, and the amount of the phosphoric acid compound is 100% by volume of the entire non-aqueous electrolyte, A non-aqueous electrolyte is disclosed which is characterized by 0.01 to 40% by volume.

Japanese Patent No. 4392726 Japanese Patent No. 4976715 Japanese Patent No. 4538886

However, in some cases, it is required to reduce the battery resistance after storage and to suppress the decrease in the open-circuit voltage during storage for conventional non-aqueous electrolyte solutions for batteries and batteries.
Therefore, the subject of the present disclosure is a non-aqueous electrolyte for batteries that can reduce battery resistance after storage and can suppress a decrease in open-circuit voltage during storage, and a lithium ion battery using this non-aqueous electrolyte for batteries. It is to provide the next battery.

Means for solving the above problems include the following aspects.
<1> an electrolyte,
a non-aqueous solvent;
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 fluorohydrocarbon group having 1 to 6 carbon atoms, and R ^a2 represents a hydrocarbon group having 1 to 6 carbon atoms or a fluorohydrocarbon group having 1 to 6 carbon atoms. show.

In formula (B), R ^b1 to R ^b9 each independently represent a hydrocarbon group having 1 to 6 carbon atoms or a fluorohydrocarbon group having 1 to 6 carbon atoms.

<2> The content of the additive A is 0.001% by mass to 30% by mass with respect to the total amount of the battery non-aqueous electrolyte,
The non-aqueous electrolyte for batteries according to <1>, 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.
<3> The non-aqueous electrolyte for a battery according to <1> or <2>, wherein the non-aqueous solvent contains a cyclic carbonate compound and a chain carbonate compound other than the compound represented by the formula (A). .
<4> Described in <3>, wherein the total ratio of the cyclic carbonate compound and the chain carbonate compound other than the compound represented by the formula (A) in the non-aqueous solvent is 80% by mass or more. non-aqueous electrolyte for batteries.
<5> The non-aqueous electrolyte for batteries according to any one of <1> to <4>, wherein the proportion of the non-aqueous solvent in the non-aqueous electrolyte for batteries is 60% by mass or more.

<6> 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 <5>,
Lithium secondary battery including.
<7> A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to <6>.

According to the present disclosure, a non-aqueous electrolyte for batteries that can reduce battery resistance after storage and suppress a decrease in open-circuit voltage during storage, and a lithium secondary battery using this non-aqueous electrolyte for batteries is 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 fluorohydrocarbon group having 1 to 6 carbon atoms, and R ^a2 represents a hydrocarbon group having 1 to 6 carbon atoms or a fluorohydrocarbon group having 1 to 6 carbon atoms. show.

In formula (B), R ^b1 to R ^b9 each independently represent a hydrocarbon group having 1 to 6 carbon atoms or a fluorohydrocarbon group having 1 to 6 carbon atoms.

According to the non-aqueous electrolyte solution of the present disclosure, it is possible to reduce the battery resistance after storage and to suppress the decrease in open-circuit voltage during storage.
Although the reason why such an effect is exhibited is not clear, the combination of the additive A and the additive B forms a coating on the electrode before the battery is stored, and the coating is less deteriorated during storage of the battery. It is considered to be for

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 fluorohydrocarbon group having 1 to 6 carbon atoms, and R ^a2 represents a hydrocarbon group having 1 to 6 carbon atoms or a fluorohydrocarbon group having 1 to 6 carbon atoms. show.

In formula (A), the C 1-6 fluorohydrocarbon group means a C 1-6 hydrocarbon group substituted with at least one fluorine atom. The fluorohydrocarbon group having 1 to 6 carbon atoms is not limited to the perfluorohydrocarbon group.

In the formula (A), the fluorohydrocarbon group having 1 to 6 carbon atoms represented by R ^a1 is a cyclic fluorohydrocarbon group whether it is a linear fluorohydrocarbon group or a branched fluorohydrocarbon group. It may be a hydrogen group.

In the formula (A), examples of the fluorohydrocarbon group having 1 to 6 carbon atoms represented by R ^a1 include:
fluoromethyl group, difluoromethyl group, trifluoromethyl group, 2,2,2-trifluoroethyl group, 1,1,2,2-tetrafluoroethyl group, perfluoroethyl group, 2,2,3,3- Fluoroalkyl groups such as a tetrafluoropropyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, a perfluorohexyl group, a perfluoroisopropyl group, and a 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-methyl-2-propenyl group, 3-fluoro-2-butenyl group, perfluorovinyl group, perfluoropropenyl group, fluoroalkenyl group such as perfluorobutenyl group;
etc.
The fluorohydrocarbon group having 1 to 6 carbon atoms represented by R ^a1 is preferably a fluoroalkyl group having 1 to 6 carbon atoms, more preferably a fluoroalkyl group having 1 to 3 carbon atoms, a fluoromethyl group, a difluoro methyl group, trifluoromethyl group, 2,2,2-trifluoroethyl group, 1,1,2,2-tetrafluoroethyl group, perfluoroethyl group, 2,2,3,3-tetrafluoropropyl group, Or a perfluoropropyl group is more preferred, and a 2,2,2-trifluoroethyl group is particularly preferred.

In formula (A), specific examples and preferred embodiments of the fluorohydrocarbon group having 1 to 6 carbon atoms represented by R ^a2 are specific examples of the fluorohydrocarbon group having 1 to 6 carbon atoms represented by R ^a1 Examples and preferred embodiments are

In the formula (A), examples of hydrocarbon groups having 1 to 6 carbon atoms represented by R ^a2 include:
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, alkyl group such as tert-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 group, 1-methyl-2 - alkenyl groups such as a propenyl group and a 2-methyl-1-propenyl group;
etc.
The hydrocarbon group having 1 to 6 carbon atoms represented by R ^a2 is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and further preferably a methyl group or an ethyl group. Methyl groups are particularly preferred.

In formula (A), R ^a2 is preferably a hydrocarbon group having 1 to 6 carbon atoms, preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, methyl group or ethyl groups are more preferred, and methyl groups are particularly preferred.

As the compound represented by formula (F2),
2,2,2-trifluoroethylmethyl carbonate, bis(2,2,2-trifluoroethyl)carbonate, perfluoroethylmethylcarbonate, or bis(perfluoroethyl)carbonate are preferred,
2,2,2-trifluoroethylmethyl carbonate (hereinafter sometimes referred to as "MFEC") is particularly preferred.

The content of additive A (the total content when additive A is two or more compounds) is preferably 0.001% by mass to 30% by mass with respect to the total amount of the non-aqueous electrolyte. , more preferably 0.001% by mass to 20% by mass, and even more preferably 0.01% by mass to 10% by mass.

<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 ^b9 each independently represent a hydrocarbon group having 1 to 6 carbon atoms or a fluorohydrocarbon group having 1 to 6 carbon atoms.

In formula (B), the hydrocarbon groups having 1 to 6 carbon atoms represented by R ^b1 to R ^b9 are respectively the hydrocarbon groups having 1 to 6 carbon atoms represented by R ^a2 in formula (A). They are synonymous, and preferred embodiments are also the same.
In formula (B), each of the fluorohydrocarbon groups having 1 to 6 carbon atoms represented by R ^b1 to R ^b9 is a fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ^a1 in formula (A). It is synonymous with hydrocarbon group, and preferred embodiments are also the same.

As the compound represented by the formula (B),
tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tris(tripropylsilyl) phosphate, tris(trivinylsilyl) phosphate or tris(trifluoromethylsilyl) phosphate is preferred,
Tris(trimethylsilyl)phosphate (hereinafter sometimes referred to as "TMSP") is particularly preferred.

The content of additive B (the total content when additive B is a compound of two or more types; the same applies hereinafter) is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte. is preferably 0.001% by mass to 5% by mass, more preferably 0.001% by mass to 3% by mass, even more preferably 0.01% by mass to 3% by mass , more preferably 0.1 to 3% by mass, more preferably 0.1 to 2% by mass, even more preferably 0.1 to 1% by mass.

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 0.01 or more and 2.0 or less, more preferably 0.01 or more and less than 1.0, still more preferably 0.01 or more and 0.5 or less, and still more preferably is 0.01 or more and 0.2 or less.

<Additive C>
The non-aqueous electrolyte of the present disclosure may further contain an additive C, which is a compound represented by formula (C) below.

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 additive C, the content of additive C is preferably 0.001% by mass to 10% by mass, and 0.001% by mass, based on the total amount of the non-aqueous electrolyte. ~5% by mass is more preferable, more preferably 0.001% by mass to 3% by mass, even more preferably 0.01% by mass to 3% by mass, and 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.

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

<Non-aqueous solvent>
The non-aqueous electrolyte contains a non-aqueous solvent.
The number of non-aqueous solvents contained in the non-aqueous electrolyte may be one, or two or more.
As the non-aqueous solvent, various known solvents can be appropriately selected.
As the non-aqueous solvent, for example, non-aqueous solvents described in paragraphs 0069 to 0087 of JP-A-2017-45723 can be used.

The non-aqueous solvent preferably contains a cyclic carbonate compound and a chain carbonate compound other than the compound represented by formula (A) (hereinafter also referred to as "specific chain carbonate compound").
In this case, each of the cyclic carbonate compound and the specific chain carbonate compound contained in the non-aqueous solvent may be one kind or two or more kinds.

Cyclic carbonate compounds include, for example, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate and 2,3-pentylene carbonate.
Among these, ethylene carbonate and propylene carbonate, which have high dielectric constants, are preferred. In the case of a battery using a negative electrode active material containing graphite, the non-aqueous solvent more preferably contains ethylene carbonate.

Specific chain carbonate compounds 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, ethyl Pentyl carbonate, dipentyl carbonate, methylheptyl carbonate, ethylheptyl carbonate, diheptyl carbonate, methylhexyl carbonate, ethylhexyl carbonate, dihexyl carbonate, methyloctyl carbonate, ethyloctyl carbonate, dioctyl carbonate, and the like.

Specific combinations of cyclic carbonates and specific chain carbonates 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, and 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, ethylene carbonate, propylene carbonate, dimethyl carbonate, methylethyl carbonate, diethyl carbonate, and the like.

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

The non-aqueous solvent may contain compounds other than the cyclic carbonate compound and the specific chain carbonate compound.
In this case, the other compound contained in the non-aqueous solvent may be of only one type, or may be of two or more types.
Other compounds include cyclic carboxylic acid ester compounds (e.g., γ-butyrolactone), cyclic sulfone compounds, cyclic ether compounds, chain carboxylic acid ester compounds, chain ether compounds, chain phosphate compounds, amide compounds, and chain carbamates. compounds, cyclic amide compounds, cyclic urea compounds, boron compounds, polyethylene glycol derivatives, and the like.
For these compounds, the description in paragraphs 0069 to 0087 of JP-A-2017-45723 can be referred to as appropriate.

The ratio of the cyclic carbonate compound and the specific chain carbonate compound in the non-aqueous solvent is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more.
The ratio of the cyclic carbonate compound and the specific chain carbonate compound in the non-aqueous solvent may be 100% by mass.

The proportion of the non-aqueous solvent in the non-aqueous electrolyte is preferably 60% by mass or more, more preferably 70% by mass or more.
The upper limit of the ratio of the non-aqueous solvent in the non-aqueous electrolyte depends on the content of other components (additive A, additive B, electrolyte, etc.), but the upper limit is, for example, 99% by mass, It is preferably 97% by mass, more preferably 90% by mass.

<Electrolyte>
The non-aqueous electrolytic solution of the present disclosure contains an electrolyte.
Any electrolyte can be used as long as it is commonly used as an electrolyte for non-aqueous electrolytes.

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 preferred.

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,
2,2,2-trifluoroethylmethyl carbonate (MFEC) as additive A (addition amount 10% by mass), and tris(trimethylsilyl)phosphate (TMSP) as additive B (addition amount 0.5% by mass)
was added to obtain a non-aqueous electrolyte.
The proportion of the non-aqueous solvent (that is, the mixed solvent of EC, DMC and EMC described above) in the obtained non-aqueous electrolyte was 79.5% by mass.

<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.

(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).

(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]
In the preparation of the non-aqueous electrolytic solution, the amount of additive B was adjusted so that additive A was not used and the amount of additive B added was maintained at 0.5% by mass. A similar operation was performed.
Table 1 shows the results.

[Comparative Example 2]
In the preparation of the non-aqueous electrolyte, the same procedure as in Example 1 was performed except that additive B was not used and the amount of additive A was adjusted so that the amount of additive A added was maintained at 10% by mass. performed the operation.
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, Comparative Example 1 in which the non-aqueous electrolyte does not contain additive A, and Compared to Comparative Example 2 containing no additive B, the battery resistance after storage was reduced, and the decrease in open circuit voltage (OCV) during storage was reduced.
In Example 1, compared with Comparative Examples 1 and 2, the battery capacity was also equivalent.

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 (7)

an electrolyte;
a non-aqueous solvent;
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);
contains
does not contain a fluorine-containing cyclic carbonate,
Non-aqueous electrolyte for batteries.

[In the formula (A), R ^a1 represents a fluorohydrocarbon group having 1 to 6 carbon atoms, and R ^a2 represents a hydrocarbon group having 1 to 6 carbon atoms or a fluorohydrocarbon group having 1 to 6 carbon atoms. represents ]

[In formula (B), R ^b1 to R ^b9 each independently represent a hydrocarbon group having 1 to 6 carbon atoms or a fluorohydrocarbon group having 1 to 6 carbon atoms. ] The content of the additive A is 0.001% by mass to 30% by mass with respect to the total amount of the non-aqueous electrolyte for batteries,
2. The non-aqueous electrolyte for batteries according to claim 1, wherein the content of said additive B is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte for batteries. 3. The non-aqueous electrolyte for a battery according to claim 1, wherein the non-aqueous solvent contains a cyclic carbonate compound and a chain carbonate compound other than the compound represented by formula (A). 4. The battery according to claim 3, wherein the total ratio of the cyclic carbonate compound and the chain carbonate compound other than the compound represented by the formula (A) in the non-aqueous solvent is 80% by mass or more. Non-aqueous electrolyte. The non-aqueous electrolyte for batteries according to any one of claims 1 to 4, wherein the proportion of the non-aqueous solvent in the non-aqueous electrolyte for batteries is 60% by mass or more. 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 5,
Lithium secondary battery including. A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to claim 6 .

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