WO2016002481A1

WO2016002481A1 - Electrolyte solution for nonaqueous electrolyte batteries, and nonaqueous electrolyte battery using same

Info

Publication number: WO2016002481A1
Application number: PCT/JP2015/067049
Authority: WO
Inventors: 孝敬森中; 幹弘高橋; 益隆新免; 誠久保; 渉河端; 寛樹松崎; 建太山本; 憲治久保; 勝也久保
Original assignee: セントラル硝子株式会社
Priority date: 2014-07-01
Filing date: 2015-06-12
Publication date: 2016-01-07
Also published as: JP2016015214A; JP6476611B2

Abstract

An electrolyte solution for nonaqueous electrolyte batteries containing a nonaqueous solvent and a solute, which contains at least lithium hexafluorophosphate as the solute, while containing at least one imide salt represented by formula M[R¹R²OPNPOR³R⁴]_m and having a phosphoryl group, but not substantially containing a bis(oxalato)borate, a difluoro(oxalato)borate, a tris(oxalato)phosphate, a difluorobis(oxalato)phosphate and a tetrafluoro(oxalato)phosphate. This electrolyte solution for nonaqueous electrolyte batteries is capable of further suppressing the amount of gas generation without deteriorating the battery characteristics.

Description

Non-aqueous electrolyte battery electrolyte and non-aqueous electrolyte battery using the same

The present invention relates to an electrolyte for a non-aqueous electrolyte battery containing at least lithium hexafluorophosphate as a solute and a non-aqueous electrolyte battery using the same.

In recent years, information-related equipment, communication equipment, such as personal computers, video cameras, digital still cameras, mobile phones, and other small-sized, high energy density power storage systems, electric vehicles, hybrid vehicles, fuel cell vehicle auxiliary power supplies, power storage, etc. Large-scale, power storage systems for power applications are attracting attention. As one candidate, non-aqueous electrolyte batteries such as lithium ion batteries, lithium batteries, and lithium ion capacitors have been actively developed.

One problem with such a non-aqueous electrolyte battery is that the battery is swollen due to gas generation accompanying the electrochemical decomposition reaction of the components contained in the electrolyte during use of the battery, and the battery characteristics are deteriorated accordingly. .
The present applicant has previously determined that the high-temperature cycle characteristics and 45 ° C. of the non-aqueous electrolyte battery can be obtained without impairing the battery characteristics by suppressing the gas generation associated with the electrochemical decomposition reaction of the components contained in the electrolyte. A patent application was filed for an invention relating to an electrolyte solution for a non-aqueous electrolyte battery for improving durability such as high-temperature storage stability (Patent Document 1).
This electrolyte is
In a non-aqueous electrolyte battery electrolyte containing a non-aqueous organic solvent and a solute,
First compound consisting of bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluorobis (oxalato) phosphate, tetrafluoro (oxalato) phosphate as additives At least one compound selected from the group;
It includes at least one compound selected from the group consisting of an imide salt having a predetermined structure and an imide salt having a sulfonate group, and an imide salt having a predetermined structure and having a phosphoryl group. .

JP 2013-051122 A

By using the electrolyte for a non-aqueous electrolyte battery described above, it is possible to suppress the generation of gas accompanying the electrochemical decomposition reaction of components contained in the electrolyte, thereby reducing the performance of the non-aqueous electrolyte battery. Although durability such as high-temperature cycle characteristics and high-temperature storage stability of 45 ° C. or higher can be improved, the amount of gas generated when used as a battery is preferably as small as possible, and the amount of gas generated can be further suppressed without impairing battery characteristics. An electrolyte for a non-aqueous electrolyte battery may be required.

The present invention provides an electrolyte for a non-aqueous electrolyte battery that can further suppress the amount of gas generated during a charge / discharge cycle without impairing the battery characteristics when used in a non-aqueous electrolyte battery, and uses the same. An object of the present invention is to provide a nonaqueous electrolyte battery.

As a result of intensive studies in view of such problems, the present inventors have
In a non-aqueous electrolyte for a non-aqueous electrolyte battery containing a non-aqueous solvent and a solute,
Containing at least lithium hexafluorophosphate as a solute,
Containing at least one imide salt having a phosphoryl group in which at least one fluorine atom is bonded to a phosphorus atom;
Substantially free of bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluorobis (oxalato) phosphate, and tetrafluoro (oxalato) phosphate, non- As an electrolyte for water electrolyte batteries,
It has been found that when the electrolyte is used in a non-aqueous electrolyte battery, the amount of gas generation can be further suppressed without impairing battery characteristics (cycle characteristics and internal resistance characteristics), and the present invention has been achieved.

That is, the present invention provides a nonaqueous electrolyte solution for a nonaqueous electrolyte battery containing a nonaqueous solvent and a solute,
Containing at least lithium hexafluorophosphate as a solute,
Containing at least one imide salt having a phosphoryl group represented by the general formula (I) (hereinafter sometimes simply referred to as “imide salt”),
Substantially free of bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluorobis (oxalato) phosphate, and tetrafluoro (oxalato) phosphate. It is the electrolyte solution for non-aqueous electrolyte batteries characterized.

[Wherein R ¹ to R ⁴ are each independently a fluorine atom or an organic group represented by —OR ⁵ ; R ⁵ is a linear or branched alkyl group, alkenyl group having 1 to 10 carbon atoms, or And at least one organic group selected from an alkynyl group, a cycloalkyl group or a cycloalkenyl group having 3 to 10 carbon atoms, and an aryl group having 6 to 10 carbon atoms, and a fluorine atom or an oxygen atom in the organic group Unsaturated bonds can also be present. M represents an alkali metal cation, an alkaline earth metal cation, or an onium cation, and m represents an integer equal to the valence of the corresponding cation. However, at least one of R ¹ to R ⁴ represents a fluorine atom. ]

In the imide salt represented by the general formula (I), the more PF bonds, the more excellent the cycle characteristics and the internal resistance characteristics when the electrolyte containing the imide salt is used in a non-aqueous electrolyte battery. Since it is easy to exhibit, it is preferable that the imide salt represented by the general formula (I) is a compound in which R ¹ to R ⁴ are all fluorine atoms.

In addition, the imide salt represented by the general formula (I) is a compound in which the organic group represented by R ⁵ is at least one group selected from a hydrocarbon group having 6 or less carbon atoms which may contain a fluorine atom. It is preferable that

In the imide salt represented by the general formula (I), the group represented by R ⁵ is a methyl group, an ethyl group, a propyl group, a vinyl group, an allyl group, an ethynyl group, a 2-propynyl group, a phenyl group, From 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group, and 1,1,1,3,3,3-hexafluoroisopropyl group A compound which is at least one selected group is preferable.

The counter cation of the imide salt represented by the general formula (I) is preferably at least one counter cation selected from the group consisting of lithium ions, sodium ions, potassium ions, and tetraalkylammonium ions.

The addition amount of the imide salt represented by the general formula (I) is preferably in the range of 0.01 to 5.0% by mass with respect to the total amount of the electrolyte for the nonaqueous electrolyte battery.

The imide salt represented by the general formula (I) is preferably highly pure, and particularly preferably the Cl (chlorine) content is 5000 mass ppm or less, particularly 1000 mass ppm or less. Further preferred.

Further, as the solute, lithium tetrafluoroborate (LiBF ₄ ), bis (fluorosulfonyl) imide lithium (LiN (FSO ₂ ) ₂ ), bis (trifluoromethanesulfonyl) imide lithium (LiN (CF ₃ SO ₂ ) ₂ ), and at least one selected from the group consisting of lithium difluorophosphate (LiPO ₂ F ₂ ) may be contained.

The non-aqueous solvent is at least one selected from the group consisting of cyclic carbonates, chain carbonates, cyclic esters, chain esters, cyclic ethers, chain ethers, sulfone compounds, sulfoxide compounds, and ionic liquids. Is preferred.

The present invention also provides a nonaqueous electrolyte battery comprising at least a positive electrode, a negative electrode, and an electrolyte for a nonaqueous electrolyte battery, wherein the electrolyte for the nonaqueous electrolyte battery is the above-described electrolysis for a nonaqueous electrolyte battery. It is a nonaqueous electrolyte battery characterized by being a liquid.

When the electrolyte of the present invention is used in a non-aqueous electrolyte battery, the amount of gas generated during a high-temperature charge / discharge cycle can be greatly suppressed, and battery characteristics (cycle characteristics, internal resistance characteristics) associated with gas generation can be reduced. ) Can be suppressed.

Hereinafter, although the present invention will be described in detail, the description of the constituent elements described below is an example of the embodiment of the present invention, and the specific contents thereof are not limited. Various modifications can be made within the scope of the gist.

The non-aqueous electrolyte battery electrolyte of the present invention is a non-aqueous electrolyte battery non-aqueous electrolyte solution containing a non-aqueous solvent and a solute.
Containing at least lithium hexafluorophosphate as a solute,
Containing at least one imide salt having a phosphoryl group represented by the general formula (I),
Substantially free of bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluorobis (oxalato) phosphate, and tetrafluoro (oxalato) phosphate. It is the electrolyte solution for non-aqueous electrolyte batteries characterized.

The electrolyte substantially comprises bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluorobis (oxalato) phosphate, and tetrafluoro (oxalato) phosphate. When the electrolyte is used in a non-aqueous electrolyte battery, the amount of gas generated can be further suppressed. “Substantially not contained” means that the concentration of the total amount of the above compounds in the electrolytic solution is 100 ppm by mass or less.

In the general formula (I), examples of the alkyl group represented by R ⁵ include methyl group, ethyl group, propyl group, isopropyl group, butyl group, secondary butyl group, tertiary butyl group, pentyl group, 2, 2 -Carbon atoms such as difluoroethyl, 2,2,2-trifluoroethyl, 2,2,3,3-tetrafluoropropyl, and 1,1,1,3,3,3-hexafluoroisopropyl Examples of the alkenyl group include vinyl group, allyl group, 1-propenyl group, isopropenyl group, 2-butenyl group, and 1,3-butadienyl group. Examples include alkenyl groups having 2 to 8 carbon atoms or fluorine-containing alkenyl groups. Examples of alkynyl groups include ethynyl group, 2-propynyl group, and 1,1 dimethyl-2-propynyl group. Examples thereof include alkynyl groups having 2 to 8 carbon atoms or fluorine-containing alkynyl groups. Examples of cycloalkyl groups include cycloalkyl groups having 3 to 10 carbon atoms such as cyclopentyl groups and cyclohexyl groups or fluorine-containing cycloalkyl groups. Examples of the cycloalkenyl group include a cycloalkenyl group having 3 to 10 carbon atoms such as a cyclopentenyl group and a cyclohexenyl group or a fluorine-containing cycloalkenyl group. Examples of the aryl group include a phenyl group, a tolyl group, and Examples thereof include aryl groups having 6 to 10 carbon atoms such as xylyl groups and fluorine-containing aryl groups.

More specifically, examples of the anion of the imide salt represented by the general formula (I) include the following compound Nos. 1-No. 10 etc. are mentioned. However, the imide salt used in the present invention is not limited by the following examples.

Compound No. 1

Compound No. 2

Compound No. 3

Compound No. 4

Compound No. 5

Compound No. 6

Compound No. 7

Compound No. 8

Compound No. 9

Compound No. 10

In the general formula (I), it is important that at least one of R ¹ to R ⁴ is a fluorine atom. The reason is not clear, but unless at least one is a fluorine atom, the effect of suppressing the internal resistance of a battery using the electrolytic solution is not sufficient.

In the above general formula (I), the organic group represented by R ⁵ is preferably at least one group selected from hydrocarbon groups having 6 or less carbon atoms which may contain a fluorine atom. When the number of carbon atoms is large, the internal resistance tends to be relatively large when a film is formed on the electrode. It is preferable that the number of carbon atoms is 6 or less because the above-mentioned internal resistance tends to be smaller. Particularly, methyl group, ethyl group, propyl group, vinyl group, allyl group, ethynyl group, 2-propynyl group, phenyl group, 2 , 2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group, and 1,1,1,3,3,3-hexafluoroisopropyl group It is preferable that at least one group is obtained because a nonaqueous electrolyte battery that is superior in cycle characteristics and internal resistance characteristics can be obtained.

The imide salt represented by the above general formula (I) is preferably highly pure, and in particular, the Cl (chlorine) content is preferably 5000 ppm by mass or less, more preferably 1000 ppm by mass or less, and still more preferably Is 100 mass ppm or less. Use of an imide salt in which Cl (chlorine) remains at a high concentration is not preferable because it tends to corrode battery members.

As a method for producing the imide salt represented by the general formula (I), an imide salt (compound No. 1) in which all of R ¹ to R ⁴ are fluorine atoms is, for example, Z. Anorg. Allg. Chem. 412 ( 1), 65-70, (1975). An imide salt in which at least one of R ¹ to R ⁴ has an organic group represented by —OR ⁵ is exemplified by, for example, Compound No. 1 can be obtained by adding a corresponding alcohol (HOR ⁵ ) and a base to react.

Moreover, the electrolytic solution of the present invention tends to be able to suppress decomposition of lithium hexafluorophosphate, which is a solute, during high temperature storage. In the imide salt represented by the general formula (I), at least one of R ¹ to R ⁴ is preferably a fluorine atom because the effect of improving the thermal stability of lithium hexafluorophosphate is easily exhibited.

Although the action mechanism for suppressing the decomposition of lithium hexafluorophosphate in the electrolytic solution of the present invention is not clear, it is due to the interaction between the imide salt and phosphorus pentafluoride which is a decomposition product of lithium hexafluorophosphate. It is considered a thing. It is known that the thermal decomposition of lithium hexafluorophosphate is first decomposed into phosphorus pentafluoride and lithium fluoride by an equilibrium reaction as shown in the following reaction formula.
LiPF ₆ ⇔ PF ₅ + LiF
In the electrolytic solution not containing the imide salt, coloring of the electrolytic solution and generation of hydrofluoric acid occur when this phosphorus pentafluoride further reacts with a solvent or alcohol or water contained in a small amount in the solvent. As phosphorus pentafluoride is consumed by reaction, it is presumed that the equilibrium of the above reaction formula is further tilted to the right and the decomposition of lithium hexafluorophosphate proceeds. Therefore, in the electrolyte solution that does not contain the imide salt, the electrolyte solution is colored by the decomposition product generated by the thermal decomposition as described above, and the electrolyte solution is denatured such as generation of hydrogen fluoride. May result. The imide salt interacts with phosphorus pentafluoride to prevent phosphorus pentafluoride from causing a reaction other than the above reaction formula, so that the equilibrium of the above reaction formula is prevented from being tilted to the right. It is estimated that the thermal stability of lithium acid acid is improved.

Further, although the mechanism of action for improving battery characteristics according to the present invention is not clear, since the imide salt is a salt having a high degree of ionic dissociation in the solution, it does not cause a decrease in the ionic conductivity of the electrolytic solution. Does not increase resistance. Further, when a fluorine atom is bonded to phosphorus of an imide salt, the electron withdrawing effect causes delocalization of electrons in the anion, and the degree of ion dissociation can be further increased. In addition, it is considered that the imide salt according to the present invention is partially decomposed at the interface between the positive electrode and the electrolytic solution and the interface between the negative electrode and the electrolytic solution to form a film. This film suppresses direct contact between the non-aqueous solvent or solute and the active material, prevents decomposition of the non-aqueous solvent or solute, and suppresses deterioration of battery performance. Although the mechanism is not clear, it is thought that when fluorine atoms are bonded to phosphorus of imide salt, the charge of the film formed by the electron withdrawing effect is biased, and the film has high lithium conductivity, that is, low resistance. . The above effect tends to increase as the number of PF bonds increases in the imide salt represented by the general formula (I).

A suitable addition amount of the imide salt used in the present invention is 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, based on the total amount of the nonaqueous electrolytic solution. Moreover, an upper limit is 5.0 mass% or less, Preferably it is 4.0 mass% or less, More preferably, it is 3.0 mass% or less. If the amount added is less than 0.01% by mass, it is not preferable because the effect of improving battery characteristics is hardly obtained. On the other hand, if the amount added exceeds 5.0% by mass, it is not preferable because it is not only useless because no further effect is obtained, but also because resistance is increased due to excessive film formation and deterioration of battery performance is likely to occur. . These imide salts may be used alone as long as they do not exceed 5.0% by mass, or two or more of them may be used in any combination and ratio according to the application.

The type of the non-aqueous solvent used in the non-aqueous electrolyte battery electrolyte of the present invention is not particularly limited, and any non-aqueous solvent can be used. Specific examples include cyclic carbonates such as propylene carbonate, ethylene carbonate, and butylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate, cyclic esters such as γ-butyrolactone and γ-valerolactone, methyl acetate, and propion. Examples include chain esters such as methyl acid, cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran and dioxane, chain ethers such as dimethoxyethane and diethyl ether, sulfone compounds such as dimethyl sulfoxide and sulfolane, and sulfoxide compounds. Moreover, although a category differs from a nonaqueous solvent, an ionic liquid etc. can also be mentioned. Moreover, the nonaqueous solvent used for this invention may be used individually by 1 type, and may mix and use two or more types by arbitrary combinations and a ratio according to a use. Of these, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate are particularly preferred from the viewpoint of electrochemical stability against redox and chemical stability related to the reaction with heat and the above solute. .

The kind of the other solute that may coexist with lithium hexafluorophosphate used in the electrolyte solution for a non-aqueous electrolyte battery of the present invention is not particularly limited, and a conventionally known lithium salt can be used. As specific examples, LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (FSO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiPF ₃ (C ₃ F ₇ ) ₃ , LiB (CF ₃ ) ₄ , LiBF ₃ (C ₂ F ₅ ), And electrolyte lithium salts represented by LiPO ₂ F _{2 and the} like. One kind of these solutes may be used alone, or two or more kinds thereof may be used in any combination and in any ratio according to the application. Among them, considering the energy density, output characteristics, life, etc. as a battery, LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiN (FSO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , and LiPO ₂ F ₂ is preferred.

The suitable concentration of these solutes (concentration combined with lithium hexafluorophosphate) is not particularly limited, but the lower limit is 0.5 mol / L or more, preferably 0.7 mol / L or more, more preferably 0.9 mol. The upper limit is 2.5 mol / L or less, preferably 2.0 mol / L or less, and more preferably 1.5 mol / L or less. If the concentration is less than 0.5 mol / L, the ionic conductivity tends to decrease and the cycle characteristics and output characteristics of the nonaqueous electrolyte battery tend to decrease. On the other hand, if the concentration exceeds 2.5 mol / L, the nonaqueous electrolyte battery is used. When the viscosity of the electrolytic solution increases, the ionic conductivity also tends to be lowered, and the cycle characteristics and output characteristics of the nonaqueous electrolytic battery may be lowered.

When a large amount of the solute is dissolved in a non-aqueous solvent at one time, the temperature of the non-aqueous electrolyte may increase due to the heat of dissolution of the solute. When the liquid temperature rises remarkably, decomposition of the lithium salt containing fluorine atoms is accelerated and hydrogen fluoride may be generated. Hydrogen fluoride is not preferable because it causes deterioration of battery performance. For this reason, the liquid temperature when dissolving the solute in the non-aqueous solvent is not particularly limited, but is preferably −20 to 80 ° C., more preferably 0 to 60 ° C.

The above is the description of the basic configuration of the electrolyte solution for a non-aqueous electrolyte battery of the present invention. Generally, the electrolyte solution for a non-aqueous electrolyte battery of the present invention is generally used as long as the gist of the present invention is not impaired. You may add the additive used in arbitrary ratios. Specific examples include cyclohexylbenzene, biphenyl, t-butylbenzene, vinylene carbonate, vinyl ethylene carbonate, difluoroanisole, fluoroethylene carbonate, propane sultone, dimethyl vinylene carbonate, etc., overcharge prevention effect, negative electrode film formation effect and positive electrode protection Examples thereof include compounds having an effect. Moreover, it is also possible to use the non-aqueous electrolyte battery electrolyte in a quasi-solid state with a gelling agent or a crosslinked polymer as used in a non-aqueous electrolyte battery called a lithium polymer battery.

Next, the configuration of the nonaqueous electrolyte battery of the present invention will be described. The non-aqueous electrolyte battery according to the present invention is characterized by using the above-described electrolyte for a non-aqueous electrolyte battery according to the present invention, and the other components are those used in general non-aqueous electrolyte batteries. Is used. That is, it comprises a positive electrode and a negative electrode capable of inserting and extracting lithium, a current collector, a separator, a container, and the like.

The negative electrode material is not particularly limited, but lithium metal, alloys of lithium and other metals or intermetallic compounds, various carbon materials, artificial graphite, natural graphite, metal oxides, metal nitrides, tin (single), A tin compound, silicon (simple substance), a silicon compound, activated carbon, a conductive polymer, or the like is used.

The positive electrode material is not particularly limited. In the case of lithium batteries and lithium ion batteries, for example, lithium-containing transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , and lithium-containing transition metals A composite oxide in which a plurality of transition metals such as Co, Mn, Ni, etc. are mixed, a part of the transition metal in the lithium-containing transition metal composite oxide is replaced with a metal other than the transition metal, olivine and LiFePO _4, LiCoPO _4, phosphoric acid compound of a transition metal such as LiMnPO ₄ called, oxides such as _{_{_{TiO 2, V 2 O 5,}}} MoO 3, TiS 2, sulfides such as FeS, or polyacetylene, polyparaphenylene, polyaniline , And conductive polymers such as polypyrrole, activated carbon, polymers that generate radicals, carbon materials, etc. It is use.

By adding acetylene black, ketjen black, carbon fiber, graphite as a conductive material, polytetrafluoroethylene, polyvinylidene fluoride, SBR resin, etc. as a binder to the positive electrode or negative electrode material, and forming into a sheet shape It can be an electrode sheet.

As a separator for preventing contact between the positive electrode and the negative electrode, a nonwoven fabric or a porous sheet made of polypropylene, polyethylene, paper, glass fiber, or the like is used.

A non-aqueous electrolyte battery having a coin shape, cylindrical shape, square shape, aluminum laminate sheet shape or the like is assembled from the above elements.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples.

[Example 1-1]
Table 1 shows the preparation conditions of the non-aqueous electrolyte, Table 2 shows the storage stability evaluation results of the electrolyte, and Table 3 shows the evaluation results of the battery using the electrolyte. In addition, the values of the cycle characteristics, internal resistance characteristics, and gas generation amount of the batteries in Table 3 are the values of the electrolyte No. 1 before standing for one month after preparation. This is a relative value when the discharge capacity retention rate and internal resistance after the cycle test of the laminate cell produced using No. 33 and the amount of gas generated due to cycle characteristic evaluation are set to 100, respectively.

A mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 2 was used as the non-aqueous solvent, LiPF ₆ was 1.0 mol / L as a solute in the solvent, and the imide compound No. 1 was used as an additive. 1 lithium salt (Cl content in the imide salt is 90 mass ppm) was dissolved to a concentration of 0.03% by mass to prepare an electrolyte for a non-aqueous electrolyte battery. The above preparation was carried out while maintaining the liquid temperature in the range of 20-30 ° C. In addition, bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluorobis (oxalato) phosphate, and tetrafluoro (oxalato) phosphate in the electrolytic solution The total concentration was less than 100 ppm by mass.

[Evaluation of storage stability of electrolyte]
Decomposition of lithium hexafluorophosphate, which is a solute, by measuring the color of the electrolyte and the amount of free acid in the electrolyte before and after leaving the prepared electrolyte at 75 ° C. for 1 month in an argon atmosphere. The inhibitory effect was evaluated. The hue of the electrolyte was evaluated using a petroleum product color tester (OME-2000 manufactured by Nippon Denshoku Industries Co., Ltd.). The measurement samples are an electrolytic solution within 1 day of storage after preparation (electrolytic solution before standing at 75 ° C.) and an electrolytic solution after 1 month of standing at 75 ° C. after preparation.
The free acid of the electrolyte was measured by neutralization titration. The measurement sample is an electrolytic solution within one day after preparation (electrolytic solution before standing at 75 ° C.) and an electrolytic solution after one month of standing at 75 ° C. after preparation. The free acid was measured at room temperature. As a titration indicator, a 0.1 w / v% bromophenol blue ethanol (50%) solution was used.

[Battery characteristics evaluation]
Using the electrolyte within one day after preparation, a cell was created using LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as the positive electrode material and graphite as the negative electrode material. evaluated. The test cell was prepared as follows.

90% by mass of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder is mixed with 5% by mass of 5% by mass of polyvinylidene fluoride (PVDF) as a binder and 5% by mass of acetylene black as a conductive material, and further with N-methylpyrrolidone. Added to paste. The paste was applied on an aluminum foil and dried to obtain a test positive electrode body. Further, 90% by mass of graphite powder was mixed with 10% by mass of polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone was further added to form a slurry. This slurry was applied on a copper foil and dried at 120 ° C. for 12 hours to obtain a test negative electrode body. Then, an electrolytic solution was immersed in a polyethylene separator to assemble a 50 mAh cell with an aluminum laminate exterior.

[High temperature cycle characteristics]
Using the above cell, a charge / discharge test was conducted at an environmental temperature of 75 ° C. to evaluate the cycle characteristics. Both charging and discharging were performed at a current density of 3.5 mA / cm ^2. After charging reached 4.3 V, 4.3 V was maintained for 1 hour, and discharging was performed up to 3.0 V, and the charge / discharge cycle was repeated. Then, the degree of deterioration of the cell was evaluated based on the discharge capacity maintenance rate after 500 cycles (cycle characteristic evaluation). The discharge capacity retention rate was determined by the following formula.
<Discharge capacity maintenance rate after 500 cycles>
Discharge capacity retention rate (%) = (discharge capacity after 500 cycles / initial discharge capacity) × 100

[Internal resistance characteristics (25 ℃)]
The cell after the cycle test was charged to 4.3 V at an ambient temperature of 25 ° C. and a current density of 0.35 mA / cm ² , and then the internal resistance of the battery was measured.

[Gas generation amount]
Before and after the high temperature cycle characteristic test, the amount of gas generation was evaluated by estimating the amount of increase in cell volume by the buoyancy method using silicon oil.

[Examples 1-2 to 1-29]
A nonaqueous electrolytic solution was prepared in the same procedure as in Example 1-1 except that the conditions for preparing the nonaqueous electrolytic solution shown in Table 1 were followed. In addition, all Cl content in the imide salt used in the Example was about 90 mass ppm. In addition, in Examples 1-24 to 1-29, other electrolytes other than the imide salt and lithium hexafluorophosphate in Example 1-1 (hereinafter, may be simply referred to as “other electrolytes”) It is an experiment example regarding the electrolyte solution which contains. In Examples 1-2 to 1-29, bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluorobis (oxalato) phosphate in the electrolytic solution The total concentration of tetrafluoro (oxalato) phosphate was less than 100 ppm by mass. Table 2 shows the results of evaluating the storage stability of the electrolytic solution, and Table 3 shows the results of evaluating batteries using the electrolytic solution.

[Comparative Examples 1-1 to 1-10]
A nonaqueous electrolytic solution was prepared in the same procedure as in Example 1-1 except that the conditions for preparing the nonaqueous electrolytic solution shown in Table 1 were followed. In Comparative Examples 1-1 to 1-3, each of the following compound Nos. 11, no. 12 lithium salt is used, or instead of compound no. 13 is an experimental example relating to an electrolytic solution using 13 (amide compound). Comparative Example 1-4 was prepared in the same manner as Example 1-1 except that neither imide salt nor other electrolyte was added. It is an experiment example regarding electrolyte solution. In Comparative Examples 1-1 to 1-4, bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluorobis (oxalato) phosphate in the electrolytic solution The total concentration of tetrafluoro (oxalato) phosphate was less than 100 ppm by mass. In addition, Comparative Examples 1-5 to 1-10, as other electrolytes, were bis (oxalato) lithium borate, difluorobis (oxalato) lithium phosphate, tetrafluoro (oxalato) lithium phosphate, difluoro (oxalato), respectively. It is an experiment example regarding the electrolyte solution which contained lithium borate and tris (oxalato) lithium phosphate. In addition, all Cl content in the imide salt used by the comparative example was about 90 mass ppm. Table 2 shows the results of evaluating the storage stability of the electrolytic solution, and Table 3 shows the results of evaluating batteries using the electrolytic solution.

Compound No. 11

Compound No. 12

Compound No. 13

When the above results are compared, in the case of containing the imide salt represented by the above general formula (I), the increase in free acid and the change in hue are suppressed even after standing at a high temperature of 75 ° C. There was a trend. In the case where no imide salt was contained (Comparative Example 1-4) or the case where an imide salt or amide compound containing no PF bond was used (Comparative Examples 1-1 to 1-3), the cycle characteristics (after the cycle test) (Capacity maintenance ratio) is relatively low and internal resistance is relatively high. In contrast, when an imide salt containing a PF bond was used, good cycle characteristics and internal resistance characteristics were exhibited. Further, even when these imide salts and other electrolytes were used in combination, good cycle characteristics and internal resistance characteristics were exhibited. Further, in Examples 1-1 to 1-29, it was confirmed that the amount of gas generated after the cycle test was further suppressed as compared with Comparative Examples 1-5 to 1-10.
Therefore, when the electrolyte solution of the present invention is used in a non-aqueous electrolyte battery, the amount of gas generation can be further suppressed without impairing the battery characteristics.

[Examples 2-1 to 2-8, Comparative examples 2-1 to 2-4]
Table 4 shows the evaluation results of the battery in which the negative electrode body used in Example 1-1 was changed. As an electrolyte for a non-aqueous electrolyte battery, a non-aqueous electrolyte No. 1 is used. Using 5, 9, 12, 19, 33, or 34, the cycle characteristics, internal resistance characteristics, and gas generation amount were evaluated in the same manner as in Example 1-1. In Examples 2-1 to 2-4 and Comparative Examples 2-1 and 2-2 in which the negative electrode active material is Li ₄ Ti ₅ O ₁₂ , the negative electrode body is 90% by mass of Li ₄ Ti ₅ O ₁₂ powder. In addition, 5% by mass of polyvinylidene fluoride (PVDF) as a binder and 5% by mass of acetylene black as a conductive agent are added, N-methylpyrrolidone is added, and the obtained paste is applied onto a copper foil and dried. The end-of-charge voltage was 2.7 V and the end-of-discharge voltage was 1.5 V during battery evaluation. In Examples 2-1 to 2-4 and Comparative Example 2-2, the values of the cycle characteristics, internal resistance characteristics, and gas generation amount of the batteries are the same as the electrolyte solution No. This is a relative value when the discharge capacity retention rate after the cycle test, the internal resistance, and the gas generation amount associated with the cycle characteristic evaluation of the laminate cell produced using No. 33 are set to 100 (Comparative Example 2-1). In Examples 2-5 to 2-8 and Comparative Examples 2-3 and 2-4 in which the negative electrode active material is graphite (silicon-containing), the negative electrode body is composed of 80% by mass of graphite powder and 10% by mass of silicon powder. 10% by weight of polyvinylidene fluoride (PVDF) as a binder, N-methylpyrrolidone is further added, and the resulting paste is applied onto a copper foil and dried to produce a battery for evaluation. The end-of-charge voltage and end-of-discharge voltage were the same as in Example 1-1. In Examples 2-5 to 2-8 and Comparative Example 2-4, the values of the cycle characteristics, internal resistance characteristics, and gas generation amount of the batteries are the same as those of the electrolyte solution No. This is a relative value when the discharge capacity retention rate after the cycle test, the internal resistance, and the gas generation amount associated with the cycle characteristic evaluation of the laminate cell produced using No. 33 are each 100 (Comparative Example 2-3).

[Examples 3-1 to 3-4, Comparative examples 3-1 to 3-2]
Table 4 shows the evaluation results of the batteries in which the positive electrode used in Example 1-1 was changed. As an electrolyte for a non-aqueous electrolyte battery, a non-aqueous electrolyte No. 1 is used. Using 5, 9, 12, 19, 33, or 34, the cycle characteristics, internal resistance characteristics, and gas generation amount were evaluated in the same manner as in Example 1-1. The positive electrode body in which the positive electrode active material is LiCoO ₂ is a mixture of 90% by mass of LiCoO ₂ powder, 5% by mass of polyvinylidene fluoride (PVDF) as a binder and 5% by mass of acetylene black as a conductive material, and N-methyl. Pyrrolidone was added, and the resulting paste was applied on an aluminum foil and dried. The end-of-charge voltage during battery evaluation was 4.2 V, and the end-of-discharge voltage was 3.0 V. In Examples 3-1 to 3-4 and Comparative Example 3-2, the values of the cycle characteristics, internal resistance characteristics, and gas generation amount of the batteries are the same as those of the electrolyte No. 1 before standing for one month after preparation. This is a relative value when the discharge capacity retention rate after the cycle test, the internal resistance, and the gas generation amount associated with the cycle characteristic evaluation of the laminate cell produced using No. 33 are each 100 (Comparative Example 3-1).

[Examples 4-1 to 4-4, Comparative Examples 4-1 to 4-2]
Table 4 shows the evaluation results of the batteries in which the positive electrode used in Example 1-1 was changed. As an electrolyte for a non-aqueous electrolyte battery, a non-aqueous electrolyte No. 1 is used. Using 5, 9, 12, 19, 33, or 34, the cycle characteristics, internal resistance characteristics, and gas generation amount were evaluated in the same manner as in Example 1-1. The positive electrode body in which the positive electrode active material is LiNi _0.8 Co _0.15 Al _0.05 O ₂ is composed of 90% by mass of LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder, 5% by mass of polyvinylidene fluoride (PVDF) as a binder, and acetylene as a conductive material. Black was mixed at 5% by mass, N-methylpyrrolidone was further added, and the obtained paste was applied on an aluminum foil and dried. The end-of-charge voltage during battery evaluation was 4.2 V, and the end-of-discharge voltage was 3.0 V. In Examples 4-1 to 4-4 and Comparative Example 4-2, the values of the cycle characteristics, internal resistance characteristics, and gas generation amount of the batteries are the same as those of the electrolyte No. 1 before standing for one month after preparation. This is a relative value when the discharge capacity retention rate, the internal resistance, and the gas generation amount associated with the cycle characteristics evaluation after the cycle test of the laminate cell produced using No. 33 are each 100 (Comparative Example 4-1).

[Examples 5-1 to 5-4, Comparative Examples 5-1 to 5-2]
Table 4 shows the evaluation results of the batteries in which the positive electrode used in Example 1-1 was changed. As an electrolyte for a non-aqueous electrolyte battery, a non-aqueous electrolyte No. 1 is used. Using 5, 9, 12, 19, 33, or 34, the cycle characteristics, internal resistance characteristics, and gas generation amount were evaluated in the same manner as in Example 1-1. In addition, the positive electrode body in which the positive electrode active material is LiFePO ₄ is obtained by adding 90% by mass of LiFePO ₄ powder coated with amorphous carbon to 5% by mass of polyvinylidene fluoride (PVDF) as a binder and 5% by mass of acetylene black as a conductive material. %, Further N-methylpyrrolidone was added, and the resulting paste was applied on an aluminum foil and dried. The end-of-charge voltage during battery evaluation was 4.1 V, and the end-of-discharge voltage was 2.5 V. In Examples 5-1 to 5-4 and Comparative Example 5-2, the values of the cycle characteristics, internal resistance characteristics, and gas generation amount of the batteries are the same as those of the electrolyte solution No. This is a relative value when the discharge capacity retention rate after the cycle test, the internal resistance, and the gas generation amount associated with the cycle characteristic evaluation of the laminate cell produced using No. 33 are each 100 (Comparative Example 5-1).

As described above, in any example using LiCoO ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , and LiFePO ₄ as the positive electrode active material, the laminate cell using the electrolyte for the non-aqueous electrolyte battery of the present invention It was confirmed that the cycle characteristics, internal resistance characteristics, and gas generation amount were superior to the corresponding comparative examples. Therefore, by using the electrolyte for a non-aqueous electrolyte battery of the present invention, a non-aqueous electrolyte battery exhibiting excellent cycle characteristics, internal resistance characteristics, and gas generation amount suppression can be obtained regardless of the type of the positive electrode active material. It was shown that.

Further, as described above, in any example using Li ₄ Ti ₅ O ₁₂ and graphite (containing silicon) as the negative electrode active material, the laminate cell using the electrolyte solution for a non-aqueous electrolyte battery of the present invention. It was confirmed that the cycle characteristics, internal resistance characteristics, and gas generation amount were superior to the corresponding comparative examples. Therefore, by using the electrolyte for a non-aqueous electrolyte battery of the present invention, a non-aqueous electrolyte battery exhibiting excellent cycle characteristics, internal resistance characteristics, and gas generation amount suppression can be obtained regardless of the type of the negative electrode active material. It was shown that.

Claims

In a non-aqueous electrolyte for a non-aqueous electrolyte battery containing a non-aqueous solvent and a solute,
Containing at least lithium hexafluorophosphate as a solute,
Containing at least one imide salt having a phosphoryl group represented by the general formula (I),
Substantially free of bis (oxalato) borate, difluoro (oxalato) borate, tris (oxalato) phosphate, difluorobis (oxalato) phosphate, and tetrafluoro (oxalato) phosphate. An electrolyte for a non-aqueous electrolyte battery.

[Wherein R 1 to R 4 are each independently a fluorine atom or an organic group represented by —OR 5 ; R 5 is a linear or branched alkyl group, alkenyl group having 1 to 10 carbon atoms, or And at least one organic group selected from an alkynyl group, a cycloalkyl group or a cycloalkenyl group having 3 to 10 carbon atoms, and an aryl group having 6 to 10 carbon atoms, and a fluorine atom or an oxygen atom in the organic group Unsaturated bonds can also be present. M represents an alkali metal cation, an alkaline earth metal cation, or an onium cation, and m represents an integer equal to the valence of the corresponding cation. However, at least one of R 1 to R 4 represents a fluorine atom. ]
The electrolyte solution for a non-aqueous electrolyte battery according to claim 1, wherein the imide salt having a phosphoryl group represented by the general formula (I) is a compound in which R 1 to R 4 are all fluorine atoms.
The imide salt having a phosphoryl group represented by the general formula (I) is at least one group selected from hydrocarbon groups having 6 or less carbon atoms in which the organic group represented by R 5 may contain a fluorine atom. The electrolyte solution for a non-aqueous electrolyte battery according to claim 1, which is a certain compound.
In the imide salt having a phosphoryl group represented by the general formula (I), the group represented by R 5 is a methyl group, an ethyl group, a propyl group, a vinyl group, an allyl group, an ethynyl group, a 2-propynyl group, a phenyl group, Group, 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group, and 1,1,1,3,3,3-hexafluoroisopropyl The electrolyte solution for nonaqueous electrolyte batteries according to claim 1 or 3, wherein the electrolyte solution is a compound that is at least one group selected from the group.
The counter cation of the imide salt having a phosphoryl group represented by the general formula (I) is at least one counter cation selected from the group consisting of lithium ion, sodium ion, potassium ion, and tetraalkylammonium ion. 5. The electrolyte for a non-aqueous electrolyte battery according to any one of 1 to 4.
The amount of the imide salt having a phosphoryl group represented by the general formula (I) is in the range of 0.01 to 5.0% by mass with respect to the total amount of the electrolyte for a nonaqueous electrolyte battery. 6. The electrolyte solution for a non-aqueous electrolyte battery according to any one of 1 to 5.
As the solute, lithium tetrafluoroborate (LiBF 4 ), bis (fluorosulfonyl) imide lithium (LiN (FSO 2 ) 2 ), bis (trifluoromethanesulfonyl) imide lithium (LiN (CF 3 SO 2 ) 2 ) And an electrolyte solution for a non-aqueous electrolyte battery according to claim 1, comprising at least one selected from the group consisting of lithium difluorophosphate (LiPO 2 F 2 ).
The non-aqueous solvent is at least one selected from the group consisting of a cyclic carbonate, a chain carbonate, a cyclic ester, a chain ester, a cyclic ether, a chain ether, a sulfone compound, a sulfoxide compound, and an ionic liquid. 8. The non-aqueous electrolyte battery electrolyte according to any one of 1 to 7.
9. A non-aqueous electrolyte battery comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolyte battery electrolyte, wherein the non-aqueous electrolyte battery electrolyte is any one of claims 1 to 8. A non-aqueous electrolyte battery characterized by being a battery electrolyte.