Electrolyte and battery

Abstract

To provide an electrolytic solution which contains a sulfonyl imide compound such as LiFSI and reduces self-discharge at a high temperature.SOLUTION: An electrolytic solution contains: a sulfonyl imide compound represented by a following formula (1) defined by M1N(R1SO2)(R2SO2) (where M1 represents an alkali metal atom; and R1 and R2 are the same or different and each represent a fluorine atom, a C1-6 alkyl group, or a C1-6 fluoroalkyl group); and a compound represented by a following formula (2) defined by M2SiO3 (where M2 represents an alkali metal atom or an alkaline earth metal atom).SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to an electrolyte and a battery. More specifically, it relates to an electrolyte that can be suitably used as a material for batteries such as lithium-ion batteries, and a battery constructed using the same. [Background technology]

[0002] In recent years, driven by growing concern for environmental issues, there has been a shift away from fossil fuels such as oil and coal as energy resources. This has increased the importance of batteries, and demand is expected to rise. Among these, rechargeable batteries, which can be repeatedly charged and discharged, are increasingly being used not only in electronic devices such as mobile phones and laptops, but also in various fields such as automobiles and aircraft. Research and development are being conducted on various types of rechargeable batteries and the materials used in them. In particular, lithium-ion batteries, with their high capacity and light weight, are the type of rechargeable battery whose future use is most anticipated, and are the most actively researched and developed.

[0003] In the research and development of such batteries, technologies to improve battery performance are being developed. For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery comprising a positive electrode containing positive electrode active material, a negative electrode, and a non-aqueous electrolyte, wherein at least one of the positive electrode, the negative electrode, and the non-aqueous electrolyte contains a basic compound having a water content of 0.001% by mass or more and 1% by mass or less. Furthermore, regarding electrolytes, Patent Document 2 discloses a technique for improving the cycle characteristics of a battery by using an electrolyte that contains a sulfonyliimide compound of a specific structure, such as lithium bisfluorosulfonylimide (LiFSI), and another alkali metal salt containing fluorine, and Patent Document 3 discloses a technique for improving ionic conductivity in low-temperature environments by using an electrolyte solution that contains an electrolyte and a sulfonyliimide compound of a specific structure, such as lithium bisfluorosulfonylimide (LiFSI), in a predetermined ratio and contains a carbonate-based solvent. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-090859 [Patent Document 2] Japanese Patent Publication No. 2013-84591 [Patent Document 3] Japanese Patent Publication No. 2013-101900 [Overview of the project] [Problems that the invention aims to solve]

[0005] As described above, while technologies using imide-based alkali metal salts with specific structures, such as LiFSI, have been disclosed to improve battery performance, there was room for improvement in the self-discharge endurance of electrolytes containing LiFSI when stored at high temperatures.

[0006] This invention has been made in view of the above-mentioned circumstances, and aims to provide an electrolyte that contains a sulfonylime compound such as LiFSI and can suppress self-discharge at high temperatures. [Means for solving the problem]

[0007] The present inventors investigated a method for suppressing self-discharge during high-temperature storage of batteries using an electrolyte containing sulfonylimide compounds such as LiFSI, and found that self-discharge at high temperatures can be suppressed by adding a silicate of a predetermined structure to the electrolyte containing the sulfonylimide compound, thus arriving at the present invention.

[0008] This invention includes the following electrolytes, etc. [1] The following formula (1); M 1 N(R 1 SO2)(R 2 SO2)(1) (In the formula, M 1 R represents an alkali metal atom. 1 and R 2represents, identically or differently, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms. A sulfonylimide compound represented by the following formula (2); M 2 SiO3(2) (In the formula, M 2 represents an alkali metal atom or an alkaline earth metal atom.) An electrolytic solution characterized by containing a compound represented by the formula. [2] Further, M 3 PF6, M 3 BF4, M 3 PO2F2, and M 3 FSO3 (M 3 represents an alkali metal atom.) The electrolytic solution according to [1] above, characterized by containing at least one selected from the group consisting of [3] The content ratio of the compound represented by the above formula (2) is 0.001% by mass or more and less than 5.0% by mass with respect to 100% by mass of the electrolytic solution. The electrolytic solution according to [1] or [2] above, characterized by this. [4] A battery characterized by being configured to include the electrolytic solution according to any one of [1] to [3] above. [5] The above battery has the following formula (3); LiNi x Co y Mn z O2(3) (In the formula, x, y, and z are numbers that satisfy x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and 0 ≤ z ≤ 1.) A battery according to [4] above, characterized by including a positive electrode containing a composite metal oxide represented by the formula and / or LiFePO4. [6] The above battery is characterized by including a negative electrode containing a negative electrode active material containing Si and being configured as described in [4] or [5] above. [Effects of the Invention]

[0009] The electrolytic solution of the present invention has the above-described configuration and can suppress self-discharge at high temperatures. Therefore, it can be suitably used for battery materials such as lithium-ion batteries. [Embodiments for Carrying Out the Invention]

[0010] Preferred embodiments of the present invention will be described below in detail, but the present invention is not limited to the following descriptions and can be modified and applied as appropriate without changing the gist of the present invention. Furthermore, embodiments combining two or more of the individual preferred embodiments of the present invention described below also constitute preferred embodiments of the present invention.

[0011] 1. Electrolyte The electrolyte of the present invention contains a sulfonylimide compound represented by formula (1) above (hereinafter also simply referred to as the sulfonylimide compound) and a silicate represented by formula (2) above (hereinafter also simply referred to as the silicate). By combining the sulfonylimide compound with the silicate, the decomposition of the sulfonylimide compound is suppressed even when the electrolyte is stored in a high-temperature environment, and self-discharge is suppressed in batteries using such an electrolyte even when stored in a high-temperature environment. When the decomposition of the sulfonylimide compound progresses, there is a risk that the battery characteristics will deteriorate due to an increase in DC resistance (DCR) and a decrease in capacity retention rate when repeatedly charged, but batteries using such an electrolyte will also be superior in terms of DCR increase rate and capacity retention rate.

[0012] In the electrolyte described above, the concentration of the sulfonylimide compound is not particularly limited, but it is preferably 0.01 to 5.0 mol / L. This allows the effects of the present invention to be fully exhibited. More preferably, it is 0.1 to 3.0 mol / L, even more preferably 0.2 to 2.5 mol / L, even more preferably 0.4 to 2.0 mol / L, even more preferably 0.6 to 1.5 mol / L, and particularly preferably 0.8 to 1.0 mol / L. The concentration of the above sulfonylimide compound is preferably 0.01 to 5.0 mol / kg, more preferably 0.1 to 3.0 mol / kg, even more preferably 0.2 to 2.5 mol / kg, even more preferably 0.4 to 2.0 mol / kg, even more preferably 0.6 to 1.5 mol / kg, and particularly preferably 0.8 to 1.0 mol / kg.

[0013] In the above electrolyte, the content of the silicate is not particularly limited, but it is preferably 0.001% by mass or more and less than 5.0% by mass, based on 100% by mass of the electrolyte. This allows the effects of the present invention to be fully exhibited. The silicate content is more preferably 0.005 to 4.0% by mass, even more preferably 0.01 to 3.0% by mass, even more preferably 0.05 to 2.0% by mass, even more preferably 0.1 to 1.5% by mass, even more preferably 0.2 to 1.0% by mass, and particularly preferably 0.3 to 0.5% by mass.

[0014] The above electrolyte contains the above sulfonylimide compound as an electrolyte, but may also contain other alkali metal salts other than the above sulfonylimide compound and silicate. The concentration of the other alkali metal salts in the electrolyte is not particularly limited, but is preferably 0 to 2.5 mol / L. More preferably 0 to 1.5 mol / L, and even more preferably 0.2 to 1.0 mol / L. The concentration of the other alkali metal salts mentioned above is preferably 0 to 2.5 mol / kg, more preferably 0 to 1.5 mol / kg, and even more preferably 0.2 to 1.0 mol / kg.

[0015] The electrolyte solution preferably has a total alkali metal salt concentration of 0.5 to 5.0 mol / L, more preferably 0.8 to 2.5 mol / L, and even more preferably 1.0 to 1.5 mol / L. The total alkali metal salt concentration of the above sulfonylimide compound and the above other alkali metal salts is preferably 0.5 to 5.0 mol / kg, more preferably 0.8 to 2.5 mol / kg, and even more preferably 1.0 to 1.5 mol / kg.

[0016] The sulfonylimide compound is preferably present in an amount of 1 to 100 mol% relative to 100 mol% of the electrolyte (the sulfonylimide compound and the other alkali metal salts) in the electrolyte solution. This allows the effects of the present invention to be fully exhibited. More preferably, it is 5 to 90 mol%, even more preferably 10 to 80 mol%, even more preferably 20 to 80 mol%, even more preferably 40 to 80 mol%, particularly preferably 50 to 85 mol%, and particularly most preferably 50 to 80 mol%. In one embodiment, the sulfonylimide compound may be present in an amount of 70 mol% or more, 80 mol% or more, or 90 mol% or more relative to 100 mol% of the electrolyte.

[0017] The solvent in the electrolyte described above is not particularly limited, but it is preferably a non-aqueous solvent, and preferably has a water content of 10% or less. This allows the effects of the present invention to be fully exhibited. The water content is more preferably 1% or less, even more preferably 1000 ppm or less, and particularly preferably 100 ppm or less. The water content may be substantially negligible (it may be as low as 0 ppm by mass). The above moisture content can be measured using a Karl Fischer moisture analyzer.

[0018] The proportion of the non-aqueous solvent in the electrolyte is not particularly limited, but it is preferably 100 to 5000 parts by mass per 100 parts by mass of the electrolyte (the sulfonylimide compound and the other alkali metal salts), more preferably 150 to 2500 parts by mass, and even more preferably 200 to 2000 parts by mass.

[0019] The electrolyte may contain other components besides the sulfonylimide compound, silicate, other alkali metal salts, and solvent. The content of other components is not particularly limited, but is preferably 0 to 5% by mass relative to 100% by mass of the electrolyte. More preferably 0 to 3% by mass, and even more preferably 0 to 2% by mass.

[0020] The essential and optional components contained in the electrolyte of the present invention will be further described below. <Sulfonylimide compounds> The above sulfonylimide compound is given by the following formula (1); M 1 N(R 1 SO2)(R 2 SO2)(1) (In the formula, M 1 R represents an alkali metal atom. 1 and R 2 The compound is represented by (which is the same or different, and represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms).

[0021] The above M 1 Examples of alkali metals in this context include lithium, sodium, potassium, rubidium, cesium, and francium. Preferably, lithium, sodium, and potassium are used, and more preferably lithium.

[0022] The above R 1 Examples of C1-C6 alkyl groups in this context include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl (amyl), and n-hexyl groups; branched alkyl groups such as i-propyl, sec-butyl, i-butyl, t-butyl, 1-methylbutyl, 1-ethylpropyl, 2-methylbutyl, i-amyl, neopentyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl, t-amyl, 1,3-dimethylbutyl, 3,3-dimethylbutyl, and 2-ethylbutyl groups; and cyclic alkyl groups such as cyclopropyl, cyclopropylmethyl, cyclobutyl, cyclobutylmethyl, cyclopentyl, and cyclohexyl groups. Linear alkyl groups are preferred among these.

[0023] The above R 1 and R 2 The number of carbon atoms in the alkyl group is preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2.

[0024] The above R 1 and R 2 In this context, a fluoroalkyl group having 1 to 6 carbon atoms is defined as one in which at least some of the hydrogen atoms bonded to the carbon atoms of the alkyl group having 1 to 6 carbon atoms are replaced with fluorine atoms. Specific examples of the alkyl groups are as described above. Examples of fluoroalkyl groups having 1 to 6 carbon atoms include fluoromethyl, difluoromethyl, trifluoromethyl, fluoroethyl, difluoroethyl, trifluoroethyl, pentafluoroethyl, fluoropropyl, fluoropentyl, and fluorohexyl groups.

[0025] The above R 1 and R 2 The number of carbon atoms in the fluoroalkyl group is preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2.

[0026] The above R 1 and R 2 Preferably, it is a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group. More preferably, it is a fluorine atom, and the above R 1 and R 2 Preferably, at least one of them is a fluorine atom. 1 and R 2 A configuration in which both atoms are fluorine atoms is one of the preferred embodiments of the present invention.

[0027] Examples of the above-mentioned sulfonylimide compounds include lithium bis(fluorosulfonyl)imide (hereinafter also referred to as LiFSI), lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium (fluorosulfonyl)(pentafluoroethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, potassium bis(fluorosulfonyl)imide, potassium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, potassium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide. Among these, lithium bis(fluorosulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, and lithium (fluorosulfonyl)(pentafluoroethylsulfonyl)imide are preferred, and lithium bis(fluorosulfonyl)imide is more preferred.

[0028] <Silicate> The above silicate is given by the following formula (2); M 2 SiO3(2) (In the formula, M 2 This is a compound represented by (where represents an alkali metal atom or an alkaline earth metal atom).

[0029] The above M 2 Examples of alkali metal atoms include lithium, sodium, potassium, rubidium, cesium, and francium. Examples of alkaline earth metal atoms include beryllium, magnesium, calcium, strontium, barium, and radium. M 2 M in SiO3 2 The number of is M 2 It depends on the valence of M. 2 If is an alkali metal atom, the above silicate is M 2 This results in 2SiO3. The above M 2 Preferably, these are lithium, sodium, potassium, magnesium, and calcium.

[0030] Specific examples of the above-mentioned silicates include Li2SiO3, Na2SiO3, K2SiO3, Rb2SiO3, Cs2SiO3, Fr2SiO3, BeSiO3, MgSiO3, CaSiO3, SrSiO3, BaSiO3, and RaSiO3. Among these, Li2SiO3, Na2SiO3, K2SiO3, MgSiO3, and CaSiO3 are preferred.

[0031] <Other alkali metal salts> Other alkali metal salts are not particularly limited as long as they are alkali metal salts other than the sulfonylimide compounds and silicates mentioned above, but examples include: alkali metal salts of fluorophosphates such as LiPF6 and LiPO2F2; alkali metal salts of fluorosulfonic acids such as LiFSO3; alkali metal salts of trifluoromethanesulfonic acids such as LiCF3SO3; alkali metal salts of perfluoroalkanesulfonylmethides such as LiC(CF3SO2)3; LiPF a (C m F 2m+1 ) 6-a Fluorophosphates such as (0≦a≦6, 1≦m≦2); alkali metal perchlorates such as LiClO4; LiBF b (C n F 2n+1 ) 4-b Examples include fluoroborates such as (0≦b≦4, 1≦n≦2); alkali metal salts of oxalatoborates such as LiBOB; cyanoborates such as lithium tetracyanoborate; and alkali metal salts such as LiAsF6, LiI, and LiSbF6.

[0032] Other alkali metal salts are preferably M 3 PF6, M 3 BF4, M 3 PO2F2 or M 3 FSO3(M 3 represents an alkali metal atom. ) and M 3 PF6, M 3 BF4, M 3PO2F2 and M 3 A form comprising at least one selected from the group consisting of FSO3 is one preferred embodiment of the present invention. More preferably as other alkali metal salts, M 3 It's PF6. Specific examples and preferred forms of the alkali metal atoms are the same as those of the alkali metal atoms in the sulfonylimide compound described above.

[0033] <Solvent> The solvent in the electrolyte of the present invention is not particularly limited as long as it can dissolve the above-mentioned electrolyte (sulfonylimide compound and other alkali metal salts), silicate, and other components described later, but it is preferably a non-aqueous solvent. Non-aqueous solvents include: linear carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and chloroethylene carbonate; ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane; lactones such as γ-butyrolactone, γ-valerolactone, and α-methyl-γ-butyrolactone; and ethyl acetate. Examples include linear carboxylic acid esters such as methyl propionate and methyl butyrate; fluorinated cyclic carbonates such as fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, tetrafluoroethylene carbonate, and 4-fluoro-5-methylethylene carbonate; fluorinated linear carbonates such as trifluorodimethyl carbonate, trifluorodiethyl carbonate, and trifluoroethylmethyl carbonate; and linear nitriles such as acetonitrile, propionitrile, succinonitrile, and adiponitrile. These solvents may be used individually or as a mixture of two or more. Preferably, the solvents are dimethyl carbonate, diethyl carbonate, ethyl methyl carbonates, and linear carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and cyclic carbonates such as 4,5-difluoroethylene carbonate.

[0034] <Other ingredients> Other components in the electrolyte of the present invention are components other than the sulfonylimide compound, silicate, other alkali metal salts, and solvent, and are not particularly limited, but include, for example, carbonate compounds such as vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, 2-vinyl ethylene carbonate, phenylethylene carbonate, and erythritol carbonate; 1,3-propanesartone, 1,4-butanesartone, 1,5-pentanesartone, 1,4-hexansartone, and 4,6-hexansartone. Sulfonic acid esters such as butansartone, methyl methanesulfonate, methyl benzenesulfonate, and methyl trifluoromethanesulfonate; sulfone compounds such as sulfolane, 3-methylsulfolane, ethylmethylsulfone, diphenylsulfone, and bis(4-fluorophenyl)sulfone; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic acid anhydride, and cyclopentanetetracarboxylic acid dianhydride. Substances, carboxylic acid anhydrides such as phenylsuccinic anhydride; nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylsucciimide; sulfamic acid (amidosulfuric acid, H3NSO3); sulfamate salts (alkali metal salts such as lithium salt, sodium salt, potassium salt; alkaline earth metal salts such as calcium salt, strontium salt, barium salt; manganese salt, copper salt, zinc salt, iron salt, cobalt) Examples include salts, other metal salts such as nickel salts; ammonium salts; guanidine salts, etc.; phosphates such as monofluorophosphates and difluorophosphates; fluorosulfonic acid compounds such as lithium fluorosulfonate (LiFSO3), sodium fluorosulfonate (NaFSO3), potassium fluorosulfonate (KFSO3), and magnesium fluorosulfonate (Mg(FSO3)2); hydrocarbon compounds such as heptane, octane, cycloheptane, cyclohexylbenzene, and amylbenzene. One or more of these can be used.

[0035] 2.Battery The electrolyte of the present invention has the above-described configuration and can sufficiently suppress self-discharge even when stored in a high-temperature environment, making it suitable for use as a battery material such as lithium-ion batteries. The present invention also includes a battery configured with the electrolyte of the present invention. Preferably, the above-mentioned battery is a battery comprising a positive electrode and a negative electrode, more preferably a separator impregnated with the electrolyte of the present invention is provided between the positive electrode and the negative electrode, and even more preferably these are housed in an outer case.

[0036] The shape of the battery according to the present invention is not particularly limited, and any conventionally known battery shape, such as cylindrical, prismatic, laminated, coin-type, or large, can be used. Furthermore, when used as a high-voltage power supply (several tens to several hundred volts) for electric vehicles, hybrid electric vehicles, etc., it can also be configured as a battery module by connecting individual batteries in series.

[0037] The above-mentioned battery is preferably an alkali metal battery, and an alkali metal battery configured with the electrolyte of the present invention is also one of the present inventions. The above-mentioned battery is more preferably a secondary battery, and a form in which the above-mentioned battery is a lithium-ion secondary battery is one of the preferred embodiments of the present invention.

[0038] The positive electrode constituting the above-mentioned battery is not particularly limited, but it is a positive electrode active material composition containing a positive electrode active material, a conductive additive, a binder, and a dispersion solvent, which is supported on a positive electrode current collector and is usually formed into a sheet.

[0039] As a method for manufacturing the positive electrode, for example, a method of applying a positive electrode active material composition to a positive electrode current collector by a doctor blade method or the like, or immersing the positive electrode current collector in the positive electrode active material composition and then drying; a method of kneading and molding the positive electrode active material composition, drying the obtained sheet, joining it to the positive electrode current collector via a conductive adhesive, pressing, and drying; a method of applying or casting a positive electrode active material composition added with a liquid lubricant onto a positive electrode current collector, molding it into a desired shape, removing the liquid lubricant, and then stretching it in a uniaxial or multi-axial direction; and the like can be mentioned.

[0040] The material of the positive electrode current collector is not particularly limited, and for example, conductive metals such as aluminum, aluminum alloy, SUS (stainless steel), and titanium can be used. Among them, aluminum is preferable from the viewpoints of being easy to process into a thin film and being inexpensive.

[0041] As the positive electrode active material, it is only necessary that it can occlude and release ions, and conventionally known positive electrode active materials are used. Specifically, M 4 CoO2, M 4 NiO2, M 4 MnO2, M 4 Ni x Co y Mn z O2 and M 4 Ni x Co y Al z O2 (x, y, z are numbers satisfying x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1.) such as composite metal oxides such as ternary oxides, M 4 p Ni q Mn (2-q) O4 (0.9 ≤ p ≤ 1.1, 0 < q < 1) nickel manganate, M 4 APO4 (A = Fe, Mn, Ni, Co) and other compounds having an olivine structure, a solid solution material incorporating a plurality of transition metals (electrochemically inert layered M 4 2MnO3 and electrochemically active layered M 4 M”O ([M” = transition metals such as Co, Ni, etc.] solid solution) (M 4Examples of positive electrode active materials include alkali metal ions (where ) and others. These positive electrode active materials may be used individually or in combination of multiple materials. The positive electrode active material is given by the following formula (3); LiRing x Co y Mn z O2(3) A composite metal oxide and / or LiFePO4 represented by the formula (wherein x, y, and z are numbers satisfying x+y+z=1, 0≦x≦1, 0≦y≦1, and 0≦z≦1) is preferred. A battery comprising a positive electrode containing such a positive electrode active material is one preferred embodiment of the present invention.

[0042] Examples of conductive additives include acetylene black, carbon black, graphite, metal powder materials, single-walled carbon nanotubes, multi-walled carbon nanotubes, and vapor-phase carbon fibers.

[0043] Examples of binders include fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber and nitrile butadiene rubber; polyamide resins such as polyamide-imide; polyolefin resins such as polyethylene and polypropylene; poly(meth)acrylic resins; polyacrylic acid; and cellulose resins such as carboxymethylcellulose. These binders may be used individually or in combination. Furthermore, these binders may be used either dissolved in a solvent or dispersed in a solvent.

[0044] The amounts of conductive additives and binders can be adjusted as appropriate, taking into consideration the intended use of the battery (e.g., emphasis on output, emphasis on energy), ionic conductivity, etc.

[0045] When manufacturing the positive electrode, solvents used in the positive electrode active material composition include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetonitrile, acetone, ethanol, ethyl acetate, and water. These solvents may be used in combination. The amount of solvent used is not particularly limited and should be determined appropriately depending on the manufacturing method and the materials used.

[0046] The negative electrode constituting the above battery is not particularly limited, but it is a negative electrode active material composition containing a negative electrode active material, a dispersion solvent, a binder, and optionally a conductive additive, which is supported on a negative electrode current collector and is usually formed into a sheet.

[0047] Conductive metals such as copper, iron, nickel, silver, and stainless steel (SUS) can be used as the material for the negative electrode current collector. However, copper is preferred from the viewpoint of being easy to process into a thin film.

[0048] As the negative electrode active material, any conventionally known negative electrode active material used in batteries can be used, as long as it is capable of intercalating and releasing ions. Specifically, metal alloys such as alkali metals and alkali metal-aluminum alloys, graphite materials such as artificial graphite and natural graphite, carbon materials such as mesophase calcined bodies made from coal and petroleum pitch, non-graphitizable carbon, Si-based negative electrode materials such as Si, Si alloys, and SiO, and Sn-based negative electrode materials such as Sn alloys can be used.

[0049] The same manufacturing method as for the positive electrode can be used for the negative electrode. Furthermore, the conductive additives, binders, and solvents used for material dispersion during the negative electrode manufacturing process are the same as those used for the positive electrode.

[0050] A separator is positioned to separate the positive and negative electrodes. The separators that make up the above-mentioned battery are not particularly limited, and commonly used separators can be used. Examples of separators include porous sheets made of polymers capable of absorbing and retaining electrolytes (e.g., polyolefin-based microporous separators and cellulose-based separators), nonwoven fabric separators, and porous metal bodies. Among these, polyolefin-based microporous separators are preferred because they are chemically stable against organic solvents.

[0051] Examples of materials for the porous sheet mentioned above include polyethylene, polypropylene, and laminates having a three-layer structure of polypropylene / polyethylene / polypropylene.

[0052] Examples of materials for the nonwoven fabric separator include cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, and glass. Depending on the mechanical strength required for the electrolyte layer, these example materials can be used individually or in combination. [Examples]

[0053] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by weight" and "%" means "mass%".

[0054] Examples 1-10, Comparative Examples 1, 2 Storage stability evaluation Dimethyl carbonate (DMC) or a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (EC / MEC = 3 / 7 (vol / vol)) was used as the solvent. LiFSI (manufactured by Nippon Shokubai Co., Ltd.) and LiPF6 (manufactured by Stella Chemifa Co., Ltd.) were added as electrolytes, and silicates were added as additives to achieve the composition shown in Table 1. After stirring for 24 hours, insoluble matter was filtered out to prepare the electrolyte. The electrolyte was analyzed immediately after preparation (initial), after storage at 40°C for 1 month, and after storage at 40°C for 3 months. The electrolyte was then analyzed by anion ion chromatography under the following conditions: F - SO4 2- The amount was measured and its storage stability was evaluated. The results are shown in Table 1. (Anion Ion Chromatography Measurement) The electrolyte solution was diluted 100-fold with ultrapure water to obtain a measurement solution. Using an ion chromatography system ICS-3000 (manufactured by Dionex Japan Corporation), the fluoride ions (F - ) and sulfate ions (SO4 2- ) contained in the electrolyte solution were measured under the following measurement conditions. Measurement Conditions Separation Mode: Ion Exchange Eluent: 7 - 18 mM KOH Aqueous Solution Detector: Conductivity Detector Column: Anion Analysis Column Ion PAC AS-17C (manufactured by Dionex Japan Corporation.)

[0055]

Table 1

[0056] From the results in Table 1, by adding silicate to the electrolyte solution, the increase in F - and SO4 2- was suppressed even when stored at 40°C for 1 month and 3 months. This effect is considered to be due to the improvement in the stability of fluorosulfonyl ions in LiFSI by silicate.

[0057] Examples 11 - 21, Comparative Examples 3 - 7 (1) Fabrication of Laminate Battery A ternary cathode (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, manufactured by Umicore), acetylene black (Denka: Denka Black), graphite (Nippon Carbon: SP270), and polyvinylidene fluoride (PVdF, manufactured by Kuraray Co., Ltd., product number: L7208) were weighed at a mass ratio of 100:3:3:3 and dispersed in NMP to prepare a slurry. The prepared slurry was applied to one side of an aluminum foil (coating weight 19.8 mg / cm 2 ) ) and dried and roll-pressed to fabricate a cathode. A commercially available artificial graphite: carbon fiber (VGCF): styrene butadiene rubber (SBR): carboxymethyl cellulose (CMC) = 100:2:1:1 composition (mass ratio) aqueous slurry was prepared and applied to one side of a copper foil (coating weight 9.8 mg / cm 2 ), dried, and roll-pressed to fabricate a negative electrode. The obtained positive electrode was cut with an effective area of 12 cm 2 , the negative electrode was 13.44 cm 2 in size, the polarity lead-out leads were welded by ultrasonic waves, opposed with a 25-μm polyethylene (PE) separator, and three sides were sealed with a laminated exterior. 700 μL of the following electrolyte was injected from the unsealed side to fabricate a 30-mAh lithium-ion battery. The electrolyte used was a mixture of EC / MEC = 3 / 7 (vol / vol) solvent with LiFSI, LiPF6, and silicate added in the ratios shown in Table 2. After injection, constant current charging was performed at 3 mA for 3 hours, one piece was cracked, and degassing was carried out by re-vacuum sealing. After the cell after degassing was stored at 25°C for 48 hours, it was charged and discharged under the following conditioning conditions to complete the evaluation battery. [Conditioning Conditions] First cycle Charge: 3 mA 4.2V constant current constant voltage charging 0.3 mA termination ⇒ Discharge: 6 mA discharge 2.75V termination Second cycle Charge: 15 mA 4.2V constant current constant voltage charging 0.6 mA termination ⇒ Discharge: 6 mA discharge 2.75V termination Third cycle Charge: 15 mA 4.2V constant current constant voltage charging 0.6 mA termination ⇒ Discharge: 30 mA discharge 2.75V termination

[0058] (2) Characteristic Evaluation Using the completed battery obtained in (1) above, OCV measurement and DCR measurement after high-temperature storage were performed by the following methods. The results are shown in Table 2. [OCV after High-Temperature Storage] The completed batteries were fully charged by constant current and constant voltage charging at 30mA, 4.2V, and 0.6mA termination. After full charge, the open circuit voltage (OCV) of the cells was measured, and the cells were stored at 60°C for 28 days. After 28 days of storage, the OCV was measured again after being stored at 25°C for 4 hours, and the initial and ΔV after 28 days of storage at 60°C were calculated as self-discharge.

[0059] <dcr> The completed battery was fully charged by constant current and constant voltage charging at 30mA, 4.2V, and 0.6mA termination. The DCR was measured at 25°C from the fully charged state. For the DCR measurement, after waiting 30 minutes after full charge completion, the battery was discharged at 6mA (0.2C) for 10 seconds. After waiting another 30 minutes, it was discharged at 30mA (1C) for 10 seconds. After waiting another 30 minutes, it was discharged at 90mA (3C) for 10 seconds. An IV line was created from the relationship between the voltage difference and current immediately before the start of discharge and 10 seconds after the start of discharge at each discharge current, and the slope of the line was calculated as the DCR. For batteries after DCR measurement, a 45°C cycle test was performed for 500 cycles, and the capacity retention rate after 500 cycles was calculated as: Capacity after 500 cycles / Initial capacity × 100. After 500 cycles, the DCR was measured at 25°C, as in the initial measurement. The cycle conditions were as follows: Charging: 4.2V 30mA (1C) 0.6mA (0.05C) termination, 10-minute rest ⇒ Discharging: 30mA (1C) 2.75V termination, 10-minute rest.

[0060] [Table 2]

[0061] As shown in Table 2, the ΔV increases as the LiFSI concentration in the electrolyte increases, and self-discharge increases. However, by using silicate, the ΔV decreases, and self-discharge is suppressed. Furthermore, the use of silicates improved the volume retention rate after the cycle test and reduced the rate of increase in DCR after the cycle test. Electrolytes with only LiPF6 as the supporting salt composition exhibited low self-discharge even without silicate addition, and the effect of adding silicate to these electrolytes on suppressing self-discharge was small. Furthermore, the improvement in capacity retention rate and DCR increase rate after 500 cycles was also small. The mechanism by which the inclusion of silicates in the LiFSI-containing electrolyte suppresses self-discharge is presumed to be due to the improved storage stability of fluorosulfonyl ions in the electrolyte, thereby suppressing electron transfer due to side reactions of decomposition products during battery storage.

[0062] Examples 22-26, Comparative Example 8 The positive electrode active material is a commercially available LiNi 0.8 Mn 0.1 Co 0.1 The positive electrode was created under the same conditions as above, except that the O2 was changed. Coating weight: 15.8 mg / cm 2 The negative electrode was created with the same composition as above, except for the change. Laminate cells were prepared using these positive and negative electrodes and an electrolyte solution prepared by adding LiFSI, LiPF6, and silicate in the proportions shown in Table 3 to an EC / MEC = 3 / 7 (vol / vol) mixed solvent. The same OCV and DCR measurements were then performed after high-temperature storage as described above. The results are shown in Table 3.

[0063] [Table 3]

[0064] From the results in Table 3, LiNi 0.8 Mn 0.1 Co 0.1 Even when using O2, self-discharge was suppressed by adding silicate to the electrolyte. It was found that even a silicate addition concentration of 0.005% by mass can suppress self-discharge.

[0065] Examples 27-29, Comparative Examples 9, 10 (1) Making laminated batteries The positive electrode active material was changed to commercially available LiFePO4, and acetylene black (HS-100) and PVdF (Kureha #L7208) were weighed in a composition (mass) ratio of 100:9:6 and dispersed in NMP to create a slurry. The prepared slurry was coated onto one side of aluminum foil (coating weight 20.20 mg / cm²). 2 The cathode was fabricated by drying and roll pressing. A negative electrode slurry with the same composition as above was applied at a coating weight of 8.8 mg / cm³. 2 The negative electrode plate was fabricated by coating, drying, and roll pressing. A 25mAh laminate battery was fabricated using the prepared positive and negative electrodes and an electrolyte solution prepared by adding LiFSI, LiPF6, and silicate in the proportions shown in Table 4 to an EC / MEC = 3 / 7 (vol / vol) mixed solvent, using the same materials and method as described above. After injecting the electrolyte, the cells were charged at a constant current of 2.5 mA for 3 hours. One cell was then split open and resealed under vacuum to remove the gas. After degassing, the cells were stored at 25°C for 48 hours, and then charged and discharged under the following conditioning conditions to complete the evaluation battery. [Conditioning conditions] Cycle 1: Charging: 2.5mA 3.6V Constant current constant voltage charging, terminates at 0.25mA ⇒ Discharging: 5mA Discharge terminates at 2.0V Cycle 2: Charging: 12.5mA 3.6V Constant current constant voltage charging, terminates at 0.5mA ⇒ Discharging: 5mA Discharge terminates at 2.0V Cycle 3: Charging: 12.5mA 3.6V Constant current constant voltage charging, terminates at 0.5mA ⇒ Discharging: 25mA Discharge terminates at 2.0V

[0066] (2) Characterization Using the completed batteries obtained in (1) above, OCV, capacity retention rate, and DCR measurements were performed after high-temperature storage using the following method. The results are shown in Table 4. <OCV and volume retention rate after high-temperature storage> The completed batteries were charged and discharged under the following conditions (25°C) to confirm their initial capacity. Charging: 3.6V 25mA constant current constant voltage charging, terminates at 0.5mA ⇒ Discharging: 2.5mA 2.0V termination Batteries with pre-measured initial capacity were charged to full capacity using a constant current and constant voltage of 25mA, 3.6V, and 0.5mA termination. The over-current voltage (OCV) after full charge was measured, and the batteries were stored at 60°C for 28 days. After storage at 25°C for 4 hours, the cell OCV was measured, and the initial and post-28-day storage ΔV values ​​were calculated as self-discharge. Batteries stored at 60°C for 28 days and then subjected to OCV measurement were discharged at a constant current of 2.5mA with a termination voltage of 2.0V. The remaining capacity after 28 days of storage at 60°C was then measured. The capacity retention rate was calculated as: remaining capacity / initial capacity × 100.

[0067] <dcr> The completed battery was fully charged by constant current and constant voltage charging at 25mA, 3.6V, and 0.5mA termination. The DCR was measured at 25°C from the fully charged state. For the DCR measurement, after waiting 30 minutes after full charge completion, the battery was discharged at 5mA (0.2C) for 10 seconds. After waiting another 30 minutes, it was discharged at 25mA (1C) for 10 seconds. After waiting another 30 minutes, it was discharged at 75mA (3C) for 10 seconds. An IV line was created from the relationship between the voltage difference and current immediately before the start of discharge and 10 seconds after the start of discharge at each discharge current, and the slope of the line was calculated as the DCR. For batteries after DCR measurement, a 45°C cycle test was performed for 500 cycles, and the capacity retention rate after 500 cycles was calculated as: Capacity after 500 cycles / Initial capacity × 100. After 500 cycles, the DCR was measured at 25°C, as in the initial measurement. The cycle conditions were as follows: Charging: 3.6V 25mA (1C) 0.5mA (0.05C) to termination, 10-minute rest ⇒ Discharging: 25mA (1C) 2.0V to termination, 10-minute rest.

[0068] [Table 4]

[0069] Because the LiFePo4 cathode exhibits a flat discharge voltage, the reduction effect of silicate addition on ΔV is smaller compared to ternary cathodes, but a reduction effect was still observed. The addition of silicate significantly improved the volume retention rate after 28 days of storage at 60°C compared to the case without silicate, confirming that self-discharge during storage at 60°C was suppressed. Even when the supporting salt composition consisted solely of LiFSI, the same self-discharge suppression effect as with mixed salts was obtained.

[0070] Examples 30, 31, Comparative Example 11 A silicon dioxide (SiO) / graphite composite material (manufactured by BTR, product number: BSO-600) as the negative electrode active material, conductive additives (manufactured by Showa Denko K.K., product number: VGCF-H® and (manufactured by Imerys, product number: Super-P®), styrene-butadiene rubber (SBR, binder) and carboxymethylcellulose (CMC, binder) were dispersed in ultrapure water to prepare a negative electrode mixture slurry (negative electrode active material: VGCF:Super-P:SBR:CMC = 90:2:3:3:2 (solid content mass ratio)). Subsequently, the obtained negative electrode mixture slurry was applied to copper foil (negative electrode current collector, manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., thickness 15 μm) with a dry coating weight of 6.8 mg / cm³. 2 The coating was applied to one side using an applicator and dried on an 80°C hot plate for 10 minutes. It was then dried in a 100°C vacuum drying oven for 12 hours. Finally, it was pressed using a roll press to achieve a density of 1.3 g / cm³. 3 A sheet-like negative electrode was obtained by press-molding until it reached this state. A 30mAh lithium-ion battery was fabricated using the same positive electrode and negative electrode as in Examples 22-26, and the same method as described above. The electrolyte was prepared by dissolving LiFSI, LiPF6, and silicate in a mixed solvent of EC / fluoroethylene carbonate (FEC) / EMC = 2 / 1 / 7 (vol / vol) at the concentrations shown in Table 5. OCV and DCR measurements were performed after high-temperature storage in the same manner as in Example 22. The results are shown in Table 5.

[0071] [Table 5]

[0072] As shown in Table 5, even when using a negative electrode active material containing Si, self-discharge was suppressed by adding silicate to the electrolyte.< / dcr> < / dcr>

Claims

1. The following formula (1); M １ N(R １ SO ２ )(R ２ SO ２ )(1) (In the formula, M １ R represents an alkali metal atom. １ and R ２ represents a fluorine atom. ) A sulfonylimide compound represented by the following formula (2); M ２ Yes ３ (2) (In the formula, M ２ An electrolyte for secondary batteries characterized by containing a compound represented by (where represents an alkali metal atom or an alkaline earth metal atom).

2. Furthermore M ３ PF ６ M ３ BF ４ M ３ PO ２ F ２ and M ３ FSO ３ (M ３ The electrolyte for a secondary battery according to claim 1, characterized by containing at least one selected from the group consisting of (where represents an alkali metal atom).

3. The electrolyte for secondary batteries according to claim 1, characterized in that the content of the compound represented by formula (2) is 0.001% by mass or more and less than 5.0% by mass, based on 100% by mass of the electrolyte.

4. A battery characterized by comprising an electrolyte for a secondary battery as described in any one of claims 1 to 3.

5. The aforementioned battery is given by the following formula (3); L)) ｘ Co ｙ Mn ｚ O ２ (3) (wherein the formula x, y, and z are numbers satisfying x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and 0 ≤ z ≤ 1.) Composite metal oxides and / or LiFePO represented by this formula ４ The battery according to claim 4, characterized in that it is configured to include a positive electrode containing

6. The battery according to claim 4, characterized in that the battery comprises a negative electrode containing a negative electrode active material containing Si.

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