Electrolytic solution and method for producing same, battery and method for manufacturing same, and vehicle equipped with battery

Abstract

The present invention relates to: [1] an electrolytic solution containing a compound represented by general formula (1), a compound represented by formula (2), an electrolyte, and a nonaqueous solvent; [2] a method for producing the electrolytic solution; [3] a battery comprising a positive electrode, a negative electrode, and the electrolytic solution; [4] a method for manufacturing the battery; and [5] a vehicle equipped with the battery.

Description

Electrolyte and manufacturing method thereof, battery and manufacturing method thereof, and vehicle equipped with the battery

[0001] The present invention relates to an electrolyte and a method for manufacturing the same, a battery and a method for manufacturing the same, and a vehicle equipped with the battery.

[0002] Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been put to practical use in a wide range of applications, such as power sources for so-called small consumer devices such as mobile phones such as smartphones and laptop computers, and on-board power sources for driving electric vehicles, etc. As a means for improving the battery characteristics of non-aqueous electrolyte secondary batteries, numerous studies have been conducted in the fields of active materials for positive and negative electrodes and additives for non-aqueous electrolytes.

[0003] In recent years, lithium ion batteries have been used as non-aqueous electrolyte secondary batteries for applications such as on-board power sources for electric vehicles and mobile phones such as smartphones. Lithium ion batteries are primarily composed of a positive electrode and a negative electrode containing a material capable of absorbing and desorbing lithium, and a non-aqueous electrolyte solution consisting of a lithium salt and a non-aqueous solvent, such as a carbonate such as ethylene carbonate (EC) or propylene carbonate (PC). Known negative electrodes for lithium secondary batteries include lithium metal, metal compounds capable of absorbing and desorbing lithium (e.g., elemental metals, oxides, and alloys with lithium), and carbon materials. In particular, non-aqueous electrolyte secondary batteries using carbon materials capable of absorbing and desorbing lithium, such as coke and graphite (artificial graphite and natural graphite), have been widely used. Because the above-mentioned negative electrode materials store and release lithium and electrons at an extremely low potential, equivalent to that of lithium metal, many solvents are likely to undergo reductive decomposition, particularly at high temperatures. Regardless of the type of negative electrode material, some of the solvent in the electrolyte undergoes reductive decomposition on the negative electrode, resulting in deposition of decomposition products, gas generation, and electrode swelling, which impede the movement of lithium ions and cause problems such as a decrease in battery characteristics, particularly high-temperature storage characteristics, and battery deformation due to electrode swelling. Furthermore, lithium secondary batteries using elemental metals or oxides, such as lithium metal, its alloys, tin, or silicon, as negative electrode materials, have high initial capacity but undergo pulverization during cycling, which accelerates the reductive decomposition of non-aqueous solvents compared to negative electrodes made of carbon materials. This results in significant decreases in battery performance, such as battery capacity and high-temperature storage characteristics, particularly at high temperatures, and battery deformation due to electrode swelling.

[0004] On the other hand, as the positive electrode, for example, LiCoO ２ , LiMn ２ O ４ , LiNiO ２ , LiFePO ４It has been found that lithium secondary batteries using LiNi, etc., undergo partial oxidative decomposition of the non-aqueous solvent in the non-aqueous electrolyte at the interface between the positive electrode material and the non-aqueous electrolyte in a charged state, generating decomposition products and gases that inhibit the desired electrochemical reactions of the battery, resulting in a deterioration in the electrochemical characteristics when used at high temperatures. ０．５ Mn １．５ O ４ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , Li ２ MnO ３ and LiMO ２ Materials capable of absorbing and releasing lithium, such as solid solutions with lithium ions (where M is a transition metal such as Co, Ni, Mn, or Fe), store and release lithium and electrons at a more noble voltage, and therefore many solvents have the potential to undergo oxidative decomposition, particularly at high temperatures. Regardless of the type of positive electrode material, the solvent in the electrolyte undergoes partial oxidative decomposition on the positive electrode, resulting in deposition of decomposed products and gas generation, which hinders the movement of lithium ions and reduces battery characteristics such as high-temperature storage characteristics.

[0005] Patent Document 1 describes an electrolyte for a lithium secondary battery containing a non-aqueous organic solvent, a lithium salt, and a specific phosphorus compound, and discloses that the electrolyte suppresses swelling of the battery, i.e., gas generation, after high-temperature storage. Patent Document 2 describes a battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains a specific cyclic sulfate ester, and when narrow spectra of sulfur atoms are measured on the surface of the negative electrode by X-ray photoelectron spectroscopy and peak separation is performed for the S2p orbital, the area ratio of Peak 1 observed in the 168.4 eV to 171.1 eV region to Peak 2 observed in the 166.3 eV to 169.0 eV region is 10 to 150, and discloses that the battery can suppress an increase in battery resistance after high-temperature storage. Patent Document 3 describes an electrolyte for a lithium secondary battery containing a non-aqueous organic solvent, a lithium salt, and a compound containing a difluorophosphorous acid structure represented by a specific chemical formula, and discloses that the electrolyte improves battery characteristics. Patent Document 4 describes a non-aqueous electrolyte containing a specific cyclic sulfate ester compound, and discloses that the electrolyte is excellent in maintaining the open circuit voltage when the battery is stored in a charged state.

[0006] International Publication No. WO 2018 / 062719 Japanese Patent Application Laid-Open No. 2022-169802 European Patent Application Publication No. 3522287 International Publication No. WO 2012 / 053644

[0007] However, the nonaqueous electrolyte secondary battery using the electrolyte solution described in Patent Document 1 has room for improvement in terms of suppressing gas generation after high-temperature storage. Furthermore, the nonaqueous electrolyte secondary batteries using the nonaqueous electrolyte solutions described in Patent Documents 2 and 4 do not disclose or suggest suppressing gas generation after high-temperature storage. Furthermore, according to the inventors' investigations, the lithium secondary battery using the electrolyte solution described in Patent Document 3 does not have a sufficient effect of suppressing gas generation.

[0008] An object of the present invention is to provide an electrolyte solution that can suppress gas generation after high-temperature storage when used in a battery, a battery using the electrolyte solution, methods for manufacturing the battery and the battery, and a vehicle equipped with the battery.

[0009] As a result of intensive research to solve the above problems, the present inventors have found that gas generation after high-temperature storage can be suppressed when an electrolytic solution containing a compound represented by the following general formula (1), a compound represented by the following formula (2), an electrolyte, and a non-aqueous solvent is used, and have completed the present invention.

[0010] That is, the gist of the present invention relates to the following [1] to

[14] : [1] An electrolytic solution containing a compound represented by the following general formula (1), a compound represented by the following formula (2), an electrolyte, and a non-aqueous solvent. (L represents a linear or branched alkylene group having 1 to 6 carbon atoms.) [2] The electrolyte solution according to [1], wherein the content of the compound represented by formula (1) in the electrolyte solution is 0.001 to 10% by mass. [3] The electrolyte solution according to [1] or [2], wherein the content of the compound represented by formula (2) in the electrolyte solution is 0.001 to 8.0% by mass. [4] The electrolyte solution according to any one of [1] to [3], wherein the mass ratio [(1):(2)] of the compound represented by formula (1) to the compound represented by formula (2) in the electrolyte solution is 94:6 to 3:97. [5] The electrolyte solution according to any one of [1] to [4], further comprising at least one carbonate compound selected from vinylene carbonate and fluoroethylene carbonate. [6] The electrolyte solution according to [5], wherein the carbonate compound is vinylene carbonate. [7] The electrolyte solution according to [5] or [6], wherein the total content of the vinylene carbonate and the fluoroethylene carbonate in the electrolyte solution is 0.001 to 10 mass%. [8] The electrolyte solution according to any one of [5] to [7], wherein the mass ratio of the total content of the vinylene carbonate and the fluoroethylene carbonate to the content of the compound represented by general formula (1) in the electrolyte solution (total [g] of vinylene carbonate and fluoroethylene carbonate / [g] of compound represented by general formula (1)) is 0.01 to 100. [9] The electrolyte solution according to any one of [1] to [8], wherein L in general formula (1) is an ethylene group.

[10] The electrolyte solution according to any one of [1] to [9], further comprising at least one anion-containing compound selected from the group consisting of an anion-containing compound having a P═O bond and a P—F bond, an anion-containing compound having an S═O bond and an S—X bond, where X represents a heteroatom, and an oxalate anion-containing compound.

[11] The electrolyte solution according to

[10] , wherein the anion-containing compound is at least one selected from the group consisting of a compound containing a difluorophosphate anion, a compound containing a fluorosulfonate anion, a compound containing a fluorosulfonylimide anion, a compound containing an alkylsulfate anion, a compound containing a bis(oxalato)borate anion, a compound containing a difluorooxalatoborate anion, and a compound containing a difluorobis(oxalato)phosphate anion.

[12] A method for producing an electrolyte solution, comprising the step of dissolving a compound represented by the following general formula (1), a compound represented by the following formula (2), and an electrolyte in a non-aqueous solvent: (L represents a linear or branched alkylene group having 1 to 6 carbon atoms.)

[13] A battery comprising a positive electrode, a negative electrode, and the electrolyte solution according to any one of [1] to

[11] .

[14] The battery according to

[13] , wherein the positive electrode contains a lithium transition metal compound.

[15] A method for manufacturing a battery, comprising the steps of housing the positive electrode and the negative electrode in a container, and injecting the electrolyte solution according to any one of [1] to

[11] into the container.

[16] A vehicle equipped with the battery according to

[13] or

[14] .

[0011] According to the electrolytic solution of the present invention, it is possible to provide an electrolytic solution capable of suppressing gas generation after high-temperature storage, and a battery using the electrolytic solution.

[0012] Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the following description is an example (typical example) of an embodiment of the present invention, and the present invention is not limited to these contents. Furthermore, the present invention can be carried out with any modifications within the scope of the gist thereof. In this specification, "α to β" means a numerical range of α or more and β or less.

[0013] <1. Electrolyte Solution> The electrolyte solution according to this embodiment contains a compound represented by general formula (1), a compound represented by formula (2), an electrolyte, and a non-aqueous solvent. The electrolyte solution according to this embodiment is preferably a non-aqueous electrolyte solution. (L represents a linear or branched alkylene group having 1 to 6 carbon atoms.) Each component will be described below.

[0014] The reason why the electrolyte solution of the present invention suppresses gas generation after high-temperature storage is unclear, but is thought to be as follows. The compound represented by general formula (1) has a fluorinated phosphorous acid structure, and the compound represented by formula (2) has a structure in which two cyclic sulfate esters are bonded. It is believed that the fluorinated phosphorous acid structure and the cyclic sulfate ester of the compound represented by general formula (1) and the compound represented by formula (2) decompose to form a mixed coating on the negative electrode active material. It is also presumed that a portion of these decomposition products reaches the positive electrode and forms a mixed coating on the positive electrode active material, thereby preventing decomposition of the non-aqueous solvent on the surface of the negative electrode active material and / or the surface of the positive electrode active material, thereby significantly suppressing gas generation. The present inventors have found that this significant suppression of gas generation cannot be achieved by combining the compound represented by general formula (1) with a general monocyclic sulfate ester. That is, the compound represented by formula (2) in which two cyclic sulfate esters are bonded, which is one of the components of the present invention, has a structure in which the decomposition products themselves have a large molecular weight and are less likely to generate gas, and also has a structure in which the decomposition products themselves have a large molecular weight and are less likely to generate gas, and -O-S(=O) ２ Since the monocyclic sulfate ester compound has more active sites such as —O— groups and O—C bonds than the monocyclic sulfate ester compound, it is believed that it is easy to quickly and firmly form a mixed coating film with the decomposition product of the compound represented by general formula (1), thereby suppressing further decomposition of the solvent and significantly suppressing gas generation.

[0015] [1-1. Compound represented by general formula (1)]

[0016]

[0017] In the general formula (1), L represents a linear or branched alkylene group having 1 to 6 carbon atoms.

[0018] The number of carbon atoms in L is more preferably 1 to 4, and even more preferably 2 to 4. The alkylene groups described above are preferred because they tend to suppress side reactions on the surface of the electrode active material.

[0019] Specific examples of the alkylene group represented by L include a linear alkylene group selected from a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, and a hexane-1,6-diyl group, an ethane-1,1-diyl group, a propane-1,2-diyl group, a butane-1,3-diyl group, a butane-1,2-diyl group, a butane-2,3-diyl group, a pentane-1,4-diyl group, a pentane-1,5-diyl group, and a hexane-1,6-diyl group. Examples of branched alkylene groups include hexane-1,3-diyl group, pentane-1,2-diyl group, pentane-2,3-diyl group, pentane-2,4-diyl group, hexane-1,5-diyl group, hexane-1,4-diyl group, hexane-1,3-diyl group, hexane-1,2-diyl group, hexane-2,3-diyl group, hexane-2,4-diyl group, hexane-2,5-diyl group, and hexane-3,4-diyl group. Among the above-mentioned alkylene groups, a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, an ethane-1,1-diyl group, a propane-1,2-diyl group, a butane-1,3-diyl group, a butane-2,3-diyl group, and a pentane-2,4-diyl group are preferred, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, a propane-1,2-diyl group, a butane-1,3-diyl group, and a butane-2,3-diyl group are more preferred, an ethylene group, a propane-1,3-diyl group, and a butane-1,4-diyl group are even more preferred, and an ethylene group is particularly preferred.

[0020] Specific examples of the compound represented by general formula (1) include compounds represented by the following formulas (A-1) to (A-23) (referred to as compounds (A-1) to (A-23)). Note that the compound represented by general formula (1) is not limited to the following examples.

[0021]

[0022] Among these, from the viewpoint of forming a homogeneous composite coating with the compound represented by formula (2), highly symmetric compounds are preferred, and compounds (A-1) to (A-10) and (A-15) are preferred. From the viewpoint of the stability of the coating to be formed, compounds (A-2) to (A-4) and compounds (A-8) to (A-10) are more preferred, and among these, compounds (A-2) to (A-4) are even more preferred.

[0023] The content of the compound represented by general formula (1) in the electrolyte solution is usually 0.001% by mass or more from the viewpoint of suitable formation of a mixed film with the compound represented by formula (2) on the negative electrode and positive electrode and enabling the production of a battery with less gas generation after high-temperature storage, preferably 0.01% by mass or more from the viewpoint of suppressing gas generation at higher temperatures, more preferably 0.1% by mass or more from the viewpoint of quickly forming a mixed film on the active material in a high-capacity battery to suppress gas generation, more preferably 0.1% by mass or more from the viewpoint of suppressing gas generation after long-term storage, and is usually 10% by mass or less, preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 1.2% by mass or less from the viewpoint of forming a highly ion-conductive and highly durable film with the minimum necessary thickness to suppress gas generation. The content of the compound represented by general formula (1) is usually 0.001 to 10% by mass, preferably 0.01 to 5.0% by mass, more preferably 0.1 to 3.0% by mass, and even more preferably 0.2 to 1.2% by mass.

[0024] There are no particular limitations on the method for incorporating the compound represented by general formula (1) into the electrolyte solution, but examples include a method of adding the compound represented by general formula (1) to a non-aqueous solvent, etc. The identification and content measurement of the compound represented by general formula (1) are carried out by nuclear magnetic resonance (NMR) spectroscopy, gas chromatography mass spectrometry (GC / MS), etc.

[0025] [1-2. Compound represented by formula (2)]

[0026]

[0027] The content of the compound represented by formula (2) in the electrolyte solution is usually 0.001% by mass or more from the viewpoint of forming a mixed film with the decomposition product of the compound represented by general formula (1) on the negative electrode and positive electrode, thereby enabling the creation of a battery with less gas generation after high-temperature storage. From the viewpoint of suppressing gas generation at higher temperatures, it is preferably 0.01% by mass or more, more preferably 0.1% by mass or more. From the viewpoint of quickly forming a mixed film on the active material in a high-capacity battery to suppress gas generation, it is even more preferably 0.5% by mass or more. Also, from the viewpoint of suppressing gas generation by minimizing the thickness of the film to form a highly ionic conductive and durable film, it is usually 8.0% by mass or less, preferably 6.0% by mass or less, and even more preferably 4.0% by mass or less. The content of the compound represented by formula (2) is usually 0.001 to 8.0% by mass, preferably 0.01 to 8.0% by mass, more preferably 0.1 to 6.0% by mass, and even more preferably 0.5 to 4.0% by mass.

[0028] There is no particular limitation on the method for incorporating the compound represented by formula (2) into the electrolyte solution, but examples include a method in which the compound represented by formula (2) is added to a non-aqueous solvent, etc. The identification and content measurement of the compound represented by formula (2) are carried out by nuclear magnetic resonance (NMR) spectroscopy, gas chromatography mass spectrometry (GC / MS), etc.

[0029] The content of the compound represented by formula (2) in the electrolyte solution is preferably 94:6 or more in the mass ratio [(1):(2)] of the compound represented by general formula (1) to the compound represented by formula (2), more preferably 80:20 or more in the compound represented by formula (2), and particularly preferably 60:40 or more in the compound represented by formula (2). Furthermore, the mass ratio [(1):(2)] of the compound represented by general formula (1) to the compound represented by formula (2) is more preferably 3:97 or less in the compound represented by formula (2), even more preferably 10:90 or less in the compound represented by formula (2), and particularly preferably 23:77 or less in the compound represented by formula (2). This range facilitates the rapid and strong formation of a mixed coating, and can more effectively suppress gas generation after high-temperature storage. The mass ratio of the compound represented by general formula (1) to the compound represented by formula (2) [(1):(2)] is preferably 94:6 to 3:97, more preferably 80:20 to 10:90, and even more preferably 60:40 to 23:77.

[0030] [1-3. Electrolyte] The electrolyte of the electrolytic solution is preferably an alkali metal salt such as lithium, sodium, or potassium. Furthermore, when the electrolytic solution according to this embodiment is used in a lithium ion battery, the counter cation in the electrolyte is preferably a lithium cation. Furthermore, when the electrolytic solution according to this embodiment is used in a sodium ion battery, the counter cation in the electrolyte is preferably a sodium ion. Furthermore, when the electrolytic solution according to this embodiment is used in a potassium ion battery, the counter cation in the electrolyte is preferably a potassium ion.

[0031] The electrolyte content in the electrolytic solution according to this embodiment is usually greater than 5% by mass and is classified into a "main salt" that is mainly responsible for ion conduction, and an "auxiliary agent" whose content is 5% by mass or less. The electrolyte in the electrolytic solution according to this embodiment may contain, in addition to the main salt, a specific anion-containing compound as an auxiliary agent. When the electrolytic solution contains a specific anion-containing compound, its content is preferably 5% by mass or less.

[0032] [1-3-1. Main Salt] The electrolyte in the electrolytic solution according to this embodiment varies depending on the type of secondary battery to which the electrolytic solution is applied, but for example, lithium salts are preferred, and sodium salts and potassium salts are also preferred.

[0033] The lithium salt is not particularly limited, and examples thereof include lithium fluoroborates, lithium fluorophosphates, lithium tungstates, lithium carboxylates, lithium sulfonates, lithium imide salts, lithium methide salts, lithium oxalate salts, and fluorine-containing organic lithium salts.

[0034] Among these, from the viewpoint of improving low-temperature output characteristics, high-rate charge / discharge characteristics, impedance characteristics, high-temperature storage characteristics, cycle characteristics, etc., LiBF is used as a lithium fluoroborate salt. ４ LiPF as lithium fluorophosphate ６ , Li ２ P.O. ３ F, LiPO ２ F ２ LiFSO as lithium sulfonate ３ , C.H. ３ SO ３ Li; LiN(FSO) as a lithium imide salt ２ ) ２ , LiN(FSO ２ ) (CF ３ SO ２ ), LiN(CF ３ SO ２ ) ２ , LiN(C ２ F ５ SO ２ ) ２ , lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide; as lithium methide salts, LiC(FSO ２ ) ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３As the lithium oxalate salt, lithium difluorooxalatoborate, lithium bis(oxalato)borate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, lithium tris(oxalato)phosphate, etc. are preferred, and LiPF ６ , LiN(FSO ２ ) ２ , lithium bis(oxalato)borate and LiFSO ３ More preferably, one or more selected from LiPF ６ is particularly preferred.

[0035] The other compounds that can be used as an electrolyte can be used alone or in combination of two or more kinds in any ratio. The combination of two or more other compounds that can be used as an electrolyte is not particularly limited, and LiPF ６ and LiN(FSO ２ ) ２ The combination of LiPF ６ and LiBF ４ The combination of LiPF ６ and LiN(CF ３ SO ２ ) ２ The combination of LiBF ４ and LiN(FSO ２ ) ２ The combination of LiBF ４ , LiPF ６ and LiN(FSO ２ ) ２ Among these, LiPF ６ and LiN(FSO ２ ) ２ The combination of LiPF ６ and LiBF ４ and LiBF ４ , LiPF ６ and LiN(FSO ２ ) ２ The combination is preferred.

[0036] The sodium salt is not particularly limited, and examples thereof include sodium fluoroborates, sodium fluorophosphates, sodium tungstates, sodium carboxylates, sodium sulfonates, sodium imide salts, sodium methide salts, sodium oxalate salts, and fluorine-containing organic sodium salts.

[0037] Among these, from the viewpoint of improving low-temperature output characteristics, high-rate charge / discharge characteristics, impedance characteristics, high-temperature storage characteristics, cycle characteristics, etc., sodium fluoroborate, NaBF ４ Fluorophosphate sodium salt: NaPF ６ , Na ２ P.O. ３ F, NaPO ２ F ２ ; NaFSO as sodium sulfonate salt ３ , C.H. ３ SO ３ Na; NaN(FSO) as sodium imide salt ２ ) ２ , NaN(FSO ２ ) (CF ３ SO ２ ), NaN(CF ３ SO ２ ) ２ , NaN(C ２ F ５ SO ２ ) ２ , sodium cyclic 1,2-perfluoroethanedisulfonylimide, sodium cyclic 1,3-perfluoropropanedisulfonylimide; as sodium methide salts, NaC(FSO ２ ) ３ , NaC(CF ３ SO ２ ) ３ , NaC(C ２ F ５ SO ２ ) ３As the sodium oxalate salt, sodium difluorooxalatoborate, sodium bis(oxalato)borate, sodium tetrafluorooxalatophosphate, sodium difluorobis(oxalato)phosphate, sodium tris(oxalato)phosphate, etc. are preferred, and NaPF ６ , NaN(FSO ２ ) ２ , sodium bis(oxalato)borate and NaFSO ３ More preferably, one or more selected from NaPF ６ is particularly preferred.

[0038] The other compounds that can be used as an electrolyte can be used alone or in combination of two or more in any ratio. The combination of two or more other compounds that can be used as an electrolyte is not particularly limited, and NaPF ６ and NaN(FSO ２ ) ２ A combination of NaPF ６ and NaBF ４ A combination of NaPF ６ and NaN(CF ３ SO ２ ) ２ A combination of NaBF ４ and NaN(FSO ２ ) ２ A combination of NaBF ４ , NaPF ６ and NaN(FSO ２ ) ２ Among these, NaPF ６ and NaN(FSO ２ ) ２ A combination of NaPF ６ and NaBF ４ and NaBF ４ , NaPF ６ and NaN(FSO ２ ) ２ The combination is preferred.

[0039] Examples of potassium salts include those in which Li and Na in the above lithium salts and sodium salts are substituted with potassium (K).

[0040] The total content of the electrolyte in this embodiment is not particularly limited. However, from the viewpoint of ensuring proper electrical conductivity for battery operation and sufficient output characteristics, it is typically 8% by mass or more, preferably 8.5% by mass or more, more preferably 9% by mass or more, and typically 18% by mass or less, preferably 17% by mass or less, more preferably 16% by mass or less, based on the total amount of the electrolyte. The content of the electrolyte is typically 8 to 18% by mass, preferably 8.5 to 17% by mass, more preferably 9 to 16% by mass. However, the content of the compounds listed in [1-3-2. Specific Anion-Containing Compounds] below is also included in the electrolyte content. Furthermore, when a compound listed in [1-5. Auxiliary Agents] below is included in the electrolyte solution, an electrolyte other than the electrolyte listed in the main salt corresponding to the auxiliary agent must be included. The electrolyte is identified and its content measured by nuclear magnetic resonance (NMR) spectroscopy.

[0041] [1-3-2. Specific Anion-Containing Compound] The electrolyte in the electrolytic solution according to this embodiment may contain a specific anion-containing compound. The specific anion-containing compound is at least one compound selected from the group consisting of an anion-containing compound having a P═O bond and a P—F bond, an anion-containing compound having an S═O bond and an S—X bond (X represents a heteroatom), and an oxalate anion-containing compound.

[0042] The specific anion-containing compound is usually an acid or a salt, preferably a salt. The counter cation in the specific anion-containing compound is preferably an alkali metal cation such as lithium, sodium, or potassium, and more preferably a lithium cation. Furthermore, when the electrolyte solution according to the present embodiment is used in a lithium ion battery, the counter cation is preferably a lithium cation. When the electrolyte solution according to the present embodiment is used in a sodium ion battery, the counter cation is preferably a sodium ion. When the electrolyte solution according to the present embodiment is used in a potassium ion battery, the counter cation is preferably a potassium ion.

[0043] The method for adding the specific anion-containing compound to the electrolytic solution is not particularly limited, but examples thereof include a method of adding a salt of the specific anion-containing compound, a method of adding one or more selected from the group consisting of lithium salts, sodium salts, and potassium salts of the specific anion-containing compound, and a method of adding a lithium salt of the specific anion-containing compound is more preferred. Also preferred is a method of adding a raw material for the specific anion-containing compound to the electrolytic solution and generating the specific anion-containing compound in the electrolytic solution.

[0044] At least one specific anion-containing compound selected from the group consisting of an anion-containing compound having a P═O bond and a P—F bond, an anion-containing compound having an S═O bond and an S—X bond, and an oxalate anion-containing compound can be used alone or in combination of two or more in any ratio.

[0045] [1-3-3. Anion-containing compound having a P—F bond and a P═O bond] An anion-containing compound having a P—F bond and a P═O bond, which is one aspect of the specific anion-containing compound in this embodiment, is, for example, PO ３ F － monofluorophosphate anions such as PO ２ F ２ － Among these, compounds containing difluorophosphate anions are preferred from the viewpoint of the balance between the output characteristics of the battery and the protection of the electrode interface.

[0046] The method for adding an anion-containing compound having a P—F bond and a P═O bond to the electrolyte is not particularly limited, and examples include a method of adding a salt of an anion-containing compound having a P—F bond and a P═O bond, a method of adding one or more selected from lithium monofluorophosphate, lithium difluorophosphate, sodium monofluorophosphate, sodium difluorophosphate, potassium monofluorophosphate, and potassium difluorophosphate is preferred, and a method of adding at least one of lithium monofluorophosphate and lithium difluorophosphate is more preferred. Also preferred is a method of adding a raw material for an anion-containing compound having a P—F bond and a P═O bond to the electrolyte and generating an anion-containing compound having a P—F bond and a P═O bond in the electrolyte.

[0047] [1-3-4. Anion-containing compound having an S═O bond and an S—X bond] In the anion-containing compound having an S═O bond and an S—X bond, which is one aspect of the specific anion-containing compound in this embodiment, X represents a heteroatom. Examples of the heteroatom include an oxygen atom, a nitrogen atom, and a fluorine atom. Examples of the anion-containing compound having an S═O bond and an S—X bond include FSO ３ － Fluorosulfonate anions such as (FSO ２ ) ２ N － , (FSO ２ ) (CF ３ SO ２ ) N － Fluorosulfonylimide anions such as (FSO ２ ) ３ C － compounds containing fluorosulfonylmethide anions such as methylsulfate anions (CH ３ SO ４ － ), ethyl sulfate anion (C ２ H ５ SO ４ －Among these, from the viewpoint of the balance between the output characteristics of the battery and the protection of the electrode interface, compounds containing a fluorosulfonate anion, a fluorosulfonylimide anion, or an alkylsulfate anion are preferred, compounds containing a fluorosulfonate anion, a fluorosulfonylimide anion, a methylsulfate anion, or an ethylsulfate anion are more preferred, and compounds containing a fluorosulfonate anion are even more preferred.

[0048] The method for adding an anion-containing compound having an S═O bond and an S—X bond to the electrolyte is not particularly limited, but examples include a method of adding a salt of an anion-containing compound having an S═O bond and an S—X bond, and a method of adding one or more selected from lithium fluorosulfonate, lithium fluorosulfonylimide, sodium fluorosulfonate, sodium fluorosulfonylimide, potassium fluorosulfonate, potassium fluorosulfonylimide, lithium methylsulfate, lithium ethylsulfate, sodium methylsulfate, sodium ethylsulfate, potassium methylsulfate, and potassium ethylsulfate is preferred, and a method of adding one or more selected from lithium fluorosulfonate, lithium fluorosulfonylimide, lithium methylsulfate, and lithium ethylsulfate is more preferred. Also preferred is a method of adding a raw material for an anion-containing compound having an S═O bond and an S—X bond to the electrolyte and generating an anion-containing compound having an S═O bond and an S—X bond in the electrolyte.

[0049] [1-3-5. Oxalate Complex Anion-Containing Compound] The oxalate complex anion-containing compound, which is one aspect of the specific anion-containing compound in this embodiment, is not particularly limited as long as it is a compound containing an anion having an oxalate complex in the molecule. The oxalate complex anion-containing compound is a compound containing an anion of an acid in which oxalic acid is coordinated or bonded to a central atom to form a complex, and examples thereof include compounds containing a boron oxalate complex anion in which oxalic acid is coordinated or bonded to a boron atom, and a phosphorus oxalate complex anion in which oxalic acid is coordinated or bonded to a phosphorus atom.

[0050] Examples of compounds containing a boron oxalate complex anion include compounds containing a bis(oxalate)borate anion and a difluorooxalateborate anion. Examples of compounds containing a phosphorus oxalate complex anion include compounds containing a tetrafluorooxalate phosphate anion, a difluorobis(oxalate)phosphate anion, a tris(oxalate)phosphate anion, and more preferably compounds containing a difluorobis(oxalate)phosphate anion. Among these, from the viewpoint of forming a stable composite coating on the surface of the electrode, compounds containing a boron oxalate complex anion are preferred, and compounds containing a bis(oxalate)borate anion are more preferred.

[0051] There is no particular limitation on the method for adding the oxalate complex anion-containing compound to the electrolyte solution. Examples of the method include adding a salt of the oxalate complex anion-containing compound, such as lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalate)phosphate, lithium tris(oxalate)phosphate, sodium bis(oxalate)borate, sodium difluorooxalateborate, sodium tetrafluorooxalate phosphate, sodium difluorobis(oxalate)phosphate, and sodium tris(oxalate). A method of adding one or more selected from lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluorooxalatephosphate, lithium difluorobis(oxalate)phosphate, and lithium tris(oxalate)phosphate is preferred, and a method of adding one or more selected from lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluorooxalatephosphate, lithium difluorobis(oxalate)phosphate, and lithium tris(oxalate)phosphate is more preferred. Also preferred is a method of adding a raw material for an oxalate complex anion-containing compound to an electrolytic solution and generating an oxalate complex anion-containing compound in the electrolytic solution.

[0052] [Content of specific anion-containing compound] When a specific anion-containing compound is contained, the content of the specific anion-containing compound in the electrolyte solution according to this embodiment is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, from the viewpoint of improving battery characteristics, particularly suppressing gas generation after high-temperature storage, and is preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less. The content of the specific anion-containing compound is preferably 0.001 to 5% by mass, more preferably 0.01 to 4% by mass, even more preferably 0.1 to 3% by mass. Note that when two or more specific anion-containing compounds are contained, the content refers to the total content of the specific anion-containing compounds.

[0053] The electrolyte solution according to this embodiment contains a specific anion-containing compound, which improves battery characteristics, particularly suppresses gas generation after high-temperature storage. While the reason for this is unclear, the specific anion-containing compound can minimize side reactions of the electrolyte solution components on the electrode surface, and this effect is thought to be more favorable within the above-mentioned range of the content of the specific anion-containing compound. The identification and content of the specific anion-containing compound are measured by nuclear magnetic resonance (NMR) spectroscopy, ion chromatography (IC), or the like.

[0054] [Mass ratio of the compound represented by the general formula (1) to the specific anion-containing compound] When a specific anion-containing compound is contained, the mass ratio of the content of the compound represented by the general formula (1) to the content of the specific anion-containing compound, that is, the mass ratio of the compound represented by the general formula (1) [g] / specific anion-containing compound [g] is, from the viewpoint of suppressing gas after high-temperature charged storage, usually 0.01 or more, preferably 0.02 or more, more preferably 0.03 or more, even more preferably 0.04 or more, still more preferably 0.05 or more, particularly preferably 0.1 or more, even more preferably 0.3 or more, even more preferably 0.6 or more, particularly preferably 0.7 or more, and usually 100 or less, preferably 30 or less, more preferably 25 or less, even more preferably 15 or less, particularly preferably 11 or less, still more preferably 10 or less, still more preferably 8 or less, even more preferably 5 or less, even more preferably 4 or less, even more preferably 3 or less, particularly preferably 2.5 or less. The mass ratio is usually 0.01 to 100, preferably 0.02 to 30, more preferably 0.03 to 25, even more preferably 0.04 to 15, still more preferably 0.05 to 11, particularly preferably 0.1 to 10, even more preferably 0.3 to 8, still more preferably 0.6 to 5, even more preferably 0.7 to 4, still more preferably 0.7 to 3, and particularly preferably 0.7 to 2.5. Note that the content of the compound represented by general formula (1) and the specific anion-containing compound means the total content when two or more of them are contained.

[0055] When the mass ratio is within the above range, the battery characteristics, particularly gas generation after high-temperature storage, can be further suppressed. Although the reason for this is unclear, it is thought that by containing the compound represented by general formula (1) and the specific anion-containing compound within the above mass ratio range, side reactions of the components of the electrolyte solution on the electrode surface can be minimized.

[0056] [Mass Ratio of Specific Anion-Containing Compound to Main Salt] When the electrolyte in the electrolytic solution according to this embodiment contains the specific anion-containing compound, the mass ratio of the content of the specific anion-containing compound to the content of the main salt constituting the electrolyte, i.e., the mass ratio expressed as specific anion-containing compound [g] / main salt [g], is usually 0.00005 or more, preferably 0.0005 or more, more preferably 0.001 or more, even more preferably 0.005 or more, even more preferably 0.01 or more, particularly preferably 0.015 or more, and is usually 0.5 or less, preferably 0.45 or less, more preferably 0.4 or less, even more preferably 0.35 or less. The mass ratio is usually 0.00005 to 0.5, preferably 0.0005 to 0.5, more preferably 0.001 to 0.45, even more preferably 0.005 to 0.4, even more preferably 0.01 to 0.35, particularly preferably 0.015 to 0.35. When two or more specific anion-containing compounds are contained, the content of the specific anion-containing compound refers to the total content thereof.

[0057] When the mass ratio is within the above range, the battery characteristics, particularly gas generation after high-temperature storage, can be further suppressed. Although the reason for this is unclear, it is thought that by containing the specific anion-containing compound and main salt within the above mass ratio range, side reactions of the electrolyte in the battery system can be minimized.

[0058] [1-4. Non-aqueous Solvent] The electrolyte solution according to this embodiment contains a non-aqueous solvent, which is a component that dissolves the above-described electrolyte.

[0059] The non-aqueous solvent is not particularly limited, and known organic solvents can be used. Examples of the organic solvent include saturated cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone; ether compounds such as dimethoxymethane, diethoxymethane, ethoxymethoxymethane, tetrahydrofuran, 1,3-dioxane, and 1,4-dioxane; and sulfone compounds such as 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, dimethyl sulfone, ethyl methyl sulfone, and monofluoromethyl methyl sulfone. Among these, saturated cyclic carbonates, chain carbonates, and chain or cyclic carboxylic acid esters are preferred, and saturated cyclic carbonates and chain carbonates are more preferred. These non-aqueous solvents can be used alone or in combination of two or more.

[0060] The combination of two or more non-aqueous solvents is not particularly limited, and examples thereof include saturated cyclic carbonates and chain carboxylic acid esters, cyclic carboxylic acid esters and chain carbonates, and saturated cyclic carbonates, chain carbonates and chain carboxylic acid esters. Among these, the combinations of saturated cyclic carbonates and chain carbonates, and saturated cyclic carbonates, chain carbonates and chain carboxylic acid esters are preferred.

[0061] [1-4-1. Saturated Cyclic Carbonate] The saturated cyclic carbonate, which is one aspect of the non-aqueous solvent in this embodiment, typically includes a saturated cyclic carbonate having an alkylene group having 2 to 4 carbon atoms. From the viewpoint of improving the battery characteristics resulting from an improved degree of lithium ion dissociation, saturated cyclic carbonates having 2 to 3 carbon atoms are preferably used.

[0062] Examples of saturated cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate and propylene carbonate are preferred, and ethylene carbonate, which is less susceptible to oxidation and reduction, is more preferred. The saturated cyclic carbonates may be used alone or in any combination and ratio of two or more.

[0063] The content of the saturated cyclic carbonate is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present invention. In the non-aqueous solvent in the electrolyte, the content is typically 3% by volume or more, preferably 5% by volume or more, and typically 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. The content of the saturated cyclic carbonate in the non-aqueous solvent in the electrolyte is typically 3 to 90% by volume, preferably 3 to 85% by volume, and more preferably 5 to 80% by volume. By setting the content within this range, a decrease in electrical conductivity due to a decrease in the dielectric constant of the electrolyte is avoided, and the battery's large-current discharge characteristics, anode stability, and cycle characteristics tend to be in favorable ranges. The oxidation / reduction resistance of the electrolyte and stability during high-temperature storage tend to be improved. In this embodiment, "volume percent" refers to the volume at 25°C and 1 atmosphere.

[0064] [1-4-2. Chain Carbonate] As the chain carbonate, which is one aspect of the non-aqueous solvent in this embodiment, one having 3 to 7 carbon atoms is usually used, and in order to adjust the viscosity of the electrolyte solution within an appropriate range, a chain carbonate having 3 to 5 carbon atoms is preferably used.

[0065] Specific examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, ethyl methyl carbonate, and methyl-n-propyl carbonate. Dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are particularly preferred.

[0066] Chain carbonates having fluorine atoms (hereinafter sometimes abbreviated as "fluorinated chain carbonates") can also be suitably used. The number of fluorine atoms in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, and preferably 4 or less. When the fluorinated chain carbonate has multiple fluorine atoms, they may be bonded to the same carbon or different carbons.

[0067] Examples of the fluorinated chain carbonate include fluorinated dimethyl carbonate derivatives such as fluoromethyl methyl carbonate, fluorinated ethyl methyl carbonate derivatives such as 2-fluoroethyl methyl carbonate, and fluorinated diethyl carbonate derivatives such as ethyl-(2-fluoroethyl) carbonate.

[0068] The chain carbonate may be used alone or in any combination of two or more kinds in any ratio.

[0069] The content of the chain carbonate in the non-aqueous solvent in the electrolyte is not particularly limited, but is usually 15% by volume or more, preferably 20% by volume or more, more preferably 25% by volume or more, and usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less. The content of the chain carbonate in the non-aqueous solvent in the electrolyte is usually 15 to 90% by volume, preferably 20 to 85% by volume, and more preferably 25 to 80% by volume. By setting the content of the chain carbonate in the above range, the viscosity of the electrolyte can be set in an appropriate range, a decrease in ionic conductivity can be suppressed, and the output characteristics of the battery can be easily set in a good range.

[0070] Furthermore, by combining a specific chain carbonate with ethylene carbonate in a specific content, the battery performance can be significantly improved.

[0071] For example, when dimethyl carbonate and ethyl methyl carbonate are selected as the specific chain carbonate, the content of ethylene carbonate is not particularly limited and can be any content as long as it does not significantly impair the effects of the present invention, but is typically 15% by volume or more, preferably 20% by volume or more, and typically 45% by volume or less, preferably 40% by volume or less, in the non-aqueous solvent of the electrolyte solution. The content of ethylene carbonate in the non-aqueous solvent of the electrolyte solution is typically 15 to 45% by volume, preferably 20 to 40% by volume. The content of dimethyl carbonate in the non-aqueous solvent of the electrolyte solution is typically 20% by volume or more, preferably 30% by volume or more, and typically 50% by volume or less, preferably 45% by volume or less. The content of dimethyl carbonate in the non-aqueous solvent of the electrolyte solution is typically 20 to 50% by volume, preferably 30 to 45% by volume. Furthermore, the content of ethyl methyl carbonate in the non-aqueous solvent in the electrolyte is usually 20% by volume or more, preferably 30% by volume or more, and usually 50% by volume or less, preferably 45% by volume or less. The content of ethyl methyl carbonate in the non-aqueous solvent in the electrolyte is usually 20 to 50% by volume, preferably 30 to 45% by volume. By keeping each content within the above ranges, excellent high-temperature stability and further suppression of gas generation tend to be achieved.

[0072] [1-4-3. Chain Carboxylic Acid Ester] Examples of the chain carboxylic acid ester, which is one aspect of the non-aqueous solvent in this embodiment, include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, methyl isobutyrate, ethyl isobutyrate, and methyl pivalate. Among these, methyl acetate, ethyl acetate, propyl acetate, and butyl acetate are preferred from the viewpoint of improving battery characteristics. Chain carboxylic acid esters in which a portion of the hydrogen atoms of the above-mentioned chain carboxylic acid esters are substituted with fluorine can also be suitably used. Examples of such fluorine-substituted chain carboxylic acid esters include methyl trifluoroacetate and ethyl trifluoroacetate.

[0073] [1-4-4. Cyclic Carboxylic Acid Ester] Examples of the cyclic carboxylic acid ester, which is one embodiment of the non-aqueous solvent in this embodiment, include γ-butyrolactone and γ-valerolactone. Among these, γ-butyrolactone is more preferable. Cyclic carboxylic acid esters in which some of the hydrogen atoms of the above-mentioned cyclic carboxylic acid esters have been substituted with fluorine atoms can also be used preferably.

[0074] [1-4-5. Ether Compounds] Preferred examples of the ether compound, which is one aspect of the non-aqueous solvent in this embodiment, include chain ethers having 3 to 10 carbon atoms, such as dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether, and cyclic ethers having 3 to 6 carbon atoms, such as tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, and 1,4-dioxane.

[0075] Among these, as the chain ethers having 3 to 10 carbon atoms, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are preferred because they have a high solvation ability for lithium ions, improve ionic dissociation, have low viscosity, and provide high ionic conductivity, and as the cyclic ethers having 3 to 6 carbon atoms, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, and the like are preferred because they provide high ionic conductivity.

[0076] The content of the ether-based compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention. In the non-aqueous solvent of the electrolyte, the content is typically 1% by volume or more, preferably 2% by volume or more, more preferably 3% by volume or more, and typically 30% by volume or less, preferably 25% by volume or less, and more preferably 20% by volume or less. The content of the ether-based compound in the non-aqueous solvent of the electrolyte is typically 1 to 30% by volume, preferably 2 to 25% by volume, and more preferably 3 to 20% by volume. If the content of the ether-based compound falls within the above range, it is easy to ensure the improvement in the degree of lithium ion dissociation of the ether and the improvement in ionic conductivity due to the reduced viscosity. Furthermore, when the negative electrode active material is a carbon-based material, the phenomenon of co-insertion of the chain ether with the lithium ion can be suppressed, thereby enabling the input / output characteristics and charge / discharge rate characteristics to be within appropriate ranges.

[0077] [1-4-6. Sulfone Compound] The sulfone compound, which is one aspect of the non-aqueous solvent in this embodiment, is not particularly limited and may be either a cyclic sulfone or a chain sulfone. In the case of a cyclic sulfone, the carbon number is usually 3 to 6, preferably 3 to 5. In the case of a chain sulfone, the carbon number is usually 2 to 6, preferably 2 to 5. In addition, the number of sulfonyl groups in one molecule of the sulfone compound is not particularly limited, but is usually 1 or 2.

[0078] Examples of cyclic sulfones include monosulfone compounds such as trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones; and disulfone compounds such as trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones. Among these, from the viewpoints of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolanes) are particularly preferred.

[0079] The sulfolanes are preferably sulfolane and / or sulfolane derivatives (hereinafter, sulfolane may also be abbreviated as "sulfolanes"). The sulfolane derivatives are preferably those in which one or more hydrogen atoms bonded to the carbon atoms constituting the sulfolane ring are substituted with a fluorine atom or an alkyl group.

[0080] Among these, 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,3-difluorosulfolane, 2-trifluoromethylsulfolane, 3-trifluoromethylsulfolane, and the like are preferred because they have high ionic conductivity and high input / output.

[0081] Examples of chain sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, pentafluoroethyl methyl sulfone, etc. Among these, dimethyl sulfone, ethyl methyl sulfone, and monofluoromethyl methyl sulfone are preferred in terms of improving the high-temperature storage stability of the electrolyte solution.

[0082] The content of the sulfone-based compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention, but is typically 0.3 vol% or more, preferably 0.5 vol% or more, more preferably 1 vol% or more, in the non-aqueous solvent of the electrolyte solution, and is typically 40 vol% or less, preferably 35 vol% or less, more preferably 30 vol% or less. The content of the sulfone-based compound in the non-aqueous solvent of the electrolyte solution is typically 0.3 to 40 vol%, preferably 0.5 to 35 vol%, more preferably 1 to 30 vol%. If the content of the sulfone-based compound is within the above range, an electrolyte solution with excellent high-temperature storage stability tends to be obtained.

[0083] [1-5. Auxiliary Agent] The electrolyte solution according to this embodiment may contain various auxiliary agents as long as the effects of the present invention are not impaired. Any conventionally known auxiliary agent can be used. The auxiliary agent can be used alone or in combination of two or more types in any ratio.

[0084] Examples of the auxiliary include cyclic carbonates having a carbon-carbon unsaturated bond, cyclic carbonates having a fluorine atom, compounds having an isocyanate group, compounds having an isocyanuric acid skeleton, sulfur-containing organic compounds, phosphorus-containing organic compounds, silicon-containing compounds, aromatic compounds, organic compounds having a cyano group, fluorine-free carboxylic acid esters, cyclic ether compounds, acid anhydrides, triple bond-containing compounds, phosphazene compounds, etc. Examples include the compounds described in WO 2015 / 111676.

[0085] Among these, at least one carbonate compound selected from the group consisting of cyclic carbonates having a carbon-carbon unsaturated bond and cyclic carbonates having a fluorine atom (hereinafter also referred to as "specific carbonate compound") is preferred.

[0086] The content of the auxiliary agent is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present invention, but is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably less than 1% by mass. The content of the auxiliary agent in the electrolyte solution is usually 0.001 to 10% by mass, preferably 0.01 to 5% by mass, more preferably 0.1 to 3% by mass, even more preferably 0.1 to 1% by mass, and particularly preferably 0.1% by mass or more but less than 1% by mass.

[0087] Here, the cyclic ether compound can be used as an auxiliary agent in the electrolytic solution, and some can also be used as a non-aqueous solvent as described in the section [1-4. Non-aqueous solvent]. When the cyclic ether compound is used as an auxiliary agent, it is used in an amount of 5% by mass or less, preferably less than 4% by mass, in the electrolytic solution.

[0088] Furthermore, borate anion-containing compounds, oxalate complex anion-containing compounds, monofluorophosphate anion-containing compounds, and difluorophosphate anion-containing compounds can be used as auxiliary agents in the electrolytic solution, and also include those that can be used as electrolytes as described in the section [1-3. Electrolytes]. When these compounds are used as auxiliary agents, they are preferably used in an amount of less than 3 mass% in the electrolytic solution.

[0089] [1-5-1. Specific Carbonate Compound] As described above, the electrolyte solution according to this embodiment preferably contains, as an auxiliary agent, at least one carbonate compound selected from the group consisting of cyclic carbonates having a carbon-carbon unsaturated bond and cyclic carbonates having a fluorine atom. These compounds can be used alone or in combination of two or more in any ratio.

[0090] When two or more specific carbonate compounds are used in combination, it is preferable to combine an unsaturated cyclic carbonate with a fluorinated cyclic carbonate, and it is more preferable to combine vinylene carbonate with a fluorinated cyclic carbonate.

[0091] [Content of Specific Carbonate Compound] The content of the specific carbonate compound in the total amount of the electrolyte solution according to this embodiment is typically 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more. It is also typically 10% by mass or less, preferably 6% by mass or less, more preferably 5% by mass or less, and even more preferably 4% by mass or less. The content of the specific carbonate compound is typically 0.001 to 10% by mass, preferably 0.01 to 6% by mass, more preferably 0.1 to 5% by mass, and even more preferably 0.5 to 4% by mass, based on the total amount of the electrolyte solution. When two or more specific carbonate compounds are contained, the "content" refers to the total content of the compounds. The content of the specific carbonate compound within the above range can improve battery characteristics, particularly durability. While the reason for this is unclear, it is believed that the inclusion of the specific carbonate compound in this ratio allows a coating to form on the electrode, minimizing side reactions of the electrolyte solution components. The identification and content of specific carbonate compounds is determined by nuclear magnetic resonance (NMR) spectroscopy.

[0092] [Mass Ratio of Specific Carbonate Compound to Compound Represented by General Formula (1)] In this embodiment, the mass ratio of the content of the specific carbonate compound to the content of the compound represented by general formula (1), i.e., the mass ratio represented by [g] of specific carbonate compound / [g] of compound represented by general formula (1), is typically 0.01 or more, preferably 0.05 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, and is typically 100 or less, preferably 50 or less, more preferably 20 or less, and even more preferably 15 or less. This mass ratio is typically 0.01 to 100, preferably 0.05 to 50, more preferably 0.3 to 20, and even more preferably 0.5 to 15. When two or more types of the compound represented by general formula (1) and two or more types of the specific carbonate compound are contained, the respective "contents" refer to the total contents thereof. When the mass ratio is within the above range, battery characteristics, particularly durability, can be improved. The reason for this is not clear, but it is thought that by containing a specific carbonate compound and a compound represented by general formula (1) within the above mass ratio range, a coating is formed on the electrode, and side reactions of the components of the electrolyte solution can be minimized.

[0093] [Mass ratio of specific carbonate compound to main salt] In the electrolyte solution according to this embodiment, the mass ratio of the content of the specific carbonate compound to the total content of the main salt constituting the electrolyte, i.e., the mass ratio expressed as specific carbonate compound [g] / main salt [g], is usually 0.00005 or more, preferably 0.0005 or more, more preferably 0.001 or more, even more preferably 0.01 or more, even more preferably 0.02 or more, particularly preferably 0.025 or more, and usually 0.5 or less, preferably 0.45 or less, more preferably 0.4 or less, even more preferably 0.35 or less. The mass ratio is usually 0.00005 to 0.5, preferably 0.0005 to 0.5, more preferably 0.001 to 0.45, even more preferably 0.01 to 0.4, even more preferably 0.02 to 0.35, particularly preferably 0.025 to 0.35. In addition, when two or more types of main salt and specific carbonate compound are contained, the above content means the total content of each. If the mass ratio is within the above range, the battery characteristics, particularly durability, can be improved. Although the reason for this is unclear, it is thought that by containing the specific carbonate compound and main salt within the above mass ratio range, a coating is formed on the electrode, minimizing side reactions of the electrolyte within the battery system.

[0094] [1-5-1-1. Cyclic Carbonate Having a Carbon-Carbon Unsaturated Bond] The cyclic carbonate having a carbon-carbon unsaturated bond (hereinafter also referred to as "unsaturated cyclic carbonate"), which is one aspect of the specific carbonate compound in this embodiment, is not particularly limited as long as it is a cyclic carbonate having a carbon-carbon double bond or a carbon-carbon triple bond. Cyclic carbonates having an aromatic ring are also included in the unsaturated cyclic carbonate.

[0095] Examples of unsaturated cyclic carbonates include vinylene carbonates, ethylene carbonates substituted with a substituent having an aromatic ring, a carbon-carbon double bond, or a carbon-carbon triple bond, phenyl carbonates, vinyl carbonates, allyl carbonates, catechol carbonates, etc. Among these, vinylene carbonates and ethylene carbonates substituted with a substituent having an aromatic ring, a carbon-carbon double bond, or a carbon-carbon triple bond are preferred.

[0096] Examples of vinylene carbonates include vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl vinylene carbonate, 4,5-vinyl vinylene carbonate, allyl vinylene carbonate, and 4,5-diallyl vinylene carbonate.

[0097] Examples of ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond include vinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, 4-methyl-5-vinyl ethylene carbonate, 4-allyl-5-vinyl ethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, 4-vinyl-5-ethynyl ethylene carbonate, 4-allyl-5-ethynyl ethylene carbonate, phenyl ethylene carbonate, 4,5-diphenyl ethylene carbonate, 4-phenyl-5-vinyl ethylene carbonate, 4-allyl-5-phenyl ethylene carbonate, allyl ethylene carbonate, 4,5-diallyl ethylene carbonate, and 4-methyl-5-allyl ethylene carbonate. Among these, vinylene carbonate, vinylethylene carbonate, and ethynylethylene carbonate are preferred because they form a more stable composite coating on the electrode, and one or more selected from vinylene carbonate and vinylethylene carbonate are more preferred, with vinylene carbonate being even more preferred.

[0098] The unsaturated cyclic carbonates can be used alone or in combination of two or more kinds in any ratio.

[0099] [1-5-1-2. Cyclic Carbonate Having a Fluorine Atom] The cyclic carbonate having a fluorine atom, which is one embodiment of the specific carbonate compound in this embodiment, is not particularly limited as long as it has a cyclic carbonate structure and contains a fluorine atom.

[0100] Examples of cyclic carbonates having fluorine atoms include fluorinated cyclic carbonates having an alkylene group having 2 to 6 carbon atoms and derivatives thereof, and more specific examples include fluorinated ethylene carbonates and derivatives thereof, and ethylene carbonates having a fluorine-containing group. In this specification, fluorinated ethylene carbonates and derivatives thereof are collectively referred to as fluoroethylene carbonate. Examples of derivatives of fluorinated ethylene carbonate include fluorinated ethylene carbonates substituted with an alkyl group (e.g., an alkyl group having 1 to 4 carbon atoms).

[0101] Among these, preferred cyclic carbonates having fluorine atoms are fluoroethylene carbonate having 1 to 8 fluorine atoms and ethylene carbonate having a fluorine-containing group having 1 to 8 fluorine atoms.

[0102] Examples of the fluoroethylene carbonate having 1 to 8 fluorine atoms and the ethylene carbonate having 1 to 8 fluorine atoms and a fluorine-containing group include monofluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4,4-difluoro-5-methylethylene carbonate, 4-( Examples of suitable fluorocarbons include 4-(fluoromethyl)-ethylene carbonate, 4-(difluoromethyl)-ethylene carbonate, 4-(trifluoromethyl)-ethylene carbonate, 4-(fluoromethyl)-4-fluoroethylene carbonate, 4-(fluoromethyl)-5-fluoroethylene carbonate, 4-fluoro-4,5-dimethylethylene carbonate, 4,5-difluoro-4,5-dimethylethylene carbonate, and 4,4-difluoro-5,5-dimethylethylene carbonate. Among these, from the viewpoints of imparting high ionic conductivity to the electrolyte and facilitating the formation of a stable interface protective coating, one or more selected from monofluoroethylene carbonate, 4,4-difluoroethylene carbonate, and 4,5-difluoroethylene carbonate are preferred.

[0103] The fluorine atom-containing cyclic carbonates can be used alone or in combination of two or more kinds in any ratio.

[0104] When the electrolyte solution according to this embodiment contains a specific carbonate, it is preferable that the electrolyte solution contains at least one selected from vinylene carbonate and fluoroethylene carbonate, from the viewpoint of imparting higher ionic conductivity to the electrolyte solution and making it easier to form a stable interface protective coating, and it is even more preferable that the specific carbonate is vinylene carbonate, from the viewpoint of making it easier to form a stable interface protective coating.

[0105] When the electrolyte solution according to this embodiment contains at least one compound selected from vinylene carbonate and fluoroethylene carbonate, the total content of vinylene carbonate and fluoroethylene carbonate in the total amount of the electrolyte solution according to this embodiment is typically 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more, and typically 10% by mass or less, preferably 6% by mass or less, more preferably 5% by mass or less, and even more preferably 4% by mass or less. The total content of vinylene carbonate and fluoroethylene carbonate in the total amount of the electrolyte solution is typically 0.001 to 10% by mass, preferably 0.01 to 6% by mass, more preferably 0.1 to 5% by mass, and even more preferably 0.5 to 4% by mass. When two or more specific carbonate compounds are contained, the "content" refers to the total content of the compounds. When the total content of vinylene carbonate and fluoroethylene carbonate is within the above range, battery characteristics, particularly durability, can be improved. Although the reason for this is unclear, it is believed that the inclusion of at least one selected from vinylene carbonate and fluoroethylene carbonate in this ratio forms a coating on the electrode, minimizing side reactions of the components in the electrolyte. The identification and content measurement of vinylene carbonate and fluoroethylene carbonate are performed by nuclear magnetic resonance (NMR) spectroscopy.

[0106] When the electrolyte solution according to this embodiment contains at least one compound selected from vinylene carbonate and fluoroethylene carbonate, the mass ratio of the total content of vinylene carbonate and fluoroethylene carbonate to the content of the compound represented by general formula (1), i.e., the mass ratio (g of vinylene carbonate and fluoroethylene carbonate) / (g of compound represented by general formula (1)), is typically 0.01 or more, preferably 0.05 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, and is typically 100 or less, preferably 50 or less, more preferably 20 or less, and even more preferably 15 or less. This mass ratio is typically 0.01 to 100, preferably 0.05 to 50, more preferably 0.3 to 20, and even more preferably 0.5 to 15. When the electrolyte solution contains two or more compounds each represented by general formula (1) and fluoroethylene carbonate, the respective "contents" refer to the total content of these compounds. When the mass ratio is within the above range, battery characteristics, particularly durability, can be improved. The reason for this is unclear, but it is thought that by containing vinylene carbonate, fluoroethylene carbonate, and the compound represented by general formula (1) within the above mass ratio range, a coating is formed on the electrode, and side reactions of the components of the electrolyte solution can be minimized.

[0107] When the electrolytic solution according to the present embodiment contains at least one selected from vinylene carbonate and fluoroethylene carbonate, the mass ratio of the total content of vinylene carbonate and fluoroethylene carbonate to the total content of the main salts constituting the electrolyte, i.e., the mass ratio expressed as total content of vinylene carbonate and fluoroethylene carbonate [g] / main salt [g], is usually 0.00005 or more, preferably 0.0005 or more, more preferably 0.001 or more, even more preferably 0.01 or more, still more preferably 0.02 or more, and particularly preferably 0.025 or more, and is usually 0.5 or less, preferably 0.45 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. The mass ratio is typically 0.00005 to 0.5, preferably 0.0005 to 0.5, more preferably 0.001 to 0.45, even more preferably 0.01 to 0.4, even more preferably 0.02 to 0.35, and particularly preferably 0.025 to 0.35. When two or more main salts and two or more fluoroethylene carbonates are contained, the above content refers to the total content of each. A mass ratio within the above range can improve battery characteristics, particularly durability. While the reason for this is unclear, it is believed that the inclusion of vinylene carbonate, fluoroethylene carbonate, and the compound represented by general formula (1) within the above mass ratio range results in the formation of a coating on the electrode, minimizing electrolyte side reactions within the battery system.

[0108] [1-5-2. Organic Compound Having an Isocyanate Group] The organic compound having an isocyanate group, which is one embodiment of the auxiliary in this embodiment, is not particularly limited as long as it is an organic compound having at least one isocyanate group in the molecule. The number of isocyanate groups in one molecule is preferably 1 to 4, more preferably 2 or 3, and even more preferably 2.

[0109] Examples of organic compounds having an isocyanate group include monoisocyanate compounds such as methyl isocyanate, ethyl isocyanate, butyl isocyanate, vinyl isocyanate, propargyl isocyanate, cyclohexyl isocyanate, phenyl isocyanate, 2-isocyanatoethyl acrylate, and 2-isocyanatoethyl methacrylate; and diisocyanate compounds such as monomethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, 1,3-diisocyanatopropane, 1,3-bis(isocyanatomethyl)cyclohexane, carbonyl diisocyanate, and 1,4-diisocyanato-2-fluorobutane. In particular, from the viewpoint of forming a stable interface protective coating, organic compounds having at least two isocyanate groups are preferred, with hexamethylene diisocyanate and 1,3-bis(isocyanatomethyl)cyclohexane being more preferred, and 1,3-bis(isocyanatomethyl)cyclohexane being even more preferred.

[0110] [1-5-3. Organic Compound Having an Isocyanuric Acid Skeleton] The organic compound having an isocyanuric acid skeleton (hereinafter also referred to as an "isocyanurate compound"), which is one embodiment of the auxiliary in this embodiment, is not particularly limited as long as it is an organic compound having at least one isocyanuric acid skeleton in the molecule. Examples of the organic compound having an isocyanuric acid skeleton include the following compounds.

[0111]

[0112] As the isocyanurate compound, particularly from the viewpoint of forming a stable interface protective coating, an isocyanurate compound having a saturated or unsaturated aliphatic hydrocarbon group which may have a halogen atom is preferred, an isocyanurate compound having an unsaturated aliphatic hydrocarbon group containing a terminal carbon-carbon unsaturated bond is more preferred, and triallyl isocyanurate is even more preferred.

[0113] [1-5-4. Sulfur-Containing Organic Compound] The sulfur-containing organic compound, which is one aspect of the auxiliary in this embodiment, is not particularly limited as long as it is an organic compound having at least one sulfur atom (S) in the molecule, but does not include the compound represented by formula (2) of the present invention. The sulfur-containing organic compound is preferably an organic compound having at least one S═O bond, and more preferably an ester compound having an S═O bond, such as a chain sulfonate ester or a cyclic sulfonate ester. However, an anion-containing compound having an S═O bond and an S—X bond is not considered to be a "sulfur-containing organic compound," but is included in the above-mentioned "anion-containing compound having an S═O bond and an S—X bond."

[0114] Examples of sulfur-containing organic compounds include methyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfan, methyl methanesulfonyloxyacetate, methyl vinylsulfonate, allyl vinylsulfonate, propargyl allylsulfonate, methoxycarbonylmethyl methanedisulfonate, ethoxycarbonylmethyl methanedisulfonate, methoxycarbonylmethyl 1,3-butanedisulfonate, ethoxycarbonylmethyl 1,3-butanedisulfonate, 1-methoxycarbonylethyl 1,3-butanedisulfonate, 1-ethoxycarbonylethyl 1,3-butanedisulfonate, butane-2,3-diyl dimethanesulfonate, and butane-1,4-diyl Chain sulfonic acid esters such as alkyl disulfonic acid esters such as dimethanesulfonate; cyclic sulfonic acid esters such as 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,5-pentane sultone, methylenemethane disulfonate, ethylenemethane disulfonate, and 2,2-dioxide-1,2-oxathiolan-4-yl acetate; 1,1-dioxidetetrahydrothiophen-3-yl methanesulfonate, and 1,1-dioxide-2,3-dihydrothiophen-3-yl Examples include cyclic sulfones such as methanesulfonate; and vinyl sulfone compounds such as divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane, and bis(2-vinylsulfonylethyl)ether.

[0115] In particular, from the viewpoint of forming a stable interface protective coating, linear or cyclic sulfonic acid esters are more preferred, cyclic sulfonic acid esters are particularly preferred, and 1,3-propane sultone and methylenemethane disulfonate are most preferred.

[0116] [1-5-5. Phosphorus-Containing Organic Compound] The phosphorus-containing organic compound, which is one aspect of the auxiliary agent in this embodiment, is not particularly limited as long as it is a compound having at least one phosphorus atom in the molecule. However, the compound represented by general formula (1) of the present invention is not included in the "phosphorus-containing organic compound." Furthermore, an anion-containing compound having a P═O bond and a P—F bond is not considered a "phosphorus-containing organic compound," but is included in the "anion-containing compound having a P═O bond and a P—F bond" as the specific anion-containing compound described above.

[0117] Examples of phosphorus-containing organic compounds include trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, ethyl-2-(diethoxyphosphoryl)acetate, and 2-propynyl-2-(diethoxyphosphoryl)acetate.

[0118] In particular, ethyl 2-(diethoxyphosphoryl)acetate or 2-propynyl-2-(diethoxyphosphoryl)acetate is preferred, with 2-propynyl-2-(diethoxyphosphoryl)acetate being more preferred.

[0119] [1-5-6. Silicon-Containing Compound] The silicon-containing compound, which is one aspect of the auxiliary agent in this embodiment, is not particularly limited as long as it is a compound having at least one silicon atom in the molecule. Examples of the silicon-containing compound include boric acid compounds such as tris(trimethylsilyl) borate, tris(trimethoxysilyl) borate, tris(triethylsilyl) borate, and tris(dimethylvinylsilyl) borate; phosphate compounds such as tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tris(triphenylsilyl) phosphate, tris(trimethoxysilyl) phosphate, and tris(dimethylvinylsilyl) phosphate; tris(trimethylsilyl) phosphite, tris(triethylsilyl) phosphite, tris(triphenylsilyl) phosphite, tris(trimethoxysilyl) phosphite, and tris(dimethylvinylsilyl) phosphite. sulfonic acid compounds such as trimethylsilyl methanesulfonate and trimethylsilyl tetrafluoromethanesulfonate; silane compounds such as tetramethylsilane, trimethylvinylsilane, dimethyldivinylsilane, methyltrivinylsilane, and tetravinylsilane; disilane compounds such as hexamethyldisilane, hexaethyldisilane, 1,1,2,2-tetramethyldisilane, and 1,2-diphenyltetramethyldisilane; and disiloxane compounds such as hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, and 1,1,3,3-tetramethyl-1,3-diphenyldisiloxane.

[0120] In particular, from the viewpoint of forming a stable interface protective coating, disilane compounds and disiloxane compounds are preferred, disiloxane compounds are more preferred, hexamethyldisiloxane and 1,3-divinyltetramethyldisiloxane are even more preferred, and 1,3-divinyltetramethyldisiloxane is particularly preferred.

[0121] [1-5-7. Aromatic Compound] The aromatic compound, which is one aspect of the auxiliary in this embodiment, is not particularly limited as long as it is a compound having an aromatic group in the molecule. Examples of the aromatic compound include aromatic compounds having a branched alkyl group such as cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, and 1-fluoro-4-tert-butylbenzene; and aromatic compounds such as biphenyl, terphenyl (o-, m-, and p-isomers), fluorobenzene, methyl phenyl carbonate, ethyl phenyl carbonate, and diphenyl carbonate.

[0122] In particular, biphenyl, terphenyl (o-, m-, p-isomer), fluorobenzene, cyclohexylbenzene, tert-butylbenzene, and tert-amylbenzene are more preferred, and biphenyl, o-terphenyl, fluorobenzene, cyclohexylbenzene, and tert-amylbenzene are even more preferred.

[0123] [1-5-8. Organic Compound Having a Cyano Group] The organic compound having a cyano group, which is one embodiment of the auxiliary in this embodiment, is not particularly limited as long as it is an organic compound having at least one cyano group in the molecule. Examples of organic compounds having a cyano group include organic compounds having one cyano group in the molecule, such as acetonitrile, propionitrile, butyronitrile, pentanenitrile, hexanenitrile, decanenitrile, undecanenitrile, dodecanenitrile, cyclohexanecarbonitrile, acrylonitrile, methacrylonitrile, and crotononitrile; organic compounds having two cyano groups in the molecule, such as succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, sebaconitrile, methylmalononitrile, ethylmalononitrile, bicyclohexyl-1,1-dicarbonitrile, 1,4-dicyanopentane, and 1,2-dicyanobenzene; and organic compounds having three cyano groups in the molecule, such as 1,2,3-propanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,3,5-cyclohexanetricarbonitrile, and 1,3,5-benzenetricarbonitrile.

[0124] In particular, from the viewpoint of forming a stable interface protective film, organic compounds having two cyano groups are preferred, succinonitrile and adiponitrile are more preferred, and adiponitrile is even more preferred.

[0125] [1-5-9. Fluorine-free carboxylic acid ester] The fluorine-free carboxylic acid ester, which is one embodiment of the auxiliary in this embodiment, is not particularly limited as long as it is a carboxylic acid ester that does not have a fluorine atom in the molecule. It is preferably a fluorine-free chain carboxylic acid ester, and more preferably a fluorine-free saturated chain carboxylic acid ester. The total number of carbon atoms in the fluorine-free chain carboxylic acid ester is preferably 3 or more, more preferably 4 or more, and preferably 7 or less, more preferably 6 or less, and even more preferably 5 or less. The total number of carbon atoms in the fluorine-free chain carboxylic acid ester is preferably 3 to 7, more preferably 3 to 6, and even more preferably 4 to 5.

[0126] Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, methyl pivalate, ethyl pivalate, n-propyl pivalate, isopropyl pivalate, n-butyl pivalate, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, methyl crotonate, ethyl crotonate, methyl 2-propionate, etc. In particular, from the viewpoint of improving the output characteristics of the battery, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and n-propyl propionate are preferred, and methyl propionate is more preferred.

[0127] [1-5-10. Cyclic Ether Compound] The cyclic ether compound, which is one embodiment of the auxiliary in this embodiment, is not particularly limited as long as it is a compound having one or more ether bonds in the molecule. Examples of the cyclic ether compound include cyclic acetal compounds such as 1,3-dioxolane, 1,3-dioxane, and 1,3,5-trioxane.

[0128] As the cyclic ether compound, a cyclic acetal compound is particularly preferred, 1,3-dioxolane or 1,3-dioxane is preferred, and 1,3-dioxane is more preferred.

[0129] [1-5-11. Acid Anhydride] The acid anhydride, which is one aspect of the auxiliary in this embodiment, is an acid anhydride having a "C(═O)—O—C(═O) group" or "C(═O)—O—S(═O) group" in the molecule. ２ group" or "S(=O) ２ -O-S(=O) ２ There are no particular limitations on the acid anhydride, so long as it is an acid anhydride having a "group". Examples of the acid anhydride include chain carboxylic acid anhydrides such as acetic anhydride, acrylic anhydride, methacrylic anhydride, cyclohexanecarboxylic anhydride, propynoic anhydride, benzoic anhydride, fluoroacetic anhydride, 4-fluorobenzoic anhydride, and acetic propionic anhydride, succinic anhydride, maleic anhydride, citraconic anhydride, glutaric anhydride, itaconic anhydride, fluorosuccinic anhydride, allylsuccinic anhydride, 1,2-oxathiolan-5-one 2,2-dioxide, and 1,2,6-oxadithiane 2,2,6,6-tetraoxide.

[0130] In particular, from the viewpoint of forming a stable interface protective film, methacrylic anhydride, succinic anhydride, maleic anhydride, and allyl succinic anhydride are preferred, with succinic anhydride and allyl succinic anhydride being more preferred.

[0131] [1-5-12. Triple Bond-Containing Compound] The triple bond-containing compound, which is one aspect of the auxiliary in this embodiment, is not particularly limited as long as it is a compound having at least one triple bond in the molecule. Examples of the triple bond-containing compound include 2-propynyl methyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, 2-propynyl 2-(methanesulfonyloxy)propionate, di(2-propynyl)oxalate, 2-butyne-1,4-diyldimethanesulfonate, and 2-butyne-1,4-diyldiformate.

[0132] In particular, 2-propynyl methyl carbonate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di(2-propynyl)oxalate, and 2-butyne-1,4-diyldimethanesulfonate are preferred, and 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di(2-propynyl)oxalate, and 2-butyne-1,4-diyldimethanesulfonate are more preferred.

[0133] [1-5-13. Phosphazene Compound] The phosphazene compound, which is one aspect of the auxiliary in this embodiment, is not particularly limited as long as it is a compound having an "N=P-N group" in the molecule. Examples of the phosphazene compound include cyclic phosphazene compounds such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene.

[0134] In particular, cyclic phosphazene compounds such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and phenoxypentafluorocyclotriphosphazene are preferred, with methoxypentafluorocyclotriphosphazene and ethoxypentafluorocyclotriphosphazene being more preferred.

[0135] [Mass ratio of main salt to auxiliary agent] When the electrolyte solution according to this embodiment contains an auxiliary agent other than a specific carbonate compound as an auxiliary agent, the mass ratio of the content of the auxiliary agent to the content of the main salt contained in the electrolyte in the electrolyte solution, that is, the mass ratio expressed as auxiliary agent [g] / main salt [g], is usually 0.00005 or more, preferably 0.0001 or more, more preferably 0.001 or more, even more preferably 0.01 or more, even more preferably 0.02 or more, particularly preferably 0.025 or more, and also usually 0.5 or less, preferably 0.45 or less, more preferably 0.4 or less, even more preferably 0.35 or less. The mass ratio is usually 0.00005 to 0.5, preferably 0.0001 to 0.5, more preferably 0.001 to 0.45, even more preferably 0.01 to 0.4, even more preferably 0.02 to 0.4, and particularly preferably 0.025 to 0.35. In addition, when two or more main salts and two or more auxiliary agents are contained, the content of the main salt and auxiliary agent refers to the total content of these. Furthermore, depending on the content of the specific anion-containing compound, the content of the specific anion-containing compound may also be included in the main salt or auxiliary agent. When the mass ratio is within the above range, the battery characteristics, particularly the rate of increase in internal resistance, can be suppressed. While the reason for this is unclear, it is thought that by containing the auxiliary agent and main salt within the above mass ratio range, a coating is formed on the electrode, minimizing electrolyte side reactions within the battery system.

[0136] [1-6. Method for Producing Electrolyte Solution] The method for producing an electrolyte solution of the present invention includes a step of dissolving the compound represented by general formula (1) above, the compound represented by formula (2) above, and the electrolyte in the non-aqueous solvent.

[0137] <2. Battery> The battery according to this embodiment includes a positive electrode and a negative electrode capable of absorbing and releasing metal ions, and an electrolyte solution, where the electrolyte solution is the electrolyte solution described in <1. Electrolyte Solution>. The battery is preferably a non-aqueous electrolyte battery, and more preferably a non-aqueous electrolyte secondary battery. The components of the battery other than the electrolyte solution will be described below using a lithium ion secondary battery as an example. Note that a lithium ion secondary battery is a secondary battery that includes a positive electrode capable of absorbing and releasing lithium ions, a negative electrode capable of absorbing and releasing lithium ions, and the electrolyte solution contains a lithium salt as the main electrolyte salt.

[0138] [2-1. Positive Electrode] The positive electrode has a positive electrode active material capable of absorbing and releasing lithium ions on at least a portion of the surface of a current collector.

[0139] [2-1-1. Positive Electrode Active Material] The positive electrode active material used in the positive electrode is not particularly limited as long as it can electrochemically absorb and release metal ions, and examples thereof include lithium transition metal compounds. The positive electrode active material (lithium transition metal compound) used in the positive electrode will be described below.

[0140] [2-1-1-1. Lithium transition metal compound] A lithium transition metal compound is a compound having a structure capable of desorbing and inserting lithium ions, and examples thereof include sulfides, phosphate compounds, silicate compounds, borate compounds, lithium transition metal composite oxides, etc. Among these, phosphate compounds and lithium transition metal composite oxides are preferred, and lithium transition metal composite oxides are more preferred.

[0141] Examples of lithium transition metal composite oxides include those having a spinel structure or an olivine structure that allow three-dimensional diffusion of lithium ions, and those having a layered structure that allows two-dimensional diffusion of lithium ions. Among these, lithium transition metal composite oxides having a layered structure are preferred from the viewpoint of improving battery capacity.

[0142] A lithium transition metal composite oxide having a spinel structure is generally represented by the following composition formula (1): Li ｘ’ M' ｙ’ O４ ...(1) (In formula (1), 0.8≦x′≦1.5, 1.9≦y′≦2.1, and M′ contains at least one transition metal element.)

[0143] As a lithium transition metal composite oxide having a spinel structure, specifically, LiMn ２ O ４ , LiCoMnO ４ , LiNi ０．５ Mn １．５ O ４ , LiCoVO ４ Examples include:

[0144] A lithium transition metal composite oxide having an olivine structure is generally represented by the following composition formula (2): Li ｘ” M” ｙ” P.O. ４ ... (2) (In formula (2), 0.8≦x″≦1.5, 0.9≦y″≦1.1, and M″ contains at least one transition metal element.)

[0145] Examples of M" include Fe, Ni, Co, and Mn. Specific examples of lithium transition metal composite oxides having an olivine structure include LiFePO ４ , etc.

[0146] A lithium transition metal composite oxide having a layered structure is generally represented by the following composition formula (3): Li １＋ｘ M ｙ O ２ ... (3) (In formula (3), -0.2≦x≦0.5, 0.5≦y≦1.1, and M contains at least one transition metal element.)

[0147] As a lithium transition metal composite oxide having a layered structure, specifically, LiCoO ２ , LiNiO ２ , LiNi ０．９０ Co ０．０５ Mn ０．０５ O ２ , LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ , LiNi ０．８０ Co ０．１５ Al ０．０５O ２ , LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ , Li １．０５ Ni ０．３３ Co ０．３３ Mn ０．３３ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , Li １．０５ Ni ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , Li １．０ Ni ０．８ Co ０．１ Mn ０．１ O ２ , LiNi ０．９１ Co ０．０６ Mn ０．０３ O ２ , LiNi ０．９１ Co ０．０６ Al ０．０３ O ２ , LiNi ０．９０ Co ０．０３ Al ０．０７ O ２ , Li １．００ Ni ０．６１ Co ０．２ 0Mn ０．１９ O ２ , Li [Li １／３ Mn ２／３ ]O ２ and solid solutions thereof.

[0148] Among the lithium transition metal composite oxides having a layered structure, from the viewpoint of achieving high capacity, a lithium transition metal composite oxide represented by the following composition formula (4) is preferred: Li １＋ｙ M1O ２ (4) (In formula (4), -0.2≦y≦0.5, M1 represents a plurality of elements including at least Ni, and the molar ratio (Ni / M1) of the content of Ni to the content of all elements included in M1 is 0.30 to 1.0.)

[0149] In the composition formula (4), the molar ratio (Ni / M1) is 0.30 or more, preferably 0.40 or more, more preferably 0.50 or more, and preferably 1.0 or less, more preferably 0.90 or less. The molar ratio (Ni / M1) is 0.30 to 1.0, preferably 0.40 to 0.90, more preferably 0.50 to 0.90. When the molar ratio (Ni / M1) is within this range, the compound represented by general formula (1) is likely to form a coating on the positive electrode, and side reactions between the positive electrode and the electrolyte are suppressed, thereby suppressing the rate of increase in internal resistance after high-temperature storage of the battery.

[0150] Specific examples of lithium transition metal oxides having a layered structure represented by composition formula (4) include LiNiO ２ , LiNi ０．９０ Co ０．０５ Mn ０．０５ O ２ , LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ , LiNi ０．８０ Co ０．１５ Al ０．０５ O ２ , LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , Li １．０５ Ni ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , Li １．０ Ni ０．８ Co ０．１ Mn ０．１ O ２ , LiNi ０．９１ Co ０．０６ Mn ０．０３ O ２ , LiNi ０．９１ Co ０．０６ Al ０．０３ O２ , LiNi ０．９０ Co ０．０３ Al ０．０７ O ２ , Li １．００ Ni ０．６１ Co ０．２ 0Mn ０．１９ O ２ etc.

[0151] Among the lithium transition metal compounds, lithium transition metal composite oxides having a layered structure are preferred from the viewpoint of improving battery capacity, and lithium transition metal composite oxides represented by the following composition formula (5) are more preferred. ａ１ Ni ｂ１ M2 ｃ１ O ２ (5) (In formula (5), M2 represents at least one element selected from the group consisting of Co, Mn, Al, Mg, Zr, Fe, Ti, and Er, and 0.80≦a1≦1.10, 0.30≦b1≦0.98, 0.00≦c1≦0.70, and 0.90≦b1+c1≦1.10.)

[0152] In the composition formula (5), b1 is 0.30 or more, preferably 0.40 or more, more preferably 0.45 or more, even more preferably 0.50 or more, and is 0.98 or less. In the composition formula (5), b1 is preferably 0.40 to 0.98, more preferably 0.45 to 0.98, even more preferably 0.50 to 0.98.

[0153] Specific examples of lithium transition metal oxides having a layered structure represented by composition formula (5) include LiNi ０．９０ Co ０．０５ Mn ０．０５ O ２ , LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ , LiNi ０．８０ Co ０．１５ Al ０．０５ O ２ , LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O２ , Li １．０５ Ni ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , Li １．０ Ni ０．８ Co ０．１ Mn ０．１ O ２ , LiNi ０．９１ Co ０．０６ Mn ０．０３ O ２ , LiNi ０．９１ Co ０．０６ Al ０．０３ O ２ , LiNi ０．９０ Co ０．０３ Al ０．０７ O ２ , Li １．００ Ni ０．６１ Co ０．２ 0Mn ０．１９ O ２ etc.

[0154] In particular, from the viewpoint of the structural stability of the lithium transition metal composite oxide, a lithium transition metal composite oxide represented by the following composition formula (6) is preferred: Li ａ２ Ni ｂ２ Co ｃ２ M3 ｄ２ O ２ (6) (In formula (6), M3 represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er, 0.80≦a2≦1.10, 0.30≦b2≦0.98, 0.01≦c2≦0.70, and 0.01≦d2≦0.60, and 0.90≦b2+c2+d2≦1.10.)

[0155] In composition formula (6), b2 is preferably 0.40 or more, more preferably 0.45 or more, and even more preferably 0.50 or more. In composition formula (6), b2 is 0.30 to 0.98, preferably 0.40 to 0.98, more preferably 0.45 to 0.98, and even more preferably 0.50 to 0.98. In composition formula (6), d2 is preferably 0.01 or more, more preferably 0.10 or more, and preferably 0.60 or less. In composition formula (6), d2 is preferably 0.01 to 0.60, and more preferably 0.10 to 0.60.

[0156] Suitable examples of the lithium transition metal composite oxide represented by the above composition formula (6) include LiNi ０．９０ Co ０．０５ Mn ０．０５ O ２ , LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ , LiNi ０．８０ Co ０．１５ Al ０．０５ O ２ , LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , Li １．０５ Ni ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , Li １．０ Ni ０．８ Co ０．１ Mn ０．１ O ２ , LiNi ０．９１ Co ０．０６ Mn ０．０３ O ２ , LiNi ０．９１ Co ０．０６ Al ０．０３ O ２ , LiNi ０．９０ Co ０．０３ Al ０．０７ O２ , Li １．００ Ni ０．６１ Co ０．２ 0Mn ０．１９ O ２ etc.

[0157] In the above composition formula (4) or (5), from the viewpoint of increasing the structural stability of the lithium transition metal oxide and suppressing structural deterioration during repeated charge and discharge, M1 or M2 preferably contains Mn or Al, and more preferably contains Mn. In the above composition formula (6), from the viewpoint of increasing the structural stability of the lithium transition metal composite oxide and suppressing structural deterioration during repeated charge and discharge, M3 preferably contains Mn or Al, and more preferably contains Mn. Identification and content measurement of the positive electrode active material are performed by wet decomposition of the sample followed by ICP emission spectroscopy.

[0158] [2-1-1-2. Introduction of a Foreign Element] The lithium transition metal oxide may further contain an element (foreign element) other than the elements contained in any of the above composition formulas (1) to (6).

[0159] [2-1-1-3. Surface Coating] The positive electrode may be one in which a substance (surface-attached substance) having a different composition from the positive electrode active material is attached to the surface of the positive electrode active material. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate. These surface-attached substances can be attached to the surface of the positive electrode active material, for example, by dissolving or suspending them in a solvent, impregnating the positive electrode active material with the substance, and drying the resulting solution.

[0160] The amount of the surface-attached substance is preferably 1 μmol / g or more, more preferably 10 μmol / g or more, and usually 1 mmol / g or less, relative to the positive electrode active material. The amount of the surface-attached substance is preferably 1 μmol / g to 1 mmol / g, more preferably 10 μmol / g to 1 mmol / g, relative to the positive electrode active material. In this specification, the positive electrode active material having the surface-attached substance attached to its surface is also referred to as the "positive electrode active material."

[0161] [2-1-1-4. Blend] The positive electrode active material may be used alone or in combination of two or more kinds in any ratio.

[0162] [2-1-2. Positive Electrode Configuration and Manufacturing Method] A positive electrode having the above-described positive electrode active material can be manufactured by a conventional method. That is, a positive electrode can be obtained by a method in which a positive electrode active material, a binder, and, if necessary, a conductive material and a thickener are mixed in a dry state to form a sheet, which is then pressed onto a positive electrode current collector, or by a coating method in which these materials are dissolved or dispersed in a liquid medium such as an aqueous solvent or an organic solvent to form a slurry, which is then applied to a positive electrode current collector and dried to form a positive electrode active material layer on the current collector. Alternatively, for example, the positive electrode active material may be roll-formed into a sheet electrode, or may be compression-molded into a pellet electrode. Below, a case in which a slurry is sequentially applied to a positive electrode current collector and dried will be described.

[0163] [2-1-2-1. Content of Positive Electrode Active Material] The positive electrode comprises a current collector and a positive electrode active material layer formed on the current collector, the content of the positive electrode active material in the positive electrode active material layer being typically 80 to 99.5 mass %.

[0164] [2-1-2-2. Electrode Density] The positive electrode active material layer obtained by applying and drying the positive electrode active material together with a binder, a conductive material, etc. is preferably compacted by a hand press, a roller press, etc. to increase the packing density of the positive electrode active material. The electrode structure when the positive electrode active material is made into an electrode is not particularly limited, but the density of the positive electrode active material layer present on the current collector is usually 1.5 to 4.5 g / cm ３ is.

[0165] [2-1-2-3. Binder] When forming a positive electrode active material layer by a coating method, the type of binder is not particularly limited as long as it is a material that can be dissolved or dispersed in a liquid medium for the slurry. Preferred binders include, for example, fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene, and CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide, due to their weather resistance, chemical resistance, heat resistance, and flame retardancy. Mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, and the like of the above polymers can also be used. The binder can be used alone or in combination of two or more types in any ratio.

[0166] When a resin is used as a binder, the weight-average molecular weight of the resin is optional as long as it does not impair the effects of the present invention, and is usually 10,000 to 3,000,000. When the molecular weight is in this range, the strength of the electrode is improved, and the electrode can be suitably formed.

[0167] The content of the binder in the positive electrode active material layer is usually 0.1 to 20% by mass.

[0168] [2-1-2-4. Conductive Material] Any known conductive material can be used as the conductive material. Specific examples include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbon-based materials such as amorphous carbon such as needle coke. The conductive material can be used alone or in combination of two or more types in any ratio.

[0169] The conductive material is usually contained in the positive electrode active material layer in an amount of 0.01 to 20% by mass.

[0170] [2-1-2-5. Current Collector] The material of the current collector that holds the positive electrode active material is not particularly limited, and any known material can be used. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, with aluminum being preferred.

[0171] The current collector may be in the form of a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punched metal, a foamed metal, or the like. Among these, a metal foil or a metal thin film is preferred. The metal thin film may be suitably formed into a mesh shape.

[0172] When the current collector of the positive electrode is in the form of a plate or film, the thickness of the current collector is not limited, but is usually 1 μm to 1 mm.

[0173] [2-1-2-6. Thickness of Positive Electrode Plate] The thickness of the positive electrode (positive electrode plate) is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the positive electrode active material layer, which is the thickness of the positive electrode plate minus the thickness of the current collector, is usually 10 to 500 μm on one side of the current collector. The positive electrode active material layer may be formed on one surface or both surfaces of the current collector.

[0174] [2-1-2-7. Surface Coating of Positive Electrode Plate] The positive electrode plate may have a substance having a different composition from the positive electrode active material attached to its surface, and the substance may be the same as the surface-attached substance that may be attached to the surface of the positive electrode active material.

[0175] [2-2. Negative Electrode] The negative electrode has a negative electrode active material capable of absorbing and releasing lithium ions on at least a portion of the surface of a current collector.

[0176] [2-2-1. Negative Electrode Active Material] There are no particular limitations on the negative electrode active material used in the negative electrode, as long as it is capable of electrochemically absorbing and releasing metal ions.

[0177] Specific examples include (i) carbon-based materials, (ii) materials containing metal elements and / or metalloid elements that can be alloyed with Li, (iii) lithium-containing metal composite oxide materials, and (iv) mixtures of the above (i) to (iii). Among these, (i) carbon-based materials, (ii) materials containing metal elements and / or metalloid elements that can be alloyed with Li, and (iv) mixtures of the above (i) to (iii) are preferred in terms of their good cycle characteristics and safety, as well as their excellent continuous charge characteristics, and (iv) is more preferably a mixture of graphite and a material containing a metal element and / or metalloid element that can be alloyed with Li. These can be used alone or in combination of two or more in any ratio.

[0178] [2-2-1-1. Carbon-based materials] (i) Examples of carbon-based materials include natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. Of these, natural graphite is preferred. The carbon-based materials can be used alone or in combination of two or more in any ratio.

[0179] Examples of natural graphite include scaly graphite, flake graphite, and / or graphite particles obtained by subjecting such graphite to spheroidization, densification, or the like. Among these, spherical or ellipsoidal graphite particles that have been subjected to spheroidization are preferred from the viewpoint of particle packing properties and charge / discharge rate characteristics. The average particle diameter (d50) of the graphite particles is typically 1 to 100 μm. Here, the average particle diameter (d50) refers to the volume-based average particle diameter (median diameter) determined by laser diffraction / scattering.

[0180] [2-2-1-2. Physical Properties of Carbon-Based Materials] Carbon-based materials used as negative electrode active materials preferably satisfy at least one of the physical properties and shape characteristics listed in (1) to (4) below, and more preferably satisfy multiple properties simultaneously. (1) X-ray Diffraction Parameters The d value (interlayer distance) of the lattice plane (002 plane) of a carbon-based material determined by X-ray diffraction using the Gakushin method is typically 0.335 to 0.360 nm. The crystallite size (Lc) of the carbon-based material determined by X-ray diffraction using the Gakushin method is typically 1.0 nm or greater. (2) Volume-Based Average Particle Size The volume-based average particle size of a carbon-based material is the volume-based average particle size (median diameter) determined by laser diffraction / scattering, and is typically 1 to 100 μm. (3) Raman R Value and Raman Half-Width Value The Raman R Value of a carbon-based material is measured using argon ion laser Raman spectroscopy and is typically 0.01 to 1.5. In addition, the carbon-based material has a 1580 cm －１ The Raman half-width in the vicinity is not particularly limited, but is usually 10 to 100 cm －１ (4) BET specific surface area The BET specific surface area of ​​a carbon-based material is the value of the specific surface area measured using the BET method, and is usually 0.1 to 100 m ２ ・g －１ is.

[0181] The negative electrode active material may contain two or more carbonaceous materials having different properties, where the properties refer to one or more characteristics selected from the group consisting of X-ray diffraction parameters, volume-based average particle size, Raman R value, Raman half-width, and BET specific surface area, as shown in (1) to (4) above.

[0182] Examples of containing two or more carbon-based materials with different properties include a case where the volume-based particle size distribution is not symmetrical about the median diameter, a case where two or more carbon-based materials with different Raman R values ​​are contained, and a case where X-ray diffraction parameters are different.

[0183] [2-2-1-3. Material containing a metal element and / or a metalloid element capable of being alloyed with Li] (ii) Any conventionally known material containing a metal element and / or a metalloid element capable of being alloyed with Li can be used. From the viewpoints of capacity and cycle life, for example, a metal or metalloid selected from the group consisting of Sb, Si, Sn, Al, As, and Zn is preferable. Furthermore, when the material containing a metal element and / or a metalloid element capable of being alloyed with Li contains two or more types of metals, the material may be an alloy material composed of an alloy of these metals.

[0184] Furthermore, materials containing metal elements and / or metalloid elements that can be alloyed with Li include oxides, nitrides, carbides, etc. of metals and / or metalloids. The material may contain two or more metals that can be alloyed with Li. Among these, materials containing Si element are preferred, and metal Si (hereinafter also referred to as "Si") or Si-containing inorganic compounds are more preferred in terms of increasing capacity. In this specification, Si or Si-containing inorganic compounds are collectively referred to as "Si compounds."

[0185] The content of the material containing a metal element and / or a metalloid element capable of forming an alloy with Li relative to the total mass of the negative electrode active material is preferably 0.1 to 25 mass %. The material containing a metal element and / or a metalloid element capable of forming an alloy with Li may be already alloyed with Li during the production of the negative electrode, which will be described later. As the material, a Si compound is preferred in terms of achieving high capacity.

[0186] The Si compound is an inorganic compound containing Si, such as SiO ｘ (0≦x≦2) and the like. Examples of metal compounds alloyed with Li include Li ｙ Si (0<y≦4.4), Li ２ｚ SiO ２＋ｚ (0<z≦2), etc.

[0187] Examples of Si compounds include Si oxide (SiO ｘ１ , 0<x1≦2) is preferred because it has a larger theoretical capacity than graphite, and amorphous Si or nano-sized Si crystals are preferred because they allow alkali ions such as lithium ions to easily enter and exit the material, making it possible to obtain a high capacity.

[0188] When the material containing a metal element and / or a metalloid element that can be alloyed with Li is in the form of particles, the average particle size (d50) of the particles is usually 0.01 to 10 μm from the viewpoint of cycle life.

[0189] [2-2-1-4. Lithium-Containing Metal Composite Oxide Material] (iii) The lithium-containing metal composite oxide material is not particularly limited as long as it is capable of absorbing and releasing lithium ions. Specifically, from the viewpoint of high current density charge / discharge characteristics, a lithium-containing metal composite oxide material containing titanium is preferred, a composite oxide of lithium and titanium (hereinafter also referred to as "lithium-titanium composite oxide") is more preferred, and a lithium-titanium composite oxide having a spinel structure is even more preferred because it significantly reduces output resistance.

[0190] Furthermore, the lithium and / or titanium of the lithium titanium composite oxide may be substituted with another metal element, for example, at least one element selected from the group consisting of Al, Ga, Cu, and Zn.

[0191] As the lithium titanium composite oxide, Li ４／３ Ti ５／３ O ４ , Li １ Ti ２ O ４ and Li ４／５ Ti １１／５ O ４ Furthermore, examples of lithium-titanium composite oxides in which part of lithium and / or titanium is substituted with other elements include Li ４／３ Ti ４／３ Al １／３ O ４ is also preferred.

[0192] [2-2-1-5. Mixture of graphite and a material containing a metal element and / or a metalloid element that can be alloyed with Li] (iv) is a mixture of the above-mentioned (i) carbon-based material, (ii) a material containing a metal element and / or a metalloid element that can be alloyed with Li, and (iii) a lithium-containing metal composite oxide material. Among these, a mixture of graphite and a material containing a metal element and / or a metalloid element that can be alloyed with Li is preferred.

[0193] The mixture of graphite and a material containing a metal element and / or a metalloid element that can be alloyed with Li may be the above-mentioned (ii) mixture in which the material containing a metal element and / or a metalloid element that can be alloyed with Li and graphite are mixed in the state of particles that are independent of each other, or it may be a composite in which the material containing a metal element and / or a metalloid element that can be alloyed with Li is present on the surface or inside of graphite particles.

[0194] The content of the material containing a metal element and / or a metalloid element that can be alloyed with Li relative to the total of the material containing a metal element and / or a metalloid element that can be alloyed with Li and graphite is usually 1 to 99 mass%.

[0195] The negative electrode active material is identified and its content is measured by alkali fusion of the sample and then ICP emission spectroscopy.

[0196] [2-2-2. Negative Electrode Configuration and Manufacturing Method] The negative electrode can be manufactured by any known method as long as it does not impair the effects of the present invention. For example, the negative electrode can be manufactured by adding a binder, a liquid medium such as an aqueous solvent or an organic solvent, and, if necessary, a thickener, a conductive material, a filler, etc. to the negative electrode active material to form a slurry, which is then applied to a current collector, dried, and pressed to form a negative electrode active material layer.

[0197] [2-2-2-1. Content of negative electrode active material] The negative electrode comprises a current collector and a negative electrode active material layer formed on the current collector, the content of the negative electrode active material in the negative electrode active material layer being typically 80 to 99.5 mass %.

[0198] [2-2-2-2. Electrode Density] The negative electrode active material layer obtained by applying and drying the negative electrode active material together with a binder, a thickener, etc. is preferably compacted by a hand press, a roller press, etc. to increase the packing density of the negative electrode active material. The electrode structure when the negative electrode active material is made into an electrode is not particularly limited, but the density of the negative electrode active material layer present on the current collector is usually 1 to 2.2 g / cm ３ is.

[0199] [2-2-2-3. Binder] The binder is not particularly limited as long as it is a material that is stable in the electrolyte solution and the liquid medium used in producing the electrodes. Specific examples include rubber-like polymers such as styrene-butadiene rubber (SBR), isoprene rubber, butadiene rubber, fluororubber, acrylonitrile-butadiene rubber (NBR), and ethylene-propylene rubber; and fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and tetrafluoroethylene-ethylene copolymer. These can be used alone or in combination of two or more in any ratio.

[0200] The content of the binder in the negative electrode active material layer is usually 0.1 to 20% by mass. In particular, when the binder contains a rubber-like polymer such as SBR as a main component, the content of the binder in the negative electrode active material layer is usually 0.1 to 5% by mass. Furthermore, when the binder contains a fluorine-based polymer such as polyvinylidene fluoride as a main component, the content of the binder in the negative electrode active material layer is usually 1 to 15% by mass.

[0201] [2-2-2-4. Thickener] A thickener is usually used to adjust the viscosity of the slurry. There are no particular limitations on the thickener, but specific examples include carboxymethyl cellulose and its salts, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, etc. These can be used alone or in combination of two or more in any ratio.

[0202] When a thickener is used, the content of the thickener in the negative electrode active material layer is usually 0.01 to 5% by mass.

[0203] [2-2-2-5. Current Collector] Any known current collector can be used as the current collector for supporting the negative electrode active material. Examples of the negative electrode current collector include metal materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel, but copper is particularly preferred from the standpoints of ease of processing and cost.

[0204] The negative electrode current collector may be in the form of a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punched metal, a foamed metal, or the like. Among these, a metal foil or a metal thin film is preferred. The metal thin film may be suitably formed into a mesh shape.

[0205] When the negative electrode current collector is in the form of a plate or film, the thickness of the current collector is not limited, but is usually 1 μm to 1 mm.

[0206] [2-2-2-6. Thickness of Negative Electrode Plate] The thickness of the negative electrode (negative electrode plate) is designed to match the thickness of the positive electrode (positive electrode plate) to be used and is not particularly limited, but the thickness of the negative electrode active material layer obtained by subtracting the thickness of the current collector from the thickness of the negative electrode material is usually 15 to 1300 μm.

[0207] [2-2-2-7. Surface Coating of Negative Electrode Plate] The negative electrode plate may have a substance (surface-attached substance) attached to its surface, the substance having a different composition from the negative electrode active material. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate.

[0208] [2-3. Separator] A separator is usually placed between the positive electrode and the negative electrode to prevent short-circuiting. In this case, the electrolyte is usually impregnated into the separator before use. There are no particular restrictions on the material or shape of the separator, and any known separator can be used as long as it does not impair the effects of the present invention.

[0209] [2-4. Battery Design] [2-4-1. Electrode Group] The electrode group may have either a laminated structure in which the positive electrode plate and the negative electrode plate are sandwiched between the separator, or a structure in which the positive electrode plate and the negative electrode plate are spirally wound with the separator sandwiched between them. The ratio of the volume of the electrode group to the internal volume of the battery (electrode group occupancy rate) is usually 40 to 90%.

[0210] [2-4-2. Current collecting structure] When the electrode group has the aforementioned laminated structure, a structure formed by bundling the metal core portions of each electrode layer and welding them to a terminal is preferably used. A structure in which multiple terminals are provided within the electrode to reduce resistance is also preferably used. When the electrode group has the aforementioned wound structure, the internal resistance can be reduced by providing multiple lead structures on each of the positive and negative electrodes and bundling them to a terminal.

[0211] [2-4-3. Protective Element] Examples of protective elements that can be used include a PTC (Positive Temperature Coefficient) element whose resistance increases with heat generation due to excessive current, a thermal fuse, a thermistor, and a valve (current cutoff valve) that cuts off the current flowing in the circuit due to a sudden increase in the internal pressure or temperature of the battery during abnormal heat generation. It is preferable to select the above protective element so that it will not operate under normal high current use, and it is more preferable to design it so that abnormal heat generation or thermal runaway does not occur even without a protective element.

[0212] [2-4-4. Exterior Body] A battery is usually constructed by housing the electrolyte solution according to this embodiment, the negative electrode, the positive electrode, the separator, etc. in an exterior body (exterior case). There are no limitations on this exterior body, and any known exterior body can be used as long as it does not impair the effects of the present invention.

[0213] The material of the outer case is not particularly limited as long as it is stable against the electrolyte solution used, but from the viewpoints of weight reduction and cost, metals such as iron, aluminum, and aluminum alloys, or laminate films are preferably used. In particular, iron is preferred from the viewpoint of pressure resistance required to activate the current cutoff valve.

[0214] Examples of exterior cases using the above metals include those in which metals are welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed, airtight structure, and those in which the above metals are used via a resin gasket to form a crimped structure.

[0215] [2-4-5. Shape] The shape of the exterior case of the battery can also be any shape, such as cylindrical, rectangular, laminated, coin-shaped, large, etc.

[0216] [2-5. Battery Manufacturing Method] The battery manufacturing method according to this embodiment includes the steps of housing the positive electrode and the negative electrode in the container and injecting the electrolyte into the container. Note that the electrolyte may be injected into the container housing the positive electrode and / or the negative electrode, or the positive electrode and / or the negative electrode may be housed in the container into which the electrolyte has been injected.

[0217] [2-6. Battery Applications] The battery according to this embodiment can be used in a variety of known applications. Specific examples of applications include laptop computers, pen-input PCs, mobile PCs, e-book players, mobile phones, mobile fax machines, mobile copiers, mobile printers, portable audio players, compact video cameras, headphone stereos, video movie players, LCD TVs, handheld vacuum cleaners, portable CDs, minidiscs, walkie-talkies, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting equipment, toys, game devices, clocks, power tools, flash devices, cameras, home backup power supplies, business backup power supplies, load-leveling power supplies, and natural energy storage power supplies. In particular, the battery according to this embodiment is preferably mounted on and used in vehicles such as automobiles, motorcycles, mopeds, and bicycles.

[0218] The present invention will be explained in more detail below by way of examples and comparative examples, but the present invention is not limited to these examples as long as it does not depart from the gist of the invention.

[0219] The compounds used in the present examples and comparative examples are as follows: 1,2-bis(difluorophosphanyloxy)ethane (compound A-2)

[0220]

[0221] 4,4'-bi(1,3,2-dioxathiolane)-2,2,2',2'-tetraoxide (compound B)

[0222]

[0223] 1,3,2-dioxathiolane-2,2-dioxide (compound C)

[0224]

[0225] Examples 1 to 4 and Comparative Examples 1 to 4 [Preparation of Positive Electrode] A lithium-nickel-cobalt-manganese composite oxide (Li １．０ Ni ０．８ Co ０．１ Mn ０．１ O ２ 90 parts by mass of the cathode active material, 7 parts by mass of acetylene black as a conductive material, and 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in an N-methylpyrrolidone solvent using a disperser to form a slurry, which was then uniformly applied to both sides of a 15 μm thick aluminum foil current collector, dried, and pressed to form a positive electrode.

[0226] [Fabrication of Negative Electrode] 98 parts by mass of graphite powder was mixed with 1 part by mass of an aqueous dispersion of sodium carboxymethyl cellulose (concentration of sodium carboxymethyl cellulose: 1% by mass) as a thickener and 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by mass) as a binder, and the mixture was mixed in a disperser to form a slurry. The resulting slurry was applied to one side of a 10 μm thick copper foil current collector, dried, and then pressed to form a negative electrode.

[0227] [Preparation of non-aqueous electrolyte] In a dry argon atmosphere, a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (volume ratio EC:EMC:DMC=3:4:3) was added to thoroughly dried LiPF as an electrolyte. ６ was dissolved at 1.0 mol / L (12.3 mass%, as the concentration in the non-aqueous electrolyte solution) to prepare a reference electrolyte solution 1. Each compound was added to this reference electrolyte solution 1 so as to obtain the content shown in Table 1 below, and vinylene carbonate was further added so that the content was 1 part by mass, thereby preparing the non-aqueous electrolyte solutions of Examples 1 to 4 and Comparative Examples 1 to 4. Here, the "content" refers to the content (% by mass) when the total non-aqueous electrolyte solution is taken as 100 parts by mass. In Table 1, "-" means that no compound was added.

[0228] [Manufacture of Non-Aqueous Electrolyte Battery] The above-mentioned positive electrode, negative electrode, and polyolefin separator were stacked in the order of negative electrode, separator, positive electrode, separator, and negative electrode to prepare a battery element. This battery element was inserted into a bag made of a laminate film with aluminum (40 μm thick) coated on both sides with a resin layer so that the positive and negative electrode terminals protruded. The prepared non-aqueous electrolyte solution was then poured into the bag and vacuum-sealed to prepare a laminated non-aqueous electrolyte battery. The non-aqueous electrolyte battery was immersed in a water bath and its volume was measured. This non-aqueous electrolyte battery was a secondary battery.

[0229] <Evaluation of Nonaqueous Electrolyte Battery> [Initial Conditioning] In a thermostatic bath at 25°C, the nonaqueous electrolyte battery prepared by the above method was charged at a constant current of 0.05C (the current value at which the rated capacity based on the discharge capacity at a 1-hour rate is discharged in 1 hour is defined as 1C; the same applies below) to 3.7V, and then discharged at a constant current of 0.2C to 2.8V. Furthermore, the nonaqueous electrolyte battery was charged at a constant current and constant voltage of 0.2C to 4.1V, and then stored at a high temperature of 60°C for 24 hours to stabilize the battery. Thereafter, the battery was discharged at a constant current of 0.2C to 2.8V at 25°C, and then charged at a constant current and constant voltage of 0.2C to a voltage of 4.25V, and then discharged at a constant current of 0.2C to 2.8V.

[0230] [High-Temperature Charge Storage Test] The nonaqueous electrolyte battery after initial conditioning was charged at a constant current and constant voltage of 0.2 C to 4.25 V, and then stored at a high temperature for 4 weeks at 60° C. Thereafter, the nonaqueous electrolyte battery was cooled to 25° C. and then discharged at a constant current of 0.2 C to 2.8 V.

[0231] [Evaluation of gas generation amount after high-temperature charged storage] The volume before and after the high-temperature charged storage test was measured by Archimedes' method, and the change in volume was taken as the gas generation amount after high-temperature charged storage. Table 1 shows the relative gas generation amount when the gas generation amount of Comparative Example 1 is set to 100%.

[0232]

[0233] Table 1 shows that nonaqueous electrolyte batteries equipped with nonaqueous electrolyte solutions (Examples 1-4) containing a compound represented by general formula (1) and a compound represented by formula (2) can suppress the amount of gas generation after high-temperature storage. This can be confirmed by comparison with nonaqueous electrolyte batteries equipped with nonaqueous electrolyte solutions (Comparative Examples 1 and 2) containing only one of the compounds represented by general formula (1) and formula (2) and a nonaqueous electrolyte solution (Comparative Example 4) containing neither of the above compounds. Furthermore, a nonaqueous electrolyte battery equipped with a nonaqueous electrolyte solution (Comparative Example 3) in which a compound represented by general formula (1) was mixed with a compound C other than the compound represented by formula (2) was unable to significantly suppress the amount of gas generation. From this, it is presumed that the nonaqueous electrolyte of the present invention quickly forms a strong mixed coating on the negative electrode and positive electrode, and it was found that the effect of significantly suppressing gas generation is a unique effect when the nonaqueous electrolyte contains the compounds represented by general formula (1) and formula (2).

[0234] The electrolyte solution according to this embodiment can be used in a battery to suppress gas generation after high-temperature storage under charge. Therefore, the battery of the present invention can be suitably used in all fields of electronic devices where batteries have traditionally been used. Furthermore, the battery according to this embodiment can be used in a variety of known applications. Specific examples of applications include laptop computers, pen-input personal computers, mobile personal computers, e-book players, mobile phones, mobile fax machines, mobile copiers, mobile printers, mobile audio players, compact video cameras, headphone stereos, video movie players, LCD televisions, handheld vacuum cleaners, portable CD players, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting equipment, toys, game devices, watches, power tools, flash devices, cameras, home backup power supplies, business backup power supplies, load-leveling power supplies, and renewable energy storage power supplies.

Claims

1. An electrolytic solution comprising a compound represented by the following general formula (1), a compound represented by the following formula (2), an electrolyte, and a non-aqueous solvent. (L represents a linear or branched alkylene group having 1 to 6 carbon atoms.) 2. The electrolyte solution according to claim 1, wherein the content of the compound represented by general formula (1) in the electrolyte solution is 0.001 to 10 mass %.

3. The electrolyte solution according to claim 1, wherein the content of the compound represented by formula (2) in the electrolyte solution is 0.001 to 8.0 mass %.

4. The electrolyte solution according to claim 1, wherein the mass ratio [(1):(2)] of the compound represented by general formula (1) to the compound represented by formula (2) in the electrolyte solution is 94:6 to 3:

97.

5. The electrolyte solution according to claim 1, further comprising at least one carbonate compound selected from vinylene carbonate and fluoroethylene carbonate.

6. The electrolyte of claim 5, wherein said carbonate compound is vinylene carbonate.

7. The electrolyte solution according to claim 5, wherein the total content of said vinylene carbonate and said fluoroethylene carbonate in said electrolyte solution is 0.001 to 10 mass %.

8. The electrolyte solution according to claim 5, wherein the mass ratio of the total content of the vinylene carbonate and the fluoroethylene carbonate to the content of the compound represented by general formula (1) in the electrolyte solution (total [g] of vinylene carbonate and fluoroethylene carbonate / [g] of the compound represented by general formula (1)) is 0.01 to 100.

9. The electrolyte solution according to claim 1, wherein L in the general formula (1) is an ethylene group.

10. The electrolyte solution according to claim 1, further comprising at least one anion-containing compound selected from the group consisting of an anion-containing compound having a P=O bond and a P-F bond, an anion-containing compound having an S=O bond and an S-X bond, where X represents a heteroatom, and an oxalate anion-containing compound.

11. The electrolyte solution according to claim 10, wherein the anion-containing compound is at least one selected from the group consisting of compounds containing difluorophosphate anions, compounds containing fluorosulfonate anions, compounds containing fluorosulfonylimide anions, compounds containing alkylsulfate anions, compounds containing bis(oxalato)borate anions, compounds containing difluorooxalatoborate anions, and compounds containing difluorobis(oxalato)phosphate anions.

12. A method for producing an electrolyte solution, comprising the step of dissolving a compound represented by the following general formula (1), a compound represented by the following formula (2), and an electrolyte in a non-aqueous solvent: (L represents a linear or branched alkylene group having 1 to 6 carbon atoms.) 13. A battery comprising a positive electrode, a negative electrode, and the electrolyte solution according to any one of claims 1 to 11.

14. The battery of claim 13, wherein the positive electrode comprises a lithium transition metal based compound.

15. A method for manufacturing a battery, comprising the steps of: housing a positive electrode and a negative electrode in a container; and injecting the electrolyte solution according to any one of claims 1 to 11 into the container.

16. A vehicle equipped with the battery according to claim 13.

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