Nonaqueous electrolyte for nonaqueous electrolyte cell, and nonaqueous electrolyte cell

Abstract

This nonaqueous electrolyte for a nonaqueous electrolyte cell comprises a nonaqueous solvent, an electrolyte salt, and an additive, wherein: the additive includes a pyrazine compound; the pyrazine compound has a pyrazine ring and at least two electron-donating groups Rx bonded to the pyrazine ring; and the at least one pair of electron-donating groups Rx is bonded to the ortho or para positions of the pyrazine ring. Alternatively, the pyrazine compound has a pyrazine ring and at least one carbonyl carbon-containing group Ry, and the carbonyl carbon of the carbonyl carbon-containing group Ry is bonded to the 2-, 3-, 5-, or 6-position of the pyrazine ring.

Description

Nonaqueous electrolyte for nonaqueous electrolyte battery and nonaqueous electrolyte battery

[0001] The present disclosure relates to a nonaqueous electrolyte for a nonaqueous electrolyte battery and a nonaqueous electrolyte battery.

[0002] A nonaqueous electrolyte battery, such as a lithium-ion secondary battery, includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. Metallic foreign matter such as copper or iron may be present in the positive electrode of a nonaqueous electrolyte battery. In such cases, the metallic foreign matter may dissolve and deposit on the negative electrode during charging and discharging of the battery. The deposition of metallic foreign matter on the negative electrode can lead to a decrease in battery characteristics (e.g., voltage).

[0003] Patent Document 1 (Japanese Patent No. 5935228) discloses "a lithium ion secondary battery including an electrolyte solution, the electrolyte solution including a lithium salt, an electrolyte solvent, and methanethiol, the methanethiol being included in an amount of 1 to 10 parts by weight relative to 100 parts by weight of the electrolyte solution, the methanethiol reacting with copper ions generated during operation of the battery to prevent the formation of dendrites due to the reduction of copper on the surface of the negative electrode."

[0004] Patent No. 5935228

[0005] Currently, there is a need for a new additive that can suppress the dissolution and precipitation of metallic foreign matter. In this situation, one of the objects of the present disclosure is to provide a nonaqueous electrolyte that can suppress the deterioration of the characteristics of nonaqueous electrolyte batteries due to the dissolution and precipitation of metallic foreign matter.

[0006] One aspect of the present disclosure is a non-aqueous electrolyte for a non-aqueous electrolyte battery, the non-aqueous electrolyte comprising: a non-aqueous solvent; an electrolyte salt; and an additive; wherein the additive comprises a pyrazine compound having a pyrazine ring and two or more electron-donating groups R bonded to the pyrazine ring. ｘ and at least one pair of the electron donating groups R ｘ relates to a non-aqueous electrolyte for a non-aqueous electrolyte battery, wherein the pyrazine ring is bonded to the ortho- or para-position.

[0007] Another aspect of the present disclosure is a non-aqueous electrolyte for a non-aqueous electrolyte battery, the non-aqueous electrolyte including a non-aqueous solvent, an electrolyte salt, and an additive, the additive including a pyrazine compound, the pyrazine compound including a pyrazine ring and at least one carbonyl carbon-containing group R ｙ and the carbonyl carbon of the carbonyl carbon-containing group is bonded to the 2-, 3-, 5-, or 6-position of the pyrazine ring.

[0008] Yet another aspect of the present disclosure relates to a nonaqueous electrolyte battery including a positive electrode containing a positive electrode active material, a negative electrode facing the positive electrode, and at least one of the nonaqueous electrolytes described above.

[0009] According to the present disclosure, it is possible to suppress the deterioration of the characteristics of non-aqueous electrolyte batteries due to the dissolution and precipitation of metallic foreign matter. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0010] 1 is a partially cutaway perspective view schematically illustrating a non-electrolytic battery according to an embodiment of the present disclosure.

[0011] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and other materials may be applied as long as the invention of the present disclosure can be implemented. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. In the following description, the expression "comprising A" can include "an embodiment substantially consisting of A" and "an embodiment consisting of A."

[0012] [Non-aqueous electrolyte] The non-aqueous electrolyte according to this embodiment is a non-aqueous electrolyte for a non-aqueous electrolyte battery. The non-aqueous electrolyte includes a non-aqueous solvent, an electrolyte salt, and an additive. The additive includes at least one of a first pyrazine compound and a second pyrazine compound described below. The non-aqueous electrolyte may be a first non-aqueous electrolyte containing only the first pyrazine compound as the additive, a second non-aqueous electrolyte containing only the second pyrazine compound as the additive, or a third non-aqueous electrolyte containing both the first pyrazine compound and the second pyrazine compound.

[0013] (First Pyrazine Compound) The first pyrazine compound comprises a pyrazine ring and two or more electron-donating groups R ｘ and two or more electron donating groups R ｘ Among these, at least one pair of electron donating groups R ｘ are bonded to the ortho- or para-position of the pyrazine ring. ｘ The first pyrazine compound having the formula (I) is hereinafter also referred to as "pyrazine compound (OP)."

[0014] The pyrazine compound (OP) is a heterocyclic compound and an aromatic compound. The pyrazine compound (OP) has the following structural formula (1):

[0015]

[0016] The pyrazine ring refers to the portion other than R1 to R4 in structural formula (1). In structural formula (1), two or more selected from R1 to R4 are electron-donating groups R ｘ Two or more electron-donating groups R ｘ At least one pair (at least two) of these have an ortho or para position relationship with respect to each other. For example, with respect to R1, R2 is in the ortho position, R3 is in the para position, and R4 is in the meta position. The bonding positions of R1 to R4 are all equivalent.

[0017] In the structural formula (1), the electron-donating group R ｘ The groups other than R1 to R4 are optional and may be hydrogen atoms. Only two of R1 to R4 are electron donating groups R1 that are in the ortho or para position relative to each other.ｘ and the remainder may be hydrogen atoms.

[0018] When metal foreign matter contaminated in a battery is exposed to the positive electrode potential, metal ions may be dissolved from the metal foreign matter into the non-aqueous electrolyte. These metal ions dissolved into the non-aqueous electrolyte migrate from the positive electrode side to the negative electrode side and precipitate on the negative electrode side. As this dissolution-precipitation reaction progresses, the precipitated metal grows into a dendrite-like structure, resulting in a decrease in the characteristics (e.g., voltage) of the non-aqueous electrolyte battery. Therefore, it is important to suppress the deterioration of characteristics due to the dissolution and precipitation of metal foreign matter in non-aqueous electrolyte batteries.

[0019] As a result of investigating various additives, the inventors of the present application have newly discovered that the use of a pyrazine compound (OP) can significantly suppress the deterioration of properties due to dissolution and precipitation of metals. The present disclosure is based on this new finding.

[0020] The reason why the use of pyrazine compounds (OP) provides such a remarkable effect is currently unknown. However, it can be considered as follows: Pyrazine compounds (OP) have two or more electron-donating groups R ｘ The basicity of the two nitrogen atoms constituting the pyrazine ring is enhanced by this. Therefore, it is presumed that the pyrazine compound (OP) captures metal ions (e.g., copper ions) in the non-aqueous electrolyte using the pyrazine ring and suppresses the reductive precipitation reaction of the metal ions at the negative electrode. At this time, the pyrazine compound (OP) becomes a ligand that coordinates with the metal ion, forming a metal complex. In such a metal complex, the ligands act as steric hindrance, resulting in significant repulsion between the metal complexes. As a result, the metal complex is diffused over a wide area in the non-aqueous electrolyte, which is thought to significantly suppress the phenomenon of localized concentration and precipitation of metal foreign matter, etc.

[0021] It is believed that the pyrazine compound (OP) not only captures metal ions but also coordinates to the surface of the positive electrode active material, thereby significantly suppressing the dissolution and precipitation of metal components from the positive electrode active material.

[0022] The content of the pyrazine compound (OP) in the non-aqueous electrolyte may be 0.01% by mass or more and 10.0% by mass or less. The content may be 0.01% by mass or more, 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 2.0% by mass or more, or 5.0% by mass or more, and may be 10.0% by mass or less, 5.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less, 0.5% by mass or less, or 0.1% by mass or less. The content may be in the range of 0.01 to 10.0% by mass, 0.1 to 10.0% by mass, 0.5 to 10.0% by mass, 1.0 to 10.0% by mass, 2.0 to 10.0% by mass, or 5.0 to 10.0% by mass. Within these ranges, the upper limit may be 5.0 mass%, 2.0 mass%, 1.0 mass%, 0.5 mass%, or 0.1 mass%, as long as the lower limit is not equal to or greater than the upper limit. By setting the content in the range of 0.1 to 5.0 mass% (e.g., 0.5 to 5.0 mass%), particularly high effects can be obtained. By setting the content to 5.0 mass% or less, the influence of the addition of the pyrazine compound (OP) on the charge / discharge characteristics of the battery can be mitigated.

[0023] The non-aqueous electrolyte may contain only one type of compound as the pyrazine compound (OP), or may contain multiple types of compounds.

[0024] Electron-donating group R ｘ Examples of the alkyl group include an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an alkenyloxy group, an alkynyloxy group, an alkylthio group, an alkenylthio group, an alkynylthio group, a phenyl group, a phenoxy group, a hydroxyphenyl group, an alkylphenyl group, a benzyl group, an amino group, a hydroxy group (—OH), and a hydroxyalkyl group.

[0025] Among them, two or more electron donating groups R ｘ Preferably, R contains at least one selected from the group consisting of an alkyl group, an alkoxy group, an alkylthio group, an amino group, and a hydroxy group. ｘ Each of the two or more electron donating groups R may independently be an alkyl group, an alkoxy group, an alkylthio group, an amino group, or a hydroxy group.ｘ may all be different groups, or at least two may be the same group.

[0026] The number of carbon atoms in the alkyl group may be, for example, in the range of 1 to 4. Specifically, the alkyl group may be, for example, at least one selected from the group consisting of a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, and an isobutyl group.

[0027] The number of carbon atoms in the alkoxy group may be, for example, in the range of 1 to 3. Specifically, the alkoxy group may be, for example, at least one selected from the group consisting of a methoxy group, an ethoxy group, a propoxy group, and an isopropoxy group.

[0028] The number of carbon atoms in the alkylthio group may be, for example, in the range of 1 to 3. Specifically, the alkylthio group may be at least one selected from the group consisting of a methylthio group, an ethylthio group, and a propylthio group.

[0029] The amino group is a primary amino group (-NH ２ The amino group may be, for example, a monoalkylamino group, a secondary amino group, or a tertiary amino group. The secondary amino group may be, for example, a monoalkylamino group. The tertiary amino group may be, for example, a dialkylamino group. The alkyl group contained in the monoalkylamino group or dialkylamino group may be, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, or the like.

[0030] The pyrazine compound (OP) is preferably a compound that dissolves in the non-aqueous solvent of the non-aqueous electrolyte. The molecular weight of the pyrazine compound (OP) may be in the range of 100 to 200 (for example, in the range of 108 to 167).

[0031] The pyrazine compounds (OP) include 2-isobutyl-3-methylpyrazine, 2,3-dimethylpyrazine, 2-ethyl-3-methylpyrazine, 2,3,5-trimethylpyrazine, 2-methoxy-3-methylpyrazine, 2,3-diethylpyrazine, 2-methyl-3-propylpyrazine, 2,3,5,6-tetramethylpyrazine, 2-ethoxy-3-methylpyrazine, 2-ethyl-3,5-dimethylpyrazine, 2-butyl-3-methylpyrazine, 2,3-diethyl-5-methylpyrazine, 2-isopropyl The pyrazine compound (OP) preferably includes at least one selected from the group consisting of 2-(2-hydroxy-3-methylpyrazine, 2-isobutyl-3-methoxypyrazine, 2,5-dimethylpyrazine, 5-methylpyrazin-2-amine, 2-hydroxy-3-methylpyrazine, and 2-(aminomethyl)-5-methylpyrazine. By using such a pyrazine compound (OP), particularly high effects can be obtained.

[0032] The pyrazine compound (OP) may be a compound in which the electron-donating group bonded to the pyrazine ring of the above-exemplified compounds is substituted with another electron-donating group.

[0033] (Second Pyrazine Compound) The second pyrazine compound comprises a pyrazine ring and at least one carbonyl carbon-containing group R ｙ and a carbonyl carbon-containing group R ｙ can be rephrased as a group having a carbonyl group (C═O group). ｙ The carbonyl carbon of the carbonyl carbon-containing group R is bonded to the 2-, 3-, 5-, or 6-position of the pyrazine ring. ｙ The second pyrazine compound having the formula (I) may be referred to as "pyrazine compound (CO)" hereinafter.

[0034] The pyrazine compound (CO) is a heterocyclic compound and an aromatic compound. The pyrazine compound (CO) has the following structural formula (2):

[0035]

[0036] The pyrazine ring refers to the portion other than R1 to R4 in structural formula (2). In structural formula (2), one or more selected from R1 to R4 is a carbonyl carbon-containing group R ｙ The bonding positions of R1 to R4 are all equivalent. Only one selected from R1 to R4 is a carbonyl carbon-containing group R ｙ and two or more of the carbonyl carbon-containing groups R ｙ That's fine too.

[0037] In structural formula (2), the carbonyl carbon-containing group R ｙ The groups other than R1 to R4 are optional, but may be hydrogen atoms. Only one or more selected from R1 to R4 are carbonyl carbon-containing groups R ｙ and the remainder may be hydrogen atoms.

[0038] When metal foreign matter contaminated in a battery is exposed to the positive electrode potential, metal ions may be dissolved from the metal foreign matter into the non-aqueous electrolyte. These metal ions dissolved into the non-aqueous electrolyte migrate from the positive electrode side to the negative electrode side and precipitate on the negative electrode side. As this dissolution-precipitation reaction progresses, the precipitated metal grows into a dendrite-like structure, resulting in a decrease in the characteristics (e.g., voltage) of the non-aqueous electrolyte battery. Therefore, it is important to suppress the deterioration of characteristics due to the dissolution and precipitation of metal foreign matter in non-aqueous electrolyte batteries.

[0039] As a result of investigating various additives, the inventors of the present application have newly discovered that the use of a pyrazine compound (CO) can also significantly suppress the deterioration of properties due to metal dissolution and precipitation. The present disclosure is based on this new finding.

[0040] The reason why the use of the pyrazine compound (CO) provides a significant effect is currently unknown. However, it can be considered as follows. The pyrazine compound (CO) contains a C═O-containing group R ｙIt is presumed that at least one of the two nitrogen atoms constituting the pyrazine ring captures metal ions (e.g., copper ions) in the non-aqueous electrolyte, thereby suppressing the reduction and precipitation reaction of the metal ions at the negative electrode. At this time, the pyrazine compound (CO) acts as a ligand that coordinates with the metal ions, forming a metal complex. In such a metal complex, the ligand of the pyrazine compound (CO) acts as a steric hindrance, resulting in significant repulsion between the metal complexes. As a result, the metal complex is diffused over a wide area in the non-aqueous electrolyte, which is thought to significantly suppress the phenomenon of localized concentration and precipitation of metal foreign matter.

[0041] It is believed that the pyrazine compound (CO) not only captures metal ions but also coordinates to the surface of the positive electrode active material, thereby significantly suppressing the dissolution and precipitation of metal components from the positive electrode active material.

[0042] The content of the pyrazine compound (CO) in the non-aqueous electrolyte may be 0.01% by mass or more and 10.0% by mass or less. The content may be 0.01% by mass or more, 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 2.0% by mass or more, or 5.0% by mass or more, and may be 10.0% by mass or less, 5.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less, 0.5% by mass or less, or 0.1% by mass or less. The content may be in the range of 0.01 to 10.0% by mass, 0.1 to 10.0% by mass, 0.5 to 10.0% by mass, 1.0 to 10.0% by mass, 2.0 to 10.0% by mass, or 5.0 to 10.0% by mass. Within these ranges, the upper limit may be 5.0 mass%, 2.0 mass%, 1.0 mass%, 0.5 mass%, or 0.1 mass%, as long as the lower limit is not greater than the upper limit. By setting the content in the range of 0.1 to 5.0 mass% (e.g., 0.5 to 5.0 mass%), particularly high effects can be obtained. By setting the content to 5.0 mass% or less, the influence of the addition of the pyrazine compound (CO) on the charge / discharge characteristics of the battery can be mitigated.

[0043] The non-aqueous electrolyte may contain only one type of compound as the pyrazine compound (CO), or may contain multiple types of compounds.

[0044] In addition, when the non-aqueous electrolyte contains a pyrazine compound (CO) and a pyrazine compound (OP), the total content of the pyrazine compound (CO) and the pyrazine compound (OP) in the non-aqueous electrolyte may be 0.01 mass% or more and 10.0 mass% or less, and may be within any of the above ranges.

[0045] Carbonyl carbon-containing group R ｙ Examples of the alkyl group include a formyl group, a ketone group, a carboxy group, an ester bond-containing group, an amide bond-containing group, an enone group, an acid halide group, an acid anhydride group, a urea bond-containing group, and a urethane bond-containing group.

[0046] Among these, one or more carbonyl carbon-containing groups R ｙ Preferably, the pyrazine compound (CO) contains at least one selected from the group consisting of a formyl group, a ketone group, a carboxy group, an ester bond-containing group, and an amide bond-containing group. ｙ When only one carbonyl carbon-containing group R ｙ is preferably an aldehyde group, a ketone group, a carboxy group, an ester bond-containing group, or an amide bond-containing group. ｙ When the compound has at least one carbonyl carbon-containing group R ｙ is preferably an aldehyde group, a ketone group, a carboxy group, an ester bond-containing group, or an amide bond-containing group. ｙ may all be different groups, or at least two may be the same group.

[0047] Carbonyl carbon-containing group R ｙ The number of carbon atoms may be, for example, in the range of 1 to 4, preferably in the range of 1 to 3, and more preferably 1 or 2.

[0048] Examples of the ketone group include an acetyl group, a 1-phenylethanone group, and a propionyl group. Examples of the ester bond-containing group include a methyl carboxylate group, an acetoxy group, and an ethyl ester group. Examples of the amide bond-containing group include an amide group and an N-methylamide group.

[0049] The pyrazine compound (CO) is preferably a compound that dissolves in the non-aqueous solvent of the non-aqueous electrolyte. The molecular weight of the pyrazine compound (CO) may be in the range of 110 to 200 (for example, in the range of 122 to 195).

[0050] The pyrazine compound (CO) preferably comprises at least one selected from the group consisting of 2-acetylpyrazine, 2-acetyl-3-methylpyrazine, methyl 2-pyrazinecarboxylate, 2-acetyl-3-ethylpyrazine, 2-acetyl-3,5-dimethylpyrazine, ethyl 3-oxo-3-pyrazin-2-ylpropionate, pyrazinamide, pyrazinecarboxylic acid, 5-methylpyrazine-2-carboxylic acid, pyrazine-2-carbohydrazide, 3-hydroxypyrazine-2-carboxamide, 3-aminopyrazine-2-carboxylic acid, methyl 3-aminopyrazine-2-carboxylate, 5-methoxypyrazine-2-carboxylic acid, and 6-fluoro-3-hydroxy-2-pyrazinecarboxamide, or may be any one compound selected from the group. By using such a pyrazine compound (CO), particularly high effects can be obtained.

[0051] The pyrazine compound (CO) is a compound having a C═O-containing group R bonded to the pyrazine ring of the compound exemplified above. ｙ with another C═O-containing group R ｙ The compound may be substituted with the following.

[0052] The content of the pyrazine compound (OP) and the content of the pyrazine compound (CO) in the non-aqueous electrolyte are determined, for example, using gas chromatography under the following conditions. Used equipment: GC-2010 Plus manufactured by Shimadzu Corporation. Column: HP-1 manufactured by J&W (film thickness 1 μm, inner diameter 0.32 mm, length 60 m). Column temperature: heated from 50° C. to 90° C. at a heating rate of 5° C. / min, maintained at 90° C. for 15 minutes, then heated from 90° C. to 250° C. at a heating rate of 10° C. / min, and maintained at 250° C. for 15 minutes. Split ratio: 1 / 50. Linear velocity: 30.0 cm / sec. Injection port temperature: 270° C. Injection volume: 1 μL. Detector: FID 290° C. (sens. 10). １ )

[0053] [Non-aqueous electrolyte battery] The non-aqueous electrolyte battery according to this embodiment includes a positive electrode containing a positive electrode active material, a negative electrode facing the positive electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte is the non-aqueous electrolyte according to this embodiment. That is, the non-aqueous electrolyte included in the non-aqueous electrolyte battery according to this embodiment may be a first non-aqueous electrolyte containing only a first pyrazine compound as the additive, a second non-aqueous electrolyte containing only a second pyrazine compound as the additive, or a third non-aqueous electrolyte containing both the first pyrazine compound and the second pyrazine compound. In other words, the non-aqueous electrolyte battery according to this embodiment includes a positive electrode, a negative electrode, and at least one of the first non-aqueous electrolyte and the second non-aqueous electrolyte.

[0054] The nonaqueous electrolyte battery may include other components. For example, the nonaqueous electrolyte battery typically further includes a separator and an exterior body. The separator is disposed between the positive electrode and the negative electrode. The exterior body houses the nonaqueous electrolyte and an electrode group including the positive electrode, the negative electrode, and the separator. There are no particular limitations on the positive electrode, the negative electrode, the separator, and the exterior body, and known components may be used.

[0055] The configuration of the nonaqueous electrolyte battery is not particularly limited as long as the effects of the present disclosure can be obtained. Examples of nonaqueous electrolyte batteries include nonaqueous electrolyte secondary batteries and nonaqueous electrolyte primary batteries. Examples of nonaqueous electrolyte secondary batteries include lithium ion secondary batteries and metal lithium secondary batteries (lithium secondary batteries). Examples of nonaqueous electrolyte primary batteries include metal lithium primary batteries. There is no limitation on the shape of the nonaqueous electrolyte battery, and it may be cylindrical or rectangular. There is no limitation on the form of the electrode group of the nonaqueous electrolyte battery, and it may be wound or stacked.

[0056] The positive electrode active material may contain a lithium transition metal composite oxide having a layered rock salt structure. The lithium transition metal composite oxide preferably contains at least one element selected from the group consisting of Co, Mn, and Al, and Ni. The proportion of Ni in the elements other than Li and oxygen (O) contained in the lithium transition metal composite oxide may be 80 atomic % or more.

[0057] Examples of components of the nonaqueous electrolyte and nonaqueous electrolyte battery of this embodiment are described below. However, the components of this embodiment are not limited to the following examples. Components of the nonaqueous electrolyte battery other than the nonaqueous electrolyte are not limited to the following examples, and known components may be used. The following mainly describes the case where the nonaqueous electrolyte battery is a lithium ion secondary battery, but components of a nonaqueous electrolyte battery other than a lithium ion secondary battery may be selected according to the battery.

[0058] [Non-aqueous electrolyte] As described above, the non-aqueous electrolyte contains a non-aqueous solvent, an electrolyte salt, and the additive described above. The additive contains at least one of a pyrazine compound (OP) and a pyrazine compound (CO). Examples of the non-aqueous solvent and the electrolyte salt are described below.

[0059] [Non-aqueous Solvent] Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, chain ethers, and cyclic ethers. Examples of cyclic carbonates include propylene carbonate (PC) and ethylene carbonate (EC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylates include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylates include methyl formate, ethyl formate, propyl formate, methyl acetate (MA), ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. Examples of chain ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. One or more hydrogen atoms of the compounds exemplified above may be substituted with fluorine atoms. The nonaqueous electrolyte may contain only one nonaqueous solvent, or may contain two or more nonaqueous solvents.

[0060] [Electrolyte Salt] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０Examples of the lithium salts include lithium carboxylates, lower aliphatic carboxylates, LiCl, LiBr, LiI, borates, and imide salts. Examples of the borates include lithium difluorooxalate borate and lithium bis(oxalate) borate. Examples of the imide salts include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ The non-aqueous electrolyte may contain only one type of electrolyte salt, or may contain two or more types of electrolyte salts.

[0061] The concentration of the electrolyte salt in the nonaqueous electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less.

[0062] The non-aqueous electrolyte may contain other additives, such as at least one selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, and vinylethylene carbonate.

[0063] A gel electrolyte containing a non-aqueous solvent, an electrolyte salt, and a matrix polymer may be used. The matrix polymer may be, for example, a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin.

[0064] [Positive Electrode] The positive electrode includes a positive electrode active material. The positive electrode typically includes a positive electrode current collector and a layer of positive electrode mixture (hereinafter referred to as a "positive electrode mixture layer") held on the positive electrode current collector. In one example of a method for forming the positive electrode mixture layer, first, the components of the positive electrode mixture are dispersed in a dispersion medium to prepare a positive electrode slurry. Next, the positive electrode slurry is applied to the surface of the positive electrode current collector to form a coating film, and the coating film is then dried to form the positive electrode mixture layer. The dried coating film may be rolled. The positive electrode mixture includes a positive electrode active material as an essential component, and may include a binder, a thickener, and the like as optional components.

[0065] [Positive Electrode Active Material] The positive electrode active material is not particularly limited as long as it can be used as a positive electrode active material for a non-aqueous electrolyte battery (e.g., a lithium ion secondary battery). Preferred positive electrode active materials include the above-mentioned lithium transition metal composite oxides.

[0066] From the viewpoint of obtaining a high capacity, it is desirable that the proportion of Ni, Rni, in the elements other than Li and oxygen contained in the lithium transition metal composite oxide is 80 atomic % or more. The proportion Rni may be 85 atomic % or more, or 90 atomic % or more. The proportion Rni may be 95 atomic % or less. When limiting the range, these lower and upper limits can be combined arbitrarily.

[0067] Hereinafter, a lithium transition metal composite oxide that satisfies the following conditions (1) to (3) may be referred to as a "composite oxide HN." (1) The composite oxide HN has a layered rock salt structure. (2) The composite oxide HN contains Ni and at least one element selected from the group consisting of Co, Mn, and Al. (3) In the composite oxide HN, the proportion of Ni to elements other than Li and oxygen is 80 atomic % or more.

[0068] The layered rock-salt structure of the composite oxide HN allows for reversible insertion and desorption of Li ions between the layers. The higher the Ni content, the more lithium ions can be extracted from the composite oxide HN during charging, thereby increasing the capacity.

[0069] On the other hand, metal components are easily dissolved from the composite oxide HN, which tends to increase the resistance of the positive electrode active material. Furthermore, the metal components dissolved from the composite oxide HN, like the dissolution and precipitation of metal foreign matter, can cause a decrease in the characteristics (e.g., voltage) of the nonaqueous electrolyte battery. In contrast, the pyrazine compound (OP) or pyrazine compound (CO) can also be coordinated to the surface of the positive electrode active material, significantly suppressing the dissolution and precipitation of metal components from the positive electrode active material.

[0070] Co, Mn, and Al contribute to stabilizing the crystal structure of the composite oxide HN having a high Ni content. However, from the viewpoint of reducing production costs, a low Co content is preferable. The composite oxide HN having a low Co content or no Co may contain Mn and Al.

[0071] In the composite oxide HN, the ratio Rco of Co to elements other than Li and oxygen is preferably 10 atomic % or less, more preferably 5 atomic % or less, and the composite oxide HN may not contain Co. From the viewpoint of stabilizing the crystal structure of the composite oxide HN, the ratio Rco of Co may be 1 atomic % or more, or 1.5 atomic % or more.

[0072] In the composite oxide HN, the ratio R of Mn to elements other than Li and oxygen may be 10 atomic % or less, or 5 atomic % or less, and may be 1 atomic % or more, 3 atomic % or more, or 5 atomic % or more.

[0073] In the composite oxide HN, the ratio Ral of Al to elements other than Li and oxygen may be 10 atomic % or less, or 5 atomic % or less. The ratio Ral of Al may be 1 atomic % or more, 3 atomic % or more, or 5 atomic % or more.

[0074] The composite oxide HN may be, for example, a compound represented by the formula: Li α Ni(1-x1-x2-yz)Co ｘ１ Mn ｘ２ Al ｙ M ｚ O ２＋β The element M is an element other than Li, Ni, Co, Mn, Al, and oxygen.

[0075] In the above formula, α, which indicates the atomic ratio of lithium, is, for example, 0.95≦α≦1.05. However, α increases or decreases with charge and discharge. In (2+β), which indicates the atomic ratio of oxygen, β satisfies −0.05≦β≦0.05.

[0076] The atomic ratio of Ni, 1-x1-x2-y-z (=v), is 0.8 or more, and may be 0.85 or more, 0.90 or more, or 0.95 or more. The atomic ratio of Ni, v, may be 0.98 or less, or 0.95 or less.

[0077] The x1, which indicates the atomic ratio of Co, is, for example, 0.1 or less (0≦x1≦0.1), and may be 0.08 or less, 0.05 or less, or 0.01 or less. When x1 is 0, this includes cases where Co is below the detection limit.

[0078] The atomic ratio x2 of Mn is, for example, 0.1 or less (0≦x2≦0.1), and may be 0.08 or less, 0.05 or less, or 0.03 or less. x2 may be 0.01 or more, or 0.03 or more. Mn contributes to stabilizing the crystal structure of the composite oxide HN. Furthermore, the inclusion of inexpensive Mn in the composite oxide HN is advantageous for cost reduction.

[0079] The atomic ratio y of Al is, for example, 0.1 or less (0≦y≦0.1), and may be 0.08 or less, 0.05 or less, or 0.03 or less. y may be 0.01 or more, or 0.03 or more. Al contributes to stabilizing the crystal structure of the composite oxide HN.

[0080] The value z representing the atomic ratio of the element M satisfies, for example, 0≦z≦0.10, and may also satisfy 0<z≦0.05 or 0.001≦z≦0.01. The lower and upper limits of these ranges can be combined in any manner.

[0081] The element M may be at least one selected from the group consisting of Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, Sc, and Y. When at least one selected from the group consisting of Nb, Sr, and Ca is contained in the composite oxide HN, it is thought that the surface structure of the composite oxide HN is stabilized, the resistance is reduced, and metal elution is further suppressed. It is more effective if the element M is unevenly distributed in the vicinity of the particle surface of the composite oxide HN.

[0082] The content of elements constituting the composite oxide HN can be measured using an inductively coupled plasma atomic emission spectroscopy (ICP-AES), an electron probe microanalyzer (EPMA), or an energy dispersive X-ray spectroscopy (EDX).

[0083] The composite oxide HN may be a secondary particle formed by agglomeration of a plurality of primary particles. The particle size of the primary particles may be 0.05 μm or more and 1 μm or less. The average particle size of the secondary particles of the composite oxide HN may be 3 μm or more and 30 μm or less, or 5 μm or more and 25 μm or less.

[0084] In this specification, the average particle size of secondary particles refers to the particle size (volume average particle size) at which the volume cumulative value is 50% in the particle size distribution measured by a laser diffraction scattering method. Such a particle size is sometimes referred to as D50. For example, an "LA-750" manufactured by Horiba Ltd. can be used as a measuring device.

[0085] The positive electrode active material may contain a lithium transition metal composite oxide other than the composite oxide HN, but preferably contains a large proportion of the composite oxide HN. The proportion of the composite oxide HN in the positive electrode active material is, for example, 90% by mass or more, or may be 95% by mass or more, or may be 100%.

[0086] (Others) As the binder, for example, a resin material is used. Examples of the binder include fluororesin, polyolefin resin, polyamide resin, polyimide resin, acrylic resin, vinyl resin, and rubber-like material (for example, styrene butadiene copolymer (SBR)). One type of binder may be used alone, or two or more types may be used in combination.

[0087] Examples of thickeners include cellulose derivatives such as cellulose ether. Examples of cellulose derivatives include carboxymethyl cellulose (CMC) and its modified forms, methyl cellulose, etc. One type of thickener may be used alone, or two or more types may be used in combination.

[0088] Examples of conductive materials include carbon nanotubes (CNTs), carbon fibers other than CNTs, and conductive particles (for example, carbon black and graphite).

[0089] The dispersion medium used in the positive electrode slurry is not particularly limited, but examples thereof include water, alcohol, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof.

[0090] The positive electrode current collector may be, for example, a metal foil. The positive electrode current collector may be porous. Examples of porous current collectors include nets, punched sheets, and expanded metals. Examples of materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloys, and titanium. The thickness of the positive electrode current collector is not particularly limited and may be in the range of 1 to 50 μm (for example, in the range of 5 to 30 μm).

[0091] [Negative Electrode] The negative electrode may include at least a negative electrode current collector and may contain a negative electrode active material. The negative electrode may include a negative electrode current collector and a layer of a negative electrode mixture (hereinafter referred to as a negative electrode mixture layer) held on the negative electrode current collector. The negative electrode mixture layer can be formed by applying a negative electrode slurry, in which the components of the negative electrode mixture are dispersed in a dispersion medium, to the surface of the negative electrode current collector and drying the slurry. The dried coating may be rolled.

[0092] The negative electrode mixture contains a negative electrode active material as an essential component, and may contain a binder, a thickener, a conductive agent, and the like as optional components.

[0093] [Negative Electrode Active Material] A material capable of electrochemically absorbing and desorbing lithium ions is preferably used as the negative electrode active material. Examples of such materials include carbonaceous materials and Si-containing materials. The negative electrode may contain one type of negative electrode active material or a combination of two or more types.

[0094] Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon). One type of carbonaceous material may be used alone, or two or more types may be used in combination. Graphite is preferred as the carbonaceous material because it has excellent charge / discharge stability and a small irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0095] Examples of the Si-containing material include simple Si, silicon alloys, silicon compounds (such as silicon oxides), and composite materials in which a silicon phase is dispersed in a lithium ion conductive phase (matrix). Examples of silicon oxides include SiO ｘ The x may be, for example, 0.5≦x<2, or 0.8≦x≦1.6. The lithium ion conductive phase may be SiO ２ At least one selected from the group consisting of a silicate phase and a carbon phase may be used.

[0096] As the binder, thickener, conductive agent, and dispersion medium used in the negative electrode slurry, for example, the materials exemplified for the positive electrode may be used.

[0097] The negative electrode current collector may be, for example, a metal foil. The negative electrode current collector may be porous. Examples of the material for the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy. The thickness of the negative electrode current collector is not particularly limited and may be in the range of 1 to 50 μm (for example, in the range of 5 to 30 μm).

[0098] [Separator] A separator is preferably disposed between the positive electrode and the negative electrode. The separator preferably has high ion permeability and adequate mechanical strength and insulating properties. The separator may be made of a microporous thin film, a woven fabric, a nonwoven fabric, or the like. The separator may be made of polyolefin (polypropylene, polyethylene, etc.), or other materials.

[0099] An example of the structure of a nonaqueous electrolyte battery is a structure in which an electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween is housed in an outer casing together with a nonaqueous electrolyte. However, this is not limited thereto, and other forms of electrode groups may also be applied. For example, a stacked electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween may also be used. The shape of the nonaqueous electrolyte battery is also not limited, and may be, for example, a cylindrical type, a prismatic type, a coin type, a button type, a laminate type, or the like. The nonaqueous electrolyte battery may be a primary battery or a secondary battery.

[0100] As an example of a nonaqueous electrolyte battery according to the present disclosure, the structure of a prismatic nonaqueous electrolyte secondary battery will be described with reference to FIG.

[0101] The nonaqueous electrolyte battery shown in FIG. 1 includes a bottomed prismatic battery case 4, an electrode group 1, and a nonaqueous electrolyte (not shown) housed within the battery case 4. The electrode group 1 includes a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator disposed therebetween. The negative electrode current collector is electrically connected to a negative electrode terminal 6 provided on a sealing plate 5 via a negative electrode lead 3. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode current collector is electrically connected to the back surface of the sealing plate 5 via a positive electrode lead 2. That is, the positive electrode is electrically connected to the battery case 4, which also serves as the positive electrode terminal. The periphery of the sealing plate 5 fits into the open edge of the battery case 4, and the fitting is laser-welded. The sealing plate 5 has an injection hole for the nonaqueous electrolyte. The injection hole is closed with a seal plug 8 after the nonaqueous electrolyte is injected. The nonaqueous electrolyte according to this embodiment is used as the nonaqueous electrolyte.

[0102] (Additional Note) The above description discloses the following technology: (Technology 1) A non-aqueous electrolyte for a non-aqueous electrolyte battery, comprising: a non-aqueous solvent; an electrolyte salt; and an additive, wherein the additive comprises a pyrazine compound, the pyrazine compound comprising a pyrazine ring and two or more electron-donating groups R bonded to the pyrazine ring. ｘ and at least one pair of the electron donating groups R ｘare bonded to the ortho-position or the para-position of the pyrazine ring. ｘ are each independently an alkyl group, an alkoxy group, an alkylthio group, an amino group, or a hydroxy group. (Technology 3) A nonaqueous electrolyte according to Technology 1 or 2, wherein the content of the pyrazine compound is 0.01 mass% or more and 10.0 mass% or less. (Technology 4) A nonaqueous electrolyte according to any one of Technology 1 to 3, wherein the alkyl group has a carbon number in the range of 1 to 4. (Technology 5) A nonaqueous electrolyte according to any one of Technology 1 to 4, wherein the alkoxy group and the alkylthio group each have a carbon number in the range of 1 to 3. (Technology 6) The pyrazine compounds include 2-isobutyl-3-methylpyrazine, 2,3-dimethylpyrazine, 2-ethyl-3-methylpyrazine, 2,3,5-trimethylpyrazine, 2-methoxy-3-methylpyrazine, 2,3-diethylpyrazine, 2-methyl-3-propylpyrazine, 2,3,5,6-tetramethylpyrazine, 2-ethoxy-3-methylpyrazine, 2-ethyl-3,5-dimethylpyrazine, 2-butyl-3-methylpyrazine, 2,3-diethyl-5-methylpyrazine, 2 2-(aminomethyl)-5-methylpyrazine, 2-isopropyl-3-methoxypyrazine, 2-methyl-3-isopropoxypyrazine, 2-ethyl-3-methylthiopyrazine, 2-sec-butyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, 2,5-dimethylpyrazine, 5-methylpyrazine-2-amine, 2-hydroxy-3-methylpyrazine, and 2-(aminomethyl)-5-methylpyrazine. (Technology 7) A nonaqueous electrolyte for a nonaqueous electrolyte battery, comprising: a nonaqueous solvent; an electrolyte salt; and an additive, wherein the additive comprises a pyrazine compound, and the pyrazine compound has a pyrazine ring and at least one carbonyl carbon-containing group R ｙ and wherein the carbonyl carbon-containing group R ｙThe carbonyl carbon-containing group R ｙ is a formyl group, a ketone group, a carboxy group, an ester bond-containing group, or an amide bond-containing group. (Technology 9) The nonaqueous electrolyte according to Technology 7 or 8, wherein the content of the pyrazine compound is 0.01 mass% or more and 10.0 mass% or less. (Technology 10) The nonaqueous electrolyte according to any one of Technology 7 to 9, wherein the number of carbon atoms in the carbonyl carbon-containing group is in the range of 1 to 4. (Technology 11) The nonaqueous electrolyte according to any one of Technologies 7 to 10, wherein the pyrazine compound includes at least one selected from the group consisting of 2-acetylpyrazine, 2-acetyl-3-methylpyrazine, methyl 2-pyrazinecarboxylate, 2-acetyl-3-ethylpyrazine, 2-acetyl-3,5-dimethylpyrazine, ethyl 3-oxo-3-pyrazin-2-ylpropionate, pyrazinamide, pyrazinecarboxylic acid, 5-methylpyrazine-2-carboxylic acid, pyrazine-2-carbohydrazide, 3-hydroxypyrazine-2-carboxamide, 3-aminopyrazine-2-carboxylic acid, methyl 3-aminopyrazine-2-carboxylate, 5-methoxypyrazine-2-carboxylic acid, and 6-fluoro-3-hydroxy-2-pyrazinecarboxamide. (Technology 12) A nonaqueous electrolyte battery comprising: a positive electrode containing a positive electrode active material; a negative electrode facing the positive electrode; and at least one of the nonaqueous electrolyte according to any one of Technologies 1 to 6 and the nonaqueous electrolyte according to any one of Technologies 7 to 11. (Technology 13) The nonaqueous electrolyte battery according to Technology 12, wherein the positive electrode active material contains a lithium transition metal composite oxide having a layered rock salt structure, the lithium transition metal composite oxide contains Ni and at least one element selected from the group consisting of Co, Mn, and Al, and a proportion of Ni to elements other than Li and oxygen contained in the lithium transition metal composite oxide is 80 atomic % or more.

[0103] The present disclosure will be specifically described below based on examples, but the present disclosure is not limited to the following examples.

[0104] (Batteries EX1 to EX6) Non-aqueous electrolyte secondary batteries were fabricated and evaluated according to the following procedure. (1) Fabrication of Positive Electrode Positive electrode active material particles NCA (LiNi ０．８８ Co ０．０９ Al ０．０３ O ２ 100 parts by mass of carbon nanotubes, 1 part by mass of polyvinylidene fluoride, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were mixed to prepare a positive electrode slurry. Next, the positive electrode slurry was applied to one side of an aluminum foil to form a coating film. Next, the coating film was dried and then rolled. In this way, the aluminum foil and the positive electrode mixture layer (thickness: 95 μm, density: 3.6 g / cm ) formed on the aluminum foil were mixed. ３ ) and a positive electrode containing the same.

[0105] (2) Preparation of Negative Electrode 98 parts by mass of negative electrode active material (graphite), 1 part by mass of sodium salt of carboxymethyl cellulose (CMC-Na), 1 part by mass of styrene-butadiene copolymer (SBR), and an appropriate amount of water were mixed to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to one side of copper foil, which serves as a negative electrode current collector, to form a coating film. Next, the coating film was dried and then rolled. In this way, a negative electrode including copper foil and a negative electrode mixture layer formed on the copper foil was obtained.

[0106] (3) Preparation of non-aqueous electrolyte (electrolytic solution) LiPF was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC = 3:7 (volume ratio)). ６ , and a pyrazine compound (OP) were dissolved in the electrolyte to prepare an electrolyte solution (non-aqueous electrolyte). ６ The concentration of the pyrazine compound (OP) was 1.0 mol / L. 2-isobutyl-3-methylpyrazine (structural formula shown in Table 1) was used as the pyrazine compound (OP). The content (concentration) of the pyrazine compound (OP) in the electrolyte solution was the value shown in Table 1.

[0107] (4) Fabrication of a Non-Aqueous Electrolyte Secondary Battery The positive electrode was cut into a predetermined shape. Next, a portion of the positive electrode mixture layer was scraped off to expose the positive electrode current collector, forming a connection area with the positive electrode lead. In this way, a positive electrode including a region functioning as a positive electrode (size: 20 mm × 20 mm) and a connection area with the positive electrode lead was obtained. Spherical copper particles (diameter: approximately 100 μm) were intentionally embedded near the center of the positive electrode mixture layer. Next, the exposed portion of the positive electrode current collector was connected to the positive electrode lead. Next, a predetermined region on the periphery of the positive electrode lead was covered with an insulating tab film. In this way, a positive electrode for evaluation was obtained.

[0108] The negative electrode was cut into the same shape as the positive electrode. Next, the same process as the positive electrode was performed to obtain a negative electrode including a region that functions as a negative electrode and a region that is connected to the negative electrode lead. Next, the exposed portion of the negative electrode current collector was connected to the negative electrode lead. Next, a predetermined region on the periphery of the negative electrode lead was covered with an insulating tab film. In this way, a negative electrode for evaluation was obtained.

[0109] A battery was fabricated using the evaluation positive and negative electrodes. First, an electrode group was obtained by arranging the positive and negative electrodes with a separator between them so that the positive electrode mixture layer and the negative electrode mixture layer faced each other. A polyethylene separator (thickness: 12 μm) was used as the separator. Next, a rectangular (size: 60 mm x 90 mm) Al laminate film (thickness: 100 μm) was cut and folded in half. Next, the 60 mm long edge of the folded laminate film was heat-sealed to form a cylindrical shape with a size of 60 mm x 45 mm. The fabricated electrode group was then placed into the cylinder. Next, the end face of the Al laminate film was aligned with the position of the heat-sealed resin of each lead and sealed. Next, electrolyte was poured into the short side of the Al laminate film that was not heat-sealed, impregnating each mixture layer with the electrolyte. Finally, the end face of the Al laminate film on the poured side was sealed. In this way, evaluation batteries EX1 to EX6 using an exterior body made of an Al laminate film were obtained.

[0110] (5) Evaluation of Self-Discharge Rate A reference battery R1 was prepared for reference. The configuration of the reference battery R1 was the same as that of battery EX1, except that no metallic copper spheres were embedded in the positive electrode and no pyrazine compound (OP) was added to the electrolyte. The resulting reference battery R1 was charged at a constant current of 0.05 C in a temperature environment of 25°C until the battery voltage reached 4.2 V. Here, 1 C is the 1-hour rate current, which is the current value that can use up the entire battery capacity in 1 hour. The battery was then discharged at a constant current of 0.05 C until the battery voltage reached 2.5 V, and a charge / discharge curve was obtained. The battery was left in an open circuit state for 20 minutes between charges and discharges.

[0111] The fabricated evaluation battery EX1 was clamped between a pair of stainless steel clamps (thickness: 2 mm) and fixed at a pressure of 0.2 MPa. Next, three hours after fabrication of battery EX1, battery EX1 was charged at a constant current of 0.05 C in a temperature environment of 25°C until the battery voltage reached 4.2 V. Next, battery EX1 was discharged at a constant current of 0.05 C until the battery voltage reached 2.5 V. Next, battery EX1 was charged until the battery voltage reached 3.58 V (state of charge SOC 28%). Then, battery EX1 was left undisturbed in a 25°C environment. Then, the battery voltage V after 48 hours of being left undisturbed in a 25°C environment was measured. １ and the battery voltage V after 72 hours ２ was measured.

[0112] Battery voltage V １ and V ２ From the charge / discharge curve of the reference battery R1, the state of charge SOC after 48 hours １ (%) and state of charge SOC after 72 hours ２ (%) was calculated based on the charge / discharge curve of the reference battery R1. Next, the self-discharge rate sd per day was calculated based on the following formula. A lower self-discharge rate sd indicates a smaller deterioration in the battery characteristics.

[0113] Self-discharge rate sd (%) = SOC １ (%)-SOC ２ (%)

[0114] The self-discharge rates sd of the other evaluation batteries were determined in the same manner as for battery EX1. Table 1 shows the evaluation results of the self-discharge rates sd of the respective batteries.

[0115]

[0116] (Batteries EX7 to EX12) Batteries EX7 to EX12 were fabricated and evaluated using the same method and conditions as batteries EX1 to EX6, except that the electrolyte was changed. 2,3-dimethylpyrazine (structural formula shown in Table 2) was used as the pyrazine compound (OP) in the electrolyte for batteries EX7 to EX12. Table 2 shows the evaluation results of the self-discharge rate (sd) of each battery.

[0117]

[0118] (Batteries EX13 to EX18) Batteries EX13 to EX18 were fabricated and evaluated using the same method and conditions as batteries EX1 to EX6, except that the electrolyte was changed. 2-methoxy-3-methylpyrazine (structural formula shown in Table 3) was used as the pyrazine compound (OP) in the electrolyte for batteries EX13 to EX18. Table 3 shows the evaluation results of the self-discharge rate (sd) of each battery.

[0119]

[0120] (Batteries EX19 to EX24) Batteries EX19 to EX24 were fabricated and evaluated using the same method and conditions as batteries EX1 to EX6, except that the electrolyte was changed. 2-methyl-3-propylpyrazine (structural formula shown in Table 4) was used as the pyrazine compound (OP) in the electrolyte for batteries EX19 to EX24. Table 4 shows the evaluation results of the self-discharge rate (sd) of each battery.

[0121]

[0122] (Batteries EX25 to EX30) Batteries EX25 to EX30 were fabricated and evaluated using the same method and conditions as batteries EX1 to EX6, except that the electrolyte was changed. 2-ethyl-3-methylthiopyrazine (structural formula shown in Table 5) was used as the pyrazine compound (OP) in the electrolyte for batteries EX25 to EX30. Table 5 shows the evaluation results of the self-discharge rate (sd) of each battery.

[0123]

[0124] (Batteries EX31 to EX36) Batteries EX31 to EX36 were fabricated and evaluated using the same method and conditions as batteries EX1 to EX6, except that the electrolyte was changed. 2,5-dimethylpyrazine (structural formula shown in Table 6) was used as the pyrazine compound (OP) in the electrolyte for batteries EX31 to EX36. Table 6 shows the evaluation results of the self-discharge rate (sd) of each battery.

[0125]

[0126] (Batteries EY1 to EY6) Batteries EY1 to EY6 were fabricated and evaluated using the same method and conditions as batteries EX1 to EX6, except that the electrolyte was changed. In the following batteries, a pyrazine compound (CO) was used instead of a pyrazine compound (OP). 2-acetylpyrazine (structural formula shown in Table 7) was used as the pyrazine compound (CO) in the electrolyte of batteries EY1 to EY6. Table 7 shows the evaluation results of the self-discharge rate (sd) of each battery.

[0127]

[0128] (Batteries EY7 to EY12) Batteries EY7 to EY12 were fabricated and evaluated using the same method and conditions as batteries EX1 to EX6, except that the electrolyte solution was changed. 2-methylpyrazinecarboxylate (structural formula shown in Table 8) was used as the pyrazine compound (CO) in the electrolyte solution for batteries EY7 to EY12. Table 8 shows the evaluation results of the self-discharge rate (sd) of each battery.

[0129]

[0130] (Batteries EY13 to EY18) Batteries EY13 to EY18 were fabricated and evaluated using the same method and conditions as batteries EX1 to EX6, except that the electrolyte solution was changed. Pyrazine amide (structural formula shown in Table 9) was used as the pyrazine compound (CO) in the electrolyte solution of batteries EY13 to EY18. Table 9 shows the evaluation results of the self-discharge rate (sd) of each battery.

[0131]

[0132] (Batteries EY19 to EY24) Batteries EY19 to EY24 were fabricated and evaluated using the same method and conditions as batteries EX1 to EX6, except that the electrolyte solution was changed. Pyrazine carboxylic acid (structural formula shown in Table 10) was used as the pyrazine compound (CO) in the electrolyte solution of batteries EY19 to EY24. Table 10 shows the evaluation results of the self-discharge rate (sd) of each battery.

[0133]

[0134] (Battery R1) Comparative battery R1 was produced in the same manner and under the same conditions as battery EX1, except that the electrolyte solution was changed. No pyrazine compound (OP) was added to the electrolyte solution of battery R1.

[0135] Comparative batteries R2 to R4 were fabricated in the same manner and under the same conditions as battery EX1, except that the electrolyte solution used in batteries R2 to R4 was changed to a compound shown in Table 11 (the structural formula of which is shown in Table 11) instead of the pyrazine compound (OP).

[0136]

[0137] Batteries EX1 to EX36 are nonaqueous electrolyte batteries according to the present disclosure. Batteries R1 to R4 are comparative examples. As shown in Tables 1 to 6 and 11, batteries EX1 to EX36 containing the pyrazine compound (OP) had lower self-discharge rates (sd) than comparative batteries R1 to R4. This is thought to be because the pyrazine compound (OP) captured dissolved copper ions.

[0138] Batteries EY1 to EY24 are nonaqueous electrolyte batteries according to the present disclosure. Batteries R1 to R4 are comparative examples. As shown in Tables 7 to 11, batteries EY1 to EY24 containing the pyrazine compound (CO) had lower self-discharge rates (sd) than the comparative batteries R1 to R4. This is thought to be because the pyrazine compound (CO) captured dissolved copper ions.

[0139] The present disclosure is applicable to non-aqueous electrolytes and non-aqueous electrolyte batteries. Although the present invention has been described with reference to presently preferred embodiments, such disclosure should not be construed as limiting. Various modifications and variations will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Therefore, the appended claims should be construed to cover all modifications and variations that do not depart from the true spirit and scope of the present invention.

[0140] 1: electrode group, 2: positive electrode lead, 3: negative electrode lead, 4: battery case, 5: sealing plate, 6: negative electrode terminal, 7: gasket, 8: sealing plug

Claims

1. A non-aqueous electrolyte for a non-aqueous electrolyte battery, comprising: a non-aqueous solvent; an electrolyte salt; and an additive, wherein the additive comprises a pyrazine compound, the pyrazine compound comprising a pyrazine ring and two or more electron-donating groups R bonded to the pyrazine ring. ｘ and at least one pair of the electron donating groups R ｘ and are bonded to the ortho- or para-position of the pyrazine ring, respectively.

2. Two or more of the electron donating groups R ｘ and each independently represent an alkyl group, an alkoxy group, an alkylthio group, an amino group, or a hydroxy group.

3. The nonaqueous electrolyte according to claim 1, wherein the content of the pyrazine compound is 0.01% by mass or more and 10.0% by mass or less.

4. The non-aqueous electrolyte according to any one of claims 1 to 3, wherein the alkyl group has 1 to 4 carbon atoms.

5. The nonaqueous electrolyte according to any one of claims 1 to 3, wherein the alkoxy group and the alkylthio group each have 1 to 3 carbon atoms.

6. The pyrazine compounds include 2-isobutyl-3-methylpyrazine, 2,3-dimethylpyrazine, 2-ethyl-3-methylpyrazine, 2,3,5-trimethylpyrazine, 2-methoxy-3-methylpyrazine, 2,3-diethylpyrazine, 2-methyl-3-propylpyrazine, 2,3,5,6-tetramethylpyrazine, 2-ethoxy-3-methylpyrazine, 2-ethyl-3,5-dimethylpyrazine, 2-butyl-3-methylpyrazine, 2,3-diethyl-5-methylpyrazine, 2 4. The nonaqueous electrolyte according to claim 1, comprising at least one selected from the group consisting of 2-isopropyl-3-methoxypyrazine, 2-methyl-3-isopropoxypyrazine, 2-ethyl-3-methylthiopyrazine, 2-sec-butyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, 2,5-dimethylpyrazine, 5-methylpyrazin-2-amine, 2-hydroxy-3-methylpyrazine, and 2-(aminomethyl)-5-methylpyrazine.

7. A non-aqueous electrolyte for a non-aqueous electrolyte battery, comprising: a non-aqueous solvent; an electrolyte salt; and an additive; wherein the additive comprises a pyrazine compound, and the pyrazine compound comprises a pyrazine ring and at least one carbonyl carbon-containing group R ｙ and wherein the carbonyl carbon-containing group R ｙ wherein the carbonyl carbon of the formula (I) is bonded to the 2-, 3-, 5- or 6-position of the pyrazine ring.

8. The carbonyl carbon-containing group R ｙ The non-aqueous electrolyte according to claim 7 , wherein is a formyl group, a ketone group, a carboxy group, an ester bond-containing group, or an amide bond-containing group.

9. The nonaqueous electrolyte according to claim 7, wherein the content of the pyrazine compound is 0.01% by mass or more and 10.0% by mass or less.

10. The nonaqueous electrolyte according to any one of claims 7 to 9, wherein the carbonyl carbon-containing group has 1 to 4 carbon atoms.

11. The nonaqueous electrolyte according to any one of claims 7 to 9, wherein the pyrazine compound comprises at least one selected from the group consisting of 2-acetylpyrazine, 2-acetyl-3-methylpyrazine, methyl 2-pyrazinecarboxylate, 2-acetyl-3-ethylpyrazine, 2-acetyl-3,5-dimethylpyrazine, ethyl 3-oxo-3-pyrazin-2-ylpropionate, pyrazinamide, pyrazinecarboxylic acid, 5-methylpyrazine-2-carboxylic acid, pyrazine-2-carbohydrazide, 3-hydroxypyrazine-2-carboxamide, 3-aminopyrazine-2-carboxylic acid, methyl 3-aminopyrazine-2-carboxylate, 5-methoxypyrazine-2-carboxylic acid, and 6-fluoro-3-hydroxy-2-pyrazinecarboxamide.

12. A nonaqueous electrolyte battery comprising: a positive electrode containing a positive electrode active material; a negative electrode facing the positive electrode; and at least one of the nonaqueous electrolyte according to any one of claims 1 to 3 and the nonaqueous electrolyte according to any one of claims 7 to 9.

13. The nonaqueous electrolyte battery according to claim 12, wherein the positive electrode active material contains a lithium transition metal composite oxide having a layered rock salt structure, the lithium transition metal composite oxide contains at least one element selected from the group consisting of Co, Mn, and Al, and Ni, and the proportion of Ni in the elements other than Li and oxygen contained in the lithium transition metal composite oxide is 80 atomic % or more.

Images