Non-aqueous electrolyte and non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte composed of a first component such as a compound represented by formula (I-1), a second component such as a compound represented by formula (II), and a third component such as a compound represented by formula (III) can reduce initial resistance. The groups in the formulas are as described in the specification.

Description

Non-aqueous electrolyte and non-aqueous electrolyte secondary battery

[0001] This disclosure relates to non-aqueous electrolytes and non-aqueous electrolyte secondary batteries.

[0002] In recent years, energy storage devices such as lithium-ion secondary batteries, which are small, lightweight, and high-output, have become even more advanced. As a result of these improvements in performance, their use is expanding not only in small electrical products but also in larger product fields such as automobiles.

[0003] Lithium-ion secondary batteries are required to meet specific requirements regarding various characteristics such as output characteristics, charge / discharge characteristics, and gas generation. However, a very important evaluation criterion is that the output degradation is minimal when stored for long periods in high-temperature environments.

[0004] Patent Document 1 discloses an invention of a non-aqueous electrolyte containing lithium trifluoromethanesulfonate (TFMSLi), lithium difluorophosphate (LiDFP), and lithium bis(oxalato)borate (LiBOB), and reports that using such a non-aqueous electrolyte reduces the resistance value at -10°C after storage at 60°C for 5 days.

[0005] Patent Document 1: International Publication No. 2018 / 181369

[0006] An object of one aspect of this disclosure is to provide a non-aqueous electrolyte that can reduce initial resistance and a non-aqueous electrolyte secondary battery using the same.

[0007] The present inventors, after diligent research to solve the aforementioned problems, have found that initial resistance can be reduced by using a non-aqueous electrolyte containing a specific first component, a specific second component, and a specific third component, and have completed the present invention. That is, one aspect of the present invention is as follows: <1> A non-aqueous electrolyte comprising: one or more first components selected from the group consisting of compounds represented by the following formula (I-1) and compounds represented by the following formula (I-2); one or more second components selected from the group consisting of compounds represented by the following formula (II); and one or more third components selected from the group consisting of compounds represented by the following formula (III), compounds represented by the following formula (IV), and compounds represented by the following formula (V).

[0008]

[0009] (In equations (I-1) and (I-2), M ＋ Each of these independently represents an alkali metal ion, ammonium ion, imidazolium ion, pyridinium ion, pyrrolidinium ion, piperidinium ion, or phosphonium ion.

[0010]

[0011] (In formula (II), R ２１ Each of these independently represents a halogen group (-X), a fluorine carbide group having 1 to 12 carbon atoms which may contain an oxa group (-O-) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a halogen group (-X) and an oxa group (-O-) as a substituent, where i represents an integer from 0 to 3.

[0012]

[0013] (In formula (III), R ３１ R represents a fluorine carbide group having 1 to 12 carbon atoms, which may contain a fluoro group (-F) and an oxa group (-O-) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms, which may contain at least one functional group selected from the group consisting of a fluoro group (-F) and an oxa group (-O-) as a substituent. ３２ This represents a hydrocarbon group having 1 to 12 carbon atoms, which may contain at least one functional group selected from the group consisting of a fluoro group (-F) and an oxa group (-O-) as a substituent, or a fluorine carbide group having 1 to 12 carbon atoms, which may contain an oxa group (-O-) as a substituent. ＋ R represents an alkali metal ion, ammonium ion, imidazolium ion, pyridinium ion, pyrrolidinium ion, piperidinium ion, or phosphonium ion. In formula (IV), R ４１Each independently represents a fluorine carbide group having 1 to 12 carbon atoms, which may contain an oxa group (-O-) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms, which may contain a fluoro group (-F) as a substituent, and j represents an integer from 1 to 4. In formula (V), R ５１ Each of these independently represents a hydrocarbon group having 1 to 12 carbon atoms or a trialkylsilyl group having 3 to 18 carbon atoms.

[0014] <2> The non-aqueous electrolyte according to <1>, wherein the total content of the first component is 0.001% by mass to 5.0% by mass relative to the total amount of the non-aqueous electrolyte. <3> The non-aqueous electrolyte according to <1> or <2>, wherein the total content of the second component is 0.001% by mass to 5.0% by mass relative to the total amount of the non-aqueous electrolyte. <4> The non-aqueous electrolyte according to any one of <1> to <3>, wherein the total content of the third component is 0.001% by mass to 5.0% by mass relative to the total amount of the non-aqueous electrolyte. <5> A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to any one of <1> to <4>. <6> The non-aqueous electrolyte secondary battery according to <5>, wherein the negative electrode comprises a current collector and a negative electrode composite layer formed on the current collector and containing a negative electrode active material, and the negative electrode active material comprises at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles. <7> The non-aqueous electrolyte secondary battery according to <5> or <6>, wherein the negative electrode active material comprises elemental carbon particles and at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles. <8> The non-aqueous electrolyte secondary battery according to any one of <5> to <7>, wherein the total mass of at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles is 30% by mass or less when the total mass of the entire negative electrode active material is 100% by mass.

[0015] According to one aspect of the present invention, a non-aqueous electrolyte that can reduce initial resistance and a non-aqueous electrolyte secondary battery using the same are provided.

[0016] Figure 1 is a schematic cross-sectional view showing a stacked non-aqueous electrolyte secondary battery precursor, which is an example of a precursor for the non-aqueous electrolyte secondary battery of this disclosure. Figure 2 is a schematic cross-sectional view showing a coin-type non-aqueous electrolyte secondary battery precursor, which is another example of a precursor for the non-aqueous electrolyte secondary battery of this disclosure.

[0017] In describing the present invention, specific examples will be given, but the invention is not limited to the following, and can be implemented with appropriate modifications, as long as it does not depart from the spirit of the invention.

[0018] In this disclosure, a numerical range expressed using "~" means a range that includes the numbers written before and after "~" as the lower and upper limits. In numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples. In this disclosure, the amount of each component in a composition means the total amount of multiple substances present in the composition if there are multiple substances corresponding to each component in the composition, unless otherwise specified. In this disclosure, a preferred combination of embodiments means a more preferred embodiment. In this disclosure, the term "process" includes not only independent processes but also processes that are not clearly distinguishable from other processes, as long as their intended purpose is achieved.

[0019] <Non-aqueous electrolyte> A non-aqueous electrolyte according to one aspect of the present invention (hereinafter sometimes abbreviated as "this non-aqueous electrolyte") comprises: "one or more first components selected from the group consisting of "compound represented by formula (I-1)" and "compound represented by formula (I-2)""; "one or more second components selected from the group consisting of "compound represented by formula (II)""; and "one or more third components selected from the group consisting of "compound represented by formula (III)", "compound represented by formula (IV)", and "compound represented by formula (V)".

[0020]

[0021] (In equations (I-1) and (I-2), M ＋each independently represents an alkali metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion.

[0022]

[0023] (In formula (II), R ２１ each independently represents a halogeno group (—X), a fluorocarbon group having 1 to 12 carbon atoms which may contain an oxa group (—O—) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a halogeno group (—X) and an oxa group (—O—) as a substituent, and i represents an integer of 0 to 3.)

[0024]

[0025] (In formula (III), R ３１ represents a fluoro group (—F), a fluorocarbon group having 1 to 12 carbon atoms which may contain an oxa group (—O—) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (—F) and an oxa group (—O—) as a substituent, R ３２ represents a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (—F) and an oxa group (—O—) as a substituent, or a fluorocarbon group having 1 to 12 carbon atoms which may contain an oxa group (—O—) as a substituent, and M ＋ represents an alkali metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion. In formula (IV), R ４１ each independently represents a fluorocarbon group having 1 to 12 carbon atoms which may contain an oxa group (—O—) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms which contains a fluoro group (—F) as a substituent, and j represents an integer of 1 to 4. In formula (V), R ５１ each independently represents a hydrocarbon group having 1 to 12 carbon atoms or a trialkylsilyl group having 3 to 18 carbon atoms.)

[0026] The inventors of this invention have conducted extensive research to solve the aforementioned problems and have found that initial resistance can be reduced by using a non-aqueous electrolyte containing the first, second, and third components. They have confirmed that initial resistance can be reduced not only at room temperature but also at low temperatures, making this non-aqueous electrolyte highly practical. The compounds represented by formula (I-1), formula (I-2), formula (II), formula (III), formula (IV), and formula (V) will be described in detail below.

[0027] [First Component] This non-aqueous electrolyte contains one or more first components selected from the group consisting of compounds represented by the following formula (I-1) and compounds represented by the following formula (I-2).

[0028] (Compound represented by formula (I-1) and compound represented by formula (I-2))

[0029]

[0030] (In equations (I-1) and (I-2), M ＋ Each of these independently represents an alkali metal ion, ammonium ion, imidazolium ion, pyridinium ion, pyrrolidinium ion, piperidinium ion, or phosphonium ion.

[0031] The compounds represented by formula (I-1) and formula (I-2) may also act as electrolytes as described later, but in this non-aqueous electrolyte, "(first) component" refers to any compound that is present in the non-aqueous electrolyte regardless of its function.

[0032] M ＋ This represents "alkali metal ions," "ammonium ions," "imidazolium ions," "pyridinium ions," "pyrrolidinium ions," "piperidinium ions," or "phosphonium ions," but as an alkali metal ion, lithium ions (Li ＋ ), sodium ions (Na ＋ ), potassium ions (K＋ Examples of ammonium ions include the ion represented by the following formula (m1), imidazolium ions include the ion represented by the following formula (m2), pyridinium ions include the ion represented by the following formula (m3), pyrrolidinium ions include the ion represented by the following formula (m4), piperidinium ions include the ion represented by the following formula (m5), and phosphonium ions include the ion represented by the following formula (m6).

[0033]

[0034] (In formulas (m1) to (m6), R' is independently a hydrogen atom (-H), or a substituent such as a halogen group, an oxa group (-O-), a carbonyl group (>C=O), or a sulfonyl group (>S (=O)) ２ (This represents a hydrocarbon group having 1 to 20 carbon atoms, which may contain at least one functional group selected from the group consisting of a secondary amino group (-NH-) and a tertiary amino group (-N<).) ＋ For example, lithium ion (Li ＋ It is especially preferable that it be of the following nature.

[0035] The compounds represented by formula (I-1) and formula (I-2) are as follows: Lithium difluorophosphate (LiPO) represented by formula (I-1-1) ２ F ２ ), Lithium monofluorophosphate (Li) represented by the following formula (I-2-1) ２ PO ３ Examples include F). This non-aqueous electrolyte may contain two or more compounds represented by formula (I-1) and a compound represented by formula (I-2).

[0036]

[0037] The content of the compound represented by formula (I-1) and the compound represented by formula (I-2) in this non-aqueous electrolyte is usually 0.001% by mass or more and 10% by mass or less, relative to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is considered to be 100% by mass), preferably 0.01% by mass or more as the lower limit, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more as the lower limit, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less as the upper limit. When the content of these compounds is within the above range, it becomes easier to reduce the initial resistance.

[0038] The total content of the first component of this non-aqueous electrolyte is usually 0.001% by mass or more and 10% by mass or less relative to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is considered as 100% by mass), preferably 0.01% by mass or more as the lower limit, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more as the lower limit, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less as the upper limit. When the content of these compounds is within the above range, it becomes easier to reduce the initial resistance.

[0039] [Second component] This non-aqueous electrolyte contains one or more second components selected from the group consisting of compounds represented by the following formula (II).

[0040] (The compound represented by formula (II))

[0041]

[0042] (In formula (II), R ２１ Each of these independently represents a halogen group (-X), a fluorine carbide group having 1 to 12 carbon atoms which may contain an oxa group (-O-) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a halogen group (-X) and an oxa group (-O-) as a substituent, where i represents an integer from 0 to 3.

[0043] The compound represented by formula (II) may also act as a non-aqueous solvent as described later, but in this non-aqueous electrolyte, the "(second) component" is defined as simply being present in the non-aqueous electrolyte regardless of its function.

[0044] R ２１ These terms independently represent "halogeno group (-X)", "a fluorine carbide group having 1 to 12 carbon atoms which may contain an oxa group (-O-) as a substituent", and "a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a halogeno group (-X) and an oxa group (-O-) as a substituent". However, "fluorine carbide group" refers to a group in which all hydrogen atoms of a hydrocarbon group are replaced with fluorine atoms. "Fluorine carbide group" is also sometimes called a "fluorinated hydrocarbon group" or "fluorinated carbon group", and is a concept that includes perfluoroalkyl groups. Furthermore, fluorine carbide groups are not limited to fluorine carbide groups having a linear structure, but may also be fluorine carbide groups having at least one structure selected from the group consisting of a branched structure, a cyclic structure, and a carbon-carbon unsaturated bond structure (carbon-carbon double bond structure and carbon-carbon triple bond structure). Furthermore, the term "hydrocarbon group" is not limited to aliphatic hydrocarbon groups having a linear structure, but may also include hydrocarbon groups having at least one structure selected from the group consisting of branched structures, cyclic structures, and carbon-carbon unsaturated bond structures (carbon-carbon double bond structures and carbon-carbon triple bond structures). The number of these structures is also not limited, so (acyclic) aliphatic hydrocarbon groups, monocyclic aliphatic hydrocarbon groups, polycyclic aliphatic hydrocarbon groups, monocyclic aromatic hydrocarbon groups, and polycyclic aromatic hydrocarbon groups are all included in "hydrocarbon groups." Naturally, alkyl groups, alkenyl groups, alkynyl groups, aryl groups, etc., are also all included in "hydrocarbon groups." Furthermore, the phrase "may contain at least one functional group selected from the group consisting of halogen groups (-X) and oxa groups (-O-) as substituents" means that the hydrogen atoms of the hydrocarbon group may be substituted with halogen groups such as fluoro groups (-F), chloro groups (-Cl), bromo groups (-Br), and iodine groups (-I), and that the carbon atoms of the hydrocarbon group may also be substituted with oxa groups (-O-).

[0045] R ２１When R is a fluorine carbide group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, and particularly preferably 4 or less. ２１ When the group is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, and particularly preferably 4 or less.

[0046] R ２１ Examples include fluoro groups (-F) and trifluoromethyl groups (-CF) ３ ), pentafluoroethyl group (-C ２ F ５ ), n-heptafluoropropyl group (-C ３ F ７ ), pentafluorophenyl group (-C ６ F ５ ), trifluoromethoxy group (-OCF ３ ), pentafluoroethoxy group (-OC ２ F ５ ), n-heptafluoropropoxy group (-OC ３ F ７ ), pentafluorophenoxy group (-OC ６ F ５ ), fluoromethyl group (-CH ２ F), difluoromethyl group (-CHF ２ ), 2,2,2-trifluoroethyl group (-CH ２ CF ３ ), p-fluorophenyl group (-C ６ H ４ F), methyl group (-CH ３ ), ethyl group (-CH ２ CH ３ ), vinyl group (-CH=CH ２ ), n-propyl group (-CH ２ CH ２ CH ３ ), i-propyl group (-CH(CH ３ ) ２ ), n-butyl group (-CH ２ CH ２ CH ２ CH ３ ), s-butyl group (-CH ２ CH (CH ３ ) ２), t-butyl group (-C(CH ３ ) ２ ), hexyl group (-CH ２ CH ２ CH ２ CH ２ CH ２ CH ３ ), cyclohexyl group (-C ６ H １１ ), phenyl group (-C ６ H ５ ), fluorophenyl group (-C ６ H ４ F), trifluoromethylphenyl group (-C ６ H ４ CF ３ ), trifluoromethoxyphenyl group (-C ６ H ４ OCF ３ Examples include the fluoro group (-F) and the trifluoromethyl group (-CF). ３ ) is particularly preferable.

[0047] i represents an integer between 0 and 3, but it is particularly preferable that it be 0.

[0048] Examples of cyclic carbonate compounds represented by formula (II) include fluoroethylene carbonate (FEC) represented by formula (II-1) below, cyclic carbonate compounds represented by formula (II-2) below, and cyclic carbonate compounds represented by formula (II-3) below. This non-aqueous electrolyte may contain two or more cyclic carbonate compounds represented by formula (II).

[0049]

[0050] The content of the compound represented by the formula (II) in the non-aqueous electrolyte is usually 0.001% by mass or more and 10% by mass or less with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). The lower limit is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more. The upper limit is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, still more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less. When the content of these compounds is within the above range, it is easy to reduce the initial resistance.

[0051] The total content of the second component of the non-aqueous electrolyte is usually 0.001% by mass or more and 10% by mass or less with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). The lower limit is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more. The upper limit is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, still more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less. When the content of these compounds is within the above range, it is easy to reduce the initial resistance.

[0052] [Third Component] The non-aqueous electrolyte contains at least one third component selected from the group consisting of a compound represented by the following formula (III), a compound represented by the following formula (IV), and a compound represented by the following formula (V).

[0053] (Compound Represented by Formula (III))

[0054]

[0055] (In formula (III), R ３１ represents a fluoro group (-F), a fluorocarbon group having 1 to 12 carbon atoms which may contain an oxa group (-O-) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F) and an oxa group (-O-) as a substituent, and R ３２represents a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F) and an oxa group (-O-), or a fluorocarbon group having 1 to 12 carbon atoms which may contain an oxa group (-O-) as a substituent, and M ＋ represents an alkali metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion.)

[0056] The compound represented by formula (III) may act as an electrolyte described later, but in this non-aqueous electrolyte, the "(third) component" may be contained in the non-aqueous electrolyte regardless of its action.

[0057] R ３１ each independently represents a "fluoro group (-F)", a "fluorocarbon group having 1 to 12 carbon atoms which may contain an oxa group (-O-) as a substituent", or a "hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F) and an oxa group (-O-) as a substituent", and "fluorocarbon group" etc. have the same meaning as described above. The oxa group (-O-) may be located at the terminal in the fluorocarbon group or hydrocarbon group. For example, it is at the position bonded to the sulfonyl group (>S(=O) ２ ) of formula (III), and may be an alkoxy group (-OR) as R ３１ .

[0058] R ３１ When R is a fluorocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less. Also, when R ３１ is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0059] R ３１ Examples of R include a fluoro group (-F), a trifluoromethyl group (-CF ３ ), a pentafluoroethyl group (-C ２ F ５), n-heptafluoropropyl group (-C ３ F ７ ), pentafluorophenyl group (-C ６ F ５ ), trifluoromethoxy group (-OCF ３ ), pentafluoroethoxy group (-OC ２ F ５ ), n-heptafluoropropoxy group (-OC ３ F ７ ), pentafluorophenoxy group (-OC ６ F ５ ), fluoromethyl group (-CH ２ F), difluoromethyl group (-CHF ２ ), 2,2,2-trifluoroethyl group (-CH ２ CF ３ ), p-fluorophenyl group (-C ６ H ４ F), methyl group (-CH ３ ), ethyl group (-CH ２ CH ３ ), vinyl group (-CH=CH ２ ), n-propyl group (-CH ２ CH ２ CH ３ ), i-propyl group (-CH(CH ３ ) ２ ), n-butyl group (-CH ２ CH ２ CH ２ CH ３ ), s-butyl group (-CH ２ CH (CH ３ ) ２ ), t-butyl group (-C(CH ３ ) ２ ), hexyl group (-CH ２ CH ２ CH ２ CH ２ CH ２ CH ３ ), cyclohexyl group (-C ６ H １１ ), phenyl group (-C ６ H ５ ), fluorophenyl group (-C ６ H ４F), trifluoromethylphenyl group (-C ６ H ４ CF ３ ), trifluoromethoxyphenyl group (-C ６ H ４ OCF ３ Examples include the fluoro group (-F) and the trifluoromethyl group (-CF). ３ ) is particularly preferable.

[0060] R ３２ This represents a "carbonic group having 1 to 12 carbon atoms that may contain at least one functional group selected from the group consisting of a fluoro group (-F) and an oxa group (-O-) as a substituent," or a "fluorine carbide group having 1 to 12 carbon atoms that may contain an oxa group (-O-) as a substituent," but "hydrocarbon group," etc., are synonymous with those mentioned above. The oxa group (-O-) may be located at the terminal end of the fluorine carbide group or hydrocarbon group, for example, at a position bonded to the carbonyl group (>C=O) of formula (III), R ３２ It may also be an alkoxy group (-OR).

[0061] R ３２ When R is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, and particularly preferably 4 or less. ３２ When the group is a fluorine carbide group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, and particularly preferably 4 or less.

[0062] R ３２ For example, a methoxy group (-OCH ３ ), ethoxy group (-OCH ２ CH ３ ), n-propoxy group (-OCH ２ CH ２ CH ３ ), t-butyroxy group (-OC(CH ３ ) ２ ), phenoxy group (-OC ６ H ５ ), fluorophenoxy group (-OC ６ H ４F), trifluoromethylphenoxy group (-OC ６ H ４ CF ３ ), trifluoromethoxyphenoxy group (-OC ６ H ４ OCF ３ ), methyl group (-CH ３ ), ethyl group (-CH ２ CH ３ ), vinyl group (-CH=CH ２ ), n-propyl group (-CH ２ CH ２ CH ３ ), i-propyl group (-CH(CH ３ ) ２ ), n-butyl group (-CH ２ CH ２ CH ２ CH ３ ), s-butyl group (-CH ２ CH (CH ３ ) ２ ), t-butyl group (-C(CH ３ ) ２ ), hexyl group (-CH ２ CH ２ CH ２ CH ２ CH ２ CH ３ ), cyclohexyl group (-C ６ H １１ ), phenyl group (-C ６ H ５ ), fluoromethyl group (-CH ２ F), difluoromethyl group (-CHF ２ ), 2,2,2-trifluoroethyl group (-CH ２ CF ３ ), p-fluorophenyl group (-C ６ H ４ F), fluorophenyl group (-C ６ H ４ F), trifluoromethylphenyl group (-C ６ H ４ CF ３ ), trifluoromethoxyphenyl group (-C ６ H ４ OCF ３ ), trifluoromethoxy group (-OCF３ ), pentafluoroethoxy group (-OC ２ F ５ ), n-heptafluoropropoxy group (-OC ３ F ７ ), pentafluorophenoxy group (-OC ６ F ５ ), trifluoromethyl group (-CF ３ ), pentafluoroethyl group (-C ２ F ５ ), n-heptafluoropropyl group (-C ３ F ７ ), pentafluorophenyl group (-C ６ F ５ Examples include the methoxy group (-OCH). ３ ), ethoxy group (-OCH ２ CH ３ ), n-propoxy group (-OCH ２ CH ２ CH ３ ) is particularly preferable.

[0063] Examples of compounds represented by formula (III) include lithium salts represented by formula (III-1), formula (III-2), formula (III-3), and formula (III-4). This non-aqueous electrolyte may contain two or more compounds represented by formula (III).

[0064]

[0065] The content of the compound represented by formula (III) in this non-aqueous electrolyte is usually 0.001% by mass or more and 10% by mass or less, relative to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is considered to be 100% by mass), preferably 0.01% by mass or more as the lower limit, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more as the lower limit, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less as the upper limit. When the content of these compounds is within the above range, it becomes easier to reduce the initial resistance.

[0066] (Compound represented by formula (IV))

[0067]

[0068] (In formula (IV), R ４１ Each of these independently represents a fluorine carbide group having 1 to 12 carbon atoms, which may contain an oxa group (-O-) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms, which may contain a fluoro group (-F) as a substituent, and j represents an integer from 1 to 4.

[0069] The compound represented by formula (IV) may also act as a non-aqueous solvent as described later, but in this non-aqueous electrolyte, the "(third) component" is defined as simply being present in the non-aqueous electrolyte regardless of its function.

[0070] R ４１ These terms independently represent "a fluorine carbide group having 1 to 12 carbon atoms that may contain an oxa group (-O-) as a substituent" or "a hydrocarbon group having 1 to 12 carbon atoms that contains a fluoro group (-F) as a substituent," but "fluorine carbide group," etc., are synonymous with the terms mentioned above.

[0071] R ４１ When R is a fluorine carbide group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, and particularly preferably 4 or less. ４１ When the group is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, and particularly preferably 4 or less.

[0072] R ４１ For example, the trifluoromethyl group (-CF ３ ), pentafluoroethyl group (-C ２ F ５ ), n-heptafluoropropyl group (-C ３ F ７ ), pentafluorophenyl group (-C ６ F ５ ), trifluoromethoxy group (-OCF ３ ), pentafluoroethoxy group (-OC ２ F ５ ), n-heptafluoropropoxy group (-OC ３ F７ ), pentafluorophenoxy group (-OC ６ F ５ ), fluoromethyl group (-CH ２ F), difluoromethyl group (-CHF ２ ), 2,2,2-trifluoroethyl group (-CH ２ CF ３ ), p-fluorophenyl group (-C ６ H ４ F), fluorophenyl group (-C ６ H ４ F), trifluoromethylphenyl group (-C ６ H ４ CF ３ ), trifluoromethoxyphenyl group (-C ６ H ４ OCF ３ Examples include the trifluoromethyl group (-CF ３ ) is particularly preferable.

[0073] j represents an integer between 1 and 4, but it is particularly preferable that it be 1.

[0074] Examples of cyclic carbonate compounds represented by formula (IV) include trifluoropropylene carbonate (TFPC) represented by formula (IV-1), cyclic carbonate compounds represented by formula (IV-2), and cyclic carbonate compounds represented by formula (IV-3). This non-aqueous electrolyte may contain two or more cyclic carbonate compounds represented by formula (IV).

[0075]

[0076] The content of the compound represented by formula (IV) in this non-aqueous electrolyte is usually 0.001% by mass or more and 10% by mass or less relative to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is considered to be 100% by mass), preferably 0.01% by mass or more as the lower limit, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more as the lower limit, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less as the upper limit. When the content of these compounds is within the above range, it becomes easier to reduce the initial resistance.

[0077] (The compound represented by formula (V))

[0078]

[0079] (In formula (V), R ５１ Each of these independently represents a hydrocarbon group having 1 to 12 carbon atoms or a trialkylsilyl group having 3 to 18 carbon atoms.

[0080] R ５１ These terms independently represent either a "hydrocarbon group with 1 to 12 carbon atoms" or a "trialkylsilyl group with 3 to 18 carbon atoms," but "hydrocarbon group," etc., are synonymous with the terms mentioned above. Also, a "trialkylsilyl group with 3 to 18 carbon atoms" is represented as -SiR ３ As shown, it is a group in which three hydrocarbon groups are bonded to a silicon atom, and the number of carbon atoms represents the total number of carbon atoms in the three hydrocarbon groups.

[0081] R ５１ When is a hydrocarbon group, the number of carbon atoms is preferably 2 or more, more preferably 3 or more, preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. ５１ When the group is a trialkylsilyl group, the number of carbon atoms is preferably 12 or less, more preferably 9 or less, even more preferably 6 or less, and particularly preferably 4 or less.

[0082] R ５１ The hydrocarbon group is a methyl group (-CH ３ ), ethyl group (-CH ２ CH ３), vinyl group (-CH=CH ２ ), n-propyl group (-CH ２ CH ２ CH ３ ), i-propyl group (-CH(CH ３ ) ２ ), n-butyl group (-CH ２ CH ２ CH ２ CH ３ ), s-butyl group (-CH ２ CH (CH ３ ) ２ ), t-butyl group (-C(CH ３ ) ２ ), cyclohexyl group (-C ６ H １１ ), phenyl group (-C ６ H ５ ) are some examples, and also R ６１ The trialkylsilyl group is a trimethylsilyl group (-Si(CH) ３ ) ３ ), triethylsilyl group (-Si(CH ２ CH ３ ) ３ Examples include i-propyl group (-CH(CH ３ ) ２ ), cyclohexyl group (-C ６ H １１ ), or trimethylsilyl group (-Si(CH ３ ) ３ ) is particularly preferable.

[0083] Examples of compounds represented by formula (V) include N,N'-di-i-propylcarbodiimide (DIC) represented by formula (V-1) below, N,N'-dicyclohexylcarbodiimide (DCC) represented by formula (V-2) below, and N,N'-bis(trimethylsilyl)carbodiimide represented by formula (V-3) below. This non-aqueous electrolyte may contain two or more compounds represented by formula (V).

[0084]

[0085] The content of the compound represented by formula (V) in this non-aqueous electrolyte is usually 0.001% by mass or more and 10% by mass or less, relative to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is considered to be 100% by mass), preferably 0.01% by mass or more as the lower limit, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more as the lower limit, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less as the upper limit. When the content of these compounds is within the above range, it becomes easier to reduce the initial resistance.

[0086] The total content of the third component in this non-aqueous electrolyte is usually 0.001% by mass or more and 10% by mass or less relative to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is considered as 100% by mass), preferably 0.01% by mass or more as the lower limit, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more as the lower limit, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less as the upper limit. When the content of these compounds is within the above range, it becomes easier to reduce the initial resistance.

[0087] (Non-aqueous solvent) Non-aqueous electrolytes generally contain a non-aqueous solvent. Various known non-aqueous solvents can be appropriately selected. There may be only one type of non-aqueous solvent, or there may be two or more types.

[0088] Examples of non-aqueous solvents include cyclic carbonates, fluorinated cyclic carbonates, linear carbonates, fluorinated linear carbonates, aliphatic carboxylic acid esters, fluorinated aliphatic carboxylic acid esters, γ-lactones, fluorinated γ-lactones, cyclic ethers, fluorinated cyclic ethers, linear ethers, fluorinated linear ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, and dimethyl sulfoxide phosphate. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of fluorinated cyclic carbonates include fluoroethylene carbonate (FEC). Examples of linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC). Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylbutyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, and ethyl trimethylbutyrate. Examples of γ-lactones include γ-butyrolactone and γ-valerolactone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane. Examples of linear ethers include 1,2-diethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane. Examples of nitriles include acetonitrile, glutalonitrile, adiponitrile, methoxyacetonitrile, and 3-methoxypropionitrile. Examples of amides include N,N-dimethylformamide.Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone.

[0089] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, linear carbonates, and fluorine-containing linear carbonates. In this case, the total proportion of cyclic carbonates, fluorine-containing cyclic carbonates, linear carbonates, and fluorine-containing linear carbonates is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the non-aqueous solvent.

[0090] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates and linear carbonates. In this case, the total proportion of cyclic carbonates and linear carbonates in the non-aqueous solvent is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the non-aqueous solvent.

[0091] The upper limit of the non-aqueous solvent content is preferably 99% by mass, more preferably 97% by mass, and even more preferably 90% by mass, relative to the total amount of the non-aqueous electrolyte. The lower limit of the non-aqueous solvent content is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, relative to the total amount of the non-aqueous electrolyte.

[0092] The intrinsic viscosity of the non-aqueous solvent is preferably 10.0 mPa·s or less at 25°C, from the viewpoint of further improving the dissociation of the electrolyte and the mobility of ions.

[0093] (Electrolytes) Non-aqueous electrolytes generally contain electrolytes.

[0094] The electrolyte preferably contains at least one of a lithium salt containing fluorine (hereinafter sometimes referred to as "fluorinated lithium salt") and a lithium salt that does not contain fluorine.

[0095] Examples of fluorinated lithium salts include inorganic acid anionic salts and organic acid anionic salts. An example of an inorganic acid anionic salt is lithium hexafluoride phosphate (LiPF). ６ ), lithium tetrafluoroborate (LiBF ４ ), lithium hexafluoride arsenate (LiAsF ６ ), lithium tantalate hexafluoride (LiTaF ６ Examples of organic acid anionic salts include lithium bis(pentafluoroethanesulfonyl)imide (Li(C)). ２ F ５ SO ２ ) ２ Examples include N). Among them, lithium hexafluoride phosphate (LiPF) is an example of a fluorinated lithium salt. ６ ) is even more preferable.

[0096] Lithium salts that do not contain fluorine include lithium perchlorate (LiClO2). ４ ), lithium aluminum tetrachloride (LiAlCl ４ ), lithium decachlorodecaborate (Li ２ B １０ Cl １０ ) are some examples.

[0097] When the electrolyte contains a fluorinated lithium salt, the content of the fluorinated lithium salt is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass, relative to the total amount of the electrolyte. ６ If it contains lithium hexafluoride phosphate (LiPF), ６ The content ratio of ) is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, relative to the total amount of electrolyte.

[0098] When the non-aqueous electrolyte contains an electrolyte, the concentration of the electrolyte in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3 mol / L or less, more preferably 0.5 mol / L or more and 2 mol / L or less.

[0099] The non-aqueous electrolyte is lithium hexafluoride phosphate (LiPF). ６ ) If it contains lithium hexafluoride phosphate (LiPF) in a non-aqueous electrolyte, ６ The concentration of the substance is preferably 0.1 mol / L or more and 3 mol / L or less, more preferably 0.5 mol / L or more and 2 mol / L or less.

[0100] <Non-aqueous electrolyte secondary battery> Another embodiment of the present invention is a non-aqueous electrolyte secondary battery comprising a "positive electrode," a "negative electrode," a "non-aqueous electrolyte," and a "separator." The "positive electrode," "negative electrode," "separator," etc. will be described in detail below.

[0101] (Positive electrode) A positive electrode can typically be manufactured by dispersing a positive electrode active material, a binder, and, if necessary, a conductive additive and a thickener in a solvent to form a slurry, applying this slurry to a current collector, drying it, and compressing it to form a positive electrode composite layer (also called a "positive electrode active material layer") on the current collector.

[0102] As the positive electrode active material, MoS ２ TiS ２ MnO ２ , V ２ O ５ Transition metal oxides or transition metal sulfides such as LiCoO ２ LiMnO ２ LiMn ２ O ４ LiNiO ２ LiNi Ｘ Co （１－Ｘ） O ２ (0<X<1), LiNi ｘ Co ｙ Mn ｚ O ２ (x, y, and z are each independently greater than 0 and less than 1.00, and the sum of x, y, and z is between 0.99 and 1.00.) (So-called "NCM"; e.g., LiNi) ０．３３ Co ０．３３ Mn ０．３３ O ２ LiNi ０．５ Co ０．３ Mn ０．２ O ２ LiNi０．５ Co ０．２ Mn ０．３ O ２ LiNi ０．６ Co ０．２ Mn ０．２ O ２ LiNi ０．８ Co ０．１ Mn ０．１ O ２ Composite oxides consisting of lithium and transition metals such as Li ｔ Ni １－ｘ－ｙ Co ｘ Al ｙ O ２ (t is between 0.95 and 1.15, x is between 0 and 0.3, y is between 0.1 and 0.2, and the sum of x and y is less than 0.5.) (So-called "NCA"; for example, LiNi ０．８ Co ０．１５ Al ０．０５ O ２ Composite oxides consisting of lithium, transition metals, and typical metals such as ); conductive polymer materials such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline composites; lithium iron phosphate (LiFePO) ４ ), Lithium manganese phosphate (LiMnPO ４ ), Lithium iron manganese phosphate (LiMn ｘ Fe １－ｘ PO ４ ; 0 < x < 1), LiCoPO2 ４ ), lithium nickel phosphate (LiNiPO ４ Examples include lithium metal phosphates such as ) and others.

[0103] Examples of binders for the positive electrode include polyvinylidene fluoride, conductive additives for the positive electrode include carbon black (e.g., acetylene black), amorphous whiskers, and graphite, and thickeners for the positive electrode include carboxymethylcellulose. Organic solvents such as N-methylpyrrolidone can be used as solvents for the slurry used to form the positive electrode.

[0104] The total content of the positive electrode active material in the positive electrode composite layer is usually 70% to 97% by mass, but preferably 75% or more by mass, and preferably 95% or less by mass, when the total content of the positive electrode composite layer is taken as 100% by mass.

[0105] Examples of materials for the positive electrode current collector include aluminum, aluminum alloy, stainless steel, nickel, titanium, tantalum, carbon cloth, and carbon paper.

[0106] (Negative electrode) A negative electrode can usually be manufactured by dispersing a negative electrode active material, a binder, and optionally a conductive additive and a thickener in a solvent to form a slurry, applying this slurry to a current collector, drying it, and compressing it to form a negative electrode composite layer (also called a "negative electrode active material layer") on the current collector.

[0107] The elements or compounds that serve as the negative electrode active material can be classified into (1) elemental carbon and carbon compounds that can be doped / dedoped with lithium ions, (2) metals and alloys that can be alloyed with lithium, and (3) oxides, nitrides, and carbides that can be doped / dedoped with lithium ions. When the negative electrode active material is elemental silicon, a particulate (powdered) elemental or compound is usually used. Furthermore, the negative electrode active material used is not limited to one type, but may be a mixture of two or more types.

[0108] The negative electrode active material preferably includes at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles, and more preferably includes elemental carbon particles and at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles. Examples of elemental carbon particles include graphite (natural graphite, artificial graphite) particles, carbon black particles, activated carbon particles, amorphous carbon particles, etc. Examples of artificial graphite include graphitized MCMB and graphitized MCF. Examples of amorphous carbon materials include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500°C or below, and mesophase pitch carbon fiber (MCF).

[0109] When the element or compound that serves as the negative electrode active material is in the form of particles (powder), its specific shape may include fibrous, spherical, potato-shaped, or flake-shaped.

[0110] When the negative electrode active material contains elemental carbon particles, the median diameter D50 of the elemental carbon is usually 1 μm to 30 μm, preferably 10 μm or more, more preferably 15 μm or more, preferably 25 μm or less, and more preferably 20 μm or less.

[0111] When the negative electrode active material contains elemental carbon particles, the BET specific surface area of ​​the elemental carbon is typically 1.0 m². ２ / g to 5.0m ２ The value is / g, preferably 2.0m ２ / g or more, more preferably 3.0m ２ / g or more, preferably 4.5m ２ / g or less, more preferably 4.0m ２ It is less than or equal to / g.

[0112] Silicon dioxide is SiO ｘ It can be expressed as follows, where x is a variable, i.e., the oxygen atom content in silicon dioxide is not particularly limited, but x is usually 0 ≤ x < 2, preferably 0.2 or more, more preferably 0.4 or more, even more preferably 0.6 or more, preferably 1.8 or less, more preferably 1.6 or less, and even more preferably 1.4 or less.

[0113] The median diameter D50 of elemental silicon particles, silicon oxide particles, or silicon carbide particles is typically 0.5 μm to 20 μm, preferably 1.0 μm or more, more preferably 3.0 μm or more, preferably 15 μm or less, and more preferably 10 μm or less.

[0114] The BET specific surface area of ​​elemental silicon particles, silicon oxide particles, or silicon carbide particles is typically 1.0 m². ２ / g to 5.0m ２ The value is / g, preferably 1.5m ２ / g or more, more preferably 2.0m ２ / g or more, preferably 4.5m ２ / g or less, more preferably 4.0m ２ It is less than or equal to / g.

[0115] When the negative electrode active material includes at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles, the total mass of the at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles is preferably 30% by mass or less when the total mass of the entire negative electrode active material is 100% by mass. When the negative electrode active material includes elemental carbon particles and at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles, the total mass of elemental silicon particles, silicon oxide particles, and silicon carbide particles in the negative electrode active material is usually 1% by mass to 20% by mass, but preferably 3% by mass or more, more preferably 5% by mass or more, preferably 18% by mass or less, and more preferably 15% by mass or less when the total mass of the entire negative electrode active material is 100% by mass.

[0116] When the negative electrode active material includes elemental carbon particles and at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles, the total mass of elemental carbon particles in the negative electrode active material is usually 70% to 99% by mass, but preferably 80% or more by mass, more preferably 85% or more by mass, preferably 95% or less by mass, and more preferably 90% or less by mass, when the total mass of the entire negative electrode active material is taken as 100% by mass. When the total mass of elemental silicon particles, etc., is within the above range, it becomes easier to ensure a balance between the energy density and capacity retention rate of the non-aqueous electrolyte secondary battery.

[0117] The total content of the negative electrode active material in the negative electrode composite layer is usually 70% to 99.5% by mass, but preferably 75% or more by mass, and preferably 99% or less by mass, when the entire negative electrode composite layer is considered to be 100% by mass.

[0118] Examples of binders for the negative electrode include styrene-butadiene rubber (SBR). The total content of the copolymer binder in the negative electrode composite layer is usually 0.1% to 5% by mass, but preferably 0.5% or more by mass, more preferably 1.0% or more by mass, preferably 3% or less by mass, and more preferably 2% or less by mass, when the entire negative electrode composite layer is considered to be 100% by mass.

[0119] The negative electrode composite layer preferably further contains a conductive additive. Examples of conductive additives for the negative electrode include carbon black (e.g., acetylene black), carbon nanotubes, amorphous whiskers, and graphite.

[0120] The total content of the conductive additive in the negative electrode composite layer is usually 0.01% to 3% by mass, when the entire negative electrode composite layer is considered to be 100% by mass, but is preferably 0.05% or more by mass, more preferably 0.1% or more by mass, preferably 2% or less by mass, and more preferably 1% or less by mass.

[0121] The negative electrode composite layer preferably further contains a thickening agent. Including a thickening agent makes it easier to adjust the viscosity of the slurry and improves productivity. Examples of thickening agents for the negative electrode include cellulose derivatives such as carboxymethylcellulose (CMC), carboxyethylcellulose, and hydroxyethylcellulose, polyoxyethylene and its modified forms, polyvinyl alcohol and its modified forms, and polysaccharides.

[0122] The total content of the thickening agent in the negative electrode composite layer is usually 0.1% to 5% by mass, when the entire negative electrode composite layer is considered as 100% by mass, but is preferably 0.5% or more by mass, more preferably 1.0% or more by mass, preferably 3% or less by mass, and more preferably 2% or less by mass.

[0123] The slurry may contain a solvent. Examples of solvents include water, acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, and ethylenediamine. The solvent may also be a mixed solvent obtained by mixing the aforementioned solvents.

[0124] Examples of materials for the negative electrode current collector include copper, nickel, stainless steel, and nickel-plated steel.

[0125] (Separator) One embodiment of the present invention is a non-aqueous electrolyte secondary battery comprising a "positive electrode," a "negative electrode," a "non-aqueous electrolyte," and a "separator." The separator is a porous resin plate. The material of the porous resin plate is a resin, a nonwoven fabric containing this resin, etc. Examples of resins include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, and polyamide. In particular, the separator is preferably a porous resin sheet with a single-layer or multi-layer structure. The material of the porous resin sheet is mainly one or more types of polyolefin resins. The thickness of the separator is preferably 5 μm or more and 30 μm or less. The separator is preferably placed between the positive electrode and the negative electrode.

[0126] <Case> The non-aqueous electrolyte secondary battery of this disclosure may include a case for housing, for example, a laminate of a positive electrode, a separator, and a negative electrode (battery element) and a non-aqueous electrolyte. The shape of the case is not particularly limited and can be appropriately selected depending on the application of the non-aqueous electrolyte secondary battery precursor of this disclosure. Examples of cases include a case including a laminate film, a case consisting of a battery can and a lid that closes the opening of the battery can, and so on.

[0127] <Specific Examples of Non-Aqueous Electrolyte Secondary Battery Precursors> The non-aqueous electrolyte secondary battery of this disclosure will be explained with specific examples. The non-aqueous electrolyte secondary battery of this disclosure is also referred to as a "lithium secondary battery." Figure 1 is a schematic cross-sectional view showing a stacked lithium secondary battery precursor, which is an example of a precursor of the non-aqueous electrolyte secondary battery of this disclosure.

[0128] As shown in Figure 1, the lithium secondary battery precursor 1 is a stacked battery precursor. More specifically, in the lithium secondary battery precursor 1, the battery element 10 is enclosed inside an outer casing 30. The outer casing 30 is made of laminate film. The battery element 10 is fitted with a positive electrode lead 21 and a negative electrode lead 22. The positive electrode lead 21 and the negative electrode lead 22 are led out in opposite directions from the inside to the outside of the outer casing 30.

[0129] As shown in Figure 1, the battery element 10 is made up of a stack of a positive electrode 11, a separator 13, and a negative electrode 12. The positive electrode 11 has a positive electrode composite layer 11B formed on both main surfaces of the positive electrode current collector 11A. The negative electrode 12 has a negative electrode composite layer 12B formed on both main surfaces of the negative electrode current collector 12A. The positive electrode composite layer 11B formed on one main surface of the positive electrode current collector 11A of the positive electrode 11 and the negative electrode composite layer 12B formed on one main surface of the negative electrode current collector 12A of the negative electrode 12 adjacent to the positive electrode 11 face each other via the separator 13.

[0130] The non-aqueous electrolyte of this disclosure is injected into the exterior casing 30 of the lithium secondary battery precursor 1. The non-aqueous electrolyte of this disclosure permeates the positive electrode composite layer 11B, the separator 13, and the negative electrode composite layer 12B. In the lithium secondary battery precursor 1, a single cell layer 14 is formed by the adjacent positive electrode composite layer 11B, the separator 13, and the negative electrode composite layer 12B. The positive electrode and the negative electrode may have their respective active material layers formed on one side of each current collector.

[0131] The lithium secondary battery precursor 1 is a stacked lithium secondary battery precursor, but the lithium secondary battery precursor of this disclosure is not limited to this, and may be, for example, a wound lithium secondary battery precursor. The wound lithium secondary battery precursor is formed by stacking a positive electrode, a separator, a negative electrode, and a separator in that order and winding them in layers. The wound lithium secondary battery precursor includes cylindrical lithium secondary battery precursors and prismatic lithium secondary battery precursors.

[0132] As shown in Figure 1, in the lithium secondary battery precursor 1, the directions in which the positive electrode lead and the negative electrode lead protrude from the inside to the outside of the outer casing 30 are opposite to the outer casing 30, but the disclosure is not limited thereto. For example, the way in which the positive electrode lead and the negative electrode lead protrude from the inside to the outside of the outer casing 30 is the same direction with respect to the outer casing 30.

[0133] An example of the lithium secondary battery of this disclosure described later is a lithium secondary battery obtained by subjecting a lithium secondary battery precursor 1 to charging and discharging.

[0134] Figure 2 is a schematic cross-sectional view showing a coin-type lithium secondary battery precursor, which is another example of a lithium secondary battery precursor of the present disclosure.

[0135] In the coin-type lithium secondary battery precursor shown in Figure 2, a disc-shaped negative electrode 42, a separator 45 injected with a non-aqueous electrolyte, a disc-shaped positive electrode 41, and, if necessary, spacer plates 47 and 48 made of stainless steel or aluminum are stacked in this order and housed between a positive electrode can 43 (hereinafter also referred to as the "battery can") and a sealing plate 44 (hereinafter also referred to as the "battery can lid"). The positive electrode can 43 and the sealing plate 44 are crimped and sealed via a gasket 46. In this example, the non-aqueous electrolyte of this disclosure is used as the non-aqueous electrolyte injected into the separator 45.

[0136] An example of the lithium secondary battery of this disclosure, as described later, is a lithium secondary battery obtained by charging and discharging a coin-type lithium secondary battery precursor shown in Figure 2.

[0137] [Lithium secondary battery and method for manufacturing the same] The method for manufacturing the lithium secondary battery of the present disclosure includes the steps of preparing the lithium secondary battery precursor of the present disclosure described above (hereinafter also referred to as the "preparation step") and the steps of charging and discharging the lithium secondary battery precursor. The lithium secondary battery of the present disclosure is a lithium secondary battery obtained by charging and discharging the lithium secondary battery precursor of the present disclosure described above.

[0138] According to the lithium secondary battery and its manufacturing method disclosed herein, the rate of increase in resistance at room temperature during high-temperature storage of the lithium secondary battery can be reduced.

[0139] The preparation step may simply be a step of preparing a pre-manufactured lithium secondary battery precursor of the present disclosure for use in the charging and discharging process, or it may be a step of manufacturing the lithium secondary battery precursor of the present disclosure. The lithium secondary battery precursor is as described above.

[0140] In the charging and discharging process, the charging and discharging of the lithium secondary battery precursor can be carried out according to known methods. In this process, the charging and discharging cycle may be repeated multiple times for the lithium secondary battery precursor. As described above, this charging and discharging preferably forms an SEI (Solid Electrolyte Interface) film on the surface of the positive electrode (particularly the positive electrode active material) and / or the negative electrode (particularly the negative electrode active material) of the lithium secondary battery precursor.

[0141] The charging and discharging process preferably involves performing a combination of charging and discharging on the lithium secondary battery precursor one or more times in an environment of 25°C to 70°C.

[0142] The following are examples of the embodiments of this disclosure, but this disclosure is not limited to these embodiments. Hereinafter, "%" refers to "mass%" unless otherwise specified.

[0143] [Example 1] <Preparation of Non-Aqueous Electrolyte> Ethylene carbonate (hereinafter sometimes abbreviated as "EC"), dimethyl carbonate (hereinafter sometimes abbreviated as "DMC"), and ethyl methyl carbonate (hereinafter sometimes abbreviated as "EMC") were mixed in a volume ratio of EC:DMC:EMC = 30:35:35. This obtained a mixed solvent as a non-aqueous solvent. LiPF was added to the obtained mixed solvent as an electrolyte. ６ The solution was dissolved so that the concentration in the final non-aqueous electrolyte was 1 mol / L, and an electrolyte (hereinafter sometimes abbreviated as "basic electrolyte") was obtained. Lithium difluorophosphate (LiPO) represented by the following formula (I-1-1) was added to the obtained basic electrolyte. ２ F ２ A non-aqueous electrolyte was obtained by adding fluoroethylene carbonate (FEC) represented by the following formula (II-1) and a lithium salt represented by the following formula (III-1) such that their respective content relative to the total amount of the final non-aqueous electrolyte (values ​​when the total amount of the non-aqueous electrolyte is considered as 100% by mass) is as shown in Table 1 (mass%).

[0144]

[0145] <Fabrication of the positive electrode> Li(Ni) as the positive electrode active material ０．５ Co ０．２ Mn ０．３ O ２ A mixture was obtained by adding (91.7% by mass) of ) (91.7% by mass), carbon black (5.5% by mass) as a conductive additive, and polyvinylidene fluoride (PVdF) (2.8% by mass) as a binder. The obtained mixture was dispersed in N-methylpyrrolidone solvent to obtain a positive electrode mixture slurry. An aluminum foil with a thickness of 20 μm was prepared as a positive electrode current collector. The obtained positive electrode mixture slurry was coated onto the aluminum foil, dried, and then rolled in a press to obtain a sheet-like positive electrode. The positive electrode consists of a positive electrode current collector and a positive electrode active material layer.

[0146] <Preparation of the negative electrode> A negative electrode slurry was obtained by mixing graphite (86.4% by mass), SiO (9.6% by mass) as the negative electrode active material, carbon black (1% by mass) as a conductive additive, 1% by mass of carboxymethylcellulose sodium dispersed in pure water as a thickener, and 2% by mass of styrene-butadiene rubber (SBR) dispersed in pure water as a binder. A copper foil with a thickness of 10 μm was prepared as the negative electrode current collector. The obtained negative electrode slurry was applied to the copper foil, dried, and then rolled in a press to obtain a sheet-like negative electrode. The negative electrode consists of a negative electrode current collector and a negative electrode active material layer.

[0147] <Preparation of the separator> A porous polyethylene film was prepared as the separator.

[0148] <Preparation of Lithium Secondary Battery Precursor> The negative electrode was punched out in a disc shape with a diameter of 14 mm, the positive electrode in a disc shape with a diameter of 13 mm, and the separator in a disc shape with a diameter of 17 mm. This yielded coin-shaped negative electrode, coin-shaped positive electrode, and coin-shaped separator. The obtained coin-shaped negative electrode, coin-shaped separator, and coin-shaped positive electrode were stacked in this order inside a stainless steel battery case (size: 2032). Next, 20 μL of non-aqueous electrolyte was poured into the battery case, impregnating the separator, positive electrode, and negative electrode with the non-aqueous electrolyte. Then, an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring were placed on the positive electrode, and the battery was sealed by crimping the battery case lid via a polypropylene gasket. As a result, a coin-shaped lithium secondary battery precursor (i.e., a lithium secondary battery before charging and discharging) having the configuration shown in Figure 2 was obtained. The size of the lithium secondary battery precursor was 20 mm in diameter and 3.2 mm in height.

[0149] <Fabrication of Lithium-ion Secondary Battery> The lithium-ion secondary battery precursor was subjected to the following processes in order: charging from 1.5V to 4.2V, holding for 5 to 50 hours, charging to 4.2V, and discharging to 2.5V, all within a temperature range of 25°C to 70°C, to obtain a lithium-ion secondary battery.

[0150] <Evaluation of Initial Room Temperature Resistance (25°C)> The lithium-ion secondary battery was charged to 3.7V, and then the DC resistance [Ω] as the initial room temperature resistance (25°C) was measured based on the voltage drop (= voltage before discharge start - voltage 10 seconds after discharge start) and the current value (i.e., the current value corresponding to the discharge rate of 0.1C to 1.0C) for each discharge rate of 0.1C to 1.0C due to "CC10s discharge". For Comparative Example 1, described later, the initial room temperature resistance (25°C) was measured by the same procedure, and the relative value of the initial room temperature resistance (25°C) of Example 1 was calculated when the initial room temperature resistance (25°C) of the lithium-ion secondary battery of Comparative Example 1 was set to 100, and this was expressed as the "Initial Room Temperature Resistance (Relative Value)" (%). The results are shown in Table 1.

[0151] <Evaluation of Initial Low-Temperature Resistance (-10°C)> A lithium-ion secondary battery was charged to 3.7V, then placed in a constant-temperature bath set to 25°C, and the DC resistance [Ω] as the initial low-temperature resistance (-10°C) was measured based on the voltage drop (= voltage before discharge - voltage 10 seconds after discharge) and the current value (i.e., the current value corresponding to the discharge rates of 0.1C to 1.0C) for each discharge rate of 0.1C to 1.0C due to a "CC10s discharge". The initial low-temperature resistance (-10°C) was measured for Comparative Example 1, described later, by the same procedure, and the relative value of the initial low-temperature resistance (-10°C) of Example 1 was calculated when the initial low-temperature resistance (-10°C) of the lithium-ion secondary battery of Comparative Example 1 was set to 100, and this was expressed as the "Initial Low-Temperature Resistance (Relative Value)" (%). The results are shown in Table 1.

[0152] [Comparative Example 1] Lithium difluorophosphate (LiPO) represented by formula (I-1-1) ２ F ２ A non-aqueous electrolyte was prepared by the same procedure as described in Example 1, except that fluoroethylene carbonate (FEC) represented by formula (II-1) and the lithium salt represented by formula (III-1) were not added, and a lithium-ion secondary battery was prepared. Furthermore, the initial room temperature resistance value (25°C) and the initial low temperature resistance value (-10°C) were measured by the same procedure as described in Example 1, and these were used as reference values ​​for the "initial low temperature resistance value (relative value)" and "initial room temperature resistance value (relative value)" in Example 1, etc.

[0153] [Examples 2-3, Comparative Examples 2-4] The same procedure as in Example 1 was followed, except that the types and contents of the components used in the preparation of the non-aqueous electrolyte were changed as shown in Table 1. The results are shown in Table 1. The components shown in Table 1 are lithium difluorophosphate (LiPO) represented by the following formula (I-1-1) ２ F ２ These are fluoroethylene carbonate (FEC) represented by the following formula (II-1), lithium salt represented by the following formula (III-1), trifluoropropylene carbonate (TFPC) represented by the following formula (IV-1), N,N'-di-i-propylcarbodiimide (DIC) represented by the following formula (V-1), and lithium salt (LiBOB) represented by the following formula (VI-1).

[0154]

[0155]

[0156] As is clear from Table 1, by using the non-aqueous electrolytes of Examples 1 to 3, which are composed of the first component, the second component, and the third component, the initial resistance can be reduced not only at room temperature (25°C) but also at low temperatures (-10°C).

[0157] The disclosure of Japanese Patent Application No. 2025-020287, filed on 10 February 2025, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

[0158] 1 Lithium secondary battery precursor 10 Battery element 11 Positive electrode 11A Positive electrode current collector 11B Positive electrode composite layer 12 Negative electrode 12A Negative electrode current collector 12B Negative electrode composite layer 13 Separator 14 Single cell layer 21 Positive electrode lead 22 Negative electrode lead 30 Outer casing 41 Positive electrode 42 Negative electrode 43 Positive electrode can 44 Sealing plate 45 Separator 46 Gasket 47, 48 Spacer plate

Claims

1. One or more first components selected from the group consisting of a compound represented by the following formula (I-1) and a compound represented by the following formula (I-2); one or more second components selected from the group consisting of a compound represented by the following formula (II); and one or more third components selected from the group consisting of a compound represented by the following formula (III), a compound represented by the following formula (IV), and a compound represented by the following formula (V). A non-aqueous electrolyte containing these components. (In formula (I-1) and formula (I-2), M ＋ independently represents an alkali metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion.) (In formula (II), R ２１ independently represents a halogeno group (-X), a fluorocarbon group having 1 to 12 carbon atoms which may contain an oxa group (-O-) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a halogeno group (-X) and an oxa group (-O-) as a substituent, and i represents an integer of 0 to 3.) (In formula (III), R ３１ represents a fluoro group (-F), a fluorocarbon group having 1 to 12 carbon atoms which may contain an oxa group (-O-) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F) and an oxa group (-O-) as a substituent, R ３２ represents a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F) and an oxa group (-O-) as a substituent, or a fluorocarbon group having 1 to 12 carbon atoms which may contain an oxa group (-O-) as a substituent, M ＋ represents an alkali metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion. In formula (IV), R ４１ Each independently represents a fluorine carbide group having 1 to 12 carbon atoms, which may contain an oxa group (-O-) as a substituent, or a hydrocarbon group having 1 to 12 carbon atoms, which may contain a fluoro group (-F) as a substituent, and j represents an integer from 1 to 4. In formula (V), R ５１ Each of these independently represents a hydrocarbon group having 1 to 12 carbon atoms or a trialkylsilyl group having 3 to 18 carbon atoms.

2. The non-aqueous electrolyte according to claim 1, wherein the total content of the first component is 0.001% by mass to 5.0% by mass relative to the total amount of the non-aqueous electrolyte.

3. The non-aqueous electrolyte according to claim 1, wherein the total content of the second component is 0.001% by mass to 5.0% by mass relative to the total amount of the non-aqueous electrolyte.

4. The non-aqueous electrolyte according to claim 1, wherein the total content of the third component is 0.001% by mass to 5.0% by mass relative to the total amount of the non-aqueous electrolyte.

5. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the non-aqueous electrolyte is the non-aqueous electrolyte described in any one of claims 1 to 4.

6. The non-aqueous electrolyte secondary battery according to claim 5, wherein the negative electrode comprises a current collector and a negative electrode composite layer formed on the current collector and containing a negative electrode active material, and the negative electrode active material comprises at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles.

7. The non-aqueous electrolyte secondary battery according to claim 6, wherein the negative electrode active material comprises elemental carbon particles and at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles.

8. The non-aqueous electrolyte secondary battery according to claim 6, wherein the total mass of at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles is 30% by mass or less when the total mass of the entire negative electrode active material is 100% by mass.

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