Non-aqueous electrolyte and non-aqueous electrolyte secondary batteries

Abstract

The objective is to provide a non-aqueous electrolyte that can reduce the resistance of a battery in the range of moderate or lower SOC, and a non-aqueous electrolyte secondary battery in which the resistance in the range of moderate or lower SOC is reduced. [Solution] A non-aqueous electrolyte containing an imide salt represented by the following formula (I) and at least one carbonate compound selected from the group consisting of the compound represented by the following formula (II-1) and the compound represented by the following formula (II-2) can reduce the resistance of a battery in the range of moderate or lower SOC. The definitions of the groups in the formulas are as described in the specification. JPEG2026052564000018.jpg32100

Description

[Technical Field]

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

[0002] Lithium-ion secondary batteries and other energy storage devices, which are small, lightweight, and high-output, have become even more high-performance in recent years. With this improvement in performance, their use is expanding not only to small electrical products but also to large products such as automobiles. Lithium-ion secondary batteries are required to meet specific requirements regarding various characteristics such as output characteristics and charge / discharge characteristics. For example, Patent Document 1 discloses a non-aqueous electrolyte containing lithium hexafluorophosphate, lithium bis(oxalate)borate, (A) a salt having an FS bond in the molecule, and (B) a salt having a PF bond in the molecule. It has been reported that such a non-aqueous electrolyte can reduce process dependence during battery break-in operation and reduce the range of variation in battery output characteristics due to the initial charge rate during battery break-in operation.

[0003] Furthermore, Patent Document 2 discloses a non-aqueous electrolyte for batteries containing additive A, represented by lithium trifluoromethylsulfonate; additive B, represented by lithium difluorophosphate; additive C, represented by lithium bis(oxalato)borate; lithium hexafluorophosphate; and a specific imide salt (e.g., lithium bis(fluorosulfonyl)imide), and reports that it can reduce battery resistance after storage. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6604014 [Patent Document 2] Japanese Patent Publication No. 2019-175578 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, in batteries such as lithium-ion secondary batteries, the resistance may be higher in the range where the State of Charge (SOC) is moderate or lower (for example, in the range where the SOC is 50% or less; the same applies hereinafter) compared to the range where the SOC is higher.

[0006] An object of one aspect of this disclosure is to provide a non-aqueous electrolyte that can reduce the resistance of a battery in the range of moderate or lower SOC, and a non-aqueous electrolyte secondary battery in which the resistance in the range of moderate or lower SOC is reduced. [Means for solving the problem]

[0007] The means for solving the above problems include the following embodiments. <1> A non-aqueous electrolyte containing an imide salt represented by the following formula (I) and at least one carbonate compound selected from the group consisting of the compound represented by the following formula (II-1) and the compound represented by the following formula (II-2).

[0008] [ka]

[0009] (In formula (I), R 11 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. 12 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. + (This represents alkali metal ions, ammonium ions, imidazolium ions, pyridinium ions, pyrrolidinium ions, piperidinium ions, or phosphonium ions.)

[0010] [ka]

[0011] (In formula (II-1), R 21 Each of these independently represents a fluorine carbide group having 1 to 12 carbon atoms, which may contain a fluoro group (-F) or 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, where i represents an integer from 1 to 4. However, R 21 At least one of these is a fluorine carbide group having 1 to 12 carbon atoms, which may contain a fluoro group (-F), 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. In formula (II-2), R 22 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 at least one functional group selected from the group consisting of a fluoro group (-F) and an oxa group (-O-) as a substituent. However, R 22 At least one of these is 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. <2> The total content of the imide salt is 0.01% to 10% by mass relative to the total amount of the non-aqueous electrolyte. <1> The non-aqueous electrolyte described above. <3> The total content of the carbonate compound is 0.1% to 30.0% by mass relative to the total amount of the non-aqueous electrolyte. <1> or <2> The non-aqueous electrolyte described above. <4> This non-aqueous electrolyte is used in a secondary battery containing at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles as the negative electrode active material. <1> ~ <3> A non-aqueous electrolyte as described in any of the following. <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 <1> ~ <4> A non-aqueous electrolyte secondary battery, which uses a non-aqueous electrolyte as described in any of the following. <6> 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. 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. <5> A non-aqueous electrolyte secondary battery as described above. <7> 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. <6> A non-aqueous electrolyte secondary battery as described above. <8> 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. <7> A non-aqueous electrolyte secondary battery as described above. [Effects of the Invention]

[0012] According to one aspect of the invention disclosed herein, a non-aqueous electrolyte that can reduce the resistance of a battery in the range of moderate or lower SOC is provided, and a lithium-ion secondary battery in which the resistance in the range of moderate or lower SOC is reduced is provided. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a lithium secondary battery (non-aqueous electrolyte secondary battery) precursor according to this disclosure. [Figure 2] 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 (non-aqueous electrolyte secondary battery) precursor of the present disclosure. [Modes for carrying out the invention]

[0014] In explaining the inventions related to this disclosure, specific examples will be given, but the inventions are not limited to the following and can be modified as appropriate, as long as they do not deviate from the spirit of the inventions related to this disclosure.

[0015] In this disclosure, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit of that 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 any multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. In this disclosure, a preferred combination of embodiments is a more preferred embodiment. In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved.

[0016] <Nonaqueous electrolyte> A non-aqueous electrolyte (hereinafter sometimes abbreviated as "this non-aqueous electrolyte") which is one aspect of the invention according to this disclosure, contains an imide salt represented by the following formula (I) (hereinafter sometimes abbreviated as "imide salt") and at least one carbonate compound (hereinafter sometimes abbreviated as "carbonate compound") selected from the group consisting of the compound represented by the following formula (II-1) and the compound represented by the following formula (II-2).

[0017] [ka]

[0018] (In formula (I), R 11represents a fluorine 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 fluorine group (-F) and an oxa group (-O-) as a substituent, R 12 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 fluorine 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.)

[0019] [Chemical formula]

[0020] (In formula (II-1), R 21 each independently represents a fluorine 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 fluorine group (-F) and an oxa group (-O-) as a substituent, and i represents an integer from 1 to 4. However, at least one of R 21 is a fluorine 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 contains a fluorine group (-F) as a substituent.) In formula (II-2), R 22 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 may contain at least one functional group selected from the group consisting of a fluorine group (-F) and an oxa group (-O-) as a substituent. However, R 22At least one of these is 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.

[0021] The inventors, after extensive research into battery resistance, have discovered that by combining the aforementioned imide salt and carbonate compound in a non-aqueous electrolyte, the battery resistance in the range of moderate or lower State of Charge (SOC) can be effectively reduced. Furthermore, it has been revealed that the non-aqueous electrolyte containing the aforementioned imide salt and carbonate compound tends to improve the capacity retention rate after charge-discharge cycles, making it a highly practical non-aqueous electrolyte. The following provides a detailed explanation of "imide salts represented by formula (I)," carbonate compounds such as "compounds represented by formula (II-1)" and "compounds represented by formula (II-2)," etc.

[0022] [Imide salt represented by formula (I)]

[0023] [ka]

[0024] R 11The term "fluoro group (-F)" represents a "fluorinated 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 fluoro group (-F) and an oxa group (-O-) as a substituent." A "fluorinated carbide group" refers to a group in which all hydrogen atoms of a hydrocarbon group are replaced with fluorine atoms. A "fluorinated carbide group" is also sometimes called a "fluorinated hydrocarbon group" or "fluorinated carbon group," and is a concept that includes perfluoroalkyl groups. Furthermore, a fluorinated carbide group is not limited to a fluorinated carbide group having a linear structure, but may also be a fluorinated carbide group 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 refer to 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." Additionally, "may contain at least one functional group selected from the group consisting of fluoro groups (-F) and oxa groups (-O-) as substituents" means that the hydrogen atoms of the hydrocarbon group may be substituted with fluoro groups (-F), and furthermore, the carbon atoms of the hydrocarbon group may be substituted with oxa groups (-O-). Furthermore, the oxa group (-O-) may be located at the terminal end of the fluorine carbide group or hydrocarbon group, for example, at the position where it is bonded to the sulfonyl group (>S(=O)2) of formula (I), R 11 It may also be an alkoxy group (-OR).

[0025] R 11When 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. 11 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.

[0026] R 11 Examples include fluoro group (-F), trifluoromethyl group (-CF3), pentafluoroethyl group (-C2F5), n-heptafluoropropyl group (-C3F7), pentafluorophenyl group (-C6F5), trifluoromethoxy group (-OCF3), pentafluoroethoxy group (-OC2F5), n-heptafluoropropoxy group (-OC3F7), pentafluorophenoxy group (-OC6F5), fluoromethyl group (-CH2F), difluoromethyl group (-CHF2), and 2,2,2-trifluoroethyl group ( -CH2CF3), p-fluorophenyl group (-C6H4F), methyl group (-CH3), ethyl group (-CH2CH3), vinyl group (-CH=CH2), n-propyl group (-CH2CH2CH3), isopropyl group (-CH(CH3)2), n-butyl group (-CH2CH2CH2CH3), s-butyl group (-CH(CH3)CH2CH3), isobutyl group (-CH2CH(CH3)2), t-butyl group (-C(CH3)3), hexyl group (-CH2CH2CH2CH2CH2CH3), cyclohexyl group (-C6H 11 Examples include phenyl groups (-C6H5), fluorophenyl groups (-C6H4F), trifluoromethylphenyl groups (-C6H4CF3), and trifluoromethoxyphenyl groups (-C6H4OCF3). Among these, the fluoro group (-F) and the trifluoromethyl group (-CF3) are particularly preferred.

[0027] R 12This represents "a hydrocarbon 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" and "fluorine carbide group" are R 11 This is equivalent to the case described above.

[0028] R 12 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. 12 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.

[0029] R 12 These include methoxy group (-OCH3), ethoxy group (-OCH2CH3), n-propoxy group (-OCH2CH2CH3), t-butyroxy group (-OC(CH3)2), phenoxy group (-OC6H5), fluorophenoxy group (-OC6H4F), trifluoromethylphenoxy group (-OC6H4CF3), trifluoromethoxyphenoxy group (-OC6H4OCF3), methyl group (-CH3), ethyl group (- CH2CH3), vinyl group (-CH=CH2), n-propyl group (-CH2CH2CH3), isopropyl group (-CH(CH3)2), n-butyl group (-CH2CH2CH2CH3), s-butyl group (-CH(CH3)CH2CH3), isobutyl group (-CH2CH(CH3)2), t-butyl group (-C(CH3)3), hexyl group (-CH2CH2CH2CH2CH2CH3), cyclohexyl group (-C6H 11Examples include phenyl group (-C6H5), fluoromethyl group (-CH2F), difluoromethyl group (-CHF2), 2,2,2-trifluoroethyl group (-CH2CF3), p-fluorophenyl group (-C6H4F), fluorophenyl group (-C6H4F), trifluoromethylphenyl group (-C6H4CF3), trifluoromethoxyphenyl group (-C6H4OCF3), trifluoromethoxy group (-OCF3), pentafluoroethoxy group (-OC2F5), n-heptafluoropropoxy group (-OC3F7), pentafluorophenoxy group (-OC6F5), trifluoromethyl group (-CF3), pentafluoroethyl group (-C2F5), n-heptafluoropropyl group (-C3F7), and pentafluorophenyl group (-C6F5). Among these, the methoxy group (-OCH3), ethoxy group (-OCH2CH3), and n-propoxy group (-OCH2CH2CH3) are particularly preferred.

[0030] 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 formula (C1) below, imidazolium ions include the ion represented by formula (C2) below, pyridinium ions include the ion represented by formula (C3) below, pyrrolidinium ions include the ion represented by formula (C4) below, piperidinium ions include the ion represented by formula (C5) below, and phosphonium ions include the ion represented by formula (C5) below.

[0031] [ka]

[0032] (In formulas (C1) to (C6), R' independently represents a hydrogen atom (-H) or a hydrocarbon group having 1 to 20 carbon atoms, which may contain at least one functional group selected from the group consisting of a halogen group (-X), an oxa group (-O-), a carbonyl group (>C=O), a sulfonyl group (>S(=O)2), a secondary amino group (-NH-), and a tertiary amino group (-N<) as a substituent.) M + For example, lithium ions (Li + It is especially preferable that it be )

[0033] Examples of imide salts represented by formula (I) include imide salts represented by any of the following formulas (I-1) to (I-20). Note that this non-aqueous electrolyte may contain two or more compounds represented by imide salts of formula (I).

[0034] [ka]

[0035] The total content of imide salts in this non-aqueous electrolyte is typically 0.01% by mass or more and 5.0% by mass or less relative to the total amount of non-aqueous electrolyte (when the total amount of non-aqueous electrolyte is considered as 100% by mass), preferably 0.05% by mass or more as the lower limit, more preferably 0.10% by mass or more, even more preferably 0.50% by mass or more, and preferably 3.0% by mass or less as the upper limit, more preferably 1.5% by mass or less, and even more preferably 1.0% by mass or less. When the total content of these compounds is within the above range, it becomes easier to reduce the resistance of the battery in the range of moderate or lower SOC, and it becomes easier to improve the capacity retention rate after charge-discharge cycles.

[0036] [Carbonate compounds] (The compound represented by formula (II-1))

[0037] [ka]

[0038] R21 These independently represent "fluoro group (-F)", "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 fluoro group (-F) and an oxa group (-O-) as a substituent". However, "hydrocarbon group" and "fluorine carbide group" are R 11 This is equivalent to the case in which (-R 21 The structure has an inserted group, which is one or more (-R) groups at a substitutable position in the ethylene carbonate structure. 21 This means that a (-R) group has been introduced. However, the substitutable position is specifically the ethylene group (-CH2CH2-) of the ethylene carbonate structure, and since the four hydrogen atoms of the ethylene group are substitutable, the introduced (-R) group is considered to have been introduced. 21 The number i, which represents the base, can be an integer from 1 to 4. That is, when i is 1, (-R 21 ) One base is introduced, and when i is 4, (-R 21 This means that four groups have been introduced. Also, "R 21 Since at least one of the members is a fluoro group (-F), 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 contains a fluoro group (-F) as a substituent, the compound represented by formula (II-1) will contain at least one fluoro group (-F).

[0039] R 21 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. 11 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.

[0040] R 21These include fluoro group (-F), trifluoromethyl group (-CF3), pentafluoroethyl group (-C2F5), n-heptafluoropropyl group (-C3F7), pentafluorophenyl group (-C6F5), trifluoromethoxy group (-OCF3), pentafluoroethoxy group (-OC2F5), n-heptafluoropropoxy group (-OC3F7), pentafluorophenoxy group (-OC6F5), fluoromethyl group (-CH2F), difluoromethyl group (-CHF2), 2,2,2-trifluoroethyl group (-CH2CF3), p-Fluorophenyl group (-C6H4F), 2-trifluoromethoxyethyl group, methyl group (-CH3), ethyl group (-CH2CH3), vinyl group (-CH=CH2), n-propyl group (-CH2CH2CH3), isopropyl group (-CH(CH3)2), n-butyl group (-CH2CH2CH2CH3), s-butyl group (-CH(CH3)CH2CH3), isobutyl group (-CH2CH(CH3)2), t-butyl group (-C(CH3)3), hexyl group (-CH2CH2CH2CH2CH2CH3), cyclohexyl group (-C6H 11 Examples include ), phenyl group (-C6H5), etc. Among these, the fluoro group (-F) is particularly preferred.

[0041] i represents an integer between 1 and 4, but it is preferably 1 or 2.

[0042] Compounds represented by formula (II-1) include any of the following formulas (II-1-1) to (II-1-11). Note that this non-aqueous electrolyte may contain two or more compounds represented by formula (II-1).

[0043] [ka]

[0044] (The compound represented by formula (II-2))

[0045] [ka]

[0046] R 22 These terms independently represent "a fluorine carbide group having 1 to 10 carbon atoms that may contain an oxa group (-O-) as a substituent" or "a hydrocarbon 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," but "fluorine carbide group" and "hydrocarbon group" are R 11 This is equivalent to the case of "R 22 Since at least one of the members is 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, the compound represented by formula (II-2) will contain at least one fluoro group (-F).

[0047] R 22 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. 12 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.

[0048] R 22Examples of fluorine carbides include trifluoromethyl group (-CF3), pentafluoroethyl group (-C2F5), n-heptafluoropropyl group (-C3F7), pentafluorophenyl group (-C6F5), trifluoromethoxy group (-OCF3), pentafluoroethoxy group (-OC2F5), n-heptafluoropropoxy group (-OC3F7), pentafluorophenoxy group (-OC6F5), fluoromethyl group (-CH2F), difluoromethyl group (-CHF2), 2,2,2-trifluoroethyl group (-CH2CF3), p -Fluorophenyl group (-C6H4F), 2-trifluoromethoxyethyl group, methyl group (-CH3), ethyl group (-CH2CH3), vinyl group (-CH=CH2), n-propyl group (-CH2CH2CH3), isopropyl group (-CH(CH3)2), n-butyl group (-CH2CH2CH2CH3), s-butyl group (-CH(CH3)CH2CH3), isobutyl group (-CH2CH(CH3)2), t-butyl group (-C(CH3)3), hexyl group (-CH2CH2CH2CH2CH2CH3), cyclohexyl group (-C6H 11 Examples include ), phenyl group (-C6H5), etc. Among these, fluoro group (-F), trifluoromethyl group (-CF3), methyl group (-CH3), ethyl group (-CH2CH3), vinyl group (-CH=CH2), n-propyl group (-CH2CH2CH3), n-butyl group (-CH2CH2CH2CH3), t-butyl group (-C(CH3)2), hexyl group (-CH2CH2CH2CH2CH2CH3), cyclohexyl group (-C6H 11 ), a phenyl group (-C6H5) is particularly preferred.

[0049] Compounds represented by formula (II-2) include any of the following formulas (II-2-1) to (II-2-5). Note that this non-aqueous electrolyte may contain two or more compounds represented by formula (II-2).

[0050] [ka]

[0051] The total content of at least one carbonate compound selected from the group consisting of the compound represented by formula (II-1) and the compound represented by formula (II-2) in this non-aqueous electrolyte is usually 0.1% by mass or more and 20.0% by mass or less, with a lower limit of preferably 0.2% by mass or more, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, particularly preferably 2.0% by mass or more, with an upper limit of preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, particularly preferably 8% by mass or less. When the total content of these compounds is within the above range, it becomes easier to reduce the resistance of the battery in the range of moderate or lower SOC, and it becomes easier to improve the capacity retention rate after charge-discharge cycles.

[0052] (Non-aqueous solvent) Non-aqueous electrolytes generally contain a non-aqueous solvent (excluding compounds represented by formula (II-1) and formula (II-2); hereinafter also simply referred to as "non-aqueous solvent"). Various known non-aqueous solvents can be appropriately selected. There may be only one non-aqueous solvent or two or more.

[0053] Examples of non-aqueous solvents include cyclic carbonates, fluorine-containing cyclic carbonates (excluding compounds represented by formula (II-1)), linear carbonates, fluorine-containing linear carbonates (excluding compounds represented by formula (II-2)), aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, γ-lactones, fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, linear ethers, fluorine-containing linear ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolanes, 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 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-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane. Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, and 3-methoxypropionitrile. Examples of amides include N,N-dimethylformamide. Examples of lactam compounds include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone.

[0054] 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, fluorinated cyclic carbonates, linear carbonates, and fluorinated 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, relative to the total amount of the non-aqueous solvent.

[0055] 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, relative to the total amount of the non-aqueous solvent.

[0056] 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.

[0057] 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.

[0058] (electrolyte) Non-aqueous electrolytes generally contain electrolytes.

[0059] 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.

[0060] Examples of fluorinated lithium salts include inorganic acid anionic salts and organic acid anionic salts. Examples of inorganic acid anionic salts include lithium hexafluoride phosphate (LiPF6), lithium borate tetrafluoride (LiBF4), lithium arsenate hexafluoride (LiAsF6), and lithium tantalate hexafluoride (LiTaF6). Examples of organic acid anionic salts include lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), and lithium bis(pentafluoroethanesulfonyl)imide (Li(C2F5SO2)2N). Among these, lithium hexafluoride phosphate (LiPF6) is even more preferred as the fluorinated lithium salt.

[0061] Lithium salts that do not contain fluorine include lithium perchlorate (LiClO4), lithium aluminate tetrachloride (LiAlCl4), and lithium decachlorodecaborate (Li2B 10 Cl 10 ) are some examples.

[0062] 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. When the fluorinated lithium salt contains lithium hexafluoride phosphate (LiPF6), the content of lithium hexafluoride phosphate (LiPF6) 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.

[0063] 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 3.0 mol / L or less, more preferably 0.5 mol / L or more and 2.0 mol / L or less.

[0064] When the non-aqueous electrolyte contains lithium hexafluoride phosphate (LiPF6), the concentration of lithium hexafluoride phosphate (LiPF6) in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3.0 mol / L or less, and more preferably 0.5 mol / L or more and 2.0 mol / L or less.

[0065] <Nonaqueous electrolyte secondary battery> Another embodiment of the invention described herein is a non-aqueous electrolyte secondary battery comprising a "positive electrode," a "negative electrode," a "non-aqueous electrolyte," and a "separator." The following provides a detailed explanation of the "positive electrode," "negative electrode," "separator," etc.

[0066] (positive electrode) Typically, a positive electrode can be manufactured by dispersing a positive electrode active material, a binder, and optionally a conductive additive and a thickener in a solvent to form a slurry, and then 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.

[0067] As for the positive electrode active material, Transition metal oxides or transition metal sulfides such as MoS2, TiS2, MnO2, and V2O5; LiCoO2, LiMnO2, LiMn2O4, LiNiO2, LiNi X Co (1-X) O2(0 <X<1)、LiNi x Co y Mn z O2(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"; for example, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiLiLi 0.5 Co 0.3 Mn 0.2 O2, LiLiLi 0.5 Co 0.2 Mn 0.3 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.8 Co0.1 Mn 0.1 Composite oxides composed of lithium and transition metals such as O2); Li t Ni 1-x-y Co x Al y O2 (where t is 0.95 or more and 1.15 or less, x is 0 or more and 0.3 or less, y is 0.1 or more and 0.2 or less, 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 Composite oxides composed of lithium, transition metals, and typical metals such as O2); Conductive polymer materials such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline composites; Lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium manganese iron phosphate (LiMn x Fe 1-x PO4; 0 < x < 1), lithium cobalt phosphate (LiCoPO4), lithium nickel phosphate (LiNiPO4), etc.; etc. can be mentioned.

[0068] Examples of the binder for the positive electrode include polyvinylidene fluoride, etc. Examples of the conductive assistant for the positive electrode include carbon black (e.g., acetylene black), amorphous whiskers, graphite, etc. Examples of the thickener for the positive electrode include carboxymethyl cellulose, etc. In addition, examples of the solvent for the slurry for forming the positive electrode include organic solvents such as N-methylpyrrolidone.

[0069] The total content of the positive electrode active material in the positive electrode mixture layer is usually 70% to 98% by mass, preferably 75% or more, and preferably 95% or less when the entire positive electrode mixture layer is 100% by mass.

[0070] Examples of materials for the positive electrode current collector include aluminum, aluminum alloy, stainless steel, nickel, titanium, tantalum, carbon cloth, and carbon paper.

[0071] (Negative electrode) Typically, a negative electrode can 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.8

[0072] 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.

[0073] The negative electrode active material preferably contains 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, and amorphous carbon particles. 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).

[0074] 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.

[0075] When the negative electrode active material contains single carbon particles, the median diameter D50 of the single 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.

[0076] When the negative electrode active material contains single carbon particles, the BET specific surface area of the single carbon is usually 1.0 m 2 / g to 5.0 m 2 / g, preferably 2.0 m 2 / g or more, more preferably 3.0 m 2 / g or more, preferably 4.5 m 2 / g or less, more preferably 4.0 m 2 / g or less.

[0077] Silicon oxide can be represented by SiO x , where x is a variable. That is, the oxygen atom content in silicon oxide is not particularly limited, but x is usually 0 ≤ x < 2, preferably 0.2 or more, more preferably 0.4 or more, still more preferably 0.6 or more, preferably 1.8 or less, more preferably 1.6 or less, and still more preferably 1.4 or less. [[ID=2\3]]

[0078] The median diameter D50 of single silicon particles, silicon oxide particles, or silicon carbide particles is usually 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.

[0079] The BET specific surface area of single silicon particles, silicon oxide particles, or silicon carbide particles is usually 1.0 m 2 / g to 5.0 m<\ 2 / g, preferably 1.5 m 2 / g or more, more preferably 2.0 m 2 / g or more, preferably 4.5 m[[ID=**39**]] 2 / g or less, more preferably 4.0 m 2 / g or less.

[0080] 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% to 20% by mass, but preferably 3% or more by mass, more preferably 5% or more by mass, preferably 18% or less by mass, and more preferably 15% or less by mass, when the total mass of the entire negative electrode active material is taken as 100% by mass.

[0081] 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 lithium-ion secondary battery.

[0082] 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.

[0083] 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 as 100% by mass.

[0084] 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.

[0085] 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 as 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] Examples of materials for the negative electrode current collector include copper, nickel, stainless steel, and nickel-plated steel.

[0090] <Separator> One embodiment of the invention described herein is a non-aqueous electrolyte secondary battery comprising a "positive electrode," a "negative electrode," a "non-aqueous electrolyte," and a "separator," wherein 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 porous resin sheet is mainly made of one or more types of polyolefin resin. The thickness of the separator is preferably 5 μm to 30 μm. The separator is preferably placed between the positive electrode and the negative electrode.

[0091] <Case> The shape of the case is not particularly limited and can be appropriately selected depending on the application of the lithium secondary battery precursor described herein. Examples of cases include cases containing laminate film, and cases consisting of a battery can and a battery can lid.

[0092] <Specific examples of lithium secondary battery precursors> Figure 1 is a schematic cross-sectional view showing a stacked lithium secondary battery precursor, which is an example of a lithium secondary battery precursor according to this disclosure.

[0093] As shown in Figure 1, lithium secondary battery precursor 1 is a stacked battery precursor. In detail, in the lithium secondary battery precursor 1, the battery element 10 is enclosed inside the 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.

[0094] 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.

[0095] 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 negative electrode may be formed with their respective active material layers on one side of their respective current collectors.

[0096] Although lithium secondary battery precursor 1 is a stacked lithium secondary battery precursor, 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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 the positive electrode can 43 (hereinafter also referred to as the "battery can") and the 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.

[0101] 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.

[0102] [Lithium secondary battery and method for manufacturing the same] The method for manufacturing a lithium secondary battery disclosed herein is: The process for preparing the lithium secondary battery precursor described above (hereinafter also referred to as the "preparation process"), The above lithium secondary battery precursor is subjected to a charging and discharging process, Includes. The lithium secondary battery of this disclosure is a lithium secondary battery obtained by subjecting the lithium secondary battery precursor of this disclosure described above to charging and discharging.

[0103] 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.

[0104] The preparation step may simply be a step of preparing a pre-manufactured lithium secondary battery precursor of the present disclosure for use in a charging and discharging step, 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.

[0105] 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 lithium secondary battery precursor may undergo multiple charging and discharging cycles. As described above, this charging and discharging process preferably forms an SEI (Solid Electrolyte Interface) film on the surface of the positive electrode (especially the positive electrode active material) and / or the negative electrode (especially the negative electrode active material) of the lithium secondary battery precursor.

[0106] The charging and discharging process preferably involves performing a combination of charging and discharging one or more times on the lithium secondary battery precursor in an environment of 25°C to 70°C. [Examples]

[0107] The following are examples of the embodiments of this disclosure, but this disclosure is not limited to the following embodiments. In the following, "%" refers to "mass%" unless otherwise specified.

[0108] [Example 1] <Preparation of non-aqueous electrolyte> Ethylene carbonate (hereinafter referred to as "EC"), dimethyl carbonate (hereinafter referred to as "DMC"), and ethyl methyl carbonate (hereinafter referred to as "EMC") were mixed at EC:DMC:EMC = 30:35:35 (volume ratio). Thereby, a mixed solvent was obtained as a non-aqueous solvent. To the obtained mixed solvent, LiPF6 as an electrolyte was dissolved so that the concentration in the finally obtained non-aqueous electrolyte became 1.0 mol / L, and an electrolyte (hereinafter also referred to as "basic electrolyte") was obtained. With respect to the obtained basic electrolyte, an imide salt represented by formula (I-1), which is a specific example of the imide salt represented by formula (I), and a compound represented by formula (II-1-1), which is a specific example of the compound represented by formula (II-1) (fluoroethylene carbonate), were each added so that the content with respect to the total amount of the finally obtained non-aqueous electrolyte became the content (mass %) described in Table 1, and a non-aqueous electrolyte was obtained.

[0109]

Chemical formula

[0110] <Fabrication of the positive electrode> LiNi as a positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (94 mass %), carbon black (3 mass %) as a conductive assistant, and polyvinylidene fluoride (PVdF) (3 mass %) as a binder were mixed to obtain a mixture. The obtained mixture was dispersed in an N-methylpyrrolidone solvent to obtain a positive electrode composite slurry. An aluminum foil with a thickness of 20 μm was prepared as a positive electrode current collector. The obtained positive electrode composite slurry was coated on the aluminum foil, dried, and then rolled with a rolling machine to obtain a sheet-shaped positive electrode. The positive electrode consists of a positive electrode current collector and a positive electrode active material layer.

[0111] <Fabrication of the negative electrode> As a negative electrode active material, 87.3 mass % of graphite and silicon oxide (SiO xA negative electrode mixture slurry was obtained by mixing 9.7% by mass of silicon monoxide (x=1), 1.5% by mass of sodium carboxymethylcellulose dispersed in pure water as a thickener, and 1.5% 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 mixture slurry was applied onto 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.

[0112] <Preparing the separator> A porous polyethylene film was prepared as a separator.

[0113] <Preparation of lithium secondary battery precursors> 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, immersing the separator, positive electrode, and negative electrode in 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-type lithium secondary battery precursor (i.e., a lithium secondary battery before charging and discharging) with 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.

[0114] <Manufacturing of lithium secondary batteries> A lithium secondary battery was obtained by repeatedly charging the above lithium secondary battery precursor to 4.2V and discharging it to 2.5V three times under a temperature range of 25°C to 70°C.

[0115] The lithium secondary batteries obtained above were subjected to the following measurements. The results are shown in Table 1. Each result is shown as a relative value with the value of Comparative Example 1 set to 100. In Table 1, "-" indicates that no additives were added.

[0116] <Measurement of initial discharge capacity> The above lithium-ion secondary battery was charged to 4.2V in a constant temperature bath at 25°C, then discharged to 2.5V, and its discharge capacity [mAh] (hereinafter also referred to as "initial discharge capacity") was measured.

[0117] <Measurement of initial resistance> After measuring the initial discharge capacity, the lithium-ion secondary battery was charged to 3.7V (SOC 50%), and the voltage drop (= voltage before discharge - voltage 10 seconds after discharge) was measured in a constant temperature bath at 25°C and -20°C for each discharge rate from 0.1C to 1.0C. Here, CC10s discharge means discharge performed at a constant current for 10 seconds. Based on the obtained voltage drop and current values ​​(i.e., current values ​​corresponding to discharge rates from 0.1C to 1.0C), the DC resistance (DCR) [Ω] as the initial resistance value was measured. The initial resistance value of Comparative Example 1, described later, was also measured using the same method, and the initial resistance value of Example 1 was calculated as a relative value when the initial resistance value of Comparative Example 1 was set to 100.

[0118] <Charge-discharge cycle test> Next, the lithium-ion secondary battery, after initial resistance measurement, was charged to 4.2V at a constant current charge rate of 0.5C in a 25°C constant temperature bath. Subsequently, it was discharged to 2.5V at a constant current charge rate of 0.5C. The above charge-discharge cycle was repeated 100 times.

[0119] <Measurement of discharge capacity retention rate after charge-discharge cycles and calculation of relative values> Next, the discharge capacity of the lithium-ion secondary battery after the charge-discharge cycle test was measured using the same method as for the initial discharge capacity. For Comparative Example 1, described later, the discharge capacity of the lithium-ion secondary battery after the charge-discharge cycle test was also measured using the same method. The discharge capacity retention rate of Example 1 after the charge-discharge cycle was calculated as a relative value, with the discharge capacity retention rate of Comparative Example 1 after the charge-discharge cycle set to 100 (see the formula below). The discharge capacity retention rate after the charge-discharge cycle in Example 1 (relative value) = (Discharge capacity retention rate after the charge-discharge cycle in Example 1) / (Discharge capacity retention rate after the charge-discharge cycle in Comparative Example 1) × 100

[0120] <Measurement of resistance value and calculation of relative value after charge-discharge cycle> Next, the resistance of the lithium-ion secondary battery after the charge-discharge cycle test was measured under the same conditions and methods as the initial resistance. For Comparative Example 1, described later, the resistance of the lithium-ion secondary battery after the charge-discharge cycle test was also measured under the same conditions and methods. The resistance of Example 1 after the charge-discharge cycle was calculated as a relative value, with the resistance of Comparative Example 1 after the charge-discharge cycle set to 100 (see the formula below). The resistance value (relative value) after the charge-discharge cycle in Example 1 = (Resistance value after the charge-discharge cycle in Example 1) / (Resistance value after the charge-discharge cycle in Comparative Example 1) × 100

[0121] [Examples 2-4, Comparative Examples 1-6] The same procedure as in Example 1 was followed, except that the types and amounts of additives in the non-aqueous electrolyte were changed as shown in Table 1. The results are shown in Table 1. The additives added to the non-aqueous electrolytes in Examples 2-4 and Comparative Examples 1-6 are as shown by the following formulas. Furthermore, each result is shown as a relative value with the value of Comparative Example 1 set to 100. Also, "-" in Table 1 means that no additive was added.

[0122] [ka]

[0123] [Table 1]

[0124] As is clear from Table 1, in a lithium-ion secondary battery using the non-aqueous electrolyte of this disclosure, which contains an imide salt represented by formula (I) and at least one carbonate compound selected from the group consisting of the compound represented by formula (II-1) and the compound represented by formula (II-2) below, the battery resistance was reduced. Specifically, the lithium-ion secondary batteries using non-aqueous electrolytes in Examples 1-4 showed reduced battery resistance compared to those in Comparative Examples 1-6, which was particularly noticeable at room temperature (25°C). Furthermore, the lithium-ion secondary batteries using non-aqueous electrolytes in Examples 1-4 also showed improved capacity retention after charge-discharge cycles. [Explanation of Symbols]

[0125] 1. Lithium secondary battery precursor 10 Battery elements 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 layers 21 Positive lead 22 Negative lead 30 Exterior 41 Positive electrode 42 Negative electrode 43 Positive electrode can 44 Sealing plate 45 Separator 46 Gasket 47, 48 Spacer plate

Claims

1. A non-aqueous electrolyte containing an imide salt represented by the following formula (I) and at least one carbonate compound selected from the group consisting of the compound represented by the following formula (II-1) and the compound represented by the following formula (II-2). 【Chemistry 1】 (In formula (I), R １１ R represents a fluorine carbide group having 1 to 12 carbon atoms, which may contain a fluoro group (-F), 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. １２ 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. ＋ (This represents alkali metal ions, ammonium ions, imidazolium ions, pyridinium ions, pyrrolidinium ions, piperidinium ions, or phosphonium ions.) 【Chemistry 2】 (In formula (II-1), R ２１ Each independently represents a fluorine carbide group having 1 to 12 carbon atoms, which may contain a fluoro group (-F), 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, where i represents an integer from 1 to 4. However, R ２１ At least one of these is a fluorine carbide group having 1 to 12 carbon atoms, which may contain a fluoro group (-F), 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. In formula (II-2), R ２２ 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 at least one functional group selected from the group consisting of a fluoro group (-F) and an oxa group (-O-) as a substituent. However, R ２２ At least one of these is 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.

2. The non-aqueous electrolyte according to claim 1, wherein the total content of the imide salt is 0.01% by mass to 10% 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 carbonate compound is 0.1% by mass to 30.0% by mass relative to the total amount of the non-aqueous electrolyte.

4. The non-aqueous electrolyte according to claim 1, which is a non-aqueous electrolyte used in a non-aqueous electrolyte secondary battery, comprising at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles as a negative electrode active material.

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

6. 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. The non-aqueous electrolyte secondary battery according to claim 5, wherein 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.

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 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.

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