Positive electrode binder, electrode mixture, electrode, and secondary battery

Abstract

Provided are: a binder in which the interface resistance between a current collector and an electrode material layer in a positive electrode of a sodium ion battery is reduced and battery characteristics are improved; and an electrode mixture, an electrode, and a secondary battery using the binder. A binder for a positive electrode of a sodium ion battery, the binder containing a copolymer having a vinylidene fluoride unit (A) and a structural unit (B) derived from at least one type of monomer selected from the group consisting of trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, a monomer represented by general formula (1), a monomer represented by general formula (2), and a monomer represented by general formula (3), and does not have a tetrafluoroethylene unit. [Formula 1] # imgabs0 # (In the formula, Rf1 is a linear or branched fluorinated alkyl group or fluorinated alkoxy group having 1-12 carbon atoms, and when both the fluorinated alkyl group and the fluorinated alkoxy group have 2 or more carbon atoms, an oxygen atom (-O-) may be included between carbon atoms. ) (In the formula, Rf2 is a linear or branched fluorinated alkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and when both the fluorinated alkyl group and the fluorinated alkoxy group have 2 or more carbon atoms, an oxygen atom (-O-) may be included between carbon atoms. ) [chemical formula 3] # imgabs2 # (In the formula, R1, R2, and R3 are each independently a hydrogen atom, a chlorine atom, or an alkyl group having 1-5 carbon atoms. And X represents a single bond or an atomic group having a molecular weight of 500 or less and having a main chain comprising 1-20 atoms. And Y represents an inorganic cation and / or an organic cation).

Description

Technical Field

[0001] The present disclosure relates to a positive electrode binder, an electrode mixture, an electrode and a secondary battery. Background Art

[0002] As electrical products have become lighter and smaller in size in recent years, the demand for electrochemical devices such as secondary batteries has increased rapidly. Furthermore, electrical products have become more high-performance and have been given functions that have never existed before, which has increased the demand for electrochemical devices that can withstand use for longer periods of time and under harsh conditions.

[0003] In addition, research has been conducted on sodium ion secondary batteries using sodium ions as charge carriers. Sodium is more abundant than lithium and can be obtained cheaply, so it has attracted attention as a low-cost and large-scale secondary battery. Patent documents 1 and 2 describe sodium ion batteries using fluorine compounds as binders.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2012-79687

[0007] Patent Document 2: Japanese Patent Application Publication No. 2014-26818 Summary of the invention

[0008] Problems to be solved by the invention

[0009] The present disclosure aims to provide a binder that reduces the interface resistance between a current collector and an electrode material layer in a positive electrode of a sodium ion battery and improves battery characteristics, and an electrode mixture, an electrode, and a secondary battery using the binder.

[0010] Means for solving problems

[0011] The present invention discloses a positive electrode binder for a sodium ion battery, comprising a copolymer having a vinylidene fluoride unit (A) and a structural unit (B) derived from at least one monomer selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene, a monomer represented by the following general formula (1), a monomer represented by the following general formula (2), and a monomer represented by the following general formula (3), and having no tetrafluoroethylene unit.

[0012] [Chemistry 1]

[0013]

[0014] (Where Rf 1It is a linear or branched fluorinated alkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms. When the fluorinated alkyl group and the fluorinated alkoxy group have 2 or more carbon atoms, they may contain an oxygen atom (-O-) between carbon atoms.

[0015] [Chemistry 2]

[0016]

[0017] (Where Rf 2 It is a linear or branched fluorinated alkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms. When the fluorinated alkyl group and the fluorinated alkoxy group have 2 or more carbon atoms, they may contain an oxygen atom (-O-) between carbon atoms.

[0018] [Chemistry 3]

[0019]

[0020] (Where R 1 , R 2 and R 3 Each is independently a hydrogen atom, a chlorine atom or an alkyl group having 1 to 5 carbon atoms. X is an atomic group having a molecular weight of 500 or less and having a single bond or a main chain consisting of 1 to 20 atoms. Y represents an inorganic cation and / or an organic cation.

[0021] The content of the vinylidene fluoride unit (A) is preferably 90 mol% to 99.5 mol% based on all monomer units in the copolymer.

[0022] The structural unit (B) is preferably a structural unit derived from at least one monomer selected from the group consisting of trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, 2,3,3,3-tetrafluoropropylene, perfluoro-(2,9,9-trihalo-5-trifluoromethyl-3,6-dioxa-8-heptene) and acrylic acid.

[0023] In addition, the structural unit (B) is preferably a structural unit derived from 2,3,3,3-tetrafluoropropylene.

[0024] The positive electrode binder may contain two or more of the copolymers.

[0025] The positive electrode binder may further contain a fluorine-containing polymer other than the copolymer.

[0026] The fluorine-containing polymer is preferably polyvinylidene fluoride or modified polyvinylidene fluoride.

[0027] The present disclosure also provides an electrode mixture, wherein the electrode active material contains a sodium composite oxide, and the electrode mixture includes the binder for the positive electrode of the sodium ion battery.

[0028] The present disclosure also provides an electrode including a current collector and an electrode material layer formed of the electrode mixture and provided on one or both surfaces of the current collector.

[0029] The present disclosure also provides a sodium ion secondary battery including the electrode.

[0030] Effects of the Invention

[0031] The present disclosure provides a binder that reduces the interface resistance between the collector and the electrode material layer in the positive electrode of a sodium ion battery and improves the battery characteristics. In addition, the electrode and secondary battery using the binder of the present disclosure reduce the interface resistance between the collector and the electrode material layer in the positive electrode. In addition, the secondary battery using the binder of the present disclosure has good battery characteristics. DETAILED DESCRIPTION

[0032] Hereinafter, the present disclosure will be described in detail.

[0033] Disclosed is a binder for use in forming a positive electrode for a sodium ion battery.

[0034] In recent years, the development of sodium ion batteries (SIBs) is advancing. The ionic radius of sodium ions is larger than that of lithium ions. Therefore, in SIBs, compared with lithium ion batteries (LiBs), the expansion and contraction of the interlayer distance in the positive electrode active material caused by charging and discharging becomes more drastic. In the electrode material layer (except the interface with the collector foil), the conductive path can be maintained despite the contraction by the binder, but at the interface with the collector foil, there is no binder between the active material and the collector foil, so it is difficult to maintain the conductive path compared with the electrode material layer (except the interface with the collector foil). Therefore, in SIBs, lower interface resistance is required at the time of electrode production.

[0035] The inventors have found that, unlike LiB, in SIBs that require electrodes with lower interface resistance, by using a binder that does not contain structural units derived from tetrafluoroethylene and contains a copolymer containing vinylidene fluoride having a specific composition as a binder component during electrode production, the conductive agent is further pressed against the collector during electrode pressing, thereby reducing the interface resistance value between the electrode collector (e.g., Al) and the electrode material layer (conductive agent / Na active material / binder).

[0036] In addition, by using the binder disclosed in the present invention, the battery performance of the sodium ion battery is also improved.

[0037] The positive electrode binder of the sodium ion battery disclosed herein comprises a copolymer having a vinylidene fluoride (VdF) unit (A) and a structural unit (B) derived from at least one monomer selected from the group consisting of trifluoroethylene (TrFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), a monomer represented by the following general formula (1), a monomer represented by the following general formula (2), and a monomer represented by the following general formula (3), and having no tetrafluoroethylene unit.

[0038] [Chemistry 4]

[0039]

[0040] (Where Rf 1 It is a linear or branched fluorinated alkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms. When the fluorinated alkyl group and the fluorinated alkoxy group have 2 or more carbon atoms, they may contain an oxygen atom (-O-) between carbon atoms.

[0041] [Chemistry 5]

[0042]

[0043] (Where Rf 2 It is a linear or branched fluorinated alkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms. When the fluorinated alkyl group and the fluorinated alkoxy group have 2 or more carbon atoms, they may contain an oxygen atom (-O-) between carbon atoms.

[0044] [Chemistry 6]

[0045]

[0046] (Where R 1 , R 2 and R 3 Each is independently a hydrogen atom, a chlorine atom or an alkyl group having 1 to 5 carbon atoms. X is an atomic group having a molecular weight of 500 or less and having a single bond or a main chain consisting of 1 to 20 atoms. Y represents an inorganic cation and / or an organic cation.

[0047] In the fluorinated monomer represented by the general formula (1), Rf 1 It is a linear or branched fluorinated alkyl group having 1 to 12 carbon atoms, or a linear or branched fluorinated alkoxy group having 1 to 12 carbon atoms. When the fluorinated alkyl group and the fluorinated alkoxy group have 2 or more carbon atoms, they may contain an oxygen atom (—O—) between carbon atoms.

[0048] R 1The fluorinated alkyl group may be a partially fluorinated alkyl group in which a part of the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms, or a perfluorinated alkyl group in which all the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms. 1 The hydrogen atom of the fluorinated alkyl group may be substituted with a substituent other than a fluorine atom, but preferably contains no substituent other than a fluorine atom.

[0049] In addition, Rf 1 The fluorinated alkoxy group may be a partially fluorinated alkoxy group in which a part of the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms, or a perfluorinated alkoxy group in which all the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms. 1 The hydrogen atom of the fluorinated alkoxy group may be substituted with a substituent other than a fluorine atom, but preferably contains no substituent other than a fluorine atom.

[0050] As Rf 1 The number of carbon atoms in the moiety is preferably 1 to 10, more preferably 1 to 6, further preferably 1 to 4, and particularly preferably 1.

[0051] As Rf 1 , preferably the general formula:

[0052] -(Rf 11 )m-(O)p-(Rf 12 -O)n-Rf 13

[0053] (Where Rf 11 and Rf 12 Rf is independently a linear or branched fluorinated alkylene group having 1 to 4 carbon atoms, 13 is a linear or branched fluorinated alkyl group having 1 to 4 carbon atoms, p is 0 or 1, m is an integer of 0 to 4, and n is an integer of 0 to 4).

[0054] R 11 and Rf 12 The fluorinated alkylene group may be a partially fluorinated alkylene group in which a part of the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms, or a perfluorinated alkylene group in which all the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms. 11 and Rf 12 The hydrogen atom of the fluorinated alkylene group may be substituted with a substituent other than a fluorine atom, but preferably contains no substituent other than a fluorine atom. 11 and Rf 12 It can be the same or different each time it occurs.

[0055] As Rf 11 The fluorinated alkylene group includes -CHF-, -CF 2 -、-CH2 -CF 2 -、-CHF-CF 2 -、-CF 2 -CF 2 -、-CF(CF 3 )-、-CH 2 -CF 2 -CF 2 -、-CHF-CF 2 -CF 2 -、-CF 2 -CF 2 -CF 2 -、-CF(CF 3 )-CF 2 -、-CF 2 -CF(CF 3 )-、-C(CF 3 ) 2 -、-CH 2 -CF 2 -CF 2 -CF 2 -、-CHF-CF 2 -CF 2 -CF 2 -、-CF 2 -CF 2 -CF 2 -CF 2 -、-CH(CF 3 )-CF 2 -CF 2 -、-CF(CF 3 )-CF 2 -CF 2 -、-C(CF 3 ) 2 -CF 2 -, etc., among which, preferably a perfluorinated alkylene group having 1 or 2 carbon atoms, more preferably -CF 2 -.

[0056] As Rf 12 The fluorinated alkylene group includes -CHF-, -CF 2 -、-CH 2 -CF 2 -、-CHF-CF 2 -、-CF 2 -CF 2 -、-CF(CF 3 )-、-CH 2 -CF 2 -CF 2 -、-CHF-CF 2-CF 2 -、-CF 2 -CF 2 -CF 2 -、-CF(CF 3 )-CF 2 -、-CF 2 -CF(CF 3 )-、-C(CF 3 ) 2 -、-CH 2 -CF 2 -CF 2 -CF 2 -、-CHF-CF 2 -CF 2 -CF 2 -、-CF 2 -CF 2 -CF 2 -CF 2 -、-CH(CF 3 )-CF 2 -CF 2 -、-CF(CF 3 )-CF 2 -CF 2 -、-C(CF 3 ) 2 -CF 2 -, etc., among which, preferably a perfluorinated alkylene group having 1 to 3 carbon atoms, more preferably -CF 2 -、-CF 2 CF 2 -、-CF 2 -CF 2 -CF 2 -、-CF(CF 3 )-CF 2 -or-CF 2 -CF(CF 3 )-.

[0057] As Rf 13 The fluorinated alkyl group may be a partially fluorinated alkyl group in which a part of the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms, or a perfluorinated alkyl group in which all the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms. 13 The hydrogen atom of the fluorinated alkyl group may be substituted by a substituent other than a fluorine atom, but preferably does not contain a substituent other than a fluorine atom (e.g., -CN, -CH 2 I. -CH 2 Br, etc.).

[0058] As Rf 13 The fluorinated alkyl group includes -CH2 F、-CHF 2 、-CF 3 、-CH 2 -CH 2 F、-CH 2 -CHF 2 、-CH 2 -CF 3 、-CHF-CH 2 F、-CHF-CHF 2 、-CHF-CF 3 、-CF 2 -CH 2 F、-CF 2 -CHF 2 、-CF 2 -CF 3 、-CH 2 -CF 2 -CH 2 F、-CHF-CF 2 -CH 2 F、-CF 2 -CF 2 -CH 2 F、-CF(CF 3 )-CH 2 F、-CH 2 -CF 2 -CHF 2 、-CHF-CF 2 -CHF 2 、-CF 2 -CF 2 -CHF 2 、-CF(CF 3 )-CHF 2 、-CH 2 -CF 2 -CF 3 、-CHF-CF 2 -CF 3 、-CF 2 -CF 2 -CF 3 、-CF(CF 3 )-CF 3 、-CH 2 -CF 2 -CF 2 -CF 3 、-CHF-CF 2 -CF 2 -CF 3 、-CF 2 -CF 2 -CF2 -CF 3 、-CH(CF 3 )-CF 2 -CF 3 ,-CF(CF 3 )-CF 2 -CF 3 ,-C(CF 3 )2-CF 3 etc., among which -CF is preferred 3 、-CHF-CF 3 , -CF 2 -CHF 2 , -CF 2 -CF 3 , -CF 2 -CF 2 -CF 3 ,-CF(CF 3 )-CF 3 , -CF 2 -CF 2 -CF 2 -CF 3 、-CH(CF 3 )-CF 2 -CF 3 or -CF(CF 3 )-CF 2 -CF 3 .

[0059] As p, 0 is preferred.

[0060] m is preferably an integer of 0 to 2, more preferably 0 or 1, and further preferably 0. When p is 0, m is also preferably 0.

[0061] n is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0.

[0062] As the repeating unit, preferably

[0063] -CH 2 -CF[-CF 3 ]-、

[0064] -CH 2 -CF[-CF 2 CF 3 ]-、

[0065] -CH 2 -CF[-CF 2 CF 2 CF 3 ]-、

[0066] -CH 2 -CF[-CF 2 CF 2 CF 2 CF 3 ]-、

[0067] -CH 2 -CF[-CF 2 -O-CF(CF 3 )-CF 2 -O-CHF-CF 3 ]-、

[0068] -CH 2 -CF[-CF 2 -O-CF(CF 3 )-CF 2 -O-CF 2 -CF 3 ]-、

[0069] -CH 2 -CF[-CF 2 -O-CF(CF 3 )-CF 2 -O-CF(CF 3 )-CF 3 ]-、

[0070] -CH 2 -CF[-CF 2 -O-CF(CF 3 )-CF 2 -O-CH(CF 3 )-CF 2 -CF 3 ]-、

[0071] -CH 2 -CF[-CF 2 -O-CF(CF 3 )-CF 2 -O-CF(CF 3 )-CF 2 -CF 3 ]-、

[0072] -CH 2 -CF[-OCF 2 OCF 3 ]-、

[0073] -CH 2 -CF[-OCF 2 CF 2 CF 2 2OCF 3 ]-、

[0074] -CH 2 -CF[-CF 2 OCFOCF 3 ]-、

[0075] -CH 2 -CF[-CF 2 OCF 2 CF 2 CF 2 OCF 3 ]-or

[0076] -CH 2 -CF[-O-CF 2 -CF 3 ]-,

[0077] More preferably -CH 2 -CF[-CF 3 ]-.

[0078] Examples of the monomer represented by the general formula (1) include 2,3,3,3-tetrafluoropropylene (1,2,3,4-yf), 2,3,3,4,4,4-hexafluoro-1-butene, and perfluoro-(2,9,9-trihalo-5-trifluoromethyl-3,6-dioxa-8-heptene) (AEHF-1). Among them, 2,3,3,3-tetrafluoropropylene (1,2,3,4-yf) is preferred.

[0079] In the fluorinated monomer (2) represented by the general formula (2), Rf 2 It is a linear or branched fluorinated alkyl group having 1 to 12 carbon atoms, or a linear or branched fluorinated alkoxy group having 1 to 12 carbon atoms. When the fluorinated alkyl group and the fluorinated alkoxy group have 2 or more carbon atoms, they may contain an oxygen atom (—O—) between carbon atoms.

[0080] R 2 The fluorinated alkyl group may be a partially fluorinated alkyl group in which a part of the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms, or a perfluorinated alkyl group in which all the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms. 2 The hydrogen atom of the fluorinated alkyl group may be substituted with a substituent other than a fluorine atom, but preferably contains no substituent other than a fluorine atom.

[0081] In addition, Rf 2 The fluorinated alkoxy group may be a partially fluorinated alkoxy group in which a part of the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms, or a perfluorinated alkoxy group in which all the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms. 2The hydrogen atom of the fluorinated alkoxy group may be substituted with a substituent other than a fluorine atom, but preferably contains no substituent other than a fluorine atom.

[0082] As Rf 2 The number of carbon atoms in the moiety is preferably 1 to 10, more preferably 1 to 6, further preferably 1 to 4, and particularly preferably 1.

[0083] As Rf 2 , preferably the general formula:

[0084] -(Rf 21 )m-(O)p-(Rf 22 -O)n-Rf 23

[0085] (Where Rf 21 and Rf 22 Rf is independently a linear or branched fluorinated alkylene group having 1 to 4 carbon atoms, 23 is a linear or branched fluorinated alkyl group having 1 to 4 carbon atoms, p is 0 or 1, m is an integer of 0 to 4, and n is an integer of 0 to 4).

[0086] R 21 and Rf 22 The fluorinated alkylene group may be a partially fluorinated alkylene group in which a part of the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms, or a perfluorinated alkylene group in which all the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms. 21 and Rf 22 The hydrogen atom of the fluorinated alkylene group may be substituted with a substituent other than a fluorine atom, but preferably contains no substituent other than a fluorine atom. 21 and Rf 22 It can be the same or different each time it occurs.

[0087] As Rf 21 The fluorinated alkylene group includes -CHF-, -CF 2 -、-CH 2 -CF 2 -、-CHF-CF 2 -、-CF 2 -CF 2 -、-CF(CF 3 )-、-CH 2 -CF 2 -CF 2 -、-CHF-CF 2 -CF 2 -、-CF 2 -CF 2 -CF 2 -、-CF(CF3 )-CF 2 -、-CF 2 -CF(CF 3 )-、-C(CF 3 ) 2 -、-CH 2 -CF 2 -CF 2 -CF 2 -、-CHF-CF 2 -CF 2 -CF 2 -、-CF 2 -CF 2 -CF 2 -CF 2 -、-CH(CF 3 )-CF 2 -CF 2 -、-CF(CF 3 )-CF 2 -CF 2 -、-C(CF 3 ) 2 -CF 2 -, etc., among which, preferably a perfluorinated alkylene group having 1 or 2 carbon atoms, more preferably -CF 2 -.

[0088] As Rf 22 The fluorinated alkylene group includes -CHF-, -CF 2 -、-CH 2 -CF 2 -、-CHF-CF 2 -、-CF 2 -CF 2 -、-CF(CF 3 )-、-CH 2 -CF 2 -CF 2 -、-CHF-CF 2 -CF 2 -、-CF 2 -CF 2 -CF 2 -、-CF(CF 3 )-CF 2 -、-CF 2 -CF(CF 3 )-、-C(CF 3 ) 2 -、-CH 2 -CF 2 -CF 2 -CF 2 -、-CHF-CF2 -CF 2 -CF 2 -、-CF 2 -CF 2 -CF 2 -CF 2 -、-CH(CF 3 )-CF 2 -CF 2 -、-CF(CF 3 )-CF 2 -CF 2 -、-C(CF 3 ) 2 -CF 2 -, etc., among which, preferably a perfluorinated alkylene group having 1 to 3 carbon atoms, more preferably -CF 2 -、-CF 2 CF 2 -、-CF 2 -CF 2 -CF 2 -、-CF(CF 3 )-CF 2 -or-CF 2 -CF(CF 3 )-.

[0089] As Rf 23 The fluorinated alkyl group may be a partially fluorinated alkyl group in which a part of the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms, or a perfluorinated alkyl group in which all the hydrogen atoms bonded to the carbon atoms are replaced by fluorine atoms. 23 The hydrogen atom of the fluorinated alkyl group may be substituted by a substituent other than a fluorine atom, but preferably does not contain a substituent other than a fluorine atom (e.g., -CN, -CH 2 I. -CH 2 Br, etc.).

[0090] As Rf 23 The fluorinated alkyl group includes -CH 2 F, -CHF 2 , -CF 3 、-CH 2 -CH 2 F, -CH 2 -CHF 2 、-CH 2 -CF 3 、-CHF-CH 2 F, -CHF-CHF 2 、-CHF-CF 3 , -CF 2 -CH 2 F, -CF2 -CHF 2 ,-CF 2 -CF 3 ,-CH 2 -CF 2 -CH 2 F, -CHF-CF 2 -CH 2 F, -CF 2 -CF 2 -CH 2 F, -CF(CF 3 )-CH 2 F, -CH 2 -CF 2 -CHF 2 ,-CHF-CF 2 -CHF 2 ,-CF 2 -CF 2 -CHF 2 ,-CF(CF 3 )-CHF 2 ,-CH 2 -CF 2 -CF 3 ,-CHF-CF 2 -CF 3 ,-CF 2 -CF 2 -CF 3 ,-CF(CF 3 )-CF 3 ,-CH 2 -CF 2 -CF 2 -CF 3 ,-CHF-CF 2 -CF 2 -CF 3 ,-CF 2 -CF 2 -CF 2 -CF 3 ,-CH(CF 3 )-CF 2 -CF 3 ,-CF(CF 3 )-CF 2 -CF 3 ,-C(CF 3 )2-CF 3 etc., among which, preferably -CF 3 , -CHF-CF 3 , -CF 2 -CHF 2 , -CF2 -CF 3 , -CF 2 -CF 2 -CF 3 ,-CF(CF 3 )-CF 3 , -CF 2 -CF 2 -CF 2 -CF 3 、-CH(CF 3 )-CF 2 -CF 3 or -CF(CF 3 )-CF 2 -CF 3 .

[0091] As p, 0 is preferred.

[0092] m is preferably an integer of 0 to 2, more preferably 0 or 1, and further preferably 0. When p is 0, m is also preferably 0.

[0093] n is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0.

[0094] As the repeating unit, preferably

[0095] -CHF-CH[-CF 3 ]-、

[0096] -CHF-CH[-CF 2 CF 3 ]-、

[0097] -CHF-CH[-CF 2 CF 2 CF 3 ]-or

[0098] -CHF-CH[-CF 2 CF 2 CF 2 CF 3 ]-,

[0099] More preferably -CHF-CH[-CF 3 ]-.

[0100] In the general formula (3), Y represents an inorganic cation and / or an organic cation. Examples of inorganic cations include cations of H, Li, Na, K, Mg, Ca, Al, Fe, etc. Examples of organic cations include NH 4 NH 3 R 15 NH 2R 15 2 、NHR 15 3 NR 15 4 (R 15 Y is preferably H, Li, Na, K, Mg, Ca, Al, NH 4 , more preferably H, Li, Na, K, Mg, Al, NH 4 , H, Li, Al, NH 4 , and H is particularly preferred. It should be noted that, for the sake of convenience, specific examples of inorganic cations and organic cations are described with symbols and valences omitted.

[0101] In the general formula (3), R 1 ~R 3 Each independently represents a hydrogen atom, a chlorine atom or an alkyl group having 1 to 5 carbon atoms. The alkyl group is a monovalent alkyl group. The number of carbon atoms in the alkyl group is preferably 4 or less. The alkyl group is preferably a methyl group or an ethyl group. 1 and R 2 R 3 Preferred is a hydrogen atom or a methyl group.

[0102] In the general formula (3), X is a single bond or an atomic group with a molecular weight of 500 or less, the main chain of which is composed of 1 to 20 atoms. The atomic group is a divalent atomic group. The atomic group is preferably a hydrocarbon group with a carbon number of 4 or less. Examples of the hydrocarbon group include alkylene and alkenylene groups with the above carbon number, among which at least one selected from the group consisting of methylene, ethylene, ethylidene, propylidene and isopropylidene is preferred, and methylene is more preferred.

[0103] The monomer represented by the general formula (3) is preferably at least one selected from the group consisting of acryloyloxypropylsuccinic acid and salts thereof, (meth)acrylic acid and salts thereof, vinylacetic acid (3-butenoic acid) and salts thereof, 3-pentenoic acid and salts thereof, 4-pentenoic acid and salts thereof, 3-hexenoic acid and salts thereof, 4-heptenoic acid and salts thereof, and 5-hexenoic acid and salts thereof.

[0104] The structural unit (B) is preferably a structural unit derived from at least one monomer selected from the group consisting of trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, 2,3,3,3-tetrafluoropropylene, perfluoro-(2,9,9-trihalo-5-trifluoromethyl-3,6-dioxa-8-heptene) and acrylic acid, and more preferably a structural unit derived from 2,3,3,3-tetrafluoropropylene.

[0105] In the copolymer, the content of the VdF unit (A) is preferably 60 mol% to 99.5 mol% based on all the monomer units in the copolymer.

[0106] When the VdF unit content is less than 60 mol %, the peel strength of the electrode becomes weak, and when it is more than 99.5 mol %, uniform coating of the slurry becomes difficult.

[0107] The copolymer preferably contains 65 mol% or more of VdF units relative to all polymerized units. If the copolymer contains 65 mol% or more, the cycle characteristics of a battery using an electrode obtained from the electrode mixture of the present disclosure tend to be better.

[0108] The composition of the copolymer can be measured using a 19F-NMR analyzer.

[0109] The content of the structural unit (B) is preferably less than 99.5 mol % relative to all polymerized units of the copolymer. If it is 99.5 mol % or more, the crystallinity of the copolymer generally decreases significantly, and as a result, the swelling property in the non-aqueous electrolyte tends to decrease.

[0110] The content of the structural unit (B) is more preferably 99 mol% or less.

[0111] When the copolymer contains the monomer unit represented by the general formula (3) as a monomer unit other than VdF, the content of the monomer unit is preferably 0.0001 mol% to 50.0 mol% relative to all monomer units, more preferably 0.01 mol% or more, further preferably 0.10 mol% or more, more preferably 5.0 mol% or less, further preferably 3.0 mol% or less, and particularly preferably 1.5 mol% or less.

[0112] When the copolymer contains the monomer unit represented by the general formula (3) as another structural unit, the content thereof can be measured by acid-base titration of the carboxylic acid group.

[0113] When the copolymer contains the monomer unit represented by the general formula (3), the content of the VdF unit in the copolymer is preferably 50.0 mol% to 99.999 mol% relative to all the monomer units, more preferably 95.0 mol% or more, further preferably 97.0 mol% or more, particularly preferably 98.5 mol% or more, more preferably 99.99 mol% or less, further preferably 99.90 mol% or less.

[0114] In addition to the above monomers, the copolymer may contain structural units (C) based on fluorinated monomers such as vinyl fluoride and fluoroalkyl vinyl ether, or non-fluorinated monomers such as ethylene and propylene, within a range not hindering the purpose of the present disclosure.

[0115] The fluoroalkyl vinyl ether is preferably a fluoroalkyl vinyl ether having a fluoroalkyl group having 1 to 5 carbon atoms, and more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) and perfluoro(propyl vinyl ether).

[0116] In the copolymer, the content of the structural unit (C) is preferably 0.0001 mol% to 50.0 mol% relative to all monomer units, more preferably 0.01 mol% or more, further preferably 0.10 mol% or more, more preferably 45.0 mol% or less, further preferably 40.0 mol% or less, particularly preferably 35.0 mol% or less.

[0117] The weight average molecular weight (polystyrene equivalent) of the copolymer is preferably 10,000 to 3,000,000, more preferably 30,000 or more, further preferably 50,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, further preferably 2,200,000 or less, particularly preferably 2,000,000 or less.

[0118] The weight average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0119] The number average molecular weight (polystyrene equivalent) of the copolymer is preferably 7,000 to 1,500,000, more preferably 21,000 or more, further preferably 35,000 or more, more preferably 1,400,000 or less, further preferably 1,200,000 or less, particularly preferably 1,100,000 or less.

[0120] The number average molecular weight can be determined by gel permeation chromatography (GPC) using dimethylformamide as solvent.

[0121] Preferred examples of the copolymer containing the monomer unit represented by the general formula (3) include a VdF / acrylic acid copolymer, a VdF / methacrylic acid copolymer, and a VdF / methyl methacrylate copolymer.

[0122] The VdF / (meth)acrylic acid copolymer contains a VdF unit and a (meth)acrylic acid unit. By using the VdF / (meth)acrylic acid copolymer as a copolymer, it is possible to easily form an electrode-forming composition, and to form a coating layer that is extremely firmly bonded to the metal foil. The content of the (meth)acrylic acid unit is preferably 0.0001 mol% to 5.0 mol%, more preferably 0.01 mol% to 3.0 mol%, and further preferably 0.10 mol% to 1.5 mol% relative to the total monomer units.

[0123] The content of the VdF unit in the VdF / (meth)acrylic acid copolymer is preferably 95.0 to 99.9999 mol %, more preferably 97.0 to 99.99 mol %, and further preferably 98.5 to 99.90 mol %, based on all monomer units.

[0124] The weight average molecular weight (polystyrene equivalent) of the VdF / (meth)acrylic acid copolymer is preferably 50,000 to 3,000,000, more preferably 80,000 or more, further preferably 100,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, further preferably 2,200,000 or less, particularly preferably 2,000,000 or less.

[0125] The number average molecular weight (polystyrene equivalent) of the VdF / (meth)acrylic acid copolymer is preferably 20,000 to 1,500,000, more preferably 40,000 or more, further preferably 70,000 or more, particularly preferably 140,000 or more, more preferably 1,400,000 or less, further preferably 1,200,000 or less, particularly preferably 1,100,000 or less.

[0126] The Mooney viscosity of the copolymer at 121° C. (ML1+10(121° C.)) is preferably 2 or more, more preferably 5 or more, further preferably 10 or more, and particularly preferably 30 or more.

[0127] The Mooney viscosity is a value measured in accordance with ASTM-D1646-15 and JIS K6300-1:2013.

[0128] The copolymer can be produced by a general free radical polymerization method using vinylidene fluoride (VdF), a monomer that becomes the structural unit (B), and other monomers other than tetrafluoroethylene as required. The polymerization method can be any of bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization, and emulsion polymerization is preferred from the perspective of easy industrial implementation.

[0129] In the polymerization, a polymerization initiator, a chain transfer agent, a surfactant and a solvent may be used, and any known substance may be used. In the polymerization of the copolymer, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator may be used as the polymerization initiator.

[0130] The oil-soluble free radical polymerization initiator may be a known oil-soluble peroxide, and representative examples thereof include: dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate; peroxyesters such as tert-butyl peroxyisobutyrate and tert-butyl peroxypivalate; dialkyl peroxides such as di-tert-butyl peroxide; and di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydro-hexadecanoyl) peroxide, di(perfluorobutanoyl) peroxide, di(perfluoropentanoyl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide. peroxide, bis(perfluorononanoyl) peroxide, bis(ω-chloro-hexafluorobutyryl) peroxide, bis(ω-chloro-decafluorohexanoyl) peroxide, bis(ω-chloro-tetrafluorooctanoyl) peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydro-dodecafluoroheptanoyl-perfluorobutyryl-peroxide, bis(dichloropentafluorobutyryl) peroxide, bis(trichlorooctafluorohexanoyl) peroxide, bis(tetrachloroundecanoyl) peroxide, bis(pentachlorotetrafluorodecanoyl) peroxide, bis(undecachlorotriacontafluorodocosanoyl) peroxide, etc.

[0131] As the water-soluble free radical polymerization initiator, it can be a known water-soluble peroxide, for example, ammonium salts, potassium salts, sodium salts of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, percarbonic acid, tert-butyl peroxymaleate, tert-butyl hydroperoxide, etc. It can also contain sulfites and reducing agents such as sulfites, and the amount thereof can be 0.1 to 20 times that of the peroxide.

[0132] The amount of the free radical polymerization initiator added is not particularly limited, and can be added all at once, sequentially, or continuously at the initial stage of polymerization in an amount that does not significantly reduce the polymerization rate (for example, a concentration of several ppm relative to water). The upper limit is the range in which the polymerization reaction heat can be removed from the device surface.

[0133] As the surfactant, nonionic surfactants, anionic surfactants, cationic surfactants, etc. can be used. The addition amount (relative to polymerization water) is preferably 10ppm to 5000ppm. More preferably, it is 50ppm to 5000ppm. In addition, as the surfactant, a reactive emulsifier can be used. The reactive emulsifier is not particularly limited as long as it is a compound having one or more unsaturated bonds and a hydrophilic group.

[0134] The solvent is preferably a solvent without chain transfer properties, such as dichloropentafluoropropane (R-225) in solution polymerization, and water, a mixture of water and a water-soluble organic solvent, or a mixture of water and a water-insoluble organic solvent in emulsion polymerization and suspension polymerization.

[0135] In the polymerization, examples of chain transfer agents include esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate, as well as isopentane, methane, ethane, propane, isopropanol, acetone, various mercaptans, carbon tetrachloride, and cyclohexane.

[0136] Bromine compounds or iodine compounds may also be used as chain transfer agents. As a polymerization method using a bromine compound or an iodine compound, for example, a method of performing emulsion polymerization in an aqueous medium under pressure in the presence of a bromine compound or an iodine compound in a substantially oxygen-free state (iodine transfer polymerization method) may be cited. As a representative example of the bromine compound or iodine compound used, for example, the general formula:

[0137] R 2 I x Br y

[0138] (where x and y are integers from 0 to 2 and satisfy 1≤x+y≤2, R 2 is a saturated or unsaturated fluorocarbon group or chlorofluorocarbon group having 1 to 16 carbon atoms, or a hydrocarbon group having 1 to 3 carbon atoms, wherein R 2 The compound shown in FIG. 1 is a compound of the type shown in FIG. 1 (containing or not containing oxygen atoms).

[0139] Examples of the iodine compound include 1,3-diiodoperfluoropropane, 2-iodoperfluoropropane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoethane, 1,3-diiodoperfluoropropane, CF 2 Br 2 BrCF 2 CF 2 Br, CF 3 CFC 2 Br, CFClBr 2 BrCF 2 CFClBr, CFBrClCFClBr, BrCF 2 CF 2 CF 2 Br, BrCF 2 CFB3 , 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 1-bromo-4-iodoperfluorobutane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluoro-1-butene, 2-bromo-4-iodoperfluoro-1-butene, mono-iodine-mono-bromine substituted bodies, di-iodine-mono-bromine substituted bodies, and (2-iodoethyl) and (2-bromoethyl) substituted bodies of benzene, etc. These compounds can be used alone or in combination with each other.

[0140] Among these, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, and 2-iodoperfluoropropane are preferably used in view of polymerization reactivity, crosslinking reactivity, and availability.

[0141] About the copolymer obtained by the above method, in the case of emulsion polymerization, the copolymer of powder state can be obtained by precipitating the dispersion liquid that completes polymerization, and washing, dehydrating, drying. Precipitation can be carried out by adding inorganic salts or inorganic acids such as aluminum sulfate or imparting mechanical shear force or freezing dispersion liquid. In the case of suspension polymerization, the copolymer of powder state can be obtained by reclaiming and drying from the dispersion liquid that completes polymerization. In the case of solution polymerization, the solution comprising polymer can be directly dried and obtained, or it can be obtained by dripping a poor solvent and refining.

[0142] In the positive electrode binder, the copolymer may be used alone or in combination of two or more. In particular, two copolymers having different molecular structures may be used in combination. The present disclosure also provides a positive electrode binder for a sodium ion battery, comprising two or more of the copolymers.

[0143] The combination of copolymers is not particularly limited and may be appropriately selected. Among them, a combination of a copolymer having a structural unit derived from a monomer represented by the above general formula (3) as the structural unit (B) and another copolymer is preferred.

[0144] When the copolymers are combined as described above, the ratio (mass ratio) of the copolymer having a structural unit derived from the monomer represented by the general formula (3) as the structural unit (B) to the other copolymers is preferably 80:20 to 99.9:0.1.

[0145] Within such a range, the effects of the present invention can be achieved.

[0146] The ratio (mass ratio) of the copolymer having a structural unit derived from the monomer represented by the general formula (3) to the other copolymers is more preferably 90:10 or more, and further preferably 95:5 or more. The ratio (mass ratio) of the copolymer having a structural unit derived from the monomer represented by the general formula (3) to the other copolymers is more preferably 99.5:0.5 or less, and further preferably 99:1 or less.

[0147] The positive electrode binder of the present disclosure may contain a blended polymer of one or more of the above copolymers and one or more of fluorinated polymers other than the above copolymers. The present disclosure is also a positive electrode binder for a sodium ion battery comprising the above copolymer and a fluorinated polymer other than the above copolymer.

[0148] The fluorine-containing polymer other than the above copolymer is not particularly limited, but among them, PVdF, modified PVdF, and the like are preferred.

[0149] Examples of modified PVdF include acrylic modified PVDF.

[0150] When the copolymer is combined with another fluorine-containing polymer, the ratio (mass ratio) of the copolymer to the other fluorine-containing polymer is preferably 0.5:99.5 to 40:60. Within such a range, the peel strength as an electrode can be maintained.

[0151] The ratio (mass ratio) of the copolymer to the other fluorine-containing polymer is more preferably 1:90 or more. The ratio (mass ratio) of the copolymer to the other fluorine-containing polymer is more preferably 35:65 or less.

[0152] The positive electrode binder of the sodium ion battery disclosed in the present invention is suitable for use in an electrode mixture for the positive electrode of the sodium ion battery. Specifically, it can constitute an electrode mixture together with a positive electrode active material and a solvent. The present invention also discloses an electrode mixture containing a sodium composite oxide as a positive electrode active material and the positive electrode binder.

[0153] (Positive electrode active material)

[0154] The positive electrode active material used in the present disclosure is not particularly limited as long as it can electrochemically store and release sodium ions.

[0155] As the positive electrode active material, there is no particular restriction as long as it can electrochemically encapsulate / release alkali metal ions. For example, it is preferred to contain an alkali metal and at least one transition metal. As a specific example, transition metal composite oxides containing alkali metals and transition metal phosphate compounds containing alkali metals can be cited. Among them, as the positive electrode active material, transition metal composite oxides containing alkali metals that can generate high voltages are particularly preferred. As the alkali metal ions, lithium ions, sodium ions, potassium ions, etc. can be cited. In a preferred embodiment, the alkali metal ions can be lithium ions or sodium ions. That is, in this embodiment, the alkali metal ion secondary battery is a sodium ion secondary battery.

[0156] Examples of the alkali metal-containing transition metal composite oxide include

[0157] Formula (3-1): MaMn2-b M 1 b O 4

[0158] (wherein, M is Na; 0.9≤a; 0≤b≤1.5; M 1 A sodium-manganese spinel composite oxide represented by at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge,

[0159] Formula (3-2): MNi 1-c M 2 c O 2

[0160] (wherein, M is Na; 0≤c≤0.5; M 2 A sodium-nickel composite oxide represented by at least one metal selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge, or

[0161] Formula (3-3): MCo 1-d M 3 d O 2

[0162] (wherein, M is Na; 0≤d≤0.5; M 3 The sodium-cobalt composite oxide is represented by at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge.

[0163] Among them, MCoO is preferred from the perspective of providing a secondary battery with high energy density and high output. 2 MMnO 2 、MNiO 2 MMn 2 O 4 、MNi 0.8 Co 0.15 Al 0.05 O 2 , or MNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 etc., and preferably the compound represented by the following general formula (3-4).

[0164] MNi h Co i Mnj M 5 k O 2 (3-4)

[0165] (where M is Na, M 5 is at least one selected from the group consisting of Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge, (h+i+j+k)=1.0, 0≤h≤1.0, 0≤i≤1.0, 0≤j≤1.5, 0≤k≤0.2.)

[0166] Examples of the alkali metal-containing transition metal phosphate compound include the following formula (70):

[0167] M e M 4 f (PO 4 ) g (70)

[0168] (where M is Na, M 4 It represents at least one selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni and Cu, and a compound represented by 0.5≤e≤3, 1≤f≤2, and 1≤g≤3).

[0169] As the transition metal of the sodium-containing transition metal phosphate compound, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. are preferred. As specific examples, NaFePO 4 、Na 3 Fe 2 (PO 4 ) 3 、NaFeP 2 O 7 etc. iron phosphates; NaCoPO 4 Cobalt phosphates, etc.; substances obtained by replacing part of the transition metal atoms serving as the main body of these sodium transition metal phosphate compounds with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

[0170] The sodium-containing transition metal phosphate compound preferably has an olivine structure.

[0171] As other positive electrode active materials, MFePO can be cited. 4 、MNi 0.8 Co 0.2 O 2 、M 1.2 Fe 0.4 Mn0.4 O 2 、 MNi 0.5 Mn 1.5 O 4 、 MV 3 O 6 、 M 2 MnO 3 etc. (where M is Na). In particular, MNi 0.5 Mn 1.5 O 4 etc. When the positive electrode active material operates the secondary battery at a voltage exceeding 4.4 V or a voltage of 4.6 V or higher, the crystal structure will not collapse, and it is preferred from this aspect. Therefore, an electrochemical device such as a secondary battery using a positive electrode material containing the exemplified positive electrode active material is preferred because even when stored at a high temperature, the residual capacity is not easily reduced, the resistance increase rate is not easily changed, and even when operating at a high voltage, the battery performance does not deteriorate.

[0172] As other positive electrode active materials, M 2 MnO 3 and MM 6 O 2 (where M is at least one metal selected from the group consisting of Li, Na, and K, and M 6 is a transition metal such as Co, Ni, Mn, Fe, etc.) solid solution materials, etc.

[0173] As the solid solution material, for example, it is an alkali metal manganese oxide represented by the general formula Mx[Mn(1 - y)M 7 y]Oz. Here, M in the formula is Na, and M 7 is composed of at least one metal element other than M and Mn, and for example, contains one or more elements selected from the group consisting of Co, Ni, Fe, Ti, Mo, W, Cr, Zr, and Sn. In addition, the values of x, y, and z in the formula are in the range of 1 < x < 2, 0 ≤ y < 1, and 1.5 < z < 3.

[0174] The average particle size of the positive electrode active material is, for example, 1 μm to 50 μm, preferably 1 μm to 20 μm, and particularly preferably 3 μm to 7 μm. This is because if the average particle size of the positive electrode active material is too small, the operability may deteriorate, and if the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode active material layer. It should be noted that the average particle size of the positive electrode active material can be obtained, for example, by measuring the particle size of the active material carrier observed by a scanning electron microscope (SEM) and averaging.

[0175] In addition, a material having a different composition attached to the surface of the positive electrode active material may also be used. Examples of the surface-attached material include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; carbon; and the like.

[0176] These surface-attached substances can be attached to the surface of the positive electrode active material by, for example, the following methods: a method of dissolving or suspending the substance in a solvent and adding it to the positive electrode active material by infiltration and drying; a method of dissolving or suspending the surface-attached substance precursor in a solvent and adding it to the positive electrode active material by infiltration and then reacting it by heating or the like; a method of adding it to the positive electrode active material precursor and simultaneously firing it; etc. It should be noted that in the case of attaching carbon, a method of mechanically attaching carbon in the form of activated carbon or the like can also be used.

[0177] The amount of the surface-attached substance is used in the following amount relative to the mass of the positive electrode active material: preferably 0.1 ppm or more, more preferably 1 ppm or more, and further preferably 10 ppm or more as the lower limit, and preferably 20% or less, more preferably 10% or less, and further preferably 5% or less as the upper limit. The surface-attached substance can inhibit the oxidation reaction of the electrolyte on the surface of the positive electrode active material and improve the battery life, but if the amount of the attached substance is too small, the effect cannot be fully manifested; if it is too much, it will hinder the entry and exit of sodium ions, and thus the resistance may increase.

[0178] The shape of the particles of the positive electrode active material may be a block shape, a polyhedron shape, a sphere shape, an ellipsoidal sphere shape, a plate shape, a needle shape, a column shape, etc. The primary particles may be aggregated to form secondary particles.

[0179] The tap density of the positive electrode active material is preferably 0.5 g / cm 3 More preferably, 0.8 g / cm 3 More preferably, 1.0 g / cm 3 Above. If the tap density of the positive electrode active material is lower than the lower limit, the amount of dispersion medium required when the positive electrode active material layer is formed increases, and the required amount of conductive material and binder increases, the filling rate of the positive electrode active material in the positive electrode active material layer is limited, and the battery capacity may be limited. By using a composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. The larger the tap density is, the better. There is no particular upper limit. However, if it is too large, the diffusion of sodium ions using the electrolyte in the positive electrode active material layer as a medium becomes rate-limiting, and sometimes the load characteristics are easily reduced. Therefore, the upper limit is preferably 4.0 g / cm3 Below, more preferably 3.7 g / cm 3 Below, more preferably 3.5 g / cm 3 the following.

[0180] It should be noted that in the present disclosure, the tap density is the powder packing density (tap density) g / cm2 when 5 to 10 g of the positive electrode active material powder is placed in a 10 ml glass cylinder and vibrated 200 times with a stroke of about 20 mm. 3 Find out.

[0181] The median diameter d50 of the particles of the positive electrode active material (secondary particle diameter in the case where the primary particles are agglomerated to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, further preferably 0.8 μm or more, and most preferably 1.0 μm or more, and preferably 30 μm or less, more preferably 27 μm or less, further preferably 25 μm or less, and most preferably 22 μm or less. If it is less than the lower limit, a high tap density product may not be obtained; if it exceeds the upper limit, the diffusion of lithium in the particles takes time, which sometimes leads to a decrease in battery performance, or when the positive electrode of the battery is made, that is, the active material and the conductive material, the binder, etc. are slurried with a solvent and coated into a thin film, causing problems such as stripes. Here, by mixing two or more of the positive electrode active materials with different median diameters d50, the filling property during the production of the positive electrode can be further improved.

[0182] It should be noted that in the present disclosure, the median diameter d50 is measured using a known laser diffraction / scattering particle size distribution measuring device. When using LA-920 manufactured by HORIBA as a particle size distribution meter, as a dispersion medium used during measurement, a 0.1% by mass sodium hexametaphosphate aqueous solution is used, and after 5 minutes of ultrasonic dispersion, the measured refractive index is set to 1.24 for measurement.

[0183] In the case where the primary particles are agglomerated to form secondary particles, the average primary particle size of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.2 μm or more, and the upper limit is preferably 5 μm or less, more preferably 4 μm or less, further preferably 3 μm or less, and most preferably 2 μm or less. If the upper limit is exceeded, it is difficult to form spherical secondary particles, which has an adverse effect on the powder filling property, or the specific surface area is greatly reduced, so the possibility of reduced battery performance such as output characteristics is sometimes increased. On the contrary, if it is lower than the lower limit, crystallization is generally not developed, so problems such as poor reversibility of charge and discharge may occur.

[0184] It should be noted that in the present disclosure, the primary particle size is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph with a magnification of 10,000 times, for any 50 primary particles, the longest value of the slice intercepted on a straight line in the horizontal direction by the left and right boundaries of the primary particles is obtained, and the average value is taken to obtain the primary particle size.

[0185] The BET specific surface area of ​​the positive electrode active material is preferably 0.1 m 2 / g or more, more preferably 0.2m 2 / g or more, more preferably 0.3m 2 / g or more, and the upper limit is preferably 50m 2 / g or less, more preferably 40m 2 / g or less, more preferably 30m 2 If the BET specific surface area is smaller than this range, the battery performance is likely to decrease, and if it is larger than this range, it is difficult to increase the tap density, and coating properties may be problematic when the positive electrode active material layer is formed.

[0186] It should be noted that in the present disclosure, the BET specific surface area is defined as: using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.), after pre-drying the sample at 150°C for 30 minutes under nitrogen flow, using a nitrogen-helium mixed gas accurately adjusted so that the relative pressure of nitrogen to atmospheric pressure becomes 0.3, the value is measured by the nitrogen adsorption BET single-point method based on the gas flow method.

[0187] When the secondary battery of the present disclosure is used as a large sodium ion secondary battery for hybrid vehicles or distributed power sources, high output is required, and therefore the particles of the positive electrode active material preferably mainly contain secondary particles.

[0188] The particles of the positive electrode active material preferably contain 0.5% to 7.0% by volume of secondary particles having an average particle size of 40 μm or less and an average primary particle size of 1 μm or less. By containing particles having an average primary particle size of 1 μm or less, the contact area with the electrolyte becomes larger, which can make the diffusion of lithium ions between the electrode and the electrolyte faster, and as a result, the output performance of the battery can be improved.

[0189] As a method for manufacturing positive electrode active materials, a common method for manufacturing inorganic compounds is used. In particular, various methods are considered for making spherical or ellipsoidal active materials, for example, the following methods can be cited: dissolving or crushing the raw material of the transition metal and dispersing it in a solvent such as water, adjusting the pH under stirring, making a spherical precursor and recovering it, drying it as needed, then adding a Na source such as sodium hydroxide and firing it at high temperature to obtain an active material.

[0190] To produce the positive electrode, the above-mentioned positive electrode active materials may be used alone, or two or more of them having different compositions may be used in any combination or ratio.

[0191] The type of the solvent used for the electrode mixture is not particularly limited as long as it can dissolve or disperse the positive electrode active material, the binder, and the conductive agent and thickener used as needed. Any of aqueous solvents and organic solvents can be used. As aqueous solvents, for example, water, mixed solvents of alcohol and water, etc. can be cited. As organic solvents, for example, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc.

[0192] As the organic solvent, a solvent represented by the general formula (4) can also be used.

[0193] General formula (4):

[0194] [Chemistry 7]

[0195]

[0196] (Where R 1 , R 2 and R 3 are independently H or an organic group, wherein R 1 , R 2 and R 3 The total number of carbon atoms is 6 or more, R 1 , R 2 and R 3 At least one of R is an organic group having a carbonyl group. 1 , R 2 and R 3 Any two of them can be bonded to form a ring. )

[0197] R 1 , R 2 and R 3 The total number of carbon atoms of R is 6 or more. 1 , R 2 and R 3 The types of the groups are selected so that the total number of carbon atoms is 6 or more. 1 , R 2 and R 3The upper limit of the total number of carbon atoms is not limited, and may be 16 or less, 14 or less, or 12 or less.

[0198] R 1 , R 2 and R 3 and are independently H or an organic group. As the organic group, an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group, an aminoalkyl group or a cycloalkyl group is preferred.

[0199] R 1 , R 2 and R 3 At least one of them is an organic group having a carbonyl group. As the organic group having a carbonyl group, an acyl group is preferred. As the acyl group, a general formula of -CO-R is preferred. 4 (Where R 4 is an alkyl group having 1 to 6 carbon atoms). When the alkyl group has 3 or more carbon atoms, it may be linear or branched. 4 When the number of carbon atoms of the alkyl group is 2 or more, a hetero atom such as an oxygen atom or a nitrogen atom or a carbonyl group may be contained between carbon atoms.

[0200] R 1 , R 2 and R 3 Any two of them may be bonded to form a ring. In addition, as the constituent atoms of the ring, heteroatoms such as oxygen atoms may be included. The ring is preferably a saturated ring. The number of ring members is not particularly limited, preferably 5 or 6. As the ring, a pyrrolidine ring, an oxazoline ring, a piperidine ring or a morpholine ring is preferred.

[0201] As the solvent, a solvent represented by the general formula (4a) is preferred.

[0202] General formula (4a):

[0203] [Chemistry 8]

[0204]

[0205] (Where R 1a is an organic group, R 2a and R 3a are independently H or an organic group, wherein R 1a , R 2a and R 3a The total number of carbon atoms is 5 or more. 1a , R 2a and R 3a Any two of them can be bonded to form a ring. )

[0206] In the general formula (4a), R 1a , R 2a and R 3aThe total number of carbon atoms of R is 5 or more. 1a , R 2a and R 3a The types of the groups are selected so that the total number of carbon atoms is 5 or more. 1a , R 2a and R 3a The upper limit of the total number of carbon atoms is not limited, and may be 15 or less, 13 or less, or 11 or less.

[0207] In the general formula (4a), R 1a The organic group is preferably an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group, an aminoalkyl group or a cycloalkyl group, and more preferably an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group or an aminoalkyl group.

[0208] In the general formula (4a), R 2a and R 3a R is independently H or an organic group. 2a and R 3a , and each of them is preferably an organic group. As the organic group, an alkyl group, an alkoxyalkyl group, an acylalkyl group, an alkenyl group, an amino group, an aminoalkyl group or a cycloalkyl group is preferred, and an alkyl group, an alkoxyalkyl group, a cycloalkyl group or an alkenyl group is more preferred.

[0209] R 1a , R 2a and R 3a Any two of them may be bonded to form a ring. 2a and R 3a Bonding and R 2a and R 3a The nitrogen atoms bonded together form a ring. In addition, as the constituent atoms of the ring, heteroatoms such as oxygen atoms may be included. The ring is preferably a saturated ring. The number of ring members is not particularly limited, preferably 5 or 6. As the ring, a pyrrolidine ring, an oxazoline ring, a piperidine ring or a morpholine ring is preferred.

[0210] The solvent is more preferably at least one selected from the group consisting of solvents represented by the general formula (4b-1) and solvents represented by the general formula (4b-2).

[0211] General formula (4b-1):

[0212] [Chemistry 9]

[0213]

[0214] (Where R 1b is alkyl, alkoxyalkyl, acylalkyl, alkenyl, amino or aminoalkyl, R 2b and R 3b are independently alkyl or alkoxyalkyl, R 1b , R2b and R 3b The total number of carbon atoms is 5 or more. 2b and R 3b Can bond with each other and with R 2b and R 3b The nitrogen atoms to which they are bonded together form a ring, which may also contain oxygen atoms as constituent atoms of the ring.)

[0215] General formula (4b-2):

[0216] [Chemistry 10]

[0217]

[0218] (wherein, ring A is a 5-membered or 6-membered amide ring, R 4b is an alkyl, cycloalkyl or alkenyl group, and ring A and R 4b The total number of carbon atoms is 5 or more.)

[0219] In the general formula (4b-1), R 1b , R 2b and R 3b The total number of carbon atoms of R is 5 or more. 1b , R 2b and R 3b The types of the groups are selected so that the total number of carbon atoms is 5 or more. 1b , R 2b and R 3b The upper limit of the total number of carbon atoms is not limited, and may be 15 or less, 13 or less, or 11 or less.

[0220] In the general formula (4b-1), R 1b is alkyl, alkoxyalkyl, acylalkyl, alkenyl, amino or aminoalkyl.

[0221] As R 1b The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms. When the alkyl group has 3 or more carbon atoms, it may be linear or branched.

[0222] As R 1b Alkoxyalkyl, preferably of the general formula: -R 1b1 -OR 1b2 (Where R 1b1 is an alkylene group having 1 to 5 carbon atoms, R 1b2 The group represented by (i) is an alkyl group having 1 to 5 carbon atoms. When the alkyl group and the alkylene group have 3 or more carbon atoms, they may be linear or branched.

[0223] As R 1b The acylalkyl group of the preferred general formula is: -R 1b3-CO-R 1b4 (Where R 1b3 is an alkylene group having 1 to 5 carbon atoms, R 1b4 The group represented by (i) is an alkyl group having 1 to 5 carbon atoms. When the alkyl group and the alkylene group have 3 or more carbon atoms, they may be linear or branched.

[0224] As R 1b Alkenyl, preferably of the general formula: -R 1b5 -CR 1b6 =CR 1b7 (Where R 1b5 is a single bond or an alkylene group having 1 to 5 carbon atoms, R 1b6 and R 1b7 (independently H or an alkyl group having 1 to 5 carbon atoms). When the alkyl group and the alkylene group have 3 or more carbon atoms, they may be straight-chain or branched. As the alkenyl group, a vinyl group is preferred.

[0225] R 1b The amino group and the aminoalkyl group have an amino group which is a monovalent functional group obtained by removing hydrogen from ammonia, a primary amine or a secondary amine. 1b In the case of amino groups, R 1b The bonded carbonyl groups together form an amide bond.

[0226] As R 1b The amino group is preferably of the general formula: -N-(R 1b8 ) 2 (Where R 1b8 is H or an alkyl group having 1 to 5 carbon atoms). When the alkyl group has 3 or more carbon atoms, it may be straight-chain or branched. As an amino group, -N-(CH 3 ) 2 or-N-(C 2 H 5 ) 2 .

[0227] As R 1b The aminoalkyl group of the preferred general formula is: -R 1b9 -N-(R 1b8 ) 2 (Where R 1b9 is an alkylene group having 1 to 5 carbon atoms, R 1b8 is H or an alkyl group having 1 to 5 carbon atoms). When the alkyl group and the alkylene group have 3 or more carbon atoms, they may be linear or branched.

[0228] In the general formula (4b-1), R 2b and R 3b are independently alkyl or alkoxyalkyl.

[0229] As R 2b and R 3b The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms. When the alkyl group has 3 or more carbon atoms, it may be linear or branched.

[0230] As R 2b and R 3b Alkoxyalkyl, preferably of the general formula: -R2 b1 -OR 2b2 (Where R 2b1 is an alkylene group having 1 to 5 carbon atoms, R 2b2 The group represented by (i) is an alkyl group having 1 to 5 carbon atoms. When the alkyl group and the alkylene group have 3 or more carbon atoms, they may be linear or branched.

[0231] R 2b and R 3b Can bond with each other and with R 2b and R 3b The nitrogen atoms bonded together form a ring, and oxygen atoms may be included as the constituent atoms of the ring. The ring is preferably a saturated ring. The number of ring members is not particularly limited, and preferably 5 or 6. As the ring, a pyrrolidine ring, an oxazoline ring, a piperidine ring or a morpholine ring is preferred.

[0232] In the general formula (4b-2), ring A and R 4b The total number of carbon atoms of ring A and R is 5 or more. 4b The types of rings and groups are selected so that the total number of carbon atoms is 5 or more. 4b The upper limit of the total number of carbon atoms is not limited, and may be 15 or less, 13 or less, or 11 or less.

[0233] Ring A is a 5-membered or 6-membered amide ring. Therefore, Ring A is composed of carbon atoms, nitrogen atoms, and an alkylene group having 3 to 4 carbon atoms. The hydrogen atom bonded to the carbon atom of the alkylene group constituting Ring A may or may not be substituted by a substituent, but preferably not be substituted by a substituent. As the substituent, an alkyl group such as a methyl group can be mentioned.

[0234] R 4b is an alkyl, cycloalkyl or alkenyl group.

[0235] As R 4b The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms. When the alkyl group has 3 or more carbon atoms, it may be linear or branched.

[0236] As R 4b The cycloalkyl group is preferably a cycloalkyl group having 3 to 10 carbon atoms.

[0237] As the cycloalkyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group or a cyclooctyl group is preferred.

[0238] As R 4b Alkenyl, preferably of the general formula: -R 4b1 -CR 4b2 =CR 4b3 (Where R 4b1 is a single bond or an alkylene group having 1 to 5 carbon atoms, R 4b2 and R 4b3 (independently H or an alkyl group having 1 to 5 carbon atoms). When the alkyl group and the alkylene group have 3 or more carbon atoms, they may be straight-chain or branched. As the alkenyl group, a vinyl group is preferred.

[0239] As the solvent, at least one selected from the group consisting of 3-methoxy-N,N-dimethylpropionamide, N-ethyl-2-pyrrolidone (NEP), N-butyl-2-pyrrolidone (NBP), acryloylmorpholine, N-cyclohexyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 3-butoxy-N,N-dimethylpropionamide, N,N,N',N'-tetraethyl urea, N,N-dimethylacetoacetamide, N-octyl-2-pyrrolidone and N,N-diethylacetamide is preferred.

[0240] As a solvent, among them, it is more preferred to select at least one of the group consisting of 3-methoxy-N, N-dimethylpropionamide, N-ethyl-2-pyrrolidone and N-butyl-2-pyrrolidone. In particular, if an electrode mixture containing 3-methoxy-N, N-dimethylpropionamide as a solvent is used, there is a tendency that the gas generation of the resulting battery is suppressed. In particular, if an electrode mixture containing N-ethyl-2-pyrrolidone (NEP) as a solvent is used, there is a tendency that the high temperature storage capacity retention rate of the resulting battery becomes higher. In particular, if an electrode mixture containing N-butyl-2-pyrrolidone (NBP) as a solvent is used, there is a tendency that the resistance of the resulting battery is difficult to increase.

[0241] The amount of the solvent in the electrode mixture is determined in consideration of coating properties on the current collector, thin film forming properties after drying, etc. In general, the ratio of the copolymer to the solvent is preferably 0.5:99.5 to 20:80 in terms of mass ratio.

[0242] The electrode mixture of the present disclosure may further contain a conductive agent as necessary.

[0243] As the conductive agent, any known conductive agent can be used. As specific examples, metal materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, needle coke, carbon nanotubes, fullerene, carbon materials such as amorphous carbon such as VGCF, etc. can be cited. It should be noted that these can be used alone or in any combination and ratio. Two or more kinds can be used together.

[0244] The conductive agent is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more in the electrode material layer, and is usually used in a manner of containing 50% by mass or less, preferably 30% by mass or less, and more preferably 15% by mass or less. If the content is lower than this range, the conductivity is sometimes insufficient. On the contrary, if the content is higher than this range, the battery capacity is sometimes reduced.

[0245] The electrode mixture disclosed herein may further contain a thickener as required. Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, polyvinyl pyrrolidone, and salts thereof. One may be used alone, or two or more may be used in any combination and ratio.

[0246] The ratio of thickener to active material is usually 0.1 mass %, preferably 0.2 mass %, more preferably 0.3 mass %, and in addition, usually 5 mass %, preferably 3 mass %, more preferably 2 mass %. If it is lower than this range, the coating property may be significantly reduced. If it is higher than this range, the ratio of active material in electrode material layer is reduced, which may cause the problem of reduced capacity of battery or the problem of increased resistance between positive active materials.

[0247] The electrode mixture may contain materials other than the above-mentioned materials. However, when the entire electrode material layer is taken as 100 mass %, the content of the above-mentioned materials is preferably 8 mass % or less, and more preferably 4 mass % or less.

[0248] In the process of preparing the electrode mixture of the present disclosure, the above-mentioned components are mixed to form a slurry. The order of mixing the components is not particularly limited, and the components may be added to a solvent and mixed.

[0249] The solid content concentration in the slurry is preferably 70% to 95% by mass. If it is within this range, the interface resistance during coating can be suppressed. In addition, the lower limit is preferably 73% by mass or more, more preferably 73.5% by mass or more, and the upper limit is preferably 85% by mass or less.

[0250] The electrode mixture disclosed in the present invention can be suitably used as an electrode material layer in a positive electrode of a sodium ion secondary battery.

[0251] An electrode including a current collector and an electrode material layer formed of the electrode mixture of the present disclosure and provided on one or both surfaces of the current collector is also one of the aspects of the present disclosure.

[0252] The sodium ion secondary battery may adopt a known structure, and typically includes a positive electrode and a negative electrode capable of storing and releasing sodium ions, and an electrolyte. A sodium ion secondary battery including the electrode of the present disclosure is also one of the present disclosures.

[0253] <Positive electrode>

[0254] The positive electrode is preferably composed of an electrode material layer containing the positive electrode active material (hereinafter sometimes referred to as a positive electrode active material layer) and a current collector.

[0255] Examples of the material of the positive electrode current collector include metals such as aluminum, titanium, tantalum, stainless steel, nickel, or alloys thereof; and carbon materials such as carbon cloth and carbon paper. Among them, metal materials, particularly aluminum or alloys thereof, are preferred.

[0256] As the shape of the current collector, in the case of metal materials, metal foil, metal cylinder, metal coil, metal plate, porous metal mesh, stamping metal, foamed metal, etc. can be mentioned, and in the case of carbon materials, carbon plate, carbon film, carbon cylinder, etc. can be mentioned. Among these, metal foil is preferred. It should be noted that the film can be appropriately formed into a mesh. The thickness of the film is arbitrary, usually more than 1 μm, preferably more than 3 μm, more preferably more than 5 μm, and usually less than 1 mm, preferably less than 100 μm, more preferably less than 50 μm. If the film is thinner than this range, the strength required as a current collector is sometimes insufficient. On the contrary, if the film is thicker than this range, sometimes the handling property is impaired.

[0257] In addition, from the perspective of reducing the electrical contact resistance between the current collector and the positive electrode active material layer, it is also preferred that a conductive additive be coated on the surface of the current collector. Examples of the conductive additive include carbon or noble metals such as gold, platinum, and silver.

[0258] The ratio of the thickness of the current collector to the positive electrode active material layer is not particularly limited, and the value of (the thickness of the positive electrode active material layer on one side before the electrolyte is injected) / (the thickness of the current collector) is preferably less than 20, more preferably less than 15, and most preferably less than 10. In addition, it is preferably more than 0.5, more preferably more than 0.8, and most preferably more than 1. If it exceeds this range, the current collector sometimes generates heat caused by Joule heat during high current density charging and discharging. If it is less than this range, the volume ratio of the current collector to the positive electrode active material increases, and the capacity of the battery sometimes decreases.

[0259] The positive electrode can be manufactured according to conventional methods. For example, a method in which a slurry of a positive electrode mixture is prepared by adding the above-mentioned binder, thickener, conductive material, solvent, etc. to the positive electrode active material, applying the slurry to a current collector, and pressing the slurry after drying to obtain a high density can be cited.

[0260] The density of the positive electrode active material layer is preferably 1.5 g / cm 3 More preferably, 2 g / cm 3 More preferably, 2.2 g / cm 3 More than 5 g / cm 3 Below, more preferably 4.5g / cm 3 Below, more preferably 4g / cm 3 If the range is exceeded, the permeability of the electrolyte to the collector / active material interface is reduced, and the charge-discharge characteristics at high current density are reduced, and sometimes high output cannot be obtained. In addition, if it is less than this range, the conductivity between the active materials is reduced, and sometimes the battery resistance increases and high output cannot be obtained.

[0261] In addition, from the perspective of high output and improved stability at high temperatures, the area of ​​the positive electrode active material layer is preferably larger than the outer surface area of ​​the battery case. Specifically, relative to the surface area of ​​the outer packaging of the secondary battery, the sum of the electrode areas of the positive electrode is preferably 15 times or more in terms of area ratio, and more preferably 40 times or more. Regarding the outer surface area of ​​the battery case, in the case of a square shape with a bottom, it refers to the total area calculated by the length, width and thickness dimensions of the shell part filled with the power generation element except the protruding portion of the terminal. In the case of a cylindrical shape with a bottom, it refers to the geometric surface area of ​​the shell part filled with the power generation element except the protruding portion of the terminal. The sum of the electrode mixture area of ​​the positive electrode refers to the geometric surface area of ​​the positive electrode mixture layer facing the mixture layer containing the negative electrode active material. In a structure where a positive electrode mixture layer is formed on both sides by a collector foil, it refers to the sum of the areas calculated for each face.

[0262] The content of the copolymer in the electrode material layer is preferably 0.1% to 5% by mass, more preferably 0.5% to 3% by mass. In addition, the lower limit is preferably 0.6% by mass or more, more preferably 1% by mass or more, and particularly preferably 1.1% by mass or more. The upper limit is preferably 2% by mass or less, more preferably 1.7% by mass or less. If the content of the copolymer in the electrode material layer is low, the flexibility of the electrode is sometimes reduced. On the contrary, if the content is too high, the battery performance is sometimes reduced.

[0263] In the case of using a blended polymer formed by combining the copolymer with one or more fluorinated polymers other than the copolymer, the content of the blended polymer in the electrode material layer is preferably 0.1% to 5% by mass, more preferably 0.5% to 3% by mass. In addition, the lower limit is preferably 0.6% by mass or more, more preferably 1% by mass or more, and particularly preferably 1.1% by mass or more. The upper limit is preferably 2% by mass or less, more preferably 1.7% by mass or less. If the content of the blended polymer in the electrode material layer is low, the flexibility of the electrode is sometimes reduced. On the contrary, if the content is too high, the battery performance is sometimes reduced.

[0264] From the aspect of high battery capacity, the content of the positive electrode active material is preferably 50% to 99.5% by mass of the electrode material layer, and more preferably 80% to 99% by mass. In addition, the content of the positive electrode active material in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. In addition, the upper limit is preferably 99% by mass or less, and more preferably 98% by mass or less. If the content of the positive electrode active material in the electrode material layer is low, the capacitance sometimes becomes insufficient. On the contrary, if the content is too high, the strength of the positive electrode is sometimes insufficient.

[0265] The thickness of the positive electrode plate is not particularly limited. From the perspective of high capacity and high output, the thickness of the composite layer after deducting the thickness of the metal foil of the core material is preferably 10 μm or more, more preferably 20 μm or more, and preferably 500 μm or less, more preferably 450 μm or less, relative to a single side of the collector as the lower limit.

[0266] In addition, a positive electrode plate having a substance having a different composition attached to the surface of the positive electrode plate may also be used. Examples of the surface-attached substance include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; carbon; and the like.

[0267] <Negative electrode>

[0268] The negative electrode is preferably composed of an electrode material layer containing a negative electrode active material (hereinafter sometimes referred to as a negative electrode active material layer) and a current collector.

[0269] (Negative electrode active material)

[0270] The negative electrode active material is not particularly limited, and examples thereof include materials selected from lithium metal, artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and carbon containing carbonaceous materials such as non-graphitizable carbon, silicon-containing compounds such as silicon and silicon alloys, Li 4 Ti 5 O 12 Among them, a substance containing at least a part of a carbonaceous material or a silicon-containing compound can be particularly preferably used.

[0271] The negative electrode active material used in the present disclosure preferably contains silicon as a constituent element. By containing silicon as a constituent element, a high-capacity battery can be produced.

[0272] As the material containing silicon, silicon particles, particles having a structure in which silicon particles are dispersed in a silicon-based compound, silicon oxide particles represented by the general formula SiOx (0.5≤x≤1.6), or mixtures thereof are preferred. By using these substances, a negative electrode mixture for a lithium ion secondary battery having higher initial charge and discharge efficiency, high capacity, and excellent cycle characteristics is obtained.

[0273] Silicon oxide in the present invention is a general term for amorphous silicon oxides, and silicon oxide before disproportionation is represented by the general formula SiOx (0.5≤x≤1.6). x is preferably 0.8≤x<1.6, and more preferably 0.8≤x<1.3. The silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metallic silicon and cooling and precipitating the generated silicon monoxide gas.

[0274] Particles having a structure in which silicon particles are dispersed in a silicon-based compound can be obtained, for example, as follows: a method in which silicon particles are mixed with a silicon-based compound and the mixture is fired; or a method in which silicon oxide particles before disproportionation represented by the general formula SiOx are heat-treated in an inactive, non-oxidizing atmosphere such as argon at a temperature of 400°C or more, preferably 800°C to 1,100°C, to carry out a disproportionation reaction. In particular, the material obtained by the latter method is preferred because the silicon crystallites are uniformly dispersed. The disproportionation reaction can make the size of silicon nanoparticles 1nm to 100nm. It should be noted that the silicon oxide in the particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is preferably silicon dioxide. It should be noted that the silicon nanoparticles (crystals) dispersed in the amorphous silicon oxide can be confirmed by transmission electron microscopy.

[0275] The physical properties of the particles containing silicon can be appropriately selected according to the target composite particles. For example, the average particle size is preferably 0.1 μm to 50 μm, and the lower limit is more preferably 0.2 μm or more, and further preferably 0.5 μm or more. The upper limit is more preferably 30 μm or less, and further preferably 20 μm or less. It should be noted that the average particle size in the present invention is expressed by the weight average particle size in the particle size distribution measurement based on the laser diffraction method.

[0276] The BET specific surface area is preferably 0.5 m 2 / g~100m 2 / g, more preferably 1m 2 / g~20m 2 / g. If the BET specific surface area is 0.5m 2 / g or more, there is no possibility of reduced adhesion when applied to the electrode and reduced battery characteristics. 2 / g or less, the proportion of silicon dioxide on the particle surface becomes large, and the battery capacity does not decrease when used as a negative electrode material for a sodium ion secondary battery.

[0277] By coating the silicon-containing particles with carbon to impart conductivity, improvement in battery characteristics is observed. Methods for imparting conductivity include mixing with conductive particles such as graphite, coating the surface of the silicon-containing particles with a carbon coating, and a combination of the two. Preferably, the coating method is a carbon coating method, and more preferably, a chemical vapor deposition (CVD) method.

[0278] In order to increase the capacity of the obtained electrode mixture, the content of the negative electrode active material is preferably more than 40 mass %, more preferably more than 50 mass %, and particularly preferably more than 60 mass % in the electrode mixture. In addition, the upper limit is preferably below 99 mass %, more preferably below 98 mass %.

[0279] (Conductive agent)

[0280] The negative electrode active material layer may further contain a conductive agent as necessary.

[0281] As the conductive agent, any known conductive material can be used. As specific examples, metal materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, needle coke, carbon nanotubes, fullerene, amorphous carbon such as VGCF, and the like can be cited. It should be noted that these can be used alone or in any combination and ratio. Two or more carbon materials can be used.

[0282] The conductive agent is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more in the negative electrode active material layer, and is usually used in a manner of containing 50% by mass or less, preferably 30% by mass or less, and more preferably 15% by mass or less. If the content is lower than this range, the conductivity is sometimes insufficient. On the contrary, if the content is higher than this range, the battery capacity is sometimes reduced.

[0283] (Binder)

[0284] The negative electrode active material layer preferably contains a binder.

[0285] As the binder, there is no particular limitation, and for example, the same binder as the binder that can be used for the positive electrode can be cited. The ratio of the binder to the negative electrode active material is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 0.6% by mass or more. In addition, it is preferably 20% by mass or less, more preferably 15% by mass or less, further preferably 10% by mass or less, and particularly preferably 8% by mass or less. If the ratio of the binder to the negative electrode active material is higher than the range, the ratio of the binder that does not contribute to the battery capacity increases, sometimes resulting in a reduction in the battery capacity. In addition, if it is lower than the range, it sometimes results in a reduction in the strength of the negative electrode.

[0286] Especially when the main component contains a rubber-like polymer represented by SBR, the ratio of the binder to the negative electrode active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. In addition, when the main component contains a fluorine-based polymer represented by polyvinylidene fluoride, the ratio relative to the negative electrode active material is usually 1% by mass or more, preferably 2% by mass or more, and more preferably 3% by mass or more, and usually 15% by mass or less, preferably 10% by mass or less, and more preferably 8% by mass or less.

[0287] The negative electrode active material layer may further contain a thermoplastic resin. Examples of the thermoplastic resin include vinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, and polyethylene oxide. One type may be used alone, or two or more types may be used in any combination and ratio.

[0288] Thermoplastic resin is generally more than 0.01 mass %, preferably more than 0.05 mass %, more preferably more than 0.10 mass %, in addition, generally below 3.0 mass %, preferably below 2.5 mass %, more preferably below 2.0 mass %.By adding thermoplastic resin, the mechanical strength of electrode can be improved.In addition, if it exceeds this scope, the ratio of electrode active material in electrode mixture is reduced, and sometimes the problem of the capacity reduction of battery or the problem of resistance increase between active material can be produced.

[0289] The negative electrode active material layer may contain a thickener.

[0290] As the thickener, the same substances as the thickeners that can be used in the positive electrode can be cited. The ratio of the thickener to the negative electrode active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less. If the ratio of the thickener to the negative electrode active material is lower than the range, the coating property is sometimes significantly reduced. In addition, if it is greater than the range, the proportion of the negative electrode active material in the negative electrode active material layer is reduced, there is a problem of reduced capacity of the battery, and sometimes the resistance between the negative electrode active materials increases.

[0291] (Other ingredients)

[0292] The negative electrode active material layer of the present disclosure may further contain other components such as a leveling agent and a reinforcing material.

[0293] The negative electrode includes a negative electrode active material layer and a current collector. The negative electrode active material layer is formed using the negative electrode mixture and can be provided on one side or both sides of the current collector.

[0294] Examples of the current collector included in the negative electrode include metal foils or metal meshes of iron, stainless steel, copper, aluminum, nickel, titanium, and the like, and carbon materials such as carbon cloth and carbon paper. Among them, copper foil is preferred.

[0295] As the shape of the current collector, in the case of metal materials, metal foil, metal cylinder, metal coil, metal plate, porous metal mesh, stamping metal, foamed metal, etc. can be mentioned, and in the case of carbon materials, carbon plate, carbon film, carbon cylinder, etc. can be mentioned. Among these, metal foil is preferred. It should be noted that the film can be appropriately formed into a mesh. The thickness of the film is arbitrary, usually more than 1 μm, preferably more than 3 μm, more preferably more than 5 μm, and usually less than 1 mm, preferably less than 100 μm, more preferably less than 50 μm. If the film is thinner than this range, the strength required as a current collector is sometimes insufficient. On the contrary, if the film is thicker than this range, sometimes the handling property is impaired.

[0296] The manufacture of the negative electrode can be carried out according to conventional methods. For example, after mixing a binder and a solvent, a negative electrode active material and the like are added to the obtained mixture and further mixed, thereby preparing a slurry-like negative electrode mixture. Then, after the obtained negative electrode mixture is evenly applied to a collector such as a metal foil or a metal mesh, the coating is dried, and a heat treatment is arbitrarily performed. The obtained dry coating is pressed as needed to form a thin negative electrode material layer on the collector to prepare a thin film electrode. In addition, the negative electrode active material and the binder and the like can be mixed first, and then a solvent is added to prepare the negative electrode mixture.

[0297] Examples of the solvent include water and an organic solvent. When the negative electrode material layer is formed using the negative electrode mixture, an organic solvent is preferred from the viewpoint of significantly reducing the possibility of water remaining in the negative electrode material layer.

[0298] Examples of the organic solvent include nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and dimethylformamide; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as tetrahydrofuran and dioxane; β-alkoxypropionamides such as β-methoxy-N,N-dimethylpropionamide, β-n-butoxy-N,N-dimethylpropionamide, and β-n-hexyloxy-N,N-dimethylpropionamide; and low-boiling-point general-purpose organic solvents such as mixed solvents thereof.

[0299] In addition, as the organic solvent, a solvent represented by the above-mentioned general formula (4) can be used.

[0300] The amount of the solvent in the negative electrode mixture is determined in consideration of coating properties on the current collector, thin film forming properties after drying, etc. Usually, the ratio of the binder to the solvent is 0.5:99.5 to 20:80 in terms of mass ratio.

[0301] The thickness of the negative electrode plate is designed according to the positive electrode plate used and is not particularly limited. The thickness of the composite layer after deducting the thickness of the metal foil of the core material is usually more than 15 μm, preferably more than 20 μm, more preferably more than 30 μm, and is usually expected to be less than 300 μm, preferably less than 280 μm, more preferably less than 250 μm.

[0302] (Electrolyte)

[0303] As the non-aqueous electrolyte solution, a solution prepared by dissolving a known electrolyte salt in a known organic solvent for dissolving the electrolyte salt can be used.

[0304] There are no particular limitations on the organic solvent used to dissolve the electrolyte salt, and known hydrocarbon solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can be used; and one or more of fluorine-based solvents such as fluoroethylene carbonate, fluoroethers, and fluorocarbonates can be used.

[0305] Examples of the electrolyte salt include NaPF 6 , NaBF 4 、NaClO 4 、NaAlF 4 、NaSbF 6 、NaTaF 6 、NaWF 7 、NaAsF 6 ,NaAlCl 4 ,NaI, NaBr, NaCl, NaB 10 Cl 10 、Na 2 SiF 6 、Na 2 PFO 3 、NaPO 2 F 2 etc. inorganic sodium salts;

[0306] NeA 5 Sodium tungstate and other products;

[0307] HCO 2 Na, CH 3 CO 2 Na, CH 2 FCO 2 Na, CHF 2 CO 2 Na, CF 3 CO 2 Na, CF 3 CH 2 CO 2 Na, CF 3 CF 2 CO 2 Na, CF 3 CF 2 CF 2 CO 2 Na, CF 3 CF 2 CF 2 CF 2 CO 2 Sodium salts of carboxylates such as Na;

[0308] FSO 3Na, CH 3 SO 3 Na, CH 2 FSO 3 Na, CHF 2 SO 3 Na, CF 3 SO 3 Na, CF 3 CF 2 SO 3 Na, CF 3 CF 2 CF 2 SO 3 Na, CF 3 CF 2 CF 2 CF 2 SO 3 Na, sodium methyl sulfate, sodium ethyl sulfate (C 2 H 5 OSO 3 Sodium salts with S=O groups such as sodium 2,2,2-trifluoroethyl sulfate, etc.

[0309] NaN(FCO) 2 、NaN(FCO)(FSO 2 )、NaN(FSO 2 ) 2 、NaN(FSO 2 )(CF 3 SO 2 )、NaN(CF 3 SO 2 ) 2 、NaN(C 2 F 5 SO 2 ) 2 、Sodium bis(perfluoroethanesulfonyl)imide、Sodium cyclic 1,2-perfluoroethane disulfonyl imide、Sodium cyclic 1,3-perfluoropropane disulfonyl imide、Sodium cyclic 1,2-ethane disulfonyl imide、Sodium cyclic 1,3-propane disulfonyl imide、Sodium cyclic 1,4-perfluorobutane disulfonyl imide、NaN(CF 3 SO 2 )(FSO 2 )、NaN(CF 3 SO 2 )(C 3 F 7 SO 2 )、NaN(CF 3 SO 2 )(C 4 F 9 SO 2)、NaN(POF 2 ) 2 etc. sodium imide salts;

[0310] NaC(FSO 2 ) 3 、NaC(CF 3 SO 2 ) 3 、NaC(C 2 F 5 SO 2 ) 3 etc. sodium methyl salts;

[0311] And formula: NaPF a (C n F 2n+1 ) 6-a (wherein a is an integer from 0 to 5, and n is an integer from 1 to 6) 3 (C 2 F 5 ) 3 、NaPF 3 (CF 3 ) 3 、NaPF 3 (iso-C 3 F 7 ) 3 、NaPF 5 (iso-C 3 F 7 )、NaPF 4 (CF 3 ) 2 、NaPF 4 (C 2 F 5 ) 2 )、NaPF 4 (CF 3 SO 2 ) 2 、NaPF 4 (C 2 F 5 SO 2 ) 2 , NaBF 3 CF 3 , NaBF 3 C 2 F 5 , NaBF 3 C 3 F 7 , NaBF 2 (CF 3 ) 2 , NaBF2 (C 2 F 5 ) 2 , NaBF 2 (CF 3 SO 2 ) 2 , NaBF 2 (C 2 F 5 SO 2 ) 2 Fluorinated organic sodium salts, NaSCN, LiB(CN) 4 、NaB(C 6 H 5 ) 4 、Na 2 (C 2 O 4 )、NaP(C 2 O 4 ) 3 、Na 2 B 12 F b H 12-b (b is an integer from 0 to 3), etc.

[0312] Among them, NaPF is particularly preferred from the viewpoint of improving output characteristics, high rate charge and discharge characteristics, high temperature storage characteristics, cycle characteristics, etc. 6 , NaBF 4 、NaSbF 6 、NaTaF 6 、NaPO 2 F 2 、FSO 3 Na, CF 3 SO 3 Na、NaN(FSO 2 ) 2 、NaN(FSO 2 )(CF 3 SO 2 )、NaN(CF 3 SO 2 ) 2 、NaN(C 2 F 5 SO 2 ) 2 、Sodium cyclic 1,2-perfluoroethane disulfonyl imide、Sodium cyclic 1,3-perfluoropropane disulfonyl imide、NaC(FSO 2 ) 3 、NaC(CF 3 SO 2 ) 3 、NaC(C2 F 5 SO 2 ) 3 , NaBF 3 CF 3 , NaBF 3 C 2 F 5 、NaPF 3 (CF 3 ) 3 、NaPF 3 (C 2 F 5 ) 3 etc., most preferably selected from NaPF 6 、NaN(FSO 2 ) 2 and NaBF 4 At least one lithium salt in the group consisting of.

[0313] The concentration of the electrolyte salt needs to be 0.8 mol / L or more, and further needs to be 1.0 mol / L or more. The upper limit also depends on the organic solvent for dissolving the electrolyte salt, but is usually 1.5 mol / L.

[0314] <Diaphragm>

[0315] The secondary battery of the present disclosure preferably further includes a separator.

[0316] The material and shape of the separator are not particularly limited as long as the electrolyte is stable and has excellent liquid retention, and a known separator can be used. Among them, it is preferred to use a porous sheet or non-woven fabric-like material formed of a material stable to the electrolyte disclosed in the present invention, using resin, glass fiber, inorganic material, etc., and having excellent liquid retention.

[0317] As materials for resin and glass fiber separators, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, glass filters, etc. can be used. Polypropylene / polyethylene two-layer membrane, polypropylene / polyethylene / polypropylene three-layer membrane, etc. These materials can be used alone or in any combination and ratio. Among them, from the perspective of good permeability of the electrolyte and good shutdown effect, the separator is preferably a porous sheet or non-woven fabric made of polyolefins such as polyethylene and polypropylene.

[0318] The thickness of the separator is arbitrary, usually 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the separator is too thin compared to the range, the insulation and mechanical strength are sometimes reduced. In addition, if it is too thick compared to the range, the battery performance such as rate characteristics is sometimes reduced, and the energy density of the electrolyte battery as a whole is sometimes reduced.

[0319] In addition, when a porous material such as a porous sheet or nonwoven fabric is used as a separator, the porosity of the separator is arbitrary, usually 20% or more, preferably 35% or more, more preferably 45% or more, and usually 90% or less, preferably 85% or less, more preferably 75% or less. If the porosity is too small compared to the range, there is a tendency for the membrane resistance to increase and the rate characteristics to deteriorate. In addition, if it is too large compared to the range, there is a tendency for the mechanical strength of the separator to decrease and the insulation to decrease.

[0320] In addition, the average pore size of the diaphragm is also arbitrary, usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. If the average pore size exceeds the above range, short circuit is likely to occur. In addition, if it is less than the above range, the membrane resistance may increase and the rate characteristics may decrease.

[0321] On the other hand, as inorganic materials, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used, and materials in the form of particles or fibers are used.

[0322] As the form, a material in the form of a thin film such as a nonwoven fabric, a woven fabric, a microporous film, etc. is used. In the case of a thin film, it is preferred to use a film with a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent thin film shape, a diaphragm can also be used in which a composite porous layer containing particles of the inorganic substance is formed on the surface of the positive electrode and / or the negative electrode using a resin binder. For example, a porous layer can be formed on both sides of the positive electrode using a fluororesin as a binder and alumina particles with a particle size of 90% less than 1 μm.

[0323] <Battery Design>

[0324] The electrode group may be any one of a laminated structure in which the separator is interposed between the positive electrode plate and the negative electrode plate, and an electrode group in which the positive electrode plate and the negative electrode plate are wound in a spiral shape with the separator interposed therebetween. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy ratio) is usually 40% or more, preferably 50% or more, and usually 90% or less, preferably 80% or less.

[0325] If the electrode group occupancy is less than the above range, the battery capacity becomes smaller. If it exceeds the above range, the void space is small, the battery temperature rises, the components expand, the vapor pressure of the liquid component of the electrolyte increases, and the internal pressure rises, which reduces the various characteristics of the battery such as the charge and discharge repetition performance and high temperature storage, and the gas release valve that releases the internal pressure to the outside may sometimes work.

[0326] The current collecting structure is not particularly limited. In order to more effectively improve the charge-discharge characteristics of the high current density caused by the electrolyte disclosed in the present invention, it is preferred to adopt a structure that reduces the resistance of the wiring part or the joint part. In the case of reducing the internal resistance in this way, the effect of using the electrolyte disclosed in the present invention can be particularly well exerted.

[0327] When the electrode group has the stacked structure, it is preferred to use a structure in which the metal core portions of each electrode layer are bundled and welded to the terminal. When the area of ​​a single electrode increases, the internal resistance increases, so it is also preferred to provide multiple terminals in the electrode to reduce the resistance. When the electrode group has the wound structure, multiple lead structures can be provided in the positive electrode and the negative electrode, respectively, and bundled on the terminal, thereby reducing the internal resistance.

[0328] The material of the housing is not particularly limited as long as it is a material that is stable to the electrolyte used. Specifically, metals such as nickel-plated steel, stainless steel, aluminum or aluminum alloy, magnesium alloy, or a laminated film (laminated film) of resin and aluminum foil are used. From the perspective of lightweight, it is preferred to use a metal such as aluminum or an aluminum alloy, or a laminated film.

[0329] In the case of using metal, there can be cited a case in which metals are welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed package structure; or a case in which the metal is used to form a riveted structure through a resin gasket. In the case of using the laminated film, there can be cited a case in which a sealed package structure is formed by thermally bonding resin layers to each other. In order to improve the sealing performance, a resin different from the resin used in the laminated film can also be sandwiched between the resin layers. In particular, in the case of forming a sealed structure by thermally bonding the resin layers through the collector terminal, since the metal is bonded to the resin, it is preferred to use a resin having a polar group or a modified resin into which a polar group is introduced as the sandwiched resin.

[0330] The sodium ion secondary battery of the present disclosure may be in any shape, such as cylindrical, square, laminated, button, large, etc. The shape and structure of the positive electrode, negative electrode, and separator may be changed according to the shape of each battery.

[0331] Example

[0332] Next, the present disclosure will be described with reference to examples, but the present disclosure is not limited to the examples.

[0333] In the following examples, "parts" and "%" mean "parts by mass" and "mass %" respectively, unless otherwise specified.

[0334] The (co)polymers used in Examples and Comparative Examples are shown in Table 1 below.

[0335] [Table 1]

[0336] (Co)polymer composition Composition ratio (molar ratio) Molecular weight 1 VdF / HFP 95 / 5 1 million 2 VdF / CTFE 97.6 / 2.4 800,000 3 VdF / 2,3,3,3-Tetrafluoropropylene 77 / 23 480,000 4 VdF / TrFE / CTFE 65 / 28 / 7 650,000 5 VdF / TrFE 80 / 20 720,000 6 VdF / AEHF-1 81.4 / 18.6 950,000 7 VdF 100 900,000 8 VdF 100 1.8 million 9 VdF / Acrylic 99 / 1 1 million

[0337] In addition, the composition and molecular weight of each polymer were measured by the following method.

[0338] (Polymer composition)

[0339] The composition of the polymer was measured by solution NMR.

[0340] Measurement device: Varian VNMRS400

[0341] Resonance frequency: 376.04 (Sfrq)

[0342] Pulse width: 30° (pw=6.8)

[0343] (Content of the Polar Group-Containing Monomer Unit in the Polymer)

[0344] The content of the monomer unit (acrylic acid unit) containing a polar group is determined by acid-base titration of the carboxyl group. Specifically, about 0.5 g of the copolymer is dissolved in acetone at a temperature of 70°C to 80°C. In order to avoid coagulation of the copolymer, 5 ml of water is added dropwise under vigorous stirring. With a neutral transfer at about -270 mV, titration is performed using an aqueous NaOH solution with a concentration of 0.1 N until the acidity is completely neutralized. The amount of the monomer unit containing a polar group contained in 1 g of the copolymer is obtained from the measurement results, and the content of the monomer unit containing a polar group is calculated.

[0345] (Weight average molecular weight)

[0346] The measurement was performed by gel permeation chromatography (GPC). AS-8010 and CO-8020 manufactured by Tosoh Corporation and columns (three GMHHR-H connected in series) and RID-10A manufactured by Shimadzu Corporation were used, dimethylformamide (DMF) as a solvent was allowed to flow at a flow rate of 1.0 ml / min, and the weight average molecular weight was calculated from the measured data (reference: polystyrene).

[0347] Examples 1 to 12, Comparative Examples 1 and 2

[0348] (Preparation of positive electrode mixture)

[0349] NaFeO 2 (manufactured by Kojundo Chemical Laboratory Co., Ltd.), a binder, and carbon black (manufactured by SUPER-P Li Imerys) were weighed so as to have a mass ratio of 97.00:1.50:1.50.

[0350] In addition, the polymer shown in Table 2 was used as a binder.

[0351] The binder was dissolved in N-methyl-2-pyrrolidone (NMP) to a concentration of 8 mass %, and a predetermined amount of NaFeO was added to the obtained NMP solution. 2 and carbon black, stirred at 100 rpm for 60 minutes using a stirrer (TKHIVIS MIX manufactured by PRIMIX), and then stirred at 100 rpm for 30 minutes while performing vacuum degassing. The stirred slurry was filtered using a Ni mesh (200 mesh) to make the particle size of the solid component uniform, thereby obtaining a positive electrode mixture.

[0352] (Fabrication of Positive Electrode Having Positive Electrode Material Layer)

[0353] The obtained positive electrode mixture was applied in an amount of 22.5 mg / cm 2 The NMP was uniformly applied on one side of a positive electrode collector (aluminum foil with a thickness of 20 μm) in a manner, and after NMP was completely volatilized, it was pressed using a roller press with a pressure of 10 t, thereby producing a positive electrode having a positive electrode material layer and a positive electrode collector.

[0354] (Preparation of Electrolyte)

[0355] NaPF 6 It was dissolved in an electrolyte solution (ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3 / 7) at a concentration of 1 mol / L.

[0356] (Production of negative electrode)

[0357] Styrene-butadiene rubber and carboxymethyl cellulose dispersed in distilled water were added to hard carbon in an amount of 1.2 mass % in terms of solid content, mixed using a disperser to form a slurry, and evenly coated on a negative electrode collector (copper foil with a thickness of 10 μm), dried to form a negative electrode mixture layer, and then compression-molded using a roller press to produce a negative electrode.

[0358] (Manufacturing of sodium ion secondary batteries)

[0359] The strip-shaped positive electrode was cut into 40mm×72mm (with a 10mm×10mm positive terminal), and the strip-shaped negative electrode was cut into 43mm×75mm (with a 10mm×10mm negative terminal), and a lead body was welded to each terminal. In addition, a microporous polyethylene film with a thickness of 20μm was cut into a size of 78mm×46mm as a separator, and the positive electrode and the negative electrode were set in a manner of sandwiching the separator, and they were placed in an aluminum laminate packaging material. Next, 2ml of electrolyte was added to each packaging material and sealed to make a laminated battery.

[0360] Table 2 shows the evaluation results.

[0361] [Determination of electrode moisture content]

[0362] In the produced electrode, the electrode moisture content (ppm) was measured by calculating the content of physically adsorbed water at 150° C. in the mixture layer of the electrode (positive electrode) after the heat drying step by the Karl Fischer method.

[0363] [Measurement of interface resistance]

[0364] The interface resistance (Ωcm) of the positive electrode was measured using an electrode resistance measurement system (HIOKI RM2610) at 25°C. 2 ).

[0365] [Determination of initial impedance]

[0366] The laminated battery produced as described above was subjected to three charge and discharge cycles at a temperature of 25°C, wherein the battery was charged at a constant current (0.2C) and a constant voltage (4.1V) and discharged at 0.2C until the discharge termination voltage reached 3.2V. Then, the voltage drop (voltage drop value 15 seconds after the start of discharge) during discharge at 0.5C, 1C, 2C, and 5C at a charging rate (SOC) of 100% was measured, and the initial impedance (Ω) was calculated from each current value and each voltage drop value.

[0367] [Determination of initial discharge capacity]

[0368] The battery was charged at 25°C at a constant current-constant voltage (0.1C cut-off) to 4.1V at a current equivalent to 0.2C, and then discharged at a constant current of 0.2C to 3.2V, which was considered as one cycle, and three cycles were performed. The discharge capacity of the third cycle was taken as the initial discharge capacity (mAh / g).

[0369] [Determination of cycle retention rate]

[0370] The above cycle was repeated for 300 cycles, and the discharge capacity was measured. The ratio of the discharge capacity after 300 cycles to the initial discharge capacity was calculated and defined as the cycle retention rate (%).

[0371]

[0372] The results in Table 2 show that the sodium ion secondary battery using the binder of the present disclosure has low interface resistance and initial internal resistance.

[0373] Industrial Applicability

[0374] The binder disclosed herein is suitable for sodium ion batteries and can be used as various power sources such as portable power sources and automotive power sources.

Claims

1. A positive electrode binder for a sodium ion battery, comprising a copolymer having a vinylidene fluoride unit (A) and a structural unit (B) derived from at least one monomer selected from the group consisting of trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, a monomer represented by the general formula (1), a monomer represented by the general formula (2) and a monomer represented by the general formula (3), and having no tetrafluoroethylene unit, [Chemistry 1] In the formula, Rf 1 A linear or branched fluorinated alkyl group or a fluorinated alkoxy group having 1 to 12 carbon atoms, wherein the fluorinated alkyl group and the fluorinated alkoxy group may contain an oxygen atom (-O-) between carbon atoms when the carbon atoms are 2 or more; [Chemistry 2] In the formula, Rf 2 A linear or branched fluorinated alkyl group or a fluorinated alkoxy group having 1 to 12 carbon atoms, wherein the fluorinated alkyl group and the fluorinated alkoxy group may contain an oxygen atom (-O-) between carbon atoms when the carbon atoms are 2 or more; [Chemistry 3] In the formula, R 1 , R 2 and R 3 Each is independently a hydrogen atom, a chlorine atom or an alkyl group having 1 to 5 carbon atoms; X is an atomic group having a molecular weight of 500 or less and having a single bond or a main chain composed of 1 to 20 atoms; and Y represents an inorganic cation and / or an organic cation.

2. The positive electrode binder for a sodium ion battery according to claim 1, in, The content of the vinylidene fluoride unit (A) is 60 mol% to 99.5 mol% based on all monomer units in the copolymer.

3. The positive electrode binder for a sodium ion battery according to claim 1 or 2, in, The structural unit (B) is a structural unit derived from at least one monomer selected from the group consisting of trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, 2,3,3,3-tetrafluoropropylene, perfluoro-(2,9,9-trihalo-5-trifluoromethyl-3,6-dioxa-8-heptene) and acrylic acid.

4. The positive electrode binder for a sodium ion battery according to claim 3, in, The structural unit (B) is a structural unit derived from 2,3,3,3-tetrafluoropropylene. 5 . The positive electrode binder for a sodium ion battery according to claim 1 , comprising two or more of the copolymers. 6 . The positive electrode binder for a sodium ion battery according to claim 1 , further comprising a fluorine-containing polymer other than the copolymer.

7. The positive electrode binder for a sodium ion battery according to claim 6, in, The fluorine-containing polymer is polyvinylidene fluoride or modified polyvinylidene fluoride.

8. An electrode mixture, in, The electrode active material contains a sodium composite oxide, and the electrode mixture contains the positive electrode binder for a sodium ion battery according to any one of claims 1 to 7. 9 . An electrode comprising a current collector and an electrode material layer formed of the electrode mixture according to claim 8 and provided on one or both surfaces of the current collector. 10 . A sodium ion secondary battery comprising the electrode according to claim 9 .

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