Secondary batteries

Abstract

In a battery according to the present invention that uses a negative electrode comprising a metal, battery life is improved by reducing the amount of gas produced, reducing resistance, and reducing the amount of precipitation, into the negative electrode, of metal elements such as Mn and Ni in the positive electrode, etc. This secondary battery includes a liquid electrolyte and a negative electrode in which a fluoropolymer is laminated onto a layer including a metal, the secondary battery being characterized in that the metal is at least one selected from lithium, sodium, magnesium, and zinc, the fluoropolymer is 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 tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, monomers represented by general formula (1), monomers represented by general formula (2), and monomers represented by general formula (3), and the liquid electrolyte contains a fluorinated ether.

Description

[Technical Field]

[0001] The present disclosure relates to secondary batteries. [Background technology]

[0002] In recent years, with the aim of further increasing the energy density of alkali metal secondary batteries, such as lithium secondary batteries, research and development has been progressing on alkali metal secondary batteries that use alkali metals with high theoretical capacities in the negative electrode.

[0003] However, secondary batteries using alkali metals have the problem that repeated charge and discharge shortens the battery life, and there is also the problem that the transition metals in the positive electrode active material dissolve and accumulate on the negative electrode, thereby reducing the battery life.

[0004] Patent Document 1 discloses an electrode in which the surface of lithium metal is coated with a polyvinylidene fluoride polymer.

[0005] Patent Document 2 discloses a protective film-forming composition containing vinylidene fluoride-hexafluoropropylene copolymer, and describes that such a protective film-forming composition is coated on a lithium metal foil film layer to form a protective film.

[0006] Patent Document 3 discloses the use of an electrolyte solution containing a fluorinated ether compound in a battery that uses lithium metal as an electrode.

[0007] Patent Document 4 discloses that the electrodes are coated with a resin.

[0008] Patent Document 5 discloses an electrode in which the surface of lithium metal is coated with a polyvinylidene fluoride polymer.

[0009] Patent Documents 6 and 7 disclose the production of an electrode using a binder composition containing a polyvinylidene fluoride polymer and an electrode active material. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2017 / 140649 [Patent Document 2] Special Table 2019-515481 [Patent Document 3] International Publication No. 2020 / 246579 [Patent Document 4] International Publication No. 2014 / 132579 [Patent Document 5] International Publication No. 2021 / 123151 [Patent Document 6] International Publication No. 2018 / 092676 [Patent Document 7] International Publication No. 2021 / 015229 Summary of the Invention [Problem to be solved by the invention]

[0011] The present disclosure aims to improve the battery life by reducing the amount of gas generated, reducing resistance, and reducing the amount of metal elements in the positive electrode, such as Mn and Ni, that are deposited on the negative electrode in a battery that uses a negative electrode made of metal. [Means for solving the problem]

[0012] The present disclosure provides: A secondary battery having a negative electrode in which a fluoropolymer is laminated on a layer containing a metal, and having a liquid electrolyte, the metal is at least one selected from lithium, sodium, magnesium, and zinc; The fluoropolymer comprises vinylidene fluoride units (A) and A copolymer having a structural unit (B) derived from at least one monomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, a monomer represented by general formula (1), a monomer represented by general formula (2), and a monomer represented by general formula (3), The secondary battery is characterized in that the liquid electrolyte contains a fluorinated ether.

[0013] [ka]

[0014] In the formula, Rf 1 is a linear or branched fluoroalkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and both the fluorinated alkyl group and the fluorinated alkoxy group, when they have 2 or more carbon atoms, can contain an oxygen atom (—O—) between carbon atoms.

[0015] [ka]

[0016] Rf 2 is a linear or branched fluoroalkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and both the fluorinated alkyl group and the fluorinated alkoxy group, when they have 2 or more carbon atoms, can contain an oxygen atom (—O—) between carbon atoms.

[0017] [ka]

[0018] In the formula, R 1 , R 2 and R 3 are each independently a hydrogen atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. X is a single bond or an atomic group whose main chain is composed of 1 to 20 atoms and has a molecular weight of 500 or less. Y represents an inorganic cation and / or an organic cation.

[0019] The copolymer preferably has a vinylidene fluoride content of 30 to 99.5 mol % based on the total monomer units.

[0020] The fluorinated ether is preferably a compound represented by the following general formula (5).

[0021] [ka] (R is an alkyl group which may contain an ether group, or a fluorinated alkyl group which may contain an ether group.)

[0022] The compound represented by the above general formula (5) is preferably at least one compound selected from the group consisting of compounds represented by the following general formulas:

[0023] [ka]

[0024] The present disclosure provides a secondary battery having a negative electrode including a laminate in which a fluoropolymer is laminated directly on a current collector, The fluoropolymer comprises vinylidene fluoride units (A) and A copolymer having a structural unit (B) derived from at least one monomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, a monomer represented by general formula (1), a monomer represented by general formula (2), and a monomer represented by general formula (3), The liquid electrolyte is also a secondary battery characterized by containing a fluorinated ether.

[0025] [ka]

[0026] In the formula, Rf 1is a linear or branched fluoroalkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and both the fluorinated alkyl group and the fluorinated alkoxy group, when they have 2 or more carbon atoms, can contain an oxygen atom (—O—) between carbon atoms.

[0027] [ka]

[0028] Rf 2 is a linear or branched fluoroalkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and both the fluorinated alkyl group and the fluorinated alkoxy group, when they have 2 or more carbon atoms, can contain an oxygen atom (—O—) between carbon atoms.

[0029] [ka]

[0030] In the formula, R 1 , R 2 and R 3 are each independently a hydrogen atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. X is a single bond or an atomic group whose main chain is composed of 1 to 20 atoms and has a molecular weight of 500 or less. Y represents an inorganic cation and / or an organic cation.

[0031] The copolymer preferably has a vinylidene fluoride content of 30 to 99.5 mol % based on the total monomer units.

[0032] The fluorinated ether is preferably a compound represented by the following general formula (5).

[0033] [ka] (R is an alkyl group which may contain an ether group, or a fluorinated alkyl group which may contain an ether group.)

[0034] The compound represented by the above general formula (5) is preferably at least one compound selected from the group consisting of compounds represented by the following general formulas:

[0035] [ka] [Effects of the Invention]

[0036] The present disclosure can provide effects such as suppressing the degradation of the positive electrode by reducing the elution of transition metals in the positive electrode active material, reducing the amount of gas generation, reducing resistance, and reducing the amount of metal elements in the positive electrode, such as Mn and Ni, that are precipitated in the negative electrode, thereby improving the battery life. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present disclosure will be described in detail below. The present disclosure provides a secondary battery having a negative electrode with a coating layer formed of a fluorine-containing polymer having a specific composition, and using a liquid electrolyte containing a fluorinated ether. By forming such a coating layer and further using a specific liquid electrolyte, the above-mentioned problems can be particularly effectively improved compared to the secondary batteries described in the above-mentioned patent documents.

[0038] The negative electrode used in the secondary battery of the present disclosure has a fluoropolymer coating layer as described in detail below. Here, the negative electrode may be one in which a fluoropolymer coating is formed directly on a negative electrode material mainly composed of a metal such as lithium metal (first embodiment), or one in which a fluoropolymer coating layer is formed on a current collector (second embodiment).

[0039] The electrode having a structure in which a coating layer made of a fluoropolymer is formed on the current collector described as the second embodiment above can also achieve the above-mentioned effects. In the second embodiment, the negative electrode is formed by directly forming a fluoropolymer coating layer on a current collector without providing a layer of metallic negative electrode material on the current collector. In this case, when such a negative electrode is laminated with other layers constituting a battery, such as a positive electrode, and then charged, an electrode reaction during charging results in the formation of a metal layer, such as lithium metal, on the current collector. This metal layer is formed between the current collector and the fluoropolymer layer. In other words, charging results in a negative electrode in which a fluoropolymer coating is formed directly on a layer of metal, such as lithium metal, which is similar to the negative electrode of the first embodiment described above. Therefore, the effects of the present disclosure are preferably exhibited.

[0040] In the negative electrode of the secondary battery of the present disclosure, the use of a fluorine-containing polymer containing the above-mentioned vinylidene fluoride unit (A) and the structural unit (B) provides a particularly favorable effect, which is presumably due to the action of enabling uniform metal deposition and suppressing the generation of dendrites due to the interaction between a specific fluorine-containing polymer layer and lithium ions.

[0041] References 6 and 7 disclose the use of similar polymers in the battery field. These are clearly different from the present disclosure in that they do not have a negative electrode in which a fluoropolymer is laminated onto a metal layer. The polymers used in the present disclosure will be described in detail below, followed by a detailed description of the negative electrode and the battery.

[0042] In the present disclosure, the negative electrode is a laminate of a fluoropolymer, which will be described in detail below. By having such a coating, the above-mentioned effects can be obtained. In the following description, a fluoropolymer containing tetrafluoroethylene, trifluoroethylene, or chlorotrifluoroethylene as the constituent unit (B) will be referred to as fluoropolymer 1. Furthermore, a fluoropolymer having as its constituent unit (B) a monomer represented by general formula (1) or a monomer represented by general formula (2) will be referred to as fluoropolymer 2 below, and a fluoropolymer having as its constituent unit (B) a monomer represented by general formula (3) will be referred to as fluoropolymer 3 below. It should be noted that the following description does not exclude the use of fluoropolymers that fall under two or more of fluoropolymers 1, 2, and 3. That is, there is no problem with using a combination of any two or more monomers selected from the group consisting of tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, a monomer represented by general formula (1), a monomer represented by general formula (2), and a monomer represented by general formula (3).

[0043] As will be described in detail below, the preferred range of copolymerization ratio varies depending on the copolymerization components used, but overall, the content of vinylidene fluoride is preferably 30 to 99.5 mol% based on the monomer units.

[0044] (Fluoropolymer 1) The fluoropolymer 1 has a structural unit based on at least one monomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, and chlorotrifluoroethylene.

[0045] The content of VdF units in fluoropolymer 1 is preferably 57.0 mol% or more, more preferably 60.0 mol% or more, and even more preferably 63.0 mol% or more, based on the total monomer units. It is preferably 95.0 mol% or less, more preferably 90.0 mol% or less, and most preferably 85.0 mol% or less.

[0046] The content of at least one monomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, and chlorotrifluoroethylene in the fluoropolymer 1 is preferably 5.0 mol% or more, more preferably 8.0 mol% or more, particularly preferably 10.0 mol% or more, and most preferably 15 mol% or more, and is preferably 43.0 mol% or less, more preferably 40.0 mol% or less, even more preferably 38.0 mol% or less, and particularly preferably 37.0 mol% or less, based on all monomer units.

[0047] Among these, preferred fluoropolymer 1 is one consisting only of VdF units, TFE units, and any non-fluorinated monomer units, with the molar ratio of VdF units to TFE units (VdF units / TFE units) being 57 / 43 to 90 / 10. That is, it is preferred that fluoropolymer 1 is a binary copolymer consisting only of VdF units and TFE units, or a ternary or higher copolymer consisting only of VdF units, TFE units, and non-fluorinated monomer units, and does not contain fluorinated monomer units other than VdF units and TFE units.

[0048] When the fluoropolymer 1 contains VdF units and TFE units, the molar ratio of VdF units to TFE units (VdF units / TFE units) is preferably 57 / 43 to 90 / 10, more preferably 60 / 40 to 89 / 11, even more preferably 63 / 37 to 88 / 12, and particularly preferably 63 / 37 to 85 / 15.

[0049] The weight average molecular weight (polystyrene equivalent) of fluoropolymer 1 is preferably 161,000 to 2,760,000, more preferably 322,000 to 2,530,000, and even more preferably 600,000 to 2,000,000. The weight average molecular weight can be measured by gel permeation chromatography (GPC) at 50°C using dimethylformamide as a solvent.

[0050] The number average molecular weight (polystyrene equivalent) of the fluoropolymer 1 is preferably 70,000 to 1,200,000, and more preferably 140,000 to 1,100,000. The number average molecular weight can be measured by gel permeation chromatography (GPC) at 50°C using dimethylformamide as a solvent.

[0051] The melting point of fluoropolymer 1 is preferably 100 to 170° C., more preferably 110 to 165° C., and even more preferably 120 to 163° C. The melting point is determined using a differential scanning calorimetry (DSC) device as the temperature corresponding to the maximum value on the heat of fusion curve obtained by increasing the temperature from 30° C. to 220° C. at a rate of 10° C. / min, then decreasing the temperature to 30° C. at 10° C. / min, and again increasing the temperature to 220° C. at a rate of 10° C. / min.

[0052] (Fluoropolymer 2) Fluorine polymer 2 is a fluoropolymer having at least one copolymerization unit selected from the group consisting of a monomer unit having a structure represented by the following general formula (1) and at least one monomer unit selected from the group consisting of a structure represented by the following general formula (2):

[0053] [ka] In the formula, Rf1 is a linear or branched fluoroalkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and when the fluorinated alkyl group or fluorinated alkoxy group has 2 or more carbon atoms, it can contain an oxygen atom (—O—) between carbon atoms. [ka] Rf2 is a linear or branched fluoroalkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and when the fluorinated alkyl group or fluorinated alkoxy group has 2 or more carbon atoms, it can contain an oxygen atom (—O—) between carbon atoms.

[0054] A fluoropolymer containing at least one copolymer unit selected from the group consisting of a monomer unit having a structure represented by the general formula (1) above and a monomer unit having a structure represented by the general formula (2) above is advantageous in that it is easy to obtain uniformity during coating.

[0055] The fluorine-containing monomer represented by the general formula (1) is Rf 1 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 each have two or more carbon atoms, they can contain an oxygen atom (—O—) between carbon atoms.

[0056] Rf 1 The fluorinated alkyl group of Rf may be a partially fluorinated alkyl group in which some of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms, or may be a perfluorinated alkyl group in which all of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms. 1 In the fluorinated alkyl group, a hydrogen atom may be substituted with a substituent other than a fluorine atom, but it is preferred that the fluorinated alkyl group does not contain any substituent other than a fluorine atom.

[0057] Also, Rf 1 The fluorinated alkoxy group of Rf may be a partially fluorinated alkoxy group in which some of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms, or may be a perfluorinated alkoxy group in which all of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms. 1 In the fluorinated alkoxy group of formula (I), a hydrogen atom may be substituted with a substituent other than a fluorine atom, but it is preferred that the fluorinated alkoxy group does not contain any substituent other than a fluorine atom.

[0058] Rf 1 The number of carbon atoms is preferably 1 to 10, more preferably 1 to 6, further preferably 1 to 4, and particularly preferably 1.

[0059] Rf1 As the general formula: -(Rf 11 ) m -(O) p -(Rf 12 -O) n -Rf 13 (In the formula, Rf 11 and Rf 12 are independently a linear or branched fluorinated alkylene group having 1 to 4 carbon atoms, Rf 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).

[0060] Rf 11 and Rf 12 The fluorinated alkylene group of Rf may be a partially fluorinated alkylene group in which some of the hydrogen atoms bonded to the carbon atoms are substituted with fluorine atoms, or may be a perfluorinated alkylene group in which all of the hydrogen atoms bonded to the carbon atoms are substituted with fluorine atoms. 11 and Rf 12 The fluorinated alkylene group Rf may have a hydrogen atom substituted with a substituent other than a fluorine atom, but preferably does not contain any substituent other than a fluorine atom. 11 and Rf 12 may be the same or different in each occurrence.

[0061] Rf 11Examples of the fluorinated alkylene group include -CHF-, -CF2-, -CH2-CF2-, -CHF-CF2-, -CF2-CF2-, -CF(CF3)-, -CH2-CF2-CF2-, -CHF-CF2-CF2-, -CF2-CF2-CF2-, -CF(CF3)-CF2-, -CF2-CF(CF3)-, -C(CF3)2-, -CH2-CF2-CF2-CF2-, -CHF-CF2-CF2-CF2-, -CF2-CF2-CF2-CF2-, -CH(CF3)-CF2-CF2-, -CF(CF3)-CF2-CF2-, -C(CF3)2-CF2- and the like. Among these, perfluorinated alkylene groups having 1 or 2 carbon atoms are preferred, and -CF2- is more preferred.

[0062] Rf 12 Fluorinated alkylene groups include -CHF-, -CF2-, -CH2-CF2-, -CHF-CF2-, -CF2-CF2-, -CF(CF3)-, -CH2-CF2-CF2-, -CHF-CF2-CF2-, -CF2-CF2-CF2-, -CF(CF3)-CF2-, -CF2-CF(CF3)-, -C(CF3)2-, -CH2-CF2-CF2-CF2-, -CHF-CF2-C Examples include F2-CF2-, -CF2-CF2-CF2-CF2-, -CH(CF3)-CF2-CF2-, -CF(CF3)-CF2-CF2-, -C(CF3)2-CF2-, and among these, perfluorinated alkylene groups having 1 to 3 carbon atoms are preferred, with -CF2-, -CF2CF2-, -CF2-CF2-CF2-, -CF(CF3)-CF2- or CF2-CF(CF3)- being more preferred.

[0063] Rf 13 The fluorinated alkyl group of Rf may be a partially fluorinated alkyl group in which some of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms, or a perfluorinated alkyl group in which all of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms. 13 The fluorinated alkyl group may have a hydrogen atom substituted with a substituent other than a fluorine atom, but preferably does not contain any substituent other than a fluorine atom (for example, -CN, -CH2I, -CH2Br, etc.).

[0064] Rf 13 Examples of the fluorinated alkyl group include -CH2F, -CHF2, -CF3, -CH2-CH2F, -CH2-CHF2, -CH2-CF3, -CHF-CH2F, -CHF-CHF2, -CHF-CF3, -CF2-CH2F, -CF2-CHF2, -CF2-CF3, -CH2-CF2-CH2F, -CHF-CF2-CH2F, -CF2-CF2-CH2F, -CF(CF3)-CH2F, -CH2-CF2-CHF2, -CHF-CF2-CHF2, -CF2-CF2-CHF2, -CF(CF3)-CHF2, -CH2-CF2-CF3, -CHF-CF2-C F3, -CF2-CF2-CF3, -CF(CF3)-CF3, -CH2-CF2-CF2-CF3, -CHF-CF2-CF2-CF2-CF3, -CF2-CF2-CF2-CF3, -CH(CF3)-CF2-CF3, -CF(CF3)-CF2-CF3, -C(CF3)2-CF3 and the like, and among these, -CF3, -CHF-CF3, -CF2-CHF2, -CF2-CF3, -CF2-CF2-CF3, -CF(CF3)-CF3, -CF2-CF2-CF2-CF3, -CH(CF3)-CF2-CF3 or CF(CF3)-CF2-CF3 are preferred.

[0065] As p, 0 is preferred.

[0066] m is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0. When p is 0, it is preferable that m is 0 as well.

[0067] n is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0.

[0068] The repeating unit is: -CH2-CF[-CF3]-, -CH2-CF[-CF2CF3]-, -CH2-CF[-CF2CF2CF3]-, -CH2-CF[-CF2CF2CF2CF3]-, -CH2-CF[-CF2-O-CF(CF3)-CF2-O-CHF-CF3]-, -CH2-CF[-CF2-O-CF(CF3)-CF2-O-CF2-CF3]-, -CH2-CF[-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF3]-, -CH2-CF[-CF2-O-CF(CF3)-CF2-O-CH(CF3)-CF2-CF3]-, -CH2-CF[-CF2-O-CF(CF3)-CF2-O-CF(CF3)-CF2-CF3]-, -CH2-CF[-OCF2OCF3]-, -CH2-CF[-OCF2CF2CF22OCF3]-, -CH2-CF[-CF2OCFOCF3]-, -CH2-CF[-CF2OCF2CF2CF2OCF3]-, or -CH2-CF[-O-CF2-CF3]- is preferred, -CH2-CF[-CF3]- is more preferred.

[0069] The fluorine-containing monomer (2) represented by the above formula (2) is Rf 2 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 each have two or more carbon atoms, they can contain an oxygen atom (—O—) between carbon atoms.

[0070] Rf 2 The fluorinated alkyl group of Rf may be a partially fluorinated alkyl group in which some of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms, or may be a perfluorinated alkyl group in which all of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms. 2 In the fluorinated alkyl group, a hydrogen atom may be substituted with a substituent other than a fluorine atom, but it is preferred that the fluorinated alkyl group does not contain any substituent other than a fluorine atom.

[0071] Also, Rf 2 The fluorinated alkoxy group of Rf may be a partially fluorinated alkoxy group in which some of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms, or may be a perfluorinated alkoxy group in which all of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms. 2 In the fluorinated alkoxy group of formula (I), a hydrogen atom may be substituted with a substituent other than a fluorine atom, but it is preferred that the fluorinated alkoxy group does not contain any substituent other than a fluorine atom.

[0072] Rf 2 The number of carbon atoms is preferably 1 to 10, more preferably 1 to 6, further preferably 1 to 4, and particularly preferably 1.

[0073] Rf 2 As the general formula: -(Rf 21 ) m -(O) p -(Rf 22 -O) n -Rf 23 (In the formula, Rf 21 and Rf 22 are independently a linear or branched fluorinated alkylene group having 1 to 4 carbon atoms, Rf 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.

[0074] Rf 21 and Rf 22 The fluorinated alkylene group of Rf may be a partially fluorinated alkylene group in which some of the hydrogen atoms bonded to the carbon atoms are substituted with fluorine atoms, or may be a perfluorinated alkylene group in which all of the hydrogen atoms bonded to the carbon atoms are substituted with fluorine atoms. 21 and Rf 22 The fluorinated alkylene group Rf may have a hydrogen atom substituted with a substituent other than a fluorine atom, but preferably does not contain any substituent other than a fluorine atom.21 and Rf 22 may be the same or different in each occurrence.

[0075] Rf 21 Examples of the fluorinated alkylene group include -CHF-, -CF2-, -CH2-CF2-, -CHF-CF2-, -CF2-CF2-, -CF(CF3)-, -CH2-CF2-CF2-, -CHF-CF2-CF2-, -CF2-CF2-CF2-, -CF(CF3)-CF2-, -CF2-CF(CF3)-, -C(CF3)2-, -CH2-CF2-CF2-CF2-, -CHF-CF2-CF2-CF2-, -CF2-CF2-CF2-CF2-, -CH(CF3)-CF2-CF2-, -CF(CF3)-CF2-CF2-, -C(CF3)2-CF2- and the like. Among these, perfluorinated alkylene groups having 1 or 2 carbon atoms are preferred, and -CF2- is more preferred.

[0076] Rf 22 Fluorinated alkylene groups include -CHF-, -CF2-, -CH2-CF2-, -CHF-CF2-, -CF2-CF2-, -CF(CF3)-, -CH2-CF2-CF2-, -CHF-CF2-CF2-, -CF2-CF2-CF2-, -CF(CF3)-CF2-, -CF2-CF(CF3)-, -C(CF3)2-, -CH2-CF2-CF2-CF2-, -CHF-CF2-C Examples include F2-CF2-, -CF2-CF2-CF2-CF2-, -CH(CF3)-CF2-CF2-, -CF(CF3)-CF2-CF2-, -C(CF3)2-CF2-, and among these, perfluorinated alkylene groups having 1 to 3 carbon atoms are preferred, with -CF2-, -CF2CF2-, -CF2-CF2-CF2-, -CF(CF3)-CF2- or CF2-CF(CF3)- being more preferred.

[0077] Rf 23 The fluorinated alkyl group of Rf may be a partially fluorinated alkyl group in which some of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms, or a perfluorinated alkyl group in which all of the hydrogen atoms bonded to the carbon atom are substituted with fluorine atoms.23 The fluorinated alkyl group may have a hydrogen atom substituted with a substituent other than a fluorine atom, but preferably does not contain any substituent other than a fluorine atom (for example, -CN, -CH2I, -CH2Br, etc.).

[0078] Rf 23 Examples of the fluorinated alkyl group include -CH2F, -CHF2, -CF3, -CH2-CH2F, -CH2-CHF2, -CH2-CF3, -CHF-CH2F, -CHF-CHF2, -CHF-CF3, -CF2-CH2F, -CF2-CHF2, -CF2-CF3, -CH2-CF2-CH2F, -CHF-CF2-CH2F, -CF2-CF2-CH2F, -CF(CF3)-CH2F, -CH2-CF2-CHF2, -CHF-CF2-CHF2, -CF2-CF2-CHF2, -CF(CF3)-CHF2, -CH2-CF2-CF3, -CHF-CF2-C F3, -CF2-CF2-CF3, -CF(CF3)-CF3, -CH2-CF2-CF2-CF3, -CHF-CF2-CF2-CF2-CF3, -CF2-CF2-CF2-CF3, -CH(CF3)-CF2-CF3, -CF(CF3)-CF2-CF3, -C(CF3)2-CF3 and the like, and among these, -CF3, -CHF-CF3, -CF2-CHF2, -CF2-CF3, -CF2-CF2-CF3, -CF(CF3)-CF3, -CF2-CF2-CF2-CF3, -CH(CF3)-CF2-CF3 or CF(CF3)-CF2-CF3 are preferred.

[0079] As p, 0 is preferred.

[0080] m is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0. When p is 0, it is preferable that m is 0 as well.

[0081] n is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0.

[0082] The repeating unit is: -CHF-CH[-CF3]-, -CHF-CH[-CF2CF3]-, -CHF-CH[-CFCFCF]-, or -CHF-CH[-CF2CF2CF2CF3]-, is preferred, -CHF-CH[-CF3]- is more preferred.

[0083] The molar ratio of vinylidene fluoride units / copolymer units in the fluoropolymer 2 is preferably 87 / 13 to 20 / 80, and from the viewpoint of solubility, more preferably 85 / 15 to 30 / 70.

[0084] The fluoropolymer 2 may have a structural unit other than vinylidene fluoride units and copolymer units. In this case, the content of the other polymers is preferably 50 mol % or less. The fluoropolymer 2 may consist of only vinylidene fluoride units and copolymer units. The content of the other polymers is more preferably 30 mol % or less, and even more preferably 15 mol % or less.

[0085] The fluoropolymer 2 may be one that uses, as the other monomer, a monomer that provides a crosslinking site. The monomer that provides the crosslinking site is not particularly limited, and examples thereof include a monomer represented by the general formula: CX 12 =CX 1 -Rf 1 CHR 1 X 2 (In the formula, X 1 is a hydrogen atom, a fluorine atom or CH3, Rf 1 represents a fluoroalkylene group, a perfluoroalkylene group, a fluoro(poly)oxyalkylene group or a perfluoro(poly)oxyalkylene group, R 1 is a hydrogen atom or CH3, X 2 is an iodine atom or a bromine atom.) an iodine- or bromine-containing monomer represented by the general formula: CF2=CFO(CF2CF(CF3)O) m(CF2) n -X 3 (wherein m is an integer of 0 to 5, n is an integer of 1 to 3, X 3 is a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, or a bromine atom, CH2=CFCF2O(CF(CF3)CF2O) m (CF(CF3)) n -X 4 (wherein m is an integer of 0 to 5, n is an integer of 1 to 3, X 4 is a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or —CH 2 OH.

[0086] Among these, at least one selected from the group consisting of CF2=CFOCF2CF(CF3)OCF2CF2CN, CF2=CFOCF2CF(CF3)OCF2CF2COOH, CF2=CFOCF2CF2CH2I, CF2=CFOCF2CF(CF3)OCF2CF2CH2I, CH2=CFCF2OCF(CF3)CF2OCF(CF3)CN, CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOH, and CH2=CFCF2OCF(CF3)CF2OCF(CF3)CH2OH is preferred.

[0087] The fluoropolymer 2 is preferably a fluoroelastomer. The fluoroelastomer is an amorphous fluoropolymer having a low glass transition temperature. It may contain repeating units based on a monomer that provides crosslinking sites, but in one embodiment of the present disclosure, it does not contain a crosslinking agent.

[0088] The fluorine-containing elastomer preferably has a glass transition temperature of 25°C or lower. More preferably, the glass transition temperature is 0°C or lower. The glass transition temperature is further preferably -5°C or lower, most preferably -10°C or lower. It can also be -20°C or lower. Here, the glass transition temperature was determined by cooling to -75°C and then raising the temperature of 10 mg of a sample at a rate of 20°C / min using a differential scanning calorimeter (X-DSC823e, manufactured by Hitachi Technoscience Corporation), to obtain a DSC curve, and the glass transition temperature was determined as the temperature at the intersection of an extension of the baseline before and after the second-order transition of the DSC curve and a tangent to the inflection point of the DSC curve.

[0089] The fluorine-containing elastomer is preferably amorphous, which means that there is no melting point peak in the DSC curve. Such amorphous fluorine-containing elastomers with a low Tg are particularly preferred in that they are easily soluble in solvents, and provide the electrodes with flexibility and ease of processing.

[0090] The above-mentioned fluorine-containing elastomer is a copolymer comprising vinylidene fluoride units, the above-mentioned copolymerization units, and, if necessary, other monomers copolymerizable therewith, and it is preferred that the molar ratio of vinylidene fluoride units / copolymerization units is 99.5 / 0.5 to 80 / 20, and the other monomer units account for 0 to 15 mol% of the total monomer units. The fluorine-containing elastomer is preferably a copolymer consisting of only vinylidene fluoride, copolymerized units and other monomers.

[0091] The fluoropolymer 2 used in the present disclosure preferably contains 0.001 to 10 mol % of structural units derived from copolymerization units (where the total of the structural units derived from vinylidene fluoride and the copolymerization units is 100 mol %), more preferably 0.01 to 5 mol %, and particularly preferably 0.01 to 3.0 mol %. Furthermore, the fluoropolymer 2 preferably contains 90 to 99.999 mol %, more preferably 95 to 99.75 mol %, and particularly preferably 96 to 99.63 mol % of structural units derived from vinylidene fluoride. When the copolymerization units are 0.01 mol % or more, the viscosity of the polymer solvent does not become too high, preventing difficulties in applying the polymer solvent.

[0092] The weight average molecular weight (polystyrene equivalent) of the fluoropolymer 2 is preferably 161,000 to 2,760,000, more preferably 322,000 to 2,530,000, and even more preferably 600,000 to 2,000,000. The weight average molecular weight can be measured by gel permeation chromatography (GPC) at 50°C using dimethylformamide as a solvent.

[0093] The number average molecular weight (polystyrene equivalent) of the fluoropolymer 2 is preferably 70,000 to 1,200,000, and more preferably 140,000 to 1,100,000. The number average molecular weight can be measured by gel permeation chromatography (GPC) at 50°C using dimethylformamide as a solvent.

[0094] The glass transition temperature of fluoropolymer 2 is preferably 25°C or lower, more preferably 20°C or lower, even more preferably 15°C or lower, even more preferably 0°C or lower, even more preferably -5°C or lower, and most preferably -10°C or lower. The glass transition temperature of fluoropolymer 2 is preferably -25°C or higher, more preferably -23°C or higher, and even more preferably -20°C or higher. Here, the glass transition temperature is determined by obtaining a DSC curve using a differential scanning calorimeter (X-DSC823e, manufactured by Hitachi Technoscience Corporation) by cooling to -75°C and then raising the temperature of 10 mg of a sample at a rate of 20°C / min, and the glass transition temperature is determined as the temperature at the intersection of an extension of the baseline before and after the second-order transition of the DSC curve and a tangent to the inflection point of the DSC curve.

[0095] The Mooney viscosity at 121°C (ML1+10(121°C)) of fluoropolymer 2 is preferably 2 or more, more preferably 5 or more, even more preferably 10 or more, and particularly preferably 15 or more, and may be 200 or less. The Mooney viscosity at 140°C (ML1+10(121°C)) of the fluoropolymer 2 is preferably 2 or more, more preferably 5 or more, even more preferably 10 or more, and particularly preferably 15 or more, and may be 200 or less. The Mooney viscosity is a value measured in accordance with ASTM-D1646-15 and JIS K6300-1:2013.

[0096] The fluoropolymer 2 has an end structure represented by the following inequality: 0.01≦([-CH2OH]+[-COOH]) / ([-CH3]+[-CF2H]+[-CH2OH]+[-CH2I]+[-OC(O)RH]+[-COOH])≦0.25 (wherein R represents an alkyl group having 1 to 20 carbon atoms.) It is more preferable that 0.03≦([-CH2OH]+[-COOH]) / ([-CH3]+[-CF2H]+[-CH2OH]+[-CH2I]+[-OC(O)RH]+[-COOH]≦0.20. By making the terminal functional group satisfy the above formula, the adhesiveness and flexibility become good, and the product has excellent functions.

[0097] That is, [-CH2OH] and [-COOH] have functional groups with high affinity, such as hydroxyl groups and carboxyl groups, and are therefore preferred in that they have high affinity with the electrolyte solution. Therefore, it is preferable to contain these functional groups in a certain proportion or more in terms of excellent adhesion. On the other hand, if the amount of [-CH2OH] or [-COOH] is excessive, flexibility will decrease. From this perspective, it is preferable that the amount of [-CH2OH] or [-COOH] is within the above-mentioned range.

[0098] Note that satisfying the above general formula does not mean that the fluoropolymer 2 has all of the functional groups [-CH], [-CFH], [-CHOH], [-CHI], [-OC(O)RH], and [-COOH] at its terminals, but rather means that the ratio of the number of these terminal groups present is within the above-mentioned range.

[0099] The amount of each end group present in the resin can be determined by NMR analysis. The NMR end group analysis was performed by the proton solution NMR method. The analytical sample was prepared as a 20 wt% solution using Acetone-d6 as the solvent, and the measurement was performed. The reference peak is the acetone peak top at 2.05 ppm. Measurement equipment: Varian VNMRS400 Resonance frequency: 399.74 (Sfrq) Pulse width: 45° Each end corresponded to the following peak positions: [-CH3]: 1.72 to 1.86 ppm [-CF2H]: 6.1 to 6.8 ppm [-CH2OH]: 3.74~3.80ppm [-CH2I]: 3.87 to 3.92 ppm [-OC(O)RH]: 1.09 to 1.16 ppm [-COOH]: 10-15 ppm The amount of functional groups is calculated from the intensity of each peak based on the integral value of each peak identified by the above-mentioned measurement, and the amount is calculated using the following formula based on the results. ([-CH2OH]+[-COOH]) / ([-CH3]+[-CF2H]+[-CH2OH]+[-CH2I]+[-OC(O)RH]+[-COOH])

[0100] Furthermore, the method for making [—CHOH] and [—COOH] fall within the above-mentioned ranges is not particularly limited, and can be controlled by known methods (for example, the selection and amount of initiator used).

[0101] To ensure good adhesion, flexibility, and solubility in solvents, the fluoropolymer 2 preferably has a number-average molecular weight (Mn) of 7,000 to 5,000,000, a weight-average molecular weight (Mw) of 10,000 to 10,000,000, and an Mw / Mn ratio of 1.0 to 30.0, and more preferably 1.5 to 25.0. The number-average molecular weight (Mn), weight-average molecular weight (Mw), and Mw / Mn are values ​​measured by GPC.

[0102] The fluoropolymer 2 can be produced by a general radical polymerization method. The polymerization method may be any of bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization, but emulsion polymerization is preferred because it is easy to carry out industrially.

[0103] In the polymerization, a polymerization initiator, a chain transfer agent, a surfactant, and a solvent can be used, and conventionally known polymerization initiators can be used. In the polymerization of the copolymer, an oil-soluble radical polymerization initiator or a water-soluble radical initiator can be used as the polymerization initiator.

[0104] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, dialkyl peroxides such as di-t-butyl peroxide, and the like. Also usable are di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluparyl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro Representative examples include di[perfluoro(or fluorochloro)acyl]peroxides such as di(hexafluorobutyryl)peroxide, di(ω-chloro-decafluorohexanoyl)peroxide, di(ω-chloro-tetradecafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundecafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undecachlorodotriacontafluorodocosanoyl)peroxide.

[0105] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium salts, potassium salts, or sodium salts of persulfuric acid, perborate, perchloric acid, perphosphoric acid, or percarbonate, t-butyl permaleate, or t-butyl hydroperoxide. A reducing agent such as sulfites or sulfites may also be contained, and the amount used may be 0.1 to 20 times the amount of the peroxide.

[0106] The amount of radical polymerization initiator to be added is not particularly limited, but may be added all at once, stepwise, or continuously at the beginning of polymerization in an amount (for example, several ppm relative to the water concentration) that does not significantly decrease the polymerization rate. The upper limit is within the range in which the heat of polymerization reaction can be removed from the equipment.

[0107] The solvent is preferably a solvent without chain transfer properties, such as dichloropentafluoropropane (R-225) in the case of solution polymerization, or water, a mixture of water and a water-soluble organic solvent, or a mixture of water and a water-insoluble organic solvent in the case of emulsion polymerization or suspension polymerization.

[0108] In the above polymerization, examples of the chain transfer agent 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.

[0109] A bromine compound or an iodine compound may be used as a chain transfer agent. Polymerization methods using a bromine compound or an iodine compound include, for example, 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). Representative examples of the bromine compound or iodine compound to be used include, for example, compounds represented by the general formula: R 2 I x Br y (wherein x and y are each an integer of 0 to 2 and satisfy 1≦x+y≦2; R2 is a saturated or unsaturated fluorohydrocarbon group or chlorofluorohydrocarbon group having 1 to 16 carbon atoms, or a hydrocarbon group having 1 to 3 carbon atoms, which may contain an oxygen atom) Examples of the compound include compounds represented by the following formula:

[0110] Examples of iodine compounds include 1,3-diiodoperfluoropropane, 2-iodoperfluoropropane, 1,3-diiodo-2-chloroperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoethane, 1,3-diiodo-n-propane, CF2Br2, BrCF2CF2Br, CF3CFBrCF2Br, CFClBr2, and BrCF2CFC. Examples include lBr, CFBrClCFClBr, BrCFCFCFBr, BrCFCFBrOCF, 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 1-bromo-4-iodoperfluorobutane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1, 2-bromo-4-iodoperfluorobutene-1, monoiodomonobromo-substituted benzene, diiodomonobromo-substituted benzene, and (2-iodoethyl) and (2-bromoethyl) substituted benzene. These compounds may be used alone or in combination with each other.

[0111] Among these, it is preferable to use 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, and 2-iodoperfluoropropane in terms of polymerization reactivity, crosslinking reactivity, availability, and the like.

[0112] In the case of emulsion polymerization, the polymer obtained by the above-mentioned method can be obtained in a powder state by coagulating the dispersion after polymerization, washing with water, dehydrating, and drying. Coagulation can be carried out by adding an inorganic salt such as aluminum sulfate or an inorganic acid, by applying mechanical shear force, or by freezing the dispersion. In the case of suspension polymerization, the polymer can be recovered from the dispersion after polymerization and dried to obtain a powder state. In the case of solution polymerization, the polymer can be obtained by drying the solution containing the polymer as it is, or by purifying it by dropping a poor solvent.

[0113] One type or two or more types may be used as the fluoropolymer 2. In particular, two types of copolymers having different molecular structures may be used in combination.

[0114] (Fluoropolymer 3) The fluoropolymer used in the present disclosure may contain a copolymer of vinylidene fluoride and a monomer represented by the above formula (3).

[0115] In the above formula (3), R 1 , R 2 and R 3 are each independently a hydrogen atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. From the viewpoint of the polymerization reaction, R 1 , R 2 is desirably a substituent with little steric hindrance, is preferably hydrogen or an alkyl group having 1 to 3 carbon atoms, and is preferably hydrogen or a methyl group.

[0116] In the above formula (3), X may be a single bond or an atomic group having a main chain composed of 1 to 20 atoms and having a molecular weight of 500 or less, but is preferably 200 or less. When X is an atomic group, there is no particular restriction on the lower limit of the molecular weight, but it is usually 15. This range is preferable in that gelation of the electrode mixture slurry can be suitably suppressed.

[0117] Furthermore, in the above formula (3), X may be a structure represented by the following formula (3-1).

[0118] -COO-X'···(3-1) In the above formula (3-1), X' is an atomic group having a main chain composed of 1 to 18 atoms and a molecular weight of 456 or less, preferably a main chain composed of 1 to 13 atoms, more preferably a main chain composed of 1 to 8 atoms, and the molecular weight is preferably 156 or less. There is no particular restriction on the lower limit of the molecular weight of the atomic group of X', but it is usually 14. This range is preferable from the viewpoint of polymerizability. The number of atoms in the main chain does not include the number of hydrogen atoms. The number of atoms in the main chain is the sum of the carboxyl group written to the right of X in formula (3) and the group (R 1 R 2 C=CR 3 The number of atoms in the skeleton of the chain connecting X and (-) with the fewest number of atoms. X may be branched by including a functional group as a side chain. X may include one or more side chains.

[0119] Y in the above general formula (3) represents an inorganic cation and / or an organic cation. Inorganic cations include cations such as H, Li, Na, K, Mg, Ca, Al, and Fe. Organic cations include NH4, NH3R. 15 , NH2R 15 2. NHR 15 3.NR 15 4(R 15 and independently represent an alkyl group having 1 to 4 carbon atoms.) Examples of cations include those mentioned above. Y is preferably H, Li, Na, K, Mg, Ca, Al, or NH4, more preferably H, Li, Na, K, Mg, Al, or NH4, still more preferably H, Li, Al, or NH4, and particularly preferably H. For convenience, specific examples of inorganic cations and organic cations are shown without the symbols and valence numbers.

[0120] Furthermore, the monomer represented by the formula (3) is preferably a polar group-containing compound. Examples of the polar group-containing compound include compounds containing a carboxyl group, an epoxy group, a hydroxyl group, a sulfonic acid group, etc., and among these, a compound containing a carboxyl group is preferred. It is preferable that the polar group-containing compound represented by the formula (3) contains a carboxyl group in terms of good binding between the electrode active material and the current collector.

[0121] Specific examples of the polar group-containing compound represented by formula (3) include acrylic acid (AA), 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, acryloyloxyethyl succinic acid (AES), acryloyloxypropyl succinic acid (APS), etc., and among these, acrylic acid, 2-carboxyethyl acrylate, acryloyloxyethyl succinic acid, and acryloyloxypropyl succinic acid are preferred. In the present disclosure, one or more polar group-containing compounds represented by formula (1) may be included.

[0122] The fluoropolymer 3 used in the present disclosure preferably contains 0.01 to 10 mol % of structural units derived from the monomer represented by formula (3) (where the sum of the structural units derived from vinylidene fluoride and the structural units derived from the monomer represented by formula (3) is 100 mol %), more preferably 0.20 to 7 mol %, and particularly preferably 0.30 to 4 mol %. Furthermore, the fluoropolymer 3 preferably contains 90 to 99.99 mol %, more preferably 93 to 99.75 mol %, and particularly preferably 96 to 99.63 mol % of structural units derived from vinylidene fluoride. When the structural units derived from the monomer represented by formula (3) are 0.01 mol % or more, the proportion of the structural units in the fluoropolymer of formula (3) is not too small, thereby suppressing gelation of the fluoropolymer solution. When the structural units derived from the monomer represented by formula (3) are 10 mol % or less, the viscosity is not too high, preventing coating difficulties.

[0123] The amount of vinylidene fluoride units in the fluoropolymer 3 and the amount of the monomer units represented by the above formula (3) are usually determined by the amount of the copolymer. 1 It can be determined by 1 H NMR spectroscopy or neutralization titration.

[0124] The fluoropolymer 3 used in the present disclosure may contain other monomer components in addition to vinylidene fluoride and the monomer represented by the above formula (3). Examples include fluorine-based monomers copolymerizable with vinylidene fluoride, hydrocarbon monomers such as ethylene and propylene, and monomers copolymerizable with the above formula (3). Examples of fluorine-based monomers copolymerizable with vinylidene fluoride include vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ethers such as perfluoromethyl vinyl ether. Examples of monomers copolymerizable with the above formula (3) include (meth)acrylic acid and alkyl (meth)acrylate compounds such as methyl (meth)acrylate. The other monomers may be used alone or in combination of two or more.

[0125] When the fluoropolymer 3 contains the other monomers described above, it preferably contains 0.01 to 10 mol % of the other monomer units, assuming that the total monomer units constituting the fluoropolymer 3 is 100 mol %.

[0126] The fluoropolymer 3 used in the present disclosure has a weight average molecular weight determined by measurement with GPC (gel permeation chromatography) generally in the range of 50,000 to 1,500,000.

[0127] The fluoropolymer 3 can be obtained by polymerizing vinylidene fluoride and at least one of the monomers represented by the formula (3) by a conventionally known method. The polymerization method is not particularly limited, but examples thereof include suspension polymerization, emulsion polymerization, and solution polymerization. Among these, aqueous suspension polymerization or emulsion polymerization is preferred for ease of post-treatment. The vinylidene fluoride and the monomer represented by the formula (3) used in the polymerization are both well-known compounds, and commercially available products may be used.

[0128] The fluoropolymer 3 is usually preferably obtained by copolymerizing 90 to 99.9 parts by mass of vinylidene fluoride and 0.1 to 10 parts by mass of the monomer represented by the above formula (3), more preferably 95 to 99.9 parts by mass of vinylidene fluoride and 0.1 to 5 parts by mass of the monomer represented by the above formula (3) (where the total of vinylidene fluoride and the monomer represented by the above formula (3) is 100 parts by mass).

[0129] The inherent viscosity ηi of the fluoropolymer 3 is preferably 0.5 dL / g to 5.0 dL / g, more preferably 1.0 dL / g to 4.0 dL / g, and even more preferably 1.5 dL / g to 3.5 dL / g. An inherent viscosity within the above range is preferable in that it prevents a decrease in the solids content of the fluororesin solution, which can lead to a decrease in productivity, and prevents uneven electrode thickness when the electrode mixture is applied, thereby facilitating electrode production. The inherent viscosity ηi can be determined by dissolving 80 mg of the polymer in 20 ml of N,N-dimethylformamide and measuring the viscosity using an Ubbelohde viscometer in a thermostatic bath at 30°C according to the following formula:

[0130] ηi=(1 / C)·ln(η / η0) In the above formula, η is the viscosity of the polymer solution, η0 is the viscosity of the solvent N,N-dimethylformamide, and C is 0.4 g / dl.

[0131] An inherent viscosity within the above range is preferable in that it does not deteriorate productivity due to a decrease in the solid content of the fluororesin solution, and does not cause unevenness in the thickness of the electrode when the electrode mixture is applied, making it easy to produce the electrode.

[0132] (Negative electrode) The negative electrode in the secondary battery of the present disclosure preferably includes a layer of at least one metal element selected from the group consisting of lithium, sodium, magnesium, and zinc in a metallic state.

[0133] In the first embodiment, it is essential that the negative electrode contains a layer of at least one metal element selected from the group consisting of lithium, sodium, magnesium, and zinc in a metallic state. In the second aspect, the electrode does not have a metallic layer when it is produced, and the metallic layer of metal elements that will be formed by subsequent charging preferably comprises at least one metal element selected from the group consisting of lithium, sodium, magnesium, and zinc.

[0134] Among these, it is most preferable to use lithium metal alone or an alloy containing lithium metal, and lithium metal alone is most preferable.

[0135] The negative electrode can be manufactured by a general method for manufacturing metal foils. When an alloy material is used, a method of forming a thin film layer (negative electrode active material layer) containing the above-mentioned negative electrode active material by a vapor deposition method, a sputtering method, a plating method, or the like can also be used.

[0136] The thickness of the negative electrode plate is designed to match the positive electrode plate to be used and is not particularly limited, but the thickness of the composite layer minus the thickness of the metal foil of the core material is usually 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and is usually 300 μm or less, preferably 280 μm or less, more preferably 250 μm or less.

[0137] (negative electrode current collector) Examples of materials for the negative electrode current collector include metals such as aluminum, titanium, tantalum, stainless steel, nickel, and copper, or alloys thereof; and carbon materials such as carbon cloth and carbon paper. Of these, metal materials, particularly aluminum, copper, and alloys thereof are preferred.

[0138] Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punched metal, and foamed metal for metal materials, and carbon plate, carbon thin film, and carbon cylinder for carbon materials. Of these, metal thin films are preferred. The thin film may be formed into a mesh shape as appropriate. The thickness of the thin film is optional, but is usually 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, and more preferably 50 μm or less. If the thin film is thinner than this range, the strength required as a current collector may be insufficient. Conversely, if the thin film is thicker than this range, handling may be impaired.

[0139] It is also preferable that the surface of the current collector is coated with a conductive additive, such as carbon or a noble metal such as gold, platinum, or silver, in order to reduce electrical contact resistance.

[0140] The thickness ratio of the current collector to the negative electrode active material layer is not particularly limited, but the value of (thickness of the negative electrode active material layer on one side immediately before injection of the liquid electrolyte) / (thickness of the current collector) is preferably 20 or less, more preferably 15 or less, and most preferably 10 or less, and is preferably 0.5 or more, more preferably 0.8 or more, and most preferably 1 or more. If the ratio exceeds this range, the current collector may generate heat due to Joule heat during high current density charge / discharge. If the ratio is below this range, the volume ratio of the current collector increases, which may reduce the battery capacity.

[0141] The fluoropolymer coating preferably has a coating thickness of 3 to 8 μm before drying. By keeping the thickness within this range, the effects of the present disclosure can be suitably exhibited.

[0142] (Method of manufacturing negative electrode) The negative electrode of the present disclosure can be produced by applying a solution of the above-described polymer onto a negative electrode material or a current collector and drying it, or by applying it by rolling. Examples of solvents for preparing a polymer solution include N-methyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone and N-butyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, diethylenetriamine, N,N-dimethylaminopropylamine, diethyl ether, propylene oxide, and tetrahydrofuran. The polymer content in the polymer solution is preferably 3 to 40 mass % relative to the entire polymer solution, and more preferably 5 to 15 mass %. The density of the coating layer after drying is 0.3 to 3.0 g / cm 3 is preferable, and more preferably 1 to 2 g / cm 3 is.

[0143] The thickness of the coating layer after drying can be calculated from the part by weight of the fluoropolymer in the polymer solution and the thickness of the coating layer on the negative electrode material or current collector. In the second embodiment, the current collector on which the coating layer is formed is freeze-dried by immersing it in liquid nitrogen, and this freeze-dried sample is cut perpendicular to the coating layer to prepare a sample for cross-sectional observation. The thickness of the coating layer after drying can also be measured by observing the cross-section of the coating layer of the sample with a scanning electron microscope (SEM).

[0144] The density of the coating layer after drying can be calculated by calculating the weight from the change in weight of the coating layer before and after drying, and dividing the weight by the volume of the coating layer after drying.

[0145] (battery) The present disclosure provides a secondary battery including the above-described negative electrode and a liquid electrolyte containing a fluorinated ether as an essential component. The above-described fluorinated ether and the liquid electrolyte containing the same are described in detail below. The use of an electrolyte containing a fluorinated ether and the above-described negative electrode is particularly advantageous in that dendrite formation can be reduced.

[0146] (fluorinated ethers) The liquid electrolyte preferably contains less than 90 mass % of fluorinated ether in the entire electrolyte solvent. The fluorinated ether is not particularly limited as long as it is an ether compound containing fluorine in part.

[0147] The fluorinated ethers include those represented by the following general formula (I): Rf 4 -O-Rf 5 (I) (In the formula, Rf 4 and Rf 5 are the same or different and are an alkyl group having 1 to 10 carbon atoms or a fluorinated alkyl group having 1 to 10 carbon atoms, provided that Rf 4 and Rf 5 At least one of the groups is a fluorinated alkyl group. By including other fluorinated ethers, the flame retardancy of the liquid electrolyte is improved, and the stability and safety at high temperatures and high voltages are also improved.

[0148] In the above general formula (I), Rf 4 and Rf 5 At least one of Rf may be a fluorinated alkyl group having 1 to 10 carbon atoms. However, from the viewpoint of further improving the flame retardancy of the liquid electrolyte and the stability and safety at high temperatures and high voltages, 4 and Rf 5 are preferably fluorinated alkyl groups having 1 to 10 carbon atoms. 4 and Rf 5 may be the same or different from each other. Among them, Rf 4 and Rf 5 are the same or different, and Rf 4 is a fluorinated alkyl group having 3 to 6 carbon atoms, and Rf 5 is more preferably a fluorinated alkyl group having 2 to 6 carbon atoms.

[0149] Rf 4 and Rf 5 If the total number of carbon atoms in Rf is too small, the boiling point of the fluorinated ether will be too low. 4 or Rf 5 If the carbon number of Rf is too large, the solubility of the electrolyte salt decreases, the compatibility with other solvents begins to be adversely affected, and the viscosity increases, resulting in a decrease in rate characteristics. 4 The carbon number of Rf is 3 or 4. 5 When the carbon number is 2 or 3, it is advantageous in that the boiling point and rate characteristics are excellent.

[0150] Such fluorinated ethers include, for example, fluorinated ethers represented by the following general formula (10). HCF2CF2-OR (10) (In the formula, R is an alkyl group which may contain an ether group, or a fluorinated alkyl group which may contain an ether group.)

[0151] In the following, first, the fluorinated ether compound represented by the general formula (10) will be described in detail, and then fluorinated ether compounds other than the fluorinated ether compound represented by the general formula (10) (hereinafter, these may be referred to as "other fluorinated ether compounds"). In the present disclosure, the fluorinated ether compound represented by the above general formula (10) may be used in combination with "other fluorinated ether compounds."

[0152] In the compound represented by the general formula (10), the fluorinated alkyl group is preferably a fluorinated alkyl group having 1 to 10 carbon atoms, more preferably a fluorinated alkyl group having 2 to 6 carbon atoms.

[0153] In the compound represented by the above general formula (10), if the number of carbon atoms in the fluoroalkyl group is too small, the boiling point will decrease and the volatility of the electrolyte will increase, and if the number of carbon atoms is too large, the viscosity will increase and the output characteristics will decrease.

[0154] The compound represented by the general formula (10) preferably has a fluorine content of 40 to 75 mass %. When the compound has a fluorine content in this range, the compound has a particularly excellent balance between non-flammability and compatibility. This is also preferred in terms of good oxidation resistance and safety. The lower limit of the fluorine content is more preferably 43% by mass, further preferably 45% by mass, and particularly preferably 50% by mass, and the upper limit is more preferably 70% by mass, and further preferably 66% by mass. The fluorine content of the fluorinated ether is a value calculated based on the structural formula of the fluorinated ether by {(number of fluorine atoms×19) / molecular weight of the fluorinated ether}×100(%).

[0155] Examples of R include -CH2CF2CF3, -CF2CFHCF3, -CF2CF2CF2H, -CH2CF2CF2H, -CH2CH2CF2CF3, -CH2CF2CFHCF3, -CF2CF2CF2CF2H, -CH2CF2CF2CF2H, -CH2CH2CF2CF2H, -CH2CF(CF3)CF2H, -CF2CF2H, -CH2CF2H, -CH2CF3, -CF2CH 3、 -CH2-CH3, CH2-CH2-CH3, CH2-CH2-CH2-CH3, -CH2CH2-O-CF2CF2H, -CH2CH2-O-CH3, -CH2CH2-O-CH2CH3, - Examples include CH2CH2-O-CF3, -CH2CH2-O-CH2CF3, -CH2CH2-O-CF2CF2H, -CH2CH2-O-CF2H, -CH2CH2-O-CH2CF2H, and the like.

[0156] Specific examples of the compound represented by the above general formula (10) include HCF2CF2-O-CH2CF2CF2H, HCF2CF2-O-CH2CF2CF3, HCF2CF2-O-CH2CF3, HCF2-CF2-O-CH2-CH2-CH3, HCF2-CF2-O-CH2-CH2-CH2-CH3, HCF2-CF2-O-CH2-CH2-CH2-CH3, HCF2-CF2-O-CH2-CH2-O-CF2-CF2H, etc.

[0157] The fluorinated ether represented by the above general formula (10) is preferably at least one fluorinated ether selected from the group consisting of fluorinated ethers represented by the following general formulae (12) to (14).

[0158] HCF2CF2-O-CH2CF2CF2H (12) HCF2CF2-O-CH2CF2CF3(13) HCF2CF2-O-CH2CF3(14)

[0159] In particular, by including the fluorinated ethers represented by the above general formulas (12) to (14) in the liquid electrolyte as an additive, it is advantageous in that the flash point of the electrolyte solution can be lowered.

[0160] Examples of the other fluorinated ethers (that is, fluorinated ethers other than those represented by the general formula (10)) include the following.

[0161] The other fluorinated ethers preferably have a fluorine content of 40 to 75% by mass. When the fluorine content is in this range, the balance between non-flammability and compatibility is particularly excellent. This is also preferred in terms of good oxidation resistance and safety. The lower limit of the fluorine content is more preferably 45% by mass, further preferably 50% by mass, and particularly preferably 55% by mass, and the upper limit is more preferably 70% by mass, and further preferably 66% by mass. The fluorine content of the other fluorinated ether is a value calculated based on the structural formula of the other fluorinated ether by {(number of fluorine atoms×19) / molecular weight of the other fluorinated ether}×100(%).

[0162] Rf 4 Examples of Rf include CF3CF2CH2-, CF3CFHCF2-, HCF2CF2CF2-, HCF2CF2CH2-, CF3CF2CH2CH2-, CF3CFHCF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CF2CH2-, HCF2CF2CH2CH2-, HCF2CF(CF3)CH2-, and the like. 4 Examples of such groups include -CH2CF2CF3, -CF2CFHCF3, -CF2CF2CF2H, -CH2CF2CF2H, -CH2CH2CF2CF3, -CH2CF2CFHCF3, -CF2CF2CF2CF2H, -CH2CF2CF2CF2H, -CH2CH2CF2CF2H, -CH2CF(CF3)CF2H, -CF2CF2H, -CH2CF2H, -CF2CH3, and the like.

[0163] Specific examples of the other fluorinated ethers include HCF2CF2CH2OCF2CFHCF3, CF3CF2CH2OCF2CFHCF3, and CF 13 OCH3, C6F 13 OC2H5, C8F 17 OCH3, C8F 17 OC2H5, CF3CFHCF2CH(CH3)OCF2CFHCF3, HCF2CF2OCH(C2H5)2, HCF2CF2OC4H9, HCF2CF2OCH2CH(C2H5)2, HCF2CF2OCH2CH(CH3)2, etc.

[0164] Among these, those containing HCF2 at one or both ends have excellent polarizability and can give other fluorinated ethers with high boiling points. The boiling point of the other fluorinated ethers is preferably 67 to 120°C, more preferably 80°C or higher, and even more preferably 90°C or higher.

[0165] Examples of such other fluorinated ethers include one or more of CF3CH2OCF2CFHCF3, CF3CF2CH2OCF2CFHCF3, HCF2CF2CH2OCF2CFHCF3, HCF2CF2CH2OCH2CF2CF2H, CF3CFHCF2CH2OCF2CFHCF3, HCF2CF2CH2OCF2CF2H, and the like. Among these, at least one selected from the group consisting of HCF2CF2CH2OCF2CFHCF3 (boiling point 106°C) and CF3CF2CH2OCF2CFHCF3 (boiling point 82°C) is preferred, as it has the advantages of a high boiling point, good compatibility with other solvents, and good solubility of electrolyte salts, and HCF2CF2CH2OCF2CFHCF3 (boiling point 106°C) is more preferred.

[0166] The content of the fluorinated ether in the liquid electrolyte is preferably less than 90 mass %. By keeping the content within this range, the liquid electrolyte can be used as a good one. That is, if the content is too high, the concentration of the liquid electrolyte increases and the ionic conductivity decreases, which shortens the battery life. The lower limit is preferably 3% by mass, more preferably 5% by mass, and the upper limit is preferably 70% by mass, more preferably 60% by mass.

[0167] When the fluorinated ether represented by the above general formula (10) is used, it is preferable that the content of the fluorinated ether is within the above range.

[0168] (Components other than fluorinated ethers in liquid electrolytes) The liquid electrolyte of the present disclosure preferably contains a component other than the fluorinated ether. Components that can be incorporated into such a liquid electrolyte are described in detail below.

[0169] The solvent preferably contains at least one selected from the group consisting of carbonates and carboxylic acid esters.

[0170] The carbonate may be a cyclic carbonate or a chain carbonate.

[0171] The cyclic carbonate may be a non-fluorinated cyclic carbonate or a fluorinated cyclic carbonate.

[0172] The non-fluorinated cyclic carbonate may be a non-fluorinated saturated cyclic carbonate, preferably a non-fluorinated saturated alkylene carbonate having an alkylene group with 2 to 6 carbon atoms, more preferably a non-fluorinated saturated alkylene carbonate having an alkylene group with 2 to 4 carbon atoms.

[0173] Among these, the non-fluorinated saturated cyclic carbonate is preferably at least one selected from the group consisting of ethylene carbonate, propylene carbonate, cis-2,3-pentylene carbonate, cis-2,3-butylene carbonate, 2,3-pentylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 1,2-butylene carbonate, and butylene carbonate, because of its high dielectric constant and suitable viscosity.

[0174] The non-fluorinated saturated cyclic carbonates may be used alone or as a mixture of two or more kinds in any combination and ratio.

[0175] When the non-fluorinated saturated cyclic carbonate is contained, the content of the non-fluorinated saturated cyclic carbonate relative to the solvent is preferably 5 to 90% by volume, more preferably 10 to 60% by volume, and even more preferably 15 to 45% by volume.

[0176] The fluorinated cyclic carbonate is a cyclic carbonate having a fluorine atom. A solvent containing the fluorinated cyclic carbonate can be suitably used even under high voltage. In this specification, the term "high voltage" refers to a voltage of 4.2 V or higher. The upper limit of the "high voltage" is preferably 4.9 V.

[0177] The fluorinated cyclic carbonate may be a fluorinated saturated cyclic carbonate or a fluorinated unsaturated cyclic carbonate.

[0178] The fluorinated saturated cyclic carbonate is a saturated cyclic carbonate having a fluorine atom, and specifically, is represented by the following general formula (A):

[0179] [ka] (In the formula, X 1 ~X 4 are the same or different and each represents -H, -CH3, -C2H5, -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond, provided that X 1 ~X 4 at least one of which is -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond. The fluorinated alkyl group is, for example, -CF3, -CF2H, -CH2F, etc.

[0180] When the liquid electrolyte of the present disclosure contains the above-mentioned fluorinated saturated cyclic carbonate, the oxidation resistance of the liquid electrolyte is improved and stable and excellent charge / discharge characteristics are obtained when the liquid electrolyte is applied to a high-voltage lithium-ion secondary battery or the like. In this specification, an "ether bond" is a bond represented by --O--.

[0181] X is a good choice due to its excellent dielectric constant and oxidation resistance. 1 ~X 4 It is preferred that one or two of the groups be -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond.

[0182] Since it is expected to reduce viscosity at low temperatures, increase flash point, and improve solubility of electrolyte salts, X 1 ~X 4is preferably —H, —F, a fluorinated alkyl group (a), a fluorinated alkyl group having an ether bond (b), or a fluorinated alkoxy group (c).

[0183] The fluorinated alkyl group (a) is an alkyl group in which at least one hydrogen atom has been substituted with a fluorine atom. The number of carbon atoms in the fluorinated alkyl group (a) is preferably 1 to 20, more preferably 1 to 17, even more preferably 1 to 7, and particularly preferably 1 to 5. If the number of carbon atoms is too large, there is a risk of reduced low-temperature characteristics and reduced solubility of the electrolyte salt. If the number of carbon atoms is too small, reduced solubility of the electrolyte salt, reduced discharge efficiency, and even increased viscosity may occur.

[0184] Among the fluorinated alkyl groups (a) above, those having one carbon atom include CFH2-, CF2H-, and CF3-. In particular, CF2H- or CF3- is preferred in terms of high-temperature storage properties, with CF3- being most preferred.

[0185] Among the above-mentioned fluorinated alkyl groups (a), those having two or more carbon atoms include those represented by the following general formula (a-1): R 8 -R 9 - (a-1) (In the formula, R 8 is an alkyl group having one or more carbon atoms which may have a fluorine atom; R 9 is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom; provided that R 1 and R 2 A preferred example is a fluorinated alkyl group represented by the formula: wherein at least one of the groups has a fluorine atom, in view of good solubility of the electrolyte salt. In addition, R 1 and R 2 may further have atoms other than carbon atoms, hydrogen atoms and fluorine atoms.

[0186] R 8 R is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. 8R is preferably a linear or branched alkyl group having 1 to 16 carbon atoms. 8 The number of carbon atoms is more preferably 1 to 6, and further preferably 1 to 3.

[0187] R 8 Specific examples of linear or branched alkyl groups include CH3-, CH3CH2-, CH3CH2CH2-, CH3CH2CH2CH2-,

[0188] [ka]

[0189] etc.

[0190] Also, R 8is a straight-chain alkyl group having a fluorine atom, CF3-, CF3CH2-, CF3CF2-, CF3CH2CH2-, CF3CF2CF2-, CF3CH2CF2-, CF3CF2CH2CH2-, CF3CF2CH2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CH2CF2-, CF3CF2CH2CH2-, CF3CF2CH2CH 2CH2-, CF3CH2CF2CH2CH2-, CF3CF2CF2CH2CH2-, CF3CF2CF2CF2CH2-, CF3CF2CH2CF2CH2-, CF3CF2CH2CH2CH2CH2-, CF3CF2C F2CF2CH2CH2-, CF3CF2CH2CF2CH2CH2-, HCF2-, HCF2CH2-, HCF2CF2-, HCF2CH2CH2-, HCF2CF2CH2-, HCF2CH2CF2-, HCF2CF2C H2CH2-, HCF2CH2CF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CH2CH2CH2-, HCF2CH2CF2CH2CH2-, HCF2CF2CF2CF2CH2-, HCF2CF2CF2 CF2CH2CH2-, FCH2-, FCH2CH2-, FCH2CF2-, FCH2CF2CH2-, FCH2CF2CF2-, CH3CF2CH2-, CH3CF2CF2-, CH3CF2CH2CF2-, CH3CF2 Examples include CF2CF2-, CH3CH2CF2CF2-, CH3CF2CH2CF2CH2-, CH3CF2CF2CF2CH2-, CH3CF2CF2CH2CH2-, CH3CH2CF2CF2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, HCFClCF2CH2-, HCF2CFClCH2-, HCF2CFClCF2CFClCH2-, HCFClCF2CFClCF2CH2-, and the like.

[0191] Also, R 8 is a branched alkyl group having a fluorine atom,

[0192] [ka]

[0193] [ka]

[0194] However, since the presence of branches such as CH3- or CF3- tends to increase viscosity, it is more preferable that the number of branches is small (one) or zero.

[0195] R 9 R is an alkylene group having 1 to 3 carbon atoms which may contain a fluorine atom. 9 R may be linear or branched. An example of the minimum structural unit constituting such a linear or branched alkylene group is shown below. 9 is composed of these alone or in combination.

[0196] (i) The smallest linear structural unit: -CH2-, -CHF-, -CF2-, -CHCl-, -CFCl-, -CCl2-

[0197] (ii) Branched chain minimum structural unit:

[0198] [ka]

[0199] Among the above examples, it is preferable to use a structural unit that does not contain Cl, since it is more stable and does not undergo a dehydrochlorination reaction with a base.

[0200] R 9 When the alkyl group is linear, it is composed only of the linear minimum structural unit described above, and among these, -CH2-, -CH2CH2-, or -CF2- is preferred. -CH2- or -CH2CH2- is more preferred in terms of further improving the solubility of the electrolyte salt.

[0201] R 9When the branched chain structure is a branched chain structure, it contains at least one of the minimum branched chain structural units described above, and is represented by the general formula -(CX a X b )-(X a is H, F, CH3 or CF3; X b is CH3 or CF3. However, X b If CF3, then X a is H or CH3) are preferred examples. These can particularly further improve the solubility of the electrolyte salt.

[0202] Preferred fluorinated alkyl groups (a) include, for example, CF3CF2-, HCF2CF2-, H2CFCF2-, CH3CF2-, CF3CHF-, CH3CF2-, CF3CF2CF2-, HCF2CF2CF2-, H2CFCF2CF2-, CH3CF2CF2-,

[0203] [ka]

[0204] [ka]

[0205] etc.

[0206] The fluorinated alkyl group (b) having an ether bond is an alkyl group having an ether bond in which at least one hydrogen atom has been substituted with a fluorine atom. The fluorinated alkyl group (b) having an ether bond preferably has 2 to 17 carbon atoms. If the number of carbon atoms is too large, the viscosity of the fluorinated saturated cyclic carbonate increases, and the number of fluorine-containing groups increases, which may result in a decrease in the dielectric constant, resulting in a decrease in the solubility of the electrolyte salt, and a decrease in compatibility with other solvents. From this perspective, the number of carbon atoms in the fluorinated alkyl group (b) having an ether bond is more preferably 2 to 10, and even more preferably 2 to 7.

[0207] The alkylene group constituting the ether moiety of the fluorinated alkyl group (b) having an ether bond may be a linear or branched alkylene group. An example of the minimum structural unit constituting such a linear or branched alkylene group is shown below.

[0208] (i) The smallest linear structural unit: -CH2-, -CHF-, -CF2-, -CHCl-, -CFCl-, -CCl2-

[0209] (ii) Branched chain minimum structural unit:

[0210] [ka]

[0211] The alkylene group may be constituted solely by these minimum structural units, or may be constituted by a combination of linear (i) units, a combination of branched (ii) units, or a combination of linear (i) and branched (ii) units. Preferred specific examples will be described later.

[0212] Among the above examples, it is preferable to use a structural unit that does not contain Cl, since it is more stable and does not undergo a dehydrochlorination reaction with a base.

[0213] More preferred fluorinated alkyl groups (b) having an ether bond include those represented by the general formula (b-1): R 10 -(OR 11 ) n2 - (b-1) (In the formula, R 10 is an alkyl group having 1 to 6 carbon atoms, which may have a fluorine atom; R 11 is an alkylene group having 1 to 4 carbon atoms, which may have a fluorine atom; n2 is an integer of 1 to 3; provided that R 3 and R 4 at least one of which has a fluorine atom).

[0214] R 10 and R11 Examples of such groups include the following, which can be appropriately combined to form the fluorinated alkyl group (b) having an ether bond represented by the above general formula (b-1), but are not limited to these.

[0215] (1)R 10 As the general formula: X c 3C-(R 12 ) n3 -(3 X c are the same or different and are either H or F;R 12 is preferably an alkylene group having 1 to 5 carbon atoms which may have a fluorine atom; and n3 is preferably an alkyl group represented by 0 or 1).

[0216] If n3 is 0, R 10 Examples include CH3-, CF3-, HCF2-, and H2CF-.

[0217] A specific example when n3 is 1 is R 10As linear chains, CF3CH2-, CF3CF2-, CF3CH2CH2-, CF3CF2CH2-, CF3CF2CF2-, CF3CH2CF2-, CF3CH2CH2CH2-, CF3CF2CH2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CH2CF2-, CF3CF2CH2CH2CH2-, CF3CF2CH2CH2CH2-, C F3CH2CF2CH2CH2-, CF3CF2CF2CH2CH2-, CF3CF2CF2CF2CH2-, CF3CF2CH2CF2CH2-, CF3CF2CH2CH2CH2CH2-, CF3CF2CF 2CF2CH2CH2-, CF3CF2CH2CF2CH2CH2-, HCF2CH2-, HCF2CF2-, HCF2CH2CH2-, HCF2CF2CH2-, HCF2CH2CF2-, HCF2CF2CH 2CH2-, HCF2CH2CF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CH2CH2CH2-, HCF2CH2CF2CH2CH2-, HCF2CF2CF2CF2CH2-, HCF2C F2CF2CF2CH2CH2-, FCH2CH2-, FCH2CF2-, FCH2CF2CH2-, CH3CF2-, CH3CH2-, CH3CF2CH2-, CH3CF2CF2-, CH3CH2CH2-, Examples include CH3CF2CH2CF2-, CH3CF2CF2CF2-, CH3CH2CF2CF2-, CH3CH2CH2CH2-, CH3CF2CH2CF2CH2-, CH3CF2CF2CF2CH2-, CH3CF2CF2CH2CH2-, CH3CF2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, and the like.

[0218] n3 is 1 and R 10 As for branched chains,

[0219] [ka]

[0220] etc.

[0221] However, if the branched chain is CH3- or CF3-, the viscosity tends to be high, so R 10 However, a straight chain structure is more preferred.

[0222] (2) -(OR 4 ) n2 In the formula, n2 is an integer of 1 to 3, preferably 1 or 2. When n2=2 or 3, R 11 may be the same or different.

[0223] R 11 Preferred specific examples of the above include the following straight-chain or branched-chain copolymers:

[0224] Examples of linear ones include -CH2-, -CHF-, -CF2-, -CH2CH2-, -CF2CH2-, -CF2CF2-, -CH2CF2-, -CH2CH2CH2-, -CH2CF2CH2-, -CH2CF2CF2-, -CH2CF2CH2-, -CH2CF2CF2-, -CF2CH2CH2-, -CF2CF2CH2-, -CF2CF2CH2-, -CF2CH2CF2-, -CF2CF2CF2-, and the like.

[0225] As branched chains,

[0226] [ka]

[0227] etc.

[0228] The fluorinated alkoxy group (c) is an alkoxy group in which at least one hydrogen atom has been substituted with a fluorine atom. The fluorinated alkoxy group (c) preferably has 1 to 17 carbon atoms, and more preferably has 1 to 6 carbon atoms.

[0229] The fluorinated alkoxy group (c) is a group represented by the general formula: X d 3C-(R 13 ) n3-O-(Three X d are the same or different and are either H or F;R 13 is preferably an alkylene group having 1 to 5 carbon atoms which may have a fluorine atom; n3 is 0 or 1; provided that three X d Fluorinated alkoxy groups represented by the following formula (1) are particularly preferred:

[0230] Specific examples of the fluorinated alkoxy group (c) include R 8 Examples of such fluorinated alkoxy groups include those in which an oxygen atom is bonded to the terminal of the alkyl group exemplified above.

[0231] The fluorine content of the fluorinated alkyl group (a), the fluorinated alkyl group having an ether bond (b), and the fluorinated alkoxy group (c) in the fluorinated saturated cyclic carbonate is preferably 10% by mass or more. If the fluorine content is too low, the effect of reducing viscosity at low temperatures and the effect of increasing the flash point may not be sufficiently obtained. From this perspective, the fluorine content is more preferably 12% by mass or more, and even more preferably 15% by mass or more. The upper limit is usually 76% by mass. The fluorine content of the fluorinated alkyl group (a), the fluorinated alkyl group having an ether bond (b), and the fluorinated alkoxy group (c) is a value calculated based on the structural formula of each group by {(number of fluorine atoms × 19) / formula weight of each group} × 100 (%).

[0232] From the viewpoint of obtaining good dielectric constant and oxidation resistance, the fluorine content of the entire fluorinated saturated cyclic carbonate is preferably 10% by mass or more, more preferably 15% by mass or more, and the upper limit is usually 76% by mass. The fluorine content of the above-mentioned fluorinated saturated cyclic carbonate is a value calculated based on the structural formula of the fluorinated saturated cyclic carbonate by {(number of fluorine atoms × 19) / molecular weight of fluorinated saturated cyclic carbonate} × 100 (%).

[0233] Specific examples of the fluorinated saturated cyclic carbonate include the following.

[0234] X 1 ~X 4 Specific examples of fluorinated saturated cyclic carbonates in which at least one of the following is -F include:

[0235] [ka] These compounds have a high withstand voltage and good solubility of electrolyte salts.

[0236] In addition,

[0237] [ka]

[0238] etc. can also be used.

[0239] X 1 ~X 4 At least one of the groups is a fluorinated alkyl group (a), and the rest are all -H. Specific examples of certain fluorinated saturated cyclic carbonates include:

[0240] [ka]

[0241] [ka]

[0242] [ka]

[0243] etc.

[0244] X 1 ~X 4Specific examples of the fluorinated saturated cyclic carbonate in which at least one of (b) is a fluorinated alkyl group having an ether bond or (c) is a fluorinated alkoxy group, and the rest are all -H include:

[0245] [ka]

[0246] [ka]

[0247] [ka]

[0248] [ka]

[0249] [ka]

[0250] [ka]

[0251] etc.

[0252] Among these, the fluorinated saturated cyclic carbonate is preferably any one of the following compounds:

[0253] [ka]

[0254] [ka]

[0255] Other examples of the fluorinated saturated cyclic carbonate include trans-4,5-difluoro-1,3-dioxolan-2-one, 5-(1,1-difluoroethyl)-4,4-difluoro-1,3-dioxolan-2-one, 4-methylene-1,3-dioxolan-2-one, 4-methyl-5-trifluoromethyl-1,3-dioxolan-2-one, 4-ethyl-5-fluoro-1,3-dioxolan-2-one, and 4-ethyl-5,5-difluoro-1,3-dioxolan-2-one. dioxolan-2-one, 4-ethyl-4,5-difluoro-1,3-dioxolan-2-one, 4-ethyl-4,5,5-trifluoro-1,3-dioxolan-2-one, 4,4-difluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-5-trifluoromethyl-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one and the like.

[0256] Of the above fluorinated saturated cyclic carbonates, fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethylethylene carbonate (3,3,3-trifluoropropylene carbonate), and 2,2,3,3,3-pentafluoropropylethylene carbonate are more preferred.

[0257] The fluorinated unsaturated cyclic carbonate is a cyclic carbonate having an unsaturated bond and a fluorine atom, and is preferably a fluorinated ethylene carbonate derivative substituted with an aromatic ring or a substituent having a carbon-carbon double bond.Specific examples include 4,4-difluoro-5-phenylethylene carbonate, 4,5-difluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, and 4,5-difluoro-4,5-diallylethylene carbonate.

[0258] The above fluorinated cyclic carbonates may be used alone or as a mixture of two or more kinds in any combination and ratio.

[0259] When the fluorinated cyclic carbonate is contained, the content of the fluorinated cyclic carbonate relative to the solvent is preferably 5 to 90% by volume, more preferably 10 to 60% by volume, and even more preferably 15 to 45% by volume.

[0260] The chain carbonate may be a non-fluorinated chain carbonate or a fluorinated chain carbonate.

[0261] Examples of the non-fluorinated chain carbonate include hydrocarbon chain carbonates such as CH3OCOOCH3 (dimethyl carbonate: DMC), CH3CH2OCOOCH2CH3 (diethyl carbonate: DEC), CH3CH2OCOOCH3 (ethyl methyl carbonate: EMC), CH3OCOOCH2CH2CH3 (methyl propyl carbonate), methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, dibutyl carbonate, methyl isopropyl carbonate, methyl-2-phenylphenyl carbonate, phenyl-2-phenylphenyl carbonate, trans-2,3-pentylene carbonate, trans-2,3-butylene carbonate, and ethyl phenyl carbonate. Among these, at least one selected from the group consisting of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate is preferred.

[0262] The non-fluorinated chain carbonates may be used alone or in any combination of two or more in any ratio.

[0263] When the non-fluorinated chain carbonate is contained, the content of the non-fluorinated chain carbonate is preferably 10 to 90% by volume, more preferably 40 to 85% by volume, and even more preferably 50 to 80% by volume, relative to the solvent.

[0264] The fluorinated chain carbonate is a chain carbonate having fluorine atoms. A solvent containing the fluorinated chain carbonate can be suitably used even under high voltage.

[0265] The fluorinated chain carbonate may be a fluorinated chain carbonate represented by the general formula (B): Rf 3 OCOOR 14 (B) (In the formula, Rf 3 is a fluorinated alkyl group having 1 to 7 carbon atoms, and R 14is an alkyl group having 1 to 7 carbon atoms which may contain a fluorine atom.

[0266] Rf 3 is a fluorinated alkyl group having 1 to 7 carbon atoms, and R 14 is an alkyl group having 1 to 7 carbon atoms which may contain a fluorine atom. The fluorinated alkyl group is an alkyl group in which at least one hydrogen atom has been substituted with a fluorine atom. 14 When is an alkyl group containing a fluorine atom, it becomes a fluorinated alkyl group. Rf 3 and R 14 The alkyl group preferably has 1 to 7 carbon atoms, more preferably 1 or 2 carbon atoms, in terms of low viscosity. If the number of carbon atoms is too large, there is a risk that the low-temperature characteristics and the solubility of the electrolyte salt may be reduced, whereas if the number of carbon atoms is too small, there may be a reduction in the solubility of the electrolyte salt, a reduction in discharge efficiency, and even an increase in viscosity.

[0267] Examples of the fluorinated alkyl group having one carbon atom include CFH2-, CF2H-, CF3-, etc. In particular, CFH2- or CF3- is preferred in terms of high-temperature storage properties.

[0268] The fluorinated alkyl group having two or more carbon atoms includes a group represented by the following general formula (d-1): R 1 -R 2 - (d-1) (In the formula, R 1 is an alkyl group having one or more carbon atoms which may have a fluorine atom; R 2 is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom; provided that R 1 and R 2 A preferred example is a fluorinated alkyl group represented by the formula: wherein at least one of the groups has a fluorine atom, in view of good solubility of the electrolyte salt. In addition, R 1 and R 2 may further have atoms other than carbon atoms, hydrogen atoms and fluorine atoms.

[0269] R 1 R is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. 1 R is preferably a linear or branched alkyl group having 1 to 6 carbon atoms. 1 The number of carbon atoms is more preferably 1 to 3.

[0270] R 1 Specific examples of linear or branched alkyl groups include CH3-, CF3-, CH3CH2-, CH3CH2CH2-, CH3CH2CH2CH2-,

[0271] [ka]

[0272] etc.

[0273] Also, R 1is a straight-chain alkyl group having a fluorine atom, CF3-, CF3CH2-, CF3CF2-, CF3CH2CH2-, CF3CF2CF2-, CF3CH2CF2-, CF3CF2CH2CH2-, CF3CF2CH2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CH2CF2-, CF3CF2CH2CH2-, CF3CF2CH2CH 2CH2-, CF3CH2CF2CH2CH2-, CF3CF2CF2CH2CH2-, CF3CF2CF2CF2CH2-, CF3CF2CH2CF2CH2-, CF3CF2CH2CH2CH2CH2-, CF3CF2C F2CF2CH2CH2-, CF3CF2CH2CF2CH2CH2-, HCF2-, HCF2CH2-, HCF2CF2-, HCF2CH2CH2-, HCF2CF2CH2-, HCF2CH2CF2-, HCF2CF2C H2CH2-, HCF2CH2CF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CH2CH2CH2-, HCF2CH2CF2CH2CH2-, HCF2CF2CF2CF2CH2-, HCF2CF2CF2 CF2CH2CH2-, FCH2-, FCH2CH2-, FCH2CF2-, FCH2CF2CH2-, FCH2CF2CF2-, CH3CF2CH2-, CH3CF2CF2-, CH3CF2CH2CF2-, CH3CF2 Examples include CF2CF2-, CH3CH2CF2CF2-, CH3CF2CH2CF2CH2-, CH3CF2CF2CF2CH2-, CH3CF2CF2CH2CH2-, CH3CH2CF2CF2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, HCFClCF2CH2-, HCF2CFClCH2-, HCF2CFClCF2CFClCH2-, HCFClCF2CFClCF2CH2-, and the like.

[0274] Also, R 1 is a branched alkyl group having a fluorine atom,

[0275] [ka]

[0276] [ka]

[0277] However, since the presence of branches such as CH3- or CF3- tends to increase viscosity, it is more preferable that the number of branches is small (one) or zero.

[0278] R 2 R is an alkylene group having 1 to 3 carbon atoms which may contain a fluorine atom. 2 R may be linear or branched. An example of the minimum structural unit constituting such a linear or branched alkylene group is shown below. 2 is composed of these alone or in combination.

[0279] (i) The smallest linear structural unit: -CH2-, -CHF-, -CF2-, -CHCl-, -CFCl-, -CCl2-

[0280] (ii) Branched chain minimum structural unit:

[0281] [ka]

[0282] Among the above examples, it is preferable to use a structural unit that does not contain Cl, since it is more stable and does not undergo a dehydrochlorination reaction with a base.

[0283] R 2 When the alkyl group is linear, it is composed only of the linear minimum structural unit described above, and among these, -CH2-, -CH2CH2-, or -CF2- is preferred. -CH2- or -CH2CH2- is more preferred in terms of further improving the solubility of the electrolyte salt.

[0284] R 2When the branched chain structure is a branched chain structure, it contains at least one of the minimum branched chain structural units described above, and is represented by the general formula -(CX a X b )-(X a is H, F, CH3 or CF3; X b is CH3 or CF3. However, X b If CF3, then X a is H or CH3) are preferred examples. These can particularly further improve the solubility of the electrolyte salt.

[0285] Specific examples of preferred fluorinated alkyl groups include CF3CF2-, HCF2CF2-, H2CFCF2-, CH3CF2-, CF3CH2-, CF3CF2CF2-, HCF2CF2CF2-, H2CFCF2CF2-, CH3CF2CF2-,

[0286] [ka]

[0287] [ka]

[0288] etc.

[0289] Among them, Rf 3 and R 14 The fluorinated alkyl group is preferably CF3-, CF3CF2-, (CF3)2CH-, CF3CH2-, C2F5CH2-, CF3CF2CH2-, HCF2CF2CH2-, CF3CFHCF2CH2-, CFH2-, or CF2H-, and from the viewpoints of high flame retardancy and good rate characteristics and oxidation resistance, CF3CH2-, CF3CF2CH2-, HCF2CF2CH2-, CFH2-, or CF2H- is more preferred.

[0290] R 14 When R is an alkyl group that does not contain a fluorine atom, it is an alkyl group having 1 to 7 carbon atoms. 14The alkyl group preferably has 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms, in terms of low viscosity.

[0291] Examples of the alkyl group not containing a fluorine atom include CH3-, CH3CH2-, (CH3)2CH-, C3H7-, etc. Among these, CH3- and CH3CH2- are preferred in terms of low viscosity and good rate characteristics.

[0292] The fluorinated chain carbonate preferably has a fluorine content of 15 to 70% by mass. When the fluorine content is within the above range, compatibility with solvents and solubility of salts can be maintained. The fluorine content is more preferably 20% by mass or more, even more preferably 30% by mass or more, and particularly preferably 35% by mass or more, and more preferably 60% by mass or less, and even more preferably 50% by mass or less. In the present disclosure, the fluorine content is determined based on the structural formula of the fluorinated chain carbonate as follows: {(number of fluorine atoms x 19) / molecular weight of fluorinated chain carbonate} x 100(%) This is the value calculated by

[0293] The fluorinated chain carbonate is preferably any one of the following compounds, because it has low viscosity.

[0294] [ka]

[0295] As the fluorinated chain carbonate, methyl 2,2,2-trifluoroethyl carbonate (F3CH2COC(=O)OCH3) is particularly preferred.

[0296] The above fluorinated chain carbonates may be used alone or as a mixture of two or more kinds in any combination and ratio.

[0297] When the fluorinated chain carbonate is contained, the content of the fluorinated chain carbonate is preferably 10 to 90% by volume, more preferably 40 to 85% by volume, and even more preferably 50 to 80% by volume, relative to the solvent.

[0298] The carboxylic acid ester may be a cyclic carboxylic acid ester or a chain carboxylic acid ester.

[0299] The cyclic carboxylic acid ester may be a non-fluorinated cyclic carboxylic acid ester or a fluorinated cyclic carboxylic acid ester.

[0300] The non-fluorinated cyclic carboxylic acid ester may be a non-fluorinated saturated cyclic carboxylic acid ester, and a non-fluorinated saturated cyclic carboxylic acid ester having an alkylene group having 2 to 4 carbon atoms is preferred.

[0301] Specific examples of non-fluorinated saturated cyclic carboxylic acid esters having an alkylene group having 2 to 4 carbon atoms include β-propiolactone, γ-butyrolactone, ε-caprolactone, δ-valerolactone, and α-methyl-γ-butyrolactone. Of these, γ-butyrolactone and δ-valerolactone are particularly preferred from the viewpoints of improving the degree of lithium ion dissociation and improving load characteristics.

[0302] The non-fluorinated saturated cyclic carboxylic acid esters may be used alone or in any combination of two or more in any ratio.

[0303] When the non-fluorinated saturated cyclic carboxylic acid ester is contained, the content of the non-fluorinated saturated cyclic carboxylic acid ester relative to the solvent is preferably 0 to 90% by volume, more preferably 0.001 to 90% by volume, even more preferably 1 to 60% by volume, and particularly preferably 5 to 40% by volume.

[0304] The chain carboxylic acid ester may be a non-fluorinated chain carboxylic acid ester or a fluorinated chain carboxylic acid ester. When the solvent contains the chain carboxylic acid ester, an increase in resistance of the liquid electrolyte after high-temperature storage can be further suppressed.

[0305] Examples of the non-fluorinated chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, tert-butyl propionate, tert-butyl butyrate, sec-butyl propionate, sec-butyl butyrate, n-butyl butyrate, methyl pyrophosphate, ethyl pyrophosphate, tert-butyl formate, tert-butyl acetate, sec-butyl formate, sec-butyl acetate, n-hexyl pivalate, n-propyl formate, n-propyl methyl ester, methyl propionate, ethyl propionate, propyl butyl ester, methyl propionate, ethyl propionate, propyl butyl ester, methyl propyl ... propyl acetate, n-butyl formate, n-butyl pivalate, n-octyl pivalate, ethyl 2-(dimethoxyphosphoryl)acetate, ethyl 2-(dimethylphosphoryl)acetate, ethyl 2-(diethoxyphosphoryl)acetate, ethyl 2-(diethylphosphoryl)acetate, isopropyl propionate, isopropyl acetate, ethyl formate, ethyl 2-propynyl oxalate, isopropyl formate, isopropyl butyrate, isobutyl formate, isobutyl propionate, isobutyl butyrate, isobutyl acetate, and the like.

[0306] Of these, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate are preferred, and ethyl propionate and propyl propionate are particularly preferred.

[0307] The non-fluorinated chain carboxylic acid esters may be used alone or as a mixture of two or more kinds in any combination and in any ratio.

[0308] When the non-fluorinated chain carboxylic acid ester is contained, the content of the non-fluorinated chain carboxylic acid ester relative to the solvent is preferably 0 to 90% by volume, more preferably 0.001 to 90% by volume, even more preferably 1 to 60% by volume, and particularly preferably 5 to 40% by volume.

[0309] The fluorinated chain carboxylic acid ester is a chain carboxylic acid ester having a fluorine atom. A solvent containing the fluorinated chain carboxylic acid ester can be suitably used even under high voltage.

[0310] The fluorinated chain carboxylic acid esters include those represented by the following general formula: R 31 COOR 32 (In the formula, R 31 and R 32 are each independently an alkyl group having 1 to 4 carbon atoms which may contain a fluorine atom, and R 31 and R 32 At least one of which contains a fluorine atom.) is preferred from the viewpoint of compatibility with other solvents and oxidation resistance.

[0311] R 31 and R 32Examples of the fluorinated alkyl groups include non-fluorinated alkyl groups such as methyl group (-CH3), ethyl group (-CH2CH3), propyl group (-CH2CH2CH3), isopropyl group (-CH(CH3)2), normal butyl group (-CH2CH2CH2CH3), and tertiary butyl group (-C(CH3)3); -CF3, -CF2H, -CFH2, -CF2CF3, -CF2CF2H, -CF2CFH2, -CH2CF3, -CH2CF2H, -CH2CFH2, -CF2CF2CF3, -CF2CF2CF2H, -CF2CF2CFH2, -CH2CF2CF3, -CH2CF 2CF2H, -CH2CF2CFH2, -CH2CH2CF3, -CH2CH2CF2H, -CH2CH2CFH2, -CF(CF3)2, -CF(CF2H)2, -CF(CFH2)2, -CH(CF3)2, -CH(CF2H)2, -CH(CFH2)2, -CF(OCH) 3)CF3, -CF2CF2CF2CF3, -CF2CF2CF2CF2H, -CF2CF2CF2CFH2, -CH2CF2CF2CF3, -CH2CF2CF2CF2H, -CH2CF2CF2CFH2, -CH2CH2CF2CF3, -CH2CH2CF2CF2H, -C H2CH2CF2CFH2, -CH2CH2CH2CF3, -CH2CH2CH2CF2H, -CH2CH2CH2CFH2, -CF(CF3)CF2CF3, -CF(CF2H)CF2CF3, -CF(CFH2)CF2CF3, -CF(CF3)CF2CF2H, -CF( CF3)CF2CFH2, -CF(CF3)CH2CF3, -CF(CF3)CH2CF2H, -CF(CF3)CH2CFH2, -CH(CF3)CF2CF3, -CH(CF2H)CF2CF3, -CH(CFH2)CF2CF3, -CH(CF3)CF2CF2H, -CH (CF3)CF2CFH2, -CH(CF3)CH2CF3, -CH(CF3)CH2CF2H, -CH(CF3)CH2CFH2, -CF2CF(CF3)CF3, -CF2CF(CF2H)CF3, -CF2CF(CFH2)CF3, -CF2CF(CF3)CF2H, - CF2CF(CF3)CFH2, -CH2CF(CF3)CF3, -CH2CF(CF2H)CF3, -CH2CF(CFH2)CF3, -CH2CF(CF3)CF2H, -CH2CF(CF3)CFH2, -CH2CH(CF3)CF3, -CH2CH(CF2H)CF3,Examples include fluorinated alkyl groups such as -CH2CH(CFH2)CF3, -CH2CH(CF3)CF2H, -CH2CH(CF3)CFH2, -CF2CH(CF3)CF3, -CF2CH(CF2H)CF3, -CF2CH(CFH2)CF3, -CF2CH(CF3)CF2H, -CF2CH(CF3)CFH2, -C(CF3)3, -C(CF2H)3, and -C(CFH2)3. Among these, methyl groups, ethyl groups, -CF3, -CF2H, -CF2CF3, -CH2CF3, -CH2CF2H, -CH2CFH2, -CH2CH2CF3, -CH2CF2CF3, -CH2CF2CF2H, and -CH2CF2CFH2 are particularly preferred in terms of compatibility with other solvents, viscosity, and oxidation resistance.

[0312] Specific examples of the fluorinated chain carboxylic acid ester include CF3CH2C(=O)OCH3 (methyl 3,3,3-trifluoropropionate), HCF2C(=O)OCH3 (methyl difluoroacetate), HCF2C(=O)OC2H5 (ethyl difluoroacetate), CF3C(=O)OCH2CH2CF3, CF3C(=O)OCH2C2F5, CF3C(=O)OCH2CF2CF2H (2,2,3,3-tetrafluoropropyl trifluoroacetate), CF3C(=O)OCH2CF3, CF3C(=O)OCH(CF3)2, ethyl pentafluorobutyrate, methyl pentafluoropropionate, ethyl pentafluoropropionate, methyl heptafluoroisobutyrate, isopropyl trifluorobutyrate, ethyl trifluoroethyl acetate, tert-butyl trifluoroacetate, and n-butyl trifluoroacetate. methyl tetrafluoro-2-(methoxy)propionate, 2,2-difluoroethyl acetate, 2,2,3,3-tetrafluoropropyl acetate, CH3C(=O)OCH2CF3 (2,2,2-trifluoroethyl acetate), 1H,1H-heptafluorobutyl acetate, methyl 4,4,4-trifluorobutyrate, ethyl 4,4,4-trifluorobutyrate, ethyl 3,3,3-trifluoropropionate, 3,3,3-trifluoropropyl 3,3,3-trifluoropropionate, ethyl 3-(trifluoromethyl)butyrate, methyl 2,3,3,3-tetrafluoropropionate, 2,2-difluorobutyl acetate, methyl 2,2,3,3-tetrafluoropropionate, methyl 2-(trifluoromethyl)-3,3,3-trifluoropropionate, methyl heptafluorobutyrate, and the like can be exemplified by one or more of these. Among these, CF3CH2C(=O)OCH3, HCF2C(=O)OCH3, HCF2C(=O)OC2H5, CF3C(=O)OCH2C2F5, CF3C(=O)OCH2CF2CF2H, CF3C(=O)OCH2CF3, CF3C(=O)OCH(CF3)2, ethyl pentafluorobutyrate, methyl pentafluoropropionate, ethyl pentafluoropropionate, methyl heptafluoroisobutyrate, isopropyl trifluorobutyrate, ethyl trifluoroacetate, tert-butyl trifluoroacetate, n-butyl trifluoroacetate, methyl tetrafluoro-2-(methoxy)propionate, 2,2-difluoroethyl acetate, 2,2,3,3-tetrafluoropropyl acetate, CH3C(=O)OCH2CF3, 1H,1H-heptafluorobutyl acetate, methyl 4,4,4-trifluorobutyrate, Ethyl 4,4,4-trifluorobutyrate, ethyl 3,3,3-trifluoropropionate, 3,3,3-trifluoropropyl 3,3,3-trifluoropropionate, ethyl 3-(trifluoromethyl)butyrate, methyl 2,3,3,3-tetrafluoropropionate, 2,2-butyl difluoroacetate, methyl 2,2,3,3-tetrafluoropropionate, methyl 2-(trifluoromethyl)-3,3,3-trifluoropropionate, and methyl heptafluorobutyrate are preferred from the viewpoints of compatibility with other solvents and good rate characteristics, and CF3CH2C(=O)OCH3, HCF2C(=O)OCH3, HCF2C(=O)OC2H5, and CH3C(=O)OCH2CF3 are more preferred, and HCF2C(=O)OCH3, HCF2C(=O)OC2H5, and CH3C(=O)OCH2CF3 are particularly preferred.

[0313] The above fluorinated chain carboxylic acid esters may be used alone or as a mixture of two or more kinds in any combination and ratio.

[0314] When the fluorinated chain carboxylic acid ester is contained, the content of the fluorinated chain carboxylic acid ester is preferably 10 to 90% by volume, more preferably 40 to 85% by volume, and even more preferably 50 to 80% by volume, relative to the solvent.

[0315] The solvent preferably contains at least one selected from the group consisting of the cyclic carbonate, the chain carbonate, and the chain carboxylic acid ester, and more preferably contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester. The cyclic carbonate is preferably a saturated cyclic carbonate. A liquid electrolyte containing a solvent having the above composition can further improve the high-temperature storage characteristics and cycle characteristics of an electrochemical device.

[0316] When the solvent contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester, the solvent preferably contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester in a total amount of 10 to 100% by volume, more preferably 30 to 100% by volume, and even more preferably 50 to 100% by volume.

[0317] When the solvent contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester, the volume ratio of the cyclic carbonate to the at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester is preferably 5 / 95 to 95 / 5, more preferably 10 / 90 or more, even more preferably 15 / 85 or more, particularly preferably 20 / 80 or more, more preferably 90 / 10 or less, even more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0318] The solvent also preferably contains at least one selected from the group consisting of the non-fluorinated saturated cyclic carbonate, the non-fluorinated chain carbonate, and the non-fluorinated chain carboxylic acid ester, and more preferably contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester. A liquid electrolyte containing a solvent of the above composition can be suitably used in electrochemical devices used at relatively low voltages.

[0319] When the solvent contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester, the solvent preferably contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester in a total amount of 5 to 100% by volume, more preferably 20 to 100% by volume, and even more preferably 30 to 100% by volume.

[0320] When the liquid electrolyte contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester, the volume ratio of the non-fluorinated saturated cyclic carbonate to the at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester is preferably 5 / 95 to 95 / 5, more preferably 10 / 90 or more, even more preferably 15 / 85 or more, particularly preferably 20 / 80 or more, more preferably 90 / 10 or less, even more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0321] The solvent also preferably contains at least one selected from the group consisting of the fluorinated saturated cyclic carbonate, the fluorinated chain carbonate, and the fluorinated chain carboxylic acid ester, and more preferably contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester. A liquid electrolyte containing a solvent of the above composition can be suitably used not only in electrochemical devices used at relatively low voltages, but also in electrochemical devices used at relatively high voltages.

[0322] When the solvent contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester, the solvent preferably contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester in a total amount of 5 to 100% by volume, more preferably 10 to 100% by volume, and even more preferably 30 to 100% by volume.

[0323] When the solvent contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester, the volume ratio of the fluorinated saturated cyclic carbonate to the at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester is preferably 5 / 95 to 95 / 5, more preferably 10 / 90 or more, even more preferably 15 / 85 or more, particularly preferably 20 / 80 or more, more preferably 90 / 10 or less, even more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0324] Furthermore, an ionic liquid can also be used as the solvent. An "ionic liquid" is a liquid composed of ions that are a combination of organic cations and anions.

[0325] The organic cation is not particularly limited, but examples thereof include imidazolium ions such as dialkylimidazolium cations and trialkylimidazolium cations; tetraalkylammonium ions; alkylpyridinium ions; dialkylpyrrolidinium ions; and dialkylpiperidinium ions.

[0326] The anions that serve as counters to these organic cations are not particularly limited, but examples thereof include PF6 anion, PF3(C2F5)3 anion, PF3(CF3)3 anion, BF4 anion, BF2(CF3)2 anion, BF3(CF3) anion, bisoxalatoborate anion, P(C2O4)F2 anion, Tf (trifluoromethanesulfonyl) anion, Nf (nonafluorobutanesulfonyl) anion, bis(fluorosulfonyl)imide anion, bis(trifluoromethanesulfonyl)imide anion, bis(pentafluoroethanesulfonyl)imide anion, dicyanoamine anion, and halide anions.

[0327] The solvent is preferably a non-aqueous solvent, and the liquid electrolyte of the present disclosure is preferably a non-aqueous liquid electrolyte. The content of the solvent in the liquid electrolyte is preferably 70 to 99.999% by mass, more preferably 80% by mass or more, and more preferably 92% by mass or less.

[0328] The liquid electrolyte of the present disclosure may further include a compound (8) represented by general formula (8).

[0329] General formula (8): [ka] (In the formula, A a+ is a metal ion, hydrogen ion or onium ion; a is an integer of 1 to 3; b is an integer of 1 to 3; p is b / a; n 203 is an integer between 1 and 4, n 201 is an integer between 0 and 8, n 202 is 0 or 1, Z 201is a transition metal, an element in group III, IV, or V of the periodic table. X 201 is O, S, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (an alkylene group, a halogenated alkylene group, an arylene group, and a halogenated arylene group may have a substituent or a heteroatom in the structure, and when n202 is 1 and n203 is 2 to 4, n 203 X's 201 may be bonded to each other). L 201 is a halogen atom, a cyano group, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, a halogenated aryl group having 6 to 20 carbon atoms (an alkylene group, a halogenated alkylene group, an arylene group, and a halogenated arylene group may have a substituent or a heteroatom in the structure, and when n201 is 2 to 8, n201 L 201 may be bonded to each other to form a ring) or -Z 203 Y 203 Y 201 , Y 202 and Z 203 are independently O, S, and NY 204 , a hydrocarbon group or a fluorinated hydrocarbon group. Y 203 and Y 204 are each independently H, F, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms (the alkyl group, halogenated alkyl group, aryl group, and halogenated aryl group may have a substituent or a heteroatom in the structure, and Y 203 or Y 204 When there are a plurality of such groups, they may be bonded to form a ring.

[0330] A a+Examples of the cations include a lithium ion, a sodium ion, a potassium ion, a magnesium ion, a calcium ion, a barium ion, a cesium ion, a silver ion, a zinc ion, a copper ion, a cobalt ion, an iron ion, a nickel ion, a manganese ion, a titanium ion, a lead ion, a chromium ion, a vanadium ion, a ruthenium ion, a yttrium ion, a lanthanoid ion, an actinoid ion, a tetrabutylammonium ion, a tetraethylammonium ion, a tetramethylammonium ion, a triethylmethylammonium ion, a triethylammonium ion, a pyridinium ion, an imidazolium ion, a hydrogen ion, a tetraethylphosphonium ion, a tetramethylphosphonium ion, a tetraphenylphosphonium ion, a triphenylsulfonium ion, and a triethylsulfonium ion.

[0331] When used for electrochemical devices, etc., a+ is preferably a lithium ion, a sodium ion, a magnesium ion, a tetraalkylammonium ion, or a hydrogen ion, and particularly preferably a lithium ion. a+ The cation valence a is an integer between 1 and 3. If it is greater than 3, the crystal lattice energy increases, making it difficult to dissolve in a solvent. Therefore, if solubility is required, a value of 1 is more preferable. The anion valence b is also an integer between 1 and 3, with 1 being particularly preferable. The constant p, which represents the ratio of the cation to the anion, is inevitably determined by the ratio of the valences of the two, b / a.

[0332] Next, the ligand portion of general formula (8) will be described. In this specification, Z in general formula (8) 201 The organic or inorganic moiety that is bonded to the ligand is called a ligand.

[0333] Z 201 is preferably Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf or Sb, and more preferably Al, B or P.

[0334] X 201 represents O, S, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms. These alkylene groups and arylene groups may have a substituent or a heteroatom in their structure. Specifically, instead of hydrogen on the alkylene group or arylene group, a halogen atom, a linear or cyclic alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group, an acyl group, an amide group, or a hydroxyl group may be substituted, or a structure in which nitrogen, sulfur, or oxygen is introduced instead of carbon on the alkylene or arylene group may be used. 202 is 1 and n 203 When is 2 to 4, there are n203 X 201 may be bonded to each other. An example of such a ligand is ethylenediaminetetraacetic acid.

[0335] L 201 is a halogen atom, a cyano group, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, a halogenated aryl group having 6 to 20 carbon atoms, or -Z 203 Y 203 (Z 203 , Y 203 The alkyl group and aryl group in this case are also represented by X 201 Similarly, the structure may have a substituent or a heteroatom, and when n201 is 2 to 8, n201 L 201 may be bonded to each other to form a ring. 201 As the anionic group, a fluorine atom or a cyano group is preferred. In the case of a fluorine atom, the solubility and dissociation degree of the salt of the anionic compound are improved, and as a result, the ionic conductivity is improved. In addition, the oxidation resistance is improved, and thus the occurrence of side reactions can be suppressed.

[0336] Y 201 , Y 202 and Z 203 are independent of each other, O, S, NY204 , hydrocarbon group or a fluorinated hydrocarbon group. 201 and Y 202 is O, S or NY 204 It is preferable that Y is O, and more preferable that Y is O. Compound (8) is characterized in that Y is not present in the same ligand. 201 and Y 202 by Z 201 Because of the bond with Z 201 This ligand forms a chelate structure. This chelate effect improves the heat resistance, chemical stability, and hydrolysis resistance of this compound. The constant n202 in this ligand is either 0 or 1, but when it is 0, the chelate ring becomes a five-membered ring, which is particularly preferable because it maximizes the chelate effect and increases stability. In this specification, a fluorinated hydrocarbon group is a group in which at least one hydrogen atom of a hydrocarbon group has been substituted with a fluorine atom.

[0337] Y 203 and Y 204 are each independently H, F, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms, and these alkyl groups and aryl groups may have a substituent or a heteroatom in their structure, and Y 203 or Y 204 When a plurality of groups are present, they may be bonded to form a ring.

[0338] In addition, the constant n related to the number of ligands mentioned above 203 is an integer of 1 to 4, preferably 1 or 2, and more preferably 2. In addition, the constant n 201 is an integer of 0 to 8, preferably an integer of 0 to 4, more preferably 0, 2 or 4. 203 When is 1, n 201 is 2, n 203 When is 2, n 201 is preferably 0.

[0339] In the general formula (8), the alkyl group, halogenated alkyl group, aryl group, and halogenated aryl group include those having other functional groups such as a branch, a hydroxyl group, or an ether bond.

[0340] Compound (8) includes compounds represented by the general formula: [ka] (In the formula, A a+ ,a,b,p,n201,Z 201 and L 201 is as defined above), or a compound represented by the general formula: [ka] (In the formula, A a+ ,a,b,p,n201,Z 201 and L 201 is as described above).

[0341] Compound (8) includes lithium oxalatoborate salts, and is represented by the following formula: [ka] Lithium bis(oxalato)borate (LIBOB), represented by the formula: [ka] Lithium difluorooxalatoborate (LIDFOB), represented by

[0342] Compound (8) also includes compounds represented by the following formula: [ka] Lithium difluorooxalatophosphanite (LIDFOP) represented by the following formula: [ka] Lithium tetrafluorooxalatophosphanite (LITFOP) represented by the following formula: [ka] Examples of suitable fluorophosphanite include lithium bis(oxalato)difluorophosphanite represented by the following formula:

[0343] Other specific examples of dicarboxylic acid complex salts in which the central element of the complex is boron include lithium bis(malonato)borate, lithium difluoro(malonato)borate, lithium bis(methylmalonato)borate, lithium difluoro(methylmalonato)borate, lithium bis(dimethylmalonato)borate, and lithium difluoro(dimethylmalonato)borate.

[0344] Specific examples of dicarboxylic acid complex salts in which the central element of the complex is phosphorus include lithium tris(oxalato)phosphate, lithium tris(malonato)phosphate, lithium difluorobis(malonato)phosphate, lithium tetrafluoro(malonato)phosphate, lithium tris(methylmalonato)phosphate, lithium difluorobis(methylmalonato)phosphate, lithium tetrafluoro(methylmalonato)phosphate, lithium tris(dimethylmalonato)phosphate, lithium difluorobis(dimethylmalonato)phosphate, and lithium tetrafluoro(dimethylmalonato)phosphate.

[0345] Specific examples of dicarboxylic acid complex salts in which the central element of the complex is aluminum include LiAl(C2O4)2 and LiAlF2(C2O4).

[0346] Among these, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate are more preferably used because of their ease of availability and their ability to contribute to the formation of a stable coating structure. As the compound (8), lithium bis(oxalato)borate is particularly preferred.

[0347] The content of compound (8) is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and is preferably 10% by mass or less, more preferably 3% by mass or less, relative to the solvent, since this provides even better cycle characteristics.

[0348] The liquid electrolyte of the present disclosure preferably further contains an electrolyte salt (excluding compounds (1) and (8)). As the electrolyte salt, any salt that can be used in a liquid electrolyte can be used, such as a lithium salt, an ammonium salt, a metal salt, a liquid salt (ionic liquid), an inorganic polymer salt, or an organic polymer salt.

[0349] The electrolyte salt of the liquid electrolyte for lithium ion secondary batteries is preferably a lithium salt. Any lithium salt can be used, and specific examples include LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, LiTaF6, LiWF7, LiAsF6, LiAlCl4, LiI, LiBr, LiCl, and LiB 10 Cl 10 Inorganic lithium salts such as Li2SiF6, Li2PFO3, LiPO2F2, etc.; Lithium tungstates such as LiWOF5; Lithium carboxylates such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, CF3CF2CF2CF2CO2Li; Lithium salts having an S=O group, such as FSO3Li, CH3SO3Li, CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, CF3CF2CF2CF2SO3Li, lithium methyl sulfate, lithium ethyl sulfate (C2H5OSO3Li), and lithium 2,2,2-trifluoroethyl sulfate; Lithium imide salts such as LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium bisperfluoroethanesulfonylimide, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, lithium cyclic 1,2-ethanedisulfonylimide, lithium cyclic 1,3-propanedisulfonylimide, lithium cyclic 1,4-perfluorobutanedisulfonylimide, LiN(CF3SO2)(FSO2), LiN(CF3SO2)(C3F7SO2), LiN(CF3SO2)(C4F9SO2), and LiN(POF2)2; Lithium methide salts such as LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3; Other, formula: LiPF a (C n F 2n+1 ) 6-a (wherein a is an integer of 0 to 5, and n is an integer of 1 to 6) (for example, fluorine-containing organic lithium salts such as LiPF3(C2F5)3, LiPF3(CF3)3, LiPF3(iso-C3F7)3, LiPF5(iso-C3F7), LiPF4(CF3)2, LiPF4(C2F5)2), LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2, LiSCN, LiB(CN)4, LiB(C6H5)4, Li2(C2O4), LiP(C2O4)3, Li2B 12 F b H 12-b (b is an integer of 0 to 3), etc.

[0350] Among these, LiPF6, LiBF4, LiSbF6, LiTaF6, LiPO2F2, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, and the like are particularly preferred because they have the effect of improving output characteristics, high-rate charge / discharge characteristics, high-temperature storage characteristics, cycle characteristics, and the like, and at least one lithium salt selected from the group consisting of LiPF6, LiN(FSO2)2, and LiBF4 is most preferred.

[0351] These electrolyte salts may be used alone or in combination of two or more. A preferred example of a combination of two or more is a combination of LiPF6 and LiBF4, or a combination of LiPF6 and LiPO2F2, C2H5OSO3Li or FSO3Li, which has the effect of improving high-temperature storage characteristics, load characteristics and cycle characteristics.

[0352] In this case, there is no limit to the amount of LiBF4, LiPO2F2, C2H5OSO3Li, or FSO3Li blended relative to 100% by mass of the entire liquid electrolyte, and it can be any amount as long as it does not significantly impair the effects of the present disclosure. However, it is usually 0.01% by mass or more, preferably 0.1% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, relative to the liquid electrolyte of the present disclosure.

[0353] Another example is the combined use of an inorganic lithium salt and an organic lithium salt, which has the effect of suppressing deterioration due to high-temperature storage. Preferred organic lithium salts include CF3SO3Li, LiN(FSO2), LiN(FSO2)(CF3SO2), LiN(CF3SO2), LiN(CF2F5SO2), lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, LiC(FSO2), LiC(CF3SO2), LiC(C2F5SO2), LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, and LiPF3(C2F5)3. In this case, the proportion of the organic lithium salt relative to 100% by mass of the entire liquid electrolyte is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, and preferably 30% by mass or less, particularly preferably 20% by mass or less.

[0354] The concentration of these electrolyte salts in the liquid electrolyte is not particularly limited as long as it does not impair the effects of the present disclosure. In order to maintain the electrical conductivity of the liquid electrolyte in a good range and ensure good battery performance, the total molar concentration of lithium in the liquid electrolyte is preferably 0.3 mol / L or more, more preferably 0.4 mol / L or more, even more preferably 0.5 mol / L or more, and is preferably 4.0 mol / L or less, more preferably 3.8 mol / L or less, even more preferably 3.5 mol / L or less.

[0355] If the total molar concentration of lithium is too low, the electrical conductivity of the liquid electrolyte may be insufficient, whereas if the concentration is too high, the electrical conductivity may decrease due to increased viscosity, which may result in reduced battery performance.

[0356] The electrolyte salt of the liquid electrolyte for the electric double layer capacitor is preferably an ammonium salt. The above ammonium salts include the following (IIa) to (IIe). (IIa) Tetraalkyl quaternary ammonium salts General formula (IIa):

[0357] [ka] (In the formula, R 1a , R 2a , R 3a and R 4a are the same or different, and each represents an alkyl group having 1 to 6 carbon atoms which may contain an ether bond; X - is an anion) Preferred examples include tetraalkyl quaternary ammonium salts represented by the following formula: In addition, ammonium salts in which some or all of the hydrogen atoms have been substituted with fluorine atoms and / or fluorine-containing alkyl groups having 1 to 4 carbon atoms are also preferred from the viewpoint of improving oxidation resistance.

[0358] Specific examples include compounds represented by the general formula (IIa-1):

[0359] [ka] (In the formula, R 1a , R 2a and X - is the same as above; x and y are the same or different and are integers of 0 to 4, and x+y=4) tetraalkyl quaternary ammonium salts represented by general formula (IIa-2):

[0360] [ka] (In the formula, R 5a is an alkyl group having 1 to 6 carbon atoms; R 6a is a divalent hydrocarbon group having 1 to 6 carbon atoms; R 7a is an alkyl group having 1 to 4 carbon atoms; z is 1 or 2; X - is an anion) an alkyl ether group-containing trialkylammonium salt represented by the formula: By introducing an alkyl ether group, it is possible to reduce the viscosity.

[0361] Anion X - may be an inorganic anion or an organic anion. Inorganic anions include, for example, AlCl4 - , BF4- , PF6 - , AsF6 - , TaF6 - , I - , SbF6 - Examples of organic anions include bisoxalatoborate anion, difluorooxalatoborate anion, tetrafluorooxalatophosphate anion, difluorobisoxalatophosphate anion, CF3COO - , CF3SO3 - , (CF3SO2)2N - , (C2F5SO2)2N - etc.

[0362] Among these, BF4 is the most popular due to its excellent oxidation resistance and ionic dissociation properties. - , PF6 - , AsF6 - , SbF6 - is preferred.

[0363] Specific preferred examples of tetraalkyl quaternary ammonium salts include EtNBF, EtNClO, EtNPF, EtNAsF, EtNSbF, EtNCFSO, EtN(CFSO)N, EtNCFSO, EtMeNBF, EtMeNClO, EtMeNPF, EtMeNAsF, EtMeNSbF, EtMeNCFSO, EtMeN(CFSO)N, and EtMeNCFSO, and particularly include EtNBF, EtNPF, EtNSbF, EtNAsF, EtMeNBF, and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium salt.

[0364] (IIb) Spirocyclic bipyrrolidinium salts General formula (IIb-1):

[0365] [ka] (In the formula, R 8a and R 9aare the same or different, and each is an alkyl group having 1 to 4 carbon atoms; X - is an anion; n1 is an integer from 0 to 5; n2 is an integer from 0 to 5) spirocyclic bipyrrolidinium salts represented by general formula (IIb-2):

[0366] [ka] (In the formula, R 10a and R 11a are the same or different, and each is an alkyl group having 1 to 4 carbon atoms; X - is an anion; n3 is an integer from 0 to 5; n4 is an integer from 0 to 5) or a spirocyclic bipyrrolidinium salt represented by general formula (IIb-3):

[0367] [ka] (In the formula, R 12a and R 13a are the same or different, and each is an alkyl group having 1 to 4 carbon atoms; X - is an anion; n5 is an integer from 0 to 5; n6 is an integer from 0 to 5) In addition, spirocyclic bipyrrolidinium salts in which some or all of the hydrogen atoms have been substituted with fluorine atoms and / or fluorine-containing alkyl groups having 1 to 4 carbon atoms are also preferred from the viewpoint of improving oxidation resistance.

[0368] Anion X - Preferred examples of (IIa) are the same as those of (IIa). Among them, BF4-, PF6-, (CF3SO2)2N-, or (C2F5SO2)2N- are preferred because of their high dissociation property and low internal resistance under high voltage.

[0369] Preferable specific examples of the spirocyclic bipyrrolidinium salt include, for example, [ka] etc.

[0370] This spirocyclic bipyrrolidinium salt is excellent in solubility in solvents, oxidation resistance, and ionic conductivity.

[0371] (IIc) Imidazolium salts General formula (IIc):

[0372] [ka] (In the formula, R 14a and R 15a are the same or different, and each is an alkyl group having 1 to 6 carbon atoms; X - is an anion) A preferred example is an imidazolium salt represented by the following formula: In addition, imidazolium salts in which some or all of the hydrogen atoms have been substituted with fluorine atoms and / or fluorine-containing alkyl groups having 1 to 4 carbon atoms are also preferred from the viewpoint of improving oxidation resistance.

[0373] Anion X - The preferred examples of (IIa) are the same as those of (IIa).

[0374] Preferred examples include

[0375] [ka] etc.

[0376] This imidazolium salt is excellent in that it has low viscosity and good solubility.

[0377] (IId): N-alkylpyridinium salts General formula (IId):

[0378] [ka] (In the formula, R 16a is an alkyl group having 1 to 6 carbon atoms; X - is an anion) Preferred examples of N-alkylpyridinium salts include those represented by the following formula: A part or all of the hydrogen atoms of the pyridinium salt are replaced with fluorine atoms and / or fluorine-containing atoms having 1 to 4 carbon atoms. Those substituted with alkyl groups are also preferred from the viewpoint of improving oxidation resistance.

[0379] Anion X - The preferred examples of (IIa) are the same as those of (IIa).

[0380] Preferred examples include

[0381] [ka] etc.

[0382] This N-alkylpyridinium salt is excellent in that it has low viscosity and good solubility.

[0383] (IIe) N,N-Dialkylpyrrolidinium Salts General formula (IIe):

[0384] [ka] (In the formula, R 17a and R 18a are the same or different, and each is an alkyl group having 1 to 6 carbon atoms; X - is an anion) Preferred examples include N,N-dialkylpyrrolidinium salts represented by the following formula: Furthermore, N,N-dialkylpyrrolidinium salts in which some or all of the hydrogen atoms have been substituted with fluorine atoms and / or fluorine-containing alkyl groups having 1 to 4 carbon atoms are also preferred from the viewpoint of improving oxidation resistance.

[0385] Anion X - The preferred examples of (IIa) are the same as those of (IIa).

[0386] Preferred examples include

[0387] [ka]

[0388] [ka] etc.

[0389] This N,N-dialkylpyrrolidinium salt is excellent in that it has low viscosity and good solubility.

[0390] Among these ammonium salts, (IIa), (IIb) and (IIc) are preferred in terms of solubility, oxidation resistance and ionic conductivity.

[0391] [ka] (wherein Me is a methyl group; Et is an ethyl group; X - , x and y are the same as in formula (IIa-1) is preferred.

[0392] Furthermore, a lithium salt may be used as the electrolyte salt for the electric double layer capacitor. Preferred examples of the lithium salt include LiPF6, LiBF4, LiN(FSO2)2, LiAsF6, LiSbF6, and LiN(SO2C2H5)2. To further improve the capacity, a magnesium salt may be used, and preferred examples of the magnesium salt include Mg(ClO4)2 and Mg(OOC2H5)2.

[0393] When the electrolyte salt is an ammonium salt, the concentration is preferably 0.7 mol / L or more. If the concentration is less than 0.7 mol / L, not only will the low-temperature characteristics deteriorate but the initial internal resistance may also increase. The concentration of the electrolyte salt is more preferably 0.9 mol / L or more. The upper limit of the concentration is preferably 2.0 mol / L or less, and more preferably 1.5 mol / L or less, from the viewpoint of low-temperature characteristics. When the ammonium salt is triethylmethylammonium tetrafluoroborate (TEMABF4), the concentration is preferably 0.7 to 1.5 mol / L in terms of excellent low-temperature properties. In the case of spirobipyrrolidinium tetrafluoroborate (SBPBF4), the concentration is preferably 0.7 to 2.0 mol / liter.

[0394] The liquid electrolyte of the present disclosure has the general formula (2): [ka] (In the formula, X 21 is a group containing at least H or C, n21 is an integer of 1 to 3, Y 21 and Z 21 are the same or different and are groups containing at least H, C, O or F; n22 is 0 or 1; Y 21 and Z 21 may be bonded to each other to form a ring.) When the liquid electrolyte contains compound (2), the capacity retention rate is more unlikely to decrease and the amount of gas generated is more unlikely to increase, even when stored at high temperatures.

[0395] If n21 is 2 or 3, then 2 or 3 Xs 21 may be the same or different. Y 21 and Z 21 If there are multiple Ys, there are multiple Ys. 21 and Z 21 may be the same or different.

[0396] X 21 As for -CY 21 Z 21 -(In the formula, Y 21 and Z 21 as above) or -CY 21 =CZ 21 -(In the formula, Y 21 and Z21 is as defined above) is preferred.

[0397] Y 21 is preferably at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2- and CF3CF2CF2-. Z 21 is preferably at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2- and CF3CF2CF2-.

[0398] Or Y 21 and Z 21 can be bonded to each other to form a carbocyclic or heterocyclic ring which may contain an unsaturated bond and which may have aromaticity. The number of carbon atoms in the ring is preferably 3 to 20.

[0399] Next, specific examples of compound (2) will be described. In the following examples, the term "analog" is used. refers to an acid anhydride obtained by replacing a part of the structure of the exemplified acid anhydride with another structure within the scope of the present disclosure, and examples thereof include dimers, trimers, tetramers, etc. composed of multiple acid anhydrides, structural isomers such as those having the same number of carbon atoms in the substituent but having a branched chain, and those in which the substituent is bonded to the acid anhydride at a different position.

[0400] Specific examples of acid anhydrides forming a five-membered ring structure include succinic anhydride, methylsuccinic anhydride (4-methylsuccinic anhydride), dimethylsuccinic anhydride (4,4-dimethylsuccinic anhydride, 4,5-dimethylsuccinic anhydride, etc.), 4,4,5-trimethylsuccinic anhydride, 4,4,5,5-tetramethylsuccinic anhydride, 4-vinylsuccinic anhydride, 4,5-divinylsuccinic anhydride, phenylsuccinic anhydride (4-phenylsuccinic anhydride), 4,5-diphenylsuccinic anhydride, Examples of the maleic anhydride include 4,4-diphenylsuccinic anhydride, citraconic anhydride, maleic anhydride, methylmaleic anhydride (4-methylmaleic anhydride), 4,5-dimethylmaleic anhydride, phenylmaleic anhydride (4-phenylmaleic anhydride), 4,5-diphenylmaleic anhydride, itaconic anhydride, 5-methylitaconic anhydride, 5,5-dimethylitaconic anhydride, phthalic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, and the like, and their analogs.

[0401] Specific examples of acid anhydrides forming a 6-membered ring structure include cyclohexanedicarboxylic anhydride (cyclohexane-1,2-dicarboxylic anhydride, etc.), 4-cyclohexene-1,2-dicarboxylic anhydride, glutaric anhydride, glutaconic anhydride, 2-phenylglutaric anhydride, and the like, and their analogs.

[0402] Specific examples of other acid anhydrides forming a cyclic structure include 5-norbornene-2,3-dicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, pyromellitic anhydride, diglycolic anhydride, and the like, and their analogs.

[0403] Specific examples of acid anhydrides that form a cyclic structure and are substituted with a halogen atom include monofluorosuccinic anhydride (4-fluorosuccinic anhydride, etc.), 4,4-difluorosuccinic anhydride, 4,5-difluorosuccinic anhydride, 4,4,5-trifluorosuccinic anhydride, trifluoromethylsuccinic anhydride, tetrafluorosuccinic anhydride (4,4,5,5-tetrafluorosuccinic anhydride), 4-fluoromaleic anhydride, 4,5-difluoromaleic anhydride, trifluoromethylmaleic anhydride, 5-fluoroitaconic anhydride, 5,5-difluoroitaconic anhydride, and analogs thereof.

[0404] Compound (2) may, among others, be glutaric anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, phenylsuccinic anhydride, 2-phenylglutaric anhydride, maleic anhydride, methylmaleic anhydride, trifluoromethyl Preferred are maleic anhydride, phenylmaleic anhydride, succinic anhydride, methylsuccinic anhydride, dimethylsuccinic anhydride, trifluoromethylsuccinic anhydride, monofluorosuccinic anhydride, and tetrafluorosuccinic anhydride, of which maleic anhydride, methylmaleic anhydride, trifluoromethylmaleic anhydride, succinic anhydride, methylsuccinic anhydride, trifluoromethylsuccinic anhydride, and tetrafluorosuccinic anhydride are more preferred, and maleic anhydride and succinic anhydride are even more preferred.

[0405] Compound (2) is represented by the general formula (3):

[0406] [ka] (In the formula, X 31 ~X 34 are the same or different groups containing at least H, C, O or F) and a compound (3) represented by the general formula (4):

[0407] [ka] (In the formula, X 41 and X 42 are the same or different and contain at least H, C, O or F).

[0408] X 31 ~X 34 are the same or different and are preferably at least one selected from the group consisting of an alkyl group, a fluorinated alkyl group, an alkenyl group, and a fluorinated alkenyl group. X 31 ~X 34 The number of carbon atoms is preferably 1 to 10, and more preferably 1 to 3.

[0409] X 31 ~X 34 are the same or different, and are more preferably at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2-, and CF3CF2CF2-.

[0410] X 41 and X 42 are the same or different and are preferably at least one selected from the group consisting of an alkyl group, a fluorinated alkyl group, an alkenyl group, and a fluorinated alkenyl group. 41 and X 42 The number of carbon atoms is preferably 1 to 10, and more preferably 1 to 3.

[0411] X 41 and X 42 are the same or different, and are more preferably at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2-, and CF3CF2CF2-.

[0412] Compound (3) is preferably any one of the following compounds:

[0413] [ka]

[0414] Compound (4) is preferably any one of the following compounds:

[0415] [ka]

[0416] The liquid electrolyte preferably contains 0.0001 to 15% by mass of compound (2) relative to the liquid electrolyte, since this further prevents a decrease in capacity retention and an increase in the amount of gas generated even when stored at high temperatures. The content of compound (2) is more preferably 0.01 to 10% by mass, further preferably 0.1 to 3% by mass, and particularly preferably 0.1 to 1.0% by mass.

[0417] When the liquid electrolyte contains both compounds (3) and (4), the capacity retention rate is less likely to decrease and the amount of gas generated is less likely to increase even when stored at high temperatures. Therefore, the liquid electrolyte preferably contains 0.08 to 2.50 mass% of compound (3) and 0.02 to 1.50 mass% of compound (4), and more preferably contains 0.80 to 2.50 mass% of compound (3) and 0.08 to 1.50 mass% of compound (4), relative to the mass of the liquid electrolyte.

[0418] The liquid electrolyte of the present disclosure may contain at least one selected from the group consisting of nitrile compounds represented by the following general formulas (1a), (1b), and (1c). [ka] (In the formula, R a and R beach independently represents a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms. n represents an integer of 1 to 10. [ka] (In the formula, R c represents a hydrogen atom, a halogen atom, an alkyl group, an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms, or NC-R c1 -X c1 -(R c1 is an alkylene group, X c1 represents an oxygen atom or a sulfur atom. d and R e each independently represents a hydrogen atom, a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms, and m represents an integer of 1 to 10. [ka] (In the formula, R f , R g , R h and R i each independently represents a group containing a cyano group (CN), a hydrogen atom (H), a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms. f , R g , R h and R i At least one of the groups is a group containing a cyano group. l represents an integer of 1 to 3. This can improve the high-temperature storage properties of the electrochemical device.The above nitrile compounds may be used alone or in any combination of two or more kinds in any ratio.

[0419] In the above general formula (1a), R a and R bare each independently a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms. Examples of halogen atoms include fluorine, chlorine, bromine, and iodine atoms, with fluorine being preferred. The alkyl group preferably has a carbon number of 1 to 5. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group. Examples of the alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms include the above-mentioned alkyl groups in which at least some of the hydrogen atoms have been substituted with halogen atoms. a and R b is an alkyl group or an alkyl group in which at least some of the hydrogen atoms are substituted with halogen atoms, R a and R b may be bonded to each other to form a ring structure (for example, a cyclohexane ring). R a and R b is preferably a hydrogen atom or an alkyl group.

[0420] In the above general formula (1a), n is an integer of 1 to 10. When n is 2 or more, n R a may all be the same, or at least some may be different. b The same applies to n. n is preferably an integer of 1 to 7, and more preferably an integer of 2 to 5.

[0421] As the nitrile compound represented by the above general formula (1a), dinitriles and tricarbonitriles are preferred. Specific examples of dinitriles include malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinonitrile, 2,2-dimethylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2,4-dimethylsuccinonitrile, 2,5-dimethylsuccinonitrile, 2,6-dimethylsuccinonitrile, 2,7-dimethylsuccinonitrile, 2,8-dimethylsuccinonitrile, 2,9-dimethylsuccinonitrile, 2,10-dimethylsuccinonitrile, 2,11-dimethylsuccinonitrile, 2,12-dimethylsuccinonitrile, 2,13-dimethylsuccinonitrile, 2,14-dimethylsuccinonitrile, 2,15-dimethylsuccinonitrile, 2,16-dimethylsuccinonitrile, 2,17-dimethylsuccinonitrile, 2,18-dimethylsuccinonitrile, 2,19-dimethylsuccinonitrile, 2,20-dimethylsuccinonitrile, 2,21-dimethylsuccinonitrile, 2,22-dimethylsuccinonitrile, 2,31-dimethylsuccinonitrile, 2,23-dimethylsuccinonitrile, 2,24-dimethylsuccinonitrile, 2,25-dimethylsuccinonitrile, 2,26-dimethylsuccinonitrile, 2,27-dimethylsuccinonitrile, 2,28-dimethylsuccinonitrile, 2,29-dimethylsuccinonitrile, 2,30-dimethylsuccinonitrile, 2,31-dimethylsuccinonitrile, 2, ,3,3-trimethylsuccinonitrile, 2,2,3,3-tetramethylsuccinonitrile, 2,3-diethyl-2,3-dimethylsuccinonitrile, 2,2-diethyl-3,3-dimethylsuccinonitrile, bicyclohexyl-1,1-dicarbonitrile, bicyclohexyl-2,2-dicarbonitrile, bicyclohexyl-3,3-dicarbonitrile, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,3-diisobutyl-2,3- Dimethylsuccinonitrile, 2,2-diisobutyl-3,3-dimethylsuccinonitrile, 2-methylglutaronitrile, 2,3-dimethylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,3,3-tetramethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 2,2,3,4-tetramethylglutaronitrile, 2,3,3,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 2,6-dicyanopentane Examples include cyclohexyl heptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,3'-(ethylenedioxy)dipropionitrile, 3,3'-(ethylenedithio)dipropionitrile, 3,9-bis(2-cyanoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, butanenitrile, phthalonitrile, etc. Among these, succinonitrile, glutaronitrile, and adiponitrile are particularly preferred. Specific examples of tricarbonitrile include pentanetricarbonitrile, propanetricarbonitrile, 1,3,5-hexanetricarbonitrile, 1,3,6-hexanetricarbonitrile, heptanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, cyclohexanetricarbonitrile, triscyanoethylamine, triscyanoethoxypropane, tricyanoethylene, and tris(2-cyanoethyl)amine. Particularly preferred are 1,3,6-hexanetricarbonitrile and cyclohexanetricarbonitrile, and most preferred is cyclohexanetricarbonitrile.

[0422] In the above general formula (1b), R c represents a hydrogen atom, a halogen atom, an alkyl group, an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms, or NC-R c1 -X c1 -(R c1 is an alkylene group, X c1 represents an oxygen atom or a sulfur atom, and R d and R e are each independently a hydrogen atom, a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms. Examples of halogen atoms, alkyl groups, and groups in which at least some of the hydrogen atoms of an alkyl group have been substituted with halogen atoms include those exemplified for the general formula (1a) above. Above NC-R c1 -X c1 -R in c1 is an alkylene group. The alkylene group is preferably an alkylene group having 1 to 3 carbon atoms. R c , R d and R e R are preferably each independently a hydrogen atom, a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms. c , R d and R eAt least one of R is preferably a halogen atom or a group in which at least some of the hydrogen atoms in an alkyl group have been substituted with halogen atoms, and more preferably a fluorine atom or a group in which at least some of the hydrogen atoms in an alkyl group have been substituted with fluorine atoms. d and R e is an alkyl group or an alkyl group in which at least some of the hydrogen atoms are substituted with halogen atoms, R d and R e may be bonded to each other to form a ring structure (for example, a cyclohexane ring).

[0423] In the above general formula (1b), m is an integer of 1 to 10. When m is 2 or more, m R d may all be the same, or at least some may be different. e The same applies to m. m is preferably an integer of 2 to 7, and more preferably an integer of 2 to 5.

[0424] Examples of the nitrile compound represented by the general formula (1b) include acetonitrile, propionitrile, butyronitrile, isobutyronitrile, valeronitrile, isovaleronitrile, lauronitrile, 3-methoxypropionitrile, 2-methylbutyronitrile, trimethylacetonitrile, hexanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, fluoroacetonitrile, difluoroacetonitrile, trifluoroacetonitrile, 2-fluoropropionitrile, 3-fluoropropionitrile, 2,2-difluoropropionitrile, 2,3-difluoropropionitrile, 3,3-difluoropropionitrile, 2,2,3-trifluoropropionitrile, 3,3,3-trifluoropropionitrile, 3,3'-oxydipropionitrile, 3,3'-thiodipropionitrile, pentafluoropropionitrile, methoxyacetonitrile, benzonitrile, etc. Among these, 3,3,3-trifluoropropionitrile is particularly preferred.

[0425] In the above general formula (1c), R f , Rg , R h and R i are each independently a group containing a cyano group (CN), a hydrogen atom, a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms. Examples of halogen atoms, alkyl groups, and groups in which at least some of the hydrogen atoms of an alkyl group have been substituted with halogen atoms include those exemplified for the general formula (1a) above. Examples of groups containing a cyano group include cyano groups and groups in which at least some of the hydrogen atoms of an alkyl group have been substituted with cyano groups. Examples of the alkyl group in this case include those exemplified for the general formula (1a) above. R f , R g , R h and R i At least one of R is a group containing a cyano group. f , R g , R h and R i At least two of R are groups containing a cyano group, and more preferably, R h and R i is a group containing a cyano group. h and R i is a group containing a cyano group, R f and R g is preferably a hydrogen atom.

[0426] In the general formula (1c), l is an integer of 1 to 3. When l is 2 or more, l R f may all be the same, or at least some may be different. g The same applies to l. l is preferably an integer of 1 to 2.

[0427] Examples of the nitrile compound represented by the general formula (1c) include 3-hexenedinitrile, mucononitrile, maleonitrile, fumaronitrile, acrylonitrile, methacrylonitrile, crotononitrile, 3-methylcrotononitrile, 2-methyl-2-butenenitrile, 2-pentenenitrile, 2-methyl-2-pentenenitrile, 3-methyl-2-pentenenitrile, and 2-hexenenitrile, of which 3-hexenedinitrile and mucononitrile are preferred, and 3-hexenedinitrile is particularly preferred.

[0428] The content of the nitrile compounds is preferably 0.2 to 7% by mass relative to the liquid electrolyte. This can further improve the high-temperature storage characteristics and safety of electrochemical devices at high voltages. The lower limit of the total content of the nitrile compounds is more preferably 0.3% by mass, and even more preferably 0.5% by mass. The upper limit is more preferably 5% by mass, even more preferably 2% by mass, and particularly preferably 0.5% by mass.

[0429] The liquid electrolyte of the present disclosure may contain a compound having an isocyanato group (hereinafter, sometimes abbreviated as "isocyanate"). The isocyanate is not particularly limited, and any isocyanate can be used. Examples of isocyanates include monoisocyanates, diisocyanates, and triisocyanates.

[0430] Specific examples of monoisocyanates include isocyanatomethane, isocyanatoethane, 1-isocyanatopropane, 1-isocyanatobutane, 1-isocyanatopentane, 1-isocyanatohexane, 1-isocyanatoheptane, 1-isocyanatooctane, 1-isocyanatononane, 1-isocyanatodecane, isocyanatocyclohexane, methoxycarbonyl isocyanate, ethoxycarbonyl isocyanate, propoxycarbonyl isocyanate, butoxycarbonyl isocyanate, methoxysulfonyl isocyanate, ethoxysulfonyl isocyanate, propoxysulfonyl isocyanate, butoxysulfonyl isocyanate, fluorosulfonyl isocyanate, methyl isocyanate, butyl isocyanate, phenyl isocyanate, 2-isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate, and ethyl isocyanate.

[0431] Specific examples of diisocyanato include 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 1,7-diisocyanatoheptane, 1,8-diisocyanatooctane, 1,9-diisocyanatononane, 1,10-diisocyanatodecane, 1,3-diisocyanatopropene, 1,4-diisocyanato-2-butene, 1,4-diisocyanato-2-fluorobutane, and 1,4-diisocyanato-2,3-difluorobutane. hexane, 1,5-diisocyanato-2-pentene, 1,5-diisocyanato-2-methylpentane, 1,6-diisocyanato-2-hexene, 1,6-diisocyanato-3-hexene, 1,6-diisocyanato-3-fluorohexane, 1,6-diisocyanato-3,4-difluorohexane, toluene diisocyanate, xylene diisocyanate, tolylene diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane (methyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane, 1,4-diisocyanatocyclohexane, dicyclohexylmethane-1,1'-diisocyanate, dicyclohexylmethane-2,2'-diisocyanate, dicyclohexylmethane-3,3'-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate bis(methyl isocyanate), bicyclo[2.2.1]heptane-2,5-diylbis(methyl isocyanate), bicyclo[2.2.1]heptane-2,6-diylbis(methyl isocyanate), 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylene diisocyanate, octamethylene diisocyanate, tetramethylene diisocyanate, and the like.

[0432] Specific examples of triisocyanates include 1,6,11-triisocyanatoundecane, 4-isocyanatomethyl-1,8-octamethylene diisocyanate, 1,3,5-triisocyanatomethylbenzene, 1,3,5-tris(6-isocyanatohex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and 4-(isocyanatomethyl)octamethylene diisocyanate.

[0433] Among these, 1,6-diisocyanatohexane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,3,5-tris(6-isocyanatohex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,4,4-trimethylhexamethylene diisocyanate, and 2,2,4-trimethylhexamethylene diisocyanate are preferred because they are easily available industrially and can keep the production costs of the liquid electrolyte low, and also from a technical viewpoint, they can contribute to the formation of a stable coating structure, and are therefore more preferably used.

[0434] The isocyanate content is not particularly limited and may be any content as long as it does not significantly impair the effects of the present disclosure, but is preferably 0.001% by mass or more and 1.0% by mass or less relative to the liquid electrolyte. When the isocyanate content is above this lower limit, a sufficient effect of improving the cycle characteristics of the nonaqueous liquid electrolyte secondary battery can be achieved. Furthermore, when the isocyanate content is below this upper limit, an increase in the initial resistance of the nonaqueous liquid electrolyte secondary battery can be avoided. The isocyanate content is more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, and more preferably 0.8% by mass or less, even more preferably 0.7% by mass or less, and particularly preferably 0.6% by mass or less.

[0435] The liquid electrolyte of the present disclosure may contain a cyclic sulfonate ester. The cyclic sulfonate ester is not particularly limited, and any cyclic sulfonate ester can be used. Examples of the cyclic sulfonate ester include saturated cyclic sulfonate esters, unsaturated cyclic sulfonate esters, saturated cyclic disulfonate esters, and unsaturated cyclic disulfonate esters.

[0436] Specific examples of saturated cyclic sulfonic acid esters include 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 2-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1,3-butane sultone, 1,4-butane sultone, 1-fluoro-1,4-butane sultone, 2-fluoro-1,4-butane sultone, 3-fluoro-1,4-butane sultone, 4-fluoro-1,4-butane sultone, 1-methyl-1,4-butane sultone, 2-methyl-1,4-butane sultone, 3-methyl-1,4-butane sultone, 4-methyl-1,4-butane sultone, and 2,4-butane sultone.

[0437] Specific examples of the unsaturated cyclic sulfonic acid ester include 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 2-fluoro-1-propene-1,3-sultone, 3-fluoro-1-propene-1,3-sultone, 1-fluoro-2-propene-1,3-sultone, 2-fluoro-2-propene-1,3-sultone, 3-fluoro-2-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, and 2-methyl-1-propene- 1-Butene-1,4-sultone, 2-Butene-1,4-sultone, 3-Butene-1,4-sultone, 1-Fluoro-1-butene-1,4-sultone, 2-Fluoro-1-butene-1,4-sultone, 3-Fluoro-1-butene-1,4-sultone, 4-Fluoro-1-butene-1,4 -sultone, 1-fluoro-2-butene-1,4-sultone, 2-fluoro-2-butene-1,4-sultone, 3-fluoro-2-butene-1,4-sultone, 4-fluoro-2-butene-1,4-sultone, 1,3-propene sultone, 1-fluoro-3-butene-1,4-sultone, 2-fluoro-3-butene-1,4-sultone, 3-fluoro-3-butene-1,4-sultone, 4-fluoro-3-butene-1,4-sultone, 1-methyl-1-butene-1,4-sultone, 2-methyl-1-butene Examples thereof include 1-methyl-1,4-sultone, 3-methyl-1-butene-1,4-sultone, 4-methyl-1-butene-1,4-sultone, 1-methyl-2-butene-1,4-sultone, 2-methyl-2-butene-1,4-sultone, 3-methyl-2-butene-1,4-sultone, 4-methyl-2-butene-1,4-sultone, 1-methyl-3-butene-1,4-sultone, 2-methyl-3-butene-1,4-sultone, 3-methyl-3-butene-1,4-sultone, and 4-methyl-3-butene-14-sultone.

[0438] Among these, 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, and 1-propene-1,3-sultone are more preferably used because they are easily available and can contribute to the formation of a stable coating structure. The content of the cyclic sulfonate ester is not particularly limited and can be any amount as long as it does not significantly impair the effects of the present disclosure, but is preferably 0.001% by mass or more and 3.0% by mass or less with respect to the liquid electrolyte.

[0439] When the content of the cyclic sulfonate ester is equal to or greater than this lower limit, the cycle characteristics of the non-aqueous liquid electrolyte secondary battery can be sufficiently improved. When the content is equal to or less than this upper limit, an increase in the manufacturing cost of the non-aqueous liquid electrolyte secondary battery can be avoided. The content of the cyclic sulfonate ester is more preferably equal to or greater than 0.01% by mass, even more preferably equal to or greater than 0.1% by mass, particularly preferably equal to or greater than 0.2% by mass, and more preferably equal to or less than 2.5% by mass, even more preferably equal to or less than 2.0% by mass, particularly preferably equal to or less than 1.8% by mass.

[0440] The liquid electrolyte of the present disclosure may further contain polyethylene oxide having a weight average molecular weight of 2,000 to 40,000 and having —OH, —OCOOH, or —COOH at its terminal. By including such a compound, the stability of the electrode interface can be improved, and the characteristics of the electrochemical device can be improved. Examples of the polyethylene oxide include polyethylene oxide monool, polyethylene oxide carboxylic acid, polyethylene oxide diol, polyethylene oxide dicarboxylic acid, polyethylene oxide triol, and polyethylene oxide tricarboxylic acid. These may be used alone or in combination of two or more. Among these, a mixture of polyethylene oxide monool and polyethylene oxide diol, and a mixture of polyethylene carboxylic acid and polyethylene dicarboxylic acid are preferred in terms of improving the properties of electrochemical devices.

[0441] If the weight-average molecular weight of the polyethylene oxide is too small, it may be susceptible to oxidative decomposition. The weight-average molecular weight is more preferably 3,000 to 40,000. The weight-average molecular weight can be measured in terms of polystyrene by gel permeation chromatography (GPC).

[0442] The content of the polyethylene oxide in the liquid electrolyte is 1 × 10 -6 ~1×10 -2 If the content of polyethylene oxide is too high, the properties of the electrochemical device may be impaired. The content of the polyethylene oxide is 5 x 10 -6 It is more preferable that it is mol / kg or more.

[0443] The liquid electrolyte of the present disclosure may further contain, as an additive, a fluorinated saturated cyclic carbonate, an unsaturated cyclic carbonate, an overcharge inhibitor, or other known auxiliary agents, etc. This can suppress deterioration of the properties of the electrochemical device.

[0444] Examples of fluorinated saturated cyclic carbonates include compounds represented by the general formula (A) described above. Among them, fluoroethylene carbonate, difluoroethylene carbonate, monofluoromethylethylene carbonate, trifluoromethylethylene carbonate, and 2,2,3,3,3-pentafluoropropylethylene carbonate (4-(2,2,3,3,3-pentafluoropropyl)-[1,3]dioxolan-2-one) are preferred. One type of fluorinated saturated cyclic carbonate may be used alone, or two or more types may be used in any combination and ratio.

[0445] The content of the fluorinated saturated cyclic carbonate is preferably 0.001 to 10% by mass, more preferably 0.01 to 5% by mass, and even more preferably 0.1 to 3% by mass, relative to the liquid electrolyte.

[0446] Examples of unsaturated cyclic carbonates include vinylene carbonates, ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond, phenyl carbonates, vinyl carbonates, allyl carbonates, and catechol carbonates.

[0447] Examples of vinylene carbonates include vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl vinylene carbonate, 4,5-divinyl vinylene carbonate, allyl vinylene carbonate, 4,5-diallyl vinylene carbonate, 4-fluoro vinylene carbonate, 4-fluoro-5-methyl vinylene carbonate, 4-fluoro-5-phenyl vinylene carbonate, 4-fluoro-5-vinyl vinylene carbonate, 4-allyl-5-fluoro vinylene carbonate, ethynyl ethylene carbonate, propargyl ethylene carbonate, methyl vinylene carbonate, and dimethyl vinylene carbonate.

[0448] Specific examples of ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond include vinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, 4-methyl-5-vinyl ethylene carbonate, 4-allyl-5-vinyl ethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, 4-vinyl-5-ethynyl ethylene carbonate, 4-allyl-5-ethynyl ethylene carbonate, Examples of the ethylene carbonate include 4-methyl-5-allylethylene carbonate, 4-methylene-1,3-dioxolan-2-one, 4,5-dimethylene-1,3-dioxolan-2-one, and 4-methyl-5-allylethylene carbonate.

[0449] Among these, preferred unsaturated cyclic carbonates are vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, vinyl vinylene carbonate, 4,5-vinyl vinylene carbonate, allyl vinylene carbonate, 4,5-diallyl vinylene carbonate, vinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, 4-methyl-5-vinyl ethylene carbonate, allyl ethylene carbonate, 4,5-diallyl ethylene carbonate, 4-methyl-5-allyl ethylene carbonate, 4-allyl-5-vinyl ethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, and 4-vinyl-5-ethynyl ethylene carbonate. Furthermore, vinylene carbonate, vinylethylene carbonate, and ethynylethylene carbonate are particularly preferred because they form a more stable interface protective film, with vinylene carbonate being the most preferred.

[0450] The molecular weight of the unsaturated cyclic carbonate is not particularly limited and may be any as long as it does not significantly impair the effects of the present disclosure. The molecular weight is preferably 50 or more and 250 or less. Within this range, the solubility of the unsaturated cyclic carbonate in the liquid electrolyte is easily ensured, and the effects of the present disclosure are easily exhibited. The molecular weight of the unsaturated cyclic carbonate is more preferably 80 or more and more preferably 150 or less.

[0451] The method for producing the unsaturated cyclic carbonate is not particularly limited, and any known method can be selected for production.

[0452] The unsaturated cyclic carbonates may be used alone or in any combination of two or more in any ratio.

[0453] The content of the unsaturated cyclic carbonate is not particularly limited and may be any content as long as it does not significantly impair the effects of the present disclosure. The content of the unsaturated cyclic carbonate is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more, based on 100% by mass of the liquid electrolyte. The content is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. Within the above range, electrochemical devices using the liquid electrolyte are likely to exhibit sufficient improvement in cycle characteristics, and it is also easy to avoid situations such as a decrease in high-temperature storage characteristics, an increase in gas generation, and a decrease in discharge capacity retention rate.

[0454] As the unsaturated cyclic carbonate, in addition to the non-fluorinated unsaturated cyclic carbonates as described above, fluorinated unsaturated cyclic carbonates can also be suitably used. The fluorinated unsaturated cyclic carbonate is a cyclic carbonate having an unsaturated bond and a fluorine atom. The number of fluorine atoms in the fluorinated unsaturated cyclic carbonate is not particularly limited as long as it is 1 or more. Among them, the number of fluorine atoms is usually 6 or less, preferably 4 or less, and most preferably 1 or 2.

[0455] Examples of the fluorinated unsaturated cyclic carbonate include fluorinated vinylene carbonate derivatives and fluorinated ethylene carbonate derivatives substituted with a substituent having an aromatic ring or a carbon-carbon double bond.

[0456] Examples of fluorinated vinylene carbonate derivatives include 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-phenylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, and 4-fluoro-5-vinylvinylene carbonate.

[0457] Examples of fluorinated ethylene carbonate derivatives substituted with a substituent having an aromatic ring or a carbon-carbon double bond include 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-allylethylene carbonate, and 4,5-difluoro-4-vinylethylene carbonate. Examples of the fluorocarbon polymerizable monomer include 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, 4,5-difluoro-4,5-diallylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4,4-difluoro-5-phenylethylene carbonate, and 4,5-difluoro-4-phenylethylene carbonate.

[0458] Among them, examples of fluorinated unsaturated cyclic carbonates include 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-vinylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, and 4,4-difluoro-4-vinylethylene carbonate. Carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-allylethylene carbonate, 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, and 4,5-difluoro-4,5-diallylethylene carbonate are more preferably used because they form stable interface protective coatings.

[0459] The molecular weight of the fluorinated unsaturated cyclic carbonate is not particularly limited and may be any value as long as it does not significantly impair the effects of the present disclosure. The molecular weight is preferably 50 or more and 500 or less. Within this range, the solubility of the fluorinated unsaturated cyclic carbonate in the liquid electrolyte is easily ensured.

[0460] The method for producing the fluorinated unsaturated cyclic carbonate is not particularly limited, and any known method can be selected for production. The molecular weight is more preferably 100 or more and more preferably 200 or less.

[0461] The fluorinated unsaturated cyclic carbonate may be used alone or in any combination and ratio of two or more. The content of the fluorinated unsaturated cyclic carbonate is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present disclosure. The content of the fluorinated unsaturated cyclic carbonate is typically, based on 100% by mass of the liquid electrolyte, preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more, and is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. Within this range, electrochemical devices using the liquid electrolyte are likely to exhibit sufficient improvement in cycle performance, and also to avoid situations such as a decrease in high-temperature storage performance, an increase in gas generation, and a decrease in discharge capacity retention rate.

[0462] The liquid electrolyte of the present disclosure may contain a compound having a triple bond. The type of compound is not particularly limited as long as it has one or more triple bonds in the molecule. Specific examples of the compound having a triple bond include the following compounds: hydrocarbon compounds such as 1-pentyne, 2-pentyne, 1-hexyne, 2-hexyne, 3-hexyne, 1-heptyne, 2-heptyne, 3-heptyne, 1-octyne, 2-octyne, 3-octyne, 4-octyne, 1-nonyne, 2-nonyne, 3-nonyne, 4-nonyne, 1-dodecyne, 2-dodecyne, 3-dodecyne, 4-dodecyne, 5-dodecyne, phenylacetylene, 1-phenyl-1-propyne, 1-phenyl-2-propyne, 1-phenyl-1-butyne, 4-phenyl-1-butyne, 4-phenyl-1-butyne, 1-phenyl-1-pentyne, 5-phenyl-1-pentyne, 1-phenyl-1-hexyne, 6-phenyl-1-hexyne, diphenylacetylene, 4-ethynyltoluene, and dicyclohexylacetylene;

[0463] 2-Propynyl methyl carbonate, 2-propynyl ethyl carbonate, 2-propynyl propyl carbonate, 2-propynyl butyl carbonate, 2-propynyl phenyl carbonate, 2-propynyl cyclohexyl carbonate, di-2-propynyl carbonate, 1-methyl-2-propynyl methyl carbonate, 1,1-dimethyl-2-propynyl methyl carbonate, 2-butynyl methyl carbonate, 3-butynyl methyl carbonate, 2-pentynyl methyl carbonate monocarbonates such as 2-butyne-1,4-diol dimethyl dicarbonate, 2-butyne-1,4-diol diethyl dicarbonate, 2-butyne-1,4-diol dipropyl dicarbonate, 2-butyne-1,4-diol dibutyl dicarbonate, 2-butyne-1,4-diol diphenyl dicarbonate, and 2-butyne-1,4-diol dicyclohexyl dicarbonate;

[0464] 2-Propynyl acetate, 2-Propynyl propionate, 2-Propynyl butyrate, 2-Propynyl benzoate, 2-Propynyl cyclohexylcarboxylate, 1,1-dimethyl-2-propynyl acetate, 1,1-dimethyl-2-propynyl propionate, 1,1-dimethyl-2-propynyl butyrate, 1,1-dimethyl-2-propynyl benzoate, 1,1-dimethyl-2-propynyl cyclohexylcarboxylate, 2-Butynyl acetate, 3-Butynyl acetate, 2-Pentynyl acetate, 3-Pentynyl acetate, 4-Pentynyl acetate, Methyl acrylate, Ethyl acrylate, propyl acrylate, vinyl acrylate, 2-propenyl acrylate, 2-butenyl acrylate, 3-butenyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, vinyl methacrylate, 2-propenyl methacrylate, 2-butenyl methacrylate, 3-butenyl methacrylate, methyl 2-propynoate, ethyl 2-propynoate, propyl 2-propynoate, vinyl 2-propynoate, 2-propenyl 2-propynoate, 2-butenyl 2-propynoate, 3-butenyl 2-propynoate, 2 Methyl 2-butynoate, Ethyl 2-butynoate, Propyl 2-butynoate, Vinyl 2-butynoate, 2-Propenyl 2-butynoate, 2-Butenyl 2-butynoate, 3-Butenyl 2-butynoate, Methyl 3-butynoate, Ethyl 3-butynoate, Propyl 3-butynoate, Vinyl 3-butynoate, 2-Propenyl 3-butynoate, 2-Butenyl 3-butynoate, 3-Butenyl 3-butynoate, Methyl 2-pentynoate, Ethyl 2-pentynoate, Propyl 2-pentynoate, Vinyl 2-pentynoate, 2-Propenyl 2-pentynoate, 2-Butenyl 2-pentynoate monocarboxylic acid esters such as 2-pentynoate, 3-butenyl 2-pentynoate, methyl 3-pentynoate, ethyl 3-pentynoate, propyl 3-pentynoate, vinyl 3-pentynoate, 2-propenyl 3-pentynoate, 2-butenyl 3-pentynoate, 3-butenyl 3-pentynoate, methyl 4-pentynoate, ethyl 4-pentynoate, propyl 4-pentynoate, vinyl 4-pentynoate, 2-propenyl 4-pentynoate, 2-butenyl 4-pentynoate, 3-butenyl 4-pentynoate, fumaric acid esters, methyl trimethylacetate, ethyl trimethylacetate;

[0465] Dicarboxylic acid esters such as 2-butyne-1,4-diol diacetate, 2-butyne-1,4-diol dipropionate, 2-butyne-1,4-diol dibutyrate, 2-butyne-1,4-diol dibenzoate, 2-butyne-1,4-diol dicyclohexanecarboxylate, hexahydrobenzo[1,3,2]dioxathiolan-2-oxide (1,2-cyclohexanediol, 2,2-dioxido-1,2-oxathiolan-4-yl acetate, 2,2-dioxido-1,2-oxathiolan-4-yl acetate, etc.;

[0466] oxalic acid diesters such as methyl 2-propynyl oxalate, ethyl 2-propynyl oxalate, propyl 2-propynyl oxalate, 2-propynyl vinyl oxalate, allyl 2-propynyl oxalate, di-2-propynyl oxalate, 2-butynylmethyl oxalate, 2-butynylethyl oxalate, 2-butynylpropyl oxalate, 2-butynylvinyl oxalate, allyl 2-butynyl oxalate, di-2-butynyl oxalate, 3-butynylmethyl oxalate, 3-butynylethyl oxalate, 3-butynylpropyl oxalate, 3-butynylvinyl oxalate, allyl 3-butynyl oxalate, and di-3-butynyl oxalate;

[0467] Phosphine oxides such as methyl(2-propynyl)(vinyl)phosphine oxide, divinyl(2-propynyl)phosphine oxide, di(2-propynyl)(vinyl)phosphine oxide, di(2-propenyl)2(-propynyl)phosphine oxide, di(2-propynyl)(2-propenyl)phosphine oxide, di(3-butenyl)(2-propynyl)phosphine oxide, and di(2-propynyl)(3-butenyl)phosphine oxide;

[0468] 2-propynyl methyl(2-propenyl)phosphinate, 2-propynyl 2-butenyl(methyl)phosphinate, 2-propynyl di(2-propenyl)phosphinate, 2-propynyl di(3-butenyl)phosphinate, 1,1-dimethyl-2-propynyl methyl(2-propenyl)phosphinate, 1,1-dimethyl-2-propynyl 2-butenyl(methyl)phosphinate, 1,1-dimethyl-2-propynyl di(2-propenyl)phosphinate, and phosphinic acid esters such as 1,1-dimethyl-2-propynyl di(3-butenyl)phosphinate, 2-propenyl methyl(2-propynyl)phosphinate, 3-butenyl methyl(2-propynyl)phosphinate, 2-propenyl di(2-propynyl)phosphinate, 3-butenyl di(2-propynyl)phosphinate, 2-propenyl 2-propynyl(2-propenyl)phosphinate, and 3-butenyl 2-propynyl(2-propenyl)phosphinate;

[0469] Methyl 2-propenylphosphonate, methyl 2-butenylphosphonate (2-propynyl), 2-propenylphosphonic acid (2-propynyl) (2-propenyl), 3-butenylphosphonic acid (3-butenyl) (2-propynyl), 2-propenylphosphonic acid (1,1-dimethyl-2-propynyl) (methyl), 2-butenylphosphonic acid (1,1-dimethyl-2-propynyl) (methyl), 2-propenylphosphonic acid (1,1-dimethyl-2-propynyl) (2-propenyl), and 3-butenylphosphonic acid (3-butenyl) (1,1-dimethyl-2-propynyl), phosphonic acid esters such as ethylphosphonic acid (2-propynyl) (2-propenyl), methylphosphonic acid (3-butenyl) (2-propynyl), methylphosphonic acid (1,1-dimethyl-2-propynyl) (2-propenyl), methylphosphonic acid (3-butenyl) (1,1-dimethyl-2-propynyl), ethylphosphonic acid (2-propynyl) (2-propenyl), ethylphosphonic acid (3-butenyl) (2-propynyl), ethylphosphonic acid (1,1-dimethyl-2-propynyl) (2-propenyl), and ethylphosphonic acid (3-butenyl) (1,1-dimethyl-2-propynyl);

[0470] phosphate esters such as (methyl)(2-propenyl)(2-propynyl)phosphate, (ethyl)(2-propenyl)(2-propynyl)phosphate, (2-butenyl)(methyl)(2-propynyl)phosphate, (2-butenyl)(ethyl)(2-propynyl)phosphate, (1,1-dimethyl-2-propynyl)(methyl)(2-propenyl)phosphate, (1,1-dimethyl-2-propynyl)(ethyl)(2-propenyl)phosphate, (2-butenyl)(1,1-dimethyl-2-propynyl)(methyl)phosphate, and (2-butenyl)(ethyl)(1,1-dimethyl-2-propynyl)phosphate;

[0471] Among these, compounds having an alkynyloxy group are preferred because they form a more stable negative electrode coating in the liquid electrolyte.

[0472] Furthermore, compounds such as 2-propynyl methyl carbonate, di-2-propynyl carbonate, 2-butyne-1,4-diol dimethyl dicarbonate, 2-propynyl acetate, 2-butyne-1,4-diol diacetate, methyl 2-propynyl oxalate, and di-2-propynyl oxalate are particularly preferred in terms of improving storage properties.

[0473] The triple bond-containing compound may be used alone or in any combination and ratio of two or more. The amount of the triple bond-containing compound relative to the total amount of the liquid electrolyte of the present disclosure is not limited, and may be any amount as long as it does not significantly impair the effects of the present disclosure. The triple bond-containing compound is typically contained in a concentration of 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and typically 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less, relative to the liquid electrolyte of the present disclosure. When the above ranges are satisfied, the effects of output characteristics, load characteristics, cycle characteristics, high-temperature storage characteristics, etc. are further improved.

[0474] In the liquid electrolyte of the present disclosure, an overcharge inhibitor can be used to effectively prevent the battery from exploding or catching fire when an electrochemical device using the liquid electrolyte is overcharged or the like.

[0475] Examples of the overcharge inhibitor include unsubstituted or alkyl group-substituted terphenyl derivatives such as biphenyl, o-terphenyl, m-terphenyl, and p-terphenyl, partially hydrogenated unsubstituted or alkyl group-substituted terphenyl derivatives, aromatic compounds such as cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, diphenylcyclohexane, 1,1,3-trimethyl-3-phenylindane, cyclopentylbenzene, cyclohexylbenzene, cumene, 1,3-diisopropylbenzene, 1,4-diisopropylbenzene, t-butylbenzene, t-amylbenzene, t-hexylbenzene, and anisole; and aromatic compounds such as 2-fluorobiphenyl, 4-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, and cyclohexyl benzene. Examples of the aromatic hydrocarbon derivative include partially fluorinated compounds of the above aromatic compounds such as xylfluorobenzene, fluorobenzene, fluorotoluene, and benzotrifluoride; fluorine-containing anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 1,6-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; aromatic acetates such as 3-propylphenyl acetate, 2-ethylphenyl acetate, benzylphenyl acetate, methylphenyl acetate, benzyl acetate, and phenethylphenyl acetate; aromatic carbonates such as diphenyl carbonate and methylphenyl carbonate; toluene derivatives such as toluene and xylene; and unsubstituted or alkyl group-substituted biphenyl derivatives such as 2-methylbiphenyl, 3-methylbiphenyl, 4-methylbiphenyl, and o-cyclohexylbiphenyl. Among these, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran, diphenylcyclohexane, 1,1,3-trimethyl-3-phenylindane, 3-propylphenyl acetate, 2-ethylphenyl acetate, benzylphenyl acetate, methylphenyl acetate, benzyl acetate, diphenyl carbonate, and methylphenyl carbonate are preferred.These may be used alone or in combination of two or more. When two or more are used in combination, it is particularly preferred to use a combination of cyclohexylbenzene with t-butylbenzene or t-amylbenzene, or a combination of at least one selected from oxygen-free aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, and t-amylbenzene with at least one selected from oxygen-containing aromatic compounds such as diphenyl ether and dibenzofuran, in terms of the balance between overcharge prevention properties and high-temperature storage properties.

[0476] The liquid electrolyte used in the battery of the present disclosure may be a carboxylic acid anhydride (excluding compound (2)). A compound represented by the following general formula (6) is preferred. The method for producing the carboxylic acid anhydride is not particularly limited, and any known method can be selected for production.

[0477] [ka] (In general formula (6), R 61 , R 62 each independently represents a hydrocarbon group having 1 to 15 carbon atoms, which may have a substituent.

[0478] R 61 , R 62 is not particularly limited in type as long as it is a monovalent hydrocarbon group. For example, it may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, or may be a group in which an aliphatic hydrocarbon group and an aromatic hydrocarbon group are bonded. The aliphatic hydrocarbon group may be a saturated hydrocarbon group or may contain an unsaturated bond (a carbon-carbon double bond or a carbon-carbon triple bond). Furthermore, the aliphatic hydrocarbon group may be either chain-like or cyclic, and if it is chain-like, it may be linear or branched. Furthermore, it may be a group in which a chain-like group and a cyclic group are bonded. In addition, R 61 and R 62 may be the same as or different from each other.

[0479] Also, R61 , R 62 When the hydrocarbon group has a substituent, the type of the substituent is not particularly limited as long as it does not contradict the spirit of the present disclosure, but examples include halogen atoms such as fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms, preferably fluorine atoms. Alternatively, examples of the substituent other than halogen atoms include substituents having functional groups such as ester groups, cyano groups, carbonyl groups, and ether groups, preferably cyano groups and carbonyl groups. 61 , R 62 The hydrocarbon group may have only one of these substituents or may have two or more of these substituents. When the hydrocarbon group has two or more substituents, the substituents may be the same or different from each other.

[0480] R 61 , R 62 The number of carbon atoms in each hydrocarbon group of R is usually 1 or more, and usually 15 or less, preferably 12 or less, more preferably 10 or less, and even more preferably 9 or less. 1 and R 2 When R and R are bonded to each other to form a divalent hydrocarbon group, the number of carbon atoms in the divalent hydrocarbon group is usually 1 or more and usually 15 or less, preferably 13 or less, more preferably 10 or less, and even more preferably 8 or less. 61 , R 62 If the hydrocarbon group has a substituent containing a carbon atom, the substituent is included in R 61 , R 62 It is preferable that the total number of carbon atoms falls within the above range.

[0481] Next, specific examples of acid anhydrides represented by the above general formula (6) will be described. In the following examples, the term "analog" refers to an acid anhydride obtained by replacing a part of the structure of the exemplified acid anhydride with another structure within the scope of the present disclosure, and examples thereof include a dimer, trimer, tetramer, etc. composed of multiple acid anhydrides, structural isomers such as those having the same number of carbon atoms in the substituent but having a branched chain, and those in which the substituent is bonded to the acid anhydride at a different position.

[0482] First, R 61 , R 62 Specific examples of acid anhydrides in which are the same are listed below.

[0483] R 61 , R 62 is a chain alkyl group, examples of which include acetic anhydride, propionic anhydride, butanoic anhydride, 2-methylpropionic anhydride, 2,2-dimethylpropionic anhydride, 2-methylbutanoic anhydride, 3-methylbutanoic anhydride, 2,2-dimethylbutanoic anhydride, 2,3-dimethylbutanoic anhydride, 3,3-dimethylbutanoic anhydride, 2,2,3-trimethylbutanoic anhydride, 2,3,3-trimethylbutanoic anhydride, 2,2,3,3-tetramethylbutanoic anhydride, 2-ethylbutanoic anhydride, and the like, as well as analogs thereof.

[0484] R 61 , R 62 Specific examples of acid anhydrides in which is a cyclic alkyl group include cyclopropanecarboxylic anhydride, cyclopentanecarboxylic anhydride, cyclohexanecarboxylic anhydride, and the like, and analogs thereof.

[0485] R 61 , R 62 is an alkenyl group, acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, 2,3-dimethylacrylic anhydride, 3,3-dimethylacrylic anhydride, 2,3,3-trimethylacrylic anhydride, 2-phenylacrylic anhydride, 3-phenylacrylic anhydride, 2,3-diphenylacrylic anhydride, 3,3-diphenylacrylic anhydride, 3-butenoic anhydride, 2-methyl-3-butenoic anhydride, 2,2-dimethyl-3-butenoic anhydride, 3-methyl-3-enoic anhydride, 2-methyl-3-methyl-3-butenoic anhydride, 2,2-dimethyl-3-methyl-3-butenoic anhydride, 3-pentenoic anhydride, 4-pentenoic anhydride, 2-cyclopentenecarboxylic anhydride, 3-cyclopentenecarboxylic anhydride, 4-cyclopentenecarboxylic anhydride, and the like, and analogs thereof.

[0486] R 61 , R 62 Specific examples of acid anhydrides in which is an alkynyl group include propynoic anhydride, 3-phenylpropynoic anhydride, 2-butynoic anhydride, 2-pentynoic anhydride, 3-butynoic anhydride, 3-pentynoic anhydride, 4-pentynoic anhydride, and analogs thereof.

[0487] R 61 , R 62 is an aryl group, include benzoic anhydride, 4-methylbenzoic anhydride, 4-ethylbenzoic anhydride, 4-tert-butylbenzoic anhydride, 2-methylbenzoic anhydride, 2,4,6-trimethylbenzoic anhydride, 1-naphthalenecarboxylic anhydride, 2-naphthalenecarboxylic anhydride, and analogs thereof.

[0488] Also, R 61 , R 62 As examples of acid anhydrides in which the halogen atoms are substituted, examples of acid anhydrides in which the halogen atoms are substituted mainly with fluorine atoms are given below, but acid anhydrides obtained by substituting some or all of these fluorine atoms with chlorine atoms, bromine atoms, or iodine atoms are also included in the exemplified compounds.

[0489] R 61 , R 62 is a chain alkyl group substituted with a halogen atom, examples of which include fluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, 2-fluoropropionic anhydride, 2,2-difluoropropionic anhydride, 2,3-difluoropropionic anhydride, 2,2,3-trifluoropropionic anhydride, 2,3,3-trifluoropropionic anhydride, 2,2,3,3-tetrapropionic anhydride, 2,3,3,3-tetrapropionic anhydride, 3-fluoropropionic anhydride, 3,3-difluoropropionic anhydride, 3,3,3-trifluoropropionic anhydride, perfluoropropionic anhydride, and analogs thereof.

[0490] R 61 , R 62Examples of acid anhydrides in which is a cyclic alkyl group substituted with a halogen atom include 2-fluorocyclopentanecarboxylic anhydride, 3-fluorocyclopentanecarboxylic anhydride, 4-fluorocyclopentanecarboxylic anhydride, and the like, and their analogs.

[0491] R 61 , R 62 Examples of acid anhydrides in which is an alkenyl group substituted with a halogen atom include 2-fluoroacrylic anhydride, 3-fluoroacrylic anhydride, 2,3-difluoroacrylic anhydride, 3,3-difluoroacrylic anhydride, 2,3,3-trifluoroacrylic anhydride, 2-(trifluoromethyl)acrylic anhydride, 3-(trifluoromethyl)acrylic anhydride, 2,3-bis(trifluoromethyl)acrylic anhydride, 2,3,3-tris(trifluoromethyl)acrylic anhydride, 2-(4-fluoroacrylic anhydride), Examples of the fluorophenyl acrylic anhydride include 2-fluoro-3-butenoic anhydride, 3-(4-fluorophenyl)acrylic anhydride, 2,3-bis(4-fluorophenyl)acrylic anhydride, 3,3-bis(4-fluorophenyl)acrylic anhydride, 2-fluoro-3-butenoic anhydride, 2,2-difluoro-3-butenoic anhydride, 3-fluoro-2-butenoic anhydride, 4-fluoro-3-butenoic anhydride, 3,4-difluoro-3-butenoic anhydride, 3,3,4-trifluoro-3-butenoic anhydride, and the like, as well as analogs thereof.

[0492] R 61 , R 62 is an alkynyl group substituted with a halogen atom, examples of which include 3-fluoro-2-propynoic anhydride, 3-(4-fluorophenyl)-2-propynoic anhydride, 3-(2,3,4,5,6-pentafluorophenyl)-2-propynoic anhydride, 4-fluoro-2-butynoic anhydride, 4,4-difluoro-2-butynoic anhydride, 4,4,4-trifluoro-2-butynoic anhydride, and analogs thereof.

[0493] R 61 , R 62Examples of acid anhydrides in which is an aryl group substituted with a halogen atom include 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, 4-trifluoromethylbenzoic anhydride, and the like, and analogs thereof.

[0494] R 61 , R 62 Examples of acid anhydrides having a substituent with a functional group such as an ester, a nitrile, a ketone, or an ether include methoxyformic anhydride, ethoxyformic anhydride, methyloxalic anhydride, ethyloxalic anhydride, 2-cyanoacetic anhydride, 2-oxopropionic anhydride, 3-oxobutanoic anhydride, 4-acetylbenzoic anhydride, methoxyacetic anhydride, 4-methoxybenzoic anhydride, and the like, and their analogs.

[0495] Next, R 61 , R 62 Specific examples of acid anhydrides having different groups are listed below.

[0496] R 61 , R 62 Although all combinations of the above-mentioned examples and their analogues are conceivable, representative examples are given below.

[0497] Examples of combinations of chain alkyl groups include acetic acid propionic anhydride, acetic acid butanoic anhydride, butanoic acid propionic anhydride, and acetic acid 2-methylpropionic anhydride.

[0498] Examples of the combination of a chain alkyl group and a cyclic alkyl group include acetic acid cyclopentanoic anhydride, acetic acid cyclohexanoic anhydride, and cyclopentanoic acid propionic anhydride.

[0499] Examples of the combination of a chain alkyl group and an alkenyl group include acetic acid acrylic anhydride, acetic acid 3-methylacrylic anhydride, acetic acid 3-butenoic anhydride, and acrylic acid propionic anhydride.

[0500] Examples of the combination of a chain alkyl group and an alkynyl group include acetic acid propynoic anhydride, acetic acid 2-butynoic anhydride, acetic acid 3-butynoic anhydride, acetic acid 3-phenylpropynoic anhydride, and propionic acid propynoic anhydride.

[0501] Examples of the combination of a chain alkyl group and an aryl group include acetic acid benzoic anhydride, acetic acid 4-methylbenzoic anhydride, acetic acid 1-naphthalenecarboxylic anhydride, and benzoic acid propionic anhydride.

[0502] Examples of combinations of a chain alkyl group and a hydrocarbon group having a functional group include acetic acid fluoroacetic anhydride, acetic acid trifluoroacetic anhydride, acetic acid 4-fluorobenzoic anhydride, fluoroacetic acid propionic anhydride, acetic acid alkyl oxalic anhydride, acetic acid 2-cyanoacetic anhydride, acetic acid 2-oxopropionic anhydride, acetic acid methoxyacetic anhydride, and methoxyacetic acid propionic anhydride.

[0503] Examples of combinations of cyclic alkyl groups include cyclopentanoic acid and cyclohexanoic acid anhydride.

[0504] Examples of combinations of a cyclic alkyl group and an alkenyl group include acrylic acid cyclopentanoic anhydride, 3-methylacrylic acid cyclopentanoic anhydride, 3-butenoic acid cyclopentanoic anhydride, and acrylic acid cyclohexanoic anhydride.

[0505] Examples of the combination of a cyclic alkyl group and an alkynyl group include propynoic cyclopentanoic anhydride, 2-butynoic cyclopentanoic anhydride, and propynoic cyclohexanoic anhydride.

[0506] Examples of the combination of a cyclic alkyl group and an aryl group include benzoic acid cyclopentanoic acid anhydride, 4-methylbenzoic acid cyclopentanoic acid anhydride, and benzoic acid cyclohexanoic acid anhydride.

[0507] Examples of combinations of a cyclic alkyl group and a hydrocarbon group having a functional group include cyclopentanoic fluoroacetic anhydride, cyclopentanoic trifluoroacetic anhydride, cyclopentanoic 2-cyanoacetic anhydride, cyclopentanoic methoxyacetic anhydride, and cyclohexanoic fluoroacetic anhydride.

[0508] Examples of combinations of alkenyl groups include acrylic acid 2-methylacrylic anhydride, acrylic acid 3-methylacrylic anhydride, acrylic acid 3-butenoic anhydride, and 2-methylacrylic acid 3-methylacrylic anhydride.

[0509] Examples of the combination of an alkenyl group and an alkynyl group include acrylic acid propynoic anhydride, acrylic acid 2-butynoic anhydride, and 2-methylacrylic acid propynoic anhydride.

[0510] Examples of combinations of an alkenyl group and an aryl group include acrylic acid benzoic acid anhydride, acrylic acid 4-methylbenzoic acid anhydride, and 2-methylacrylic acid benzoic acid anhydride.

[0511] Examples of combinations of an alkenyl group and a hydrocarbon group having a functional group include acrylic fluoroacetic anhydride, acrylic trifluoroacetic anhydride, acrylic 2-cyanoacetic anhydride, acrylic methoxyacetic anhydride, and 2-methylacrylic fluoroacetic anhydride.

[0512] Examples of combinations of alkynyl groups include propynoic acid 2-butynoic acid anhydride, propynoic acid 3-butynoic acid anhydride, and 2-butynoic acid 3-butynoic acid anhydride.

[0513] Examples of a combination of an alkynyl group and an aryl group include benzoic acid propynoic anhydride, 4-methylbenzoic acid propynoic anhydride, and benzoic acid 2-butynoic anhydride.

[0514] Examples of the combination of an alkynyl group and a hydrocarbon group having a functional group include propynoic acid fluoroacetic anhydride, propynoic acid trifluoroacetic anhydride, propynoic acid 2-cyanoacetic anhydride, propynoic acid methoxyacetic anhydride, and 2-butynoic acid fluoroacetic anhydride.

[0515] Examples of combinations of aryl groups include benzoic acid 4-methylbenzoic acid anhydride, benzoic acid 1-naphthalenecarboxylic acid anhydride, and 4-methylbenzoic acid 1-naphthalenecarboxylic acid anhydride.

[0516] Examples of the combination of an aryl group and a hydrocarbon group having a functional group include benzoic acid fluoroacetic anhydride, benzoic acid trifluoroacetic anhydride, benzoic acid 2-cyanoacetic anhydride, benzoic acid methoxyacetic anhydride, and 4-methylbenzoic acid fluoroacetic anhydride.

[0517] Examples of combinations of hydrocarbon groups having functional groups include fluoroacetic acid trifluoroacetic anhydride, fluoroacetic acid 2-cyanoacetic anhydride, fluoroacetic acid methoxyacetic anhydride, and trifluoroacetic acid 2-cyanoacetic anhydride.

[0518] Among the acid anhydrides forming the chain structure, preferred are acetic anhydride, propionic anhydride, 2-methylpropionic anhydride, cyclopentanecarboxylic anhydride, cyclohexanecarboxylic anhydride, acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, 2,3-dimethylacrylic anhydride, 3,3-dimethylacrylic anhydride, 3-butenoic anhydride, 2-methyl-3-butenoic anhydride, propynoic anhydride, 2-butynoic anhydride, benzoic anhydride, 2-methylbenzoic anhydride, 4-methylbenzoic anhydride, 4-tert-butylbenzoic anhydride, trifluoroacetic anhydride, 3,3,3-trifluoroacetic anhydride, 2-methyl-3-butenoic ... Examples of the acrylic anhydride include fluoropropionic anhydride, 2-(trifluoromethyl)acrylic anhydride, 2-(4-fluorophenyl)acrylic anhydride, 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, methoxyformic anhydride, and ethoxyformic anhydride, and more preferably, acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, benzoic anhydride, 2-methylbenzoic anhydride, 4-methylbenzoic anhydride, 4-tert-butylbenzoic anhydride, 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, methoxyformic anhydride, and ethoxyformic anhydride.

[0519] These compounds are preferred from the viewpoint that they can appropriately form bonds with the lithium oxalate salt to form a coating having excellent durability, thereby improving the charge / discharge rate characteristics, input / output characteristics, and impedance characteristics, particularly after a durability test.

[0520] The molecular weight of the carboxylic acid anhydride is not limited and may be any value as long as it does not significantly impair the effects of the present disclosure, but is usually at least 90, preferably at least 95, and usually at most 300, preferably at most 200. When the molecular weight of the carboxylic acid anhydride is within the above range, an increase in the viscosity of the liquid electrolyte can be suppressed, and the film density can be optimized, thereby appropriately improving durability.

[0521] The method for producing the carboxylic acid anhydride is not particularly limited, and any known method can be selected for production. The nonaqueous liquid electrolyte of the present disclosure may contain any one of the above-described carboxylic acid anhydrides alone, or may contain two or more of them in any combination and ratio.

[0522] The content of the carboxylic acid anhydride in the liquid electrolyte of the present disclosure is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present disclosure, but it is desirable to include it in a concentration of typically 0.01% by mass or more, preferably 0.1% by mass or more, and typically 5% by mass or less, preferably 3% by mass or less, relative to the liquid electrolyte of the present disclosure. When the content of the carboxylic acid anhydride is within the above range, the effect of improving cycle characteristics is easily exhibited, and the battery characteristics are easily improved due to suitable reactivity.

[0523] Other known auxiliary agents can be used in the liquid electrolyte of the present disclosure, such as hydrocarbon compounds such as pentane, heptane, octane, nonane, decane, cycloheptane, benzene, furan, naphthalene, 2-phenylbicyclohexyl, cyclohexane, 2,4,8,10-tetraoxaspiro[5.5]undecane, and 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane; Fluorine-containing aromatic compounds such as fluorobenzene, difluorobenzene, hexafluorobenzene, benzotrifluoride, monofluorobenzene, 1-fluoro-2-cyclohexylbenzene, 1-fluoro-4-tert-butylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-2-cyclohexylbenzene, and fluorinated biphenyls; Carbonate compounds such as erythritan carbonate, spiro-bis-dimethylene carbonate, and methoxyethyl-methyl carbonate; Ether compounds such as dioxolane, dioxane, 2,5,8,11-tetraoxadodecane, 2,5,8,11,14-pentaoxapentadecane, ethoxymethoxyethane, trimethoxymethane, glyme, and ethyl monoglyme; Ketone compounds such as dimethyl ketone, diethyl ketone, and 3-pentanone; Acid anhydrides such as 2-allylsuccinic anhydride; Ester compounds such as dimethyl oxalate, diethyl oxalate, ethyl methyl oxalate, di(2-propynyl) oxalate, methyl 2-propynyl oxalate, dimethyl succinate, di(2-propynyl) glutarate, methyl formate, ethyl formate, 2-propynyl formate, 2-butyne-1,4-diyl diformate, 2-propynyl methacrylate, and dimethyl malonate; Amide compounds such as acetamide, N-methylformamide, N,N-dimethylformamide, and N,N-dimethylacetamide; Ethylene sulfate, vinylene sulfate, ethylene sulfite, methyl fluorosulfonate, ethyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfan, sulfolene, diphenyl sulfone, N,N-dimethylmethanesulfonamide, N,N-diethylmethanesulfonamide, methyl vinylsulfonate, ethyl vinylsulfonate, allyl vinylsulfonate, propargyl vinylsulfonate, methyl allylsulfonate, ethyl allylsulfonate, allyl allylsulfonate, propargyl allylsulfonate, 1,2-bis(vinylsulfonyloxy)ethane, propanedisulfonic anhydride, sulfobutyric anhydride, sulfobenzoic anhydride, sulfopropionic anhydride, ethanedisulfonic anhydride, methylenemethanedisulfonate, 2-propynyl methanesulfonate, pentenesulfite, pentafluorophenylmethanesulfonate, propylene sulfate, propylene sulfite, propane sultone, butylene sulfite, butane-2,3-diyldimethanesulfonate, 2-butyne-1,4-diyldimethanesulfonate, 2-propynyl vinylsulfonate, bis(2-vinylsulfonylethyl) ether, 5-vinyl-hexahydro-1,3,2-benzodioxathiol-2-oxide, 2-propynyl 2-(methanesulfonyloxy)propionate, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxy sulfur-containing compounds such as 3-sulfo-propionic anhydride, trimethylenemethane disulfonate, 2-methyltetrahydrofuran, trimethylenemethane disulfonate, tetramethylene sulfoxide, dimethylenemethane disulfonate, difluoroethyl methyl sulfone, divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane, ethylenebismethyl sulfonate, ethylenebisethyl sulfonate, ethylene sulfate, and thiophene 1-oxide; Nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide, nitromethane, nitroethane, and ethylenediamine; Trimethyl phosphite, triethyl phosphite, triphenyl phosphite, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, diethyl ethylphosphonate, dimethyl vinylphosphonate, diethyl vinylphosphonate, ethyl diethylphosphonoacetate, methyl dimethylphosphinate, ethyl diethylphosphinate, trimethylphosphine oxide, triethylphosphine oxide, bis(2,2-difluoroethyl) 2,2,2-trifluoroethyl phosphate, bis(2,2,3,3-tetrafluoroethyl) phosphate Bis(2,2,2-trifluoroethyl) 2,2,2-trifluoroethyl phosphate, bis(2,2,2-trifluoroethyl)methyl phosphate, bis(2,2,2-trifluoroethyl)ethyl phosphate, bis(2,2,2-trifluoroethyl) 2,2-difluoroethyl phosphate, bis(2,2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl phosphate, tributyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(1,1,1,3,3,3-hexafluoropropan-2-yl) phosphate, trioctyl phosphate, 2-phenyl phosphate Nylphenyldimethyl, 2-phenylphenyldiethyl phosphate, (2,2,2-trifluoroethyl)(2,2,3,3-tetrafluoropropyl)methyl phosphate, methyl 2-(dimethoxyphosphoryl)acetate, methyl 2-(dimethylphosphoryl)acetate, methyl 2-(diethoxyphosphoryl)acetate, methyl 2-(diethylphosphoryl)acetate, methyl methylenebisphosphonate, ethyl methylenebisphosphonate, methyl ethylenebisphosphonate, ethyl ethylenebisphosphonate, methyl butylenebisphosphonate Phosphorus-containing compounds such as ethyl butylenebisphosphonate, 2-propynyl 2-(dimethoxyphosphoryl) acetate, 2-propynyl 2-(dimethylphosphoryl) acetate, 2-propynyl 2-(diethoxyphosphoryl) acetate, 2-propynyl 2-(diethylphosphoryl) acetate, tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tris(trimethoxysilyl) phosphate, tris(trimethylsilyl) phosphite, tris(triethylsilyl) phosphite, tris(trimethoxysilyl) phosphite, and trimethylsilyl polyphosphate; Boron-containing compounds such as tris(trimethylsilyl) borate and tris(trimethoxysilyl) borate; silane compounds such as dimethoxyaluminoxytrimethoxysilane, diethoxyaluminoxytriethoxysilane, dipropoxyaluminoxytriethoxysilane, dibutoxyaluminoxytrimethoxysilane, dibutoxyaluminoxytriethoxysilane, titanium tetrakis(trimethylsiloxide), titanium tetrakis(triethylsiloxide), and tetramethylsilane; These may be used alone or in combination of two or more. The addition of these auxiliary agents can improve the capacity retention and cycle characteristics after high-temperature storage. Among these other auxiliary agents, phosphorus-containing compounds are preferred, and tris(trimethylsilyl) phosphate and (tristrimethylsilyl) phosphite are preferred.

[0524] The amount of the other auxiliary agents is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present disclosure. The amount of the other auxiliary agents is preferably 0.01% by mass or more and 5% by mass or less, based on 100% by mass of the liquid electrolyte. Within this range, the effects of the other auxiliary agents are easily exerted, and it is easy to avoid a deterioration in battery characteristics such as high-load discharge characteristics. The amount of the other auxiliary agents is more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and more preferably 3% by mass or less, even more preferably 1% by mass or less.

[0525] The liquid electrolyte used in the battery of the present disclosure may further contain additives such as cyclic and chain carboxylic acid esters, ether compounds, nitrogen-containing compounds, boron-containing compounds, organosilicon-containing compounds, non-flammable (flame retardant) agents, surfactants, high-dielectric additives, cycle performance and rate performance improvers, and sulfone-based compounds, within the scope that does not impair the effects of the present disclosure.

[0526] Examples of the cyclic carboxylic acid ester include those having a total carbon atom number of 3 to 12 in the structural formula. Specific examples include gamma-butyrolactone, gamma-valerolactone, gamma-caprolactone, epsilon-caprolactone, 3-methyl-γ-butyrolactone, etc. Among these, gamma-butyrolactone is particularly preferred from the viewpoint of improving the characteristics of electrochemical devices due to an improved degree of lithium ion dissociation.

[0527] The amount of the cyclic carboxylic acid ester blended as an additive is typically preferably 0.1% by mass or more, more preferably 1% by mass or more, based on 100% by mass of the solvent. Within this range, the electrical conductivity of the liquid electrolyte is improved, and the large-current discharge characteristics of the electrochemical device are likely to be improved. Furthermore, the amount of the cyclic carboxylic acid ester blended is preferably 10% by mass or less, more preferably 5% by mass or less. By setting the upper limit in this way, the viscosity of the liquid electrolyte is kept within an appropriate range, a decrease in electrical conductivity is avoided, an increase in negative electrode resistance is suppressed, and the large-current discharge characteristics of the electrochemical device are likely to be within a favorable range.

[0528] Furthermore, as the cyclic carboxylic acid ester, a fluorinated cyclic carboxylic acid ester (fluorine-containing lactone) can also be suitably used. Examples of the fluorine-containing lactone include those represented by the following formula (C):

[0529] [ka]

[0530] (In the formula, X 15 ~X 20 are the same or different and are each -H, -F, -Cl, -CH3, or a fluorinated alkyl group; provided that X 15 ~X 20 at least one of which is a fluorinated alkyl group) is mentioned.

[0531] X 15 ~X 20Examples of the fluorinated alkyl group in include -CFH2, -CF2H, -CF3, -CH2CF3, -CF2CF3, -CH2CF2CF3, -CF(CF3)2, and the like, with -CH2CF3 and -CH2CF2CF3 being preferred due to their high oxidation resistance and safety-improving effect.

[0532] X 15 ~X 20 is a fluorinated alkyl group, -H, -F, -Cl, -CH3 or a fluorinated alkyl group is 15 ~X 20 The substitution may be at only one position or at multiple positions, preferably 1 to 3 positions, more preferably 1 to 2 positions, in view of good solubility of the electrolyte salt.

[0533] The substitution position of the fluorinated alkyl group is not particularly limited, but X is preferred because it provides a good synthesis yield. 17 and / or X 18 But especially X 17 or X 18 is preferably a fluorinated alkyl group, particularly -CH2CF3 or -CH2CF2CF3. X other than a fluorinated alkyl group 15 ~X 20 is -H, -F, -Cl or CH3, and is preferably -H in view of good solubility of the electrolyte salt.

[0534] In addition to those represented by the above formula, the fluorine-containing lactones include, for example, those represented by the following formula (D):

[0535] [ka]

[0536] (In the formula, either A or B is CX 226 X 227 (X 226 and X 227 Is it the same? or different, each of which is -H, -F, -Cl, -CF3, -CH3 or an alkylene group in which a hydrogen atom may be substituted with a halogen atom and which may contain a heteroatom in the chain), and the other is an oxygen atom; Rf 12 is a fluorinated alkyl group or a fluorinated alkoxy group which may have an ether bond; X 221 and X 222 are the same or different and are each -H, -F, -Cl, -CF3 or -CH3; X 223 ~X 225 are the same or different, and each represents an alkyl group in which a hydrogen atom may be replaced by -H, -F, -Cl, or a halogen atom and which may contain a heteroatom in the chain; n=0 or 1). and the like.

[0537] The fluorine-containing lactone represented by formula (D) includes a fluorine-containing lactone represented by the following formula (E):

[0538] [ka]

[0539] (In the formula, A, B, Rf 12 , X 221 , X 222 and X 223 is the same as formula (D) A five-membered ring structure represented by the following formula (F):

[0540] [ka]

[0541] (In the formula, Rf 12 , X 221 , X 222 , X 223 , X 226 and X 227 is equation (D) are the same) and a fluorine-containing lactone represented by the following formula (G):

[0542] [ka]

[0543] (In the formula, Rf 12 , X 221 , X 222 , X 223 , X 226 and X 227 is equation (D) are the same) There is a fluorine-containing lactone represented by the formula:

[0544] Among these, the present invention is particularly advantageous in that it can exhibit excellent properties such as a high dielectric constant and a high withstand voltage, and in that it has good solubility of the electrolyte salt and good reduction in internal resistance, thereby improving the properties of the liquid electrolyte of the present disclosure.

[0545] [ka] etc. By incorporating a fluorinated cyclic carboxylic acid ester, effects such as improved ionic conductivity, improved safety, and improved stability at high temperatures can be obtained.

[0546] Examples of the chain carboxylic acid ester include those having a total carbon number in the structural formula of 3 to 7. Specific examples include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isobutyl propionate, n-butyl propionate, methyl butyrate, isobutyl propionate, t-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, and isopropyl isobutyrate.

[0547] Among these, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, etc. are preferred from the viewpoint of improving ionic conductivity due to reduced viscosity.

[0548] The ether compound is preferably a chain ether having 2 to 10 carbon atoms or a cyclic ether having 3 to 6 carbon atoms. Examples of chain ethers having 2 to 10 carbon atoms include dimethyl ether, diethyl ether, di-n-butyl ether, dimethoxymethane, methoxyethoxymethane, diethoxymethane, dimethoxyethane, methoxyethoxyethane, diethoxyethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol, diethylene glycol dimethyl ether, pentaethylene glycol, triethylene glycol dimethyl ether, triethylene glycol, tetraethylene glycol, tetraethylene glycol dimethyl ether, and diisopropyl ether.

[0549] Examples of cyclic ethers having 3 to 6 carbon atoms include 1,2-dioxane, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, metaformaldehyde, 2-methyl-1,3-dioxolane, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-(trifluoroethyl)dioxolane, 2,2-bis(trifluoromethyl)-1,3-dioxolane, and fluorinated compounds thereof. Among these, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, and crown ether are preferred in terms of their high solvation ability for lithium ions and improved ionic dissociation, and dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferred because they have low viscosity and provide high ionic conductivity.

[0550] Examples of the nitrogen-containing compound include nitriles, fluorine-containing nitriles, carboxylic acid amides, fluorine-containing carboxylic acid amides, sulfonic acid amides, fluorine-containing sulfonic acid amides, acetamide, and formamide. Also usable are 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxaziridinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide. However, the nitrile compounds represented by the general formulas (1a), (1b), and (1c) are not included in the nitrogen-containing compound.

[0551] Examples of the boron-containing compound include boric acid esters such as trimethyl borate and triethyl borate, boric acid ethers, and alkyl borates.

[0552] Examples of the organic silicon-containing compound include (CH3)4-Si, (CH3)3-Si-Si(CH3)3, and silicone oil.

[0553] Examples of the flame retardant (flame retardant) agent include phosphate esters and phosphazene compounds. Examples of the phosphate esters include fluorine-containing alkyl phosphate esters, non-fluorine-containing alkyl phosphate esters, and aryl phosphate esters. Among these, fluorine-containing alkyl phosphate esters are preferred because they can exert a flame retardant effect even in small amounts.

[0554] Examples of the phosphazene compound include methoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, dimethylaminopentafluorocyclotriphosphazene, diethylaminopentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene.

[0555] Specific examples of the fluorine-containing alkyl phosphate ester include the fluorine-containing dialkyl phosphate ester described in JP-A-11-233141, the cyclic alkyl phosphate ester described in JP-A-11-283669, and the fluorine-containing trialkyl phosphate ester.

[0556] As the non-combustible (flame retardant) agent, (CH3O)3P=O, (CF3CH2O)3P=O, (HCF2CH2O)3P=O, (CF3CF2CH2)3P=O, (HCF2CF2CH2)3P=O, and the like are preferred.

[0557] The surfactant may be any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant, but is preferably one containing a fluorine atom in terms of improving cycle characteristics and rate characteristics.

[0558] The content of the surfactant is preferably 0.01 to 2% by mass in the liquid electrolyte, since it is possible to reduce the surface tension of the liquid electrolyte without reducing the charge-discharge cycle characteristics.

[0559] Examples of the high-dielectric additive include sulfolane, methylsulfolane, γ-butyrolactone, and γ-valerolactone.

[0560] Examples of the cycle performance and rate performance improver include methyl acetate, ethyl acetate, tetrahydrofuran, and 1,4-dioxane.

[0561] Furthermore, the liquid electrolyte used in the battery of the present disclosure may be further combined with a polymer material to form a gel-like (plasticized) gel liquid electrolyte.

[0562] Examples of such polymer materials include conventionally known polyethylene oxide, polypropylene oxide, and modified products thereof (see Japanese Patent Application Laid-Open Nos. 8-222270 and 2002-100405); polyacrylate polymers, polyacrylonitrile, fluororesins such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers (see Japanese Patent Application Laid-Open Nos. 4-506726, 8-507407, and 10-294131); and composites of such fluororesins with hydrocarbon resins (see Japanese Patent Application Laid-Open Nos. 11-35765 and 11-86630). In particular, polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers are preferably used as polymer materials for gel electrolytes.

[0563] In addition, the liquid electrolyte used in the battery of the present disclosure may also contain the ion-conducting compound described in Japanese Patent Application No. 2004-301934.

[0564] The ion-conducting compound has the formula (101): A-(D)-B (101) [Wherein D is a group represented by formula (201): -(D1) n -(FAE) m -(AE) p -(Y) q - (201) (Wherein D1 is a compound represented by formula (2a):

[0565] [ka]

[0566] (wherein Rf represents a fluorine-containing ether group which may have a crosslinkable functional group; R 10 is a group or bond connecting Rf to the main chain) an ether unit having a fluorine-containing ether group in the side chain, represented by the formula: FAE is expressed by the formula (2b):

[0567] [ka]

[0568] (wherein Rfa represents a hydrogen atom or a fluorinated alkyl group which may have a crosslinkable functional group; R 11 is the group or bond connecting Rfa to the main chain) an ether unit having a fluorinated alkyl group in the side chain, represented by the formula: AE is represented by the formula (2c):

[0569] [ka]

[0570] (In the formula, R 13 represents a hydrogen atom, an alkyl group which may have a crosslinkable functional group, an aliphatic cyclic hydrocarbon group which may have a crosslinkable functional group, or an aromatic hydrocarbon group which may have a crosslinkable functional group; R 12 is R 13 and the main chain) Ether units denoted by ; Y is expressed by the formulas (2d-1) to (2d-3):

[0571] [ka]

[0572] A unit containing at least one of the following: n is an integer from 0 to 200; m is an integer from 0 to 200; p is an integer from 0 to 10,000; q is an integer from 1 to 100; provided that n+m is not 0, and the bonding order of D1, FAE, AE, and Y is not specified); A and B may be the same or different and are each a hydrogen atom, an alkyl group which may contain a fluorine atom and / or a crosslinkable functional group, a phenyl group which may contain a fluorine atom and / or a crosslinkable functional group, a -COOH group, -OR (R is a hydrogen atom or an alkyl group which may contain a fluorine atom and / or a crosslinkable functional group), an ester group, or a carbonate group (however, when the terminal of D is an oxygen atom, it is not a -COOH group, -OR, ester group, or carbonate group) The compound is an amorphous fluorine-containing polyether compound having a fluorine-containing group in the side chain, represented by the formula:

[0573] The liquid electrolyte used in the battery of the present disclosure may contain a sulfone-based compound. As the sulfone-based compound, cyclic sulfones having 3 to 6 carbon atoms and chain sulfones having 2 to 6 carbon atoms are preferred. The number of sulfonyl groups in one molecule is preferably 1 or 2.

[0574] Examples of cyclic sulfones include monosulfone compounds such as trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones; and disulfone compounds such as trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones. Among these, from the viewpoints of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolanes) are particularly preferred.

[0575] The sulfolanes are preferably sulfolane and / or sulfolane derivatives (hereinafter, sulfolane may also be abbreviated as "sulfolanes"). The sulfolane derivatives are preferably those in which one or more hydrogen atoms bonded to the carbon atoms constituting the sulfolane ring are substituted with a fluorine atom or an alkyl group.

[0576] Among them, 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,2-difluorosulfolane, 2,3-difluorosulfolane, 2,4-difluorosulfolane, 2,5-difluorosulfolane, 3,4-difluorosulfolane, 2-fluoro-3-methylsulfolane, 2-fluoro-2-methylsulfolane, 3-fluoro-3-methylsulfolane, 3-fluoro-2-methylsulfolane, 4-fluoro-3-methylsulfolane, 4-fluoro-2-methylsulfolane, 5-fluoro-3-methylsulfolane , 5-fluoro-2-methylsulfolane, 2-fluoromethylsulfolane, 3-fluoromethylsulfolane, 2-difluoromethylsulfolane, 3-difluoromethylsulfolane, 2-trifluoromethylsulfolane, 3-trifluoromethylsulfolane, 2-fluoro-3-(trifluoromethyl)sulfolane, 3-fluoro-3-(trifluoromethyl)sulfolane, 4-fluoro-3-(trifluoromethyl)sulfolane, 3-sulfolene, 5-fluoro-3-(trifluoromethyl)sulfolane, and the like are preferred because they have high ionic conductivity and high input / output.

[0577] Examples of chain sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, n-propyl ethyl sulfone, di-n-propyl sulfone, isopropyl methyl sulfone, isopropyl ethyl sulfone, diisopropyl sulfone, n-butyl methyl sulfone, n-butyl ethyl sulfone, t-butyl methyl sulfone, t-butyl ethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, and perfluoroethyl methyl sulfone. Examples thereof include fluoromethyl-n-propyl sulfone, ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, di(trifluoroethyl) sulfone, perfluorodiethyl sulfone, fluoromethyl-n-propyl sulfone, difluoromethyl-n-propyl sulfone, trifluoromethyl-n-propyl sulfone, fluoromethyl isopropyl sulfone, difluoromethyl isopropyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl-n-propyl sulfone, trifluoroethyl isopropyl sulfone, pentafluoroethyl-n-propyl sulfone, pentafluoroethyl isopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-t-butyl sulfone, pentafluoroethyl-n-butyl sulfone, and pentafluoroethyl-t-butyl sulfone.

[0578] Among these, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, isopropyl methyl sulfone, n-butyl methyl sulfone, t-butyl methyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, trifluoromethyl-n-propyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-t-butyl sulfone, trifluoromethyl-n-butyl sulfone, trifluoromethyl-t-butyl sulfone, and the like are preferred because of their high ionic conductivity and high input / output.

[0579] The content of the sulfone-based compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present disclosure, but is usually 0.3 vol% or more, preferably 0.5 vol% or more, more preferably 1 vol% or more, and usually 40 vol% or less, preferably 35 vol% or less, more preferably 30 vol% or less, based on 100 vol% of the solvent. If the content of the sulfone-based compound is within the above range, it is easy to obtain an effect of improving durability such as cycle characteristics and storage characteristics, and it is also possible to keep the viscosity of the nonaqueous liquid electrolyte within an appropriate range, avoid a decrease in electrical conductivity, and keep the input / output characteristics and charge / discharge rate characteristics of the nonaqueous liquid electrolyte secondary battery within appropriate ranges.

[0580] From the viewpoint of improving output characteristics, the liquid electrolyte used in the battery of the present disclosure also preferably contains, as an additive, at least one compound (7) selected from the group consisting of lithium fluorophosphate salts (excluding LiPF) and lithium salts having an S=O group. When compound (7) is used as an additive, it is preferable to use a compound other than compound (7) as the electrolyte salt.

[0581] Examples of the lithium fluorophosphate salts include lithium monofluorophosphate (LiPO3F) and lithium difluorophosphate (LiPO2F2). Examples of the lithium salts having the S=O group include lithium monofluorosulfonate (FSO3Li), lithium methylsulfate (CH3OSO3Li), lithium ethylsulfate (C2H5OSO3Li), and lithium 2,2,2-trifluoroethylsulfate. Of these, LiPO2F2, FSO3Li, and C2H5OSO3Li are preferred as compound (7).

[0582] The content of compound (7) is preferably 0.001 to 20 mass %, more preferably 0.01 to 15 mass %, further preferably 0.1 to 10 mass %, and particularly preferably 0.1 to 7 mass %, relative to the liquid electrolyte.

[0583] The liquid electrolyte used in the battery of the present disclosure may further contain other additives as needed, such as metal oxides and glass.

[0584] The liquid electrolyte used in the battery of the present disclosure preferably contains 5 to 200 ppm of hydrogen fluoride (HF). The inclusion of HF can promote film formation by the additives described above. If the HF content is too low, the film-forming ability on the negative electrode decreases, and the electrochemical device performance tends to deteriorate. If the HF content is too high, the oxidation resistance of the liquid electrolyte tends to decrease due to the influence of HF. The liquid electrolyte used in the battery of the present disclosure, even if it contains HF within the above range, does not decrease the high-temperature storage recovered capacity rate of the electrochemical device. The HF content is more preferably 10 ppm or more, and even more preferably 20 ppm or more, and more preferably 100 ppm or less, more preferably 80 ppm or less, and particularly preferably 50 ppm or less. The HF content can be measured by neutralization titration.

[0585] The liquid electrolyte used in the batteries of the present disclosure can be prepared by any method using the components described above.

[0586] (positive electrode) In the battery of the present disclosure, the positive electrode is not particularly limited, but may be one composed of a positive electrode active material layer containing a positive electrode active material and a current collector.

[0587] The positive electrode active material is not particularly limited as long as it can electrochemically absorb and release ions of at least one metal selected from lithium, sodium, magnesium, and zinc, but is preferably, for example, a material containing an alkali metal and at least one transition metal, such as an alkali metal-containing transition metal composite oxide, an alkali metal-containing transition metal phosphate compound, a sulfur-based material, or a conductive polymer. Among these, alkali metal-containing transition metal composite oxides that produce high voltage are particularly preferred as the positive electrode active material. Examples of the alkali metal ions include lithium ions and sodium ions. In a preferred embodiment, the alkali metal ions may be lithium ions. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery.

[0588] Examples of the alkali metal-containing transition metal composite oxide include: Formula: MaMn 2-b M 1 b O4 (Wherein, M is at least one metal selected from the group consisting of Li and Na; 0.5≦a; 0≦b≦1.5; M 1 is 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), Formula:MNi 1-c M 2 c O2 (Wherein, M is at least one metal selected from the group consisting of Li and Na; 0≦c≦0.5; M 2 is 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 Formula:MCo 1-d M 3 d O2 (Wherein, M is at least one metal selected from the group consisting of Li and Na; 0≦d≦0.5; M 3 is 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) In the above, M is preferably one metal selected from the group consisting of Li and Na, and is Li or Na, and more preferably Li.

[0589] Among these, MCoO2, MMnO2, MNiO2, MMn2O4, and MNi are the most popular because they can provide high energy density and high output secondary batteries. 0.8 Co 0.15 Al 0.05 O2 or MNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and the like are preferred, and a compound represented by the following general formula (3) is preferred. MNi h Co i Mn j M 5 k O2(3) (Wherein, M is M 5 represents at least one element selected from the group consisting of Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, and (h+i+j+k)=1.0, 0≦h≦1.0, 0≦i≦1.0, 0≦j≦1.5, and 0≦k≦0.2.

[0590] The alkali metal-containing transition metal phosphate compound is, for example, a compound represented by the following formula (4): M e M 4 f (PO4) g (In the formula, M is at least one metal selected from the group consisting of Li and Na, and M 4 represents at least one selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni, and Cu, and 0.5≦e≦3, 1≦f≦2, 1≦g≦3). In the above, M is preferably a metal selected from the group consisting of Li and Na, and more preferably Li.

[0591] The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, cobalt phosphates such as LiCoPO4, and lithium transition metal phosphate compounds in which a portion of the transition metal atoms that constitute the main components of these lithium transition metal phosphate compounds has been substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si. The lithium-containing transition metal phosphate compound is preferably one having an olivine structure.

[0592] Other positive electrode active materials include MFePO4 and MNi 0.8 Co 0.2 O2, M 1.2 Fe 0.4 Mn 0.4 O2, MNi 0.5 Mn 1.5 O2, MV3O6, M2MnO3, M MnO3, etc. In particular, M2MnO3, MNi 0.5 Mn 1.5Positive electrode active materials such as O2 are preferable in that the crystal structure does not collapse even when the secondary battery is operated at a voltage exceeding 4.4 V or at a voltage of 4.6 V or higher. Therefore, an electrochemical device such as a secondary battery using a positive electrode material containing the positive electrode active material exemplified above is preferable because the remaining capacity hardly decreases even when stored at a high temperature, the resistance increase rate hardly changes, and the battery performance does not deteriorate even when operated at a high voltage.

[0593] As other positive electrode active materials, solid solution materials of M2MnO3 and MM 6 O2 (where M is at least one metal selected from the group consisting of Li and Na, and M 6 is a transition metal such as Co, Ni, Mn, Fe, etc.) and the like can also be mentioned.

[0594] As the above solid solution material, for example, it is an alkali metal manganate represented by the general formula Mx[Mn(1-y)M 7 y]Oz. Here, M in the formula is at least one metal selected from the group consisting of Li and Na, and M 7 consists 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. Also, the values of x, y, and z in the formula are in the ranges of 0.5 < x < 2, 0 ≤ y < 1, and 1.5 < z < 3. Among them, a manganese-containing solid solution material in which LiNiO2 or LiCoO2 is solid-solved based on Li2MnO3 such as Li 1.2 Mn 0.5 Co 0.14 Ni 0.14 O2 is preferable in that it can provide an alkali metal ion secondary battery having a high energy density.

[0595] In addition, it is preferable to include lithium phosphate in the positive electrode active material because the continuous charging characteristics are improved. There is no limitation on the use of lithium phosphate, but it is preferable to mix and use the above-mentioned positive electrode active material and lithium phosphate. The amount of lithium phosphate used is preferably at least 0.1% by mass, more preferably at least 0.3% by mass, still more preferably at least 0.5% by mass, and preferably at most 10% by mass, more preferably at most 8% by mass, still more preferably at most 5% by mass, based on the total of the above positive electrode active material and lithium phosphate.

[0596] Examples of the sulfur-based material include materials containing sulfur atoms, and at least one selected from the group consisting of elemental sulfur, metal sulfides, and organic sulfur compounds is preferable, and elemental sulfur is more preferable. The metal sulfide may be a metal polysulfide. The organic sulfur compound may be an organic polysulfide.

[0597] Examples of the metal sulfide include LiS x a compound represented by (0 < x ≦ 8); Li2S x a compound represented by (0 < x ≦ 8); a compound having a two-dimensional layered structure such as TiS2 or MoS2; general formula Me x a Chevrel compound having a strong three-dimensional skeleton structure represented by Mo6S8 (Me is various transition metals including Pb, Ag, Cu, etc.) and the like.

[0598] Examples of the organic sulfur compound include carbon sulfide compounds and the like.

[0599] The organic sulfur compound may be supported on a material having pores such as carbon and used as a carbon composite material. The sulfur content in the carbon composite material is preferably 10 to 99% by mass, more preferably 20% by mass or more, still more preferably 30% by mass or more, particularly preferably 40% by mass or more, and preferably 85% by mass or less, with respect to the carbon composite material, because the cycle performance is further improved and the overvoltage is further reduced. When the positive electrode active material is the above elemental sulfur, the sulfur content contained in the positive electrode active material is equal to the content of the above elemental sulfur.

[0600] Examples of conductive polymers include p-doped conductive polymers and n-doped conductive polymers, as well as polyacetylenes, polyphenylenes, heterocyclic polymers, ionic polymers, ladder and network polymers, etc.

[0601] Alternatively, a substance having a different composition may be attached to the surface of the positive electrode active material, such as an oxide, such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, or bismuth oxide; a sulfate, such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, or aluminum sulfate; a carbonate, such as lithium carbonate, calcium carbonate, or magnesium carbonate; or carbon.

[0602] These surface-attaching substances can be attached to the surface of the positive electrode active material by, for example, a method of dissolving or suspending the substance in a solvent, impregnating the positive electrode active material, and then drying, a method of dissolving or suspending a surface-attaching substance precursor in a solvent, impregnating the positive electrode active material, and then reacting the surface-attaching substance by heating, or a method of adding the substance to a positive electrode active material precursor and simultaneously calcining the surface-attaching substance, etc. When carbon is attached, a method of mechanically attaching the carbonaceous material in the form of, for example, activated carbon, etc., after the surface-attaching substance is attached can also be used.

[0603] The amount of the surface-attached substance is, by mass relative to the positive electrode active material, preferably 0.1 ppm or more as the lower limit, more preferably 1 ppm or more, and even more preferably 10 ppm or more, and preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less as the upper limit. The surface-attached substance can suppress the oxidation reaction of the liquid electrolyte on the surface of the positive electrode active material and improve the battery life, but if the amount of attachment is too small, the effect will not be fully exerted, and if it is too large, the movement of lithium ions is hindered, which may increase the resistance.

[0604] The shape of the particles of the positive electrode active material may be any of the conventional shapes such as block, polyhedron, sphere, oval sphere, plate, needle, column, etc. Furthermore, primary particles may aggregate to form secondary particles.

[0605] 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 That is all. If the tap density of the positive electrode active material is below the above lower limit, the amount of dispersion medium required when forming the positive electrode active material layer increases, and the amounts of conductive material and binder required also increase, which may restrict the filling rate of the positive electrode active material in the positive electrode active material layer and restrict the battery capacity. By using a composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. Generally, the higher the tap density, the better, and there is no particular upper limit. However, if the tap density is too high, the diffusion of lithium ions in the positive electrode active material layer using the liquid electrolyte as a medium becomes rate-limiting, and the load characteristics may be easily reduced. Therefore, the upper limit is preferably 4.0 g / cm. 3 or less, more preferably 3.7 g / cm 3 More preferably 3.5 g / cm or less 3 The following is the result. In the present disclosure, the tap density is the powder packing density (tap density) g / cm when 5 to 10 g of positive electrode active material powder is placed in a 10 ml glass measuring cylinder and tapped 200 times with a stroke of approximately 20 mm. 3 is required.

[0606] The median diameter d50 of the positive electrode active material particles (the secondary particle diameter when primary particles aggregate to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and most preferably 1.0 μm or more, and is preferably 30 μm or less, more preferably 27 μm or less, even more preferably 25 μm or less, and most preferably 22 μm or less. Below the lower limit, a high tap density product may not be obtained. Above the upper limit, lithium diffusion within the particles takes too long, resulting in reduced battery performance and problems such as streaking during battery positive electrode preparation, i.e., when the active material, conductive material, binder, etc. are slurried with a solvent and applied as a thin film. Mixing two or more of the above positive electrode active materials with different median diameters d50 can further improve the packing properties during positive electrode preparation.

[0607] In the present disclosure, the median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using a HORIBA LA-920 as the particle size distribution analyzer, the measurement is performed using a 0.1% by mass aqueous solution of sodium hexametaphosphate as the dispersion medium, and after ultrasonic dispersion for 5 minutes, the measurement is performed with a refractive index set to 1.24.

[0608] When primary particles aggregate to form secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more, with an upper limit of preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less. If the average particle diameter exceeds the upper limit, it may be difficult to form spherical secondary particles, adversely affecting powder packing, or the specific surface area may be significantly reduced, potentially resulting in a decrease in battery performance, such as output characteristics. Conversely, if the average particle diameter is below the lower limit, problems such as poor charge / discharge reversibility may occur due to underdeveloped crystals.

[0609] In the present disclosure, the primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at 10,000x magnification, the longest intercept value of a horizontal line at the left and right boundary lines of a primary particle is determined for any 50 primary particles, and the average value is calculated.

[0610] 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, whereas if it is larger, it becomes difficult to increase the tap density, which may easily cause problems with the coating properties when forming the positive electrode active material layer.

[0611] In the present disclosure, the BET specific surface area is defined as a value measured by a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.) using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3, after which the sample is pre-dried at 150°C for 30 minutes under a nitrogen flow, by a nitrogen adsorption BET single-point method using a gas flow method.

[0612] When the secondary battery of the present disclosure is used as a large-scale lithium-ion secondary battery for hybrid vehicles or distributed power sources, high output is required, and therefore it is preferable that the particles of the positive electrode active material are mainly secondary particles. The particles of the positive electrode active material preferably contain 0.5 to 7.0 volume % of fine particles having an average secondary particle size of 40 μm or less and an average primary particle size of 1 μm or less. By including fine particles having an average primary particle size of 1 μm or less, the contact area with the liquid electrolyte increases, allowing for faster diffusion of lithium ions between the electrode and the liquid electrolyte, resulting in improved output performance of the battery.

[0613] The cathode active material is produced by a method generally used for producing inorganic compounds. In particular, various methods can be considered for producing spherical or oval-spherical active materials, such as dissolving or pulverizing and dispersing raw materials of transition metals in a solvent such as water, adjusting the pH while stirring, producing and recovering spherical precursors, drying them as necessary, and then adding a Li source such as LiOH, Li2CO3, or LiNO3 and baking them at a high temperature to obtain the active material.

[0614] For the production of a positive electrode, the above-mentioned positive electrode active materials may be used alone, or two or more of different compositions may be used in any combination or ratio. In this case, a preferred combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 Examples of such a material include a combination of LiMn2O4 such as O2 or a combination of LiCoO ...

[0615] The content of the positive electrode active material is preferably 50 to 99.5% by mass of the positive electrode mixture, more preferably 80 to 99% by mass, in terms of high battery capacity. 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. The upper limit is preferably 99% by mass or less, more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electrical capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

[0616] The positive electrode mixture preferably further contains a binder, a thickener, and a conductive material. Any material can be used as the binder as long as it is safe for the solvents and liquid electrolytes used in the electrode production. Examples of such binders include resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, chitosan, alginic acid, polyacrylic acid, polyimide, cellulose, and nitrocellulose; rubber-like polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or hydrogenated products thereof; and EPDM ( Examples of suitable polymers include thermoplastic elastomeric polymers such as ethylene-propylene-diene terpolymers, styrene-ethylene-butadiene-styrene copolymers, styrene-isoprene-styrene block copolymers, and hydrogenated products thereof; soft resinous polymers such as syndiotactic 1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride copolymers, and tetrafluoroethylene-ethylene copolymers; and polymer compositions with ionic conductivity for alkali metal ions (especially lithium ions). These may be used alone or in any combination and ratio of two or more.

[0617] The content of the binder, expressed as the proportion of the binder in the positive electrode active material layer, is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 1.5% by mass or more, and usually 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass or less, and most preferably 10% by mass or less. If the proportion of the binder is too low, the positive electrode active material cannot be sufficiently held, resulting in insufficient mechanical strength of the positive electrode and deterioration of battery performance such as cycle characteristics. On the other hand, if the proportion is too high, it may lead to a decrease in battery capacity and conductivity.

[0618] Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphated starch, casein, polyvinylpyrrolidone, and salts thereof. One type may be used alone, or two or more types may be used in any combination and ratio.

[0619] The ratio of the thickener to the active material is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% 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 is below this range, the coating properties may be significantly reduced. If the ratio is above this range, the ratio of the active material in the positive electrode active material layer may decrease, which may cause problems such as a decrease in battery capacity or an increase in resistance between the positive electrode active materials.

[0620] Any known conductive material can be used as the conductive material. Specific examples include metal materials such as copper and nickel; graphite (e.g., natural graphite and artificial graphite); carbon black (e.g., acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black); and carbon materials such as needle coke, carbon nanotubes, fullerenes, and amorphous carbon (e.g., VGCF). These materials may be used alone or in any combination and ratio of two or more. The conductive material is typically present in the positive electrode active material layer in an amount of at least 0.01% by mass, preferably at least 0.1% by mass, and more preferably at least 1% by mass, and typically at most 50% by mass, preferably at most 30% by mass, and more preferably at most 15% by mass. A content below this range may result in insufficient conductivity. Conversely, a content above this range may result in a decrease in battery capacity.

[0621] The solvent for forming the slurry is not particularly limited as long as it can dissolve or disperse the positive electrode active material, conductive material, binder, and optional thickener. Either an aqueous or organic solvent can be used. Examples of aqueous solvents include water and mixtures of alcohol and water. Examples of organic solvents include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and 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; and aprotic polar solvents such as hexamethylphosphalamide and dimethyl sulfoxide.

[0622] Examples of materials for the positive electrode current collector include metals such as aluminum, titanium, tantalum, stainless steel, and nickel, or alloys thereof; and carbon materials such as carbon cloth and carbon paper. Of these, metal materials, particularly aluminum or its alloys, are preferred.

[0623] Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, roughened metal foil, expanded metal, punched metal, and foamed metal for metal materials, and carbon plate, carbon thin film, and carbon cylinder for carbon materials. Of these, metal thin films are preferred. The thin film may be formed into a mesh shape as appropriate. The thickness of the thin film is optional, but is usually 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, and more preferably 50 μm or less. If the thin film is thinner than this range, the strength required as a current collector may be insufficient. Conversely, if the thin film is thicker than this range, handling may be impaired.

[0624] In addition, it is also preferable that the surface of the current collector is coated with a conductive additive, from the viewpoint of reducing the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of the conductive additive include carbon and precious metals such as gold, platinum, and silver.

[0625] The thickness ratio of the current collector to the positive electrode active material layer is not particularly limited, but the value of (thickness of the positive electrode active material layer on one side immediately before injection of the liquid electrolyte) / (thickness of the current collector) is preferably 20 or less, more preferably 15 or less, and most preferably 10 or less, and is preferably 0.5 or more, more preferably 0.8 or more, and most preferably 1 or more. If the ratio exceeds this range, the current collector may generate heat due to Joule heat during high current density charge / discharge. If the ratio is below this range, the volume ratio of the current collector to the positive electrode active material increases, which may reduce the battery capacity.

[0626] The positive electrode may be manufactured by a conventional method, for example, by adding the above-mentioned binder, thickener, conductive material, solvent, etc. to the above-mentioned positive electrode active material to form a slurry positive electrode mixture, which is then applied to a current collector, dried, and pressed to increase density.

[0627] The densification can be performed by a hand press, a roller press, etc. 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 or more, and preferably 5 g / cm 3 or less, more preferably 4.5 g / cm 3 More preferably, 4 g / cm or less 3 The range is as follows. If the temperature exceeds this range, the permeability of the liquid electrolyte near the current collector / active material interface will decrease, which may result in a decrease in charge / discharge characteristics, especially at high current densities, and high output may not be obtained. If the temperature falls below this range, the conductivity between the active materials will decrease, which may increase the battery resistance and prevent high output.

[0628] When using the liquid electrolyte used in the battery of the present disclosure or the liquid electrolyte used in the alkali metal secondary battery of the present disclosure, the area of ​​the positive electrode active material layer is preferably larger than the external surface area of ​​the battery exterior case in order to improve high output and stability at high temperatures. Specifically, the total electrode area of ​​the positive electrode relative to the surface area of ​​the secondary battery exterior is preferably 15 times or more, and more preferably 40 times or more. In the case of a bottomed prismatic battery exterior case, the external surface area refers to the total area calculated from the length, width, and thickness of the case portion filled with the power generating elements, excluding the terminal protrusions. In the case of a bottomed cylindrical battery exterior case, the external surface area refers to the geometric surface area of ​​the case portion filled with the power generating elements, excluding the terminal protrusions, approximated as a cylinder. The total electrode 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 in which a positive electrode mixture layer is formed on both sides of a current collector foil, the total area refers to the sum of the areas calculated separately for each surface.

[0629] The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the mixture layer minus the thickness of the metal foil of the core material is preferably 10 μm or more, more preferably 20 μm or more, as a lower limit on one side of the current collector, and is also preferably 500 μm or less, more preferably 450 μm or less.

[0630] Alternatively, a material having a different composition may be attached to the surface of the positive electrode plate, such as an oxide, such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, or bismuth oxide; a sulfate, such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, or aluminum sulfate; a carbonate, such as lithium carbonate, calcium carbonate, or magnesium carbonate; or carbon.

[0631] (separator) The secondary battery of the present disclosure preferably further includes a separator. The separator may be made of any known material or shape as long as it is stable to the liquid electrolyte and has excellent liquid retention properties, and among these, it is preferable to use a porous sheet or nonwoven fabric-like material that is made of a material that is stable to the liquid electrolyte used in the battery of the present disclosure or the liquid electrolyte used in the alkali metal secondary battery of the present disclosure, such as a resin, glass fiber, or inorganic material, and has excellent liquid retention properties.

[0632] Materials that can be used for the resin and glass fiber separator include, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, glass filters, etc. These materials may be used alone or in any combination and ratio of two or more, such as polypropylene / polyethylene two-layer films and polypropylene / polyethylene / polypropylene three-layer films. Among these, the separator is preferably a porous sheet or nonwoven fabric made from a polyolefin such as polyethylene or polypropylene, because of its excellent liquid electrolyte permeability and shutdown effect.

[0633] The thickness of the separator is optional, but is 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 thinner than the above range, the insulating properties and mechanical strength may be reduced. On the other hand, if the separator is thicker than the above range, not only may the battery performance such as rate characteristics be reduced, but also the energy density of the entire liquid electrolyte battery may be reduced.

[0634] Furthermore, when a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is optional, but is usually 20% or more, preferably 35% or more, more preferably 45% or more, and is usually 90% or less, preferably 85% or less, more preferably 75% or less. If the porosity is too low, the membrane resistance tends to increase, resulting in poor rate performance. If the porosity is too high, the mechanical strength of the separator tends to decrease, resulting in poor insulation.

[0635] The average pore size of the separator can also be any value, but is 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 circuits are likely to occur. If the average pore size is below the above range, the membrane resistance increases, which may result in a decrease in rate characteristics.

[0636] On the other hand, inorganic materials include, for example, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate, and these are used in particulate or fibrous form.

[0637] As for the form, a thin film such as a nonwoven fabric, a woven fabric, or a microporous film is used. In the thin film form, a film with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition to the above independent thin film form, a separator can be used in which a composite porous layer containing the above inorganic particles is formed on the surface layer of the positive electrode and / or negative electrode using a resin binder. For example, a porous layer can be formed on both sides of the positive electrode using alumina particles with 90% particle diameters of less than 1 μm and a fluororesin as a binder.

[0638] (Battery design) The electrode group may have either a laminated structure in which the positive electrode plate and the negative electrode plate are sandwiched between the separator, or a structure in which the positive electrode plate and the negative electrode plate are spirally wound with the separator sandwiched between them. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy ratio) is ) is usually 40% or more, preferably 50% or more, and is usually 90% or less, preferably 80% or less.

[0639] If the electrode group occupancy rate is below the above range, the battery capacity will be small, whereas if it exceeds the above range, the void space will be small, and the battery will become hot, causing the components to expand and the vapor pressure of the electrolyte liquid components to increase, resulting in an increase in internal pressure, which will degrade various battery characteristics such as repeated charge / discharge performance and high-temperature storage, and may even cause the gas release valve that releases internal pressure to the outside to operate.

[0640] The current collection structure is not particularly limited, but in order to more effectively achieve improved high current density charge / discharge characteristics with the liquid electrolyte used in the battery of the present disclosure or the liquid electrolyte used in the alkali metal secondary battery of the present disclosure, it is preferable to use a structure that reduces the resistance of wiring portions and joint portions. When the internal resistance is reduced in this manner, the effects of using the liquid electrolyte used in the battery of the present disclosure or the liquid electrolyte used in the alkali metal secondary battery of the present disclosure are particularly well exhibited.

[0641] When the electrode group has the above-mentioned laminated structure, a structure formed by bundling the metal core portions of each electrode layer and welding them to a terminal is preferably used. When the area of ​​a single electrode is large, the internal resistance increases, so it is also preferably used to reduce the resistance by providing multiple terminals within the electrode. When the electrode group has the above-mentioned wound structure, the internal resistance can be reduced by providing multiple lead structures on each of the positive electrode and negative electrode and bundling them to a terminal.

[0642] The material of the outer case is not particularly limited as long as it is stable against the liquid electrolyte used. Specifically, metals such as nickel-plated steel sheet, stainless steel, aluminum or aluminum alloy, magnesium alloy, or a laminate film of resin and aluminum foil (laminate film) can be used. From the viewpoint of weight reduction, metals such as aluminum or aluminum alloy and laminate film are preferably used.

[0643] Examples of exterior cases using metals include those in which metals are welded together to form a sealed, airtight structure by laser welding, resistance welding, or ultrasonic welding, or those in which the metals are used via a resin gasket to form a crimped structure. Examples of exterior cases using the above-mentioned laminate film include those in which resin layers are heat-sealed to form a sealed, airtight structure. In order to improve sealing properties, a resin different from the resin used in the laminate film may be interposed between the resin layers. In particular, when a sealed structure is formed by heat-sealing the resin layers via a current collecting terminal, a resin having a polar group or a modified resin into which a polar group has been introduced is preferably used as the interposed resin, since the metal and the resin are bonded together.

[0644] The shape of the secondary battery of the present disclosure is arbitrary, and examples thereof include cylindrical, prismatic, laminated, coin, large, etc. The shapes and configurations of the positive electrode, negative electrode, and separator can be changed according to the shape of each battery. [Example]

[0645] The present disclosure will be specifically described below based on examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

[0646] Types of fluoropolymers Polymer A: Fluorocopolymer containing vinylidene fluoride (VdF) units and tetrafluoroethylene (TFE) units VdF / TFE=81 / 19 (mol %) Weight average molecular weight: 970000 Melting point: 128°C

[0647] Polymer B: Fluorocopolymer containing VdF units and trifluoroethylene (TrFE) units VdF / TrFE=80 / 20 (mol %) Weight average molecular weight: 720000 Melting point: 165℃

[0648] Polymer C: Fluoropolymer containing VdF units, TrFE units, and chlorotrifluoroethylene (CTFE) units VdF / TrFE / CTFE=65 / 28 / 7 (mol %) Weight average molecular weight: 650000 Melting point: 170℃

[0649] Polymer D: Fluorocopolymer containing VdF units and acrylic acid units VdF / acrylic acid=99 / 1 (mol%) Weight average molecular weight: 1120000 Melting point: 161°C

[0650] Polymer E: Fluoropolymer containing VdF units and 2,3,3,3-tetrafluoropropene units VdF / 2,3,3,3-tetrafluoropropene=77 / 23 Weight average molecular weight: 480000 Tg: -13℃ Mooney viscosity: ML1+10 (121°C): 25

[0651] Polymer F: Fluorocopolymer containing VdF units and perfluoro-(2,9,9-trihaloid-5-trifluoromethyl-3,6-dioxa-8-heptene) (AEHF-1) units VdF / AEHF-1=81.4 / 18.6 Weight average molecular weight: 950000 Tg: -27℃ Mooney viscosity: (ML1+10 (121℃)): 15 AEHF-1 is a compound represented by the following general formula: [ka]

[0652] Polymer G: (Comparative Polymer) Fluoropolymer containing VdF units and hexafluoropropylene (HFP) units VdF / HFP=95:5 Weight average molecular weight: 870000 Melting point: 141°C

[0653] Types of fluorinated ethers (E-1)HCF2-CF2-O-CH2-CF2-CF2H (E-2)HCF2-CF2-O-CH2-CH2-CH3 (E-3)HCF2-CF2-O-CH2-CH2-CH2-CH3 (E-4)HCF2-CF2-O-CH2-CF3 (E-5)HCF2-CF2-O-CH2-CH2-O- CF2-CF2H (E-6)CF3-CF2-CH2-O-CH2-CF2-CF3

[0654] Lithium salts LiPF6 LiFSI: Lithium bis(fluorosulfonyl)imide LiBOB: Lithium bis(oxalato)borate

[0655] Cyclic carbonate EC: Ethylene carbonate FEC: Fluoroethylene carbonate

[0656] Chain carbonate EMC: Ethyl methyl carbonate DMC: Dimethyl carbonate

[0657] Other solvents GBL: gamma-butyrolactone DME: Dimethoxyethane

[0658] (Method for measuring weight-average molecular weight) Measurements were made by gel permeation chromatography (GPC). Calculations were made using data measured using Tosoh AS-8010, CO-8020, and columns (three GMHHR-H columns connected in series) and Shimadzu RID-10A, with dimethylformamide (DMF) as the solvent at a flow rate of 1.0 ml / min (reference: polystyrene).

[0659] (Method for measuring Tg) A DSC curve was obtained by heating 10 mg of a sample at a rate of 20°C / min using a differential scanning calorimeter (Hitachi Technoscience, X-DSC823e). The glass transition temperature (Tg) was determined as the temperature at the intersection of the extension of the baseline before and after the second-order transition of the DSC curve and the tangent to the inflection point of the DSC curve.

[0660] (Method for measuring Mooney viscosity) <Mooney viscosity (ML1+10 (121℃, 140℃))> Measurements were performed in accordance with ASTM-D1646-15 and JIS K6300-1:2013. Measuring equipment: MV2000E model manufactured by ALPHA TECHNOLOGIES Rotor rotation speed: 2 rpm Measurement temperature: 121℃, 140℃

[0661] (Examples 1 to 17, Comparative Examples 1 to 6) (Coating on current collector) Eight parts by weight of various fluoropolymers were dissolved in N-methyl-2-pyrrolidone (NMP) as a solvent to obtain protective film-forming compositions.

[0662] The protective film-forming composition was coated to a thickness of 5 μm on the top of copper foil (15 μm) as a negative electrode current collector using a doctor blade. The coated composition was dried at approximately 100°C. An electrode was cut out to a size of 40 mm x 40 mm. The thickness of the coating after drying was 0.4 μm, and the density of the coating layer after drying was 1.6 g / cm. 3 In Comparative Examples 2 and 3, copper foil without the coating was used as the electrode.

[0663] Separately, LiCoO2, a conductive agent (Super-P, Timcal Ltd.), polyvinylidene fluoride (PVdF), and NMP were mixed to obtain a positive electrode composition. In this positive electrode composition, the mixing weight ratio of LiCoO2, the conductive agent, and PVDF was 97:1.5:1.5.

[0664] The above positive electrode composition was coated on top of an aluminum foil (thickness: about 15 μm) and dried under vacuum at about 110 °C to obtain a positive electrode. The obtained positive electrode was cut into a size of 39 mm × 39 mm to fabricate an electrode.

[0665] A polyethylene / polypropylene separator was interposed between the positive electrode obtained by the above process and the negative electrode current collector foil to manufacture a laminate cell. Here, various electrolytic solutions were obtained from the combinations of the Li salts and solvents described in Table 1 between the above positive electrode and the negative electrode.

[0666] <High-temperature storage characteristic evaluation test> The coin cell manufactured above was charged at a constant current-constant voltage up to 4.4 V at a current corresponding to 0.2C at 25 °C (hereinafter referred to as CC / CV charging. (0.1C cut)), then discharged at a constant current of 0.2C to 3V. Taking this as one cycle, the initial discharge capacity was determined from the discharge capacity of the third cycle. Here, 1C represents the current value for discharging the reference capacity of the battery in one hour. For example, 0.2C represents a current value that is 1 / 5 of that. After performing CC / CV charging (0.1C cut) up to 4.4V again, high-temperature storage was carried out under the conditions of 65 °C for 36 hours. After the battery was sufficiently cooled, the volume was measured by the Archimedes method, and the amount of gas generated was determined from the volume change before and after storage. Next, it was discharged at 0.2C to 3V at 25 °C, the remaining capacity after high-temperature storage was measured, and the ratio of the remaining capacity to the initial discharge capacity was determined, and this was taken as the storage capacity maintenance rate (%). (Remaining capacity) / (Initial discharge capacity)×10 = Storage capacity maintenance rate (%)

[0667] <Evaluation of IV resistance> After evaluation of the initial discharge capacity, the battery was charged at a constant current of 0.2 C at 25°C to half the initial discharge capacity. The battery was discharged at 2.0 C at 25°C, and the voltage was measured 10 seconds later. The resistance was calculated from the voltage drop during discharge and used as the IV resistance. The resistance increase rate (%) was calculated from the resistance before and after high-temperature storage. (Resistance after high-temperature storage) / (Resistance before high-temperature storage) x 100 = Resistance increase rate (%)

[0668] <Measurement of the amount of transition metal eluted from the positive electrode> After measuring the storage capacity, the cell was disassembled, the negative electrode was washed with DMC, and the transition metals deposited on the negative electrode were removed. The amount of Ni dissolved from the DMC solution containing the transition metals was determined by quantifying Ni content using ICP emission spectrometry. The amount of Ni dissolved from the positive electrode was assumed to be the amount deposited on the negative electrode. The results are shown in Table 1.

[0669] (Thickness of coating layer after drying) The thickness of the coating layer after drying was calculated from the part by weight of the fluoropolymer in the protective film-forming composition and the thickness of the coating layer before drying.

[0670] (Dry coating layer density) The weight was calculated from the change in weight of the coating layer before and after drying, and the weight was divided by the volume of the coating layer after drying to calculate the density of the coating layer after drying.

[0671] [Table 1]

[0672] (Examples 18 to 26, Comparative Examples 7 to 10) (Coating on Li metal) Eight parts by weight of various fluoropolymers were dissolved in N-methyl-2-pyrrolidone (NMP) as a solvent to obtain protective film-forming compositions.

[0673] The protective film-forming composition was coated on a lithium metal thin film (thickness: about 15 μm) to a thickness of about 8 μm using a doctor blade. The coated result was dried at about 25°C and then heat-treated in vacuum at about 40°C to prepare a lithium anode with a protective film formed on the lithium metal. A cutout electrode measuring 20 mm x 20 mm was prepared. The thickness of the coating after drying was 0.4 μm, and the density of the coating layer after drying was 1.6 g / cm. 3 It was.

[0674] Separately, LiNi 0.8 Mn 0.1 Co 0.1 LiCoO, a conductive agent (Super-P, Timcal Ltd.), polyvinylidene fluoride (PVdF), and NMP were mixed to obtain a positive electrode composition in a weight ratio of 97.5:1.25:1.25.

[0675] The positive electrode composition was coated on an aluminum foil (thickness: about 15 μm) and dried in vacuum at about 110° C. to obtain a positive electrode. The obtained positive electrode was cut into a size of 19 mm × 19 mm to prepare an electrode.

[0676] A laminate cell was fabricated by placing a polyethylene / polypropylene separator between the cathode obtained by the above process and a lithium metal anode. Various electrolyte solutions were prepared between the cathode and anode using the combinations of Li salts and solvents listed in Table 2.

[0677] <High-temperature storage characteristic evaluation test> The coin cells manufactured as described above were charged at 25°C with a constant current up to 4.3 V at a current corresponding to 0.2C (hereinafter referred to as CC / CV charging) (0.1C cut), then discharged at a constant current of 0.2C down to 3V. This was taken as one cycle, and the initial discharge capacity was determined from the discharge capacity of the third cycle. Here, 1C represents the current value at which the reference capacity of the battery is discharged in one hour. For example, 0.2C represents a current value that is 1 / 5 of that. After performing CC / CV charging (0.1C cut) up to 4.3V again, high-temperature storage was carried out under the conditions of 45°C for 48 hours. After sufficiently cooling the battery, the volume was measured by the Archimedes method, and the amount of gas generated was determined from the volume change before and after storage. Next, it was discharged at 0.2C at 25°C down to 3V, the remaining capacity after high-temperature storage was measured, and the ratio of the remaining capacity to the initial discharge capacity was determined, which was taken as the storage capacity retention rate (%). (Remaining capacity) / (Initial discharge capacity)×100 = Storage capacity retention rate (%)

[0678] <Evaluation of internal resistance The battery for which the evaluation of the initial discharge capacity had been completed was charged at 25°C with a constant current of 0.2C to a capacity that was half of the initial discharge capacity. This was discharged at 2.0C at 25°C, and the voltage at 10 seconds was measured. The resistance was calculated from the voltage drop during discharge and taken as the internal resistance. The resistance increase rate (%) was calculated from the resistance before and after high-temperature storage. (Resistance after high-temperature storage) / (Resistance before high-temperature storage)×100 = Resistance increase rate (%)

[0679] <Measurement of the amount of transition metal eluted from the positive electrode After disassembling the cell after the storage capacity measurement, the negative electrode was washed with DMC, and the transition metal deposited on the negative electrode was taken out. The amount of transition metal eluted was determined by quantifying Mn in the DMC solution containing the transition metal by ICP emission analysis. It was assumed that the amount of Mn eluted from the positive electrode was the amount deposited on the negative electrode. The results are shown in Table 2.

[0680] (Thickness of the coating layer after drying) The thickness of the coating layer after drying was calculated from the parts by weight of the fluoropolymer in the protective film-forming composition and the thickness of the coating layer on the lithium metal foil.

[0681] (Dry coating layer density) The weight was calculated from the change in weight of the coating layer before and after drying, and the weight was divided by the volume of the coating layer after drying to calculate the density of the coating layer after drying.

[0682] [Table 2]

[0683] From the results in Tables 1 and 2, it can be determined that the secondary battery of the present disclosure has excellent effects in terms of capacity retention rate, amount of gas generated, rate of resistance increase, amount of Mn elution, and amount of Ni elution, and that deterioration of the negative electrode is suppressed, thereby achieving the effect of improving battery life. [Industrial Applicability]

[0684] The secondary battery of the present disclosure can be used as various general secondary batteries.

Claims

1. A secondary battery having a negative electrode in which a fluoropolymer is laminated on a layer containing a metal, and having a liquid electrolyte, the metal is at least one selected from lithium, sodium, magnesium, and zinc; The fluoropolymer comprises vinylidene fluoride units (A) and A structural unit (B) derived from at least one monomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, a monomer represented by general formula (1), a monomer represented by general formula (2), and a monomer represented by general formula (3). is a copolymer having A secondary battery characterized in that the liquid electrolyte contains a fluorinated ether. 【Chemistry 1】 In the formula, Rf １ is a linear or branched fluoroalkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and when the fluorinated alkyl group or fluorinated alkoxy group has 2 or more carbon atoms, it can contain an oxygen atom (—O—) between carbon atoms. 【Chemistry 2】 Rf ２ is a linear or branched fluoroalkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and when the fluorinated alkyl group or fluorinated alkoxy group has 2 or more carbon atoms, it can contain an oxygen atom (—O—) between carbon atoms. 【Transformation 3】 In the formula, R １ , R ２ and R ３ are each independently a hydrogen atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. X is a single bond or an atomic group having a main chain consisting of 1 to 20 atoms and a molecular weight of 500 or less. Y represents an inorganic cation and / or an organic cation.

2. 2. The secondary battery according to claim 1, wherein the copolymer contains 30 to 99.5 mol % of vinylidene fluoride based on the total amount of monomer units.

3. 3. The secondary battery according to claim 1, wherein the fluorinated ether is a compound represented by the following general formula (5): 【Chemistry 4】 (R is an alkyl group which may contain an ether group, or a fluorinated alkyl group which may contain an ether group.)

4. 4. The secondary battery according to claim 3, wherein the compound represented by the general formula (5) is at least one compound selected from the group consisting of compounds represented by the following general formulas: 【Transformation 5】

5. A secondary battery having a negative electrode including a laminate in which a fluoropolymer is laminated directly on a current collector, The fluoropolymer comprises vinylidene fluoride units (A) and A structural unit (B) derived from at least one monomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, a monomer represented by general formula (1), a monomer represented by general formula (2), and a monomer represented by general formula (3). is a copolymer having A secondary battery characterized in that the liquid electrolyte contains a fluorinated ether. 【Transformation 6】 In the formula, Rf １ is a linear or branched fluoroalkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and when the fluorinated alkyl group or fluorinated alkoxy group has 2 or more carbon atoms, it can contain an oxygen atom (—O—) between carbon atoms. 【Transformation 7】 Rf ２ is a linear or branched fluoroalkyl group or fluorinated alkoxy group having 1 to 12 carbon atoms, and when the fluorinated alkyl group or fluorinated alkoxy group has 2 or more carbon atoms, it can contain an oxygen atom (—O—) between carbon atoms. 【Transformation 8】 In the formula, R １ , R ２ and R ３ are each independently a hydrogen atom, a chlorine atom, or an alkyl group having 1 to 5 carbon atoms. X is a single bond or an atomic group having a main chain consisting of 1 to 20 atoms and a molecular weight of 500 or less. Y represents an inorganic cation and / or an organic cation.

6. 6. The secondary battery according to claim 5, wherein the copolymer has a vinylidene fluoride content of 30 to 99.5 mol % based on the total monomer units.

7. 7. The secondary battery according to claim 5, wherein the fluorinated ether is a compound represented by the following general formula (5): 【Chemistry 9】 (R is an alkyl group which may contain an ether group, or a fluorinated alkyl group which may contain an ether group.)

8. 8. The secondary battery according to claim 7, wherein the compound represented by the general formula (5) is at least one compound selected from the group consisting of compounds represented by the following general formulas: 【Chemistry 10】

Images