Ionic conductive compound, electrolyte for lithium ion secondary battery, composite solid electrolyte for lithium ion secondary battery, and lithium ion secondary battery

Abstract

To provide an ionic conductive compound that can inhibit side reactions with a sulfide-based solid electrolyte while exhibiting high lithium ion conductivity, and to provide an electrolyte for a lithium ion secondary battery, a composite solid electrolyte for a lithium ion secondary battery, and a lithium ion secondary battery employing the ionic conductive compound.SOLUTION: An ionic conductive compound having a specific oxetane skeleton.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ion-conductive compound, an electrolyte for a lithium ion secondary battery, a composite solid electrolyte for a lithium ion secondary battery, and a lithium ion secondary battery. [Background technology]

[0002] All-solid-state batteries are batteries that have a solid electrolyte layer between a positive electrode layer and a negative electrode layer, and have the advantage that safety devices can be more easily simplified compared to liquid-based batteries that have an electrolyte solution containing a flammable organic solvent.

[0003] Among all-solid-state batteries, all-solid-state lithium-ion batteries have attracted attention because they have a high energy density due to the use of a battery reaction involving the movement of lithium ions, and because they use a solid electrolyte instead of an electrolytic solution containing an organic solvent as the electrolyte between the positive electrode and the negative electrode (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-107414 Summary of the Invention [Problem to be solved by the invention]

[0005] Sulfide-based solid electrolytes are sometimes used as inorganic solid electrolytes in all-solid-state batteries. However, sulfide-based solid electrolytes generally undergo side reactions when in contact with other materials constituting the battery, which can lead to decomposition of the sulfide-based solid electrolyte itself. Therefore, there is a demand for materials that can suppress side reactions with sulfide-based solid electrolytes and suppress decomposition reactions of the sulfide-based solid electrolyte.

[0006] Furthermore, because there are few contact points between inorganic solid electrolytes, other electrolytes have been added to inorganic solid electrolytes to improve ionic conductivity. In conventional technology, polyether-based polymers, primarily composed of polyethylene oxide (PEO), a polymer electrolyte, have been used as other electrolytes added to inorganic solid electrolytes. However, the inventors' research has revealed that conventional polyether-based polymers have room for improvement in terms of suppressing side reactions with sulfide-based solid electrolytes and providing high lithium ion conductivity. Lithium ion conductivity is a property that can be calculated by the product of ionic conductivity and lithium ion transport number. Many inventions in this technical field generally aim to improve ionic conductivity. This invention is novel in that it focuses on the ionic transport number, which is a trade-off between ionic conductivity and lithium ion transport number, and also focuses on the properties calculated from the ionic transport number.

[0007] An object of the present invention is to provide an ion-conductive compound that can suppress side reactions with sulfide-based solid electrolytes and has high lithium ion conductivity, an electrolyte for a lithium ion secondary battery that uses the ion-conductive compound, a composite solid electrolyte for a lithium ion secondary battery, and a lithium ion secondary battery. [Means for solving the problem]

[0008] As a result of extensive investigations to achieve the above object, the present inventors have found that a specific ion-conductive compound can suppress side reactions with a sulfide-based solid electrolyte and has high lithium ion conductivity, and have completed the present invention.

[0009] The aspects of the present invention are as follows. Item 1 An ion-conductive compound having an oxetane skeleton represented by the following general formula (A): [ka] [In the formula, R 1 is an alkyl group having 1 to 6 carbon atoms, and R 2 is a hydrogen atom, -CH2O(CH2)a O(CH2) b an alkylene glycol alkyl ether group represented by H, -CHOR 8 or a bridging group containing an ethylenically unsaturated double bond represented by -CH2O(CH2) c (CHR 6 ) d (CH2) e R 7 The number of repeating units, a, is an integer of 1 to 8, and the number of repeating units, b, is an integer of 0 to 6. R 8 is an acrylic group, a methacrylic group, an allyl group, or a methallyl group. 6 are the same or different and are a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R 7 represents a hydrogen atom, a hydroxyl group, a nitrile group, a trifluoromethyl group, an alkoxy group, or a cyclic ether group which may have a substituent. c, which is the number of repeating units, is an integer from 0 to 4, d, which is the number of repeating units, is an integer from 0 to 4, and e, which is the number of repeating units, is an integer from 0 to 10.] Section 2 Item 1. An electrolyte for a lithium ion secondary battery, comprising the ion-conductive compound according to item 1 and a lithium salt compound. Section 3 Item 3. A composite solid electrolyte for lithium ion secondary batteries, comprising an inorganic solid electrolyte and the electrolyte for lithium ion secondary batteries according to Item 2. Section 4 Item 4. A composite solid electrolyte for a lithium ion secondary battery according to Item 3, wherein the inorganic solid electrolyte is a sulfide-based solid electrolyte. Section 5 Item 3. A lithium ion secondary battery using the electrolyte for lithium ion secondary batteries according to Item 2. Section 6 Item 3. A lithium ion secondary battery using the composite solid electrolyte for lithium ion secondary batteries according to Item 3 or 4. [Effects of the Invention]

[0010] The ion-conductive compound of the present invention is a compound having a specific structure, and therefore can suppress side reactions with sulfide-based solid electrolytes and has high lithium ion conductivity. DETAILED DESCRIPTION OF THE INVENTION

[0011] The ion-conductive compound of the present invention has an oxetane skeleton represented by the general formula (A), which makes it possible to suppress side reactions with sulfide-based solid electrolytes and to have high lithium ion conductivity.

[0012] The reason why the above effects are obtained in the present invention is not clear, but is presumed to be as follows. R in formula (A) 1 is an alkyl group having 1 to 6 carbon atoms, which tends to cause steric hindrance and can suitably suppress coordination of lithium ions to ether oxygen, thereby achieving a higher ion transport number (lithium ion conductivity) and suppressing side reactions with the sulfide-based solid electrolyte.

[0013] <Ion-conductive compounds> The ion-conductive compound of the present invention has an oxetane skeleton represented by the following general formula (A). [ka] [In the formula, R 1 is an alkyl group having 1 to 6 carbon atoms, and R 2 is a hydrogen atom, -CH2O(CH2) a O(CH2) b an alkylene glycol alkyl ether group represented by H, -CHOR 8 or a bridging group containing an ethylenically unsaturated double bond represented by -CH2O(CH2) c (CHR 6 ) d (CH2) e R 7 The number of repeating units, a, is an integer of 1 to 8, and the number of repeating units, b, is an integer of 0 to 6. R 8 is an acrylic group, a methacrylic group, an allyl group, or a methallyl group. 6 are the same or different and are a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R 7represents a hydrogen atom, a hydroxyl group, a nitrile group, a trifluoromethyl group, an alkoxy group, or a cyclic ether group which may have a substituent. c, which is the number of repeating units, is an integer from 0 to 4, d, which is the number of repeating units, is an integer from 0 to 4, and e, which is the number of repeating units, is an integer from 0 to 10.]

[0014] R in formula (A) 1 The alkyl group having 1 to 6 carbon atoms (preferably 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms) may be linear or branched, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, and a hexyl group. Of these, a methyl group and an ethyl group are preferred.

[0015] R in formula (A) 2 -CH2O(CH2) a O(CH2) b The alkylene glycol alkyl ether group represented by H has excellent molecular mobility and has a structure that maintains an appropriate distance between oxygen atoms, resulting in a high ion transport number (lithium ion conductivity).

[0016] R in formula (A) 2 In the formula (A), a is an integer of 1 to 8, preferably an integer of 1 to 7, more preferably an integer of 1 to 6, even more preferably an integer of 1 to 5, particularly preferably an integer of 1 to 4, most preferably an integer of 1 to 3, and most preferably an integer of 1 to 2. 2 In the formula, b is an integer of 0 to 6, preferably an integer of 0 to 4, more preferably an integer of 1 to 3, and even more preferably an integer of 1 to 2.

[0017] R in formula (A) 2 -CH2OR 8 The crosslinking group containing an ethylenically unsaturated double bond represented by the formula (I) is capable of crosslinking, and therefore can form a polymer by crosslinking.

[0018] R in formula (A) 2 In R 8is an acrylic group, a methacrylic group, an allyl group, or a methallyl group, preferably an acrylic group, a methacrylic group, or an allyl group, more preferably a methacrylic group or an allyl group, and even more preferably an allyl group.

[0019] R in formula (A) 2 -CH2O(CH2) c (CHR 6 ) d (CH2) e R 7 The group represented by the formula (I) does not allow lithium ions to be coordinated, and therefore a high ion transport number (lithium ion conductivity) can be obtained.

[0020] R in formula (A) 2 In R 6 The alkyl group having 1 to 4 carbon atoms (preferably 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms) may be linear or branched, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group. Of these, a methyl group and an ethyl group are preferred.

[0021] R in formula (A) 2 In R 6 As the alkyl group, an alkyl group having 1 to 4 carbon atoms is preferred.

[0022] R in formula (A) 2 In R 7 Examples of the alkoxy group include alkoxy groups having 1 to 6 carbon atoms (preferably 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms). The alkoxy group may be linear or branched, and examples include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentoxy, and n-hexyloxy. Of these, methoxy and ethoxy groups are preferred.

[0023] R in formula (A) 2 In R 7The number of ring members of the cyclic ether group, which may have a substituent, is preferably 3 to 10, more preferably 3 to 8, and even more preferably 3 to 6. The number of oxygen atoms in the cyclic ether group is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 3. In this specification, the number of ring members refers to the number of atoms constituting the skeleton of the ring, and for example, in the case of a 5-membered ring, it is 5.

[0024] Examples of the substituent that the cyclic ether group has include a carbonyl group, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having an alkyl group having 1 to 4 carbon atoms. Of these, a carbonyl group and an alkyl group having 1 to 4 carbon atoms are preferred, and a carbonyl group is more preferred. Examples of the alkyl group having 1 to 4 carbon atoms include R 6 The same applies to the alkyl group having 1 to 4 carbon atoms as in the above, including the preferred embodiments. Similarly, the alkyl group having 1 to 4 carbon atoms contained in the alkoxy group can also be used as the alkyl group having 1 to 4 carbon atoms as in the above, including the preferred embodiments. 6 The same applies to the alkyl group having 1 to 4 carbon atoms, including preferred embodiments.

[0025] R 7 The cyclic ether group, which may have a substituent, preferably has a substituent. The cyclic ether group preferably has a carbonate group (-O-(C=O)-O-) in the group. 7 Preferred embodiments of the cyclic ether group which may have a substituent are shown below, where * represents a bond. [ka]

[0026] R in formula (A) 2 In R 7 R is preferably a hydrogen atom, a nitrile group, a trifluoromethyl group, an alkoxy group, or a cyclic ether group which may have a substituent, more preferably a hydrogen atom, a nitrile group, a trifluoromethyl group, or a cyclic ether group which may have a substituent, and even more preferably a trifluoromethyl group. 7 As the alkyl group, a hydrogen atom, a nitrile group, a trifluoromethyl group, and a cyclic ether group which may have a substituent are also preferred.

[0027] R in formula (A) 2 In the formula (A), c is an integer of 0 to 4, preferably an integer of 1 to 3, more preferably an integer of 1 to 2, and even more preferably an integer of 1. d is an integer of 0 to 4, preferably an integer of 0 to 3, more preferably an integer of 0 to 2, and even more preferably an integer of 0. R in formula (A) 2 In the formula, e is an integer of 0 to 10, preferably an integer of 0 to 8, more preferably an integer of 0 to 6, still more preferably an integer of 0 to 2, and particularly preferably an integer of 0.

[0028] R in formula (A) 2 As an example, -CH2O(CH2) a O(CH2) b an alkylene glycol alkyl ether group represented by H, -CHOR 8 a bridging group containing an ethylenically unsaturated double bond represented by -CH2O(CH2) c (CHR 6 ) d (CH2) e R 7 A group represented by the formula: -CH2O(CH2) is preferred. a O(CH2) b an alkylene glycol alkyl ether group represented by H, -CHOR 8 A crosslinking group containing an ethylenically unsaturated double bond represented by the formula: -CH2O(CH2) is more preferred. a O(CH2) b An alkylene glycol alkyl ether group represented by H is more preferred.

[0029] Preferred embodiments of the ion-conductive compound having an oxetane skeleton represented by formula (A) are shown below. Among them, the compounds represented by formulas (A-1), (A-2), (A-3), (A-4), and (A-9) are preferred, the compounds represented by formulas (A-1), (A-2), and (A-3) are more preferred, and the compound represented by formula (A-1) is even more preferred. [ka]

[0030] <Method for producing an ion-conductive compound having an oxetane skeleton represented by formula (A)> The method for producing the ion-conductive compound having an oxetane skeleton represented by formula (A) of the present invention is not particularly limited, and a person skilled in the art can appropriately produce it by a known synthesis method, etc. For example, the ion-conductive compound having an oxetane skeleton represented by formula (A) can be obtained by reacting an oxetane alcohol with a halogenated alkyl ether.

[0031] <Electrolyte for lithium-ion secondary batteries> The electrolyte for a lithium ion secondary battery of the present invention is not particularly limited as long as it contains the ion-conductive compound of the present invention, but it preferably contains the ion-conductive compound of the present invention and a lithium salt compound. Here, the ion-conductive compound of the present invention may be used alone or in combination of two or more kinds.

[0032] The electrolyte for a lithium ion secondary battery of the present invention is usually a liquid electrolyte at room temperature, and is preferably made into a gel electrolyte by mixing with a polymer or other high molecular weight substance. Furthermore, in this specification, a solid electrolyte refers to an electrolyte that is solid (does not exhibit fluidity) at room temperature. Here, in this specification, room temperature refers to the temperature range in which a power supply is expected to operate normally. The temperature range in which a power supply is expected to operate normally has an upper limit of about 120°C, or in some cases about 60°C, and a lower limit of about -40°C, or in some cases about -20°C.

[0033] In the electrolyte for lithium ion secondary batteries of the present invention, the content of the ion-conductive compound of the present invention in 100% by mass of the ion-conductive compounds is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may even be 100% by mass, which tends to more suitably achieve the effects of the present invention. In this specification, the content of the ion-conductive compound can be determined by nuclear magnetic resonance spectroscopy. Furthermore, in this specification, the ion-conductive compound means a compound that can conduct ions.

[0034] The lithium salt compound is preferably a lithium salt compound having a wide potential window, such as those commonly used in lithium ion batteries. Examples of lithium salt compounds include LiBF, LiPF, LiClO, LiCF, Li(CF, SO)N, LiN(CF, SO)(LiTFSI), LiN(SFO)(LiFSI), LiN(CF, SO), and LiN[CF, SC(CF, SO)]. These compounds may be used alone or in combination of two or more.

[0035] When the electrolyte for lithium ion secondary batteries of the present invention contains a lithium salt compound, the content of the lithium salt compound is preferably 10 to 200 parts by mass, more preferably 15 to 100 parts by mass, and even more preferably 20 to 50 parts by mass, relative to 100 parts by mass of the ion-conductive compound (preferably the ion-conductive compound of the present invention). This tends to more suitably achieve the effects of the present invention. In this specification, the notation "to" means that the value is equal to or greater than the value before the notation "to" and equal to or less than the value after the notation "to". In addition, in this specification, the content of the lithium salt compound means the total content when multiple types of lithium salt compounds are contained as the lithium salt compound. The same applies to other contents.

[0036] In the electrolyte for lithium ion secondary batteries of the present invention, the total content of the ion-conductive compound (preferably the ion-conductive compound of the present invention) and the lithium salt compound is preferably 60 mass % or more, more preferably 80 mass % or more, even more preferably 90 mass % or more, particularly preferably 95 mass % or more, based on 100 mass % of the electrolyte for lithium ion secondary batteries of the present invention, and may even be 100 mass %. This tends to more suitably achieve the effects of the present invention.

[0037] The lithium ion secondary battery electrolyte of the present invention may contain a room-temperature molten salt, which means a salt that is at least partially liquid at room temperature.

[0038] Room-temperature molten salts are also called ionic liquids, and known examples include pyridine-based, aliphatic amine-based, and alicyclic amine-based quaternary ammonium organic cations. These may be used alone or in combination of two or more. Examples of quaternary ammonium organic cations include imidazolium ions such as dialkylimidazolium and trialkylimidazolium ions, tetraalkylammonium ions, alkylpyridinium ions, pyrazolium ions, pyrrolidinium ions, and piperidinium ions.

[0039] The lithium ion secondary battery electrolyte of the present invention may contain a plasticizer. The plasticizer is not particularly limited, but dicyano compounds and branched ether compounds are preferred. These may be used alone or in combination of two or more.

[0040] The lithium ion secondary battery electrolyte of the present invention may contain, in addition to the above components, for example, a reaction initiator, a cross-linking aid, a binder, etc. These may be used alone or in combination of two or more. Since the ion-conductive compound of the present invention can suppress side reactions with sulfide-based solid electrolytes while remaining a low molecular weight and has high lithium ion conductivity, it is also preferable that the lithium ion secondary battery electrolyte of the present invention does not contain a reaction initiator or a cross-linking aid.

[0041] Examples of the reaction initiator include a thermal reaction initiator and a photoreaction initiator, which may be used alone or in combination of two or more.

[0042] As the thermal reaction initiator, a radical initiator selected from organic peroxides, azo compounds, etc. is used. As the organic peroxide, those usually used for crosslinking purposes, such as ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, and peroxyesters, are used, and as the azo compound, those usually used for crosslinking purposes, such as azonitrile compounds, azoamide compounds, and azoamidine compounds, are used.

[0043] As the photoreaction initiator, radical initiators such as alkylphenones, benzophenones, acylphosphine oxides, titanocenes, triazines, bisimidazoles, and oxime esters are used.

[0044] The crosslinking aid may be any of ethylene glycol diacrylate, ethylene glycol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane triacrylate, allyl methacrylate, allyl acrylate, diallyl maleate, triallyl isocyanurate, maleimide, phenylmaleimide, maleic anhydride, etc. These may be used alone or in combination of two or more.

[0045] The electrolyte for a lithium ion secondary battery of the present invention can be prepared using a conventionally known method, for example, by adding a lithium salt compound or the like to the ion-conductive compound of the present invention as needed, and mixing them.

[0046] The lithium ion conductivity (25°C) of the electrolyte for lithium ion secondary batteries of the present invention is preferably 1 x 10 -5 (S / cm) or more, more preferably 5×10 -5 (S / cm) or more, more preferably 8×10 -5 (S / cm) or more, particularly preferably 1×10 -4 (S / cm) or more, and the upper limit is not particularly limited, but for example, 5×10 -3 (S / cm) or less. In this specification, the lithium ion conductivity of an electrolyte for a lithium ion secondary battery is calculated as the product of the ionic conductivity and the lithium ion transport number, and specifically, is measured by the method described in the examples.

[0047] <Composite solid electrolyte for lithium-ion secondary batteries> The composite solid electrolyte for a lithium ion secondary battery of the present invention (sometimes simply referred to as the composite solid electrolyte) comprises an inorganic solid electrolyte and the lithium ion secondary battery electrolyte of the present invention (the ion-conductive compound of the present invention). Because the composite solid electrolyte of the present invention contains the lithium ion secondary battery electrolyte of the present invention (the ion-conductive compound of the present invention) in addition to the inorganic solid electrolyte, it is believed that the contact area at the interface between the electrode material layer and the solid electrolyte layer is larger than when the solid electrolyte is formed solely from an inorganic solid electrolyte. As a result, the interfacial resistance between the electrode and the electrolyte is reduced, and excellent charge / discharge characteristics are exhibited. Furthermore, within the composite solid electrolyte, the lithium ion secondary battery electrolyte of the present invention (the ion-conductive compound of the present invention) is believed to reduce the internal resistance of the composite solid electrolyte by forming adhesion between the inorganic solid electrolyte particles. The lithium ion secondary battery electrolyte of the present invention (the ion-conductive compound of the present invention) may be used alone or in combination of two or more.

[0048] Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. These may be used alone or in combination of two or more. In the composite solid electrolyte of the present invention, the inorganic solid electrolyte is contained, for example, in the form of particles, and has a structure in which the particles of the inorganic solid electrolyte are tightly adhered to each other by the electrolyte for lithium ion secondary batteries of the present invention (the ion-conductive compound of the present invention).

[0049] The oxide-based solid electrolyte is not particularly limited as long as it contains oxygen, has the ionic conductivity of a metal belonging to Group 1 or 2 of the periodic table, and has electronic insulation properties.

[0050] Specific compounds that make up oxide-based solid electrolytes include Li x La y TiO3 [x=0.3~0.7, y=0.3~0.7] (LLT), Li x La y Zr z M m O n(M is at least one element selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, and x satisfies 5≦x≦10, y satisfies 1≦y≦4, z satisfies 1≦z≦4, m satisfies 0≦m≦2, and n satisfies 5≦n≦20.) Li x B y M z O n (wherein M is at least one element selected from C, S, Al, Si, Ga, Ge, In, and Sn, x satisfies 0≦x≦5, y satisfies 0≦y≦1, z satisfies 0≦z≦1, and n satisfies 0≦n≦6), Li x (Al,Ga) y (Ti,Ge) z Si a P m O n (where 1≦x≦3, 0≦y≦1, 0≦z≦2, 0≦a≦1, 1≦m≦7, 3≦n≦13), Li (3-2x) M x DO (x represents a number of 0 or more and 0.1 or less, M represents a divalent metal atom, and D represents a halogen atom or a combination of two or more halogen atoms), Li x Si y O z (1≦x≦5, 0 <y≦3、1≦z≦10)、Li x S y O z (1≦x≦3, 0 <y≦2、1≦z≦10)、Li3BO3-Li2SO4、Li2O-B2O3-P2O5、Li2O-SiO2、Li6BaLa2Ta2O 12 , LiPO (4-3 / 2w) N w (w<1), Li with LISICON (Lithium super ionic conductor) type crystal structure 3.5 Zn 0.25 GeO4, La with perovskite crystal structure 0.55 Li 0.35 TiO3, LiTi2P3O with NASICON (sodium super ionic conductor) type crystal structure 12 , Li (1+x+y) (Al,Ga) x (Ti,Ge) (2-x) Si yP (3-y) O 12 (where 0≦x≦1, 0≦y≦1), and Li7La3Zr2O12 having a garnet-type crystal structure. Phosphorus compounds containing Li, P, and O are also desirable. Examples include lithium phosphate (Li3PO4), LiPON, LiPOD (wherein D is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc.), and the like, in which some of the oxygen in lithium phosphate has been substituted with nitrogen. LiAON (wherein A is at least one selected from Si, B, Ge, Al, C, Ga, etc.) and the like can also be preferably used.

[0051] Among them, Li x La y TiO3 [x=0.3~0.7, y=0.3~0.7] (LLT), Li x La y Zr z M m O n (M is at least one element selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, and x satisfies 5≦x≦10, y satisfies 1≦y≦4, z satisfies 1≦z≦4, m satisfies 0≦m≦2, and n satisfies 5≦n≦20.) Li7La3Zr2O 12 (LLZ), Li3BO3, Li3BO3-Li2SO4, Li3BO3-Li2CO3, Li x (Al,Ga) y (Ti,Ge) z Si a P m O n (However, 1≦x≦3, 0≦y≦1, 0≦z≦2, 0≦a≦1, 1≦m≦7, 3≦n≦13) is preferred.

[0052] The sulfide-based solid electrolyte is not particularly limited as long as it contains sulfur, has the ionic conductivity of a metal belonging to Group 1 or 2 of the periodic table, and has electronic insulation properties.

[0053] The sulfide-based solid electrolyte may be a glass-based sulfide solid electrolyte or a glass-ceramic-based sulfide solid electrolyte. These may be used alone or in combination of two or more. The glass-based sulfide solid electrolyte can be obtained by vitrifying raw materials. The glass-ceramic-based sulfide solid electrolyte can be obtained, for example, by heat-treating a glass-based sulfide solid electrolyte. In addition, the sulfide-based solid electrolyte preferably has a crystalline structure. Examples of the crystalline structure include a Thio-LISICON-type crystalline structure, an LGPS-type crystalline structure, and an Argyrodite-type crystalline structure.

[0054] Examples of glass-based sulfide solid electrolytes include Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, etc. These may be used alone or in combination of two or more.

[0055] Examples of sulfide-based solid electrolytes having a crystalline structure include Li 10 GeP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li 9.42 Si 1.02 P 2.1 S 9.96 O 2.24 LGPS-type sulfide solid electrolytes such as Li6PS5Cl, Li 6.6 Ge 0.6 P 0.4 S5I, Li7Ge3PS 12 Argyrodite-type sulfide solid electrolytes such as Li 4.275 Ge 0.61 Ga 0.25Examples of suitable sulfide solid electrolytes include Thio-LISICON-type sulfide solid electrolytes such as LiSnS4, Li4SnS4, and β-Li3PS4. Among these, argyrodite-type sulfide solid electrolytes and Thio-LISICON-type sulfide solid electrolytes are preferred, with argyrodite-type sulfide solid electrolytes being more preferred. These may be used alone or in combination of two or more.

[0056] The sulfide-based solid electrolyte is preferably a sulfide-based solid electrolyte having high ionic conductivity from the viewpoint of improving the electrical characteristics of the all-solid-state lithium ion secondary battery. Specific examples of the ionic conductivity include sulfide-based solid electrolytes having a conductivity of 1×10 -4 S / cm or more is preferable, and 1×10 -3 It is more preferable that the viscosity is S / cm or more.

[0057] The inorganic solid electrolyte is preferably a sulfide-based solid electrolyte. The ion-conductive compound of the present invention can suppress side reactions with the sulfide-based solid electrolyte and has high lithium ion conductivity, so that the effects of the present invention can be more suitably exhibited.

[0058] When the inorganic solid electrolyte is in the form of particles, the particle size is, for example, 0.01 to 100 μm, and preferably 0.1 to 20 μm.

[0059] In the composite solid electrolyte for lithium ion secondary batteries of the present invention, the mass ratio of the inorganic solid electrolyte to the electrolyte for lithium ion secondary batteries of the present invention (preferably the ion-conductive compound of the present invention) is not particularly limited, but from the viewpoint of more suitably exhibiting excellent charge-discharge characteristics in the secondary battery, the content of the electrolyte for lithium ion secondary batteries of the present invention (preferably the ion-conductive compound of the present invention) per 100 parts by mass of the inorganic solid electrolyte is preferably 0.1 to 1000 parts by mass, more preferably 0.5 to 800 parts by mass, even more preferably 5 to 600 parts by mass, and particularly preferably 10 to 400 parts by mass.

[0060] In the composite solid electrolyte for lithium ion secondary batteries of the present invention, the total content of the inorganic solid electrolyte and the electrolyte for lithium ion secondary batteries of the present invention is preferably 60 mass % or more, more preferably 80 mass % or more, still more preferably 90 mass % or more, particularly preferably 95 mass % or more, and may even be 100 mass %, based on 100 mass % of the composite solid electrolyte for lithium ion secondary batteries of the present invention. This tends to more suitably achieve the effects of the present invention.

[0061] The composite solid electrolyte for a lithium ion secondary battery of the present invention may contain, in addition to the inorganic solid electrolyte and the electrolyte for a lithium ion secondary battery of the present invention, for example, a crosslinkable polymer, a reaction initiator, a crosslinking aid, a binder, etc. These may be used alone or in combination of two or more kinds.

[0062] The composite solid electrolyte for lithium ion secondary batteries of the present invention can be prepared by using a conventionally known method, for example, by mixing an inorganic solid electrolyte with the electrolyte for lithium ion secondary batteries of the present invention (the ion-conductive compound of the present invention). Specifically, the composite solid electrolyte can be produced by a method in which the inorganic solid electrolyte is dispersed in a solvent containing the electrolyte for lithium ion secondary batteries of the present invention (the ion-conductive compound of the present invention) to prepare a composite solid electrolyte slurry, and the slurry is then sprayed and dried in hot air to obtain the composite solid electrolyte, or by a method in which the solvent of the dispersed slurry is evaporated to dryness by heating under atmospheric pressure or reduced pressure.

[0063] The dispersion solvent can be water, an organic solvent, or a mixture of these in any ratio. Whether the resulting dispersion slurry is a homogeneous solution or the solute insoluble in the dispersion solvent is an inorganic solid electrolyte and / or the lithium-ion secondary battery electrolyte of the present invention, it can be prepared by the above-mentioned general preparation method. The composite solid electrolyte obtained by removing only the dispersion solvent is preferably obtained by removing as much of the remaining dispersion solvent and water as possible. For example, this can be achieved by heating at 30°C to 200°C and evacuating the mixture for 1 hour to 48 hours. The composite solid electrolyte of the present invention obtained by removing the dispersion solvent not only has a high ion transport number (lithium ion conductivity) but also contains the ion-conductive compound of the present invention, which is a liquid component, thereby reducing the porosity and increasing the particle interface adhesion during layer formation. Polar solvents are preferred as the organic solvent. Specifically, acetonitrile, ethyl alcohol, methyl alcohol, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, dioxane, methyl ethyl ketone, methyl isobutyl ketone, etc. can be used alone or in combination. Note that if the lithium-ion secondary battery electrolyte of the present invention (the ion-conductive compound of the present invention) is liquid, a dispersion solvent may not be used.

[0064] <Lithium-ion secondary battery> The lithium ion secondary battery of the present invention is a lithium ion secondary battery that uses the electrolyte for lithium ion secondary batteries of the present invention. The lithium ion secondary battery of the present invention is not particularly limited as long as it uses the electrolyte for lithium ion secondary batteries of the present invention. A preferred embodiment is a lithium ion secondary battery that uses the composite solid electrolyte for lithium ion secondary batteries of the present invention. The layered structure of the secondary battery may be, for example, a layered structure in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are layered in this order, and it is preferable to use the composite solid electrolyte for lithium ion secondary batteries of the present invention in any of the layers, and more preferably in the negative electrode layer.

[0065] In the secondary battery of the present invention, it is preferable to use the composite solid electrolyte for lithium ion secondary batteries of the present invention in any of the above-mentioned layers. As described above, the composite solid electrolyte for lithium ion secondary batteries of the present invention has a high ion transport number (lithium ion conductivity), and since the ion-conducting compound of the present invention is a liquid component, it can penetrate into non-contact surfaces between solid components. Therefore, the composite solid electrolyte for lithium ion secondary batteries of the present invention increases the contact area within each layer, which effectively reduces the interfacial resistance of the solid electrolyte layer, and it is thought that the secondary battery of the present invention exhibits excellent charge-discharge characteristics.

[0066] The secondary battery of the present invention includes at least a positive electrode, a negative electrode, and a solid electrolyte layer. As described above, the composite solid electrolyte for a lithium ion secondary battery of the present invention is preferably used in any of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer, and more preferably used in the negative electrode layer.

[0067] Known solid electrolyte layers, positive electrode layers, and negative electrode layers can be used.

[0068] The solid electrolyte layer contains at least the inorganic solid electrolyte described above, and may further contain the composite solid electrolyte for a lithium ion secondary battery of the present invention, a binder, a thickener, and a conductive aid, if necessary.

[0069] When the composite solid electrolyte for a lithium ion secondary battery of the present invention is used in a solid electrolyte layer, the content of the composite solid electrolyte for a lithium ion secondary battery of the present invention is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.5 parts by mass or more, based on 100 parts by mass of the components of the solid electrolyte layer, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less.

[0070] The method for producing the solid electrolyte layer is not particularly limited, and a common method can be used, for example, by uniformly applying a solid electrolyte paste (coating liquid) containing a solid electrolyte, a conductive additive, a binder, the composite solid electrolyte for a lithium ion secondary battery of the present invention, a solvent, etc. to an appropriate thickness by a doctor blade method, a silk screen method, or the like.

[0071] For example, in the doctor blade method, the solid electrolyte paste is uniformly applied to an appropriate thickness using a blade with a specified slit width. After application, excess organic solvent is removed by drying, for example, with hot air at 100°C or under reduced pressure at 80°C. After drying, the solid electrolyte layer is produced by press molding using a press machine.

[0072] In the positive electrode layer and the negative electrode layer, for example, an electrode material layer, that is, a positive electrode material layer or a negative electrode material layer, is provided on a current collector.

[0073] Known current collectors can be used for the positive electrode layer and the negative electrode layer. Specifically, metals such as aluminum, nickel, stainless steel, gold, platinum, and titanium are used as the current collector for the positive electrode layer. Metals such as copper, nickel, stainless steel, gold, platinum, and titanium are used as the current collector for the negative electrode layer.

[0074] The positive electrode material layer and the negative electrode material layer contain at least a positive electrode active material and a negative electrode active material, respectively, and may further contain a conductive additive, a binder, a thickener, the inorganic solid electrolyte described above, and the composite solid electrolyte for a lithium ion secondary battery of the present invention.

[0075] The positive electrode active material used in the present invention is a lithium metal-containing composite oxide powder having any one of the following compositions: LiMO2, LiM2O4, Li2MO3, and LiMEO4. In this formula, M is primarily composed of a transition metal and contains at least one of Co, Mn, Ni, Cr, Fe, and Ti. M is composed of a transition metal, but may also contain other elements such as Al, Ga, Ge, Sn, Pb, Sb, Bi, Si, P, and B. E contains at least one of P and Si. The particle size of the positive electrode active material is preferably 50 μm or less, and more preferably 20 μm or less. These active materials have an electromotive force of 3 V (vs. Li / Li+) or more.

[0076] Specific examples of the positive electrode active material include lithium cobalt oxide, lithium nickel oxide, nickel / cobalt / lithium manganese oxide (ternary system), spinel-type lithium manganese oxide, and lithium iron phosphate.

[0077] The negative electrode active material used in the present invention is a carbon material (natural graphite, artificial graphite, amorphous carbon, etc.) having a structure (intercalation compound) capable of absorbing and desorbing alkali metal ions such as lithium ions, or a metal such as lithium, an aluminum-based compound, a tin-based compound, a silicon-based compound, or a titanium-based compound capable of absorbing and desorbing alkali metal ions such as lithium ions. In the case of a powder, the particle size is preferably 10 nm or more and 100 μm or less, more preferably 20 nm or more and 20 μm or less. A mixed active material of a metal and a carbon material may also be used.

[0078] When the composite solid electrolyte for a lithium ion secondary battery of the present invention is used in the anode material layer and / or the cathode material layer, the content of the composite solid electrolyte for a lithium ion secondary battery of the present invention is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the components of the anode material layer or the cathode material layer, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less.

[0079] When a conductive additive is used, a known conductive additive can be used, and examples thereof include conductive carbon black such as graphite, furnace black, acetylene black, and ketjen black, carbon fibers such as carbon nanotubes, and metal powders. These conductive additives may be used alone or in combination of two or more.

[0080] The binder may be one or more compounds selected from fluororesins such as PVdF, fluororubbers, acrylic rubbers, modified acrylic rubbers, styrene-butadiene rubbers, acrylic polymers, and vinyl polymers. These binders are added in an amount of preferably 5 parts by mass or less, more preferably 3 parts by mass or less, for example, 0.01 to 2 parts by mass, per 100 parts by mass of the active material.

[0081] Specific examples of thickeners include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, and salts thereof (alkali metal salts such as sodium salts, and ammonium salts), polyvinyl alcohol, polyacrylates, polyethylene oxide, etc. These thickeners may be used alone or in combination. These thickeners are added in an amount of preferably 5 parts by mass or less, more preferably 3 parts by mass or less, for example, 0.01 to 2 parts by mass, per 100 parts by mass of the active material. Furthermore, when the viscosity of the coating liquid is low, a thickener can be used in combination.

[0082] The method for producing the positive electrode layer and the negative electrode layer, which include the current collector and the positive electrode material layer and the negative electrode material layer, is not particularly limited and a common method can be used. For example, the method can be performed by uniformly applying a paste (coating liquid) of the positive electrode material and the negative electrode material, which are composed of the positive electrode active material or the negative electrode active material, the composite solid electrolyte for a lithium ion secondary battery of the present invention, a conductive additive, a binder, a solvent such as water or N-methyl-2-pyrrolidone (NMP), and, if necessary, a thickener, onto the surface of the current collector to an appropriate thickness by a doctor blade method, a silk screen method, or the like.

[0083] For example, in the doctor blade method, the paste is applied to a metal electrode substrate, and then uniformly applied to an appropriate thickness using a blade with a specified slit width. After the active material is applied to the electrode, the electrode is dried, for example, with hot air at 100°C or under reduced pressure at 80°C to remove excess organic solvent. After drying, the electrode is press-molded using a press machine to produce the electrode.

[0084] The method for manufacturing the secondary battery of the present invention is not particularly limited, and the battery is manufactured by a known method, comprising at least a positive electrode, a negative electrode, and a solid electrolyte. For example, in the case of a coin-type lithium-ion battery, the positive electrode, the solid electrolyte, and the negative electrode are inserted into an outer can. Then, the battery is joined to a sealing body by tab welding or the like, and the sealing body is sealed and crimped to obtain a storage battery. The shape of the battery is not limited, and examples include coin type, cylindrical type, and sheet type, and a structure in which two or more batteries are stacked may also be used.

[0085] The secondary battery of the present invention is preferably an all-solid-state battery, which allows for a higher level of safety.

[0086] The ion-conductive compound of the present invention, the electrolyte for a lithium ion secondary battery using the ion-conductive compound, the composite solid electrolyte for a lithium ion secondary battery, and the lithium ion secondary battery can suppress side reactions with sulfide-based solid electrolytes and have high lithium ion conductivity, and are therefore useful in, for example, on-board storage batteries for electric vehicles, hybrid vehicles, and the like, storage batteries for home power storage, and storage batteries for electronic devices such as mobile phones and personal computers. [Example]

[0087] The present invention will be specifically explained by way of examples and comparative examples, but the present invention is not limited to these.

[0088] [Production Example 1-1] (Synthesis of Cyclic Ether Compound 1) A flask was charged with 320 parts by mass of 3-ethyl-3-oxetanemethanol and 694 parts by mass of potassium hydroxide, and 5024 parts by mass of 1,3-dimethyl-2-imidazolidinone was added as a solvent. The mixture was stirred at room temperature for 1 hour. The reaction solution was cooled to 10°C, and 967 parts by mass of 1-bromo-4-methoxybutane was added dropwise while maintaining stirring. After the addition was completed, the mixture was allowed to react for 44 hours. The oil-water separation was then performed, and the resulting organic layer was concentrated to obtain 420 parts by mass of cyclic ether compound 1.

[0089] [Production Example 1-2] (Synthesis of Cyclic Ether Compound 2) Cyclic ether compound 2 was obtained in the same manner as in Production Example 1-1, except that 1-bromo-4-methoxybutane was changed to 1-bromo-3-methoxypropane.

[0090] [Production Example 1-3] (Synthesis of Cyclic Ether Compound 3) Cyclic ether compound 3 was obtained in the same manner as in Production Example 1-1, except that 1-bromo-4-methoxybutane was changed to 2-bromoethyl methyl ether.

[0091] [Production Example 1-4] (Synthesis of Cyclic Ether Compound 4) Cyclic ether compound 4 was obtained in the same manner as in Production Example 1-1, except that 1-bromo-4-methoxybutane was changed to 1,1,1-trifluoro-2-iodoethane.

[0092] [Production Example 1-5] (Synthesis of Cyclic Ether Compound 5) Cyclic ether compound 5 was obtained in the same manner as in Production Example 1-1, except that 1-bromo-4-methoxybutane was changed to allyl bromide.

[0093] The structures of the resulting cyclic ether compounds are shown below. [ka] 1 H-NMR(400 MHz, δ, ppm from tetramethylsilane (TMS) in CDCl3): 0.87 (t, 3H, J = 7.6 Hz), 1.61 - 1.67 (m, 4H), 1.73 (q, 2H, J = 7.5 Hz), 3.32 (s, 3H), 3.36 - 3.40 (m, 2H), 3.45 - 3.50 (m, 2H), 3.52 (s, 2H), 4.36 (d, 2H, J = 6.0 Hz), 4.44 (d, 2H, J = 5.5 Hz) 13 C - NMR (100 MHz, δ, ppm from TMS in CDCl3): 8.34, 26.4, 26.5, 26.9, 43.5, 58.7, 71.4, 72.7, 73.5, 78.7

Chem.

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Chem.

[0094] In the following experiments, sulfolane manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., diethylene glycol dimethyl ether manufactured by Kishida Chemical Co., Ltd., and dibutyl ether manufactured by Tokyo Chemical Industry Co., Ltd. were used.

[0095] [Example 1] To 100 parts by mass of the obtained cyclic ether compound 1, LiN(FSO2)2 as a lithium salt compound was added in the amount shown in Table 1 and mixed to prepare a dissolved cyclic ether compound electrolyte.

[0096] [Examples 2 to 6, Comparative Examples 1 to 3] An ether compound electrolyte was obtained in the same manner as in Example 1, except that the composition was changed as shown in Table 1.

[0097] The ether compound and the resulting ether compound electrolyte were evaluated as follows, and the results are shown in Table 1.

[0098] [Evaluation of ionic conductivity of ether compound electrolytes] The ionic conductivity of the ether compound electrolyte was measured using an electric conductivity meter (ES-51, manufactured by Horiba, Ltd.) at a temperature of 25°C.

[0099] [Evaluation of Li-ion transport numbers in ether compound electrolytes] An ether compound electrolyte was applied to a nonwoven fabric separator, and then the separator-containing ether compound electrolyte was sandwiched between Li foils to prepare a Li symmetric cell. An AC impedance test and chronoamperometry measurement were performed using a potentio / galvanostat (BioLogic SP-300) at 25°C. (AC impedance test before polarization) A Li symmetric cell using an ether compound electrolyte was prepared and subjected to AC impedance testing using a potentio / galvanostat. The interfacial resistance was calculated from the size of the semicircular arc derived from the interfacial resistance obtained from the Cole-Cole plot. The test temperature was set to 25°C. Measurements were performed at a voltage amplitude of 20 mV and a measurement frequency range of 7 MHz to 100 mHz. (Chronoamperometry test) After conducting an AC impedance test, the open circuit voltage (OCV) was measured for 1 minute, followed by chronoamperometry. The test temperature was 25°C. The measurement was performed at a DC voltage of 20 mV for 3 hours, and the initial current value and the steady-state current value after 3 hours were measured. (AC impedance test after polarization) After the chronoamperometry test, the open circuit voltage (OCV) was measured for 1 minute, and then an AC impedance test was performed. The interfacial resistance was calculated from the size of the semicircular arc derived from the interfacial resistance obtained from the Cole-Cole plot. (Calculation of Li-ion transport number) The Li-ion transport number was calculated from the interfacial resistance values ​​before and after polarization, the initial current value obtained in the chronoamperometry test, and the steady-state current value according to the following formula. t Li+ =(I s ×(V-I0×R0))) / ((I0×(VI s ×R s )) t Li+ : Li-ion transport numbers of ether compound electrolytes I0: Initial current value of chronoamperometry test (A) I s : Steady-state current value (A) in chronoamperometry test R0: Interface resistance before polarization (Ω) R s :Interfacial resistance value after polarization (Ω) V: DC voltage (V)

[0100] [Evaluation of lithium ion conductivity] Lithium ion conductivity can be calculated by multiplying the ionic conductivity and the lithium ion transport number. -4 (S / cm) or more, the ionic conductivity that a solid electrolyte normally has is not impaired. Lithium ion conductivity = ionic conductivity × lithium ion transference number

[0101] [Evaluation of degradation of sulfide solid electrolytes] 1.6 parts by mass of an ether compound was added to 0.8 parts by mass of an argyrodite-type sulfide solid electrolyte (Li6PS5Cl, manufactured by NEI) and mixed. The argyrodite-type sulfide solid electrolyte was immersed in the ether compound for 24 hours. After that, the ether compound was removed by vacuum heating and drying. The solid sulfide solid electrolyte was filled into a solid-state NMR sample tube and analyzed using a nuclear magnetic resonance (NMR) spectrometer. 31 P-NMR tests were carried out. ( 31 P-NMR test) Measurements were carried out using an NMR device (device name: ECA400WB, manufactured by JEOL Ltd.). 3- Spectra derived from the unit and P2S7 produced by the decomposition reaction of sulfide solid electrolyte 4- Resistance was evaluated based on the presence or absence of spectra originating from the unit. A score of ◯ was given when no spectra generated by the decomposition reaction of the sulfide solid electrolyte were detected, and an X was given when spectra generated by the decomposition reaction of the sulfide solid electrolyte were detected. A score of ◯ indicates that side reactions with the sulfide-based solid electrolyte can be suppressed. Measurement temperature: room temperature Rotation speed: 10kHz Accumulation count: 16 times Repeat wait time: 2,000 seconds Chemical shift standard: ammonium dihydrogen phosphate (1 ppm)

[0102] [Table 1]

[0103] From Table 1, it was found that the ion-conductive compounds of the examples having the oxetane skeleton represented by the general formula (A) can suppress side reactions with sulfide-based solid electrolytes and have high lithium ion conductivity. [Industrial Applicability]

[0104] The ion-conductive compound of the present invention, the electrolyte for a lithium ion secondary battery using the ion-conductive compound, the composite solid electrolyte for a lithium ion secondary battery, and the lithium ion secondary battery can suppress side reactions with sulfide-based solid electrolytes and have high lithium ion conductivity, and are therefore useful in, for example, on-board storage batteries for electric vehicles, hybrid vehicles, and the like, storage batteries for home power storage, and storage batteries for electronic devices such as mobile phones and personal computers.

Claims

1. An ion-conductive compound having an oxetane skeleton represented by the following general formula (A): 【Chemical 1】 [In the formula, R １ is an alkyl group having 1 to 6 carbon atoms, and R ２ is a hydrogen atom, -CH ２ O (CH ２ ) ａ O (CH ２ ) ｂ an alkylene glycol alkyl ether group represented by H, —CH ２ OR ８ or a bridging group containing an ethylenically unsaturated double bond represented by —CH ２ O (CH ２ ) ｃ (CHR ６ ) ｄ (CH ２ ) ｅ R ７ The number of repeating units, a, is an integer of 1 to 8, and the number of repeating units, b, is an integer of 0 to 6. ８ is an acrylic group, a methacrylic group, an allyl group, or a methallyl group. ６ are the same or different and are a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R ７ represents a hydrogen atom, a hydroxyl group, a nitrile group, a trifluoromethyl group, an alkoxy group, or a cyclic ether group which may have a substituent. The number of repeating units, c, is an integer from 0 to 4, the number of repeating units, d, is an integer from 0 to 4, and the number of repeating units, e, is an integer from 0 to 10.]

2. An electrolyte for a lithium ion secondary battery, comprising the ion-conductive compound according to claim 1 and a lithium salt compound.

3. A composite solid electrolyte for a lithium ion secondary battery, comprising an inorganic solid electrolyte and the electrolyte for a lithium ion secondary battery according to claim 2.

4. 4. The composite solid electrolyte for a lithium ion secondary battery according to claim 3, wherein the inorganic solid electrolyte is a sulfide-based solid electrolyte.

5. A lithium ion secondary battery using the electrolyte for lithium ion secondary batteries according to claim 2.

6. A lithium ion secondary battery using the composite solid electrolyte for lithium ion secondary batteries according to claim 3.

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