Electrolytes and Energy Storage Devices

Abstract

Provided is technology pertaining to an electrolyte having exceptional ion conductivity and exceptional strength. This electrolyte is characterized by containing an ionic liquid, an inorganic oxide, and a binder, and moreover is characterized in that: a polycarbonate polyol and a polyisocyanate are used as raw materials in the binder; and at least one functional group selected from the group consisting of C1-4 trialkoxysilyl groups, epoxy groups, and oxetanyl groups is provided at the end of the binder.

Description

[Technical Field]

[0001] The present invention relates to an electrolyte and an electricity storage device. [Background technology]

[0002] BACKGROUND ART It has been known for some time that secondary batteries are used as power sources for portable terminals such as notebook computers, mobile phones, and PDAs (Personal Digital Assistants) (for example, Patent Document 1).

[0003] Patent Documents 1 and 2 describe secondary batteries that include an electrolyte using polyvinylidene fluoride (PVDF) as a binder, and a separator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-090777 [Patent Document 2] Japanese Patent Application Publication No. 2017-017041 Summary of the Invention [Problem to be solved by the invention]

[0005] The technologies described in Patent Documents 1 and 2 are both premised on the use of a separator. However, if the electrolyte has sufficient strength, a separator is not necessary. Furthermore, electrolytes are generally required to have excellent ionic conductivity. Therefore, there has been a demand for the development of a technology relating to an electrolyte that has sufficient strength and excellent ionic conductivity. [Means for solving the problem]

[0006] The present invention has been made to solve the above problems, and can be realized in the following forms.

[0007] According to one aspect of the present invention, there is provided an electrolyte comprising an ionic liquid, an inorganic oxide, and a binder, the binder being made from polycarbonate polyol and polyisocyanate, and having at least one functional group selected from the group consisting of a trialkoxysilyl group having 1 to 4 carbon atoms, an epoxy group, and an oxetanyl group at its terminal.

[0008] According to this embodiment, an electrolyte having excellent ionic conductivity and strength can be provided.

[0009] The electrolyte of the above form may further contain an additive different from the inorganic oxide, and the additive may be at least one of a boron compound and an aluminum compound.

[0010] According to this embodiment, an electrolyte having excellent ionic conductivity and strength can be provided.

[0011] In the electrolyte of the above form, the additive Agent is the boron compound, and the number of moles of the boron compound may be 0.55 mol / kg or less per 1 kg of the electrolyte.

[0012] According to this embodiment, the ionic conductivity can be effectively improved with a small amount of additives.

[0013] In the electrolyte of the above form, the additive Agent is the aluminum compound, and the number of moles of the aluminum compound may be 0.05 mol / kg or less per 1 kg of the electrolyte.

[0014] According to this embodiment, the ionic conductivity can be effectively improved with a small amount of additives.

[0015] In the electrolyte of the above type, the additive may be a borate ester.

[0016] According to this embodiment, an electrolyte having excellent ionic conductivity and strength can be provided.

[0017] In the electrolyte of the above form, the borate ester may be at least one of trimethyl borate and triethyl borate.

[0018] According to this embodiment, an electrolyte having excellent ionic conductivity and strength can be provided.

[0019] In the electrolyte of the above embodiment, the inorganic oxide may include at least one of silicon oxide and aluminum oxide.

[0020] According to this embodiment, an electrolyte having excellent ionic conductivity and strength can be provided.

[0021] In the electrolyte of the above embodiment, the weight average molecular weight of the binder may be 10,000 or more and 120,000 or less.

[0022] According to this embodiment, the transport number can be improved.

[0023] According to another aspect of the present invention, there is provided an electricity storage device including the electrolyte of the above aspect. DETAILED DESCRIPTION OF THE INVENTION

[0024] Preferred embodiments of the present invention will now be described.

[0025] <Electrolyte> An electrolyte according to an embodiment of the present invention includes an ionic liquid, an inorganic oxide, and a binder. The binder is made from polycarbonate polyol and polyisocyanate, and is characterized in that the binder has at least one functional group selected from the group consisting of a trialkoxysilyl group having 1 to 4 carbon atoms, an epoxy group, and an oxetanyl group at its terminal. This embodiment provides an electrolyte that has excellent ionic conductivity and strength. The electrolyte according to this embodiment is in a quasi-solid or gel state.

[0026] <Binder> (Polycarbonate polyol) The polycarbonate polyol is not particularly limited, and for example, polycarbonate polyols commonly used in the art can be used, such as carbonate polyols of 1,6-hexanediol, carbonate polyols of 1,4-butanediol and 1,6-hexanediol, carbonate polyols of 1,5-pentanediol and 1,6-hexanediol, and carbonate polyols of 3-methyl-1,5-pentanediol and 1,6-hexanediol. More specifically, examples thereof include PCDL T-6001, T-6002, T-5651, T-5652, T-5650J, T-4671, and T-4672 manufactured by Asahi Kasei Corporation, Kuraray Polyol C-590, C-1050, C-1050R, C-1090, C-2050, C-2050R, C-2070, C-2070R, C-2090, C-2090R, C-3090, C-3090R, C-4090, C-4090R, C-5090, C-5090R, C-1065N, C-2065N, C-1015N, and C-2015N manufactured by Kuraray Co., Ltd., and ETERNACOLL (registered trademark) manufactured by Ube Industries, Ltd. Examples include UH-50, UH-100, UH-200, UH-300, UM-90(3 / 1), UM-90(1 / 1), UM-90(1 / 3), and UC-100.

[0027] (Polyisocyanate) The polyisocyanate is not particularly limited, but examples thereof include organic polyisocyanates. The organic polyisocyanate is not particularly limited, but examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, and araliphatic polyisocyanates. Examples of aliphatic polyisocyanates include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate. Examples of alicyclic polyisocyanates include isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, etc. Examples of aromatic polyisocyanates include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4' Examples of suitable polyisocyanates include 1,4-diphenylmethane diisocyanate (MDI), 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate. Examples of aromatic aliphatic polyisocyanates include dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α,α-tetramethylxylylene diisocyanate. Examples of suitable polyisocyanates include dimers or trimers of these organic polyisocyanates, and modified products such as biuretized isocyanates. Only one type of polyisocyanate may be used, or two or more types may be used in combination.

[0028] As the polyisocyanate, aromatic polyisocyanates and alicyclic polyisocyanates are preferred, and alicyclic polyisocyanates are more preferred. Specifically, as the polyisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, and hydrogenated diphenylmethane diisocyanate are preferred.

[0029] In this embodiment, the binder has at least one functional group selected from the group consisting of a trialkoxysilyl group having 1 to 4 carbon atoms, an epoxy group, and an oxetanyl group at its terminal. Specifically, the functional group is provided at the terminal of the polyisocyanate of the binder. From the viewpoint of excellent ionic conductivity, it is preferable that the polyisocyanate has a trialkoxysilyl group having 1 to 4 carbon atoms at its terminal.

[0030] Examples of a method for introducing at least one functional group selected from the group consisting of a trialkoxysilyl group having 1 to 4 carbon atoms, an epoxy group, and an oxetanyl group into the terminal of the polyisocyanate side of the binder include a method of reacting a compound having the functional group and an active hydrogen group with the terminal of the polyisocyanate side of the binder.

[0031] Examples of compounds having a trialkoxysilyl group having 1 to 4 carbon atoms and an active hydrogen group include alkoxysilyl compounds having a primary amino group and alkoxysilyl compounds having a primary amino group and a secondary amino group. Specific examples include γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ alkoxysilyl group-containing monoamines such as N-β(aminoethyl)γ-aminopropyltrimethoxysilane (N-2-(aminoethyl)-3-aminopropyltrimethoxysilane), N-β(aminoethyl)γ-aminopropyltriethoxysilane (N-2-(aminoethyl)-3-aminopropyltriethoxysilane), N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane (N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane), and N-β(aminoethyl)γ-aminopropylmethyldiethoxysilane (N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane).

[0032] Examples of compounds having an epoxy group and an active hydrogen group include 2,3-epoxy-1-propanol (glycidol) and 1-[4-(2-hydroxyethyl)phenoxy]-2,3-epoxypropane.

[0033] Examples of compounds having an oxetanyl group and an active hydrogen group include (3-ethyloxetan-3-yl)methanol and 3-oxetanol.

[0034] Polyols other than polycarbonate polyols may also be used as raw materials for the binder, such as polyolefin polyols, polyhydric alcohols, polyether polyols, polyester polyols, polyether ester polyols, polyacrylic polyols, polyacetal polyols, polysiloxane polyols, and fluorine polyols.

[0035] In this specification, polyolefin polyol refers to a polymer or copolymer of a diolefin having 4 to 12 carbon atoms, such as butadiene or isoprene, containing hydroxyl groups. The polyolefin polyol is not particularly limited, but examples thereof include copolymers of a diolefin having 4 to 12 carbon atoms and an α-olefin having 2 to 22 carbon atoms. The method for incorporating hydroxyl groups is not particularly limited, but examples thereof include reacting a diene monomer with hydrogen peroxide. Furthermore, the remaining double bonds may be hydrogenated to form saturated aliphatic polyols. Examples of such polyolefin polyols include the "NISSO-PB G" series manufactured by Nippon Soda Co., Ltd., the "Poly bd" series and "Epol (registered trademark)" manufactured by Idemitsu Kosan Co., Ltd., and the "Kraysol (registered trademark)" series manufactured by Cray Valley.

[0036] In this specification, the term "polyhydric alcohol" refers to a polyol having three or more hydroxyl groups in one molecule. The polyhydric alcohol is not particularly limited, but examples thereof include polyhydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol, and oxyalkylene derivatives thereof. Examples of the polyhydric alcohol include ester compounds of these polyhydric alcohols or oxyalkylene derivatives with polycarboxylic acids, polycarboxylic anhydrides, or polycarboxylic acid esters. The use of a polyhydric alcohol is preferred because it provides excellent film strength.

[0037] The polyether polyol is not particularly limited, but examples thereof include alkylene derivatives of polyhydric alcohols, polytetramethylene glycol, and polythioether polyols.

[0038] The polyester polyols and polyether ester polyols are not particularly limited, but examples thereof include esters of polyhydric alcohols or polyether polyols with polycarboxylic acids or polycarboxylic acid anhydrides, etc. Furthermore, examples of the polyester polyols and polyether ester polyols include castor oil polyols and polycaprolactone polyols.

[0039] Among the other polyols, polyether polyols and polyester polyols are preferred. One or more of the other polyols can be used. The other polyols may also be used in combination with a compound having one hydroxyl group.

[0040] The weight-average molecular weight of the binder is not particularly limited, but is preferably 5,000 to 300,000, and more preferably 10,000 to 120,000. From the viewpoint of improving the transference number, the weight-average molecular weight of the binder is further preferably 25,000 to 100,000, and particularly preferably 33,000 to 50,000. Here, the weight-average molecular weight is a value measured using GPC column chromatography under the following conditions. Pump: Shimadzu LC-20AD Column: Showa Denko Shodex OH pak SB-806M (8.0 mm diameter x 300 mm) x 2 Mobile phase: 50mmol / L lithium bromide in N,N-dimethylformamide ·Flow rate: 0.5mL / min ·Temperature: 50℃ Column heater: Shimadzu CTO-20A Detector: Differential refractometer (RI) Shimadzu RID-20A ·Injection volume: 100μL Autosampler: Shimadzu SIL-20AHT

[0041] <Binder manufacturing method> The method for producing the binder is not particularly limited, and known methods can be used. Examples of methods for producing the binder include the following: First, a compound having at least one functional group selected from the group consisting of a trialkoxysilyl group having 1 to 4 carbon atoms, an epoxy group, and an oxetanyl group, and an active hydrogen group, is reacted with a polyisocyanate, a polycarbonate polyol, or the like at 30°C to 130°C for about 0.5 to 10 hours, and then cooled to 5°C to 45°C as necessary to obtain the binder. Any organic solvent, such as N-methyl-2-pyrrolidone (NMP), can be used as the solvent. In this case, the ratio of the total isocyanate group equivalent of the polyisocyanate to the total active hydrogen group equivalent of the polycarbonate polyol, the compound having at least one functional group selected from the group consisting of a trialkoxysilyl group having 1 to 4 carbon atoms, an epoxy group, and an oxetanyl group and an active hydrogen group, and the other compounds having active hydrogen groups (total isocyanate group equivalent / total active hydrogen group equivalent) is preferably 0.9 to 1.0. In this specification, the active hydrogen group refers to a hydroxy group, a primary amino group, or a secondary amino group.

[0042] <Inorganic oxides> The electrolyte of this embodiment includes an inorganic oxide. Examples of inorganic oxides include, but are not limited to, silicon oxide, titanium oxide, aluminum oxide (alumina), zirconium oxide, hafnium oxide, niobium oxide, tantalum oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, tin oxide, and lead oxide. Alternatively, an oxide-based solid electrolyte (SE: Solid Electrolyte) may be used. Examples of oxide-based solid electrolytes include, but are not limited to, LICGC (registered trademark, composition: Li2O-Al2O3-SiO2-P2O5-TiO2) manufactured by OHARA Corporation. Examples of inorganic oxides include, but are not limited to, silicon oxide and aluminum oxide, and aluminum oxide is more preferred.

[0043] <Additives> It is preferable to add an additive other than inorganic oxides to the electrolyte. This additive is preferably at least one of a boron compound and an aluminum compound. Adding this additive to the electrolyte is believed to bond the functional groups at the ends of the binder with the additive, further improving ionic conductivity.

[0044] The amount of this additive is not particularly limited, but when the additive is a boron compound, it is preferably 0.4 parts by mass or more, and more preferably 0.8 parts by mass or more, per 100 parts by mass of electrolyte. When the additive is a boron compound, it is preferably 2.2 parts by mass or less, more preferably 1.6 parts by mass or less, and even more preferably 1.2 parts by mass or less, per 100 parts by mass of electrolyte. When the additive is an aluminum compound, it is preferably 0.04 parts by mass or more, and even more preferably 0.08 parts by mass or more, per 100 parts by mass of electrolyte. When the additive is an aluminum compound, it is preferably 0.4 parts by mass or less, more preferably 0.32 parts by mass or less, and even more preferably 0.24 parts by mass or less, per 100 parts by mass of electrolyte.

[0045] The molar amount of the additive is not particularly limited, but when the additive is a boron compound, it is preferably 0.1 mol / kg or more, more preferably 0.2 mol / kg or more, per 1 kg of electrolyte. When the additive is a boron compound, it is preferably 0.55 mol / kg or less, more preferably 0.4 mol / kg or less, and even more preferably 0.3 mol / kg or less, per 1 kg of electrolyte. When the additive is an aluminum compound, it is preferably 0.005 mol / kg or more, more preferably 0.01 mol / kg or more, per 1 kg of electrolyte. When the additive is an aluminum compound, it is preferably 0.05 mol / kg or less, more preferably 0.04 mol / kg or less, and even more preferably 0.03 mol / kg or less, per 1 kg of electrolyte. Compared to when a boron compound is added, the addition of an aluminum compound tends to improve ionic conductivity with a small amount of addition.

[0046] The boron compound is not particularly limited, but examples thereof include boric acid esters, borane compounds, boronic acids, and boronic acid anhydrides. The boric acid ester is not particularly limited, but examples thereof include trimethyl borate (TMB), triethyl borate, tripropyl borate, tributyl borate, triisobutyl borate, tri-t-butyl borate, triphenyl borate, tritriyl borate, and trimethoxyboroxine. The borane compound is not particularly limited, but examples thereof include dimethylamine borane, trimethylamine borane, triethylamine borane, and morpholine borane. The boronic acid is not particularly limited, but examples thereof include propylboronic acid, isopropylboronic acid, butylboronic acid, and t-butylboronic acid. Examples of the boron compound include butylboronic acid, phenylboronic acid, etc. The boronic acid anhydride is not particularly limited, but examples thereof include propylboronic acid anhydride, isopropylboronic acid anhydride, butylboronic acid anhydride, t-butylboronic acid anhydride, phenylboronic acid anhydride, etc. The boron compound is preferably a boric acid ester, and more preferably trimethyl borate (TMB) or triethyl borate.

[0047] The aluminum compound is not particularly limited, but examples thereof include aluminum alkoxides. The aluminum alkoxide is not particularly limited, but examples thereof include aluminum methoxide, aluminum ethoxide, aluminum isopropoxide (AIP), aluminum sec-butoxide, etc. The aluminum compound is preferably aluminum isopropoxide (AIP).

[0048] <Ionic liquid> The electrolyte of this embodiment contains an ionic liquid. The cation of the ionic liquid is not particularly limited, but examples include butylpyridinium, 1-ethyl-3-methylimidazolium (EMIm), 1-butyl-3-methylimidazolium (BMIm), 1,2-dimethyl-3-propylimidazolium, 1-methyl-1-propylpiperidinium, 1-butyl-1-methylpyrrolidinium, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium (DEME), 1-methyl-1-propylpyrrolidinium (P13), N-methyl-N-propylpiperidinium (PP13), and N-ethyl-N-butylpyrrolidinium (P24). As the cation of the ionic liquid, 1-ethyl-3-methylimidazolium (EMIm) is preferred due to its excellent electrical properties.

[0049] The anion of the ionic liquid is not particularly limited, but examples thereof include bis(fluorosulfonyl)imide (FSI), bis(trifluoromethanesulfonyl)imide (TFSI), tris(trifluoromethanesulfonyl)methide, fluorosulfonyl(trifluoromethanesulfonyl)imide, bis(perfluoroethylsulfonyl)amide (BETI), tetrafluoroborate (BF4), trifluoromethanetrifluoroborate (CF3BF3), pentafluoroethyltrifluoroborate (CF3CF2BF3), hexafluorophosphate (PF6), etc. As the anion of the ionic liquid, bis(fluorosulfonyl)imide (FSI) is preferred because of its excellent electrical properties.

[0050] Examples of the electrolyte salt used in the electrolyte of this embodiment include lithium salts. Examples of the lithium salt include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), and lithium bisfluorosulfonylimide (LiFSI). As the electrolyte salt, lithium bisfluorosulfonylimide (LiFSI) is preferred because of its excellent electrical properties. Such lithium salts are desirably contained in the electrolyte solution at a concentration of typically 0.1 to 2.0 mol / L, preferably 0.3 to 1.5 mol / L.

[0051] The concentration of the electrolyte salt is not particularly limited, but from the viewpoint of suppressing an excessive increase in resistance value during charge and discharge, it is preferably 0.5 mol / kg or more per 1 kg of electrolyte, more preferably 0.7 mol / kg or more, even more preferably 1.0 mol / kg or more, and particularly preferably 2.0 mol / kg or more. Furthermore, the concentration of the electrolyte salt is not particularly limited, but from the viewpoint of suppressing a decrease in ionic conductivity due to an increase in viscosity, it is preferably 3.5 mol / kg or less per 1 kg of electrolyte, more preferably 3.3 mol / kg or less, and even more preferably 3.0 mol / kg or less.

[0052] The amount of inorganic oxide is not particularly limited, but is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 43 parts by mass or more per 100 parts by mass of electrolyte, and is preferably 55 parts by mass or less, more preferably 53 parts by mass or less, and even more preferably 50 parts by mass or less per 100 parts by mass of electrolyte.

[0053] The amount of the electrolyte solution using an ionic liquid is not particularly limited, but is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 43 parts by mass or more per 100 parts by mass of the electrolyte. The amount of the electrolyte solution using an ionic liquid is preferably 55 parts by mass or less, more preferably 53 parts by mass or less, and even more preferably 50 parts by mass or less per 100 parts by mass of the electrolyte.

[0054] The amount of binder is not particularly limited, but is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more per 100 parts by mass of electrolyte, and is preferably 15 parts by mass or less, more preferably 13 parts by mass or less, and even more preferably 10 parts by mass or less per 100 parts by mass of electrolyte.

[0055] <Other> If necessary, various commonly used additives may be further used, including, but not limited to, weather resistance agents, antibacterial agents, antifungal agents, pigments, rust inhibitors, dyes, film-forming aids, inorganic crosslinking agents, organic crosslinking agents, silane coupling agents, antiblocking agents, viscosity modifiers, leveling agents, antifoaming agents, dispersants, light stabilizers, antioxidants, ultraviolet absorbers, inorganic fillers, organic fillers, plasticizers, lubricants, and antistatic agents.

[0056] The organic crosslinking agent is not particularly limited, but examples thereof include blocked isocyanate crosslinking agents, epoxy crosslinking agents, carbodiimide crosslinking agents, oxazoline crosslinking agents, and melamine crosslinking agents.

[0057] The dispersant is not particularly limited, but any known dispersant having dispersing properties can be used, including, for example, celluloses such as hydroxymethylcellulose, carboxymethylcellulose and alkali metal salts thereof, methylcellulose, ethylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose; cellulose nanofibers such as the chemically modified cellulose nanofibers described in Japanese Patent Nos. 5,626,828 and 5,921,960; polycarboxylic acid compounds such as polyacrylic acid and sodium polyacrylate; compounds having a vinylpyrrolidone structure such as polyvinylpyrrolidone; polyurethane, polyester, polyacrylamide, polyethylene oxide, polyvinyl alcohol, sodium alginate, xanthan gum, carrageenan, guar gum, agar, and starch. Among these, carboxymethylcellulose salts are preferred.

[0058] The electricity storage device of the present invention may be a known electricity storage device, and is not particularly limited, but examples thereof include a lithium secondary battery and a lithium ion capacitor.

[0059] Next, a lithium secondary battery as the power storage device of this embodiment will be described. The lithium secondary battery of this embodiment includes a pair of electrodes, a positive electrode and a negative electrode, and an electrolyte held between the positive electrode and the negative electrode.

[0060] The positive electrode includes a positive electrode substrate and a positive electrode active material layer provided on the surface of the positive electrode substrate. Similarly, the negative electrode includes a negative electrode substrate and a negative electrode active material layer provided on the surface of the negative electrode substrate, and the negative electrode active material layer is in contact with the electrolyte.

[0061] The positive electrode substrate functions as a current collector that collects electrons generated by the electrochemical reaction of the positive electrode active material layer. The negative electrode substrate functions as a current collector that collects electrons generated by the electrochemical reaction of the negative electrode active material layer. The positive electrode substrate and the negative electrode substrate are not particularly limited, and known metal plates or metal foils can be used.

[0062] The positive electrode active material used in the positive electrode active material layer of the lithium secondary battery of this embodiment is not particularly limited as long as it is capable of inserting and extracting lithium ions. Examples include metal oxides such as CuO, Cu2O, MnO2, V2O5, CrO3, MoO3, Fe2O3, Ni2O3, and CoO3; composite oxides of lithium and transition metals such as LixCoO2, LixNiO2, LixMn2O4, and LiFePO4; metal chalcogenides such as TiS2, MoS2, and NbSe3; and conductive polymer compounds such as polyacene, polyparaphenylene, polypyrrole, and polyaniline. Among these, composite oxides of lithium and one or more transition metals selected from cobalt, nickel, and manganese, commonly known as high-voltage systems, are preferred because of their ability to release lithium ions and provide high voltages. Specific examples of composite oxides of cobalt, nickel, manganese and lithium include LiCoO2, LiMnO2, LiMn2O4, LiNiO2, and LiNi x Co (1-x) O2, LiMn a Ni b Co c(a+b+c=1). These lithium composite oxides may also be doped with small amounts of elements such as fluorine, boron, aluminum, chromium, zirconium, molybdenum, or iron, or may have their particle surfaces treated with carbon, MgO, Al2O3, or SiO2. Two or more of the above positive electrode active materials may also be used in combination.

[0063] The negative electrode active material used in the negative electrode active material layer of this embodiment can be any known active material that can insert and extract metallic lithium or lithium ions, without any particular limitation. For example, carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, and easily graphitizable carbon can be used. Metallic materials such as metallic lithium, alloys, and tin compounds, lithium transition metal nitrides, crystalline metal oxides, amorphous metal oxides, silicon compounds, and conductive polymers can also be used. Specific examples include Li4Ti5O 12 , NiSi5C6, etc.

[0064] A conductive agent is used in the positive electrode and negative electrode of the lithium secondary battery of this embodiment. Any electron-conductive material that does not adversely affect battery performance can be used as the conductive agent without any particular limitation. Typically, carbon black such as acetylene black or ketjen black is used, but other conductive materials such as natural graphite (e.g., scaly graphite, flake graphite, or clay-like graphite), artificial graphite, carbon whiskers, carbon fibers, metal (e.g., copper, nickel, aluminum, silver, or gold) powder, metal fibers, or conductive ceramic materials may also be used.

[0065] The current collector for the electrode active material of the lithium secondary battery of this embodiment can be any electron conductor that does not adversely affect the constructed battery. For example, as the positive electrode current collector, aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymers, conductive glass, etc., as well as aluminum or copper whose surface has been treated with carbon, nickel, titanium, silver, etc., for the purpose of improving adhesion, conductivity, and oxidation resistance, can be used. As the negative electrode current collector, copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymers, conductive glass, Al-Cd alloys, etc., as well as copper whose surface has been treated with carbon, nickel, titanium, silver, etc., for the purpose of improving adhesion, conductivity, and oxidation resistance, can be used. These current collector materials can also be surface-oxidized. In addition to foils, molded bodies such as films, sheets, nets, punched or expanded materials, laths, porous materials, and foams can also be used. There are no particular limitations on the thickness, but a thickness of 1 to 100 μm is typically used.

[0066] The electrode of the lithium secondary battery of this embodiment can be manufactured by mixing the materials that make up the active material layer to prepare a slurry-like electrode material, applying it to a substrate, and volatilizing the dispersion medium.

[0067] The electrode material of this embodiment can use a thickener such as a water-soluble polymer as a viscosity adjuster for slurrying. Specifically, one or more selected from the group consisting of celluloses such as carboxymethyl cellulose salts, methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl methyl cellulose; polycarboxylic acid compounds such as polyacrylic acid and sodium polyacrylate; compounds having a vinylpyrrolidone structure such as polyvinylpyrrolidone; polyacrylamide, polyethylene oxide, polyvinyl alcohol, sodium alginate, xanthan gum, carrageenan, guar gum, agar, and starch can be used, with carboxymethyl cellulose salts being preferred.

[0068] The method and order of mixing the electrode materials are not particularly limited. For example, the active material and the conductive agent can be mixed in advance and used. In this case, a mortar, a mill mixer, a ball mill such as a planetary ball mill or a shaker ball mill, a mechanofusion, or the like can be used for mixing.

[0069] The lithium secondary battery of this embodiment does not necessarily require a separator. When a separator is used, any separator used in a typical lithium secondary battery can be used without any particular limitation, and examples thereof include porous resins such as polyethylene, polypropylene, polyolefin, and polytetrafluoroethylene, ceramics, and nonwoven fabrics.

[0070] The lithium secondary battery according to this embodiment can be formed into any shape, such as a cylindrical shape, a coin shape, a rectangular shape, or any other shape. The basic configuration of the battery is the same regardless of the shape, and the design can be modified depending on the purpose. For example, in the case of a cylindrical battery, a negative electrode formed by applying a negative electrode active material to a negative electrode current collector and a positive electrode formed by applying a positive electrode active material to a positive electrode current collector are wound together, and the wound body is housed in a battery can, and a non-aqueous electrolyte is poured into the battery can with insulating plates placed above and below it, and the battery can is sealed. In addition, when applied to a coin-type lithium secondary battery, a disc-shaped negative electrode, an electrolyte, a disc-shaped positive electrode, and a stainless steel plate are stacked and housed in a coin-type battery can, and a non-aqueous electrolyte is poured into the battery can and sealed. [Example]

[0071] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0072] Example 1 An electrolyte solution (IL electrolyte) was prepared by dissolving the lithium salt lithium bis(fluorosulfonyl)imide (LiFSI, Kishida Chemical Co., Ltd., lithium battery grade (LBG)) at a ratio of 1.0 mol / kg in the ionic liquid-based electrolyte solvent 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImFSI, Daiichi Kogyo Seiyaku Co., Ltd., product name: Elexel IL-110). A coating material was then prepared by mixing 50 parts by mass of alumina as an inorganic oxide, 45 parts by mass of the electrolyte, and 5 parts by mass of Binder 1 (solids content) in a planetary centrifugal mixer.

[0073] Binder 1 was prepared by the following method. First, polycarbonate diol (product 77 parts by weight of PCDL T5652 (manufactured by Asahi Kasei Corporation, weight-average molecular weight 2000), 1 part by weight of trimethylolpropane (molecular weight 134.7), 14 parts by weight of isophorone diisocyanate (molecular weight 222), 140 parts by weight of NMP, and 0.048 parts by weight of Sn catalyst (product name T-320) were added to a separable flask and heated and stirred at 80°C for approximately 2 hours to allow the reaction to proceed until the f-NCO content reached 1.23%. Next, 5 parts by weight of 3-aminopropyltriethoxysilane (product name KBM-903, manufactured by Shin-Etsu Chemical Co., Ltd., molecular weight 179.3) and 72 parts by weight of NMP were added to the separable flask and allowed to react by stirring at room temperature for approximately 1 hour. The obtained reactive polyurethane solution (solid content concentration 33% by mass) was diluted to a solid content concentration of 10% by mass by adding 660 parts by mass of NMP to obtain Binder 1. Binder 1 has a trimethoxysilyl group at its terminal.

[0074] The paint was then applied to a stainless steel (SUS) plate as a substrate. The solvent was then removed by heating and drying, and the crosslinking reaction was allowed to proceed, producing test specimens. The heating and drying was carried out at 80°C for 16 hours.

[0075] <Examples other than Example 1 and Comparative Examples> Test pieces were prepared in the same manner as in Example 1, except that the composition was changed to that shown in the table below.

[0076] Here, in Example 3, Binder 2 was used instead of Binder 1. Also, in Example 17, Binder 2 was used instead of Binder 1. Binder 2 was produced by the following manufacturing method. First, 77 parts by mass of polycarbonate diol (product name: ETERNACOLL UH-200, manufactured by Ube Industries, Ltd., weight average molecular weight 2000), 1 part by mass of trimethylolpropane (molecular weight 134.7), 17 parts by mass of hydrogenated MDI (molecular weight 262), 160 parts by mass of NMP, and 0.048 parts by mass of Sn catalyst (product name: T-320) were added to a separable flask, and the mixture was heated and stirred at 80°C for about 2 hours, allowing the reaction to occur until the f-NCO content reached 0.54%. Next, 3.2 parts by weight of 3-ethyl-3-hydroxymethyloxetane (manufactured by Toagosei Co., Ltd., product name: Aron Oxetane OXT-101) and 72 parts by weight of NMP were added to a separable flask and allowed to react by stirring at room temperature for approximately 1 hour. The resulting reactive polyurethane solution (solids concentration 33% by weight) was diluted with 650 parts by weight of NMP to a solids concentration of 10% by weight, yielding Binder 2. Binder 2 has an oxetanyl group at its terminal.

[0077] In Examples 7 to 16 and Examples 18 to 21, Binder 4 was used instead of Binder 1. Binder 4 was produced by the following method: First, 77 parts by mass of polycarbonate diol (product name: PCDL T5652, manufactured by Asahi Kasei Corporation, weight average molecular weight 2000), 1 part by mass of polyol (product name: DK Polyol G-480, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), 14 parts by mass of isophorone diisocyanate (molecular weight 222), 140 parts by mass of NMP, and 0.048 parts by mass of Sn catalyst (product name: T-320) were added to a separable flask, and then the mixture was heated and stirred at 80°C for approximately 2 hours, allowing the reaction to occur until the f-NCO content reached 1.23%. Next, 5 parts by weight of 3-aminopropyltriethoxysilane (product name: KBM-903, Shin-Etsu Chemical, molecular weight 179.3) and 72 parts by weight of NMP were added to a separable flask and allowed to react by stirring at room temperature for approximately 1 hour. The resulting reactive polyurethane solution (solid content concentration 33% by weight) was diluted to a solid content concentration of 10% by weight by adding 660 parts by weight of NMP to obtain Binder 4. Binder 4 has a trimethoxysilyl group at its terminal.

[0078] In Examples 4 and 5, boric acid was used as an additive together with inorganic oxides and binders. In Examples 8, 10, 12 to 15, and 17, trimethyl borate (TMB) was added as an additive together with the inorganic oxide, binder, etc., and then the mixture was stirred. In Example 6, aluminum isopropoxide (AIP) was added as an additive together with the inorganic oxide, binder, etc., and then the mixture was stirred. In Example 18, aluminum isopropoxide (AIP) was added as an additive together with the inorganic oxide, binder, etc., and then the mixture was stirred.

[0079] In Example 19, an oxide-based solid electrolyte (SE, product name: LICGC (registered trademark), composition: Li2O-Al2O3-SiO2-P2O5-TiO2, manufactured by OHARA) was used as the inorganic oxide instead of alumina.

[0080] Here, in Comparative Example 1, Binder 3 was used instead of Binder 1. Binder 3 was produced by the following manufacturing method. First, 77 parts by mass of polycarbonate diol (product name: PCDL T5652, manufactured by Asahi Kasei Corporation, weight average molecular weight 2,000), 1 part by mass of trimethylolpropane (molecular weight 134.7), 14 parts by mass of isophorone diisocyanate (molecular weight 222), 140 parts by mass of NMP, and 0.048 parts by mass of Sn catalyst (product name T-320) were added to a separable flask, and then heated and stirred at 80°C for about 2 hours, allowing the reaction to occur until the f-NCO content reached 1.23%. Next, 3.6 parts by mass of dibutylamine (molecular weight 129.2) and 72 parts by mass of NMP were added to the separable flask, and then allowed to react by stirring at room temperature for about 1 hour. The obtained reactive polyurethane solution (solid content concentration 33% by mass) was diluted to a solid content concentration of 10% by mass by adding 660 parts by mass of NMP to obtain Binder 3. The weight average molecular weights of Binders 1, 2, and 3 were all 30,000. The weight average molecular weight of Binder 4 was 35,000.

[0081] In Comparative Example 2, a binder in which polyvinylidene fluoride (PVDF) and hexafluoropropylene (HFP) were mixed in a mixing ratio (by mass) of 95:5 was used. Also in Comparative Example 3, a binder in which polyvinylidene fluoride (PVDF) and hexafluoropropylene (HFP) were mixed in a mixing ratio (by mass) of 95:5 was used.

[0082] In Comparative Example 3, trimethyl borate (TMB) was added as an additive together with the inorganic oxide, binder, etc., and then stirred.

[0083] <Evaluation> (ionic conductivity) The thickness (film thickness) of the electrolyte obtained in each example or comparative example was measured. Then, the test piece was subjected to electrochemical impedance (EIS) measurement at a frequency of 1 MHz to 0.1 Hz using an impedance analyzer (product name: SP-150) manufactured by Bio-Logic SAS, to obtain the bulk resistance value. The ionic conductivity was calculated by dividing the electrolyte film thickness by the bulk resistance value (unit: mS / cm). The larger the calculated value, the better the ionic conductivity.

[0084] (transportation number) The electrolyte obtained in each Example or Comparative Example was sandwiched between two sheets of lithium foil to prepare a lithium symmetric cell. The impedance of the lithium symmetric cell and the current decay versus input voltage were measured. The lithium ion transport number was then calculated using the following equation (1).

[0085]

number

[0086] (Lithium ion conductivity) The lithium ion conductivity (unit: mS / cm) of the electrolyte obtained in each Example or Comparative Example was calculated by multiplying the above-mentioned ionic conductivity value by the transport number value.

[0087] (Membrane strength) The electrolyte membrane obtained in each Example or Comparative Example was checked to see if it could be peeled off from the substrate by hand. If it could be peeled off, it had excellent membrane strength.

[0088] Evaluation criteria 〇: Peelable ×: Cannot be peeled off

[0089] The experimental results are shown below.

[0090] [Table 1]

[0091] [Table 2]

[0092] [Table 3]

[0093] By comparing the Examples and Comparative Examples, it was found that the use of the binder of the present embodiment makes it possible to obtain an electrolyte having excellent ionic conductivity and strength. It was also found that the addition of an additive further improves the ionic conductivity. [Industrial Applicability]

[0094] The electrolyte of this embodiment can be used in electricity storage devices (for example, electrodes for lithium secondary batteries, etc.) The obtained electricity storage device can be used in various portable devices such as mobile phones, notebook computers, personal digital assistants (PDAs), video cameras, and digital cameras, as well as medium-sized or large-sized electricity storage devices installed in electric bicycles, electric vehicles, etc.

[0095] The present invention is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit of the present invention. For example, the technical features in the embodiments and examples corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

Claims

1. an electrolyte including an ionic liquid, an inorganic oxide, and a binder; The binder is made from polycarbonate polyol and polyisocyanate, The binder has at least one functional group selected from the group consisting of a trialkoxysilyl group having 1 to 4 carbon atoms, an epoxy group, and an oxetanyl group at its terminal. Electrolytes.

2. 10. The electrolyte of claim 1, further comprising: containing an additive different from the inorganic oxide, The electrolyte, wherein the additive is at least one of a boron compound and an aluminum compound.

3. 3. The electrolyte of claim 2, The additive is the boron compound, and the number of moles of the boron compound per 1 kg of the electrolyte is 0.55 mol / kg or less. Electrolytes.

4. The electrolyte according to claim 2 , wherein the additive is the aluminum compound, An electrolyte, characterized in that the number of moles of the aluminum compound per 1 kg of the electrolyte is 0.05 mol / kg or less.

5. 4. The electrolyte according to claim 2, wherein the additive is a borate ester.

6. The electrolyte of claim 5 An electrolyte, wherein the borate ester is at least one of trimethyl borate and triethyl borate.

7. 7. An electrolyte according to any one of claims 1 to 6, An electrolyte comprising at least one of silicon oxide and aluminum oxide as the inorganic oxide.

8. The electrolyte according to claim 1 , wherein the weight average molecular weight of the binder is 10,000 or more and 120,000 or less.

9. 9. A battery comprising an electrolyte according to claim 1 , Energy storage device.

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