Electrolyte with oxidation corrosion suppression capability

Abstract

To provide an electrolyte for a power storage device that can suppress oxidation corrosion of an electrode current collector and provide excellent battery characteristics.SOLUTION: An electrolyte for a power storage device including water or an organic solvent as a solvent contains a trifluoroacetate (TFA) salt. The TFA salt reacts with aluminum metal present within a secondary battery to form a passivation film, thereby providing suppression capability against oxidation corrosion of the aluminum metal. The aluminum metal constitutes the material forming a cathode current collector and / or an anode current collector in the power storage device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrolyte for suppressing oxidative corrosion of aluminum metal contained in an electrode current collector or the like in an electricity storage device, and an electricity storage device containing the electrolyte. The present invention also relates to a method for suppressing surface oxidative corrosion, a surface coating agent, and an electrode current collector having a passivation film on its surface. [Background technology]

[0002] Current lithium-ion batteries use highly flammable nonaqueous (organic solvent) electrolytes, which have led to numerous fires and explosions. For this reason, active research has been conducted on aqueous secondary batteries, which use nonflammable, fire-extinguishing water as the electrolyte solvent (e.g., Patent Document 1). Aqueous secondary batteries are highly safe and offer manufacturing cost advantages because they eliminate the need for a water-free environment during the battery manufacturing process. However, the operating voltage of aqueous secondary batteries is 2 V or less, which is lower than that of conventional organic lithium-ion batteries (4 V class). Therefore, increasing the voltage (higher energy density) is key to the widespread use of aqueous secondary batteries. In particular, active corrosion of current collectors containing aluminum (Al) metal occurs in aqueous electrolytes, which has been pointed out as a cause of severe battery degradation. Therefore, aqueous electrolytes capable of realizing oxidation resistance of Al current collectors have not yet been put into practical use.

[0003] Aluminum metal is abundant in the earth's crust, lightweight, and easily processed, making it an essential material for achieving low-cost, high-energy-density batteries. In nonaqueous electrolytes, the HF produced by the decomposition of electrolytes (e.g., LiPF6, LiBF6, LiBOB, LiDFOB) forms a passive film (AlF3) on the aluminum metal surface, suppressing its corrosion. This mechanism is thought to occur as follows: 1) lithium salts react (hydrolyze) with trace amounts of water impurities in the electrolyte to produce hydrogen fluoride (HF), and 2) HF reacts with the aluminum oxide film to form AlF3. However, it has been reported that the protective function of aluminum current collectors decreases in highly oxidizing and high-temperature environments (e.g., above 4.0 V and 40°C). [ka]

[0004] Furthermore, LiPF6 salt is easily hydrolyzed, making it unsuitable for use in aqueous electrolytes. Therefore, imide salts such as LiTFSI (LiN(SO2CF3)2), LiBETI (LiN(SO2C2F5)2), and LiPTFSI (LiN(SO2CF3)(SO2C2F5)) are used as electrolyte salts in aqueous electrolytes because they do not hydrolyze. However, these imide salts lack the ability to form passive films, which can cause oxidation and corrosion of the Al current collector in aqueous electrolytes, resulting in battery degradation. Even when a trace amount of HF is added to the electrolyte, it is difficult to form an AlF3 film on the electrode surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2020-155277 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, an object of the present invention is to provide an electrolyte solution for an electricity storage device that can suppress oxidation corrosion of an electrode current collector and provide excellent battery characteristics. [Means for solving the problem]

[0007] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have found that by using an electrolyte containing a metal salt with trifluoroacetate (TFA) as the anion, a passivation film is formed on the surface of an Al current collector in an aqueous electrolyte, thereby suppressing Al metal oxidative corrosion and providing excellent battery characteristics. Furthermore, they have found that this high oxidative corrosion resistance also functions in non-aqueous solvent systems. Based on these findings, the present invention has been completed.

[0008] That is, in one aspect, the present invention relates to an electrolyte solution for an electricity storage device and an electricity storage device containing the electrolyte solution, and more specifically, <1> an electrolyte solution for an electricity storage device, comprising water or an organic solvent as a solvent, and containing a trifluoroacetate (TFA) salt, the TFA salt reacting with aluminum metal present in a secondary battery to form a passivation film, thereby inhibiting oxidation corrosion of the aluminum metal, and the aluminum metal being a material constituting a positive electrode current collector and / or a negative electrode current collector in the electricity storage device; <2> The passive film has the following formula (1): AlO x (OH) y F z (1) (wherein x is 0 to 1.5; y is 0 to 3; and z is 0 to 3), <1> Described in electrolyte; <3> The concentration of the TFA salt in the electrolytic solution is 0.1% by weight or more. <1> Electrolyte solution according to <4> The TFA salt is a salt of a metal selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, and transition metals. <1> Electrolyte solution according to <5> The power storage device is a lithium ion secondary battery, a sodium ion secondary battery, or a potassium ion secondary battery. <1> Electrolyte solution according to <6> Positive electrode, negative electrode, positive electrode current collector, negative electrode current collector, and the above <1> ~ <5> an electricity storage device comprising the electrolytic solution according to any one of the preceding items, wherein the positive electrode current collector and / or the negative electrode current collector contain aluminum metal, and the positive electrode current collector and / or the negative electrode current collector have a passivation coating formed on their surfaces by a reaction with the TFA salt in the electrolytic solution; <7> The above has a positive electrode with a voltage of 3.0 V or higher relative to lithium metal. <6> The electricity storage device according to <8> The battery is a lithium ion secondary battery, a sodium ion secondary battery, or a potassium ion secondary battery. <6> The electricity storage device according to This provides:

[0009] In another aspect, the present invention also relates to a method for inhibiting oxidation corrosion of a surface, a surface coating agent, and an electrode current collector having a passivation film on its surface, more specifically, <9> A method for inhibiting oxidation corrosion on the surface of an electrode current collector containing aluminum metal, comprising: <1> ~ <5> forming a passivation film on a positive electrode current collector and / or a negative electrode current collector using the electrolytic solution according to any one of the above items; <10> a coating agent for the surface of an electrode current collector, which reacts with aluminum metal contained in the positive electrode current collector and / or the negative electrode current collector to form a passivation film, the coating agent comprising a trifluoroacetate (TFA) salt; <11> an electrode current collector for an electricity storage device, comprising aluminum metal and having a passivation coating on its surface; <12> The positive electrode current collector or the negative electrode current collector, <11> The present invention provides an electrode current collector according to the above item. [Effects of the Invention]

[0010] The electrolyte of the present invention can achieve high oxidation resistance of an Al current collector in an aqueous electrolyte and provide excellent battery characteristics. This allows the Al current collector to be applied to aqueous energy storage devices, contributing to the realization of low-cost, highly safe, and high-energy-density aqueous batteries. Furthermore, because this high oxidation resistance is also effective in non-aqueous electrolytes, it is useful for achieving high-stability operation and long life for various energy storage devices, including current lithium-ion batteries. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of the formation of a passive film on the surface of an Al current collector. [Figure 2] FIG. 2 is a graph showing the results of linear sweep voltammetry (LSV) for the electrolyte solutions of the present invention and comparative examples (Example 1 and Comparative Example 1). [Figure 3]FIG. 3 is a graph showing the results of LSV for the electrolyte solutions of the present invention and comparative examples (Example 2 and Comparative Examples 2 to 4). [Figure 4] FIG. 4 is a graph showing the results of chronoamperometry carried out on the electrolyte solution of the present invention (Example 1). [Figure 5] FIG. 5 shows the results of X-ray photoelectron spectroscopy (XPS) analysis of the surface of an Al current collector. [Figure 6] FIG. 6 shows the results of time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis of the surface of an Al current collector. [Figure 7] FIG. 7 is a graph showing the results of LSV for the Na aqueous electrolyte of the present invention. [Figure 8] FIG. 8 is a graph showing the results of LSV in an organic solvent-based electrolyte solution. [Figure 9] FIG. 9 is a graph comparing the performance of aqueous batteries before and after the addition of TFA salt. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following describes embodiments of the present invention. The scope of the present invention is not limited to these descriptions, and other than the following examples, the present invention can be implemented with appropriate modifications within the scope that does not depart from the spirit of the present invention.

[0013] 1. Electrolyte of the Present Invention The electrolyte solution of the present invention is an electrolyte solution for an electricity storage device containing water or an organic solvent as a solvent, 1) Contains a trifluoroacetate (TFA) salt; 2) The TFA salt reacts with the aluminum metal present in the secondary battery to form a passivation film, thereby inhibiting the oxidation corrosion of the aluminum metal; 3) The aluminum metal that reacts with the TFA salt is a material that constitutes the positive electrode current collector and / or the negative electrode current collector in the electricity storage device. It is characterized by:

[0014] This is based on the new finding that by using a salt with TFA as the anion, a passivation film can be formed on the surface of the Al current collector, suppressing Al metal oxidation corrosion and providing excellent battery characteristics.

[0015] More specifically, the TFA anion (CF3COO - ) and water (the solvent in aqueous electrolytes, or the trace amounts of water present in non-aqueous electrolytes) react with aluminum oxide (Al2O3) on the surface of the Al current collector to form an Al metal complex represented by the following formula (1). This metal complex then functions as a passive film that inhibits oxidation corrosion of the aluminum metal (Figure 1). [ka]

[0016] In formula (1), x is 0 to 1.5; y is 0 to 3; and z is 0 to 3.

[0017] As described above, the electrolytic solution of the present invention is characterized by being able to form a passivation film on the surface of the Al current collector and inhibit oxidation corrosion of the Al metal. Below, we will further explain representative specific examples of each component constituting the electrolytic solution.

[0018] (A) TFA salt The TFA salt used in the present invention is a TFA anion (CF3COO - The TFA salt is not particularly limited as long as it is a salt containing an alkali metal, an alkaline earth metal, or a transition metal, but is typically a salt of an alkali metal, an alkaline earth metal, or a transition metal. The alkali metal can be lithium, sodium, or potassium, and the alkaline earth metal can be magnesium or calcium. Zinc or the like can be used as the transition metal. For example, when the electrolyte solution of the present invention is used in a lithium ion secondary battery, the TFA salt is preferably lithium TFA.

[0019] The concentration of the TFA salt in the electrolyte solution of the present invention is preferably 0.1 wt % or more, more preferably 1 wt % or more, based on the total weight of the electrolyte solution. A high concentration of the TFA salt is advantageous in that it can achieve high oxidation resistance of the electricity storage device. The upper limit of the concentration of the TFA salt is not particularly limited, but can be, for example, 20 wt %.

[0020] (B) Solvent component The solvent in the electrolytic solution of the present invention may be any known solvent that has been conventionally known as being usable as an electrolytic solution for an electricity storage device such as a secondary battery, and may be water or an organic solvent.

[0021] Typically, the electrolyte solution of the present invention is an aqueous electrolyte solution, with water as the main solvent. However, it is also possible to use a mixed solvent containing other organic solvents in addition to water. Such organic solvents are soluble in water, and examples thereof include alcohols such as methanol, and aprotic polar solvents such as acetone, acetonitrile, and dimethyl sulfoxide. Even in such mixed solvents, the proportion of water can be 1 to 100% by volume, preferably 10% by volume or more, more preferably 50% by volume or more, and particularly preferably 90% by volume or more. Most desirable is a completely aqueous electrolyte solution containing 100% by volume of water.

[0022] The electrolytic solution of the present invention may also be a non-aqueous solvent (organic solvent) system that does not contain water. Examples of such solvents include carbonates such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane; dimethoxymethane (DMM), dimethyl ether, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, 1,4-dioxane, and tetrahydrofuran. Examples of suitable organic solvents include ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran; esters such as methyl formate, methyl acetate, and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amines such as triethylamine; amides such as N,N-dimethylformamide (DMF) and N,N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide (DMSO), sulfolane, and 1,3-propane sultone; ketones such as acetone; and organic solvents containing fluorine substituents. These may be used alone or in combination. However, the present invention is not limited to these. Preferably, the solvent is an aprotic organic solvent.

[0023] For example, typical solvents that can be used include 1,2-dimethoxyethane (DME), hydrofluoroether (HFE), ethylene carbonate (EC), propylene carbonate (PC), fluorinated linear carbonate (FEMC), 1,4-dioxane, sulfolane, toluene, and diethylene glycol dimethyl ether (diglyme).

[0024] (C) Other ingredients In addition to the TFA salt, the electrolyte solution of the present invention may further contain a supporting electrolyte known in the art. In the case of a lithium-ion secondary battery, such a supporting electrolyte may be selected from the group consisting of LiPF, LiBF, LiClO, LiNO, LiCl, LiSO, LiS, lithium difluoro(oxalato)borate (LiDFOB), and lithium bis(oxalato)borate (LiBOB), and any combination thereof. Most preferably, the electrolyte solution of the present invention does not contain any metal salt other than the TFA salt, and the TFA salt functions as a supporting electrolyte together with the passivation film-forming agent.

[0025] Other examples of supporting electrolytes include metal salts containing anions preferably containing one or more groups selected from the group consisting of fluorosulfonyl, trifluoromethanesulfonyl, and perfluoroethanesulfonyl groups. For example, examples of such anions include bis(fluorosulfonyl)imide ([N(FSO)] - ), (fluorosulfonyl)(trifluorosulfonyl)imide ([N(CF3SO2)(FSO2)] - ), bis(trifluoromethanesulfonyl)imide ([N(CF3SO2)2] - ), bis(perfluoroethanesulfonyl)imide ([N(C2F5SO2)2] - ) or (perfluoroethanesulfonyl)(trifluoroethanemethanesulfonyl)imide ([N(C2F5SO2)(CF3SO2)] - ) is preferred.

[0026] For example, specific examples of lithium salts used as supporting electrolytes include lithium bis(fluorosulfonyl)imide (LiFSI), lithium (fluorosulfonyl)(trifluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(perfluoroethanesulfonyl)imide (LiBETI), and lithium (perfluoroethanesulfonyl)(trifluoroethanemethanesulfonyl)imide. Lithium bis(fluorosulfonyl)amide (LiFSI) is preferred. These salts are preferred because they have weak cation-anion interactions and high ionic conductivity even at high concentrations.

[0027] Those skilled in the art can determine the appropriate concentration of the supporting electrolyte in the electrolyte solution. For example, in the case of a lithium ion secondary battery, the concentration can be within a range that allows for reversible intercalation and deintercalation of lithium ions into the negative electrode carbon material, as long as precipitation of the lithium salt does not occur. Typically, the molar ratio of the solvent to the lithium salt is preferably within a range of 1:20 to 1:0.5. An excessively low concentration of the lithium salt can result in low ionic conductivity, while an excessively high concentration can cause adverse effects such as high viscosity, so it is desirable for the lithium salt to be within these ranges.

[0028] The electrolyte solution of the present invention may also contain other components as needed to improve its functions, etc. Examples of other components include conventionally known overcharge inhibitors, dehydrating agents, deoxidizing agents, and property-improving aids for improving capacity retention and cycle characteristics after high-temperature storage.

[0029] Examples of overcharge inhibitors include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially fluorinated compounds of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; and fluorine-containing anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, and 2,6-difluoroaniol. One type of overcharge inhibitor may be used alone, or two or more types may be used in combination.

[0030] When the electrolyte solution contains an overcharge inhibitor, the content of the overcharge inhibitor in the electrolyte solution is preferably 0.01 to 5% by mass. By adding 0.1% by mass or more of the overcharge inhibitor to the electrolyte solution, it becomes easier to prevent explosion or fire of the electricity storage device due to overcharge, and the electricity storage device can be used more stably.

[0031] Examples of dehydrating agents include molecular sieves, sodium sulfate, magnesium sulfate, calcium hydride, sodium hydride, potassium hydride, and lithium aluminum hydride. The solvent used in the electrolytic solution of the present invention may be one that has been dehydrated with the dehydrating agent and then rectified. Alternatively, a solvent that has been dehydrated with the dehydrating agent alone without rectification may be used.

[0032] Examples of the characteristic improving aid for improving the capacity retention characteristics and cycle characteristics after high-temperature storage include carboxylic acid anhydrides such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, and phenylsuccinic anhydride; sulfur-containing compounds such as ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, diphenyl sulfone, methyl phenyl sulfone, dibutyl disulfide, dicyclohexyl disulfide, tetramethylthiuram monosulfide, N,N-dimethylmethanesulfonamide, and N,N-diethylmethanesulfonamide; hydrocarbon compounds such as heptane, octane, and cycloheptane; and fluorine-containing aromatic compounds such as fluoroethylene carbonate (FEC), fluorobenzene, difluorobenzene, hexafluorobenzene, and benzotrifluoride. These property improvement assistants may be used alone or in combination of two or more. When the electrolytic solution contains a property improvement assistant, the content of the property improvement assistant in the electrolytic solution is preferably 0.01 to 5 mass %.

[0033] 2. Electricity storage device of the present invention As described above, the present invention also relates to an electricity storage device comprising a positive electrode, a negative electrode, a positive electrode current collector, a negative electrode current collector, and the above-described electrolyte. When the positive electrode current collector and / or the negative electrode current collector contain aluminum metal, the use of the above-described electrolyte can form a passivation film on the surface of the Al current collector, suppressing oxidation corrosion of the Al metal and providing excellent battery characteristics. Examples of electricity storage devices include lithium ion secondary batteries, sodium ion secondary batteries, potassium ion secondary batteries, lithium metal batteries, electric double layer capacitors, and alkali metal ion capacitors.

[0034] (A) Negative electrode The negative electrode in the power storage device of the present invention may have an electrode configuration known in the art. For example, when the power storage device is a lithium ion battery, an example of the negative electrode includes an electrode containing a negative electrode active material capable of electrochemically absorbing and releasing lithium ions. Such a negative electrode active material may be a known negative electrode active material for lithium ion secondary batteries, and examples thereof include carbonaceous materials such as natural graphite, highly oriented pyrolytic graphite (HOPG), and amorphous carbon. Further examples include lithium metal, or metal compounds containing lithium, such as alloys, metal oxides, metal sulfides, and metal nitrides. For example, examples of alloys containing lithium include lithium aluminum alloys, lithium tin alloys, lithium lead alloys, and lithium silicon alloys. Furthermore, examples of metal oxides containing lithium include lithium titanate (Li4Ti5O 12 Examples of metal nitrides containing lithium include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride. These negative electrode active materials may be used alone or in combination of two or more. Of these, lithium titanate is preferred as the negative electrode active material.

[0035] When the electricity storage device is a sodium ion battery, an electrode containing a negative electrode active material capable of electrochemically absorbing and releasing sodium ions can be used. For example, instead of the above-mentioned lithium metal, etc., sodium metal, or a metal compound containing sodium, such as an alloy, metal oxide, metal sulfide, or metal nitride, can be used.

[0036] When the power storage device is a potassium ion secondary battery, an example of the electrode includes a negative electrode active material capable of electrochemically absorbing and releasing potassium ions. As such a negative electrode active material, known negative electrode active materials for potassium ion secondary batteries can be used, and examples thereof include carbonaceous materials such as graphitizable carbon and non-graphitizable carbon (hard carbon). Further examples include metal compounds such as alloys and metal oxides containing potassium. Examples of alloys containing potassium include potassium aluminum alloys, potassium tin alloys, potassium lead alloys, and potassium silicon alloys. Furthermore, examples of metal compounds containing potassium include potassium titanate (K2Ti3O7 or K4Ti5O 12 ) and potassium-containing titanium oxides. These negative electrode active materials may be used alone or in combination of two or more. Among them, potassium titanate is preferred as the negative electrode active material for potassium ion secondary batteries.

[0037] When the power storage device is an electric double layer capacitor, the negative electrode preferably contains an active material that undergoes a deposition-dissolution reaction of lithium metal. Examples of active materials that undergo a deposition-dissolution reaction of lithium metal include lithium metal, alloys containing lithium element, and metal compounds such as metal nitrides. Examples of alloys containing lithium element include lithium aluminum alloys, lithium tin alloys, lithium lead alloys, and lithium silicon alloys. Examples of metal nitrides containing lithium element include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride. In addition, lithium titanate (Li4Ti5O 12 ) or lithium titanium niobate (TiNb2O7) can also be used.

[0038] When the power storage device is an electric double layer capacitor, the negative electrode contains a polarizable electrode material. The polarizable electrode material may be any material used in ordinary electric double layer capacitors, such as activated carbon produced from various raw materials. Activated carbon with a large specific surface area is preferred.

[0039] When the power storage device is an alkali metal ion capacitor, the negative electrode contains a material capable of absorbing and releasing alkali metal ions. Examples of such materials include graphite-containing materials such as natural graphite or artificial graphite. Materials such as alkali metal titanates, which exhibit redox capacity at a constant potential by inserting and desorbing cations such as alkali metal ions, may also be used. When using a material that does not contain alkali metals as the negative electrode active material, a compound containing a large amount of alkali metal may be added to the negative electrode or positive electrode, and the alkali metal may be pre-doped into the negative electrode active material.

[0040] When the power storage device is a secondary battery, the negative electrode may contain only the negative electrode active material, or may contain at least one of a conductive material and a binder in addition to the negative electrode active material, and may be in the form of a negative electrode mixture attached to a negative electrode current collector. For example, when the negative electrode active material is in foil form, the negative electrode may contain only the negative electrode active material. On the other hand, when the negative electrode active material is in powder form, the negative electrode may contain the negative electrode active material and a binder. Methods for forming a negative electrode using a powdered negative electrode active material include a doctor blade method and a molding method using a pressure press. The same applies when the power storage device is a capacitor.

[0041] Examples of conductive materials that can be used include carbon materials, conductive fibers such as metal fibers, metal powders such as copper, silver, nickel, and aluminum, and organic conductive materials such as polyphenylene derivatives. Examples of carbon materials that can be used include graphite, soft carbon, hard carbon, carbon black, ketjen black, acetylene black, graphite, activated carbon, carbon nanotubes, and carbon fibers. Furthermore, mesoporous carbon obtained by burning synthetic resins containing aromatic rings, petroleum pitch, and the like can also be used.

[0042] Preferred examples of binders include fluorine-based resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and ethylene tetrafluoroethylene (ETFE), as well as carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyethylene, and polypropylene. The negative electrode current collector may be a rod, plate, foil, or mesh containing aluminum, copper, nickel, stainless steel, or the like.

[0043] (B) Positive electrode The positive electrode of the secondary battery of the present invention can be any electrode configuration known in the art, but preferably has a voltage of 3.0 V or higher versus lithium metal. For example, when the secondary battery is a lithium-ion battery, the positive electrode active material can be a lithium-containing transition metal oxide containing one or more transition metals, such as lithium cobalt oxide (LiCoO), lithium manganese oxide (LiMnO), or lithium nickel oxide (LiNiO), a transition metal sulfide, a metal oxide, a lithium-containing polyanion compound containing one or more transition metals, such as lithium iron phosphate (LiFePO) or lithium iron pyrophosphate (LiFePO), or a sulfur-based compound (LiS). The positive electrode may contain a conductive material or a binder, or a catalyst that promotes the oxidation-reduction reaction of oxygen. Lithium manganese oxide is preferred.

[0044] When the power storage device is a sodium-ion secondary battery, examples of the positive electrode active material include sodium cobaltate (NaCoO), sodium manganate (NaMnO), sodium nickelate (NaNiO), and sodium vanadate (NaVO). Examples of the positive electrode active material include sodium-containing transition metal oxides containing one or more transition metals, such as sodium ferrate (NaFeO), transition metal sulfides, metal oxides, sodium iron phosphate (NaFePO), and sodium-containing phosphate compounds containing one or more transition metals, such as sodium vanadium phosphate (NaVP2O7), sodium vanadium fluorophosphate (NaV2(PO4)2F3), and sodium iron fluorophosphate (Na2FePO4F). The positive electrode may contain a conductive material or a binder. Furthermore, oxygen or an oxygen-containing metal salt, such as sodium oxide, may be used as the positive electrode active material. A positive electrode containing such a positive electrode active material may also contain a catalyst that promotes the oxidation-reduction reaction of oxygen in the positive electrode active material. A preferred positive electrode active material is a transition metal oxide containing excess sodium (such as manganese, cobalt, iron, nickel, or copper). A high-surface-area material, such as activated carbon, can also be used in the positive electrode to create a reaction field for efficiently redoxing atmospheric oxygen and extracting capacity.

[0045] When the power storage device is a potassium-ion secondary battery, examples of the positive electrode active material include potassium cobaltate (KCoO), potassium manganate (KMnO), potassium nickelate (KNiO), and potassium vanadate (KVO). Potassium-containing transition metal oxides containing one or more transition metals, such as potassium ferrate (KFeO), transition metal sulfides, metal oxides, potassium iron phosphate (KFePO), and potassium phosphate compounds containing one or more transition metals, such as potassium cobalt phosphate (KCoPO), potassium cobalt fluorophosphate (KCoPOF), and potassium iron fluorophosphate (KFePOF). The positive electrode may contain a conductive material or a binder. Oxygen or an oxygen-containing metal salt, such as potassium oxide, may also be used as the positive electrode active material. A positive electrode containing such a positive electrode active material may also contain a catalyst that promotes the oxidation-reduction reaction of oxygen in the positive electrode active material. A preferred positive electrode active material is a transition metal oxide containing an excess of potassium (such as manganese, cobalt, iron, nickel, or copper). A high-surface-area material, such as activated carbon, can also be used in the positive electrode to create a reaction field for efficiently redoxing atmospheric oxygen and extracting capacity.

[0046] When the power storage device is a lithium metal battery, examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO2), lithium manganese spinel (LiMn2O4), lithium nickel oxide (LiNiO2), etc., or lithium-containing transition metal oxides, transition metal sulfides, metal oxides, lithium iron phosphate (LiFePO4), lithium iron pyrophosphate (Li2FeP2O7), etc., which contain one or more transition metals in their compositions, or lithium-containing polyanion compounds, which contain one or more transition metals in their compositions. The positive electrode may contain a conductive material or a binder.

[0047] When the power storage device is a capacitor, the positive electrode contains a polarizable electrode material. The polarizable electrode material may be any of those described for the negative electrode. The polarizable electrode material may also be a conductive polymer such as polyacene or a material used in redox capacitors, such as 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), which increases capacitance through the adsorption and desorption of anions. Materials such as potassium manganate with a spinel structure or potassium iron phosphate with an olivine structure, which exhibit redox capacitance at a constant potential of 3 V or higher by inserting and desorbing cations such as alkali metal ions, may also be used.

[0048] The conductive material and binder may be the same as those used for the negative electrode.

[0049] The positive and negative electrode current collectors may be made of aluminum metal in the form of a rod, plate, foil, mesh, etc. However, in addition to aluminum metal, other materials such as copper, nickel, and stainless steel may also be used.

[0050] (C) Separator The separator used in the electricity storage device of the present invention is not particularly limited as long as it has the function of electrically separating the positive electrode layer and the negative electrode layer. Examples of the separator include porous sheets made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide, and porous insulating materials such as nonwoven fabrics and glass fiber nonwoven fabrics.

[0051] (D) Shape of the energy storage device The shape of the electricity storage device of the present invention is not particularly limited as long as it can accommodate a positive electrode, a negative electrode, and an electrolyte solution, and examples thereof include a cylindrical shape, a coin shape, a flat plate shape, a laminate shape, etc. The case for accommodating the electricity storage device may be an open-to-air case or a sealed case.

[0052] Although the electrolyte solution of the present invention is suitable for use in secondary batteries, its use in primary batteries is not excluded.

[0053] 3. Method for inhibiting oxidation corrosion, coating agent, and current collector of the present invention The use of the above-mentioned electrolyte solution makes it possible to form a passivation film on the surface of an Al current collector, inhibit oxidative corrosion of the Al metal, and provide excellent battery characteristics. Therefore, in another aspect, the present invention relates to a method for inhibiting oxidative corrosion on the surface of an electrode current collector containing aluminum metal. Specifically, the method of the present invention includes a step of forming a passivation film on a positive electrode current collector and / or a negative electrode current collector using the above-mentioned electrolyte solution.

[0054] In another aspect, the present invention relates to a coating agent for electrode current collector surfaces, which reacts with aluminum metal contained in a positive electrode current collector and / or a negative electrode current collector to form a passivation film, the coating agent comprising a trifluoroacetate (TFA) salt. As described above, the TFA salt is preferably a salt having an alkali metal, alkaline earth metal, or transition metal as the cation.

[0055] In yet another aspect, the present invention can also be said to relate to an electrode current collector for an electricity storage device, which contains aluminum metal and has a passivation coating on its surface.

[0056] Here, details of the electrolyte solution containing TFA salt, the current collector, etc. are as described above. [Example]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] 1. Verification of Al passivation in aqueous electrolyte (Li aqueous system) We investigated the passivation of Al in aqueous electrolytes containing LiTFA salts by linear sweep voltammetry (LSV). As comparative examples, we performed similar experiments using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(perfluoroethanesulfonyl)imide (LiBETI), lithium triflate (LiOTf), and lithium acetate (LiAc).

[0059] The electrolytes used had the compositions shown in Table 1. These electrolytes were prepared by dissolving an alkali metal salt in a predetermined solvent in a glove box filled with Ar. [Table 1]

[0060] The specific measurement procedure was as follows: a three-electrode cell was prepared with aluminum, platinum, and Ag / AgCl (sat.KCl) as the working electrode, counter electrode, and reference electrode, respectively; after injecting the electrolyte, linear sweep voltammetry (LSV) was performed at a sweep rate of 0.1 mV / s.

[0061] The results are shown in Figures 2 and 3. Figure 2 shows a comparison of the current-potential curves in Example 1 and Comparative Example 1. Figure 3 shows a comparison of the current-potential curves in Example 2 and Comparative Examples 2 to 4. As a result, the aqueous electrolytes of Examples 1 and 2 containing TFA salt showed a voltage drop of 5.0 V (vs. Li / Li + ) or higher. In contrast, in Comparative Examples 1 to 4, a current derived from the oxidative decomposition of Al was observed.

[0062] 2. Verification of oxidation resistance in aqueous electrolyte Next, the oxidation resistance of the electrolytes of Examples 1 and 2 was investigated using chronoamperometry. The experimental procedure involved injecting the electrolytes of Examples 1 and 2 into a three-electrode cell using aluminum, platinum, and Ag / AgCl (sat.KCl) as the working electrode, counter electrode, and reference electrode, respectively, and then performing chronoamperometry. The electrode potential was increased from 4.0 V to 10 V (vs. Li / Li+) in 0.5 V increments and maintained at each potential for 10 hours. The results are shown in Figure 4.

[0063] As shown in FIG. 4, in the electrolyte of Example 1, the voltage drop of 10 V (vs. Li / Li + This indicates that even higher oxidation resistance can be achieved by increasing the concentration of TFA salt.

[0064] 3.Surface analysis The surface of the Al current collector when the electrolyte of the present invention (Example 1) was used was analyzed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). As a result, as shown in Figures 5 and 6, in the electrolyte containing TFA, the signal derived from Al disappeared, and AlO x (OH) y F z This confirmed that a passive film had been formed on the surface of the Al current collector.

[0065] 4. Application to Na-water systems An LSV test was carried out in the same manner as in 1 above using NaTFA salt. The specific experimental procedure was as follows: a three-electrode cell was prepared using aluminum, platinum, and Ag / AgCl (sat.KCl) as the working electrode, counter electrode, and reference electrode, respectively; after injecting the electrolyte, linear sweep voltammetry (LSV) was carried out at a sweep rate of 0.1 mV / s. As a comparative example, Na(PTFSI) 0.55 (HTFSI) 0.45 The results are shown in Figure 7.

[0066] As shown in Figure 7, aqueous Na(PTFSI)0.55 (HTFSI) 0.45 It can be seen that adding a small amount (1 wt%) of NaTFA as an additive to the electrolyte improves the oxidation resistance of aluminum from 3.4 V (vs. Na / Na+) to 4.4 V (vs. Na / Na+). It was found that increasing the amount of NaTFA added to 5 wt% further suppresses aluminum oxidation to above 5.0 V (vs. Na / Na+).

[0067] 5. Application to organic solvent systems Next, an electrolyte solution was prepared by replacing the solvent with propylene carbonate (PC), and an LSV test was performed in the same manner as in 1 above. Specifically, a three-electrode cell was prepared using aluminum, lithium metal, and lithium metal as the working, counter, and reference electrodes, respectively. After injecting the electrolyte, linear sweep voltammetry (LSV) was performed at a sweep rate of 0.1 mV / s. LiTFSI was used as a comparative example. The results are shown in Figure 8.

[0068] As a result, in the organic solvent electrolyte containing LiTFSI, a current due to the oxidative decomposition of Al was observed from around 4.1 V (vs. Li / Li+). In contrast, in the electrolyte containing a small amount (1 wt%) of TFA salt as an additive, a current due to the oxidative decomposition of Al was observed from around 4.7 V (vs. Li / Li+). + ) improved the oxidation resistance of aluminum. It was found that by increasing the amount of LiTFA added to 10 wt%, the oxidation of aluminum could be further suppressed to above 5.0 V (vs. Li / Li+).

[0069] 6. Application to aqueous batteries Next, we considered application to an actual battery system. The positive electrode (LiMn2O4 positive electrode active material / aluminum positive electrode current collector), the negative electrode (Li4Ti5O 12 We fabricated an aqueous battery consisting of a negative electrode active material and an aluminum negative electrode current collector. 0.6 (TFSI) 0.4 A small amount (1 wt%) of LiTFA was added to the aqueous electrolyte (1 / 1.2) and the capacity degradation behavior of the battery was observed. The results are shown in Figure 9.

[0070] As a result, Li(PTFSI) 0.6 (TFSI) 0.4 In the case of a 1 / 1.2 aqueous electrolyte, the aluminum current collector was oxidized, and the battery capacity significantly decreased with repeated charge and discharge. In contrast, in the case of a battery using an electrolyte containing a small amount of LiTFA (1 wt%), the oxidation of the aluminum current collector was highly suppressed by the addition of LiTFA, and it was confirmed that the battery maintained more than 80% of its capacity even after more than 100 charge and discharge cycles. This is more than seven times the performance improvement compared to a battery without LiTFA added.

Claims

1. An electrolyte solution for an electricity storage device containing water or an organic solvent as a solvent, including the trifluoroacetate (TFA) salt, the TFA salt reacts with aluminum metal present in the secondary battery to form a passivation film, thereby inhibiting oxidation corrosion of the aluminum metal; The aluminum metal is a material that constitutes a positive electrode current collector and / or a negative electrode current collector in the electricity storage device. The electrolyte solution is characterized by:

2. The passive film has the following formula (1): AlO ｘ (OH) ｙ F ｚ (1) (wherein x is 0 to 1.5; y is 0 to 3; and z is 0 to 3.)

3. 2. The electrolyte solution according to claim 1, wherein the concentration of the TFA salt in the electrolyte solution is 0.1% by weight or more.

4. 2. The electrolyte solution of claim 1, wherein the TFA salt is a salt of a metal selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, and transition metals.

5. The electrolyte solution according to claim 1 , wherein the electricity storage device is a lithium ion secondary battery, a sodium ion secondary battery, or a potassium ion secondary battery.

6. An electricity storage device comprising a positive electrode, a negative electrode, a positive electrode current collector, a negative electrode current collector, and the electrolyte solution according to any one of claims 1 to 5, the positive electrode current collector and / or the negative electrode current collector contains aluminum metal, the positive electrode current collector and / or the negative electrode current collector has a passivation coating formed on its surface by reaction with the TFA salt in the electrolyte solution; Energy storage device.

7. The electricity storage device according to claim 6 , having a positive electrode having a voltage of 3.0 V or higher versus lithium metal.

8. The electricity storage device according to claim 6 , which is a lithium ion secondary battery, a sodium ion secondary battery, or a potassium ion secondary battery.

9. A method for inhibiting oxidation corrosion on a surface of an electrode current collector containing aluminum metal, comprising: A method comprising forming a passivation film on a positive electrode current collector and / or a negative electrode current collector using the electrolyte solution according to any one of claims 1 to 5.

10. A coating agent for the surface of an electrode current collector, which reacts with aluminum metal contained in the positive electrode current collector and / or the negative electrode current collector to form a passivation film, the coating agent comprising a trifluoroacetate (TFA) salt.

11. An electrode current collector for an electricity storage device, comprising aluminum metal and having a passivation coating on its surface.

12. The electrode current collector according to claim 11 , which is a positive electrode current collector or a negative electrode current collector.

Images