JP2013114934A - Metal salt, electrode protective film forming agent, secondary battery electrolyte including the salt, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal salt having a protective film forming ability at a positive electrode and useful for an electrode protective film forming agent excellent in safety, an electrode protective film forming agent using the metal salt, a secondary battery electrolyte, and further a secondary battery.SOLUTION: A metal salt comprises a constituent (A) and a constituent (B). (A): metal cation and (B): cyano methane sulfonate-based anion represented by the following formula:OSOCF(CN)(1) (where, n represents an integer of 1-3.)

Description

  The present invention relates to a novel metal salt, and further relates to an electrode protective film forming agent having an electrode protective film forming ability and excellent electrolyte performance, an electrolyte for a secondary battery containing such a metal salt, and a secondary battery. Is.

  In recent years, power storage devices such as batteries and capacitors have become widespread in information electronic devices such as notebook computers, mobile phones, and PDAs, and more comfortable portability has been demanded, resulting in smaller, thinner, lighter, and higher performance. Progressing rapidly. In particular, secondary batteries typified by lithium secondary batteries are being considered for application in electric vehicles that are expected to be the next generation of vehicles, and further increases in capacity and output are required. Yes.

A lithium secondary battery is configured by sandwiching an electrolyte between a positive electrode and a negative electrode. Such an electrolyte is composed of an organic solvent such as propylene carbonate or diethyl carbonate, a lithium salt such as LiPF ₆ or LiBF ₄ , and electrode protection. It is manufactured by dissolving additives such as a film forming agent.

As the electrode protective film forming agent, vinylene carbonate or the like is generally used, but although it can form a protective film on the negative electrode, it does not have a protective function for the positive electrode and can fully utilize the potential region of the positive electrode active material. Absent. For example, a high-performance material having an oxidation potential of 5 V or higher (vs Li / Li ⁺ ) has been developed as a positive electrode active material, and an organic solvent or a lithium salt counter anion is present on the surface of the positive electrode material containing the positive electrode active material. Because of oxidative decomposition, these positive electrode active materials cannot be utilized. Further, in order to ensure the safety of the battery even in an overcharged state, an electrolyte having a high oxidation resistance potential is desired even when the oxidation resistance potential is 6 V or more (vs Li / Li ⁺ ), and even 0.1 V. Furthermore, in the above-mentioned battery for electric vehicles, ensuring safety is the utmost proposition, and there is a demand for an effective electrode protective film forming material in order to avoid the risk of ignition or explosion due to a short circuit.

  Various electrode protective film forming materials have been proposed from the viewpoint of improving the performance and safety of the above-described battery. For example, compounds such as 1,3-propane sultone have been proposed (for example, Patent Document 1). ~ 5).

JP 2002-367675 A JP 2002-373704 A JP 2005-026091 A JP 2007-134282 A Japanese Unexamined Patent Publication No. 2009-140641

  However, in the disclosed techniques of Patent Documents 1 to 5, as in the case of vinylene carbonate, SEI (Solid Electrolyte Interface) is formed on the negative electrode to increase the use potential on the reduction side, but an effective protective film cannot be formed on the positive electrode. .

  Therefore, in the present invention, under such a background, a metal salt useful for an electrode protective film forming agent having a protective film forming ability in the positive electrode and excellent in safety, an electrode protective film forming agent using such a metal salt, and An object of the present invention is to provide an electrolyte for a secondary battery, and further a secondary battery.

  However, as a result of intensive research in view of such circumstances, the present inventors have found that a metal salt composed of a sulfonate anion having a metal cation and a cyano group is excellent in ability to form a protective film in the positive electrode, and completed the present invention. did.

That is, the gist of the present invention relates to a metal salt comprising components (A) and (B).
(A) Metal cation (B) Cyanomethanesulfonate anion represented by the following general formula (1)

(Chemical formula 1)
^{_{- OSO 2 CF (3-n}} ) (CN) n (1)
(Here, n is an integer of 1 to 3.)

  Furthermore, the present invention provides an electrode protective film forming agent containing the metal salt, a secondary battery electrolyte, and a secondary battery obtained by sandwiching the metal salt between a positive electrode and a negative electrode, particularly lithium secondary battery. The present invention relates to a secondary battery.

  The metal salt of the present invention has an ability to form a positive electrode protective film, is effective as an electrode protective film forming agent, and further provides an electrolyte for a secondary battery and a secondary battery that are excellent in safety and battery characteristics. be able to.

3 is a chart showing ESI-MS (−) of the metal salt of Example 1. FIG. 3 is a chart showing ¹³ C-NMR of the metal salt of Example 1. FIG. 2 is a chart showing ¹⁹ F-NMR of the metal salt of Example 1. FIG.

The present invention is described in detail below.
In addition, the monovalence and divalence used in this invention represent the stable valence of each metal cation.

  The metal salt of the present invention is a metal salt comprising a metal cation (A) and a cyanomethanesulfonate anion (B) represented by the following general formula (1).

(Chemical formula 2)
^{_{- OSO 2 CF (3-n}} ) (CN) n (1)
(Here, n is an integer of 1 to 3.)

  Examples of the metal cation (A) of the present invention include monovalent metal cations such as lithium cation, sodium cation, potassium cation and silver cation, divalent metal cations such as magnesium cation, calcium cation and copper cation, aluminum and the like. Among these metal cations, monovalent metal cations such as lithium cation, sodium cation, and potassium cation are preferable, and sodium cation is particularly preferable from the viewpoint of purity. The lithium cation is preferred.

As the metal cation used in the present invention, it is possible to use a metal cation having a different valence, or to use a monovalent metal cation and a divalent metal cation together to form a mixture of metal salts.

In the cyanomethanesulfonate anion (B) of the present invention, in the above general formula (1), n is preferably 1 or 2 from the viewpoint of the ability to form an electrode protective film, and particularly preferably the conductivity of the electrolyte. 1 in terms of rate.

  A remarkable effect of the metal salt of the present invention is that when a battery is charged and discharged, a small amount of anion decomposition products form an electrochemically stable SEI (Solid Electrolyte Interface) on the surface of the positive electrode material. In addition to protecting the electrode, it is also possible to inhibit further decomposition of the electrolyte. This effect makes it possible to use a wide potential region inherently possessed by the positive electrode active material and to stabilize the potential window of the battery.

  It is not clear by what mechanism the anion of the present invention forms SEI, but it is presumed that the cyano group, fluorine, and / or sulfur of the anion reacts with the electrode surface to form stable SEI. The above-described electrode protective film forming agent such as vinylene carbonate generally forms a protective film on the negative electrode to stabilize the reduction potential. However, the metal salt of the present invention forms a protective film on the positive electrode. The oxidation potential can be stabilized. Naturally, by using both in combination, a battery that operates stably over a wide range of potentials can be manufactured.

Hereinafter, specific examples of the production of the metal salt of the present invention will be described by taking n = 1 as an example. The chemical formula of such a metal salt is M ^{m +} · ^m− [OSO ₂ CF ₂ CN] _m . Here, when M is a monovalent metal cation such as lithium, sodium, or potassium, m is 1. When M is a divalent metal cation such as magnesium, calcium, or copper, m is 2.

  1 to 10 equivalents, preferably 1 to 5 equivalents of sodium bicarbonate and usually 1 to 10 equivalents, preferably 1 to 5 equivalents of a metal salt of dithionite were added to the halogenated difluoroacetamide. Thereafter, ultrapure water is added, and 2-amino-1,1-difluoro-2-oxoethane is stirred at room temperature to 70 ° C., preferably at room temperature to 40 ° C. for 1 to 5 hours, preferably 2 to 4 hours. A metal salt of sulfinic acid can be obtained. As the halogenated difluroacetamide, for example, chlorodifluroacetamide, bromodifluoroacetamide, and iododifluroacetamide are preferable, and bromodifluroacetamide and iododifluoroacetamide are particularly preferable from the viewpoint of reactivity. The reaction is preferably performed in an inert gas atmosphere. As the reaction solvent, for example, acetone, methyl ethyl ketone, acetonitrile, tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and the like are preferable, and acetonitrile and acetone are preferable from the viewpoint of solubility.

  Next, 1 to 10 equivalents of an oxidizing agent is usually added to the metal salt of 2-amino-1,1-difluoro-2-oxoethanesulfinic acid and stirred in water, and usually room temperature to 60 ° C., preferably room temperature. The reaction is usually carried out at -40 ° C for several minutes to several hours, preferably 1-2 hours, to obtain a metal salt of 2-amino-1,1-difluoro-2-oxoethanesulfonic acid. As the oxidizing agent, for example, potassium chromate, potassium permanganate, hydrogen peroxide and the like are preferable, and hydrogen peroxide water is particularly preferable from the viewpoint of solubility in water.

  Furthermore, the metal salt of 2-amino-1,1-difluoro-2-oxoethanesulfonic acid is usually -20 ° C to room temperature, preferably -15 ° C to room temperature, and 1 to 10 equivalents of dehydrating agent, preferably Add 1 to 5 equivalents, stir for several minutes to several hours, preferably 10 minutes to 2 hours, then heat to room temperature to 100 ° C, preferably 50 to 80 ° C, and distill off the solvent and by-products under reduced pressure. Thus, a metal salt of 1-cyano-1,1-difluoromethanesulfonic acid is obtained. Examples of the dehydrating agent include thionyl chloride, diphosphorus pentoxide, acetic anhydride, trifluoroacetic anhydride, pyridine and the like. From the viewpoint of reactivity, diphosphorus pentoxide and trifluoroacetic anhydride are preferable, and particularly in terms of purification. To trifluoroacetic anhydride is preferred.

  The obtained metal salt composed of 1-cyano-1,1-difluoromethanesulfonic acid is preferably purified in order to remove the generated metal halide and impurities. Examples of the purification technique include filtration, extraction, washing, column chromatography, reprecipitation, recrystallization, adsorption, and the like. Among these, recrystallization is preferable from the viewpoint of improving electrochemical characteristics. Furthermore, the obtained metal salt is preferably vacuum-dried from the viewpoint of improving electrochemical characteristics, and is preferably stored in a dry atmosphere.

Thus, although the metal salt of the present invention is obtained, the metal salt of the present invention is excellent in an electrode protective film forming function and is very useful as an electrode protective film forming agent.
And in this invention, the electrolyte for secondary batteries which has an electrode protective film formation function, especially the electrolyte for lithium secondary batteries can be formed by mix | blending the metal salt of this invention and lithium salt with electrolyte solution. .
When the metal salt of the present invention is a lithium salt, an electrolyte can be formed simply by blending the lithium salt into an electrolytic solution.

Examples of the lithium salt include LiBF ₄ , LiF, LiCl, LiBr, LiI, LiPF ₆ , LiOH, LiCO ₂ H, LiCO ₂ CH ₃ , LiCO ₂ CF ₃ , LiSO ₂ CH ₃ , LiSO ₂ CF ₃ , LiCN, LiN. _{(CN) 2, LiC (CN} ) 3, LiSCN, LiN (SO 2 CF 3) 2, LiN (SO 2 F) 2 and the like. Among these, from the viewpoint of solubility in organic solvents, LiBF ₄ , LiPF ₆ , LiCO ₂ H, LiCO ₂ CH ₃ , LiCO ₂ CF ₃ , LiSO ₂ CH ₃ , LiSO ₂ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ More preferably, LiBF ₄ , LiPF ₆ , LiCO ₂ H, LiCO ₂ CH ₃ , LiCO ₂ CF ₃ , LiSO ₂ CH ₃ , and LiSO ₂ CF ₃ are preferable from the viewpoint of the stability of the counter anion.

  As the electrolytic solution used in the present invention, known ones such as organic solvents and ionic liquids can be used. Examples of the organic solvent include carbonate solvents (propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, etc.), amide solvents (N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N -Methylacetamide, N-ethylacetamide, N-methylpyrrolidinone, etc.), lactone solvents (γ-butyllactone, γ-valerolactone, δ-valerolactone, 3-methyl-1,3-oxazolidine-2-one Etc.), alcohol solvents (ethylene glycol, propylene glycol, glycerin, methyl cellosolve, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, diglycerin, polyoxyalkylene glycol cyclo Xylenediol, xylene glycol, etc.), ether solvents (methylal, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-2-methoxyethane, alkoxy polyalkylene ethers, etc.), nitrile solvents (benzo Nitrile, acetonitrile, 3-methoxypropionitrile, etc.), phosphoric acids and phosphoric acid ester solvents (eg orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, polyphosphoric acid, phosphorous acid, trimethyl phosphate, etc.), 2-imidazolidinones (1,3 -Dimethyl-2-imidazolidinone, etc.), pyrrolidones, sulfolane solvents (sulfolane, tetramethylene sulfolane, etc.), furan solvents (tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, etc.), dioxolane, dioxane, etc. And this Et alone or as a mixture of two or more solvents can be used. Among these, carbonate-based solvents, ether-based solvents, furan-based solvents, and sulfolane-based solvents are preferable from the viewpoint of the conductivity of the obtained electrolyte, and sulfolane-based solvents are particularly preferable from the viewpoint of battery safety.

Examples of the ionic liquid include, as an anion, a chlorine anion, a bromine anion, an iodine anion, BF ₄ ⁻ , BF ₃ CF ₃ ⁻ , BF ₃ C ₂ F ₅ ⁻ , PF ₆ ⁻ , NO ₃ ⁻ , CF ₃ CO. ₂ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (FSO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) (FSO ₂ ) N ⁻ , (CN) ₂ N ⁻ , (CN) Examples thereof include ionic liquids containing ₃ C ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , AlCl ₄ ⁻ , Al ₂ Cl ₇ ^{− and the} like. Corresponding cations include, for example, 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1- Dialkylimidazolium cations such as octyl-3-methylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1,2,3-trimethylimidazolium, 1,2-dimethyl-3-ethylimidazolium, etc. Examples include alkyl imidazolium cations such as trialkyl imidazolium cations. In addition to imidazolium cations, examples include ionic liquids containing quaternary ammonium cations, pyridinium cations, quaternary phosphonium cations, and the like. These ionic liquids can be used alone or in combination of two or more. Among these, an ionic liquid composed of an imidazolium cation is preferably used from the viewpoint of the conductivity of the obtained electrolyte.

  The content of the metal salt in the electrolyte of the present invention is preferably 0.1 to 20% by weight, more preferably 0.2 to 10% by weight, still more preferably 0, when the entire electrolyte is 100% by weight. .3 to 5% by weight, particularly preferably 0.3 to 3% by weight. If the amount of the metal salt is too small, the ability of the electrolyte to form an electrode protective film tends to be reduced.

  Thus, although the electrolyte of the present invention using the metal salt of the present invention is obtained, the oxidation resistance potential of the electrolyte is preferably 6 V or more (vs Li / Li +). A more preferable range of the oxidation resistance potential is 6.5 V or more, more preferably 6.8 V or more, and particularly preferably 7 V or more. If the oxidation resistance potential is too small, it tends to be difficult to apply to automobile batteries that require high capacity and high output.

Here, the oxidation resistance potential is measured by a method described later, but the peak detected with a minute amount of decomposition of the electrolyte is ignored. Usually, when an electrode protective film is formed during the measurement, a minute current peak is observed, but this peak does not detract from the gist of the present invention, and a sufficient electrode protective film is formed by repeated measurement. After being done, it will disappear. Specifically, peaks with a current density of less than 1 mA / cm ² are ignored.

  The electrolyte of the present invention preferably has a conductivity of 5 mS / cm or more at 25 ° C., more preferably 7 mS / cm or more, still more preferably 9 mS / cm or more, and particularly preferably 10 mS / cm or more. The upper limit of the conductivity at 25 ° C. is usually 100 mS / cm. If the conductivity at 25 ° C. is too small, high-speed charge / discharge of the battery tends to be difficult.

  Furthermore, in the present invention, the electrical conductivity at low temperature is important. For example, the electrical conductivity of the electrolyte at −20 ° C. is preferably 0.01 mS / cm or more, more preferably 0.1 mS / cm. More preferably, it is 1 mS / cm or more, and particularly preferably 2 mS / cm or more. In addition, the upper limit of the conductivity at −20 ° C. is usually 10 mS / cm. If the conductivity at −20 ° C. is too small, the operation of the battery in a cold region tends to be difficult.

  Thus, the electrolyte of the present invention can be obtained. The metal salts used may be used alone or in combination of two or more. For example, those having different metal cations, those having different n in the general formula (1), etc. Two or more types may be used in combination.

  You may mix | blend well-known electrode protective film forming agents other than this invention with the electrolyte obtained using the metal salt of this invention as needed.

  Examples of the electrode protective film forming agent other than the present invention include vinylene carbonate, 1,3-propane sultone, ethylene sulfite, triethyl borate, and butyl methyl sulfonate. Among these, vinylene carbonate is particularly preferable from the viewpoint of forming stable SEI on the negative electrode side.

  The content of the electrode protective film forming agent is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 3 parts by weight, particularly preferably 100 parts by weight of the entire electrolyte. 0.3 to 1 part by weight. When the content is too large, the conductivity of the electrolyte tends to decrease, and when the content is too small, the effect of stabilizing the potential window of the lithium secondary battery tends to be difficult to obtain.

Next, a secondary battery obtained by using the electrolyte of the present invention, particularly a lithium secondary battery will be described.
In the present invention, the lithium secondary battery is produced by sandwiching the electrolyte of the present invention obtained above between a positive electrode and a negative electrode.

  Such a positive electrode is preferably a composite positive electrode. A composite positive electrode refers to a composition in which a positive electrode active material is mixed with a conductive additive such as ketjen black or acetylene black, a binder such as polyvinylidene fluoride, and an ion conductive polymer as required. It is applied to a conductive metal plate.

  Examples of the positive electrode active material include an inorganic active material, an organic active material, and a composite thereof. However, an inorganic active material or a composite of an inorganic active material and an organic active material has a large energy density. This is preferable.

As the inorganic active material, Li _0.3 MnO ₂ , Li ₄ Mn ₅ O ₁₂ , V ₂ O ₅ , LiFePO ₄ , LiMnO _3, etc. in the 3V system, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _{1 / 3} Mn _1/3 Co _1/3 O ₂ , LiNi _1/2 Mn _1/2 O ₂ , LiNi _0.8 Co _0.2 O ₂ , LiMnPO ₄ , Li ₂ MnO _3, etc. In the 5V system, Li ₂ MnO ₃ And metal oxides such as LiNi _0.5 Mn _1.5 O ₂ , metal sulfides such as TiS ₂ , MoS ₂ and FeS, and composite oxides of these compounds and lithium. Examples of the organic active material include conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyparaphenylene, organic disulfide compounds, carbon disulfide, and active sulfur.

  With regard to the negative electrode, for example, a metal-based negative electrode in which a negative electrode active material is directly applied to a current collector, an active material such as a conductive polymer, a carbon body, and an oxide with a binder such as polyvinylidene fluoride on an alloy-based current collector. Examples thereof include a negative electrode coated with a substance.

Examples of the negative electrode active material include lithium metal and silicon metal, alloys of metals such as lithium, silicon, aluminum, lead, tin, silicon, and magnesium, metal oxides such as SnO ₂ and TiO ₂ , polypyridine, polyacetylene, polythiophene, or Examples thereof include cation-doped conductive polymers composed of these derivatives, carbon bodies capable of occluding lithium, and in particular, when the electrolyte of the present invention is used, lithium metal and silicon metal having high energy density are preferable. .

  In the present invention, when such lithium metal is used, the thickness of the lithium metal is preferably 1 to 500 μm, more preferably 10 to 100 μm, and particularly preferably 20 to 50 μm. It is economical and preferable to use a thin lithium foil as the lithium metal.

  The lithium secondary battery of the present invention is manufactured by sandwiching an electrolyte between the positive electrode and the negative electrode, but it is preferable to use a separator from the viewpoint of preventing a short circuit. Specifically, a lithium secondary battery is obtained by impregnating a separator with an electrolyte and sandwiching the separator between a positive electrode and a negative electrode.

  As the separator, those having low resistance to ion migration of lithium ions are used, and for example, selected from polypropylene, polyethylene, polyester, polytetrafluoroethylene, polyvinyl alcohol, and saponified ethylene-vinyl acetate copolymer. Examples thereof include a microporous film made of one or more materials, an organic or inorganic nonwoven fabric, or a woven fabric. In these, the microporous film and glass nonwoven fabric which consist of polypropylene or polyethylene are preferable at the point of short circuit prevention and economical efficiency.

  Although it does not specifically limit as a form of the lithium secondary battery of this invention, The battery cell of various forms, such as a coin, a sheet | seat, a cylinder, is mentioned.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded.
In the examples, “parts” and “%” mean weight basis.
The measurement conditions for each characteristic are as follows.

(conductivity)
Using a CG-511B cell made by Toa DKK as a measurement cell, immersed in an electrolyte for 5 hours, and then measured by an alternating current impedance method using an electrochemical measurement system “Solartron 1280Z” (manufactured by Solartron, UK). . The AC amplitude was measured at 5 mV, and the frequency range was 20 k to 0.1 Hz.

(Oxidation resistance)
As a measurement cell, a V-4C voltammetry cell manufactured by BAES Co., Ltd. was used, and an electrode manufactured by BAS Co., Ltd. was used. Glassy carbon (diameter 1 mm) was used for the working electrode, platinum was used for the counter electrode, and lithium was used for the reference electrode. The potential sweep rate was 5 mV / sec, and the temperature was 25 ° C. As a measuring apparatus, an electrochemical measuring system “Solartron 1280Z” (manufactured by Solartron, UK) was used. The limiting current density was ± 1 mA / cm ^2, and the potential reaching +1 mA / cm ² was defined as oxidation resistance potential (V).

Example 1
[Production of metal salt (I)]
(1) Production of iododifluoroacetamide 200 g of ethyl iododifluoroacetate was placed in a 500 mL Erlenmeyer flask, dissolved by adding 120 mL of diethyl ether, and 97.1 g of 28% aqueous ammonia solution was added while cooling with ice. The solution was stirred at room temperature for 3 hours, extracted by adding 200 ml of ether and 100 ml of ultrapure water, and the ether layer was collected. Further, the aqueous layer was washed twice with 50 ml of ether, the ether layer was collected, collected together with the previous ether layer, and concentrated. To the obtained product, 50 ml of hexane was added, filtered under reduced pressure through a membrane filter (manufactured by Nippon Millipole) having a pore size of 0.45 μm, the residue was recovered, and 129 g of iododifluoroacetamide was collected by vacuum drying at 50 ° C. for 3 hours. 73%) was obtained.

(2) Preparation of sodium 2-amino-1,1-difluoro-2-oxoethanesulfinate 49.7 g of iododifluoroacetamide obtained in (1) was placed in a 500 mL Erlenmeyer flask under an argon atmosphere, and 300 ml of acetonitrile was added. In addition, 38.0 g of sodium hydrogen carbonate, 59.0 g of sodium dithionite, and 300 ml of ultrapure water were added in order, and the mixture was stirred at room temperature for 2 hours, followed by filtration and concentration. 100 ml of methanol was added to the obtained product, filtered, and the filtrate was concentrated and dried at 60 ° C. under vacuum for 3 hours to obtain 40.6 g of sodium 2-amino-1,1-difluoro-2-oxoethanesulfinate (recovery). 100%).

(3) Preparation of sodium 2-amino-1,1-difluoro-2-oxoethanesulfonate 2-amino-1,1-difluoro-2-oxoethanesulfinic acid obtained in (2) in a 2 L Erlenmeyer flask Add 40.0 g of sodium, add 1 L of ultrapure water to dissolve, add 52 ml of 30% hydrogen peroxide and 179 mg of sodium tungstate dihydrate successively, stir at room temperature for 2 hours, and then manganese oxide until no bubbles appear The mixture was stirred at room temperature for 30 minutes, filtered, and the filtrate was concentrated and vacuum dried at 60 ° C. for 3 hours to obtain 25 g of sodium 2-amino-1,1-difluoro-2-oxoethanesulfonate (yield 81). %).

(4) Preparation of sodium 1-cyano-1,1-difluoromethanesulfonate 2-amino-1,1-difluoro-2-oxo obtained in (3) in a 200 ml four-necked round bottom flask under an argon atmosphere Add 15.5 g of sodium ethanesulfonate, dissolve in 110 ml of dehydrated dimethylformamide, add 14.1 ml of trifluoroacetic anhydride so that the temperature does not exceed 5 ° C., stir for 30 minutes under ice cooling, and then heat to 80 ° C. The solvent and by-products were distilled off under reduced pressure, and the residue was vacuum-dried at 80 ° C. for 2 hours, then allowed to cool to room temperature, dissolved in 30 ml of dehydrated acetonitrile, recrystallized by adding 60 ml of dichloromethane, Filtration under reduced pressure through a 45 μm membrane filter (manufactured by Nihon Millipole), the residue was recovered, 100 ml of acetonitrile was added and dissolved, Filtration under reduced pressure using a 0.45 μm membrane filter (manufactured by Nihon Millipole), the filtrate was concentrated and vacuum dried at 60 ° C. for 3 hours to obtain white powder of sodium 1-cyano-1,1-difluoromethanesulfonate ( 7.66 g (50%) of metal salt (I) was obtained.

The obtained metal salt (I) was identified using the following analyzer.
That is, for the analyzer, mass spectrometry was performed using “JMS-T100LP AccuTOF LC-plus” manufactured by JEOL Ltd., and NMR was measured using “Unity-300” (solvent: heavy water) manufactured by Varian. The main chart attributions are shown below. The ESI-MS (-), ¹³ C-NMR and ¹⁹ F-NMR charts are shown in FIGS.

・ ESI-MS (-)
m / z = 155.95333
・¹³ C-NMR
110.34 ppm [t, Hz = 41.7 Hz, CN]
107.20 ppm [t, Hz = 279.1 Hz, CF ₂ ]
・¹⁹ F-NMR
−99.57 ppm [s, CF ₂ ]

[Production of electrolyte (I)]
0.37 g (0.001 mol) of the obtained metal salt (I) (sodium 1-cyano-1,1-difluoromethanesulfonate) and 7.6 g (0.05 mol) of LiPF ₆ were used as an electrolyte. Dissolved in 100 g of carbonate (50% by volume) / dimethyl carbonate (50% by volume) to obtain an electrolyte (I).
Various characteristics of the obtained electrolyte (I) are as shown in Table 1. It has high conductivity and a wide potential window even at low temperatures, and it was confirmed that it has excellent electrochemical characteristics.
Moreover, the obtained electrolyte (I) can manufacture a lithium secondary battery as follows, for example, and is useful as an electrolyte for lithium secondary batteries.

[Manufacture of lithium secondary batteries]
(1) Preparation of positive electrode 9.0 g of LiCoO ₂ powder, 0.5 g of ketjen black, and 0.5 g of polyvinylidene fluoride were mixed, and 7.0 g of 1-methyl-2-pyrrolidone was further added and mixed well in a mortar. A positive electrode slurry is obtained. The obtained positive electrode slurry was applied on a 20 μm thick aluminum foil using a wire bar in the air, dried at 100 ° C. for 15 minutes, and further dried at 130 ° C. for 1 hour under reduced pressure to obtain a film thickness of 30 μm. A composite positive electrode is produced.

(2) Battery assembly The above electrolyte (I) is impregnated into a separator (Celguard # 2400 manufactured by Celgard Inc., thickness 20 μm) and a composite positive electrode, and a separator and a lithium foil (thickness) as a negative electrode are formed on the composite positive electrode. 50 μm), and inserted into a 2032 coin cell and sealed to obtain a lithium secondary battery.

Example 2
0.74 g (0.002 mol) of the metal salt (I) obtained in the same manner as in Example 1 and 7.6 g (0.05 mol) of LiPF _{6 were} mixed with ethylene carbonate (50 vol%) / dimethyl carbonate (50 vol). %) Was dissolved in 100 g to prepare an electrolyte (II) and evaluated in the same manner as in Example 1.

Example 3
0.74 g (0.002 mol) of the metal salt (I) obtained in the same manner as in Example 1 and 15.2 g (0.1 mol) of LiPF _{6 were} mixed with ethylene carbonate (50 vol%) / dimethyl carbonate (50 vol). %) Was dissolved in 100 g to prepare an electrolyte (III) and evaluated in the same manner as in Example 1.

Comparative Example 1
An electrolyte was prepared by dissolving 7.6 g (0.05 mol) of LiPF _{6 in} 100 g of ethylene carbonate (50 vol%) / dimethyl carbonate (50 vol%), and evaluated in the same manner as in Example 1.
The results are as shown in Table 1.

  As is clear from the evaluation results of the above examples and comparative examples, the electrolytes of the examples have excellent conductivity at low temperatures, excellent oxidation resistance, and a wide potential window with respect to the electrolytes of the comparative examples. Therefore, it is very effective as an electrolyte for a secondary battery, particularly a lithium secondary battery.

  The metal salt of the present invention is excellent in the electrode protective film forming function, excellent in performance as an electrolyte such as having high conductivity and a wide potential window, and also excellent in safety, secondary It is very useful as an electrolyte for batteries, particularly for lithium secondary batteries. It is also useful as an electrolyte for other secondary batteries, primary batteries, capacitors, capacitors, actuators, electrochromic elements, various sensors, dye-sensitized solar cells, fuel cells, and further, antistatic agents, polymerization initiators. It is also useful as an ion exchange membrane material or an ion glass material.

[Production of electrolyte (I)]
Using 0.37 g ( 0.002 mol) of the obtained metal salt (I) (sodium 1-cyano-1,1-difluoromethanesulfonate) and 7.6 g (0.05 mol) of LiPF ₆ as an electrolyte, ethylene was used. Dissolved in 100 g of carbonate (50% by volume) / dimethyl carbonate (50% by volume) to obtain an electrolyte (I).
Various characteristics of the obtained electrolyte (I) are as shown in Table 1. It has high conductivity and a wide potential window even at low temperatures, and it was confirmed that it has excellent electrochemical characteristics.
Moreover, the obtained electrolyte (I) can manufacture a lithium secondary battery as follows, for example, and is useful as an electrolyte for lithium secondary batteries.

Example 2
0.74 g ( 0.004 mol) of the metal salt (I) obtained in the same manner as in Example 1 and 7.6 g (0.05 mol) of LiPF _{6 were} mixed with ethylene carbonate (50 vol%) / dimethyl carbonate (50 vol). %) Was dissolved in 100 g to prepare an electrolyte (II) and evaluated in the same manner as in Example 1.

Example 3
0.74 g ( 0.004 mol) of metal salt (I) obtained in the same manner as in Example 1 and 15.2 g (0.1 mol) of LiPF _{6 were} mixed with ethylene carbonate (50 vol%) / dimethyl carbonate (50 vol). %) Was dissolved in 100 g to prepare an electrolyte (III) and evaluated in the same manner as in Example 1.

Claims (6)

A metal salt comprising components (A) and (B).
(A) Metal cation (B) Cyanomethanesulfonate anion represented by the following general formula (1)
^{_{- OSO 2 CF (3-n}} ) (CN) n (1)
(Here, n is an integer of 1 to 3.) The metal salt according to claim 1, wherein component (B) is a cyanofluoromethanesulfonate anion. The metal salt according to claim 1 or 2, wherein the component (A) is a monovalent metal cation. An electrode protective film forming agent comprising the metal salt according to claim 1. An electrolyte for a secondary battery comprising the metal salt according to any one of claims 1 to 3. 6. A secondary battery comprising the secondary battery electrolyte according to claim 5 sandwiched between a positive electrode and a negative electrode.

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