JP2012248515A - Metal salt, electrode protection film forming agent, secondary battery electrolyte including the same, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal salt having a protection film forming capability at a positive electrode and useful for an electrode protection film forming agent excellent in safety, and provide an electrode protection film forming agent, a secondary battery electrolyte and further a secondary battery, using the metal salt.SOLUTION: The metal salt comprises a composition (A1) or (A2) and a composition (B). (A1) represents a monovalent metal cation (where, excluding a lithium cation), (A2) represents a divalent metal cation, and (B) represents a cyano fluorophosphate-based anion represented by the following general formula (1).P(CN)F...(1) (where, n represents an integer of 1-5.)

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 as 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 It aims at providing the electrolyte for secondary batteries, and also a secondary battery.

  However, as a result of intensive studies in view of such circumstances, the present inventors have found that a metal salt comprising a specific metal cation and a phosphate anion having a cyano group and a fluorine atom is excellent in the ability to form a protective film in the positive electrode. The present invention has been completed.

That is, the gist of the present invention relates to a metal salt comprising components (A1) and (B).
(A1) Monovalent metal cation (excluding lithium cation)
(B) Cyanofluorophosphate anion represented by the following general formula (1)

[Chemical 1]
^{_{- P (CN) n F 6}} -n ··· (1)
(Here, n is an integer of 1 to 5.)

Or it is related with the metal salt which consists of component (A2) and (B).
(A2) Divalent metal cation (B) Cyanofluorophosphate anion represented by the following general formula (1)

[Chemical 2]
^{_{- P (CN) n F 6}} -n ··· (1)
(Here, n is an integer of 1 to 5.)

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

  The metal salt of the present invention has a positive electrode protective film-forming ability, is effective as an electrode protective film forming agent, and can provide a secondary battery electrolyte and a secondary battery that are excellent in safety.

3 is a chart showing ³¹ P-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. 3 is a chart showing ESI (+) of the metal salt of Example 1. FIG. 3 is a chart showing ESI (−) 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 comprises a specific monovalent metal cation (A1) or a specific divalent metal cation (A2) and a cyanofluorophosphate anion (B) represented by the following general formula (1). It is a metal salt.

[Chemical 3]
^{_{- P (CN) n F 6}} -n ··· (1)
(Here, n is an integer of 1 to 5.)

  The metal cation (A1) of the present invention may be a monovalent metal cation, and examples thereof include a sodium cation, a potassium cation, and a silver cation. Among these metal cations, from the viewpoint of solubility in an electrolytic solution. A potassium cation and a silver cation are preferred, and a silver cation is particularly preferred from the viewpoint of purity. Two or more metal cations (A1) may be used.

  Further, the metal cation (A2) of the present invention may be a divalent metal cation, and examples thereof include a magnesium cation, a calcium cation, and a copper cation. Among these metal cations, the conductivity of the electrolyte may be mentioned. From the viewpoint, magnesium cation and calcium cation are preferable, and calcium cation is particularly preferable from the viewpoint of reduction resistance of the electrolyte. Two or more metal cations (A2) may be used.

As the metal cation of the present invention, a monovalent metal cation (A1) and a divalent metal cation (A2) can be used in combination to form a mixture of metal salts.

As the cyanofluorophosphate anion (B) of the present invention, in the general formula (1), n is preferably 2 to 4 from the viewpoint of the ability to form an electrode protective film, and particularly preferably, the conductivity of the electrolyte. 3 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 prevent 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 stabilizes the potential window of the battery.

  The mechanism by which the anion of the present invention forms SEI is not clear, but it is presumed that the cyano group, fluorine, and / or phosphorus 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.

  Generally, when a metal salt is dissolved in an electrolytic solution, the resulting electrolyte has a higher viscosity than the electrolytic solution. As a result, for example, in a lithium secondary battery, the mobility of lithium cations decreases, and the conductivity and charge / discharge rate of the electrolyte decrease. This phenomenon is not preferable for a large-capacity battery that requires a relatively large amount of lithium cations and an electric vehicle battery that requires high-speed charge / discharge.

  However, the metal salt of the present invention contains a metal cation (A1) or (A2), but when dissolved in an electrolytic solution, it avoids an increase in the viscosity of the electrolyte, develops a high electrical conductivity, and charges the battery at high speed. Allow discharge. The effect is remarkable when n in the general formula (1) is 2 to 4, but in such a case, since an anion contains a geometric isomer, it is presumed that the mixture avoids the increase in viscosity. . In particular, when n in the general formula (1) is 3, the anion has geometric isomers (facial and meridional), and both geometric isomers have an asymmetric chemical structure. This is presumed to avoid increasing the viscosity of the electrolyte.

Hereinafter, specific examples of the production of the metal salt of the present invention will be described by taking n = 3 as an example. The chemical formula of such a metal salt is ^{m +} M · ^m− [P (CN) ₃ F ₃ ] _m . Here, when M is a monovalent metal cation such as sodium, potassium or silver, m is 1. When M is a divalent metal cation such as magnesium, calcium, or copper, m is 2.

  1 to 10 equivalents, preferably 3 to 8 equivalents of a cyano compound is added to 1 mole of phosphorus trichloride and stirred. Usually, the temperature is -30 to 120 ° C, preferably 20 to 120 ° C, particularly preferably 30 to 110 ° C. Usually, the reaction is carried out for several minutes to several tens of hours, preferably 10 minutes to 50 hours, particularly preferably 1 to 24 hours to obtain the desired tricyanophosphine. The reaction is preferably performed in an inert gas atmosphere, and particularly preferably performed in a dry atmosphere. Examples of the reaction solvent include acetone, methyl ethyl ketone, acetonitrile, dichloromethane, dichloroethylene, chloroform, tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), carbon tetrachloride, benzene, toluene, xylene and the like, propylene carbonate ( PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and the like are preferable, and toluene and xylene are particularly preferable from the viewpoint of reactivity. Examples of the cyano compound include hydrogen cyanide, trimethylsilyl cyanide, potassium cyanide, sodium cyanide, silver cyanide, copper cyanide and the like. Among these, silver cyanide and copper cyanide are preferable in terms of purity.

  Next, 1-2 equivalents of halogen is added to tricyanophosphine, and the mixture is stirred in a reaction solvent. Usually, it is −196 to 50 ° C., preferably −78 to 40 ° C., usually several minutes to several hours, preferably The reaction is carried out for 10 minutes to 2 hours to obtain dihalotricyanophosphine. The reaction is preferably performed in an inert gas atmosphere, and particularly preferably performed in a dry atmosphere. As the reaction solvent, polar solvents such as acetone, methyl ethyl ketone, acetonitrile, dichloromethane, dichloroethylene, chloroform, tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), propylene carbonate (PC), ethylene carbonate (EC), Electrolytic solutions such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) are preferable, and dichloromethane and acetonitrile are particularly preferable. The halogen used includes fluorine, chlorine, bromine and iodine, but chlorine is preferred from the viewpoint of reactivity. It is also possible to use a halogenating agent such as sulfuryl chloride instead of halogen. In this case, dihalotricyanophosphine can be obtained by removing by-produced sulfur dioxide by argon substitution.

  Furthermore, lithium trihalotricyanophosphate can be obtained by lithiation of dihalotricyanophosphine using a lithiating agent such as lithium halide. More specifically, 1 to 10 equivalents of lithium halide is added to 1 equivalent of dihalotricyanophosphine, and is usually −196 to 100 ° C., preferably −78 to 80 ° C., particularly preferably −78 to 60 ° C. Lithium trihalotricyanophosphate is obtained by reacting at a temperature of usually several minutes to several tens of hours, preferably 1 to 24 hours, particularly preferably 2 to 8 hours.

  Examples of the lithium halide include LiF, LiCl, LiBr, and LiI. Among these, LiCl is preferable in terms of reactivity. In this case, lithium trichlorotricyanophosphate is obtained.

Lithium trihalotricyanophosphate is fluorinated using a fluorinating agent containing a monovalent metal cation such as sodium cation, potassium cation or silver cation, or a divalent metal cation such as magnesium cation, calcium cation or copper cation. To obtain a metal salt of trifluorotricyanophosphate. More specifically, 3 to 10 equivalents of a fluorinating agent is added to 1 equivalent of lithium trihalotricyanophosphate, and usually 0 to 100 ° C, preferably 20 to 80 ° C, particularly preferably 25 to 60 ° C. The metal salt of trifluorotricyanophosphate is usually obtained by reacting for several minutes to several tens of hours, preferably 1 to 24 hours, particularly preferably 2 to 8 hours. Reaction solvents include acetone, methyl ethyl ketone, acetonitrile, dichloromethane, dichloroethylene, chloroform, tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC). ), Diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and the like, and dichloromethane and acetonitrile are particularly preferred from the viewpoint of solubility. The fluorinating _{agent, NaF, KF, AgF, MgF} 2, CaF 2, CuF 2, NaBF 4, KBF 4, AgBF 4, Mg (BF 4) 2, Ca (BF 4) 2, Cu (BF 4) 2 Among these, AgBF ₄ is preferable from the viewpoint of reactivity.

  The obtained metal salt comprising trifluorotricyanophosphate is preferably purified in order to remove the generated metal halide and impurities. Examples of the purification technique include techniques such as filtration, extraction, washing, column chromatography, reprecipitation, and adsorption. Among these, extraction with acetonitrile or dimethyl carbonate 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 lithium secondary batteries which has an electrode protective film formation function can be formed by mix | blending the metal salt of this invention, and lithium salt with electrolyte 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 is more preferable, and 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- Alkyl imidazolium cations such as octyl-3-methylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1,2,3-trimethylimidazolium, 1,2-dimethyl-3-ethylimidazolium In addition to imidazolium cations, ionic liquids containing quaternary ammonium cations, pyridinium cations, quaternary phosphonium cations, and the like can be given. 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.

  In the electrolyte obtained using the metal salt of the present invention, an electrode protective film forming agent other than the present invention may be blended as necessary.

  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. If the content is too large, the conductivity of the electrolyte tends to decrease, and if it is too small, the effect of stabilizing the potential window of the lithium secondary battery tends not to be obtained.

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 and acetylene black, a binder such as polyvinylidene fluoride, and if necessary, an ion conductive polymer. 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).

(Analysis equipment)
Mass spectrometry (MS) uses “JMS-T100LP AccuTOF LC-plus” manufactured by JEOL Ltd., IR spectrum uses “Avatar 360” manufactured by Nicolet, NMR uses “Unity-300” (solvent: heavy acetonitrile) manufactured by Varian. ).

Example 1
[Production of metal salt (1)]
Under a stream of argon, 40.17 g (0.30 mol) of silver cyanide and 150 mL of dehydrated xylene were added to a 500 mL four-necked flask, and 8.74 mL (0.10 mol) of phosphorus trichloride was added dropwise in an ice bath using a dropping funnel. did. Then, after heating to 100 degreeC and stirring for 5 hours, the reaction liquid was filtered and the deposit was obtained. To the resulting precipitate, 150 mL of dehydrated diethyl ether was added and filtered, and the obtained filtrate was concentrated to obtain 10 g of white solid tricyanophosphine. The analysis results of the obtained tricyanophosphine are shown below.
³¹ P-NMR -132.5 ppm
IR 2190cm ^-1 [CN]

  Next, 1.87 g (0.028 mol) of lithium chloride in 20 mL of dehydrated dichloromethane was added to a 100 mL three-necked flask in an argon stream, and 1.2 equivalents (0.034 mol) of chlorine gas was blown into the cooled to −78 ° C. It is. Further, 3.05 g (0.028 mol) of tricyanophosphine dissolved in 20 mL of acetonitrile was added dropwise. Thereafter, the temperature was gradually raised to room temperature and stirred for 2 hours. Thereafter, the reaction solution was filtered, and the obtained filtrate was concentrated to obtain an ocherous solid. Further, dehydrated acetonitrile was added to the obtained solid, followed by filtration, and the filtrate was concentrated to obtain 6.081 g of a pale yellow solid. The analysis result of the obtained solid was as follows and confirmed to be lithium trichlorotricyanophosphate.

MS (−) m / z = 213.92696 [PCl ₃ (CN) ₃ ]
IR 2200cm ^-1 [CN]
³¹ P-NMR −333.579 ppm [s, P]

Next, 36.9 g (0.190 mol) of silver tetrafluoroborate (AgBF ₄ ) and 100 mL of dehydrated dichloromethane were added to a 300 mL three-necked flask in an argon stream, and 10 mL of dehydrated acetonitrile was added and dissolved in an ice bath. Thereto was added dropwise 6.0 g (0.0027 mol) of lithium trichlorotricyanophosphate dissolved in 25 mL of dehydrated acetonitrile. After stirring at room temperature for 2 hours, the reaction solution was filtered, and the resulting filtrate was concentrated. Further, after washing with 400 mL of ultrapure water and filtration, the obtained precipitate was vacuum-dried to obtain 3.77 g of an ocher solid. The analysis result of the obtained solid was as follows and was confirmed to be a silver salt of trifluorotricyanophosphate (metal salt (1)).

MS (+) m / z = 188.92361 [Ag + 2CH 3 CN]
MS (−) m / z = 166.00182 [PF ₃ (CN) ₃ ]
IR 2200cm ^-1 [CN]
³¹ P-NMR 218.964 ppm [q, Hz = 740.8 Hz, P]
¹⁹ F-NMR -36.6605 ppm [d, Hz = 740.8 Hz, F]
[Manufacture of electrolyte (1)]
0.37 g (0.001 mol) of the obtained metal salt (1) and 7.6 g (0.05 mol) of LiPF ₆ were used as an electrolytic solution. Ethylene carbonate (50 vol%) / dimethyl carbonate (50 vol%) 100 g To obtain an electrolyte (1).
Various characteristics of the obtained electrolyte are as shown in Table 1. It was confirmed that the electrochemical characteristics were excellent by having high conductivity and a wide potential window even at low temperatures.
Moreover, the obtained electrolyte (1) 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 (1) is impregnated into a separator (Celguard # 2400 manufactured by Celgard, 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.

Comparative Example 1
7.6 g (0.05 mol) of LiPF ₆ was dissolved in 100 g of ethylene carbonate (50% by volume) / dimethyl carbonate (50% by volume) to prepare an electrolyte, which was 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 lithium secondary battery.

  The metal salt of the present invention is excellent in the function of forming an electrode protective film, is excellent in performance as an electrolyte such as having high conductivity and a wide potential window, and is excellent in safety. It is very useful as an electrolyte for 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.

Claims (5)

A metal salt comprising components (A1) and (B).
(A1) Monovalent metal cation (excluding lithium cation)
(B) Cyanofluorophosphate anion represented by the following general formula (1)
^{_{- P (CN) n F 6}} -n ··· (1)
(Here, n is an integer of 1 to 5.) A metal salt comprising components (A2) and (B).
(A2) Divalent metal cation (B) Cyanofluorophosphate anion represented by the following general formula (1)
^{_{- P (CN) n F 6}} -n ··· (1)
(Here, n is an integer of 1 to 5.) 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 claim 1 or 2. A secondary battery comprising the electrolyte according to claim 4 sandwiched between a positive electrode and a negative electrode.

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