JP2012216419A - Electricity storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electricity storage device capable of stably operating in a high voltage region.SOLUTION: An electricity storage device of the present invention includes a positive electrode, a negative electrode and an electrolyte. The electrolyte includes a cyanoborate salt represented by the following general formula (1) and a solvent, and (i) a positive electrode potential in a full charge state is 4.0-5.5 V based on lithium, or (ii) the positive electrode includes a positive electrode active material exhibiting a discharge voltage of 3.5-5.5 V based on lithium. M([B(CN)(XR)])(1) (In the formula, Mrepresents a monovalent, divalent or trivalent organic or inorganic cation, Xrepresents O or S, Rrepresents H or a hydrocarbon group having 1-10 carbon atoms, n represents an integer of 1-3, and (a) represents an integer of 0-3.)

Description

  The present invention relates to an electricity storage device.

  Electric power storage devices such as electrolytic capacitors, electric double layer capacitors, lithium ion capacitors, and lithium ion secondary batteries are used as power sources for mobile phones, personal computers, and electric vehicles and hybrid vehicles. Various researches aimed at improving the characteristics of

  Among the above electricity storage devices, lithium ion secondary batteries use lithium as a constituent material, so the size and weight of the battery can be reduced, and the electric capacity compared to the conventionally used secondary batteries. It has the feature that is large. Therefore, various studies have been conducted for the purpose of improving the electric capacity, input / output characteristics, and cycle characteristics of the lithium ion secondary battery.

  For example, as an attempt to improve the characteristics of an electricity storage device from the electrode surface, Patent Document 1 discloses a graphite material whose surface is coated with a low crystalline carbon material and a graphitizable carbon material having a predetermined degree of graphitization. A negative electrode carbon material in combination with is disclosed. Patent Document 2 discloses secondary particles obtained by agglomerating primary particles of lithium nickel composite oxide having different aspect ratios, and the length direction of some primary particles is the center direction of the secondary particles. It is disclosed that a material having a structure suitable for the above can be a positive electrode material capable of high power discharge and excellent in cycle durability at high temperatures.

JP 2009-117240 A WO 2006-118279

  In order to improve the characteristics of lithium ion secondary batteries, in particular, to achieve high energy density, in addition to optimizing the negative electrode and the positive electrode, as described above, the use of a positive electrode material having a high lithium-based discharge voltage is used. Is effective. In this case, it is necessary that the electrolytic solution is not easily decomposed even when operated under a high voltage.

However, even if a positive electrode material having a high discharge voltage is used, electrolytes such as LiPF ₆ and LiBF ₄ used in current electrolyte solutions have a low withstand voltage, so that it is difficult to obtain sufficient battery characteristics. We have found that.

  The present invention has been made paying attention to the circumstances as described above, and an object thereof is to provide an electric storage device that can be stably operated in a high voltage range.

The electricity storage device of the present invention that can achieve the above object includes a positive electrode, a negative electrode, and an electrolytic solution, and the electrolytic solution includes a cyanoborate salt represented by the following general formula (1) and a solvent, and
(I) The positive electrode potential when fully charged is 4.0 V to 5.5 V on the basis of lithium, or (ii) the positive electrode active material in which the positive electrode exhibits a discharge voltage of 3.5 V to 5.5 V on the basis of lithium. It has the feature in including.
M ^{n +} ([B (CN) _4-a (X ² R ¹³ ) _a ] ⁻ ) _n (1)
(In the formula, M ^{n +} is a monovalent, divalent or trivalent organic or inorganic cation, X ² is O or S, R ¹³ is H or a hydrocarbon group having 1 to 10 carbon atoms, and n is an integer of 1 to 3. A represents an integer of 0 to 3)

In the electrolytic solution according to the present invention, in the formula (1), M ^{n +} is preferably Li ⁺ , and a solvent containing γ-butyrolactone is preferably used as the solvent. Moreover, it is preferable that the electrical storage device of this invention has a separator which consists of glass fiber between the said positive electrode and a negative electrode.

  As the electricity storage device of the present invention, a lithium ion secondary battery is preferable.

  ADVANTAGE OF THE INVENTION According to this invention, the electrical storage device which can operate | move stably in a high voltage range is obtained.

FIG. 1 is a graph showing the results of the charge / discharge test of Experimental Example 1.

The electricity storage device of the present invention includes a positive electrode, a negative electrode, and an electrolytic solution, and the electrolytic solution includes a cyanoborate salt represented by the general formula (1) and a solvent, and
(I) The positive electrode potential when fully charged is 4.0 V to 5.5 V on the basis of lithium, or (ii) the positive electrode active material in which the positive electrode exhibits a discharge voltage of 3.5 V to 5.5 V on the basis of lithium. It has the characteristic in including.

<Cyanoborate salt>
First, the cyanoborate salt contained in the electrolytic solution used in the present invention will be described. The cyanoborate salt according to the present invention is an organic or inorganic cation: M ^{n +} and a cyanoborate anion: [B (CN) _4-a (X ² R ¹³ ) _a as represented by the general formula (1). ] ^- a compound consisting of a.

Cyanoborate anion: [B (CN) _4-a (X ² R ¹³ ) _a ] ⁻
Cyano anions according to the present invention, boron, cyano group: -CN and, -X ² R ¹³ group is attached general _{formula: [B (CN) 4-} a (X 2 R 13) a] - Table Has a structure. In the above general formula, since a is an integer of 0 to 3, the cyanoborate anion according to the present invention includes a tetracyanoborate anion in which a is 0: [B (CN) ₄ ] ⁻ ; A tricyanoborate anion: [B (CN) ₃ X ² R ¹³ ] ⁻ ; a is a dicyanoborate anion: [B (CN) ₂ (X ² R ¹³ ) ₂ ] ⁻ ; a is 3 Cyanoborate anions: [B (CN) (X ² R ¹³ ) ₃ ] ⁻ ; In addition, as a cyanoborate anion, what a is 0 or 1 in the said general formula is preferable.

In the anion represented by the above general formula, X ² represents O or S. X ² is preferably O. R ¹³ represents H or a hydrocarbon group having 1 to 10 carbon atoms. Note that the hydrocarbon group may have a substituent, and in this case, the number of carbons constituting the substituent is not included in the above-described number of carbons. The hydrocarbon group may contain a hetero atom (O, N, Si, etc.) in a part thereof, and further, a part or all of the hydrogen atoms of the hydrocarbon group are F, Cl, Br and It may be substituted with a halogen atom such as I. As the hydrocarbon group, a linear, branched or cyclic saturated and / or unsaturated hydrocarbon group having 1 to 10 carbon atoms is preferable, and a more preferable hydrocarbon group is an alkyl group having 1 to 10 carbon atoms, Examples thereof include a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, and a benzyl group. Specific examples of the hydrocarbon group R ¹³ include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a sec-butyl group, a pentyl group, a hexyl group, and an octyl group. Linear or branched alkyl group; cycloalkyl group such as cyclohexyl group and cyclopentyl group; alkenyl group such as vinyl group; aryl group such as phenyl group, methylphenyl group, methoxyphenyl group, dimethylphenyl group and naphthyl group ; Preferred are methyl group, ethyl group, propyl group, isopropyl group, butyl group and phenyl group.

Specific cyanoborate anions include tetracyanoborate anions represented by [B (CN) ₄ ] ⁻ ; [B (CN) ₃ (OMe)] ⁻ , [B (CN) ₃ (OEt)] ⁻ , [B (CN) ₃ (Oi-Pr)] ⁻ (“-i-” indicates “iso”, the same applies hereinafter), [B (CN) ₃ (OBu)] ⁻ , [B ( CN) ₃ (OPh)] ⁻ etc .; alkoxytricyanoborate anions such as [B (CN) ₃ (SMe)] ⁻ etc .; thioalkoxytricyanoborate anions such as [B (CN) ₂ (OMe) ₂ ] ⁻ , [ _{B (CN) 2 (OEt)} 2] -, [B (CN) 2 (O-i-Pr) 2] -, [B (CN) 2 (OBu) 2] -, [B (CN) 2 (OPh ) _2] ^-, etc. dialkoxy dicyano borate anion; [B (CN) (OMe ) 3] -, [B (CN) ( ^{_{Et) 3] -, [B}} (CN) (O-i-Pr) 3] -, [B (CN) (OBu) 3] -, [B (CN) (OPh) 3] - or the like of the trialkoxy cyano Borate anion.

Organic or inorganic cation: M ^{n +}
Next, the organic or inorganic cation M ^{n +} constituting the cyanoborate salt according to the present invention will be described. The organic cation M ^{n +} constituting the cyanoborate salt according to the present invention has the general formula (2): L ⁺ -R _S (wherein L represents C, Si, N, P, S or O, R Are the same or different organic groups and may be bonded to each other, s represents the number of R bonded to L, and is 3 or 4. Here, s is directly related to the valence of element L and L The onium cation represented by (the value determined by the number of double bonds to be bonded) is preferable.

  The “organic group” represented by R means a group having at least one hydrogen atom, fluorine atom, or carbon atom. The “group having at least one carbon atom” only needs to have at least one carbon atom, and may have another atom such as a halogen atom or a hetero atom, a substituent, or the like. Good. Examples of the substituent include amino group, imino group, amide group, ether bond group, thioether bond group, ester group, hydroxyl group, alkoxy group, carboxyl group, carbamoyl group, cyano group, disulfide group, nitro group. Group, nitroso group, sulfonyl group and the like.

  Examples of the onium cation represented by the general formula (2) include those represented by the following general formula.

(R in the formula is the same as in the general formula (2))

  Among the six onium cations represented by the above general formula, those in which L is N, P, S or O are more preferable, and onium cations in which L is N are more preferable. The said onium cation may be used independently and may use 2 or more types together. Specifically, examples of the onium cation in which L is N, P, S, or O include those represented by the following general formulas (3) to (5).

  General formula (3):

At least one of 15 types of heterocyclic onium cations represented by the formula:

Examples of the organic groups R ^{1 to} R ⁸ include the same organic groups R exemplified in the general formula (2). More specifically, R ^{1 to} R ⁸ are a hydrogen atom, a fluorine atom, or an organic group, and examples of the organic group include a straight chain, a branched chain, or a ring (provided that R ^{1 to} R ⁸ are bonded to each other to form a ring). Are preferably a hydrocarbon group having 1 to 18 carbon atoms or a fluorine group, and more preferably a hydrocarbon group having 1 to 8 carbon atoms or a fluorine group. Moreover, the organic group may contain the substituent illustrated about the said General formula (2), hetero atoms, such as N, O, and S, and a halogen atom.

  General formula (4):

(Wherein R ^{1 to} R ¹² are the same as R ^{1 to} R ^{8 in} the general formula (3))
At least one of nine types of saturated ring onium cations represented by the formula:

  General formula (5):

(Wherein R ^{1 to} R ⁴ are the same as R ^{1 to} R ^{8 in} the general formula (3))
A chain onium cation represented by

For example, the chain onium cation (5) includes tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, tetraheptylammonium, tetrahexylammonium, tetraoctylammonium, triethylmethylammonium, methoxyethyldiethylmethylammonium, Trimethylphenylammonium, benzyltrimethylammonium, benzyltriethylammonium, benzyltributylammonium, dimethyldistearylammonium, diallyldimethylammonium, 2-methoxyethoxymethyltrimethylammonium, tetrakis (pentafluoroethyl) ammonium, N-methoxytrimethylammonium, N-ethoxy Trimethylammoni And quaternary ammoniums such as N-propoxytrimethylammonium, tertiary ammoniums such as trimethylammonium, triethylammonium, tributylammonium, diethylmethylammonium, dimethylethylammonium, dibutylmethylammonium, dimethylammonium, diethylammonium Secondary ammoniums such as dibutylammonium, methylammonium, ethylammonium, butylammonium, hexylammonium, octylammonium primary ammoniums, and ammonium compounds represented by NH ₄ .

  Among the onium cations of (3) to (5) above, an onium cation containing a nitrogen atom is more preferable, and a more preferable one is the following general formula:

(Wherein, R ¹ to R ¹² are the same as R ¹ to R ⁸ of general formula (3).)
And at least one of six kinds of onium cations represented by the formula:

  Among the six kinds of onium cations, chain quaternary ammonium such as tetraethylammonium, tetrabutylammonium and triethylmethylammonium, chained tertiary ammonium such as triethylammonium, tributylammonium, dibutylmethylammonium and dimethylethylammonium, Pyrrolidiniums such as 1-ethyl-3-methylimidazolium and imidazolium such as 1,2,3-trimethylimidazolium, N, N-dimethylpyrrolidinium and N-ethyl-N-methylpyrrolidinium are readily available. It is more preferable because it exists. More preferred are quaternary ammonium and imidazolium. From the viewpoint of reduction resistance, quaternary ammonium such as tetraethylammonium, tetrabutylammonium and triethylmethylammonium classified into the chain onium cation is more preferable.

The inorganic cations ^{M n +, Li +, Na} +, K +, Cs +, 1 monovalent inorganic cations M ¹⁺ of Pb ^{+ like; Mg 2+, Ca 2+, Zn} 2+, Pd 2+, Sn 2 ^{+, Hg 2+, Rh 2+,} Cu 2+, Be 2+, Sr 2+, 2 divalent inorganic cations M ²⁺ of Ba ^2+, and the like; and trivalent inorganic cation M ³ of Ga ³⁺ etc. ⁺ . Among these, Li ⁺ , Na ⁺ , Mg ²⁺ and Ca ²⁺ are preferable because they have a small ionic radius and can be easily used as an electricity storage device, and a more preferable inorganic cation M ^{n +} is Li ⁺ .

Cyanoborate salt: M ^{n +} ([B (CN) _4-a (X ² R ¹³ ) _a ] ⁻ ) _n
The cyanoborate salt according to the present invention includes all the combinations of the above cation and anion. Specific cyanoborate salts include triethylmethylammonium tetracyanoborate, tetraethylammonium tetracyanoborate, 1-ethyl-3-methylimidazolium tetracyanoborate, tetramethylammonium tricyanomethoxyborate, tetraethylammonium tricyanomethoxyborate, Triethylmethylammonium tricyanomethoxyborate, triethylmethylammonium tricyanoisopropoxyborate, triethylmethylammonium tricyanobutoxyborate, triethylmethylammonium tricyanophenoxyborate, triethylmethylammonium tricyano (pentafluorophenoxy) borate, triethylmethylammonium tricyano (Trimethylsiloxy) borate Riethylmethylammonium tricyanomethylthioborate, triethylmethylammonium tricyano (hexafluoroisopropoxy) borate, 1-ethyl-3-methylimidazolium tricyanomethoxyborate, triethylammonium tricyanomethoxyborate, tributylammonium tricyanomethoxyborate, Salts of organic cations such as triethylmethylammonium dicyanodimethoxyborate, triethylmethylammonium cyanotrimethoxyborate, etc .; lithium tetracyanoborate, lithium tricyanomethoxyborate, sodium tricyanomethoxyborate, magnesium bis (tricyanomethoxyborate), lithium tricia Noisopropoxyborate, lithium tricyanobutoxyborate, lithium Um tricyanophenoxyborate, lithium tricyano (pentafluorophenoxy) borate, lithium tricyano (trimethylsiloxy) borate, lithium tricyano (hexafluoroisopropoxy) borate, lithium tricyanomethylthioborate, lithium dicyanodimethoxyborate, lithium cyanotri And salts of inorganic cations such as methoxyborate. Among these, triethylmethylammonium tetracyanoborate, lithium tetracyanoborate, triethylmethylammonium tricyanomethoxyborate, lithium tricyanomethoxyborate, and lithium tricyanophenoxyborate are preferable.

<Method for producing cyanoborate salt>
The cyanoborate salt according to the present invention may be produced, for example, by the method described in International Publication No. 2010/021391, etc., specifically, it is produced by reacting a cyanide compound with a boron compound. be able to.

Cyanide compound As the CN source of the cyanoborate salt represented by the general formula (1), it is preferable to use a cyanide compound. Examples of the cyanide include metal cyanides; ammonium cyanide compounds; silyl cyanides; hydrogen cyanide.

As said metal cyanide, the cyanide of the above-mentioned inorganic cation ^{Mn +} is mentioned. Preferred metal cyanides include KCN, NaCN, LiCN, Zn (CN) ₂ , Ga (CN) ₃ , Pd (CN) ₂ , Sn (CN) ₂ , Hg (CN) ₂ , Rh (CN) ₂ , Cu ( CN) ₂ and PbCN.

Examples of the ammonium cyanide compound include compounds composed of an onium cation having L as N and a cyanide ion (CN ⁻ ) among the onium cations exemplified as the organic cation M ^{n +} . Preferably, a salt of chain quaternary ammonium such as tetrabutylammonium cyanide, tetraethylammonium cyanide and triethylmethylammonium cyanide and cyanide ion, triethylammonium cyanide, dibutylmethylammonium cyanide and dimethylethylammonium cyanide. Salts of chain tertiary ammonium such as nido and cyanide ion, imidazolium and cyanide ion such as 1-ethyl-3-ethylimidazolium cyanide and 1,2,3-trimethylimidazolium cyanide And salts of pyrrolidinium and cyanide ions such as salts, N, N-dimethylpyrrolidinium cyanide and N-ethyl-N-methylpyrrolidinium cyanide.

  Examples of silyl cyanides include trimethylsilyl cyanide, triethylsilyl cyanide, triisopropylsilyl cyanide, alkyldimethyl cyanide such as ethyldimethylsilyl cyanide, isopropyldimethylsilyl chloride, tert-butyldimethylsilyl cyanide; dimethylphenylsilyl cyanide; And alkylarylsilyl cyanides such as phenyldimethylsilyl cyanide.

  In addition, a commercially available thing may be used for a cyanide compound, and what was synthesize | combined by the well-known method may be used.

-Boron compound A boron compound becomes a boron source of the cyanoborate salt based on this invention. Accordingly, the boron compound is not particularly limited as long as it contains boron. For example, ZBX ¹ ₄ (Z represents a hydrogen atom or an alkali metal atom, and X ¹ represents a hydrogen atom or a halogen atom. Similarly, ZB (X ² R ¹³ ) ₄ (R ¹³ is the same as the hydrocarbon group R ¹³ in the general formula (1), and X ² is O or S. The same applies hereinafter), BX ¹ ₃ , BX ¹ ₃ -complex, B (X ² R ¹³ ) ₃ , B (X ² R ¹³ ) ₃ -complex, Na ₂ B ₄ O ₇ , ZnO.B ₂ O ₃ and NaBO ₃ It is preferable that it is at least one kind.

The ^{_{ZBX 1 4, HBF 4, KBF}} 4, KBBr 4, LiBF 4, NaBH 4 , and examples of the _{^{ZB (X 2 R 13) 4}} , NaB (OH) 4, KB (OH) 4, LiB ( OH) _{4 and the} like. Examples of BX ¹ ₃ include BH ₃ , BF ₃ , BCl ₃ , BBr ₃ , and BI _3. Examples of B (X ² R ¹³ ) ₃ include boric acid; B (OMe ) ₃ and B (OEt) ₃ , B (Oi-Pr) ₃ , B (Ot-Bu) ₃ (wherein -t- represents “tert”; the same shall apply hereinafter), B (OPh) ₃ , B (OTMS) ₃ , B (O (C ₆ F ₅ )) ₃ , B (OCH (CF ₃ ) ₂ ) ₃ , B (On-Bu) ₃ , (where −n− is “normal” .. indicating "hereinafter the same) borate esters such as; B (SMe) ₃ and _{B (SEt) 3, B (} S-i-Pr) 3, B (S-t-Bu) 3 B (SPh) borate thioesters such as _3; and the like, BX ¹ ₃ - ^{complex, B (X 2 R 13)} 3 - complexes, as is diethyl ether, tripropyl ether, tri butyl ether such as tetrahydrofuran Ammonia, methylamine, ethylamine, butylamine, hexylamine, octylamine, dimethylamine, diethylamine, dibutylamine, dihexylamine, dicyclohexylamine, trimethylamine, triethylamine, tributylamine, triphenylamine, guanidine, aniline, morpholine, pyrrolidine, And a complex of amines such as methylpyrrolidine and the above BX ¹ ₃ or B (X ² R ¹³ ) ₃ . Among these, NaBH ₄ , BH ₃ , BF ₃ , BCl ₃ , BBr ₃ , B (OMe) ₃ , B (OEt) ₃ , B (SMe) ₃ , B (SEt) ₃ , Na having relatively high reactivity ₂ B ₄ O ₇ and B (OH) ₃ are preferable, and BF ₁ , BCl ₃ , BBr _3, etc., where X ¹ is a halogen atom, BX ¹ ₃ , B (OMe) ₃ , B (OEt) _3, etc. Boric acid ester ^{2 in} which ² is O and R ¹³ has an alkoxy group having 1 to 4 carbon atoms: B (OR ¹³ ) ₃ is more preferred, and most preferred are BCl ₃ , B (OMe) ₃ and B (OEt ₃ ). The said boron compound may be used independently and may be used in combination of 2 or more type.

  The blending ratio of the raw materials may be changed in accordance with the number of cyano groups bonded to boron in the cyanoborate salt that is the target product, whereby a monocyanoborate salt that is a monosubstituted cyano group From this, a dicyanoborate salt (disubstituted product), a tricyanoborate salt (trisubstituted product), and a tetracyanoborate salt that is a tetrasubstituted product of a cyano group can be obtained. For example, the amount of the boron compound used relative to the cyan compound is preferably 0.5: 1 to 100: 1 (cyan compound: boron compound, molar ratio). More preferably, the ratio is 0.8: 1 to 80: 1, still more preferably 1: 1 to 50: 1, still more preferably 1: 1 to 40: 1, and still more preferably 3: 1 to 1. 40: 1, particularly preferably 4: 1 to 20: 1, even more preferably 4: 1 to 10: 1, and most preferably 4: 1 to 5: 1. If the amount of cyanide compound is too small, the amount of the desired cyanoborate salt may be reduced or a by-product may be formed. On the other hand, if the amount is too large, the amount of impurities derived from CN increases, It tends to be difficult to purify.

The reaction between the cyanide compound and the boron compound is preferably carried out in the presence of the above-mentioned organic or inorganic cation M ^{n +} salt or amine. In particular, when a metal cyanide is used as a cyanide, an amine or an organic or inorganic cation is used when an alkylsilylcyanide or alkylarylsilylcyanide is used as a cyanide in the presence of a salt of an organic or inorganic cation ^{Mn +.} When hydrogen cyanide is used as a cyanide in the presence of a salt of M ^{n +} , it is recommended that the reaction between a cyanide compound and a boron compound be performed in the presence of an amine.

Examples of the organic or inorganic cation constituting the salt of the organic or inorganic cation include the organic or inorganic cation M ^{n +} described above. On the other hand, as anions constituting the salt of the organic or inorganic cation M ^{n +} , halide ions, hydroxide ions (OH ⁻ ), cyanate ions (OCN ⁻ ), thiocyanate ions (SCN ⁻ ), alkoxy ions (RO ^- ), Sulfate ion, nitrate ion, acetate ion, carbonate ion, perchlorate ion, alkyl sulfate ion, alkyl carbonate ion and the like. Among these, halide ions (F ⁻ , Cl ⁻ , Br ⁻ and I ⁻ ) are preferable, and among the halide ions, Cl ⁻ or Br ⁻ is particularly preferable.

Preferred salts of organic or inorganic cation M ^{n +} include triethylammonium bromide, tributylammonium bromide, triethylmethylammonium bromide, 1-ethyl-3-methylimidazolium bromide, lithium bromide, triethylammonium chloride, tributylammonium chloride, triethylmethylammonium. Examples include chloride, 1-ethyl-3-methylimidazolium chloride, triethylmethylammonium chloride, and lithium chloride. More preferred halogen salts of organic or inorganic cations are triethylammonium bromide, triethylmethylammonium bromide, lithium bromide, triethylammonium chloride, triethylmethylammonium chloride, lithium chloride, and more preferably triethylammonium bromide, triethylmethylammonium bromide, Lithium bromide.

  Examples of the amine include chain amines such as triethylamine, tributylamine, butyldimethylamine, diethylamine, dibutylamine, butylamine, hexylamine, octylamine and guanidine, piperidine, 1,4-diazabicyclo [2.2.2] octane (DABCO ), Imidazoline, diazabicyclononene (DBN) and cyclic amines such as diazabicycloundecene (DBU), and aromatic amines such as pyridine, imidazole, methylimidazole and pyrazine.

The amount of the salt of the organic or inorganic cation M ^{n +} is 100: 1 to 1: 100 (the salt of the organic or inorganic cation M ^{n +} : boron compound, mol when the metal cyanide is cyanide). Ratio) is preferable (more preferably 50: 1 to 1:50, more preferably 20: 1 to 1:20). When alkylsilyl cyanide or alkylarylsilyl cyanide is used as cyanide, boron is preferable. It is preferable to be 0.1: 1 to 10: 1 (boron compound: amine and / or ammonium salt, molar ratio) with respect to the compound (more preferably 0.2: 1 to 5: 1, still more preferably). 0.5: 1 to 2: 1), when hydrogen cyanide is used as cyanide, it is preferably 0.02: 1 to 50: 1 (hydrogen cyanide: amine, molar ratio) (more preferably .05: 1 to 20: 1, more preferably from 0.1: 1 to 10: 1). If the amount of the organic or inorganic cation salt or amine used for the boron compound or the amount of the amine used for hydrogen cyanide is too small, it may be difficult to produce a cyanoborate salt efficiently. May increase and purification may be difficult.

  In the above production method, a reaction solvent may be used. The reaction solvent is not particularly limited as long as it dissolves the above raw materials, and water or an organic solvent is used. Examples of organic solvents include hydrocarbon solvents such as toluene, xylene, benzene and hexane, chlorine solvents such as chloroform, dichloromethane, dichloroethane, chlorobenzene and dichlorobenzene, diethyl ether, cyclohexyl methyl ether, dibutyl ether, dimethoxyethane, and dioxane. Ether solvents such as tetrahydrofuran, ester solvents such as ethyl acetate and butyl acetate, ketone solvents such as 2-butanone and methyl isobutyl ketone, alcohol solvents such as methanol, ethanol, 2-propanol and butanol, acetonitrile and valero Examples include nitrile, propylene carbonate, dimethyl sulfoxide, dimethylformamide, N-methyl-2-pyrrolidone and the like. These reaction solvents may be used alone or in combination of two or more.

  The conditions for reacting the above starting materials are not particularly limited and may be appropriately adjusted according to the progress of the reaction. For example, the reaction temperature is preferably 20 ° C to 180 ° C. More preferably, it is 40 degreeC-120 degreeC, More preferably, it is 50 degreeC-80 degreeC. The reaction time is preferably 1 hour to 50 hours, more preferably 5 hours to 40 hours, and even more preferably 10 hours to 30 hours.

  In the above manufacturing method, the order of adding and mixing the above-described raw materials is not particularly limited. In the case where an organic or inorganic cation salt or amine is used, a reaction solvent and an organic or inorganic cation salt or amine are mixed in advance, and then the remaining raw material boron compound and cyanide are added to the mixed solution. It is preferred to add the compound. More preferably, a boron compound is added to a salt solution of an organic or inorganic cation or a mixed solution of an amine and a reaction solvent, and then a cyanide compound is added.

  After the reaction, purification may be performed to increase the purity of the produced cyanoborate salt. Although the purification method is not particularly limited, for example, washing with water, organic solvents, and mixed solvents thereof, adsorption purification method, reprecipitation method, liquid separation extraction method, recrystallization method, crystallization method, and purification method by chromatography Is mentioned.

  The cyanoborate salt obtained by the above production method may further undergo a cation exchange reaction. Since the characteristics of the cyanoborate salt represented by the general formula (1) depend on the cation species, cyanoborate salts having different characteristics can be easily obtained by performing a cation exchange reaction.

  The cation exchange reaction may be performed by reacting the cyanoborate salt represented by the general formula (1) obtained by the above production method with an ionic substance having a desired cation. It does not specifically limit as an ionic substance, For example, the salt of the above-mentioned organic or inorganic cation is mentioned. The conditions for the cation exchange reaction are not particularly limited, and the reaction temperature and time may be appropriately adjusted according to the progress of the reaction. Moreover, you may use a solvent as needed, for example, the reaction solvent mentioned above is used preferably.

<Electrolyte>
Next, the electrolytic solution according to the present invention will be described. The electrolytic solution provided in the electricity storage device of the present invention is a cyanoborate salt represented by the above general formula (1): M ^{n +} ([B (CN) _4-a (X ² R ¹³ ) _a ] ⁻ ) _n And a solvent.

  Examples of the solvent that can be suitably used in the electrolytic solution according to the present invention include an aprotic solvent in which the cyanoborate salt can be dissolved. Specifically, a solvent having a large dielectric constant, high solubility of an electrolyte salt, a boiling point of 60 ° C. or higher, and a wide electrochemical stability range is preferable. More preferably, it is an organic solvent (non-aqueous solvent) having a low water content. Examples of such organic solvents include ethylene glycol dimethyl ether (1,2-dimethoxyethane), ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, crown ether, triethylene glycol dimethyl ether, Ethers such as tetraethylene glycol dimethyl ether, 1,4-dioxane, 1,3-dioxolane; dimethyl carbonate, ethyl methyl carbonate (methyl ethyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate, methyl phenyl carbonate, etc. Chain carbonates of ethylene carbonate (ethylene carbonate), propylene carbonate (propylene carbonate), 2,3-dimethylethylene carbonate, butyrate , Cyclic carbonates such as vinylene carbonate and 2-vinylethylene carbonate; aliphatic carboxylic acid esters such as methyl formate, methyl acetate, propionic acid, methyl propionate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate; Aromatic carboxylic acid esters such as methyl acid and ethyl benzoate; cyclic carboxylic acid esters such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone; trimethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, Phosphate esters such as triethyl phosphate; Nitriles such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, isobutyronitrile; benzonitrile , Tolunitrile Aromatic nitriles; amides such as N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidinone, N-vinylpyrrolidone; dimethylsulfone, ethylmethylsulfone , Sulfur compounds such as diethyl sulfone, sulfolane, 3-methyl sulfolane, 2,4-dimethyl sulfolane: alcohols such as ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether; dimethyl sulfoxide, methyl ethyl sulfoxide Sulfoxides such as diethyl sulfoxide; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H) -pyrimidi Non, 3-methyl-2-oxazolidinone and the like can be mentioned. Among these, chain carbonic acid esters, cyclic carbonic acid esters, aliphatic carboxylic acid esters, cyclic carboxylic acid esters, ethers are more preferable, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, More preferred are γ-butyrolactone, γ-valerolactone, and the like. The said solvent may be used individually by 1 type, and may be used in combination of 2 or more type. Moreover, when using together 2 or more types of solvent, it is preferable that (gamma) -butyrolactone is included.

  The electrolytic solution according to the present invention may contain a polymer as the solvent. Examples of the polymer that can be used as the solvent contained in the electrolytic solution according to the present invention include polyether polymers such as polyethylene oxide (PEO) and polypropylene oxide, methacrylic polymers such as polymethyl methacrylate (PMMA), and polyacrylonitrile (PAN). And the like, fluorinated polymers such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene, and copolymers thereof. In addition, a polymer gel obtained by mixing these polymers with another organic solvent is also one suitable form of the solvent constituting the electrolytic solution according to the present invention. When a polymer gel electrolyte in which the above-described electrolyte is dissolved and dispersed in such a polymer gel instead of using the above solvent alone is used, self-discharge is reduced, so that the voltage holding characteristic in a high voltage state is improved. Therefore, it can be said that using the polymer gel which combined the above-mentioned polymer or a polymer and another organic solvent as an organic solvent is also one of the suitable aspects of the electrolyte solution which concerns on this invention.

  In the electricity storage device, the polymer electrolyte solution (including the polymer, the organic solvent, and the electrolyte) is usually used in the state of a film and sandwiched between electrodes. Therefore, when the polymer can maintain sufficient film strength, it may contain a solvent (polymer gel electrolyte). In this case, the content of the solvent is preferably 1% by mass to 99% by mass in 100% by mass of the electrolyte material. If the amount of the solvent is too small, it may be difficult to obtain sufficient ionic conductivity. On the other hand, if the amount of the solvent is too large, the ionic concentration in the electrolyte easily changes due to volatilization of the solvent, and stable ionic conductivity is obtained. Because it is difficult to be done. More preferably, it is 1.5 mass% or more, More preferably, it is 20 mass% or more, More preferably, it is 50 mass% or more, More preferably, it is 85 mass% or less, More preferably, it is 75 mass% or less, More preferably, 65 It is below mass%.

  The polymer gel electrolytic solution is a method in which an electrolytic solution is dropped onto a polymer formed by a conventionally known method to impregnate and carry an electrolyte and an organic solvent; the polymer and the electrolyte are melted at a temperature equal to or higher than the melting point of the polymer. After mixing, a film can be formed and manufactured by a method of impregnating with an organic solvent. On the other hand, an intrinsic polymer electrolyte is a method in which an electrolyte solution previously dissolved in an organic solvent and a polymer are mixed, and then this is formed into a film by a casting method or a coating method, and the organic solvent is volatilized; It can be produced by a method in which a polymer and an electrolyte are melted, mixed and molded.

The electrolyte solution according to the present invention may contain an electrolyte other than the cyanoborate salt. As other electrolytes, those having a large dissociation constant in the electrolytic solution are preferable. Examples of the cation species contained in the other electrolyte include the above-described monovalent inorganic cation and divalent inorganic cation. Among these, Li ⁺ , Na ⁺ , Mg ²⁺ and Ca ²⁺ are preferable, and Li ⁺ is more preferable. On the other hand, as anionic species, PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , [C (CN) ₃ ] ⁻ , N [(CN) ₂ ] ⁻ , N [(SO ₂ CF ₃ ) ₂ ] ⁻ , N [(SO ₂ F) ₂ ] ⁻ , CF ₃ (SO ₃ ) ⁻ , C [(CF ₃ SO ₂ ) ₃ ] ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ and dicyanotriazolate ion (DCTA). . Among these, PF ₆ ⁻ and BF ₄ ⁻ are more preferable, and BF ₄ ⁻ is particularly preferable. Specifically, lithium tetrafluoroborate containing Li ⁺ as the cation component and BF ₄ ⁻ as the anion component is preferable as another electrolyte.

  When the other electrolyte is used, the abundance thereof is preferably 1% by mass or more and 50% by mass or less in a total of 100% by mass of the cyanoborate salt and the other electrolyte. If the amount is less than 1% by mass, the absolute amount of ions may not be sufficient, and the electrical conductivity may be decreased. If the amount exceeds 50% by mass, the movement of ions may be significantly inhibited. More preferably, it is 5 mass% or more, More preferably, it is 10 mass% or more, More preferably, it is 40 mass% or less, More preferably, it is 30 mass% or less. From the viewpoint of achieving both high energy density and stable operation of the electricity storage device, it is desirable to use only the compound represented by the general formula (1) as the electrolyte.

  The electrolyte concentration (cyanoborate salt or the total amount of the cyanoborate salt and other electrolyte) in the electrolytic solution according to the present invention is preferably 1% by mass or more, and preferably less than the saturation concentration. If it is less than 1% by mass, the ionic conductivity is lowered, which is not preferable. More preferably, it is 5 mass% or more, and more preferably 50 mass% or less, and still more preferably 40 mass% or less. If the electrolyte concentration is too low, it may be difficult to obtain the desired electrical conductivity. On the other hand, if the concentration is too high, the viscosity of the electrolytic solution is particularly noticeable in a low temperature range (about −20 ° C.). As a result, the charge transfer efficiency may be lowered, or the electrolyte (cyanoborate salt or other electrolyte) may be separated and deposited in the electrolytic solution, which may adversely affect the device. In addition, there is a problem of cost increase due to a large amount of electrolyte used.

  The electrolytic solution according to the present invention may further contain an additive. Examples of such additives include a dissolution aid for improving the solubility of the tetracyanoborate salt and other electrolytes. Although it does not specifically limit as a specific dissolution aid, For example, an amine compound is mentioned as a preferable additive. Specifically, trimethylamine, triethylamine, tributylamine, dimethylethylamine, dimethylbutylamine, diethylbutylamine, hexamethylenetetramine, DABCO (diazabicyclooctane), DBU (diazabicycloundecene), TMEDA (tetramethylethylenediamine) and N -Methylimidazole etc. are mentioned, DBU, TMEDA and N-methylimidazole are preferable.

<Power storage device>
Next, the electricity storage device of the present invention will be described. The electricity storage device of the present invention includes a positive electrode, a negative electrode, and an electrolytic solution, and the electrolytic solution includes a cyanoborate salt represented by the general formula (1) and a solvent, and (i) a positive electrode at full charge The potential is 4.0 V to 5.5 V based on lithium, or (ii) the positive electrode includes a positive electrode active material that exhibits a discharge voltage of 3.5 V to 5.5 V based on lithium. Is.

  In the electricity storage device of the present invention, the positive electrode potential at the time of full charge is preferably 4.0 V or more, more preferably 4.3 V or more, further preferably 4.6 V or more, even more preferably, based on lithium. Is 4.9V or more. Therefore, the electricity storage device of the present invention can be charged to such a high potential. In addition, although the positive electrode potential at the time of a full charge is so preferable that it is high, it is preferable that it is 5.5 V or less from a safety viewpoint. More preferably, it is 5.4V or less, More preferably, it is 5.3V or less.

The positive electrode potential at the time of full charge is obtained by measuring the potential between two electrodes using a general potentiostat using Li metal as a reference electrode (reference electrode) and a positive electrode made of any material as a working electrode. Desired. When a material other than Li metal is used as the reference electrode, the actual measurement value can be converted to a positive electrode potential measured on the basis of the standard electrode potential value. For example, when an Ag electrode is used as a reference electrode (Ag / Ag ⁺ , standard electrode potential: 0.799 V), and when a Li metal is used as a reference electrode (Li / Li ⁺ , standard electrode potential: −3.045 V) Since the potential differs by about 3.8 V, it can be converted to the positive electrode potential measured on the basis of lithium by adding 3.8 V to the actual measurement value.

  More specifically, the positive electrode potential at the time of full charge means a value obtained by adding an operating voltage based on the lithium standard of the negative electrode to the charge end voltage when the charge / discharge test is performed (for example, using graphite as the negative electrode). In the case of using lithium titanate, 0.2 V is applied, and in the case of using Li as the negative electrode, the end-of-charge voltage may be the positive electrode potential at the time of full charge). The lithium-based operating voltage means a flat portion (plateau) voltage observed in a charge / discharge curve when the battery is operated using the negative electrode and Li as electrodes.

  The end-of-charge voltage when the charge / discharge test is performed may be set within a range in which the positive electrode material described later can be stably charged without causing decomposition or deterioration, and the capacity can be sufficiently taken out by discharge.

  The positive electrode and the negative electrode provided in the electricity storage device of the present invention are each composed of a current collector, a positive electrode active material or a negative electrode active material, a conductive agent, a binder (binder material), and the like. This material is formed on a positive electrode or negative electrode current collector into a thin coating film, a sheet shape or a plate shape.

  As the positive electrode, a positive electrode current collector, a positive electrode active material, a conductive agent and a binder are used. Examples of the positive electrode current collector include aluminum and stainless steel.

Examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiNi _(1-x) Co _x O ₂ , LiNi _(1-x) Mn _x O ₂ , LiNi _(1-x) Al _x O ₂ , LiNi _{x. Mn y Co (1-xy)} O 2, LiNi x Co y Al (1-xy) O 2, Li 2 MnO 3 -LiMO 2 (M = Co, Ni, Mn), LiMn 2 O 4, LiM x Mn ( _2-x) O ₄ (M = Cr, Fe, Co, Ni, Cu, Al), LiMPO ₄ (M = Fe, Mn, Co, Ni), Li ₂ MSiO ₄ (M = Mn, Fe, Co), LiMVO ₄ (M = Co, Ni), LiMBO ₃ (M = Mn, Fe), M ₂ (XO ₄ ) ₃ (M = transition metal, X = S, P, As, Mo, W), Li ₃ M ₂ (PO ₄ ) ₃ (M = Fe, V, Ti) Among these, LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiNi _0.5 Co _0.5 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.75 Al _0.25 O ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiMPO ₄ (M = Fe, Mn, Co, Ni) and LiMVO ₄ (M = Co, Ni) are preferable.

In order to increase the output, it is preferable to use, as the positive electrode active material, a material that can increase the potential at full charge to 4.0 V or higher with respect to lithium. Examples of such a material include a positive electrode active material having a lithium-based discharge voltage of 3.5 to 5.5 V determined by the following measurement among the above positive electrode active materials. Specifically, LiCoO ₂ (3.9V), LiNiO ₂ (3.9V), LiNi _0.5 Mn _0.5 O ₂ (3.9V), LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (3. 9V), LiNi _0.8 Co _0.15 Al _0.05 O ₂ (3.7 V), LiMn ₂ O ₄ (4.0 V), LiNi _0.5 Mn _1.5 O ₄ (4.7 V), LiMnPO ₄ (4.1 V), LiCoPO ₄ ( _{4.8V), LiNiPO 4 (5.1V)} , LiNiVO 4 (4.8V), LiCoVO 4 (4.2V) , and the like. The numerical value in parentheses after the positive electrode active material indicates the discharge voltage of the positive electrode active material. Such positive electrode active materials include, for example, Japanese Patent No. 3593322, Japanese Patent No. 412568, Japanese Patent No. 3568826, Japanese Patent No. 3589542, Japanese Patent No. 4234418, Japanese Patent Application Laid-Open No. 10-27611, and Japanese Patent Application Laid-Open No. 11-16572. No. 4,581,157, JP 2001-143704, JP 3606289, JP 2001-185145, JP 2002-63904, JP 3461800, JP 2004-95534, JP 2007-119304, J. Org. Electrochem. Soc. , 152, pp. A1434-A1440 (2005), J. MoI. Power. Sources, 189, p. 397 (2009), Electrochem. Solid State Lett. , 3, p. 178 (2000), J.A. Power. Sources, 142, p. 389 (2005), J.A. Electrochem. Soc. 141, 279 (1994), Electrochim. Acta. 45, 295 (1999) and the like. Among the positive electrode active materials described above, it is a recommended embodiment of the present invention to use a positive electrode active material capable of raising the potential at full charge to 4.0 V or more on the basis of lithium.

  Here, the lithium-based discharge voltage is a flat portion (plateau) observed in a charge / discharge curve when a battery is operated using a positive electrode composed of the positive electrode active material as a positive electrode and Li as a negative electrode. Means voltage.

  The positive electrode active material is preferably powdery (granular), and preferably has a particle diameter of 10 nm or more and 500 μm or less. The particle diameter is more preferably 20 nm or more and 100 μm or less, further preferably 50 nm or more and 50 μm or less, particularly preferably 100 nm or more and 30 μm or less, and further preferably 10 μm or less. Here, the average particle diameter is a value of a volume average particle diameter measured by a laser diffraction particle size distribution measuring apparatus. The nominal value of the seller may be referred to.

  The negative electrode is not particularly limited, and for example, any known negative electrode used in a lithium ion secondary battery can be used. Specifically, a negative electrode current collector, a negative electrode active material, a conductive agent, and Those composed of a binder or the like are preferably used. Examples of the negative electrode current collector include copper, nickel, and stainless steel.

  As a negative electrode active material, the conventionally well-known negative electrode active material used with a lithium ion secondary battery can be used, for example. Specifically, carbon materials such as natural graphite, artificial graphite, amorphous carbon, coke and mesophase pitch carbon fiber, graphite, amorphous carbon hard carbon, C-Si composite material, lithium-aluminum alloy, lithium -One or more of lithium alloys such as magnesium alloy, lithium-indium alloy, lithium-thallium alloy, lithium-lead alloy, lithium-bismuth alloy, titanium, tin, iron, molybdenum, niobium, vanadium and zinc And metal oxides containing metal sulfides. Among these, metallic lithium and carbon materials that can occlude and release alkali metal ions are more preferable.

  As the conductive agent, carbon black such as acetylene black and ketjen black, natural graphite, thermally expanded graphite, carbon fiber, metal fiber such as ruthenium oxide, titanium oxide, aluminum, and nickel are preferable. These can use 1 type (s) or 2 or more types. Among these, acetylene black and ketjen black are more preferable in that the conductivity can be effectively improved with a small amount. Although the compounding quantity of a electrically conductive agent changes also with the kind of active material to be used, it is preferable to set it as 1 mass part-10 mass parts with respect to 100 mass parts of a positive electrode or a negative electrode active material, and 3 mass parts-5 mass parts. It is more preferable that

  As the binder substance, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, fluoroolefin copolymer crosslinked polymer, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, phenol resin, and the like are suitable. These can use 1 type (s) or 2 or more types. The blending amount of the binder material varies depending on the type of the active material to be used, but is preferably 0.5 parts by mass to 10 parts by mass with respect to 100 parts by mass of the positive electrode or the negative electrode active material. More preferably, it is 5 parts by mass.

  As a method for forming the positive electrode and the negative electrode, for example, (1) a binder material is added and mixed in a mixture of an electrode active material of a positive electrode or a negative electrode and acetylene black as a conductive agent, and then applied onto each current collector. And (2) a method in which an electrode active material and a binder material are mixed and molded, integrated with a current collector, and then heat-treated in an inert atmosphere to form an electrode as a sintered body. It is. In addition, when using the activated carbon fiber cloth obtained by activating a carbon fiber cloth, you may use as an electrode as it is, without using a binder substance.

  In the electricity storage device of the present invention, a separator is provided between the positive electrode and the negative electrode in order to prevent short circuit. The separator may be provided by a method in which the separator is sandwiched between the positive electrode and the negative electrode, or a method in which each electrode is opposed to each other with a gap using a holding unit.

As the separator, it is preferable to use a porous thin film that does not chemically react with the cyanoborate salt of the general formula (1), other electrolytes, or the like in the operating temperature range of the electricity storage device. The material of the separator is preferably paper; polyolefin (polypropylene, polyethylene, etc.); cellulose; organic material such as aramid; organic porous material such as aramid fiber; inorganic material such as glass fiber; In particular, when an electricity storage device is operated under a high voltage, a high insulating property is required, and therefore a separator made of an inorganic material, a polyolefin material, or a mixture thereof is suitable. From the viewpoint of insulating properties, polypropylene (PP) film, polyethylene (PE) film, or laminated film in which these films are laminated (for example, PP / PE / PP _three- layer film); polyolefin-based materials and inorganic-based materials And the like, which are formed by applying or impregnating the above organic material to a porous sheet containing cellulose; and the like are suitable as the separator. From the viewpoint of miniaturization of the electricity storage device, a separator made of an organic material or an organic porous material that can be easily thinned is preferable. On the other hand, a separator made of an inorganic material such as glass fiber is related to the present invention. This is preferable because the wettability to the electrolytic solution is good.

The above-described electrolytic solution is used as the electrolytic solution of the electricity storage device of the present invention. The cation: M ^{n +} and the cyanoborate anion: [B (CN) _4-a (X ² R ¹³ ) _a ] ⁻ contained in the electrolytic solution according to the present invention are compounds containing these anions and / or cations. It comes from. The compound that generates these ions may be derived from the cyanoborate salt represented by the general formula (1) or may be derived from another electrolyte. As described above, the electrolyte solution according to the present invention preferably contains lithium ions. However, when the cyanoborate salt of the general formula (1) does not contain lithium ions, the electrolyte solution according to the present invention is used. Lithium ions contained in the electrolytic solution are derived from other electrolytes.

The concentration of lithium ions in the electrolytic solution is preferably 5.0 × 10 ⁻⁴ mass% or more and 5 mass% or less. More preferably, it is 2.5 × 10 ⁻³ mass% or more, further preferably 1.0 × 10 ⁻² mass% or more, more preferably 3 mass% or less, and further preferably 2 mass% or less. is there. On the other hand, the concentration of the cyanoborate anion is preferably 0.1% by mass or more and 50% by mass or less. More preferably, it is 1 mass% or more, More preferably, it is 5 mass% or more, More preferably, it is 40 mass% or less, More preferably, it is 30 mass% or less. When both the lithium ion and the cyanoborate anion are present in the electrolyte solution in an excessively small amount, it may be difficult to obtain a desired electrical conductivity. On the other hand, when the concentration is too high, particularly in a low temperature range. Although it becomes remarkable at (about −20 ° C.), the viscosity of the electrolytic solution increases, and the charge transfer efficiency may be lowered, or lithium cyanoborate may precipitate in the electrolytic solution, which may adversely affect the electrode and the like. Further, a large amount of use leads to an increase in cost.

The concentration of the cyanoborate salt represented by the general formula (1) and other electrolytes in the electrolytic solution is not particularly limited as long as the lithium ion amount and the cyanoborate anion amount fall within the above ranges. For example, M ^{n +} The concentration of the cyanoborate salt of the general formula (1) in which is lithium ion is 0.01% by mass or more and preferably less than 50% by mass. When the concentration of the electrolyte is within the above range, it is preferable because it shows good electric conductivity. The concentration of the cyanoborate salt is more preferably 0.05% by mass or more, further preferably 0.1% by mass or more, more preferably 30% by mass or less, and further preferably 20% by mass. It is as follows. If the concentration is too low, it may be difficult to obtain the desired electrical conductivity. On the other hand, if the concentration is too high, the viscosity of the electrolytic solution is particularly remarkable in a low temperature range (about −20 ° C.). This may increase the charge transfer efficiency or may cause separation and precipitation of the cyanoborate salt in the electrolytic solution, which may adversely affect the electrode. In addition, the use of a large amount of cyanoborate salt causes an increase in cost.

  In the electricity storage device of the present invention, a polymer electrolyte or a polymer gel electrolyte may be used as the electrolyte. The polymer electrolyte is obtained by supporting an electrolyte on a polymer serving as a base material. For example, a polymer electrolyte obtained by impregnating a polymer with the electrolytic solution of the present invention (polymer gel electrolytic solution) or a cyano compound represented by the general formula (1) Examples include an intrinsic polymer electrolyte in which a borate salt or the other electrolyte described above is dissolved in a base polymer. In the present invention, it is preferable to use a polymer electrolyte containing lithium ions and cyanoborate anions. Examples of the polymer serving as a base material for the polymer electrolyte include polyether copolymers such as polyethylene oxide and polypropylene oxide, and among them, polyethylene oxide is preferably used.

  The electricity storage device of the present invention only needs to have a positive electrode, a negative electrode, and an electrolytic solution, and may include a plurality of cells each having the positive electrode, the negative electrode, and the electrolytic solution as one unit. If it is provided with the said structure, the shape of the electrical storage device of this invention will not be limited, All conventionally well-known shapes, such as a coin type | mold, a winding cylindrical type | mold, a lamination | stacking square type | mold, an aluminum lamination type | mold, can be employ | adopted. Moreover, the said exterior case is not specifically limited, What is necessary is just to employ | adopt conventionally well-known things, such as a product made from aluminum and steel.

  A lithium ion secondary battery is mentioned as an electrical storage device of this invention which has the said structure.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[NMR measurement]
Using a “Unity Plus” (400 MHz) manufactured by Varian, ¹ H-NMR and ¹³ C-NMR spectra were measured, and the structure of the sample was analyzed based on the peak intensity of protons and carbon. ^For the measurement of ¹¹ B-NMR spectrum, “Advance 400M” (400 MHz) manufactured by Bruker was used.

In addition, the measurement of a NMR spectrum measured the measurement sample which dissolved the reaction solution or the obtained salt so that the density | concentration might be 1 mass%-5 mass% in heavy dimethyl sulfoxide, and does not contain a boron element, but is made from aluminum oxide. Were measured at room temperature (25 ° C.) and 64 times of integration. In the measurement of ¹ H-NMR and ¹³ C-NMR spectra, tetramethylsilane was used as a standard substance, and in the measurement of ¹¹ B-NMR spectrum, diethyl etherate of boron trifluoride was used as a standard substance.

Synthesis Example 1 Synthesis of Ionic Compound (Lithium Tetracyanoborate) 44.4 g (200 mmol) of tributylammonium chloride previously heated and dried in a 1 L eggplant flask equipped with a stirrer, a reflux tube and a withdrawal device, and a dropping funnel. ) Was added. After replacing the inside of the container with nitrogen, 109.0 g (1100 mmol) of trimethylsilylcyanide (TMSCN) was added at room temperature, and the mixture was stirred and mixed. Next, 200 mL (200 mmol) of a 1 mol / L p-xylene solution of boron trichloride was slowly dropped from the dropping funnel. After completion of the dropping, the reaction vessel was heated to 150 ° C., and the reaction was performed while extracting trimethylsilyl chloride (TMSCl, boiling point: about 57 ° C.) as a by-product from the reflux extraction portion.

  After stirring with heating for 30 hours, the inside of the reaction vessel was depressurized with a diaphragm pump, and the p-xylene solution of TMSCN was distilled off from the reflux outlet. Thereafter, 45 g of the crude product and 225 g of ethyl acetate were placed in a 500 mL beaker equipped with a stirrer, and dissolved by stirring for 5 minutes. )) Was added and stirred for 10 minutes. The obtained activated carbon suspension was filtered through a membrane filter (0.2 μm, PTFE), the solvent was distilled off, and the residue was dried to obtain the target product, tributylammonium tetracyanoborate (yellow solid) (yield) : 48.2 g (160 mmol), yield: 80%).

  Various physical properties of the obtained tributylammonium tetracyanoborate were measured by the above measuring method. The results are as follows.

¹ H-NMR (d ₆ -DMSO) δ 2.98 (m, 6H), 1.4 to 1.8 (m, 6H), 1.2 to 1.3 (m, 6H), 0.94 (m, 9H)
¹³ C-NMR (d ₆ -DMSO) δ 121.9 (m), 52.7 (s), 26.2 (s), 20.3 (s), 14.4 (s)
¹¹ B-NMR (d ₆ -DMSO) δ -39.6 (s)

  Subsequently, 48.2 g (160 mmol) of the obtained tributylammonium tetracyanoborate, 200 g of butyl acetate, 4.6 g (192 mmol) of lithium hydroxide monohydrate, and 200 g of ultrapure water were added to a 500 ml beaker equipped with a stirrer. Was added and stirred for 1 hour. Thereafter, the mixed solution was transferred to a separatory funnel and allowed to stand to separate into two layers. Among these, the pale yellow solid obtained by separating and concentrating the lower layer (aqueous layer) was mixed with 200 g of acetonitrile and stirred. Thereafter, the obtained solution was filtered through a membrane filter (0.2 μm, made of PTFE), and the solvent was distilled off to obtain lithium tetracyanoborate (LiTCB, white solid) as a target product (yield: 13). .6 g (112 mmol), yield: 70%). The obtained white solid was dried under reduced pressure at 150 ° C. for 3 days.

⁷ Li-NMR (d ₆ -DMSO) δ 0.02 (s)
¹³ C-NMR (d ₆ -DMSO) δ 121.9 (m)
¹¹ B-NMR (d ₆ -DMSO) δ -39.6 (s)

Experimental Example 1 Charge / Discharge Test A CR2032 type coin cell was prepared using the lithium tetracyanoborate synthesized in Synthesis Example 1 and a commercially available γ-butyrolactone (LIB grade, manufactured by Kishida Chemical Co., Ltd.), and a charge / discharge test was performed. .

The coin cell uses LiNi _0.5 Mn _1.5 O ₄ with a lithium-based discharge voltage of 4.7 V for the positive electrode and lithium foil (thickness: 0.5 mm, manufactured by Honjo Metal Co., Ltd.) for the negative electrode. The glass non-woven fabrics were opposed to each other and filled with a γ-butyrolactone solution (electrolytic solution) of lithium tetracyanoborate having a concentration of 7% by mass (0.7 M).

Using the produced coin cell, a charge / discharge test was performed using a charge / discharge test apparatus (“Battery Labo System [BS2501 Series]”, manufactured by Keiki Keiki Center Co., Ltd.). The measurement conditions are shown below. Moreover, the charging / discharging curve at the time of initial charging / discharging is shown in FIG.
(Measurement condition)
Charge / discharge rate: 0.2C
Charging / discharging mode: Constant current mode Charging / discharging range: 3.5V-4.9V

  In the electricity storage device having the above configuration, the positive electrode potential at the time of full charge is 4.9 V, and charging and discharging are possible without severe decomposition of the electrolyte even under a high voltage condition of 4.9 V from FIG. It can be seen that the electricity storage device of the present invention can be stably operated even when operated in a high voltage range.

  According to the present invention, it is considered that an electricity storage device that can operate stably in a high voltage range can be provided.

Claims (6)

Comprising a positive electrode, a negative electrode and an electrolyte;
The electrolytic solution includes a cyanoborate salt represented by the following general formula (1) and a solvent, and
A power storage device, wherein the positive electrode potential at full charge is 4.0 V to 5.5 V with respect to lithium.
M ^{n +} ([B (CN) _4-a (X ² R ¹³ ) _a ] ⁻ ) _n (1)
(In the formula, M ^{n +} is a monovalent, divalent or trivalent organic or inorganic cation, X ² is O or S, R ¹³ is H or a hydrocarbon group having 1 to 10 carbon atoms, and n is an integer of 1 to 3. A represents an integer of 0 to 3) Comprising a positive electrode, a negative electrode and an electrolyte;
The electrolytic solution includes a cyanoborate salt represented by the following general formula (1) and a solvent, and
The electricity storage device, wherein the positive electrode includes a positive electrode active material exhibiting a discharge voltage of 3.5 V to 5.5 V on a lithium basis.
M ^{n +} ([B (CN) _4-a (X ² R ¹³ ) _a ] ⁻ ) _n (1)
(In the formula, M ^{n +} is a monovalent, divalent or trivalent organic or inorganic cation, X ² is O or S, R ¹³ is H or a hydrocarbon group having 1 to 10 carbon atoms, and n is an integer of 1 to 3. A represents an integer of 0 to 3) The electricity storage device according to claim 1, wherein M ^{n + in the} formula is Li ⁺ .   The electricity storage device according to claim 1, wherein the solvent contains γ-butyrolactone.   The electrical storage device in any one of Claims 1-4 which has the separator which consists of glass fiber between the said positive electrode and a negative electrode. It is a lithium ion secondary battery, The electrical storage device in any one of Claims 1-5.