JP2018115122A - Lithium cyanofluoro borate, nonaqueous electrolyte containing lithium cyanofluoro borate and electricity storage device having the nonaqueous electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide lithium cyanofluoro borate capable of exhibiting more stable property than conventional technologies after use at high temperature and storage at high temperature in an application such as an electricity storage device, and a nonaqueous electrolyte containing the salt.SOLUTION: There is provided a nonaqueous electrolyte containing a salt represented by Li BF(CN)(1), where X is an integer of 1 to 3, having content of a compound having an isocyanide group (-NC group), which is an impurity, of 0.02 mol% or less, preferably a salt represented by the formula (1) and having the content of the compound having the isocyanide group of 2×10mol/L. There is provided a nonaqueous electrolyte further preferably containing one or more kind of nonaqueous solvent selected from chain carbonate, cyclic carbonate, chain ester, lactone or ether.SELECTED DRAWING: None

Description

  The present invention relates to a novel cyanofluoroborate lithium salt, a novel non-aqueous electrolyte containing the cyanofluoroborate lithium salt, and a novel electricity storage device having the non-aqueous electrolyte. Specifically, a novel cyanofluoroborate lithium salt, a novel nonaqueous electrolytic solution containing the cyanofluoroborate lithium salt, and a nonaqueous electrolyte in which the compound having an isocyanide group (—NC group) as an impurity is a specific amount or less. The present invention relates to a novel power storage device having an electrolytic solution.

  In recent years, portable electronic devices, mobile phones, video cameras, and the like have spread rapidly, and the demand for lightweight, high-performance secondary batteries used for them has greatly increased. In addition, development of larger-capacity electricity storage devices is being promoted for in-vehicle applications and natural energy storage applications. When used as a large-capacity power storage device, it is required to have a longer life and a wider operating temperature range than those of conventional devices (in higher temperature and lower temperature regions). It is supposed to be used.)

In many cases, an electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent is used as the electrolytic solution used in these power storage devices. As the non-aqueous solvent, for example, a mixed solvent containing at least a non-aqueous solvent such as ethylene carbonate, propylene carbonate, and diethyl carbonate is generally used. Then, as the lithium _salt, such as LiPF 6, LiBF ₄ is employed.

  In addition, as a negative electrode active material of a lithium ion secondary battery in an electricity storage device, a carbonaceous material capable of occluding and releasing lithium ions, and a metal or alloy using silicon or tin aiming at high capacity System materials are known. At present, carbonaceous natural graphite, artificial graphite, amorphous carbon and the like are mainly used. On the other hand, as the positive electrode active material, a transition metal composite oxide capable of inserting and extracting lithium ions is used. Typical examples of transition metals are cobalt, nickel, manganese, iron and the like.

  Since such a lithium ion secondary battery uses a highly active positive electrode and negative electrode, it is known that the charge / discharge capacity is reduced by repeated use due to side reaction between the electrode and the electrolyte. In particular, there is a problem that the capacity decreases or the resistance increases when stored at high temperature. Therefore, in the lithium ion secondary battery, various studies have been made on a non-aqueous solvent, an electrolyte, and the like that are components of the electrolytic solution in order to improve battery characteristics.

  Among them, the development of nonaqueous electrolytes using cyanoborate lithium salts is underway (see, for example, Patent Documents 1 to 3). Specifically, according to the methods described in these patent documents, the nonaqueous electrolytic solution contains a cyanofluoroborate anion, is electrochemically stable, and further improves conductivity at low and high temperatures. It can be set as the electrolyte solution suitable for an electrical storage device.

International publication WO2015 / 186568 pamphlet International Publication WO2016 / 111151 Pamphlet JP2015-103288A

  However, according to the study by the present inventors, in recent years, the demand for power storage devices has increased further, even when a non-aqueous electrolyte containing a relatively stable cyanofluoroborate anion is used. I found that there was room for improvement.

  For example, in the methods described in Patent Documents 1 and 3, when only a cyanofluoroborate lithium salt is used as an electrolyte salt, the characteristics after storage at high temperatures (for example, 80 to 85 ° C.) tend to deteriorate. It was in. Specifically, Patent Document 3 shows that the storage maintenance ratio (the ratio of the discharge capacity after storage) is at most 80%, and Patent Document 1 shows that the resistance value is about four times higher. ing. Moreover, in patent document 2, although it is not described about the use at high temperature, in the result that the present inventors made additional trials, the characteristics at high temperature tended to be lowered.

  In power storage devices for which high performance has been demanded in recent years, lithium (Li) ion batteries have a large capacity, and therefore, application from a power source of a portable device to a medium to large capacity power source is being studied. However, Li-ion batteries are greatly degraded when stored at high temperatures in a charged state. Therefore, for example, when used at a high temperature in summer, it is required to further suppress deterioration during charging at a high temperature in order to use it for a medium to large capacity power source.

  Therefore, an object of the present invention is to provide a lithium cyanofluoroborate salt that can exhibit more stable characteristics than those of the prior art after use at high temperature and storage at high temperature in applications such as power storage devices. It is providing the non-aqueous electrolyte containing a salt.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. And the tendency of the electrolyte solution which the characteristic of an electrical storage device falls after use and storage at high temperature was investigated. Then, it was found that when the concentration of the cyanofluoroborate lithium salt is relatively high, or when the concentration of the cyanofluoroborate anion is high, the characteristics are deteriorated. Based on this, it was considered that impurities contained in the cyanofluoroborate lithium salt may have an adverse effect, and the analysis was performed. As a result, it was found that the impurity “isocyanide group (—NC group) -containing compound” contained in the cyanofluoroborate lithium salt was the cause. By reducing this impurity, it was found that the above problems could be solved, and the present invention was completed. It came to do.

That is, the first aspect of the present invention is
(1) A cyanofluoroborate lithium salt represented by the following formula (1), wherein the content of a compound having an isocyanide group (—NC group) as an impurity is 0.02 mol% or less.

Li · BF _X (CN) _4-X (1)
(X is an integer of 1 to 3).

Furthermore, the second aspect of the present invention provides
Cyanofluoroborate lithium salt represented by the following formula (1) Li · BF _X (CN) _4-X (1)
(X is an integer of 1 to 3)
And the content of the compound having an isocyanide group is 2 × 10 ⁻⁴ mol / L.

In the second invention, it is preferable to include the cyanofluoroborate lithium salt of the first invention,
(3) Cyanofluoroborate lithium salt Li · BF _X (CN) _4-X represented by the following formula (1) in which the content of the compound having an isocyanide group is 0.02 mol% or less (1)
(X is an integer of 1 to 3)
It is preferable that it is a non-aqueous electrolyte containing.

  Moreover, it is preferable that 2nd this invention takes the following structures.

  (4) The method according to (2) or (3), further comprising at least one nonaqueous solvent selected from the group consisting of a chain carbonate, a cyclic carbonate, a chain ester, a lactone and an ether. Non-aqueous electrolyte.

  (5) The nonaqueous electrolyte solution according to any one of (2) to (4), further comprising a lithium salt other than the cyanofluoroborate lithium salt of (1).

  (6) The non-aqueous electrolyte according to any one of (2) to (5) above, wherein the total concentration of all lithium salts contained in the non-aqueous electrolyte is 0.3 to 4 mol / L.

Furthermore, the third aspect of the present invention provides
(7) A power storage device comprising a positive electrode, a negative electrode, and the nonaqueous electrolytic solution according to any one of (2) to (6).

In the third invention,
(8) The electricity storage device according to (7), which is a lithium battery, a lithium ion battery, or a lithium ion capacitor.

The fourth aspect of the present invention is
(9) Precipitating crystals of a lithium cyanofluoroborate salt represented by the following formula (1) in a mixed solution containing acetonitrile and at least one solvent selected from alcohols and halogen solvents. A process for producing a lithium cyanofluoroborate salt.
Li · BF _X (CN) _4-X (1)
(X is an integer of 1 to 3).

  The present invention is a cyanofluoroborate lithium salt having a low content of a compound having an isocyanide group as an impurity. The non-aqueous electrolyte containing the lithium cyanofluoroborate provides an electricity storage device that is excellent in use at high temperatures (including use after storage at high temperatures), particularly when used as an electrolyte for electricity storage devices. it can.

The present invention is a cyanofluoroborate lithium salt represented by the following formula (1) in which the content of a compound having an isocyanide group (—NC group) as an impurity is 0.02 mo% or less.
Li · BF _X (CN) _4-X (1)
In formula, X is an integer of 1-3.

  By using a non-aqueous electrolyte containing a cyanofluoroborate lithium salt as described above as an electrolyte for an electricity storage device, the effect of suppressing a decrease in discharge capacity after storage at high temperature, and after storage at high temperature The effect of suppressing the increase in the resistance value is exhibited (hereinafter, these effects may be simply referred to as “effects at high temperature use”). In the following, description will be given in order.

(Cyanofluoroborate lithium salt)
In the present invention, the cyanofluoroborate lithium salt has the following formula (1):
Li · BF _X (CN) _4-X (1)
(Hereinafter, sometimes simply referred to as “cyanofluoroborate lithium salt”). X is an integer of 1 to 3, that is, the cyanofluoroborate lithium salt is at least selected from Li · BF (CN) ₃ , Li · BF ₂ (CN) ₂ , and LiBF ₃ (CN). It contains one kind of salt. Among these, in consideration of the productivity of itself, the ease of purification, and the performance when blended with a non-aqueous electrolyte, it is selected from Li · BF (CN) ₃ and Li · BF ₂ (CN) _2. Preferably it is at least one salt.

(Impurity contained in cyanofluoroborate lithium salt; compound having isocyanide group)
In the present invention, the compound having an isocyanide group which is an impurity must be 0.02 mo% or less in the cyanofluoroborate lithium salt. This compound having an isocyanide group is considered to exist as Li · BF ₂ (NC) (CN) and Li · BF (NC) (CN) _{2 in the} cyanofluoroborate lithium salt. As will be described in the section of the non-aqueous electrolyte, if there is a cation other than Li, in the state in which the solvent was distilled off from the non-aqueous ^{_{electrolyte, BF 2 (NC) (CN}} ) -, BF (NC) ( CN) ₂ ⁻ anion can be quantified in the form of a salt formed with Li ions and cations other than Li. And the compound which has this isocyanide group can be measured by the method as described in the following Example.

When quantifying the compound having an isocyanide group contained in the cyanofluoroborate lithium salt, it can be quantified by measurement of ¹⁹ F-NMR. However, when the non-aqueous electrolyte containing the cyanofluoroborate lithium salt is used, the content of the compound having an isocyanide group is also reduced. Therefore, in the present invention, quantification of the “compound having an isocyanide group” contained in the cyanofluoroborate lithium salt itself, and the “compound having an isocyanide group” contained in the nonaqueous electrolytic solution containing the cyanofluoroborate lithium salt The following method was employed for quantification.

Specifically, first, a sample in which a cyanofluoroborate lithium salt before purification and a cyanofluoroborate lithium salt after purification were mixed at different quantitative ratios was prepared. Quantification of the “compound having an isocyanide group” in each sample was performed by ¹⁹ F-NMR measurement. Next, Raman measurement was performed on each sample that was quantified, and a calibration curve by Raman measurement (a calibration curve showing a correlation between the peak ratio of the cyano group and the isocyanide group and the content of the “compound having an isocyanide group”) was obtained. Created. In the present invention, the “compound having an isocyanide group” was quantified using a calibration curve based on this Raman measurement. When the measurement sample was salt, the Raman measurement was performed as it was, and quantified with the calibration curve. In the case of the electrolytic solution, after removing the solvent by vacuum drying, the residue was subjected to Raman measurement, and the content of the “compound having an isocyanide group” contained in the electrolytic solution was measured. In the electrolyte solution, the content of the “compound having an isocyanide group” contained in the cyanofluoroborate lithium salt is determined by measuring the concentration of the cyanofluoroborate salt contained in the solvent by NMR or the like, and the “isocyanide group contained in the electrolyte solution”. It was calculated from the measured value of “compound having”. In addition, when the compound which has an isocyanide group is contained 0.1 mol% or more, it can fully quantify also by a ¹⁹ F-NMR measurement.

  It is known that an isocyanide group has a higher reactivity than a cyano group and is likely to react at a relatively high temperature, for example, 60 ° C. or higher. As a result, it is considered that the cyanofluoroborate lithium salt containing “the compound having an isocyanide group” in excess of 0.02 mol% is discolored or easily decomposed. And, when a cyanofluoroborate lithium salt containing a large amount of “compound having an isocyanide group”, for example, containing more than 0.02 mo% is added to the non-aqueous electrolyte, the characteristics of the electricity storage device when used at high temperatures are reduced. Conceivable. Therefore, in order to further enhance the storage stability of the cyanofluoroborate lithium salt itself and the effect at high temperature use of the electricity storage device, the amount of the compound having an isocyanide group is more preferably 0.01 mol% or less, More preferably, it is 0.005 mol% or less, and especially preferably 0.001 mol% or less. The lower limit of the content of the compound having an isocyanide group is most preferably 0 mol%, but is 0.001 mol% in view of industrial production.

(Method for producing cyanofluoroborate lithium salt)
As the cyanofluoroborate lithium salt, for example, a method in which a cyanide compound of lithium metal is dissolved in an organic solvent such as acetonitrile and acetone and BF ₃ gas is blown can be employed. Also, a method of reacting a cyanide compound of lithium metal with a BF ₃ addition compound such as boron trifluoride ether BF ₃ · OEt _{2 in} the presence of an aprotic solvent such as acetonitrile, diethyl ether, tetrahydrofuran, and dimethoxyethane Can be synthesized. In addition, it can be synthesized by reacting a lithium boron fluoride lithium salt such as LiBF ₄ with a silicon cyanide compound such as trimethylsilyl cyanide.

In addition to the above method, a method in which a cyanofluoroborate salt other than the lithium salt is once produced and then the cation is lithium can be employed. For example, first, the above BF ₃ gas is blown into a solution obtained by dissolving an alkali metal or alkaline earth metal cyanide other than lithium, such as potassium, sodium, magnesium and calcium, in an organic solvent, and cyanofluoroborate. An alkali metal or alkaline earth metal salt is synthesized. Alternatively, a BF ₃ adduct such as boron trifluoride ether BF ₃ .OEt _{2 is} allowed to act in the presence of an aprotic solvent to synthesize an alkali metal or alkaline earth metal salt of cyanofluoroborate. In addition, an alkali metal or alkaline earth metal salt of cyanofluoroborate can be synthesized by reacting an alkali metal or alkaline earth metal salt of boron fluoride with a silicon cyanide compound such as trimethylsilyl cyanide. Next, salt exchange may be performed by allowing an inorganic lithium salt such as lithium hydroxide, lithium carbonate, or lithium halide to act on the obtained alkali metal or alkaline earth metal salt of cyanofluoroborate.

  The compound “compound having an isocyanide group” as an impurity is prepared by synthesizing the above lithium salt, other alkali metal salt or alkaline earth metal salt (hereinafter sometimes simply referred to as “cyanofluoroborate salt”). It is thought to be a by-product when doing. Specifically, when a boron atom and a cyano group are reacted, a compound having an isocyanide group at the same time is considered to be a byproduct. Therefore, it is considered difficult to reduce the compound having an isocyanide group during production. According to the study by the present inventors, it has been found that the cyanofluoroborate lithium salt produced by the above method contains a compound having an isocyanate group in an amount of more than 0.02 mol% and about 2 mol% or less.

(Method for reducing compounds having an isocyanide group)
Therefore, the present inventors tried to reduce “compounds having an isocyanide group (impurities)” by purification. A cyanofluoroborate lithium salt containing the impurity in a mixed solution of acetonitrile and at least one solvent selected from alcohols and halogenated solvents (hereinafter sometimes referred to simply as “mixed solution”) It was found that the “compound having an isocyanide group” can be efficiently reduced by crystallizing. Specific examples of the halogen-based solvent contained in the mixed solution include methylene chloride, chloroform, carbon tetrachloride and the like. Examples of the alcohol include methanol, ethanol, isopropyl alcohol and the like.

  As a crystallization method, a known method can be adopted. The amount of the mixed solvent to be used may be appropriately determined depending on the kind of cyanofluoroborate lithium salt, the temperature at the time of crystallization, etc. Among them, in order to improve operability and improve the effect of reducing impurities, 0 The mixed solution is preferably used in an amount of 50 parts by mass or more and 700 parts by mass or less with respect to 100 parts by mass of the cyanofluoroborate lithium salt containing a compound having an isocyanide group exceeding 0.02 mol%, and more preferably 100 parts by mass or more and 600 parts by mass or more. It is preferable to use an amount equal to or less than part by mass. Moreover, in the said mixed solution, it is preferable that the ratio of acetonitrile and the other solvent (at least 1 sort (s) of solvent chosen from alcohol and a halogen-type solvent) shall be the following ratios. Specifically, when acetonitrile is 100 parts by mass, the other solvent is preferably 10 parts by mass to 500 parts by mass, and more preferably 10 parts by mass to 300 parts by mass.

  The temperature at which the crystallization is performed is not particularly limited, but it is preferable that the crystal is precipitated at a temperature of 10 ° C. or higher and 30 ° C. or lower because impurities tend not to be sufficiently reduced if the temperature is too low. . In addition, for example, if the temperature at which cyanofluoroborate lithium containing “compound having an isocyanide group” exceeding 0.02 mol% is dissolved in the mixed solution is too high, other impurities tend to increase. The temperature is preferably 40 ° C. or higher and 75 ° C. or lower.

  As a matter of course, the crystallization operation can be repeatedly performed. Furthermore, a cyanofluoroborate lithium salt containing 0.02 mol% or less of “compound having an isocyanide group” can be crystallized in the mixed solution.

By purifying by the above method, impurities other than the compound having an isocyanide group can be reduced. For example, the metal concentration other than Li is 5 × 10 ⁻³ mol% or less for Na, 7 × 10 ⁻⁴ mol% or less for K, 2 × 10 ⁻³ mol% or less for Ca, and 1 × 10 ⁻⁴ mol for Fe. % Or less.

By the above method, the “compound having an isocyanide group” can be reduced. Among these, the optimum conditions vary depending on the composition of the cyanofluoroborate lithium salt. Specifically, preferred conditions for crystallization of Li · BF (CN) ₃ or Li · BF ₂ (CN) _2, which are suitable cyanofluoroborate lithium salts, are different. In particular, the type and amount of the mixed solution differ depending on the type of lithium cyanofluoroborate. Next, the optimum conditions for crystallization due to the difference in the types of these cyanofluoroborate lithium salts will be described.

(Suitable conditions for crystallizing Li · BF ₂ (CN) ₂ )
In order to crystallize Li · BF ₂ (CN) ₂ in a solvent containing acetonitrile and reduce the compound having an isocyanide group as an impurity, it is preferable to employ the following method. Specifically, Li · BF ₂ (CN) ₂ containing a compound having an isocyanide group is preferably crystallized in a mixed solution containing acetonitrile and a halogen-based solvent, particularly chloroform.

In this case, it is preferable to use 100 parts by mass or more and 700 parts by mass or less of a mixed solution containing acetonitrile and a halogenated solvent with respect to 100 parts by mass of Li · BF ₂ (CN) ₂ containing a compound having an isocyanide group. 200 parts by mass or more and 600 parts by mass or less are preferable. In this case, in the mixed solution containing acetonitrile and the halogen solvent, when acetonitrile is 100 parts by mass, the halogen solvent is 50 parts by mass or more and 500 parts by mass or less, and further 100 parts by mass or more and 300 parts by mass or less. It is preferable to do.

Further, the temperature at which Li · BF ₂ (CN) ₂ containing “the compound having an isocyanide group” is dissolved in a mixed solution containing acetonitrile and a halogen-based solvent is preferably 40 ° C. or higher and 75 ° C. or lower. On the other hand, the temperature at which the Li · BF ₂ (CN) ₂ crystals are precipitated is preferably 10 ° C. or higher and 30 ° C. or lower.

According to the above method, it can be reduced efficiently compound from _Li · BF _{2 (CN)} 2 having an isocyanide group. As a result, the obtained Li · BF ₂ (CN) ₂ is considered to have improved heat resistance, but it is difficult to discolor even if it is held at a high temperature exceeding 80 ° C.

(Suitable conditions for crystallizing Li · BF (CN) ₃ )
In order to crystallize Li · BF (CN) ₃ in a solvent containing acetonitrile and reduce impurities “compound having an isocyanide group”, the following method is preferably employed. Specifically, it is preferable to crystallize Li · BF (CN) ₃ containing a compound having an isocyanide group in a mixed solution of acetonitrile and alcohol, particularly, a mixed solution containing acetonitrile and ethanol.

In this case, it is preferable to use 50 parts by mass or more and 300 parts by mass or less of a mixed solution containing acetonitrile and alcohol with respect to 100 parts by mass of Li · BF (CN) ₃ including the “compound having an isocyanide group”. Furthermore, it is preferable to use 100 to 250 parts by mass. In this case, in the mixed solution containing acetonitrile and alcohol, when acetonitrile is 100 parts by mass, the alcohol is preferably 10 parts by mass to 100 parts by mass, and more preferably 10 parts by mass to 50 parts by mass. .

Further, the temperature at which Li · BF (CN) ₃ containing “the compound having an isocyanide group” is dissolved in the mixed solution is preferably 40 ° C. or higher and 75 ° C. or lower. On the other hand, the temperature at which the Li · BF (CN) ₃ crystals are precipitated is preferably 10 ° C. or higher and 30 ° C. or lower.

If the above method is followed, the compound which has an isocyanide group from Li * BF (CN) ₃ can be reduced efficiently. As a result, the obtained Li · BF (CN) ₃ is considered to have improved heat resistance, but even when held at a high temperature exceeding 80 ° C., it is difficult to discolor.
Next, the nonaqueous electrolytic solution of the present invention will be described.

(Nonaqueous electrolyte)
The nonaqueous electrolytic solution of the present invention contains a cyanofluoroborate lithium salt represented by the above formula (1), and the content of the “compound having an isocyanide group” is 2 × 10 ⁻⁴ mol / L or less. Electrolytic solution. In addition, this non-aqueous electrolyte refers to the electrolyte which does not contain water. However, water of 1000 ppm mass or less mixed unavoidably is not excluded. However, water is most preferably 0 ppm in mass.

As the cyanofluoroborate lithium salt represented by the formula (1), it is preferable to use at least the main component having 0.02 mol% or less of the “compound having an isocyanide group”. When a cyanofluoroborate lithium salt is used as an electrolyte, a cyanofluoroborate lithium salt in which the “compound having an isocyanide group” is 0.02 mol% or less and a cyanofluoroborate in which the “compound having an isocyanide group” exceeds 0.02 mol%. By using both of the borate lithium salt, a nonaqueous electrolytic solution in which the content of the “compound having an isocyanide group” is 2 × 10 ⁻⁴ mol / L or less can be obtained. However, when a higher-performance nonaqueous electrolytic solution is used, a nonaqueous electrolytic solution can be produced by using a cyanofluoroborate lithium salt in which the “compound having an isocyanide group” is 0.02 mol% or less. preferable.

When a large amount of the “compound having an isocyanide group” is present in the nonaqueous electrolytic solution of the present invention, the effect at the time of high temperature use is reduced when used as an electrolytic solution for an electricity storage device. Therefore, the concentration of the “compound having an isocyanide group” contained in the non-aqueous electrolyte is more preferably 1 × 10 ⁻⁴ mol / L or less, and further preferably 2 × 10 ⁻⁵ mol / L or less. preferable. The lower limit of the concentration of the “compound having an isocyanide group” is most preferably 0 mol / L or less, but considering industrial production, the lower limit of the content of the compound having an isocyanide group contained in the nonaqueous electrolytic solution The value is 1 × 10 ⁻⁷ mol / L.

  In the nonaqueous electrolytic solution of the present invention, the content of all lithium salts contained in the nonaqueous electrolytic solution is preferably 0.3 to 4 mol / L, and usually 0.3 mol / L in the nonaqueous electrolytic solution. As mentioned above, More preferably, it is 0.5 mol / L or more, More preferably, it is 0.7 mol / L or more, Usually, 4 mol / L or less, More preferably, it is 3 mol / L or less, More preferably, it is 1.5 mol / L or less. If it is this density | concentration, the density | concentration of the viscosity of electrolyte solution is appropriate, and the density | concentration of the lithium ion which is a medium of an electric current is too small, and can obtain appropriate electrical conductivity. The total lithium salt content is represented by the formula (1) which is an essential component and a lithium salt other than the cyanofluoroborate lithium salt represented by the formula (1), which is blended as necessary. The total content of lithium cyanofluoroborate.

  Among them, the content of the cyanofluoroborate lithium salt represented by the formula (1) in the non-aqueous electrolyte is preferably 0.3 to 4 mol / L, more preferably 0.5 to 3 mol / L, and still more preferably. Is 0.7 to 1.5 mol / L.

(Other lithium salts)
In the present invention, as described above, other lithium salts other than the cyanofluoroborate lithium salt represented by the formula (1) can be included. Other lithium salts include CF ₃ SO ₃ Li, LiN (FSO ₂ ) ₂ , LiN (FSO ₂ ) (CF ₃ SO ₂ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ). ₂ , lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiC (FSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluorooxalate phosphate, lithium difluorobisoxalatophosphate, LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiPF ₃ (CF ₃ ) _{3, LiPF 3 (C 2 F} 5) 3 organolithium salt such as Etc. and LiPF _6, inorganic lithium salts such as LiBF _4, LiClO ₄ and the like. Among these, in order to exert an excellent effect, it is preferably at least one lithium compound selected from the group consisting of LiPF ₆ , LiBF ₄ , LiBF ₂ CN ₂ , and LiBFCN ₃ , and LiPF ₆ , and / or LiBF ₄ is more preferable. Furthermore, in view of solubility in organic solvent (non-aqueous solvent) and conductivity, LiPF ₆ is particularly preferable.

  The other lithium salts may be used alone or in combination of two or more.

  The blending ratio of these other lithium salts is preferably less than 50 mol% and more preferably 30 mol% or less in the total lithium salt. Here, as described above, the total lithium salt is the total of lithium salts contained in the nonaqueous electrolytic solution, that is, the total of the cyanofluoroborate lithium salt represented by the formula (1) and other lithium salts. Represents.

  When the other lithium salt is blended, depending on the salt to be blended, the viscosity of the non-aqueous electrolyte increases and the electrical conductivity decreases, or the electrochemical stability and high-temperature stability of the non-aqueous electrolyte decrease. There is a fear. Therefore, an embodiment in which no other lithium salt is contained is preferable.

<Nonaqueous electrolyte; other additives>
The nonaqueous electrolytic solution of the present invention may contain an additive used for an existing battery or an electrolytic solution of an electric double layer capacitor. The electrolyte for a lithium ion battery contains various additives for the purpose of flame retardancy and cycle characteristics improvement, but the existing additive can be used as it is for the non-aqueous electrolyte. Examples of the additive include unsaturated carbonates containing double bonds and fluorinated carbonates.

  Specific examples of the unsaturated carbonate containing a double bond include vinylene carbonate and vinyl ethylene carbonate. Specific examples of the fluorinated carbonate include a fluorinated dimethyl carbonate derivative and a fluorinated ethyl methyl carbonate derivative. And fluorinated diethyl carbonate derivatives.

(Configuration of non-aqueous electrolyte)
The non-aqueous electrolyte of the present invention can be classified into the following two. That is, one is a non-electrolytic solution containing an organic solvent as a non-aqueous solvent. The other is a non-electrolytic solution that does not contain an organic solvent and uses an ionic substance as a non-aqueous solvent as a non-aqueous solvent. Each will be described below.

((I) -1 Nonaqueous electrolytic solution containing organic solvent)
When the non-aqueous electrolyte contains an organic solvent, it is a non-aqueous electrolyte in which at least the cyanofluoroborate lithium salt represented by the formula (1) is dissolved in a non-aqueous solvent that is an organic solvent, The compound having an isocyanide group must be 2 × 10 ⁻⁴ mol / L or less.

((I) -2 non-aqueous solvent; organic solvent)
The non-aqueous solvent that is an organic solvent preferably contains at least one selected from the group consisting of a chain carbonate, a cyclic carbonate, a chain ester, a lactone, and an ether. This non-aqueous solvent does not contain water. Examples of the organic solvent that can be used in the present invention include the following organic solvents (non-aqueous solvents).

  As the chain carbonate, a chain carbonate having 3 to 6 carbon atoms is preferable. Specific examples of the chain carbonate include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

  As a cyclic carbonate, a C3-C6 cyclic carbonate is preferable. Specific examples of the cyclic carbonate include ethylene carbonate and propylene carbonate.

  As the chain ester, a chain ester having 3 to 6 carbon atoms is preferable. Specific examples of the chain ester include ethyl propionate, methyl propionate, ethyl acetate, and methyl acetate.

  Examples of the lactone include lactones having 3 to 6 carbon atoms. Specific examples of the lactone include γ-butyrolactone.

  As ether, C3-C8 ether is preferable. Specific ethers include dimethoxyethane, ethoxymethoxyethane, diethoxyethane, and triethylene glycol dimethyl ether.

  Of the organic solvents (nonaqueous solvents) exemplified above, those that are solid when the electrolytic solution is prepared or used are mixed with the above-mentioned other organic solvents (nonaqueous solvents) that are liquid. It can be used as a mixed solvent.

  Organic solvents other than those described above are generally unsuitable as electrolyte solutions because of insufficient electrochemical stability, low solubility of electrolyte salts, high viscosity and low electrical conductivity.

  The said solvent may be used individually by 1 type, or may use 2 or more types together. For example, it is known that good solubility and high electrical conductivity can be obtained by combining a high dielectric constant solvent such as cyclic carbonate with a low viscosity solvent such as chain carbonate and chain ester. These can be preferably used.

  Among them, it is preferable to use a cyclic carbonate in that the solubility of the electrolyte salt is good and the electrochemical stability is high. Furthermore, considering the solubility of the lithium salt and the performance of the resulting electrolyte (excellent electrical conductivity and electrochemical stability), a mixed solvent of chain carbonate and cyclic carbonate is used as the non-aqueous solvent. It is preferable to do.

  When the mixed solvent is used, the viscosity of the electrolytic solution can be easily adjusted and the electrical conductivity can be increased when the linear carbonate content in the mixed solvent is 15% or more by volume% (23 ° C.). Therefore, it is suitable. In addition, when the chain carbonate content is 90% or less in terms of volume% (23 ° C.), a decrease in electrical conductivity due to a decrease in the dielectric constant of the solvent can be reduced. For this reason, when a mixed solvent is used, the chain carbonate content is preferably 15% to 90%, the cyclic carbonate content is preferably 10% to 85%, and the chain carbonate content is 20% to 85%. %, More preferably the cyclic carbonate content is 15% to 80%, the chain carbonate content is 25% to 80%, and the cyclic carbonate content is 20% to 75%. Preferred (however, the total volume% of the chain carbonate and cyclic carbonate at 23 ° C. is 100%). Among the above mixed solvents, when ethylene carbonate is used as the cyclic carbonate, the linear carbonate is 40% to 85% and the ethylene carbonate is 15% to 60% as volume% (23 ° C.). The chain carbonate is more preferably 45% to 80%, and the ethylene carbonate is more preferably 20% to 55%.

((I) -3 Nonaqueous Electrolyte Production Method Containing Organic Solvent)
The nonaqueous electrolytic solution of the present invention can be obtained, for example, by adding a lithium salt to the nonaqueous solvent of the organic solvent and further adding a predetermined amount of additives. At this time, it is preferable that the organic solvent, other additives and the like are purified in advance and have as few impurities as possible. Moreover, it is desirable to carry out in a low moisture environment such as a dry room in order to avoid mixing of moisture.

((Ii) -1 Nonaqueous electrolyte using ionic substance as nonaqueous solvent)
This non-aqueous electrolyte preferably has a lithium cation ratio of 1 to 60 mol% in a total of 100 mol% of the lithium cation and the organic onium cation. The proportion of the lithium cation is usually 1 mol% or more, more preferably 3 mol% or more, particularly preferably 5 mol% or more, and usually 40 mol% or less, preferably 30 mol% or less. If it is in the said range, the ratio of the lithium cation which is a medium of an electric current is not too small, the range of the viscosity of electrolyte solution is suitable, and appropriate electrical conductivity can be obtained. When the ratio of lithium cations is lower than this range, there is a possibility that current will hardly flow. Moreover, when the ratio of a lithium ion is too high, there exists a possibility that the viscosity of a non-aqueous electrolyte may become high or lithium salt may precipitate easily. That is, when the lithium cation ratio is out of the range of 1 to 60 mol%, high electric conductivity may not be obtained. Therefore, from the viewpoint of obtaining preferable electrical conductivity, the proportion of the lithium cation is preferably 1 to 40 mol%, more preferably 3 to 40 mol%, and further preferably 5 to 30 mol%. The nonaqueous electrolytic solution of the present invention has high lithium salt solubility. Therefore, even when the proportion of the lithium cation is relatively high, precipitation of the lithium salt can be suppressed.

In the nonaqueous electrolytic solution of the present invention, an anion is represented by the following formula (2) in 100 mol% of the anion contained in the ionic substance.
^{_{BF a (CN) 4-a}} - (2)
(In formula (I), a is an integer of 1 to 3)
It is preferable to consist of a cyanofluoroborate anion represented by That is, it is an anion portion excluding lithium of the cyanofluoroborate lithium salt represented by the formula (1).

  The proportion of the cyanofluoroborate anion is 30 mol% or more, preferably 60 mol% or more, particularly preferably 90 mol% or more, and most preferably 100 mol% in 100 mol% of anions contained in the ionic substance. is there. The electrolytic solution containing the cyanofluoroborate anion has the advantages of high electrochemical stability and high conductivity. Further, by including the cyanofluoroborate anion, the ionic substance can have a low viscosity and a low melting point.

In said formula (2), a is an integer of 1-3. Therefore, the nonaqueous electrolytic solution of the present invention contains at least one selected from the group consisting of BF (CN) ₃ ⁻ , BF ₂ (CN) ₂ ⁻ and BF ₃ (CN) ⁻ as the cyanofluoroborate anion. These cyanofluoroborate anions may be used alone or in combination of two or more. Among these, it is preferable to use tricyanofluoroborate anion (BF (CN) ₃ ⁻ ) and dicyanodifluoroborate anion (BF ₂ (CN) ₂ ⁻ ) alone or as a mixture. In the case of a mixture, it is preferable to use 1 to 99 mol% of tricyanofluoroborate anion and 1 to 99 mol% of dicyanodifluoroborate anion in 100 mol% of anions.

All the anions contained in the non-aqueous electrolyte of the present invention may be the cyanofluoroborate anion, but other anions may be contained. As the other anion, an existing anion can be used without particular limitation. As other anions, for example, CF ₃ SO ₃ ⁻ , N (FSO ₂ ) ₂ ⁻ , N (FSO ₂ ) (CF ₃ SO ₂ ) ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , N (C ₂ F ₅ SO ₂ ) ₂ ⁻ , cyclic 1,2-perfluoroethanedisulfonylimide anion, cyclic 1,3-perfluoropropane disulfonylimide anion, C (FSO ₂ ) ₃ ⁻ , C (CF ₃ SO ₂ ) ₃ ⁻ , C (C ₂ F ₅ SO ₂ ) ₃ ⁻ , bisoxalatoborate anion, difluorooxalatoborate anion, tetrafluorooxalatophosphate anion, difluorobisoxalatophosphate anion, BF ₃ CF ₃ ⁻ , BF ₃ C ₂ Anions constituting organic lithium salts such as F ₅ ⁻ , PF ₃ (CF ₃ ) ₃ ⁻ , B (CN) ₄ ⁻ and PF ₃ (C ₂ F ₅ ) ₃ ⁻ ; PF ₆ ⁻ , BF ₄ ⁻ and ClO ₄ ^- inorganic, such as lithium Examples include anions constituting um salts. Among them, BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (FSO ₂ ) ₂ N ^{− and the} like are particularly preferably used because an electrolytic solution having high electrochemical stability and high conductivity can be obtained. I can do things.

((Ii) -2 Method for producing non-aqueous electrolyte using ionic substance as non-aqueous solvent)
The method for producing the ionic substance constituting the nonaqueous electrolytic solution of the present invention is not particularly limited. For example, the following formula (3)
_{^{A + · BF a (CN)}} 4-a - (3)
(In formula (3), A ⁺ represents an organic onium cation, and a is an integer of 1 to 3)
In the cyanofluoroborate salt represented by the following formula (4) in the range of 1 to 60 mol% of the lithium cation in 100 mol% of all cations,
Li ⁺ · X ⁻ (4)
(In formula (4), X ⁻ represents an anion)
It can obtain by melt | dissolving lithium salt shown by these.

The organic onium cation A ⁺ in the above formula (3) is preferably an organic ammonium cation or an aromatic heterocyclic compound cation. In the case where an organic ammonium cation or an aromatic heterocyclic compound cation is present, BF ₂ (NC) (CN) ⁻ , BF (NC) (CN) ₂ in the state where the solvent is distilled off from the nonaqueous electrolytic solution. The anion of ⁻ can be quantified in the form of a salt with Li ion and a cation other than Li (in this case, an organic ammonium cation or an aromatic heterocyclic compound cation).

The cyanofluoroborate salt represented by the above formula (3) is
Following formula (5)
_{^{M + · BF a (CN)}} 4-a - (5)
(In Formula (5), a is an integer of 1-3 and M ^<+> is a metal ion.)
Can be obtained by a salt exchange method in which a metal salt of a cyanofluoroborate anion and a halogen salt of an organic onium cation are mixed, or a direct quaternization method in which an organic onium cation precursor is reacted with an asymmetric anion precursor. . Among these, the salt exchange method is preferably used because of the ease of reaction. The metal salt represented by the formula (5) corresponds to the “cyanofluoroborate salt” described in (Method for producing cyanofluoroborate lithium salt).

Among the cyanofluoroborate salts represented by the formula (5), when M ⁺ is a lithium ion, that is, when the cyanofluoroborate lithium salt represented by the formula (1) is used, the lithium ion battery is used. It can be suitably used for (a lithium battery, a lithium ion battery, a lithium ion capacitor, etc.). In addition, when a cyanofluoroborate lithium salt in which the “compound having an isocyanide group” is reduced to 0.02 mol% or less is used, the content of the compound having an isocyanide group contained in the non-aqueous electrolyte is reduced. Can do.

In the present invention, the nonaqueous electrolytic solution is preferably one in which the anion represented by the formula (2) is 100 mol% in 100 mol% of the anion contained in the ionic substance, and X ⁻ represented by the formula (4) is cyano. It is preferably a fluoroborate anion (a cyanofluoroborate lithium salt represented by the formula (1)).

  The non-aqueous electrolyte described above can be used as an electrolyte for an electricity storage device. Next, the electricity storage device will be described.

<Power storage device>
The non-aqueous electrolyte can be used for power storage devices such as lithium batteries (lithium primary batteries), lithium ion batteries (lithium secondary batteries), and lithium ion capacitors. Among these, it is more preferable to use as a lithium battery and a lithium ion battery, and it is most preferable to use as a lithium ion battery. Further, the nonaqueous electrolytic solution may be used in a gel form as well as in a liquid form. Furthermore, the non-aqueous electrolyte of the present invention can be used for a solid polymer electrolyte.

The electricity storage device of the present invention is a nonaqueous electrolytic solution containing a cyanofluoroborate lithium salt represented by the above formula (1) in which “the compound having an isocyanide group” is 0.02 mol% or less, or represented by the above formula (1). The non-aqueous electrolyte containing the cyanofluoroborate lithium salt and the “compound having an isocyanide group” at 2 × 10 ⁻⁴ mol / L or less is used, so that the effect at high temperature use can be enhanced. .

<Lithium battery>
The lithium battery includes a negative electrode, a positive electrode, a separator disposed between the positive electrode and the negative electrode, and the nonaqueous electrolytic solution of the present invention.

  The lithium battery has the same configuration as the known lithium battery except for the non-aqueous electrolyte. Usually, the positive electrode and the negative electrode are laminated through a porous film impregnated with the non-aqueous electrolyte, and these are the cases. It has the form stored in. Therefore, the shape of the lithium battery is not particularly limited, and may be any of a cylindrical shape, a square shape, a laminate shape, a coin shape, a large size, and the like.

  In the negative electrode, at least one selected from the group consisting of lithium and lithium alloys is used as an active material.

  The positive electrode contains a positive electrode active material, and preferably further contains a conductive material and a binder. As the positive electrode active material, materials commonly used in the field of lithium batteries can be used as they are, and among them, metal oxides such as manganese dioxide, graphite fluoride, thionyl chloride and the like can be preferably used. Manganese dioxide is particularly preferable because of its good discharge characteristics.

  The nonaqueous electrolytic solution of the present invention containing the polyvalent onium compound represented by the formula (1) can suppress an increase in resistance after high-temperature storage and can reduce a decrease in discharge capacity at a low temperature.

<Lithium ion battery>
The lithium ion battery includes a negative electrode and a positive electrode that can occlude and release lithium ions, a separator disposed between the positive electrode and the negative electrode, and the nonaqueous electrolytic solution of the present invention.

  The lithium ion battery is the same as the known lithium ion battery in terms of the configuration other than the non-aqueous electrolyte, and usually the positive electrode and the negative electrode are laminated through the porous film impregnated with the non-aqueous electrolyte, These have the form accommodated in the case. Therefore, the shape of the lithium ion battery is not particularly limited, and may be any of a cylindrical shape, a square shape, a laminate shape, a coin shape, a large size, and the like.

  A negative electrode used for a lithium ion battery has a negative electrode active material layer on a current collector. The negative electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. Specific examples thereof include carbonaceous materials, alloy-based materials, lithium-containing metal composite oxide materials, and the like. These may be used individually by 1 type, and may be used together combining 2 or more types arbitrarily.

  Any positive electrode active material can be used without particular limitation as long as it can electrochemically occlude and release lithium ions. The positive electrode active material is preferably a material containing lithium and at least one transition metal. Specific examples include lithium transition metal composite oxides and lithium-containing transition metal phosphate compounds. These positive electrode active materials may be used alone or in any combination of two or more.

  The nonaqueous electrolytic solution of the present invention containing a cyanofluoroborate salt in which the isocyanide group in the salt is 0.02 mol% or less based on the nitrile group can remarkably suppress an increase in resistance after high-temperature storage.

<Lithium ion capacitor>
A lithium ion capacitor (LIC) is a power storage device that uses a carbon material such as graphite as a negative electrode and stores energy using lithium ion intercalation thereto. Examples of the positive electrode include those using an electric double layer between an activated carbon electrode and an electrolytic solution, those using a π-conjugated polymer electrode doping / dedoping reaction, and the like.

  Since the above-mentioned electrolytic solution is used as the electrolytic solution, LIC can remarkably suppress an increase in resistance after high-temperature storage.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not limited to a following example. First, a method for analyzing isocyanide groups in the sialofluoroborate of the present invention will be described.

(Method for analyzing isocyanide groups in sialofluoroborate)
The compounds having an isocyanide group contained in the sialofluoroborate lithium salt represented by the formula (1) were quantified by the following methods (1) and (2).

(1) NMR measurement 10-20 mg of the cyanofluoroborate lithium salt produced in Production Examples / Examples / Comparative Examples was dissolved in about 1 ml of deuterated methanol, and ¹⁹ F- was measured by JEOL nuclear magnetic resonance apparatus JNM-ECA400II. NMR was measured. The chemical shift value of the ¹⁹ F-NMR spectrum was determined using the KF peak (-125.3 ppm) in the aqueous solution as a standard value. The (BF (CN) ₃ ⁻ ) anion is near −211 ppm, the (BF (NC) (CN) ₂ ⁻ ) anion (compound having an isocyanide group) is −182 ppm, and the (BF ₂ (CN) ₂ ⁻ ) anion is In the vicinity of −153 ppm, in each of the (BF ₂ (NC) (CN) ⁻ ) anion (compound having an isocyanide group), a quadruple line appeared in the vicinity of −124 ppm, and this was quantified by integrating.

(2) Raman measurement Next, in order to quantify the compound having an isocyanide group contained in the nonaqueous electrolytic solution, a calibration curve was prepared by the following method. First, the powder obtained by vacuum drying of the non-aqueous electrolyte was directly measured with JASCO NSR-7100. The (BF (CN) ₃ ⁻ ) anion is 2230 cm ⁻¹ , the (BF (NC) (CN) ₂ ⁻ ) anion is 2162 cm ⁻¹ , the (BF ₂ (CN) ₂ ⁻ ) anion is 2231 cm ⁻¹ , (BF ₂ ( For the NC) (CN) ⁻ ) anion, a peak was observed at 2166 cm ⁻¹ . The concentration of the “compound having an isocyanide group” with respect to the cyanofluoroborate salt is calculated from the above CN and NC ratio. By converting the concentration of the cyanofluoroborate in the nonaqueous electrolyte, the “isocyanide group in the nonaqueous electrolyte” The “compound with” concentration was determined.

In each sample, the amount of “compound having an isocyanide group” is quantified by the NMR measurement of (1). Therefore, the peak intensity of the (BF (CN) ₃ ⁻ ) anion and (BF ₂ (CN) ₂ ⁻ ) anion cyanofluoroborate anion measured in the Raman measurement of (2),
The ratio of the (BF (NC) (CN) ₂ ⁻ ) anion and the peak intensity of the compound having an isocyanide group of the (BF ₂ (NC) (CN) ⁻ ) anion;
From the quantitative results measured by NMR in (1), a calibration curve was created to determine the relationship between the peak intensity ratio and the content of the “compound having an isocyanide group”.

In the non-aqueous electrolyte using the (BF (CN) ₃ ⁻ ) anion, the intensity ratio of peak (2162 cm ⁻¹ ) / peak (2230 cm ⁻¹ ) in the Raman spectrum was measured, and (BF ₂ (CN) ₂ ^-) in the non-aqueous electrolyte solution using an anion, by measuring the intensity ratio of the peak (2166cm ^-1) / peak (2231cm ^-1), it was determined the content of "the compound having an isocyanide group".

Note that even when the anion of BF ₂ (NC) (CN) ⁻ , BF (NC) (CN) ₂ ^— forms a salt with Li ion or a cation other than Li, ¹⁹ F-NMR, and In the Raman measurement, the observed peak position hardly changes. Moreover, (2) The value calculated | required using the analytical curve created by the Raman measurement, and the fixed_quantity | quantitative_assay result calculated | required using (1) NMR became the same.

(Measurement method of other impurities)
For impurities other than “compound having an isocyanide group”, 0.2 g of a sample was weighed, ultrapure water was added and completely dissolved, and a solution adjusted to a total amount of 100 g was prepared as an ICP light emitting device (thermoscience). Fick, iCAP 6500 DUO) and ion chromatography (Nihon Dionex, ICS-2100).

Production Example 1 Synthesis of LiBF (CN) ₃ 9.4 g of LiBF ₄ was placed in a well-dried round bottom flask with a cooling tube, and the inside was replaced with nitrogen. Further, 70 g of trimethylsilylcyanide was added, heated to 125 ° C. in an oil bath and refluxed for 1 week. After returning to room temperature, vacuum drying was performed at a temperature of 80 ° C. or lower to obtain 9.4 g of a crude product. 30 ml of acetonitrile was added to the residue, stirred and filtered to obtain 8.9 g (77%) of light yellow powder.

When 3 mg of a pale yellow powder was dissolved in 4 ml of deuterated methanol and a ¹⁹ F-NMR spectrum was measured, a quadruple line of B F (CN) ₃ near −211 ppm and a B F ₂ (CN) ₂ near −153 ppm. A quadruple line due to B F (NC) (CN) ₂ was observed around -182 ppm. From the respective peak area ratios, the abundance ratio of each boron anion was BF (CN) ₃ : BF ₂ (CN) ₂ : BF (NC) (CN) ₂ = 100: 2.9: 1.1. From this, it was confirmed that the concentration of the “compound having an isocyanide group (NC group)” in LiBF (CN) ₃ was 1.1 mol%. This value was the same as the value calculated using the calibration curve from the Raman measurement of (2). The results are summarized in Table 2 together with the amounts of other impurities.

Production Example 2 Synthesis of LiBF ₂ (CN) ₂ 5 g of acetonitrile was added to a round bottom flask containing 3.0 g of KCN, and 5.5 ml of BF ₃ etherate was added dropwise using a dropping funnel and stirred for 2 hours. The solution portion was collected, and the residue was washed several times with acetonitrile with a total amount of 20 ml. The washing solution and the previously recovered solution portion were combined and distilled under reduced pressure to obtain 2.3 g of a light yellow powder. The obtained powder was dissolved in 25 ml of water, 2.5 ml of concentrated hydrochloric acid and 3 ml of tripropylamine were added and stirred, and further 25 ml of methylene chloride was added to extract the methylene chloride layer. This was dried under reduced pressure and then vacuum dried at room temperature overnight. Thereafter, 5 ml of ethanol and 0.3 g of lithium hydroxide were added to the obtained dried product and stirred for 4 hours, followed by drying under reduced pressure. The residue was extracted with 15 ml of acetonitrile. The extract was dried under reduced pressure and then vacuum dried overnight to obtain 1.9 g of white powder.

When 3 mg of white powder was dissolved in 4 ml of deuterated methanol and a ¹⁹ F-NMR spectrum was measured, a quadruple line of B F ₂ (CN) ₂ near −153 ppm and B F ₂ (NC) near −124 ppm ( A quadruple line due to CN) was observed. The respective area ratios were BF ₂ (CN) ₂ : BF ₂ (NC) (CN) = 100: 3.4. From this, it was confirmed that the concentration of the “compound having an isocyanide group (NC group)” in LiF ₂ (CN) ₂ was 1.7 mol%. This value was the same as the value calculated using the calibration curve from the Raman measurement of (2). The results are summarized in Table 1 together with the amounts of other impurities.

The LiBF ₂ (CN) ₂ 2.9 g prepared in Example 1 LiBF ₂ (CN) ₂ in the purified preparation example 2 were collected in a recovery flask, acetonitrile 5.5 g (7.0 ml) added to the 60 ° C. in an oil bath Upon heating, the LiBF ₂ (CN) ₂ was completely dissolved. Further, 7.4 g (5 ml) of chloroform was added, and after stirring well, the mixture was allowed to stand at a temperature range of 13 ° C. to 23 ° C. for 30 minutes. White needle crystals precipitated in the mixed solution were filtered under reduced pressure with a funnel, and the filtrate was washed with a mixed solution containing 3.5 ml of acetonitrile and 2.5 ml of chloroform. Then, it vacuum-dried at 85 degreeC for 8 hours, and collect | recovered 1.7 g of white needle-like crystals. The obtained crystals were measured by the Raman measurement method of (2) above, and the content of the “compound having an isocyanide group” was confirmed to be 1.7 mol% before purification, but 0.0055 mol% after purification. became. The results are summarized in Table 1 together with other impurities.

Example 2
In Example 1, a mixed solution containing 5.5 g (7.0 ml) of acetonitrile and 6.6 g (4.5 ml) of chloroform was used and heated to 60 ° C. in an oil bath, and the LiBF ₂ (CN) ₂ was completely removed. Was dissolved in the temperature range of 13 ° C. to 23 ° C. for 30 minutes, and the same operation as in Example 1 was performed to obtain 1.3 g of LiBF ₂ (CN) ₂ crystals. The obtained crystals were measured by the Raman measurement method of (2) above, and the content of the “compound having an isocyanide group” was confirmed to be 1.7 mol% before purification, but 0.0077 mol% after purification. became. The results are summarized in Table 1 together with other impurities.

Comparative Example 1
In Example 1, instead of the mixed solution. The same operation as in Example 1 was carried out except that 5.5 g (7.0 ml) of acetonitrile was used for recrystallization. 2.1 g of reddish brown crystals were obtained. The obtained crystals were measured by the Raman measurement method of (2) above, and the content of the “compound having an isocyanide group” was confirmed to be 1.7 mol% before purification, but 1.6 mol% after purification. there were.

Comparative Example 2
In Example 1, the same operation was performed using only 5.0 ml of chloroform. A reddish brown liquid was obtained, which was filtered using 5A filter paper and then vacuum dried to obtain 2.8 g of a reddish brown substance. When the content of the “compound having an isocyanide group” was confirmed by measuring the obtained substance by the Raman measurement method of (2) above, it was 1.7 mol% before purification, but it was 1.7 mol% after purification. there were.

Comparative Examples 3-6
In Example 1, instead of acetonitrile, the same volume of γ-butyrolactone (Comparative Example 3), propylene carbonate (Comparative Example 4), dioxane (Comparative Example 5), tetrahydrofuran; THF (Comparative Example 6) was used. The same operation was performed to precipitate crystals. The amount of impurities in the obtained crystal is summarized in Table 1.

Comparative Example 7
2.9 g of LiBF ₂ (CN) ₂ produced in Production Example 2 was dissolved in 5 g of ethanol, stored in a container containing 1 g of molecular sieve for 2 days (48 hours), and then filtered using 5A filter paper. Ethanol was removed under reduced pressure, followed by vacuum drying at 85 ° C. for 8 hours to obtain 2.3 g of pale yellow crystals. The obtained substance was measured by the Raman measurement method of (2) above, and the content of the “compound having an isocyanide group” was confirmed to be 1.7 mol% before purification, but it was 0.055 mol% after purification. there were.

Example 3 LiBF (CN) takes LiBF of 3.0g obtained in ₃ Purification Preparation 1 (CN) ₃ placed in an eggplant-shaped flask 100 ml, 5 ml of acetonitrile (3.9 g) and 1 ml (0.8 g) Of ethanol was added, stoppered with a cock and heated to 70 ° C. for complete dissolution. The solution was cooled to 23 ° C. and left to precipitate crystals (left for 10 hours). After removing the solution by decantation, 3 ml (2.4 g) of acetonitrile was added and mixed, and then acetonitrile was removed. Further, 3 ml (4.0 g) of methylene chloride was similarly added and mixed, and then methylene chloride was removed. Then, it vacuum-dried and 1.0g of transparent crystals were obtained. The compound having an isocyanide group was 1.1 mol%, but it was 0.013 mol% after purification. The results are summarized in Table 2 together with other impurities.

Example 4
In Example 3, the same operation as in Example 3 was performed, except that a mixed solution containing 4 ml (3.1 g) of acetonitrile and 1.5 ml (1.2 g) of ethanol was used. Crystals of LiBF (CN) ₃ 1 .4 g was obtained. The obtained crystals were measured by the Raman measurement method of (2) above, and the content of the “compound having an isocyanide group” was confirmed. As a result, it was 1.1 mol% before purification, but was 0.008 mol% after purification. became. The results are summarized in Table 2 together with other impurities.

Comparative Example 8
In Example 3, except that ethanol was not added, the same operation as in Example 2 was performed to obtain pale yellow crystals. The obtained crystals were measured by the Raman measurement method of (2) above, and the content of the “compound having an isocyanide group” was confirmed to be 1.1 mol% before purification, but 0.9 mol% after purification. there were.

Comparative Examples 9-12
In Example 3, instead of acetonitrile, the same volume of γ-butyrolactone (Comparative Example 9), propylene carbonate (Comparative Example 10), dioxane (Comparative Example 11), tetrahydrofuran; THF (Comparative Example 12) was used. The same operation was performed to precipitate crystals. The amount of impurities in the obtained crystal is summarized in Table 2.

Comparative Example 13
The same operation was carried out except that 2.9 g of LiBF (CN) ₃ was used instead of 2.9 g of LiBF ₂ (CN) _{2 of} Comparative Example 7 to obtain 2.3 g of light yellow powder 2.3 g. The obtained substance was measured by the Raman measurement method of (2) above, and when the content of “compound having an isocyanide group” was confirmed, it was 1.1 mol% before purification, but 4.3 × 10 ⁻² after purification. mol%.

Example 5
5.39 g of lithium dicyanodifluoroborate (LiBF ₂ (CN) ₂ ) obtained in Example 1 was mixed with a commercially available mixed solvent of ethylene carbonate (EC) -diethyl carbonate (DEC) (nonaqueous solvent; volume ratio EC : DEC = 1: 1) was added and dissolved to prepare a non-aqueous electrolyte solution to 50 ml. At this time, lithium dicyanodifluoroborate in the obtained nonaqueous electrolytic solution was 1.0 mol / L. Moreover, the “compound having an isocyanide group” contained in the obtained nonaqueous electrolytic solution was 5.5 × 10 ⁻⁵ mol / L. The concentration of the “compound having an isocyanide group” contained in the nonaqueous electrolytic solution is calculated from the value calculated from the concentration of the “compound having an isocyanide group” contained in LiBF ₂ (CN) ₂ , and the nonelectrolytic solution. The actual value of the “compound having an isocyanide group” contained therein (the value measured by the Raman measurement method in (2) above) was the same value.

  The obtained non-aqueous electrolyte was used for a battery by the method (3) below, and evaluation was performed by conducting the tests (4) and (5).

(3) Production of battery The positive electrode was made into a slurry with LiNi _1/3 Co _1/3 MN _1/3 O 293 parts as an active material, 4 parts of acetylene black as a conductive material, and 3 parts of polyvinylidene fluoride as a binder. The current collector foil was coated with an applicator, dried at 120 ° C. for 10 minutes and then pressed.

  The negative electrode was prepared in the same process as the positive electrode, using 93 parts of graphite as an active material, 2 parts of acetylene black as a conductive material, and 5 parts of polyvinylidene fluoride as a binder.

  As the separator, a polyethylene microporous film (thickness 20 μm, porosity 40%) was used.

The positive electrode and negative electrode prepared above were punched out to 30 × 50 mm ² , dried at 170 ° C. for 10 hours, respectively, opposed to each other through a separator and inserted into an aluminum laminate, and the non-aqueous prepared in Example 1 The electrolyte was injected, impregnated under reduced pressure, and vacuum sealed to produce a single-layer laminate cell (battery) for battery performance evaluation.

(4) Charge capacity and discharge capacity The initial charge / discharge characteristics (charge capacity and discharge capacity) of the battery prepared in (3) and the discharge capacity measured by evaluation of low temperature operability were measured by the following methods. The charge capacity and discharge capacity measured in the evaluation of the initial charge / discharge characteristics, and the discharge capacity measured in the evaluation of low temperature operability were measured with a charge / discharge test apparatus (HJ0501SD8 manufactured by Hokuto Denko). The conditions of the charge / discharge test were as follows: CCCV charge (0.05C cut) to 4.2V at a current corresponding to 0.2C at room temperature 23 ° C, and then discharged to 2.7V at a current corresponding to 0.2C. . Charging / discharging was repeated under these conditions, and the third result was defined as initial charge / discharge characteristics.

(5) Evaluation of high-temperature storage performance and evaluation of low-temperature operability The resistance measured in the following evaluation of high-temperature storage performance and low-temperature operability was measured with VersaSTAT4 manufactured by Toyo Technica.

<High temperature storage performance>
After the initial charge / discharge test of the battery prepared in (3), the resistance was measured (initial resistance value). Then, it preserve | saved for 10 days at 85 degreeC, and resistance was measured again (resistance after high temperature preservation | save).

  Table 3 summarizes the evaluation results, components used, and amounts used.

Example 6
In Example 5, the same operation as in Example 5 was performed, except that lithium dicyanodifluoroborate containing 7.7 × 10 ⁻³ mol% of the “compound having an isocyanide group” prepared in Example 2 was used. Produced. In addition, the evaluations (4) and (5) were performed. The results are shown in Table 3.

Comparative Example 14
In Example 5, the same operation as in Example 5 was performed, except that lithium dicyanodifluoroborate containing 5.5 × 10 ⁻² mol% of the “compound having an isocyanide group” prepared in Comparative Example 7 was used. Produced. In addition, the evaluations (4) and (5) were performed. The results are shown in Table 3.

Comparative Example 15
A battery was produced in the same manner as in Example 5 except that lithium dicyanodifluoroborate containing 1.1 mol% of the “compound having an isocyanide group” produced in Production Example 2 was used in Example 5. In addition, the evaluations (4) and (5) were performed. The results are shown in Table 3.

Example 7
In Example 5, the same operation as in Example 5 was performed, except that 1.3 × 10 ⁻² mol% lithium tricyanofluoroborate (LiBF (CN) ₃ ) obtained in Example 3 was used. Was made. In addition, the evaluations (4) and (5) were performed. The results are shown in Table 4.

Example 8
In Example 7, the same operation as in Example 7 was performed, except that lithium tricyanofluoroborate containing 8 × 10 ⁻³ mol% of the “compound having an isocyanide group” obtained in Example 4 was used. Produced. In addition, the evaluations (4) and (5) were performed. The results are shown in Table 4.

Comparative Examples 16 and 17
In Example 8, LiBF (CN) ₃ containing 4.3 × 10 ⁻² mol% of the “compound having an isocyanide group” produced in Comparative Example 13 (Comparative Example 16) and “having an isocyanide group” produced in Production Example 1 A battery was produced in the same manner as in Example 8 except that LiBF (CN) ₃ containing 1.1 mol% of “Compound” (Comparative Example 17) was used, and the same evaluation was performed. The results are shown in Table 4.

Example 9
Lithium dicyanodifluoro prepared in Example 1 was added to 98 g of a commercially available mixed solvent of 1 mol / L LiPF ₆ in ethylene carbonate (EC) -diethyl carbonate (DEC) (nonaqueous solvent; volume ratio EC: DEC = 1: 1). A nonaqueous electrolytic solution in which 2 g of borate was dissolved was prepared. Using this non-aqueous electrolyte, a battery was produced in the same manner as in Example 5, and evaluated in the same manner. The results are shown in Table 5.

Example 10
In Example 9, a battery was produced in the same manner as in Example 9, except that lithium tricyanofluoroborate produced in Example 3 was used instead of lithium dicyanodifluoroborate produced in Example 1. The same evaluation was performed. The results are shown in Table 5.

Comparative Example 18
In Example 9, a battery was produced in the same manner as in Example 9, except that lithium dicyanodifluoroborate produced in Production Example 1 was used instead of lithium dicyanodifluoroborate produced in Example 1. Similar evaluations were made. The results are shown in Table 5.

Comparative Example 19
In Example 10, a battery was produced in the same manner as in Example 12 except that lithium tricyanofluoroborate produced in Production Example 2 was used instead of lithium tricyanofluoroborate produced in Example 3. The same evaluation was performed. The results are shown in Table 5.

Example 13
In Example 11, commercially available 2.2 g of lithium dicyanodifluoroborate salt (0.02 mol) prepared in Example 1 and 12.2 g of commercially available electrolyte-grade LiPF ₆ salt (0.08 mol) for Li-ion batteries A non-aqueous electrolyte that was completely dissolved in a mixed solvent of ethylene carbonate (EC) -diethyl carbonate (DEC) (non-aqueous solvent; volume ratio EC: DEC = 1: 1) and made up to 100 ml was used. LiCoO2 is used in place of LiNi _1/3 Co _1/3 MN _1/3 O2 as the positive electrode active material, charging to 4.35V instead of CCCV charging to 4.2V, and discharging to 2.7V instead of 2. Discharge up to 5V. A battery was produced in the same manner as in Example 11 except for the changes as described above, and an initial evaluation was performed in the same manner. Then, after charging and storing at 85 ° C. for 10 days, the battery was discharged at room temperature, and the discharge capacity was measured. From this result, storage retention ratio (%) = (discharge capacity after storage / discharge capacity before storage) × 100 was calculated. The results are summarized in Table 6.

Comparative Example 20
In Example 13, a battery was produced in the same manner as in Example 13, except that lithium dicyanodifluoroborate produced in Production Example 2 was used instead of lithium dicyanodifluoroborate produced in Example 1. Similar evaluations were made. The results are shown in Table 6.

Claims (9)

A cyanofluoroborate lithium salt represented by the following formula (1) in which the content of a compound having an isocyanide group (—NC group) as an impurity is 0.02 mol% or less.
Li · BF _X (CN) _4-X (1)
(In the formula, X is an integer of 1 to 3). Cyanofluoroborate lithium salt represented by the following formula (1) Li · BF _X (CN) _4-X (1)
(Wherein X is an integer of 1 to 3)
And a content of the compound having an isocyanide group is 2 × 10 ⁻⁴ mol / L or less. Cyanofluoroborate lithium salt represented by the following formula (1) in which the content of the compound having an isocyanide group is 0.02 mol% or less Li · BF _X (CN) _4-X (1)
(Wherein X is an integer of 1 to 3)
The nonaqueous electrolytic solution according to claim 2, comprising:   The nonaqueous electrolytic solution according to claim 2 or 3, further comprising at least one nonaqueous solvent selected from the group consisting of a chain carbonate, a cyclic carbonate, a chain ester, a lactone, and an ether.   Furthermore, lithium salts other than the cyanofluoroborate lithium salt shown by said Formula (1) are included, The non-aqueous electrolyte in any one of Claims 2-4 characterized by the above-mentioned.   The non-aqueous electrolyte solution according to claim 2, wherein the total concentration of all lithium salts contained in the non-aqueous electrolyte solution is 0.3 to 4 mol / L.   A power storage device comprising a positive electrode, a negative electrode, and the nonaqueous electrolytic solution according to claim 2.   The power storage device according to claim 7, wherein the power storage device is a lithium battery, a lithium ion battery, or a lithium ion capacitor. Acetonitrile,
At least one solvent selected from alcohols and halogenated solvents;
A crystal of a cyanofluoroborate lithium salt represented by the following formula (1) is precipitated in a mixed solution containing:
Li · BF _X (CN) _4-X (1)
(X is an integer of 1 to 3).