JP2017004638A - Electrolyte salt, non-aqueous electrolyte containing the electrolyte salt, and electricity storage device using the same - Google Patents

Abstract

An electrolyte salt, a non-aqueous electrolyte, and an electricity storage device including the non-aqueous electrolyte that have both stability at high temperatures and high conductivity at low temperatures.
A cyanofluoroborate lithium salt represented by the following general formula (I): Li.BF _X (CN) _{4 -X} (I) (where X is an integer of 1 to 3),
And an electrolyte salt containing a lithium salt other than the cyanofluoroborate lithium salt,
An electrolyte salt comprising 0.05 mol or more and less than 1 mol of the cyanofluoroborate / lithium salt with respect to 1 mol of a lithium salt other than the cyanofluoroborate / lithium salt.
[Selection] Figure 1

Description

  The present invention relates to a novel electrolyte salt, a novel non-aqueous electrolyte containing the electrolyte salt, and a novel electricity storage device using the non-aqueous electrolyte.

  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, secondary batteries are being developed for in-vehicle applications or natural energy storage applications. For automotive applications, the operating environment temperature is assumed to be -30 ° C to 60 ° C, and it is assumed that the usage environment is severer than the temperature range that has been used in the past. The ionic conductivity of is required. Especially in a high temperature environment, since the cell is enlarged, not only the use environment but also a constant relatively high temperature is exposed by self-heating, and the upper limit temperature of 45 ° C. at which a conventional lithium ion battery is used. Improvement of durability at a higher temperature of 60 ° C. or higher has become an important development issue.

  In addition, in the case of a vehicle-mounted battery or a natural energy storage battery, operation at −30 ° C. is assumed as a use condition, and ion conductivity at a low temperature is also required. In order to avoid a decrease in ionic conductivity at low temperatures, a low-viscosity organic solvent (such as a mixed solvent of ethylene carbonate and ethyl methyl carbonate) is usually used, but most low-viscosity organic solvents are vapors. When the pressure is high and a short circuit occurs in the battery due to dendrite deposition, there is a problem that the safety is lowered, for example, fire is easily generated.

In many cases, an electrolytic solution in which a lithium salt is dissolved in a nonaqueous solvent is used as an electrolytic solution used in an electricity storage device such as the secondary battery. Furthermore, as the non-aqueous solvent, for example, a mixed solvent such as ethylene carbonate, propylene carbonate, and diethyl carbonate is generally used. As the lithium salt, LiPF ₆ , LiBF ₄ or the like is used.

  In addition, as a negative electrode active material of a lithium ion secondary battery, a carbonaceous material capable of inserting and extracting lithium ions, and a metal or alloy-based material using silicon or tin etc. aiming at high capacity, etc. Currently, carbonaceous materials such as natural graphite, artificial graphite, and amorphous carbon are mainly used. 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 positive electrode and a negative electrode with high activity, it is known that the charge / discharge capacity decreases due to a side reaction between the electrode and the electrolyte solution. In order to improve, various studies have been made on non-aqueous solvents, electrolytes, and additives that are components of the electrolytic solution.

The compound (electrolyte salt) used as the electrolyte is LiPF ₆ and LiBF _{4 as} described above. In addition, lithium bistrifluoromethylsulfonylimide (LITFSI), lithium bisfluorosulfonylimide (LiFSI), LiClO ₄ , lithium bis [pentafluoroethanesulfonyl] imide, lithium [trifluoromethanesulfonyl] [nonafluorobutanesulfonyl] imide, lithium Cyclohexafluoropropane-1,3-bis [sulfonyl] imide, lithium bis [oxalate (2-)] borate, lithium trifluoromethyl trifluoroborate, lithium pentafluoroethyl trifluoroborate, lithium heptafluoropropyl trifluoroborate, Lithium tris [pentafluoroethyl] trifluorophosphate, lithium dicyanodifluoroborate, lithium tricyano Ruoroboreto, it has been studied also lithium salt such as lithium tetracyanoborate. Among them, LiPF ₆ and LiBF ₄ are mainly used, and LiPF ₆ is preferably used in consideration of solubility in an organic solvent and conductivity.

And in order to improve the performance of a lithium ion battery, the development which combines the combination of said electrolyte salt and another additive with electrolyte salt is made | formed. For example, an electrolyte salt composition in which LiPF ₆ is used as a main electrolyte salt and LiTFSI or LiFSI is combined therewith has been developed (for example, see Patent Documents 1 to 3). More specifically, Patent Document 1 uses a combination of LiPF ₆ and LiFSI as an electrolyte salt and γ-butyrolactone as a nonaqueous solvent for the purpose of improving the remaining / recovery capacity after charge storage. An example using a solvent is shown. Patent Document 2 shows an example in which a combination of LiPF ₆ and LiTFSI is used as an electrolyte salt and a fluorinated cyclic ester is blended for the purpose of improving high-temperature cycle characteristics. Furthermore, Patent Document 3 uses a combination of LiPF ₆ and LiFSI as an electrolyte salt for the purpose of improving the remaining charge after high temperature and using it under high voltage, and blending fluorinated cyclic carbonate An example is shown.

JP 2004-165151 A JP 2006-294375 A JP 2010-129449 A

  According to the methods described in Patent Documents 1 to 3, a lithium ion battery having excellent performance can be manufactured.

  However, in the above method, although the use characteristics at high temperature are improved, what is actually shown is the characteristics up to 60 ° C., and the characteristics at temperatures exceeding 60 ° C. are shown. Absent. In recent years, the use of lithium ion batteries has been expanded, and repeated use at 60 ° C. is assumed in the usage situation. In addition, in-vehicle applications and the like, the in-vehicle temperature may exceed 70 ° C. under hot weather, and it is desired to maintain characteristics at higher temperatures. At present, there is no development that can fully satisfy these requirements.

For example, LiPF _{6 and the} like are extremely susceptible to hydrolysis and are poor in thermal stability and are known to decompose at 60 ° C. or higher. Use of LiPF ₆ alone at a temperature exceeding 60 ° C. Is difficult. Furthermore, LiPF ₆ reacts with a small amount of moisture to generate hydrogen fluoride (HF). Specifically, during high-temperature storage, LiPF 6 is thermally decomposed (LiPF ₆ → LiF + PF ₅ ), and the generated PF ₅ reacts with water to generate HF. Further, HF and PF5 is also conceivable to cause decomposition of the water is more PF ₆ reacts with an organic solvent to generate water. HF is known to dissolve and corrode metal materials of battery containers and current collectors, and to dissolve positive electrode active materials to elute transition metals and cause battery deterioration. Such deterioration of the battery characteristics occurs even when a slight thermal decomposition of LiPF ₆ occurs in the electrolyte, and occurs remarkably during long-term storage and continuous charge / discharge of the battery. Become.

  Accordingly, an object of the present invention is to provide an electrolyte salt that is electrochemically stable over a wide range and can improve stability at high temperatures, particularly stability at temperatures exceeding 60 ° C., and a non-aqueous solution containing the electromodified salt. It is in providing an electrolyte solution and an electrical storage device using the same. Furthermore, to provide a power storage device with higher performance, it is to provide a power storage device that can be used in a wider temperature range, and in particular, to provide a power storage device that exhibits excellent characteristics even at temperatures below 0 ° C. There is.

  The inventors of the present invention have made extensive studies to solve the above problems. And the mechanism of decomposition | disassembly of the conventional lithium salt (electrolyte salt) was examined, and the method of suppressing the decomposition | disassembly was examined. Specifically, in order to prevent the lithium salt from degrading while not degrading its performance, an additive that can itself act as an excellent electrolyte salt and trap the decomposition product of the main lithium salt is useful. I thought that it might be. As a result, it has been found that the above problem can be solved by using a lithium salt having a cyano group as an additive, and the present invention has been completed.

That is, the present invention relates to the following [1] to [8], for example.
[1] Cyanofluoroborate / lithium salt represented by the following general formula (I) Li · BF _X (CN) _{4 -X} (I) (where X is an integer of 1 to 3),
And an electrolyte salt containing a lithium salt other than the cyanofluoroborate lithium salt,
An electrolyte salt comprising 0.05 mol or more and less than 1 mol of the cyanofluoroborate / lithium salt with respect to 1 mol of a lithium salt other than the cyanofluoroborate / lithium salt.
[2] The electrolyte salt according to [1], wherein the lithium salt other than the cyanofluoroborate / lithium salt is LiPF ₆ or LiBF ₄ .
[3] A non-aqueous electrolyte obtained by dissolving the electrolyte salt according to [1] or [2] in a non-aqueous solvent, wherein the total concentration of all lithium salts contained in the non-electrolyte solution is 0.3 to A non-aqueous electrolyte characterized by being 4 mol / L.
[4] The nonaqueous electrolytic solution according to [3], wherein the nonaqueous solvent is at least one selected from the group consisting of a chain carbonate, a cyclic carbonate, a chain ester, a lactone, and an ether.
[5] The non-aqueous electrolyte according to [3] or [4], which is used for an electricity storage device.
[6] The nonaqueous electrolytic solution according to [3] or [4], which is used for a lithium battery, a lithium ion battery, or a lithium ion capacitor.
[7] An electricity storage device comprising a positive electrode, a negative electrode, and the nonaqueous electrolytic solution according to [3] or [4].
[8] The electricity storage device according to [7], which is a lithium battery, a lithium ion battery, or a lithium ion capacitor.

ADVANTAGE OF THE INVENTION According to this invention, the electrolyte salt which can improve the electrical conductivity in low temperature, especially stability at high temperature, the nonaqueous electrolyte containing this electrolyte salt, and an electrical storage device using the same can be provided. Specifically, by using an electrolytic solution in which an electrolyte salt obtained by combining a lithium salt such as LiPF ₆ and the cyanofluoroborate salt represented by the general formula (I) is used, compared with a conventional electrolytic solution. An electrolytic solution having a wide operating temperature range, which has an equivalent electrical conductivity at room temperature, high conductivity at low temperatures, and is less likely to deteriorate charge / discharge characteristics even after being stored at high temperature after charging, can be obtained. In particular, a lithium battery that is suitably used as a non-aqueous electrolyte for an in-vehicle power storage device or a non-aqueous electrolyte for a large-sized battery for storing natural energy, has low electrochemical characteristics at high temperatures, and operates in a low-temperature environment, An electric storage device such as a lithium ion battery or a lithium ion capacitor can be obtained.

FIG. 4 is a diagram showing measurement results of initial charge / discharge characteristics of Example 1. It is the figure which showed the measurement result of the initial stage charge / discharge characteristic of the comparative example 1. It is the figure which showed the measurement result of the initial stage charge / discharge characteristic of the comparative example 2.

[Electrolyte salt]
The electrolyte salt of the present invention contains at least two types of lithium salts as electrolyte salts. One lithium salt is a cyanofluoroborate / lithium salt represented by the following general formula (I) (hereinafter also referred to as lithium salt (I)).
_{Li · BF X (CN) 4} -X (I) ( provided that, X is an integer of 1 to 3.).

  The electrolyte salt of the present invention is composed of a lithium salt other than the lithium salt (I) (hereinafter also referred to as other lithium salt) as a main component, and a combination of the other lithium salt and the lithium salt (I). Is. First, the lithium salt (I) will be described.

<Lithium salt (I)>
The electrolyte salt of the present invention contains a cyanofluoroborate lithium salt represented by the following general formula (I) as an electrolyte salt.
Li · BF _X (CN) _4-X (I)
In the above formula, X is an integer of 1 to 3.

That is, Li · BF (CN) ₃ , Li · BF ₂ (CN) ₂ and Li · BF ₃ (CN) are used as the lithium salt (I) in the present invention. When X is 0, that is, Li · B (CN) ₄ has problems of insufficient electrochemical stability and low electrical conductivity at a low temperature. Therefore, when combined with other lithium salts, Can not improve. On the other hand, when X is 4, that is, LiBF ₄ has low electrical conductivity, the performance cannot be improved when combined with other lithium salts. In addition, a compound substituted with another group instead of the fluorine atom (F) has a problem of low electrochemical stability and low electrical conductivity, and when combined with other lithium salts, The performance cannot be improved. On the other hand, the lithium salt (I) has the lithium salt (I) because the boron atom is substituted with both a fluorine atom and a cyano group, and the symmetry is lower than that of PF ₆ or BF _4. It is considered that it can be used as the electrolyte salt of the present invention because it has sufficient electrochemical stability by itself and high electrical conductivity particularly at low temperature.

Li · BF ₂ (CN) ₂ and Li · BF (CN) ₃ are relatively stable against water. Therefore, even if some moisture is mixed in, it is difficult to decompose and HF or the like that degrades battery performance is unlikely to occur.

In addition, it is estimated that the lithium salt (I) is likely to trap other decomposition products of the lithium salt, such as HF, etc., and further decomposition of the electrolyte caused by the generation of HF and corrosion of the electrode. It is thought that it can be suppressed. Furthermore, since the ion radius and molecular weight of the anion are small and the symmetry of the anion is low, it is difficult to deposit in a non-aqueous solvent, and the interaction between the compounds is small because the polarity of the anion is small. When combined with salt, it is considered that the performance of the non-aqueous electrolyte at low temperatures can be improved.
Next, the manufacturing method of this lithium salt (I) is demonstrated.

<Method for producing lithium salt (I)>
The lithium salt (I) can be synthesized by a known method. For example, a lithium metal cyanide compound is dissolved in an organic solvent such as acetonitrile and acetone, and BF ₃ gas is blown, or lithium metal It can be synthesized by a method in which a cyanide compound is reacted 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. .

In addition to the above method, the above BF ₃ gas is added to 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. BF ₃ addition compound such as boron trifluoride ether BF ₃ .OEt _{2 is} allowed to act in the presence of an aprotic solvent to synthesize a corresponding alkali metal or alkaline earth metal salt of cyanofluoroborate, This includes a method of synthesizing the lithium salt (I) by performing salt exchange by allowing an inorganic lithium salt such as lithium hydroxide, lithium carbonate, or lithium halide to act.

  Further, when the synthesized lithium salt (I) is used for the non-aqueous electrolyte of the present invention, it is preferable to sufficiently remove impurities by, for example, sufficiently washing with water and drying. Specifically, the metal concentration other than Li is 1000 ppm or less, Na is 20 ppm or less, K is 10 ppm or less, Ca is 10 ppm or less, Fe is 3 ppm or less, and Pb is 10 ppm or less. Preferable (both lithium salt (I) is 100% by mass).

  The electrolyte salt of the present invention contains a lithium salt other than the lithium salt (I) as a main component. Next, other lithium salts will be described.

<Other lithium salts>
The electrolyte salt of the present invention contains a lithium salt other than the lithium salt (I) as a main component. As other lithium salts, existing lithium salts other than the lithium salt (I) can be used without particular limitation. Specifically, as other lithium salts, 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-perfluoropropanedisulfonylimide, LiC (FSO 2) 3,} LiC (CF 3 SO 2) 3, LiC (C ₂ F ₅ SO ₂ ) ₃ , lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluorooxalatophosphate, lithium difluorobisoxalatophosphate, LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiPF _{3 (CF 3) 3, LiPF} 3 (C 2 F 5) 3 and the like organic Lithium salts, and LiPF _6, LiBF _4, and inorganic lithium salts such as LiClO ₄ and the like. Among these, considering the action mechanism of the lithium salt (I), a lithium salt having a fluorine (F) atom in the molecule is preferable, and an inorganic lithium salt of LiPF ₆ or LiBF ₄ is more preferable. In particular, when LiPF ₆ decomposes at 60 ° C., the present invention exhibits a remarkable effect. The other lithium salts may be used alone or in combination of two or more.

[Mixing ratio of electrolyte salt]
The electrolyte salt of the present invention contains 0.05 mol or more and less than 1 mol of lithium salt (I) with respect to 1 mol of the other lithium salt. When the amount of the lithium salt (I) used is 1 mol or more and less than 0.05 mol, the effect of improving the performance of other lithium salts is reduced, which is not preferable. In order to further increase the blending effect of the lithium salt (I), the lithium salt (I) is preferably 0.05 mol or more and 0.5 mol or less with respect to 1 mol of the other lithium salt. More preferably, the amount is from 05 mol to 0.3 mol.

  The electrolyte salt described above can be dissolved in a non-aqueous solvent and used as a non-aqueous electrolyte. Next, the nonaqueous solvent will be described.

<Non-aqueous electrolyte>
<Nonaqueous solvent>
The organic solvent (nonaqueous solvent) used for the nonaqueous electrolytic solution of the present invention is not particularly limited and can be used. When used in Li-ion batteries and Li-ion capacitors, the battery electrolytes include 1) electrochemical stability in the range of use, 2) high solubility in electrolyte salts, and 3) high electrical conductivity due to low viscosity. Is required. In particular, lithium-ion batteries have a charge / discharge potential of about 0 to 4.5 V vs. Li + / Li, which is very wide compared to other batteries, and the solvents that can be used are limited. Chain carbonates, cyclic carbonates, chain-like A solvent selected from the group consisting of esters, lactones and ethers is preferred. Examples of preferable organic solvents 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 usually unsuitable as electrolytes 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 carbonates with a low viscosity solvent such as chain carbonates and chain esters. These can be preferably used.

  Among them, in consideration of the solubility of the lithium salt (I) and the performance of the obtained electrolyte (excellent electrical conductivity and electrochemical stability), a chain carbonate or a cyclic carbonate should be used as a non-aqueous solvent. In particular, it is preferable to use a mixed solvent of a chain carbonate and a cyclic carbonate.

  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%.

  Moreover, since high electrical conductivity can be obtained, it is also preferable to use lactone as a non-aqueous solvent.

  By applying the non-aqueous electrolyte containing this non-aqueous solvent to the battery, it is possible to provide a battery having both high temperature stability and high conductivity at low temperature.

<Additives other than lithium salt>
The non-aqueous electrolyte of the present invention may also contain an additive used for an existing battery or an electric double layer capacitor electrolyte. 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.

<Characteristics of non-aqueous electrolyte>
In the non-aqueous electrolyte of the present invention, the content of all lithium salts (total of other lithium salts and lithium salts) contained in the non-aqueous electrolyte is not particularly limited. Among these, Preferably it is 0.3-4 mol / L, More preferably, it is 0.5-3 mol / L, More preferably, it is 0.7-1.5 mol / L. If the total lithium salt content in the non-aqueous electrolyte is 0.3 to 4 mol / L, the concentration of lithium ions as the current medium is not too small, and the viscosity range of the electrolyte is appropriate and appropriate. Electrical conductivity can be obtained.

  The non-aqueous electrolyte of the present invention (non-electrolytic solution in which an electrolyte salt combining other lithium salt and lithium salt (I) is dissolved in a non-aqueous solvent) is at a high temperature, specifically at a high temperature exceeding 60 ° C. The reason why the storage characteristics can be greatly improved is not necessarily clear, but is considered as follows.

For example, hexafluorophosphate lithium salt (LiPF ₆ ), which is another lithium salt, starts decomposing at around 60 ° C. and is unstable to water, reacts with moisture and decomposes to generate HF. It is a sensitive compound. A lithium ion battery or the like reacts with a solvent or the like at the time of charging, and moisture can easily be generated by the reaction. Therefore, it is considered that LiPF ₆ decomposes at a high temperature (LiPF ₆ → LiF + PF ₅ ), and the generated PF ₅ reacts with an organic solvent that is an electrolyte component to generate water and further decompose (PF ₅ water and Is considered to react with and generate HF). With respect to this decomposition mechanism, it is presumed that the lithium salt (I) to be blended has trapped HF, particularly fluorine ions (F ions) generated during the decomposition, and changed them into harmless forms. That is, F ions generated at the time of decomposition are replaced with CN groups of the lithium salt (I), and the CN ions form a SEI (Solid Electrolyte Interface) film on the electrode surface, thereby suppressing the decomposition of other lithium salts, It is thought that the cycle characteristics at high temperature can be greatly improved. Therefore, when other lithium salt has a fluorine (F) atom in a molecule | numerator, this invention is considered to exhibit the especially outstanding effect.

  Moreover, although the nonaqueous electrolyte of this invention is demonstrated in detail in the following Example, the characteristic in low temperature can also be improved. The reason for this is not clear, but is estimated as follows. The ionic diameter and molecular weight of the anion of the lithium salt (I) are relatively smaller than the ionic diameter and molecular weight of other lithium salt anions, and the symmetry is low. In particular, the molecular weight of the hexafluorophosphate anion is small and the symmetry is low. Therefore, in the non-electrolytic solution of the present invention in which the lithium salt (I) is blended, it is considered that the electrolyte salt hardly precipitates even at a low temperature, and the characteristics at a low temperature can be maintained. In addition, since the polarity of the anion of the lithium salt (I) is small and the interaction between the compounds is small, it is considered that the non-electrolytic solution of the present invention can maintain the characteristics at low temperatures.

<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 uses the other lithium salt and lithium salt (I) as the non-aqueous electrolyte solution, so that it does not deteriorate even when stored at a high temperature of 60 ° C. or higher. It has an electrical conductivity higher than that of the liquid, and can be made into an electrochemically stable electrolyte. This effect is higher than when other lithium salt alone or lithium salt (I) is used alone.

<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 non-aqueous electrolyte of the present invention using the lithium salt (I) and other lithium salts has little deterioration even when stored at a high temperature of 60 ° C. or higher, and is discharged at a current higher than that of an existing lithium battery from room temperature to low temperature. A possible battery can be obtained.

<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.

  Lithium ion batteries are excellent in electrochemical properties at high temperatures even when the end-of-charge voltage is 4.2 V or higher, particularly 4.3 V or higher. Moreover, the lithium ion battery in this invention can be charged / discharged at -40-100 degreeC.

  The non-aqueous electrolyte of the present invention using the lithium salt (I) and other lithium salts has little deterioration even when stored at a high temperature of 60 ° C. or higher, and has a current higher than that of an existing lithium ion battery from room temperature to low temperature. It can be set as the secondary battery which can be charged / discharged.

<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, the LIC can achieve both electrochemical stability at high temperature and high conductivity at low temperature.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these.

(1) Production of battery The positive electrode is made into a slurry form of LiNi _1/3 Co _1/3 Mn _1/3 O293 part 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 prepared in Examples and Comparative Examples. The electrolyte was injected, impregnated under reduced pressure, and vacuum sealed to produce a single-layer laminate cell (battery) for battery performance evaluation.

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

(3) 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 conducting an initial charge / discharge test of the batteries prepared in Examples and Comparative Examples, 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).

<Low temperature operability>
After conducting the initial charge / discharge test of the batteries prepared in Examples and Comparative Examples, the discharge capacity and resistance were measured at −30 ° C. (resistance).

Example 1
2 g of Li · BF ₂ (CN) ₂ was dissolved in 98 g of a mixed solution of ethylene carbonate (EC) -diethyl carbonate (DEC) of 1 mol / L LiPF ₆ (1: 1 23 ° C. volume ratio) purchased from Kishida Chemical Co., Ltd. (1 mol / L LiPF ₆ 0.24 mol / l Li · BF ₂ (CN) ₂ added solution) to prepare a non-aqueous electrolyte. Thereafter, a single-layer laminate cell for battery performance evaluation was produced by the method described in (1) Production of battery. Thereafter, battery characteristics were evaluated according to (2) charge capacity and discharge capacity, (3) evaluation of high-temperature storage performance, and evaluation of low-temperature operability. The evaluation results, the components used, and the amounts used are summarized in Table 1. The measurement results of the initial charge / discharge characteristics are shown in FIG.

Comparative Example 1
Single layer laminate for battery performance evaluation in the same manner as in Example 1 except that a mixed solution (1: 1) of ethylene carbonate (EC) -diethyl carbonate (DEC) of 1 mol / L LiPF ₆ purchased from Kishida Chemical Co., Ltd. was used. A cell was prepared and evaluated in the same manner. The results are summarized in Table 1, and the measurement results of the initial charge / discharge characteristics are shown in FIG.

Comparative Example 2
25 ml of diethyl carbonate (DEC) was added to 33 g of ethylene carbonate (EC) and dissolved. Further, 5.39 g of Li · BF ₂ (CN) ₂ was added and stirred to completely dissolve, and ethylene carbonate (EC) -diethyl carbonate ( A nonaqueous electrolytic solution in which Li · BF ₂ (CN) ₂ was dissolved in a 1: 1 (23 ° C. volume ratio) mixed solvent of DEC at a concentration of 1 mol / L was prepared. A single-layer laminate cell for battery performance evaluation was prepared in the same manner as in Example 1 except that the prepared electrolytic solution was used, and the same evaluation was performed. The results are summarized in Table 1, and the measurement results of the initial charge / discharge characteristics are shown in FIG.

  As shown in Table 1, it was found from the evaluation results of the initial charge / discharge characteristics that the battery produced in Example 1 exhibited the same initial charge / discharge characteristics as the battery produced in Comparative Example 2 at room temperature.

  In addition, from the evaluation results of the high temperature storage performance, the battery produced in Example 1 has a small increase in resistance compared with the battery produced in Comparative Example 1 after high temperature storage (85 ° C., 10 days). It was found to be stable.

  Furthermore, from the evaluation results of the low temperature operability, the battery produced in Example 1 has a higher discharge capacity at a low temperature and a lower resistance than the battery produced in Comparative Example 2, and thus has excellent battery performance at a low temperature. I understood that.

Surprisingly, the non-aqueous electrolyte (Example 1) in which 0.24 mol / L LiBF ₂ CN ₂ and 1 mol / L LiPF ₆ were dissolved in a solution of EC: DEC 1: 1 was LiPF which is easily thermally decomposed. Compared to a 1 mol / L LiBF ₂ CN ₂ non-aqueous electrolyte containing no ₆ (Comparative Example 2), the increase in resistance after storage at high temperatures and the increase in resistance at low temperatures are suppressed. Was maintained and the performance at low temperature was improved.

Claims (8)

Cyanofluoroborate lithium salt represented by the following general formula (I) Li.BF _X (CN) _{4 -X} (I) (where X is an integer of 1 to 3),
And an electrolyte salt containing a lithium salt other than the cyanofluoroborate lithium salt,
An electrolyte salt comprising 0.05 mol or more and less than 1 mol of the cyanofluoroborate / lithium salt with respect to 1 mol of a lithium salt other than the cyanofluoroborate / lithium salt. 2. The electrolyte salt according to claim 1, wherein the lithium salt other than the cyanofluoroborate lithium salt is LiPF ₆ or LiBF ₄ . A non-aqueous electrolyte obtained by dissolving the electrolyte salt according to claim 1 or 2 in a non-aqueous solvent,
A nonaqueous electrolytic solution, wherein the total concentration of all lithium salts contained in the nonelectrolytic solution is 0.3 to 4 mol / L.   The non-aqueous electrolyte according to claim 3, wherein the non-aqueous solvent is at least one selected from the group consisting of a chain carbonate, a cyclic carbonate, a chain ester, a lactone, and an ether.   The nonaqueous electrolytic solution according to claim 3 or 4, wherein the nonaqueous electrolytic solution is used in an electricity storage device.   The nonaqueous electrolytic solution according to claim 3 or 4, which is used for a lithium battery, a lithium ion battery, or a lithium ion capacitor.   An electrical storage device comprising a positive electrode, a negative electrode, and the nonaqueous electrolytic solution according to claim 3.   The power storage device according to claim 7, which is a lithium battery, a lithium ion battery, or a lithium ion capacitor.

Images