JP4405779B2 - Ether complex salt - Google Patents

Description

  The present invention provides a novel ether complex salt useful as an electrolyte.

  2. Description of the Related Art In power storage devices such as lithium primary batteries and lithium secondary batteries that have been widely used in recent years, charging and discharging are performed by movement of alkali metal ions. Accompanying the downsizing and high performance of portable devices in which these electricity storage devices are used, energy storage devices are required to have higher energy density. In order to obtain high energy density in such electricity storage devices, electrolyte solution It is preferable that the concentration of alkali metal ions in the interior is high and the ionic conductivity of the electrolyte is large.

  Alkali metal salts such as lithium hexafluorophosphate and lithium bistrifluoromethanesulfonimide are used as a source of such alkali metal ions, but these alkali metal salts are generally solid, It can be used as an electrolytic solution by dissolving in a solvent. As such an organic solvent, polar solvents such as propylene carbonate, ethylene carbonate and γ-butyrolactone, and low viscosity solvents such as dimethyl carbonate are used.

  However, a polar solvent capable of dissolving alkali metal at a high concentration has a high viscosity, and the ionic conductivity of the obtained electrolytic solution tends to be low. On the other hand, a solvent having a low viscosity has a low polarity, and it is difficult to dissolve an alkali metal at a high concentration. Therefore, usually, a method of using both a high-viscosity and highly polar solvent and a low-viscosity solvent in a mixed manner to achieve both ionic concentration and ionic conductivity has been mainly adopted. The limit is about 5 to 2 mol / l.

  Moreover, since these organic solvents are volatile and flammable, they also have environmental effects, ignition problems during overheating, and the like.

  As one of methods for solving the above problems, a method using a so-called room temperature molten salt has also been proposed. In other words, the room temperature molten salt is a compound that is dissociable into ions but is liquid at room temperature, and since it is non-volatile, there is no risk of ignition. A method for reducing the environmental impact and safety problems caused by the volatile organic solvent by dissolving in a room temperature molten salt (see, for example, Patent Document 1), or an alkali metal salt that itself becomes a room temperature molten salt is used. A method has been proposed (see, for example, Non-Patent Document 1).

Japanese Patent Laid-Open No. 10-168028 Fujinami, “Journal of Power Source”, published June 1, 2003, Elsevier, 119-121, p. 438-441

  However, when these conventionally known room temperature molten salts are used as a solvent, the solubility of the alkali metal salt in the room temperature molten salt is low, so the concentration of the alkali metal salt is not limited, but the alkali metal salt is dissolved. When it does, there existed a problem that a viscosity will rise and an ionic conductivity will also fall. Further, conventionally known alkali metal salts that themselves become room temperature molten salts, although the alkali metal salt concentration can be improved, the viscosity is still high, and there is still much room for improvement in terms of ionic conductivity.

  Accordingly, there has been a demand for the development of a room temperature molten salt composed of an alkali metal ion that has a low viscosity in itself and that exhibits sufficient ionic conductivity by itself without using it in combination with a solvent.

  As a result of intensive studies to solve the above problems, the present inventors have found that an alkali metal ether complex salt having an ether having a specific structure as a ligand shows a liquid state even at room temperature. It came to complete. That is, the present invention provides the following general formula (I)

(In the formula, R ^1, R ³ are different from each other, each of the total number of carbon atoms represents an alkyl group substituted by an unsubstituted or halogen atoms from 1 to 4, the number of carbon atoms R ² is constituting the main chain 2 And an alkyl group having 2 to 4 carbon atoms in total or an alkylene group which may be substituted with a halogen atom , M represents an alkali metal, and X represents a halogen atom.)

  Since the ether complex salt of the present invention is in a liquid state even at room temperature and has a low viscosity, it can be used as an electrolytic solution without using any other solvent, and the energy density of the electricity storage device can be improved. Moreover, safety can also be improved by using the present ether complex salt as a solvent.

  The ether complex of the present invention has the following general formula (I)

(Wherein R ¹ and R ³ are different from each other and each represents an optionally substituted alkyl group having 1 to 4 carbon atoms, R ² has ² to 4 carbon atoms constituting the main chain, and A compound having a structure of 2 to 4 carbon atoms which may be substituted, M represents an alkali metal, and X represents a halogen atom.

R ¹ and R ³ in the general formula (I) are different alkyl groups having 1 to 4 carbon atoms which are different from each other (in addition, when the total carbon number has a substituent, Including carbon atoms of substituents).

If these R ¹ and R ³ are the same group, such an ether chain salt is presumed to have high symmetry, but since the melting point is high and it becomes a solid at around room temperature, The effect which the invention aims at cannot be obtained. R ¹ and R ³ may have the same alkyl group moiety other than a substituent as long as they are different groups (that is, a group in which an alkyl group having the same carbon number is substituted by a substituent having a different number or type), In order to obtain better physical properties, it is preferable that the alkyl group portion other than the substituent is different.

In addition, as the number of carbons increases, the viscosity tends to increase, and when R ¹ or R ³ is an alkyl group having 5 or more carbon atoms, the ionic conductivity is low, which is also an object of the present invention. It becomes difficult to obtain conductivity.

  The alkyl group may have a substituent, but considering that the ether complex salt of the present invention is used as an electrolyte of an electrochemical device such as a power storage device, there is an electrochemically unstable group. Therefore, it is preferable that it is an unsubstituted alkyl group, or that the substituent is a halogen atom such as a fluorine atom or a chlorine atom, a cyano group or an alkoxy group, and is unsubstituted or substituted by a halogen atom. More preferably, it is an alkyl group formed.

The alkyl group shown as R ¹ or R ³ will be described with specific examples. A methyl group, an ethyl group, an n-propyl group, a sec-propyl group, an n-butyl group, a sec-butyl group. Unsubstituted alkyl groups such as tert-butyl group; fluoroalkyl groups such as monofluoromethyl group, trifluoromethyl group and pentafluoroethyl group; chloro such as trichloromethyl group, 2-chloroethyl group and pentachloroethyl group Alkyl groups; and the like.

The combination of these groups as R ¹ and R ³ is not particularly limited as long as R ¹ and R ³ are different from each other, but in particular, the raw materials can be easily obtained in the synthesis, and the ether complex salt A combination of a methyl group and an ethyl group is particularly preferable in that the viscosity of the resin can be lowered.

In the above formula (I), R ² is an alkylene group, and the main chain thereof has 2 to 4 carbon atoms. That is, the ring constituted by R ² , two oxygen atoms and the alkali metal M takes a 5- to 7-membered ring. The compound having 1 carbon in the main chain in R ² has low stability and cannot be obtained as a stable compound near room temperature. On the other hand, when the number of carbons in the main chain is 5 or more, not only the chemical stability is lowered, but also the ionic conductivity is lowered. R ² is particularly preferably one having 2 carbon atoms constituting the main chain.

R ² may be substituted if the total carbon number is 2 to 4 (the total carbon number is the number including the carbon atom of the substituent when it has a substituent). If the total number of carbon atoms is 5 or more, the ionic conductivity is still not sufficient.

The alkylene group may have a substituent. For the same reason as described for R ¹ and R ³ , the alkylene group may be an unsubstituted alkylene group, or the substituent may be a methyl group, an ethyl group or the like. An alkyl group such as a group, a halogen atom such as a fluorine atom or a chlorine atom, a cyano group or an alkoxy group is preferable, and an unsubstituted or substituted alkylene group is more preferable.

Specific examples of the group suitable for R ² are explained below. Examples thereof include unsubstituted alkylene groups such as ethylene group, trimethylene group and tetramethylene group; alkyl-substituted alkylene groups such as propylene group and butylene group; Fluoroalkylene groups such as ethylene group, 1,1-difluoroethylene group and hexafluorotrimethylene group; Chloroalkylene groups such as tetrachloroethylene group, 1,2-dichloroethylene group and 1,1-dichloroethylene group; Can do.

  In the above formula (I) of the present invention, M is an alkali metal atom. Specifically, lithium, sodium and potassium are preferable. Of these, lithium is particularly preferred because of the high stability of the cation moiety.

X in the formula (I) is a halogen atom. Specific examples include fluorine, chlorine, bromine and iodine. Of these, fluorine is preferred because of its high stability and oxidation resistance. In the anion represented as BX ₄ ^— , X may be different halogen atoms, but are preferably the same from the viewpoint of ease of synthesis and stability. The most preferred anions, BF ₄ ^- is (boron tetrafluoride anion).

The method for producing the ether complex salt of the present invention is not particularly limited, but a method for producing an alkali metal boron halide salt and ether in a 1: 1 reaction is preferable from the viewpoint of easy reaction. Specifically, a complexing reaction occurs by mixing an alkali metal boron halide salt represented by M-BX ₄ and an ether represented by R ¹ —O—R ² —O—R ³ , The ether complex salt of the present invention is obtained. When mixing these, the amount of the alkali metal boron halide salt and the ether is not particularly limited, and an equimolar amount may be mixed, or one of them may be used in excess. When ether is used in excess, the ether complex salt of the present invention can be easily obtained by distilling off unreacted ether. Since the ether complex salt of the present invention does not decompose or volatilize near the boiling point of the ether used as a raw material, a high purity ether complex salt can be obtained with a high yield by this method. In addition, when an excessive amount of alkali metal boron halide salt is used, unreacted alkali metal boron halide salt may be separated by filtration.

  In view of the efficiency of the reaction and the ease of separation from the unreacted raw material, a method in which an excess amount of ether and an alkali metal boron halide salt are reacted and then the excess amount of ether is distilled off is suitable.

  The reaction temperature and time are not particularly limited, but in general, the reaction is completed within a few minutes to several hours at a temperature below the boiling point of the starting ether used with stirring.

Specific examples of ethers represented by R ¹ —O—R ² —O—R ³ that can be suitably used in such production methods include 1-ethoxy-2-methoxyethane and 1-methoxy-2-propoxyethane. Dialkoxyethanes such as 1-butoxy-2-methoxyethane, 1-ethoxy-2-propoxyethane, 1-ethoxy-2-trifluoromethoxyethane, 1-pentafluoroethoxy-2-trifluoromethoxyethane, -Substituted dialkoxyethanes such as ethoxy-1,1,2,2-tetrafluoro-2-methoxyethane, 1,2-difluoro-1-pentafluoroethoxy-2-trifluoromethoxyethane, 1-ethoxy-3 -Dialkoxypropanes such as methoxypropane and 1-ethoxy-3-propoxypropane It can be. Among them, 1-ethoxy-2-methoxyethane, 1-methoxy-2-propoxyethane, 1-pentafluoroethoxy-2-yl is preferable in that an ether complex salt having the above-described preferable R ¹ , R ² and R ³ can be obtained. Dialkoxyethanes such as trifluoromethoxyethane are preferred.

Examples of M-BX ₄ include LiBF ₄ , LiBCl ₄ , and NaBF ₄ , with LiBF ₄ being particularly preferable.

  The ether complex salt of the present invention thus obtained is a hardly volatile liquid, and its chemical structure can be confirmed by NMR.

  The ether complex salt of the present invention is hygroscopic, and the ether complex salt generally contains moisture due to moisture remaining from the production raw material remaining or mixing of moisture in the production process. In this case, it may be dried by performing concentration, azeotropic dehydration or the like. If the amount of water in the ether complex salt is too high, the heat resistance of the ether complex salt may be drastically lowered. Although the details are unknown, the boron halide anion is decomposed to produce hydrogen halide, and the hydrogen halide decomposes the ether ligand to produce an alcohol, which decomposes the boron halide anion. It is presumed that this is the mechanism. For this reason, it is preferable that the water content in an ether complex salt is 1000 ppm or less.

The ether complex salt of the present invention thus obtained generally has a low melting point and high ionic conductivity. Therefore, the electrolyte of an electricity storage device such as a lithium primary battery, a lithium secondary battery, or an electrochemical capacitor, or an electrochromic display element It is preferably used as an electrolyte for plating, an electrolyte for plating, a solvent for reaction and the like. In addition, by using such an electrolyte composed of an ether complex salt to construct electrochemical devices such as lithium primary batteries, lithium secondary batteries, electrochemical capacitors, and electrochromic elements, electrochemical devices with good low-temperature characteristics can be obtained. The present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.
Example 1
7.16 g (68 mmol) of ethoxymethoxyethane was added to 3.22 g (34 mmol) of lithium tetrafluoroborate, and the mixture was stirred at room temperature for 1 hour in a nitrogen atmosphere. The reaction solution was concentrated under reduced pressure at 1 mmHg at 40 ° C. to obtain 6.8 g of a colorless and transparent liquid. When the structure was confirmed using NMR using 1,4-bistrifluoromethylbenzene as a reference substance, 1H-NMR 1.10 ppm (t, 3H), 3.25 ppm (s, 3H), 3.41 to 3.45 ( m, 4H), 3.46 to 3.49 (q, 2H), 19F-NMR -164.68 ppm (s, 1F), -164.74 (s, 3F), lithium tetrafluoroborate ethoxymethoxy It was confirmed to be an ethane complex. The liquid had a water content of 800 ppm and an ionic conductivity of 1.3 mS / cm.

Example 2
3.58 g (34 mmol) of ethoxymethoxyethane was added to 3.22 g (34 mmol) of lithium tetrafluoroborate and stirred at room temperature for 1 hour under a nitrogen atmosphere, and 6.8 g of a lithium tetrafluoroborate ethoxymethoxyethane complex as a colorless transparent liquid. Got. The amount of water was 8000 ppm.

Comparative Example 1
When 0.90 g (10 mmol) of dimethoxyethane was added to 2.87 g (10 mmol) of lithium bistrifluoromethanesulfonimide and stirred at 70 ° C. for 1 hour in a nitrogen atmosphere, a colorless and transparent liquid was obtained. The liquid was cooled to room temperature and crystallized to obtain 3.77 g of a colorless solid. When confirmed by NMR, it was a lithium bistrifluoromethanesulfonimide dimethoxyethane complex. Melting point 69 ° C.

Comparative Example 2
When 1.04 g (10 mmol) of ethoxymethoxyethane was added to 2.87 g (10 mmol) of lithium bistrifluoromethanesulfonimide and stirred at 70 ° C. for 1 hour in a nitrogen atmosphere, a colorless and transparent liquid was obtained. The liquid was cooled to room temperature and crystallized to obtain 3.91 g of a colorless solid. It was confirmed by NMR that it was a lithium bistrifluoromethanesulfonimide ethoxymethoxyethane complex. Melting point 56 ° C.

Claims (4)

The following general formula (I)

(In the formula, R ^1, R ³ are different from each other, each of the total number of carbon atoms represents an alkyl group substituted by an unsubstituted or halogen atoms from 1 to 4, the number of carbon atoms R ² is constituting the main chain 2 And an alkyl group having 2 to 4 carbon atoms in total or an alkylene group which may be substituted with a halogen atom , M represents an alkali metal, and X represents a halogen atom.)
Ether complex salt represented by   A liquid electrolyte comprising the ether complex salt according to claim 1.   An electrolytic solution comprising the ether complex salt according to claim 1.   The electrolytic solution according to claim 3, which does not contain a solvent.