JP2008130623A - Electrolyte for electrochemical device using room temperature molten salt and electrochemical device - Google Patents

Abstract

【選択図】なし[Problem] To provide a novel room temperature molten salt electrolyte exhibiting low viscosity and high electrical conductivity, and by using the electrolyte, in a severe external environment over a wide temperature range from extremely low temperature to high temperature. To provide an electrochemical device that operates safely and exhibits excellent electrical properties.
An electrolyte for an electrochemical device comprising a compound represented by the following general formula 1, an electric double layer capacitor, a lithium ion secondary battery, and a dye-sensitized solar cell using the same Electrochemical devices such as.
[Chemical 1]

[Selection figure] None

Description

  The present invention relates to a room temperature molten salt electrolyte used for an electrochemical device typified by a lithium secondary battery, an electric double layer capacitor and the like, and an electrochemical device using the electrolyte.

  In recent years, various secondary batteries and electric double layer capacitors with high energy density are attracting attention as power storage devices used for power supplies for electronic devices, power storage power supplies, electric vehicle power supplies, etc. Has been.

  In general, electrolytes used in these electrochemical devices include linear alkyl quaternary ammonium salts such as tetraethylammonium salts and quaternary phosphonium salts in aprotic solvents such as γ-butyrolactone and propylene carbonate. A solution in which a solid electrolyte salt is dissolved at room temperature is known.

  On the other hand, it has been proposed to use a room-temperature molten salt type compound that exhibits a liquid state at room temperature as an electrolyte for an electrochemical device. This is because the room temperature molten salt type compound has characteristics such as non-volatility and flame retardancy, so it does not require an organic solvent that has been used in conventional electrolytes, and a safer electrochemical device can be obtained. This is because.

  As these room temperature molten salt electrolytes for electrochemical devices, Patent Document 1 discloses room temperature molten salts such as N, N'-dialkylimidazolium salts and N-alkylpyridinium salts.

  However, since the room temperature molten salt disclosed in the document has high viscosity and low electrical conductivity, an electrochemical device produced using the room temperature molten salt has a drawback that the internal resistance increases.

  In addition, since electrochemical devices are expected to be exposed to harsh external environments, the electrolyte must have characteristics that allow the electrochemical devices to operate stably over a wide temperature range from extremely low temperatures to high temperatures. However, there is a need for a room temperature molten salt electrolyte that satisfies this requirement.

JP 2004-111184 A

  The object of the present invention is to provide a novel room temperature molten salt electrolyte exhibiting low viscosity and high conductivity, and by using the electrolyte, a severe external temperature over a wide temperature range from extremely low temperature to high temperature. To provide an electrochemical device that operates safely even in an environment and exhibits excellent electrical properties.

  As a result of intensive studies to solve the above problems, the present inventors have found that a quaternary ammonium compound salt having an isoxazolium cation structure exhibits high flame retardancy, low viscosity, high electrical conductivity, It has been found that the electrolyte is suitable for an electrochemical device having a low freezing point and expected to be operated in a wide temperature range, and the present invention has been completed. That is, this invention is a thing of the following 1-3.

  1. An electrolyte for electrochemical devices, comprising a compound represented by the following general formula 1.

In the formula, R ₁ represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, and R ₂ , R ₃ and R ₄ represent a substituent selected from the group consisting of a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. , A represents an acid component.

  2. In the general formula 1, the acid component A is at least 1 selected from the group consisting of a tetrafluoroborate anion, a hexafluorophosphate anion, an imide anion represented by the following general formula 2 and a methide anion represented by the following general formula 3. 2. The electrolyte for electrochemical devices as described in 1 above, which is a seed.

In the formula, R ₅ and R _{6 each} represents a fluoroalkyl group, a cyano group, a fluoroalkylsulfonyl group, a fluorosulfonyl group, a fluoroalkylcarbonyl group, or a fluorophosphonyl group. Further, a ring structure may be formed by two groups of R ₅ and R ₆ .

In the formula, R ₇ , R ₈ and R ₉ each independently represents a fluoroalkyl group, a cyano group, a fluoroalkylsulfonyl group, a fluorosulfonyl group, a fluoroalkylcarbonyl group or a fluorophosphonyl group.

Among these, preferred acid component A is BF ₄ , PF ₆ , N (CN) ₂ , C (CN) ₃ , N (FSO ₂ ) ₂ , CF ₃ SO ₃ , N (CF ₃ SO ₂ ) ₂ , From the group consisting of N (C ₂ F ₅ SO ₂ ) ₂ , N (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), C (CF ₃ SO ₂ ) ₃ and C (C ₂ F ₅ SO ₂ ) ₃ It is one kind selected.

  3. An electrochemical device using the electrolyte for an electrochemical device according to 1 or 2 above.

  The electrolyte for electrochemical devices of the present invention exhibits a liquid state in a very wide temperature range, and exhibits a low viscosity and a high electrical conductivity. The electrochemical device using the electrolyte of the present invention exhibits excellent characteristics over a temperature range of at least about −40 ° C. to + 150 ° C.

  Hereinafter, the present invention will be described in detail.

  The electrolyte for an electrochemical device of the present invention contains a quaternary ammonium compound having an isoxazolium structure represented by the general formula 1. The isoxazolium salt is a room temperature molten salt and exhibits high flame retardancy. Further, the isoxazolium compound having the structure of the general formula 1 has an N—O bond in the unsaturated heteromonocycle, and is particularly low-viscosity and excellent in high conductivity.

  The isoxazolium compound represented by the formula 1 is obtained by the following production method.

  First, an alkyl halide is allowed to act on an isoxazole derivative in an aqueous solution to obtain a halide of the isoxazolium derivative, and then an equivalent equivalent of the acid component A is added to the aqueous isoxazolium halide solution. After metathesis, the by-product is removed and dried under reduced pressure to obtain the desired isoxazolium compound salt.

In the general formula 1, R ₁ is a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, and R ₂ , R ₃ and R ₄ are a substituent selected from the group consisting of a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Represents a group, and A represents an acid component.

Among these, considering the ease of synthesis and economy, R ₁ is a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, R ₂ , R ₃ , R ₄ , and R ₅ are each a hydrogen atom or 1 to 1 carbon atom. An alkyl group of 3 is preferred.

  Specific preferred examples of the cation of the isoxazolium compound in the present invention include 2,5-dimethylisoxazolium, 2-ethyl-5-methylisoxazolium, 2-propyl-3-methylisoxazolium, 2-butyl-3-methylisoxazolium, 2-pentyl-3-methylisoxazolium, 2-hexyl-3-methylisoxazolium, 2,3,5-trimethylisoxazolium, 2- Ethyl-3,5-dimethylisoxazolium, 2-propyl-3,5-dimethylisoxazolium, 2-butyl-3,5-dimethylisoxazolium, 2-pentyl-3,5-dimethyliso Oxazolium, 2-hexyl-3,5-dimethylisoxazolium, 2,3,4,5-tetramethylisoxazolium, 2 Ethyl-3,4,5-trimethylisoxazolium, 2-propyl-3,4,5-trimethylisoxazolium, 2-butyl-3,4,5-trimethylisoxazolium, 2-pentyl- Examples include 3,4,5-trimethylisoxazolium and 2-hexyl-3,4,5-trimethylisoxazolium, but the present invention is not limited thereto. In addition, 2 or more types of these cations may be mixed.

In the isoxazolium compound represented by the above general formula 1, preferred acid component A includes tetrafluoroborate anion (BF ₄ ⁻ ), hexafluorophosphate anion (PF ₆ ⁻ ), and the above general formula 2. It is preferable that it is at least 1 sort (s) chosen from the group which consists of the imide anion and the metide anion represented by the said General formula 3. By selecting these anions, a salt that is liquid at room temperature, has a low viscosity, exhibits high conductivity, and is low in volatility and stable can be obtained.

Among them, A representing an acid component includes BF ₄ , PF ₆ , N (CN) ₂ , C (CN) ₃ , N (FSO ₂ ) ₂ , CF ₃ SO ₃ , N (CF ₃ SO ₂ ) ₂ , From the group consisting of N (C ₂ F ₅ SO ₂ ) ₂ , N (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), C (CF ₃ SO ₂ ) ₃ and C (C ₂ F ₅ SO ₂ ) ₃ What is chosen is preferred.

Among these, BF ₄ , PF ₆ , N (FSO ₂ ) ₂ , and N (CF ₃ SO ₂ ) ₂ are particularly preferable in consideration of low viscosity, high conductivity, and the like.

  The electrolyte for electrochemical devices of the present invention exhibits a liquid state in a very wide temperature range and exhibits a sufficient electrical conductivity. Specifically, the extremely wide temperature range referred to here is a range from approximately −40 ° C. to 150 ° C.

  When used as an electrolyte of an electrochemical device, an organic solvent that is not an ionic compound may be used in combination so that the advantages such as flame retardancy, non-volatility, and high conductivity are not impaired. Examples of organic solvents that are not ionic compounds include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate Chain carbonates such as ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate, methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, Ethers such as 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or the like Examples thereof include a single derivative or a mixture of two or more thereof, but are not limited thereto.

In addition, the electrolyte of the present invention may contain a lithium salt such as LiN (CF ₃ SO ₂ ) ₂ or LiBF ₄ as the electrolyte. In particular, in an electrochemical device using lithium ions as carrier ions, such as a lithium battery, a device having excellent electrical characteristics can be obtained.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited at all by the Example.

Example 1
An isoxazolium salt represented by the general formula 1 by adding 2-ethyl-3,5-dimethylisoxazolium iodide and lithium bis (trifluoromethanesulfonyl) imide to water at room temperature and stirring for 2 hours 2-ethyl-3,5-dimethylisoxazolium bis (trifluoromethanesulfonyl) imide (hereinafter referred to as “invention product 1”) in which R ₁ = 2, R ₂ , R ₄ = 1, and R ₃ = 0 Was synthesized. Inventive product 1 had an electric conductivity of 8.4 mS / cm at a temperature of 25 ° C. and a viscosity of 30 cP.

Example 2
The isoxazolium salt represented by the general formula 1 by adding 2-propyl-3,5-dimethylisoxazolium iodide and lithium bis (trifluoromethanesulfonyl) imide to water at room temperature and stirring for 2 hours 2-propyl-3,5-dimethylisoxazolium bis (trifluoromethanesulfonyl) imide (hereinafter referred to as “invention product 2”) in which R ₁ = 3, R ₂ , R ₄ = 1, and R ₃ = 0 Was synthesized. Inventive product 2 had an electric conductivity of 6.5 mS / cm at a temperature of 25 ° C. and a viscosity of 31 cP.

Example 3
In the isoxazolium salt represented by the general formula 1 by adding 2-ethyl-3,5-dimethylisoxazolium iodide and lithium bis (fluorosulfonyl) imide to water at room temperature and stirring for 2 hours , R ₁ = 2, R ₂ , R ₄ = 1, R ₃ = 0, 2-ethyl-3,5-dimethylisoxazolium bis (fluorosulfonyl) imide (hereinafter referred to as “invention product 3”). ) Was synthesized. Inventive product 3 had an electric conductivity of 17.0 mS / cm at a temperature of 25 ° C. and a viscosity of 21 cP.

Comparative Example 1
1-methyl-3-propylimidazolium bis (trifluoromethanesulfonyl) imide is added by adding 1-methyl-3-propylimidazolium iodide and lithium bis (trifluoromethanesulfonyl) imide to water at room temperature and stirring for 2 hours. (Hereinafter referred to as “Comparative Product 1”) was synthesized. The conductivity of Comparative Product 1 at a temperature of 25 ° C. was 5.2 mS / cm, and the viscosity was 35 cP.

  Next, an electric double layer capacitor was produced as an electrochemical device using the inventive products 1 to 3 and the comparative product 1 as electrolytes. The positive electrode and the negative electrode are active materials (activated carbon: Nippon Enviro Chemicals Co., Ltd., Shirahama KA), conductive materials (Ketjen Black: Lion Co., Ltd., ECP-600JD), and binder (PTFE: Mitsui DuPont Fluoro Chemical Co., Ltd.) 30-J). The weight composition ratio was active material: conductive material: binder = 80 parts: 10 parts: 10 parts. These mixtures were sufficiently kneaded while adding ethanol, and rolled to obtain a sheet electrode having a thickness of 0.85 mm on average. This sheet electrode is punched with a punch having a diameter of 15 mm, and bonded to a case and a cap (both made of SUS316) welded with a current collector (17 mm diameter plate) with a conductive adhesive, respectively. Part and a negative electrode part were obtained. The electrolyte was poured into each of these electrodes, impregnated under reduced pressure at 3 mmHg for 10 minutes, and then assembled with a polypropylene non-woven fabric as a separator, a polypropylene gasket attached to a cap, and fitted with a caulking machine to a 2032 size. Coin type electric double layer capacitor was completed.

  The obtained electric double layer capacitor was subjected to a charge / discharge test at an ambient temperature of −40 ° C. to 120 ° C. The capacitor is allowed to stand for 30 minutes or more at a predetermined measurement temperature. After the capacitor reaches the predetermined temperature, 2.5 V is applied as a rated voltage for 30 minutes, and then the capacitance is discharged at a constant current of 2 mA. The time until the voltage between the terminals was changed from 2V to 1V was calculated from the IR drop when the internal resistance was discharged at 30 mA. Further, the lower limit value of discharge was set to 0.9V. Measurement was started from −40 ° C., and the measurement temperature was sequentially raised to the high temperature side for testing. The results for each capacitor are shown in Table 1.

As shown in Table 1, in the evaluation at −40 ° C., the comparative product showed no electrostatic capacity, and the internal resistance could not be measured. Moreover, it was a result that an electrostatic capacity did not express at 120 degreeC also on the high temperature side.
On the other hand, the product of the present invention exhibits very excellent electrical characteristics (capacitance and internal resistance) in the range of 0 ° C. to 120 ° C., and does not solidify even in the extremely low temperature range of −40 ° C. Expressed. From this, it is clear that the product of the present invention is an electrolyte for electrochemical devices applicable to a very wide temperature range.

  The electrolyte of the present invention can be suitably used not only for the electric double layer capacitor described above but also for various electrochemical devices such as an electrochemical capacitor, a lithium ion secondary battery, and a dye-sensitized solar cell.

Claims (3)

An electrolyte for electrochemical devices, comprising a compound represented by the following general formula 1.

(Wherein R ₁ represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, and R ₂ , R ₃ and R ₄ represent a substituent selected from the group consisting of a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. And A represents an acid component.) In the general formula 1, the acid component A is at least 1 selected from the group consisting of a tetrafluoroborate anion, a hexafluorophosphate anion, an imide anion represented by the following general formula 2 and a methide anion represented by the following general formula 3. The electrolyte for electrochemical devices according to claim 1, which is a seed.

(In the formula, R ₅ and R ₆ represent a fluoroalkyl group, a cyano group, a fluoroalkylsulfonyl group, a fluorosulfonyl group, a fluoroalkylcarbonyl group, or a fluorophosphonyl group. Also, two groups of R ₅ and R ₆ May form a ring structure.

(In the formula, R ₇ , R ₈ and R ₉ each independently represents a fluoroalkyl group, a cyano group, a fluoroalkylsulfonyl group, a fluorosulfonyl group, a fluoroalkylcarbonyl group or a fluorophosphonyl group.)   An electrochemical device comprising the electrolyte for an electrochemical device according to claim 1 or 2.