JP5684138B2 - Electric storage device and electrolyte used therefor - Google Patents

Description

  The present invention relates to an electricity storage device such as an electric double layer capacitor, a lithium ion capacitor, and a lithium ion secondary battery, and an electrolyte solution and an additive for an electrolyte solution provided in these electricity storage devices.

  Electric storage devices such as electrolytic capacitors, electric double layer capacitors, lithium ion capacitors, and lithium ion secondary batteries are used in a wide range of fields such as power supplies for mobile phones, personal computers, and power supplies for electric vehicles and hybrid vehicles. . Various studies have been made for the purpose of improving the characteristics of these electricity storage devices.

  An electric double layer capacitor is an electricity storage device that can be charged / discharged more rapidly than a secondary battery, has high charge / discharge efficiency, and is excellent in cycle characteristics. As shown in Patent Document 1, the electric double layer capacitor is provided with a cell composed of two polarizable electrodes and an electrolytic solution with a separator interposed therebetween.

  In recent years, research has been conducted from various viewpoints such as an electrode material surface and an electrolyte material surface in order to increase the energy density of an electric double layer capacitor. For example, Patent Document 2 discloses 1-ethyl-3-methylimidazolium tetracyanoborate as a compound that is excellent in thermal stability and electrochemical stability, and is used as an electrolyte even in the absence of a solvent. .

  Lithium ion capacitors have a structure that combines a negative electrode of a lithium ion secondary battery and a positive electrode of an electric double layer, and can store lithium ions as a negative electrode material while utilizing the principle of a general electric double layer capacitor. This is a capacitor whose energy density is improved by using lithium-ion supported on the negative electrode using a simple carbon-based material. This lithium ion capacitor combines the characteristics of a secondary battery such as high energy density with the characteristics of an electric double layer capacitor that can be rapidly charged and discharged, has high charge and discharge efficiency, and has excellent cycle characteristics. It is expected as a next-generation power storage device that can replace electric double layer capacitors and conventional secondary batteries.

  Thus, studies for practical application of lithium ion capacitors have been repeated. For example, Patent Document 3 discloses a method for efficiently supporting lithium ions on a negative electrode.

  Since lithium ion secondary batteries use lithium as a constituent material, they can be reduced in size and weight, and have a feature that their electric capacity is larger than that of conventionally used secondary batteries. It is an electricity storage device.

  Therefore, various studies have been conducted for the purpose of improving the electric capacity, input / output characteristics, and cycle characteristics of the lithium ion secondary battery. For example, Patent Document 4 discloses a negative electrode carbon material in which a graphite material whose surface is coated with a constant crystalline carbon material and an easily graphitizable carbon material having a predetermined degree of graphitization are combined. Patent Document 5 discloses secondary particles obtained by agglomerating primary particles of lithium nickel composite oxide having different aspect ratios, and the length direction of some primary particles is the center direction of the secondary particles. It is disclosed that a material having a structure suitable for the above can be a positive electrode material capable of high power discharge and excellent in cycle durability at high temperatures.

  Attempts have also been made to improve the electricity storage device characteristics by improving the electrolytic solution such as durability and low temperature characteristics. For example, in Patent Document 6, an ammonium salt having a structure in which an imidazole ring and an amine are bonded to an alkylene group is used as an additive for an electrolytic solution, so that crystals of other ion conductive salts contained in the electrolytic solution are used. And prevention of dendrite formation of metals. Patent Document 7 describes that the use of lithium difluoro [oxolato-O, O ′] lithium borate as an additive improves the low-temperature characteristics and further improves the durability. In Patent Document 8, when an organometallic compound having a specific structure is used as an additive for a non-aqueous electrolyte, an insulating film having heat resistance is formed on the surface of the positive electrode by a decomposition byproduct of the additive, and as a result. Patent Document 9 describes that an electrolytic solution containing a fluorinated ether having a specific structure is excellent in withstand voltage, and that this non-aqueous electrolytic solution secondary battery has improved safety against overcharging. It is described that the battery provided with can be charged at a high voltage.

JP-A-2005-64435 Special table 2009-527074 gazette JP 2006-286919 A JP 2009-117240 A WO 2006-118279 JP 2009-105028 A JP 2008-166342 A Japanese Patent No. 3934557 JP 2006-86134 A

In order to realize high energy density of the electric double layer capacitor, it is important that electrolysis or the like hardly occurs even when the electric double layer capacitor is operated at a high potential. However, carbonate solvents such as propylene carbonate and ammonium or alkyl group-substituted ammonium, which have been used as an electrolytic solution for electric double layer capacitors, as a cation component, tetrafluoroborate (BF ₄ ⁻ ), hexafluorophosphate ( In a system using an electrolyte containing PF ₆ ⁻ ) or the like as an anion component, it can be operated only in a potential range of about 2.5 V to 3 V (vs. Li / Li ⁺ ), and further improvement has been desired. .

  In order to achieve higher energy density of lithium ion capacitors, it is also effective to increase the withstand voltage of lithium ion capacitors in addition to optimization from the electrode surface, such as increase of electrode surface area and increase of lithium ion loading. Therefore, it is important that the electrolyte is stable and does not easily undergo electrolysis even when operated under high voltage.

Furthermore, in order to improve the characteristics of the lithium ion secondary battery, in particular, to achieve high energy density, in addition to optimizing the negative electrode and the separator as described above, the use of a positive electrode material having a high redox potential is used. Is effective. Further, in this case, it is important that the electrolytic solution is hardly decomposed even when operated under a high voltage and is stable. Further, from the viewpoint of cycle characteristics, there is a demand for a stable electrolytic solution that is difficult to decompose even when a currently used positive electrode material (redox potential 4.2 V (vs. Li ^/ Li ⁺ ) or less) is used. .

  As described above, in order to realize high energy density of various power storage devices, it is necessary to operate the power storage device under a high voltage. From such a viewpoint, as an electrolyte provided in the power storage device, Are also required to be difficult to disassemble.

  The present invention has been made paying attention to the above-described circumstances, and the object thereof is to provide an electricity storage device such as an electric double layer capacitor, a lithium ion capacitor, and a lithium ion secondary battery that operate stably even in a high voltage range. Is to provide.

  Another object of the present invention is to provide an electrolyte solution for an electricity storage device that can stably operate the electricity storage device even in a high voltage range.

The electrolytic solution of the present invention that has achieved the above object is represented by the general formula (1): Kt ⁺ [B (CN) ₄ ] ⁻ (wherein Kt ⁺ represents an onium cation and / or an inorganic cation). The present invention includes a ionic compound and an aprotic organic solvent, and has a withstand voltage of 6.9 V or more and 13.8 V or less (vs. Li ^/ Li ⁺ ) when LSV measurement is performed. I have it.

In the electrolytic solution of the present invention, the concentration of the ionic compound represented by the general formula (1) is preferably 0.01% by mass or more and less than 50% by mass. When the cation Kt ⁺ contained in the ionic compound represented by the general formula (1) is an onium cation, it is at least one cation selected from the group consisting of compounds represented by the following general formula. Is preferred.
(R ^{1 to} R ¹² each independently represent a hydrogen atom, a fluorine atom, or an organic group)

On the other hand, when the cation Kt ⁺ is an inorganic cation, the cation Kt ⁺ is preferably at least one cation selected from the group consisting of Li, Na, Mg and Ca.
In the present invention, an ionic compound represented by the general formula (1): Kt ⁺ [B (CN) ₄ ] ⁻ (wherein Kt ⁺ represents an onium cation and / or an inorganic cation) And an electrolytic solution containing an aprotic organic solvent and having a withstand voltage of 0 V or more and less than 6.9 V (vs. Li ^/ Li ⁺ ) when the LSV measurement is performed.

Furthermore, the present invention also includes an electricity storage device including the above-described electrolytic solution. Further, as the electricity storage device of the present invention, it is desirable that the positive electrode potential at full charge is 4 V (vs. Li ^/ Li ⁺ ) or more. A lithium ion secondary battery, a lithium ion capacitor, and an electric double layer capacitor are recommended embodiments of the electricity storage device of the present invention.

  According to the present invention, it is possible to provide an electrolytic solution in which decomposition does not easily occur in a high voltage range, particularly in an oxidation side high voltage range. In addition, it is considered that the electricity storage device of the present invention provided with this electrolytic solution hardly operates even when operated at a high potential, and can operate stably.

It is a graph which shows the result of Experimental example 1-1. It is a graph which shows the result of Experimental example 1-2. It is a figure which shows the LSV measurement result of Experimental example 2-1. It is a figure which shows the LSV measurement result of Experimental example 2-1, 2-2. It is a figure which shows the LSV measurement result of Experimental example 2-3, 2-4. It is a figure which shows the LSV measurement result of Experimental example 2-5. It is a figure which shows the LSV measurement result of Experimental example 2-6. It is a figure which shows the cyclic voltammogram result of Experimental example 3-1. It is a figure which shows the cyclic voltammogram result of Experimental example 3-2. It is a figure which shows the LSV measurement result of Experimental example 4-1. It is a figure which shows the LSV measurement result of Experimental example 4-2, 4-3. It is a figure which shows the LSV measurement result of Experimental example 4-4. It is a figure which shows the LSV measurement result of Experimental example 4-5. It is a figure which shows the LSV measurement result of Experimental example 4-6. It is a figure which shows the electric current amount retention of Experimental example 5-1 to Experimental example 5-3. It is a graph which shows the charging / discharging test result of Experimental example 6.

<Electrolyte>
As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that general formula (1): Kt ⁺ [B (CN) ₄ ] ⁻ (wherein Kt ⁺ is an onium cation and / or Or an ionic compound represented by an inorganic cation) can be used as an electrolyte, so that the withstand voltage of the electrolyte can be improved, and the electricity storage device can be stably operated even when charging and discharging are repeated under a high voltage. The present invention has been completed.

The electrolytic solution of the present invention is an ionic compound represented by the general formula (1): Kt ⁺ [B (CN) ₄ ] ⁻ (wherein Kt ⁺ represents an onium cation and / or an inorganic cation). And an aprotic organic solvent, and having a voltage resistance of 6.9 V or more and 13.8 V or less (vs. Li ^/ Li ⁺ ) when LSV measurement is performed under the following conditions.

  Usually, the organic solvent is decomposed under a high voltage, so that the electrolyte is deteriorated. However, the present inventors can decompose even under a high voltage that greatly exceeds the withstand voltage of a commonly known solvent by using the electrolytic solution according to the present invention containing the ionic compound represented by the general formula (1). It has been found that the current does not flow and the electrolyte does not easily deteriorate. That is, the electrolytic solution containing the ionic compound according to the present invention has improved withstand voltage, so that charge / discharge cycle characteristics are improved in an electricity storage device using this electrolytic solution. In addition, the effect of improving the withstand voltage characteristics and cycle characteristics is also obtained when the electrolyte is added with other ionic compounds in addition to the ionic compound represented by the general formula (1). It is obtained similarly. The present inventors do not clearly grasp the reason why such an effect is obtained, but consider it as follows. Tetracyanoborate added to the electrolyte causes some reaction in the system when the electricity storage device equipped with the electrolyte operates under high-voltage conditions. As a result, the reaction product generated on the electrode surface is simulated. A protective film is formed. Thereby, decomposition of other electrolytes and solvents is suppressed, and as a result, it is considered that the electricity storage device can be stably operated without causing decomposition of the electrolytic solution even in a high voltage range. In particular, tetracyanoborate, which is an anionic component of the ionic compound represented by the general formula (1), has excellent electric resistance (improvement of oxidation resistance on the positive electrode side) and is hardly decomposed even when used under high voltage. Therefore, if the electrolytic solution of the present invention containing tetracyanoborate is used, the electricity storage device can be stably operated even under a high voltage, and as a result, a high energy density can be secured.

Here, “having withstand voltage at 6.9 V or more and 13.8 V or less (vs. Li ^/ Li ⁺ )” means that when LSV measurement is performed under the conditions described later, 6.9 V to 13.8 V It means that no current exceeding the reference current value flows in the range, that is, it is difficult for the electrolyte to decompose. Therefore, an energy storage device including the electrolytic solution of the present invention having the above withstand voltage can be charged to a high potential, and even when operated at a high potential, the electrolyte and the electrode are unlikely to deteriorate. Will be expensive. It can be said that the higher the voltage at which a current higher than the reference current value is observed, the higher the performance of the electrolyte solution. Accordingly, the electrolyte solution of the present invention preferably has a withstand voltage of 7 V or more and 13.8 V (lithium standard), more preferably has a withstand voltage of 8 V to 13.8 V (lithium standard). Those having a withstand voltage of ˜13.8 V (lithium standard) are more preferable.

  In addition, the range which shows a withstand voltage is calculated | required by measuring a decomposition potential by the linear sweep voltammetry (LSV) measurement demonstrated below.

In linear sweep voltammetry, a propylene carbonate solution or a γ-butyrolactone solution having a predetermined electrolyte concentration (the total amount of an ionic compound represented by the general formula (1) and another electrolyte described later) is used as an electrolyte, and a glassy carbon electrode ( Electrode surface area: 1mmφ (0.785mm ² )) as working electrode, Ag electrode as reference electrode, platinum electrode as counter electrode, tripolar electrochemical cell with salt bridge, and standard voltammetry tool (“HSV- 100 "or" HSV-3000 "(both manufactured by Hokuto Denko Co., Ltd.), in a glove box at a temperature of 30 ° C, sweep rate: 100 mV / s, sweep range: -5 V to 10 V (vs. Ag / Ag ⁺ ) And measure the decomposition potential when a current of 0.03 mA flows. Note that the oxidation decomposition potential can be measured when scanning to a higher potential side than the natural potential, and the reduction decomposition potential can be measured when scanning to a lower potential side than the natural potential. The concentration of the electrolytic solution is 1 mol / L when the cation Kt ⁺ is an onium cation, and 0.7 mol / L when the cation Kt ⁺ is an inorganic cation (for example, a metal cation).

  In the evaluation of the withstand voltage, by setting the reference current value to be lower than 0.03 mA, it can be confirmed that the electrolytic solution has a higher performance. That is, it can be said that the electrolyte is so high in performance that no slight current is observed when measured under the above-mentioned LSV measurement conditions. For example, the lower reference current value is preferably 0.02 mA, and the higher the potential at which a current of 0.02 mA flows when measured under the above conditions, the higher the performance of the electrolyte. A more preferable reference current value is 0.01 mA, more preferably 0.005 mA, and still more preferably 0.004 mA.

Further, the present invention includes an ionic compound represented by the general formula (1): Kt ⁺ [B (CN) ₄ ] ⁻ and an aprotic organic solvent, and the reference current value is set to 0.02 mA. Except for this, an electrolytic solution having a withstand voltage of 0 V or more and less than 6.9 V (vs. Li ^/ Li ⁺ ) when the LSV measurement is performed under the same conditions as described above is also included. The LSV measurement conditions other than the reference current value are as described above, and “having a withstand voltage at 0 V or more and less than 6.9 V (vs. Li ^/ Li ⁺ )” was measured under the above-described conditions. In this case, it means that the current of the reference current value (0.02 mA) or more does not flow in the range of 0 V or more and less than 6.9 V, that is, the electrolyte does not decompose.

In addition, even in the withstand voltage evaluation at 0 V or more and less than 6.9 V (Li / Li ⁺ ), it can be confirmed that the electrolyte is a higher performance electrolyte by similarly setting the reference current value to be lower than 0.02 mA. . For example, the lower reference current value is preferably 0.015 mA, more preferably 0.01 mA, still more preferably 0.005 mA, and still more preferably 0.004 mA.
When the LSV measurement is performed under the above conditions, the electrolytic solution having a voltage resistance of 0 V or more and less than 6.9 V (vs. Li ^/ Li ⁺ ) is, for example, purified (for example, a recrystallization method or an electrolysis method described later) It is preferable that the ionic compound represented by the above general formula (1) obtained by the above method is included.

First, the ionic compound contained in the electrolytic solution of the present invention will be described.
The ionic compound represented by the general formula (1) is an onium cation and / or an inorganic cation as the cation component Kt ⁺ , and tetracyanoborate ([B (CN) ₄ ] ⁻ ; In some cases, the compound has.

The onium cation is represented by the general formula (2): L ⁺ -R _S (wherein L represents C, Si, N, P, S or O, and R is the same or different and represents a hydrogen atom, fluorine Represents an atom or an organic group, and may be bonded to each other when R is an organic group, s represents the number of R bonded to L, and is 3, 4 or 5. Those represented by the valence of the element L and the number of double bonds directly bonded to L are preferred.

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

Examples of the onium cation represented by the general formula (2) include those represented by the following general formula.
(R in the formula is the same as in the general formula (2))

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

General formula (3);
At least one of 15 types of heterocyclic onium cations represented by the formula:

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

General formula (4);
(Wherein R ^{1 to} R ¹² are the same as R ^{1 to} R ^{8 in} the general formula (3))
At least one of nine types of saturated ring onium cations represented by the formula:

General formula (5);
(Wherein R ^{1 to} R ⁴ are the same as R ^{1 to} R ^{8 in} the general formula (3))
A chain onium cation represented by

For example, the chain onium cation (5) includes tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, tetraheptylammonium, tetrahexylammonium, tetraoctylammonium, triethylmethylammonium, methoxyethyldiethylmethylammonium, Quaternary ammoniums such as trimethylphenylammonium, benzyltrimethylammonium, benzyltributylammonium, benzyltriethylammonium, dimethyldistearylammonium, diallyldimethylammonium, 2-methoxyethoxymethyltrimethylammonium and tetrakis (pentafluoroethyl) ammonium, trimethylammonium , Triethylan Tertiary ammoniums such as nium, diethylmethylammonium, dimethylethylammonium and dibutylmethylammonium, secondary ammoniums such as dimethylammonium, diethylammonium and dibutylammonium, methylammonium, ethylammonium, butylammonium, hexylammonium and octyl Examples include ammonium primary ammoniums, N-methoxytrimethylammonium, N-ethoxytrimethylammonium, N-propoxytrimethylammonium, and ammonium compounds represented by NH ₄ .

Among the onium cations of the above general formulas (3) to (5), an onium cation containing a nitrogen atom is more preferable, and a more preferable one is the following general formula:
(Wherein, R ¹ to R ¹² are the same as R ¹ to R ⁸ of general formula (3).)
And at least one of six kinds of onium cations represented by the formula:

  Among the above 6 kinds of onium cations, linear quaternary ammonium such as tetraethylammonium, tetrabutylammonium and triethylmethylammonium, linear tertiary ammonium such as triethylammonium, dibutylmethylammonium and dimethylethylammonium, 1-ethyl Since imidazolium such as -3-methylimidazolium and 1,2,3-trimethylimidazolium, pyrrolidinium such as N, N-dimethylpyrrolidinium and N-ethyl-N-methylpyrrolidinium are readily available, preferable. More preferred are quaternary ammonium and imidazolium. From the viewpoint of reduction resistance, quaternary ammonium such as tetraethylammonium, tetrabutylammonium and triethylmethylammonium classified into the chain onium cation is more preferable.

On the other hand, as inorganic cations, alkaline metal cations such as Li ⁺ , Na ⁺ and K ⁺ , alkaline earth metal cations such as Mg ²⁺ and Ca ²⁺ , Zn ²⁺ , Ga ³⁺ , Cu ^2+, etc. Examples include 4-period metal cations, fifth-period metal cations such as Pd ²⁺ , Sn ²⁺ , and Rh ²⁺ , and sixth-period transition metal cations such as Hg ²⁺ and Pb ²⁺ . Among these, Li ⁺ , Na ⁺ , Mg ²⁺ and Ca ²⁺ cations are preferable because they have a small ionic radius and can be easily used as an electricity storage device. Further, Li ⁺ cations are easily dissolved in an organic solvent and are non-aqueous. Since it can utilize as electrolyte solution, it is preferable.

  Therefore, as the ionic compound represented by the general formula (1), tetraethylammonium tetracyanoborate, tetrabutylammonium tetracyanoborate, triethylmethylammonium tetracyanoborate and lithium tetracyanoborate are particularly preferable.

  The ionic compound represented by the general formula (1) is obtained by reacting a compound having TCB as an anion with a compound containing the onium cation or inorganic cation (for example, triethylmethylammonium chloride or tributylammonium chloride). It can be obtained by cation exchange by a conventional method. The TCB-containing compound may be a commercially available compound, and further a method of reacting a cyanide (metal cyanide such as zinc or copper, ammonium cyanide, or trimethylcyanide) with a boron compound. Alternatively, it can also be produced by the method described in WO2004 / 072089.

In general, in order to increase the durability of the electrolyte, materials that make up the electrolyte, such as electrolytes and organic solvents, must be made of high-purity materials that easily reduce residual halogen components that easily undergo electrolysis and impurities such as moisture. It is required to use. Therefore, in order to obtain a high withstand voltage electrolytic solution, the ionic compound represented by the general formula (1) may be subjected to a purification step as necessary. The timing of carrying out the purification step is not particularly limited. For example, the purification step may be performed at the raw material stage used for the production of the ionic compound represented by the general formula (1), or the raw material may be reacted. Thereafter, the obtained ionic compound may be purified. Furthermore, when performing a cation exchange reaction, you may perform a refinement | purification process in any step before and after the process of manufacturing the electrolyte solution containing an ionic compound before and after a cation exchange reaction.
Any conventionally known method can be employed as the purification method. Conventionally known methods include, for example, washing with water, organic solvents, and mixed solvents thereof; oxidizing agent treatment; adsorption purification method; reprecipitation method; liquid separation extraction method; recrystallization method; crystallization method; Purification method by electrolysis; electrolysis method by voltage application and the like. These purification methods may be carried out in combination of two or more. Among the above purification methods, the recrystallization method and the electrolysis method are particularly preferable. Although there is no restriction | limiting in particular as a solvent used for a recrystallization method, For example, the aprotic organic solvent used for the electrolyte solution mentioned later and water are suitable.

  On the other hand, the electrolysis method is a method in which an ionic compound is dissolved in a solvent and a voltage is applied to the solution to electrolyze impurities. Although there is no restriction | limiting in particular as a solvent which can be used by an electrolysis method, The aprotic organic solvent used for the electrolyte solution mentioned later is especially suitable. Although there is no restriction | limiting in particular in the electrode used when applying a voltage, For example, it is preferable to use the carbon type electrodes, such as a glassy carbon and activated carbon, and the metal and metal oxide type electrode which are generally used with the battery. Moreover, 0V-13.8V (Li reference | standard) is suitable for the voltage value to apply, More preferably, it is 0.5V-10V, More preferably, it is 1V-8V.

  The density | concentration of the ionic compound represented by the said General formula (1) in electrolyte solution is 0.01 mass% or more, and it is preferable that it is less than 50 mass%. The electrolytic solution of the present invention exhibits high electrical conductivity when the concentration of the electrolyte is in the above range. The concentration of the ionic compound is more preferably 0.1% by mass or more, still more preferably 1% by mass or more, still more preferably 5% by mass or more, and more preferably 45% by mass. % Or less, and more preferably 40% by mass or less. If the concentration is too low, it may be difficult to obtain desired electrical conductivity (improvement of ion conductivity, voltage resistance, etc.). On the other hand, if the concentration is too high, it is particularly low temperature range (about −20 ° C. ), The concentration of the electrolytic solution increases, the electrical conductivity decreases, or the ionic compound separates and precipitates in the electrolytic solution, which may adversely affect the device (electrode, etc.). Moreover, the problem of the cost rise by a large amount use of an ionic compound also arises.

In the electrolytic solution according to the present invention, only the ionic compound represented by the general formula (1) may be included as an electrolyte, but other electrolytes other than the ionic compound of the general formula (1) are included. It may be. By using another electrolyte, the absolute amount of ions in the electrolytic solution can be increased, and the electrical conductivity can be improved. Even when other electrolytes are used, if the component derived from the ionic compound of the general formula (1) is contained in the electrolytic solution, the voltage resistance on the positive electrode side can be improved. This is one of the characteristics when the ionic compound represented by the general formula (1) is used. Therefore, as an aspect of the electrolytic solution according to the present invention, an aspect 1 in which only the ionic compound of the general formula (1) (Kt ⁺ is lithium ion) is included; the ionic compound of the general formula (1) (Kt ⁺ is lithium) Embodiment 2 including only ions and onium cations); Embodiment 3 including an ionic compound of general formula (1) (Kt ⁺ is a lithium ion) and another electrolyte; Ionic compound of general formula (1) (Kt ⁺ Is an onium cation) and another electrolyte; and an ionic compound of the general formula (1) (Kt ⁺ is a lithium ion and an onium cation) and another electrolyte are included.

As other electrolytes, those having a large dissociation constant in the electrolyte and having an anion that is difficult to solvate with an aprotic solvent described later are preferable. Examples of cation species constituting other electrolytes include alkali metal ions such as Li ⁺ , Na ⁺ and K ⁺ , alkaline earth metal ions such as Ca ²⁺ and Mg ²⁺ , and onium cations. Chain quaternary ammonium or lithium ions are preferred. On the other hand, as anion species, PF ₆ ⁻ , BF ₄ ⁻ , Cl ⁻ , Br ⁻ , ClO ₄ ⁻ , AlCl ₄ ⁻ , C [(CN) ₃ ] ⁻ , N [(CN) ₂ ] ⁻ , N [( SO ₂ CF ₃ ) ₂ ] ⁻ , N [(SO ₂ F) ₂ ] ⁻ , CF ₃ (SO ₃ ) ⁻ , C [(CF ₃ SO ₂ ) ₃ ] ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ and dicyanotri An azolate ion (DCTA) etc. are mentioned. Among these, PF ₆ ⁻ and BF ₄ ⁻ are more preferable, and BF ₄ ⁻ is particularly preferable.

Specifically, alkali metal salts or alkaline earth metal salts of trifluoromethanesulfonic acid such as LiCF ₃ SO ₃ , NaCF ₃ SO ₃ , KCF ₃ SO ₃ ; LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ Alkali metal salts and alkaline earth metal salts of perfluoroalkanesulfonic acid imides such as CF ₂ SO ₂ ) ₂ and LiN (FSO ₂ ) ₂ ; Alkali metal salts of hexafluorophosphoric acid such as LiPF ₆ , NaPF ₆ and KPF ₆ and alkaline earth metal salts; LiClO _4, NaClO ₄ perchlorate alkali metal salt or an alkaline earth metal such as salts; LiBF _4, tetrafluoroborate of NaBF _{4 such; LiAsF 6, LiI, LiSbF 6} , LiAlO 4, Alkali metal salts such as LiAlCl ₄ , LiCl, NaI, NaAsF ₆ , and KI; fourth of perchloric acid such as tetraethylammonium perchlorate Quaternary ammonium salts; quaternary ammonium salts of tetrafluoroboric acid such as (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ , and (C ₂ H ₅ ) ₄ NPF ₆ Quaternary ammonium salts; quaternary phosphonium salts such as (CH ₃ ) ₄ P · BF ₄ and (C ₂ H ₅ ) ₄ P · BF ₄ are preferred. Among these, alkali metal salts and / or alkaline earth metal salts are preferable. Further, from the viewpoint of solubility in an aprotic organic solvent and ion conductivity, LiPF ₆ , LiBF ₄ , LiAsF ₆ , alkali metal salt or alkaline earth metal salt of perfluoroalkanesulfonic acid imide, A quaternary ammonium salt is preferable, and a chain quaternary ammonium salt is preferable from the viewpoint of reduction resistance. As the alkali metal salt, a lithium salt, a sodium salt, and a potassium salt are preferable, and as the alkaline earth metal salt, a calcium salt and a magnesium salt are preferable. More preferred is a lithium salt.

  The abundance of the other electrolyte is preferably 0.1% by mass or 90% by mass or less in a total of 100% by mass of the ionic compound represented by the general formula (1) and the other electrolyte. It is. If the amount of other electrolytes is too small, it may be difficult to obtain the effect of using other electrolytes (for example, the absolute amount of ions is not sufficient and the electrical conductivity is reduced). When there is too much quantity, there exists a possibility that the movement of ion may be inhibited greatly. More preferably, it is 1 mass% or more, More preferably, it is 5 mass% or more, More preferably, it is 80 mass% or less, More preferably, it is 70 mass% or less.

  In addition, the electrolyte concentration (total amount of the ionic compound represented by the general formula (1) and other electrolytes) in the electrolytic solution according to the present invention is preferably 0.01% by mass or more, and is preferably a saturated concentration or less. . If it is less than 0.01% by mass, the ionic conductivity is lowered, which is not preferable. More preferably, it is 0.5 mass% or more, More preferably, it is 1 mass% or more, More preferably, it is 5 mass% or more. The electrolyte concentration in the electrolytic solution is more preferably less than 50% by mass, and still more preferably 40% by mass or less.

Examples of the organic solvent contained in the electrolytic solution according to the present invention include an aprotic organic solvent in which the ionic compound represented by the general formula (1) and the other electrolyte described above can be dissolved.
As the aprotic organic solvent, a solvent having a large dielectric constant, a high solubility of the electrolyte salt, a boiling point of 60 ° C. or higher, and a wide electrochemical stability range is preferable. More preferably, it is an organic solvent (non-aqueous solvent) having a low water content. Examples of such organic solvents include ethylene glycol dimethyl ether (1,2-dimethoxyethane), ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, crown ether, triethylene glycol dimethyl ether, Ethers such as tetraethylene glycol dimethyl ether, 1,4-dioxane, 1,3-dioxolane; dimethyl carbonate, ethyl methyl carbonate (methyl ethyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate, methyl phenyl carbonate, etc. Chain carbonates of ethylene carbonate (ethylene carbonate), propylene carbonate (propylene carbonate), 2,3-dimethylethylene carbonate, butyrate , Cyclic carbonates such as vinylene carbonate and 2-vinylethylene carbonate; aliphatic carboxylic acid esters such as methyl formate, methyl acetate, propionic acid, methyl propionate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate; Aromatic carboxylic acid esters such as methyl acid and ethyl benzoate; carboxylic acid esters such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone; trimethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, phosphorus Phosphate esters such as triethyl acid; Nitriles such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, isobutyronitrile; N-methyl Formamide, N-eth Amides such as formamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidinone, N-methylpyrrolidone, N-vinylpyrrolidone; dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methyl Sulfur compounds such as sulfolane and 2,4-dimethylsulfolane: alcohols such as ethylene glycol, propylene glycol, ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; sulfoxides such as dimethyl sulfoxide, methyl ethyl sulfoxide and diethyl sulfoxide; benzo Aromatic nitriles such as nitrile and tolunitrile; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H) -pyrimidinone, 3-methyl-2-oxazolidinone and the like can be mentioned, and one or more of these are preferable. Among these, carbonic acid esters, aliphatic carboxylic acid esters, carboxylic acid esters, and ethers are more preferable, carbonates such as ethylene carbonate and propylene carbonate, and carboxylic acid esters such as γ-butyrolactone and γ-valerolactone. Are more preferred, and propylene carbonate and γ-butyrolactone are even more preferred.

  In addition, a polymer can also be used as the organic solvent in the electrolytic solution of the present invention. Examples of such a polymer include polyether polymers such as polyethylene oxide (PEO) and polypropylene oxide, methacrylic polymers such as polymethyl methacrylate (PMMA), nitrile polymers such as polyacrylonitrile (PAN), and poly (vinylidene fluoride) (PVdF ), Fluoropolymers such as poly (vinylidene fluoride) -hexafluoropropylene, and copolymers thereof. In addition, a polymer gel obtained by mixing these polymers with another organic solvent is also one suitable form of the organic solvent constituting the electrolytic solution of the present invention. When a polymer gel electrolyte in which the above-described electrolyte is dissolved and dispersed in such a polymer gel instead of using an organic solvent alone is used, self-discharge is reduced, and voltage holding characteristics in a high voltage state are improved. Therefore, it can also be said that using the polymer gel which combined the above-mentioned polymer or a polymer and another organic solvent as an organic solvent is one of the suitable aspects of the electrolyte solution of this invention.

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

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

  When the ionic compound represented by the general formula (1) and the other electrolyte described above are difficult to dissolve in the aprotic organic solvent, the electrolyte solution is used to improve the solubility of the ionic compound or the other electrolyte. A solubilizing agent may be added. Although it does not specifically limit as a solubilizing agent, For example, an amine compound is mentioned as a preferable additive. Specifically, trimethylamine, triethylamine, tributylamine, dimethylethylamine, dimethylbutylamine, diethylbutylamine, hexamethylenetetramine, DABCO (diazabicyclooctane), DBU (diazabicycloundecene), TMEDA (tetramethylethylenediamine) and N -Methylimidazole etc. are mentioned, DBU, TMEDA and N-methylimidazole are preferable.

  The compounding amount of the auxiliary agent is preferably 0.01 parts by mass or more and less than 50 parts by mass with respect to 100 parts by mass in total of the ionic compound represented by the general formula (1) and the other electrolyte. More preferably, they are 0.05 mass part or more and 20 mass parts or less, More preferably, they are 0.1 mass part or more and 10 mass parts or less.

  The ionic compound represented by the general formula (1) may be used as a main component of the electrolyte as described above, but may be used as an additive of the electrolytic solution.

  When using the ionic compound of General formula (1) as an additive, the usage-amount of an additive shall be 0.01 mass% or more and less than 50 mass% in the total 100 mass% of the main electrolyte and additive mentioned later. Is preferred. If the amount of the additive is too large, the charge transfer efficiency may be reduced, or an ionic compound may be deposited in the electrolyte solution, which may adversely affect the electrode. Further, a large amount of use leads to an increase in cost. On the other hand, when the amount is too small, it is difficult to obtain the effects of using additives such as suppression of decomposition of the electrolytic solution, suppression of deterioration of the electrode, and improvement of electric resistance characteristics. Preferably they are 0.1 mass% or more and 40 mass% or less, More preferably, they are 0.5 mass% or more and 25 mass% or less, More preferably, they are 1 mass% or more and 10 mass% or less.

  The main electrolyte used together with the additive of the present invention is one that dissociates into ions in the electrolyte and functions as a charge carrier. As a main compound, the compound illustrated as said other electrolyte can be used.

The electrolyte concentration in the electrolytic solution (the total amount of the additive represented by the general formula (1) and the main electrolyte) is preferably 0.01% by mass or more, and preferably less than the saturation concentration. If it is less than 0.01% by mass, the ionic conductivity is lowered, which is not preferable. More preferably, it is 0.5 mass% or more, More preferably, it is 1 mass% or more, More preferably, it is 5 mass% or more. The electrolyte concentration in the electrolytic solution is more preferably 50% by mass or less, and further preferably 40% by mass or less.
As the solvent, the above-mentioned aprotic solvent may be used. Moreover, in order to improve the solubility of electrolyte, you may use the said dissolution aid.

<Power storage device>
The electricity storage device of the present invention is an ionic compound represented by the general formula (1): Kt ⁺ [B (CN) ₄ ] ⁻ (wherein Kt ⁺ represents an onium cation and / or an inorganic cation). And an electrolytic solution of the present invention that includes an aprotic organic solvent and exhibits voltage resistance at 6.9 V to 13.8 V (vs. Li / Li ⁺ ) when LSV measurement is performed under predetermined conditions. It has characteristics in the place of inclusion.

In the electricity storage device of the present invention having the above configuration, the positive electrode potential at full charge is preferably 4 V (vs. Li ^/ Li ⁺ ) or more, more preferably 4.3 V or more, and still more preferably 4.6 V. Or more, more preferably 5.0 V or more. Therefore, the electricity storage device of the present invention can be charged to a high potential. In addition, the electricity storage device of the present invention has a high energy density because the electrolyte and the electrode hardly deteriorate even when operated at such a high potential.

  In these devices, the use of an electrolytic solution having a high withstand voltage characteristic leads to an increase in the storage capacity. For example, in other conventional electricity storage devices using water as a solvent, the working voltage is set low to prevent electrolysis of water, and there are few merits of using a high withstand voltage electrolyte. However, a lithium ion battery, a lithium ion capacitor, and an electric double layer capacitor use a non-aqueous electrolyte, and a high capacity can be achieved by using a high withstand voltage electrolyte. For this reason, further increase in capacity is required for these devices. Therefore, it is considered that when the electrolytic solution of the present invention is used for these power storage devices, a high withstand voltage can be achieved and a high capacity of the device can be realized. Therefore, in the present invention, the electrolytic solution of the present invention is used particularly for lithium ion batteries, lithium ion capacitors, and electric double layer capacitors.

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

  Moreover, it is preferable that the withstand voltage of the electrical storage device of this invention is 6V (lithium standard, silver standard 2.2V) or more. More preferably, it is 7V or more, More preferably, it is 8V or more, More preferably, it is 10V or more. The electricity storage device of the present invention can be stably operated even at 6 V or more, and has a high energy density. In addition, withstand voltage is a value measured by the method as described in the Example mentioned later here. Note that in this specification, the value of the decomposition potential measured by linear sweep voltammetry described below is used as the withstand voltage of the electricity storage device (lithium ion secondary battery, electric double layer capacitor, and lithium ion capacitor) of the present invention.

Linear sweep voltammetry uses a propylene carbonate solution or a γ-butyrolactone solution of a predetermined electrolyte (the total amount of the ionic compound represented by the general formula (1) and the above-mentioned other electrolyte) as an electrolyte solution. (Electrode surface area: 1 mmφ (0.785 mm ² )) as a working electrode, Ag electrode as a reference electrode, platinum electrode as a counter electrode, and a three-pole electrochemical cell equipped with a salt bridge and a standard voltammetry tool (“HSV -100 ", manufactured by Hokuto Denko Co., Ltd.) in a glove box at a temperature of 30 ° C, sweep rate: 100 mV / s, sweep range: -5 V to 10 V (vs. Ag / Ag ⁺ ), 0.03 mA Measure the decomposition potential (withstand voltage) when the current flows. Note that the oxidation decomposition potential can be measured when scanning to a higher potential side than the natural potential, and the reduction decomposition potential can be measured when scanning to a lower potential side than the natural potential. The concentration of the electrolytic solution is 1 mol / L when the cation Kt ⁺ is an onium cation, and 0.7 mol / L when the cation Kt ⁺ is an inorganic cation (metal or the like).

  The power storage device of the present invention includes a portable information terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle, an electric vehicle, a hybrid electric vehicle, a power supply device for momentary power interruption, a power regeneration power device, a solar cell, and a backup power supply device It can use suitably for various uses, such as these.

  Examples of the electricity storage device using the electrolytic solution of the present invention include lithium ion secondary batteries, electrolytic capacitors, electric double layer capacitors, and lithium ion capacitors. Among these, (1) lithium ion secondary The battery, (2) the electric double layer capacitor, and (3) the lithium ion capacitor will be described in more detail.

(1) Lithium ion secondary battery A lithium ion secondary battery is comprised as a basic component by the positive electrode, a negative electrode, the separator interposed between a positive electrode and a negative electrode, and the electrolyte solution of this invention. The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, and an electrolytic solution, and the electrolytic solution includes lithium ions, tetracyanoborate; [B (CN) ₄ ] ⁻ , and an aprotic organic solvent. And has a feature. The lithium ion secondary battery having the above configuration can operate stably even when charging and discharging are repeated under a high voltage.

Such a lithium ion secondary battery is preferably a non-aqueous electrolyte lithium ion secondary battery that is a lithium ion secondary battery other than the water electrolyte. This lithium ion secondary battery uses a carbon material such as graphite as a negative electrode active material, which will be described later, and a compound containing a metal oxide such as LiCoO ₂ as a positive electrode active material. In the secondary battery, at the time of charging, for example, a reaction of C ₆ Li → 6C + Li + e occurs in the negative electrode, and electrons (e) generated on the negative electrode surface are ion-conducted in the electrolytic solution and move to the positive electrode surface. On the surface, for example, a reaction of CoO ₂ + Li + e → LiCoO ₂ occurs, and a current flows from the negative electrode to the positive electrode. On the other hand, at the time of discharging, a reverse reaction at the time of charging occurs, and a current flows from the positive electrode to the negative electrode. Thus, in a lithium ion secondary battery, electricity is stored or supplied by a chemical reaction caused by ions.

  The electrolytic solution provided in the lithium ion secondary battery of the present invention contains lithium ions, tetracyanoborate, and an aprotic organic solvent. Lithium ions and tetracyanoborate each function as a charge carrier in the electrolyte. In particular, tetracyanoborate is excellent in electric withstand characteristics (an effect of improving the withstand voltage on the positive electrode side) and hardly decomposes even when used under a high voltage. Therefore, the lithium ion secondary battery of the present invention can be stably operated even under a high voltage and has a high energy density.

  As the electrolytic solution of the lithium ion secondary battery of the present invention, the electrolytic solution of the present invention is preferably used. The lithium ions and tetracyanoborate contained in the electrolytic solution according to the present invention are derived from compounds containing these anions and / or cations. The compound that generates these ions may be derived from the ionic compound represented by the general formula (1), or may be derived from another electrolyte. In addition, when lithium ion is not contained in the ionic compound of General formula (1), the lithium ion contained in the electrolyte solution which concerns on this invention comes from another electrolyte.

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

The concentration of the ionic compound represented by the general formula (1) and the other electrolyte in the electrolytic solution is not particularly limited as long as the lithium ion amount and the tetracyanoborate amount fall within the above ranges. For example, Kt ⁺ The ionic compound concentration of the general formula (1) in which is an onium cation is 0.01% by mass or more and preferably less than 50% by mass. When the concentration of the electrolyte is within the above range, it is preferable because it shows good electric conductivity. The concentration of the ionic compound is more preferably 0.05% by mass or more, further preferably 0.1% by mass or more, more preferably 20% by mass or less, and further preferably 10% by mass. It is as follows. If the concentration is too low, it may be difficult to obtain the desired electrical conductivity. On the other hand, if the concentration is too high, the viscosity of the electrolytic solution is particularly remarkable in a low temperature range (about −20 ° C.). The charge transfer efficiency may be increased, and the ionic compound may be separated and deposited in the electrolytic solution, which may adversely affect the electrode. In addition, the use of a large amount of an ionic compound causes an increase in cost.

  Moreover, in the lithium ion secondary battery of this invention, you may use the above-mentioned polymer electrolyte or polymer gel electrolyte solution as electrolyte. The polymer electrolyte is obtained by supporting an electrolyte on a polymer as a base material. For example, a polymer electrolyte obtained by impregnating a polymer with the electrolytic solution of the present invention (polymer gel electrolytic solution) or an ion of the general formula (1) And those obtained by dissolving a soluble compound or the other electrolyte in a base polymer (intrinsic polymer electrolyte). In the present invention, it is preferable to use a polymer electrolyte containing lithium ions and tetracyanoborate. Examples of the polymer serving as a base material for the polymer electrolyte include polyether copolymers such as polyethylene oxide and polypropylene oxide, and among them, polyethylene oxide is preferably used.

  The lithium ion secondary battery of the present invention has a positive electrode, a negative electrode, and an electrolytic solution. A separator is provided between the positive electrode and the negative electrode in order to prevent a short circuit due to contact between the two.

  Each of the positive electrode and the negative electrode is composed of a current collector, a positive electrode active material or a negative electrode active material, a conductive agent, a binder (binder material), and the like. It is formed by forming a thin coating film, sheet or plate on the top.

The positive electrode is not particularly limited, and a known positive electrode can be used. For example, a positive electrode current collector, a positive electrode active material, a conductive agent, a binder, and the like are used. Examples of the positive electrode current collector include aluminum and stainless steel. Examples of the positive electrode active material include LiNiVO ₄ , LiCoPO ₄ , LiCoVO ₄ , LiCrMnO ₄ , LiCr _x Mn _2−x O ₄ (0 <x <0.5), LiCr _0.2 Ni _0.4 Mn _1.4 O ₄ , LiPtO ₃ , Li _x Fe ₂ (SO ₄ ) ₃ , LiFeO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiCoO ₂ , LiMn _1.6 Ni _0.4 O ₄ , LiFePO ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _{1/2 Mn 1/2 O 2, LiNi 0.8} Co 0.2 O 2, LiNiO 2, Li 1 + x (Fe 0.4 Mn 0.4 Co 0.2) 1-x O 2 or the like can be used. Among these, LiMn ₂ O ₄ , LiCoO ₂ , LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and LiNi _0.8 Co _0.2 O ₂ , NMC (= LiNiMnCo) _{1 / 302} , NCA (= Ni _0.8 Co _0.15 Al _0.05 ) O ₂ is preferred. In order to increase the output, it is preferable to use a material having a high potential of 4 V or more as the positive electrode material. Examples of the material having a high potential include LiCoO ₂ (4.2 V), LiCr _x Mn _2−x O ₄ (0 <x <0.5) (4.2 V), LiCr _0.2 Ni _0.4 Mn _1.4 O ₄ ( _4.7 V), LiNi _0.5 Mn _1.5 O ₄ (4.7 V), LiCoPO ₄ (4.8 V), LiNiPO ₄ (5.1 V), NMC (= LiNiMnCo) _1/302 (4.2 V), NCA (= Ni _0.8 Co _0.15 Al _0.05 ) O ₂ (4.2 V) and the like.

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

  The negative electrode is not particularly limited, and any known negative electrode used in a lithium ion secondary battery can be used. Specifically, a negative electrode current collector, a negative electrode active material, a conductive agent, a binder, and the like Those composed of are preferably used. These materials are the same for the positive electrode, but are formed by forming a thin coating film, sheet or plate on the negative electrode current collector.

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

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

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

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

  In the lithium ion secondary battery of the present invention, the contact between the positive electrode and the negative electrode is achieved by a method in which a separator is sandwiched between the positive electrode and the negative electrode, or a method in which each electrode is opposed to each other with a gap using a holding means. It is preferable to prevent short circuit.

  As the separator, it is preferable to use a porous thin film that does not cause a chemical reaction with the ionic compound of the above general formula (1) and other electrolytes in the operating temperature range. As the material of the separator, paper; organic materials such as polyolefin (polypropylene, polyethylene, etc.) and aramid; organic porous materials such as aramid fiber; inorganic materials such as glass fiber; In particular, when an electricity storage device is operated under a high voltage, a high insulating property is required, and therefore a separator made of an inorganic material, a polyolefin material, or a mixture thereof is suitable. From an insulating viewpoint, a polypropylene (PP) film, a polyethylene (PE) film, or a laminated film in which these films are laminated (for example, a PP / PE / PP three-layer film); a polyolefin-based material and an inorganic-based material A molded body of the above mixture; a product obtained by applying or impregnating the organic material to a porous sheet containing cellulose; and the like are suitable as a separator.

Note that an electrolyte such as LiPF ₆ that has been used in a conventional electrolytic solution is decomposed even with a small amount of water contained in the electrolytic solution to generate hydrogen fluoride (HF). This hydrogen fluoride not only dissolves the electrode active material, but also reacts with and dissolves an inorganic material for a separator such as glass fiber, thereby increasing the internal resistance of the electricity storage device. However, since the anion (TCB) of the ionic compound represented by the general formula (1) does not contain fluorine (F), an insulating inorganic material such as a metal oxide such as ceramic or glass fiber Can also be used as a separator material. The insulating inorganic material may be used alone or in a form mixed with an organic material as a filler.

  The lithium ion secondary battery of the present invention only needs to have a positive electrode, a negative electrode, and an electrolyte, and may include a plurality of cells each having the positive electrode, the negative electrode, and the electrolyte as one unit. Good. If it has the said structure, the shape of the lithium ion secondary battery of this invention will not be limited, Conventionally well-known shapes, such as a coin type | mold, a winding cylinder type | mold, a lamination | stacking square type | mold, an aluminum lamination type | mold, can be employ | adopted. Moreover, the said exterior case is not specifically limited, What is necessary is just to employ | adopt conventionally well-known things, such as those made from aluminum and steel.

  The lithium ion secondary battery of the present invention is configured with a positive electrode and a negative electrode facing each other with a separator interposed therebetween, and an electrolytic solution that fills between these electrodes as basic components. In the lithium ion secondary battery of the present invention, electric energy is accumulated and taken out when lithium ions move between the positive electrode and the negative electrode by occlusion and release of lithium ions at each electrode.

(2) Electric Double Layer Capacitor The electric double layer capacitor is composed of a polarizable electrode (negative electrode, positive electrode) and an electrolytic solution as basic components.

The electric double layer capacitor of the present invention has the electrolytic solution of the present invention comprising a pair of polarizable electrodes facing each other with a separator, the ionic compound represented by the general formula (1) and an aprotic solvent. However, it has characteristics. In the ionic compound represented by the general formula (1), the cation Kt ⁺ is preferably an onium cation. In the electric double layer capacitor of the present invention, the above-described polymer electrolyte or polymer gel electrolyte may be used as the electrolyte.
The electric double layer capacitor having the above configuration has a higher positive electrode potential when fully charged than conventional ones, and can operate stably even when charging and discharging are repeated under a high voltage.

  In the electric double layer capacitor of the present invention, one of the opposing polarizable electrodes functions as a positive electrode and the other functions as a negative electrode. A polarizable electrode is provided on a current collecting electrode, and is composed of a positive or negative electrode active material, a conductive agent, a binder (binder material), and the like. It is formed by forming a thin coating film, sheet or plate on the extreme.

Examples of the electrode active material include activated carbon fibers, activated carbon particles, activated carbon such as activated carbon particles, porous metal oxides, porous metals, and conductive polymers. In addition, activated carbon is suitable for the negative electrode, and activated carbon, porous metal oxide, porous metal, and conductive polymer are suitable for the positive electrode. Among these, activated carbon is preferable, and activated carbon having an average pore diameter of 2.5 nm or less is preferable. Here, the average pore diameter is a value measured by the BET method by nitrogen adsorption. The specific surface area of the activated carbon varies depending on the capacitance per unit area (F / m ² ) depending on the carbonaceous species, the decrease in the bulk density accompanying the increase in the specific surface area, etc. is preferably a specific surface area of 500m ² / g~2500m ² / g, more preferably 1000m ² / g~2000m ² / g.

  As the method for producing the activated carbon, plant-based wood, sawdust, coconut husk, pulp waste liquid, fossil fuel-based coal, heavy petroleum oil, or pyrolyzed coal and petroleum-based pitch, petroleum coke, Carbon aerogel, mesophase carbon, tar pitched fiber, synthetic polymer, phenol resin, furan resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, polyamide resin, ion exchange resin, liquid crystal polymer, plastic disposal It is preferable to use an activation method in which a raw material such as a product or a waste tire is carbonized and then activated.

  The activation method includes (1) a gas activation method in which a carbonized raw material is brought into contact with water vapor, carbon dioxide gas, oxygen, and other oxidizing gas at a high temperature, and (2) the carbonized raw material is mixed with zinc chloride, phosphoric acid, Evenly impregnated with sodium phosphate, calcium chloride, potassium sulfide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium sulfate, potassium sulfate, calcium carbonate, boric acid, nitric acid, etc. in an inert gas atmosphere And a chemical activation method in which activated carbon is obtained by dehydration and oxidation reaction of the chemical, and any of them may be used.

  The activated carbon obtained by the above activation method may be subjected to a heat treatment to remove unnecessary surface functional groups or to develop the crystallinity of carbon to increase electrical conductivity. The heat treatment is preferably performed in an inert gas atmosphere such as nitrogen, argon, helium, or xenon, preferably at a temperature of 500 ° C. to 2500 ° C., more preferably 700 ° C. to 1500 ° C. Examples of the shape of the activated carbon include crushing, granulation, granule, fiber, felt, woven fabric, and sheet shape. Among these, the shape of the activated carbon is preferably granular. In this case, the average particle diameter of the activated carbon is preferably 30 μm or less from the viewpoint of improving the bulk density of the electrode and reducing the internal resistance. Here, the average particle diameter is a value of a volume average particle diameter measured by a laser diffraction particle size distribution measuring device. The nominal value of the seller may be referred to.

  As the electrode active material, a carbon material having the above specific surface area other than activated carbon may be used. For example, carbon nanotubes, diamond produced by plasma CVD, or the like may be used.

  As the conductive agent, carbon black such as acetylene black and ketjen black, natural graphite, thermally expanded graphite, carbon fiber, metal fiber such as ruthenium oxide, titanium oxide, aluminum, and nickel are preferable. These can use 1 type (s) or 2 or more types. Among these, acetylene black and ketjen black are more preferable in that the conductivity can be effectively improved with a small amount. The blending amount of the conductive agent varies depending on the bulk density of the activated carbon, but is preferably 5 to 50 parts by mass with respect to 100 parts by mass of the activated carbon, and preferably 10 to 30 parts by mass. More preferred.

  As the binder substance, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, fluoroolefin copolymer crosslinked polymer, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, phenol resin, and the like are suitable. These can use 1 type (s) or 2 or more types. As a compounding quantity of a binder substance, although it changes with kinds, shapes, etc. of activated carbon, it is preferable to set it as 0.5 mass part-30 mass parts with respect to 100 mass parts of activated carbon, and 2 mass parts-30 mass parts. More preferably.

  The current collecting electrode is used for taking out the electric capacity stored in the polarizable electrode to the outside. Examples of the collecting electrode include aluminum foil, copper foil, and metal fibers such as aluminum and nickel.

  As a method for forming the polarizable electrode (positive electrode and negative electrode), for example, (1) polytetrafluoroethylene as a binder material is added and mixed into a mixture of activated carbon as an electrode active material and acetylene black as a conductive agent. Then, it is applied on the collector electrode and press-molded. (2) Activated carbon and binder materials such as pitch, tar, phenol resin, etc. are mixed, molded, integrated with the collector electrode, and then heat-treated in an inert atmosphere. Thus, a method of forming an electrode as a sintered body and (3) a method of sintering only activated carbon and a binder material or activated carbon to form an electrode are suitable. In addition, when using the activated carbon fiber cloth obtained by activating a carbon fiber cloth, you may use as an electrode as it is, without using a binder substance.

  In the electric double layer capacitor of the present invention, contact or short circuit between the polarizable electrodes can be achieved by a method in which the separator is sandwiched between the polarizable electrodes or a method in which the polarizable electrodes are opposed to each other with a spacing using a holding means. It is preferable to prevent.

  As the separator, it is preferable to use a porous thin film that does not cause a chemical reaction with the ionic compound of the above general formula (1) and other electrolytes in the operating temperature range. As the material of the separator, nonwoven fabric made of cellulose fibers such as kraft paper and Manila hemp paper, fiber material made of inorganic fibers such as ceramic fibers, porous sheet containing aliphatic polyketone fibers, porous sheet containing cellulose, latex And the like impregnated with a polymer such as

  The electric double layer capacitor of the present invention only needs to have a pair of polarizable electrodes and a non-aqueous electrolyte that are opposed to each other via a separator, and a pair of polarizable electrodes that are opposed to each other via a separator. A plurality of cells each having a water electrolyte as a unit may be provided. As long as it has the above configuration, the shape of the electric double layer capacitor of the present invention is not limited, and any conventionally known shape such as a coin shape, a wound cylindrical shape, a laminated square shape, and an aluminum laminated shape can be adopted.

  The electric double layer capacitor of the present invention includes a pair of polarizable electrodes opposed via a separator and an electrolytic solution that fills the gap between the polarizable electrodes as basic components. In the electric double layer capacitor of the present invention, electric charges are stored in the electric double layer generated at the interface between the polarizable electrode and the electrolytic solution by the physical adsorption / desorption of ions. And the stored electric charge is taken out as electrical energy through the current collecting electrode.

(3) Lithium Ion Capacitor A lithium ion capacitor uses a carbon-based material that can store lithium ions as a negative electrode material while using the principle of a general electric double layer capacitor. It is an improved capacitor, and the principle of charging and discharging is different between the positive electrode and the negative electrode, and has a structure in which the negative electrode of the lithium ion secondary battery and the positive electrode of the electric double layer capacitor are combined.

The lithium ion capacitor of the present invention includes a positive electrode, a negative electrode, and an electrolytic solution, the positive electrode is a polarizable electrode, the negative electrode includes a negative electrode active material capable of occluding and releasing lithium ions, and the electrolytic solution Is characterized in that it contains lithium ions, tetracyanoborate; [B (CN) ₄ ] ^- , and an aprotic organic solvent.

  The lithium ion capacitor having the above configuration can operate stably even when charging and discharging are repeated under a high voltage.

  The electrolytic solution provided in the lithium ion capacitor of the present invention contains lithium ions, tetracyanoborate, and an aprotic organic solvent. Lithium ions and tetracyanoborate each function as a charge carrier in the electrolyte. In particular, tetracyanoborate is excellent in electric withstand characteristics (an effect of improving the withstand voltage on the positive electrode side) and hardly decomposes even when used under a high voltage. Therefore, the lithium ion capacitor of the present invention can be stably operated even under a high voltage and has a high energy density.

The electrolyte solution of the present invention is preferably used as the electrolyte solution of the lithium ion capacitor of the present invention. The lithium ions and tetracyanoborate contained in the electrolytic solution according to the present invention are derived from compounds containing these anions and / or cations. The compound that generates these ions is an ion represented by the general formula (1): Kt ⁺ [B (CN) ₄ ] ⁻ (in the formula (1), Kt ⁺ represents a lithium ion and / or an onium cation). It may be derived from a functional compound or may be derived from another electrolyte. In addition, when lithium ion is not contained in the ionic compound of General formula (1), the lithium ion contained in the electrolyte solution which concerns on this invention comes from another electrolyte.

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

  The lithium ion capacitor of the present invention has a positive electrode (polarizable electrode), a negative electrode, and an electrolytic solution. A separator is provided between the positive electrode and the negative electrode in order to prevent a short circuit due to contact between the two.

  Each of the positive electrode and the negative electrode includes a current collecting electrode, a positive electrode active material or a negative electrode active material, a conductive agent, a binder (binder material), and the like, and each electrode has these materials on the current collecting electrode. It is formed by forming a thin coating film, a sheet shape or a plate shape.

As the positive electrode active material, activated carbon, a porous metal oxide, a porous metal, and a conductive polymer are suitable. As the activated carbon, those having an average pore diameter of 2.5 nm or less are preferable. Here, the average pore diameter is a value measured by the BET method by nitrogen adsorption. The specific surface area of the activated carbon varies depending on the capacitance per unit area (F / m ² ) depending on the carbonaceous species, the decrease in the bulk density accompanying the increase in the specific surface area, etc. is preferably a specific surface area of 500m ² / g~2500m ² / g, more preferably 1000m ² / g~2000m ² / g.

  As the method for producing the activated carbon, plant-based wood, sawdust, coconut husk, pulp waste liquid, fossil fuel-based coal, heavy petroleum oil, or pyrolyzed coal and petroleum-based pitch, petroleum coke, Carbon aerogel, mesophase carbon, tar pitched fiber, synthetic polymer, phenol resin, furan resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, polyamide resin, ion exchange resin, liquid crystal polymer, plastic disposal It is preferable to use an activation method in which a raw material such as a product or a waste tire is carbonized and then activated.

  The activation method includes (1) a gas activation method in which a carbonized raw material is brought into contact with water vapor, carbon dioxide gas, oxygen, and other oxidizing gas at a high temperature, and (2) the carbonized raw material is mixed with zinc chloride, phosphoric acid, Evenly impregnated with sodium phosphate, calcium chloride, potassium sulfide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium sulfate, potassium sulfate, calcium carbonate, boric acid, nitric acid, etc. in an inert gas atmosphere And a chemical activation method in which activated carbon is obtained by dehydration and oxidation reaction of the chemical, and any of them may be used.

  The activated carbon obtained by the above activation method may be subjected to a heat treatment to remove unnecessary surface functional groups or to develop the crystallinity of carbon to increase electrical conductivity. The heat treatment is preferably performed in an inert gas atmosphere such as nitrogen, argon, helium, or xenon, preferably at a temperature of 500 ° C. to 2500 ° C., more preferably 700 ° C. to 1500 ° C. Examples of the shape of the activated carbon include crushing, granulation, granule, fiber, felt, woven fabric, and sheet shape. Among these, the shape of the activated carbon is preferably granular. In this case, the average particle diameter of the activated carbon is preferably 30 μm or less from the viewpoint of improving the bulk density of the electrode and reducing the internal resistance. Here, the average particle diameter is a value of a volume average particle diameter measured by a laser diffraction particle size distribution measuring device. The nominal value of the seller may be referred to.

  As the positive electrode active material, a carbon material having the above specific surface area other than activated carbon may be used. For example, carbon nanotubes or diamond produced by plasma CVD may be used.

As the negative electrode active material, a material capable of inserting and extracting lithium ions is used. Examples of such materials include pyrolytic carbon; coke such as pitch coke, needle coke, and petroleum coke; graphite; glassy carbon; an organic polymer compound obtained by firing and carbonizing a phenol resin, a furan resin, or the like at an appropriate temperature. Sintered body; carbon fiber; carbon material such as activated carbon; polymer such as polyacetylene, polypyrrole, polyacene; lithium-containing transition metal oxide or transition metal sulfide such as Li ₄ / 3Ti ₅ / 3O ₄ , TiS ₂ ; and alkali metal Al alloying, Pb, Sn, Bi, metals such as Si, the alkali metal can be inserted interstitially, AlSb, Mg ₂ Si, intermetallic compounds cubic such NiSi ₂ or, Li _3- Lithium nitrogen compounds such as _f G _f N (G: transition metal, f: real number greater than 0 and less than 0.8) are suitable. These can use 1 type (s) or 2 or more types. Among these, a carbon material is more preferable.

  As the conductive agent, carbon black such as acetylene black and ketjen black, natural graphite, thermally expanded graphite, carbon fiber, metal fiber such as ruthenium oxide, titanium oxide, aluminum, and nickel are preferable. These can use 1 type (s) or 2 or more types. Among these, acetylene black and ketjen black are more preferable in that the conductivity can be effectively improved with a small amount. The blending amount of the conductive agent varies depending on the bulk density of the activated carbon, but is preferably 5 to 50 parts by mass with respect to 100 parts by mass of the activated carbon, and preferably 10 to 30 parts by mass. More preferred.

  As the binder substance, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, fluoroolefin copolymer crosslinked polymer, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, phenol resin, and the like are suitable. These can use 1 type (s) or 2 or more types. As a compounding quantity of a binder substance, although it changes with kinds, shapes, etc. of activated carbon, it is preferable to set it as 0.5 mass part-30 mass parts with respect to 100 mass parts of activated carbon, and 2 mass parts-30 mass parts. More preferably.

  The current collecting electrode is used for taking out the electric capacity stored in the positive electrode (polarizable electrode) and the negative electrode to the outside. For example, aluminum or stainless steel is used as the positive electrode current collecting electrode, and aluminum, copper, nickel, or the like is used as the negative electrode current collecting electrode.

  As a method for forming the positive electrode and the negative electrode, for example, (1) a binder material is added and mixed into a mixture of an electrode active material of a positive electrode or a negative electrode and acetylene black, which is a conductive agent, and then applied onto each collector electrode. (2) A method of press molding, (2) A method in which an electrode active material and a binder material are mixed and molded, integrated with a collector electrode, and then heat-treated in an inert atmosphere to form a sintered body as an electrode, (3) A method of sintering only activated carbon and a binder substance or activated carbon to form an electrode is suitable. In addition, when using the activated carbon fiber cloth obtained by activating a carbon fiber cloth, you may use as an electrode as it is, without using a binder substance.

  In addition, it is preferable that the negative electrode produced as described above occlude lithium ions by a chemical method or an electrochemical method. This lowers the potential of the negative electrode, so that a wider voltage range can be used. As a result, the energy density of the lithium ion capacitor is improved. As a method for occluding lithium ions, any conventionally known method can be adopted. For example, a method in which a negative electrode and a lithium metal are opposed to each other through a separator in an electrolytic solution, and constant current charging is performed. Among them, a method in which the negative electrode and lithium metal are brought into contact with each other and heated may be mentioned.

  In the lithium ion capacitor of the present invention, contact between the positive electrode and the negative electrode or a short circuit by a method in which a separator is sandwiched between the positive electrode and the negative electrode or a method in which each electrode is opposed to each other with a gap using a holding means. It is preferable to prevent this.

  As the separator, it is preferable to use a porous thin film that does not cause a chemical reaction with the ionic compound of the above general formula (1) and other electrolytes in the operating temperature range. As the material of the separator, those exemplified as the separator of a lithium ion secondary battery or an electric double layer capacitor are suitable.

  The lithium ion capacitor of the present invention only needs to have a positive electrode, a negative electrode, and an electrolytic solution, and may include a plurality of cells each having the positive electrode, the negative electrode, and the electrolytic solution as one unit. If it is provided with the said structure, the shape of the lithium ion capacitor of this invention will not be limited, All conventionally well-known shapes, such as a coin type | mold, a winding cylindrical type | mold, a lamination | stacking square type | mold, an aluminum lamination type | mold, are employable.

  The lithium ion capacitor of the present invention is composed of a positive electrode and a negative electrode that face each other with a separator interposed therebetween, and an electrolyte solution that fills between these electrodes as a basic component. In the lithium ion capacitor of the present invention, charges are stored in the electric double layer generated at the interface between the positive electrode and the electrolyte by physical adsorption / desorption of ions, while in the negative electrode, lithium ions are occluded in the negative electrode active material. As a result, electric charge is stored. And when the stored electric charge is taken out as electric energy through the current collecting electrode, ions attached to the positive electrode are separated from the electrode, and lithium ions occluded in the negative electrode active material are also released.

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

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

[Measurement of ion conductivity]
The ionic compound obtained in the following production example was dissolved in γ-butyrolactone (GBL) or propylene carbonate (PC) to prepare an ionic compound solution having a concentration of 35% by mass.

  Using an impedance analyzer ("SI1260" manufactured by Solartron Co., Ltd.) and using a SUS electrode, the ionic conductivity of the ionic compound solution was measured by a complex impedance method under a temperature condition of 25 ° C.

[Measurement of thermal decomposition start temperature]
10 mg of the ionic compound obtained in the following production example was put in an aluminum pan, heated at 5 ° C./min, and the temperature when it was reduced by 2% from the initial mass was measured by a differential thermothermal gravimetric simultaneous measurement device (manufactured by Seiko Instruments Inc. “ EXSTAR6000 TG / DTA ”).

Production Example 1 Synthesis of Ionic Compound 1 30.3 g of triethylmethylammonium chloride (Et ₃ MeNCl) previously heated and dried in a 1 L eggplant flask equipped with a stirrer, a reflux tube and a drawing device, and a dropping funnel 200 mmol) was added. After replacing the inside of the container with nitrogen, 109.0 g (1100 mmol) of trimethylsilylcyanide (TMSCN) was added at room temperature, and the mixture was stirred and mixed. Next, 200 mL (200 mmol) of a 1 mol / L p-xylene solution of boron trichloride was slowly dropped from the dropping funnel. After completion of the dropping, the reaction vessel was heated to 150 ° C., and the reaction was performed while extracting trimethylsilyl chloride (TMSCl, boiling point: about 57 ° C.) as a by-product from the reflux extraction portion.

  After stirring with heating for 30 hours, the inside of the reaction vessel was depressurized with a diaphragm pump, and the p-xylene solution of TMSCN was distilled off from the reflux outlet. Thereafter, 45 g of the crude product and 225 g of ethyl acetate were placed in a 500 mL beaker equipped with a stirrer, and dissolved by stirring for 5 minutes, and then 135 g of activated carbon (Carlabafine (registered trademark) manufactured by Nippon Enviro Chemical Co., Ltd.). )) Was added and stirred for 10 minutes. The obtained activated carbon suspension is filtered through a membrane filter (0.2 μm, made of PTFE), the solvent is distilled off, and the resulting white yellow solid is dried under reduced pressure at 80 ° C. for 3 days to be the target product. Triethylmethylammonium tetracyanoborate (TEMATCB, pale yellow solid) was obtained (yield: 37.9 g (164 mmol), yield: 82%, melting point: 115 ° C.).

Various physical properties of triethylmethylammonium tetracyanoborate obtained by the above measuring method were measured. The results are as follows.
Ionic conductivity (25 ° C.): 0.018 S / cm
Thermal decomposition start temperature: 280 ° C
¹ H-NMR (d6-DMSO) δ 3.23 (q, J = 6.8 Hz, 6H), 2.86 (s, 3H), 1.18 (t, J = 6.8 Hz, 9H)
¹³ C-NMR (d6-DMSO) δ 112.5 (m), 55.2 (s), 46.2 (s), 7.7 (s)
¹¹ B-NMR (d6-DMSO) δ-39.6 (s)

Production Example 2 Synthesis of Ionic Compound 2 (1-Ethyl-3-methylimidazolium Tetracyanoborate) The inside of a 50-ml flask equipped with a stirrer, a dropping funnel and a reflux tube was purged with nitrogen, and the room temperature was maintained under a nitrogen atmosphere. Here, 3.0 g (15.8 mmol) of 1-ethyl-3-methylimidazolium bromide, 9.26 g (78.9 mmol) of zinc (II) cyanide, 10 ml of toluene, 2.8 g of boron tribromide ( 11.2 mmol), and the contents were stirred for 2 days while heating the contents in a 130 ° C. oil bath. Two days later, toluene in the flask was distilled off under reduced pressure to obtain a black solid. The obtained solid was pulverized in a mortar and then placed in a beaker equipped with a stirrer, and 200 ml of chloroform was added thereto twice to extract the product into a chloroform layer. Subsequently, the obtained chloroform solution was transferred to a separatory funnel and washed with 200 ml of water, and then the organic layer was separated and concentrated by an evaporator to obtain an oily crude product. This was purified by column chromatography (developing solvent, mixed solution of diethyl ether and chloroform) using neutral alumina as a filler, fractions containing the product were separated, the solvent was distilled off, To give 1-ethyl-3-methylimidazolium tetracyanoborate (EMIMTCB) as a product (yellow oil, yield: 1.0 g (4.4 mmol), yield: 38%, melting point: 15 ° C).
¹ H-NMR (d6-DMSO) δ 8.41 (s, 1H), 7.34 (d, J = 21.6Hz, 2H), 3.81 (s, 3H), 1.45 (t, J = 7.2Hz, 3H)
¹³ C-NMR (d6-DMSO) δ 136.5 (s), 132.2 (m), 122.9 (s), 45.8 (s), 36.8 (s), 15.4 (s)
¹¹ B-NMR (d6-DMSO) δ-39.6 (s)

Production Example 3 Synthesis of Ionic Compound 3 (Lithium Tetracyanoborate) 44.4 g of tributylammonium chloride previously heated and dried in a 1 L eggplant flask equipped with a stirrer, a reflux tube and a withdrawal device, and a dropping funnel ( 200 mmol) was added. After replacing the inside of the container with nitrogen, 109.0 g (1100 mmol) of trimethylsilylcyanide (TMSCN) was added at room temperature, and the mixture was stirred and mixed. Next, 200 mL (200 mmol) of a 1 mol / L p-xylene solution of boron trichloride was slowly dropped from the dropping funnel. After completion of the dropping, the reaction vessel was heated to 150 ° C., and the reaction was performed while extracting trimethylsilyl chloride (TMSCl, boiling point: about 57 ° C.) as a by-product from the reflux extraction portion.

  After stirring with heating for 30 hours, the inside of the reaction vessel was depressurized with a diaphragm pump, and the p-xylene solution of TMSCN was distilled off from the reflux outlet. Thereafter, 45 g of the crude product and 225 g of ethyl acetate were placed in a 500 mL beaker equipped with a stirrer, and dissolved by stirring for 5 minutes, and then 135 g of activated carbon (Carlabafine (registered trademark) manufactured by Nippon Enviro Chemical Co., Ltd.). )) Was added and stirred for 10 minutes. The obtained activated carbon suspension was filtered through a membrane filter (0.2 μm, PTFE), the solvent was distilled off, and the residue was dried to obtain the target product, tributylammonium tetracyanoborate (yellow solid) (yield) : 48.2 g (160 mmol), yield: 80%).

Various physical properties of the obtained tributylammonium tetracyanoborate were measured by the above measuring method. The results are as follows.
¹ H-NMR (d6-DMSO) δ 2.98 (m, 6H), 1.4 to 1.8 (m, 6H), 1.2 to 1.3 (m, 6H), 0.94 (m, 9H)
¹³ C-NMR (d6-DMSO) δ 121.9 (m), 52.7 (s), 26.2 (s), 20.3 (s), 14.4 (s)
¹¹ B-NMR (d6-DMSO) δ-39.6 (s)

Subsequently, 48.2 g (160 mmol) of the obtained tributylammonium tetracyanoborate, 200 g of butyl acetate, 4.6 g (192 mmol) of lithium hydroxide monohydrate, and 200 g of ultrapure water were added to a 500 ml beaker equipped with a stirrer. Was added and stirred for 1 hour. Thereafter, the mixed solution was transferred to a separatory funnel and allowed to stand to separate into two layers. Among these, the pale yellow solid obtained by separating and concentrating the lower layer (aqueous layer) was mixed with 200 g of acetonitrile and stirred. Thereafter, the obtained solution was filtered through a membrane filter (0.2 μm, made of PTFE), and the solvent was distilled off to obtain lithium tetracyanoborate (LiTCB, white solid) as a target product (yield: 13). .6 g (112 mmol), yield: 70%). The obtained white solid was dried under reduced pressure at 150 ° C. for 3 days.
⁷ Li-NMR (d6-DMSO) δ 0.02 (s)
¹³ C-NMR (d6-DMSO) δ 121.9 (m)
¹¹ B-NMR (d6-DMSO) δ-39.6 (s)

Experimental Example 1 Measurement of Ionic Conductivity Experimental Example 1-1
The ionic compound 1 (TEMATCB) obtained in Production Example 1 is dissolved in propylene carbonate (PC) to prepare an electrolytic solution having the concentration shown in Table 1, and the ionic conductivity at −20 ° C., 0 ° C., and 25 ° C. Was measured.

Ion conductivity was measured according to the method described above except that six types of measurement sample solutions having different concentrations were used. The results are shown in Table 1 and FIG.

  As can be seen from FIG. 1, the ionic conductivity increases as the concentration of the ionic compound increases at any temperature, but after showing the maximum ionic conductivity at a concentration of about 50% by mass, the ions gradually increase as the concentration increases. It can be seen that the conductivity tends to decrease. As described above, the ionic conductivity decreases on the high concentration side because the increase in the ionic compound concentration increases the electrolyte viscosity, the decrease in the amount of the ionic compound present in the dissociated state in the electrolyte, or the ionic compound This is thought to be because the number of ions that can be carriers in the electrolyte decreased due to the deposition of.

Experimental Example 1-2
The ionic compound 2 (EMIMTCB) obtained in Production Example 2 was dissolved in propylene carbonate (PC) to prepare an electrolytic solution having a concentration shown in Table 2, and the temperature was measured at 25 ° C. in the same manner as in Experimental Example 1-1. Ionic conductivity was measured. The concentration of 100% by mass means that the electrolyte was adjusted with only the ionic compound 2 (no solvent) and the ionic conductivity was measured. The results are shown in Table 2 and FIG.

  From Table 2, it can be seen that, as in Experimental Example 1-1, the ionic conductivity tends to decrease as the concentration of the ionic compound increases, and good ionic conductivity is exhibited at a concentration of 50% by mass or less.

Experimental example 2 Withstand voltage range LSV measurement (linear sweep voltammetry)
Experimental Example 2-1
Using the ionic compound 1 (TEMATCB) obtained in Production Example 1, the withstand voltage range was measured.

  The withstand voltage range is measured in a glove box at 30 ° C using a tripolar electrochemical cell and a standard voltammetry tool (“HSV-100”, manufactured by Hokuto Denko). The potential when the value reached 0.03 mA was defined as the oxidative decomposition potential. The results are shown in FIG. The measurement conditions are as follows.

(Measurement condition)
Working electrode: Glassy carbon electrode (manufactured by BAS, product number: 11-2411, electrode surface area 1 mmφ (0.785 mm ² ))
Reference electrode: Ag electrode (Reference solution: acetonitrile solution of silver nitrate and tetrabutylammonium perchlorate (silver nitrate concentration 0.01M, tetrabutylammonium perchlorate concentration 0.1M))
Counter electrode: platinum electrode Salt bridge: 0.1 M acetonitrile solution of tetrabutylammonium perchlorate Ionic compound concentration: 1 mol / L (24% by mass)
Solvent: Propylene carbonate Sweep speed: 100 mV / s
Sweep range: natural potential to ± 5 V (vs. Ag / Ag +)

Experimental Example 2-2
A sample obtained by purifying the ionic compound 1 (TEMATCB) obtained in Production Example 1 by a recrystallization method using butyl acetate as a solvent, a standard voltammetric tool (“HZ-3000”, Hokuto Denko Co., Ltd.) LSV measurement was performed under the same conditions as in Experimental Example 2-1, except that the voltage was swept from -5V to 10V (Ag / Ag + reference). The results obtained at this time are shown in FIG. 4 together with the LSV measurement results of Experimental Example 2-1.

(Recrystallization method)
10 g of butyl acetate was added to 10 g of TEMATCB, and this solution was stirred at 80 ° C. for 1 hour. The resulting solution was allowed to stand at −15 ° C. for 2 hours, and the precipitated white solid was filtered off to purify TEMATCB (recrystallized purified product, yield: 4.0 g, yield 40%).
FIG. 4 shows that the peak current value during the voltage sweep is smaller in Experimental Example 2-2 (recrystallized purified product) than in Experimental Example 2-1 (Experimental Example 2-1: 0.011 mA, Experimental Example 2-2: 0.005 mA). This is considered to be because impurities were reduced by recrystallization purification. From this result, it was found that a higher performance electrolyte can be obtained by performing recrystallization.

Experimental Example 2-3, 2-4
Using the ionic compound 1 (TEMATCB) obtained in Production Example 1, purification by electrolysis was performed according to the following procedure, and LSV measurement was performed on samples before and after purification by electrolysis. The results are also shown in FIG. 5 (sample after purification by electrolysis method: Experimental Example 2-3, sample before purification by electrolysis method: Experimental Example 2-4).

(Electrolysis method)
Using a 25 mass% propylene carbonate solution of TEMATCB, using a standard voltammetric tool (“HZ-3000”, manufactured by Hokuto Denko), working electrode: glassy carbon (manufactured by BAS, product number: 11-2411, electrode surface area: 1 mmφ (0.785 mm ² ), reference electrode: Ag electrode (reference solution: silver nitrate and acetonitrile solution of tetrabutylammonium perchlorate (silver nitrate concentration 0.01 M, tetrabutylammonium perchlorate concentration 0.1 M)), counter electrode: Platinum electrode, salt bridge: A 0.1 M tetrabutylammonium perchlorate acetonitrile solution was used and swept from 0 V to 5 V (vs. Ag / Ag +) at 100 mV / sec.

  As shown in FIG. 5, by performing the electrolysis purification, the peak current seen in the vicinity of 1 to 2.5 V (vs. Ag / Ag +) in the sample before the electrolysis purification (Experimental Example 2-4) is greatly reduced. It was found to be less than 0.004 mA (Experimental Example 2-3). From this result, it was found that a higher performance electrolyte can be obtained by subjecting the electrolyte of the present invention to an electrolysis purification process.

Experimental Example 2-5
Except for using a standard voltammetry tool (“HZ-3000”, manufactured by Hokuto Denko Co., Ltd.) and sweeping the voltage from −5 V to 10 V (Ag / Ag + reference), the same as in Experimental Example 2-1. LSV measurement was performed under conditions. The results are shown in FIG.

From FIG. 6, in Experiment 2-5, the voltage was increased to 10 V and the measurement was performed, but no current exceeding 0.03 mA was observed. When this is converted to a lithium electrode standard, it becomes about 13.8 V (vsLi / Li ⁺ ), and even if the electric double layer capacitor of the present invention provided with the electrolytic solution is operated in a high voltage range of about 14 V, the electrolytic solution and the electrode Therefore, it is considered that the energy density is higher than that of the conventional electric double layer capacitor.

Experimental Example 2-6
LSV measurement was performed in the same manner as in Experimental Example 2-1 except that commercially available triethylmethylammonium tetrafluoroborate (TEMABF ₄ , manufactured by Kishida Chemical Co., Ltd.) was used as the ionic compound (electrolytic solution: 1.0 M TEMABF ₄ propylene carbonate solution, TEMABF ₄ concentration: 25% by mass). The results are shown in FIG.

From FIG. 3, in Experimental Example 2-1 (TEMATCB), no current was observed even in the vicinity of 5 V, and no current was observed even in a voltage range exceeding 5 V. This is about 8.8 V (vs. Li / Li ⁺ ) when converted to a lithium electrode standard, and the electric double layer capacitor of the present invention provided with the electrolytic solution has a high voltage of about 9 V (vs. Li ^/ Li ⁺ ). Even when operated in the range, the electrolyte and the electrode are unlikely to deteriorate, so it is considered to have a higher energy density than the conventional electric double layer capacitor.

On the other hand, in Experimental Example 2-6 (FIG. 7, TEMABF ₄ ), a current value of 0.03 mA was observed at 2.41 V (vs. Ag / Ag ⁺ ). It can be confirmed that it has been reached. When this is converted on the basis of a lithium electrode, it is about 6.2V. Therefore, it can be seen that the electric double layer capacitor including the electrolytic solution of Experimental Example 2-6 is difficult to operate in the high voltage range because the electrolytic solution is decomposed in the voltage range of 6.2 V or higher. From these results, it can be seen that the electric double layer capacitor of the present invention can operate stably in a high voltage range as compared with the conventional electric double layer capacitor containing TEMABF ₄ as an electrolyte.

  Practically, the electric double layer capacitor provided with the electrolyte solution of Experimental Example 2-6 has a positive electrode potential of about 4.2 V at full charge in consideration of long-term stability and safety (lithium It is recommended that it be used within the range of the standard). Considering the experimental result that the decomposition start potential in Experimental Example 2-6 is 6.2 V (lithium reference), a potential lower by about 2.0 V from the above measured value is a practical full charge in consideration of safety. It becomes the positive electrode potential.

  On the other hand, from the result of Experimental Example 2-1, since it is stable without decomposition up to 8.8 V in terms of lithium electrode, in the case of Experimental Example 2-1, the positive electrode at full charge Even if the potential is about 6.8 V (lithium standard), it can be safely used.

Experimental Example 3 Cyclic Voltammetry Cyclic voltammetry (CV) measurement was performed as a full cell evaluation of an electric double layer capacitor and a half cell evaluation of a lithium ion capacitor.

  In this experimental example, in order to evaluate the basic performance of an electric double layer capacitor and a lithium ion capacitor, an experiment was performed using an electrode and a separator equivalent to those used in these devices. Therefore, from this experimental result, the charge / discharge characteristics in the electric double layer capacitor and the charge / discharge characteristics in the half cell condition of the lithium ion capacitor can be evaluated.

Experimental example 3-1
Cyclic voltammetry was performed using the ionic compound 1 (TEMATCB) obtained in Production Example 1.

Cyclic voltammetry was performed using an electrochemical measurement device (“HZ-3000”, manufactured by Hokuto Denko Co., Ltd.) using a triode cell as an electrode in an atmosphere at 25 ° C. Note that an ACF electrode using activated carbon fiber cloth (specific surface area 2000 m ² / g, manufactured by Kuraray Chemical Co., Ltd.) was used for the working electrode and the counter electrode in the triode cell, and an Ag electrode was used for the reference electrode. The separator used was a filter paper “A-2” manufactured by Toyo Filter Paper Co., Ltd., which was dried at 100 ° C. for 1 hour.

The measurement uses 1.0 M TEMATCB propylene carbonate solution (TEMATCB concentration: 25% by mass) as the electrolytic solution, the sweep rate is 5 mV / s, and between -1.0 V and 2.5 V (vs. Ag / Ag ⁺ ). I went there. The results are shown in FIG. The specific capacitance calculated from the result of CV measurement was 81.6 [Fg ⁻¹ ]. Therefore, it is considered that the electric double layer capacitor including the electrode and the electrolytic solution has a specific capacity of 81.6 [Fg ⁻¹ ].

Experimental Example 3-2
Cyclic voltammetry was performed in the same manner as in Experimental Example 3-1, except that commercially available triethylmethylammonium tetrafluoroborate (TEMABF ₄ , manufactured by Kishida Chemical Co., Ltd.) was used as the ionic compound (1.0 M TEMABF ₄ propylene carbonate solution, TEMABF ₄ concentration: 25% by mass). The results are shown in FIG.

  From FIG. 8, in Experimental Example 3-1, which includes the ionic compound according to the present invention, the 10th cycle shows the same hysteresis as the 5th cycle. Therefore, the electric double layer capacitor and the lithium ion capacitor of the present invention are stable without causing decomposition of the electrolyte or deterioration of the electrode even in a high voltage range of 2.5 V (about 6.3 V on the lithium standard). It can be seen that charging and discharging can be repeated.

On the other hand, in FIG. 9 (Experimental example 3-2), the hysteresis in the first cycle and the hysteresis after the second cycle are completely different. This is probably because the electrolyte solution, particularly TEMABF ₄ used as the electrolyte, was oxidatively decomposed in a high voltage range. As described above, since the noise considered to be derived from the decomposition product was seen in the cyclic voltammogram of FIG. 9, the specific capacity could not be calculated in Experimental Example 3-2.

  As is clear from Experimental Examples 1 to 3, the electric double layer capacitor and the lithium ion capacitor of the present invention are resistant to decomposition of the electrolytic solution and electrode deterioration even in a high voltage range, and can operate stably. . Therefore, the electric double layer capacitor of the present invention is suitable for a power source for mobile phones, personal computers, automobiles, and the like.

Experimental example 4 Withstand voltage range LSV measurement (linear sweep voltammetry)
Experimental example 4-1
Using the ionic compound 3 (LiTCB) obtained in Production Example 3 as the electrolyte, the withstand voltage range was measured. The measurement was the same as in Experimental Example 2-1, except that a standard voltammetric tool (“HZ-3000”, manufactured by Hokuto Denko Co., Ltd.) was used as the measurement device, and the measurement conditions were changed as follows. (Electrolytic solution: 0.7 M LiTCB γ-butyrolactone solution, LiTCB concentration: 7% by mass). The results are shown in FIG.

(Measurement condition)
Working electrode: Glassy carbon electrode (manufactured by BAS, product number: 11-2411, electrode surface area 1 mmφ (0.785 mm ² ))
Reference electrode: Ag electrode (Reference solution: Acetonitrile solution of silver nitrate and tetrabutylammonium perchlorate (silver nitrate concentration 0.01M, tetrabutylammonium perchlorate concentration 0.1M)
Counter electrode: platinum electrode Salt bridge: 0.1 M acetonitrile solution of tetrabutylammonium perchlorate Ionic compound concentration: 0.7 mol / L (7% by mass)
Solvent: γ-butyrolactone Sweep speed: 100 mV / s
Sweeping range: natural potential to ± 10 V (vs. Ag / Ag +)

Experimental example 4-2, 4-3
Except for using 7% by mass LiTCB γ-butyrolactone solution as the electrolytic solution, electrolysis purification was performed in the same manner as in Experimental Example 2-3, and LSV measurement was performed using samples before and after electrolysis purification. It was. The results are also shown in FIG.

  From FIG. 11, in LiTCB (Experimental Example 4-2), as in the case of TEMATCB (Experimental Example 2-3), electrolysis purification was performed, and in Experimental Example 4-3 (before electrolytic purification), 1 to It was found that the peak current seen in the vicinity of 2.5 V was greatly reduced and was less than 0.015 mA (Experimental Example 4-2). From this result, it was found that a higher performance electrolyte can be obtained by subjecting the electrolyte of the present invention to electrolysis purification.

Experimental Example 4-4
LSV measurement was performed in the same manner as in Experimental Example 4-1 except that commercially available lithium tetrafluoroborate (LiBF ₄ , LBG grade, manufactured by Kishida Chemical Co., Ltd.) was used as the electrolyte (electrolytic solution: 0.8M LiBF ₄ γ-butyrolactone solution, LiBF ₄ concentration: 7% by mass).
The results are shown in FIG.

Experimental Example 4-5
The LSV measurement of the LiTCB solution (0.7 M LiTCB γ-butyrolactone solution) was performed under the same conditions as in Experimental Example 4-3 except that the voltage was swept from −5 V to 10 V (Ag / Ag ⁺ reference). . The results are shown in FIG.

From FIG. 13, it was confirmed that even if the sweep voltage range is 10 V (Ag / Ag ⁺ ), 0.03 mA or more does not flow in Experimental Example 4-3 (LiTCB). In addition, 10V on the basis of Ag corresponds to about 13.8V on the basis of Li (battery initial characteristic evaluation).

Experimental Example 4-6
LSV measurement was performed in the same manner as in Experimental Example 4-1 except that a commercially available lithium hexafluorophosphate (LiPF ₆ , LBG grade, manufactured by Kishida Chemical Co., Ltd.) was used as the electrolyte (electrolyte: 0. 0). 5M LiPF ₆ γ-butyrolactone solution, LiPF ₆ concentration: 7% by mass). The results are shown in FIG.

From FIG. 10, in Experimental Example 4-1 (LiTCB), no current is observed even in the vicinity of 5 V (Ag / Ag ⁺ reference), and a voltage range exceeding 5 V (silver electrode reference), particularly 10 V ( No current was observed even in a voltage range exceeding the silver electrode standard). In addition, 5V on the basis of the silver electrode is about 8.8V (vs. Li / Li ⁺ ) in terms of the lithium electrode. Therefore, even if the lithium ion capacitor or lithium ion secondary battery of the present invention having an electrolytic solution containing tetracyanoborate is operated in a high voltage range of about 9 V to 14 V (lithium electrode standard), the electrolytic solution and the electrode deteriorate. Therefore, it is considered to have a higher energy density than conventional lithium ion capacitors and lithium ion secondary batteries.

On the other hand, in Experimental Example 2-6 (TEMABF ₄ ), 2.41 V (silver electrode reference, FIG. 7), and in Experimental Example 4-4 (LiBF ₄ ), 4.62 V (silver electrode reference, FIG. 12), the experiment In Example 4-6 (LiPF ₆ ), a current value of 0.03 mA was observed at 4.09 V (silver electrode reference, FIG. 14). Therefore, it can be seen that when these electrolytes are used alone, the oxidative decomposition potential is reached at about 2V to 4V. When this is converted on the basis of a lithium electrode, it becomes 6.2V to 8.4V. Therefore, in a lithium ion capacitor or lithium ion secondary battery that uses TEMABF ₄ , LiBF ₄ or LiPF ₆ as an electrolyte and employs an electrolytic solution that does not contain tetracyanoborate, the electrolytic solution is decomposed in a voltage range up to about 8V. It can be seen that it is difficult to operate in a higher voltage range than this. From this result, it can be seen that the lithium ion capacitor and the lithium ion secondary battery of the present invention provided with an electrolytic solution containing lithium ions, tetracyanoborate and an aprotic organic solvent can operate stably even in a high voltage range. .

  Therefore, as is clear from Experimental Example 4 described above, the lithium ion capacitor and the lithium ion secondary battery of the present invention are resistant to decomposition of the electrolytic solution and electrode deterioration even in a high voltage range and can operate stably. is there. Therefore, the lithium ion capacitor and the lithium ion secondary battery of the present invention are suitable for power supplies for mobile phones, personal computers, automobiles, and the like.

Experimental Example 5 Basic Charge / Discharge Test Experimental Examples 5-1 to 5-3
LiTCB solution obtained in Production Example 3 (0.6 M LiTCB γ-butyrolactone solution, Experimental Example 5-1), commercially available LiPF ₆ (LBG grade, manufactured by Kishida Chemical Co., Ltd.) solution (0.6 M LiPF ₆ γ -Butyrolactone solution, Experimental Example 5-2), and LiTCB + LiPF ₆ solution obtained by mixing these two electrolytic solutions (concentration of each electrolyte: 0.1 M (LiTCB), 0.9 M (LiPF ₆ ), Experimental Example 5-3 ) Was subjected to a basic charge / discharge test using a standard voltammetric tool (“HSV-100”, manufactured by Hokuto Denko). The results are shown in FIG.

(Measurement condition)
Working electrode: LiCoO ₂ (“Pioxel (registered trademark) C100”, manufactured by Pionics)
Reference electrode: Li metal Counter electrode: Li metal Sweep potential range: 3 to 4.5 V (Li standard)
Sweep speed: 0.1 mV / s

LiCoO ₂ is a positive electrode that is used as a standard for lithium secondary batteries, and similarly, lithium metal is a negative electrode that is used as a standard for lithium secondary batteries. In this experimental example, in order to measure initial characteristics as a lithium secondary battery, normally used electrodes were selected as a working electrode, a reference electrode, and a counter electrode.

From FIG. 15, when the sweep voltage range was 3 V to 4.5 V (Li reference), Experimental Example 5-1 (LiTCB) showed 90% current amount retention even at the 10th cycle. On the other hand, the current holding ratio in the 10th cycle of Experimental Example 5-2 (LiPF ₆ ) was about 40%. From this, it can be seen that LiTCB (Experimental Example 5-1) exhibits excellent cycle characteristics even under high voltage conditions as compared with a conventional electrolyte using LiPF ₆ (Experimental Example 5-2). Furthermore, in the electrolytic solution of Experimental Example 5-3 in which LiTCB was added to LiPF _{6 at} a molar ratio of about 9: 1, the cycle characteristics were higher than that of the electrolytic solution containing LiPF ₆ alone (Experimental Example 5-2). A result of improvement was obtained (10th cycle, current holding ratio 50%). From this, LiTCB not only becomes an electrolyte solution with high cycle characteristics when used alone as an electrolyte, but also exhibits cycle characteristics of the electrolyte solution when LiTCB is used as an additive to other electrolytes. It was found to have an improving effect.

Experimental Example 6 Charge / Discharge Test Ionic Compound 3 (LiTCB; Experimental Example 6-1) Obtained in Production Example 3 above, Commercial Lithium Hexafluorophosphate (LiPF ₆ , LBG Grade, Kishida Chemical Co., Ltd .; Experimental Example A CR2032 type coin cell was prepared using 6-2), and a charge / discharge test was performed.

The coin cell uses LiCoO ₂ (“Cell Seed (registered trademark) C-8G”, manufactured by Nippon Chemical Industry Co., Ltd.) for the positive electrode, and lithium foil (thickness: 0.5 mm, manufactured by Honjo Metal Co., Ltd.) for the negative electrode. And a negative electrode with a separator (“Hypore (registered trademark) NSN9615B”, manufactured by Asahi Kasei E-Materials Co., Ltd.) facing each other, and a 7% by mass (0.7 M) LiTCB γ-butyrolactone solution (electrolyte) Satisfied and produced.

  First, the produced coin cell was stabilized at room temperature (25 ° C.) for 4 hours, and the discharge capacity after the first and 10 cycles was measured with a charge / discharge test apparatus (“ACD-01”, manufactured by Asuka Electronics Co., Ltd.) The capacity retention rate after 10 cycles was calculated. In addition, the charging / discharging rest time of 30 minutes was provided at the time of each charging / discharging.

In addition, the electrolyte solution was changed to an ethylene carbonate (EC) / ethyl methyl carbonate (EMC) solution (EC / EMC = 50/50 (volume ratio)) of LiPF ₆ having a concentration of 14% by mass (1.0 M). Similarly, a coin cell was produced and a charge / discharge test was performed. The measurement conditions are shown below. The results are shown in Table 3 and FIG.

(Measurement condition)
Charge / discharge rate: 0.2C
Charging / discharging mode: Constant current mode Charging / discharging range: 2.5V-4.0V (Li standard)

From Table 3, the lithium ion secondary battery of Experimental Example 6-1 using an electrolytic solution containing TCB as an anion was first discharged compared to the example of Experimental Example 6-2 containing PF ₆ ⁻ and not containing TCB. It can be seen that both the capacity and the capacity retention after 10 cycles show high values. Further, FIG. 16 shows that Experimental Example 6-1 is superior in cycle characteristics as compared to Experimental Example 6-2. From this result, it can be seen that an electrolytic solution containing TCB as an anion has a high withstand voltage, and oxidative decomposition of the electrolytic solution hardly occurs during charging.

  Therefore, the lithium ion secondary battery of the present invention including an electrolytic solution containing lithium ions, tetracyanoborate, and an aprotic organic solvent is unlikely to cause decomposition of the electrolytic solution or deterioration of the electrode derived therefrom. It is thought that it can operate stably.

  As is clear from the above experimental examples 4 to 6, the lithium ion secondary battery of the present invention can be stably operated even in a high voltage range without causing the decomposition of the electrolytic solution and the deterioration of the electrode. Therefore, the lithium ion secondary battery of the present invention is suitable for power sources for mobile phones, personal computers, automobiles, and the like.

Experimental Example 7 LSV measurement (linear sweep voltammetry)
Experimental Example 7-1
Commercially available lithium hexafluorophosphate (LiPF ₆ , LBG grade, manufactured by Kishida Chemical Co., Ltd.) as a main electrolyte was dissolved in propylene carbonate to prepare a measurement solution (7% by mass), and electrochemical characteristics were measured. . In Experimental Example 7-1, the ionic compound for additive was not used. LSV measurement was performed using a tripolar electrochemical cell and a standard voltammetric tool (“HZ-3000”, manufactured by Hokuto Denko) in a glove box at 30 ° C., and the current value was 0.03 mA. The oxidative decomposition potential (withstand voltage range) was measured. The results are shown in Table 4. The measurement conditions are as follows. The sweep range is appropriately adjusted within ± 10 V (vs. Ag ^/ Ag ⁺ ) from the natural potential according to the type of electrolyte used and the measurement conditions, and when the limit current is reached within the range. Finished the measurement at that time.

(Measurement condition)
Working electrode: Glassy carbon electrode (manufactured by BAS, product number: 11-2411, electrode surface area 1 mmφ (0.785 mm ² ))
Reference electrode: Ag electrode (Reference solution: Acetonitrile solution of silver nitrate and tetrabutylammonium perchlorate (silver nitrate concentration 0.01M, tetrabutylammonium perchlorate concentration 0.1M)
Counter electrode: platinum electrode Salt bridge: 0.1 M acetonitrile solution of tetrabutylammonium perchlorate Solvent: propylene carbonate Sweep speed: 100 mV / s
Sweeping range: Natural potential to within ± 10 V (vs. Ag ^/ Ag ⁺ )
Limit current: 1mA

Experimental Example 7-2
Using the commercially available lithium hexafluorophosphate (LiPF ₆ , LBG grade, manufactured by Kishida Chemical Co., Ltd.) as the main electrolyte and the ionic compound 3 (LiTCB) obtained in Production Example 3 as the ionic compound for the additive, A measurement solution was prepared by dissolving in propylene carbonate so that the concentrations shown in Table 4 were obtained, and electrochemical characteristics were measured in the same manner as in Experimental Example 7-1. The results are shown in Table 4. In addition, the decomposition potential in Table 4 is a voltage measurement value based on a silver electrode.

Experimental Example 7-3
Using commercially available lithium hexafluorophosphate (LiPF ₆ , LBG grade, manufactured by Kishida Chemical Co., Ltd.) as the main electrolyte and ionic compound 1 (TEMATCB) obtained in Production Example 1 as the ionic compound for additives, these were used. A measurement solution was prepared by dissolving in propylene carbonate so that the concentrations shown in Table 4 were obtained, and electrochemical characteristics were measured in the same manner as in Experimental Example 7-1. The results are shown in Table 4.

Experimental Example 7-4
A measurement solution was prepared in the same manner as in Experimental Example 7-4, except that the concentrations of the main electrolyte and additive were changed to the concentrations shown in Table 4, respectively, and the chemistry was performed in the same procedure as in Experimental Example 7-1. The characteristics were measured. The results are shown in Table 4.

Experimental Example 7-5
Except that the ionic compound for additive was not used and a propylene carbonate solution (18% by mass) of triethylmethylammonium tetrafluoroborate was used as the measurement solution, the electrochemical characteristics were the same as in Experimental Example 7-1. Measurements were made. The results are shown in Table 4.

Experimental Examples 7-6 to 7-8
Commercially available triethylmethylammonium tetrafluoroborate (TEMABF ₄ ) was used as the main electrolyte, and ionic compound 1 (TEMATCB) obtained in Production Example 1 was used as the ionic compound for the additive. The electrochemical characteristics were measured in the same manner as in Experimental Example 7-1 except that the measurement solution was prepared by dissolving in propylene carbonate. The results are shown in Table 4.

  In Table 4, the concentration 1 means the concentration in the electrolytic solution, and the concentration 2 means the ratio of the main electrolyte and the additive to the total amount.

From Table 4, in Experimental Example 7-1 in which no additive was used, a current value of 0.03 mA was observed at 3.07 V (withstand voltage: about 6.9 V (vs. Li ^/ Li ⁺ )). On the other hand, the current value of 0.03 mA was observed in Experimental Example 7-2 using LiTCB as an additive was 3.74 V (withstand voltage: about 7.5 V (vs. Li ^/ Li ⁺ )). It can be seen that the decomposition potential can be increased by using the additive according to the present invention. Further, from the results of Experimental Example 7-1, Experimental Examples 7-3 and 7-4, Experimental Example 7-5, and Experimental Examples 7-6 to 7-8, the improvement effect of the decomposition potential is not dependent on the type of cation. It turns out that it is what is obtained. It has been confirmed that the effect of improving the decomposition potential can be obtained even when the amount of the additive used is less than 1% by mass.

The reason why the above effect was obtained is that when an ionic compound having tetracyanoborate as an anion is used as an additive, a pseudo protective film is formed on the electrode surface by some reaction. It is presumed that the deterioration of the liquid or electrode was suppressed. On the other hand, in Experimental Example 7-5 in which the additive was not used, it is considered that the current value increased with the increase in voltage, and the decomposition of the electrolyte and the electrode proceeded without being suppressed. From these results, among the additives according to the present invention, when the onium cation salt of TCB is used, even when operated under a high voltage, it is difficult to cause decomposition of the electrolytic solution and deterioration of the electrode, and stably. It is considered that an electricity storage device that operates and has a high energy density is obtained.
From the results of Experimental Example 7, it can be seen that various power storage devices including an electrolytic solution containing the additive according to the present invention in addition to the main electrolyte can operate stably even in a higher voltage range.

  As described above, by using the ionic compound according to the present invention as an additive, decomposition of the electrolytic solution in a high voltage region can be suppressed. Therefore, it is considered that various power storage devices provided with the electrolytic solution containing the additive of the present invention can be stably operated even in a high voltage range without causing decomposition of the electrolytic solution or electrode deterioration. Therefore, various power storage devices provided with the electrolytic solution of the present invention are suitable for power supplies for mobile phones, personal computers, automobiles, and the like.

Claims (10)

Formula ^{(1): Kt + [B} (CN) 4] - ( in the formula (1), Kt ⁺ represents a non-machine cationic) ionic compound represented by, and,
An aprotic organic solvent,
When the LSV measurement is performed, the positive electrode potential at full charge is 4 V (vs. Li ^/ Li ⁺ ) , characterized by having a withstand voltage of 6.9 V or more and 13.8 V or less (vs. Li ^/ Li ⁺ ). The electrolytic solution for an electricity storage device as described above .   The electrolytic solution according to claim 1, wherein the concentration of the ionic compound represented by the general formula (1) is 0.01% by mass or more and less than 50% by mass. The electrolytic solution according to claim 1, wherein the aprotic organic solvent is at least one selected from ethylene carbonate, propylene carbonate, γ-butyrolactone, and γ-valerolactone. The electrolytic solution according to any one of claims 1 to 3, wherein the cation Kt ⁺ is at least one cation selected from the group consisting of Li, Na, Mg, and Ca. It is an electrolyte solution for lithium ion secondary batteries, The electrolyte solution as described in any one of Claims 1-4. An electrical storage device comprising the electrolytic solution according to any one of claims 1 to 5. The electricity storage device according to claim 6, wherein the positive electrode potential at full charge is 4 V (vs. Li ^/ Li ⁺ ) or more.   The electricity storage device according to claim 6, which is a lithium ion secondary battery.   The electricity storage device according to claim 6, wherein the electricity storage device is a lithium ion capacitor.   The electricity storage device according to claim 6, which is an electric double layer capacitor.