WO2020241686A1

WO2020241686A1 - Electrochemical device including three-layer system electrolytic solution

Info

Publication number: WO2020241686A1
Application number: PCT/JP2020/020918
Authority: WO
Inventors: 大平　昭博; 縁佐藤; 晃次野田; 雅司國武
Original assignee: 国立研究開発法人産業技術総合研究所
Priority date: 2019-05-29
Filing date: 2020-05-27
Publication date: 2020-12-03

Abstract

[Problem] To provide an electrochemical device that can be used for both water-soluble and water-insoluble active materials, and that enables ion transport effectively even without using a solid electrolyte membrane. [Solution] This electrochemical device includes: (a) at least one pair of a positive electrode and a negative electrode; (b) an aqueous layer including one of a positive electrode electrolytic solution and a negative electrode electrolytic solution; (c) a non-aqueous layer including the other of the positive electrode electrolytic solution and the negative electrode electrolytic solution; and (d) an emulsion layer including both the positive electrode electrolytic solution and the negative electrode electrolytic solution, and being interposed between the aqueous layer and the non-aqueous layer without any intermixing therewith.

Description

Electrochemical device containing three-layer electrolyte

Cross reference

This application claims priority based on Japanese Patent Application No. 2019-100337 filed on May 29, 2019 and Japanese Patent Application No. 2019-190284 filed on October 17, 2019 in Japan. All the contents of the application are incorporated herein by reference. In addition, all the patents, patent applications and contents described in the documents cited in the present application are incorporated herein by reference as they are.

The present invention relates to a technical field related to an electrochemical device. More specifically, the electrolytic solution can be charged and discharged by a three-layer system consisting of an aqueous layer, a non-aqueous layer (oil layer) and an emulsion layer without using a solid electrolyte membrane. Regarding secondary batteries and redox flow batteries.

Power generation systems that use natural energy such as solar power and wind power that do not generate warming gas such as carbon dioxide are being actively introduced in Japan, mainly in Europe and the United States. In order to use such renewable energy effectively and flexibly, a large-capacity power storage system using a storage battery (secondary battery) that can freely put in and take out the generated electricity is also required. As the large-capacity storage battery, a lithium ion battery, a lithium ion capacitor, a NAS battery (sodium-sulfur battery), a lead storage battery, and a redox flow battery have been put into practical use.

Conventional redox flow batteries use inorganic redox active substances such as vanadium and bromine under strong acidity such as sulfuric acid. Therefore, there is a problem that the risk and toxicity of the electrolytic solution itself is high, and the abundance of the vanadium compound on the earth is limited, so that the cost fluctuates sharply. Therefore, as a recent movement, there have been many reports using organic redox molecules that are non-corrosive, safe, and low-cost instead of inorganic electrolytes. For example, organic compounds such as quinones, phenothiazines, viologens, nitrooxides, pyridines, methoxybenzenes, quinoxalines and phthalimide derivatives are used in place of metal compounds. Most organic molecules are non-toxic, environmentally friendly and durable. Electrochemical and physicochemical properties such as oxidation-reduction potential and solubility of these molecules can be modified by chemical modification. Some organic molecules are capable of multiple electron transfers, which allows them to have a high charge storage capacity.

Also, unlike other secondary batteries, the redox flow battery has a high degree of freedom in design because the capacity and output can be designed independently, and it is easy to increase the size. The volume portion is determined by the concentration and amount of electrolyte. The output portion is controlled by the electrode area of the cell, the current collector plate, the electrode area, and the number of stacked single cells when the electrolyte membrane is a single cell, depending on the purpose. As for the capacitance part, not only inorganic type but also organic type electrolytic solution has been developed, and the energy density has been improved. For the output part, the output density can be improved by improving the materials that make up the single cell and designing the cell. The positive and negative electrodes constituting the single cell are made of carbon material, and the electrolyte membrane responsible for ion transport is generally a polymer electrolyte membrane or a glass electrolyte. By using a solid electrolyte membrane having a cation or anion transporting ability, the charges of the positive and negative electrode electrolytes are compensated and charging / discharging becomes possible. Further, the electrolyte membrane is required to have selective permeability that moves only ions without moving the active material in the positive and negative electrode electrolytes to the electrolytes on the opposite sides. With the diversification of electrolytes in this way, the role of the electrolyte membrane is becoming even more important.

However, with respect to the diversification of electrolytes, the types of solid electrolyte membranes such as polymer electrolyte membranes and glass electrolyte membranes are limited, and their applicability is limited. For example, there is currently no practical solid electrolyte membrane for realizing a redox flow battery in which an aqueous electrolyte solution and a non-aqueous electrolyte solution are used for the positive electrode or the negative electrode, respectively, which can be expected to improve the energy density.

Under such circumstances, a redox flow battery that does not use a solid electrolyte membrane has been proposed. For example, it is a battery system consisting of three layers in which a non-aqueous electrolyte solution is used as a positive electrode and a negative electrode electrolyte (oil layer) and an aqueous layer is arranged between the positive and negative electrode oil layers (see Patent Document 1 and Non-Patent Document 1). In this case, the aqueous layer plays the role of the solid electrolyte membrane. Ions are transported between the oil layer and the water layer, and the redox reaction of the active material in each of the positive and negative oil layers proceeds.

Further, a redox flow battery composed of only an aqueous electrolyte and a non-aqueous electrolyte has been proposed (see Patent Document 2, Non-Patent Documents 2 and 3). It is composed of two layers, the aqueous electrolyte is an aqueous layer and the non-aqueous electrolyte is an oil layer. The aqueous layer is the positive electrode and the oil layer is the negative electrode. In this case, the ion transport for charge compensation is performed at the interface between the aqueous layer and the oil layer, and the redox reaction of the active material in the electrolytic solution proceeds in each layer to operate as a rechargeable secondary battery.

In these three-layer and two-layer liquid redox flow batteries, a battery cell that can be charged and discharged easily and easily can be produced simply by introducing an aqueous layer and an oil layer. Therefore, the material cost for the solid electrolyte membrane is high. It leads to reduction of battery cell manufacturing cost and maintenance cost.

WO2017 / 186836A1 ES2633601A1

However, the three-layer system in which the oil layer is the positive electrode and the negative electrode described in Patent Document 1 has an advantage that an electromotive force higher than the voltage of electrolysis of water can be obtained, but a water-soluble active material is used. It cannot be done, and the types of active materials are limited. Further, there is a problem that the resistance of the positive and negative electrode oil layers becomes large, and as a result, the voltage efficiency decreases. The same applies to the case of a two-layer system, in which ion transport is performed only at the interface between the aqueous layer and the oil layer, so that the relatively high output characteristics inherent in the redox flow battery are sacrificed, and the redox activity is reduced. There are problems such as electron exchange of substances easily occurring and low charge / discharge stability, and it is not possible to show superiority over other secondary batteries such as lithium ion batteries.

The present invention has been made to solve such a problem, and the object thereof is that both water-soluble and water-insoluble active materials can be used, and a solid electrolyte membrane is not used. It is also to provide an electrochemical device that enables ion transport between an aqueous layer and an oil layer.

In order to solve the above problems, the electrochemical device according to the embodiment of the present invention includes (a) an aqueous layer containing at least a pair of positive electrode and negative electrode, and (b) an aqueous layer containing one of a positive electrode electrolyte and a negative electrode electrolyte. (C) A non-aqueous layer containing the other of the positive electrode electrolytic solution and the negative electrode electrolytic solution, and (d) containing both the positive electrode electrolytic solution and the negative electrode electrolytic solution, and being mixed with both the aqueous layer and the non-aqueous layer. It is characterized by including an emulsion layer interposed between them without any need.
The positive electrode electrolyte contains a positive electrode active material composed of metal ions, an organic metal compound and / or an organic compound, and the negative electrode electrolytic solution is a negative electrode composed of a metal ion, an organic metal compound and / or an organic compound which is the same as or different from the positive electrode active material. It preferably contains an active material.
The aqueous layer contains an aqueous solvent consisting mainly of water, and the non-aqueous layer contains dichloromethane, benzotrifluoride, 2-butanone, propylene carbonate and 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR). It preferably contains at least one non-aqueous solvent selected from the group consisting of ₁₄ TFSI). The aqueous layer and the non-aqueous layer can contain supporting salts that are soluble in their respective solvents.
The emulsion layer is preferably a bicontinuous microemulsion layer containing an aqueous solvent, a non-aqueous solvent, a surfactant and a co-surfactant, and may be in the form of a liquid or semi-solid. In addition, the emulsion layer can contain the respective supporting electrolytes contained in the aqueous layer and the non-aqueous layer.
A preferred embodiment of the electrochemical device is a secondary battery that can be charged and discharged by a redox reaction between a positive electrode active material and a negative electrode active material.

A redox flow battery as another embodiment of the present invention comprises (a) an aqueous layer containing at least a pair of positive and negative electrodes and (b) one of a positive electrode and a negative electrode, and a positive electrode and a negative electrode. A battery cell containing a non-aqueous layer containing the other, and an emulsion layer containing both a positive electrode electrolytic solution and a negative electrode electrolytic solution and interposing between the aqueous layer and the non-aqueous layer without being mixed with each other, and (c). ) An electrolytic solution tank for storing each of the positive electrode electrolytic solution and the negative electrode electrolytic solution, and (d) an electrolytic solution circulation device for connecting each electrolytic solution tank and the battery cell to circulate the positive electrode electrolytic solution and the negative electrode electrolytic solution. It is characterized by being prepared.

According to the present invention, an electrochemical device capable of using both water-soluble and water-insoluble active materials and enabling ion transport between an aqueous layer and an oil layer without using a solid electrolyte membrane is provided. Can be provided.

FIG. 1 is a schematic view of a small test cell containing the three-layer electrolytic solution of one embodiment. FIG. 2 is a schematic view of a redox flow battery according to another embodiment. FIG. 3 is a flow chart showing a step of preparing the three-layer electrolytic solution according to the embodiment. FIG. 4 shows an example of the concentration range of the surfactant and the auxiliary surfactant forming a three-layer system in the electrolytic solution containing 1 M sodium chloride aqueous solution and dichloromethane. FIG. 5 shows an example of the concentration range of the surfactant and the auxiliary surfactant forming a three-layer system in the electrolytic solution containing 1 M aqueous sodium chloride solution and dichloromethane containing 0.1 M tetrabutylammonium perchlorate. Shown. FIG. 6 shows the results of cyclic voltammetry measured with the oil layer side as the working electrode in Example 1. FIG. 7 shows the results of cyclic voltammetry measured with the aqueous layer side as the working electrode in Example 1. FIG. 8 shows the results of cyclic voltammetry measured with the oil layer side as the working electrode in Comparative Example 1. FIG. 9 shows the results of cyclic voltammetry measured with the aqueous layer side as the working electrode in Comparative Example 1. FIG. 10 shows the results of a charge / discharge experiment using a three-layer electrolytic solution containing a low-concentration positive electrode active material in Example 2. FIG. 11 shows the results of the cycle stability of the charge / discharge experiment using the three-layer electrolytic solution containing the positive electrode active material having a low concentration in Example 2. FIG. 12 shows the results of a charge / discharge experiment using a three-layer electrolytic solution containing a high-concentration positive electrode active material in Example 2. FIG. 13 shows the results of a charge / discharge experiment using a two-layer electrolyte in Comparative Example 2. FIG. 14 shows the results of cycle stability in a charge / discharge experiment using a two-layer electrolyte in Comparative Example 2. FIG. 15 shows the change in capacity at the time of discharge for each cycle in the charge / discharge cycle test of the three-layer system and the two-layer system.

1 Small test cell 2 Redox flow

battery

10, 20

Positive electrode

11, 21 Negative electrode 12 Silver-silver

chloride Reference electrode

13, 23

Positive electrode electrolyte

14, 24

Negative electrode electrolyte

15, 25

Emulsion layer

16, 26

Power supply

17, 27

Load

31, 32 Pump 41 Positive electrode electrolyte tank 42 Negative electrode electrolyte tank

Next, a preferred embodiment of the present invention will be described with reference to the drawings. It should be noted that the embodiments described below do not limit the invention according to the claims, and all of the elements and combinations thereof described in the embodiments are essential for the means for solving the present invention. Is not always the case. Also, disclosures of all patent and non-patent documents cited herein are incorporated herein by reference in their entirety.

<Electrochemical device>
FIG. 1 is a schematic view of a small test cell containing a three-layer electrolyte. In FIG. 1, the small test cell 1 includes a positive electrode electrolytic solution (aqueous layer) 13 in contact with a positive electrode (cathode) 10, a negative electrode electrolytic solution (non-aqueous layer) 14 in contact with a negative electrode (anode) 11, and these. It has an emulsion layer 15 interposed between the two. The emulsion layer 15 is immiscible with neither the aqueous layer 13 nor the non-aqueous layer 14, but contains a surfactant and an auxiliary surfactant together with the aqueous solvent and the non-aqueous solvent. Therefore, the supporting electrolyte that is soluble in both an aqueous solvent and a non-aqueous solvent can transfer substances to the aqueous layer and the non-aqueous layer via the emulsion layer. Charging and discharging can be performed by connecting the power supply device 16 or the load (resistance circuit) 17 between the positive electrode 10 and the negative electrode 11.

A silver-silver chloride reference electrode 12 is arranged on the emulsion layer 15, and by connecting to a potentiometer, the redox state of each active material contained in the positive electrode electrolytic solution and the negative electrode electrolytic solution during charging / discharging can be confirmed. be able to. To give an example of a redox reaction, for example, a positive electrode electrolyte solution containing an aqueous solvent containing hydroquinone as a positive electrode active material and a non-aqueous solution containing 2,3-dimethylanthraquinone (2,3-DMAQ) as a negative electrode active material. When a negative electrode electrolytic solution containing a solvent is used, the following charge / discharge reactions are considered to occur.

In the present embodiment, the positive electrode electrolytic solution is an aqueous layer and the negative electrode electrolytic solution is a non-aqueous layer. However, by changing the type of solvent and active material contained in each electrolytic solution, on the contrary, the positive electrode electrolytic solution is used. Can be used as a non-aqueous layer, and the negative electrode electrolytic solution can be used as an aqueous layer. For example, when a non-aqueous solvent containing ferrocene as the positive electrode active material is used as the positive electrode electrolytic solution and an aqueous solvent containing 2,7-anthraquinone disulfonate sodium as the negative electrode active material is used as the negative electrode electrolytic solution, the following It is considered that a charge / discharge reaction occurs.

Next, a more specific configuration and operation of the present invention will be described using other embodiments. FIG. 2 is a schematic view of a redox flow battery according to another embodiment.

<Redox flow battery>
The redox flow battery 2 typically has a power source 26 such as a power plant (for example, a photovoltaic generator, a wind power generator, or other general power plant) and an electric power system via an AC / DC converter. It is connected to a load 27 such as a consumer or a consumer, charges the power plant as a power supply source, and discharges the load as a power supply target. In performing the above charging and discharging, the following battery system including a redox flow battery 2 and a circulation mechanism (tank, piping, pump) for circulating an electrolytic solution in the battery 2 is constructed.

The redox flow battery 2 includes a positive electrode electrolyte 23 (aqueous layer or non-aqueous layer) in contact with the positive electrode 20 and a negative electrode electrolyte 24 (non-aqueous layer or aqueous layer) in contact with the negative electrode 21. A battery cell is provided which separates the

liquids

23 and 24 and also contains an emulsion layer 25 sandwiched between two immiscible liquid layers, which contain both positive electrode and negative electrode electrolytic solutions that appropriately allow ions to pass through. A tank 41 for the positive electrode electrolytic solution is connected to the positive electrode electrolytic solution 23 via a pipe. A tank 42 for the negative electrode electrolytic solution is connected to the negative electrode electrolytic solution 24 via a pipe. The piping is provided with

pumps

31 and 32 for circulating the electrolytic solution. The redox flow battery 2 circulates and supplies the positive electrode electrolyte of the tank 41 and the negative electrode electrolyte of the tank 42 to the battery cells by using pipes and pumps, respectively, to supply the metal and the organic metal compound in the electrolyte of each electrode. Charging and discharging are performed along with the redox reaction of active materials such as organic molecules.

In the present embodiment, since both continuous microemulsion layers 25 carry the function of the conventional solid electrolyte membrane, it is not necessary to use a cation exchange membrane or an anion exchange membrane, but the porous layer for stabilizing the emulsion layer is not necessary. Membranes and support materials can be used. Examples of the porous film and the support material include, but are not limited to, a ceramic film and a glass filter.

(Positive electrode electrolyte)
The positive electrode electrolyte is either water-based or non-aqueous, but it is a solvent different from the negative electrode electrolyte. For example, if the positive electrode electrolyte is water-based (water layer), the negative electrode electrolyte is selected to be non-aqueous (oil layer). .. Metal ions such as iron, manganese, vanadium, and cerium as active materials, or organometallic compounds containing the metal and whose ligand is an organic molecule (ferrocene, manganocene, vanadocene, (ferrocenemethyl) trimethylammonium chloride, 1, Organic molecules such as 1'-bis [3- (trimethylammonio) propyl] ferrocene dichloride) or hydroquinone, acid blue, biolic acid, indigo, TEMPO, 4OH-TEMPO or 9-aminoaclysine, with particular preference being Hydroquinone, ferrocene, (ferroceneylmethyl) trimethylammonium chloride, 1,1'-bis [3- (trimethylammonio) propyl] ferrocene dichloride.

(Negative electrode electrolyte)
The negative electrode electrolyte is either aqueous or non-aqueous, but it is a solvent different from that of the positive electrolyte, and contains metal ions such as titanium, copper, zinc, cobalt, or the metal as an active material, or the ligand. Organic metal compounds consisting of organic molecules (titanocene, nickerosen, cobaltene), phthalimide, fluorenone, camphorquinone, anthraquinone, naphthoquinone, benzoquinone, anthraquinone monosulfonic acid, anthraquinone disulfonic acid, naphthoquinone monosulfonic acid, naphthoquinone disulfonic acid, methylbiologene , Acid blue and the like, and particularly preferred are phthalimide, fluorenone, camphorquinone, anthraquinone, anthraquinone disulfonic acid and acid blue.

(Aqueous layer)
In the present embodiment, the aqueous layer contains an aqueous solvent mainly composed of water. The content of water in the solvent containing water is preferably 60 to 100% by mass, more preferably 80 to 100% by mass. The water is preferably ion-exchanged water in order to strictly adjust the concentration of coexisting supporting salts. The organic solvent that can be contained in the aqueous solvent may be any one of methanol, ethanol, and ethylene glycol, or a combination thereof.

Further, the aqueous layer can contain a supporting salt as an electrolyte. By containing the supporting salt, the electrical conductivity of the electrolytic solution can be improved, and the energy efficiency and energy density of the battery can be improved. Supporting salts that can be added to the aqueous solvent (aqueous layer) include, for example, methanesulfonic acid, trifluoromethanesulfonic acid, sulfuric acid, hydrochloric acid, hydrobromic acid, nitric acid, perchloric acid, sodium methanesulfonate, potassium methanesulfonate, and the like. Lithium trifluoromethanesulfonate, sodium trifluoromethanesulfonate, potassium trifluoromethanesulfonate, lithium chloride, sodium chloride, potassium chloride, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride, lithium bromide, sodium bromide, odor Potassium bromide, tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, lithium nitrate, sodium nitrate, potassium nitrate, tetramethylammonium nitrate, tetrabutylammonium nitrate, lithium perchlorate, excess Examples thereof include sodium chlorate, tetramethylammonium perchlorate, tetraethylammonium perchlorate, tetrabutylammonium perchlorate, lithium hydroxide, sodium hydroxide, potassium hydroxide and the like. The aqueous layer can be used as either a positive electrode or a negative electrode electrolytic solution.

(Non-aqueous layer)
In this embodiment, the non-aqueous layer contains a non-aqueous solvent that is immiscible with water. The non-aqueous solvent is not particularly limited as long as it can dissociate the electrolyte contained as the supporting salt and functions as a field for an electrochemical reaction, but is preferably at least one of dichloromethane, benzotrifluoride, 2-butanone and propylene carbonate. Including one. It may also be an ionic liquid such as 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR ₁₄ TFSI).

The supporting salts contained in the non-aqueous layer (oil layer) include p-toluenesulfonic acid, sodium methanesulfonate, potassium methanesulfonate, lithium trifluoromethanesulfonate, sodium trifluoromethanesulfonate, potassium trifluoromethanesulfonate, and the like. Tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride, tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, tetramethylammonium nitrate, tetrabutylammonium nitrate, perchlorate Lithium, sodium perchlorate, tetramethylammonium perchlorate, tetraethylammonium perchlorate, tetrabutylammonium perchlorate, lithium hexafluorophosphate, lithium borofluoride, 1-butyl-1-methylpyrrolidinium chloride, 1 -Butyl-1-methylpyrrolidinium bromide, 1-ethyl-1-methylpyrrolidinium bromide, 1-butylpyridinium chloride, 1-butylpyridinium bromide, 1-butyl-4-methylpyridinium bromide, 1-butyl-3 -Methylpyridinium chloride, 1-butyl-3-methylpyridinium bromide, 1-butyl-4-methylpyridinium chloride, 1-ethylpyridinium chloride, 1-ethylpyridinium bromide, 1-ethyl-2-methylpyridinium bromide, 1-ethyl Examples thereof include -4-methylpyridinium bromide, 1-propylpyridinium chloride, tributyl-n-octylphosphonium bromide, tetrabutylphosphonium bromide, tributylhexadecylphosphonium bromide, trihexyl (tetradecyl) phosphonium chloride and the like. The non-aqueous layer can be used as either a positive electrode or a negative electrode electrolytic solution.

(Emulsion layer)
The emulsion layer contains the above-mentioned aqueous solvent and non-aqueous solvent, and contains a surfactant and an auxiliary surfactant in order to form both continuous microemulsion layers between the aqueous layer and the non-aqueous layer. In microemulsion, which is a micromixed solution of water and oil in a thermodynamically equilibrium state, by using a surfactant and / or an auxiliary surfactant having an appropriate hydrophilic lipophilic balance (HLB) value, It is known that it is a phase state positioned between the O / W phase state and the W / O phase state, and can form a state in which both the aqueous phase and the oil phase are not closed (the state of both continuous phases). (For example, see Kawano et al. "Surfactant of Surfactant Pourous Organogels, Hydrogels, and Bicontinous Organo / HydroHybrid Gelsmulus43.

The surfactant is not particularly limited to cationic, anionic, nonionic and amphoteric surfactants, but the cationic surfactants include, for example, amines, quaternary ammonium salts (for example, tetramethylammonium chloride), and Examples thereof include polymers containing a quaternary ammonium salt. Examples of the anionic surfactant include sulfonic acids (for example, sodium dodecyl sulfate), carboxylic acids, and polymers having phosphoric acid. Examples of the nonionic surfactant include ether-containing compounds such as jigglime and polymers containing ether (for example, polyethylene glycol octadecyl ether). Further, examples of the zwitterionic surfactant include a carboxylate, an amino acid salt, and a surfactant having a betaine structure.

The auxiliary surfactant has the effect of adjusting the hydrophilic lipophilic balance of the surfactant, and aliphatic primary or secondary alcohols are used. Preferably, it is a linear or molecular C2-C6 monoalcohol. Examples of alcohols are ethanol, 1-butanol, 2-butanol, 3-methyl-1-butanol, 2-methyl-1-propanol, 1-pentanol, 1-propanol, 2-propanol and any mixture thereof. is there. One of these may be used alone, or two or more thereof may be used in any ratio and combination. Particularly preferred are 2-butanol and sodium dodecyl sulfate.

(Preparation method of three-layer electrolyte)
The method for preparing the electrolytic solution in the present embodiment will be described with reference to FIG. FIG. 3 is a flow chart showing a step of preparing the three-layer electrolytic solution according to the embodiment. In step S1, sodium chloride is dissolved in ion-exchanged water, and a predetermined concentration of hydrophilic active material is added to prepare an aqueous layer. Next, in step S2, a second electrolytic solution for forming an oil layer is added to the electrolytic solution by adding a lipophilic active substance having a predetermined concentration to a dichloromethane solution containing tetrabutylammonium perchlorate. In step S3, a predetermined amount of sodium dodecyl sulfate, which is a surfactant, and 2-butanol, which is an auxiliary surfactant, are added. In step S4, these are stirred and allowed to stand for 30 minutes to 1 hour to form a three-layer electrolytic solution containing both continuous emulsion layers. At this time, a three-layer system is formed in a system in which water and dichloromethane are used as an aqueous solvent and a non-aqueous solvent, respectively, regardless of the presence or absence of the supporting electrolytes sodium chloride and tetrabutylammonium perchlorate. The concentration range of each component forming this three-layer system can be controlled by the concentration of the surfactant and the auxiliary surfactant.

FIG. 4 shows an example of the concentration range of the surfactant and the auxiliary surfactant that form a three-layer system. FIG. 4 shows changes in the emulsion layer due to changes in the concentrations of sodium dodecyl sulfate, which is a surfactant, and 2-butanol, which is an auxiliary surfactant, when 4 mL of a 1 M sodium chloride aqueous solution is used as an aqueous layer and 4 mL of dichloromethane is used as an oil layer. ing. A three-layer system is formed in a concentration range of sodium dodecyl sulfate of 0.35 M to 0.5 M and a concentration range of 2-butanol of 1.4 M to 2 M. In the figure, ◯ is the precipitate formation, □ is the emulsion in which water is incorporated into the oil layer (WO: Water in Oil), ▲ is the double continuous microemulsion (BME), and ◇ is the emulsion in which oil is incorporated into the aqueous layer (OW: Oil). in Water) is shown. The concentration of sodium dodecyl sulfate is calculated based on the volume of the aqueous layer, and the concentration of 2-butanol is calculated based on the sum of the volume of the aqueous layer and the volume of 2-butanol added.

FIG. 5 shows the experimental results when tetrabutylammonium perchlorate was added as a supporting electrolyte to the above-mentioned dichloromethane. In FIG. 5, the concentrations of sodium dodecyl sulfate as a surfactant and 2-butanol as an auxiliary surfactant when a 1 M aqueous sodium chloride solution is used as an aqueous layer and a dichloromethane containing 0.1 M tetrabutylammonium perchlorate as an oil layer are used. It is a figure which showed the change of the emulsion layer by the change. A three-layer system is formed in a concentration range of sodium dodecyl sulfate of 0.22M to 0.52M and a concentration range of 2-butanol of 1.3M to 1.6M. In the figure, ◯ indicates precipitation formation, □ indicates an emulsion (WO) in which water is incorporated into an oil layer, ▲ indicates a bicontinuous microemulsion (BME), and ◇ indicates an emulsion in which oil is incorporated into an aqueous layer (OW). The concentration of sodium dodecyl sulfate is calculated based on the volume of the aqueous layer, and the concentration of 2-butanol is calculated based on the sum of the volume of the aqueous layer and the volume of 2-butanol added.

From the results of FIGS. 4 and 5, a three-layer system is formed in the system having the aqueous layer and the dichloromethane as the oil layer regardless of the presence or absence of the supporting electrolyte, and the range in which the three-layer system is formed is the surfactant and the auxiliary surfactant. It shows that it can be controlled by the concentration of the agent. Further, the volumes of the aqueous solvent and the non-aqueous solvent to be mixed are not limited to 1: 1 and can be freely changed to some extent. The thickness of the emulsion layer formed between the aqueous layer and the oil layer can be freely adjusted by appropriately selecting the capacity of the aqueous layer, the oil layer and the emulsion layer, and the capacity and shape of the battery cell to be used.

Next, examples will be given and the present invention will be described in more detail, but the present invention is not limited to these examples.

(Example 1) Preparation of positive electrode and negative electrode electrolytes containing both continuous microemulsion layers and electrochemical measurement in a three-layer battery cell (cyclic voltamogram measurement)
A 0.3 M tetrabutylammonium perchlorate-dichloromethane solution containing 10 mM ferrocene was prepared as a positive electrode electrolyte. As a negative electrode electrolyte, a 0.3 M aqueous sodium chloride solution containing 10 mM sodium 2,7-anthraquinone disulfonate was prepared. When 4 mL of the positive electrode electrolyte, 5.5 mL of the negative electrode electrolyte, 0.6 g of sodium dodecyl sulfate, and 2.25 mL of 2-butanol were mixed, and then stirred and allowed to stand, between the aqueous layer and the oil layer. A three-layer electrolytic solution containing both continuous microemulsion layers was formed in. FIG. 6 shows the results of the current-potential curve obtained by filling the small test cell shown in FIG. 1 and performing cyclic voltammetry measurement at a sweep rate of 1 mV / s with the oil layer side as the working electrode.

On the other hand, FIG. 7 shows the results of the current-potential curve obtained by cyclic voltammetry measurement at a sweep rate of 1 mV / s with the aqueous layer side as the working electrode using a small test cell filled with the same three-layer electrolytic solution as described above. Shown.
In FIG. 6, the redox peak was clearly observed. The peak on the oxidation side is confirmed to be around 0.55V, and the peak on the reduction side is confirmed to be 0.23V. In FIG. 7, an oxidation peak is observed at −0.46 V and a reduction peak is observed at −0.58 V. Further, these redox peaks appear at the same potential even after repeating the cycle, indicating that the active material stably undergoes a redox reaction.

(Comparative Example 1) Preparation of positive electrode and negative electrode electrolytes and electrochemical measurement in a two-layer battery cell (cyclic voltamogram measurement)
A 0.3 M tetrabutylammonium perchlorate-dichloromethane solution containing 10 mM ferrocene was prepared as a positive electrode electrolyte. As a negative electrode electrolyte, a 0.3 M aqueous sodium chloride solution containing 10 mM sodium 2,7-anthraquinone disulfonate was prepared. A two-layer electrolyte obtained by mixing 4 mL of a positive electrode electrolyte and 5.5 mL of a negative electrode electrolyte is placed in a small test cell shown in FIG. 1, and a sweep rate of 1 mV / with the oil layer side as the working electrode. The current-potential curve obtained by cyclic voltammetry measurement in s is shown in FIG.

On the other hand, FIG. 9 shows the results of the current-potential curve obtained by cyclic voltammetry measurement at a sweep rate of 1 mV / s with the aqueous layer side as the working electrode using a small test cell containing the same two-layer electrolytic solution as above. Shown.
Comparing the voltamograms of the oil reservoirs of FIGS. 6 and 8, the peak on the oxidation side of FIG. 8 is unclear as compared with the three-layer system of FIG. This suggests that the reaction resistance in the two-layer oil layer is larger than that in the three-layer oil layer, which can cause a loss of voltage efficiency such as an increase in overvoltage during charging and discharging.

(Example 2) Preparation of positive electrode and negative electrode electrolytes containing both continuous microemulsion layers, charge / discharge and cycle test in a three-layer battery cell (three-layer cycle test using a low-concentration active material)
A 0.3 M tetrabutylammonium perchlorate-dichloromethane solution containing 1 mM ferrocene was prepared as the positive electrode electrolyte. As the negative electrode electrolyte, a 0.3 M aqueous sodium chloride solution containing 1 mM sodium 2,7-anthraquinone disulfonate was prepared. When 4 mL of the positive electrode electrolyte, 5.5 mL of the negative electrode electrolyte, 1.2 g of sodium dodecyl sulfate, and 2.25 mL of 2-butanol were mixed, and then stirred and allowed to stand, between the aqueous layer and the oil layer. A three-layer electrolytic solution containing both continuous microemulsion layers was formed in. FIG. 10 shows the results of a charge / discharge experiment under a constant current of 1 mA / cm ² performed using a small test cell filled with this. In the figure, the vertical axis shows the cell voltage and the horizontal axis shows the charge / discharge time. A indicates the time required for charging, B indicates the pause time when no current is applied (no current is flowing), and C indicates the time required for discharging.

In addition, FIG. 11 shows the results of cycle stability of a charge / discharge experiment conducted using a small test cell containing the same three-layer electrolyte. From FIG. 10, it can be seen that charging / discharging is proceeding with a pause time in between. It decreased from 2.1V to 1.6V during the rest period of 30 seconds. Immediately after the start of discharge, the voltage drops from 1.6V to 1.4V, and the voltage gradually drops due to the discharge. The decrease of 0.2V immediately after discharge is due to overvoltage. FIG. 11 is a diagram showing charge / discharge cycle stability under the same conditions as in FIG. The solid line shows the change in cell voltage, and the dotted line shows the change in potential of the negative electrode electrolyte (based on Ag / AgCl arranged in the emulsion layer). Since there is no difference between the cell voltage change during 30 cycles, the time required for charging / discharging within one cycle, and the potential change of the negative electrode electrolyte, side reactions such as decomposition of the electrolyte occur. It does not occur, indicating that charging and discharging are proceeding stably.

(Three-layer cycle test using high-concentration active material)
A 1.0 M tetrabutylammonium perchlorate-dichloromethane solution containing 20 mM ferrocene was prepared as the positive electrode electrolyte. As the negative electrode electrolyte, a 0.3 M aqueous sodium chloride solution containing 10 mM sodium 2,7-anthraquinone disulfonate was prepared. When 4 mL of the positive electrode electrolyte, 5.5 mL of the negative electrode electrolyte, 0.65 g of sodium dodecyl sulfate, and 1.25 mL of 2-butanol were mixed, and then stirred and allowed to stand, between the aqueous layer and the oil layer. A three-layer electrolytic solution containing both continuous microemulsion layers was formed in. FIG. 12 shows the results of a charge / discharge experiment conducted using a small test cell filled with this.

FIG. 12 shows the results of performing charge / discharge cycles 5 times with the active material concentration of the positive electrode electrolytic solution increased 20 times and the active material concentration of the negative electrode electrolytic solution increased 10 times. The solid line shows the change in cell voltage, and the dotted line shows the change in potential of the negative electrode electrolyte (based on Ag / AgCl arranged in the emulsion layer). Similar to FIG. 11, since the cell voltage change during 5 cycles, the time required for charging / discharging within 1 cycle, and the potential change of the negative electrode electrolytic solution were not observed to be different between cycles, the electrolytic solution was used. It shows that side reactions such as decomposition do not occur and charging and discharging proceed stably even at high concentrations. This indicates that a battery that can be charged and discharged stably can be manufactured even if the active material concentration is increased, that is, the energy density is increased.

(Comparative Example 2) Charge / Discharge and Cycle Test in a Two-Layer Battery Cell A 1.0 M tetrabutylammonium perchlorate-dichloromethane solution containing 20 mM ferrocene was prepared as a positive electrode electrolyte. As the negative electrode electrolyte, a 0.3 M aqueous sodium chloride solution containing 10 mM sodium 2,7-anthraquinone disulfonate was prepared. FIG. 13 shows the results of a charge / discharge experiment conducted using a small test cell containing a two-layer electrolytic solution obtained by mixing 4 mL of a positive electrode electrolyte solution and 5.5 mL of a negative electrode electrolyte solution.

In addition, FIG. 14 shows the results of cycle stability of a charge / discharge experiment conducted using a small test cell containing the same two-layer electrolyte.
In FIG. 13, the vertical axis represents the cell voltage and the horizontal axis represents the charge / discharge time. A indicates the time required for charging, B indicates the pause time when no current is applied (no current is flowing), and C indicates the time required for discharging. From FIG. 13, it can be seen that charging / discharging is proceeding with a pause time in between. It dropped from 2.1V to 1.36V during the 60 second rest period. Immediately after the start of discharge, the voltage drops from 1.36 V to 1.28 V, and the voltage gradually drops due to the discharge. Compared with the result of FIG. 10, there is no significant difference in the voltage at which the discharge is gradually started.

FIG. 14 shows the result of performing the charge / discharge cycle 5 times. The solid line shows the change in cell voltage, and the dotted line shows the change in potential of the negative electrode electrolyte (based on Ag / AgCl arranged in the aqueous layer). Unlike the case of the three-layer system shown in FIG. 11, the time required for charging / discharging within one cycle tends to gradually decrease as the cycle is repeated. This indicates that the reactivity of the active material gradually decreases. Since it is composed of only an aqueous layer and an oil layer, it is considered that the battery capacity is reduced due to a decrease in the active material concentration due to mutual movement of the active material and electron exchange during repeated charging and discharging.

(Example 3) Comparison of cycle characteristics between three-layer and two-layer battery cells (preparation of three-layer electrolyte and charge / discharge cycle test)
A 1.0 M tetrabutylammonium perchlorate-dichloromethane solution containing 20 mM ferrocene was prepared as the positive electrode electrolyte. As the negative electrode electrolyte, a 0.6 M aqueous sodium chloride solution containing 10 mM sodium 2,7-anthraquinone disulfonate was prepared. When 4 mL of the positive electrode electrolyte, 5.5 mL of the negative electrode electrolyte, 0.65 g of sodium dodecyl sulfate, and 1.25 mL of 2-butanol were mixed, and then stirred and allowed to stand, between the aqueous layer and the oil layer. A three-layer electrolytic solution containing both continuous microemulsion layers was formed in. Using a small test cell filled with this, the charge / discharge cycle was repeated 10 times with a current density of 0.32 mA / cm ² , an upper limit voltage of 1.6 V during charging, and a lower limit voltage of 0 V during discharge.

(Preparation of two-layer electrolyte and charge / discharge cycle test)
A 1.0 M tetrabutylammonium perchlorate-dichloromethane solution containing 20 mM ferrocene was prepared as the positive electrode electrolyte. As the negative electrode electrolyte, a 0.6 M aqueous sodium chloride solution containing 10 mM sodium 2,7-anthraquinone disulfonate was prepared. Using a small test cell containing a two-layer electrolyte obtained by mixing 4 mL of positive electrode electrolyte and 5.5 mL of negative electrode electrolyte, a current density of 0.32 mA / cm ² was used during charging. The charge / discharge cycle was repeated 10 times with an upper limit voltage of 2.1 V and a lower limit voltage of 0.2 V at the time of discharge.

FIG. 15 shows the change in capacity at the time of discharge for each cycle in the charge / discharge cycle test of the three-layer system and the two-layer system. Comparing the results of the three-layer system and the two-layer system, it is observed that the discharge capacity of the two-layer system gradually decreases as the number of cycles increases. On the other hand, the three-layer system has a larger discharge capacity than the two-layer system, and no decrease in capacity with the cycle is observed. This indicates that in the three-layer system, the active materials in the positive electrode and negative electrode electrolytes are stably present in each layer, and the capacity as a battery is large and stable by repeating the redox reaction. ing.

The electrochemical device of the present invention does not use a solid electrolyte membrane, and can easily and easily produce a secondary battery. Further, both an aqueous electrolytic solution and a non-aqueous electrolytic solution can be used, and a redox flow battery using an electrolytic solution having excellent energy efficiency and energy density can be provided.

Claims

(A) At least a pair of positive and negative electrodes
(B) An aqueous layer containing one of a positive electrode electrolyte and a negative electrode electrolyte,
(C) A non-aqueous layer containing the other of the positive electrode electrolytic solution and the negative electrode electrolytic solution, and
(D) An emulsion layer containing both the positive electrode electrolytic solution and the negative electrode electrolytic solution and intervening between the aqueous layer and the non-aqueous layer without being miscible.
Electrochemical devices including.
The electrochemical device according to claim 1, wherein the positive electrode electrolytic solution contains a positive electrode active material composed of a metal ion, an organometallic compound and / or an organic compound.
The electrochemical device according to claim 2, wherein the negative electrode electrolytic solution contains a negative electrode active material composed of a metal ion, an organometallic compound and / or an organic compound that are the same as or different from the positive electrode active material.
The aqueous layer consists of an aqueous solvent mainly composed of water, methanesulfonic acid, trifluoromethanesulfonic acid, sulfuric acid, hydrochloric acid, hydrobromic acid, nitrate, perchloric acid, sodium methanesulfonate, potassium methanesulfonate, trifluoromethanesulfon. Lithium acid, sodium trifluoromethanesulfonate, potassium trifluoromethanesulfonate, lithium chloride, sodium chloride, potassium chloride, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride, lithium bromide, sodium bromide, potassium bromide, Tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, lithium nitrate, sodium nitrate, potassium nitrate, tetramethylammonium nitrate, tetrabutylammonium nitrate, lithium perchlorate, sodium perchlorate Includes at least one supporting electrolyte selected from the group consisting of tetramethylammonium perchlorate, tetraethylammonium perchlorate, tetrabutylammonium perchlorate, lithium hydroxide, sodium hydroxide, and potassium hydroxide. The electrochemical device according to any one of 1 to 3.
The non-aqueous layer is at least one selected from the group consisting of dichloromethane, benzotrifluoride, 2-butanone, propylene carbonate and 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR 14 TFSI). Two non-aqueous solvents: p-toluenesulfonic acid, sodium methanesulfonate, potassium methanesulfonate, lithium trifluoromethanesulfonate, sodium trifluoromethanesulfonate, potassium trifluoromethanesulfonate, tetramethylammonium chloride, tetraethylammonium chloride, chloride Tetrabutylammonium, tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, tetramethylammonium nitrate, tetrabutylammonium nitrate, lithium perchlorate, sodium perchlorate, perchloric acid Tetramethylammonium, tetraethylammonium perchlorate, tetrabutylammonium perchlorate, lithium hexafluorophosphate, lithium borofluoride, 1-butyl-1-methylpyrrolidinium chloride, 1-butyl-1-methylpyrrolidinium bromide , 1-Ethyl-1-methylpyrrolidinium bromide, 1-butylpyridinium chloride, 1-butylpyridinium bromide, 1-butyl-4-methylpyridinium bromide, 1-butyl-3-methylpyridinium chloride, 1-butyl-3 -Methylpyridinium bromide, 1-butyl-4-methylpyridinium chloride, 1-ethylpyridinium chloride, 1-ethylpyridinium bromide, 1-ethyl-2-methylpyridinium bromide, 1-ethyl-4-methylpyridinium bromide, 1-propyl Claims 1-4, comprising at least one supporting electrolyte selected from the group consisting of pyridinium chloride, tributyl-n-octylphosphonium bromide, tetrabutylphosphonium bromide, tributylhexadecylphosphonium bromide, and trihexyl (tetradecyl) phosphonium chloride. The electrochemical device according to any one item.
The electrochemical device according to any one of claims 1 to 5, wherein the emulsion layer is a bicontinuous microemulsion layer containing the aqueous solvent, the non-aqueous solvent, a surfactant and an auxiliary surfactant.
The electrochemical device according to any one of claims 1 to 6, wherein the emulsion layer is a liquid or a semi-solid.
The electrochemical device according to any one of claims 1 to 7, wherein the emulsion layer contains the supporting electrolytes contained in the aqueous layer and the non-aqueous layer.
The electrochemical device according to any one of claims 1 to 8, which is a secondary battery capable of charging and discharging by a redox reaction between the positive electrode active material and the negative electrode active material.
(A) At least a pair of positive and negative electrodes
(B) An aqueous layer containing one of a positive electrode electrolyte and a negative electrode electrolyte, a non-aqueous layer containing the other of the positive electrode electrolyte and the negative electrode electrolyte, and the aqueous layer containing both the positive electrode electrolyte and the negative electrode electrolyte. A battery cell containing an emulsion layer interposed between the layers and the non-aqueous layer without being mixed with each other.
(C) An electrolytic solution tank for storing each of the positive electrode electrolytic solution and the negative electrode electrolytic solution, and
(D) An electrolytic solution circulation device that connects each of the electrolytic solution tanks and the battery cell to circulate the positive electrode electrolytic solution and the negative electrode electrolytic solution.
Redox flow battery with.