WO2019124300A1

WO2019124300A1 - Electrolyte solution and redox flow battery

Info

Publication number: WO2019124300A1
Application number: PCT/JP2018/046317
Authority: WO
Inventors: 賢太郎渡邉; 淳一秋山; 学織地
Original assignee: 昭和電工株式会社
Priority date: 2017-12-19
Filing date: 2018-12-17
Publication date: 2019-06-27
Also published as: JP2021028866A; TW201931658A

Abstract

This electrolyte solution includes alkali metal ions and vanadium ions, the total concentration of alkali metal ions being 0.3–2.0 M.

Description

Electrolyte and redox flow battery

The present invention relates to an electrolytic solution and a redox flow battery comprising the electrolytic solution. Priority is claimed on Japanese Patent Application No. 2017-242312, filed Dec. 19, 2017, the content of which is incorporated herein by reference.

A redox flow battery is known as a large capacity storage battery. In general, a redox flow battery has a positive electrode chamber provided with a positive electrode, a negative electrode chamber provided with a negative electrode, and a diaphragm made of an ion exchange membrane sandwiched between these two electrode chambers. In general, a redox flow battery supplies an electrolytic solution to each of the two electrode chambers to perform charging and discharging. Hereinafter, in the present specification, the electrolytic solution supplied to the positive electrode chamber is referred to as a positive electrode electrolytic solution, and the electrolytic solution supplied to the negative electrode chamber is referred to as a negative electrode electrolytic solution. In general, a redox flow battery uses, as an active material, an aqueous electrolyte solution containing metal ions whose valence changes by oxidation / reduction. For example, an iron-chromium (Fe-Cr) redox flow battery using a positive electrode electrolyte containing iron ions and a negative electrode electrolyte containing chromium ions, a positive electrode electrolyte containing manganese ions and a negative electrode electrolyte containing titanium ions The manganese-titanium (Mn-Ti) redox flow battery to be used, the all-vanadium (VV) redox flow battery using a positive electrode electrolyte containing vanadium ions and the negative electrode electrolyte, and the like can be mentioned. In particular, development of all-vanadium-based (V-V) redox flow batteries is widely pursued worldwide.

In the all-vanadium-based redox flow battery, the following reactions occur in the positive electrode chamber (positive electrode) and the negative electrode chamber (negative electrode) during charge and discharge.
Positive electrode: VO ₂ ⁺ + H ₂ O → VO ₂ ⁺ + 2H ⁺ + e ⁻ (charge)
VO ²⁺ + H ₂ O ← VO ₂ ⁺ + 2H ⁺ + e ⁻ (discharge)
The negative ^{^{^{electrode: V 3+ + e - → V}}} 2+ ( charging)
^{^{^{V 3+ + e - ← V 2+}}} ( discharge)

However, in a redox flow battery, when charge and discharge are repeated, a phenomenon called crossover occurs. Crossover is a phenomenon in which an active material (especially metal ion) and a solvent move between a positive electrode chamber and a negative electrode chamber through a diaphragm. In the crossover, the active material in the positive electrode chamber and the active material in the negative electrode chamber are mixed, and the concentration of the active material and the amount of the electrolyte become unbalanced between the positive electrode chamber and the negative electrode chamber. That is, the crossover significantly reduces the electrical capacity of the redox flow battery. At present, various devices have been tried because it is difficult to prevent crossover with only an ion exchange membrane widely used as a diaphragm.

According to Patent Document 1, the redox flow battery described in the same document includes an organic radical positive / negative active material having a higher electromotive force than vanadium ions and an ion exchange membrane having a pore diameter which does not pass through the positive / negative active material. It is stated that the occurrence of over has been suppressed. However, this method is not suitable for redox flow batteries in which metal ions are used as an active material.

In Patent Document 2, “a positive electrode cell and a negative electrode cell separated by a diaphragm, a positive electrode and a negative electrode built in each cell, a positive electrode tank for introducing and discharging an electrolytic solution for the positive electrode to the positive electrode cell, and a negative electrode cell An electrolyte flow type battery comprising a negative electrode tank for introducing and discharging a negative electrode electrolyte, provided in a communicating pipe connecting both tanks at a position lower than the liquid level of the electrolytic solution in each tank, and a communicating pipe Based on the detected valve, the means for detecting the state of charge, and the detection result by means for detecting the state of charge, the valve is opened when the state of charge of the battery is lower than the specified state, and the amount of And a valve opening and closing mechanism. Although this electrolytic solution flow type battery is suggested to rebalance the amount of electrolytic solution, the equipment becomes complicated and the cost increases.

JP, 2017-117752, A Japanese Patent Application Laid-Open No. 11-204124

The object of the present invention is made in view of the above-mentioned problems, and is to provide an electrolytic solution capable of suppressing a decrease in electric capacity due to crossover and a redox flow battery provided with the same.

The present inventors diligently studied to solve the problems described above. As a result, by using an electrolyte containing alkali metal ions and vanadium ions in a redox flow battery, the reduction in redox flow battery capacity caused by the crossover of vanadium ions is suppressed, and the cycle life of the battery is improved. The present invention has been completed.

The present invention includes the following inventions [1] to [8].
[1] The electrolyte according to the first aspect of the present invention contains an alkali metal ion and a vanadium ion, and the total concentration of the alkali metal ions is 0.3 M to 2.0 M.
[2] In the electrolytic solution of the above-mentioned [1], the alkali metal ion may be at least one selected from sodium ion and potassium ion.
[3] In the electrolyte solution of the above [1] or [2], the concentration of the vanadium ion may be 1.0 M to 4.0 M.
[4] The electrolyte solution of the above [1] to [3] may contain a sulfate ion.
[5] In the electrolyte solution of the above [1] to [4], the concentration of the sulfate ion may be 1.0 M to 10.0 M.
[6] The electrolytic solution of the above [1] to [5] may further contain at least one anion selected from the group consisting of fluoride ion, chloride ion, bromide ion, and phosphate ion .
[7] In the electrolyte solution of the above [1] to [6], the total concentration of the anions may be 0.01 M to 2.0 M.
[8] A redox flow battery according to a second aspect of the present invention comprises the electrolytic solution of the above [1] to [7].

ADVANTAGE OF THE INVENTION According to this invention, when used for a redox flow battery, the electrolyte solution which can suppress a capacity | capacitance fall can be provided, and a redox flow battery provided with the same.

It is a figure which shows the relationship between the density | concentration of sodium ion and discharge capacity reduction rate in Examples 1-5 and a comparative example. It is a figure which shows the relationship between the density | concentration of the sodium ion and Coulomb efficiency in Examples 1-5 and a comparative example. It is a figure which shows the relationship between the density | concentration of sodium ion and cell resistance in Examples 1-5 and a comparative example. It is a schematic diagram of the redox flow battery used by the example and the comparative example.

Hereinafter, preferred embodiments of the present invention will be described in detail. In addition, this invention is not limited only to the following embodiment, It can change suitably and can be implemented in the range which has the effect. For example, materials, dimensions, numerical values, amounts, ratios, characteristics, and the like can be omitted, added, or changed without departing from the spirit of the present invention.

[Electrolyte solution]
The electrolytic solution according to this embodiment contains an alkali metal ion and a vanadium ion, and the total concentration of the alkali metal ions is 0.3 M to 2.0 M. Here, M shown as a unit of concentration means volume molar concentration, that is, mol / liter (mol / L). The following also shows the same meaning. For example, 0.3 M in the present specification indicates 0.3 mol / L. Moreover, the electrolyte solution which concerns on this embodiment can be preferably used as electrolyte solution for redox flow batteries so that it may mention later.

[Alkali metal ion]
The alkali metal ions in the electrolytic solution are not limited to these, and examples thereof include lithium ion (Li ⁺ ), sodium ion (Na ⁺ ), potassium ion (K ⁺ ), rubidium ion (Rb ⁺ ), And at least one selected from cesium ions (Cs ⁺ ). Among them, sodium ion (Na ⁺ ) and potassium ion (K ⁺ ) are preferable, and sodium ion (Na ⁺ ) is more preferable, from the viewpoint of cost control. When such an electrolytic solution is used in a redox flow battery, it is possible to suppress a decrease in battery capacity caused by crossover of vanadium ions in the electrolytic solution. Also, from the viewpoint of suppressing an increase in cell resistance, the total concentration of alkali metal ions in the electrolytic solution is 0.3 M to 2.0 M, preferably 0.3 M to 1.5 M, more preferably 0.3 M to 1. It is 0 M, more preferably 0.4 M to 0.8 M. The raw material which is dissolved in the electrolytic solution to generate an alkali metal ion is not particularly limited, but in terms of handling safety, a salt containing the alkali metal ion is preferable. From the viewpoint of improving the stability of the electrolytic solution and the ion conductivity, a halogen salt, a sulfate or a mixture of a halogen salt and a sulfate of the metal ion is particularly preferable.

[Vanadium ion]
The vanadium ions in the electrolyte solution are divalent vanadium ions (V 2 ⁺ ), trivalent vanadium ions (V ³ ⁺ ), tetravalent vanadium ions (VO ₂ ⁺ ), and pentavalent vanadium ions (VO ₂ ⁺ ). At least one of the That is, for example, trivalent vanadium ion (V ³⁺ ) and tetravalent vanadium ion (VO ²⁺ ) may be used in combination. As a raw material which melt | dissolves in the said electrolyte solution and produces | generates such a vanadium ion, the vanadium salt which can be melt | dissolved in water or acidic aqueous solution is preferable. From the viewpoint of high solubility in water, vanadium oxide sulfate (VOSO ₄ ) is more preferable. The total concentration of vanadium ions in the electrolytic solution is preferably 1.0 M to 4.0 M. Within this range, generation of vanadium precipitates is suppressed while securing energy density. More preferably, it is 1.0 M to 3.0 M, particularly preferably 1.0 M to 2.5 M. For example, the total concentration of vanadium ions may be 1.0 M to 1.5 M, 1.5 M to 2.0 M, 1.0 M to 2.0 M, or 2.0 M to 3.0 M, as necessary. It is good also as a range. As a specific example, it may be 1.8 M.

[Sulfate ion]
It is preferable that the electrolytic solution in the present embodiment contains a sulfate ion (SO ₄ ²⁻ ). In the presence of a modest amount of sulfate ion, the vanadium ion tends to dissolve more stably. The concentration of sulfate ion is preferably 1.0 M to 10.0 M, more preferably 1.0 M to 8.0 M, and still more preferably 2.0 M to 6.0 M for stabilization of vanadium ion. In addition, as necessary, for example, 3.0 M to 6.0 M, 4.0 M to 6.0 M, 4.0 M to 5.5 M, or 4.3 M to 5.3 M may be used. Examples of the raw material which dissolves in the electrolytic solution to generate sulfate ions include sulfuric acid or a sulfate of vanadium, and the like, and preferably sulfuric acid in terms of keeping the electrolytic solution acidic.

[Anion other than sulfate ion]
The electrolytic solution according to the present embodiment is at least one selected from the group consisting of fluoride ion (F ⁻ ), chloride ion (Cl ⁻ ), bromide ion (Br ⁻ ), and phosphate ion (PO ₄ ^3- ). It is preferable to further contain the anion of Among these, chloride ion - and more preferably contains ^(Cl). The electrolytic solution according to the present embodiment is considered to further increase the ion conductivity of the electrolytic solution and the reactivity of the metal ion by further containing an appropriate amount of the anion. Therefore, in the redox flow battery having the electrolyte containing the anion, the internal resistance of the battery is reduced. Furthermore, the effect of improving the solubility of vanadium ions in the electrolytic solution can also be obtained. The total concentration of the anions is preferably 0.01 M to 2.0 M, more preferably 0.1 M to 1.5 M, still more preferably 0.1 M to 1.0 M. As a raw material which melt | dissolves in the said electrolyte solution and produces the said anion, the acid containing the said anion, and a vanadium salt are preferable. Moreover, the electrolyte solution concerning this embodiment does not necessarily need to be a structure which has an anion. That is, the total concentration of anions may be 0.00M.

[Redox flow battery]
The redox flow battery according to the present embodiment is characterized by including the electrolyte solution. The redox flow battery of the present invention can adopt a known configuration. For example, it may be a redox flow battery as shown as a preferred example in FIG. FIG. 4 is a schematic view of a redox flow battery used in an experiment according to an example to be described later, and is an example of a redox flow battery according to the present embodiment. The redox flow battery shown in FIG. 4 includes the battery cell 2, the positive electrode electrolyte solution tank 12, the positive electrode return pipe 13, the positive electrode return pipe 14, the negative electrode electrolyte tank 22, the negative electrode return pipe 23, and the negative electrode return pipe 24. And pumps 15 and 25. The tank 12 for positive electrode electrolyte, the positive electrode forward pipe 13, the positive electrode return pipe 14, the negative electrode electrolyte tank 22, the negative electrode forward pipe 23, the negative electrode return pipe 24, and the

pumps

15 and 25 are known redox What is used for a flow battery can be applied. The battery cell 2 includes a positive electrode cell 11, a negative electrode cell 21, and a diaphragm that separates the positive electrode cell 11 and the negative electrode cell 21. The positive electrode cell 11 and the negative electrode cell 21 respectively have the positive electrode 10 and the negative electrode 20 inside. The electrolytic solution according to the embodiment is circulated in the positive electrode cell 11 and the negative electrode cell 21. The positive electrode 10 and the negative electrode 20 can use the electrode used for a well-known redox flow battery.

The electrolytic solution is stored in the positive electrode electrolytic tank 12, and is supplied to the positive electrode cell 11 by the pump 15 through the positive electrode outward pipe 13. The flow rate of the electrolytic solution supplied to the positive electrode cell 11 can be appropriately selected, and it is preferable to sufficiently supply an amount of the active material necessary to obtain a desired output. In addition, after performing the charge and discharge in the positive electrode cell 11, the electrolytic solution returns to the positive electrode electrolytic solution tank 12 through the positive electrode return path pipe 14, and circulates the same path again. The discharge amount of the electrolytic solution from the positive electrode cell 11 can be made to be substantially the same flow rate as the supply amount into the positive electrode cell 11.
The electrolytic solution also circulates to the negative electrode cell 21 in the same manner as the circulation to the positive electrode cell 11. That is, the electrolytic solution is stored in the negative electrode electrolytic solution tank 22, and is supplied to the negative electrode cell 21 by the pump 25 through the negative electrode outward pipe 23. The flow rate of the electrolytic solution supplied to the negative electrode cell 21 can be appropriately selected, and it is preferable to sufficiently supply an amount of the active material necessary to obtain a desired output. In addition, after the electrolyte solution is charged and discharged in the negative electrode cell 21, the electrolytic solution returns to the negative electrode electrolyte tank 22 through the negative electrode return pipe 24 and circulates in the same path again.

The electrolytic solution supplied to the battery cell 2 contributes to the reaction when charging and discharging in the positive electrode 10 and the negative electrode 20. Charging and discharging use electric power from an external power generation unit (not shown). Electric power is supplied from the power generation unit and supplied to the positive electrode 11 and the negative electrode 21 via an external AC / DC converter (not shown).
As the diaphragm 30 which separates the positive electrode cell 11 and the negative electrode cell 21, a known ion exchange membrane can be used.

The redox flow battery concerning this embodiment can control a fall of the electric capacity by crossover, and can improve cycle life by the composition concerned.

EXAMPLES The present invention will be more specifically described below based on examples, but the present invention is not limited to these examples.

Example 1
(Preparation of electrolyte)
A solution of sulfuric acid (H ₂ SO ₄ ) in 100 ml of a 4.0 M aqueous sulfuric acid solution, 0.03 mol sodium sulfate (Na ₂ SO ₄ ), 0.09 mol vanadium sulfate (V ₂ (SO ₄ ) ₃ ), 0 18 mol of vanadium oxide sulfate (VOSO ₄ ) was added, and pure water was added so as to make the solution volume 200 ml, and stirred to prepare 200 ml of an electrolytic solution.

(Measurement of charge and discharge characteristics)
The schematic diagram of the redox flow battery used for experiment is shown in FIG. The battery cell 2 used a carbon felt (AAF 304 ZS) manufactured by Toyobo Co., Ltd. with an area of 50 cm ² (5 cm × 10 cm) as the positive electrode 10 and the negative electrode 20, and Nafion (trademark) 212 as an ion exchange membrane. Prepare 50 ml of each of the prepared electrolytes as a positive electrode electrolytic solution and a negative electrode electrolytic solution, and circulate the electrolytic solution at a flow rate of 50 ml / min through the positive electrode cell 11 and the negative electrode cell 21 to a current of 10 A (current density 0 Charging / discharging was performed at ^{2 A} / cm ² ). First, charging was performed, charging was stopped when the voltage reached 1.75 V, and then discharging was performed, and discharging was finished when the voltage reached 1.0 V. This charge / discharge was further repeated for 49 cycles (50 cycles in total), and charge time (h), discharge time (h), and cell voltage (V) during charge / discharge were measured for each cycle. The cell voltage at the half of the charging time is V ₁ , and the cell voltage at the half of the discharging time is V ₂ . And as the following formula, the Coulomb efficiency (%) of the 10th cycle (cyc10), the cell resistance (Ω · cm ² ), and the discharge capacity of the 10th cycle (cyc10) and the 50th cycle (cyc50) The reduction rate (hereinafter referred to as the discharge capacity reduction rate) was determined.
· Charge capacity (Ah) = charge current × charge time · discharge capacity (Ah) = discharge current × discharge time · coulomb efficiency (%) = ([discharge capacity] / [charge capacity]) × 100
・ Cell resistance (Ω · cm ² ) = (V ₁ −V ₂ ) / (2 × current density)
· Discharge capacity reduction ratio (%) = (1-[discharge capacity (cyc50)] / [discharge capacity (cyc10))) × 100

[Examples 2 to 5, Comparative Examples 1 and 2]
A 200 ml electrolytic solution was prepared in the same manner as in Example 1 except that the amount of sodium sulfate added was as shown in Table 1, and the charge / discharge characteristics were measured.

[Example 6]
A mixed aqueous solution was obtained by mixing 100 ml of a sulfuric acid aqueous solution having a sulfuric acid (H ₂ SO ₄ ) concentration of 4.0 M and 10 ml of a hydrochloric acid aqueous solution having a hydrochloric acid concentration of 10.0 M. In the mixed aqueous solution, 0.06 mol sodium sulfate (Na ₂ SO ₄ ), 0.09 mol vanadium sulfate (V ₂ (SO ₄ ) ₃ ) and 0.18 mol vanadium oxide sulfate (VOSO ₄ ) are added. Pure water was added to the solution so that the solution volume became 200 ml, and stirred to prepare 200 ml of an electrolyte. And the measurement of the charge / discharge characteristic was implemented similarly to Example 1.

Table 1 summarizes the amounts of raw materials used to make the electrolyte in the above Examples and Comparative Examples. Table 2 shows the electrolytic solution compositions of the examples and the comparative examples and the measurement results of the charge and discharge characteristics.

As apparent from Table 2 and FIGS. 1 and 2, when 0.3 M of sodium ion as an alkali metal ion is contained in the electrolytic solution, the discharge capacity reduction rate becomes sufficiently low, and the concentration of sodium ion in the electrolytic solution is As it increased, the rate of reduction of the discharge capacity decreased further, and the coulombic efficiency increased. From these, it was confirmed that the crossover of the electrolyte solution containing vanadium ion can be suppressed when the electrolyte solution containing vanadium ion further contains an appropriate amount of alkali metal ion. On the other hand, as shown in FIG. 3, with the increase of the amount of sodium ions in the electrolytic solution, an increase in cell resistance was also observed, and it was found that the consumption of power due to the cell resistance was high. From the viewpoint of achieving both suppression of crossover and suppression of rise in cell resistance, it was found that the concentration of sodium ion is 0.3 M to 2.0 M, and particularly 0.3 M to 1.0 M is preferable.
The comparative examples 1 and 2 which do not contain alkali metal ions or have a small amount of alkali metal ions were inferior in the obtained characteristics as compared with the examples.

In Example 6, it is presumed that the ion conductivity of the electrolytic solution and the reactivity of the vanadium ion are improved by further including a chloride ion as an anion other than the sulfate ion. Therefore, compared to Example 2, the cell resistance could be reduced while suppressing the decrease in discharge capacity caused by the crossover of vanadium ions. Such an electrolytic solution can be suitably used particularly for high current density (charge / discharge current density is 100 mA / cm ² or more) redox flow battery.

INDUSTRIAL APPLICABILITY The redox flow battery of the present invention can be applied to the storage of electric power in power stations, substations and the like, and can be used for reduction of electricity charges, measures against voltage sags, and the like.

DESCRIPTION OF SYMBOLS 1 redox flow battery 2 battery cell 10 positive electrode 11 positive electrode cell 12 positive electrode electrolyte tank 13 positive outgoing pipe 14 positive return pipe 15 pump 20 negative electrode 21 negative cell 22 negative electrolyte tank 23 negative outgoing pipe 24 negative return pipe 25 pump 30 diaphragm

Claims

An electrolytic solution containing an alkali metal ion and a vanadium ion, wherein the total concentration of the alkali metal ion is 0.3M to 2.0M.
The electrolytic solution according to claim 1, wherein the alkali metal ion is at least one selected from sodium ion and potassium ion.
The electrolytic solution according to claim 1 or 2, wherein the concentration of the vanadium ion is 1.0M to 4.0M.
The electrolytic solution according to any one of claims 1 to 3, which contains a sulfate ion.
The electrolytic solution according to claim 4, wherein the concentration of the sulfate ion is 1.0M to 10.0M.
The electrolytic solution according to any one of claims 1 to 5, further comprising at least one anion selected from the group consisting of fluoride ions, chloride ions, bromide ions, and phosphate ions.
The electrolytic solution according to claim 6, wherein the total concentration of the anion is 0.01M to 2.0M.
A redox flow battery comprising the electrolytic solution according to any one of claims 1 to 7.