KR102088601B1 - Membraneless redox flow battery - Google Patents

Abstract

Disclosed is a redox flow battery which comprises: a first electrolyte solution comprising tetrabutylammonium chloride; and a second electrolyte solution comprising tetraethylammonium chloride, wherein the redox flow battery does not include a separator.

Description

Redox flow battery without membrane {MEMBRANELESS REDOX FLOW BATTERY}

The present invention is a first electrolyte solution containing tetrabutylammonium chloride; And a second electrolyte solution comprising tetraethylammonium chloride, wherein the redox flow cell does not contain a separator.

Redox Flow Battery (RFB) is attracting attention as a core technology of renewable energy such as solar energy and wind energy as a large-scale energy storage device. Unlike the existing lithium and sodium secondary batteries, in the case of the redox flow battery, the active material is dissolved in the electrolyte solution, and each active material in the positive electrode and the negative electrode undergoes a redox reaction, thereby expressing the capacity to be charged and discharged. Has a mechanism. Since the capacity and voltage of the battery are determined by the redox reaction between the active materials in the electrolyte supplied from the external storage, it has the advantage that it can be freely set, and the capacity of the entire battery can be controlled by adjusting the size of the external storage. In addition, since the redox reaction of the redox couple, which is an active material, occurs on the surfaces of the positive electrode and the negative electrode, the life of the battery compared to a conventional battery such as a lithium ion battery that undergoes a reaction in which ions are inserted / detached inside the electrode active material This has the advantage of being longer. In addition, the redox flow battery may increase the life of the electrode because the electrode itself does not react.

Redox flow batteries may be divided into an aqueous system and a non-aqueous system according to the type of electrolyte solution containing the redox active material. Aqueous Redox Flow Battery (ARFB), which uses water as the solvent of the electrolyte, has advantages in terms of high ionic conductivity, stability, and economics, and many studies have been conducted on water-based redox flow batteries. The water-based redox flow battery mainly uses a metal having high solubility in an aqueous electrolyte as an active material. Typically, vanadium ions are most frequently used, but there is a demand for materials that can replace them in consideration of their economic feasibility, resource scarcity, and environmental aspects, and organic active materials are attracting attention as substitutes. When using an organic active material, it is natural-friendly and more economical than metal, and has the advantage of being able to more easily change the redox potential difference and solubility through the introduction of various functional groups.

The structure of a typical redox flow cell is shown in FIG. 1. There are three key factors influencing the performance of the redox flow battery, which are electrodes, electrolytes, and ion exchange membranes, that is, separators. In particular, the ion exchange membrane is an element that affects self-discharge and overvoltage of the redox flow battery, and is located between the positive electrode electrolyte and the negative electrode electrolyte to exchange ions of a specific polarity and size through chemical and physical properties. In order to obtain a continuous redox reaction of the battery, only the ions that transfer electrons without mixing the positive electrode electrolyte and the negative electrode electrolyte must be able to pass through the ion exchange membrane. Therefore, the ion exchange membrane is an essential component in a typical redox flow cell. However, such an ion exchange membrane interferes with the flexibility of the battery design and has a problem of increasing the battery manufacturing cost due to its high price.

Accordingly, the present inventors intend to provide a redox flow battery having no ion exchange membrane.

Korean Patent Application Publication No. 10-2014-0119479 (2014-10-10)

An object of the present invention is to provide a redox flow battery that does not contain a separator.

As one aspect for achieving the above object, the present invention

A first electrolyte solution comprising tetrabutylammonium chloride; And

A redox flow cell comprising a second electrolyte solution comprising tetraethylammonium chloride, wherein the redox flow cell does not include a separator, thereby providing a redox flow cell.

Hereinafter, the redox flow battery in the present invention will be described in detail.

In order to solve the problems caused by the separator of the redox flow battery, the present disclosure provides a redox flow battery having no separator or membrane.

The two electrolytes of the redox flow battery according to the present disclosure, the first electrolyte and the second electrolyte, have different densities. Due to this difference in density and a special combination of tetrabutylammonium chloride and tetraethylammonium chloride contained in the electrolyte, the first electrolyte and the second electrolyte are not mixed with each other, and are divided into two layers of solutions in the upper part and the lower part. . A liquid-liquid interface may be formed between the solutions of the upper and lower layers. Through such a liquid-liquid interface, the movement of ions or salts for charge balance can occur freely. However, self-discharge due to movement of the active material in the electrolytic solution through the liquid-liquid interface is suppressed, so that the battery can be driven. Therefore, it is possible to provide a redox flow battery without a separator.

Normally, depending on the dissolution characteristics of the active material of the redox flow battery, the electrolyte is often an acid base, but the electrolyte according to the present disclosure has a neutral pH condition, and the redox flow battery according to the present disclosure may be capable of operating under a neutral pH condition. have. Therefore, unlike other acidic and basic batteries, it is possible to reduce the risk and increase the durability of the battery.

The first electrolyte solution may include tetrabutylammonium chloride at a concentration of about 0.1 to about 15M, about 1M to about 10M, about 2M to about 8M, about 3M to about 7M, or about 5M. The second electrolyte may include tetraethylammonium chloride at a concentration of about 0.1 to about 20M, about 1M to about 15M, about 5M to about 15M, about 7M to about 12M, or about 10M. The concentration of tetrabutylammonium chloride in the first electrolyte may be lower than the concentration of tetraethylammonium chloride in the second electrolyte. The ratio of the concentration of tetraethylammonium chloride to the concentration of tetrabutylammonium chloride may be 1 to 10, 1 to 5, more than 1 and 5 or less, more than 1 and 3 or less, or about 2.

Specifically, in the redox flow battery according to the present disclosure, each of the electrolyte solutions includes an active material. The first electrolyte solution may be a positive electrode electrolyte solution containing a positive electrode active material, and the second electrolyte solution may be a negative electrode electrolyte solution containing a negative electrode active material, and vice versa. The active material included in the electrolyte may be any active material that can be commonly used in redox flow batteries. In one embodiment, the active material may include ferricyanide / ferrocyanide. Each of the active materials may be present in the electrolyte solution at a concentration of 0.05 M to 3.0 M, specifically, at a concentration of 0.05M to 2M, and more specifically, at a concentration of 0.1M to 1.5M.

 The electrolyte may be an aqueous electrolyte. The solvent of the aqueous electrolyte solution may be an aqueous solvent. The water-based solvent may be water or a mixture of water and a hydrophilic solvent. Here, the hydrophilic solvent may include one or more selected from the group consisting of methanol, ethanol, n-propanol, isopropyl alcohol, n-butanol, t-butanol, ethylene glycol and diethylene glycol.

The electrolyte solution includes one of tetraethylammonium chloride and tetrabutylammonium chloride, and contains both an active material and a solvent, and may further include an electrolyte. The electrolyte solution may include at least one metal salt selected from H ₂ SO ₄ , Li ₂ SO ₄ , Na ₂ SO ₄ , K ₂ SO ₄ , LiCl, KOH, KCl, H ₃ PO ₄ , HNO ₃ and combinations thereof as an electrolyte. Can. The metal salt may be present in the electrolyte solution at a concentration of 0.05 M to 3 M, specifically 0.1 M to 2 M, and more specifically 0.1 M to 1.5 M.

The redox flow battery may include an anode and a cathode as electrodes. In addition, the battery may include a positive electrode electrolyte reservoir and a negative electrode electrolyte reservoir that respectively receive the positive electrode electrolyte solution and the negative electrode electrolyte solution, and may include a pump for pumping them respectively. The pump may be set to an operating condition of 10 to 50 rpm, preferably 20 to 40 rpm, to be set to a flow rate of 10 to 50 mL / min, preferably 20 to 30 mL / min.

The anode and cathode of the present invention may be any one or more selected from the group consisting of gold (Au), tin (Sn), titanium (Ti), platinum-titanium (Pt-Ti), iridium-titanium oxide (IrO-Ti), and carbon. You can. The electrode must have excellent electrical conductivity and mechanical strength, and must be chemically and electrochemically stable. In addition, when applied to a battery, it should be able to show high efficiency, be inexpensive, and be a material that reversibly undergoes an oxidation / reduction reaction with an active material. In consideration of these criteria, as described above, from the group consisting of gold (Au), tin (Sn), titanium (Ti), platinum-titanium (Pt-Ti), iridium-titanium oxide (IrO-Ti) and carbon materials Any one or more selected ones may be used as an electrode, and other materials that maintain stability in acids and bases while satisfying the above criteria may be used as electrodes. The carbon material has an advantage of low cost, high chemical resistance in acid and base electrolytes, and easy surface treatment. In particular, in the case of the carbon felt among the carbon materials, it has advantages such as chemical resistance, stability in a wide voltage range, and high strength. In addition, in order to increase the strength of these electrode materials, polyvinylidene (PVDF), high density polyethylene (HDPE), polyvinyl acetate (PVA), polyolefine, etc. A carbon polymer composite electrode may be used by mixing the binder with a conductive material such as carbon black or graphite fiber.

It is understood that the term “about” refers to a range of numbers that a person skilled in the art will consider to be equivalent to the stated value in terms of achieving the same function or result.

Since the redox flow battery according to the present disclosure does not include a separator, problems caused by the redox flow battery can be eliminated. For example, the redox flow battery according to the present disclosure can reduce the cost for the separator and allow a more free form in battery design.

1 shows the structure of a typical redox flow cell.
Figure 2 shows the structure of a redox flow battery without a separator according to the present invention.
Figure 3 shows the results of layer separation and NMR analysis of the electrolyte solution confirmed in Experimental Example 1.
Figure 4 shows the results of the three-electrode experiment confirmed in Experimental Example 2.
Figure 5 confirms the electrode activity of the redox flow battery confirmed in Experimental Example 3.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, various changes may be made to the embodiments, and the scope of the patent application right is not limited or limited by these embodiments. It should be understood that all modifications, equivalents, or substitutes for the embodiments are included in the scope of rights.

The terms used in the examples are for illustrative purposes only and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the embodiment belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

In addition, in the description with reference to the accompanying drawings, the same reference numerals are assigned to the same components regardless of reference numerals, and redundant descriptions thereof will be omitted. In describing the embodiments, when it is determined that detailed descriptions of related known technologies may unnecessarily obscure the subject matter of the embodiments, detailed descriptions thereof will be omitted.

Throughout this specification, "%" used to indicate the concentration of a specific substance, unless otherwise specified, solids / solids (weight / weight)%, solids / liquids (weight / volume)%, and The liquid / liquid is (volume / volume)%.

Production Example 1: Preparation of electrolyte

A solution of tetraethylammonium chloride in distilled water having a concentration of 10 M was prepared. In addition, a solution of tetrabutylammonium chloride in distilled water having a concentration of 5 M was prepared. After mixing these solutions with each other to form a mixed solution, ferrocyanide and ferricyanide as active materials were added to the mixed solution so that they were each 0.01 M, thereby preparing an electrolytic solution.

The electrolytic solution was sufficiently stirred for 1 hour or more. After stirring, it was still placed at 30 ° C for one day. Then it was confirmed that it is completely divided into two layers, as shown in FIG. The divided supernatant and lower layer were separated and stored respectively. At this time, it can be confirmed in Experimental Examples 2 and 3 that ferrocyanide and ferricyanide are dissolved in both the supernatant and the lower layer.

Experimental Example 1: H of electrolyte ^One -NMR analysis

H ¹ -NMR analysis of each of the two electrolytes obtained in Preparation Example 1 was performed (using Agilent technologies (USA), DD2 700). In addition, for comparison, tetraethylammonium chloride and tetrabutylammonium chloride were also subjected to H ¹ -NMR analysis. Fig. 3 shows the obtained NMR results.

The upper right of FIG. 3 shows the results of NMR analysis of the supernatant solution and tetrabutylammonium chloride, and the lower right solution of FIG. 3 shows the results of NMR analysis of the lower layer solution and tetraethylammonium chloride. Looking at the results of the supernatant, it can be seen that the supernatant in the electrolytic solution contained tetrabutylammonium chloride, and not tetraethylammonium chloride. On the other hand, looking at the results of the lower layer solution, it can be seen that the lower layer solution in the electrolytic solution contains tetraethylammonium chloride and does not include tetrabutylammonium chloride.

Experimental Example 2: 3-electrode experiment to confirm electrode activity

A three-electrode experiment was performed using the electrolyte obtained in Preparation Example 1.

An Ag / AgCl (RE-1B, Japan) electrode was used as a reference electrode, a Pt wire was used as a counter electrode, and a glassy carbon electrode (Glassy Carbon Electrdoe; GCE) was used as a working electrode. After immersing the three electrodes thus prepared in an electrolyte, a cyclic voltammetry test was performed. The voltage was changed in an external device to measure the amount of current generated at that voltage. The experiment was carried out using the supernatant in the electrolytic solution, and the same was repeated using the lower layer. Each result is shown in FIG. 4.

It can be confirmed that the electrode reaction occurs in both the case of using the supernatant and the case of using the lower layer. That is, it can be confirmed that ferrocyanide and ferricyanide as active materials exist in both the supernatant and the lower layer.

Experimental Example 3: Preparation of redox flow battery

A battery was manufactured using the electrolyte obtained in Production Example 2.

As shown in FIG. 2, a current collector plate, a positive electrode plate (reduction electrode), a flow frame, and a positive electrode plate (oxide electrode), and a current collector plate were stacked and assembled in this order to prepare a battery. Graphite electrodes were used for both anodes and cathodes. Battery activity was confirmed using a symmetric cell structure in which the positive electrode electrolyte and the negative electrode electrolyte were identical (Goulet MA, Aziz MJ.Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods.Journal of The Electrochemical Society. 2018; 165 (7) : A1466-A1477).

After the electrolyte solution of the upper and lower layers obtained in Preparation Example 1 was placed in each of the electrolyte reservoirs, the electrolyte was circulated using a pump in the battery. Thereafter, a constant current was supplied from an external device to measure voltage change in charging and discharging of the battery.

A single cell test was performed at a current density of 10 mA cm-2. Charging was carried out to 0.6V, and discharge was performed to -0.6V. As a result of the experiment, the battery was continuously operated without a decrease in charge / discharge time per cycle (decrease in capacity). The results thereof are shown in FIG. 5. It was confirmed that the battery system was normally operated based on the active material dissolved in the supernatant and the lower layer. This means that the redox flow cell without a membrane of the present specification can operate normally even though it does not contain a membrane. That is, it was confirmed that even without a membrane, the movement of the active material between the upper layer solution and the lower layer solution was suppressed and the battery was driven.

As described above, although the embodiments have been described by a limited drawing, a person skilled in the art can apply various technical modifications and variations based on the above. For example, the described techniques are performed in a different order than the described method, and / or the components of the described system, structure, device, circuit, etc. are combined or combined in a different form from the described method, or other components Alternatively, even if replaced or substituted by equivalents, appropriate results can be achieved.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (5)

A first electrolyte solution comprising tetrabutylammonium chloride; And
A redox flow battery comprising a second electrolyte comprising tetraethylammonium chloride, wherein the redox flow battery does not contain a separator.
The redox flow battery of claim 1, wherein a liquid-liquid interface is formed between the first electrolyte solution and the second electrolyte solution.
The redox flow battery of claim 1, wherein the first electrolyte solution and the second electrolyte solution are both aqueous electrolyte solutions.
The redox flow battery of claim 1, wherein the concentration of tetrabutylammonium chloride in the first electrolyte is lower than the concentration of tetraethylammonium chloride in the second electrolyte.
The redox flow battery of claim 1, wherein the density of the first electrolyte is lower than that of the second electrolyte.

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