Preparing method of electrolyte solution for redox battery, electrolyte solution for redox battery prepared by the method and sealed type redox battery comprising the same

Abstract

The present invention relates to a method for preparing an electrolyte that functions as a liquid electrode in a redox battery, comprising the steps of: adding an organic phase solvent and a metal extractant to an aqueous solution containing an active material whose acid value changes according to redox; and separating the organic phase containing metal impurities from the aqueous solution to remove the metal impurities, wherein when the internal pressure is measured while performing a charge-discharge test under the battery structure and charge-discharge conditions as described below using the electrolyte, the increase in the final pressure measured after the 100th discharge relative to the reference pressure measured after the 11th discharge is 1 kPa or less. - Battery structure: A sealed structure with 138g of electrolyte and a solid electrode area of ​​99×99mm. - Charging conditions: Charge at constant current at 25 ℃ and 1.6 A (1 C) until 1.53 V or 2 Wh is reached. - Discharge conditions: Discharge at constant current at 25 ℃ and 1.6 A (1 C) until 1.1 V is reached. The present invention has the effect of significantly reducing the gas generated during the charging and discharging process of a redox battery by removing impurities that cause gas generation.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing an electrolyte for a redox battery, and more specifically, to a method for manufacturing an electrolyte for a redox battery capable of reducing gas generation during the charging and discharging process, an electrolyte for a redox battery manufactured according to the method, and a sealed redox battery containing the same. Background Technology

[0002] Recently, the introduction of new and renewable energy is being promoted globally as a measure to address environmental issues and the depletion of petroleum energy. However, since the power output of new and renewable energy is affected by environmental factors such as weather, the importance of Energy Storage Systems (ESS), which act as a buffer between generation capacity and consumption and demand, is increasing.

[0003] In a redox battery, charging and discharging are performed as the oxidation state of a metal ion pair called a redox couple changes. Examples of redox couples include Cr / Cr, V / Sn, V / Fe, and V / V. Among these, the vanadium redox battery using vanadium is the closest to practical application.

[0004] A vanadium redox cell includes a cathode in which the oxidation state of vanadium changes to 2 and 3, and an anode in which the oxidation state of vanadium changes to 4 and 5.

[0005] Anode: VO2 + + 2H + + e - ↔ VO 2+ + H2O

[0006] Cathode: V 2+ - e - ↔ V 3+

[0007] In this context, unlike conventional secondary batteries where the active material undergoing charging and discharging is in a solid form, redox batteries utilize a liquid electrode in which the active material is dissolved in an electrolyte. This allows for an increase in power storage capacity through the simple method of increasing the amount of the liquid electrode (electrolyte). Utilizing this characteristic, many developments are underway in the form of redox flow batteries (RFBs), where an electrolyte storage device is installed outside the battery cell where the reaction takes place, and the electrolyte moves between the inside and outside of the cell.

[0008] Although redox batteries are known to have fewer side reactions compared to other batteries, hydrogen gas and the like can be generated due to the reaction of impurities contained in the electrolyte. While gases generated in redox flow batteries affect the pH of the electrolyte and consequently reduce lifespan, their impact is not significant within the structure of the flow battery through which the electrolyte moves, and it is possible to capture or remove the gases within the flow battery structure. (Republic of Korea Registered Patent No. 10-2219191, Republic of Korea Published Patent No. 10-2019-0059618)

[0009] Meanwhile, due to structural problems with flow batteries, the utility of redox flow batteries is limited, and thus, the development of new types of redox batteries is underway. This technology, which has been developed for vanadium redox batteries and is named a vanadium ion battery (VIB) to differentiate it from flow batteries, differs from conventional flow battery methods in that the liquid electrode moves outside the cell, and the vanadium electrolyte, which is the liquid electrode, is located only within the internal space of a sealed cell structure and does not move outside.

[0010] In such vanadium ion batteries, gas generation due to side reactions, which was not a major issue in conventional flow batteries, can cause very serious problems by increasing the pressure inside the sealed cell. Prior art literature

[0011] Republic of Korea Registered Patent No. 10-2219191 Republic of Korea Published Patent No. 10-2019-0059618 The problem to be solved

[0012] The present invention aims to solve the problems of the aforementioned prior art and provides a method for manufacturing an electrolyte for a redox battery that can minimize gas generation due to side reactions. means of solving the problem

[0013] A method for manufacturing an electrolyte for a redox battery according to the present invention for achieving the above objective is a method for manufacturing an electrolyte that functions as a liquid electrode in a redox battery, comprising the steps of: adding an organic phase solvent and a metal extractant to an aqueous solution containing an active material whose acid value changes according to redox; and separating the organic phase containing metal impurities from the aqueous solution to remove the metal impurities, wherein when the internal pressure is measured while performing a charge-discharge test under the battery structure and charge-discharge conditions as described below using the electrolyte, the increase in the final pressure measured after the 100th discharge relative to the reference pressure measured after the 11th discharge is 1 kPa or less.

[0014] - Battery structure: A sealed structure with 138g of electrolyte and a solid electrode area of ​​99×99mm.

[0015] - Charging conditions: Charge at constant current at 25 ℃ and 1.6 A (1 C) until 1.53 V or 2 Wh is reached.

[0016] - Discharge conditions: Discharge at constant current at 25 ℃ and 1.6 A (1 C) until 1.1 V is reached.

[0017] Based on the volume of the above aqueous solution, the organic solvent may be added in the range of 2 to 20 percent.

[0018] The extractant may be added in the range of 0.3 to 1.5% based on the volume of the above aqueous solution.

[0019] After adding the organic phase solvent and the metal extractant, stirring is performed, and it is preferable to perform stirring while heating to a temperature of 60°C or lower.

[0020] The above metal extractant may be used as one or a mixture of extractants capable of removing one or more elements from the group consisting of Ni, Cu, Ru, Rh, Pd, Ag, Sb, Te, Os, Ir, Pt, and Au.

[0021] The above aqueous solution contains vanadium ions as an active material, and the metal extractant may use one or more selected from TOPO (Trioctylphosphine oxide), TBP (Tributyl phosphate), DBP (dibutyl phthalate) and Alamine 336.

[0022] An electrolyte for a redox battery according to another embodiment of the present invention is an electrolyte that functions as a liquid electrode in a redox battery, and is characterized by adding an organic phase solvent and a metal extractant to an aqueous solution containing an active material whose acid value changes according to redox, and removing metal impurities by phase separation of the organic phase containing metal impurities, such that when the internal pressure is measured while performing a charge-discharge test under the battery structure and charge-discharge conditions as described below, the increase in the final pressure measured after the 100th discharge relative to the reference pressure measured after the 11th discharge is 1 kPa or less.

[0023] - Battery structure: A sealed structure with 138g of electrolyte and a solid electrode area of ​​99×99mm.

[0024] - Charging conditions: Charge at constant current at 25 ℃ and 1.6 A (1 C) until 1.53 V or 2 Wh is reached.

[0025] - Discharge conditions: Discharge at constant current at 25 ℃ and 1.6 A (1 C) until 1.1 V is reached.

[0026] A sealed redox battery according to another embodiment of the present invention comprises: a housing having a sealed internal space; an electrolyte containing an active material that fills the space inside the housing and whose acid value changes according to redox; a separator separating the space inside the housing; and a pair of solid electrodes each installed on both sides of the separator and which move electrons according to the reaction of the active material contained in the electrolyte, wherein the electrolyte is prepared by adding an organic phase solvent and a metal extractant and removing metal impurities by phase-separating the organic phase containing metal impurities, and wherein, when the internal pressure is measured while performing a charge-discharge test under the battery structure and charge-discharge conditions as described below, the increase in the final pressure measured after the 100th discharge relative to the reference pressure measured after the 11th discharge is 1 kPa or less.

[0027] - Battery structure: A sealed structure with 138g of electrolyte and a solid electrode area of ​​99×99mm.

[0028] - Charging conditions: Charge at constant current at 25 ℃ and 1.6 A (1 C) until 1.53 V or 2 Wh is reached.

[0029] - Discharge conditions: Discharge at constant current at 25 ℃ and 1.6 A (1 C) until 1.1 V is reached. Effects of the invention

[0030] The present invention, configured as described above, has the effect of significantly reducing the gas generated during the charging and discharging process of a redox battery by removing impurities that cause gas generation.

[0031] In addition, the electrolyte for a redox battery according to the present invention has an excellent effect of preventing problems caused by increased internal pressure in a sealed redox battery by minimizing gas generation due to side reactions even during long-term charging and discharging processes through the removal of metal impurities. Brief explanation of the drawing

[0032] FIG. 1 is a flowchart for explaining a method for manufacturing an electrolyte for a redox battery according to an embodiment of the present invention. Figure 2 is the result of measuring the change in internal pressure according to the number of charge and discharge cycles of a test cell manufactured using an electrolyte according to an embodiment and a comparative example of the present invention. Specific details for implementing the invention

[0033] An embodiment according to the present invention will be described in detail with reference to the attached drawings.

[0034] However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited only to the embodiments described below. The shapes and sizes of elements in the drawings may be exaggerated for clearer explanation, and elements indicated by the same reference numerals in the drawings are the same elements.

[0035] Furthermore, throughout the specification, when a part is described as being "connected" to another part, this includes not only cases where they are "directly connected" but also cases where they are "electrically connected" with other components interposed between them. Additionally, when a part is described as "including" or "equipped" with a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion or equipping of additional components.

[0036] Furthermore, terms such as "first," "second," etc., are intended to distinguish one component from another, and the scope of rights shall not be limited by these terms. For example, the first component may be named the second component, and similarly, the second component may be named the first component.

[0037] FIG. 1 is a flowchart for explaining a method for manufacturing an electrolyte for a redox battery according to an embodiment of the present invention.

[0038] First, prepare an aqueous solution used as the electrolyte for the redox battery.

[0039] The prepared aqueous solution is an aqueous solution that can be used as a liquid electrode for a redox battery, containing an active material whose acid value changes according to redox. It may be prepared using a method for manufacturing electrolytes for redox flow batteries known to date. The present invention aims to manufacture an electrolyte for a redox battery that reduces gas generation by decreasing metal-induced side reactions compared to conventionally used electrolytes for redox batteries. Since this objective can be achieved through subsequent impurity removal, the method for manufacturing electrolytes for redox flow batteries used conventionally can be applied without limitation.

[0040] Next, a solvent and an extractant are added to the prepared aqueous solution.

[0041] The added solvent is an organic phase solvent to facilitate the removal of impurities, and can be added in a range of 2 to 20 percent based on the volume of the aqueous solution. If the organic phase solvent exceeds 20 percent relative to the aqueous solution, the amount of extractant contained in the organic phase decreases due to the increase in the solvent, resulting in a decrease in extraction effect; furthermore, the manufacturing cost increases as the amount of additional solvent increases. On the other hand, when the organic phase solvent is less than 2 percent relative to the aqueous solution, there is a problem in that the extraction effect decreases because the amount of organic solvent capable of dissolving the extractant is insufficient, causing the viscosity of the organic solvent containing the extractant to increase and consequently the dispersion to be low. The type of organic phase solvent can be applied without limitation within a range that does not impair the features of the present invention, and kerosene, triglycerol (edible oil), etc., may be used.

[0042] Various extractants capable of removing metals that cause gas generation may be applied as the added extractant, and can be added in a range of 0.3 to 1.5% based on the volume of the aqueous solution. If the extractant exceeds 1.5% based on the volume of the aqueous solution, the manufacturing cost increases without a significant increase in the effect of removing impurities in the electrolyte. On the other hand, if the extractant is less than 0.3% based on the volume of the aqueous solution, the amount of extractant used decreases and the manufacturing cost is lowered; however, this results in a negligible effect of extracting metal ions from the electrolyte, ultimately leading to a problem where the removal of impurities from the electrolyte is not sufficiently achieved. In the present invention, the amount of extractant added has an economical effect, as it allows for the removal of impurities that cause gas generation with a very small amount compared to the amount of conventional general extractants used, due to the use of an organic solvent.

[0043] The inventor of the present invention analyzed the electrolyte generally used in vanadium redox flow batteries and identified Ni, Cu, Ru, Rh, Pd, Ag, Sb, Te, Os, Ir, Pt, and Au as impurities that cause gas generation. By removing at least some of these, the inventor developed the present invention, which can significantly reduce the amount of gas generated compared to conventional methods. Various metal extractants that remove only impurities without removing redox couples contained in the aqueous solution can be applied, and the specific level of impurity removal will be explained in detail later.

[0044] The inventors of the present invention conducted experiments on six extractants, PC88A (Mono-2-ethylhexyl (2-Ethylhexyl)phosphonate), TOPO (Trioctylphosphine oxide), TBP (Tributyl phosphate), DBP (dibutyl phthalate), HDEHP (Di-(2-ethylhexyl)phosphoric acid), and Alamine336, and confirmed that they can all extract and remove Pd, Ag, Au, and Pb. It was also confirmed that PC88A and HDEHP cannot be used in vanadium redox batteries because they also extract vanadium. In addition, one or a mixture of extractants capable of removing one or more of Ni, Cu, Ru, Rh, Pd, Ag, Sb, Te, Os, Ir, Pt, and Au, which are the causes of gas generation, without removing redox couples contained in aqueous solutions, may be used. The extractant may be used after dilution to a concentration range of 5 to 25 mM.

[0045] Then, the aqueous solution to which the solvent and extractant have been added is stirred to extract impurities, and the organic phase from which the metal impurities have been extracted is phase-separated to remove the metal impurities.

[0046] The organic phase and the aqueous solution containing the added metal extractant are sufficiently stirred so that the added metal extractant can remove trace amounts of metal impurities contained in the aqueous solution. At this time, the aqueous solution may be heated to accelerate the extraction process, and stirring can be performed while heating to a temperature of 60°C or lower to reduce the time required for extraction. However, since heating to too high a temperature may cause water to volatilize from the mixed solution and alter the physical properties of the electrolyte, it is preferable to heat to a temperature of 60°C or lower.

[0047] After extraction by a metal extractant is performed, if stirring is stopped, the aqueous solution and the organic solvent separate into phases. Since the extracted metal impurities are dissolved in the organic solvent, the electrolyte for a redox battery according to the present invention, from which metal impurities are further removed, can be prepared by separating the phase-separated organic solvent and the aqueous solution.

[0048] The process of separating the phase-separated organic solvent and the aqueous solution is not particularly limited, and methods such as separating by discharging only the aqueous solution from a discharge port located at the bottom by utilizing the characteristic of phase separation such that the organic solvent is located above the aqueous solution may be applied.

[0049] Hereinafter, the effects of the present invention and the level of impurity removal required for the electrolyte according to the present invention are explained using the electrolyte prepared by the method for preparing an electrolyte for a redox battery according to the present invention.

[0050] First, an aqueous solution used as the electrolyte for a vanadium redox flow battery was prepared.

[0051] The prepared aqueous solution is an electrolyte for a vanadium redox flow battery prepared by a general method, with a concentration of 1.7 M, and although the metal impurity content was not confirmed, it is at a level suitable for use in a general flow battery. Specifically, 26 g of 99.9% vanadium metal, 108 g of commonly used 98% V2O5 powder, 235 mL of 98% aqueous sulfuric acid solution, and 600 mL of ultrapure water were mixed and stirred sufficiently at room temperature, and then additional ultrapure water was added to make the volume of the solution 1 L to prepare an aqueous solution having an oxidation state of vanadium of 3.5.

[0052] For such a vanadium redox flow battery electrolyte, kerosene, an organic phase solvent, and an extractant were added and stirred under the following conditions, and then only the phase-separated aqueous solution was collected through the lower discharge port.

[0053] aqueous solution (ℓ) Kerosene (ml) extractant (g) Stirring temperature (°C) Stirring time (h) Comparative Example 1 1 × × × × Comparative Example 2 1 200 4.5 25 2 Example 1 1 200 4.5 25 14 Example 2 1 200 4.5 50 2

[0054] Comparative Example 1 used a conventional electrolyte for a vanadium redox flow battery without applying the method of the present invention, and Comparative Example 2 performed short stirring for 2 hours without heating during the stirring process, creating an environment where it is difficult for the extractant to function sufficiently.

[0055] In Example 1, as in Comparative Example 2, no heat was applied during the stirring process, but stirring was carried out for 14 hours, and in Example 2, stirring was carried out for 2 hours while heated to 50°C using a heating mantle. The extractant used was TBP (tributyl phosphate), which is cost-effective and does not remove vanadium.

[0056] A battery cell was constructed by sequentially stacking a solid electrode made of carbon felt, a carbon current collector, and a metal current collector on both sides of a separator inside a cell housing, and an electrolyte prepared by the above method was injected into the sealed battery cell using a vacuum post-injection process to manufacture a test cell, and charge-discharge experiments were performed with a pressure gauge attached to the injection port.

[0057] The separator used was an ion-selective separator generally used in vanadium redox batteries, and the area of ​​the carbon felt, which is the solid electrode, is 99×99 mm. The carbon current collector is a separator containing carbon, and the metal current collector is a current collector containing aluminum. The amount of electrolyte injected, which functions as the liquid electrode of the redox battery, is 138 g, and the pressure gauge used is a Sensys product with a measurement range of -100 to 100 kPa and an accuracy of 25 ℃ ±0.5% FS.

[0058] For the test cell of the above-described structure, a charging and discharging process was performed 100 times at 25°C, charging with a constant current of 1.6 A (1 C) until it reached 1.53 V or 2 Wh, and discharging with a constant current of 1.6 A (1 C), the same as the charging, until it reached 1.1 V.

[0059] Pressure was measured after performing discharge, and the first 10 times were excluded as they were treated as the stabilization process of the test cell, and the pressure from the 11th time was used as the reference pressure and the pressure was measured from the 11th time to the 100th time.

[0060] Figure 2 is the result of measuring the change in internal pressure according to the number of charge and discharge cycles of a test cell manufactured using an electrolyte according to an embodiment and a comparative example of the present invention.

[0061] The difference in pressure at the 11th cycle is that in the case of Comparative Examples 1 and 2, the pressure continuously increased even during the 1 to 10 charge-discharge cycles. Even when based on the pressure at the 11th cycle, which is the stabilization process of the test cell, the internal pressure continuously increased in the case of Comparative Examples 1 and 2.

[0062] In contrast, in the case of Examples 1 and 2, the reference pressure measured after the 11th cycle was lower than that of Comparative Examples 1 and 2, and it can be confirmed that there was almost no change in pressure even during the process of repeating the charge-discharge experiment 100 times.

[0063] The electrolyte for a redox battery manufactured by the method of the present invention has the effect of preventing gas generation within the electrolyte even during long-term charging and discharging by removing impurities that are the cause of side reactions generating gas during the charging and discharging process.

[0064] The electrolyte for a redox battery produced by the method of the present invention has the effect of making maintenance easier compared to the conventional method even when applied to a conventional flow battery method, but it exhibits an even more superior effect in a redox battery, such as a vanadium ion battery (VIB), in which the liquid electrode vanadium electrolyte is located only in the internal space of a sealed cell structure and does not move to the outside.

[0065] To this end, a method for manufacturing an electrolyte for a redox battery according to one embodiment of the present invention is carried out by the above-described manufacturing method, and is characterized in that impurities are removed such that the increase in the final pressure measured after the 100th cycle with respect to the reference pressure measured after the 11th cycle in a charge-discharge experiment on the above-described test cell is 1 kPa or less.

[0066] When impurities are removed to this extent, problems caused by gas generation do not occur within the service life of a closed redox battery such as a vanadium ion battery (VIB).

[0067] In addition, an electrolyte for a redox battery according to another form of the present invention is characterized by being manufactured by the above-described manufacturing method such that the increase in the final pressure measured after the 100th cycle with respect to the reference pressure measured after the 11th cycle in a charge-discharge experiment on the above-described test cell is 1 kPa or less.

[0068] Furthermore, a redox battery according to another form of the present invention is characterized in that, unlike a flow battery, the electrolyte, which is a liquid electrode, is located only inside a sealed housing, and the electrolyte used is manufactured by the above-described manufacturing method such that the increase in the final pressure measured after the 100th cycle with respect to the reference pressure measured after the 11th cycle in the charge-discharge experiment for the above-described test cell is 1 kPa or less.

[0069] The present invention has been described above through preferred embodiments. However, the aforementioned embodiments are merely illustrative of the technical concept of the present invention, and those skilled in the art will understand that various modifications are possible within the scope of the technical concept of the present invention. Therefore, the scope of protection of the present invention should be interpreted by the matters described in the claims rather than by specific embodiments, and all technical concepts within an equivalent scope should also be interpreted as being included within the scope of rights of the present invention.

Claims

Claim 1 A method for preparing an electrolyte that functions as a liquid electrode in a redox battery, comprising the step of adding an organic phase solvent and a metal extractant to an aqueous solution containing an active material whose acid value changes according to redox; A method for manufacturing an electrolyte for a redox battery, comprising the step of removing metal impurities by phase-separating an organic phase containing metal impurities from the above aqueous solution, wherein, when measuring the internal pressure while performing a charge-discharge test under the battery structure and charge-discharge conditions as described below using the electrolyte, the increase in the final pressure measured after the 100th discharge relative to the reference pressure measured after the 11th discharge is 1 kPa or less. - Battery structure: A sealed structure having 138 g of electrolyte and a solid electrode area of ​​99 × 99 mm - Charging condition: Charging with a constant current at 25 ℃ and 1.6 A (1 C) until reaching 1.53 V or 2 Wh - Discharging condition: Discharging with a constant current at 25 ℃ and 1.6 A (1 C) until reaching 1.1 V Claim 2 A method for manufacturing an electrolyte for a redox battery according to claim 1, characterized in that the organic phase solvent is added in a range of 2 to 20 percent based on the volume of the aqueous solution. Claim 3 A method for manufacturing an electrolyte for a redox battery according to claim 1, characterized in that the extractant is added in a range of 0.3 to 1.5% based on the volume of the aqueous solution. Claim 4 A method for manufacturing an electrolyte for a redox battery according to claim 1, characterized in that stirring is performed after adding an organic phase solvent and a metal extractant, while stirring is performed while heating to a temperature of 60°C or lower. Claim 5 A method for manufacturing an electrolyte for a redox battery according to claim 1, characterized in that the metal extractant used is one or a mixture of extractants capable of removing one or more elements from the group consisting of Ni, Cu, Ru, Rh, Pd, Ag, Sb, Te, Os, Ir, Pt, and Au. Claim 6 A method for manufacturing an electrolyte for a redox battery according to claim 1, wherein the aqueous solution comprises vanadium ions as an active material, and the metal extractant uses one or more selected from TOPO (Trioctylphosphine oxide), TBP (Tributyl phosphate), DBP (dibutyl phthalate), and Alamine 336. Claim 7 An electrolyte for a redox battery that functions as a liquid electrode, characterized in that, by adding an organic phase solvent and a metal extractant to an aqueous solution containing an active material whose acid value changes according to redox, and removing metal impurities by phase separation of the organic phase containing metal impurities, the increase in the final pressure measured after the 100th discharge cycle relative to the reference pressure measured after the 11th discharge cycle is 1 kPa or less when measuring the internal pressure while performing charge-discharge tests under the battery structure and charge-discharge conditions as described below. - Battery structure: A sealed structure having 138 g of electrolyte and a solid electrode area of ​​99 × 99 mm. - Charging conditions: Charging with a constant current at 25 ℃ and 1.6 A (1 C) until 1.53 V or 2 Wh is reached. - Discharging conditions: Discharging with a constant current at 25 ℃ and 1.6 A (1 C) until 1.1 V is reached. Claim 8 A housing having a sealed internal space; an electrolyte containing an active material that fills the space inside the housing and whose acid value changes according to oxidation and reduction; and a separator that separates the space inside the housing; A sealed redox battery comprising a pair of solid electrodes, each installed on both sides of a separator, which move electrons according to the reaction of an active material contained in an electrolyte, wherein the electrolyte is prepared by adding an organic phase solvent and a metal extractant, and removing metal impurities by phase-separating the organic phase containing metal impurities, characterized in that when internal pressure is measured while performing a charge-discharge test under the battery structure and charge-discharge conditions as described below, the increase in the final pressure measured after the 100th discharge cycle relative to the reference pressure measured after the 11th discharge cycle is 1 kPa or less. - Battery structure: A sealed structure having 138 g of electrolyte and a solid electrode area of ​​99 × 99 mm - Charging conditions: Charging with a constant current at 25 ℃ and 1.6 A (1 C) until 1.53 V or 2 Wh is reached - Discharging conditions: Discharging with a constant current at 25 ℃ and 1.6 A (1 C) until 1.1 V is reached

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