Method for preparing electrolyte for redox battery, electrolyte prepared thereby for redox battery, and sealed redox battery comprising same

Abstract

The present invention relates to a method for preparing an electrolyte that functions as a liquid electrode in a redox battery, the method 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 oxidation and reduction; and separating an organic phase containing metal impurities from the aqueous solution to remove the metal impurities. When a charge / discharge test is performed using the electrolyte with the following battery structure and charge / discharge conditions, the increase in final pressure measured after the 100th discharge relative to the reference pressure measured after the 11th discharge is 1 kPa or less: – Battery structure: sealed structure with 138 g of electrolyte and a solid electrode area of 99 × 99 mm, – Charging condition: 25 °C, constant current charging at 1.6 A (1 C) until reaching 1.53 V or 2 Wh, – Discharging condition: 25 °C, constant current discharging at 1.6 A (1 C) until reaching 1.1 V. The present invention significantly reduces gas generation during the charge / discharge process by removing impurities that cause gas evolution in redox batteries.

Description

Method for producing an electrolyte for a redox battery, an electrolyte for a redox battery produced thereby, and a sealed redox battery comprising the same

[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 a charge / discharge process, an electrolyte for a redox battery manufactured thereby, and a sealed redox battery including the same.

[0002] Recently, the adoption of renewable energy sources has been promoted globally to address environmental issues and the depletion of petroleum energy. However, because the power generation output of renewable energy sources is affected by environmental factors such as weather, the importance of energy storage systems (ESS) to act as a buffer between power generation capacity and consumption and demand is increasing.

[0003] A redox battery is a battery that charges and discharges by changing the oxidation number of a pair of metal ions called a redox couple. There are various types of redox couples such as Cr / Cr, V / Sn, V / Fe, and V / V. Among these, the one closest to practical use is the vanadium redox battery using vanadium.

[0004] A vanadium redox battery includes a cathode in which the oxidation states of vanadium change between divalent and trivalent, and an anode in which the oxidation states of vanadium change between tetravalent and pentavalent.

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

[0006] Cathode: V 2+ - e - ↔ V 3+

[0007] At this time, unlike general secondary batteries in which the active material through which electricity is charged and discharged is in a solid form, redox batteries adopt the form of liquid electrodes in which the active material through which electricity is charged and discharged is dissolved in an electrolyte, thereby increasing the amount of electricity stored through a simple method of increasing the amount of liquid electrode (electrolyte). Taking advantage of this characteristic, many developments are being conducted in the form of redox flow batteries (RFBs), in which an electrolyte storage device is installed outside the battery cell where the reaction is performed, and the electrolyte moves inside and outside the battery cell.

[0008] Redox batteries are known to have fewer side reactions than other types of batteries, but reactions with impurities in the electrolyte can still produce gases like hydrogen gas. While these gases can alter the pH of the electrolyte and, consequently, reduce its lifespan, the impact is minimal within the structure of the flow battery, where the electrolyte flows. Furthermore, the gas can be captured or removed within the flow battery structure (Korean Patent No. 10-2219191, Korean Patent Publication No. 10-2019-0059618).

[0009] Meanwhile, due to structural issues with flow batteries, the usability of redox flow batteries is limited, and the development of a new type of redox battery is underway. This technology, developed for vanadium redox batteries and named vanadium ion batteries (VIBs) to differentiate it from flow batteries, differs from the conventional flow battery method in that the liquid electrode moves outside the cell. In addition, the vanadium electrolyte, which is the liquid electrode, is located only in the internal space of the sealed cell structure and does not move outside.

[0010] In these vanadium ion batteries, gas generation due to side reactions, which was not a major problem in conventional flow batteries, can cause very serious problems in that it increases the pressure inside the sealed cell.

[0011] The present invention is intended to solve the problems of the above-mentioned prior art and to provide a method for manufacturing an electrolyte for a redox battery that can minimize gas generation due to side reactions.

[0012] In order to achieve the above object, the present invention provides a method for producing an electrolyte for a redox battery, which functions as a liquid electrode in a redox battery, comprising: a step of adding an organic solvent and a metal extractant to an aqueous solution containing an active material whose acid value changes depending on redox; and a step of removing metal impurities by separating an organic phase containing metal impurities from the aqueous solution, wherein when a charge-discharge test is performed using the electrolyte under the following battery structure and charge-discharge conditions and the internal pressure is measured, the increase in the final pressure measured after the 100th discharge with respect to the reference pressure measured after the 11th discharge is 1 kPa or less.

[0013] - Battery structure: Sealed structure with 138g of electrolyte and solid electrode area of ​​99×99mm

[0014] - Charging conditions: Constant current charging at 25℃, 1.6 A (1 C) until reaching 1.53 V or 2 Wh

[0015] - Discharge conditions: Constant current discharge at 25 ℃, 1.6 A (1 C) current until reaching 1.1 V.

[0016] The solvent of the organic phase may be added in the range of 2 to 20% based on the volume of the aqueous solution.

[0017] The extractant may be added in a range of 0.3 to 1.5% based on the volume of the aqueous solution.

[0018] After adding the organic solvent and metal extractant, stirring is performed, and it is preferable to perform the stirring while heating to a temperature of 60°C or lower.

[0019] The above metal extractant may be 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.

[0020] The above aqueous solution contains vanadium ions as an active material, and the metal extractant may be one or more selected from TOPO (Trioctylphosphine oxide), TBP (Tributyl phosphate), DBP (dibutyl phthalate), and Alamine336.

[0021] 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, wherein an organic solvent and a metal extractant are added to an aqueous solution containing an active material whose acid value changes depending on oxidation-reduction, and the organic phase containing metal impurities is phase-separated to remove the metal impurities, and when a charge-discharge test is performed under the following battery structure and charge-discharge conditions and the internal pressure is measured, the increase in the final pressure measured after the 100th discharge with respect to the reference pressure measured after the 11th discharge is 1 kPa or less.

[0022] - Battery structure: Sealed structure with 138g of electrolyte and solid electrode area of ​​99×99mm

[0023] - Charging conditions: Constant current charging at 25℃, 1.6 A (1 C) until reaching 1.53 V or 2 Wh

[0024] - Discharge conditions: Constant current discharge at 25 ℃, 1.6 A (1 C) current until reaching 1.1 V.

[0025] A sealed redox battery according to another embodiment of the present invention comprises: a housing having a sealed internal space; an electrolyte filled in the internal space of the housing and containing an active material whose acid value changes depending on redox; a separator separating the internal space of the housing; and a pair of solid electrodes installed on each side of the separator and moving electrons depending on the reaction of the active material included in the electrolyte, wherein the electrolyte is prepared by adding an organic solvent and a metal extractant and separating an organic phase containing metal impurities to remove metal impurities, and when a charge-discharge test is performed under the following battery structure and charge-discharge conditions, the internal pressure is measured, and the increase in the final pressure measured after the 100th discharge with respect to the reference pressure measured after the 11th discharge is 1 kPa or less.

[0026] - Battery structure: Sealed structure with 138g of electrolyte and solid electrode area of ​​99×99mm

[0027] - Charging conditions: Constant current charging at 25℃, 1.6 A (1 C) until reaching 1.53 V or 2 Wh

[0028] - Discharge conditions: Constant current discharge at 25 ℃, 1.6 A (1 C) current until reaching 1.1 V.

[0029] The present invention, configured as described above, has the effect of significantly reducing gas generated during the charging and discharging process of a redox battery by removing impurities that cause gas generation.

[0030] In addition, the electrolyte for a redox battery of the present invention has an excellent effect of minimizing gas generation due to side reactions even during a long-term charge / discharge process through the removal of metal impurities, thereby preventing problems due to an increase in internal pressure in a sealed redox battery.

[0031] Figure 1 is a flowchart for explaining a method for manufacturing an electrolyte for a redox battery according to an embodiment of the present invention.

[0032] Figure 2 shows the results of measuring the change in internal pressure according to the number of charge / discharge cycles of a test cell manufactured using an electrolyte according to an embodiment and a comparative example of the present invention.

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

[0034] However, the embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited 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 symbols in the drawings are the same elements.

[0035] Throughout the specification, when a part is said to be "connected" to another part, this includes not only the cases where it is "directly connected" but also the cases where it is "electrically connected" with another element in between. Furthermore, when a part is said to "include" or "comprise" a component, this does not mean that it excludes other components, but rather that it can include or comprise other components, unless otherwise specifically stated.

[0036] Additionally, terms such as "first," "second," etc. are intended to distinguish one component from another and should not limit the scope of the rights. For example, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component.

[0037]

[0038] Figure 1 is a flowchart for explaining a method for manufacturing an electrolyte for a redox battery according to an embodiment of the present invention.

[0039] First, prepare an aqueous solution used as an electrolyte for a redox battery.

[0040] The aqueous solution prepared is an aqueous solution that can be used as a liquid electrode of a redox battery, including an active material whose acid value changes depending on redox, and may be prepared through a method for preparing an electrolyte for a redox flow battery known to date. The present invention aims to prepare an electrolyte for a redox battery that reduces side reactions due to metals and thus reduces gas generation compared to conventional electrolytes for redox batteries, and since this purpose can be achieved by removing impurities that are performed thereafter, a method for preparing an electrolyte for a redox flow battery that has been conventionally used can be applied without limitation.

[0041] Add the solvent and extractant to the prepared aqueous solution.

[0042] The added solvent is applied as an organic solvent to facilitate the removal of impurities, and can be added in the range of 2 to 20% based on the volume of the aqueous solution. When the organic solvent exceeds 20% of the aqueous solution, the amount of extractant contained in the organic phase decreases due to the increase in the solvent, which reduces the extraction effect, and also increases the manufacturing cost because the additional amount of solvent increases. On the other hand, when the organic solvent is less than 2% of the aqueous solution, the amount of organic solvent that can dissolve the extractant is insufficient, so the viscosity of the organic solvent including the extractant increases and the dispersibility decreases accordingly, which causes a problem of reduced extraction effect. The type of organic solvent can be applied without limitation as long as it does not impair the characteristics of the present invention, and kerosene, triglycerol (edible oil), etc. can be used.

[0043] The extractant added can be a variety of extractants capable of removing metals that cause gas generation, and can be added in the 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 significantly increasing 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, lowering the manufacturing cost. However, this results in a minimal effect of extracting metal ions in the electrolyte, and ultimately, there is a problem that impurities in the electrolyte are not sufficiently removed. The amount of extractant added in the present invention has an economical effect of removing impurities that cause gas generation even with a very small amount compared to the amount of conventional general extractants used, as an organic solvent is used.

[0044] The inventor of the present invention analyzed the electrolyte generally used in a vanadium redox flow battery and identified Ni, Cu, Ru, Rh, Pd, Ag, Sb, Te, Os, Ir, Pt, and Au as impurities that cause gas generation, and developed the present invention which can significantly reduce the amount of gas generation compared to the prior art by removing at least some of these, and a metal extractant that removes only impurities without removing the redox couple contained in an aqueous solution can be applied in various ways, and the specific level of impurity removal will be described in detail later.

[0045] The inventor of the present invention performed 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 commonly extract and remove Pd, Ag, Au, and Pb, and that PC88A and HDEHP cannot be used in vanadium redox batteries because they extract vanadium together. In addition, extractants that can remove one or more of Ni, Cu, Ru, Rh, Pd, Ag, Sb, Te, Os, Ir, Pt, and Au, which are causes of gas generation, without removing the redox couple contained in the aqueous solution, can be used alone or in combination. The concentration of the extractant can be diluted and used in the range of 5 to 25 mM.

[0046] Then, the aqueous solution containing the solvent and extractant is stirred to extract impurities, and the organic phase from which the metal impurities are extracted is separated to remove the metal impurities.

[0047] The organic phase and the aqueous solution containing the added metal extractant are sufficiently stirred to allow the metal extractant to remove trace amounts of metal impurities contained in the aqueous solution. The aqueous solution can be heated to facilitate rapid extraction, and the time required for extraction can be shortened by heating to a temperature below 60°C while stirring. At this time, heating to a temperature below 60°C is preferred, as excessive heating can cause water volatilization from the mixed solution, which can alter the properties of the electrolyte.

[0048] After extraction using a metal extractant is performed, stirring is stopped, the aqueous solution and the organic solvent are phase separated, and the extracted metal impurities are dissolved in the organic solvent. Therefore, by separating the phase-separated organic solvent and the aqueous solution, an electrolyte for a redox battery of the present invention with additional metal impurities removed can be manufactured.

[0049] The process for separating the phase-separated organic solvent and aqueous solution is not particularly limited, and a method for separating only the aqueous solution by discharging it from the discharge port located at the bottom can be applied, utilizing the characteristic of the organic solvent being phase-separated to be located at the top of the aqueous solution.

[0050]

[0051] Hereinafter, the effects of the present invention and the level of impurity removal required for the electrolyte according to the present invention will be described using the electrolyte manufactured by the method for manufacturing the electrolyte for a redox battery according to the present invention.

[0052] First, an aqueous solution used as an electrolyte for a vanadium redox flow battery was prepared.

[0053] The prepared aqueous solution is an electrolyte for a vanadium redox flow battery manufactured by a general method, and has a concentration of 1.7 M. Although the content of metal impurities was not confirmed, it is at a level that can be used in a general flow battery. Specifically, 26 g of 99.9% vanadium metal, 108 g of 98% V2O5 powder commonly used, 235 mL of 98% sulfuric acid aqueous solution, and 600 mL of ultrapure water were mixed and stirred sufficiently at room temperature. Then, ultrapure water was additionally added so that the volume of the solution became 1 L, thereby manufacturing an aqueous solution in which the oxidation number of vanadium was 3.5.

[0054] For the electrolyte for this vanadium redox flow battery, kerosene, an organic solvent, and an extractant were added and stirred under the following conditions, and only the phase-separated aqueous solution was collected through the discharge port at the bottom.

[0055] Aqueous solution (ℓ) Kerosene (㎖) Extractant (g) Stirring temperature (℃) Stirring time (h) Comparative example 11×××× Comparative example 212004.5252 Example 112004.52514 Example 212004.5502

[0056] Comparative Example 1 used a conventional vanadium redox flow battery electrolyte without applying the method of the present invention, and Comparative Example 2 performed a short stirring of 2 hours without heating during the stirring process, which is an environment in which it is difficult for the extractant to function sufficiently. In Example 1, like Comparative Example 2, no heat was applied during the stirring process, but stirring was performed for 14 hours, and in Example 2, stirring was performed for 2 hours while heating to 50°C using a heating mantle. The extractant used was TBP (tributyl phosphate), which is excellent in price without removing vanadium.

[0057] A battery cell was constructed by sequentially stacking a solid electrode composed of carbon felt on both sides centered on a separator inside a cell housing, a carbon current collector, and a metal current collector, and an electrolyte manufactured by the above method was injected into the sealed battery cell through a vacuum post-injection process to manufacture a test cell, and a charge / discharge experiment was performed with a pressure gauge attached to the injection port.

[0058] The separator used is an ion-selective separator generally used in vanadium redox batteries, and the area of ​​the carbon felt solid electrode is 99 × 99 mm. The carbon collector is a separator containing carbon, and the metal collector is a collector containing aluminum. The amount of electrolyte that functions as the liquid electrode of the redox battery is 138 g, and the pressure gauge used is a product of Sensys with a measurement range of -100 to 100 kPa and an accuracy of 25 ℃ ±0.5% FS.

[0059] For the test cell of the above structure, a charge-discharge process was performed 100 times, in which the battery was charged at a constant current of 1.6 A (1 C) at 25°C until it reached 1.53 V or 2 Wh, and then discharged at a constant current of 1.6 A (1 C) at the same current as the charge until it reached 1.1 V.

[0060] The pressure was measured after performing the discharge, and the first 10 times were excluded as they were treated as a stabilization process of the test cell, and the pressure of the 11th time was used as the reference pressure, and the pressure was measured from the 11th to the 100th time.

[0061] Figure 2 shows the results of measuring the change in internal pressure according to the number of charge / discharge cycles of a test cell manufactured using an electrolyte according to an embodiment and a comparative example of the present invention.

[0062] The difference in pressure in the 11th cycle is because, in the case of Comparative Examples 1 and 2, the pressure continued to increase even during the 1st to 10th charge / discharge cycle. Even when the stabilization process of the test cell was based on the pressure in the 11th cycle, the internal pressure in the case of Comparative Examples 1 and 2 continued to increase.

[0063] In contrast, in the case of Examples 1 and 2, the reference pressure measured after the 11th cycle was lower than in Comparative Examples 1 and 2, and it can be confirmed that there was almost no change in pressure even during 100 repetitions of the charge / discharge experiment.

[0064] 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 that generate gas during the charging and discharging process.

[0065] The electrolyte for a redox battery manufactured by the method of the present invention has the effect of making maintenance easier compared to conventional methods even when applied to a conventional flow battery, but it exhibits an even more outstanding effect in a redox battery, for example, a vanadium ion battery (VIB), in which the vanadium electrolyte, which is a liquid electrode, is located only in the internal space of a sealed cell structure and does not move to the outside.

[0066] To this end, a method for manufacturing an electrolyte for a redox battery according to one embodiment of the present invention is performed by the above-described manufacturing method, and is characterized in that impurities are removed so 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.

[0067] When impurities are removed to this extent, no problems due to gas generation occur during the service life of sealed redox batteries such as vanadium ion batteries (VIB).

[0068] In addition, the electrolyte for a redox battery according to another form of the present invention is characterized in that it is manufactured by the above-described manufacturing method, and is manufactured so 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.

[0069] 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, and 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.

[0070]

[0071] The present invention has been described above through preferred embodiments. However, the above-described embodiments are merely illustrative of the technical idea of ​​the present invention. Those skilled in the art will understand that various changes may be made without departing from the technical idea of ​​the present invention. Therefore, the scope of protection of the present invention should be interpreted not by specific embodiments, but by the matters described in the claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included within the scope of the rights of the present invention.

Claims

1. A method for manufacturing an electrolyte that functions as a liquid electrode in a redox battery, A step of adding an organic solvent and a metal extractant to an aqueous solution containing an active material whose acid value changes depending on redox; and It includes a step of removing metal impurities by separating an organic phase containing metal impurities from the above aqueous solution, A method for manufacturing an electrolyte for a redox battery, characterized in that when a charge-discharge test is performed using the above electrolyte under the following battery structure and charge-discharge conditions and the internal pressure is measured, the increase in the final pressure measured after the 100th discharge with respect to the reference pressure measured after the 11th discharge is 1 kPa or less. - Battery structure: Sealed structure with 138g of electrolyte and solid electrode area of ​​99×99mm - Charging conditions: Constant current charging at 25℃, 1.6 A (1 C) until reaching 1.53 V or 2 Wh - Discharge conditions: Constant current discharge at 25 ℃, 1.6 A (1 C) current until reaching 1.1 V.

2. In claim 1, A method for producing an electrolyte for a redox battery, characterized in that the organic solvent is added in a range of 2 to 20% based on the volume of the aqueous solution.

3. In claim 1, A method for producing an electrolyte for a redox battery, characterized in that the extractant is added in a range of 0.3 to 1.5% based on the volume of the aqueous solution.

4. In claim 1, A method for producing an electrolyte for a redox battery, characterized in that stirring is performed after adding an organic solvent and a metal extractant, and stirring is performed while heating to a temperature of 60°C or lower.

5. In claim 1, A method for producing an electrolyte for a redox battery, characterized in that the metal extractant 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.

6. In claim 1, The above aqueous solution contains vanadium ions as an active material, A method for producing an electrolyte for a redox battery, characterized in that the metal extractant uses at least one selected from TOPO (Trioctylphosphine oxide), TBP (Tributyl phosphate), DBP (dibutyl phthalate), and Alamine336.

7. As an electrolyte that functions as a liquid electrode in a redox battery, By adding an organic solvent and a metal extractant to an aqueous solution containing an active material whose acid value changes depending on redox, and separating the organic phase containing metal impurities, the metal impurities are removed. An electrolyte for a redox battery, characterized in that when the internal pressure is measured while performing a charge / discharge test under the following battery structure and charge / discharge conditions, the increase in the final pressure measured after the 100th discharge with respect to the reference pressure measured after the 11th discharge is 1 kPa or less. - Battery structure: Sealed structure with 138g of electrolyte and solid electrode area of ​​99×99mm - Charging conditions: Constant current charging at 25℃, 1.6 A (1 C) until reaching 1.53 V or 2 Wh - Discharge conditions: Constant current discharge at 25 ℃, 1.6 A (1 C) current until reaching 1.1 V.

8. A housing having a sealed internal space; An electrolyte containing an active material that is filled in the space inside the housing and whose acid value changes depending on redox; A separator separating the space inside the housing; and It includes a pair of solid electrodes installed on each side of the separator and moving electrons according to the reaction of the active material contained in the electrolyte. A sealed redox battery characterized in that, when the internal pressure is measured while performing a charge / discharge test under the battery structure and charge / discharge conditions below by adding an organic solvent and a metal extractant to the electrolyte and separating the organic phase containing the metal impurities to remove the metal impurities, the increase in the final pressure measured after the 100th discharge with respect to the reference pressure measured after the 11th discharge is 1 kPa or less. - Battery structure: Sealed structure with 138g of electrolyte and solid electrode area of ​​99×99mm - Charging conditions: Constant current charging at 25℃, 1.6 A (1 C) until reaching 1.53 V or 2 Wh - Discharge conditions: Constant current discharge at 25 ℃, 1.6 A (1 C) current until reaching 1.1 V.

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