A high-temperature-resistant vanadium flow battery electrolyte, and a method for preparing and using the same

Abstract

The application provides a high-temperature-resistant vanadium flow battery electrolyte, a preparation method and application thereof. m P x M y V z O n of a general formula, wherein P is a phosphorus element, V is a vanadium element, M is any one or more of Mo, W, Nb and Ta elements; m, n, x, y and z are all greater than 0 and include but are not limited to integers, and the ratio of x, y and z is 0.05-2:0.1-10:1. The electrolyte provided by the application takes vanadium pentoxide as a main active raw material, and takes one or two of molybdenum trioxide, tungsten trioxide, niobium pentoxide and tantalum pentoxide as a secondary active raw material, which is helpful to improve the energy density of the battery and improve the high-temperature-resistant stability of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a high-temperature resistant vanadium redox flow battery electrolyte, its preparation method, and its application. Background Technology

[0002] Vanadium redox flow batteries store energy in a sulfuric acid electrolyte containing vanadium ions in different valence states. An external pump introduces the electrolyte into the battery reactor, allowing for the interconversion of chemical and electrical energy stored in the solution. The vanadium electrolyte is a crucial component. As the active material in the battery's electrochemical reactions, the electrolyte acts as a carrier for electron transfer to generate electrical energy. Its concentration and quantity directly determine the battery's energy storage capacity, while its performance directly affects the overall battery efficiency and lifespan.

[0003] In practical applications, the dissolution of vanadium ions is affected by concentration and temperature, resulting in limited stability. Once precipitation occurs during use, it can cause blockages in the battery reactor and electrolyte delivery pipelines, severely impacting the battery system's lifespan and efficiency. Therefore, electrolyte stability is a primary consideration in the use of vanadium redox flow batteries. The electrolyte in vanadium redox flow batteries is typically composed of vanadium ions, but their low solubility in sulfuric acid solution leads to a low energy density (25 Wh / kg), and precipitation easily occurs at elevated temperatures (>50°C). Therefore, increasing the electrolyte concentration and maintaining stability under elevated temperatures is of great significance. Currently, a common method to address this issue is to add stabilizers to the electrolyte to maintain stability within a certain concentration and temperature range. However, the protective effect is still limited; vanadium electrolytes still precipitate under prolonged high temperatures (>50°C). Furthermore, adding different protective agents to the anode and cathode can lead to diffusion and side reactions during continuous battery cycling, gradually causing an imbalance in the electrolytes and reducing battery efficiency. Therefore, improving the stability of the electrolyte at high temperatures is a problem that urgently needs to be solved in vanadium redox flow batteries.

[0004] CN107546403A discloses a positive electrode electrolyte protected by an organic polymer, but the organic matter is at risk of degradation during battery charging and discharging. CN105762395A discloses a method for preparing a positive electrode electrolyte using composite additives, adding one or more of potassium, sodium, and ammonium salts such as phosphates, dihydrogen phosphates, and dihydrogen phosphates as composite additives to the positive electrode electrolyte. CN106876767A introduces molybdate as a positive electrode stabilizer, and CN105322207A introduces phosphorus-containing heteropolyacids as additives to the positive electrode electrolyte to suppress energy decay under high-temperature conditions. However, these methods only introduce stabilizers into the positive electrode electrolyte, which will lead to charge imbalance between the anode and cathode electrolytes with long-term use. Furthermore, the amount of additive is difficult to control; too little additive cannot stabilize the electrolyte at high temperatures for extended periods, while too much additive leads to a significant decrease in voltage efficiency and energy efficiency. Summary of the Invention

[0005] This invention provides a high-temperature resistant vanadium redox flow battery electrolyte, its preparation method, and its application. It has high energy density and can operate stably at high temperatures.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a high-temperature resistant vanadium redox flow battery electrolyte, which has H... m P x M y V z O n The general formula is , where P is phosphorus, V is vanadium, and M is any one or more of Mo, W, Nb, and Ta; m, n, x, y, and z are all greater than 0 and include, but are not limited to, integers, and the ratio of x, y, and z is 0.05 to 1:0.1 to 10:1.

[0007] Furthermore, the ratio of x, y, and z in the general formula is 0.1–0.4:0.5–2:1.

[0008] Furthermore, the ratio of y to z is ≥0.8.

[0009] Furthermore, H m P x M y V z O n In the general formula, P x M y V z Typical composition ratios include P3M9V 18 P3M 12 V 18 P3M 18 V7, P3M 10 V 10 P3V 10M 16 PM8V4, PM9V3, P2M 14 V4 or P2M 12 V6.

[0010] The general formula of the electrolyte only describes the proportional relationship of the elements, and its existence in solution is in the form of H containing the classical Keggin structure. 3+i PV i M 12-i O 40 Compounds (where i = 1–4), H with Dawson structure 6+i P2V i M 18-i O 62 Compounds (where i = 1–8), H9PV with typical structure 14 O 42 H6V 10 O 28 VO2 + VO 2+ PO4 3- A mixture of one or more ions. The concentration of ions in the mixture changes with the solution concentration, temperature, and pH conditions. The ions in the solution decompose, recombine, and interconvert to reach a dynamic equilibrium, ultimately forming a mixture with H+. m P x M y V z O n A mixture of general formulas.

[0011] The present invention also relates to an electrolyte prepared using the electrolyte described above, wherein the concentration of vanadium in the electrolyte is 1.7 to 2.2 mol / L.

[0012] Furthermore, the electrolyte also contains sulfuric acid, with a concentration of 0.5–3 mol / L.

[0013] The present invention also relates to a method for preparing the electrolyte, comprising the following steps:

[0014] S1, General Formula H m P x M y V z O n In the preparation of electrolytes, metal M is added in the form of oxide, and V is added in the form of V2O5. The raw materials are weighed according to the proportion and added to water and mixed. P in the general formula is added in the form of phosphoric acid. After adding phosphoric acid according to the proportion, the mixture is heated to boiling and refluxed until all the solid oxides are dissolved.

[0015] S2. Add sulfuric acid to the solution obtained in S2, mix well, and concentrate under reduced pressure below 100℃ to the target concentration to obtain the electrolyte.

[0016] Furthermore, when the oxides of M and V in S1 are added to water, hydrogen peroxide is added to promote dissolution; the amount added is 5-20% of the mass of the liquid.

[0017] The present invention also relates to the application of electrolyte in vanadium redox flow batteries.

[0018] Furthermore, before the electrolyte is injected, the vanadium ions are reduced to an average valence of 3.5 by a reducing gas, and then stored in a polypropylene tank before being pumped into the anode and cathode of the electrolytic cell filled with graphite felt.

[0019] The present invention has the following beneficial effects:

[0020] 1. The H involved in this invention m P x M y V z O n In the general electrolyte, not only does V undergo redox reactions during charge and discharge to store charge, but metal M also undergoes redox reactions during charge and discharge to store charge. Vanadium-containing flow batteries, which are not limited to an integer ratio of vanadium ions, have high energy density. The concentration of variable-valence ions capable of redox reactions is higher than that of all-vanadium flow batteries, with vanadium ion concentrations reaching as high as 1.7–2.2 mol / L. The volumetric charge storage density is greater than 45–59 Ah / L, and the gravimetric energy density is greater than 48–63 Wh / kg, which is higher than the gravimetric energy density (30–40 Wh / kg) of traditional all-vanadium flow batteries.

[0021] 2. The electrolyte provided by this invention is a complex formed by vanadium, metal M, and phosphorus. Therefore, it exhibits high thermal stability in batteries, and can withstand 80°C without precipitation when the vanadium ion concentration is 1.7 mol / L. Compared with the traditional all-vanadium redox flow battery's ability to withstand a temperature of 45°C, the flow battery of this invention demonstrates superior heat resistance.

[0022] 3. This invention relates to the property that different redox ions in the electrolyte have a property that is not limited to an integer ratio. The M:V ratio can exist stably in a wide range of 0.1 to 10:1. It does not require that the two different elements have a regular ratio. Therefore, it has great flexibility in electrolyte formulation and is beneficial to engineering applications. Attached Figure Description

[0023] Figure 1 To synthesize P3Mo 10 V 10 Electrolyte solution 31 P NMR spectrum.

[0024] Figure 2 To synthesize P3Mo 10 V 10 After the electrolyte solution undergoes a 240-hour reaction in an 80°C water bath... 31 P NMR spectrum.

[0025] Figure 3 P3Mo 10 V 10 Battery capacity as measured by electrolyte solution cycling test. Detailed Implementation

[0026] The following embodiments are further illustrations of the present invention, but are not intended to limit the scope of the invention.

[0027] Example 1: Synthesis and Analysis of a Typical High-Temperature Vanadium Battery Electrolyte

[0028] 3.64 g of vanadium pentoxide and 5.8 g of molybdenum trioxide were suspended in 1200 mL of water and stirred at room temperature. 180 mL of hydrogen peroxide was added, and the mixture was stirred for 2 hours while maintaining the temperature below 10°C, resulting in a brown solution. 1.2 g of phosphoric acid (98 wt%) was added, and the solution was heated to boiling until the solid powder dissolved. The solution was then concentrated under vacuum at 80°C to 20 mL. At this point, the electrolyte was bright red, and all vanadium was in its highest valence state (+5). A portion of the electrolyte was taken, and heavy water was added before use. 31 P NMR characterization of the electrolyte in solution yielded results shown in Figure 1. Multiple peaks were observed between -3 and -4 ppm, indicating that the electrolyte was a series of mixtures. This electrolyte is designated as Example 1-2, and its general formula is abbreviated as P3Mo based on the ratio of x, y, and z. 10 V 10 And so on.

[0029] Example 2: High-Temperature Endurance Test of Typical High-Temperature Vanadium Battery Electrolyte

[0030] Following the method described in Example 1, electrolytes containing different elemental ratios were synthesized and prepared as high-temperature vanadium battery electrolytes. Each electrolyte contained 1.5 mol / L sulfuric acid. Then, 20 mL of each electrolyte was taken and heated in an 80°C water bath. The reaction time of the precipitate formed was observed and recorded, and compared with the reaction time of the highest oxidation state (VO2). + The results are shown in Table 1, with 2SO4 solution as a control.

[0031] Table 1. Stabilization time and precipitation amount of different vanadium battery electrolytes in an 80℃ water bath.

[0032]

[0033] As shown in Table 1, Mo plays a role in stabilizing the high-valence state V, where P in the general formula... x My V z The ratio of y:z is crucial. If y:z < 0.8:1 (as in Examples 1-7), the stability of vanadium decreases; when y:z ≥ 0.8:1, it can still maintain stability in solution for a long time at a high temperature of 80℃. The proportion of P should not be too high or too low; too high a proportion easily leads to phosphate precipitation, while too low a proportion easily leads to vanadium precipitation. After 240 hours of reaction in an 80℃ water bath, P3Mo 10 V 10 P 2.4 Mo 10 V 10 P3Mo 18 V7, P3W 10 V 10 No precipitate formed in the solution. Take the P3Mo solution after the reaction. 10 V 10 Part of the electrolyte, after adding heavy water, is used 31 P NMR characterizes the state of the electrolyte in solution, and the results are as follows: Figure 2 As shown, this indicates that P3Mo 10 V 10 There was no significant change.

[0034] Example 3: Charge and Discharge Test

[0035] The synthesized P3Mo was used respectively 10 V 10 P3Mo8V 10 P3W 10 V 10 An electrolyte solution with a concentration of 0.17 mol / L was prepared by adding sulfuric acid to a concentration of 1.5 mol / L. 50 ml of this solution was pumped into the anode, and another 50 ml was pumped into the cathode to assemble a vanadium redox flow cell. The anode and cathode were separated by a Nafion proton exchange membrane, and graphite felt was used as the electrode with an active surface area of ​​50 cm². 2 Using conductive graphite as the bipolar plate, the charge / discharge current density at room temperature is 80 mA / cm². 2 The cutoff voltage is 1.0-1.55V. Table 2 shows the coulombic efficiency, voltage efficiency, energy efficiency, and battery capacity of the different synthesized electrolytes during charge and discharge. The experimental results show that the synthesized electrolyte exhibits high coulombic efficiency, voltage efficiency, and energy efficiency during charge and discharge. It also exceeds the theoretical charge capacity of vanadium storage (2.27 Ah), because the added stabilizing component Mo can also undergo redox reactions on the electrode, participating in charge storage and charge / discharge.

[0036] Table 2. Coulombic efficiency, voltage efficiency, energy efficiency, and battery capacity of different electrolytes during charge and discharge.

[0037] Example 3-1 <![CDATA[P3Mo 10 In 10 ]]> 96 88 84 2.6 Example 3-2 <![CDATA[P3Mo8V 10 ]]> 92 83 81 2.4 Example 3-3 <![CDATA[P3W 10 In 10 ]]> 95 86 82 2.7

[0038] Example 4: Cyclic Charge-Discharge Test

[0039] Using the synthesized P3Mo 10 V 10 An electrolyte solution with a concentration of 0.17 mol / L was prepared by adding sulfuric acid to bring the sulfuric acid concentration in the solution to 1.5 mol / L. 50 ml of the solution was pumped into the anode and 50 ml was pumped into the cathode to assemble a vanadium redox flow cell. Other test conditions were the same as in Example 3. Figure 3 The battery capacity decay was shown after 100 cycles, with the capacity remaining relatively stable at around 2.6 Ah. This indicates that the electrolyte solution can operate stably for extended periods.

Claims

1. A high-temperature resistant vanadium redox flow battery electrolyte, characterized in that: This electrolyte has H m P x M y V z O n The general formula is given by , where P is phosphorus, V is vanadium, and M is any one or more of Mo, W, Nb, and Ta; m, n, x, y, and z are all greater than 0 and include, but are not limited to, integers, and the ratio of x, y, and z is 0.05~1:0.1~10:

1.

2. The electrolyte according to claim 1, characterized in that: The ratio of x, y, and z in the general formula is 0.1~0.4:0.5~2:

1.

3. The electrolyte according to claim 1, characterized in that: The ratio of y to z is ≥0.

8.

4. The electrolyte according to claim 1, characterized in that: H m P x M y V z O n In the general formula, P x M y V z Typical composition ratios include P3M9V 18 P3M 12 V 18 P3M 18 V7, P3M 10 V 10 P3V 10 M 16 PM8V4, PM9V3, P2M 14 V4 or P2M 12 V6.

5. An electrolyte prepared using the electrolyte according to any one of claims 1 to 4, characterized in that: The concentration of vanadium in the electrolyte is 1.7~2.2 mol / L.

6. The electrolyte according to claim 5, characterized in that: The electrolyte also contains sulfuric acid, with a concentration of 0.5~3 mol / L.

7. The method for preparing the electrolyte according to claim 6, characterized in that, Includes the following steps: S1, General Formula H m P x M y V z O n In the preparation of electrolytes, metal M is added in the form of oxide, and V is added in the form of V2O5. The raw materials are weighed according to the proportion and added to water and mixed. P in the general formula is added in the form of phosphoric acid. After adding phosphoric acid according to the proportion, the mixture is heated to boiling and refluxed until all the solid oxides are dissolved. S2. Add sulfuric acid to the solution obtained in S2, mix well, and concentrate under reduced pressure below 100℃ to the target concentration to obtain the electrolyte.

8. The preparation method according to claim 7, characterized in that: When adding the oxides of M and V in S1 to water, add hydrogen peroxide to promote dissolution; the amount added is 5-20% of the mass of the liquid.

9. The application of the electrolyte according to claim 5 or 6 in a vanadium redox flow battery.

10. The application according to claim 9, characterized in that: Before the electrolyte is injected, the vanadium ions are reduced to an average valence of 3.5 by a reducing gas, and then stored in a polypropylene tank before being pumped into the anode and cathode of an electrolytic cell filled with graphite felt.

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