A vanadium iron chromium electrolyte based on hydrochloric acid, a preparation method thereof and a flow battery

Abstract

This application discloses a hydrochloric acid-based vanadium-iron-chromium electrolyte, its preparation method, and a flow battery, relating to the field of batteries. The hydrochloric acid-based vanadium-iron-chromium electrolyte contains 1.0~2.5 mol / L vanadium ions, 0.15~2.0 mol / L ferrous ions, 0.1~1.7 mol / L chromium ions, 3.0~4.5 mol / L hydrogen ions, and 0.001~0.05 mol / L hydrogen evolution inhibitor. The technical solution of this application utilizes a hydrochloric acid-based vanadium-iron-chromium electrolyte formed with specific concentrations of vanadium ions, ferrous ions, chromium ions, hydrogen ions, and a hydrogen evolution inhibitor. This electrolyte is suitable for use as the positive and negative electrode electrolytes in flow batteries, significantly improving the energy efficiency and cycle stability of the flow battery. Furthermore, the introduction of relatively inexpensive iron reduces the system's dependence on expensive vanadium resources and lowers production costs.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to a hydrochloric acid-based vanadium iron chromium electrolyte, its preparation method, and a flow battery. Background Technology

[0002] With the vigorous development and promotion of renewable energy globally, energy storage technology has become crucial for addressing the intermittency and volatility issues associated with renewable energy. Flow batteries, due to their unique advantages such as independent energy storage and power output, long cycle life, high safety, and deep discharge capability, have shown enormous application potential in large-scale energy storage. In flow batteries, the composition, concentration, and preparation process of the electrolyte all significantly impact battery performance and lifespan. Currently, common electrolytes include vanadium redox electrolytes and iron-chromium electrolytes.

[0003] Iron-chromium electrolytes are prone to side reactions such as hydrogen evolution, which consume active materials and increase the electrolyte pH, accelerating ligand exchange and creating a vicious cycle that affects battery performance. While flow batteries using all-vanadium electrolytes offer excellent performance, vanadium resources are relatively scarce, resulting in higher costs. Summary of the Invention

[0004] The main objective of this application is to propose a hydrochloric acid-based vanadium iron chromium electrolyte, its preparation method, and a flow battery, aiming to solve the problems of high cost and poor cycle stability of electrolytes in the prior art.

[0005] In a first aspect, this application provides a hydrochloric acid-based vanadium-iron-chromium electrolyte, wherein the hydrochloric acid-based vanadium-iron-chromium electrolyte contains 1.0~2.5 mol / L of vanadium ions, 0.15~2.0 mol / L of ferrous ions, 0.1~1.7 mol / L of chromium ions, 3.0~4.5 mol / L of hydrogen ions, and 0.001~0.05 mol / L of hydrogen evolution inhibitor; wherein the molar content of ferrous ions and the molar content of chromium ions are both lower than the molar content of vanadium ions; the vanadium ions include trivalent vanadium ions and tetravalent vanadium ions, and the molar ratio of the trivalent vanadium ions to the tetravalent vanadium ions is 1:1; the chromium ions are trivalent chromium ions, and the difference in molar content between the ferrous ions and the chromium ions is <0.4 mol / L.

[0006] By adopting the above technical solution, a hydrochloric acid-based vanadium-iron-chromium electrolyte formed with specific concentrations of vanadium ions, ferrous ions, chromium ions, hydrogen ions, and hydrogen evolution inhibitors can significantly improve the rate and reversibility of electrode reactions, reduce overpotential, and significantly improve the energy efficiency of flow batteries. This composite electrolyte is suitable for both the positive and negative electrode electrolytes of flow batteries, effectively suppressing hydrogen evolution side reactions and cross-contamination of the electrolyte, reducing the loss of active materials, resulting in high capacity retention during multiple charge-discharge cycles and significantly improving the cycle stability of flow batteries. Furthermore, this composite electrolyte can operate smoothly at temperatures ranging from -35℃ to 50℃ without crystallization, exhibiting excellent overall performance and suitability for large-scale energy storage applications. The electrolyte of this application introduces relatively inexpensive iron, reducing the system's dependence on expensive vanadium resources. The raw materials are widely available, and the preparation process is simple, reducing production costs. Hydrogen evolution inhibitors can form a protective film on the electrode surface, reducing or even blocking the contact between hydrogen ions and the active sites of the electrode, effectively suppressing hydrogen evolution side reactions, while not affecting the target reaction, thus ensuring the electrochemical performance of the fabricated flow battery.

[0007] In the technical solution of this application, the molar content of ferrous ions is controlled to be higher than that of chromium ions. The reason is: (1) The standard electrode potential of ferrous ions is about 0.77V, and the standard electrode potential of chromium ions is about -0.41V. The potential difference between the two is the core of the battery's electromotive force. In order to avoid the preferential over-oxidation of chromium ions during charging (generating unstable Cr), 6 (2) During charging, the positive electrode reaction (Fe²⁺-e⁻→Fe³⁺) and the negative electrode reaction (Cr³⁺+e⁻→Cr²⁺) of the flow battery have a 1:1 electron transfer ratio. However, in actual operation, chromium ions are prone to undergo a "disproportionation reaction" (2Cr³⁺→Cr²⁺+Cr). 4 (⁺), leading to a loss of effective concentration. Increasing the initial content of ferrous ions can compensate for the potential loss of chromium ions, but the initial content of ferrous ions should not be increased too much to effectively maintain the overall charge balance of the electrolyte and avoid rapid capacity decay of the battery.

[0008] Optionally, the difference in molar content between the ferrous ions and the chromium ions is 0.05~0.15 mol / L.

[0009] By adopting the above technical solution and further optimizing the difference in molar content between ferrous ions and chromium ions, the overall charge balance of the electrolyte and the stability of each component in the electrolyte can be effectively improved, thereby increasing the energy efficiency and cycle stability of the prepared flow battery.

[0010] Preferably, the hydrochloric acid-based vanadium-iron-chromium electrolyte contains 1.8~2.2 mol / L vanadium ions, 0.34~0.70 mol / L ferrous ions, 0.29~0.55 mol / L chromium ions, 3.0~4.0 mol / L hydrogen ions, and 0.005~0.030 mol / L hydrogen evolution inhibitor.

[0011] Optionally, the molar content of the hydrogen evolution inhibitor is 0.5% to 1.3% of the molar content of vanadium ions.

[0012] By adopting the above technical solution and further optimizing the dosage of hydrogen evolution inhibitor, the stability of each component in the electrolyte can be better balanced, and the hydrogen evolution side reaction can be effectively suppressed, thereby improving the electrochemical performance of the flow battery.

[0013] Optionally, the hydrogen evolution inhibitor is selected from at least one of ethylenediaminetetraacetic acid, N,N′-ethylenediaminedisuccinic acid, oxalic acid, and phosphoric acid.

[0014] By adopting the above technical solution and using specific hydrogen evolution inhibitors, the hydrogen evolution side reaction can be effectively suppressed, and the stability of each component can be improved, thereby ensuring the electrochemical performance of the prepared flow battery.

[0015] Optionally, the hydrogen evolution inhibitor comprises ethylenediaminetetraacetic acid and oxalic acid, and the molar ratio of ethylenediaminetetraacetic acid to oxalic acid is (2.1~3.2):1.

[0016] By adopting the above technical solution and optimizing the components and ratios of the hydrogen evolution inhibitor, the hydrogen evolution side reaction can be effectively suppressed, the stability of each component can be improved, and the electrochemical performance of the prepared flow battery can be guaranteed.

[0017] Preferably, the molar ratio of ethylenediaminetetraacetic acid to oxalic acid is 2.6:1.

[0018] Secondly, this application also provides a method for preparing the hydrochloric acid-based vanadium iron chromium electrolyte according to any one of the above claims, comprising the following steps:

[0019] S10. In a protective atmosphere, vanadium source and reducing agent are added to hydrochloric acid to carry out a reduction reaction, resulting in a solution containing tetravalent vanadium.

[0020] S20. The tetravalent vanadium solution obtained in step S10 is reacted under electrolytic reduction conditions to reduce some tetravalent vanadium ions to trivalent vanadium ions, forming a vanadium solution with the same molar content of trivalent vanadium ions and the same molar content of tetravalent vanadium ions.

[0021] S30. Add the iron source and chromium source to the vanadium solution obtained in step S20, stir to dissolve, add hydrogen evolution inhibitor, and adjust the hydrogen ion concentration of the mixture to the target concentration to obtain the hydrochloric acid-based vanadium-iron-chromium electrolyte.

[0022] By employing the above technical solution, an inert gas is used to create a protective atmosphere throughout the preparation of the hydrochloric acid-based vanadium-iron-chromium electrolyte. This eliminates oxygen in the system and prevents the oxidation of ferrous ions, which would affect the electrochemical activity of the resulting electrolyte. In preparing the hydrochloric acid-based vanadium-iron-chromium electrolyte, a vanadium source is dissolved in hydrochloric acid, and a reducing agent is added to reduce the high-valence vanadium in the vanadium source to tetravalent vanadium, yielding a tetravalent vanadium solution. Electrolytic reduction is then used to reduce some of the tetravalent vanadium ions in the tetravalent vanadium solution to trivalent vanadium ions. During the reaction, the molar content of trivalent and tetravalent vanadium ions in the reaction system is monitored in real time until they are equal, at which point the electrolytic reduction reaction ends, yielding a 3.5-valent vanadium solution. An iron source and a chromium source are added to the 3.5-valent vanadium solution, and after complete dissolution, a hydrogen evolution inhibitor is added, and the hydrogen ion concentration of the system is adjusted to obtain the hydrochloric acid-based vanadium-iron-chromium electrolyte. The entire preparation process is simple, and the flow battery made using this electrolyte has good overall performance and is suitable for large-scale energy storage applications.

[0023] Optionally, in step S10, the reducing agent is selected from at least one of oxalic acid, glucose, and glycerol.

[0024] By adopting the above technical solution and using at least one of oxalic acid, glucose and glycerol as a reducing agent, the high-valence vanadium in the vanadium source can be reduced to tetravalent vanadium more fully to obtain a tetravalent vanadium solution, and no other metal ions will be introduced to interfere with the activity and stability of the system, thus ensuring the electrochemical activity of the prepared electrolyte.

[0025] Optionally, in step S10, the vanadium source includes vanadium pentoxide; and / or,

[0026] The concentration of the hydrochloric acid is 32-38 wt%; and / or,

[0027] The protective atmosphere includes nitrogen or argon; and / or,

[0028] The reduction reaction occurs at a temperature of 50-70℃. The reduction reaction ends when the solution turns completely dark blue and no yellow precipitate is found, yielding a solution containing tetravalent vanadium.

[0029] Optionally, in step S20, during the electrolytic reduction reaction, the molar content of trivalent vanadium ions and tetravalent vanadium ions in the solution is detected by potentiometric titration until the molar content of trivalent vanadium ions and tetravalent vanadium ions are equal, at which point the electrolytic reduction reaction ends.

[0030] Optionally, in step S30, the chromium source includes chromium trichloride hexahydrate; and / or,

[0031] The iron source is selected from at least one of ferrous chloride tetrahydrate or iron powder; and / or,

[0032] The hydrogen ion concentration of the mixture was adjusted using hydrochloric acid with a concentration of 35-37 wt%.

[0033] Thirdly, this application also provides a flow battery, including a positive electrode electrolyte and a negative electrode electrolyte, wherein both the positive electrode electrolyte and the negative electrode electrolyte are made of the hydrochloric acid-based vanadium iron chromium electrolyte described in any of the above claims.

[0034] By adopting the above technical solution, the hydrochloric acid-based vanadium iron chromium electrolyte prepared in this application is used as the positive and negative electrode electrolyte of the flow battery. The resulting flow battery has high energy density and excellent cycle stability.

[0035] In summary, this application includes at least one of the following beneficial technical effects:

[0036] 1. The technical solution of this application employs a hydrochloric acid-based vanadium-iron-chromium electrolyte formed with specific concentrations of vanadium ions, ferrous ions, chromium ions, hydrogen ions, and hydrogen evolution inhibitors. This electrolyte is suitable for use as the positive and negative electrode electrolyte in flow batteries, significantly improving the rate and reversibility of electrode reactions, reducing overpotential, and thus significantly improving the energy efficiency of flow batteries. This composite electrolyte also effectively suppresses hydrogen evolution side reactions and cross-contamination of the electrolyte, reducing the loss of active materials and resulting in high capacity retention during multiple charge-discharge cycles, significantly improving the cycle stability of flow batteries. Furthermore, the introduction of relatively inexpensive iron reduces the system's dependence on expensive vanadium resources, lowering production costs.

[0037] 2. The preparation process of the hydrochloric acid-based vanadium iron chromium electrolyte provided in this application is simple, and the flow battery made using this electrolyte has good comprehensive performance and is suitable for large-scale energy storage applications.

[0038] 3. By controlling the molar content of ferrous ions to be higher than that of chromium ions, the overall charge balance of the electrolyte and the stability of each component in the electrolyte can be effectively improved, thereby increasing the energy efficiency and cycle stability of the prepared flow battery.

[0039] 4. Hydrogen evolution inhibitors can effectively suppress hydrogen evolution side reactions and improve the stability of each component, thereby ensuring the electrochemical performance of the prepared flow battery. Attached Figure Description

[0040] Figure 1 This is a graph showing the energy efficiency and capacity retention of the battery corresponding to Embodiment 1 of this application. Detailed Implementation

[0041] The present application will be further described in detail below with reference to the embodiments. Example 1

[0042] A method for preparing a hydrochloric acid-based vanadium iron chromium electrolyte includes the following steps:

[0043] S10. Add 0.7L of 37wt% hydrochloric acid to the reaction vessel, start the stirring device and stir at a rate of 200rpm, and introduce nitrogen gas at a rate of 60mL / min. Add 1mol of vanadium pentoxide to the hydrochloric acid, control the temperature of the solution at 60℃, and add 1mol of anhydrous oxalic acid to carry out the reduction reaction. When the color of the solution changes completely from yellow to dark blue and there is no yellow precipitate, the reduction reaction ends and a solution containing tetravalent vanadium is obtained.

[0044] S20. The tetravalent vanadium solution is reacted under electrolytic reduction conditions. During the electrolytic reduction reaction, the molar content of trivalent vanadium ions and tetravalent vanadium ions in the solution is detected by potentiometric titration until the molar content of trivalent vanadium ions and tetravalent vanadium ions are equal. The electrolytic reduction reaction ends when the molar content of trivalent vanadium ions and tetravalent vanadium ions are equal, and a vanadium solution with a molar content of trivalent vanadium ions and tetravalent vanadium ions (i.e., 3.5 vanadium solution) is obtained.

[0045] S30. Add 0.29 mol of chromium trichloride hexahydrate (CrCl3·6H2O) and 0.34 mol of ferrous chloride tetrahydrate (FeCl2·4H2O) to a vanadium solution with a valence of 3.5 valence. After stirring and dissolving, filter the solution under vacuum using a 0.22 μm acid-resistant filter membrane to remove impurities and obtain a clear mixture. Add 0.01 mol of ethylenediaminetetraacetic acid (hydrogen evolution inhibitor) to the mixture and add deionized water to bring the volume to 1 L. Stir thoroughly and add 37 wt% hydrochloric acid to adjust the hydrogen ion concentration to 3.5 mol / L to obtain a hydrochloric acid-based vanadium iron chromium electrolyte.

[0046] In step S20, the electrolytic reduction reaction of the tetravalent vanadium solution includes: adding the tetravalent vanadium solution obtained in step S10 to the positive and negative electrode electrolytic cells of the electrolytic cell, respectively, and pumping it into the battery chamber so that the tetravalent vanadium solution comes into contact with the corresponding porous carbon electrode, and the proton exchange membrane separates the positive and negative electrode electrolytes. During charging, the external circuit provides electrons, and at the negative electrode / electrolyte interface, V 4+ After gaining electrons at the electrode surface, it is reduced to V. 3+ That is, part of the V in the solution 4+ Reduction to V 3+ During electrolysis, the V in the negative electrode electrolytic cell is detected. 3+ and V 4+ The molar content, up to V 3+ and V4+ When the molar content is equal, the electrolytic reduction reaction ends.

[0047] Examples 2-4

[0048] Examples 2-4 are based on Example 1, the difference being that in step S30, the amounts of chromium trichloride hexahydrate and ferrous chloride tetrahydrate are different; the other steps remain the same as in Example 1. Specifically,

[0049] In Example 2, the molar amount of chromium trichloride hexahydrate was 0.15 mol, and the molar amount of ferrous chloride tetrahydrate was 0.16 mol.

[0050] In Example 3, the molar amount of chromium trichloride hexahydrate was 0.55 mol, and the molar amount of ferrous chloride tetrahydrate was 0.70 mol.

[0051] In Example 4, the molar amount of chromium trichloride hexahydrate was 0.85 mol, and the molar amount of ferrous chloride tetrahydrate was 1.05 mol. Comparative Example 1

[0052] This comparative example is based on Example 1, except that in step S30, 0.01 mol of ethylenediaminetetraacetic acid is not added, while the other steps are the same as in Example 1. Comparative Example 2

[0053] This comparative example is based on Example 1, except that in step S30, the molar amount of ferrous chloride tetrahydrate is 0.69 mol, while the other steps are the same as in Example 1. Comparative Example 3

[0054] This comparative example is based on Example 1, except that in step S10, an equimolar amount of sodium oxalate is used to replace anhydrous oxalic acid, while the other steps remain the same as in Example 1.

[0055] Performance Test 1

[0056] The hydrochloric acid-based vanadium iron chromium electrolytes prepared in Examples 1-4 and Comparative Examples 1-3 were used as positive and negative electrode electrolytes to assemble flow batteries, and the constant current charge-discharge performance of the hydrochloric acid-based vanadium iron chromium electrolytes was tested.

[0057] Among them, 160mA / cm 2 The current density and charge / discharge cutoff voltages were 1.65V and 0.8V, respectively. The energy efficiency (%) of the battery after 100 effective charge / discharge cycles and the capacity retention rate (%) of the battery after 100 effective charge / discharge cycles were tested. The test results are shown in Table 1 below.

[0058] Wherein, the battery capacity retention rate = (Q 100 / Q)*100%, where Q 100 Q refers to the discharge energy at the 100th effective cycle, while Q refers to the maximum discharge energy obtained in 100 effective cycles.

[0059] Table 1. Battery energy efficiency and capacity retention

[0060]

[0061] Based on Examples 1-4, Comparative Examples 1-3, and the experimental results in Table 1, it can be seen that the hydrochloric acid-based vanadium-iron-chromium electrolyte formed by using specific concentrations of vanadium ions, ferrous ions, chromium ions, hydrogen ions, and hydrogen evolution inhibitors in the technical solution of this application is suitable for the positive and negative electrode electrolytes of flow batteries. It can significantly improve the rate and reversibility of electrode reactions, reduce overpotential, and significantly improve the energy efficiency of flow batteries. This composite electrolyte can also effectively suppress hydrogen evolution side reactions and cross-contamination of the electrolyte, reducing the loss of active materials and resulting in high capacity retention during multiple charge-discharge cycles, thus significantly improving the cycle stability of flow batteries.

[0062] Comparative Example 1, lacking the hydrogen evolution inhibitor ethylenediaminetetraacetic acid (EDTA), could not effectively suppress the hydrogen evolution side reaction and could not improve the stability of each component in the system, thus affecting the electrochemical performance of the prepared flow battery. Comparative Example 2 added an excessive amount of ferrous chloride tetrahydrate relative to chromium trichloride hexahydrate, affecting the overall charge balance of the electrolyte and the stability of each component, leading to a decrease in the energy efficiency and cycle stability of the prepared flow battery. Comparative Example 3 used sodium oxalate as a reducing agent, introducing new metal salt ions, which affected the electrochemical activity of the system, thereby impacting the electrochemical performance of the prepared flow battery.

[0063] Examples 5-7

[0064] Examples 5-7 are based on Example 3, the difference being that the molar amount of ethylenediaminetetraacetic acid used in step S30 is different, while the other steps remain the same as in Example 3. Specifically,

[0065] In Example 5, the molar amount of ethylenediaminetetraacetic acid was 0.002 mol.

[0066] In Example 6, the molar amount of ethylenediaminetetraacetic acid was 0.026 mol.

[0067] In Example 7, the molar amount of ethylenediaminetetraacetic acid was 0.040 mol.

[0068] Examples 8-12

[0069] Examples 8-12 are based on Example 6, the difference being that in step S30, other hydrogen evolution inhibitors are used instead of ethylenediaminetetraacetic acid; the other steps remain the same as in Example 6. Specifically,

[0070] In Example 8, an equimolar amount of N,N′-ethylenediaminedisuccinic acid was used to replace ethylenediaminetetraacetic acid.

[0071] In Example 9, an equimolar amount of anhydrous oxalic acid was used to replace ethylenediaminetetraacetic acid.

[0072] In Example 10, the hydrogen evolution inhibitor was a mixture of ethylenediaminetetraacetic acid (EDTA) and anhydrous oxalic acid, with a molar ratio of EDTA to anhydrous oxalic acid of 2.1:1, and the sum of the molar amounts of EDTA and anhydrous oxalic acid was 0.01 mol.

[0073] In Example 11, the hydrogen evolution inhibitor was a mixture of ethylenediaminetetraacetic acid (EDTA) and anhydrous oxalic acid, with a molar ratio of EDTA to anhydrous oxalic acid of 2.6:1, and the sum of the molar amounts of EDTA and anhydrous oxalic acid was 0.01 mol.

[0074] In Example 12, the hydrogen evolution inhibitor was a mixture of ethylenediaminetetraacetic acid (EDTA) and anhydrous oxalic acid, with a molar ratio of EDTA to anhydrous oxalic acid of 3.2:1, and the sum of the molar amounts of EDTA and anhydrous oxalic acid was 0.01 mol.

[0075] Performance Test 2

[0076] The vanadium iron chromium hydrochloride electrolytes prepared in Examples 5-12 were used as positive and negative electrode electrolytes to assemble flow batteries, and the constant current charge-discharge performance of the vanadium iron chromium hydrochloride electrolytes was tested. The test method was the same as that in performance test 1, and the test results are shown in Table 2 below.

[0077] Table 2 Battery energy efficiency and capacity retention

[0078]

[0079] As shown in Table 2, Examples 5-7, based on Example 3, investigated the effect of the molar amount of the hydrogen evolution inhibitor ethylenediaminetetraacetic acid (EDTA) on the electrochemical performance of the prepared flow battery. Example 6 was the preferred example. Examples 8-12, based on Example 6, investigated the effect of the type of hydrogen evolution inhibitor on the electrochemical performance of the prepared flow battery. When the hydrogen evolution inhibitor was a mixture of EDTA and oxalic acid, and the molar ratio of their amounts was (2.1-3.2):1, the electrochemical performance of the prepared flow battery could be further improved.

[0080] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be covered within the scope of protection of this application.

Claims

1. A vanadium iron-chromium electrolyte based on hydrochloric acid, characterized in that, The hydrochloric acid-based vanadium iron chromium electrolyte contains vanadium ions 1.0-2.5 mol / L, ferrous ions 0.15-2.0 mol / L, chromium ions 0.1-1.7 mol / L, hydrogen ions 3.0-4.5 mol / L, and hydrogen evolution inhibitors 0.001-0.05 mol / L; The molar content of the ferrous ions and the molar content of the chromium ions are both lower than the molar content of the vanadium ions; The vanadium ions include trivalent vanadium ions and tetravalent vanadium ions, and the ratio of the molar content of the trivalent vanadium ions to the molar content of the tetravalent vanadium ions is 1:1; The chromium ions are trivalent chromium ions, and the difference between the molar content of the ferrous ions and the molar content of the chromium ions is <0.4 mol / L; The hydrogen evolution inhibitors are selected from at least one of ethylenediaminetetraacetic acid, N,N'-ethylenediamine disuccinic acid, oxalic acid, and phosphoric acid.

2. The hydrochloric acid-based vanadium iron chromium electrolyte according to claim 1, characterized in that, The difference between the molar content of the ferrous ions and the molar content of the chromium ions is 0.05-0.15 mol / L.

3. The hydrochloric acid-based vanadium iron chromium electrolyte of claim 1, wherein, The molar content of the hydrogen evolution inhibitors is 0.5-1.3% of the molar content of the vanadium ions.

4. The hydrochloric acid-based vanadium iron chromium electrolyte of claim 1, wherein, The hydrogen evolution inhibitors include ethylenediaminetetraacetic acid and oxalic acid, and the ratio of the molar content of the ethylenediaminetetraacetic acid to the molar content of the oxalic acid is (2.1-3.2):

1.

5. A process for the preparation of a vanadium iron-chromium electrolyte hydrochloride according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: S10. In a protective atmosphere, a vanadium source and a reducing agent are added to hydrochloric acid to perform a reduction reaction to obtain a tetravalent vanadium-containing solution; S20. The tetravalent vanadium-containing solution obtained in the step S10 is reacted under electrolytic reduction conditions to reduce part of the tetravalent vanadium ions into trivalent vanadium ions to form a vanadium solution with equal molar content of trivalent vanadium ions and tetravalent vanadium ions; S30. An iron source and a chromium source are added to the vanadium solution obtained in the step S20, stirred and dissolved, hydrogen evolution inhibitors are added, and the hydrogen ion concentration in the mixed solution is adjusted to a target concentration to obtain the hydrochloric acid-based vanadium iron chromium electrolyte.

6. The process for the preparation of hydrochloric vanadium iron chromium electrolyte according to claim 5, characterized in that, In the step S10, the reducing agent is selected from at least one of oxalic acid, glucose, and glycerol; and / or, The vanadium source includes vanadium pentoxide; and / or, The concentration of the hydrochloric acid is 32-38 wt%; and / or, The protective atmosphere includes nitrogen or argon; and / or, The temperature of the reduction reaction is 50-70℃, and the reduction reaction ends when the color of the solution is completely changed into deep blue and there is no yellow precipitate, to obtain the tetravalent vanadium-containing solution.

7. The process for the preparation of vanadium iron chromium electrolyte hydrochloride according to claim 5, characterized in that, In the step S20, during the electrolytic reduction reaction, the molar content of the trivalent vanadium ions and the tetravalent vanadium ions in the solution is detected by using a potential titration method, and the electrolytic reduction reaction ends when the molar content of the trivalent vanadium ions and the tetravalent vanadium ions is equal.

8. The process for the preparation of vanadium iron chromium electrolyte hydrochloride according to claim 5, characterized in that, In the step S30, the chromium source includes chromium chloride hexahydrate; and / or, The iron source is selected from at least one of ferrous chloride tetrahydrate or iron powder; and / or, The hydrogen ion concentration in the mixed solution is adjusted by using hydrochloric acid with a concentration of 35-37 wt%.

9. A flow battery, characterized in that, The method comprises the following steps: The positive electrolyte and the negative electrolyte both use the hydrochloric acid-based vanadium iron chromium electrolyte according to any one of claims 1-4.

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