Flow battery electrolyte, preparation thereof and flow battery

Abstract

The invention discloses a flow battery electrolyte, preparation thereof and a flow battery. The electrolyte comprises a positive electrode electrolyte and a negative electrode electrolyte, the positive electrode electrolyte contains vanadium ions, the negative electrode electrolyte contains titanium ions and chromium ions, and both the positive electrode electrolyte and the negative electrode electrolyte contain acid and compounds containing sulfonic acid groups. The preparation method of the electrolyte comprises the following steps: mixing acid and a sulfonic acid group-containing compound to obtain a solvent, dissolving a vanadium compound by adopting the solvent, and filtering to obtain first filtrate; adjusting the average valence state of vanadium ions to be 4, filtering and taking filtrate to obtain a positive electrode electrolyte; dissolving a titanium compound and a chromium compound by adopting the solvent, and filtering to obtain a second filtrate; and adding water into the second filtrate, and adjusting the concentrations of titanium ions and chromium ions to obtain the negative electrode electrolyte. The electrolyte, a positive electrode, an ion conduction membrane and a negative electrode are further assembled into the flow battery. The electrolyte and the flow battery have the characteristics of high energy density and low cost.

Description

Technical Field

[0001] The present invention relates to a battery electrolyte and its preparation and application, and in particular to a liquid flow battery electrolyte and its preparation and a liquid flow battery. Background Art

[0002] All-vanadium liquid flow batteries have the characteristics of identical positive and negative electrolyte elements and separated power and capacity. However, due to the relatively high price of vanadium, the initial investment of the product is high and the payback time is long, which restricts the further development and application of all-vanadium liquid flow battery energy storage technology.

[0003] Chinese patent CN116826126A discloses an iron-vanadium electrolyte and an iron-vanadium flow battery, the iron-vanadium flow battery includes a single cell system consisting of a positive electrode, a positive electrolyte, an ion exchange membrane, a negative electrolyte and a negative electrode, the single cell system is connected in series to obtain a battery stack: the battery stack is connected to the positive electrode storage tank and the negative electrode storage tank through a pipeline and a circulation pump to form a loop, and the circulation pump drives the positive electrode electrolyte and the negative electrode electrolyte to circulate inside the battery stack respectively. The iron-vanadium electrolyte includes the positive electrode electrolyte and the negative electrode electrolyte in the iron-vanadium flow battery, and the positive electrode electrolyte and the negative electrode electrolyte include iron ions, vanadium ions, sulfate ions and chloride ions. The total reaction electrode potential in this invention is only 1.03V, and the energy density is lower than that of the all-vanadium flow battery. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a liquid flow battery electrolyte to solve the problems of low energy density and total reaction electrode potential of existing electrolytes. Another purpose of the present invention is to propose a method for preparing the above-mentioned liquid flow battery electrolyte to solve the problem of how to obtain liquid flow battery electrolyte. The third purpose of the present invention is to provide a liquid flow battery with high energy density and low negative electrode potential.

[0005] Technical solution: The liquid flow battery electrolyte described in the present invention includes a positive electrode electrolyte and a negative electrode electrolyte, the positive electrode electrolyte contains vanadium ions, the negative electrode electrolyte contains titanium ions and chromium ions, and the positive electrode electrolyte and the negative electrode electrolyte both contain acid and a sulfonic acid group-containing compound.

[0006] The present invention introduces a titanium-chromium-based energy storage medium into the negative electrode of the battery, and utilizes its excellent redox properties to achieve efficient conversion of divalent and trivalent titanium ions and chromium ions and chromium. In addition, compared with the divalent vanadium ions in the negative electrode of the all-vanadium liquid flow battery, they are easily oxidized to trivalent vanadium ions, resulting in valence imbalance. The titanium-chromium-based energy storage medium is relatively stable after contact with air, ensuring the safe and stable operation of the battery. Finally, since the price of the titanium-chromium energy storage medium is lower than that of the vanadium-based energy storage medium, the battery cost can be greatly reduced.

[0007] The present invention introduces a vanadium-based energy storage medium into the positive electrode part of the battery, and utilizes its excellent redox performance to achieve efficient conversion between low-valent vanadium ions and high-valent vanadium ions.

[0008] The present invention couples a vanadium-based energy storage medium with a titanium-chromium-based energy storage medium to solve the problem of instability and high price of directly using a vanadium-based energy storage medium at the negative electrode, thereby achieving more stable electric energy output.

[0009] Preferably, the acid is a strong inorganic acid, and the compound containing a sulfonic acid group is at least one of hydroxymethanesulfonic acid, dimethanesulfonic acid, and aminoethylsulfinic acid.

[0010] Preferably, the acid is at least one of sulfuric acid and hydrochloric acid, and the methanesulfonic acid derivative is a mixture of hydroxymethanesulfonic acid and dimethanesulfonic acid in a mass ratio of 1-5:1-5.

[0011] Preferably, the molar concentration ratio of V ions:Ti ions:Cr ions in the positive electrode electrolyte and the negative electrode electrolyte is 0.5-2.5:0.5-2.5:0.25-1.25.

[0012] Preferably, the vanadium ion concentration in the positive electrode electrolyte is 0.5-2.5 mol / L, the titanium ion concentration in the negative electrode electrolyte is 0.5-2.5 mol / L, and the chromium ion concentration is 0.25-1.25 mol / L.

[0013] In some embodiments, the pH range of the positive electrode electrolyte and the negative electrode electrolyte is 0-3.0.

[0014] The second aspect of the present invention discloses a method for preparing the above-mentioned liquid flow battery electrolyte, comprising the following steps:

[0015] (1) mixing an acid and a compound containing a sulfonic acid group to obtain a solvent, dissolving a vanadium compound with the solvent, and filtering to obtain a first filtrate;

[0016] (2) adjusting the average valence of vanadium ions to tetravalent, filtering the filtrate, adding water to adjust the vanadium ion concentration to obtain a positive electrode electrolyte;

[0017] (3) dissolving the titanium compound and the chromium compound using the solvent, and filtering to obtain a second filtrate;

[0018] (4) Adding water to the second filtrate to adjust the concentrations of titanium ions and chromium ions to obtain a negative electrode electrolyte.

[0019] Preferably, the vanadium compound comprises V 2 O 5 , VO 2 、V 2 O 3 、(VO 2 ) 2 SO4 、VOSO 4 , VO 2 Cl、VOCl 2 、VCl 3 、VCl 2 One or more of the titanium compounds include TiCl 3 、TiO 2 、TiSO 4 、TiOSO 4 , Ti, the chromium compound comprises CrCl 2 CrSO 4 , Cr or more.

[0020] Preferably, the vanadium compound comprises V 2 O 5 , VO 2 、(VO 2 ) 2 SO 4 、VOSO 4 VOCl 2 One or more of .

[0021] Preferably, in step (1), the molar ratio of the acid to the compound containing the sulfonic acid group is 100:2-15, and the solid-liquid ratio of the vanadium compound to the solvent is 0.052-0.673 g / mL; in step (2), the method for adjusting the average valence state of the vanadium ion is: adding a reducing agent to the first filtrate, the reducing agent is oxalic acid with a final concentration of 1.8-2.5 mol / L; in step (3), the solid-liquid ratio of the titanium compound: the chromium compound: the solvent is 0.061-0.385 g: 0.021-0.490 g: 1 mL.

[0022] A third aspect of the present invention provides a liquid flow battery, comprising the above-mentioned liquid flow battery electrolyte, a positive electrode, an ion conductive membrane and a negative electrode.

[0023] The redox pairs of the positive and negative electrodes of the above-mentioned vanadium-titanium-chromium flow battery are VO 2 + / VO 2+ 、Ti 3+ / Ti 2+ and Cr 2+ / Cr, the standard potential difference is 1.90-1.92V, and the VO 2 + Ions lose electrons to form VO 2+ ions, Ti in the negative electrolyte 3+ Reducing to Ti 2+ , while Cr 2+It is reduced to generate Cr which is deposited on the negative electrode, and the discharge process is the opposite.

[0024] The reaction equation of vanadium-titanium-chromium flow battery is:

[0025] Ti 3+ +e - →Ti 2+

[0026] Cr 2+ +2e - →Cr

[0027] VO 2+ +H 2 O→VO 2 + +2H + +e -

[0028] Ti 3+ +Cr 2+ +3VO 2+ +3H 2 O=Ti 2+ +Cr+3VO 2 + +6H +

[0029] The specific reactions during the charge and discharge process are as follows:

[0030] Negative electrode: During the charging process, the trivalent titanium ions are reduced to divalent titanium ions, and the divalent chromium ions are reduced to elemental chromium; during the discharging process, the divalent titanium ions of the negative electrode are oxidized to trivalent titanium ions, and elemental chromium is oxidized to divalent chromium ions. Through the action of the diaphragm, the products and intermediates between the negative electrode and the positive electrode do not interfere with each other, ensuring the independent redox reaction of the titanium-chromium-based energy storage medium.

[0031] During the charging process, a reduction reaction of the titanium-chromium energy storage medium occurs:

[0032] Ti 3+ +e - →Ti 2+

[0033] Cr 2+ +2e - →Cr

[0034] During the discharge process, an oxidation reaction of the titanium-chromium energy storage medium occurs:

[0035] Ti 2+ →Ti 3+ +e -

[0036] Cr→Cr 2++2e -

[0037] Positive electrode: During the charging process, the 4-valent vanadium ions in the positive electrode are oxidized to 5-valent vanadium ions on the positive electrode carbon felt; during the discharging process, the 5-valent vanadium ions in the positive electrode undergo a reduction reaction to generate 4-valent vanadium ions. Through the action of the diaphragm, the products and intermediate products between the negative electrode and the positive electrode do not interfere with each other, ensuring the independent redox reaction of the vanadium-based energy storage medium.

[0038] During the charging process, the 4-valent vanadium ions undergo an oxidation reaction to form 5-valent vanadium ions:

[0039] VO 2+ +H 2 O→VO 2 + +2H + +e -

[0040] During the discharge process, the reduction reaction of pentavalent vanadium ions occurs to form tetravalent vanadium ions:

[0041] VO 2 + +2H + +e - →VO 2+ +H 2 O

[0042] Coupling system: The negative electrode containing titanium-chromium-based energy storage medium and the positive electrode containing vanadium-based energy storage medium are placed in the same system, separated by a diaphragm to ensure that the reactions between the positive and negative electrodes are carried out separately. Ensure that there is an external circuit connection between the two systems to ensure that the new liquid flow battery system can be used for electrical energy storage and output.

[0043] Total charging reaction: Ti 3+ +Cr 2+ +3VO 2+ +3H 2 O=Ti 2+ +Cr+3VO 2 + +6H +

[0044] Total discharge reaction: Ti 2+ +Cr+3VO 2 + +6H + =Ti 3+ +Cr 2+ +3VO 2+ +3H 2 O

[0045] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0046] The electrolyte of the present invention and the battery composed of the electrolyte have the characteristics of high energy density and low cost. The present invention reduces the amount of vanadium by introducing titanium-chromium-based energy storage medium, successfully solves the problem of unstable and high price of low-priced vanadium in the negative electrode of current liquid flow batteries, and achieves more stable power output. The application of the electrolyte is expected to promote the development of liquid flow batteries and the efficient use of energy, which is of great significance to sustainable development and the green energy industry.

[0047] Compared with the all-vanadium liquid flow battery, the negative electrode potential of the vanadium-titanium-chromium liquid flow battery in the present invention is reduced from -0.25V to -0.91V, which effectively avoids the occurrence of hydrogen evolution reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The discharge process reaction principle diagram of the vanadium-titanium-chromium liquid flow battery in the present invention;

[0049] Figure 2 This is a reaction principle diagram of the charging process of the vanadium-titanium-chromium liquid flow battery in the present invention. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0051] Embodiment 1: A flow battery electrolyte, comprising a positive electrode electrolyte and a negative electrode electrolyte, wherein the positive electrode electrolyte contains vanadium ions with a final concentration of 1.8 mol / L, the negative electrode electrolyte contains titanium ions with a final concentration of 0.6 mol / L and chromium ions with a final concentration of 0.6 mol / L, and the positive electrode electrolyte and the negative electrode electrolyte both contain sulfuric acid and a sulfonic acid group-containing compound, wherein the sulfonic acid group-containing compound is a mixture of hydroxymethanesulfonic acid and dimethanesulfonic acid in a mass ratio of 1:1. The negative electrode electrolyte also contains water. The pH of the positive electrode electrolyte and the negative electrode electrolyte are both around 1.0.

[0052] The method for preparing the above-mentioned liquid flow battery electrolyte comprises the following steps:

[0053] (1) Concentrated sulfuric acid and a compound containing a sulfonic acid group are mixed in a molar ratio of 100:7 to obtain a solvent, and the solvent is used to dissolve V 2 O 5 , V 2 O 5 The solid-liquid ratio to the solvent is 0.327 g / mL, and the first filtrate is obtained by filtration;

[0054] (2) adding oxalic acid with a final concentration of 1.8 mol / L to the first filtrate to adjust the average valence of the vanadium ions to 4, filtering the filtrate and adding water to adjust the vanadium ion concentration to obtain a positive electrode electrolyte;

[0055] (3) Dissolve TiCl using the solvent described in step (1) 3 and CrSO 4 , filter and take the second filtrate; TiCl 3 :CrSO 4 : The solid-liquid ratio of the solvent is 0.092g:0.235g:1mL

[0056] (4) Add water to the second filtrate to adjust the concentrations of titanium ions and chromium ions to the target final concentrations to obtain a negative electrode electrolyte.

[0057] according to Figure 1 The structure of the vanadium-titanium-chromium liquid flow battery is assembled by using the positive electrolyte, negative electrolyte, positive electrode, negative electrode and ion conductive membrane. The electrode material is carbon felt.

[0058] Embodiment 2: The rest is the same as Embodiment 1, except that:

[0059] The positive electrode electrolyte contains vanadium ions with a final concentration of 1.0 mol / L, the negative electrode electrolyte contains titanium ions with a final concentration of 0.8 mol / L and chromium ions with a final concentration of 0.5 mol / L, and the positive electrode electrolyte and the negative electrode electrolyte both contain sulfuric acid and a sulfonic acid group-containing compound, and the sulfonic acid group-containing compound is a mixture of hydroxymethanesulfonic acid and dimethanesulfonic acid in a mass ratio of 5:1. The negative electrode electrolyte also contains water. The pH of the positive electrode electrolyte and the negative electrode electrolyte are both around 3.0.

[0060] In step (1), concentrated sulfuric acid and a compound containing a sulfonic acid group are mixed at a molar ratio of 100:15 to obtain a solvent, and the solvent is used to dissolve VO 2 , VO 2 The solid-liquid ratio to the solvent is 0.083 g / mL, and the first filtrate is obtained by filtration;

[0061] No oxidizing agent or reducing agent is added in step (2);

[0062] In step (3), the solvent described in step (1) is used to dissolve TiO 2 and CrCl 2 , filter and take the second filtrate; TiO 2 :CrCl 2 : The solid-liquid ratio of the solvent is 0.063g:0.133g:1mL.

[0063] Embodiment 3: The rest is the same as Embodiment 1, except that:

[0064] The positive electrode electrolyte contains vanadium ions with a final concentration of 2.5 mol / L, the negative electrode electrolyte contains titanium ions with a final concentration of 2 mol / L and chromium ions with a final concentration of 0.5 mol / L, and the positive electrode electrolyte and the negative electrode electrolyte both contain sulfuric acid and a compound containing a sulfonic acid group, and the compound containing a sulfonic acid group is a mixture of hydroxymethanesulfonic acid and dimethanesulfonic acid in a mass ratio of 1:5. The negative electrode electrolyte also contains water. The pH of the positive electrode electrolyte and the negative electrode electrolyte are both around 1.5.

[0065] In step (1), concentrated sulfuric acid and a compound containing a sulfonic acid group are mixed in a molar ratio of 100:10 to obtain a solvent, and the solvent is used to dissolve (VO 2 ) 2 SO 4 , (VO 2 ) 2 SO 4 The solid-liquid ratio to the solvent is 0.655 g / mL, and the first filtrate is obtained by filtration;

[0066] In step (2), oxalic acid with a final concentration of 2.5 mol / L is used as a reducing agent;

[0067] In step (3), the solvent described in step (1) is used to dissolve TiSO 4 and Cr, filter and take the second filtrate; TiSO 4 The solid-liquid ratio of Cr:solvent is 0.291g:0.025g:1mL.

[0068] Embodiment 4: All other aspects are the same as Embodiment 1, except that:

[0069] The positive electrode electrolyte contains vanadium ions with a final concentration of 2.0 mol / L, the negative electrode electrolyte contains titanium ions with a final concentration of 2.0 mol / L and chromium ions with a final concentration of 1.0 mol / L, and the positive electrode electrolyte and the negative electrode electrolyte both contain sulfuric acid and a sulfonic acid group-containing compound, and the sulfonic acid group-containing compound is a mixture of hydroxymethanesulfonic acid and dimethanesulfonic acid in a mass ratio of 2:3. The negative electrode electrolyte also contains water. The pH of the positive electrode electrolyte and the negative electrode electrolyte are both around 0.5.

[0070] In step (1), concentrated sulfuric acid and a compound containing a sulfonic acid group are mixed at a molar ratio of 100:5 to obtain a solvent, and the solvent is used to dissolve VOSO 4 , VOSO 4 The solid-liquid ratio to the solvent is 0.506 g / mL, and the first filtrate is obtained by filtration;

[0071] No oxidizing agent or reducing agent is added in step (2);

[0072] In step (3), the solvent described in step (1) is used to dissolve TiOSO 4and CrCl 2 , filter and take the second filtrate; TiOSO 4 :CrCl 2 : The solid-liquid ratio of the solvent is 0.319g:0.122g:1mL.

[0073] Embodiment 5: All other aspects are the same as Embodiment 1, except that:

[0074] The positive electrode electrolyte contains vanadium ions with a final concentration of 2.0 mol / L, the negative electrode electrolyte contains titanium ions with a final concentration of 2.0 mol / L and chromium ions with a final concentration of 1 mol / L, and the positive electrode electrolyte and the negative electrode electrolyte both contain hydrochloric acid and a sulfonic acid group-containing compound, and the sulfonic acid group-containing compound is a mixture of hydroxymethanesulfonic acid and dimethanesulfonic acid in a mass ratio of 4:3. The negative electrode electrolyte also contains water. The pH of the positive electrode electrolyte and the negative electrode electrolyte are both around 3.0.

[0075] In step (1), concentrated hydrochloric acid and a compound containing a sulfonic acid group are mixed in a molar ratio of 100:12 to obtain a solvent, and the solvent is used to dissolve VOCl 2 , VOCl 2 The solid-liquid ratio to the solvent is 0.275 g / mL, and the first filtrate is obtained by filtration;

[0076] No oxidizing agent or reducing agent is added in step (2);

[0077] In step (3), the solvent described in step (1) is used to dissolve Ti and CrSO 4 , filter and take the second filtrate; Ti:CrSO 4 : The solid-liquid ratio of the solvent is 0.095g:0.148g:1mL.

[0078] Embodiment 6: All other aspects are the same as Embodiment 1, except that:

[0079] In step (1), concentrated sulfuric acid and a compound containing a sulfonic acid group are mixed in a molar ratio of 100:2 to obtain a solvent, and the solvent is used to dissolve V 2 O 3 , VO 2 Cl, VCl 3 and VCl 2 A mixture of 1:1:1:1 was prepared, and the insoluble matter was removed by filtration to obtain a first filtrate; the solid-liquid ratio of the vanadium compound to the solvent was 0.205 g / mL.

[0080] Comparative Example 1: The rest is the same as Example 1, except that:

[0081] No CrSO is added to the negative electrolyte 4 .

[0082] Comparative Example 2: The rest is the same as Example 1, except that:

[0083] No TiCl is added to the negative electrode electrolyte 3 .

[0084] Comparative Example 3: The rest is the same as Example 1, except that:

[0085] CrSO 4 Replaced by FeSO 4 .

[0086] Comparative Example 4: The rest is the same as Example 1, except that:

[0087] TiCl 3 Replaced by MnCl 2 .

[0088] Comparative Example 5: The rest is the same as Example 1, except that:

[0089] TiCl 3 Replaced by ZnCl 2 .

[0090] Comparative Example 6: The rest is the same as Example 1, except that:

[0091] A mixture of hydroxymethanesulfonic acid and dimethanesulfonic acid in a mass ratio of 1:1 was replaced by methanesulfonic acid.

[0092] Comparative Example 7: The rest is the same as Example 1, except that:

[0093] The dimethanesulfonic acid was replaced by 1,2-benzenedimethanesulfonic acid disodium salt.

[0094] Comparative Example 8: The rest is the same as Example 1, except that:

[0095] Replace hydroxymethanesulfonic acid with aminoethylsulfinic acid.

[0096] Comparative Example 9: The rest is the same as Example 1, except that:

[0097] TiCl 3 and CrSO 4 Replaced by VOSO 4 The concentration of vanadium ions in the positive electrode electrolyte is 1M; the concentration of vanadium ions in the negative electrode electrolyte is 2M, and an all-vanadium liquid flow battery is prepared.

[0098] The energy density, standard potential difference and negative electrode potential of the flow batteries prepared in Examples 1-5 and Comparative Examples 1-9 were measured; the single cells prepared in each Example and Comparative Example were connected in series to obtain a vanadium-titanium-chromium flow battery stack system, and the efficiency at the stack outlet was measured.

[0099] Table 1 Effect of the selection of metal ions and solvent system in the electrolyte on battery performance

[0100]

[0101]

[0102] It can be seen from the results in Table 1 that the combination of titanium ions and chromium ions can significantly reduce the negative electrode potential, increase the potential difference, and effectively improve the energy density of the flow battery. When titanium ions or chromium ions are used alone, the performance of the battery is greatly reduced. When any of the titanium ions and chromium ions are replaced by iron ions, manganese ions or zinc ions commonly used in existing flow batteries, no significant improvement in battery performance can be achieved. On the contrary, in some examples, the performance of the flow battery will be reduced. In addition, the synergistic effect of titanium ions and chromium ions also depends on a specific solvent system. Only when hydroxymethanesulfonic acid and dimethanesulfonic acid are used in combination can better battery performance be obtained.

Claims

1. A flow battery electrolyte, characterized in that: The invention comprises a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte contains vanadium ions, the negative electrode electrolyte contains titanium ions and chromium ions, and both the positive electrode electrolyte and the negative electrode electrolyte contain acid and a compound containing a sulfonic acid group.

2. The liquid flow battery electrolyte according to claim 1, characterized in that: The molar concentration ratio of V ions:Ti ions:Cr ions in the positive electrode electrolyte and the negative electrode electrolyte is 0.5-2.5:0.5-2.5:0.25-1.

25.

3. The liquid flow battery electrolyte according to claim 1, characterized in that: The vanadium ion concentration in the positive electrode electrolyte is 0.5-2.5 mol / L, the titanium ion concentration in the negative electrode electrolyte is 0.5-2.5 mol / L, and the chromium ion concentration is 0.25-1.25 mol / L.

4. The liquid flow battery electrolyte according to claim 1, characterized in that: The acid is an inorganic strong acid, and the compound containing a sulfonic acid group is at least one of hydroxymethanesulfonic acid, dimethanesulfonic acid, and aminoethylsulfinic acid.

5. The liquid flow battery electrolyte according to claim 4, characterized in that: The acid is at least one of sulfuric acid and hydrochloric acid, and the methanesulfonic acid derivative is a mixture of hydroxymethanesulfonic acid and dimethanesulfonic acid in a mass ratio of 1-5:1-5.

6. The method for preparing a flow battery electrolyte according to any one of claims 1 to 5, characterized in that: The steps include: (1) mixing an acid and a compound containing a sulfonic acid group to obtain a solvent, dissolving a vanadium compound with the solvent, and filtering to obtain a first filtrate; (2) adjusting the average valence of vanadium ions to tetravalent, filtering the filtrate, adding water to adjust the vanadium ion concentration to obtain a positive electrode electrolyte; (3) dissolving the titanium compound and the chromium compound using the solvent, and filtering to obtain a second filtrate; (4) Adding water to the second filtrate to adjust the concentrations of titanium ions and chromium ions to obtain a negative electrode electrolyte.

7. The liquid flow battery electrolyte according to claim 6, characterized in that: The vanadium compounds include one or more of V2O5, VO2, V2O3, (VO2)2SO4, VOSO4, VO2Cl, VOCl2, VCl3, and VCl2; the titanium compounds include one or more of TiCl3, TiO2, TiSO4, TiOSO4, and Ti; and the chromium compounds include one or more of CrCl2, CrSO4, and Cr.

8. The liquid flow battery electrolyte according to claim 7, characterized in that: The vanadium compound includes one or more of V2O5, VO2, (VO2)2SO4, VOSO4, and VOCl2.

9. The method for preparing a flow battery electrolyte according to claim 6, characterized in that: In step (1), the molar ratio of the acid to the compound containing a sulfonic acid group is 100:2-15, and the solid-liquid ratio of the vanadium compound to the solvent is 0.052-0.673 g / mL; in step (2), the method for adjusting the average valence state of the vanadium ion is: adding a reducing agent to the first filtrate, wherein the reducing agent is oxalic acid with a final concentration of 1.8-2.5 mol / L; in step (3), the solid-liquid ratio of the titanium compound: the chromium compound: the solvent is 0.061-0.385 g: 0.021-0.490 g: 1 mL.

10. A liquid flow battery, characterized in that: It comprises the liquid flow battery electrolyte according to any one of claims 1 to 5, a positive electrode, an ion conductive membrane and a negative electrode.

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