Electrolyte of all-vanadium redox flow battery and preparation method of electrolyte

Abstract

The invention relates to the technical field of all-vanadium redox flow battery electrolytes, and discloses an all-vanadium redox flow battery electrolyte and a preparation method thereof, and the all-vanadium redox flow battery electrolyte comprises sulfuric acid, a vanadium ion active substance and a composite additive composed of lithium phosphate and soluble trivalent cerium salt. According to the invention, lithium phosphate and trivalent cerium salt are compounded, phosphate ions and pentavalent vanadium ions form a stable complex, and hydrolytic polymerization and V2O5 precipitation of the complex at high temperature are effectively inhibited; meanwhile, by means of the variable valence state of the trivalent cerium ions, the stabilizing effect is enhanced, and the trivalent cerium ions serve as a redox medium to accelerate reaction kinetics of V4 + / V5 + couple. According to the synergistic system, the precipitation amount of the electrolyte stored at 50 DEG C for a long time is reduced to 0.015-0.025 g / L, the stable V < 5 + > working concentration is increased to 2.2-2.8 mol / L, and the contradiction between high energy density and high-temperature operation stability is solved.

Description

Technical Field

[0001] This invention belongs to the field of vanadium redox flow battery electrolyte technology, specifically relating to an electrolyte for vanadium redox flow batteries and its preparation method; particularly relating to a highly stable electrolyte with lithium phosphate and trivalent cerium ions as composite additives, suitable for high energy density vanadium redox flow battery energy storage systems. Background Technology

[0002] As a key technology for large-scale energy storage, the commercial application of vanadium redox flow batteries has long been limited by a prominent technical contradiction: there is an irreconcilable conflict between improving energy density and ensuring high-temperature operational stability. The physicochemical root of this contradiction lies in the inherent thermodynamic instability of pentavalent vanadium ions, the positive electrode active material.

[0003] To achieve higher energy density, the total vanadium concentration in the electrolyte must be increased. However, during charging, V... 4+ Oxidation to produce VO2 + This leads to VO2 in the positive electrode electrolyte + The local concentration of VO2 increases rapidly and instantaneously at a specific stage. When the system temperature exceeds 40°C, this high concentration of VO2... + It will pass through "2VO2" + +H₂O→V₂O₅↓+2H₂O + "This reversible reaction leads to irreversible homogeneous polymerization, resulting in the precipitation of solid vanadium pentoxide (V2O5), which deteriorates the electrochemical reaction kinetics." Summary of the Invention

[0004] The purpose of this invention is to provide an electrolyte for a vanadium redox flow battery and its preparation method, which solves the problem of existing vanadium redox flow battery electrolytes being unsuitable for use at temperatures >40℃ and high concentrations. 5+ The problem of easy precipitation of ions and the corrosiveness or poor thermal stability of existing additives is addressed by achieving the effects of widening the working temperature window of the electrolyte, improving the solubility of vanadium ions, and ensuring long-term operational stability.

[0005] Based on the above concept, the technical solution adopted by this invention is as follows: According to a first aspect of the present invention, an electrolyte for a vanadium redox flow battery is provided, comprising sulfuric acid, vanadium ion active material, and a composite additive composed of lithium phosphate and a soluble trivalent cerium salt.

[0006] Optionally, the soluble trivalent cerium salt is at least one of cerium sulfate, cerium nitrate, or cerium chloride.

[0007] In some embodiments, the concentration of lithium phosphate in the electrolyte is from 0.05 mol / L to 0.15 mol / L.

[0008] In some embodiments, the concentration of cerium ions in the electrolyte of the soluble trivalent cerium salt is from 0.01 mol / L to 0.10 mol / L.

[0009] In some embodiments, the molar ratio of lithium phosphate to cerium ions is 1.5:1 to 5:1.

[0010] In some embodiments, the concentration of pentavalent vanadium ions in the electrolyte is from 2.2 mol / L to 2.8 mol / L.

[0011] According to a second aspect of the present invention, a method for preparing an electrolyte for a vanadium redox flow battery is provided. Includes the following steps: S1: Dissolve the vanadium compound in sulfuric acid solution and stir to obtain a basic vanadium electrolyte; S2: Add lithium phosphate to the basic vanadium electrolyte and stir until completely dissolved; S3: Continue to add soluble trivalent cerium salt to the solution obtained in step S2, and stir until completely dissolved to obtain the composite additive electrolyte.

[0012] According to a third aspect of the present invention, an all-vanadium redox flow battery is provided, comprising: Positive electrolyte; Negative electrode electrolyte; Ion exchange membrane; Positive electrode; And the negative electrode, The positive electrode electrolyte is the electrolyte of the vanadium redox flow battery described above.

[0013] The beneficial effects of this invention are as follows: 1. This invention utilizes the complexation of lithium phosphate and trivalent cerium salt to form a stable complex between phosphate ions and pentavalent vanadium ions, effectively inhibiting their hydrolysis and polymerization at high temperatures and the precipitation of V₂O₅. Simultaneously, the trivalent cerium ions, due to their variable valence state, not only enhance the aforementioned stabilizing effect but also significantly accelerate the precipitation of V₂O₅ as a redox medium. 4+ / V 5+ Reaction kinetics of the redox couple. This synergistic system reduces the amount of precipitate in the electrolyte to 0.015-0.025 g / L during long-term storage at 50°C, and stabilizes V... 5+ The working concentration was increased to 2.2-2.8 mol / L, resolving the contradiction between high energy density and high-temperature operational stability.

[0014] 2. The composite additive of this invention optimizes the ionic environment and reduces electrochemical polarization during the precipitation suppression process, thereby increasing the energy efficiency of the battery to 84.5%-85.8%. In addition, the system does not contain corrosive components such as chloride ions, posing no risk of corrosion to the battery's metal components. Furthermore, the lithium phosphate and cerium salts used are stable in strong acid environments, avoiding the problem of easy decomposition of organic additives at high temperatures. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the charging of the all-vanadium redox flow battery of the present invention; Figure 2 This is a schematic diagram of the discharge of the all-vanadium redox flow battery of the present invention; Figure 3 This is a flowchart illustrating the preparation process of the electrolyte of the present invention. Detailed Implementation

[0016] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0017] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise defined, the technical or scientific terms used in this application should be understood in their ordinary sense by one of ordinary skill in the art to which this invention pertains. The words “a” or “one” and similar terms used in this application specification and claims do not indicate a limitation of quantity, but rather indicate the presence of at least one. “A plurality” means two or more. The words “comprising” or “including” and similar terms mean that the element or object preceding “comprising” or “including” covers the element or object listed following “comprising” or “including” and its equivalents, and does not exclude other elements or objects. The words “connected” or “linked” and similar terms are not limited to physical or mechanical connections and can include electrical connections, whether direct or indirect. The words “above” and / or “below” and similar terms are for ease of description only and are not limited to a location or spatial orientation. The singular forms “a,” “the,” and “the” used in this application specification and appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0018] The technical concept of this invention includes: In vanadium redox flow batteries, pentavalent vanadium ions in the positive electrode electrolyte are highly susceptible to hydrolysis and polymerization, forming V₂O₅ precipitates at temperatures exceeding 40°C or under high concentration conditions. This leads to loss of active material, blockage of flow channels, and degradation of battery performance. Furthermore, while existing chlorine-containing additives (such as LiCl) can improve stability, Cl… - It is prone to corrosion of metal components such as titanium tube heat exchangers and bipolar plates, with a corrosion rate of up to 0.015 mm / year; organic additives (such as EDTA) are easily decomposed at medium and high temperatures, making them unsuitable for long-term operation at temperatures above 45°C, and difficult to ensure long-term stable operation at high temperatures and high concentrations.

[0019] Therefore, this invention proposes to introduce lithium phosphate and trivalent cerium salt to construct a composite additive system. This system utilizes the reaction of phosphate ions and V... 5+ The coordination effect of cerium ions inhibits their polymerization and precipitation, and enhances the electrode reaction kinetics by leveraging the variable valence state of cerium ions. The two form a synergistic stable structure through a specific ratio and addition order, which reduces electrochemical polarization while inhibiting precipitation, and does not introduce corrosive components, thereby comprehensively solving the problems of electrolyte stability and performance improvement under high temperature and high concentration conditions.

[0020] Therefore, this invention aims to obtain a vanadium redox flow battery electrolyte that combines high-temperature stability, high concentration tolerance, low polarization characteristics, and good material compatibility by designing and optimizing the composition, ratio, and preparation process of the composite additive, in order to meet the increasingly demanding requirements of energy storage application environments.

[0021] This application provides an electrolyte for a vanadium redox flow battery and a method for preparing the same, comprising sulfuric acid, vanadium ion active material, and a composite additive composed of lithium phosphate and soluble trivalent cerium salt.

[0022] This invention utilizes the complexation of lithium phosphate and trivalent cerium salt to form a stable complex between phosphate ions and pentavalent vanadium ions, effectively inhibiting their hydrolysis and polymerization at high temperatures and the precipitation of V₂O₅. Simultaneously, the trivalent cerium ions, due to their variable valence state, not only enhance the aforementioned stabilizing effect but also significantly accelerate the V₂O₅ precipitation process as a redox mediator. 4+ / V 5+ Reaction kinetics of the redox couple. This synergistic system reduces the amount of precipitate in the electrolyte to 0.015-0.025 g / L during long-term storage at 50°C, and stabilizes V... 5+ The working concentration was increased to 2.2-2.8 mol / L, resolving the contradiction between high energy density and high-temperature operational stability. Simultaneously, the composite additives optimized the ionic environment and reduced electrochemical polarization during precipitation suppression, improving the battery's energy efficiency to 84.5%-85.8%. Furthermore, the system contains no corrosive components such as chloride ions, posing no risk of corrosion to battery metal components. The lithium phosphate and cerium salts used are stable in strongly acidic environments, preventing the easy decomposition of organic additives at high temperatures.

[0023] The method for preparing the electrolyte of an all-vanadium redox flow battery described in this application includes the following steps: S1: Dissolve the vanadium compound in sulfuric acid solution and stir to obtain a basic vanadium electrolyte; S2: Add lithium phosphate to the basic vanadium electrolyte and stir until completely dissolved; S3: Continue to add soluble trivalent cerium salt to the solution obtained in step S2, and stir until completely dissolved to obtain the composite additive electrolyte.

[0024] The vanadium redox flow battery described in this application includes: Positive electrolyte; Negative electrode electrolyte; Ion exchange membrane; Positive electrode; And the negative electrode.

[0025] The following is in conjunction with the appendix Figures 1 to 3 This application provides a detailed description of the electrolyte for an all-vanadium redox flow battery and its preparation method.

[0026] Example 1 A 2.5 mol / L sulfuric acid solution (950 ml) was prepared under 35°C water bath and mechanical stirring conditions. While maintaining this temperature and stirring, vanadium oxysulfate was added to the solution, and stirring continued for 2 hours to obtain V. 4+ A clarified base vanadium electrolyte with a concentration of approximately 2.4 mol / L.

[0027] Maintaining the system at 35°C with continuous stirring, lithium phosphate was added to the above-mentioned basic electrolyte to achieve a concentration of 0.05 mol / L, and stirring was continued for 60 minutes until completely dissolved. Subsequently, cerium sulfate was added to introduce cerium ions to a concentration of 0.01 mol / L, and stirring was continued for 40 minutes until completely dissolved. The resulting solution was filtered through a 1 μm filter membrane, and the filtrate was diluted with water to a final volume of 1.0 L to obtain the composite additive electrolyte.

[0028] Battery Assembly: The above-mentioned composite additive electrolyte is injected into the storage tank as the positive electrode electrolyte. The negative electrode electrolyte is prepared by dissolving vanadium sulfate in a 2.5 mol / L sulfuric acid solution to form a 1.0 L solution with a total vanadium concentration of approximately 2.2 mol / L. 3+ Electrolyte. The electrolyte was reduced by passing hydrogen gas through it to obtain a product with a yield of V... 3+ / V 2+ A negative electrode electrolyte dominated by redox couples, wherein V 2+ The concentration is approximately 1.0 mol / L.

[0029] Example 2 A 3.5 mol / L sulfuric acid solution (950 ml) was prepared under 35°C water bath and mechanical stirring conditions. While maintaining this temperature and stirring, vanadium oxysulfate was added to the solution, and stirring continued for 2 hours to obtain V. 4+ A clarified basic vanadium electrolyte with a concentration of approximately 2.6 mol / L.

[0030] Maintaining the system at 35°C with continuous stirring, lithium phosphate was added to the above-mentioned basic electrolyte to achieve a concentration of 0.1 mol / L, and stirring was continued for 60 minutes until completely dissolved. Subsequently, cerium sulfate was added to introduce cerium ions to a concentration of 0.05 mol / L, and stirring was continued for 40 minutes until completely dissolved. The resulting solution was filtered through a 1 μm filter membrane, and the filtrate was diluted with water to a final volume of 1.0 L to obtain the composite additive electrolyte.

[0031] Battery Assembly: The above-mentioned composite additive electrolyte is injected into the storage tank as the positive electrode electrolyte. The negative electrode electrolyte is prepared by dissolving vanadium sulfate in a 3.5 mol / L sulfuric acid solution to form a 1.0 L solution with a total vanadium concentration of approximately 2.6 mol / L. 3+ Electrolyte. The electrolyte was reduced by passing hydrogen gas through it to obtain a product with a yield of V... 3+ / V 2+ A negative electrode electrolyte dominated by redox couples, wherein V 2+ The concentration is approximately 1.2 mol / L.

[0032] Example 3 A 5.0 mol / L sulfuric acid solution (950 ml) was prepared under 35°C water bath and mechanical stirring conditions. While maintaining this temperature and stirring, vanadium oxysulfate was added to the solution, and stirring continued for 2 hours to obtain V. 4+ A clarified basic vanadium electrolyte with a concentration of approximately 3.0 mol / L.

[0033] Maintaining the system at 35°C with continuous stirring, lithium phosphate was added to the above-mentioned basic electrolyte to achieve a concentration of 0.15 mol / L, and stirring was continued for 60 minutes until completely dissolved. Subsequently, cerium sulfate was added to introduce cerium ions to a concentration of 0.1 mol / L, and stirring was continued for 40 minutes until completely dissolved. The resulting solution was filtered through a 1 μm filter membrane, and the filtrate was diluted with water to a final volume of 1.0 L to obtain the composite additive electrolyte.

[0034] Battery Assembly: The above-mentioned composite additive electrolyte is injected into the storage tank as the positive electrode electrolyte. The negative electrode electrolyte is prepared by dissolving vanadium sulfate in a 5.0 mol / L sulfuric acid solution to form a 1.0 L solution with a total vanadium concentration of approximately 3.0 mol / L. 3+Electrolyte. The electrolyte was reduced by passing hydrogen gas through it to obtain a product with a yield of V... 3+ / V 2+ A negative electrode electrolyte dominated by redox couples, wherein V 2+ The concentration is approximately 1.4 mol / L.

[0035] Example 4 A 3.5 mol / L sulfuric acid solution (950 ml) was prepared under 35°C water bath and mechanical stirring conditions. While maintaining this temperature and stirring, vanadium oxysulfate was added to the solution, and stirring continued for 2 hours to obtain V. 4+ A clarified basic vanadium electrolyte with a concentration of approximately 2.6 mol / L.

[0036] Maintaining the system at 35°C with continuous stirring, lithium phosphate was added to the above-mentioned basic electrolyte to achieve a concentration of 0.1 mol / L, and stirring was continued for 60 minutes until completely dissolved. Subsequently, cerium nitrate was added to introduce cerium ions to a concentration of 0.05 mol / L, and stirring was continued for 40 minutes until completely dissolved. The resulting solution was filtered through a 1 μm filter membrane, and the filtrate was diluted with water to a final volume of 1.0 L to obtain the composite additive electrolyte.

[0037] Battery Assembly: The above-mentioned composite additive electrolyte is injected into the storage tank as the positive electrode electrolyte. The negative electrode electrolyte is prepared by dissolving vanadium sulfate in a 3.5 mol / L sulfuric acid solution to form a 1.0 L solution with a total vanadium concentration of approximately 2.6 mol / L. 3+ Electrolyte. The electrolyte was reduced by passing hydrogen gas through it to obtain a product with a yield of V... 3+ / V 2+ A negative electrode electrolyte dominated by redox couples, wherein V 2+ The concentration is approximately 1.2 mol / L.

[0038] Comparative Example 1 Everything else is the same as in Example 2, except that: No additives were added.

[0039] A 3.5 mol / L sulfuric acid solution was prepared under 35℃ water bath and mechanical stirring conditions. Maintaining this temperature and stirring, vanadium oxysulfate was added to the solution, and stirring continued for 2 hours to obtain V. 4+ A clarified basic vanadium electrolyte with a concentration of approximately 2.6 mol / L.

[0040] The electrolyte contains no added lithium phosphate or cerium salt. The resulting solution was filtered through a 1 μm filter membrane to obtain the control positive electrode electrolyte.

[0041] Battery assembly: The above-mentioned positive electrode electrolyte is injected into the storage tank. The negative electrode electrolyte is prepared by dissolving vanadium sulfate in a 3.5 mol / L sulfuric acid solution to achieve a total vanadium concentration of approximately 2.6 mol / L. 3+ The electrolyte was brought to a final volume of 1.0 L. Hydrogen gas was then passed through the electrolyte for reduction treatment to obtain a product with a volume of V. 3+ / V 2+ A negative electrode electrolyte dominated by redox couples, wherein V 2+ The concentration is approximately 1.2 mol / L.

[0042] Comparative Example 2 Everything else is the same as in Example 2, except that: No soluble trivalent cerium salts were added.

[0043] A 3.5 mol / L sulfuric acid solution (950 ml) was prepared under 35°C water bath and mechanical stirring conditions. While maintaining this temperature and stirring, vanadium oxysulfate was added to the solution, and stirring continued for 2 hours to obtain V. 4+ A clarified basic vanadium electrolyte with a concentration of approximately 2.6 mol / L.

[0044] Maintaining the system at 35°C and continuously stirring, lithium phosphate was added to the above-mentioned basic electrolyte to achieve a concentration of 0.10 mol / L. Stirring continued for 60 minutes until completely dissolved. No cerium salts were added to this electrolyte. The resulting solution was filtered through a 1 μm filter membrane to obtain a control cathode electrolyte containing only lithium phosphate.

[0045] Battery assembly: The above-mentioned positive electrode electrolyte is injected into the storage tank. The negative electrode electrolyte is prepared by dissolving vanadium sulfate in a 3.5 mol / L sulfuric acid solution to achieve a total vanadium concentration of approximately 2.6 mol / L. 3+ The electrolyte was brought to a final volume of 1.0 L. Hydrogen gas was then passed through the electrolyte for reduction treatment to obtain a product with a volume of V. 3+ / V 2+ A negative electrode electrolyte dominated by redox couples, wherein V 2+ The concentration is approximately 1.2 mol / L.

[0046] Comparative Example 3 Everything else is the same as in Example 2, except that: No lithium phosphate was added.

[0047] A 3.5 mol / L sulfuric acid solution was prepared under 35℃ water bath and mechanical stirring conditions. Maintaining this temperature and stirring, vanadium oxysulfate was added to the solution, and stirring continued for 2 hours to obtain V. 4+ A clarified basic vanadium electrolyte with a concentration of approximately 2.6 mol / L.

[0048] The system was maintained at 35°C with continuous stirring. Cerium sulfate was added to the above-mentioned basic electrolyte to introduce cerium ion concentrations identical to those in Example 1, at 0.01 mol / L. Stirring continued for 40 minutes until complete dissolution. No lithium phosphate was added to this electrolyte. The resulting solution was filtered through a 1 μm filter membrane, and the filtrate was diluted with water to 1.0 L to obtain a control positive electrode electrolyte containing only cerium salts.

[0049] Battery assembly: The above-mentioned positive electrode electrolyte is injected into the storage tank. The negative electrode electrolyte is prepared by dissolving vanadium sulfate in a 3.5 mol / L sulfuric acid solution to achieve a total vanadium concentration of approximately 2.6 mol / L. 3+ The electrolyte was brought to a final volume of 1.0 L. Hydrogen gas was then passed through the electrolyte for reduction treatment to obtain a product with a volume of V. 3+ / V 2+ A negative electrode electrolyte dominated by redox couples, wherein V 2+ The concentration is approximately 1.2 mol / L.

[0050] Table 1. Comparison of electrolyte performance between different embodiments and comparative examples

[0051] V at high temperature 5+ Ion precipitation is a key issue limiting the operating temperature window and energy density of vanadium redox flow batteries. Experimental data show that after standing at 50°C for 200 hours, the V₂O₅ precipitation in Examples 1-4 containing composite additives ranged from 0.015 to 0.025 g / L, while the precipitation in Comparative Example 1 without any additives reached as high as 0.085 g / L. Even compared to single-additive systems, the advantages of composite additives are significant: the precipitation in Comparative Example 2, containing only lithium phosphate, was 0.045 g / L, and the precipitation in Comparative Example 3, containing only cerium salts, was 0.075 g / L, both higher than any of the examples.

[0052] This significant improvement in stability stems from phosphate (PO4) 3- ) and trivalent cerium ions (Ce 3+ The synergistic effect of PO4. On the one hand, PO4 3- Can be used with V 5+ Formation of thermodynamically stable VO2(PO4) 3- The complex has a low formation energy, effectively competing for and blocking V. 5+ The reaction pathway of polymerization between ions via "vanadium-oxygen bridging bonds" (VOV) inhibits 2VO2. + +H2O V₂O₅↓+2H⁺ + This precipitation reaction. On the other hand, the introduced Ce... 3+ The stabilizing effect was further enhanced, Ce 3+ With PO43- and V 5+ A dynamic ternary composite structure is formed in solution. This structure not only physically blocks V through steric hindrance effects. 5+ The ions approach each other, and Ce 3+ / Ce 4+ The presence of redox couples can act as an "electron buffer," absorbing excessively high local oxidation potential and preventing V from being absorbed. 5 + Excessive aggregation and disproportionation. Therefore, composite additives significantly improve the long-term stability of electrolytes at high temperatures through a dual mechanism of "chemical coordination stabilization" and "physical spatial shielding".

[0053] The electrolyte system of this invention can support higher concentrations of V 5+ Stable existence. In Examples 1-3, V 5+ The concentrations reached 2.2, 2.4, and 2.8 mol / L, respectively, and maintained a low precipitation rate even during high-temperature testing. In contrast, the traditional sulfuric acid system (Comparative Example 1) showed a lower precipitation rate. 5+ The saturated solubility of lithium is typically below 2.0 mol / L. Even with the addition of lithium phosphate alone (Comparative Example 2), the increase in solubility is relatively limited (approximately 2.1 mol / L).

[0054] Improved tolerance to high concentrations and lithium ions (Li + The introduction of ) and its compound synergistic effect are closely related. Li + With the large amount of SO4 present in the electrolyte 2- The formation of weakly interacting ion pairs partially "shields" the interaction between sulfate and vanadium oxide ions (VO2). + The strong electrostatic interaction between vanadium ions weakens the hydrogen bond network formed by sulfate bridging between vanadium ions, allowing more V to escape. 5+ Ions can be stably dispersed in a solvated form. Meanwhile, PO4... 3- With V 5+ Specific coordination and Ce 3+ The synergistic stabilizing effect further enhances V 5+ The solvation sheath's structural strength prevents dehydration and condensation. Therefore, the electrolyte system of this invention overcomes the limitations of traditional sulfuric acid systems on vanadium concentration, providing a key material foundation for achieving higher energy density all-vanadium redox flow batteries.

[0055] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. The invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0056] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. An electrolyte for a vanadium redox flow battery, characterised in that, The composite additive comprises sulfuric acid, a vanadium ion active substance, and a lithium phosphate and soluble trivalent cerium salt.

2. The electrolyte of a vanadium redox flow battery according to claim 1, characterized in that, The soluble trivalent cerium salt is at least one of cerium sulfate, cerium nitrate, or cerium chloride.

3. The electrolyte of a vanadium redox flow battery according to claim 1, characterized in that, The lithium phosphate has a concentration of 0.05 mol / L to 0.15 mol / L in the electrolyte.

4. The electrolyte of a vanadium redox flow battery according to claim 1, characterized in that, The soluble trivalent cerium salt has a concentration of 0.01 mol / L to 0.10 mol / L of cerium ions in the electrolyte.

5. The electrolyte of a vanadium redox flow battery according to claim 1, characterized in that, The molar ratio of the lithium phosphate to the cerium ions is 1.5:1 to 5:

1.

6. The electrolyte of a vanadium redox flow battery according to claim 1, characterized in that, The concentration of the pentavalent vanadium ions in the electrolyte in a charged state is 2.2 mol / L to 2.8 mol / L.

7. The electrolyte of a vanadium redox flow battery according to claim 1, characterized in that, The concentration of the sulfuric acid is 2.5 mol / L to 5.0 mol / L.

8. A method of preparing an electrolyte for a vanadium redox flow battery as claimed in any one of claims 1 to 7, characterised in that, The method comprises the following steps: S1: dissolving a vanadium compound in a sulfuric acid solution, stirring, to obtain a basic vanadium electrolyte; S2: adding lithium phosphate to the basic vanadium electrolyte, stirring until completely dissolved; S3: continuing to add a soluble trivalent cerium salt to the solution obtained in step S2, stirring until completely dissolved, to obtain the composite additive electrolyte.

9. A full vanadium redox flow battery comprising a positive electrolyte; a negative electrolyte; an ion exchange membrane; a positive electrode; and a negative electrode, the positive electrolyte being the electrolyte of the full vanadium redox flow battery according to any one of claims 1 to 7.

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