Positive electrode electrolyte of all-vanadium redox flow battery, and flow battery

Abstract

Disclosed in the present invention are a positive electrode electrolyte of an all-vanadium redox flow battery, and a flow battery. The positive electrode electrolyte comprises an active material, a supporting electrolyte and an additive, wherein the active material comprises VO2 + / VO2+; and the additive comprises a transition metal salt, cations in the transition metal salt are selected from at least one of Ti4+, Cr3+, Mn2+, Co2+, Ni2+, Cu2+, Cd2+ and Ce3+, anions are selected from at least one of SO4 2-, HSO4 -, PO4 3-, HPO4 2-, H2PO4 -, BrO3 - and IO3 -, and the concentration of the transition metal salt is greater than or equal to 0.05 moL L-1. In the present application, by changing the chemical environment around VO2 + via transition metal ions, pentavalent vanadium ions are prevented from dehydration condensation to generate a V2O5 precipitate; therefore, the high-temperature stability of the electrolyte is significantly improved, and stable and efficient operation can be achieved at a high temperature.

Description

All-vanadium redox flow battery cathode electrolyte and redox flow battery Technical Field

[0001] The present application belongs to the field of energy storage technology, and in particular relates to an all-vanadium liquid flow battery positive electrode electrolyte and a liquid flow battery. Background Art

[0002] Achieving carbon peak and carbon neutrality is currently a key strategic goal for my country. However, my country's power system accounts for over 40% of CO2 emissions. Therefore, shifting the energy structure and developing a power system dominated by renewable energy is crucial. The construction of this power system is inseparable from the support of energy storage technology. Among various energy storage technologies, electrochemical energy storage has attracted widespread attention due to its high efficiency, fast response, and unrestricted geographical location, providing technical support for achieving the dual carbon goals.

[0003] As a type of electrochemical energy storage, flow batteries offer design flexibility and high safety. All-vanadium flow batteries are currently the most mature and widely used flow battery system. They utilize the valence state changes of vanadium ions at the positive and negative electrodes to store and release electrical energy. They offer high safety and excellent cycle performance, making them a leading technology for large-scale energy storage.

[0004] However, the cathode electrolyte of all-vanadium flow battery is unstable at high temperature, VO2 + Ions easily dehydrate and condense to form V2O5 precipitates, limiting the operating temperature range of all-vanadium flow batteries. Excessive temperature rise in a region of the system can lead to precipitation, rendering the entire system useless. Therefore, the high-temperature stability of all-vanadium electrolytes is crucial. To ensure electrolyte stability during battery operation, a heat exchange system is often required for temperature regulation, which increases system costs and power consumption. Therefore, improving the high-temperature stability of all-vanadium flow battery electrolytes has become a key issue in promoting their further development.

[0005] Summary of the Invention

[0006] In view of this, the present application provides a positive electrode electrolyte for an all-vanadium liquid flow battery and a liquid flow battery, the main purpose of which is to solve the technical problem that the positive electrode electrolyte of the all-vanadium liquid flow battery is unstable at high temperatures.

[0007] In one aspect, the present application provides a positive electrode electrolyte for an all-vanadium redox flow battery, wherein the positive electrode electrolyte for the all-vanadium redox flow battery comprises an active material, a supporting electrolyte, and an additive;

[0008] Wherein, the active substance includes VO2 + / VO 2+ ;

[0009] The additive includes a transition metal salt.

[0010] The all-vanadium redox flow battery electrolyte containing transition metal ions proposed in this application uses VO2 + / VO 2+ As the active material, the negative electrode uses V 2+ / V 3+ As the active material, sulfuric acid is used as the supporting electrolyte, and inorganic salts containing transition metal ions are used as additives to improve the high-temperature instability of the cathode electrolyte of the all-vanadium flow battery, thereby improving the capacity retention rate and cycle stability of the all-vanadium flow battery during high-temperature operation. + The change in the surrounding chemical environment (water and ambient air) prevents the dehydration and condensation of pentavalent vanadium ions to form V2O5 precipitation, significantly improving the electrolyte's high-temperature stability. All-vanadium redox flow batteries employing the electrolyte described in this application can achieve stable and efficient operation at high temperatures. Furthermore, due to the altered chemical environment surrounding the vanadium ions, crosstalk in the electrolyte is significantly reduced, resulting in all-vanadium redox flow batteries utilizing this electrolyte exhibiting higher coulombic efficiency.

[0011] Optionally, the counter anion in the cathode electrolyte of the all-vanadium redox flow battery is SO4 2- .

[0012] Optionally, the cation in the transition metal salt is selected from Ti 4+ Cr 3+ 、Mn 2+ 、Co 2+ 、Ni 2+ 、Cu 2+ 、Cd 2+ and Ce 3+ At least one of .

[0013] Optionally, the anion in the transition metal salt is selected from SO4 2- 、HSO4 - PO4 3- 、HPO4 2- 、H2PO4 - BrO3 - and IO3 - At least one of the following, Cl cannot be used - .

[0014] Preferably, the cation is selected from Ti 4+ Cr 3+ , or Ce 3+ .

[0015] Preferably, the anion is selected from SO4 2- 、HSO4 - PO4 3- 、HPO4 2-、H2PO4 - .

[0016] Optionally, the concentration of the transition metal salt is greater than or equal to 0.05 mol L -1 ~0.8mol L -1 .

[0017] Optionally, the concentration of the transition metal salt is 0.2 to 0.3 mol L -1 .

[0018] Optionally, the concentration of the transition metal salt is selected from 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 mol L -1 Any value in between or any range of values ​​between them.

[0019] Optionally, the positive electrode electrolyte is an acidic solution.

[0020] Optionally, the concentration of vanadium ions in the active material is 0.1 to 2.5 mol L -1 .

[0021] Optionally, the concentration of vanadium ions in the active material is 1.5 to 2.0 mol L -1 .

[0022] Optionally, the concentration of vanadium ions in the active material is selected from 0.1, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, 2.2, 2.5 mol L -1 Any value in between or any range of values ​​between them.

[0023] Optionally, the supporting electrolyte comprises sulfuric acid.

[0024] Optionally, the concentration of the sulfuric acid is 1 to 6 mol L -1 .

[0025] Optionally, the concentration of the sulfuric acid is 2 to 3 mol L -1 .

[0026] Optionally, the concentration of the sulfuric acid is selected from 1, 2, 3, 4, 5, 6 mol L -1 Any value in between or any range of values ​​between them.

[0027] Optionally, the Cl - Not more than 0.15 mol L -1 .

[0028] In a second aspect, the present application provides an all-vanadium redox flow battery, comprising a positive electrode electrolyte and a negative electrode electrolyte; the positive electrode electrolyte is the above-mentioned all-vanadium redox flow battery positive electrode electrolyte.

[0029] Optionally, the negative electrode electrolyte includes an active material, a supporting electrolyte and an additive;

[0030] Wherein, the active substance includes V 2+ / V 3+ ;

[0031] The additive includes a transition metal salt.

[0032] Optionally, the supporting electrolyte comprises sulfuric acid.

[0033] Optionally, the vanadium ion concentration in the positive electrode electrolyte is equal to the vanadium ion concentration in the negative electrode electrolyte.

[0034] Optionally, the transition metal salt in the negative electrode electrolyte is selected from at least one of the transition metal salts in the positive electrode electrolyte; (the transition metal salt in the positive electrode electrolyte and the transition metal salt in the negative electrode electrolyte may be the same or different).

[0035] Optionally, the transition metal salt in the negative electrode electrolyte is the same as the transition metal salt in the positive electrode electrolyte (the same type of substance and / or the same concentration are selected to prevent the positive electrode ions and the negative electrode ions from cross-contaminating).

[0036] The formula of the positive electrode electrolyte in this application is the same as that of the negative electrode liquid. Through different charge and discharge operations, VO2 + / VO 2+ Ion positive electrolyte and V 2+ / V 3+ ion negative electrolyte.

[0037] The vanadium concentrations of the positive and negative electrodes in this application are equal, the positive electrode is the sum of the concentrations of tetravalent and pentavalent vanadium ions, and the negative electrode is the sum of the concentrations of divalent and trivalent vanadium ions.

[0038] The high temperature environment of the all-vanadium redox flow battery in this application is preferably 40-60°C.

[0039] Compared with the prior art, this application has the following beneficial effects:

[0040] (1) The present application provides an all-vanadium flow battery electrolyte containing transition metal ions, which changes the chemical environment around the vanadium ions by adding transition metal ion salt additives, thereby inhibiting VO2 +The side reaction of dehydration condensation of ions to generate V2O5 significantly improves the thermal stability of the electrolyte. The all-vanadium redox flow battery operated with the electrolyte exhibits excellent capacity retention and cycle stability at high temperatures.

[0041] (2) The present application provides an all-vanadium liquid flow battery electrolyte containing transition metal ions, which has low battery polarization and good voltage efficiency. Compared with batteries without additives, the addition of transition metal salts does not significantly increase the solution impedance and charge transfer impedance of the electrolyte, thereby achieving higher voltage efficiency, and the performance is comparable to that of electrolytes without additives.

[0042] (3) The present application provides an all-vanadium liquid flow battery electrolyte containing transition metal ions. Since the transition metal salt changes the chemical environment around the vanadium ions, the all-vanadium liquid flow battery using the electrolyte described in the present application can significantly reduce the cross-talk of active substances in the electrolyte, thereby improving the coulombic efficiency of the battery.

[0043] (4) The present application provides an all-vanadium liquid flow battery electrolyte containing transition metal ions. The additive can exist stably under strongly acidic and strongly oxidizing conditions, does not react with the original electrolyte components, does not participate in the electrochemical reaction, and has almost no effect on the original electrochemical reaction of the all-vanadium liquid flow battery, thereby ensuring the long-term stable operation of the all-vanadium liquid flow battery.

[0044] (5) The present application provides an all-vanadium liquid flow battery electrolyte containing transition metal ions, which has abundant additive sources, is cheap and easy to obtain, has high solubility, is simple to prepare, and is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG1 is a digital image of the pentavalent vanadium ion electrolyte solution state at the beginning and 30 days after heating in a 50° C. water bath in Example 1 of the present application;

[0046] FIG2 is a graph showing battery efficiency versus charge and discharge capacity after 150 cycles of the battery in Example 1 of the present application;

[0047] FIG3 is a constant current charge and discharge curve diagram of the battery in Example 1 of the present application;

[0048] FIG4 is a digital image of the state of the pentavalent vanadium ion electrolyte solution at the beginning and 7 hours after heating in a 50° C. water bath in Comparative Example 1 of the present application;

[0049] FIG5 is a graph showing battery efficiency versus charge and discharge capacity after 50 cycles of the battery in Comparative Example 1 of the present application;

[0050] FIG6 is a constant current charge and discharge curve diagram of the battery in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0051] The present application will be further described below in conjunction with specific embodiments. The following description is merely a few embodiments of the present application and does not limit the present application in any form. Although the present application discloses the preferred embodiments below, it is not intended to limit the present application. Any person skilled in the art who, without departing from the scope of the technical solution of the present application, makes slight changes or modifications using the above disclosed technical content is equivalent to an equivalent implementation case and falls within the scope of the technical solution.

[0052] Unless otherwise specified, the raw materials in the examples of this application were purchased from commercial channels and used directly without any special treatment.

[0053] Example 1

[0054] Preparation of all-vanadium redox flow battery electrolyte:

[0055] The electrolyte consists of 1.5 mol L -1 of vanadyl sulfate, 2.25 mol L -1 of sulfuric acid, 0.3 mol L -1 An aqueous solution composed of chromium sulfate (the positive electrolyte and the negative electrolyte have the same formula).

[0056] Assembly of all-vanadium redox flow battery:

[0057] The battery structure includes stainless steel end plates, graphite plate current collectors, two pieces of carbon felt with an area of ​​6×8 cm and a thickness of 5 mm as positive and negative electrodes, commercial Nafion115 or PBI as diaphragms, annular silicone pads, annular liquid flow frames, electrolyte storage tanks and pumps, and pipelines. The battery is assembled according to the conventional liquid flow battery structure (end plates, annular silicone pads, current collectors, annular silicone pads, annular liquid flow frames with positive electrodes inside, annular silicone pads, diaphragms, annular silicone pads, annular liquid flow frames with sodium electrodes inside, annular silicone pads, current collectors, annular silicone pads, and end plates stacked in sequence) and assembly process.

[0058] Thermal stability test of pentavalent vanadium electrolyte for all-vanadium redox flow battery:

[0059] Preparation of pentavalent vanadium electrolyte: The volume of positive electrolyte is 100 mL, the volume of negative electrolyte is 55 mL, and the flow rate of electrolyte is 60 ml min -1 , PBI membrane as separator. Constant current charging was adopted, and the current density was from 200mA cm -2 Gradually decrease to 10 mA cm -2The charge cutoff voltage is 1.7V. After charging, transfer 20mL of the positive electrolyte, which is the pentavalent vanadium electrolyte, to a 40mL glass bottle and place it in a 50°C water bath. Observe and record the formation of a reddish-brown precipitate. A value greater than a certain time indicates that no reddish-brown precipitate was observed during that time period; a value less than a certain time indicates that reddish-brown precipitate was observed during that time period; and a value between two times indicates that precipitate was observed between those two times.

[0060] All-vanadium redox flow battery cycle performance test:

[0061] The initial volume of the positive electrode electrolyte used in the battery performance test was 120 mL, and the volume of the negative electrode electrolyte was 60 mL. The flow rate of the electrolyte was about 60 mL min -1 The battery cycle performance test adopts constant current charge and discharge mode, and the current density used is 80mA cm -2 . During the test, the charging cutoff voltage was 1.65V, and the discharging cutoff voltage was 0.8V. After the first cycle of charging, 60mL of positive electrode electrolyte was taken, and the battery was connected to continue the charge and discharge cycle. The coulomb efficiency, voltage efficiency, energy efficiency and charge and discharge capacity under different cycle numbers were recorded by the Arbin charge and discharge instrument. The energy efficiency in the table is the average efficiency of the first 10 cycles. The stable cycle number means that the coulomb efficiency, voltage efficiency, energy efficiency and charge and discharge capacity have not changed dramatically in the cycle. At the same time, the attenuation of various parameters during the long cycle process is within the expected range, which can still ensure the normal operation of the battery, and the battery can be restored to its original performance by means of regenerating the electrolyte.

[0062] Examples 2 to 17

[0063] The difference between Examples 2 to 17 and Example 1 is that the vanadium ion concentration, sulfuric acid concentration, additive type, and additive concentration are different, as shown in Table 1; the battery assembly process, thermal stability test, and cycle performance test are exactly the same as those in Example 1.

[0064] Example 18

[0065] Preparation of all-vanadium redox flow battery electrolyte:

[0066] The electrolyte consists of 1.5 mol L -1 of vanadyl sulfate, 2.25 mol L -1 of sulfuric acid, 0.27 molL -1 of chromium sulfate, 0.03 mol L -1 Chromium chloride aqueous solution

[0067] The assembly process, thermal stability test and cycle performance test of the all-vanadium redox flow battery in Example 18 are exactly the same as those in Example 1.

[0068] Example 19

[0069] Preparation of all-vanadium redox flow battery electrolyte:

[0070] The electrolyte consists of 1.5 mol L -1 of vanadyl sulfate, 2.25 mol L -1 of sulfuric acid, 0.25 molL -1 of chromium sulfate, 0.05 mol L -1 Chromium chloride aqueous solution

[0071] The assembly process, thermal stability test and cycle performance test of the all-vanadium redox flow battery in Example 18 are exactly the same as those in Example 1.

[0072] Example 20

[0073] Preparation of all-vanadium redox flow battery electrolyte:

[0074] The electrolyte consists of 1.5 mol L -1 of vanadyl sulfate, 2.25 mol L -1 of sulfuric acid, 0.05 mol L -1 of chromium sulfate, 0.05 mol L -1 of titanium sulfate, 0.05 mol L -1 Manganese sulfate, 0.05 mol L -1 of cobalt sulfate, 0.05 mol L -1 of nickel sulfate, 0.05 mol L -1 of copper sulfate to form an aqueous solution.

[0075] The assembly process, thermal stability test and cycle performance test of the all-vanadium redox flow battery in Example 19 are exactly the same as those in Example 1.

[0076] Comparative Example 1

[0077] Preparation of all-vanadium redox flow battery electrolyte:

[0078] The electrolyte consists of 1.5 mol L -1 of vanadyl sulfate, 2.25 mol L -1 An aqueous solution of sulfuric acid.

[0079] The assembly process, thermal stability test and cycle performance test of the all-vanadium redox flow battery in Comparative Example 1 are exactly the same as those in Example 1.

[0080] Comparative Examples 2 to 10

[0081] Comparative Examples 2 to 10 differ from Comparative Example 1 in that the vanadium ion concentration, sulfuric acid concentration, additive type, and additive concentration are different, as shown in Table 1. The battery assembly process, thermal stability test, and cycle performance test are exactly the same as those in Example 1.

[0082] Comparative Example 11

[0083] Preparation of all-vanadium redox flow battery electrolyte:

[0084] The electrolyte consists of 1.5 mol L -1 of vanadyl sulfate, 2.25 mol L -1 of sulfuric acid, 0.23 mol -1 of chromium sulfate, 0.07 mol L -1 of chromium chloride to form an aqueous solution.

[0085] The assembly process, thermal stability test and cycle performance test of the all-vanadium redox flow battery in Comparative Example 11 are exactly the same as those in Example 1.

[0086] Table 1. Examples 1 to 17 and Comparative Examples 1 to 5

[0087] The thermal stability test data from Example 1 in Table 1 demonstrates that the addition of an inorganic transition metal salt (Cr2(SO4)3) as an additive prolongs the time it takes for pentavalent vanadium ions to form vanadium pentoxide precipitates, significantly improving the thermal stability of the all-vanadium flow battery electrolyte (Figure 1). Batteries operating at high temperatures using the invented all-vanadium flow battery electrolyte exhibit excellent cycle stability and capacity retention, significantly increasing the number of stable cycles, and exhibiting excellent coulombic efficiency and energy efficiency (Figure 2).

[0088] The thermal stability test results for Comparative Example 1 in Table 1 show that, due to the absence of a transition metal salt, the time it takes for pentavalent vanadium ions to precipitate vanadium pentoxide is relatively short, resulting in poor thermal stability of the electrolyte (Figure 4). During high-temperature operation of the battery, precipitation can form in the positive electrolyte, causing pipe blockage and, in turn, battery capacity loss (Figure 5).

[0089] Combining Example 1 and Comparative Example 1, the charge and discharge curves are shown in Figures 3 and 6, Cr 3+ The addition of ions does not participate in the electrochemical reaction, and the entire reaction process still only involves the electrochemical reaction of the all-vanadium liquid flow battery.

[0090] From the data of high temperature stability time of Example 1, Example 2, Example 3, Examples 8-13, Comparative Example 2, Comparative Example 3, Comparative Examples 7-9 in Table 1, it can be seen that the type of cation selected as the additive to the electrolyte has a great influence on the thermal stability of the electrolyte.3+ 、Ce 3+ 、Ti 4+ 、Cu 2+ 、Co 2+ 、Mn 2+ 、Ni 2+ 、Cd 2+ When these transition metals are added, they further enhance the chemical environment surrounding the vanadium ions, prolonging the precipitation time of pentavalent vanadium ions to form vanadium pentoxide, thereby improving the thermal stability of the all-vanadium flow battery electrolyte. This improved electrolyte thermal stability allows the battery to cycle stably for longer periods, facilitating the long-term energy storage application of all-vanadium flow batteries. Example 20 also demonstrates that using a combination of cation additives in a certain ratio can also improve the thermal stability of the electrolyte.

[0091] Example 1, Example 3 and Comparative Example 10 illustrate that anions must exclude impurities Cl - , Cl - It has a negative effect on the high temperature stability of the electrolyte. The comparison of Examples 18 and 19 with Comparative Example 11 shows that Cl - The concentration should not exceed 0.15 mol L -1 , while Cl - The lower the concentration, the better the stabilization effect.

[0092] In combination with Example 1, Example 4, 6-7 and Comparative Examples 4-5, the concentration of the additive will also have a great impact on the thermal stability of the all-vanadium liquid flow battery electrolyte. When chromium sulfate is used as an additive, the higher the concentration of the additive, the longer the stability time of the pentavalent vanadium ion electrolyte. When the concentration of the additive is lower than a certain concentration, the stability time of the electrolyte cannot meet the requirements of high-temperature operation of the battery, resulting in capacity loss of the battery. When the concentration of the additive is large, the higher the ion concentration will affect the physical properties such as viscosity and conductivity of the electrolyte, thereby affecting the voltage efficiency of the battery. Therefore, the concentration of the transition metal salt is 0.05 mol L -1 ~0.8mol L -1 The optimal concentration is 0.2~0.3 mol L considering thermal stability and battery efficiency. -1 .

[0093] In combination with Examples 1-3, Examples 8-13 and Comparative Examples 6-7, compared with other additives that improve the thermal stability of the electrolyte, the transition metal additives protected by this patent can simultaneously ensure that the electrolyte has good thermal stability (at least 10 days or more) and good energy efficiency (at least 80% or more), meeting the long-term stable and efficient operation of the battery.

[0094] By comparing the thermal stability of Example 5 and Comparative Example 6, the transition metal ion-containing all-vanadium flow battery electrolyte increases the vanadium ion concentration to 2 mol L -1 The stability time of the pentavalent vanadium ion electrolyte can still meet the thermal stability requirements of the battery at high temperature operation. The electrolyte can effectively widen the battery operating temperature window, improve the battery's energy density, and ensure the battery's energy efficiency.

[0095] In combination with Example 1 and Examples 14-17, the concentration of vanadium within the range (0.1 to 2.5 mol L -1 ) and sulfuric acid concentration (1~6mol L -1 ) changes in the electrolyte can still maintain good thermal stability, but considering the energy efficiency and the energy density and low temperature performance of the actual application process, it is more appropriate to choose a vanadium ion concentration of 1.5 to 2.0 mol L -1 The concentration of sulfuric acid is 2-3 mol L -1 .

[0096] Based on the above analysis, the all-vanadium liquid flow battery electrolyte containing transition metal ions in this application has good thermal stability. The all-vanadium liquid flow battery operated with it has excellent capacity retention and cycle stability at high temperatures, and has higher coulombic efficiency.

[0097] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A positive electrolyte for an all-vanadium redox flow battery, characterized in that: The positive electrode electrolyte of the all-vanadium liquid flow battery comprises an active material, a supporting electrolyte and an additive; Wherein, the active substance includes VO2 + / VO 2+ ; The additive includes a transition metal salt.

2. The positive electrode electrolyte of an all-vanadium redox flow battery according to claim 1, characterized in that: The cation in the transition metal salt is selected from Ti 4+ Cr 3+ , Mn 2+ 、Co 2+ 、Ni 2+ , Cu 2+ 、Cd 2+ and Ce 3+ At least one of .

3. The positive electrode electrolyte of an all-vanadium redox flow battery according to claim 1, characterized in that: The anion in the transition metal salt is selected from SO4 2- 、HSO4 - PO4 3- 、HPO4 2- 、H2PO4 - BrO3 - and IO3 - At least one of .

4. The positive electrode electrolyte of an all-vanadium redox flow battery according to claim 1, characterized in that: The concentration of the transition metal salt is 0.05 mol L -1 ~0.8mol L -1 .

5. The positive electrode electrolyte of an all-vanadium redox flow battery according to claim 1, characterized in that: The concentration of the transition metal salt is 0.2 to 0.3 mol L -1 .

6. The positive electrode electrolyte of an all-vanadium redox flow battery according to claim 1, characterized in that: The positive electrode electrolyte is an acidic solution; The concentration of vanadium ions in the active material is 0.1 to 2.5 mol L -1 .

7. The positive electrode electrolyte of an all-vanadium redox flow battery according to claim 1, characterized in that: The concentration of vanadium ions in the active material is 1.5 to 2.0 mol L -1 .

8. The positive electrode electrolyte of an all-vanadium redox flow battery according to claim 1, characterized in that: The supporting electrolyte includes sulfuric acid.

9. The positive electrode electrolyte of the all-vanadium redox flow battery according to claim 8, characterized in that: The concentration of sulfuric acid is 1 to 6 mol L -1 .

10. The positive electrode electrolyte of an all-vanadium redox flow battery according to claim 8, characterized in that: The concentration of sulfuric acid is 2 to 3 mol L -1 .

11. A positive electrode electrolyte for an all-vanadium redox flow battery according to any one of claims 1 to 10, characterized in that: It is best not to contain Cl - ; When there is Cl - When impurities are present, Cl - The concentration should be less than or equal to 0.15 mol L -1 , preferably less than or equal to 0.10 mol L -1 , more preferably less than or equal to 0.03 mol L -1 , the best is Cl-free - .

12. An all-vanadium redox flow battery, comprising a positive electrode electrolyte and a negative electrode electrolyte; characterized in that: The positive electrode electrolyte is the positive electrode electrolyte of the all-vanadium redox flow battery according to any one of claims 1 to 11.

13. The all-vanadium redox flow battery according to claim 12, further characterized in that the negative electrode electrolyte comprises an active material, a supporting electrolyte and an additive; in, The active substance includes V 2+ / V 3+ ; The additive includes a transition metal salt.

14. The all-vanadium liquid flow battery according to claim 13, further characterized in that the supporting electrolyte comprises sulfuric acid.

15. The all-vanadium redox flow battery according to claim 13, further characterized in that the transition metal salt in the negative electrode electrolyte is selected from at least one of the transition metal salts in the positive electrode electrolyte. 16 . The all-vanadium redox flow battery according to claim 13 , further characterized in that the transition metal salt in the negative electrode electrolyte is the same as the transition metal salt in the positive electrode electrolyte.

17. The all-vanadium liquid flow battery according to claim 13, further characterized in that the vanadium ion concentration in the positive electrode electrolyte is equal to the vanadium ion concentration in the negative electrode electrolyte.

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