Preparation method for 3 / 4-valent vanadium sulfate-hydrochloric acid electrolyte

Abstract

The present invention provides a preparation method for a 3 / 4-valent vanadium sulfate-hydrochloric acid electrolyte, comprising the following steps: adding hydrochloric acid into a 4-valent vanadium sulfate electrolyte to prepare a 4-valent vanadium sulfate-hydrochloric acid electrolyte; preparing a (4+x)-valent vanadium sulfate electrolyte; using the (4+x)-valent vanadium sulfate electrolyte and the 4-valent vanadium sulfate-hydrochloric acid electrolyte respectively as positive and negative electrode electrolytes of an all-vanadium redox flow battery to perform charging electrolysis, to obtain a (4+y)-valent vanadium sulfate electrolyte and a 3-valent vanadium sulfate-hydrochloric acid electrolyte at positive and negative electrodes, respectively; and adding oxalic acid into the obtained (4+y)-valent vanadium sulfate electrolyte for reduction to re-obtain the (4+x)-valent vanadium sulfate electrolyte, wherein the re-obtained (4+x)-valent vanadium sulfate electrolyte can be further used to prepare the 3-valent vanadium sulfate-hydrochloric acid electrolyte. The preparation method for a 3 / 4-valent vanadium sulfate-hydrochloric acid electrolyte provided by the present invention features high efficiency and low costs, and the obtained 3 / 4-valent vanadium sulfate-hydrochloric acid electrolyte has a high concentration and a wide operating temperature range.

Description

3. Preparation method of 4-valent sulfate vanadium electrolyte Technical Field

[0001] The present invention relates to the technical field of all-vanadium redox flow batteries, and in particular to a method for preparing a trivalent or tetravalent vanadium sulfate electrolyte. Background Art

[0002] All-vanadium liquid flow batteries use vanadium electrolytes of different valence states to circulate from bottom to top through the positive and negative electrodes to carry out electrochemical reactions, realizing the mutual conversion of electrical energy and chemical energy. They combine high power, high energy, high efficiency, and fast response, and have high safety, long life, low cost, pollution-free, and easy site selection. They have become the preferred technology for large-capacity and long-term energy storage, and are the key technical support for achieving the energy revolution and dual carbon goals.

[0003] All-vanadium redox flow batteries typically consist of a power unit (stack), an energy storage unit (vanadium electrolyte and storage tank), a vanadium electrolyte delivery unit (piping, valves, circulation pumps, heat exchangers, etc.), and a battery management system. The stack consists of end plates that fasten the inlet plate, current collector, and multiple monolithic cells. The monolithic cells are composed of positive and negative electrode flow frame plates, positive and negative electrodes, ion-conducting membranes, bipolar plates, and seals.

[0004] The electrochemical reaction, standard electrode potential and standard electromotive force of the all-vanadium redox flow battery are as follows:

[0005] Negative electrode: V 2+ -e= V 3+ E°=-0.25V

[0006] Positive electrode: VO2 + +2H + +e=VO 2+ +H2O E°=1.00V

[0007] Battery: V 2+ +VO2 + +2H + =V 3+ +VO 2+ +H2O E°=1.25V

[0008] The vanadium electrolyte usually prepared is 3.5-valent vanadium sulfate electrolyte, that is, equimolar trivalent vanadium ions V 3+ and tetravalent vanadium ion VO 2+However, when 3.5-valent vanadium electrolyte is used as the positive and negative electrolytes in all-vanadium flow batteries, it must undergo a pre-charging process. This involves converting the 3.5-valent vanadium electrolyte to a 4-valent vanadium electrolyte at the positive electrode and to a 3-valent vanadium electrolyte at the negative electrode before normal all-vanadium flow battery charging and discharging can proceed. However, this pre-charging process for the 3.5-valent vanadium electrolyte is not only time-consuming and consumes a huge amount of electricity, but also causes irreversible water migration between the positive and negative vanadium electrolytes, widening the concentration difference between the positive and negative vanadium electrolytes and reducing the capacity of the all-vanadium flow battery and the stability of the vanadium electrolyte.

[0009] In addition, the stability of vanadium sulfate electrolyte at medium and low temperatures is poor, and VOSO4 crystals are easily precipitated during use. Therefore, the concentration of vanadium sulfate electrolyte is low, usually around 1.6M. Once the concentration exceeds 2M, a large amount of VOSO4 crystals will precipitate from the positive electrode vanadium sulfate electrolyte even at room temperature. The precipitation of VOSO4 crystals not only greatly reduces the concentration of tetravalent vanadium ions VO in the positive electrode vanadium electrolyte, but also greatly reduces the concentration of tetravalent vanadium ions VO in the positive electrode vanadium electrolyte. 2+ The concentration and capacity of the all-vanadium liquid flow battery can be affected, and it is easy to cause the ceramic pump shaft and graphite sleeve of the positive electrode vanadium electrolyte circulation pump to stick and lock, making it impossible to start the pump.

[0010] What is more serious is that the high temperature stability of vanadium sulfate electrolyte is extremely poor. When the temperature exceeds 40℃, the pentavalent vanadium ion VO2 in the positive electrode vanadium electrolyte will + It is very easy to absorb hot water and precipitate a large amount of insoluble V2O5:

[0011] 2VO2 + +H2O=V2O5↓+2H + , ΔH>0

[0012] The precipitation of V2O5 not only greatly reduces the pentavalent vanadium ion VO2 in the positive electrolyte, but also greatly reduces the + The concentration and capacity of the all-vanadium liquid flow battery are greatly affected, and it is very easy to clog the microporous flow channels of the graphite felt electrode and the branch flow channels of the liquid frame plate in the all-vanadium liquid flow battery stack, which in turn leads to failure of the vanadium electrolyte, corrosion of the bipolar plates, and scrapping of the battery stack. Therefore, the all-vanadium liquid flow battery using vanadium sulfate electrolyte must be equipped with a heat exchanger to control the temperature of the vanadium sulfate electrolyte below 40°C. However, the all-vanadium liquid flow battery equipped with a heat exchanger is not only complex in structure and increases the cost, but the heat exchanger itself consumes a lot of electricity, resulting in the energy efficiency of the all-vanadium liquid flow battery energy storage system reduced by about 10%, thereby significantly increasing the cost of using the all-vanadium liquid flow battery and greatly reducing the rate of return on investment.

[0013] Chinese patent ZL 201210407114.9 discloses a method for preparing a trivalent or tetravalent vanadium sulfate electrolyte, comprising the following steps:

[0014] (3) The nmol VO(HSO4)2 electrolyte mother solution and the nmol VO(HSO4)2+(1.5~2)nmol HCl negative electrode electrolyte mother solution are placed at the positive and negative electrodes of the all-vanadium redox flow battery for charging, respectively. After full charge, the nmol VO2HSO4+nmol H2SO4 positive electrode electrolyte mother solution (I) is obtained at the positive electrode; and the nmol V(HSO4)2Cl+(0.5~1)nmol HCl negative electrode electrolyte is obtained at the negative electrode.

[0015] (4) Add 0.5 nmol H2C2O4·2H2O to the nmol VO2HSO4+nmol H2SO4 positive electrode electrolyte mother solution (I) obtained in step (3), and react at 60-80°C until no bubbles are generated to obtain nmol VO(HSO4)2 positive electrode electrolyte mother solution (II).

[0016] (5) Add (1.5-2) nmol HCl to the nmol VO(HSO4)2 positive electrode electrolyte mother solution (II) obtained in step (4) to obtain nmol VO(HSO4)2+(1.5-2) nmol HCl positive electrode electrolyte.

[0017] A large number of experiments have shown that the above method has two serious flaws:

[0018] First, this method requires that nmol VO(HSO4)2 electrolyte mother solution and nmol VO(HSO4)2+(1.5~2)nmol HCl negative electrode electrolyte mother solution be fully charged at the same time, that is, the tetravalent vanadium ions VO in the positive electrode electrolyte must be fully charged. 2+ All oxidized to pentavalent vanadium ions VO2 + At the same time, the 4-valent vanadium ion VO in the negative electrode electrolyte 2+ All reduced to trivalent vanadium ions V 3+ , in order to obtain n mol VO2HSO4+n mol H2SO4 positive electrode electrolyte mother solution (I) at the positive electrode, and n mol V(HSO4)2Cl+(0.5~1)n mol HCl negative electrode electrolyte at the negative electrode, and this takes a very long time to complete, partly because HSO4 in VO(HSO4)2 electrolyte mother solution - Ionization is very insufficient, H + The concentration is low, the conductivity is low, and the charging reaction rate is slow. On the other hand, more importantly, as the charging reaction proceeds, the tetravalent vanadium ions VO in the positive and negative electrolytes 2+ The concentration is getting lower and lower and tends to 0, the charging reaction rate is getting slower and slower and tends to 0, and the charging current is getting smaller and smaller and tends to 0, so it takes a long time to convert the 4-valent vanadium ion VO 2+All oxidized to pentavalent vanadium ions VO2 + , the tetravalent vanadium ion VO 2+ All reduced to trivalent vanadium ions V 3+ .

[0019] Secondly, this method requires adding 0.5n mol H2C2O4·2H2O oxalic acid to the nmol VO2HSO4+n mol H2SO4 positive electrode electrolyte mother solution (I) to completely reduce it to nmol VO(HSO4)2 positive electrode electrolyte mother solution (II). It also takes a long time to complete because as the reduction reaction proceeds, the pentavalent vanadium ion VO2 in the positive electrode electrolyte mother solution (I) + The concentration and oxalic acid concentration will decrease and approach 0 at the same time, and the reaction rate will slow down and approach 0, so it will take a long time to convert the pentavalent vanadium ion VO2 in the positive electrode electrolyte mother solution (I) into + All reduced to tetravalent vanadium ions VO 2+ ;

[0020] If the incompletely reduced positive electrolyte mother solution (I) is added with hydrochloric acid and used as the positive electrolyte for charging the all-vanadium redox flow battery, the unreacted oxalic acid in the positive electrolyte will react with the newly generated pentavalent vanadium ions VO2 + Oxidation-reduction reaction occurs, generating a large amount of CO2 bubbles in the positive electrode electrolyte, which will frequently cause the positive electrode electrolyte magnetic circulation pump to be disconnected, idle, or even burn out, making it impossible for the all-vanadium redox flow battery to charge smoothly.

[0021] Therefore, there is an urgent need for an efficient and low-cost method for preparing trivalent and tetravalent vanadium sulfate electrolyte. Summary of the Invention

[0022] The technical problem to be solved by the present invention is to provide an efficient and low-cost method for preparing a high-concentration, wide-operating-temperature 3.4-valent vanadium sulfate electrolyte, so as to overcome the defects of the current electrolytic preparation methods of 3.5-valent vanadium sulfate electrolyte and 3.4-valent vanadium sulfate electrolyte.

[0023] In order to solve the above technical problems, the present invention provides a method for preparing a trivalent or tetravalent vanadium sulfate electrolyte, comprising the following steps:

[0024] adding hydrochloric acid to a tetravalent vanadium sulfate electrolyte to prepare a tetravalent vanadium sulfate hydrochloride electrolyte;

[0025] preparing a (4+x)-valent vanadium sulfate electrolyte;

[0026] The (4+x)-valent vanadium sulfate electrolyte and the tetravalent vanadium sulfate hydrochloride electrolyte are used as the positive and negative electrolytes of the all-vanadium redox flow battery for charging and electrolysis, respectively, to obtain a (4+y)-valent vanadium sulfate electrolyte and a trivalent vanadium sulfate hydrochloride electrolyte at the positive and negative electrodes, respectively, wherein 1>y>x>0;

[0027] The (4+y)-valent vanadium sulfate electrolyte is reduced with oxalic acid to obtain a (4+x)-valent vanadium sulfate electrolyte, wherein x≥0.1 and y≥0.9;

[0028] The (4+x)-valent vanadium sulfate electrolyte obtained again is continued to be used as the positive and negative electrolytes of the all-vanadium liquid flow battery for charging and electrolysis together with the 4-valent vanadium sulfate hydrochloride electrolyte, and the 3-valent vanadium sulfate hydrochloride electrolyte is prepared at the negative electrode.

[0029] Furthermore, the preparation method of the (4+x)-valent vanadium sulfate electrolyte comprises:

[0030] The tetravalent vanadium sulfate electrolyte and the tetravalent vanadium sulfate hydrochloride electrolyte are used as the positive and negative electrolytes of the all-vanadium redox flow battery, respectively, and the (4+z)-valent vanadium sulfate electrolyte is obtained at the positive electrode, and the trivalent vanadium sulfate hydrochloride electrolyte is obtained at the negative electrode;

[0031] The (4+z)-valent vanadium sulfate electrolyte is reduced by adding oxalic acid to obtain a (4+x)-valent vanadium sulfate electrolyte, wherein 1>z>x>0.

[0032] Furthermore, the tetravalent vanadium sulfate electrolyte is prepared by reducing vanadium pentoxide with sulfuric acid and oxalic acid solution.

[0033] The present invention provides a method for preparing trivalent and tetravalent vanadium sulfate electrolytes. Unlike conventional electrolytic preparation of vanadium electrolytes in which both the positive and negative electrolytes are tetravalent vanadium electrolytes, the present invention provides a positive electrode electrolyte with a vanadium valence between four and five. By using the tetravalent vanadium sulfate electrolyte and the (4+x)-valent vanadium sulfate electrolyte as the negative and positive electrolytes of an all-vanadium redox flow battery, respectively, for charging and electrolysis, a trivalent vanadium sulfate electrolyte is directly obtained at the negative electrode. Oxalic acid is then added to the (4+y)-valent vanadium sulfate electrolyte obtained at the positive electrode in a stoichiometric ratio to reduce the resulting (4+x)-valent vanadium sulfate electrolyte, where 1>y>x>0. This cycle is repeated to continuously obtain a trivalent vanadium sulfate electrolyte at the negative electrode, while the corresponding tetravalent vanadium sulfate electrolyte can be directly obtained by adding hydrochloric acid to the tetravalent vanadium sulfate electrolyte.

[0034] Therefore, the method for preparing a 3- and 4-valent vanadium sulfate electrolyte provided by the present invention has the following beneficial effects:

[0035] First, during charging and electrolysis of the all-vanadium liquid flow battery of the present invention, it is only necessary to oxidize the vanadium in the positive electrode electrolyte from a valence of (4+x) to a valence of (4+y), where 1>y>x>0. That is, it is only necessary to oxidize part of the tetravalent vanadium to a valence of pentavalent vanadium, and it is not necessary to oxidize all of the tetravalent vanadium to a valence of pentavalent vanadium. Therefore, the electrolysis reaction rate is fast, which greatly shortens the time of the electrolysis step and improves the preparation efficiency.

[0036] Secondly, the present invention only needs to quantitatively add oxalic acid according to a stoichiometric ratio to the sulfuric acid solution of (4+y)-valent vanadium ions obtained at the positive electrode after charging and electrolysis of the all-vanadium redox flow battery to reduce the sulfuric acid solution of (4+x)-valent vanadium ions, wherein 1>y>x>0, that is, only part of the pentavalent vanadium needs to be reduced to a tetravalent vanadium, and it is not necessary to reduce all of the pentavalent vanadium to a tetravalent vanadium. Therefore, the reduction reaction rate is also very fast, which greatly shortens the time of the reduction step and further improves the preparation efficiency.

[0037] Furthermore, since the present invention keeps the pentavalent vanadium in excess relative to the oxalic acid reducing agent in the reduction step of the cathode electrolyte after the charging electrolysis of the all-vanadium redox flow battery, not only the reduction reaction rate is fast and the reduction step time is short, but also no oxalic acid reducing agent remains in the cathode electrolyte after the reduction, thus avoiding the reaction of unreacted oxalic acid with the newly generated pentavalent vanadium ion VO2 + A redox reaction occurs and a large amount of CO2 bubbles are generated in the positive electrode electrolyte, which fundamentally prevents the positive electrode electrolyte magnetic circulation pump from being disconnected, idling, or even burning out during the next charging and electrolysis, ensuring the smooth progress of subsequent electrolysis steps.

[0038] In addition, the present invention can prepare 3- and 4-valent vanadium sulfate electrolytes with a high concentration of more than 1.8M and a wide operating temperature range of 20-60°C. When used in all-vanadium liquid flow batteries, they not only have high energy efficiency and high energy density, but also completely eliminate the need for a pre-charging process for the 3.5-valent vanadium sulfate electrolyte, saving a large amount of time and electrical energy. This avoids irreversible water migration between the positive and negative vanadium electrolytes and completely overcomes the serious defects of the vanadium sulfate electrolyte, namely, the easy precipitation of VOSO4 crystals at low temperatures and the extremely easy precipitation of insoluble V2O5 precipitates at temperatures above 40°C, which lead to a significant decrease in battery capacity, blockage of the battery stack, and even scrapping. The invention can operate stably within a wide temperature range of -20-60°C, eliminating the cost and energy consumption of the heat exchanger required for the vanadium sulfate electrolyte, significantly improving the energy efficiency of the all-vanadium liquid flow battery energy storage system by approximately 10%, greatly reducing the cost of using the all-vanadium liquid flow battery, significantly improving the rate of return on investment, and shortening the payback period.

[0039] Therefore, the present invention provides a method for preparing a 3- and 4-valent vanadium sulfate electrolyte. The method uses a 4-valent vanadium sulfate electrolyte and a (4+x)-valent vanadium sulfate electrolyte (x>0) as the negative and positive electrolytes of an all-vanadium liquid flow battery for charging electrolysis to prepare the 3- and 4-valent vanadium sulfate electrolytes. This method completely overcomes the serious defects of the traditional electrolysis preparation method in which both the positive and negative electrolytes are 4-valent vanadium electrolytes and the 3.5-valent vanadium sulfate electrolyte. The method not only has outstanding advantages such as rapid electrolysis and quick reduction, but also has the advantages of low preparation cost and high return on investment for the preparation of high-concentration and wide-operating-temperature 3- and 4-valent vanadium sulfate electrolytes. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG1 is a flow chart of a method for preparing a trivalent or tetravalent vanadium sulfate electrolyte according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] 1 , a method for preparing a trivalent or tetravalent vanadium sulfate electrolyte provided by an embodiment of the present invention includes the following steps:

[0042] Step 1) adding hydrochloric acid to a tetravalent vanadium sulfate electrolyte to prepare a tetravalent vanadium sulfate hydrochloride electrolyte.

[0043] Step 2) preparing a (4+x)-valent vanadium sulfate electrolyte. The preparation method of the (4+x)-valent vanadium sulfate electrolyte comprises:

[0044] First, a tetravalent vanadium sulfate electrolyte and a tetravalent vanadium sulfate hydrochloride electrolyte are used as the positive and negative electrolytes of the all-vanadium redox flow battery, respectively, and charged and electrolyzed to obtain a (4+z)-valent vanadium sulfate electrolyte at the positive electrode and a trivalent vanadium sulfate hydrochloride electrolyte at the negative electrode;

[0045] Then, oxalic acid is added to the (4+z)-valent vanadium sulfate electrolyte in a stoichiometric ratio, and the (4+z)-valent vanadium sulfate electrolyte is reduced to obtain a (4+x)-valent vanadium sulfate electrolyte, wherein 1>z>x>0.

[0046] Step 3) Using (4+x)-valent vanadium sulfate electrolyte and 4-valent vanadium sulfate hydrochloride electrolyte as the positive and negative electrolytes of the all-vanadium redox flow battery respectively for charging electrolysis, a (4+y)-valent vanadium sulfate electrolyte is obtained at the positive electrode and a 3-valent vanadium sulfate hydrochloride electrolyte is obtained at the negative electrode, wherein 1>y>x>0.

[0047] Step 4) oxalic acid is added to the (4+y)-valent vanadium sulfate electrolyte in a stoichiometric ratio to reduce the (4+y)-valent vanadium sulfate electrolyte to a (4+x)-valent vanadium sulfate electrolyte, wherein x≥0.1 and y≥0.9.

[0048] The (4+x)-valent vanadium sulfate electrolyte obtained again is continued to be used as the positive and negative electrolytes of the all-vanadium liquid flow battery for charging electrolysis with the 4-valent vanadium sulfate hydrochloride electrolyte, respectively, to obtain the 3-valent vanadium sulfate hydrochloride electrolyte at the negative electrode and the (4+y)-valent vanadium sulfate electrolyte at the positive electrode.

[0049] The (4+y)-valent vanadium sulfate electrolyte obtained at the positive electrode is then reduced to (4+x)-valent vanadium sulfate electrolyte using oxalic acid. This can then continue to participate in the charging electrolysis of the all-vanadium redox flow battery, producing trivalent vanadium sulfate electrolyte at the negative electrode. This cycle is repeated, and the negative electrode can continuously produce trivalent vanadium sulfate electrolyte.

[0050] The tetravalent vanadium sulfate electrolyte is prepared by reducing vanadium pentoxide with sulfuric acid and oxalic acid solution.

[0051] The present invention provides a method for preparing a 3- and 4-valent vanadium sulfate electrolyte, which completely overcomes the serious defects of traditional electrolyte electrolysis preparation methods in which 3.5-valent vanadium sulfate electrolyte and positive and negative electrode electrolytes are both 4-valent vanadium electrolytes. The method has the advantages of rapid electrolysis and quick reduction, and can be used for the efficient and low-cost preparation of high-concentration and wide-operating-temperature 3- and 4-valent vanadium sulfate electrolytes.

[0052] The following examples illustrate the method for preparing a trivalent and tetravalent vanadium sulfate electrolyte provided by the present invention.

[0053] Example 1

[0054] Preparation of 1250L 1.8MV(HSO4)2Cl+HCl trivalent sulfate vanadium hydrochloride electrolyte and 1250L 1.8MVO(HSO4)2+2HCl quadrivalent sulfate vanadium hydrochloride electrolyte

[0055] Step 1: Preparation of 1758L 1.6M VO(HSO4)2+H2SO4 4-valent vanadium sulfate electrolysis mother liquor

[0056] 0.5V2O5+3H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+H2SO4+CO2+2.5H2O

[0057] V2O5: 1758*1.6*0.5*182=256(kg)

[0058] H2SO4: 1758*1.6*3*98.1=828(kg)

[0059] H2C2O4·2H2O: 1758*1.6*0.5*126=177(kg)

[0060] Add 400 L of pure water to the reactor. Slowly add 828 kg of H₂SO₄ and 177 kg of H₂C₂O₄·2H₂O while stirring. Slowly add 256 kg of V₂O₅ and allow to react until no bubbles form. Filter the solution and add pure water to obtain 1758 L of 1.6 M VO(HSO₄)₂ + H₂SO₄ tetravalent vanadium sulfate electrolysis mother liquor.

[0061] Step 2: Preparation of two 800L 2.8125M VO(HSO4)2 4-valent vanadium sulfate electrolytes

[0062] 0.5V2O5+2H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2+2.5H2O

[0063] V2O5: 2*800*2.8125*0.5*182=410(kg)

[0064] H2SO4: 2*800*2.8125*2*98.1=883(kg)

[0065] H2C2O4·2H2O: 2*800*2.8125*0.5*126=284(kg)

[0066] Add 600L of pure water to a reactor. Slowly add 883kg of H₂SO₄ and 284kg of H₂C₂O₄·2H₂O while stirring. Slowly add 410kg of V₂O₅ and allow to react until no bubbles form. Filter the solution, divide equally, and add pure water to each to obtain two 800L portions of 2.8125M VO(HSO₄)₂ tetravalent vanadium sulfate electrolyte.

[0067] Step 3: Prepare two 1250L 1.8M VO(HSO4)2+2HCl 4-valent sulfate vanadium electrolytes

[0068] Add 164 kg of HCl to each of the two 800 L 2.8125 M VO(HSO4)2 4-valent vanadium electrolytes in step 2, and add pure water to each to obtain two 1250 L 1.8 M VO(HSO4)2 + 2HCl 4-valent vanadium electrolytes.

[0069] HCl: 1250*1.8*2*36.46=164(kg)

[0070] A portion of 1250L of 1.8M VO(HSO4)2+2HCl 4-valent sulfate vanadium hydrochloride electrolyte was stored; another portion of 1250L of 1.8M VO(HSO4)2+2HCl 4-valent sulfate vanadium hydrochloride electrolyte was used to prepare 1250L of 1.8M V(HSO4)2Cl+HCl 3-valent sulfate vanadium hydrochloride electrolyte.

[0071] Step 4: Preparation of 1250L 1.8MV (HSO4)2Cl+HCl trivalent sulfate vanadium electrolyte

[0072] The other 1250L 1.8M VO(HSO4)2+2HCl 4-valent vanadium sulfate electrolyte prepared in step 3 was used as the negative electrolyte for 37 5kW all-vanadium redox flow battery stacks. The 1758L 1.6M VO(HSO4)2+H2SO4 4-valent vanadium sulfate mother solution prepared in step 1 was used as the positive electrolyte. The battery was charged for 1630Ah.

[0073] SOC － =37*1630 / (1250*1.8*26.8)=100%

[0074] SOC + =37*1630 / (1758*1.6*26.8)=80%

[0075] Negative electrode: VO(HSO4)2+2HCl+H + +e=V(HSO4)2Cl+HCl+H2O

[0076] Positive electrode: VO(HSO4)2+H2O-H + -e=VO2HSO4+H2SO4

[0077] At the negative electrode, 1250L of 1.8MV (HSO4)2Cl+HCl trivalent vanadium sulfate electrolyte was obtained and stored; at the positive electrode, 1758L of 1.6M 0.8VO2HSO4+0.2VO(HSO4)2+1.8H2SO4 4.8valent vanadium sulfate electrolyte mother liquor was obtained.

[0078] Step 5: Preparation of 1758L 1.6M 0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1-valent vanadium sulfate electrolysis mother liquor

[0079] Step 4: Add 124 kg of H2C2O4·2H2O to 1758 L of 1.6M 0.8VO2HSO4+0.2VO(HSO4)2+1.8H2SO4 4.8-valent vanadium sulfate electrolysis mother liquor and stir until no bubbles are generated to obtain 1758 L of 1.6M 0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1-valent vanadium sulfate electrolysis mother liquor:

[0080] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2+2H2O

[0081] H2C2O4·2H2O: 0.7*1758*1.6*0.5*126=124(kg)

[0082] Step 6: Preparation of 1250L 1.8MV (HSO4)2Cl + HCl trivalent sulfate vanadium electrolyte and 1250L 1.8M VO (HSO4)2 + 2HCl quadrivalent sulfate vanadium electrolyte

[0083] Repeat steps 2 and 3, storing 1250L of 1.8M VO(HSO4)2+2HCl 4-valent vanadium sulfate electrolyte; using another 1250L of 1.8M VO(HSO4)2+2HCl 4-valent vanadium sulfate electrolyte as the negative electrolyte for a 37-cell 5kW all-vanadium redox flow battery stack; using 1758L of 1.6M0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1-valent vanadium sulfate mother liquor as the positive electrolyte, and charging for 1630Ah:

[0084] SOC － =37*1630 / (1250*1.8*26.8)=100%

[0085] SOC + =37*1630 / (1758*1.6*26.8)+10%=80%+10%=90%

[0086] Negative electrode: VO(HSO4)2+2HCl+H + +e=V(HSO4)2Cl+HCl+H2O

[0087] Positive electrode: VO(HSO4)2+H2O-H + -e=VO2HSO4+H2SO4

[0088] 1250L 1.8MV (HSO4)2Cl+HCl trivalent vanadium sulfate electrolyte was obtained at the negative electrode and stored; 1758L 1.6M 0.9VO2HSO4+0.1VO(HSO4)2+1.9H2SO4 4.9valent vanadium sulfate electrolyte mother liquor was obtained at the positive electrode.

[0089] Step 7: Preparation of 1758L 1.6M 0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1-valent vanadium sulfate electrolysis mother liquor

[0090] Add 141.8 kg of H2C2O4·2H2O to 1758 L of 1.6M 0.9VO2HSO4+0.1VO(HSO4)2+1.9H2SO4 4.9-valent vanadium sulfate electrolysis mother liquor and stir until no bubbles are generated to obtain 1758 L of 1.6M0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1-valent vanadium sulfate electrolysis mother liquor:

[0091] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2+2H2O

[0092] H2C2O4·2H2O: 0.8*1758*1.6*0.5*126=141.8(kg)

[0093] Step 8: Repeat steps 6 and 7 to continuously prepare 1250 L of 1.8 MV (HSO4)2Cl + HCl trivalent sulfate vanadium hydrochloride electrolyte and 1250 L of 1.8 M VO (HSO4)2 + 2HCl quadrivalent sulfate vanadium hydrochloride electrolyte.

[0094] Example 2

[0095] Preparation of 800L 2.2MV(HSO4)2Cl+HCl trivalent sulfate vanadium hydrochloride electrolyte and 800L 2.2MVO(HSO4)2+2HCl quadrivalent sulfate vanadium hydrochloride electrolyte

[0096] Step 1: Preparation of 1376L 1.6M VO(HSO4)2+H2SO4 4-valent vanadium sulfate electrolysis mother liquor

[0097] 0.5V2O5+3H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+H2SO4+CO2+2.5H2O

[0098] V2O5: 1376*1.6*0.5*182=200(kg)

[0099] H2SO4: 1376*1.6*3*98.1=648(kg)

[0100] H2C2O4·2H2O: 1376*1.6*0.5*126=139(kg)

[0101] Add 400 L of pure water to the reactor. Slowly add 648 kg of H₂SO₄ and 139 kg of H₂C₂O₄·2H₂O while stirring. Slowly add 200 kg of V₂O₅ and allow to react until no bubbles form. Filter the solution and add pure water to obtain 1376 L of 1.6 M VO(HSO₄)₂ + H₂SO₄ tetravalent vanadium sulfate electrolysis mother liquor.

[0102] Step 2: Preparation of two 470L 3.75M VO(HSO4)2 4-valent vanadium sulfate electrolytes

[0103] 0.5V2O5+2H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2+2.5H2O

[0104] V2O5: 2*470*3.75*0.5*182=321(kg)

[0105] H2SO4: 2*470*3.75*2*98.1=692(kg)

[0106] H2C2O4·2H2O: 2*470*3.75*0.5*126=222(kg)

[0107] Add 500L of pure water to a reactor. Slowly add 692kg of H₂SO₄ and 222kg of H₂C₂O₄·2H₂O while stirring. Slowly add 321kg of V₂O₅ and allow to react until no bubbles form. Filter the solution, divide equally, and add pure water to each to obtain two 470L portions of 3.75M VO(HSO₄)₂ vanadium sulfate electrolyte.

[0108] Step 3: Preparation of two 800L 2.2M VO(HSO4)2+2HCl 4-valent sulfate vanadium electrolytes

[0109] Add 128 kg of HCl to each of the two 470 L 3.75 M VO(HSO4)2 4-valent vanadium electrolytes prepared in step 2, and add pure water to each to obtain two 800 L 2.2 M VO(HSO4)2 + 2HCl 4-valent vanadium electrolytes.

[0110] HCl: 800*2.2*2*36.46=128(kg)

[0111] One portion of 800L 2.2M VO(HSO4)2+2HCl 4-valent sulfate vanadium hydrochloride electrolyte was stored; another portion of 800L 2.2M VO(HSO4)2+2HCl 4-valent sulfate vanadium hydrochloride electrolyte was used to prepare 800L 2.2MV(HSO4)2Cl+HCl 3-valent sulfate vanadium hydrochloride electrolyte.

[0112] Step 4: Preparation of 800L 2.2MV (HSO4)2Cl+HCl trivalent sulfate vanadium electrolyte

[0113] Another 800L portion of 2.2M VO(HSO4)2+2HCl 4-valent vanadium sulfate electrolyte prepared in step 3 was used as the negative electrolyte for 37 5kW all-vanadium redox flow battery stacks. 1376L of 1.6M VO(HSO4)2+H2SO4 4-valent vanadium sulfate mother solution prepared in step 1 was used as the positive electrolyte. The battery was charged for 1275Ah.

[0114] SOC － =37*1275 / (800*2.2*26.8)=100%

[0115] SOC + =37*1275 / (1376*1.6*26.8)=80%

[0116] Negative electrode: VO(HSO4)2+2HCl+H + +e=V(HSO4)2Cl+HCl+H2O

[0117] Positive electrode: VO(HSO4)2+H2O-H + -e=VO2HSO4+H2SO4

[0118] At the negative electrode, 800L of 2.2MV (HSO4)2Cl+HCl trivalent vanadium sulfate electrolyte was obtained and stored; at the positive electrode, 1376L of 1.6M 0.8VO2HSO4+0.2VO(HSO4)2+1.8H2SO4 4.8valent vanadium sulfate electrolyte mother liquor was obtained.

[0119] Step 5: Preparation of 1376L 1.6M 0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1-valent vanadium sulfate electrolysis mother liquor

[0120] In step 4, 97.1 kg of H2C2O4·2H2O was added to 1376 L of 1.6M 0.8VO2HSO4+0.2VO(HSO4)2+1.8H2SO4 4.8-valent vanadium sulfate electrolysis mother liquor, and the mixture was stirred until no bubbles were generated to obtain 1376 L of 1.6M 0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1-valent vanadium sulfate electrolysis mother liquor:

[0121] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2+2H2O

[0122] H2C2O4·2H2O: 0.7*1376*1.6*0.5*126=97.1(kg)

[0123] Step 6: Preparation of 800L 2.2MV (HSO4)2Cl + HCl trivalent sulfate vanadium electrolyte and 800L 2.2MVO (HSO4)2 + 2HCl quadrivalent sulfate vanadium electrolyte

[0124] Repeat steps 2 and 3, storing 800L of 2.2M VO(HSO4)2+2HCl 4-valent vanadium sulfate electrolyte; use another 800L of 2.2M VO(HSO4)2+2HCl 4-valent vanadium sulfate electrolyte as the negative electrolyte for 37 5kW all-vanadium redox flow battery stacks, and use 1376L of 1.6M0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1-valent vanadium sulfate mother liquor as the positive electrolyte. Charge for 1275Ah:

[0125] SOC － =37*1275 / (800*2.2*26.8)=100%

[0126] SOC + =37*1275 / (1376*1.6*26.8)+10%=80%+10%=90%

[0127] Negative electrode: VO(HSO4)2+2HCl+H + +e=V(HSO4)2Cl+HCl+H2O

[0128] Positive electrode: VO(HSO4)2+H2O-H + -e=VO2HSO4+H2SO4

[0129] 800L 2.2MV (HSO4)2Cl+HCl trivalent vanadium sulfate electrolyte was obtained at the negative electrode and stored; 1376L 1.6M 0.9VO2HSO4+0.1VO(HSO4)2+1.9H2SO4 4.9valent vanadium sulfate electrolyte mother liquor was obtained at the positive electrode.

[0130] Step 7: Preparation of 1376L 1.6M 0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1-valent vanadium sulfate electrolysis mother liquor

[0131] Add 111 kg of H2C2O4·2H2O to 1376 L of 1.6M 0.9VO2HSO4+0.1VO(HSO4)2+1.9H2SO4 4.9-valent vanadium sulfate electrolysis mother liquor and stir until no bubbles are generated to obtain 1376 L of 1.6M 0.1VO2HSO4+0.9VO(HSO4)2+1.1H2SO4 4.1-valent vanadium sulfate electrolysis mother liquor:

[0132] VO2HSO4+H2SO4+0.5H2C2O4·2H2O=VO(HSO4)2+CO2+2H2O

[0133] H2C2O4·2H2O: 0.8*1376*1.6*0.5*126=111(kg)

[0134] Step 8: Repeat steps 6 and 7 to continuously prepare 800 L of 2.2 MV (HSO4)2Cl + HCl trivalent sulfate vanadium hydrochloride electrolyte and 800 L of 2.2 M VO (HSO4)2 + 2HCl quadrivalent sulfate vanadium hydrochloride electrolyte.

[0135] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a trivalent or tetravalent vanadium sulfate electrolyte, characterized in that: The steps include: adding hydrochloric acid to a tetravalent vanadium sulfate electrolyte to prepare a tetravalent vanadium sulfate hydrochloride electrolyte; preparing a (4+x)-valent vanadium sulfate electrolyte; The (4+x)-valent vanadium sulfate electrolyte and the tetravalent vanadium sulfate hydrochloride electrolyte are used as the positive and negative electrolytes of the all-vanadium redox flow battery for charging and electrolysis, respectively, to obtain a (4+y)-valent vanadium sulfate electrolyte and a trivalent vanadium sulfate hydrochloride electrolyte at the positive and negative electrodes, respectively, wherein 1>y>x>0; The (4+y)-valent vanadium sulfate electrolyte is reduced with oxalic acid to obtain a (4+x)-valent vanadium sulfate electrolyte, wherein x≥0.1 and y≥0.9; The (4+x)-valent vanadium sulfate electrolyte obtained again is continued to be used as the positive and negative electrolytes of the all-vanadium liquid flow battery for charging and electrolysis together with the 4-valent vanadium sulfate hydrochloride electrolyte, and the 3-valent vanadium sulfate hydrochloride electrolyte is prepared at the negative electrode.

2. The method for preparing a trivalent or tetravalent vanadium sulfate electrolyte according to claim 1, wherein: The preparation method of the (4+x)-valent vanadium sulfate electrolyte comprises: The tetravalent vanadium sulfate electrolyte and the tetravalent vanadium sulfate hydrochloride electrolyte are used as the positive and negative electrolytes of the all-vanadium redox flow battery, respectively, and the (4+z)-valent vanadium sulfate electrolyte is obtained at the positive electrode, and the trivalent vanadium sulfate hydrochloride electrolyte is obtained at the negative electrode; The (4+z)-valent vanadium sulfate electrolyte is reduced by adding oxalic acid to obtain a (4+x)-valent vanadium sulfate electrolyte, wherein 1>z>x>0.

3. The method for preparing a trivalent or tetravalent vanadium sulfate electrolyte according to claim 1 or 2, wherein: The tetravalent vanadium sulfate electrolyte is prepared by reducing vanadium pentoxide with sulfuric acid and oxalic acid solution.

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