Method for preparing all-vanadium redox flow battery electrolyte with different valence states by utilizing multivalent vanadium oxide or mixture of multivalent vanadium oxide

Abstract

The invention discloses a method for preparing all-vanadium redox flow battery electrolyte with different valence states by utilizing multivalent vanadium oxide or a mixture thereof. According to the method, various vanadium oxides (such as vanadium tetraoxide, vanadium trioxide, vanadium pentoxide and vanadium oxides with unknown valence states) or mixtures thereof and vanadium oxides with uncertain proportions and random oxygen contents are used, and low-concentration dilute sulphuric acid is combined, so that the process flow is simplified, and the preparation of the high-purity electrolyte is realized. The method comprises the following specific steps: determining the concentration of vanadium ions and sulfuric acid of the required electrolyte, adding the raw materials according to the proportion for dissolving, and adjusting the valence state of the electrolyte through an electrolytic bath to finally obtain an electrolyte product meeting the commercialization requirement and simultaneously obtain products with additional values, such as hydrogen or oxygen. According to the method, the preparation cost and the energy consumption are reduced, electrolyte with various concentrations and valence states can be provided according to different requirements, and the method is suitable for different scenes.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid flow batteries, and in particular relates to a method for preparing electrolytes of all-vanadium liquid flow batteries with different valence states by using multivalent vanadium oxides or mixtures thereof. Background Art

[0002] The core components of all-vanadium flow batteries include positive and negative electrode chambers, vanadium electrolyte and ion exchange membrane. Among them, vanadium electrolyte is the key to system performance, stability and cost. Vanadium electrolyte is generally composed of acidic solutions corresponding to different valence states of vanadium, which stores and releases electrical energy through redox reactions during the battery charging and discharging process. For example, the negative electrode electrolyte is positive divalent (V 2+ ) and positive trivalent (V 3+ ) vanadium ions mutually transform; positive tetravalent (VO 2+ ) and pentavalent (VO 2 + ) realizes the charging and discharging process of the positive electrolyte. However, an important challenge facing the current all-vanadium flow battery technology is how to prepare reliable vanadium electrolyte more efficiently and at a lower cost. However, there are many problems with the existing preparation methods of vanadium electrolytes, such as low purity, high cost, complex process, large equipment loss, large environmental impact, and the need to add additives. For example, Chinese patent application CN1598063A discloses a method for preparing an electrolyte for an all-vanadium ion flow battery, wherein sulfuric acid is first prepared into a 1:1 dilute sulfuric acid, and then vanadium trioxide is first added, followed by vanadium pentoxide, to react to obtain a vanadium sulfate solution; then Na2SO4, emulsifier OP and other additives are added; then the vanadium sulfate solution is placed at the cathode of the electrolytic cell, and a sodium sulfate sulfuric acid solution with the same ionic strength is placed at the anode of the electrolytic cell for electrolysis to obtain a vanadium electrolyte for a vanadium battery in which 4-valent vanadium and 3-valent vanadium each account for 50% of the total vanadium; due to the additional addition of electrolyte sodium sulfate, the permeation of sodium ions across the membrane during the electrolysis process will lead to the introduction of impurity ions, and the purity of the electrolyte is correspondingly reduced. In order to overcome these problems, it is particularly important to develop an efficient, environmentally friendly and economically feasible method for preparing a high-purity vanadium electrolyte.

[0003] In addition, the preparation of vanadium electrolytes traditionally relies on chemically pure vanadium oxides, and the target product is obtained through multiple chemical reactions and cumbersome process steps. For example, Chinese patent application CN 106941186 A discloses a method for preparing vanadium electrolytes, comprising the following steps: (1) using ammonium metavanadate with a purity of 99.0-99.5 wt% as a raw material, dissolving vanadium, filtering to obtain a purified vanadium solution, and acidic ammonia precipitation to obtain an ammonium polyvanadate solid phase; (2) calcining the ammonium polyvanadate solid phase under a reducing atmosphere to obtain a mixture containing vanadium tetroxide and vanadium trioxide; wherein the molar ratio of vanadium tetroxide to vanadium trioxide is (0.95-1.05):1; (3) acid dissolving the mixture to obtain a vanadium electrolyte. Chinese patent application CN 117902626 A provides a method and device for preparing vanadium electrolyte from crude vanadium, the method provided comprises: (1) providing a crude vanadium raw material solution, adjusting the pH value to 8-9, then adding an impurity remover to remove impurities once, and obtaining a primary impurity removal product; (2) adding a reducing agent of sodium thiosulfate and sulfuric acid with a value of 1.2-5 times the theoretical amount of vanadium to the primary impurity removal product to control the pH value of the solution to 1.5-4, and performing a primary reduction to obtain a primary reduction product and a filter residue containing tetravalent vanadium; (3) adjusting the pH value of the primary reduction product to 2-5, and performing a secondary impurity removal to obtain a secondary impurity removal liquid; (4) performing extraction and stripping treatment on the secondary impurity removal liquid to obtain an extraction product containing a tetravalent vanadium electrolyte; (5) performing electrolytic reduction treatment on the extraction product to obtain a 3.5-valent vanadium electrolyte. These methods are not only time-consuming and labor-intensive, but also cannot avoid the introduction of a large number of impurities, which affects the electrochemical properties of the vanadium electrolyte. Therefore, developing a new method to prepare vanadium electrolytes with different valence states directly from multivalent vanadium oxides and their mixtures will have a profound impact on the commercial application of all-vanadium flow batteries. Summary of the invention

[0004] In order to solve the shortcomings and deficiencies of the prior art, the object of the present invention is to provide a method for preparing all-vanadium liquid flow battery electrolytes of different valence states using vanadium oxides.

[0005] Based on the electrolyte preparation method of the present invention, by using simple vanadium oxide raw materials, one or more of vanadium trioxide (V2O3), vanadium tetroxide (V2O4) and vanadium pentoxide (V2O5), or a mixture of vanadium oxides of unknown valence, and safer low-concentration dilute sulfuric acid, an all-vanadium liquid flow battery electrolyte can be finally obtained, in which the vanadium ion concentration in the electrolyte is 0.01-4 mol / L and the sulfate concentration is 0.1-6 mol / L (the specific electrolyte concentration depends on the product requirements and the solubility of the active substance at the corresponding temperature). At the same time, according to different research purposes and usage scenarios, the valence of the electrolyte product can also be adjusted in a targeted manner.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing electrolytes of all-vanadium liquid flow batteries with different valence states using vanadium oxides comprises the following steps:

[0008] Step 1: Raw material preparation and dissolution

[0009] The mass of the required raw material vanadium oxide is determined according to the vanadium ion and sulfate concentration of the target electrolyte, and the vanadium oxide and low-concentration dilute sulfuric acid are added to a reactor, fully stirred and dissolved to obtain a preliminary electrolyte.

[0010] Step 2: Electrolysis to adjust the valence state

[0011] The preliminary electrolyte is electrolyzed in an electrolytic cell to reduce (reduce the valence) or oxidize (increase the valence) the electrolyte to obtain an electrolyte with an integer valence (i.e., positive divalent, trivalent, tetravalent, or pentavalent); or the prepared electrolytes with different integer valences are mixed in a fixed volume according to demand to obtain an electrolyte with a non-integer valence.

[0012] In this step, the final valence state of the electrolyte can be controlled by adjusting the electrolysis time, current density or electrolytic cell configuration (such as electrode materials, hydrogen or oxygen evolution catalysts), wherein the electrolysis time and current density can be determined by calculating the theoretical capacity according to the concentration and volume of the electrolyte, that is, electrolysis time × current density × electrode area = electrolyte capacity = n × F × C × V (n is the number of electron transfers, F is the Faraday constant, which is about 96485C / mol, C is the concentration of the electrolyte (in mol / L), and V is the volume of the electrolyte (in L). Furthermore, electrolytes of different valence states can also be mixed by volume ratio to prepare electrolyte products for different application requirements. For example, a standard commercial 3.5-valent electrolyte can be obtained by mixing positive tetravalent and positive trivalent electrolytes in a volume ratio of 1:1.

[0013] Preferably, in step 1, the vanadium ion concentration in the target electrolyte is 0.01-4 mol / L, and the sulfate concentration is 0.1-6 mol / L.

[0014] Preferably, the stirring and dissolving in step 1 is carried out at a temperature of room temperature to 80° C., and for a time of 30 minutes to 24 hours, depending on the dissolution conditions.

[0015] Preferably, the concentration of the low-concentration dilute sulfuric acid in step 1 is 2 to 8 mol / L, more preferably 2 to 5 mol / L.

[0016] Preferably, the vanadium oxide in step 1 is V2O4, or V2O3 and V2O4, or V2O3 and V2O5, or V2O4 and V2O5, or V2O3, V2O4 and V2O5; or V2O x(3 < x < 5). The dosage of the vanadium oxide meets the following requirements: Assuming that the vanadium ion concentration of the final target product electrolyte is X mol / L, if the vanadium oxide is V2O4, the mass of vanadium oxide required per liter of the target electrolyte is 0.5×165.88b g, where b = 0.5X; if the vanadium oxide is V2O3 and V2O4, the mass of vanadium oxide required per liter of the target electrolyte is 0.5×149.88a + 0.5×165.88b g, where a + b = 0.5X; if the vanadium oxide is V2O3 and V2O5, the mass of vanadium oxide required per liter of the target electrolyte is 0.5×149.88a + 0.5×181.88c g, where a + c = 0.5X; if the vanadium oxide is V2O4 and V2O5, the mass of vanadium oxide required per liter of the target electrolyte is 0.5×165.88b + 0.5×181.88c g, where b + c = 0.5X; if the vanadium oxide is V2O3, V2O4 and V2O5, the total mass of vanadium oxide required per liter of the target electrolyte is 0.5×(149.88a + 165.88b + 181.88c) g, a + b + c = 0.5X; if the vanadium oxide is V2O x , 3 < x < 5, the mass of vanadium oxide required per liter of the target electrolyte is 0.5×(101.88 + 16x) g.

[0017] More preferably, when the vanadium oxide described in Step 1 is V2O3 and V2O5, the molar ratio of the two is preferably 1:1.

[0018] Preferably, the electrode material of the electrolytic cell described in Step 2 is a carbon-based material such as graphite carbon felt, carbon paper or carbon cloth.

[0019] Preferably, a hydrogen evolution or oxygen evolution catalyst is further added during the electrolysis process described in Step 2. Among them, the hydrogen evolution catalyst preferably uses a commercial platinum / carbon catalyst, and other commercial low-cost hydrogen evolution catalysts can also be used; the oxygen evolution catalyst preferably uses a low-cost oxygen evolution catalyst such as manganese dioxide. The use of the catalyst can reduce the electrolytic cell voltage and improve the energy efficiency. If the material cost is to be saved, the catalyst can be not used.

[0020] Preferably, the specific steps for adjusting the valence state of the electrolyte by using the electrolytic cell in Step 2 are as follows: First, introduce a certain volume of the preliminary electrolyte into one side of the electrolytic cell, then introduce sulfuric acid with the same volume as the preliminary electrolyte introduced into the electrolytic cell and the same concentration as the dilute sulfuric acid described in Step 1 into the other side of the electrolytic cell, and perform electrolysis using a constant current. Control the electrolysis depth by adjusting the cut-off voltage to obtain the required electrolyte.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] 1. Compared with the traditional method, the advantages of the present invention are that it significantly reduces production costs and energy consumption, improves the purity and stability of the electrolyte, and is suitable for a variety of different application scenarios and requirements.

[0023] 2. The method of the present invention can reduce the requirement for oxygen content in the vanadium oxide used, that is, the purity problem of the vanadium oxide raw material caused by mixed oxide raw materials or air oxidation will not affect the final electrolyte product. At the same time, since vanadium oxides of different valence states can promote the dissolution of each other, the dissolution process of the oxide can be completed using safer dilute sulfuric acid, which greatly improves the safety of the preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the X-ray diffraction pattern of vanadium oxide raw materials (V2O3 and V2O5);

[0025] Figure 2 is the X-ray diffraction pattern of the vanadium oxide raw material (V2O4);

[0026] Figure 3 The cyclic voltammetry curves of the electrolyte prepared in Example 3 at different scanning speeds are shown in the figure. It can be seen from the figure that the peak current increases with the increase of the scanning speed;

[0027] Figure 4 The peak current-scan rate relationship in the cyclic voltammetry curve of the electrolyte prepared in Example 3 is that the peak current and the square root of the scan rate are linearly related, proving that the redox of the vanadium electrolyte is a diffusion-controlled process;

[0028] Figure 5 The electrolyte prepared in Example 3 is adjusted to the voltage-capacity curve of the positive electrode tetravalent electrolyte;

[0029] Figure 6 The electrolyte prepared in Example 7 is adjusted to the voltage-capacity curve of the negative electrode trivalent electrolyte;

[0030] Figure 7 The electrolyte prepared in Example 4 was adjusted to the voltage-capacity curve of a commercial 3.5-valent electrolyte;

[0031] Figure 8 is the UV-visible absorption spectrum of the 3.5-valent electrolyte prepared in Example 4;

[0032] Fig. 9 The voltage-capacity curve of the charge-discharge test of the all-vanadium liquid flow battery using the prepared 3.5-valent electrolyte in Example 4;

[0033] Fig.10 It is a schematic diagram of the electrolytic cell structure in the electrolysis step. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below in conjunction with embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials involved in the present invention can be directly purchased from the market. For process parameters not specifically noted, conventional techniques can be referred to.

[0035] The present invention provides a method for preparing electrolytes of different valence states of vanadium redox flow batteries using vanadium oxides, comprising the following steps:

[0036] Step 1: Raw material preparation and dissolution

[0037] According to the vanadium ion and sulfate ion concentrations of the target electrolyte, determine the mass of the required raw material vanadium oxide. Put the vanadium oxide and low-concentration dilute sulfuric acid into the reaction kettle in proportion and stir well to dissolve to obtain a preliminary electrolyte. The vanadium oxide is V2O4, V2O3 and V2O4, V2O3 and V2O5, V2O4 and V2O5, V2O3, V2O4 and V2O5, or V2O x , where 3 < x < 5; the concentration of the dilute sulfuric acid is 2 - 8 mol / L. The temperature for stirring and dissolving is from room temperature to 80 °C, and the time is from 30 minutes to 24 hours, depending on the dissolution situation.

[0038] Step 2: Electrochemical adjustment of valence

[0039] Use an electrolytic cell to electrolyze the preliminary electrolyte to reduce (lower the valence state) or oxidize (raise the valence state) the electrolyte to adjust the valence state of the electrolyte and obtain the required electrolyte; or directly mix the preliminary electrolytes of different valence states by volume ratio to obtain the required electrolyte.

[0040] Specifically, in the method of the present invention, the preparation of the standard electrolyte mainly includes two steps: quantitative dissolution and valence adjustment:

[0041] (1) First, determine the vanadium ion concentration and sulfuric acid concentration of the target electrolyte. Then, according to the concentration of the target electrolyte and the reaction equation, determine the ratio and mass of the required raw materials, including accurately proportioning the vanadium oxide raw materials (V2O3, V2O4, V2O5, V2O x (3 < x < 5), etc.) and dilute sulfuric acid of the corresponding concentration.

[0042] V2O3 + 6H + = 2V 3+ + 3H2O

[0043] V2O4 + 4H + = 2VO 2+ + 2H2O

[0044]

[0045] The molecular weight of V2O3 is 149.88 g / mol, the molecular weight of V2O4 is 165.88 g / mol, and the molecular weight of V2O5 is 181.88 g / mol. The molar ratios of their dissolution reactions with sulfuric acid are 1:3, 1:2, and 1:1 respectively. That is, assuming the vanadium ion concentration in the final target electrolyte is X mol / L, if the vanadium oxide is V2O4, the required mass is 0.5×165.88b g / L, where b = 0.5X; if the vanadium oxides are V2O3 and V2O4, the required mass is 0.5×149.88a + 0.5×165.88b g / L, where a + b = 0.5X; if the vanadium oxides are V2O3 and V2O5, the required mass is 0.5×149.88a + 0.5×181.88c g / L, where a + c = 0.5X; if the vanadium oxides are V2O4 and V2O5, the required mass is 0.5×165.88b + 0.5×181.88c g / L, where b + c = 0.5X; if the vanadium oxides are V2O3, V2O4, and V2O5, the total mass of V2O3, V2O4, and V2O5 in the starting raw materials is 0.5×(149.88a + 165.88b + 181.88c) g / L, a + b + c = 0.5X; if the starting raw material is a mixed vanadium oxide V2O x (3 < x < 5), the required mass is 0.5×(101.88 + 16x) g / L.

[0046] Different ratios of a, b, and c can complete the valence control of the electrolyte before electrolysis, but at the same time, different ratios will also affect the kinetics of dissolution and the solubility of vanadium ions. The final theoretical valence of the electrolyte is: (6a + 8b + 10c) / X.

[0047] When the vanadium oxides described in Table 1 are V2O3 and V2O5, the valence states of the electrolyte under ideal conditions obtained based on different a and c values

[0048] a\c 0.1 0.2 0.3 0.4 0.5 0.1 4.000 4.333 4.500 <![CDATA[4.600 * ]]> <![CDATA[4.667 * ]]> 0.2 3.667 4.000 4.200 4.333 4.429 0.3 3.5 3.800 4.000 4.143 4.250 0.4 <![CDATA[3.400 * ]]> 3.667 3.857 4.000 4.111 0.5 <![CDATA[3.333 * ]]> 3.571 3.750 3.889 4.000

[0049] Using the above equations, the specific values of a, b, and c required can be determined. Put the prepared raw materials into the reaction kettle and stir and dissolve at room temperature to 80 °C for 30 minutes to 24 hours to obtain a preliminary electrolyte (*: In actual operation, the solubility at room temperature is limited to a certain extent).

[0050] (2) Use an electrolytic cell for electrolysis adjustment, and adjust the valence of the electrolyte to meet the needs of different usage scenarios. Specifically: First, a certain volume of preliminary electrolyte is passed into one side of the electrolytic cell, and then sulfuric acid of the same volume as the preliminary electrolyte passed into the electrolytic cell and the same concentration as the dilute sulfuric acid described in step 1 is passed into the other side of the electrolytic cell (if you want to reduce the electrolyte valence, the electrolyte side is connected to the negative electrode, the sulfuric acid side is connected to the positive electrode, and if you want to increase the electrolyte valence, the electrolyte side is connected to the positive electrode, and the sulfuric acid side is connected to the negative electrode.), use a constant current for electrolysis, and control the electrolysis depth by adjusting the cut-off voltage. The sulfuric acid side can load the corresponding hydrogen evolution (when increasing the electrolyte valence) or oxygen evolution (when reducing the electrolyte valence) catalyst, and collect the produced hydrogen or oxygen at the same time as a valuable industrial byproduct.

[0051] When reducing the electrolyte (taking the valence state to 3 as an example):

[0052] Negative electrode reaction: VO 2+ +2H + +e - =V 3+ +H2O

[0053] Positive electrode reaction: 2H2O-4e - =4H + +O2

[0054] Total reaction: 4VO 2+ +H2O+4H + =4V 3+ +O2

[0055] When the electrolyte is oxidized (taking the valence state increased to 4 as an example):

[0056] Negative electrode reaction: 2H + +2e - =H2

[0057] Positive electrode reaction: V 3+ +H2O=VO 2+ +2H + +e -

[0058] Total response: 2V 3+ +2H2O=2VO 2+ +2H + +H2

[0059] (3) Since it is difficult to control the electrolysis depth of electrolytes with non-integer valence by adjusting the cut-off voltage, the final product can be mixed in a certain proportion according to actual needs, and the electrolyte with integer valence (i.e., divalent, trivalent, tetravalent, and pentavalent) can be obtained by electrolysis, and then mixed in a certain volume according to needs, and finally the desired commercial electrolyte product can be obtained.

[0060] Example 1: Preparation of standard positive trivalent negative electrode electrolyte using vanadium oxide raw materials (V2O3 and V2O5)

[0061] The following is an example of preparing a 1L volume of a trivalent negative electrode electrolyte with a vanadium ion concentration of 1 mol / L and a sulfate concentration of 4 mol / L to provide a detailed calculation step description.

[0062] (1) First, according to the required concentration, the reaction equation determines the ratio and mass of the required raw materials, including the accurate proportion of the vanadium oxide raw materials (V2O3 and V2O5) and the corresponding concentration of dilute sulfuric acid, a = c = 0.25. The weight of vanadium trioxide (V2O3) is: 0.5 × 149.88 × 0.25g, and the weight of vanadium pentoxide (V2O5) is: 0.5 × 181.88 × 0.25g.

[0063] (2) The vanadium oxide raw materials vanadium trioxide and vanadium pentoxide are sequentially put into a reaction kettle and dissolved in 0.8L of dilute sulfuric acid with a concentration of 5 mol / L, and then water is added to 1L. The mixture is stirred and dissolved at room temperature for 5 hours to obtain a preliminary tetravalent electrolyte.

[0064] (3) The initial tetravalent electrolyte is passed into the electrolytic cell, and sulfuric acid of equal volume and concentration is passed into the other side of the electrolytic cell. The purpose here is to reduce the valence state of the electrolyte. The electrolyte side is connected to the negative electrode, and the sulfuric acid side is connected to the positive electrode. Use 100mA / cm 2 When electrolysis is performed at a constant current, a stable voltage platform can be observed. The corresponding cut-off voltage is set, and the electrolysis is stopped after all the electrolyte is reduced to trivalent.

[0065] Example 2: Preparation of standard positive trivalent negative electrode electrolyte using vanadium oxide raw material (V2O4)

[0066] The following is an example of preparing a 1L volume of a trivalent negative electrode electrolyte with a vanadium ion concentration of 1 mol / L and a sulfate concentration of 4 mol / L to provide a detailed calculation step description.

[0067] (1) First, according to the required concentration, the reaction equation determines the ratio and mass of the required raw materials, including the accurate proportion of the vanadium oxide raw material (V2O4) and the corresponding concentration of dilute sulfuric acid, that is, b = 0.5. The weight of the required raw material vanadium tetroxide (V2O4) is: 0.5×165.88g.

[0068] (2) The vanadium oxide raw material vanadium tetroxide (V2O4) was put into a reactor and dissolved in 0.8L of dilute sulfuric acid with a concentration of 5 mol / L, and then water was added to 1L. The mixture was stirred and dissolved at room temperature for 5 hours to obtain a preliminary tetravalent electrolyte.

[0069] (3) The initial tetravalent electrolyte was introduced into the electrolytic cell, and sulfuric acid of equal volume and concentration was introduced into the other side of the electrolytic cell. The electrolyte side was the negative electrode, and the sulfuric acid side was the positive electrode. The current was 100 mA / cm 2 When electrolysis is performed at a constant current, a stable voltage platform can be observed. The corresponding cut-off voltage is set, and the electrolysis is stopped after all the electrolyte is reduced to trivalent.

[0070] Example 3: Preparation of standard tetravalent positive electrode electrolyte using vanadium oxide raw materials (V2O3 and V2O5)

[0071] The following is an example of preparing a 1L volume of a trivalent negative electrode electrolyte with a vanadium ion concentration of 1 mol / L and a sulfate concentration of 4 mol / L to provide a detailed calculation step description.

[0072] (1) First, according to the required concentration, the reaction equation determines the ratio and mass of the required raw materials, including the accurate proportion of the vanadium oxide raw materials (V2O3 and V2O5) and the corresponding concentration of dilute sulfuric acid, a = c = 0.25. The weight of vanadium trioxide (V2O3) is: 0.5 × 149.88 × 0.25g, and the weight of vanadium pentoxide (V2O5) is: 0.5 × 181.88 × 0.25g.

[0073] (2) The vanadium oxide raw materials vanadium trioxide and vanadium pentoxide are sequentially put into a reaction kettle and dissolved in 0.8L of dilute sulfuric acid with a concentration of 5 mol / L, and then water is added to 1L. The mixture is stirred and dissolved at room temperature for 5 hours to obtain a preliminary tetravalent electrolyte.

[0074] (3) Due to the exothermic oxidation and other problems that may exist during the dissolution process, the actual valence state of the initial tetravalent electrolyte may be slightly higher than tetravalent. The initial tetravalent electrolyte is passed into the electrolytic cell, and sulfuric acid of equal volume and concentration is passed into the other side of the electrolytic cell. The electrolyte side is the negative electrode, and the sulfuric acid side is the positive electrode. Use 100mA / cm 2 When electrolysis is performed at a constant current, a stable voltage platform can be observed. The corresponding cut-off voltage is set, and the electrolysis is stopped after all the electrolyte is reduced to tetravalent.

[0075] Example 4: Preparation of a standard tetravalent positive electrode electrolyte using vanadium oxide raw material (V2O4)

[0076] The following is an example of preparing a standard trivalent negative electrode electrolyte with a volume of 1L and a vanadium ion concentration of 1 mol / L and a sulfate concentration of 4 mol / L, and a detailed calculation step description is given.

[0077] (1) First, according to the required concentration, the reaction equation determines the ratio and mass of the required raw materials, including the accurate proportion of the vanadium oxide raw material (V2O4) and the corresponding concentration of dilute sulfuric acid, that is, b = 0.5. The weight of the required raw material vanadium tetroxide (V2O4) is: 0.5×165.88g.

[0078] (2) The vanadium oxide raw material vanadium tetroxide (V2O4) was put into a reactor and dissolved in 0.8L of dilute sulfuric acid with a concentration of 5 mol / L, and then water was added to 1L. The mixture was stirred and dissolved at room temperature for 5 hours to obtain a preliminary tetravalent electrolyte.

[0079] (3) Due to the exothermic oxidation and other problems that may exist during the dissolution process, the actual valence state of the initial tetravalent electrolyte may be slightly higher than tetravalent. The initial tetravalent electrolyte is passed into the electrolytic cell, and sulfuric acid of equal volume and concentration is passed into the other side of the electrolytic cell. The electrolyte side is the negative electrode, and the sulfuric acid side is the positive electrode. Use 100mA / cm 2 When electrolysis is performed at a constant current, a stable voltage platform can be observed. The corresponding cut-off voltage is set, and the electrolysis is stopped after all the electrolyte is reduced to tetravalent.

[0080] Example 5: Preparation of a standard commercial 3.5-valent electrolyte using vanadium oxide raw material (V2O4)

[0081] The following is an example of preparing a standard commercial 3.5-valent negative electrode electrolyte with a volume of 1L and a vanadium ion concentration of 1 mol / L and a sulfate concentration of 4 mol / L, and a detailed calculation step is explained.

[0082] (1) First, according to the required concentration, the reaction equation determines the ratio and mass of the required raw materials, including the accurate proportion of the vanadium oxide raw material (V2O4) and the corresponding concentration of dilute sulfuric acid, that is, b = 0.5. The weight of the required raw material vanadium tetroxide (V2O4) is: 0.5×165.88g.

[0083] (2) The vanadium oxide raw material vanadium tetroxide (V2O4) was put into a reactor and dissolved in 0.8L of dilute sulfuric acid with a concentration of 5 mol / L, and then water was added to 1L. The mixture was stirred and dissolved at room temperature for 5 hours to obtain a preliminary tetravalent electrolyte.

[0084] (3) The initial tetravalent electrolyte was introduced into the electrolytic cell, and sulfuric acid of equal volume and concentration was introduced into the other side of the electrolytic cell. The electrolyte side was the negative electrode, and the sulfuric acid side was the positive electrode. The current was 100 mA / cm 2 The electrolysis was carried out at a constant current, and the capacity of the entire electrolyte was calculated to be 26.8014Ah. A stable voltage platform was observed, and the electrolysis was stopped when the voltage reached 13.4007Ah.

[0085] Example 6: Preparation of standard commercial 3.5-valent negative electrode electrolyte

[0086] Based on the standard trivalent negative electrode electrolyte in the preceding embodiments 1 and 2 and the standard tetravalent electrolyte in the preceding embodiments 3 and 4, the desired commercial 3.5-valent electrolyte can be obtained by mixing in a volume ratio of 1:1.

[0087] Example 7: Preparation of a standard commercial 3.5-valent negative electrode electrolyte using vanadium oxide of unknown valence

[0088] The following is an example of preparing a 1L volume of a trivalent negative electrode electrolyte with a vanadium ion concentration of 1 mol / L and a sulfate concentration of 4 mol / L to provide a detailed calculation step description.

[0089] (1) First, according to the required concentration and reaction equation, the ratio and mass of the required raw materials are determined, including the accurate weight of vanadium oxide and the corresponding concentration of dilute sulfuric acid. The vanadium content in the mixed oxide is 60.14%, that is, the molecular weight of the corresponding oxide is 169.4 g / mol. The raw material is calculated to be V2O 4.22 The required raw materials (V2O 4.22 )Weight: 0.5×169.4g.

[0090] (2) The mixed oxide raw material was put into a reactor and dissolved in 0.8 L of dilute sulfuric acid with a concentration of 5 mol / L, and then water was added to 1 L. The mixture was stirred and dissolved at room temperature for 5 hours to obtain a preliminary positive 4.22-valent electrolyte.

[0091] (3) The initial positive 4.22-valent electrolyte was introduced into the electrolytic cell, and sulfuric acid of equal volume and concentration was introduced into the other side of the electrolytic cell. The electrolyte side was the negative electrode, and the sulfuric acid side was the positive electrode. The current was 100 mA / cm 2 When electrolysis is performed at a constant current, a stable voltage platform can be observed. The corresponding cut-off voltage is set, and the electrolysis is stopped after all the electrolyte is reduced to trivalent.

[0092] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing electrolytes of all-vanadium redox flow batteries with different valence states using vanadium oxides, characterized in that: The following steps are involved: Step 1: Raw material preparation and dissolution According to the vanadium ion and sulfate ion concentrations of the target electrolyte, determine the dosage of the raw material vanadium oxide required, and put the vanadium oxide and dilute sulfuric acid into a reaction kettle, and stir and dissolve them充分搅拌溶解 to obtain a preliminary electrolyte; the vanadium oxide is V2O4, V2O3 and V2O4, V2O3 and V2O5, V2O4 and V2O5, V2O3, V2O4 and V2O5, or V2O x , where 3 < x < 5; the concentration of the dilute sulfuric acid is 2 to 8 mol / L; the temperature of the stirring and dissolving is from room temperature to 80 °C, and the time is from 30 minutes to 24 hours; Step 2: Electrolysis to adjust the valence state A certain volume of preliminary electrolyte is passed into one side of the electrolytic cell, and then sulfuric acid of the same volume as the preliminary electrolyte passed into the electrolytic cell and the same concentration as the dilute sulfuric acid described in step 1 is passed into the other side of the electrolytic cell, and electrolysis is performed using a constant current, and the electrolysis depth is controlled by adjusting the cut-off voltage to obtain an electrolyte with an integer valence state.

2. The method according to claim 1, characterized in that Step 2 also includes mixing the prepared electrolytes of different integer valence states in a fixed volume according to demand to obtain an electrolyte of non-integer valence state.

3. The method according to claim 1, characterized in that In step 1, the vanadium ion concentration in the target electrolyte is 0.01-4 mol / L, and the sulfate concentration is 0.1-6 mol / L.

4. The method according to claim 1, characterized in that: The concentration of the dilute sulfuric acid in step 1 is 2-5 mol / L.

5. The method according to claim 1, characterized in that The dosage of the vanadium oxide in the first step meets the following requirements: Assuming that the vanadium ion concentration of the final target product electrolyte is X mol / L, if the vanadium oxide is V2O4, the mass of vanadium oxide required per liter of the target electrolyte is 0.5×165.88b g, where b = 0.5X; if the vanadium oxide is V2O3 and V2O4, the mass of vanadium oxide required per liter of the target electrolyte is 0.5×149.88a + 0.5×165.88b g, where a + b = 0.5X; if the vanadium oxide is V2O3 and V2O5, the mass of vanadium oxide required per liter of the target electrolyte is 0.5×149.88a + 0.5×181.88c g, where a + c = 0.5X; if the vanadium oxide is V2O4 and V2O5, the mass of vanadium oxide required per liter of the target electrolyte is 0.5×165.88b + 0.5×181.88c g, where b + c = 0.5X; if the vanadium oxide is V2O3, V2O4 and V2O5, the total mass of vanadium oxide required per liter of the target electrolyte is 0.5×(149.88a + 165.88b + 181.88c) g, a + b + c = 0.5X; if the vanadium oxide is V2O x , 3 < x < 5, the mass of vanadium oxide required per liter of the target electrolyte is 0.5×(101.88 + 16x) g.

6. The method according to claim 1, characterized in that In step 2, the electrode material of the electrolytic cell is graphite carbon felt, carbon paper or carbon cloth.

7. The method according to claim 1, characterized in that In step 2, a hydrogen or oxygen evolution catalyst is also added during the electrolysis process.

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