Vanadium chromium electrolyte, its manufacturing method and flow battery made from same

Abstract

The present application discloses a vanadium-chromium electrolyte, a method for producing the same, and a flow battery comprising the same. The vanadium-chromium electrolyte contains an active material and a free acid, which ionizes to become a proton conductive agent, and the active material contains at least vanadium ions and chromium ions. The present application also discloses a method for producing the vanadium-chromium electrolyte, which includes the steps of dissolving a vanadium compound in the free acid and filtering to obtain a mixed solution of the free acid and vanadium ions, electrolytically reducing vanadium to an average valence of 3.5 to 4, adding a chromium compound, stirring and dissolving, and filtering, and adding water and auxiliary reagents and adjusting the concentration to prepare the vanadium-chromium electrolyte. The vanadium-chromium electrolyte of the present application has the advantages of high vanadium utilization, high energy density, and low watt-hour cost. When applied to a flow battery, it can improve the energy density of the solution and reduce battery costs.

Description

[Technical Field]

[0001] This application claims priority from a Chinese patent application filed with the China Patent Office on September 15, 2022, bearing application number CN202211120529.8 and entitled "Vanadium chromium electrolyte, its manufacturing method, and flow battery made therefrom," the contents of which are incorporated herein by reference.

[0002] This application relates to flow battery technology, and more particularly to a vanadium chromium electrolyte, a method for making the same, and a flow battery comprising the same. [Background technology]

[0003] As an alloy additive, vanadium can improve the strength and toughness of steel, playing an important role in the field of alloy steel. Although vanadium resources are abundant, the production volume of vanadium extracted from vanadium-titanium magnetite depends on the steelmaking production volume, and the vanadium content of the concentrated vanadium slag is low, which makes the cost of vanadium extraction high. Currently, vanadium is mainly used as a steelmaking additive, and its price is greatly influenced by the steel market.

[0004] Flow batteries are batteries that use a liquid to load the active material. A pump pumps the active liquid to the electrodes, where an oxidation-reduction reaction occurs, enabling the storage and release of electricity. Because the solvent used is water, its safety performance is significantly superior to that of lithium and sodium-ion batteries, which use organic solvents. In addition, flow batteries' excellent cycle performance and recyclability mean that their lifetime costs are significantly lower than those of lithium-ion and sodium-ion batteries. Flow batteries are expected to be applied in the energy storage field.

[0005] All-vanadium flow batteries are the most popular type of flow battery. Their advantages—the same elemental composition on both the positive and negative electrodes, the separate power and energy units, and the easy recovery of vanadium solution—have made them popular in the energy storage market in recent years. However, due to the high price of vanadium, the initial investment cost of vanadium batteries is significantly higher than that of lithium batteries. Furthermore, vanadium's limited solubility in aqueous solutions results in a narrow voltage window, resulting in low energy density. While increasing the vanadium concentration is necessary to increase energy density, the high-temperature stability of pentavalent vanadium requires a lower vanadium concentration. Clearly, flow batteries using only vanadium as the active material cannot achieve both high-temperature stability and high energy density.

[0006] As the charge level increases, the concentration of available active materials in the solution decreases, and if the battery is continuously charged at a high current, the current will corrode the carbon felt at the positive electrode, damaging the battery, and a serious hydrogen evolution reaction will occur at the negative electrode. Therefore, in actual operation, to protect the battery, it is common to control the charge SOC, which will result in a low utilization rate of vanadium.

[0007] Iron-chromium batteries utilize the potential of divalent and trivalent iron at the positive electrode and the potential of divalent and trivalent chromium at the negative electrode. Iron-chromium flow batteries are significantly less expensive than vanadium flow batteries. However, due to the low activity of chromium and the presence of trivalent chromium degradation, the chromium activity is lost after long-term cycling, resulting in a significant decrease in electrical capacity. This necessitates a higher reaction temperature, which improves battery efficiency but exacerbates the hydrogen evolution reaction. Furthermore, as cycling progresses, iron ions gradually migrate to the anode, rapidly disrupting the battery balance. Because the potential of divalent and trivalent iron is only +0.77V, if the average valence offset of the electrolyte becomes high, it is difficult to restore it to its original state, which is another fatal drawback of iron-chromium batteries. At high temperatures, the battery assembly requirements are very stringent, requiring the use of high-temperature-resistant fluoroplastics. Therefore, while the electrolyte cost of iron-chromium batteries is significantly lower than that of all-vanadium flow batteries, the cell stack cost is significantly higher. Summary of the Invention [Problem to be solved by the invention]

[0008] To solve the problems of conventional all-vanadium electrolytes, such as low vanadium utilization, narrow voltage window, and low energy density, and the inability of iron-chromium electrolytes to operate stably for a long period of time, a vanadium-chromium electrolyte is provided. This electrolyte has the advantages of high vanadium utilization, high energy density, and low watt-hour cost. When applied to flow batteries, it can improve the energy density of the solution and reduce battery costs. [Means for solving the problem]

[0009] In a first aspect, a vanadium chromium electrolyte is provided, the electrolyte including an active material and a free acid, the free acid being ionized to become a proton conducting agent, and the active material including at least vanadium ions and chromium ions.

[0010] Furthermore, the active material is a vanadium compound and a chromium compound.

[0011] Furthermore, the vanadium compound is VO2, V2O3, VO 13 , V2O5, CrVO4, VOSO4, V2(SO4)3, vanadium dichloride VCl2, vanadium oxide dichloride VOCl2 and vanadium trichloride VCl3.

[0012] Furthermore, the vanadium compound is preferably one or more of vanadium dichloride VCl2, vanadium oxide dichloride VOCl2, vanadium trichloride VCl3 and VO2.

[0013] Furthermore, the chromium compound is one or more of chromium trichloride, chromium dichloride, chromium sulfate, chromium vanadate, and Cr2O3.

[0014] Furthermore, the chromium compound is preferably chromium trichloride and / or chromium dichloride.

[0015] Furthermore, the concentration of the vanadium ions ranges from 0.1 to 5 mol / L, and preferably from 0.5 to 3 mol / L.

[0016] Furthermore, the concentration of the chromium ions is 0.1 to 2 mol / L, and preferably 0.4 to 2 mol / L.

[0017] Research has revealed the following: Chromium has low reactivity, and as the battery cycles, it degrades, resulting in a loss of battery activity. To address this, the solution temperature must typically be raised, e.g., to above 65°C, to increase chromium activity and prevent its degradation. However, this leads to a serious hydrogen evolution reaction and the energy consumption associated with maintaining high temperatures, significantly reducing the energy efficiency of chromium. Typically, the DC side energy efficiency of iron-chromium batteries is only about 70%. A certain concentration of vanadium exhibits excellent activating properties, with divalent vanadium in particular acting as a bridge in the solution. During battery operation, divalent vanadium attached to the electrode surface catalyzes the activity of divalent and trivalent chromium and inhibits the formation of inactive chromium complex ions.

[0018] Therefore, furthermore, the ratio of the amount of vanadium to chromium in the vanadium chromium electrolyte used in the negative electrode is ≧0.3, that is, V:Cr≧0.3, and more preferably, the ratio of the amount of vanadium to chromium is ≧0.5.

[0019] In addition, the ion exchange membrane of the flow battery cannot completely prevent the movement of chromium ions and vanadium ions in the vanadium chromium electrolyte, and during charge-discharge cycles, the vanadium ions and chromium ions move between both sides of the ion exchange membrane, causing changes in the concentrations of the electrolyte on both sides. Here, the concentration range of the electrolyte is only the initial concentration, and vanadium chromium electrolytes whose concentrations increase or decrease after charge-discharge cycles are derivatives of the vanadium chromium electrolyte.

[0020] During the charge and discharge process of a battery, the amounts of vanadium and chromium involved in the electrochemical reaction in the negative electrode electrolyte are equal to the amount of vanadium involved in the electrochemical reaction in the positive electrode electrolyte, but the total amount of vanadium in the positive electrode electrolyte does not necessarily have to be equal to the sum of the total amount of vanadium and the total amount of chromium in the negative electrode electrolyte. Based on the above principle, the formulation and design of the positive and negative electrode electrolytes may be determined by setting the initial vanadium and chromium concentrations to be the same and calculating the volume ratio of the positive and negative electrodes based on the amounts of vanadium and chromium involved in the reaction, or by setting the initial volumes to be the same and calculating the corresponding concentrations of vanadium and chromium involved in the reaction based on the amounts of vanadium and chromium involved in the reaction. The initial volumes and concentrations of the positive and negative electrode electrolytes may be different, but the change in the electron number of the active material involved in the reaction may be the same. In actual applications, the initial formulation design may be changed depending on changes in the environment and the application purpose.

[0021] Furthermore, the concentration (P) of the phosphorus compound in the vanadium chromium electrolyte is 0 to 1 mol / L, preferably 0.05 to 0.6 mol / L. The addition of the phosphorus compound can improve the stability of pentavalent vanadium. The phosphorus compound is one or more of phosphoric acid, sodium phosphate, ammonium phosphate, metaphosphoric acid, sodium metaphosphate, ammonium metaphosphate, pyrophosphoric acid, sodium pyrophosphate, ammonium pyrophosphate, and P2O5.

[0022] Furthermore, the contents of Ti, Cd, Pb, Ni, Co, Cu and Mo in the vanadium chromium electrolyte are all less than 2 mg / L.

[0023] Furthermore, the contents of Ti, Cd, Pb, Ni, Co, Cu and Mo in the vanadium chromium electrolyte are all less than 0.1 mg / L.

[0024] Furthermore, the free acid is a mixture of one or more of hydrochloric acid, sulfuric acid, phosphoric acid, and methanesulfonic acid. The free acid is preferably a mixture of one or more of hydrochloric acid, phosphoric acid, and methanesulfonic acid.

[0025] Furthermore, the concentration of free hydrogen ions in the vanadium chromium electrolyte is 0.1 to 5 mol / L, preferably 0.5 to 4 mol / L, and more preferably 1 to 3 mol / L.

[0026] In a second aspect, there is provided a method for producing a vanadium chromium electrolyte, the method comprising: Step 1: dissolving a vanadium compound using a free acid and filtering the solution to obtain a mixed solution of the free acid and vanadium ions; Step 2: electrolytically reducing vanadium until the average valence is 3.5 to 4; Step 3: adding a chromium compound, stirring and dissolving, and then filtering; and step 4 of adding pure water and auxiliary reagents and adjusting the concentrations to prepare a vanadium chromium electrolyte solution.

[0027] Additionally, the auxiliary reagents include, but are not limited to, phosphorus compounds.

[0028] Furthermore, the electrolytic reduction in step 2 uses a battery structure in which the anode is a tetravalent vanadium solution and the cathode is a mixed solution, and after charging, the valence of the vanadium ions in the anode is increased to pentavalent and the valence of the vanadium ions in the mixed solution in the cathode is decreased to 3.5 to 4.

[0029] In a third aspect, there is further provided the use of the vanadium chromium electrolyte in the field of flow batteries.

[0030] Furthermore, the vanadium chromium electrolyte is used as a positive electrode electrolyte and / or a negative electrode electrolyte of a flow battery.

[0031] Furthermore, when the vanadium chromium electrolyte is used as the positive electrode electrolyte and the negative electrode electrolyte of a flow battery, the concentrations of vanadium and chromium in the positive electrode electrolyte and the negative electrode electrolyte may differ, but the total amount of vanadium in the positive electrode electrolyte is the same as the sum of the amounts of vanadium and chromium in the negative electrode electrolyte.

[0032] In a fourth aspect, a vanadium chromium flow battery is provided, which includes a positive electrode, a negative electrode, and an ionic membrane, and uses the vanadium chromium electrolyte as the positive electrode electrolyte and / or the negative electrode electrolyte.

[0033] Furthermore, the ionic membrane is a proton exchange membrane, allowing hydrogen ions to pass freely across the membrane.

[0034] Furthermore, the operating temperature of the vanadium chromium flow battery is 0°C to 50°C, and preferably 10°C to 45°C.

[0035] Furthermore, the energy density of the vanadium chromium flow battery is 30 to 50 Wh / L, preferably 35 to 50 Wh / L, and more preferably 40 to 50 Wh / L.

[0036] Furthermore, the vanadium chromium flow battery operates at room temperature and uses PP or PE materials for the electrode plate frame, eliminating the need for fluorine materials. Based on the principles of the present application, there is no need to use precious metals, lead, or bismuth-deposited carbon felt for the electrodes, reducing costs and preventing the hydrogen evolution reaction.

[0037] The operating principle of the vanadium chromium flow battery according to the present invention is as follows.

[0038] Positive electrode is VO2 + / VO 2+ The negative electrode is V 3+ / V 2+ , Cr 3+ / Cr 2+ The potential of the electrode is used to form an electrochemical couple.

[0039] V 3+ / V 2+ , Cr 3+ / Cr 2+ Although the standard potentials of both are lower than the hydrogen potential, they can exist stably in aqueous solution, provided that the concentration of the hydrogen-generating element in the solution is controlled due to reaction kinetics, thereby enabling the charging and discharging of batteries.

[0040] positive electrode (1) H2O+VO 2+ =VO2 + +2H + +e+0.991V negative electrode (1)V 3+ +e = V 2+ -0.225V (2)Cr 3+ +e = Cr 2+ -0.407V The discharge process is reversed. [Effects of the Invention]

[0041] The present application provides a vanadium chromium electrolyte, a method for producing the same, and a flow battery containing the same, which have the following beneficial effects:

[0042] (1) Because the potential of Cr(III) / Cr(II) is lower than that of V(III) / V(II), the battery's voltage window is broadened, and the average battery voltage is increased from +1.25 V, the average discharge voltage of vanadium batteries, to approach +1.4 V. When charging the same amount of electricity, the battery's energy density is improved by approximately 12%. Compared to vanadium flow batteries, the flow battery of the present application has an improved solution energy density, which can be increased from less than 30 Wh / L for all-vanadium flow batteries to more than 40 Wh / L.

[0043] (2) The charge / discharge SOC of the electrolyte of the present invention is significantly higher than that of the electrolyte of an all-vanadium flow battery. When charging at a high SOC, the potential of chromium in the negative electrode solution is lower, so that even if all of the vanadium is reduced, the occurrence of a hydrogen generation reaction can be avoided. At the positive electrode, the presence of chromium allows all of the vanadium to be oxidized to a pentavalent state, and Cr 6+ / Cr 3+The standard electrode potential of vanadium flow batteries is 1.23 V, which is lower than the chlorine and oxygen evolution potentials. This ensures that the carbon electrode will not be destroyed when vanadium is completely oxidized to pentavalent form, and prevents the generation of chlorine gas. This improves the vanadium utilization rate, from 80% to 100% in hydrochloric acid systems, significantly reducing the cost of vanadium flow batteries. At the same time, by substituting chromium for some of the vanadium at the same energy density, battery costs can also be significantly reduced.

[0044] (3) Compared with iron-chromium flow batteries, the present flow battery improves the cathode potential from +0.77V to +0.99V, and can achieve cathode recovery using common reducing agents, achieving long-term stable operation of the battery. Under the action of vanadium, the activity of chromium is released, and at room temperature, an energy efficiency of over 80% and a coulombic efficiency of over 95% can be achieved.

[0045] (4) By adding chromium to the vanadium solution and assembling it into a battery, the electrochemical reaction activity of chromium can be significantly improved, avoiding the charge / discharge process at high temperatures (50-65°C), reducing the requirements for the system's cell stack, and reducing the side reaction of hydrogen generation. Even when the charge / discharge reaction is performed at 25°C, a battery efficiency of 96% CE and 85% EE can be achieved. By using chromium instead of vanadium, the battery cost can be significantly reduced, the OCV can be increased to 1.6V, and the battery energy density can be increased to over 40Wh / L. [Brief explanation of the drawings]

[0046] [Figure 1] 1 is a curve showing the change in capacity of an all-vanadium flow battery versus charge / discharge cycles. [Figure 2] 1 is a curve showing the change in capacity of a vanadium chromium battery versus charge and discharge cycles. [Figure 3] 1 is a charge / discharge cycle-efficiency curve of an all-vanadium flow battery. [Figure 4] 1 is a charge / discharge cycle-efficiency curve of a vanadium chromium flow battery. [Figure 5] 1 is a charge / discharge cycle-voltage curve of a vanadium chromium flow battery. [Figure 6] This is the structure of a vanadium chromium flow battery. DETAILED DESCRIPTION OF THE INVENTION

[0047] The following clearly and completely describes the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. It should be noted that the embodiments described here are only some of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, all other embodiments that a person skilled in the art can obtain without any creative effort fall within the scope of protection of the present application.

[0048] The present disclosure provides numerous different embodiments or examples for realizing different structures of the present application. To simplify the present disclosure, the present application describes components and arrangements in specific examples. These are for illustrative purposes only and are not intended to limit the present application. Furthermore, while the present application may duplicate reference numbers and / or characters in different examples, this duplication is for the purposes of simplicity and clarity and does not imply a relationship between the various embodiments and / or arrangements discussed. Additionally, while the present application provides examples of various specific processes and materials, those skilled in the art will recognize that other processes may be applied and / or other materials may be used.

[0049] Example 1 This example discloses a vanadium chromium flow battery having high energy density, and the vanadium chromium electrolyte used in the vanadium chromium flow battery includes an anode electrolyte and a cathode electrolyte. In the negative electrode electrolyte, the concentration of V is 1.95 mol / L, and Cr 3+ 0.7 mol / L, Cl - 9.8 mol / L, phosphoric acid 0.05 mol / L, In the positive electrode electrolyte, the concentration of V is 1.95 mol / L, and Cr 3+ 0.7 mol / L, Cl -9.8 mol / L, and phosphoric acid 0.05 mol / L. The method for producing the electrolyte solution of this example is as follows. In step 1, VO2 is dissolved using hydrochloric acid and filtered to obtain a mixed solution of free acid and vanadium ions. In step 2, vanadium is reduced until its average valence becomes 3.5 to 4. In step 3, chromium trichloride is added, stirred to dissolve, and filtered. In step 4, water is added to adjust the concentration and prepare the electrolyte solution.

[0050] Comparative Example 1 This comparative example discloses an all-vanadium flow battery electrolyte, the components and contents of which are shown in Table 1.

[0051] Table 1 shows the components and contents of the electrolytes of Comparative Example 1 and Example 1.

[0052] [Table 1]

[0053] In order to examine the performance of the electrolytes of Example 1 and Comparative Example, both were used in a flow battery, and the performance was examined. The flow battery includes, in order, a positive conductive plate, a positive electrolyte, a positive frame, a positive electrode, an ion exchange membrane, a negative electrode, a negative electrolyte, a negative frame, and a negative conductive plate, which are compressed together to form a battery structure.

[0054] The positive electrode frame defines a cavity, the positive electrode is placed in the frame, the electrolyte is in contact with the electrode, and an electrochemical reaction occurs at the electrode.

[0055] The negative electrode electrolyte and the positive electrode electrolyte of Example 1 were placed in a volume ratio of 1:1.36 on both sides of the double flow battery shown in FIG. 6, and pumped into the negative electrode cavity body and the positive electrode cavity body of the battery, respectively. The charge-discharge cycle was carried out at 30°C, and the current was 100 mA / cm. 2 The constant current charging was performed at 50 mA / cm. The cutoff voltage of the constant current charging was 1.65 V.2 Constant voltage charging at 100mA / cm 2 The charge-discharge cycle curves are shown in Figures 2, 4, and 5. Similarly, the electrolyte (V1.65M) of the all-vanadium flow battery of Comparative Example 1 was placed on both sides of the double flow battery at a volume ratio of 1:1 and pumped into the positive and negative electrode cavities of the battery, respectively. The charge-discharge cycle was performed at 30°C with a current of 100 mA / cm. 2 The cut-off voltage was 1.55 V and the constant current was 50 mA / cm. 2 Constant voltage charging at 100mA / cm 2 The charge-discharge cycle experiment showed that the energy density of the vanadium chromium flow battery of Example 1 was 43 Wh / L, and the energy density of the all-vanadium flow battery of Control Example 1 was 26 Wh / L.

[0056] Compared with the vanadium concentration of the all-vanadium mixed acid system of Comparative Example 1, the vanadium consumption per unit energy of the electrolyte of Example 1 is reduced from 5.775 kg V2O5 / KWh to 4.13 kg V2O5 / KWh, reducing the vanadium consumption by 28.5% and increasing the CrCl3.6H2O / KWh by 4.34 kg, with a reduction cost of 300 RMB / KWh.

[0057] Example 2 This example discloses a high energy density flow battery, and the vanadium electrolytes employed in this vanadium flow battery include a negative electrode electrolyte and a positive electrode electrolyte. In the negative electrode electrolyte, the concentration of V is 2.5 mol / L, and 3+ 0.5mol / L, Cl 9.2mol / L, SO4 2- 0.6 mol / L, In the positive electrode electrolyte, the concentration of V is 3 mol / L, and Cr 3+ 0.3 mol / L, Cl 8.1 mol / L, SO4 2- It is 0.9 mol / L. The manufacturing procedures and test methods for the negative and positive electrode electrolytes were essentially the same as those in Example 1, except for the type and content of the active material. The negative and positive electrode electrolytes were placed in a double flow battery at a volume ratio of 1:1, and pumped into the positive and negative electrode cavities of the battery, respectively, and then subjected to charge-discharge cycles at room temperature. The negative and positive electrolytes were placed in a double flow battery with a volume ratio of 1:1, and pumped into the negative and positive cavity bodies of the battery, respectively. The charge-discharge cycle was carried out at 30°C and 100mA / cm 2 The constant current charging was performed at 50 mA / cm. The cutoff voltage of the constant current charging was 1.65 V. 2 Constant voltage charging at 100mA / cm 2 The charge-discharge cycle curves are shown in Figures 1 and 3. Similarly, the electrolyte (V1.65M) of the all-vanadium flow battery of Comparative Example 1 was placed on both sides of the double flow battery at a volume ratio of 1:1 and pumped into the positive and negative electrode cavities of the battery, respectively. The charge-discharge cycle was performed at 30°C and at a current of 100 mA / cm. 2 The cut-off voltage was 1.55 V and the constant current was 50 mA / cm. 2 Constant voltage charging at 100mA / cm 2 The charge-discharge cycle experiment shows that the energy density of the vanadium chromium flow battery of this example is 50 Wh / L.

[0058] Example 3 Based on Example 2, 0.12 mol / L of H3PO4 was added to the positive and negative electrode electrolytes. In other words, the concentration of V in the negative electrode electrolyte is 2.5 mol / L, and Cr 3+ 0.5mol / L, Cl 9.2mol / L, SO4 2 -0.6 mol / L, 0.12 mol / L H3PO4, In the positive electrode electrolyte, the concentration of V is 3 mol / L, and Cr 3+ 0.3 mol / L, Cl 8.1 mol / L, SO4 2- 0.9 mol / L and 0.12 mol / L H3PO4. The manufacturing procedures and test methods for the negative and positive electrode electrolytes were basically the same as those in Example 1, except for the type and content of the active material. The negative and positive electrode electrolytes were placed in a double flow battery with a volume ratio of 1:1, and pumped into the negative and positive electrode cavity bodies of the battery, respectively. Charge-discharge cycles were performed at 30°C and 100 mA / cm. 2 The constant current charging was performed at 50 mA / cm. The cutoff voltage of the constant current charging was 1.65 V. 2 Constant voltage charging at 100mA / cm 2 The charge-discharge cycle curves are shown in Figures 1 and 3. Similarly, the electrolyte (V1.65M) of the all-vanadium flow battery of Comparative Example 1 was placed on both sides of the double flow battery at a volume ratio of 1:1 and pumped into the positive and negative electrode cavities of the battery, respectively. The charge-discharge cycle was performed at 30°C and at a current of 100 mA / cm. 2 The cut-off voltage was 1.55 V and the constant current was 50 mA / cm. 2 Constant voltage charging at 100mA / cm 2 The charge-discharge cycle experiment shows that the energy density of the vanadium chromium flow battery of this example is 52 Wh / L.

[0059] The batteries of Examples 2 and 3 were each charged to 95% SOC, and at this time, the ratio of the amount of pentavalent vanadium in the positive electrode electrolyte to the total amount of vanadium, VO 2+ / V 総量 The positive electrode electrolyte was sealed and stored at 30, 40, and 50°C for 1 to 5 days to observe its stability. As can be seen from the data in Table 2, after adding phosphorus, precipitation occurred on the fifth day at 50°C, indicating that phosphorus-added compounds can significantly improve the high-temperature stability of the positive electrode electrolyte.

[0060] Table 2 shows the stability experiments.

[0061] [Table 2] Note that √ indicates that there is no change in the stability of the solution, and × indicates that precipitation occurs.

[0062] Example 4 This embodiment discloses a high energy density flow battery, and the vanadium electrolytes employed in this vanadium flow battery include an anode electrolyte and a cathode electrolyte. In the negative electrode electrolyte, the concentration of V is 1 mol / L, and 3+ 1.5 mol / L, Cl - 10 mol / L, In the positive electrode electrolyte, the concentration of V is 1.5 mol / L, and Cr 3+ 0.3 mol / L, Cl - It is 6.8 mol / L. The manufacturing procedures and test methods for the negative and positive electrode electrolytes were basically the same as those in Example 1, except for the type and content of the active material. The negative and positive electrode electrolytes were placed in a double flow battery with a volume ratio of 1:1.67, and pumped into the negative and positive electrode cavity bodies of the battery, respectively. Charge-discharge cycles were performed at 30°C, with a current of 100 mA / cm. 2 The constant current charging was performed at 50 mA / cm. The cutoff voltage of the constant current charging was 1.65 V. 2 Constant voltage charging at 100mA / cm 2 The charge-discharge cycle experiment shows that the vanadium chromium flow battery of this example has an energy density of 54 Wh / L and an energy efficiency of 81%. Although the battery energy density in this example does not reach 40 Wh / L, the vanadium consumption per unit energy is 62% of that of the standard 1.65M electrolyte for the entire vanadium flow battery. Furthermore, lowering the vanadium concentration is advantageous for improving the high-temperature stability of the positive electrode electrolyte. The positive electrode electrolyte in this example can operate stably at temperatures above 50°C.

[0063] Example 5 This example discloses a flow battery, and the vanadium chromium electrolyte employed in this flow battery includes an anode electrolyte and a cathode electrolyte. In the negative electrode electrolyte, the concentration of V is 0.8 mol / L, and the concentration of Cr is 3+ 0.9 mol / L, Cl - 8 mol / L, In the positive electrode electrolyte, the concentration of V is 1.5 mol / L, and Cr 3+ 0.2 mol / L, Cl - It is 6.8 mol / L. The manufacturing procedures and test methods for the negative and positive electrode electrolytes were basically the same as those in Example 1, except that the type and content of the active material were adjusted. The negative and positive electrode electrolytes were placed in the battery at a volume ratio of 1:1.13, and pumped into the negative and positive electrode cavity bodies of the battery, respectively. The batteries were maintained at 30°C and subjected to charge-discharge cycles at 100 mA / cm. 2 The constant current charging was performed at 50 mA / cm. The cutoff voltage of the constant current charging was 1.65 V. 2 Constant voltage charging at 100mA / cm 2 The battery is discharged at a constant current of 1 V, with a cutoff voltage of 1 V and an energy efficiency of 86% during the charge-discharge cycle.

[0064] Example 6 This example discloses a flow battery, and the vanadium chromium electrolyte employed in this flow battery includes an anode electrolyte and a cathode electrolyte. In the negative electrode electrolyte, the concentration of V is 0.2 mol / L, and 3+ 1.5 mol / L, Cl - 8 mol / L, In the positive electrode electrolyte, the concentration of V is 1.5 mol / L, and Cr 3+ 0.2 mol / L, Cl - It is 6.8 mol / L. The manufacturing procedures and test methods for the negative and positive electrode electrolytes were basically the same as those in Example 1, except that the type and content of the active material were adjusted. The negative and positive electrode electrolytes were placed in the battery at a volume ratio of 1:1.13, and pumped into the negative and positive electrode cavity bodies of the battery, respectively. The batteries were maintained at 30°C and subjected to charge-discharge cycles at 100 mA / cm. 2 The constant current charging was performed at 50 mA / cm. The cutoff voltage of the constant current charging was 1.65 V.2 Constant voltage charging at 100mA / cm 2 The battery is discharged at a constant current of 1 V, with a cut-off voltage of 1 V. The energy efficiency of the charge / discharge cycle is 70%.

[0065] Comparing Example 6 and Example 5, the only difference between the two is the molar ratio of vanadium to chromium in the negative electrode: the molar ratio of vanadium to chromium in Example 6 is 0.13, while the molar ratio of vanadium to chromium in Example 5 is 0.89; otherwise, they are identical. As can be seen from the detection results, when the vanadium to chromium ratio is in a low range, the battery efficiency of the chromium is low, similar to that of an iron-chromium battery. This is because when the vanadium concentration is low, the activity of the chromium is not easily improved by catalysis by the vanadium.

[0066] Finally, it should be noted that the above embodiments are merely for illustrating the technical solutions of the present application, and are not intended to limit the same. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified or equivalently substituted for some or all of the technical features therein. Furthermore, such modifications or substitutions do not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the present application.

Claims

1. The catalyst comprises an active material and a free acid, the free acid being ionized to become a proton conductive agent, and the active material comprises at least vanadium ions and chromium ions. Vanadium chromium electrolyte.

2. The active material is a vanadium compound and a chromium compound.

2. The vanadium chromium electrolyte according to claim 1.

3. The vanadium compound is VO ２ , V ２ O ３ , V ６ O １３ , V ２ O ５ , CrVO ４ , VOSO ４ , V ２ (SO ４ ) ３ , VCl ２ , VOCl ２ and VCl ３ One or more selected from The vanadium chromium electrolyte according to claim 2.

4. The chromium compounds include chromium trichloride, chromium dichloride, chromium sulfate, chromium vanadate, and Cr ２ O ３ One or more selected from The vanadium chromium electrolyte according to claim 2.

5. The concentration range of the vanadium ions is 0.1 to 5 mol / L. The vanadium chromium electrolyte according to claim 1 or 2.

6. The concentration range of the vanadium ions is 0.5 to 3 mol / L; The vanadium chromium electrolyte according to claim 5.

7. The concentration of the chromium ions is 0.1 to 2 mol / L. The vanadium chromium electrolyte according to claim 1 or 3.

8. The concentration of the chromium ions is 0.4 to 2 mol / L. The vanadium chromium electrolyte according to claim 7.

9. The concentration of the phosphorus compound in the vanadium chromium electrolytic solution is 0 to 1 mol / L.

2. The vanadium chromium electrolyte according to claim 1.

10. The concentration of the phosphorus compound in the vanadium chromium electrolytic solution is 0.05 to 0.6 mol / L. The vanadium chromium electrolyte according to claim 9.

11. The phosphorus compounds include phosphoric acid, sodium phosphate, ammonium phosphate, metaphosphoric acid, sodium metaphosphate, ammonium metaphosphate, pyrophosphoric acid, sodium pyrophosphate, ammonium pyrophosphate, and P ２ O ５ One or more selected from The vanadium chromium electrolyte according to claim 9.

12. The contents of Ti, Cd, Pb, Ni, Co, Cu and Mo in the vanadium chromium electrolyte are all less than 2 mg / L; 2. The vanadium chromium electrolyte according to claim 1.

13. The free acid is one or a mixture of two or more acids selected from hydrochloric acid, sulfuric acid, phosphoric acid, and methanesulfonic acid.

2. The vanadium chromium electrolyte according to claim 1.

14. The concentration of free hydrogen ions in the vanadium chromium electrolyte is 0.1 to 5 mol / L.

2. The vanadium chromium electrolyte according to claim 1.

15. Step 1: dissolving a vanadium compound using a free acid and filtering the resulting solution to obtain a mixed solution of the free acid and vanadium ions; Step 2: electrolytically reducing vanadium until the average valence is 3.5 to 4; Step 3: adding a chromium compound, stirring and dissolving the mixture, and then filtering the mixture; Step 4: adding pure water and auxiliary reagents and adjusting the concentration to prepare a vanadium chromium electrolyte; Method for producing vanadium chromium electrolyte.

16. The electrolytic reduction in step 2 uses a battery structure in which the anode is a tetravalent vanadium solution and the cathode is a mixed solution, and after charging, the valence of the vanadium ions in the anode is increased to pentavalent and the valence of the vanadium ions in the mixed solution in the cathode is decreased to 3.5 to 4. The method for producing the vanadium chromium electrolyte according to claim 15.

17. Use of the vanadium chromium electrolyte according to any one of claims 1 to 14 in the field of flow batteries.

18. A vanadium chromium flow battery comprising a positive electrode, a negative electrode, and an ionic membrane, wherein the vanadium chromium electrolyte according to any one of claims 1 to 14 is used as the positive electrode electrolyte and / or the negative electrode electrolyte. Vanadium chromium flow battery.

19. The operating temperature of the vanadium chromium flow battery is 0°C to 50°C.

20. The vanadium chromium flow battery of claim 18.

20. The energy density of the vanadium chromium flow battery is 30 to 50 Wh / L.

20. The vanadium chromium flow battery of claim 18.

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