Vanadium-chromium electrolyte, preparation method therefor, and flow battery comprising same

Abstract

A vanadium-chromium electrolyte, a preparation method therefor, and a flow battery comprising same. The vanadium-chromium electrolyte comprises an active substance and a free acid; the free acid is ionized and thereupon serves as a proton conductor, and the active substance at least comprises vanadium ions and chromium ions. The preparation method for the vanadium-chromium electrolyte comprises the following steps: dissolving a vanadium compound by using said free acid, filtering, and obtaining a mixed solution of free acid and vanadium ions; carrying out electrolytic reduction on vanadium to an average valence state of 3.5-4; adding a chromium compound, stirring and dissolving, and filtering; and adding water and an auxiliary reagent, adjusting the concentration, and obtaining the vanadium-chromium electrolyte. The vanadium-chromium electrolyte has the advantages of high vanadium utilization, high energy density, and low watt-hour costs; when same is used in a flow battery, same can improve the energy density of a solution, and reduces the cost of the battery.

Description

A vanadium-chromium electrolyte, its preparation method and liquid flow battery composed of the same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 15, 2022, with application number CN202211120529.8 and application name “A vanadium-chromium electrolyte, its preparation method and a flow battery composed thereof”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to liquid flow battery technology, and in particular to a vanadium-chromium electrolyte, a preparation method thereof, and a liquid flow battery composed thereof. Background Art

[0003] As an alloying additive, vanadium improves the strength and toughness of steel and plays a crucial role in alloy steel. While vanadium resources are plentiful, the yield from vanadium-titanium magnetite depends on steelmaking output, and the low vanadium content in the enriched slag results in high vanadium extraction costs. Currently, vanadium is primarily used as a steelmaking additive, and its price is significantly influenced by the steel market.

[0004] A flow battery uses a liquid-loaded active material. The active liquid is pumped into the electrodes, where a redox reaction occurs, storing and releasing electrical energy. Because it uses water as a solvent, its safety performance is significantly superior to that of lithium- and sodium-ion batteries, which use organic solvents. Furthermore, due to its excellent cycling performance and recoverability, its lifecycle cost is significantly lower than that of lithium-ion and sodium-ion batteries. Flow batteries hold great promise in the energy storage field.

[0005] All-vanadium redox flow batteries are the most prominent type of redox flow battery. Their advantages, including identical elemental composition on both the positive and negative electrodes, separation of power and energy units, and easy vanadium liquid recovery, have made them popular in the energy storage market in recent years. However, the high price of vanadium makes the initial investment cost of vanadium batteries significantly higher than that of lithium batteries. Furthermore, vanadium's limited solubility in aqueous solutions and narrow voltage window result in low energy density. Redox flow batteries composed solely of vanadium as the active material cannot achieve both high-temperature stability and high energy density.

[0006] A higher charge level reduces the concentration of available active substances in the solution. Continuing to charge at high currents can corrode the carbon felt at the positive electrode, damaging the battery, and cause severe hydrogen evolution at the negative electrode. Therefore, in practice, the charge SOC is often controlled to protect the battery, resulting in lower vanadium utilization.

[0007] In iron-chromium batteries, the positive electrode utilizes the potential of divalent and trivalent iron, while the negative electrode utilizes the divalent and trivalent potential of chromium. At the same time, the cost of iron-chromium flow batteries is significantly lower than that of vanadium flow batteries. However, due to the low activity of chromium and the aging of trivalent chromium, chromium loses its activity after long-term cycling, and the capacitance decreases significantly. This requires increasing the reaction temperature, so achieving higher battery efficiency may lead to severe hydrogen evolution reactions. In addition, as the cycle progresses, iron ions gradually migrate to the anode, causing the battery to quickly become unbalanced. Because the potential of divalent / trivalent iron is only +0.77V, once the average valence state of the electrolyte shifts and increases, it is difficult to restore it to its initial state. This is also a fatal flaw of iron-chromium batteries. High temperatures place extremely stringent requirements on battery assembly, requiring the use of high-temperature-resistant fluoroplastics. Therefore, although the cost of the electrolyte in iron-chromium batteries is much lower than that of all-vanadium flow batteries, the cost of the battery stack is significantly higher. Technical issues

[0008] Existing all-vanadium electrolytes have low vanadium utilization, a narrow voltage window range, and low energy density, while iron-chromium electrolytes cannot operate stably for a long time. Therefore, a vanadium-chromium electrolyte has been proposed. This electrolyte has the advantages of high vanadium utilization, high energy density, and low watt-hour cost. When used in liquid flow batteries, it can increase the energy density of the solution and reduce battery costs. Technical Solutions

[0009] In a first aspect, a vanadium-chromium electrolyte is provided, comprising an active substance and a free acid, wherein the free acid acts as a proton conductor after ionization, and the active substance contains at least vanadium ions and chromium ions.

[0010] Furthermore, the active substances are vanadium compounds and chromium compounds.

[0011] Furthermore, the vanadium compound is VO2, V2O3, V6O 13 , one or more of V2O5, CrVO4, VOSO4, V2(SO4)3, vanadium dichloride VCl2, vanadium oxychloride VOCl2 and vanadium trichloride VCl3.

[0012] Furthermore, the vanadium compound is preferably one or more of vanadium dichloride VCl2, vanadium oxychloride 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, preferably from 0.5 to 3 mol / L.

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

[0017] Research has found that chromium has low reactivity and ages over time, leading to battery inactivity loss. Typically, the solution temperature needs to be raised, for example, to above 65°C, to enhance chromium activity and inhibit chromium aging. However, this leads to severe hydrogen evolution reactions and energy loss from maintaining high temperatures, significantly reducing chromium's energy efficiency. Typically, the DC side energy efficiency of an iron-chromium battery is only around 70%. A certain concentration of vanadium can have a significant activation effect, especially divalent vanadium, which acts as a bridge in the solution. During the battery process, divalent vanadium attached to the electrode surface catalyzes the activity of divalent and trivalent chromium, inhibiting the formation of inert chromium complex ions.

[0018] Therefore, further, the mass ratio 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 mass ratio of vanadium to chromium is ≥0.5.

[0019] It's important to note that the ion exchange membrane of a flow battery cannot completely block the migration of chromium and vanadium ions in the vanadium-chromium electrolyte. During charge-discharge cycles, vanadium and chromium ions migrate between the two sides of the ion exchange membrane, causing changes in the electrolyte concentration on both sides. The electrolyte concentration range described here only represents the initial concentration. A vanadium-chromium electrolyte with an increased or decreased concentration after charge-discharge cycles is a derivative of the vanadium-chromium electrolyte.

[0020] During the battery charge and discharge process, the amount of vanadium and chromium participating in the electrochemical reaction in the negative electrolyte is equal to the amount of vanadium participating in the electrochemical reaction in the positive electrolyte, but this does not mean that the total amount of vanadium in the positive electrolyte must be equal to the sum of the total amount of vanadium and total chromium in the negative electrolyte. Based on the above principles, the preparation strategy for the positive and negative electrolytes can be to set the same initial vanadium and chromium mass concentration, and calculate the positive and negative electrode volume ratio based on the amount of vanadium and chromium participating in the reaction; or to set the same initial volume, and calculate the corresponding concentration of the positive and negative electrodes based on the amount of vanadium and chromium participating in the reaction; the initial volume and concentration of the positive and negative electrolytes can be set to be different, but the change in the number of electrons of the active substances participating in the reaction is the same. In actual applications, the initial preparation strategy can be changed according to changes in the environment and different application purposes.

[0021] Furthermore, the concentration of the phosphorus compound (P) 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 one or a mixture of hydrochloric acid, sulfuric acid, phosphoric acid and methanesulfonic acid. The free acid is preferably one or a mixture of hydrochloric acid, phosphoric acid and methanesulfonic acid.

[0025] Furthermore, the free hydrogen ion concentration 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, a method for preparing a vanadium-chromium electrolyte is provided, comprising the following steps:

[0027] Step 1. dissolving a vanadium compound with a free acid and filtering to obtain a mixed solution of the free acid and vanadium ions;

[0028] Step 2. Electrolytically reducing vanadium to an average valence of 3.5 to 4;

[0029] Step 3. Add chromium compound, stir to dissolve, and filter;

[0030] Step 4. Add pure water and auxiliary reagents, adjust the concentration, and prepare a vanadium-chromium electrolyte.

[0031] Furthermore, the auxiliary reagent includes but is not limited to a phosphorus compound.

[0032] Furthermore, the electrolytic reduction in step 2 is as follows: a battery structure is adopted, the anode is a tetravalent vanadium solution, the cathode is a mixed solution, after charging, the valence of the vanadium ions at the anode increases to pentavalent, and the valence of the vanadium ions in the cathode mixed solution decreases to 3.5-4.

[0033] In a third aspect, a use of a vanadium-chromium electrolyte in the field of flow batteries is provided.

[0034] Furthermore, the vanadium-chromium electrolyte is used as the positive electrode electrolyte and / or negative electrode electrolyte of a liquid flow battery.

[0035] Furthermore, when the vanadium-chromium electrolyte is applied to the positive and negative electrolytes of a flow battery, the concentrations of vanadium and chromium in the positive and negative electrolytes may be different, but the total amount of vanadium in the positive electrolyte is the same as the sum of the amounts of vanadium and chromium in the negative electrolyte.

[0036] In a fourth aspect, a vanadium-chromium flow battery is provided, comprising a positive electrode, a negative electrode and an ion membrane, wherein the positive electrode electrolyte and / or the negative electrode electrolyte adopts the above-mentioned vanadium-chromium electrolyte.

[0037] Furthermore, the ion membrane is a proton exchange membrane, which can allow hydrogen ions to pass freely on both sides of the membrane.

[0038] Furthermore, the operating temperature of the vanadium-chromium flow battery is 0-50°C, preferably 10-45°C.

[0039] 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.

[0040] Furthermore, the vanadium-chromium flow battery operates at room temperature and uses PP or PE materials as the plate frame, eliminating the need for fluorine materials. Based on the principles of this application, there is no need to use precious metals or lead or bismuth deposited carbon felt as electrodes, reducing costs and preventing hydrogen evolution reactions.

[0041] The working principle of the vanadium-chromium flow battery in this application is as follows:

[0042] Positive electrode uses VO2 + / VO 2+ The negative electrode uses V 3+ / V 2+ Cr 3+ / Cr 2+ potential, forming an electrochemical couple.

[0043] Although V 3+ / V 2+ Cr 3+ / Cr 2+ The standard potential of both is lower than the hydrogen potential, but due to the reaction kinetics, under the premise of controlling the concentration of hydrogen element in the solution, both can exist stably in the aqueous solution, thereby realizing the charge and discharge of the battery.

[0044] positive electrode

[0045] (1)H2O+VO 2+ =VO2 + +2H + +e +0.991V

[0046] negative electrode

[0047] (1)V 3+ +e ＝ V 2+ -0.225V

[0048] (2)Cr 3+ +e ＝Cr 2+ -0.407V

[0049] The discharge process is the opposite. Beneficial effects

[0050] The present application provides a vanadium-chromium electrolyte, a preparation method thereof, and a flow battery containing the same, which have the following beneficial effects:

[0051] (1) Since the Cr(III) / Cr(II) potential is lower than V(III) / V(II), the voltage window of the battery is widened, and the average battery voltage is increased from the average discharge voltage of the vanadium battery from +1.25V to nearly +1.4V. When the same amount of electricity is charged, the energy density of the battery is increased by about 12%. Compared with the vanadium liquid flow battery, the liquid flow battery of the present application improves the energy density of the solution, which can be increased from less than 30Wh / L of the all-vanadium liquid flow battery to more than 40Wh / L.

[0052] (2) The charge and discharge SOC of the electrolyte of the present application is significantly higher than that of the all-vanadium liquid flow battery electrolyte. When charging at a high SOC, the potential of chromium in the negative electrode solution is lower. Even if all the vanadium is reduced, the occurrence of hydrogen evolution reaction can still be avoided. At the positive electrode, due to the presence of chromium, all the vanadium can be oxidized to pentavalent. 6+ / Cr 3+ The standard electrode potential is 1.23V, lower than the potentials for chlorine and oxygen evolution. Therefore, even when vanadium is completely oxidized to pentavalent, the carbon electrode remains intact and chlorine production is prevented. This increases vanadium utilization from 80% in the hydrochloric acid system to 100%, significantly reducing the cost of vanadium flow batteries. Using chromium to replace some vanadium at the same energy density can also significantly reduce battery costs.

[0053] (3) Compared with the iron-chromium flow battery, the flow battery of the present application increases the positive electrode potential from +0.77V to +0.99V, and can use common reducing agents to achieve positive electrode recovery, thereby achieving long-term stable operation of the battery; under the action of vanadium, the activity of chromium is released, and only at room temperature, an energy efficiency of more than 80% and a coulombic efficiency of more than 95% can be obtained;

[0054] (4) Adding chromium to a vanadium solution and assembling it into a battery can significantly improve the electrochemical activity of chromium, avoid the use of high-temperature (50-65°C) charging and discharging processes, reduce the system's requirements for the battery stack, and reduce the hydrogen evolution side reaction. When the charging and discharging reaction is carried out at 25°C, a battery efficiency of 96% CE and 85% EE can still be achieved. Replacing vanadium with chromium can significantly reduce battery costs, increase OCV to 1.6V, and increase battery energy density to over 40Wh / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is the capacity change curve of the all-vanadium redox flow battery charge and discharge cycle;

[0056] Figure 2 is the capacity change curve of the vanadium-chromium battery charge and discharge cycle;

[0057] Figure 3 is the charge and discharge cycle - efficiency curve of the all-vanadium redox flow battery;

[0058] Figure 4 is the charge and discharge cycle - efficiency curve of the vanadium-chromium flow battery;

[0059] Figure 5 is a charge and discharge cycle-voltage curve of a vanadium-chromium flow battery;

[0060] Figure 6 shows the structure of a vanadium-chromium flow battery.

[0061] Implementation Methods of the Application

[0062] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0063] The disclosure of the present application provides many different embodiments or examples for realizing the different structures of the present application. In order to simplify the disclosure of the present application, the components and settings of specific examples are described in the present application. Of course, they are merely examples, and the purpose is not to limit the present application. In addition, the present application may repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present application provides various specific process and material examples, but those of ordinary skill in the art will appreciate the application of other processes and / or the use of other materials.

[0064] Example 1

[0065] This embodiment discloses a vanadium-chromium flow battery with high energy density. The vanadium-chromium electrolyte used in the vanadium-chromium flow battery includes a negative electrode electrolyte and a positive electrode electrolyte.

[0066] The concentration of negative electrode electrolyte V is 1.95 mol / L, Cr 3+ 0.7mol / L, Cl - 9.8 mol / L, phosphoric acid 0.05 mol / L;

[0067] The concentration of V in the positive electrolyte is 1.95 mol / L, and the concentration of Cr 3+ 0.7mol / L, Cl - 9.8mol / L, phosphoric acid 0.05mol / L.

[0068] The preparation method of the electrolyte of this embodiment is as follows:

[0069] Step 1. Dissolve VO2 with hydrochloric acid and filter to obtain a mixed solution of free acid and vanadium ions;

[0070] Step 2. reducing vanadium to an average valence of 3.5 to 4;

[0071] Step 3. Add chromium trichloride, stir to dissolve, and filter;

[0072] Step 4. Add water to adjust the concentration to prepare the electrolyte.

[0073] Comparative Example 1

[0074] This comparative example discloses an all-vanadium redox flow battery electrolyte, the components and contents of which are shown in Table 1.

[0075] Table 1 Components and contents of electrolytes in Control Example 1 and Example 1

[0076] To test the performance of the electrolytes of Example 1 and the control example, both were used in a flow battery and their performance was tested. The flow battery comprises, in order: a positive conductive plate, a positive electrolyte, a positive electrode frame, a positive electrode, an ion exchange membrane, a negative electrode, a negative electrolyte, a negative electrode frame, and a negative conductive plate, which are compressed to form a battery structure.

[0077] The positive electrode frame forms a cavity, the positive electrode is placed in the frame, the electrolyte contacts the electrode, and an electrochemical reaction occurs on the electrode.

[0078] The negative electrolyte and positive electrolyte of Example 1 were placed on both sides of the dual-flow battery shown in FIG6 at a volume ratio of 1:1.36 and pumped into the negative and positive electrode cavities of the battery, respectively. The battery was charged and discharged at 30°C and 100 mA / cm 2 , constant current charging cut-off voltage is 1.65V, constant voltage charging to 50mA / cm 2 , 100mA / cm 2 , constant current discharge, cut-off voltage 1V, charge and discharge cycle curves are shown in Figures 2, 4 and 5. Similarly, the electrolyte (V1.65M) of the all-vanadium redox flow battery of Control Example 1 was placed on both sides of the dual-flow battery in a volume ratio of 1:1 and pumped into the positive and negative electrode cavities of the battery respectively at 30°C for charge and discharge cycles with a constant current of 100mA / cm 2 Charging, cut-off voltage is 1.55V, constant voltage charging to 50mA / cm 2 ;100mA / cm 2The constant current discharge and cut-off voltage were 1V, and the cycle curves were shown in Figures 1 and 3. The charge and discharge cycle experiments showed that the energy density of the vanadium-chromium redox flow battery of Example 1 was 43Wh / L, while the energy density of the all-vanadium redox flow battery of Comparative Example 1 was 26Wh / L.

[0079] Compared with the vanadium concentration of the all-vanadium mixed acid system in Control Example 1, the amount of vanadium consumed per unit energy in the electrolyte of Example 1 was reduced from 5.775 kg V2O5 / KWh to 4.13 kg V2O5 / KWh, a 28.5% reduction in vanadium usage and an increase of 4.34 kg CrCl3.6H2O / KWh, resulting in a cost reduction of RMB 300 / KWh.

[0080] Example 2

[0081] This embodiment discloses a high energy density liquid flow battery. The vanadium liquid flow battery uses a vanadium electrolyte including a negative electrode electrolyte and a positive electrode electrolyte.

[0082] The concentration of negative electrode electrolyte V is 2.5 mol / L, Cr 3+ 0.5mol / L, Cl 9.2mol / L, SO4 2- 0.6mol / L;

[0083] The concentration of V in the positive electrolyte is 3 mol / L, and the concentration of Cr 3+ 0.3mol / L, Cl 8.1mol / L, SO4 2- 0.9mol / L.

[0084] The preparation steps and testing methods for the negative and positive electrolytes were essentially the same as those in Example 1, except that the type and content of the active material were adjusted. The negative and positive electrolytes were placed in a 1:1 volume ratio in a dual-flow battery and pumped into the positive and negative electrode cavities, respectively. Charge and discharge cycles were performed at room temperature.

[0085] According to the volume ratio of negative electrolyte to positive electrolyte of 1:1, the double flow battery was placed and pumped into the negative electrode cavity and positive electrode cavity of the battery respectively. The charge and discharge cycle was carried out at 30℃ and 100mA / cm 2 , constant current charging cut-off voltage is 1.65V, constant voltage charging to 50mA / cm 2 , 100mA / cm 2 , constant current discharge, cut-off voltage 1V, charge and discharge cycle curves are shown in Figures 1 and 3. Similarly, the electrolyte of the all-vanadium redox flow battery in Control Example 1 (V1.65M) was placed on both sides of the dual-flow battery in a volume ratio of 1:1 and pumped into the positive and negative electrode cavities of the battery respectively at 30°C for charge and discharge cycles with a constant current of 100mA / cm 2 Charging, cut-off voltage is 1.55V, constant voltage charging to 50mA / cm 2;100mA / cm 2 The discharge was carried out at a constant current and the cut-off voltage was 1 V. The charge and discharge cycle experiments showed that the energy density of the vanadium-chromium redox flow battery of this embodiment was 50 Wh / L.

[0086] Example 3

[0087] Based on Example 2, 0.12 mol / L H3PO4 was added to the positive and negative electrolytes respectively, namely:

[0088] The concentration of negative electrode electrolyte V is 2.5 mol / L, Cr 3+ 0.5mol / L, Cl 9.2mol / L, SO4 2- 0.6mol / L, 0.12mol / L H3PO4;

[0089] The concentration of V in the positive electrolyte is 3 mol / L, and the concentration of Cr 3+ 0.3mol / L, Cl 8.1mol / L, SO4 2- 0.9mol / L, 0.12mol / L H3PO4;

[0090] The preparation steps and testing methods of the negative and positive 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 electrolytes were placed in a dual-flow battery at a volume ratio of 1:1 and pumped into the negative and positive electrode cavities of the battery, respectively. The battery was charged and discharged at 30°C and 100 mA / cm 2 , constant current charging cut-off voltage is 1.65V, constant voltage charging to 50mA / cm 2 , 100mA / cm 2 , constant current discharge, cut-off voltage 1V, charge and discharge cycle curves are shown in Figures 1 and 3. Similarly, the electrolyte of the all-vanadium redox flow battery in Control Example 1 (V1.65M) was placed on both sides of the dual-flow battery in a volume ratio of 1:1 and pumped into the positive and negative electrode cavities of the battery respectively at 30°C for charge and discharge cycles with a constant current of 100mA / cm 2 Charging, cut-off voltage is 1.55V, constant voltage charging to 50mA / cm 2 ;100mA / cm 2 The discharge was carried out at a constant current and the cut-off voltage was 1 V. The charge and discharge cycle experiments showed that the energy density of the vanadium-chromium redox flow battery of this embodiment was 52 Wh / L.

[0091] The batteries of Examples 2 and 3 were charged to 95% SOC respectively. At this time, the mass ratio of pentavalent vanadium in the positive electrolyte to the total vanadium was VO2 + / V 总=95%. The positive electrolyte was sealed and placed at 30, 40, and 50°C for 1-5 days to observe its stability. As shown in Table 2, after adding phosphorus, precipitation did not appear until the fifth day at 50°C. Adding phosphorus compounds significantly improves the high-temperature stability of the positive electrolyte.

[0092] Table 2 Stability test

[0093] Note: √ means the solution is stable and unchanged, × means precipitation occurs

[0094] Example 4

[0095] This embodiment discloses a high energy density liquid flow battery. The vanadium liquid flow battery uses a vanadium electrolyte including a negative electrode electrolyte and a positive electrode electrolyte.

[0096] The concentration of negative electrode electrolyte V is 1 mol / L, Cr 3+ 1.5mol / L, Cl - 10mol / L;

[0097] The concentration of V in the positive electrolyte is 1.5 mol / L, and the concentration of Cr 3+ 0.3mol / L, Cl - 6.8mol / L.

[0098] The preparation steps and testing methods of the negative and positive 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 electrolytes were placed in a dual-flow battery at a volume ratio of 1:1.67 and pumped into the negative and positive electrode cavities of the battery, respectively. Charge and discharge cycles were performed at 30°C and 100 mA / cm 2 , constant current charging cut-off voltage is 1.65V, constant voltage charging to 50mA / cm 2 , 100mA / cm 2 The constant current discharge has a cut-off voltage of 1 V. The charge and discharge cycle experiments show that the vanadium-chromium redox flow battery of this embodiment has an energy density of 54 Wh / L and an energy efficiency of 81%.

[0099] While the battery energy density in this example does not reach 40Wh / L, the amount of vanadium consumed per unit energy is 62% of the standard 1.65M electrolyte used in all-vanadium redox flow batteries. Furthermore, reducing the vanadium concentration improves the high-temperature stability of the cathode electrolyte. The cathode electrolyte in this example can operate stably at temperatures above 50°C.

[0100] Example 5

[0101] This embodiment discloses a liquid flow battery, wherein the vanadium-chromium electrolyte used in the liquid flow battery includes a negative electrode electrolyte and a positive electrode electrolyte.

[0102] The concentration of negative electrode electrolyte V is 0.8 mol / L, Cr 3+ 0.9mol / L, Cl - 8mol / L;

[0103] The concentration of V in the positive electrolyte is 1.5 mol / L, and the concentration of Cr 3+ 0.2mol / L, Cl - 6.8mol / L.

[0104] The preparation steps and testing methods of the negative and positive 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 electrolytes were placed in a battery at a volume ratio of 1:1.13 and pumped into the negative and positive electrode cavities, respectively. The battery was maintained at 30°C for charge and discharge cycles at 100 mA / cm 2 , constant current charging cut-off voltage is 1.65V, constant voltage charging to 50mA / cm 2 , 100mA / cm 2 The constant current discharge has a cut-off voltage of 1V and the energy efficiency of the charge and discharge cycle is 86%.

[0105] Example 6

[0106] This embodiment discloses a liquid flow battery, wherein the vanadium-chromium electrolyte used in the liquid flow battery includes a negative electrode electrolyte and a positive electrode electrolyte.

[0107] The concentration of V in the negative electrode electrolyte is 0.2 mol / L, and the concentration of Cr 3+ 1.5mol / L, Cl - 8mol / L;

[0108] The concentration of V in the positive electrolyte is 1.5 mol / L, and the concentration of Cr 3+ 0.2mol / L, Cl - 6.8mol / L.

[0109] The preparation steps and testing methods of the negative and positive 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 electrolytes were placed in a battery at a volume ratio of 1:1.13 and pumped into the negative and positive electrode cavities, respectively. The battery was maintained at 30°C for charge and discharge cycles at 100 mA / cm 2 , constant current charging cut-off voltage is 1.65V, constant voltage charging to 50mA / cm 2 , 100mA / cm 2 Constant current discharge, cut-off voltage 1 V. Energy efficiency of charge and discharge cycle 70%.

[0110] The only difference between Example 6 and Example 5 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 that in Example 5 is 0.89. All other aspects are identical. The test results indicate that within the low vanadium-chromium ratio range, the chromium battery efficiency is low, similar to that of iron-chromium batteries, because when the vanadium concentration is low, the activity of chromium is difficult to be improved by vanadium catalysis.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A vanadium-chromium electrolyte comprising an active substance and a free acid, wherein the free acid acts as a proton conductor after ionization, and the active substance contains at least vanadium ions and chromium ions.

2. The vanadium-chromium electrolyte according to claim 1, wherein The active substances are vanadium compounds and chromium compounds.

3. The vanadium-chromium electrolyte according to claim 2, wherein: The vanadium compound is VO2, V2O3, V6O 13 , one or more of V2O5, CrVO4, VOSO4, V2(SO4)3, VCl2, VOCl2 and VCl3.

4. The vanadium-chromium electrolyte according to claim 2, wherein: The chromium compound is one or more of chromium trichloride, chromium dichloride, chromium sulfate, chromium vanadate and Cr2O3.

5. The vanadium-chromium electrolyte according to claim 1 or 2, wherein: The concentration of the vanadium ions ranges from 0.1 to 5 mol / L.

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

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

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

9. The vanadium-chromium electrolyte according to claim 1, wherein: The concentration of the phosphorus compound in the vanadium-chromium electrolyte is 0-1 mol / L.

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

11. The vanadium-chromium electrolyte according to claim 9, wherein: 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.

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

13. The vanadium-chromium electrolyte according to claim 1, wherein: The free acid is one or a mixture of hydrochloric acid, sulfuric acid, phosphoric acid and methanesulfonic acid.

14. The vanadium-chromium electrolyte according to claim 1, wherein: The free hydrogen ion concentration in the vanadium-chromium electrolyte is 0.1-5 mol / L.

15. A method for preparing a vanadium-chromium electrolyte, comprising the following steps: Step 1. dissolving a vanadium compound with a free acid and filtering to obtain a mixed solution of the free acid and vanadium ions; Step 2. Electrolytically reducing vanadium to an average valence of 3.5 to 4; Step 3. Add chromium compound, stir to dissolve, and filter; Step 4. Add pure water and auxiliary reagents, adjust the concentration, and prepare vanadium-chromium electrolyte.

16. The method for preparing a vanadium-chromium electrolyte according to claim 15, wherein: The electrolytic reduction in step 2 is as follows: a battery structure is adopted, the anode is a tetravalent vanadium solution, the cathode is a mixed solution, after charging, the valence of the vanadium ions at the anode increases to pentavalent, and the valence of the vanadium ions in the cathode mixed solution decreases to 3.5-4.

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

18. A vanadium-chromium flow battery comprising a positive electrode, a negative electrode and an ion membrane, wherein: The positive electrode electrolyte and / or the negative electrode electrolyte adopts the vanadium-chromium electrolyte described in any one of claims 1-14.

19. The vanadium-chromium flow battery according to claim 18, wherein: The operating temperature of the vanadium-chromium flow battery is 0-50°C.

20. The vanadium-chromium flow battery according to claim 18, wherein: The energy density of the vanadium-chromium redox flow battery is 30 to 50 Wh / L.