An electrolyte for a vanadium redox flow battery and a preparation method thereof

Abstract

The present invention belongs to the field of vanadium battery electrolytes, and discloses a vanadium redox flow battery electrolyte and a preparation method thereof, including preparing vanadium-containing oxides by using ammonium metavanadate; preparing an electrolyte precursor by using the vanadium-containing oxides; and electrolyzing the electrolyte precursor by using an asymmetric electrolysis device to obtain a +3.5-valent electrolyte. The present invention uses asymmetric electrolysis to oxidize a vanadium oxide solution reduced to below +3.5 valence to +3.5 valence to obtain a +3.5-valent electrolyte. The cathode chamber uses a trivalent vanadium sulfate solution, and the cathode solution is recycled by introducing oxygen without returning to the anode for oxidation, greatly improving the electrolysis efficiency; the present invention uses ammonium metavanadate for self-reduction-dissolution-asymmetric electrolysis to prepare the electrolyte, with a short process, high efficiency, no need to use a reducing agent, low cost and high purity of the electrolyte product.

Description

Technical Field

[0001] The present invention belongs to the field of vanadium battery electrolytes, and particularly relates to a vanadium redox flow battery electrolyte and a preparation method thereof. Background Art

[0002] At present, vanadium battery electrolytes are generally prepared using high-purity vanadium. Since vanadium pentoxide has extremely low solubility in water and sulfuric acid, it needs to be reduced to tetravalent vanadium with high solubility to prepare the electrolyte. The methods for preparing the electrolyte are mainly divided into two types, one is the electrolysis method, and the other is the chemical reduction method. The preparation of the electrolyte adopts the method of first reduction and then electrolysis. Vanadium pentoxide is quickly dissolved and reduced to tetravalent crude liquid by a reducing agent, and then further electrolytic reduction is carried out through an electrolysis device to prepare a 3.5-valent electrolyte.

[0003] The patent technology of "A production process and system for vanadium battery electrolyte" (CN108777316A) provides a preparation method for vanadium battery electrolyte. Using liquid SO2 as a reducing agent, the suspension slurry prepared from sulfuric acid and vanadium pentoxide is directly reduced in a pressure reaction kettle in the liquid phase, and then the positive and negative electrolytes of the vanadium battery are prepared by a one-step method using a diaphragm electrolytic cell. Although no impurities are introduced and the process is simple in this preparation process, due to the low solubility of SO2 and the residues in the reaction being difficult to remove, the utilization rate of SO2 is low and it is easy to cause large environmental pollution. The patent technology of "Preparation method of vanadium battery electrolyte" (CN101800339B) uses oxalic acid to directly reduce vanadium pentoxide to prepare vanadium battery electrolyte. This preparation process uses oxalic acid as a reducing agent. Although the preparation efficiency is high and the process is simple, the cost is too high and the residual oxalic acid is difficult to remove, which affects the performance of the electrolyte. The patent technology of "A vanadium redox flow battery electrolyte and a preparation method thereof" (CN10880L052A) proposes a method for preparing vanadium battery electrolyte. This technology uses a two-step method of chemical dissolution and electrolysis to prepare the electrolyte, and the reducing agent is selected from propionic acid, succinic acid, glycerol, benzyl alcohol, malonic acid, glutaric acid, methanol, etc. The reduction efficiency in the preparation process is low and the cost of the reducing agent is high. The patent technology of "A method for preparing the negative electrolyte of vanadium battery using V2O5" (CN105655620B) proposes a method for preparing vanadium battery electrolyte. Vanadium pentoxide is heated and activated in an aqueous sulfuric acid solution, and then a trivalent vanadium electrolyte is prepared by the copper-sodium thiosulfate-ammonia combined method. Although this method has a low cost and a fast reaction rate, the preparation process is complex and it is easy to introduce impurities such as sodium and ammonia.

[0004] At present, the preparation technology of vanadium battery electrolyte mainly uses vanadium pentoxide as raw material to prepare vanadium battery electrolyte by reduction first and then electrolysis. The reducing agents mainly include substances such as SO2, oxalic acid, propionic acid, succinic acid, glycerol, benzyl alcohol, malonic acid, glutaric acid, methanol, copper and sodium thiosulfate. Since the reducing agents used cannot simultaneously meet the requirements of high efficiency, pollution-free, no impurity residue and low cost, the production process of the electrolyte is complex, the reaction rate is slow, the cost is high, there is pollution and impurity residue. Therefore, developing a high-efficiency and low-cost electrolyte preparation technology is an urgent problem to be solved in the popularization and application process of vanadium batteries in the energy storage field. Summary of the Invention

[0005] In order to overcome the defects of the above-mentioned existing technologies, the purpose of the present invention is to provide a vanadium redox flow battery electrolyte and its preparation method. By subjecting high-purity ammonium metavanadate to high-temperature treatment in an inert atmosphere, ammonia gas and vanadium pentoxide are decomposed. The ammonia gas gradually reduces the vanadium pentoxide to low-valent vanadium oxides. The amount of ammonia gas generated by the decomposition of ammonium metavanadate is sufficient, and the valence state of the vanadium oxides will be reduced to below 3.5. Then, an asymmetric electrolysis device is used to oxidize the vanadium ions to 3.5 valence to prepare the electrolyte.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] A preparation method of a vanadium redox flow battery electrolyte, comprising the following steps:

[0008] Using ammonium metavanadate to prepare vanadium-containing oxides;

[0009] Using the vanadium-containing oxides to prepare an electrolyte precursor;

[0010] Using an asymmetric electrolysis device to electrolyze the electrolyte precursor to obtain a 3.5-valent electrolyte.

[0011] Further, using ammonium metavanadate to prepare vanadium-containing oxides, including:

[0012] Using a heating furnace to heat ammonium metavanadate to 350-550 °C and keep it warm for 0.5-2 h;

[0013] Cooling the heating furnace to below 70 °C to obtain vanadium-containing oxides.

[0014] Further, before using a heating furnace to heat ammonium metavanadate to 350-550 °C and keep it warm for 0.5-2 h, it includes:

[0015] Placing ammonium metavanadate into the heating furnace, evacuating the heating furnace and filling it with inert gas, repeating it more than 3 times and then pumping negative pressure for 3-6 min.

[0016] Further, using vanadium-containing oxides to prepare an electrolyte precursor, including:

[0017] Mix the vanadium-containing oxide with the first deionized water and a sulfuric acid solution with a mass fraction of 98%, and react for 15 - 30 minutes;

[0018] Add the second deionized water to the mixed solution after the reaction, stir and react at a temperature of 25 - 100 °C for 1 - 4 hours, and filter to obtain the electrolyte precursor.

[0019] Furthermore, the liquid-solid ratio of the vanadium-containing oxide to the first deionized water is 0.6 - 1.2 mL / g;

[0020] The liquid-solid ratio of the vanadium-containing oxide to the sulfuric acid solution is 2 - 3 mL / g;

[0021] The liquid-solid ratio of the vanadium-containing oxide to the second deionized water is 5 - 7 mL / g.

[0022] Furthermore, use an asymmetric electrolysis device to electrolyze the electrolyte precursor to obtain a +3.5-valent electrolyte, including:

[0023] Use the electrolyte precursor as the anolyte of the asymmetric electrolysis device, and a trivalent sulfuric acid solution as the catholyte of the asymmetric electrolysis device, and perform constant-current electrolysis until a +3.5-valent electrolyte is obtained;

[0024] The anode electrode material of the asymmetric electrolysis device is a catalytic metal-coated titanium-based electrode, and the catalytic metal includes one or more of ruthenium, iridium, tin, and platinum. The cathode electrode material of the asymmetric electrolysis device includes any one of carbon felt, graphite felt, carbon paper, and graphite plate.

[0025] Furthermore, in the trivalent sulfuric acid solution, the vanadium concentration is 1.5 - 1.8 mol / L, and the sulfate concentration is 4.0 - 4.5 mol / L.

[0026] Furthermore, performing constant-current electrolysis includes:

[0027] Control the electrolysis current density to be 40 - 500 mA / cm 2 .

[0028] Furthermore, performing constant-current electrolysis also includes:

[0029] Introduce oxygen or air into the cathode chamber of the asymmetric electrolysis device during the constant-current electrolysis process.

[0030] On the other hand, the present invention discloses a vanadium redox flow battery electrolyte prepared by the above method.

[0031] The technical effects and advantages of the present invention:

[0032] The present invention uses asymmetric electrolysis to oxidize a vanadium oxide solution reduced to a valence of less than 3.5 to a valence of 3.5, thereby obtaining a 3.5-valence electrolyte. A trivalent vanadium sulfuric acid solution is used in the cathode chamber. By introducing oxygen, the cathode solution is recycled, eliminating the need to return to the anode for oxidation, thereby significantly improving the electrolysis efficiency.

[0033] The present invention adopts ammonium metavanadate self-reduction-dissolution-asymmetric electrolysis to prepare the electrolyte, which has a short process, high efficiency, no need to use a reducing agent, and the electrolyte product has low cost and high purity;

[0034] The invention uses ammonium metavanadate as a raw material and fully utilizes ammonia generated by its high-temperature decomposition for reduction, thereby avoiding ammonia pollution generated by calcining ammonium metavanadate and reducing production energy consumption at a low processing temperature.

[0035] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a flow chart of a method for preparing an electrolyte for an all-vanadium redox flow battery. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] Figure 1 This is a flow chart of a method for preparing an all-vanadium redox flow battery electrolyte according to the present invention. Figure 1 As shown, the present invention provides a method for preparing an electrolyte for an all-vanadium redox flow battery, comprising:

[0039] Preparation of vanadium-containing oxides using ammonium metavanadate;

[0040] preparing an electrolyte precursor using the vanadium-containing oxide;

[0041] An asymmetric electrolysis device is used to electrolyze an electrolyte precursor to obtain a 3.5-valent electrolyte.

[0042] Further, when preparing vanadium-containing oxide using ammonium metavanadate, first place ammonium metavanadate in a heating furnace, evacuate the heating furnace and then fill it with an inert gas. After repeating this process more than 3 times, apply a negative pressure for 3 - 6 minutes. Then, use the heating furnace to heat ammonium metavanadate to 350 - 550 °C and keep it warm for 0.5 - 2 hours. Then, cool the heating furnace to below 70 °C to obtain vanadium-containing oxide.

[0043] Further, when preparing an electrolyte precursor using the vanadium-containing oxide, mix the vanadium-containing oxide with deionized water and a 98% sulfuric acid solution by mass, react for 15 - 30 minutes, and then add deionized water to the reacted mixed solution. Stir and react at a temperature of 25 - 100 °C for 1 - 4 hours, and then filter to obtain the electrolyte precursor. Among them, the liquid-solid ratio of the vanadium-containing oxide to the first deionized water is 0.6 - 1.2 mL / g; the liquid-solid ratio of the vanadium-containing oxide to the sulfuric acid solution is 2 - 3 mL / g; the liquid-solid ratio of the vanadium-containing oxide to the second deionized water is 5 - 7 mL / g.

[0044] Further, when electrolyzing the electrolyte precursor using an asymmetric electrolysis device, use the electrolyte precursor as the anolyte of the asymmetric electrolysis device, and use a trivalent sulfuric acid solution as the catholyte of the asymmetric electrolysis device for constant current electrolysis. During the electrolysis process, control the electrolysis current density to be 40 - 500 mA / cm 2 , and simultaneously introduce oxygen or air into the cathode chamber of the asymmetric electrolysis device until a 3.5-valent electrolyte is obtained. Among them, in the trivalent sulfuric acid solution, the vanadium concentration is 1.5 - 1.8 mol / L, and the sulfate concentration is 4.0 - 4.5 mol / L.

[0045] On the other hand, the present invention also discloses an all-vanadium redox flow battery electrolyte prepared by the method described in claims 1 - 9 above.

[0046] Example 1

[0047] S1. Take 120 g of ammonium metavanadate and place it in a heating furnace. Evacuate the heating furnace and then fill it with an inert gas. Repeat this process 3 times, then apply a negative pressure for 6 minutes and close the furnace door, and start heating up.

[0048] S2. Heat the heating furnace to 450 °C, subject ammonium metavanadate to high-temperature treatment for 1 hour. After the heating is completed, wait for the temperature of the heating furnace to drop to 60 °C, take out the solid to obtain vanadium-containing oxide with a valence below 3.5.

[0049] S3. Add 100 mL of the first deionized water to the vanadium-containing oxide, then add 300 mL of a 98% sulfuric acid solution by mass, stir and react for 20 minutes, then add 600 mL of the second deionized water, stir and react at a temperature of 90 °C for 3 hours, and then filter to obtain the electrolyte precursor.

[0050] S4. Place the electrolyte precursor in the anode chamber of the asymmetric electrolytic cell. Fill the cathode chamber of the electrolytic cell with a vanadium(III) sulfate solution having a vanadium concentration of 1.6 mol / L and a sulfate concentration of 4.3 mol / L. Then, perform constant current electrolysis while controlling the current density at 300 mA / cm 2 , and introduce oxygen into the cathode chamber during the electrolysis process. Stop the electrolysis until the valence state of the electrolyte reaches 3.5 to obtain a 3.5-valent electrolyte.

[0051] Example 2

[0052] S1. Take 120 g of ammonium metavanadate and place it in a heating furnace. Evacuate the heating furnace and then refill it with an inert gas, repeating this process 5 times. Then, evacuate to a negative pressure for 3 minutes and close the furnace door before starting to raise the temperature.

[0053] S2. Raise the temperature of the heating furnace to 550 °C and subject the ammonium metavanadate to high-temperature treatment for 0.5 h. After the heating is completed, wait for the temperature of the heating furnace to drop to 70 °C and then take out the solid to obtain a vanadium oxide with a valence state below 3.5.

[0054] S3. Add 72 mL of first deionized water to the vanadium oxide, then add 240 mL of sulfuric acid solution with a mass fraction of 98%. Stir and react for 30 minutes, then add 720 mL of second deionized water and stir and react at 100 °C for 4 h. Filter to obtain the electrolyte precursor.

[0055] S4. Place the electrolyte precursor in the anode chamber of the asymmetric electrolytic cell. Fill the cathode chamber of the electrolytic cell with a vanadium(III) sulfate solution having a vanadium concentration of 1.5 mol / L and a sulfate concentration of 4.0 mol / L. Then, perform constant current electrolysis while controlling the current density at 500 mA / cm 2 , and introduce oxygen into the cathode chamber during the electrolysis process. Stop the electrolysis until the valence state of the electrolyte reaches 3.5 to obtain a 3.5-valent electrolyte.

[0056] Example 3

[0057] S1. Take 120 g of ammonium metavanadate and place it in a heating furnace. Evacuate the heating furnace and then refill it with an inert gas, repeating this process 4 times. Then, evacuate to a negative pressure for 5 minutes and close the furnace door before starting to raise the temperature.

[0058] S2. Raise the temperature of the heating furnace to 350 °C and subject the ammonium metavanadate to high-temperature treatment for 2 h. After the heating is completed, wait for the temperature of the heating furnace to drop to 50 °C and then take out the solid to obtain a vanadium oxide with a valence state below 3.5.

[0059] S3. Add 144 mL of first deionized water to the vanadium oxide, then add 360 mL of sulfuric acid solution with a mass fraction of 98%, stir and react for 15 min, then add 840 mL of second deionized water, stir and react at 25 °C for 1 h, and filter to obtain the electrolyte precursor.

[0060] S4. Place the electrolyte precursor in the anode chamber of the asymmetric electrolytic cell, and fill the cathode chamber of the electrolytic cell with a trivalent vanadium-containing sulfuric acid solution. The vanadium concentration in the trivalent vanadium-containing sulfuric acid solution is 1.8 mol / L, and the sulfate concentration is 4.5 mol / L. Then, perform constant current electrolysis, control the current density at 40 mA / cm 2 , and introduce oxygen into the cathode chamber during electrolysis until the valence state of the electrolyte reaches 3.5, then stop electrolysis to obtain a 3.5-valent electrolyte.

[0061] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of an electrolyte for an all-vanadium redox flow battery, characterized in that, The method includes the following steps: Prepare vanadium-containing oxide using ammonium metavanadate; Prepare an electrolyte precursor using the vanadium-containing oxide; Electrolyze the electrolyte precursor using an asymmetric electrolysis device to obtain a +3.5-valent electrolyte; The preparation of vanadium-containing oxide using ammonium metavanadate includes: Heat ammonium metavanadate to 350-550 °C using a heating furnace and hold for 0.5-2 h; Cool the heating furnace to below 70 °C to obtain vanadium-containing oxide; The preparation of the electrolyte precursor using the vanadium-containing oxide includes: Mix the vanadium-containing oxide with deionized water and a 98% sulfuric acid solution by mass, and react for 15-30 min; Add deionized water to the reacted mixed solution, stir and react at 25-100 °C for 1-4 h, and filter to obtain the electrolyte precursor; The electrolysis of the electrolyte precursor using an asymmetric electrolysis device to obtain a +3.5-valent electrolyte includes: Use the electrolyte precursor as the anolyte of the asymmetric electrolysis device and a trivalent vanadium sulfate solution as the catholyte of the asymmetric electrolysis device for constant current electrolysis until a +3.5-valent electrolyte is obtained; The constant current electrolysis further includes: Introduce oxygen or air into the cathode chamber of the asymmetric electrolysis device during the constant current electrolysis process.

2. The preparation method of an all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, Before heating ammonium metavanadate to 350-550 °C using the heating furnace and holding for 0.5-2 h, it includes: Place ammonium metavanadate in the heating furnace, evacuate the heating furnace and then fill it with an inert gas, repeat more than 3 times and then draw a negative pressure for 3-6 min.

3. The preparation method of an all-vanadium redox flow battery electrolyte according to claim 1, wherein The liquid-solid ratio of the vanadium-containing oxide to the first deionized water is 0.6-1.2 mL / g; The liquid-solid ratio of the vanadium-containing oxide to the sulfuric acid solution is 2-3 mL / g; The liquid-solid ratio of the vanadium-containing oxide to the second deionized water is 5-7 mL / g.

4. The preparation method of an all-vanadium redox flow battery electrolyte according to claim 1, wherein The anode electrode material of the asymmetric electrolysis device is a catalytic metal-coated titanium-based electrode, the catalytic metal includes one or more of ruthenium, iridium, tin, and platinum, and the cathode electrode material of the asymmetric electrolysis device includes any one of carbon felt, graphite felt, carbon paper, and graphite plate.

5. The preparation method of an all-vanadium redox flow battery electrolyte according to claim 1, wherein In the trivalent vanadium sulfate solution, the vanadium concentration is 1.5-1.8 mol / L and the sulfate concentration is 4.0-4.5 mol / L.

6. The preparation method of an electrolyte for a vanadium redox flow battery according to claim 1, wherein, The constant current electrolysis includes: Control the electrolytic current density to be 40 - 500 mA / cm 2 .

7. An electrolyte for an all-vanadium redox flow battery, characterized in that, The electrolyte is prepared by the method described in any one of claims 1-6.

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