Vanadium bromine flow battery electrolyte, preparation thereof and flow battery

Abstract

The application discloses a vanadium-bromine flow battery electrolyte, a preparation method thereof and a flow battery. The electrolyte comprises a positive electrolyte and a negative electrolyte. The positive electrolyte contains water, bromine ions and an additive. The additive is a pyridine derivative and / or an imidazole derivative. The negative electrolyte contains an acid, vanadium ions and water. The preparation method comprises the following steps: mixing a bromine source with water, and then adding the pyridine derivative and / or the imidazole derivative to obtain the positive electrolyte; dissolving a vanadium source with an acid, and then filtering to obtain a filtrate; adding water to the filtrate, and then adjusting the concentration of vanadium ions to a target final concentration to obtain the negative electrolyte. The flow battery comprises the above-mentioned vanadium-bromine flow battery electrolyte, a positive electrode, an ion-conducting membrane and a negative electrode. The application solves the problems of low energy density, high price and cost, zinc dendrite and positive bromine volatilization of the current flow battery by introducing the coupling of a vanadium-based energy storage medium and a bromine oxygen reduction-oxidation couple.

Description

Technical Field

[0001] The present invention relates to a liquid flow battery electrolyte and its preparation, in particular to a vanadium-bromine liquid flow battery electrolyte and its preparation and a liquid flow battery. Background Art

[0002] Traditional flow batteries have the following problems:

[0003] High cost: Traditional flow batteries, such as all-vanadium flow batteries, use expensive vanadium ions as active materials in both their positive and negative electrodes, resulting in high electrolyte costs. This shortcoming limits their application in energy storage.

[0004] Low energy density: Traditional flow batteries, such as all-vanadium flow batteries, have limited vanadium ion solubility. If the concentration exceeds a certain range, pentavalent vanadium ions will easily precipitate to form V2O5. Therefore, due to the limitation of vanadium ion concentration in the cathode electrolyte, the electrolyte concentration cannot be too high, resulting in low energy density.

[0005] Deposition problem of negative electrode metal zinc: In traditional flow batteries, such as zinc-bromine flow batteries, Zn 2+ After receiving two electrons, zinc is converted into elemental zinc and deposited at the negative electrode. As charging progresses, zinc continues to accumulate on the surface of the already deposited zinc metal. This process, due to inherent factors such as uneven electrode material resistance and electrode edge effects, can lead to the formation of zinc dendrites. The continued growth of zinc dendrites can penetrate the battery separator, causing a short circuit and rendering the battery useless.

[0006] Cathode bromine volatilization: When a bromine-based battery is fully charged, the bromine in the cathode electrolyte exists as Br2. As the electrolyte temperature rises, Br2 volatilizes, limiting the maximum operating temperature of the electrolyte and, in turn, narrowing the battery's effective operating temperature range. Summary of the Invention

[0007] Objectives of the invention: The present invention aims to provide a vanadium-bromine flow battery electrolyte that addresses the problems of low energy density and volatilization of bromine in the cathode. Another objective is to provide a method for preparing the vanadium-bromine flow battery electrolyte, addressing the issue of how to obtain such electrolyte. A third objective is to provide a flow battery with high energy density and a wide effective operating temperature range.

[0008] Technical solution: The vanadium-bromine flow battery electrolyte described in the present invention includes a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte contains water, bromide ions and additives, and the additives are pyridine derivatives and / or imidazole derivatives. The negative electrode electrolyte contains acid, vanadium ions and water.

[0009] The inherent safety and long life of the vanadium-based energy storage medium in the negative electrode allows for efficient storage of chemical energy and release of electrical energy. Compared to traditional flow batteries, such as zinc-bromine flow batteries, which suffer from metallic zinc deposition at the negative electrode, this design enables efficient and stable system operation.

[0010] The bromine redox couple at the positive electrode is low-cost, stable at room temperature, and not easily decomposed. It produces no harmful substances during use and is environmentally friendly. It also has a high energy density, enabling long-term, stable energy output.

[0011] Introducing additives into the positive electrode electrolyte can effectively inhibit the volatilization of positive electrode bromine and significantly improve the stability of the electrolyte under high temperature conditions, thereby optimizing the overall performance of the battery.

[0012] Preferably, the molar concentration ratio of vanadium ions:bromide ions:additive in the positive electrode electrolyte and the negative electrode electrolyte is 1-2.5:0.5-1.5:0.02-0.5.

[0013] Preferably, the final concentration of bromide ions in the positive electrode electrolyte is 0.5-1.5 mol / L, the final concentration of vanadium ions in the negative electrode electrolyte is 1.0-2.5 mol / L, the final concentration of the additive is 0.02-0.5 mol / L, and the final concentration of the acid is 3 mol / L.

[0014] Preferably, the acid is an inorganic strong acid, the pyridine derivative is 1-ethyl-4-methylpyridinium bromide, and the imidazole derivative is 1,2-dimethylimidazole.

[0015] Preferably, the acid is at least one of sulfuric acid and hydrochloric acid, and the additive is a mixture of 1-ethyl-4-methylpyridinium bromide and 1,2-dimethylimidazole in a molar ratio of 1-3:1-3.

[0016] A second aspect of the present invention provides a method for preparing the above-mentioned vanadium-bromine flow battery electrolyte, comprising the following steps:

[0017] (1) mixing a bromine source with water and then adding a pyridine derivative and / or an imidazole derivative to obtain a positive electrode electrolyte;

[0018] (2) dissolving the vanadium source with acid and filtering the filtrate;

[0019] (3) Add water to the filtrate and adjust the vanadium ion concentration to the target final concentration to obtain the negative electrode electrolyte.

[0020] Preferably, the bromine source includes one or more of HBr, NaBr, KBr4, and Br2; the vanadium source includes one or more of V2O5, VO2, V2O3, (VO2)2SO4, VOSO4, VO2Cl, VOCl2, VCl3, and VCl2.

[0021] Preferably, the vanadium source includes one or more of V2O5, VO2, (VO2)2SO4, VOSO4, and VOCl2, and the bromine source is HBr.

[0022] Preferably, in step (2), the molar ratio of the acid to the vanadium source is 4-8:1.5-2.0, the acid is sulfuric acid, and the water is deionized water.

[0023] A third aspect of the present invention provides a flow battery comprising the above-mentioned vanadium-bromine flow battery electrolyte, a positive electrode, an ion-conducting membrane and a negative electrode.

[0024] The vanadium-based energy storage medium-bromine redox couple coupled system structure design combines vanadium-based energy storage materials with bromine redox couples to form a battery system. During the charging process, the trivalent vanadium ions at the negative electrode are reduced to divalent vanadium ions, while the bromide ions at the positive electrode are deposited on the positive electrode to form bromine, thereby storing electrical energy; during the discharge process, the divalent vanadium ions at the negative electrode are oxidized to trivalent vanadium ions, and the bromine at the positive electrode undergoes a redox reaction to generate bromide ions, thereby outputting electrical energy. The specific working principle is as follows:

[0025] Negative electrode: During charging, trivalent vanadium ions are reduced to divalent vanadium ions; during discharge, divalent vanadium ions in the negative electrode are oxidized to trivalent vanadium ions. The separator prevents the products and intermediates between the negative and positive electrodes from interfering with each other, ensuring the independent redox reactions of the vanadium energy storage medium.

[0026] During the charging process, a reduction reaction of the vanadium energy storage medium occurs:

[0027] V 3+ +e - →V 2+

[0028] During the discharge process, an oxidation reaction of the vanadium energy storage medium occurs:

[0029] V 2+ →V 3+ +e -

[0030] Positive Electrode: During charging, bromide ions at the positive electrode deposit on the positive electrode carbon felt to form bromine. During discharge, the bromine at the positive electrode undergoes a reduction reaction to form bromide ions. The separator prevents the products and intermediates between the negative and positive electrodes from interfering with each other, ensuring the independent redox reactions of the bromine redox couple.

[0031] During the charging process, an oxidation reaction of bromide ions occurs to form bromine:

[0032] 2Br - →Br2+2e -

[0033] During the discharge process, bromine reduction reaction occurs to form bromide ions:

[0034] Br2+2e - →2Br -

[0035] Coupled system: A negative electrode containing a vanadium-based energy storage medium and a positive electrode containing a bromine redox couple are placed in the same system, separated by a separator to ensure that the reactions between the positive and negative electrodes proceed separately. An external circuit is ensured between the two systems, ensuring that the new flow battery system can be used for both energy storage and output.

[0036] Total charging reaction: V2(SO4)3+2HBr=2VSO4+Br2+H2SO4

[0037] Total discharge reaction: 2VSO4+Br2+H2SO4=V2(SO4)3+2HBr

[0038] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0039] 1. This invention introduces a vanadium-based energy storage medium into the battery's negative electrode. Leveraging its excellent redox properties, it achieves efficient conversion between low-valent and high-valent vanadium ions. Furthermore, this vanadium-based energy storage medium is more stable than the zinc-based energy storage medium used in the negative electrode of zinc-bromine flow batteries, eliminating the zinc dendrite problem.

[0040] 2. This invention introduces a bromine redox couple into the battery's positive electrode, leveraging its excellent redox properties to achieve efficient conversion of bromide ions into bromine. Furthermore, unlike the pentavalent vanadium ions in the positive electrode of all-vanadium flow batteries, which readily precipitate to form V2O5 at high concentrations, this bromine redox couple eliminates the risk of precipitation, ensuring safe and stable battery operation while improving battery energy density. Finally, because the bromine redox couple is less expensive than metal pairs, it can significantly reduce battery costs.

[0041] 3. Improve battery power output efficiency: The present invention couples vanadium-based energy storage media with bromine redox couples to solve the problems of zinc dendrites caused by direct use of zinc-based energy storage media at the negative electrode and low energy density, high cost, and poor stability caused by direct use of vanadium redox couples at the positive electrode, thereby achieving more stable power output.

[0042] 4. Expanding the effective operating temperature range of the battery: The present invention improves the stability of positive electrode bromine in high temperature environments by adding 1-ethyl-4-methylpyridinium bromide and 1,2-dimethylimidazole to the electrolyte, thereby ensuring safe and stable operation of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1Schematic diagram of the discharge process of the vanadium-bromine flow battery of the present invention;

[0044] Figure 2 Schematic diagram of the charging process of the vanadium-bromine flow battery in the present invention. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further described below.

[0046] Example 1: A vanadium-bromine flow battery electrolyte comprises a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte contains water, bromide ions, and an additive, wherein the additive is a mixture of 1-ethyl-4-methylpyridinium bromide and 1,2-dimethylimidazole. The negative electrode electrolyte contains sulfuric acid, vanadium ions, and water. The final bromide ion concentration in the positive electrode electrolyte is 1.0 mol / L, the final vanadium ion concentration in the negative electrode electrolyte is 1.5 mol / L, the final concentration of the additive is 0.1 mol / L, and the final concentration of the sulfuric acid is 3 mol / L.

[0047] The preparation method of the above-mentioned vanadium-bromine flow battery electrolyte is as follows:

[0048] (1) HBr was mixed with deionized water and then a mixture of 1-ethyl-4-methylpyridinium bromide and 1,2-dimethylimidazole in a molar ratio of 1:1 was added to obtain a positive electrode electrolyte, ensuring that the final concentration of bromide ions in the positive electrode electrolyte was 1.0 mol / L, the final concentration of vanadium ions in the negative electrode electrolyte was 1.5 mol / L, the final concentration of 1-ethyl-4-methylpyridinium bromide was 0.05 mol / L, the final concentration of 1,2-dimethylimidazole was 0.05 mol / L, and the final concentration of sulfuric acid was 3 mol / L.

[0049] (2) dissolving VOSO4 with sulfuric acid at a molar ratio of sulfuric acid to vanadium source of 6:1.7, and filtering to obtain the filtrate;

[0050] (3) Deionized water is added to the filtrate to adjust the vanadium ion concentration to the target final concentration to obtain the negative electrode electrolyte.

[0051] according to Figure 1 The structure is a vanadium-bromine flow battery assembled using the above-mentioned positive electrolyte, negative electrolyte, positive electrode, negative electrode and ion conductive membrane. The electrode material is carbon felt.

[0052] Example 2: The rest is the same as Example 1, except that:

[0053] The final concentration of bromide ions in the positive electrode electrolyte is 1.5 mol / L, the final concentration of vanadium ions in the negative electrode electrolyte is 1.0 mol / L, the final concentration of 1-ethyl-4-methylpyridinium bromide is 0.25 mol / L, the final concentration of 1,2-dimethylimidazole is 0.25 mol / L, the final concentration of additives is 0.5 mol / L, and the final concentration of acid is 3 mol / L.

[0054] Replace HBr with NaBr.

[0055] Replace VOSO4 with V2O5.

[0056] The molar ratio of the sulfuric acid to the vanadium source is 4:1.5.

[0057] Example 3: The rest is the same as Example 1, except that:

[0058] The final concentration of bromide ions in the positive electrode electrolyte is 0.5 mol / L, the final concentration of vanadium ions in the negative electrode electrolyte is 2.5 mol / L, the final concentration of 1-ethyl-4-methylpyridinium bromide is 0.01 mol / L, the final concentration of 1,2-dimethylimidazole is 0.01 mol / L, the final concentration of additives is 0.02 mol / L, and the final concentration of acid is 3 mol / L.

[0059] Replace HBr with KBr4.

[0060] Replace VOSO4 with (VO2)2SO4.

[0061] The molar ratio of the acid to the vanadium source is 8:2.0.

[0062] Example 4: The rest are the same as Example 1, except that:

[0063] The final concentration of bromide ions in the positive electrode electrolyte is 1.0 mol / L, the final concentration of vanadium ions in the negative electrode electrolyte is 2.0 mol / L, the final concentration of 1-ethyl-4-methylpyridinium bromide is 0.05 mol / L, the final concentration of 1,2-dimethylimidazole is 0.15 mol / L, the final concentration of additives is 0.2 mol / L, and the final concentration of acid is 3 mol / L.

[0064] In step (1), a mixture of 1-ethyl-4-methylpyridinium bromide and 1,2-dimethylimidazole in a molar ratio of 1:3 is added.

[0065] Replace HBr with Br2.

[0066] Replace VOSO4 with VO2Cl.

[0067] Sulfuric acid was replaced by hydrochloric acid.

[0068] Example 5: The rest are the same as Example 1, except that:

[0069] The final concentration of bromide ions in the positive electrode electrolyte is 0.8 mol / L, the final concentration of vanadium ions in the negative electrode electrolyte is 1.8 mol / L, the final concentration of 1-ethyl-4-methylpyridinium bromide is 0.1 mol / L, the final concentration of 1,2-dimethylimidazole is 0.05 mol / L, the final concentration of additives is 0.15 mol / L, and the final concentration of acid is 3 mol / L.

[0070] In step (1), a mixture of 1-ethyl-4-methylpyridinium bromide and 1,2-dimethylimidazole in a molar ratio of 2:1 is added.

[0071] Replace VOSO4 with VCl3.

[0072] Sulfuric acid was replaced by hydrochloric acid.

[0073] Comparative Example 1: The rest are the same as Example 1, except that:

[0074] 1,2-Dimethylimidazole was replaced by 1-ethyl-4-methylpyridinium bromide.

[0075] Comparative Example 2: All other aspects are the same as in Example 1, except that:

[0076] 1-Ethyl-4-methylpyridinium bromide was replaced by 1,2-dimethylimidazole.

[0077] Comparative Example 3: The rest are the same as Example 1, except that:

[0078] No additives are added to the positive electrode electrolyte.

[0079] Comparative Example 4: The rest are the same as Example 1, except that:

[0080] 1-Ethyl-4-methylpyridinium bromide was replaced with 4-methyl-3-bromopyridine.

[0081] Comparative Example 5: The rest are the same as Example 1, except that:

[0082] Replace 1,2-dimethylimidazole with imidazole.

[0083] The properties of the electrolytes prepared in Examples 1-5 and Comparative Examples 1-5 were measured respectively.

[0084] Different electrolytes were used to assemble the flow battery. The positive electrode of the flow battery was set as a sealed cavity, and a bromine gas detection probe was set in the cavity. The probe did not come into contact with the positive electrode electrolyte. The flow battery was charged and discharged 10 times. The bromine gas concentration at the positive electrode before and after charge and discharge was detected. The bromine gas concentration difference was calculated according to the following formula:

[0085] Bromine gas concentration difference = average bromine gas concentration of the positive electrode after charge and discharge - average bromine gas concentration of the positive electrode before charge and discharge.

[0086] Circulate the electrolyte in the temperature zone and test whether there is precipitation. No precipitation means that it can operate in this temperature zone.

[0087] Here are the results:

[0088] Table 1 Energy density and operating temperature range of different flow battery electrolytes

[0089]

[0090] As can be seen from the results in Table 1, the addition of additives has almost no effect on the energy density of the electrolyte. However, Comparative Example 3 shows that the addition of additives can significantly reduce the volatilization of positive electrode bromine and increase the upper limit of the operating temperature. Comparative Examples 1 and 2 show that when 1-ethyl-4-methylpyridinium bromide or 1,2-dimethylimidazole is used alone, the inhibitory effect on bromine volatilization is weak, and the upper limit of the operating temperature is increased by a small margin. However, when 1-ethyl-4-methylpyridinium bromide is used in combination with 1,2-dimethylimidazole, the volatilization of bromine is greatly reduced, and the operating temperature range is greatly expanded. Comparative Examples 4 and 5 show that among the many imidazole derivatives and brominated pyridinium derivatives, only specific types have the effect of expanding the temperature range and inhibiting bromine volatilization.

Claims

1. A vanadium-bromine flow battery electrolyte, characterized in that: The invention comprises a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte contains water, bromide ions and an additive, wherein the additive is a mixture of 1-ethyl-4-methylpyridinium bromide and 1,2-dimethylimidazole in a molar ratio of 1-3:1-3. The negative electrode electrolyte contains acid, vanadium ions and water.

2. The vanadium-bromine flow battery electrolyte according to claim 1, characterized in that: The molar concentration ratio of vanadium ions:bromide ions:additives in the positive electrode electrolyte and the negative electrode electrolyte is 1-2.5:0.5-1.5:0.02-0.

5.

3. The vanadium-bromine flow battery electrolyte according to claim 1, characterized in that: The final concentration of bromide ions in the positive electrode electrolyte is 0.5-1.5 mol / L, the final concentration of vanadium ions in the negative electrode electrolyte is 1.0-2.5 mol / L, the final concentration of the additive is 0.02-0.5 mol / L, and the final concentration of the acid is 3 mol / L.

4. The vanadium-bromine flow battery electrolyte according to claim 1, characterized in that: The acid is a strong inorganic acid.

5. The vanadium-bromine flow battery electrolyte according to claim 1, characterized in that: The acid is at least one of sulfuric acid and hydrochloric acid.

6. The method for preparing the electrolyte for vanadium-bromine flow battery according to any one of claims 1 to 5, characterized in that: The steps include: (1) mixing a bromine source with water and then adding 1-ethyl-4-methylpyridinium bromide and 1,2-dimethylimidazole in a molar ratio of 1-3:1-3 to obtain a positive electrode electrolyte; (2) Dissolve the vanadium source with acid and filter the filtrate; (3) Add water to the filtrate and adjust the vanadium ion concentration to the target final concentration to obtain the negative electrode electrolyte.

7. The method for preparing the electrolyte for vanadium-bromine flow battery according to claim 6, characterized in that: The bromine source includes one or more of HBr, NaBr, and Br2; the vanadium source includes one or more of V2O5, VO2, V2O3, (VO2)2SO4, VOSO4, VO2Cl, VOCl2, VCl3, and VCl2.

8. The method for preparing the electrolyte for vanadium-bromine flow battery according to claim 7, characterized in that: The vanadium source includes one or more of V2O5, VO2, (VO2)2SO4, VOSO4, and VOCl2, and the bromine source is HBr.

9. The method for preparing the electrolyte for vanadium-bromine flow battery according to claim 6, characterized in that: In step (2), the molar ratio of the acid to the vanadium source is 4-8:1.5-2.0, and the acid is sulfuric acid; in step (3), the water is deionized water.

10. A flow battery, characterized in that: The invention comprises the vanadium-bromine flow battery electrolyte according to any one of claims 1 to 5, a positive electrode, an ion-conducting membrane and a negative electrode.

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