A cobalt-tungsten acid-halogen flow battery

Abstract

The application discloses a cobalt-tungsten acid-halogen liquid flow battery, which adopts an aqueous solution of keggin type cobalt-tungsten acid or a mixed aqueous solution of keggin type cobalt-tungsten acid and hydrobromic acid and hydroiodic acid as a negative electrolyte of the battery, and the mixed aqueous solution of keggin type cobalt-tungsten acid and hydrobromic acid and hydroiodic acid as a positive electrolyte. The Keggin type cobalt-tungsten acid-halogen mixed electrolyte of the application can further improve the energy density of the battery on the basis of maintaining the osmotic pressure balance of the positive and negative electrodes of the battery, and meanwhile, the optimal energy efficiency of the liquid flow battery can be achieved by regulating the composition and concentration of the positive and negative electrolytes. The manufacturing method is simple, and the battery has high stability and high capacity density.

Description

Technical Field

[0001] This invention belongs to the field of energy and chemical technology, and in particular to the field of flow battery technology. Specifically, it relates to a flow battery that uses keggin-type cobalt tungstate and halogens as electroactive materials. Background Technology

[0002] Electrochemical energy storage and conversion technology, as a clean and efficient energy storage technology, has become a hot topic pursued by researchers, countries, and related companies worldwide. Among them, flow batteries (RFBs) have become a promising large-scale energy storage technology due to their advantages such as the ability to independently and flexibly design power and energy storage capacity (power modules and energy storage modules are separated), the use of highly fluid liquid or quasi-solid materials with fast kinetic reaction speeds, high safety due to deep charge-discharge capability, and long cycle life.

[0003] Currently, the more mature flow batteries mainly include systems such as all-vanadium, all-chromium, iron-chromium, and zinc-bromine. However, the electroactive materials in these systems are generally small, positively charged metal ions. These batteries commonly suffer from electrolyte leaching or cross-contamination, severely impacting their energy efficiency and lifespan. Therefore, developing novel electroactive materials for flow batteries is essential.

[0004] Heteropolyacids and halogens are both highly stable and electrochemically active anions. Due to charge repulsion, they are difficult to pass through conventional proton exchange membranes. Furthermore, electrolytes using heteropolyacids and halogens as electroactive materials have high half-cell capacities, demonstrating significant potential as novel electroactive materials for flow batteries. However, common heteropolyacid electroactive materials, such as Keggin-type phosphotungstic acid, Keggin-type silicotungstic acid, and Dawson-type phosphotungstic acid, are only used in the negative electrode, while halogens such as bromine and iodine are only used in the positive electrode. The large molecular weight of heteropolyacids results in low water content in heteropolyacid solutions, creating a significant osmotic pressure difference with smaller molecule solutions like halogens. When these two are directly combined in a flow battery, the positive electrode electrolyte permeates to the negative electrode under osmotic pressure, making it difficult to ensure stable operation of the flow battery.

[0005] To address the aforementioned issues, the commonly used strategy is to mix the positive and negative electrode active materials to create a mixed electrolyte for use at both electrodes of the battery, balancing the osmotic pressure and improving battery stability. However, the active materials used to balance osmotic pressure often cannot function at the other electrode; for example, the active material used at the positive electrode cannot function at the negative electrode, increasing the energy storage cost of the battery. Simultaneously, the ionic strength of the solution increases significantly after mixing the active materials, causing a substantial decrease in the solubility of each active material, further reducing the battery's energy density. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a cobalt tungstate-halogen flow battery. This battery employs a Keggin-type cobalt tungstate and halogen mixed electrolyte, which can further improve the battery's energy density while maintaining the osmotic pressure balance between the positive and negative electrodes.

[0007] The complete technical solution of this invention includes:

[0008] A cobalt tungstate-halogen flow battery, the flow battery comprising a positive electrode and a negative electrode, the negative electrode being connected to a negative electrode electrolyte, and the positive electrode being connected to a positive electrode electrolyte; characterized in that the negative electrode electrolyte is an aqueous solution of keggin-type cobalt tungstate, or a mixed aqueous solution of keggin-type cobalt tungstate with hydrobromic acid and hydroiodic acid; and the positive electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstate with hydrobromic acid and hydroiodic acid.

[0009] Furthermore, the flow battery also includes a proton exchange membrane located between the positive and negative electrodes.

[0010] Furthermore, the positive and negative electrodes are respectively connected to the positive and negative electrolytes through infusion tubes, and an infusion pump for delivering the electrolyte is provided on the infusion tubes.

[0011] Furthermore, the positive and negative electrode materials include, but are not limited to, graphite felt, carbon felt, and carbon paper.

[0012] Furthermore, the proton exchange membrane is 211 proton exchange membrane.

[0013] Furthermore, the molecular formula of the keggin-type cobalt tungstate is H6[CoW]. 12 O 40 The hydrobromic acid has the molecular formula HBr, and the hydroiodic acid has the molecular formula HI. The negative electrode reaction that occurs in the flow battery is as follows:

[0014]

[0015]

[0016] The positive electrode reaction that occurs in a flow battery is as follows:

[0017]

[0018]

[0019] Furthermore, the negative electrode electrolyte is a keggin-type cobalt tungstic acid aqueous solution with a concentration of 0.2-0.8M; the positive electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydrobromic acid, with the cobalt tungstic acid concentration of 0.2-0.8M and the hydrobromic acid concentration of 0.6-3.6M.

[0020] Furthermore, the negative electrode electrolyte is a keggin-type cobalt tungstic acid aqueous solution with a concentration of 0.2-0.8M; the positive electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydroiodic acid, with the cobalt tungstic acid concentration of 0.2-0.8M and the hydrobromic acid concentration of 0.6-3.6M.

[0021] Furthermore, the negative electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydrobromic acid, with a cobalt tungstic acid concentration of 0.2-0.8 M; the positive electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydrobromic acid, with a cobalt tungstic acid concentration of 0.2-0.8 M and a hydrobromic acid concentration of 0.6-3.6 M; and the concentration of hydrobromic acid in the negative electrode electrolyte is less than or equal to the concentration of hydrobromic acid in the positive electrode electrolyte.

[0022] Furthermore, the negative electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydroiodic acid, with a cobalt tungstic acid concentration of 0.2-0.8 M; the positive electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydroiodic acid, with a cobalt tungstic acid concentration of 0.2-0.8 M and a hydroiodic acid concentration of 0.6-3.6 M; and the concentration of hydroiodic acid in the negative electrode electrolyte is less than or equal to the concentration of hydroiodic acid in the positive electrode electrolyte.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) Keggin-type cobalt tungstate (H6[CoW) 12 O 40 It can be used as an electroactive material for both the positive and negative electrodes of the battery, and can better balance the osmotic pressure of the electrolyte. Compared with flow batteries that use heteropoly acids only at the negative electrode, it has better stability.

[0026] (2) Adding halogens to the positive electrode electrolyte as electroactive materials can increase the positive electrode capacity density of the cobalt tungstate flow battery, thereby increasing the overall capacity density of the flow battery.

[0027] (3) The method of the present invention is simple and can achieve the optimal energy efficiency of flow battery by adjusting the composition and concentration of positive and negative electrode electrolytes. Attached Figure Description

[0028] Figure 1 The working principle of the flow battery of the present invention is shown.

[0029] Figure 2 A comparison of the voltage characteristic curves of the flow battery in this embodiment of the invention.

[0030] Figure 3 This is a comparison of the efficiency cycle performance of the flow batteries in this embodiment of the invention.

[0031] Figure 4 This is a comparison of the capacity cycle performance of flow batteries according to embodiments of the present invention.

[0032] In the diagram: 1-Proton exchange membrane; 2-Electrode material; 3-Infusion pump; 4-Infusion tube; 5-Negative electrolyte; 6-Positive electrolyte. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The purpose of this invention is to overcome the above-mentioned shortcomings of existing flow batteries and provide a novel heteropolyacid flow battery with high energy efficiency, long cycle life, and safety and reliability.

[0035] Keggin-type cobalt tungstate (H6[CoW) 12 O 40 Cobalt tungstic acid (CTA) is a heteropolyacid that can be used as the electroactive material for both the positive and negative electrodes of a battery. Using CTA at both electrodes can effectively balance the osmotic pressure of the electrolyte. However, CTA undergoes a four-electron transfer redox reaction of tungsten at the negative electrode, but only a single-electron redox reaction of cobalt occurs at the positive electrode. Therefore, its capacity density at the positive electrode is much lower than that at the negative electrode, resulting in a lower overall energy density of the CTA flow battery. Therefore, this invention adds halogens such as bromine and iodine to the positive electrode of the CTA flow battery. While maintaining the osmotic pressure balance of the electrolyte, this replenishes the capacity density of the positive electrode, thereby effectively improving the overall energy density of the flow battery.

[0036] Figure 1 The figure shows the structure and working principle of the flow battery of the present invention. The flow battery of the present invention includes a proton exchange membrane 1 located in the middle. Positive and negative electrode materials 2 are respectively provided on both sides of the proton exchange membrane 1. The electrode materials 2 are respectively connected to their respective positive and negative electrolytes through the infusion pipes 4. The infusion pipes 4 are equipped with infusion pumps 3 for conveying electrolytes. The negative electrode material is connected to the negative electrolyte 5, and the positive electrode material is connected to the positive electrolyte 6.

[0037] Preferably, the electrode material of the flow battery of the present invention is selected from carbon-based materials such as graphite felt, carbon felt, and carbon paper, and the proton exchange membrane is adopted. 211 proton exchange membrane.

[0038] The operating performance of a flow battery according to an embodiment of the present invention is as follows: Figure 2 , Figure 3 , Figure 4 As shown. Figure 2 , Figure 3 , Figure 4 In the illustrated embodiment (Example 1), the negative electrode electrolyte composition is 0.4M cobalt tungstate + 1.2M hydrobromic acid, and the positive electrode electrolyte composition is 0.4M cobalt tungstate + 1.2M hydrobromic acid. The volume ratio of the positive and negative electrode electrolytes is 1:1. The performance of the flow battery is determined by... Figure 2 voltage characteristic curve, Figure 3 Efficiency, cycle performance and Figure 4 The capacity cycling performance is characterized.

[0039] Example 1

[0040] The electrode material for the flow battery is graphite felt, and the proton exchange membrane is made of... A 211 proton exchange membrane was used. The negative electrode electrolyte consisted of 0.4M cobalt tungstate + 1.2M hydrobromic acid, with a volume of 7.5 mL; the positive electrode electrolyte also consisted of 0.4M cobalt tungstate + 1.2M hydrobromic acid, with a volume of 7.5 mL. The electrolyte flow rate was 100 mL / min. This flow battery exhibits high capacity, energy efficiency, and good stability. Figure 2-4 As shown, at 200mA / cm 2 At the given current density, the capacity is 120mAh, the coulombic efficiency is 95%, the energy efficiency is 70%, which gradually increases to 73% during cycling. The capacity decreases from 120mAh to 98mAh within 100 cycles, with a capacity retention of 99.8% per cycle.

[0041] Example 2

[0042] The electrode material for the flow battery is graphite felt, and the proton exchange membrane is made of... 211 proton exchange membrane. The negative electrode electrolyte consists of 0.2M cobalt tungstate (7.5 mL); the positive electrode electrolyte consists of 0.2M cobalt tungstate + 0.6M hydrobromic acid (7.5 mL). The electrolyte flow rate is 100 mL / min. At 200 mA / cm²... 2 At a current density, it has a capacity of 60mAh, a coulombic efficiency of 93%, an average energy efficiency of 69%, and a capacity retention of 99.7% per cycle.

[0043] Example 3

[0044] The electrode material for the flow battery is graphite felt, and the proton exchange membrane is made of... 211 proton exchange membrane. The negative electrode electrolyte consists of 0.8M cobalt tungstate + 2.4M hydrobromic acid, with a volume of 7.5 mL; the positive electrode electrolyte consists of 0.8M cobalt tungstate + 3.6M hydrobromic acid, with a volume of 7.5 mL. The electrolyte flow rate is 100 mL / min. At 200 mA / cm²... 2 At a current density of 200mAh, the capacity is 90%, the coulombic efficiency is 90%, the average energy efficiency is 65%, and the capacity retention is 99.8% per cycle.

[0045] Comparative Example 1

[0046] The electrode material for the flow battery is graphite felt, and the proton exchange membrane is made of... 211 proton exchange membrane. The negative electrode electrolyte is 0.4M cobalt tungstate, with a volume of 7.5 mL; the positive electrode electrolyte is 0.4M cobalt tungstate, with a volume of 7.5 mL. The electrolyte flow rate is 100 mL / min.

[0047] like Figure 2 , Figure 3 , Figure 4 As shown, at 200mA / cm 2 At a current density, the capacity is 50mAh, the coulombic efficiency is 95%, the energy efficiency is 53%, which gradually decreases to 50% during cycling. The capacity decays from 50mAh to 10mAh in 100 cycles, with a capacity retention of 99.2% per cycle.

[0048] Depend on Figure 2-4 It can be seen that the cobalt tungstate-halogen flow battery constructed in this invention (Example 1) has higher capacity and energy efficiency and better cycle stability compared with the cobalt tungstate flow battery (Comparative Example 1).

[0049] Comparative Example 2

[0050] The electrode material for the flow battery is graphite felt, and the proton exchange membrane is made of... 211 proton exchange membrane. The negative electrode electrolyte is 0.4M cobalt tungstate, 7.5 mL in volume; the positive electrode electrolyte is 2.5M hydroiodic acid, 7.5 mL in volume. The electrolyte flow rate is 100 mL / min.

[0051] like Figure 2-4 As shown, at 200mA / cm 2 At the given current density, the capacity is 120mAh, the coulombic efficiency is 60%, the energy efficiency is 30%, which rises to 44% during cycling and then gradually decreases back to 40%. The capacity only decreases from 120mAh to 50mAh within 40 cycles, with a capacity retention of 98.5% per cycle.

[0052] Depend on Figure 2-4It can be seen that the cobalt tungstate-halogen flow battery constructed in this invention (Example 1) has higher capacity and energy efficiency and better cycle stability compared with the flow battery (Comparative Example 2) in which cobalt tungstate is only used as the negative electrode electrolyte.

[0053] The above-described embodiments are merely some implementation methods of this application. For those skilled in the art, various modifications and improvements can be made without departing from the inventive concept of this application, and these all fall within the protection scope of this application.

Claims

1. A cobalt tungstate-halogen flow battery, the flow battery comprising a positive electrode and a negative electrode, the negative electrode being connected to a negative electrolyte, and the positive electrode being connected to a positive electrolyte; characterized in that, The negative electrode electrolyte is an aqueous solution of keggin-type cobalt tungstic acid, or a mixed aqueous solution of keggin-type cobalt tungstic acid, hydrobromic acid, and hydroiodic acid; the positive electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid, hydrobromic acid, and hydroiodic acid. The molecular formula of the keggin-type cobalt tungstate is H6[CoW]. 12 O 40 The hydrobromic acid has the molecular formula HBr, and the hydroiodic acid has the molecular formula HI; the positive electrode reaction occurring in the flow battery is as follows: or:

2. The cobalt tungstate-halogen flow battery according to claim 1, characterized in that, The flow battery also includes a proton exchange membrane located between the positive and negative electrodes.

3. The cobalt tungstate-halogen flow battery according to claim 1, characterized in that, The positive and negative electrodes are respectively connected to the positive and negative electrolytes through infusion pipes, and an infusion pump for delivering the electrolyte is provided on the infusion pipes.

4. The cobalt tungstate-halogen flow battery according to claim 1, characterized in that, The positive and negative electrode materials include graphite felt, carbon felt, and carbon paper.

5. A cobalt tungstate-halogen flow battery according to claim 2, characterized in that, The proton exchange membrane is 211 proton exchange membrane.

6. A cobalt tungstate-halogen flow battery according to claim 4, characterized in that, The negative electrode reaction that occurs in a flow battery is as follows:

7. A cobalt tungstate-halogen flow battery according to any one of claims 1-6, characterized in that, The negative electrode electrolyte is a keggin-type cobalt tungstic acid aqueous solution with a concentration of 0.2-0.8M; the positive electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydrobromic acid, with the cobalt tungstic acid concentration of 0.2-0.8M and the hydrobromic acid concentration of 0.6-3.6M.

8. A cobalt tungstate-halogen flow battery according to any one of claims 1-6, characterized in that, The negative electrode electrolyte is a keggin-type cobalt tungstic acid aqueous solution with a concentration of 0.2-0.8M; the positive electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydroiodic acid, with the cobalt tungstic acid concentration of 0.2-0.8M and the hydrobromic acid concentration of 0.6-3.6M.

9. A cobalt tungstate-halogen flow battery according to any one of claims 1-6, characterized in that, The negative electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydrobromic acid, with a cobalt tungstic acid concentration of 0.2-0.8 M; the positive electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydrobromic acid, with a cobalt tungstic acid concentration of 0.2-0.8 M and a hydrobromic acid concentration of 0.6-3.6 M; and the concentration of hydrobromic acid in the negative electrode electrolyte is less than or equal to the concentration of hydrobromic acid in the positive electrode electrolyte.

10. A cobalt tungstate-halogen flow battery according to any one of claims 1-6, characterized in that, The negative electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydroiodic acid, with a cobalt tungstic acid concentration of 0.2-0.8 M; the positive electrode electrolyte is a mixed aqueous solution of keggin-type cobalt tungstic acid and hydroiodic acid, with a cobalt tungstic acid concentration of 0.2-0.8 M and a hydroiodic acid concentration of 0.6-3.6 M; and the concentration of hydroiodic acid in the negative electrode electrolyte is less than or equal to the concentration of hydroiodic acid in the positive electrode electrolyte.

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