Alkaline zinc-iron flow battery electrolyte and use thereof

Abstract

The application provides a kind of alkaline zinc iron liquid flow battery electrolyte and its application, belong to liquid flow battery technical field.The negative electrode electrolyte of the application is prepared into suspension by dissolving zinc bromide in strong alkali solution;The concentration difference exists in the alkali concentration of positive and negative electrode electrolyte, and the alkali concentration of positive electrode electrolyte is lower than that in negative electrode electrolyte.The use of positive and negative electrode electrolyte of the application can effectively alleviate the migration problem of alkaline zinc iron liquid flow battery electrolyte, improve the energy density of negative electrode electrolyte, widen the applicable temperature range of battery, and improve the reliability of battery.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, specifically relating to an alkaline zinc-iron flow battery electrolyte and its application. Background Technology

[0002] With my country's rapid social progress and economic development, we have also paid a heavy price – massive energy consumption and severe environmental pollution. Therefore, to resolve the conflict between humanity and nature, clean and renewable energy sources (such as wind and solar power) will inevitably be widely utilized. However, these clean and renewable energy sources are often discontinuous and unstable, requiring energy storage facilities during their utilization. Zinc-iron flow batteries, due to their high safety, low cost, and high power density, hold promise as large-scale or distributed energy storage systems for power facilities, promoting the high-quality application of clean and renewable energy.

[0003] Zinc-iron flow batteries are a highly competitive energy storage technology that utilizes an alkaline aqueous electrolyte, offering advantages such as low cost and high safety. The negative electrode utilizes the deposition and dissolution reaction of zinc, exhibiting a low potential in the alkaline electrolyte (-1.2V vs. the standard hydrogen electrode), with the electrochemical reaction involving the transfer of two electrons. The positive electrode electrolyte is composed of potassium ferrocyanide or sodium ferrocyanide dissolved in an alkaline solution, with a potential of 0.5V relative to the standard hydrogen electrode. It is low-cost, highly reversible, and exhibits a high electrochemical reaction rate.

[0004] However, traditional zinc-iron flow batteries experience electrolyte migration and precipitation of active materials in the positive electrode electrolyte during operation, shortening the battery's cycle life and resulting in poor low-temperature performance. Developing a high-performance electrolyte that can effectively alleviate these problems has become a crucial research topic, thereby improving the performance of zinc-iron flow batteries and driving their rapid development. Summary of the Invention

[0005] Therefore, the purpose of this invention is to provide a novel composition of the positive and negative electrolytes for an alkaline zinc-iron flow battery and their applications.

[0006] The objective of this invention is achieved through the following means:

[0007] This invention provides an alkaline zinc-iron flow battery electrolyte, comprising a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte is composed of a transparent solution formed by a mixed aqueous solution of ferrocyanide and a strong alkali, and the negative electrode electrolyte is composed of a suspension formed by a mixed aqueous solution of zinc bromide and a strong alkali, wherein the suspended solids in the suspension are zinc hydroxide.

[0008] Furthermore, the ferrocyanide is one or a combination of two or more of potassium ferrocyanide, sodium ferrocyanide, lithium ferrocyanide, magnesium ferrocyanide, and calcium ferrocyanide.

[0009] Furthermore, the ferrocyanide is one or a combination of two of sodium ferrocyanide and potassium ferrocyanide.

[0010] Furthermore, the strong base is one or a combination of two or more of sodium hydroxide, lithium hydroxide, and potassium hydroxide.

[0011] Furthermore, the concentration of ferrocyanide in the positive electrode electrolyte is 0.05–0.7 mol / L, and the concentration of the strong base is 0.5–2 mol / L.

[0012] Furthermore, the concentration of zinc bromide in the negative electrode electrolyte is 0.4–1.2 mol / L, and the concentration of strong alkali is 2–6 mol / L; the molar ratio of zinc bromide to alkali is 1:12.5–1:2, preferably 1:10–1:5.

[0013] Furthermore, the alkali concentration in the negative electrode electrolyte is higher than that in the positive electrode electrolyte, with a difference of 1–6 mol / L, preferably 2–4 mol / L.

[0014] Furthermore, the ferrocyanide in the positive electrode electrolyte is sodium ferrocyanide with a concentration of 0.5 mol / L; the strong base is potassium hydroxide with a concentration of 1.25-1.75 mol / L.

[0015] Furthermore, the concentration of zinc bromide in the negative electrode electrolyte is 0.5-1.0 mol / L; the strong base is potassium hydroxide with a concentration of 4.5-5 mol / L.

[0016] Furthermore, in addition to the zincate ions dissolved in the strongly alkaline solution being reduced to elemental zinc during charging, the suspended zinc hydroxide in the electrolyte also dissolves into the strongly alkaline solution and continues to be reduced to elemental zinc, participating in the electrochemical reaction of the battery.

[0017] Another aspect of the present invention provides an alkaline zinc-iron flow battery assembled using the above-described alkaline zinc-iron flow battery electrolyte.

[0018] Furthermore, the alkaline zinc-iron flow battery comprises a battery module consisting of one or more single cells connected in series or parallel.

[0019] Furthermore, the alkaline zinc-iron flow battery is equipped with a storage tank containing positive / negative electrolyte, a circulation pump, and a circulation pipeline.

[0020] Furthermore, the alkaline zinc-iron flow battery also includes a positive current collector, a negative current collector, positive / negative electrodes, and an ion-conducting membrane.

[0021] Furthermore, the electrodes are made of carbon felt or carbon paper.

[0022] Compared with the prior art, the beneficial effects achieved by this invention are as follows:

[0023] 1. The electrolyte of the present invention effectively alleviates the electrolyte migration problem in alkaline zinc-iron flow batteries: The present invention greatly alleviates the problem of large-scale electrolyte migration from the negative electrode to the positive electrode by adjusting the alkali concentration in the positive and negative electrode electrolytes, the osmotic pressure provided by bromide ions, and the dissolution and precipitation of suspended matter, thereby effectively reducing the system maintenance cost and improving the cycle life of the battery.

[0024] 2. The electrolyte of this invention effectively improves the energy density of the negative electrode electrolyte: Traditional negative electrode electrolytes rely solely on the amount of zincate formed by zinc salt and / or zinc oxide solution in an alkaline electrolyte to determine the energy density. The electrolyte of this invention overcomes the limitation of the dissolved form on the energy density of the negative electrode electrolyte, and improves the energy density of the negative electrode electrolyte by using a suspension form.

[0025] 3. The electrolyte of this invention improves the reliability of single cells / stacks of zinc-iron flow batteries: The increased energy density of the negative electrode electrolyte of this invention allows for a suitable reduction in the concentration of ferricyanide in the positive electrode while maintaining the same overall energy density as the total positive and negative electrode electrolytes in traditional zinc-iron flow batteries. This avoids battery failure caused by positive electrode electrolyte precipitation due to changes in ambient temperature, which could lead to blockage of the positive electrode electrolyte circulation path, and broadens the applicable temperature range of the battery. Attached Figure Description

[0026] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0027] Figure 1 The graph shows the cycle efficiency of a zinc-iron flow battery with a comparative electrolyte.

[0028] Figure 2 The diagram shows the cycle efficiency of the zinc-iron flow battery using the electrolyte of this invention. Detailed Implementation

[0029] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0030] In the examples and comparative examples, the alkaline zinc-iron flow battery is a single-cell battery. The battery includes a storage tank containing positive and negative electrolytes, a circulation pump, and circulation piping. The battery comprises a positive current collector, a negative current collector, a carbon felt electrode, and a polybenzimidazole membrane, with an electrode area of ​​9 cm². 2Test conditions: Charging cutoff voltage is 2.2V, discharging cutoff voltage is 0.1V.

[0031] Example 1

[0032] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2 Constant current charge-discharge was performed, with charging for 1 hour. The positive electrode electrolyte was 0.5 mol / L sodium ferrocyanide + 1.25 mol / L potassium hydroxide, 90 mL; the negative electrode electrolyte was a suspension prepared with 0.8 mol / L zinc bromide + 5 mol / L potassium hydroxide, 30 mL. The concentration ratio of zinc bromide to negative electrode alkali was 1:6.25, and the concentration difference between the negative and positive electrode electrolytes was 3.75.

[0033] The negative electrode electrolyte has an energy density of 42.88 Ah / L, and no significant deposition of the positive electrode electrolyte was observed at 0℃. The average coulombic efficiency for the first 100 charge-discharge cycles was approximately 98.1%, and the average energy efficiency was approximately 90.4% (e.g., ...). Figure 2 (As shown); after 200 hours of charge-discharge cycles, less than 5 mL of electrolyte migrated from the positive electrode to the negative electrode.

[0034] Example 2

[0035] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2 Constant current charge-discharge was performed, with charging for 1 hour. The positive electrode electrolyte was 0.5 mol / L sodium ferrocyanide + 1.75 mol / L potassium hydroxide, 90 mL; the negative electrode electrolyte was a suspension prepared with 0.8 mol / L zinc bromide + 4.5 mol / L potassium hydroxide, 30 mL. The concentration ratio of zinc bromide to negative electrode alkali was 1:6.25, and the concentration difference between the negative and positive electrode electrolytes was 2.75.

[0036] The energy density of the negative electrode electrolyte is 42.88 Ah / L, and no significant deposition of the positive electrode electrolyte occurs at 0℃. The average coulombic efficiency is approximately 97.9% and the average energy efficiency is approximately 90.1% for the first 100 charge-discharge cycles. After 200 hours of charge-discharge cycles, less than 5 mL of electrolyte migrates from the negative electrode to the positive electrode.

[0037] Example 3

[0038] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2 Constant current charge-discharge was performed, with charging for 1 hour. The positive electrode electrolyte was 0.5 mol / L sodium ferrocyanide + 1.25 mol / L potassium hydroxide, 90 mL; the negative electrode electrolyte was a suspension prepared with 0.5 mol / L zinc bromide + 5 mol / L potassium hydroxide, 30 mL. The concentration ratio of zinc bromide to negative electrode alkali was 1:10, and the concentration difference between the negative and positive electrode electrolytes was 3.75.

[0039] The energy density of the negative electrode electrolyte is 26.8 Ah / L, and no significant deposition of the positive electrode electrolyte occurs at 0℃. The average coulombic efficiency is approximately 97.5% and the average energy efficiency is approximately 89.8% in the first 100 charge-discharge cycles. After 200 hours of charge-discharge cycles, less than 5 mL of electrolyte migrates from the negative electrode to the positive electrode.

[0040] Example 4

[0041] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2 Constant current charge-discharge was performed, with charging for 1 hour. The positive electrode electrolyte was 0.5 mol / L sodium ferrocyanide + 1.25 mol / L potassium hydroxide, 90 mL; the negative electrode electrolyte was a suspension prepared with 1 mol / L zinc bromide + 5 mol / L potassium hydroxide, 30 mL. The concentration ratio of zinc bromide to negative electrode alkali was 1:5, and the concentration difference between the negative and positive electrode electrolytes was 3.75.

[0042] The energy density of the negative electrode electrolyte is 53.6 Ah / L, and no significant precipitation of the positive electrode electrolyte occurs at 0℃. The average coulombic efficiency is approximately 97.7% and the average energy efficiency is approximately 89.3% for the first 100 charge-discharge cycles. After 200 hours of charge-discharge cycles, less than 5 mL of electrolyte migrates from the positive to the negative electrode.

[0043] Comparative Example 1

[0044] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2 Constant current charge-discharge was performed, with charging for 1 hour. The positive electrode electrolyte was 0.5 mol / L sodium ferrocyanide + 1.25 mol / L potassium hydroxide, 90 mL; the negative electrode electrolyte was a suspension of 2.5 mol / L zinc bromide + 5 mol / L potassium hydroxide, 30 mL. The concentration ratio of zinc bromide to negative electrode alkali was 1:2, and the concentration difference between the negative and positive electrode electrolytes was 3.75.

[0045] Due to excessive zinc bromide in the negative electrode and low alkali concentration, the solid content in the negative electrode electrolyte is too high, the circulation path of the negative electrode electrolyte is blocked, the circulation pump cannot effectively deliver the negative electrode active material to the electrode surface, the battery cannot cycle 100 times, and the voltage soars to the cutoff voltage of 2.2V when the charging time is less than 1 hour.

[0046] Comparative Example 2

[0047] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2 Constant current charge-discharge was performed, with charging for 1 hour. The positive electrode electrolyte was 0.5 mol / L sodium ferrocyanide + 2 mol / L potassium hydroxide, 90 mL; the negative electrode electrolyte was a suspension prepared with 0.8 mol / L zinc bromide + 2 mol / L potassium hydroxide, 30 mL. The concentration ratio of zinc bromide to negative electrode alkali was 1:2.5, and the concentration difference between the negative and positive electrode electrolytes was 0.

[0048] The energy density of the negative electrode electrolyte is 42.88 Ah / L. Due to the low alkali concentration, the solid content in the negative electrode electrolyte is too high, the circulation path of the negative electrode electrolyte is blocked, and the circulation pump cannot effectively deliver the negative electrode active material to the electrode surface. When charging is less than 1 hour, the voltage soars to 2.2V.

[0049] Comparative Example 3

[0050] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2 Constant current charge-discharge was performed, with charging for 1 hour. The positive electrode electrolyte was 0.5 mol / L sodium ferrocyanide + 1 mol / L potassium hydroxide, 90 mL; the negative electrode electrolyte was a suspension prepared with 0.8 mol / L zinc bromide + 8 mol / L potassium hydroxide, 30 mL. The concentration ratio of zinc bromide to negative electrode alkali was 1:10, and the concentration difference between the negative and positive electrode electrolytes was 7.

[0051] The energy density of the negative electrode electrolyte is 42.88 Ah / L. When the battery has not cycled 100 times, the charging voltage spikes to the cutoff voltage of 2.2V. Because the electrolyte migrates only more than 10 mL from the positive to the negative electrode, electrolyte precipitates out from the positive electrode, blocking the supply line to the positive electrode active material. Without an active material supply, the charging voltage at the positive electrode increases rapidly.

[0052] Comparative Example 4

[0053] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2 Constant current charge-discharge was applied, with charging for 1 hour. The positive electrode electrolyte was 0.8 mol / L sodium ferrocyanide + 3 mol / L potassium hydroxide, 60 mL, heated until completely dissolved. The negative electrode electrolyte was 0.4 mol / L zinc oxide + 3.8 mol / L sodium hydroxide transparent solution, 60 mL. The concentration difference between the negative and positive electrode electrolytes was 0.8.

[0054] The negative electrode electrolyte has an energy density of 21.44 Ah / L. Supersaturation and deposition of the positive electrode are visible at room temperature, necessitating filtration of the positive electrode electrolyte with carbon felt for battery cycling. The average coulombic efficiency for the first 100 charge-discharge cycles is approximately 98.7%, and the average energy efficiency is approximately 90.6% (e.g., ...). Figure 1 (As shown); After 200 hours of charge-discharge cycles, more than 10 mL of electrolyte migrated from the negative electrode to the positive electrode. This was mainly due to the small concentration difference of the alkali in the electrolyte between the negative and positive electrodes. The negative electrode electrolyte lacked bromide ions and suspended solids, causing it to be unable to maintain a stable concentration during charge-discharge, resulting in a large amount of electrolyte migrating from the negative electrode to the positive electrode.

[0055] Comparative Example 5

[0056] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2Constant current charge and discharge, charging for 1 hour, positive electrode electrolyte is 0.8 mol / L sodium ferrocyanide + 3 mol / L potassium hydroxide, 90 mL; negative electrode electrolyte is a suspension prepared of 0.8 mol / L zinc oxide + 4 mol / L potassium hydroxide, 30 mL.

[0057] The negative electrode electrolyte has an energy density of 42.88 Ah / L. Significant precipitation occurs in the positive electrode electrolyte at room temperature, necessitating filtration of the positive electrode electrolyte with carbon felt for battery cycling. The average coulombic efficiency for the first 100 charge-discharge cycles is approximately 97.8%, and the average energy efficiency is approximately 90.1%. After 200 hours of charge-discharge cycling, more than 10 mL of electrolyte migrates from the negative electrode to the positive electrode. This is mainly due to the excessively high alkali concentration in the positive electrode electrolyte and the absence of bromide ions in the negative electrode electrolyte, leading to a large-scale migration of water from the negative electrode electrolyte to the positive electrode electrolyte.

[0058] Comparative Example 6

[0059] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2 Constant current charge-discharge was applied, with charging for 1 hour. The positive electrode electrolyte was 0.5 mol / L sodium ferrocyanide + 3.5 mol / L potassium hydroxide, 90 mL, heated until completely dissolved. The negative electrode electrolyte was a suspension of 0.8 mol / L zinc bromide + 4 mol / L potassium hydroxide, 30 mL. The concentration ratio of zinc bromide to negative electrode alkali was 1:5, and the concentration difference between the negative and positive electrode electrolytes was 0.5.

[0060] The energy density of the negative electrode electrolyte is 42.88 Ah / L. The average coulombic efficiency of the first 100 charge-discharge cycles is about 96.7%, and the average energy efficiency is about 89.1%. After 200 hours of charge-discharge cycles, due to the small concentration difference between the negative and positive electrode electrolytes, more than 10 mL of electrolyte migrates from the negative electrode to the positive electrode.

[0061] Comparative Example 7

[0062] The zinc-iron liquid flow single cell was operated at 40 mA / cm 2 Constant current charge-discharge was performed, with charging for 1 hour. The positive electrode electrolyte was 0.5 mol / L sodium ferrocyanide + 1.25 mol / L potassium hydroxide, 90 mL; the negative electrode electrolyte was a clear solution prepared with 0.2 mol / L zinc bromide + 5 mol / L potassium hydroxide, 30 mL. The concentration ratio of zinc bromide to negative electrode alkali was 1:25, and the concentration difference between the negative and positive electrode electrolytes was 3.75.

[0063] The energy density of the negative electrode electrolyte is 10.72 Ah / L. Due to the low energy density of the negative electrode electrolyte, it cannot provide enough zinc source to be deposited on the negative electrode. The battery cannot cycle 100 times. When the charging time is less than 1 hour, the voltage spikes to the cutoff voltage of 2.2V.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An alkaline zinc-iron flow battery electrolyte, characterized in that, It includes a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte is composed of a transparent solution formed by a mixed aqueous solution of ferrocyanide and a strong base, and the negative electrode electrolyte is composed of a suspension formed by a mixed aqueous solution of zinc bromide and a strong base. The concentration of ferrocyanide in the positive electrode electrolyte is 0.05~0.7 mol / L, and the concentration of the strong base is 0.5~2 mol / L; the concentration of zinc bromide in the negative electrode electrolyte is 0.4~1.2 mol / L, and the concentration of the strong base is 2~6 mol / L; the molar ratio of zinc bromide to base is 1:10-1:

5. The alkali concentration in the negative electrode electrolyte is higher than that in the positive electrode electrolyte, with a difference of 1~6 mol / L.

2. The alkaline zinc-iron flow battery electrolyte according to claim 1, characterized in that, The ferrocyanide is one or a combination of two or more of potassium ferrocyanide, sodium ferrocyanide, lithium ferrocyanide, magnesium ferrocyanide, and calcium ferrocyanide.

3. The alkaline zinc-iron flow battery electrolyte according to claim 2, characterized in that, The ferrocyanide is one or a combination of two of sodium ferrocyanide and potassium ferrocyanide.

4. The alkaline zinc-iron flow battery electrolyte according to claim 1, characterized in that, The strong base is one or a combination of two or more of sodium hydroxide, lithium hydroxide, and potassium hydroxide.

5. The alkaline zinc-iron flow battery electrolyte according to claim 1, characterized in that, The difference between the alkali concentration in the negative electrode electrolyte and the alkali concentration in the positive electrode electrolyte is 2~4 mol / L.

6. An alkaline zinc-iron flow battery, characterized in that, The electrolyte of the alkaline zinc-iron flow battery is the alkaline zinc-iron flow battery electrolyte according to any one of claims 1-5.

7. The alkaline zinc-iron flow battery according to claim 6, characterized in that, The alkaline zinc-iron flow battery comprises a battery module consisting of one or more single cells connected in series or parallel.

8. The alkaline zinc-iron flow battery according to claim 6, characterized in that, The alkaline zinc-iron flow battery is equipped with a storage tank containing positive / negative electrolyte, a circulation pump, and circulation pipelines.

9. The alkaline zinc-iron flow battery according to claim 6, characterized in that, The alkaline zinc-iron flow battery also includes a positive electrode current collector, a negative electrode current collector, positive / negative electrodes, and an ion-conducting membrane.

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