A negative electrode electrolyte and battery for alkaline zinc-based flow batteries

Abstract

This invention discloses a negative electrode electrolyte and battery for alkaline zinc-based flow batteries, belonging to the field of electrochemical energy storage technology. The negative electrode electrolyte comprises an alkaline zincate solution and a sulfone additive with a concentration of 0.05-5.0 mol / L. The alkaline zincate solution contains tetrahydroxy zinc ions. The sulfone additive, through its oxygen and sulfur functional groups, forms a moderate complexation with the tetrahydroxy zinc ions, partially substituting the hydroxyl groups, thereby effectively suppressing the hydrogen evolution side reaction during zinc deposition. Simultaneously, this moderate complexation does not hinder the transport and deposition of zinc ions, promoting uniform zinc deposition. Applying the negative electrode electrolyte of this invention to an alkaline zinc-based flow battery can significantly improve the battery's coulombic efficiency, energy efficiency, and cycle life. Experiments show that adding dimethyl sulfone can increase the cycle life of a zinc-iron flow battery from 172 cycles to 379 cycles. This invention is simple, low-cost, and easy to implement, and is of great significance for promoting the development of low-cost, long-life zinc-based flow batteries.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a negative electrode electrolyte for an alkaline zinc-based flow battery and an alkaline zinc-based flow battery containing the electrolyte. Background Technology

[0002] To achieve the "dual carbon" goal, renewable energy sources, represented by wind and solar power, have been vigorously developed. However, their inherent intermittency and volatility pose challenges to the stable operation of the power grid, necessitating large-scale energy storage technologies for peak shaving. Flow batteries, due to their long cycle life, high safety, and the ability to independently design power and capacity, are considered one of the most promising large-scale energy storage technologies. Currently, vanadium redox flow battery technology is relatively mature, but the high cost of vanadium resources limits further reductions in its cost.

[0003] Zinc is abundant, inexpensive, and highly electrochemically active, making alkaline zinc-based flow batteries (such as zinc-iron flow batteries) with zinc anodes a promising alternative technology. However, in strongly alkaline environments, zinc mainly exists as tetrahydroxyzinc ions ([Zn(OH)4]²⁻), which are prone to hydrogen evolution side reactions during charge and discharge, accompanied by uneven zinc deposition (dendritic growth). This leads to reduced battery coulombic efficiency, rapid capacity decay, and short cycle life, severely hindering the commercial application of this technology.

[0004] To suppress hydrogen evolution and dendrite growth, a common method is to add organic additives to the electrolyte. Existing technologies have attempted to use citric acid, tetrabutylammonium bromide, and vanillin as additives. However, these additives often have excessively strong binding forces with zinc ions. While they can suppress hydrogen evolution, they also severely hinder zinc ion transport kinetics, affecting the battery's rate performance and energy efficiency. Therefore, developing an additive that can moderately regulate interfacial processes, effectively suppressing hydrogen evolution without affecting zinc ion deposition kinetics, is crucial for advancing alkaline zinc-based flow batteries.

[0005] Furthermore, while there are existing reports of using sulfone compounds (such as sulfolane) in aqueous zinc-metal batteries, their mechanisms of action (e.g., formation of reverse micelle structures) and application scenarios (neutral / weakly acidic static batteries) are fundamentally different from the strongly alkaline, flowing system flow batteries that this invention focuses on. In particular, the chemical form of zinc ions ([Zn(OH)4]²⁻) is completely different in alkaline environments (Zn²⁺ hydrated ions) compared to neutral environments, making the mechanism and effect of additives unpredictable. Currently, there are no reports on using sulfone compounds as trace additives in alkaline zinc-based flow batteries, and on their ability to synergistically suppress hydrogen evolution and promote uniform deposition through moderate complexation with tetrahydroxyzinc ions. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a negative electrode electrolyte and battery for alkaline zinc-based flow batteries. This electrolyte, by introducing specific types and concentrations of sulfone additives, can generate appropriately sized complexing forces with tetrahydroxyzinc ions in an alkaline environment, effectively suppressing hydrogen evolution side reactions and promoting uniform zinc deposition, thereby significantly improving the battery's coulombic efficiency, energy efficiency, and cycle life.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a negative electrode electrolyte for an alkaline zinc-based flow battery, comprising an alkaline zincate solution and a sulfone additive dissolved therein; wherein the alkaline zincate solution contains tetrahydroxyzinc ions, and the concentration of the sulfone additive is from 0.05 mol / L to 5.0 mol / L.

[0008] Preferably, the sulfone additive is selected from one or more of sulfolane, cyclopentyl sulfone, dimethyl sulfone, phenylethyl sulfone, diethyl sulfone, polyether sulfone, polyphenylene sulfone, and hydroxydiphenyl sulfone. More preferably, it is sulfolane or dimethyl sulfone.

[0009] Preferably, the concentration of the sulfone additive is from 0.1 mol / L to 0.5 mol / L. Within this concentration range, the additive achieves the best effect and the optimal cost-effectiveness.

[0010] Preferably, the alkaline zincate solution is obtained by dissolving a zinc salt in an aqueous inorganic alkaline solution; the zinc salt is selected from one or more of zinc sulfate, zinc hydroxide, zinc chloride, zinc oxide, and zinc nitrate; and the inorganic alkaline is potassium hydroxide and / or sodium hydroxide.

[0011] The inventors have discovered that the sulfone additives, through their polar functional groups such as oxygen and sulfur, exhibit moderate complexation with tetrahydroxyzinc ions. This complexation partially replaces the hydroxyl groups in [Zn(OH)4]²⁻, thereby stabilizing zinc ions, reducing their activity, and effectively inhibiting the direct hydrogen evolution reaction of hydroxyl groups on the electrode surface. Simultaneously, this complexing force is "appropriately strong," avoiding the excessive binding of zinc ions that leads to sluggish deposition kinetics, as seen in some strong complexing agents, while also appropriately regulating the desolvation and deposition process of zinc ions at the electrode / electrolyte interface, guiding uniform nucleation and growth of zinc, and inhibiting dendrite formation.

[0012] In a second aspect, the present invention provides an alkaline zinc-based flow battery, comprising a positive electrode electrolyte, a negative electrode electrolyte, a positive electrode, a negative electrode, and an ion exchange membrane disposed between the positive and negative electrodes, wherein the negative electrode electrolyte is any one of the negative electrode electrolytes described in the first aspect above.

[0013] Preferably, the electrode materials for the negative and positive electrodes are independently selected from carbon felt, graphite felt, zinc foam, or copper foam, with carbon felt being the most preferred. Preferably, when the electrode is carbon felt, its compression ratio is 10% to 60%, preferably 20%. A suitable compression ratio helps optimize electrolyte distribution and electrode conductivity. Preferably, the ion exchange membrane is a Nafion membrane, a porous membrane, or a composite membrane.

[0014] Preferably, the alkaline zinc-based flow battery is an alkaline zinc-iron flow battery, an alkaline zinc-manganese flow battery, or an alkaline zinc-nickel flow battery, and is particularly suitable for alkaline zinc-iron flow batteries.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention introduces specific sulfone compounds as trace additives into the negative electrode electrolyte of an alkaline zinc-based flow battery. By utilizing their unique complexing effect with tetrahydroxy zinc ions under a strongly alkaline environment, the invention synergistically achieves effective suppression of hydrogen evolution side reactions and effective promotion of uniform zinc deposition.

[0016] 2. The additives of this invention have significant effects. Experiments show that after adding 0.3 mol / L sulfolane, the battery performance at 80 mAcm⁻¹ is improved. -2 The energy efficiency was improved from 72% to 75%, and the coulombic efficiency was improved from 98% to 99%. More importantly, after adding 0.2 mol / L dimethyl sulfone, the cycle life of the battery was significantly extended from 172 cycles to 379 cycles, an improvement of more than 120%, achieving unexpected technical results.

[0017] 3. The method of the present invention is simple to operate. It only requires adding sulfone additives and mixing them evenly when preparing the negative electrode electrolyte. No complicated equipment or subsequent processing is required. It is easy to implement in existing battery production processes, has low cost, and is suitable for large-scale production applications.

[0018] 4. The sulfone compounds used in this invention are chemically stable, have good compatibility in strongly alkaline environments, and will not introduce new side reactions or accelerate electrolyte decomposition, which is beneficial to the long-term stable operation of the battery. Attached Figure Description

[0019] Figure 1 The rate performance of the alkaline zinc-iron flow battery with added sulfolane in Example 1 is shown in the graph at different current densities.

[0020] Figure 2 The graph shows the rate performance of the alkaline zinc-iron flow battery without additives in Comparative Example 1 at different current densities.

[0021] Figure 3 The graph shows the long-cycle performance of the alkaline zinc-iron flow battery with added dimethyl sulfone in Example 2.

[0022] Figure 4 The graph shows the long-cycle performance of the alkaline zinc-iron flow battery without additives in Comparative Example 2. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto. Unless otherwise specified, the reagents and materials used in the embodiments of the present invention can be purchased commercially. Example 1: Alkaline zinc-iron flow battery with added sulfolane and its rate performance test Preparation of negative electrode electrolyte: Sodium hydroxide (NaOH) was dissolved in deionized water to prepare an alkaline solution with a concentration of 3 mol / L. Zinc oxide (ZnO) was then added as a zinc source, and the solution was stirred thoroughly to form an alkaline zincate solution containing tetrahydroxyzinc ions. Finally, sulfolane was added to this solution to bring the final concentration to 0.3 mol / L, and the mixture was stirred until homogeneous to obtain the negative electrode electrolyte.

[0024] Positive Electrolyte Preparation: Dissolve 0.8 mol / L sodium hexacyanoferrate (Na4Fe(CN)6·10H2O) in 3 mol / L potassium hydroxide (KOH) solution to obtain the positive electrolyte. Battery Assembly: A Nafion 212 membrane was used as the ion exchange membrane. Two 6 cm × 6 cm carbon felt pieces (compression ratio 20%) were used as the positive and negative electrodes, respectively. The Nafion 212 membrane was sandwiched in between and secured with bipolar plates to assemble a single flow battery cell. The positive and negative electrolyte volumes were each 50 mL, placed in separate storage tanks and circulated using a peristaltic pump.

[0025] Battery testing: The battery was tested using the Blue Battery testing system at 25°C. First, the battery was allowed to stand for 3 minutes. The test procedure was as follows: at 40mA cm... -2 The capacitor was charged to a capacity of 720 mAh at a current density, and then discharged to a cutoff voltage of 0.1 V at the same current density. Then, it was discharged sequentially at 60, 80, 100, 120, 140, and 160 mA cm⁻¹. -2 Rate testing was conducted at various current densities, with six cycles at each current density.

[0026] Test results are as follows Figure 1 As shown. At 80 mA cm -2 At the specified current density, the battery achieved a coulombic efficiency (CE) of 99%, an energy efficiency (EE) of 75%, and a voltage efficiency (VE) of 75%. This indicates that the addition of sulfolane maintains excellent electrochemical performance over a wide current density range.

[0027] Comparative Example 1: Alkaline zinc-iron flow battery without additives (as a comparison with Example 1) Except for not adding any sulfone additives to the negative electrode electrolyte, the other steps, materials, and test conditions are exactly the same as in Example 1.

[0028] Test results are as follows Figure 2 As shown. At 80 mA cm -2 At the specified current density, the battery exhibits a coulombic efficiency (CE) of 98%, an energy efficiency (EE) of 72%, and a voltage efficiency (VE) of 73%. Compared to Example 1, all efficiencies decreased, particularly the energy efficiency, which dropped by 3 percentage points. This is primarily due to the more severe hydrogen evolution side reaction at the negative electrode without additives, and the potentially more uneven zinc deposition, leading to increased polarization and decreased efficiency.

[0029] Example 2: Alkaline zinc-iron flow battery with added dimethyl sulfone and its long-cycle performance test The battery assembly method is similar to that in Example 1, except that the sulfone additive added to the negative electrode electrolyte is dimethyl sulfone, with a concentration of 0.2 mol / L.

[0030] Battery testing: Charge-discharge cycle testing was conducted at 25°C and a constant current density of 80 mA cm⁻². The battery was charged to a capacity of 720 mAh, and the discharge cutoff voltage was 0.1 V.

[0031] Test results are as follows Figure 3 As shown, the battery using dimethyl sulfone additive operated very stably, maintaining stable operation for 379 cycles before showing significant degradation. This indicates that the additive effectively extends the battery's cycle life. This is mainly due to the addition of sulfone additives to the negative electrode electrolyte. Sulfone compounds contain oxygen and sulfur functional groups with moderate polarity, which can combine with zinc ions, inhibiting the hydrogen evolution side reaction of tetrahydroxyzinc ions during deposition. Simultaneously, it promotes uniform deposition of zinc on the negative electrode, increasing electrode polarization, thereby reducing the charge transfer rate to zincate and slowing down the nucleation rate of zinc deposition, significantly improving the cycle life of the alkaline zinc-iron flow battery.

[0032] Comparative Example 2: Alkaline zinc-iron flow battery without additives (as a comparison with Example 2) Except for the absence of any additives, the battery assembly and testing conditions were the same as in Example 2.

[0033] Test results are as follows Figure 4 As shown, the unadded battery began to degrade in performance after only 172 stable cycles. Compared to Example 2, the cycle life was shortened by approximately 207 cycles, a decrease of over 54%. This comparison strongly demonstrates the significant and unexpected effect of the sulfone additives of this invention in improving the cycle life of alkaline zinc-based flow batteries.

[0034] Example 3: Effect of different carbon felt compression ratios on battery performance The battery was assembled and the electrolyte (with 0.3 mol / L sulfolane added) was prepared according to the method of Example 1. The compression ratio of the carbon felt was adjusted to 15%, 20%, 25%, and 30% by varying the thickness of the electrode frame and sealing gasket. The electrolyte was prepared at 80 mA cm⁻¹. -2 Battery performance was tested at current density. The results are shown in Table 1 below.

[0035] As shown in Table 1, with the increase of carbon felt compression ratio, the EE and VE of alkaline zinc-based flow batteries first increase and then decrease. When the compression ratio is 20%, the alkaline zinc-based flow battery has the best performance. Therefore, the carbon felt compression ratio of alkaline zinc-based flow batteries is preferably 20%.

[0036] Example 4: Effect of different sulfolane concentrations on battery performance The battery was assembled according to the method of Example 1, except that the concentration of sulfolane in the negative electrode electrolyte was changed to 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, and 0.4 mol / L. The electrolyte was then heated at 80 mA cm⁻¹. -2 Battery performance was tested at current density. The results are shown in Table 2 below.

[0037] As can be seen from Table 2, the alkaline zinc-based flow battery with a sulfolane concentration of 0.3 mol / L exhibits the best performance. Therefore, the preferred sulfolane additive concentration for alkaline zinc-based flow batteries is 0.3 mol / L.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A negative electrode electrolyte for alkaline zinc-based flow batteries, characterized in that, The mixture comprises an alkaline zincate solution and a sulfone additive dissolved therein; the alkaline zincate solution contains tetrahydroxyzinc ions, and the concentration of the sulfone additive is from 0.05 mol / L to 5.0 mol / L.

2. The negative electrode electrolyte according to claim 1, characterized in that, The sulfone additive is selected from at least one of sulfolane, cyclopentyl sulfone, dimethyl sulfone, phenylethyl sulfone, diethyl sulfone, polyether sulfone, polyphenylene sulfone, and hydroxydiphenyl sulfone.

3. The negative electrode electrolyte according to claim 2, characterized in that, The sulfone additive is sulfolane or dimethyl sulfone.

4. The negative electrode electrolyte according to claim 3, characterized in that, The concentration of the sulfone additive is from 0.1 mol / L to 0.5 mol / L.

5. The negative electrode electrolyte according to claim 1, characterized in that, The alkaline zincate solution is obtained by dissolving a zinc salt in an inorganic alkaline aqueous solution; the zinc salt is selected from at least one of zinc sulfate, zinc hydroxide, zinc chloride, zinc oxide, and zinc nitrate; the inorganic alkali is selected from at least one of potassium hydroxide and sodium hydroxide.

6. The negative electrode electrolyte according to any one of claims 1 to 5, characterized in that, The sulfone additives partially replace the hydroxyl groups on the tetrahydroxy zinc ion by complexing with the oxygen and sulfur functional groups in their molecules.

7. An alkaline zinc-based flow battery, comprising a positive electrode electrolyte, a negative electrode electrolyte, a positive electrode, a negative electrode, and an ion exchange membrane disposed between the positive and negative electrodes, characterized in that, The negative electrode electrolyte is the negative electrode electrolyte according to any one of claims 1 to 6.

8. The alkaline zinc-based flow battery according to claim 7, characterized in that, The electrode materials for the negative and positive electrodes are independently selected from carbon felt, graphite felt, zinc foam, or copper foam; the ion exchange membrane is a Nafion membrane, a porous membrane, or a composite membrane.

9. The alkaline zinc-based flow battery according to claim 8, characterized in that, When the electrode is a carbon felt, its compression ratio is 10% to 60%.

10. The alkaline zinc-based flow battery according to claim 7, characterized in that, The alkaline zinc-based flow battery is an alkaline zinc-iron flow battery, an alkaline zinc-manganese flow battery, or an alkaline zinc-nickel flow battery.

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