Non-aqueous electrolyte zinc-bromine battery without hydrogen evolution

Abstract

The invention discloses a non-aqueous electrolyte zinc-bromine battery without hydrogen evolution. The non-aqueous electrolyte zinc-bromine battery comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm, the positive electrode is a porous conductive support electrode, and the surface is coated with composite slurry containing a bromine complexing agent and activated carbon; the negative electrode is zinc foil; the electrolyte is a non-aqueous organic electrolyte and comprises an acetonitrile and tetrahydrofuran mixed solvent, a zinc bromide main salt, lithium bis (trifluoromethanesulfonyl) imide or lithium bis (fluoromethanesulfonyl) imide conducting salt and an alkyl or benzyl ammonium bromide cationic surfactant complexing agent. By adopting the aprotic organic solvent, the electrolytic reaction of water is avoided, the problem of hydrogen evolution of a traditional aqueous zinc-bromine battery is solved, and potential safety hazards are eliminated; the mixed solvent system obviously improves the solubility and ionic conductivity of zinc bromide; and the complexing agent in the positive electrode and the electrolyte can effectively complex bromine, so that self-discharge is reduced. The coulombic efficiency of the battery is stabilized at 92% or above, the capacity retention ratio is greater than 90% after 100 cycles, and the battery shows excellent safety performance and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a zinc-bromine battery using a non-aqueous organic electrolyte, specifically a non-flowing zinc-bromine battery that can avoid hydrogen evolution and improve safety performance. Background Technology

[0002] With the rapid development of renewable energy, large-scale energy storage technology has become key to the energy transition. Zinc-bromine batteries, as a battery system with high theoretical energy density (430 Wh / kg), abundant resources, and low cost, have enormous application potential in the field of large-scale energy storage.

[0003] Currently, zinc-bromine batteries are mostly used in flow battery systems. However, zinc-bromine flow batteries require expensive auxiliary components such as circulation pumps, piping systems, and reactors, resulting in complex systems and high costs. Non-flowing zinc-bromine batteries can significantly reduce costs, simplify battery structure, and have better application prospects.

[0004] Existing non-fluid zinc-bromine batteries all use aqueous electrolyte systems. In aqueous electrolytes, water molecules readily undergo electrolytic reactions during charging and discharging, especially under high voltage or low pH conditions, leading to hydrogen and oxygen evolution side reactions on the electrode surface, producing hydrogen and oxygen gas. According to the reaction mechanism of zinc-bromine batteries, zinc dissolution and deposition reactions occur at the negative electrode, while bromine redox reactions occur at the positive electrode. During this process, the hydrogen and oxygen evolution side reactions on the electrode surface lead to continuous gas accumulation. For example, Chinese patent document CN118538967A discloses an aqueous zinc-bromine battery using zinc bromide aqueous solution as the electrolyte, but this battery is prone to hydrogen evolution reactions during charging, resulting in battery bulging, changes in electrolyte concentration, and safety hazards. It also reduces the battery's coulombic efficiency and cycle life.

[0005] To address the hydrogen evolution problem, researchers have proposed various solutions. Chinese patent document CN117855630A discloses a zinc-bromine battery electrolyte with added hydrogen evolution inhibitors, which suppresses hydrogen evolution by adding a small amount of organic solvent; however, the effect is limited and it affects the battery's electrochemical performance. Chinese patent document CN118335917A describes a zinc-bromine battery with a modified zinc anode, reducing hydrogen evolution by passivating the zinc anode with trivalent chromium salts; however, the process is complex and cannot completely eliminate hydrogen evolution.

[0006] Existing zinc-bromine battery technology mainly suffers from the following problems: the unavoidable hydrogen evolution reaction in aqueous electrolytes leads to battery safety hazards; existing hydrogen evolution suppression methods have limited effectiveness and affect battery performance; research on non-aqueous electrolyte systems is still immature, and there is a lack of high-performance electrolyte formulations suitable for zinc-bromine batteries.

[0007] Therefore, developing a non-aqueous electrolyte system that can effectively dissolve zinc bromide, has good ion transport performance, and avoids hydrogen evolution is of great significance for promoting the practical application of zinc-bromine batteries. Summary of the Invention

[0008] The purpose of this invention is to provide a non-aqueous electrolyte zinc-bromine battery without hydrogen evolution. By designing a suitable composition and ratio of non-aqueous organic electrolyte, the hydrogen evolution problem existing in the existing aqueous zinc-bromine batteries is solved, thereby improving the safety and cycle stability of the battery.

[0009] The technical solution adopted in this invention is: a non-aqueous zinc-bromine battery without hydrogen evolution, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that: the positive electrode is a porous conductive support electrode, the surface of which is coated with a composite slurry containing a bromine complexing agent and activated carbon; the negative electrode is zinc foil; the electrolyte is a non-aqueous organic electrolyte, comprising: a mixed electrolyte solvent: acetonitrile and tetrahydrofuran, with a mass ratio of 1:(0.3-3), and may add no more than 30% by weight of a third polar organic solvent; the main salt: zinc bromide, with a concentration of 0.5-6.0 mol / L; the conductive salt: lithium bis(trifluoromethanesulfonylimide) or lithium bis(fluoromethanesulfonylimide) with a concentration of 1-30 g / L; and the complexing agent: an alkyl or benzyl ammonium bromide cationic surfactant with a concentration of 0.01-1 mol / L.

[0010] Furthermore, the mass ratio of acetonitrile to tetrahydrofuran in the mixed solvent is preferably 1:(0.8-1.2).

[0011] Further, the preferred concentrations of each component in the electrolyte are: zinc bromide 1.5-4.0 mol / L, the concentration of the conductive salt lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluoromethanesulfonyl)imide 5-15 g / L, and the alkyl or benzyl ammonium bromide cationic surfactant tetrapropylammonium bromide at a concentration of 0.05-0.5 mol / L. The third polar organic solvent may be selected from at least one of propylene carbonate, ethylene carbonate, dimethyl sulfoxide, or N,N-dimethylformamide.

[0012] Furthermore, the composite slurry coated on the positive electrode surface consists of: alkyl or benzyl ammonium bromide cationic surfactant, activated carbon, polyvinylidene fluoride (PVDF), and acetylene black, in a mass ratio of (2-8):(1-3):(0.5-2):(0.5-2); the slurry dispersant is N-methylpyrrolidone (NMP).

[0013] Furthermore, the alkyl or benzyl ammonium bromide cationic surfactant in the battery composite slurry is tetrapropylammonium bromide (TPABr), accounting for 40% to 70% of the total mass of the slurry.

[0014] This invention also provides a method for preparing the above-mentioned zinc-bromine battery, comprising the following steps:

[0015] (1) Negative electrode preparation: The zinc sheet is polished with 400-mesh sandpaper until the surface is bright and the oxide layer is removed; it is soaked in 2% citric acid solution for 1 hour to remove surface impurities; it is rinsed with deionized water and anhydrous ethanol in sequence, and dried in a vacuum drying oven at 60℃ for 2 hours.

[0016] (2) Preparation of positive electrode: Weigh alkyl or benzyl ammonium bromide cationic surfactant, activated carbon, PVDF and acetylene black in a mass ratio of (2-8): (1-3): (0.5-2): (0.5-2), add an appropriate amount of NMP and stir evenly to make a slurry; coat the slurry evenly on the surface of the porous positive electrode and dry it in a vacuum drying oven at 120℃ for 12 hours.

[0017] (3) Electrolyte preparation: Mix acetonitrile and tetrahydrofuran in a mass ratio; add alkyl or benzyl ammonium bromide cationic surfactants in sequence and stir until completely dissolved; finally add lithium bis(trifluoromethanesulfonylimide) or lithium bis(fluoromethanesulfonylimide) and continue stirring until uniform and transparent to obtain a non-aqueous organic electrolyte.

[0018] (4) Battery assembly: The prepared zinc sheet is used as the negative electrode, the porous conductive material coated with slurry is used as the positive electrode, the polypropylene porous membrane is used as the separator, the prepared organic electrolyte is injected, and the soft pack battery is assembled in a glove box and vacuum sealed.

[0019] (5) Battery activation: Activate the battery by constant current charge and discharge for 10 cycles using a current density of 0.1C.

[0020] The beneficial effects of this invention are:

[0021] (1) Completely solve the hydrogen evolution problem: The use of non-protic organic solvents avoids the electrolysis reaction of water, eliminates hydrogen evolution and oxygen evolution, and improves the safety of the battery.

[0022] (2) Improved solubility and conductivity: The acetonitrile-tetrahydrofuran mixed solvent system significantly improved the solubility of zinc bromide (up to 4 mol / L or more) while ensuring good ionic conductivity (>10 mS / cm).

[0023] (3) Suppressing polybromination diffusion: TPABr complexing agent in the positive electrode and electrolyte can effectively complex bromine to form stable polybromination anion complexes, reduce the volatilization and diffusion of bromine, and reduce self-discharge.

[0024] (4) Excellent electrochemical performance: The battery coulombic efficiency is stable at over 92%, and the capacity retention rate is greater than 90% after 100 cycles, showing good cycle stability.

[0025] (5) Simple structure and low cost: Compared with the flow battery system, the static battery structure of the present invention is simple and does not require auxiliary equipment such as circulation pump, which greatly reduces the system cost. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the organic electrolyte zinc-bromine battery of the present invention.

[0027] Figure 2 Comparison of the battery's appearance before and after charging and discharging.

[0028] Figure 3 This is a charge / discharge voltage-capacity curve for Example 1.

[0029] Figure 4 The graph shows the coulomb efficiency of Example 1 as a function of the number of cycles.

[0030] Figure 5 The graph shows the capacity retention rate as a function of the number of cycles in Example 1. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0032] Comparative Example 1 (Aqueous Electrolyte)

[0033] Polish the zinc sheet surface with 400-grit sandpaper until it is shiny, remove the oxide layer, cut it into 30mm×30mm square pieces, spot weld nickel tabs, and dry it in a vacuum drying oven at 60℃ for 1 hour.

[0034] A slurry was prepared by mass ratio of TPABr: activated carbon: PVDF: acetylene black = 6:2:1:1. The slurry was stirred evenly with NMP as a dispersant and then uniformly coated onto a carbon felt. The slurry was then vacuum dried at 120°C for 10 hours.

[0035] Prepare a 3 mol / L zinc bromide aqueous solution, add 0.2 mol / L tetrapropylammonium bromide, and stir to dissolve to obtain an aqueous electrolyte. Assemble a pouch cell and vacuum seal it.

[0036] Charge-discharge tests were conducted at a current density of 2 mA / cm². The results showed that the battery capacity dropped sharply after 80 cycles, a large amount of gas was generated inside the battery, and obvious bulging occurred, posing a safety hazard.

[0037] Comparative Example 2 (Pure Acetonitrile Electrolyte)

[0038] The negative electrode preparation was the same as in Comparative Example 1.

[0039] The preparation of the positive electrode is the same as in Comparative Example 1.

[0040] Take 10 mL of acetonitrile, add zinc bromide to a concentration of 0.5 mol / L, add 0.1 g of lithium bis(trifluoromethanesulfonylimide) (10 g / L), add TPABr to a concentration of 0.1 mol / L, and stir until completely dissolved to obtain a transparent electrolyte.

[0041] The battery was assembled and tested at a current density of 2 mA / cm². The results showed that no gas was generated inside the battery, and no bulging occurred after 100 cycles. However, the capacity was relatively small due to the low zinc bromide concentration.

[0042] Comparative Example 3 (pure tetrahydrofuran electrolyte)

[0043] The preparation of the negative and positive electrodes is the same as in Comparative Example 1.

[0044] Take 10 mL of tetrahydrofuran, add 2.25 g of zinc bromide (1.0 mol / L), add 0.1 g of lithium bis(trifluoromethanesulfonylimide), add TPABr to a concentration of 0.2 mol / L, and stir until completely dissolved.

[0045] Test results: The battery showed no hydrogen evolution and no bulging after 100 cycles. Tetrahydrofuran provided better solubility for zinc bromide, but its conductivity was relatively low.

[0046] Example 1 (Acetonitrile-tetrahydrofuran mixed electrolyte)

[0047] Negative electrode preparation: Polish the zinc sheet to a mirror finish with sandpaper, soak it in 2% citric acid solution for 1 hour, clean it with deionized water and ethanol, vacuum dry it, and spot weld the electrode tabs.

[0048] Positive electrode preparation: Prepare TPABr complexing agent slurry, coat it on carbon felt, and spot weld the electrode tabs.

[0049] Electrolyte preparation: Mix 5 mL of tetrahydrofuran and 5 mL of acetonitrile, add 4.49 g of zinc bromide (2.0 mol / L), add 0.1 g of lithium bis(trifluoromethanesulfonylimide) (10 g / L), and add TPABr to a concentration of 0.2 mol / L. Stir magnetically for 2 hours until completely dissolved to obtain a colorless and transparent electrolyte. Tetrahydrofuran improves the solubility of ZnBr2, and acetonitrile improves the conductivity; the two work synergistically to optimize the electrolyte performance, while LiTFSI significantly improves the conductivity of the system.

[0050] Performance testing: Current density 2 mA / cm², cutoff voltage 0.8-2.0 V. Test results show:

[0051] No gas is generated inside the battery, and there is no bulging after 100 cycles; the average coulombic efficiency is ≥92%; the capacity retention rate after 100 cycles is >90%; the plateau voltage is stable at around 1.4 V; and the specific capacity reaches 85 mAh / g.

[0052] Figure 2 The comparison of the battery's appearance before and after charging and discharging shows that there is no change in the battery's appearance and no bulging. Figure 3 Typical charge-discharge curves are shown, with a clear and stable plateau. Figure 4 The coulomb efficiency is shown to be above 92 and stable. Figure 5 This indicates excellent capacity retention, maintaining over 90% even after 100 cycles.

[0053] The above embodiments demonstrate that the present invention employs an acetonitrile-tetrahydrofuran mixed solvent system, combined with a positive electrode that can fix bromine, successfully solving the hydrogen evolution problem in zinc-bromine batteries and achieving safe and stable electrochemical performance.

Claims

1. A non-aqueous electrolyte zinc-bromine battery without hydrogen evolution, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that: The positive electrode is a porous conductive support electrode, coated with a composite slurry containing a bromine complexing agent and activated carbon; the negative electrode is zinc foil; the electrolyte is a non-aqueous organic electrolyte comprising: a mixed electrolyte solvent: acetonitrile and tetrahydrofuran, in a mass ratio of 1:(0.3-3), and may contain no more than 30% by weight of a third polar organic solvent; a main salt: zinc bromide, with a concentration of 0.5-6.0 mol / L; a conductive salt: lithium bis(trifluoromethanesulfonylimide) or lithium bis(fluoromethanesulfonylimide), with a concentration of 1-30 g / L; and a complexing agent: an alkyl or benzyl ammonium bromide cationic surfactant, with a concentration of 0.01-1 mol / L.

2. The non-aqueous electrolyte zinc-bromine battery without hydrogen evolution according to claim 1, characterized in that: The preferred mass ratio of acetonitrile to tetrahydrofuran in the mixed solvent is 1:(0.8-1.2).

3. The non-aqueous electrolyte zinc-bromine battery without hydrogen evolution according to claim 1, characterized in that: The concentrations of each component in the electrolyte are as follows: zinc bromide 1.5-4.0 mol / L, conductive salt is lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluoromethanesulfonyl)imide with a concentration of 5-15 g / L, and alkyl or benzyl ammonium bromide cationic surfactant is tetrapropylammonium bromide with a concentration of 0.05-0.5 mol / L.

4. The non-aqueous electrolyte zinc-bromine battery without hydrogen evolution according to claim 1, characterized in that: The third polar organic solvent is selected from at least one of propylene carbonate, ethylene carbonate, dimethyl sulfoxide, or N,N-dimethylformamide.

5. The non-aqueous electrolyte zinc-bromine battery without hydrogen evolution according to claim 1, characterized in that: The composite slurry coated on the positive electrode surface consists of: alkyl or benzyl ammonium bromide cationic surfactant, activated carbon, polyvinylidene fluoride, and acetylene black, in a mass ratio of (2-8):(1-3):(0.5-2):(0.5-2).

6. The non-aqueous electrolyte zinc-bromine battery without hydrogen evolution according to claim 5, characterized in that: The alkyl or benzyl ammonium bromide cationic surfactant in the composite slurry is tetrapropylammonium bromide, accounting for 40% to 70% of the total mass of the slurry.

7. The method for preparing a non-aqueous electrolyte zinc-bromine battery without hydrogen evolution according to any one of claims 1-6, characterized in that... Includes the following steps: (1) Negative electrode preparation: The zinc sheet is polished with 400-mesh sandpaper until the surface is bright, soaked in 2% citric acid solution for 1 hour, rinsed with deionized water and anhydrous ethanol in turn, and dried in a vacuum drying oven at 60℃ for 2 hours; (2) Positive electrode preparation: The alkyl or benzyl ammonium bromide cationic surfactant, activated carbon, polyvinylidene fluoride and acetylene black are weighed in the mass ratio (2-8):(1-3):(0.5-2):(0.5-2), and an appropriate amount of N-methylpyrrolidone is added and stirred evenly to make a slurry. The slurry is evenly coated on the surface of the porous positive electrode and dried in a vacuum drying oven at 120℃ for 12 hours; (3) Electrolyte preparation: Acetonitrile and tetrahydrofuran are mixed in the mass ratio, and zinc bromide and alkyl or benzyl ammonium bromide cationic surfactant are added in turn. The mixture is stirred until completely dissolved, and finally lithium bis(trifluoromethanesulfonylimide) or lithium bis(fluoromethanesulfonylimide) is added. The mixture is stirred until uniform and transparent to obtain a non-aqueous organic electrolyte; (4) Battery assembly: The prepared zinc sheet is used as the negative electrode, the porous conductive material coated with slurry is used as the positive electrode, the polypropylene porous membrane is used as the separator, the prepared organic electrolyte is injected, and the soft pack battery is assembled in a glove box and vacuum sealed.

8. The application of the hydrogen-evolution-free, non-aqueous electrolyte zinc-bromine battery according to claims 1 to 7 in new energy and energy storage.

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