Non-hydrogen-evolution non-aqueous electrolyte zinc-bromine battery

Abstract

The application discloses a non-hydrogen-evolution non-aqueous electrolyte zinc-bromine battery, which comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm. The positive electrode is a porous conductive support electrode, and the surface of the positive electrode is coated with a composite slurry containing a bromine complexing agent and activated carbon; the negative electrode is a zinc foil; the electrolyte is a non-aqueous organic electrolyte, which comprises a mixed solvent of acetonitrile and tetrahydrofuran, zinc bromide main salt, lithium bis-trifluoromethanesulfonimide or lithium bis-fluoromethanesulfonimide conductive salt and an alkyl or benzyl bromide ammonium cationic surfactant complexing agent. The application adopts an aprotic organic solvent, avoids the electrolytic reaction of water, solves the hydrogen evolution problem of a traditional water-based zinc-bromine battery, eliminates the safety hazard, and significantly improves the solubility and ionic conductivity of zinc bromide in a mixed solvent system. The complexing agent in the positive electrode and the electrolyte can effectively complex bromine and reduce self-discharge. The coulombic efficiency of the battery is stable at more than 92%, the capacity retention rate is greater than 90% after 100 cycles, and the battery exhibits excellent safety performance and cycle stability.

Description

TECHNICAL FIELD

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

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

[0003] Currently, the application of zinc-bromine batteries is mostly concentrated in flow battery systems. However, zinc-bromine flow batteries require expensive auxiliary components such as circulating pumps, pipeline systems, and reactors, resulting in complex systems and high costs. Non-flowing zinc-bromine batteries can greatly reduce costs and simplify battery structure, with better application prospects.

[0004] Non-flowing zinc-bromine batteries in the prior art all use aqueous electrolyte systems. In aqueous electrolyte, water molecules are prone to electrolytic reactions during charging and discharging, especially under high voltage or low pH conditions, which can cause hydrogen and oxygen evolution side reactions on the electrode surface. According to the reaction mechanism of zinc-bromine batteries, zinc dissolution and deposition reactions occur at the negative electrode, and bromine oxidation and reduction reactions occur at the positive electrode. In this process, the hydrogen and oxygen evolution side reactions on the electrode surface can cause continuous gas accumulation. For example, Chinese patent document CN118538967A discloses a water-based zinc-bromine battery that uses zinc bromide aqueous solution as electrolyte, but the battery is prone to hydrogen evolution during charging, which can cause battery bulging, electrolyte concentration changes, and safety hazards, and also reduces the coulombic efficiency and cycle life of the battery.

[0005] To solve the problem of hydrogen evolution, researchers have proposed various solutions. Chinese patent document CN117855630A discloses a zinc-bromine battery electrolyte with hydrogen evolution inhibitors, which can inhibit hydrogen evolution by adding a small amount of organic solvent, but the effect is limited and can affect the electrochemical performance of the battery. Chinese patent document CN118335917A describes a zinc-bromine battery with a modified zinc negative electrode, which reduces hydrogen evolution by passivating the zinc negative electrode with trivalent chromium salt, but the processing process is complex and cannot completely eliminate hydrogen evolution.

[0006] The existing zinc-bromine battery technology mainly has the following problems: The inevitable hydrogen evolution reaction in the aqueous electrolyte leads to safety hazards in the battery; The existing hydrogen evolution inhibition methods have limited effect and affect the performance of the battery; The non-aqueous electrolyte system is not mature, and there is a lack of high-performance electrolyte formulations suitable for zinc-bromine batteries.

[0007] Therefore, it is of great significance to develop a non-aqueous electrolyte system capable of effectively dissolving zinc bromide, having good ion transmission performance, and avoiding hydrogen evolution phenomenon, for promoting the practical application of zinc bromide batteries. SUMMARY

[0008] The present application aims to provide a non-aqueous electrolyte zinc bromide battery without hydrogen evolution, by designing a suitable non-aqueous organic electrolyte composition and ratio, to solve the existing hydrogen evolution problem of the existing aqueous zinc bromide battery, and to improve the safety and cycle stability of the battery.

[0009] The technical scheme adopted by the present application is: a non-aqueous electrolyte zinc bromide 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, the mass ratio being 1:(0.3-3), and a third polar organic solvent with a weight of not more than 30% can be added; main salt: zinc bromide, concentration 0.5-6.0 mol / L; conductive salt: lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluoromethanesulfonyl)imide, concentration 1-30 g / L; complexing agent: alkyl or benzyl ammonium bromide cationic surfactant, concentration 0.01-1 mol / L.

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

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

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

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

[0014] The application also provides a preparation method of the zinc-bromine battery, comprising the following steps:

[0015] (1) Negative electrode preparation: polish the zinc sheet with 400 mesh sandpaper to make the surface bright and remove the oxide layer; soak in a 2% mass fraction citric acid solution for 1 hour to remove surface impurities; rinse with deionized water and anhydrous ethanol in sequence, and dry in a 60°C vacuum drying oven for 2 hours.

[0016] (2) Positive electrode preparation: take alkyl or benzyl ammonium bromide cationic surfactant, activated carbon, PVDF and acetylene black according to the mass ratio (2-8):(1-3):(0.5-2):(0.5-2), add an appropriate amount of NMP to stir and uniformly prepare a slurry; uniformly coat the slurry on the surface of the porous positive electrode, and dry in a 120°C vacuum drying oven for 12 hours.

[0017] (3) Electrolyte preparation: mix acetonitrile and tetrahydrofuran according to the mass ratio; add alkyl or benzyl ammonium bromide cationic surfactant in sequence, and stir until completely dissolved; finally, add lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluoromethanesulfonyl)imide, and continue to stir until uniform and transparent to obtain a non-aqueous organic electrolyte.

[0018] (4) Battery assembly: use the treated zinc sheet as the negative electrode, the porous conductive material coated with the slurry as the positive electrode, and a polypropylene porous film as the separator, and then inject the prepared organic electrolyte to assemble a soft package battery in a glove box and vacuum package.

[0019] (5) Battery activation: perform constant current charge and discharge activation at a current density of 0.1C for 10 cycles.

[0020] The application has the following beneficial effects:

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

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

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

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

[0025] (5) Simple structure and low cost: compared with a liquid flow battery system, the static battery of the application has a simple structure and does not need auxiliary equipment such as a circulating pump, thereby greatly reducing the system cost. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the organic electrolyte zinc-bromine battery of the application.

[0027] Figure 2 It is a contrastive diagram of the appearance forms before and after charging and discharging of the battery.

[0028] Figure 3 It is a charging and discharging voltage-capacity curve diagram of Example 1.

[0029] Figure 4 It is a diagram of the change of the coulombic efficiency with the cycle number of Example 1.

[0030] Figure 5 It is a diagram of the change of the capacity retention rate with the cycle number of Example 1. DETAILED DESCRIPTION

[0031] The application will be further described in detail below in combination with the drawings and examples.

[0032] Comparative Example 1 (aqueous electrolyte)

[0033] The surface of the zinc sheet was polished to be bright with 400-mesh sandpaper to remove the oxide layer, and was cut into a 30 mm x 30 mm square sheet, and was spot-welded with a nickel tab, and was dried in a 60℃ vacuum drying oven for 1 hour.

[0034] A slurry was prepared according to the mass ratio TPABr: activated carbon: PVDF: acetylene black = 6:2:1:1, and was uniformly stirred with NMP as a dispersant, and the slurry was uniformly coated on the carbon felt, and was vacuum dried at 120℃ for 10 hours.

[0035] A 3 mol / L zinc bromide aqueous solution was prepared, 0.2 mol / L tetrapropylammonium bromide was added, and stirring and dissolution were performed to obtain an aqueous electrolyte. A soft-pack battery was assembled and vacuum packaged.

[0036] Charging and discharging tests were performed at a current density of 2 mA / cm². The results showed that the battery capacity sharply decreased when cycled to 80 times, a large amount of gas was generated in the battery, obvious bulging phenomenon occurred, and there was a safety hazard.

[0037] Comparative Example 2 (pure acetonitrile electrolyte)

[0038] The negative electrode was prepared as in Comparative Example 1.

[0039] The positive electrode was prepared 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. Due to the low zinc bromide concentration, the capacity was relatively small.

[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 appearance of the battery before and after charging and discharging is shown, and it can be seen that the appearance of the battery does not change, and there is no bulging phenomenon. Figure 3 Typical charging and discharging curves are shown, and the platform is obvious and stable. Figure 4 The coulombic efficiency is shown to be above 92 and stable. Figure 5 It is shown that the capacity retention rate is excellent, and is still maintained above 90% after 100 cycles.

[0053] The above examples show that the acetonitrile-tetrahydrofuran mixed solvent system is used, combined with a positive electrode that can fix bromine, the problem of hydrogen evolution of the zinc-bromine battery is successfully solved, and safe and stable electrochemical performance is achieved.

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: an aprotic mixed electrolyte solvent: acetonitrile and tetrahydrofuran, in a mass ratio of 1:(0.3-3), optionally adding no more than 30% by weight of a third aprotic polar organic solvent, the third aprotic polar organic solvent being selected from at least one of propylene carbonate, ethylene carbonate, dimethyl sulfoxide, or N,N-dimethylformamide; the main salt: zinc bromide, with a concentration of 0.5-6.0 mol / L; the conductive salt: lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluoromethanesulfonyl)imide, with a concentration of 1-30 g / L; and the complexing agent: 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 mass ratio of acetonitrile to tetrahydrofuran in the aprotic mixed electrolyte 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 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).

5. The non-aqueous electrolyte zinc-bromine battery without hydrogen evolution according to claim 4, 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.

6. The method for preparing a non-aqueous electrolyte zinc-bromine battery without hydrogen evolution according to any one of claims 1-5, 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 sequence, and dried in a vacuum drying oven at 60℃ for 2 hours; (2) Positive electrode preparation: alkyl or benzyl ammonium bromide cationic surfactant, activated carbon, polyvinylidene fluoride and acetylene black are weighed in the mass ratio of (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: Mix acetonitrile and tetrahydrofuran in mass ratio, add zinc bromide and alkyl or benzyl ammonium bromide cationic surfactants in sequence, stir until completely dissolved, and finally add lithium bis(trifluoromethanesulfonylimide) or lithium bis(fluoromethanesulfonylimide) and continue stirring until uniform and transparent to obtain a non-aqueous organic electrolyte; (4) Battery assembly: Use the treated zinc sheet as the negative electrode, the porous conductive material coated with slurry as the positive electrode, and the polypropylene porous membrane as the separator, inject the prepared organic electrolyte, assemble into a soft pack battery in a glove box and vacuum seal it.

7. The application of the hydrogen-evolution-free, non-aqueous electrolyte zinc-bromine battery according to any one of claims 1-5 in the field of energy storage.

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