Biphase diaphragm-free zinc-bromine battery electrolyte, preparation method and application

Abstract

The invention provides a double-phase diaphragm-free zinc-bromine battery electrolyte, a preparation method and application, belongs to the technical field of energy storage batteries, and aims to solve the problems that an organic solvent of an existing double-phase diaphragm-free zinc-bromine battery electrolyte has safety risks, the solubility of active substances is not high, and the service life of the battery is prolonged. And when a specific ionic liquid is used as an organic phase, the bromine fixation function is single. Imidazole bromine salt and zinc bromide are jointly dissolved in water, and an ionic liquid phase and a water phase are formed by adjusting the adding amount of the zinc bromide. The solubility of the bromine species in the ionic liquid phase is far greater than that in the water phase, and the imidazole bromine salt can be complexed with the bromine species to form a polybromine complex, so that the ionic liquid phase can be used as a positive electrode electrolyte of a two-phase zinc-bromine battery. The raw materials of the prepared dual-phase electrolyte all participate in the electrode reaction of the zinc-bromine battery, bromine species are dissolved and fixed in an ionic liquid phase under the condition that other organic solvents or ionic liquid is not introduced, diffusion of the bromine species to a water phase is reduced, and the self-discharge phenomenon of the zinc-bromine battery is reduced. And the preparation method of the electrolyte is simple, greatly simplifies the manufacturing process of the battery, and is easy to popularize and apply.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage batteries, and in particular relates to the preparation and application of an electrolyte. Background Art

[0002] In traditional zinc-bromine flow batteries, the separator is an essential part, which is used to separate the positive and negative electrolytes and prevent the bromide in the positive electrolyte (such as bromide ions Br ⁻ , bromine element Br2, polybrominates Br3 ⁻ etc.) and zinc ions in the negative electrode electrolyte (Zn 2+ ) and metallic zinc (Zn), can effectively avoid the chemical reaction between bromide and zinc, reduce self-discharge, and improve the efficiency and stability of the battery. Zinc-bromine flow batteries often use Nafion membranes and non-selective microporous polymer membranes. The high cost of Nafion membranes has hindered the marketization of zinc-bromine flow batteries; non-selective microporous polymer membranes are low in cost and suitable for large-scale applications. However, in research, it was found that after a period of use, non-selective microporous polymer membranes are often deformed due to factors such as bromide corrosion, which reduces the zinc deposition space, thereby reducing the surface capacity, the electrolyte utilization rate and the actual energy density of the battery. In order to solve the problems of traditional membranes, membrane-free zinc-bromine batteries came into being. Through special electrolyte design, the use of membranes is avoided, which can reduce costs and system complexity.

[0003] Patent CN 117855630 A discloses a zinc-bromine battery with organic-aqueous self-stratification. The organic electrolyte solvent is selected from one or more of tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, succinonitrile, dimethylformamide, and dimethylacetamide, and the solute is selected from one or more of zinc bromide, magnesium bromide, sodium bromide, potassium bromide, lithium bromide, and elemental bromine. The aqueous electrolyte solvent is water, and the solute is selected from one or more of zinc sulfate, zinc chloride, zinc perchlorate, zinc acetate, and zinc trifluoromethanesulfonate. This dual-phase electrolyte is prepared by utilizing the principle of incompatibility between the organic and aqueous phases. On the one hand, the maximum concentration of the organic phase electrolyte in this patent is 2.0 mol / L. Excessive concentration will increase the density of the upper organic phase and destroy the original self-stratified structure of the battery. On the other hand, it is well known that there are certain safety issues with the use of organic solvents in batteries. Some organic solvents themselves are toxic, have poor thermal stability, and pose a risk of flammability and explosion.

[0004] Patent CN 115954556 A discloses an aqueous liquid electrode battery based on self-adsorption and self-stratification. A water-soluble imidazole salt and a water-soluble salt containing bis(trifluoromethylsulfonyl)imide ions are dissolved separately in deionized water. The two solutions are then mixed and allowed to stand to form two layers: an ionic liquid and an aqueous solution. This method replaces organic solvents with a hydrophobic ionic liquid formed by imidazole cations and bis(trifluoromethylsulfonyl)imide anions, avoiding the safety risks associated with organic solvents. This ionic liquid exhibits strong adsorption for halogens through its inherent three-dimensional hydrogen bond network, achieving the goal of fixing halogen compounds at the positive electrode.

[0005] Patent CN119092770A discloses a homogeneous, high-temperature-resistant zinc-bromine flow battery electrolyte, its preparation method, and application. A certain amount of ionic liquid imidazolium bromide and / or pyrrole bromide is mixed with a certain amount of ZnBr2 and stirred at high temperature for a certain period of time to produce a pure ionic liquid electrolyte for use in zinc-bromine flow batteries. The flow battery structure consists of a battery module assembled by sequentially arranging a positive terminal plate, a current collector, a graphite plate, a positive electrode, a diaphragm, a negative electrode, a graphite plate, a current collector, and a negative terminal plate. The positive and negative electrolyte reservoirs, as well as a circulation pump and circulation piping, are connected. Both the positive and negative electrolytes in this patent utilize the prepared ionic liquid-based electrolyte. The technical problem addressed is the phase separation problem between the oil-phase polybromine complex and the aqueous electrolyte. Summary of the Invention

[0006] To address the safety risks and low solubility of organic solvents in existing biphasic, membraneless zinc-bromine battery electrolytes for active materials, as well as the limited bromine-fixing function of certain ionic liquids as the organic phase, the present invention proposes a biphasic, membraneless zinc-bromine battery electrolyte, a preparation method, and a biphasic, membraneless zinc-bromine battery. An imidazole bromide salt and zinc bromide are dissolved in water, and by adjusting the amount of zinc bromide added, an ionic liquid phase and an aqueous phase are formed. The solubility of bromine species in the ionic liquid phase is much greater than in the aqueous phase, and the imidazole bromide salt can complex bromine species to form a polybromine complex. Therefore, the ionic liquid phase can be used as the positive electrode electrolyte for biphasic zinc-bromine batteries. The raw materials of the biphasic electrolyte prepared in the present invention all participate in the zinc-bromine battery electrode reactions. Without the introduction of other organic solvents or ionic liquids, the bromine species can be effectively dissolved and fixed in the ionic liquid phase, reducing the diffusion of bromine species into the aqueous phase and minimizing the self-discharge of zinc-bromine batteries. The simple electrolyte preparation method greatly simplifies the battery manufacturing process and facilitates widespread application.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for preparing a biphasic diaphragm-free zinc-bromine battery electrolyte comprises the following steps: dissolving imidazolium bromide and zinc bromide weighed in a certain proportion in water, stirring the mixture thoroughly and then allowing the mixture to stand. The electrolyte then automatically separates into layers, wherein the upper layer is an aqueous phase and the lower layer is an ionic liquid phase. The upper aqueous phase and the lower ionic liquid phase constitute the biphasic diaphragm-free zinc-bromine battery electrolyte.

[0008] As a preferred technical solution of the present invention, the imidazolium bromide is one or more of 1-butyl-3-methyl imidazolium bromide, 1-pentyl-3-methyl imidazolium bromide, and 1-hexyl-3-methyl imidazolium bromide. As an ionic liquid, the imidazolium bromide forms an oily polybromo complex through the electrostatic interaction between the imidazolium cation and the polybromo anion, which can dissolve the oily polybromo complex. Simultaneously, the imidazolium bromide has good solubility, and its solubility in water usually increases as the branch chain length shortens.

[0009] As a preferred technical solution of the present invention, the mass ratio of the imidazolium bromide, zinc bromide and water is 1:(0.06~1.26):1, preferably 1:(0.3~1):1. The mass ratio of zinc bromide will change the physical properties of the electrolyte. When the mass ratio of zinc bromide is low, whether the electrolyte is single-phase or biphasic is determined by the water solubility of the imidazolium bromide. Even if the water solubility of the selected imidazolium bromide is poor and a biphasic electrolyte is formed, it cannot be directly applied to membraneless biphasic zinc-bromine batteries because the concentration of the solute zinc bromide is too low and the battery capacity formed is also low, which is of little significance. Increasing the mass ratio of zinc bromide will form a biphasic electrolyte with a clear dividing line, with the upper layer being the aqueous phase and the lower layer being the ionic liquid phase. And as the mass ratio of zinc bromide increases, the volume ratio of the ionic liquid phase will also increase accordingly. The biphasic electrolyte at this time is suitable as the electrolyte of membraneless biphasic zinc-bromine batteries. The aqueous phase and the ionic liquid phase both maintain a certain degree of mutual solubility and are separate phases. This helps increase the conduction rate of ions and electrons between the two phases and reduces interfacial impedance. At the same time, the ionic liquid phase, through complexation and its solubility advantage for polybrominated compounds, fixes the bromine species produced by the positive electrode in the lower layer, reducing diffusion into the upper aqueous phase. This ensures that even in the absence of a membrane barrier, the positive and negative active materials do not contact each other, reducing the self-discharge of the zinc-bromine battery and improving battery performance. Further increasing the mass percentage of zinc bromide will cause the electrolyte to become single-phase again, and it will also be unsuitable for zinc-bromine batteries without a separator.

[0010] Dissolving imidazolium bromide and zinc bromide in water in the above mass ratio and stirring thoroughly will form an unstable emulsion, which will automatically separate into layers after standing. As a preferred technical solution of the present invention, the standing time is 12 to 24 hours.

[0011] The present invention also provides a two-phase membrane-free zinc-bromine battery electrolyte prepared by the preparation method, which consists of an upper aqueous phase electrolyte and a lower ionic liquid phase electrolyte.

[0012] A two-phase, diaphragm-free zinc-bromine battery, unlike traditional zinc-bromine flow batteries, features a simple structure, easy installation, and low cost. It comprises the aforementioned electrolyte, a positive electrode, a negative electrode, and a current collector. The electrolyte is placed in a transparent container, and the positive and negative electrodes are secured to the current collectors. The positive electrode is immersed in the lower ionic liquid electrolyte, while the negative electrode is immersed in the upper aqueous electrolyte.

[0013] As a preferred technical solution of the present invention, the positive electrode is a carbon material, including one or more of carbon felt, carbon cloth, carbon paper, and conductive carbon plastic.

[0014] As a preferred technical solution of the present invention, the negative electrode is one or more of zinc foil, zinc sheet and carbon material, and the carbon material includes one or more of carbon felt, carbon cloth, carbon paper and conductive carbon plastic.

[0015] As a preferred technical solution of the present invention, the current collector is one or more of high-purity titanium wire and titanium foil.

[0016] Beneficial effects of the present invention: (1) The raw materials of the electrolyte provided by the present invention are simple and easy to obtain, and the preparation method is easy to operate.

[0017] (2) The electrolyte raw materials provided by the present invention all participate in the electrode reaction of the zinc-bromine battery. Without introducing other organic solvents or ionic liquids, the selected ionic liquid has the ability to complex with bromine, which can effectively dissolve and fix the bromine species in the lower ionic liquid phase, greatly reducing the diffusion of bromine species to the upper aqueous phase and reducing the self-discharge phenomenon of the zinc-bromine battery.

[0018] (3) The battery structure provided by the present invention is flexible, and the distance between the positive and negative electrodes can be freely adjusted, leaving space for the deposition of zinc in the negative electrode.

[0019] (4) The battery provided by the present invention has no separator, which reduces material costs and simplifies the battery manufacturing process.

[0020] (5) The electrolyte provided by the present invention introduces a water phase in addition to the ionic liquid phase, which increases the ionic and electronic conductivity and is beneficial to improving the battery efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1This is a photo of the two-phase electrolyte prepared in Example 1.

[0023] Figure 2 This is a photo of the two-phase electrolyte prepared in Example 2.

[0024] Figure 3 This is a photo of the two-phase electrolyte prepared in Example 3.

[0025] Figure 4 This is a photo of the electrolyte prepared in Comparative Example 1.

[0026] Figure 5 This is a photo of a two-phase separatorless zinc-bromine battery (Example 1) before charging.

[0027] Figure 6 This is a photo of the biphasic separatorless zinc-bromine battery (Example 1) after charging. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0029] Example 1 A method for preparing a biphasic diaphragm-free zinc-bromine battery electrolyte comprises the following steps: 15 g of 1-butyl-3-methylimidazole bromide, 15 g of zinc bromide, and 15 mL of water were added to a 30 mL quartz electrolytic cell. After thorough stirring, the mixture was allowed to stand for 12 h and then separated into layers. The upper layer was an aqueous phase, and the lower layer was an ionic liquid phase. The upper aqueous phase and the lower ionic liquid phase constituted the described biphasic membraneless zinc-bromine battery electrolyte.

[0030] Use high-purity titanium wire to fix the carbon felt, wrap polytetrafluoroethylene tape on the surface of the titanium wire to prevent the titanium wire from directly contacting the positive and negative electrolytes. Then fix the titanium wire into a certain structure so that the carbon felt is immersed in the upper and lower electrolytes respectively. Figure 5 , the two-phase diaphragmless zinc-bromine battery is assembled.

[0031] After connecting the positive and negative electrodes of the electrochemical workstation, set the charge and discharge current to 1 mA / cm 2 After the battery is charged, Figure 6 As shown, a layer of silver-grey zinc metal is deposited on the carbon felt in the upper electrolyte, and the lower electrolyte changes from colorless to orange-red, indicating that bromine species are generated and fixed in the lower electrolyte.

[0032] Example 2 A method for preparing a biphasic diaphragm-free zinc-bromine battery electrolyte comprises the following steps: 15 g of 1-butyl-3-methylimidazole bromide, 10 g of zinc bromide, and 15 mL of water were added to a 30 mL quartz electrolytic cell. After thorough stirring, the mixture was allowed to stand for 20 h and then separated into two layers: an upper layer of aqueous phase and a lower layer of ionic liquid phase. The upper aqueous phase and the lower ionic liquid phase constituted the described biphasic membraneless zinc-bromine battery electrolyte.

[0033] Assemble the two-phase diaphragm-free zinc-bromine battery according to Example 1, replace the negative electrode carbon felt with a zinc sheet, and set the battery charge and discharge current to 3 mA / cm 2 .

[0034] Example 3 A method for preparing a biphasic diaphragm-free zinc-bromine battery electrolyte comprises the following steps: 15 g of 1-butyl-3-methylimidazole bromide, 5 g of zinc bromide and 15 mL of water were added to a 30 mL quartz electrolytic cell. After thorough stirring, the mixture was allowed to stand for 24 h and then separated into two layers: an upper layer of water and a lower layer of ionic liquid. The upper layer of water and the lower layer of ionic liquid constituted the described biphasic membraneless zinc-bromine battery electrolyte.

[0035] The two-phase diaphragm-free zinc-bromine battery was assembled according to Example 1, the positive electrode carbon felt was replaced with a graphite plate, and the charge and discharge current of the battery was set to 5 mA / cm 2 .

[0036] Example 4 A method for preparing a biphasic diaphragm-free zinc-bromine battery electrolyte comprises the following steps: 15 g of 1-pentyl-3-methylimidazole bromide, 10 g of zinc bromide and 15 mL of water were added to a 30 mL quartz electrolytic cell. After thorough stirring, the mixture was allowed to stand for 20 h and then separated into two layers: an upper layer of water and a lower layer of ionic liquid. The upper layer of water and the lower layer of ionic liquid constituted the described biphasic membraneless zinc-bromine battery electrolyte.

[0037] Assemble the two-phase diaphragm-free zinc-bromine battery according to Example 1, replace the positive electrode carbon felt with a graphite plate, and the negative electrode carbon felt with a zinc sheet. Set the battery charge and discharge current to 2 mA / cm 2 .

[0038] Example 5 A method for preparing a biphasic diaphragm-free zinc-bromine battery electrolyte comprises the following steps: 15 g of 1-hexyl-3-methylimidazole bromide, 10 g of zinc bromide, and 15 mL of water were added to a 30 mL quartz electrolytic cell. After thorough stirring, the mixture was allowed to stand for 20 h and then separated into two layers: an upper layer of water and a lower layer of ionic liquid. The upper and lower layers of water constituted the dual-phase membraneless zinc-bromine battery electrolyte.

[0039] Assemble the two-phase diaphragm-free zinc-bromine battery according to Example 1, replace the positive electrode carbon felt with a graphite plate, and the negative electrode carbon felt with a zinc sheet. Set the battery charge and discharge current to 4 mA / cm 2 .

[0040] Comparative Example 1 Take 15g of 1-butyl-3-methylimidazole bromide, 20g of zinc bromide and 15mL of water, add them to a 30mL quartz electrolytic cell, stir thoroughly, and let it stand for 24h.

[0041] The same method as in Example 1 was used to assemble a diaphragm-free zinc-bromine battery, and the charge and discharge current of the battery was set to 1 mA / cm 2 .

[0042] Comparative Example 2 Prepare a conventional zinc-bromine flow battery electrolyte (2 M zinc bromide, 3 M potassium chloride, and 0.4 M 1-methyl-1-ethylpyrrolidone bromide), and add 20 mL to a quartz electrolytic cell for later use.

[0043] The same method as in Example 1 was used to assemble a diaphragm-free zinc-bromine battery, and the charge and discharge current of the battery was set to 1 mA / cm 2 .

[0044] Comparative Example 3 Take 0.2 mol of 1-butyl-3-methylimidazole bromide and 0.1 mol of ZnBr2 and add them into a 250 mL single-necked round-bottom flask. Use an oil bath to heat and stir the round-bottom flask. Stir and react at 70°C for 48 hours to obtain a light yellow ionic liquid electrolyte for use.

[0045] The same method as in Example 1 was used to assemble a diaphragm-free zinc-bromine battery, and the charge and discharge current of the battery was set to 1 mA / cm 2 .

[0046] Comparative Example 4 Take 15 mL of dichloromethane and 15 mL of water, add them to a 30 mL quartz electrolytic cell, stir thoroughly and let it stand to form a two-phase electrolyte for use.

[0047] The same method as in Example 1 was used to assemble a diaphragm-free zinc-bromine battery, and the charge and discharge current of the battery was set to 1 mA / cm 2 .

[0048] like Figures 1-3As shown, the electrolytes prepared in Examples 1 to 3 are all biphasic; Figure 4 As shown, after adding excess zinc bromide in Comparative Example 1, the electrolyte is single-phase.

[0049] Table 1 Battery test results corresponding to the electrolytes obtained in Examples and Comparative Examples After cycling, the average coulombic efficiency of the biphasic, membrane-free zinc-bromine batteries assembled in Examples 1-5 remained stable at 95%-97%, indicating no significant self-discharge and excellent stability. The average energy efficiency and average voltage efficiency decreased with increasing charge and discharge current, due to increased concentration polarization and internal resistance losses caused by increased current density.

[0050] After adding an excess of zinc bromide in Comparative Example 1, the electrolyte was single-phase, and the assembled diaphragm-free zinc-bromine battery was unable to prevent the diffusion of polybromine compounds to the negative electrode, and the battery could not operate normally. In the diaphragm-free zinc-bromine battery assembled in Comparative Example 2, its electrolyte was a single aqueous phase, and 1-methyl-1-ethylpyrrolidone bromide, a bromine complexing agent, was evenly distributed in the electrolyte system. The polybromine complex produced by the positive electrode gradually diffused into the entire electrolyte system, directly contacting the zinc produced by the negative electrode, resulting in severe self-discharge, and the battery could not operate normally. In the diaphragm-free zinc-bromine battery assembled in Comparative Example 3, its electrolyte was a single ionic liquid phase, similar to a single aqueous phase. The polybromine complex diffused into the entire electrolyte system and contacted zinc, resulting in self-discharge. In addition, the electrolyte had high viscosity and low electronic conductivity, and the battery could not operate normally. In the diaphragm-free zinc-bromine battery assembled in Comparative Example 4, the organic solvent dichloromethane was used as the organic phase, which naturally separated from the aqueous phase to form a two-phase electrolyte. Dichloromethane has a greater solubility for bromine than water and can fix a small amount of polybrominated species, but it has no bromine complexing ability. In the presence of a large amount of bromine species, some bromine species will still diffuse into the aqueous phase and come into contact with zinc, causing self-discharge and the battery cannot operate for a long time.

[0051] The electrolyte raw materials provided by the present invention all participate in the electrode reaction of the zinc-bromine battery. Without introducing other organic solvents or ionic liquids, the selected ionic liquid has bromine complexing ability, which can effectively dissolve and fix bromine species in the lower ionic liquid phase, greatly reducing the diffusion of bromine species to the upper aqueous phase, and reducing the self-discharge phenomenon of the zinc-bromine battery.

[0052] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a biphasic diaphragm-free zinc-bromine battery electrolyte, characterized in that: Imidazole bromide and zinc bromide are dissolved in water, stirred thoroughly and then allowed to stand. The electrolyte is automatically separated into layers, with the upper layer being a water phase and the lower layer being an ionic liquid phase. The upper water phase and the lower ionic liquid phase constitute the dual-phase membraneless zinc-bromine battery electrolyte.

2. The method for preparing a biphasic membrane-free zinc-bromine battery electrolyte according to claim 1, wherein: The imidazolium bromide is one or more of 1-butyl-3-methylimidazolium bromide, 1-pentyl-3-methylimidazolium bromide, and 1-hexyl-3-methylimidazolium bromide.

3. The method for preparing a biphasic membraneless zinc-bromine battery electrolyte according to claim 1, wherein: The mass ratio of the imidazolium bromide, zinc bromide and water is 1:(0.06~1.26):

1.

4. The method for preparing a biphasic membrane-free zinc-bromine battery electrolyte according to claim 1, wherein: The standing time is 12 to 24 hours.

5. The biphasic diaphragmless zinc-bromine battery electrolyte prepared by the preparation method according to any one of claims 1 to 4, characterized in that: It consists of an upper aqueous electrolyte and a lower ionic liquid electrolyte.

6. A two-phase membrane-less zinc-bromine battery comprising the electrolyte according to claim 5, a positive electrode, a negative electrode and a current collector.

7. The two-phase diaphragmless zinc-bromine battery according to claim 6, characterized in that: The positive electrode is made of carbon material, including one or more of carbon felt, carbon cloth, carbon paper, and conductive carbon plastic.

8. The two-phase membrane-less zinc-bromine battery according to claim 6, characterized in that: The negative electrode is one or more of zinc foil, zinc sheet and carbon material, and the carbon material includes one or more of carbon felt, carbon cloth, carbon paper and conductive carbon plastic.

9. The two-phase diaphragmless zinc-bromine battery according to claim 6, characterized in that: The current collector is one or more of high-purity titanium wire and titanium foil.

10. The two-phase diaphragmless zinc-bromine battery according to claim 6, characterized in that: The electrolyte is placed in a transparent container, and the positive electrode and negative electrode are fixed with current collectors respectively. The positive electrode is immersed in the lower ionic liquid phase electrolyte, and the negative electrode is immersed in the upper aqueous phase electrolyte.

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