Electrolyte for zinc-bromine flow battery, preparation method of electrolyte and zinc-bromine flow battery

Abstract

The invention belongs to the technical field of electrochemical energy storage, and discloses an electrolyte for a zinc-bromine flow battery, a preparation method of the electrolyte and the zinc-bromine flow battery, raw materials of the electrolyte comprise the following components: zinc salt, potassium salt, an additive and a solvent; the potassium salt is a compound mixture of potassium bromide and potassium bromate; the additive comprises an organic complexing agent and an inorganic corrosion inhibitor; wherein the organic complexing agent comprises an organic zinc complexing agent and an organic bromine complexing agent; the organic zinc complexing agent is crown ether; the organic bromine complexing agent is imidazole bromine salt or pyridine bromine salt; the inorganic corrosion inhibitor is a compound of sodium molybdate, zinc sulfate, sodium dihydrogen phosphate and deionized water; growth of zinc dendrites can be remarkably inhibited, the energy density of the battery is improved, and escape of hydrogen bromide is effectively prevented, so that the performance and the stability of the zinc-bromine flow battery are comprehensively improved, the service life of the battery is prolonged, and the use cost and the safety risk of the battery are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, relates to the field of zinc-bromine flow batteries, and particularly relates to an electrolyte for a zinc-bromine flow battery, a preparation method thereof, and a zinc-bromine flow battery. Background Art

[0002] With the continuous growth of energy demand and the vigorous development of renewable energy, efficient and reliable energy storage technologies have become the key to solving energy storage and utilization problems; as a highly potential electrochemical energy storage device, the zinc-bromine flow battery has many advantages such as high energy density, low cost, and easy access to raw materials, significantly reducing the economic threshold for large-scale energy storage applications; at the same time, the zinc-bromine flow battery is environmentally friendly and can reduce environmental pollution problems that may be brought by traditional energy storage technologies; therefore, it shows broad application prospects in the fields of energy storage supporting for renewable energy power generation, peak shaving and frequency modulation of power grids, etc.

[0003] However, the existing zinc-bromine flow batteries still face some problems to be solved urgently in practical applications. For example, the growth of zinc dendrites and the escape of hydrogen bromide lead to low battery performance and stability and high safety risks, seriously affecting the practical application and commercial development of zinc-bromine flow batteries.

[0004] Specifically, the growth of zinc dendrites is a key problem that seriously affects battery performance and safety; during the charge and discharge process of a zinc-bromine flow battery, when zinc ions deposit on the negative electrode surface, due to the unevenness of the electrode surface and the difference in ion transport, zinc dendrites are likely to form; zinc dendrites will continue to grow. Once they pierce the battery separator, it will cause an internal short circuit of the battery, greatly reducing the battery performance, shortening the battery cycle life, and even possibly triggering safety accidents; the escape of hydrogen bromide is also a problem that cannot be ignored; during the operation of a zinc-bromine flow battery, due to the influence of chemical reactions in the electrolyte and environmental factors, hydrogen bromide may escape from the electrolyte; due to the strong corrosiveness of hydrogen bromide, it will not only cause changes in the electrolyte composition, affecting the electrochemical performance of the battery, but also corrode the equipment of the battery system and the surrounding environment, increasing the equipment maintenance cost and safety risks; in addition, although the existing zinc-bromine flow batteries have certain advantages in energy density, there is still room for improvement; in some application scenarios with high requirements for energy density, such as electric vehicles, portable electronic devices, etc., the current energy density level limits the further promotion and application of zinc-bromine flow batteries.

[0005] Therefore, there is an urgent need to develop an electrolyte that can effectively inhibit the growth of zinc dendrites, improve the energy density of the battery, and prevent the escape of hydrogen bromide to promote the practical application and commercial development of zinc-bromine flow batteries. Summary of the Invention

[0006] In view of the technical problems existing in the prior art, the present invention provides an electrolyte for a zinc-bromine flow battery, a preparation method thereof, and a zinc-bromine flow battery, so as to solve the problems that the existing zinc-bromine flow battery has the growth of zinc dendrites and the escape of hydrogen bromide, resulting in low battery performance and stability and high safety risks, seriously affecting the practical application and commercial development of zinc-bromine flow batteries.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides an electrolyte for a zinc-bromine flow battery, and the raw materials include the following components: zinc salt, potassium salt, additive and solvent;

[0009] The potassium salt is a compound mixture of potassium bromide and potassium bromate;

[0010] The additive includes an organic complexing agent and an inorganic corrosion inhibitor; among them, the organic complexing agent includes an organic zinc complexing agent and an organic bromine complexing agent; the organic zinc complexing agent is a crown ether; the organic bromine complexing agent is an imidazole bromide or a pyridine bromide;

[0011] The inorganic corrosion inhibitor is a complex of sodium molybdate, zinc sulfate, sodium dihydrogen phosphate and deionized water.

[0012] Further, the zinc salt is a mixture of zinc bromide and zinc tetrafluoroborate.

[0013] Further, based on zinc ions, the concentration of the zinc salt is 2.1-3.2 mol / L; among them, the molar ratio of zinc bromide to zinc tetrafluoroborate is 1:(0.05-0.2).

[0014] Further, based on potassium ions, the concentration of the potassium salt is 1.5-2.2 mol / L; among them, the molar ratio of potassium bromide to potassium bromate is (0.093-0.186):0.6.

[0015] Further, the concentration of the organic zinc complexing agent is 0.3-0.6 mol / L, and the concentration of the organic bromine complexing agent is 0.5-0.8 mol / L.

[0016] Further, the organic zinc complexing agent is one of 18-crown(ether)-6 and dicyclohexano-18-crown-6; the organic bromine complexing agent is one of 2-bromomethylpyridine bromide and 1-butyl-3-methylimidazole bromide.

[0017] Further, based on zinc sulfate, the concentration of the inorganic corrosion inhibitor is 0.093 - 0.186 mol / L; in the inorganic corrosion inhibitor, the mass - volume percentage concentration of sodium molybdate is 2% - 4%, the mass - volume percentage concentration of zinc sulfate is 3% - 6%, the mass - volume percentage concentration of sodium dihydrogen phosphate is 1% - 3%, and the balance is deionized water.

[0018] The present invention also provides a preparation method for an electrolyte used in a zinc - bromine flow battery, including:

[0019] Dissolve a zinc salt in a solvent and stir until completely dissolved;

[0020] Add a potassium salt and stir until completely dissolved;

[0021] Add an additive and perform high - speed shear dispersion to obtain a mixed solution;

[0022] Filter the mixed solution using a microporous filter membrane with a preset pore size to obtain an electrolyte for a zinc - bromine flow battery.

[0023] The present invention also provides a zinc - bromine flow battery including the electrolyte for a zinc - bromine flow battery described above.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The present invention provides an electrolyte for a zinc - bromine flow battery, which can significantly inhibit the growth of zinc dendrites, improve the energy density of the battery, and effectively prevent the escape of hydrogen bromide, thereby comprehensively improving the performance and stability of the zinc - bromine flow battery, extending the service life of the battery, and reducing the use cost and safety risk of the battery; specifically, by introducing potassium bromate into the potassium salt, the deposition and stripping modes of zinc at the negative electrode can be changed to reduce the potential of the negative electrode, significantly expanding the working voltage window of the zinc - bromine flow battery, and then significantly improving the working voltage and energy density of the battery; secondly, by adding an organic complexing agent and an inorganic corrosion inhibitor, the reaction kinetics of both electro - couples can be catalyzed and improved simultaneously, thereby improving the energy efficiency of the zinc - bromine flow battery; in addition, using imidazole bromide or pyridine bromide as an organic bromine complexing agent can effectively complex the bromine generated during the charging process of the battery positive electrode, prevent its diffusion and volatilization, avoid the escape of hydrogen bromide, reduce the harm to the battery system and the environment, and thus achieve long - term stable cycling of the flow battery, reducing the maintenance cost and safety risk of the equipment; secondly, through the synergistic effect of the organic zinc complexing agent and the inorganic corrosion inhibitor, a stable zinc ion transport channel is constructed in the electrolyte, effectively restricting the uneven deposition of zinc ions on the electrode surface, thereby significantly inhibiting the growth of zinc dendrites and improving the cycle life and safety of the battery. Description of the Drawings

[0026] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0027] Figure 1 It is a flowchart for the preparation of the electrolyte for the zinc-bromine flow battery provided by the present invention. Specific embodiments

[0028] In order to make the technical problems, technical solutions and beneficial effects solved by the present application more clearly understood, the following will combine the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application; obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0029] The present invention provides an electrolyte for a zinc-bromine flow battery, and the raw materials include the following components: zinc salt, potassium salt, additive and solvent.

[0030] The zinc salt is a mixture of zinc bromide and zinc tetrafluoroborate; calculated as zinc ions, the concentration of the zinc salt is 2.1 - 3.2 mol / L; among them, the molar ratio of zinc bromide to zinc tetrafluoroborate is 1:(0.05 - 0.2); the potassium salt is a compound mixture of potassium bromide and potassium bromate; calculated as potassium ions, the concentration of the potassium salt is 1.5 - 2.2 mol / L; among them, the molar ratio of potassium bromide to potassium bromate is (0.093 - 0.186):0.6; the additive includes an organic complexing agent and an inorganic corrosion inhibitor, and the organic complexing agent includes an organic zinc complexing agent and an organic bromine complexing agent.

[0031] The concentration of the organic zinc complexing agent is 0.3 - 0.6 mol / L, and the organic zinc complexing agent is a crown ether; among them, the organic zinc complexing agent is one of 18-crown(ether)-6 and dicyclohexano-18(crown)-6.

[0032] The concentration of the organic bromine complexing agent is 0.5 - 0.8 mol / L, and the organic bromine complexing agent is an imidazole bromide or a pyridine bromide; among them, the organic bromine complexing agent is one of 2-bromomethylpyridine bromide and 1-butyl-3-methylimidazole bromide.

[0033] The inorganic corrosion inhibitor is a complex of sodium molybdate, zinc sulfate, sodium dihydrogen phosphate and deionized water; based on zinc sulfate, the concentration of the inorganic corrosion inhibitor is 0.2 - 0.4 mol / L; among them, in the inorganic corrosion inhibitor, the mass - volume percentage concentration of sodium molybdate is 2% - 4%, the mass - volume percentage concentration of zinc sulfate is 3% - 6%, the mass - volume percentage concentration of sodium dihydrogen phosphate is 1% - 3%, and the balance is deionized water.

[0034] The solvent is deionized water.

[0035] Preparation process:

[0036] As shown in the Figure 1 attachment, the electrolyte for a zinc - bromine flow battery according to the present invention includes the following steps:

[0037] Step 1: Dissolve the zinc salt in the solvent and stir until completely dissolved;

[0038] Step 2: Add the potassium salt and stir until completely dissolved;

[0039] Step 3: Add the additive and perform high - speed shear dispersion to obtain a mixed solution;

[0040] Step 4: Filter the mixed solution with a microporous filter membrane with a preset pore size to obtain the electrolyte for a zinc - bromine flow battery.

[0041] Electrolyte design principle:

[0042] For the electrolyte for a zinc - bromine flow battery according to the present invention, by introducing potassium bromate in the potassium salt and utilizing the reducibility of potassium bromate, the deposition and stripping of zinc at the negative electrode of the battery can be changed, thereby reducing the potential of the negative electrode of the battery, and further broadening the working voltage window of the zinc - bromine flow battery, so that the working voltage and energy density of the battery are significantly improved compared with the existing zinc - bromine flow battery.

[0043] Specifically, during the charging process, BrO3 - undergoes a reduction reaction on the surface of the negative electrode, and its reduction reaction process is: BrO3 - +6H + +6e - →Br - +3H2O; this reduction reaction can consume H + in the electrolyte, thereby increasing the local pH value of the negative electrode, inhibiting the hydrogen evolution reaction (HER), and further reducing the interference of side reactions on the zinc deposition at the negative electrode of the battery; secondly, the Br - generated by the reduction reaction can react with Zn 2+ to form a stable ZnBr4 2- complex, and its complexation reaction process is Zn 2+ +4Br- →ZnBr4 2- , to reduce the free Zn in the electrolyte through complexation 2+ activity; According to the Nernst equation, the equilibrium potential (E) of zinc becomes more negative as the Zn 2+ activity decreases, making the theoretical potential of zinc deposition more negative and the absolute value increases, resulting in an overall decrease in the negative electrode potential; In addition, the ZnBr4 2- complex regulates the nucleation and growth process of zinc by adsorbing on the electrode surface, promoting uniform and dense zinc deposition and reducing dendrite formation; At the same time, the reduction reaction of BrO3 - can inhibit the concentration of local current density, further reduce the polarization overpotential, and make the actual deposition potential closer to the thermodynamic equilibrium value; Thus, through the synergistic effect of the reduction of the negative electrode potential and the positive electrode reaction (Br2 / Br - oxidation), the total voltage of the battery is significantly increased, the voltage window is broadened, and the energy density increases accordingly.

[0044] In the present invention, by adding an organic complexing agent and an inorganic corrosion inhibitor to the electrolyte, it can catalyze and enhance the reaction kinetics of the positive and negative electrode couples of the battery; that is, on the zinc negative electrode side, the organic complexing agent and the inorganic corrosion inhibitor jointly inhibit dendrites, reduce electrode polarization, and the sodium molybdate passivation film reduces corrosion; on the bromine positive electrode side, imidazole bromide can stably complex Br2, accelerate the redox reaction, synchronously optimize the reaction kinetics of the positive and negative electrodes, reduce side reactions, and significantly improve the energy efficiency; Secondly, through the synergistic effect of the organic zinc complexing agent and the inorganic corrosion inhibitor, a stable zinc ion transport channel is constructed in the electrolyte, effectively restricting the uneven deposition of zinc ions on the electrode surface, thereby significantly inhibiting the growth of zinc dendrites and improving the cycle life and safety of the battery.

[0045] Specifically, using imidazole bromide or pyridine bromide as the organic bromine complexing agent can effectively complex the bromine generated during the charging process of the positive electrode of the flow battery to form a stable ionic liquid complex BMIMBr3 - ; Among them, the organic bromine complexing agent acts as a reaction intermediate to accelerate the redox reaction of bromine, reduce the activation energy of Br - →Br2, improve the positive electrode reaction rate, thereby preventing the diffusion and volatilization of Br2 and causing harm to the battery system and the environment, so as to achieve long-term stable cycling of the flow battery.

[0046] Secondly, using crown ether as the organic zinc complexing agent, the complex formed by crown ether and zinc ions can regulate the transport rate and direction of zinc ions, making zinc ions reach the electrode surface more evenly; Specifically, crown ether forms a stable complex with Zn 2+ through its cyclic cavity, which can significantly reduce the free Zn in the solution 2+ activity; According to the Nernst equation, Zn2+ The decrease in activity shifts the equilibrium potential of zinc deposition negatively, reduces the polarization overpotential, and thus enhances the reversibility of zinc deposition / stripping. Moreover, the formed stable complex serves as an "ion carrier" to guide the uniform diffusion of Zn 2+ to the electrode surface, forming a stable zinc ion transport channel, avoiding dendrite growth caused by excessive local concentration. The uniform ion distribution makes the zinc deposition denser, reducing the short-circuit risk caused by dendrite piercing the separator.

[0047] In addition, the inorganic corrosion inhibitor forms a physical barrier on the electrode surface, which can inhibit the corrosion of zinc and hinder the growth of zinc dendrites. Specifically, sodium molybdate in the inorganic corrosion inhibitor has a passivation effect, and molybdate ions (MoO4 2- ) adsorb on the negative electrode surface and form a dense ZnMoO4 passivation film, inhibiting the corrosion reaction of zinc caused by hydrogen evolution. The reduction of side reactions reduces the energy loss and directly improves the energy efficiency (EE). Through the H2PO4 - / HPO4 2- buffer system, the pH of the electrolyte is stably maintained in the range of 2-4, avoiding the side reaction of Br - being oxidized to Br2 due to excessive local acidity, ensuring the stability of the positive and negative electrode reactions. Secondly, the addition of zinc sulfate replenishes the Zn 2+ consumed in the electrolyte during deposition, maintaining the continuity of zinc deposition. At the same time, zinc sulfate and the corrosion inhibitor synergistically inhibit dendrite growth, further optimizing the cycle life and effectively improving the energy efficiency of the zinc-bromine flow battery.

[0048] Examples 1-5

[0049] Taking Example 1 as an example, Example 1 provides an electrolyte for a zinc-bromine flow battery, and the raw materials include the following components: zinc salt, potassium salt, additive and solvent.

[0050] Based on zinc ions, the concentration of the zinc salt is 2.1 mol / L; the zinc salt is a mixture of zinc bromide and zinc tetrafluoroborate; among them, the molar ratio of zinc bromide to zinc tetrafluoroborate is 1:0.05.

[0051] Based on potassium ions, the concentration of the potassium salt is 1.5 mol / L; the potassium salt is a compound mixture of potassium bromide and potassium bromate; among them, the molar ratio of potassium bromide to potassium bromate is 0.2:0.6.

[0052] The additive includes an organic zinc complexing agent, an organic bromine complexing agent and an inorganic corrosion inhibitor.

[0053] The concentration of the organic zinc complexing agent is 0.3 mol / L, and the organic zinc complexing agent is 18-crown-(ether)-6.

[0054] The concentration of the organic bromine complexing agent is 0.5 mol / L, and the organic bromine complexing agent is 1-butyl-3-methylimidazolium bromide.

[0055] Calculated as zinc sulfate, the concentration of the inorganic corrosion inhibitor is 0.148 mol / L; the inorganic corrosion inhibitor is prepared from the following raw materials: sodium molybdate with a mass-volume percentage concentration of 3.5%, zinc sulfate with a mass-volume percentage concentration of 4.8%, sodium dihydrogen phosphate with a mass-volume percentage concentration of 2.4%, and the balance being deionized water.

[0056] The solvent is deionized water.

[0057] Preparation method:

[0058] The preparation process of the electrolyte for the zinc-bromine flow battery described in Example 1 of this embodiment includes the following steps:

[0059] Step 1: Dissolve 2.0 mol of zinc bromide and 0.10 mol of zinc tetrafluoroborate in 200 mL of deionized water, and stir for 15 min until completely dissolved.

[0060] Step 2: Add 0.375 mol of potassium bromide and 1.125 mol of potassium bromate, then add 200 mL of deionized water, and stir for 15 min until completely dissolved.

[0061] Step 3: Add 0.3 mol of 18-crown-(ether)-6, 0.5 mol of 1-butyl-3-methylimidazolium bromide, and 500 mL of the inorganic corrosion inhibitor, and perform high-speed shear dispersion for 30 min. Add deionized water to make up the volume to 1 L to obtain a mixed solution; wherein, calculated as zinc sulfate, the concentration of the inorganic corrosion inhibitor is 0.148 mol / L.

[0062] Step 4: Filter the mixed solution through a 0.22-μm microporous filter membrane to remove impurity particles and undissolved substances in the solution, and obtain the electrolyte for the zinc-bromine flow battery.

[0063] Example 1 of this embodiment also provides a zinc-bromine flow battery, including a positive electrode, a negative electrode, a separator, and an electrolyte; wherein, the electrolyte uses the electrolyte for the zinc-bromine flow battery described in Example 1 of this embodiment; wherein, the positive electrode, the negative electrode, and the separator all use common materials for zinc-bromine flow batteries, and this Example 1 does not limit this.

[0064] The following specifically describes the component characteristics of the electrolytes for zinc-bromine flow batteries in Examples 1-5; wherein, the component characteristics of the electrolytes for zinc-bromine flow batteries in Examples 1-5 are shown in Table 1.

[0065] Table 1 Component distribution table of the electrolytes for zinc-bromine flow batteries in Examples 1-5

[0066]

[0067]

[0068] Among them, in Example 1, the organic zinc complexing agent is 18-crown(ether)-6, and the organic bromine complexing agent is 1-butyl-3-methylimidazolium bromide; in Example 2, the organic zinc complexing agent is 18-crown(ether)-6, and the organic bromine complexing agent is 1-butyl-3-methylimidazolium bromide; in Example 3, the organic zinc complexing agent is 18-crown(ether)-6, and the organic bromine complexing agent is 1-butyl-3-methylimidazolium bromide; in Example 4, the organic zinc complexing agent is dicyclohexano-18-crown-6, and the organic bromine complexing agent is 2-bromomethylpyridine bromide; in Example 5, the organic zinc complexing agent is dicyclohexano-18-crown-6, and the organic bromine complexing agent is 2-bromomethylpyridine bromide.

[0069] It should be noted that in Examples 1-5, the volume of the inorganic corrosion inhibitor is 500 mL, and the concentration of the inorganic corrosion inhibitor is represented by zinc sulfate; among them, the component characteristics of the inorganic corrosion inhibitor are shown in Table 2.

[0070] Table 2 Component allocation table of inorganic corrosion inhibitor

[0071] Sodium molybdate Zinc sulfate Sodium dihydrogen phosphate Deionized water Example 1 3.5％ 4.8％ 2.4％ Balance Example 2 2.0％ 3.0％ 1.0％ Balance Example 3 2.6％ 4.0％ 1.5％ Balance Example 4 3.1％ 5.0％ 2.0％ Balance Example 5 4.0％ 6.0％ 3.0％ Balance

[0072] Comparative Example 1

[0073] In Comparative Example 1, except for not adding potassium bromate, organic zinc complexing agent, organic bromine complexing agent, and inorganic corrosion inhibitor, other operations are the same as those in Example 1, and the detailed process will not be elaborated here.

[0074] Comparative Example 2

[0075] In Comparative Example 2, except for not adding the organic bromine complexing agent, other operations are the same as those in Example 1, and the detailed process will not be elaborated here.

[0076] Comparative Example 3

[0077] In Comparative Example 3, except for not adding the organic zinc complexing agent, other operations are the same as those in Example 1, and the detailed process will not be elaborated here.

[0078] Comparative Example 4

[0079] In Comparative Example 4, except for not adding the inorganic corrosion inhibitor, other operations are the same as those in Example 1, and the detailed process will not be elaborated here.

[0080] Comparative Example 5

[0081] In Comparative Example 5, except for not adding potassium bromate, other operations are the same as those in Example 1, and the detailed process will not be elaborated here.

[0082] The component characteristics of the electrolytes in Comparative Examples 1-5 are specifically described below; among them, the component characteristics of the electrolytes in Comparative Examples 1-5 are shown in Table 3.

[0083] Table 3 Composition table of the electrolytes in Comparative Examples 1-5

[0084] Name Zinc bromide Zinc tetrafluoroborate Potassium bromide Potassium bromate Organic zinc complexing agent Organic bromine complexing agent Inorganic corrosion inhibitor Comparative example 1 2.0 0.10 0.375 / / / / Comparative example 2 2.0 0.10 0.375 1.125 0.3 / 0.149 Comparative example 3 2.0 0.10 0.375 1.125 / 0.5 0.149 Comparative example 4 2.0 0.10 0.375 / 0.3 0.5 0.149 Comparative example 5 2.0 0.10 0.375 1.125 0.3 0.5 /

[0085] Among them, in Comparative Examples 1-5, the organic zinc complexing agent is 18-crown(ether)-6, the organic bromine complexing agent is 1-butyl-3-methylimidazolium bromide, and the volume and composition of the inorganic corrosion inhibitor are the same as those of the inorganic corrosion inhibitor in Example 1 above.

[0086] The performance test results of the electrolytes for zinc-bromine flow batteries described in Examples 1-5 and the electrolytes described in Comparative Examples 1-5 are described below, specifically as follows:

[0087] It should be noted that the electrolytes for zinc-bromine flow batteries described in Examples 1-5 and the electrolytes described in Comparative Examples 1-5 are respectively applied to zinc-bromine flow batteries for performance testing. The experimental conditions are as follows: the electrode is carbon felt, and the separator is a microporous polyolefin separator; among them, the electrode area is 9 cm 2 ; the charge-discharge current density is 620 mA / cm 2 , the charging time is 1 h, and the discharge cut-off voltage is 0.6 V; the test performances of the batteries assembled in Examples 1-5 and Comparative Examples 1-5 are all under the same conditions; among them, the performance test results are shown in Table 4.

[0088] Table 4 Performance test results table of zinc-bromine flow batteries

[0089]

[0090]

[0091] It can be seen from Table 4 that the values of the Coulomb efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) in Examples 1-5 are all greater than the values of the Coulomb efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) in Comparative Examples 1-5, indicating that by using the electrolytes for zinc-bromine flow batteries described in Examples 1-5, the performance of the battery can be comprehensively improved, including longer service life, better power output, faster charging ability, and higher energy utilization rate.

[0092] The specific reasons for the analysis are as follows:

[0093] Comparing the above Comparative Examples 1-5 with Example 1 above respectively, the comparison results show that:

[0094] From Comparative Example 1, when zinc bromate, organic zinc complexing agent, organic bromine complexing agent and inorganic corrosion inhibitor are not added, it will lead to insufficient battery performance; from Comparative Example 2, when the organic bromine complexing agent is not added, the bromine generated during the charging process of the positive electrode of the flow battery cannot be effectively complexed, and the diffusion and volatilization of bromine will damage the battery system, affect the stable cycle of the battery, and cause its performance to decline; from Comparative Example 3, when the organic zinc complexing agent is not added, the zinc ions at the negative electrode cannot form a stable complex, effectively regulate the transport rate and direction of zinc ions, and make the zinc ions reach the electrode surface more evenly, resulting in uneven deposition of zinc ions at the negative electrode, thus causing the battery performance to decline; from Comparative Example 4, when the battery without potassium bromate is charged, the hydrogen evolution side reaction at the negative electrode will interfere with zinc deposition, unable to inhibit the concentration of local current density, reduce the polarization overpotential, and the battery performance is affected; from Comparative Example 5, when the inorganic corrosion inhibitor is not added, a physical barrier cannot be formed on the electrode surface, the corrosion of zinc cannot be inhibited, resulting in uneven zinc deposition, and the growth of zinc dendrites cannot be inhibited, ultimately leading to a decline in battery performance.

[0095] In summary, the electrolyte for a zinc-bromine flow battery described in the present invention, through the electrolyte composed of zinc salt, potassium salt, solvent and additive, effectively restricts the uneven deposition of zinc ions on the electrode surface under the synergistic action of each component of the additive, thus significantly inhibiting the growth of zinc dendrites and improving the cycle life and safety of the battery.

[0096] The above embodiments are only one of the implementation manners capable of implementing the technical solution of the present invention. The scope of protection required by the present invention is not limited only by this embodiment, but also includes any changes, substitutions and other implementation manners that are easily conceivable by those skilled in the art within the technical scope disclosed by the present invention.

Claims

1. An electrolyte for a zinc-bromine flow battery, characterized in that, The raw materials include the following components: zinc salts, potassium salts, additives and solvents; The potassium salt is a compound mixture of potassium bromide and potassium bromate; The additives include an organic complexing agent and an inorganic corrosion inhibitor; among them, the organic complexing agent includes an organic zinc complexing agent and an organic bromine complexing agent; the organic zinc complexing agent is a crown ether; the organic bromine complexing agent is an imidazole bromide or a pyridine bromide; The inorganic corrosion inhibitor is a complex of sodium molybdate, zinc sulfate, sodium dihydrogen phosphate and deionized water.

2. An electrolyte for a zinc-bromine flow battery according to claim 1, characterized in that, The zinc salt is a mixture of zinc bromide and zinc tetrafluoroborate.

3. An electrolyte for a zinc-bromine flow battery according to claim 2, characterized in that, Calculated as zinc ions, the concentration of the zinc salt is 2.1 - 3.2 mol / L; among them, the molar ratio of zinc bromide to zinc tetrafluoroborate is 1:(0.05 - 0.2).

4. An electrolyte for a zinc-bromine flow battery according to claim 1, characterized in that, Calculated as potassium ions, the concentration of the potassium salt is 1.5 - 2.2 mol / L; among them, the molar ratio of potassium bromide to potassium bromate is (0.093 - 0.186):0.

6.

5. An electrolyte for a zinc-bromine flow battery according to claim 1, characterized in that, The concentration of the organic zinc complexing agent is 0.3 - 0.6 mol / L, and the concentration of the organic bromine complexing agent is 0.5 - 0.8 mol / L.

6. An electrolyte for a zinc bromine flow battery according to claim 1, characterized in that, The organic zinc complexing agent is one of 18-crown(ether)-6 and dicyclohexano-18(crown)-6; the organic bromine complexing agent is one of 2-bromomethylpyridine bromide and 1-butyl-3-methylimidazole bromide.

7. An electrolyte for a zinc-bromine flow battery according to claim 1, characterized in that, Calculated as zinc sulfate, the concentration of the inorganic corrosion inhibitor is 0.093 - 0.186 mol / L; in the inorganic corrosion inhibitor, the mass-volume percentage concentration of sodium molybdate is 2% - 4%, the mass-volume percentage concentration of zinc sulfate is 3% - 6%, the mass-volume percentage concentration of sodium dihydrogen phosphate is 1% - 3%, and the balance is deionized water.

8. A method for preparing an electrolyte for a zinc-bromine flow battery according to any one of claims 1-7, characterized in that, It includes: Dissolve the zinc salt in the solvent and stir until completely dissolved; Add the potassium salt and stir until completely dissolved; Add the additives and perform high-speed shearing dispersion to obtain a mixed solution; Filter the mixed solution with a microporous filter membrane with a preset pore size to obtain the electrolyte for a zinc-bromine flow battery.

9. A zinc-bromine flow battery, characterized in that, It includes the electrolyte for a zinc-bromine flow battery according to any one of claims 1 - 7.

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