Combined negative electrode additive for zinc-bromine flow battery, negative electrode electrolyte, preparation method of combined negative electrode additive and negative electrode electrolyte, and zinc-bromine flow battery

Abstract

The invention discloses a combined negative electrode additive for a zinc-bromine flow battery, a negative electrode electrolyte, a preparation method of the negative electrode electrolyte and the zinc-bromine flow battery, and belongs to the technical field of electrochemical energy storage, and the combined negative electrode additive for the zinc-bromine flow battery comprises indium trichloride and glycine in a molar ratio of 1: (3.33-60); during charging, indium ions in indium trichloride are reduced into metal indium on the surface of the electrode, the metal indium and the post-deposited zinc generate a nanoscale alloy layer in situ, electric field distribution is homogenized, and zinc dendritic crystal growth is inhibited; carboxyl and amino of glycine are used as electron donors to form a water-soluble complex with zinc ions, so that the reduction kinetics of the zinc ions on the surface of the electrode is slowed down; polar functional groups of glycine are adsorbed on active sites on the surface of a zinc electrode, zinc ion deposition is blocked, energy distribution of the electrode and an electrolyte interface is changed, zinc is guided to perform transverse two-dimensional growth, zinc dendrite growth is inhibited, hydroxyl ions are neutralized, and hydrogen evolution reaction is inhibited. The coulombic efficiency of the zinc-bromine flow battery is 95.4%-97.0%; the energy efficiency ranges from 81.85% to 84.49%; and the voltage efficiency is 85.8%-87.1%.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a combined negative electrode additive for zinc-bromine flow batteries, a negative electrode electrolyte and its preparation method, and zinc-bromine flow batteries. Background Technology

[0002] With the increasing importance of clean energy, the demand for energy storage technologies is becoming more diversified. Flow batteries, as a highly efficient and sustainable medium- to long-term energy storage technology, have attracted much attention. Zinc-bromine flow batteries, due to their high energy density, low cost, and environmental friendliness, are an important branch of flow batteries. However, zinc-bromine flow batteries face a severe challenge at the negative electrode—the formation of zinc dendrites and the hydrogen evolution reaction. During zinc deposition, influenced by the microenvironment at the electrode-electrolyte interface, the reduced zinc tends to preferentially grow along a specific crystal orientation, eventually forming a dendritic structure with a tree-like morphology. With continuous charge-discharge cycles, these zinc dendrites continue to grow in the kinetically dominant direction, significantly reducing the interfacial stability of the electrochemical system. When the zinc dendrites grow to a critical size, their tips penetrate the separator, causing damage to the internal battery structure and triggering a series of irreversible battery failure mechanisms. On the one hand, the bromine at the positive electrode can shuttle through the punctured separator, significantly reducing the coulombic efficiency of the zinc-bromine flow battery and thus severely affecting its performance. On the other hand, contact between zinc dendrites and the positive electrode can cause a short circuit, directly leading to battery failure and severely limiting the lifespan and stability of the zinc-bromine flow battery, becoming a key factor hindering its widespread application. The hydrogen evolution reaction (HER) can affect battery performance, safety, and economy in multiple dimensions. Firstly, the hydrogen ions and water consumed in the HER are irreversible, and the generated hydroxide ions can trigger a zinc passivation layer. Secondly, the HER causes a localized increase in pH on the electrode surface, leading to a loose, porous zinc deposition layer and accelerating zinc dendrite growth. Simultaneously, the hydrogen evolution poses certain safety hazards to the system.

[0003] Chinese patent application CN121260860A discloses the use of dimethylformamide as a co-solvent and the introduction of saponin and cinnamaldehyde as binary additives. By forming an adsorption layer and electrostatic repulsion network on the electrode surface to regulate zinc ion distribution, dendrite formation and hydrogen evolution are suppressed to some extent. However, saponin, as a natural product, may have issues with compositional fluctuations and stability, while cinnamaldehyde has certain toxicity and environmental concerns. Furthermore, the modification effect on the electrode surface may not be durable or thorough enough. Chinese patent application CN121011691A focuses primarily on improving the positive electrode reaction kinetics and overall electrolyte performance. Its negative electrode side uses a buffer system composed of sodium acetate and sodium citrate to stabilize pH, and optionally adds dicarboxylic acid to regulate zinc deposition. This approach emphasizes macroscopic pH stability and complexation, but lacks the ability to actively and in-situ reconstruct the microstructure of the electrode surface, and may be insufficient in fundamentally homogenizing the electric field and suppressing dendrite nucleation.

[0004] Therefore, developing a negative electrode electrolyte for zinc-bromine flow batteries and its preparation method to fundamentally and persistently suppress the growth of zinc dendrites and the occurrence of hydrogen evolution side reactions, thereby comprehensively improving the coulombic efficiency, energy efficiency, and cycle stability of the battery, is of great significance for improving the performance of zinc-bromine flow batteries and promoting their practical application. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a combined negative electrode additive, a negative electrode electrolyte and its preparation method for zinc-bromine flow batteries, and a zinc-bromine flow battery, so as to solve the technical problems of zinc dendrite formation and hydrogen evolution reaction in the negative electrode operation of existing zinc-bromine flow batteries.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a combined negative electrode additive for zinc-bromine flow batteries, comprising: indium trichloride and glycine; the molar ratio of indium trichloride to glycine is 1:(3.33~60).

[0007] Preferably, the molar ratio of indium trichloride to glycine is 1:(6.67~10).

[0008] This invention discloses a negative electrode electrolyte for a zinc-bromine flow battery, comprising: an electrolyte, a supporting electrolyte, a solvent, and a negative electrode additive; the negative electrode additive is the aforementioned combined negative electrode additive for zinc-bromine flow batteries; the molar concentration of indium trichloride in the zinc-bromine flow battery negative electrode electrolyte is 0.005-0.030 mol / L; and the molar concentration of glycine in the zinc-bromine flow battery negative electrode electrolyte is 0.10-0.30 mol / L.

[0009] Preferably, the molar concentration of the electrolyte is 2.0-2.5 mol / L.

[0010] Preferably, the electrolyte is a zinc bromide solution; the solvent is deionized water.

[0011] Preferably, the molar concentration of the supporting electrolyte is 2.0-3.0 mol / L.

[0012] Preferably, the supporting electrolyte is potassium chloride.

[0013] The present invention also discloses a method for preparing the above-mentioned zinc-bromine flow battery negative electrode electrolyte, comprising: adding an electrolyte, a supporting electrolyte and a negative electrode additive to a solvent in sequence, stirring until completely dissolved, to obtain the zinc-bromine flow battery negative electrode electrolyte.

[0014] The present invention also discloses a zinc-bromine flow battery, comprising the above-mentioned zinc-bromine flow battery negative electrode electrolyte.

[0015] Preferably, the coulombic efficiency of the zinc-bromine flow battery is 95.4%-97.0%; the energy efficiency is 81.85%-84.49%; and the voltage efficiency is 85.8%-87.1%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a combined negative electrode additive for zinc-bromine flow batteries. This additive is used during the charging process of zinc-bromine flow batteries to preferentially reduce indium ions to form a zinc-indium alloy layer, and utilizes the amino and carboxyl groups of glycine to complex and adsorb zinc ions onto the electrode surface, synergistically inhibiting zinc dendrite growth and hydrogen evolution reaction. During charging, indium ions of indium trichloride are preferentially reduced to metallic indium on the electrode surface. The metallic indium and subsequently deposited zinc form a nanoscale alloy layer in situ, thereby homogenizing the electric field distribution and inhibiting zinc dendrite growth. The carboxyl and amino groups of glycine act as electron donors, forming water-soluble complexes with zinc ions, slowing down the reduction kinetics of zinc ions on the electrode surface. The polar functional groups of glycine adsorb onto the active sites on the zinc electrode surface through electrostatic interactions or coordination bonds, blocking zinc ion deposition, altering the energy distribution, guiding zinc to undergo lateral two-dimensional growth, and inhibiting zinc dendrite growth. It also neutralizes hydroxide ions, inhibiting the hydrogen evolution reaction and ensuring high reversibility of zinc deposition and dissolution reactions. The synergistic effect of indium trichloride and glycine solves the problems of zinc dendrite growth and hydrogen evolution reaction, endowing the electrolyte with multiple functions such as inhibiting zinc dendrite growth, inhibiting hydrogen evolution reaction, stabilizing interfacial pH, and inducing uniform zinc deposition. Indium trichloride acts as a nucleating agent, optimizing the initial deposition of zinc through an in-situ alloying mechanism; while glycine acts as a complexing agent, adsorbent, and pH buffer, regulating the deposition process from multiple dimensions.

[0017] This invention discloses a negative electrode electrolyte for a zinc-bromine flow battery. During battery charging, indium ions derived from indium trichloride are preferentially reduced to metallic indium on the electrode surface. These indium atoms then form a nanoscale zinc-indium alloy layer with subsequently deposited zinc. This in-situ generated alloy layer has a uniform surface morphology and excellent conductivity, which can homogenize the electric field distribution on the electrode surface, eliminate the tip effect of traditional zinc electrodes, and allow zinc ions to be deposited uniformly in a two-dimensional layered manner, thereby suppressing the formation of zinc dendrites. Furthermore, the formation of this alloy layer provides basic modification to the electrode surface, guiding subsequent zinc deposition. The carboxyl and amino groups in glycine molecules can act as electron donors, forming water-soluble complexes with zinc ions. The formation of these complexes effectively reduces the concentration and activity of free zinc ions in the electrolyte. The reduction of free zinc ions slows down the reduction kinetics of zinc ions on the electrode surface. By slowing down the deposition process, zinc deposition becomes more controlled and uniform, which is beneficial for forming a dense and smooth zinc deposition layer. The carboxyl and amino groups of glycine preferentially adsorb onto highly active sites such as defects and grain boundaries on the electrode surface, reducing surface energy and decreasing the deposition energy barrier for zinc ions across the electrode surface. This results in a uniform adsorption layer that prevents preferential deposition of zinc ions at these highly active sites, inhibiting dendrite growth. The carboxyl and amino groups in glycine can also neutralize the OH groups produced by hydrogen evolution. - This maintains the pH value at the interface, thereby preventing the formation of zinc hydroxide or zinc oxide precipitates from the source, and keeping the zinc reaction highly reversible.

[0018] This invention discloses a method for preparing a negative electrode electrolyte for a zinc-bromine flow battery. Indium trichloride ions can be uniformly reduced on the electrode surface and form an alloy layer with zinc, thereby effectively homogenizing the electric field distribution and inhibiting zinc dendrite growth. The carboxyl and amino groups of glycine can also uniformly form water-soluble complexes with zinc ions, slowing down the zinc ion reduction kinetics. Furthermore, their polar functional groups are uniformly adsorbed on the active sites on the zinc electrode surface, guiding zinc to undergo lateral two-dimensional growth and neutralizing hydroxide ions, thus inhibiting the hydrogen evolution reaction. This ensures the component activity and overall performance of the electrolyte, thereby guaranteeing the stable operation of the zinc-bromine flow battery.

[0019] This invention discloses a zinc-bromine flow battery. By integrating the aforementioned zinc-bromine flow battery negative electrode electrolyte into the zinc-bromine flow battery system, during charging, the negative electrode electrolyte is pumped to the negative electrode side of the electrochemical reaction unit. Indium ions of indium trichloride in the electrolyte are preferentially reduced to metallic indium on the negative electrode surface, subsequently forming a nanoscale alloy layer with the deposited zinc in situ. This alloy layer effectively homogenizes the electric field distribution, thereby inhibiting the growth of zinc dendrites. Simultaneously, glycine in the negative electrode electrolyte forms water-soluble complexes with zinc ions through its carboxyl and amino groups as electron donors, slowing down the reduction kinetics of zinc ions on the electrode surface. Furthermore, glycine utilizes its polar functional groups to adsorb onto the active sites on the zinc electrode surface through electrostatic interactions or coordination bonds, blocking zinc ion deposition, altering the energy distribution, and guiding zinc to undergo lateral two-dimensional growth, further inhibiting the formation of zinc dendrites. In addition, glycine can neutralize hydroxide ions, effectively suppressing the occurrence of hydrogen evolution side reactions. By fully utilizing the advantages of the negative electrode electrolyte, stable and efficient zinc deposition / dissolution is achieved during charge-discharge cycles, thereby ensuring long-term stable operation and high efficiency of the battery. The battery structure provides the site for electrochemical reactions and the channel for electrolyte circulation, while the negative electrode electrolyte provides an optimized electrochemical reaction environment. The two work synergistically to solve the performance degradation problems caused by zinc dendrite formation and hydrogen evolution reaction in traditional zinc-bromine flow batteries.

[0020] Furthermore, by introducing indium trichloride and glycine as negative electrode additives into the negative electrode electrolyte, indium ions of indium trichloride are preferentially reduced to form metallic indium on the electrode surface, and then form a nanoscale alloy layer in situ with the subsequently deposited zinc. This alloy layer can homogenize the electric field distribution and effectively inhibit the growth of zinc dendrites, thereby reducing short circuits and active material loss caused by dendrites piercing the separator, significantly improving coulombic efficiency. Simultaneously, the carboxyl and amino groups of glycine act as electron donors, forming water-soluble complexes with zinc ions, slowing down the reduction kinetics of zinc ions on the electrode surface. Furthermore, its polar functional groups adsorb onto the active sites on the zinc electrode surface through electrostatic interactions or coordination bonds, blocking zinc ion deposition, altering the energy distribution, and guiding zinc to undergo lateral two-dimensional growth, further inhibiting dendrite formation. Glycine can also neutralize hydroxide ions, inhibiting the hydrogen evolution reaction, reducing energy loss, ensuring coulombic efficiency and energy efficiency, and effectively suppressing side reactions, thus ensuring effective charge transfer and achieving a high coulombic efficiency of 95.4%-97.0%. Meanwhile, due to the suppression of dendrite growth and hydrogen evolution reaction, the electrode surface reaction is more uniform and stable, reducing polarization loss during charging and discharging, and achieving a high voltage efficiency of 85.8%-87.1% and an energy efficiency of 81.85%-84.49%. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0023] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0024] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0025] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0026] In this invention, unless otherwise specified, the numerical range "a~b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that the range includes real numbers between "6~22" in this document; "6~22" is simply an abbreviation for these numerical combinations.

[0027] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0028] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0029] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0030] Existing zinc-bromine flow batteries face two major technical challenges during negative electrode operation: zinc dendrite formation and hydrogen evolution reaction (HER). The zinc dendrite problem arises because, during zinc deposition during battery charging, the microenvironment at the electrode-electrolyte interface causes the reduced zinc to preferentially grow along specific crystal orientations, eventually forming a dendritic structure. With continuous charge-discharge cycles, these zinc dendrites continue to grow, severely reducing the interfacial stability of the electrochemical system. When the zinc dendrites grow to a critical size, they penetrate the battery separator, triggering a shuttle phenomenon of bromine at the positive electrode, leading to a significant decrease in coulombic efficiency. Simultaneously, contact between zinc dendrites and the positive electrode can cause a short circuit, severely limiting the lifespan and stability of the zinc-bromine flow battery. The HER problem arises because zinc has a low hydrogen evolution overpotential, making the HER reaction highly likely to occur. The HER irreversibly consumes hydrogen ions and water in the electrolyte, generating hydroxide ions, which in turn trigger the formation of a zinc passivation layer. In addition, the hydrogen evolution reaction can also cause a local increase in pH value on the electrode surface, which makes the zinc deposit layer loose and porous, accelerates the growth of zinc dendrites, and the generated gas also poses certain safety hazards to the battery system.

[0031] This invention addresses the two core technical challenges of zinc dendrite formation and hydrogen evolution reaction by introducing two key additives—indium trichloride and glycine—into the negative electrode electrolyte. Indium trichloride, as a negative electrode additive, inhibits zinc dendrite formation and the hydrogen evolution reaction through preferential deposition and alloying of indium, as well as by increasing the hydrogen evolution overpotential. Glycine, added as a negative electrode additive, aims to regulate zinc deposition morphology and suppress zinc dendrite growth and the hydrogen evolution reaction through complexation, adsorption, and pH buffering capabilities.

[0032] This invention provides a method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh the required amounts of solvent, electrolyte, supporting electrolyte, and negative electrode additive; S2: Add the electrolyte to the solvent and stir until completely dissolved; S3: Add the supporting electrolyte to the solution prepared in step S2 and stir until completely dissolved; S4: Add the negative electrode additive to the solution prepared in step S3 and stir until completely dissolved; S5: Adjust the volume to the required level using solvent.

[0033] The negative electrode electrolyte of a zinc-bromine flow battery includes: electrolyte, supporting electrolyte, negative electrode additive, and solvent; Preferably, the solvent is deionized water.

[0034] Preferably, the electrolyte is a 2.0-2.5 mol / L zinc bromide solution, ensuring that the negative electrode electrolyte has suitable ion concentration and transport performance, providing sufficient active zinc ions to support efficient electrochemical reactions, while avoiding solubility problems or increased viscosity due to excessive concentration, and insufficient energy density and mass transfer limitations due to excessively low concentration. The optimized electrolyte concentration works synergistically with indium trichloride and glycine. Indium ions in indium trichloride preferentially reduce to form an alloy layer, homogenizing the electric field; glycine guides the lateral growth of zinc and inhibits hydrogen evolution through complexation and adsorption.

[0035] Preferably, the supporting electrolyte is potassium chloride at a concentration of 2.0-3.0 mol / L, ensuring that the negative electrode electrolyte has excellent ionic conductivity. At this suitable concentration, the electrolyte can provide sufficient ion carriers, effectively reducing the ohmic resistance of the electrolyte, thereby promoting the rapid migration of zinc ions in the electrolyte.

[0036] Preferably, the negative electrode additive comprises 0.005-0.030 mol / L indium trichloride and 0.10-0.30 mol / L glycine. The molar concentration of indium trichloride (0.005-0.030 mol / L) ensures that during charging, an appropriate amount of indium ions are preferentially reduced on the electrode surface compared to zinc ions, allowing the formed metallic indium to form a nanoscale alloy layer in situ with the subsequently deposited zinc. The formation of this alloy layer is crucial for homogenizing the electric field distribution on the electrode surface, effectively eliminating localized high electric field regions and thus inhibiting the formation and growth of zinc dendrites. The molar concentration of glycine (0.10-0.30 mol / L) ensures that glycine effectively inhibits zinc dendrite growth and hydrogen evolution reaction on the electrode surface, while avoiding negative effects from excessively high or low concentrations.

[0037] This invention addresses the problems of zinc dendrite formation and hydrogen evolution reaction at both the microscopic and macroscopic levels through the synergistic effect of indium trichloride and glycine. The specific working principle is as follows: The mechanism by which indium trichloride inhibits zinc dendrite growth is as follows: During battery charging, indium ions are preferentially reduced to metallic indium at the electrode surface. These pre-deposited indium atoms do not form dendrites independently, but instead form an extremely thin, nanoscale alloy layer with the subsequently deposited zinc. This in-situ generated zinc-indium alloy layer homogenizes the electric field distribution, promoting uniform zinc deposition and resulting in a uniform, flat, and dendrite-free deposition morphology. This alloying effect at the micro-interface fundamentally optimizes the zinc nucleation process.

[0038] The mechanism by which indium trichloride inhibits the hydrogen evolution reaction: The addition of indium trichloride significantly increases the hydrogen evolution overpotential, making it extremely difficult for the hydrogen evolution reaction to occur in aqueous electrolytes. This effectively inhibits the occurrence of the hydrogen evolution reaction, improves coulombic efficiency, and enhances the stability of the electrolyte.

[0039] The mechanism by which glycine inhibits zinc dendrite growth: The carboxyl and amino groups in the glycine molecule can act as electron donors, forming stable water-soluble complexes with zinc ions. This complexation reduces the amount of free Zn in the electrolyte. 2+ The concentration and activity of Zn are thus reduced, thereby slowing down the growth of Zn. 2+ The reduction kinetics at the electrode surface slow down and control the zinc deposition process, promoting the formation of a dense, smooth zinc deposit layer rather than disordered dendrites. Furthermore, the polar functional groups of glycine can adsorb onto the active sites on the zinc electrode surface through electrostatic interactions or coordination bonds, forming an adsorption layer. This physically prevents preferential deposition of zinc ions at these highly active sites and alters the energy distribution at the electrode-electrolyte interface, guiding zinc towards lateral two-dimensional growth rather than vertical dendrite growth, thus resulting in a smoother zinc deposit layer. Glycine can also induce more uniform nucleation of zinc on the electrode surface by altering the solvation structure and transport mechanism of zinc ions.

[0040] The mechanism by which glycine inhibits the hydrogen evolution reaction: Glycine is an amphoteric substance with buffering capacity, and its effective buffering range covers the working pH range of the zinc-bromine battery negative electrode. It can promptly neutralize the hydroxide ions generated by the hydrogen evolution reaction, stabilizing the interfacial pH and thus effectively inhibiting the continued occurrence of the hydrogen evolution reaction. Simultaneously, the carboxyl and amino groups in glycine can neutralize the OH- ions generated by hydrogen evolution. - This maintains the pH value at the interface, thereby preventing the formation of zinc hydroxide or zinc oxide precipitates from the source, and keeping the zinc reaction highly reversible.

[0041] Synergistic Effect of Indium Trichloride and Glycine: Indium trichloride and glycine achieve perfect synergy. Indium trichloride mainly addresses the hydrogen evolution problem and improves coulombic efficiency through microscopic interface alloying and optimized nucleation; glycine mainly solves the zinc dendrite problem by controlling the macroscopic morphology to achieve smooth deposition. These two additives work together at different scales to effectively solve the two most important problems faced by the negative electrode of zinc-bromine flow batteries: zinc dendrite formation and hydrogen evolution reaction. This greatly improves the battery's coulombic efficiency, voltage efficiency, and energy efficiency, and extends the battery's cycle life.

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Therefore, the following detailed description of the embodiments is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 0.664g indium trichloride (0.030mol / L), and 0.751g glycine (0.10mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0044] Example 2 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 0.664g indium trichloride (0.030mol / L), and 1.126g glycine (0.15mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0045] Example 3 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 0.664g indium trichloride (0.030mol / L), and 1.501g glycine (0.20mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0046] Example 4 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 0.664g indium trichloride (0.030mol / L), and 1.877g glycine (0.25mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0047] Example 5 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 0.664g indium trichloride (0.030mol / L), and 2.252g glycine (0.30mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0048] Example 6 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 0.111g indium trichloride (0.005mol / L), and 0.751g glycine (0.10mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0049] Example 7 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 0.221g indium trichloride (0.010mol / L), and 0.751g glycine (0.10mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0050] Example 8 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 0.332g indium trichloride (0.015mol / L), and 0.751g glycine (0.10mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0051] Example 9 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 0.442g indium trichloride (0.020mol / L), and 0.751g glycine (0.10mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0052] Example 10 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 0.553g indium trichloride (0.025mol / L), and 0.751g glycine (0.10mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0053] Example 11 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 45.04g zinc bromide (2.0mol / L), 14.91g potassium chloride (2.0mol / L), 0.111g indium trichloride (0.005mol / L), and 0.751g glycine (0.10mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0054] Example 12 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 56.30g zinc bromide (2.5mol / L), 18.64g potassium chloride (2.5mol / L), 0.664g indium trichloride (0.030mol / L), and 2.252g glycine (0.30mol / L); S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine and indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0055] Comparative Example 1 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L) and 22.37g potassium chloride (3.0mol / L). S2: Mix zinc bromide with deionized water until homogeneous; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Adjust the volume to 100ml with the deionized water mixture.

[0056] Comparative Example 2 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), and 0.111g indium trichloride (0.005mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0057] Comparative Example 3 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), and 0.332g indium trichloride (0.015mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0058] Comparative Example 4 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), and 0.664g indium trichloride (0.030mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add indium trichloride to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0059] Comparative Example 5 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), and 0.751g glycine (0.10mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0060] Comparative Example 6 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), and 1.501g glycine (0.20mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0061] Comparative Example 7 A method for preparing a negative electrode electrolyte for a zinc-bromine flow battery, comprising: S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), and 2.252g glycine (0.30mol / L). S2: Mix zinc bromide with deionized water until completely dissolved; S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved; S4: Add glycine to the solution prepared in S3 and stir until completely dissolved; S5: Adjust the volume to 100ml with deionized water.

[0062] Table 1. Composition of key components in the zinc-bromine flow battery negative electrode electrolytes prepared in Examples 1-12 and Comparative Examples 1-7.

[0063] Table 2. Comparison of single-cell performance test results of zinc-bromine flow battery negative electrode electrolytes prepared in Examples 1-12 and those prepared in Comparative Examples 1-7.

[0064] To test the performance of the zinc-bromine flow battery negative electrode electrolytes prepared in Examples 1-12 and Comparative Examples 1-7, zinc-bromine flow battery negative electrode electrolytes prepared in Examples 1-12 and Comparative Examples 1-7 were assembled with positive electrode electrolytes to form zinc-bromine flow batteries. The positive electrode electrolyte consisted of 2.0 mol / L zinc bromide, 1.5 mol / L potassium chloride, and 0.4 mol / L 1-methyl-1-ethylpyrrolidine ammonium bromide. Both the carbon positive and negative electrode materials were carbon felt, and the separator was a Daramic porous membrane. The test current density was 20 mA cm⁻¹. 2 The zinc-bromine flow battery was used as the test object for electrochemical performance testing, including energy efficiency, voltage efficiency, and coulombic efficiency. The results are shown in Table 2.

[0065] Table 1 shows the composition of key components of the zinc-bromine flow battery negative electrode electrolytes prepared in Examples 1-12 and Comparative Examples 1-7; Table 2 compares the performance test results of single cells assembled with the zinc-bromine flow battery negative electrode electrolytes prepared in Examples 1-12 and Comparative Examples 1-7. As shown in the tables, compared with Comparative Example 1, adding indium trichloride alone (Comparative Examples 2-4) or glycine alone (Comparative Examples 5-7) can improve various efficiencies of the battery, and the performance increases with increasing additive concentration. This indicates that both additives have a positive effect when used alone. When indium trichloride and glycine are used in combination (Examples 1-12), the battery performance is significantly improved compared to adding them alone. For example, Comparative Example 4 (0.030 M indium trichloride only) had a coulombic efficiency of 93.2% and an energy efficiency of 78.85%; Comparative Example 7 (0.30 M glycine only) had a coulombic efficiency of 93.5% and an energy efficiency of 79.01%; while Example 5, which combined the two (0.030 M indium trichloride and 0.30 M glycine), achieved a coulombic efficiency of 97.0% and an energy efficiency of 84.49%. This demonstrates a synergistic effect between indium trichloride and glycine. The zinc-bromine flow battery using the zinc-bromine flow battery negative electrode electrolyte prepared in this invention has a coulombic efficiency of 95.4%-97.0%, an energy efficiency of 81.85%-84.49%, and a voltage efficiency of 85.8%-87.1%. By adding indium trichloride as an additive to the negative electrode electrolyte of a zinc-bromine flow battery, indium ions are preferentially reduced to metallic indium on the electrode surface during charging. These pre-deposited indium atoms do not form dendrites individually, but instead form an extremely thin, nanoscale alloy layer with the subsequently deposited zinc. This in-situ generated alloy layer homogenizes the electric field distribution, ensuring uniform zinc deposition. The uniform deposition morphology and absence of dendrite growth allow the battery to withstand thousands of cycles without failure due to short circuits or electrode pulverization. Zinc has a very low hydrogen evolution overpotential and readily undergoes hydrogen evolution reaction, which is the primary cause of low coulombic efficiency, gas production, and electrolyte instability. The addition of indium trichloride increases the hydrogen evolution overpotential, meaning that hydrogen evolution reaction on this surface is extremely difficult to occur in aqueous electrolytes. By introducing glycine as a negative electrode additive, the carboxyl and amino groups in the glycine molecule can act as electron donors, forming stable water-soluble complexes with zinc ions. This complexation reduces the free Zn in the electrolyte. 2+ The concentration and activity of Zn ions are reduced, thereby slowing down the reduction kinetics of zinc ions on the electrode surface. 2+The deposition process becomes slower and more controllable, which is conducive to the formation of a dense and smooth zinc deposition layer, rather than a disordered dendrite that is prone to piercing the separator. The carboxyl and amino groups of glycine can preferentially adsorb onto highly active sites such as defects and grain boundaries on the electrode surface, reducing the surface energy at these sites. This reduces the difference in deposition energy barriers for zinc ions across the electrode surface, resulting in a uniform adsorption layer. This makes the electrochemical potential energy across the electrode surface more consistent, guiding zinc to undergo lateral two-dimensional growth rather than vertical dendrite growth, thus obtaining a smoother zinc deposition layer. Glycine induces more uniform nucleation of zinc on the electrode surface by altering the solvation structure and transport mode of zinc ions. Furthermore, glycine is an amphoteric substance with buffering capacity; its effective buffering range covers the working pH range of the zinc-bromine battery negative electrode, and it can promptly neutralize OH-. - The ions stabilize the interface pH, thereby effectively inhibiting the continued occurrence of the hydrogen evolution reaction. Zn in the electrolyte... 2+ Will react with OH - The reaction produces non-conductive Zn(OH)₂ or ZnO, forming an insulating passivation layer. The carboxyl and amino groups in glycine can neutralize the OH groups produced by hydrogen evolution. - This prevents the formation of zinc hydroxide or zinc oxide precipitation at the source, maintaining high reversibility and coulombic efficiency in the zinc reaction. Glycine regulates the macroscopic morphology, resulting in a smooth deposition layer and resolving the zinc dendrite problem; indium trichloride has a microscopic interface alloying effect, fundamentally eliminating hydrogen evolution and optimizing nucleation. The two additives work together at different scales to effectively inhibit zinc dendrite and hydrogen evolution reactions, achieving a synergistic improvement in coulombic efficiency, voltage efficiency, and energy efficiency, thus extending battery cycle life.

[0066] In summary, the zinc-bromine flow battery disclosed in this invention, comprising a combined negative electrode additive, a negative electrode electrolyte, and their preparation method, and a zinc-bromine flow battery, firstly, preferentially reduces indium ions of indium trichloride and forms a nanoscale alloy layer with zinc in situ. This alloy layer can homogenize the electric field distribution, fundamentally changing the nucleation and growth mechanism of zinc and effectively inhibiting dendrite formation. This in-situ alloying strategy is uncommon in existing technologies, and its homogenization effect on the electric field distribution is a key innovation in solving the dendrite problem. Secondly, glycine, through its unique molecular structure, forms a complex with zinc ions, slowing down the reduction kinetics of zinc ions and making the zinc deposition process more controllable. On the other hand, its polar functional groups adsorb on the electrode surface, guiding zinc to undergo lateral two-dimensional growth, further optimizing the deposition morphology. In addition, glycine's amphoteric buffering capacity effectively neutralizes hydroxide ions, stabilizing the interface pH and thus significantly inhibiting the hydrogen evolution reaction. This is a multifunctional effect that is difficult to achieve simultaneously with a single additive in existing technologies. This invention not only solves the problems of short circuits and shortened battery life caused by zinc dendrite growth, but also effectively suppresses energy loss and safety hazards caused by hydrogen evolution reaction. Through the synergistic effect of indium trichloride and glycine, precise control of zinc deposition morphology and effective suppression of side reactions are achieved, thereby significantly improving the coulombic efficiency, voltage efficiency, and energy efficiency of the zinc-bromine flow battery, and extending the battery's cycle life. Simultaneously, the stability of electrode reactions and the reduction of polarization losses ensure the effective utilization of charge and discharge voltage, thus achieving high voltage efficiency. The synergistic effect of high coulombic efficiency and high voltage efficiency ultimately enables this zinc-bromine flow battery to exhibit excellent energy conversion and storage capabilities, significantly improving overall energy efficiency and providing a more efficient and economical solution for the practical application of zinc-bromine flow batteries.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A combined negative electrode additive for zinc-bromine flow batteries, characterized in that, include: Indium trichloride and glycine; the molar ratio of indium trichloride to glycine is 1:(3.33~60).

2. The combined negative electrode additive for zinc-bromine flow batteries according to claim 1, characterized in that, The molar ratio of indium trichloride to glycine is 1:(6.67~10).

3. A zinc-bromine flow battery negative electrode electrolyte, characterized in that, include: Electrolyte, supporting electrolyte, solvent, and negative electrode additive; the negative electrode additive is the combined negative electrode additive for zinc-bromine flow batteries as described in claim 1 or 2; the molar concentration of indium trichloride in the negative electrode electrolyte of the zinc-bromine flow battery is 0.005-0.030 mol / L; the molar concentration of glycine in the negative electrode electrolyte of the zinc-bromine flow battery is 0.10-0.30 mol / L.

4. The zinc-bromine flow battery negative electrode electrolyte according to claim 3, characterized in that, The molar concentration of the electrolyte is 2.0-2.5 mol / L.

5. The zinc-bromine flow battery negative electrode electrolyte according to claim 3, characterized in that, The electrolyte is zinc bromide solution; the solvent is deionized water.

6. The zinc-bromine flow battery negative electrode electrolyte according to claim 3, characterized in that, The molar concentration of the supporting electrolyte is 2.0-3.0 mol / L.

7. The zinc-bromine flow battery negative electrode electrolyte according to claim 3, characterized in that, The supporting electrolyte is potassium chloride.

8. The method for preparing the negative electrode electrolyte of the zinc-bromine flow battery according to any one of claims 3-7, characterized in that, include: Electrolyte, supporting electrolyte and negative electrode additive are added to solvent in sequence and stirred until completely dissolved to obtain the negative electrode electrolyte of zinc-bromine flow battery.

9. A zinc-bromine flow battery, characterized in that, Includes the zinc-bromine flow battery negative electrode electrolyte as described in any one of claims 3-7.

10. The zinc-bromine flow battery according to claim 9, characterized in that, The zinc-bromine flow battery has a coulombic efficiency of 95.4%-97.0%, an energy efficiency of 81.85%-84.49%, and a voltage efficiency of 85.8%-87.1%.

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