A membrane-free anode-free zinc-bromine battery and a preparation method thereof

Abstract

The application provides a membrane-free and anode-free zinc-bromine battery and a preparation method thereof. The battery comprises an open insulated container, a first graphite felt and a second graphite felt. The first graphite felt serves as a positive electrode current collector, the second graphite felt serves as a negative electrode current collector, the first graphite felt and the second graphite felt are independently arranged in the container, and the first graphite felt and the second graphite felt are connected by a wire. The container contains an anode electrolyte and a cathode electrolyte. The anode electrolyte and the cathode electrolyte contain a bifunctional additive. The bifunctional additive can coexist in a first configuration and a second configuration in the electrolyte to inhibit the crossover of bromine species between the positive electrode and the negative electrode. Spectroscopic characterization confirms that the bifunctional additive can effectively reduce the crossover of bromine species between the positive electrode and the negative electrode, significantly prolong the cycle life of the battery, and the membrane-free and anode-free zinc-bromine battery can be stably operated for 1451 cycles (about 740 hours) at a current density of 10 mA / cm 2 The average coulombic efficiency is as high as 99.97%.

Description

Technical Field

[0001] This invention relates to the field of technology, and in particular to a membrane-free, anode-free zinc-bromine battery and its preparation method. Background Technology

[0002] Aqueous zinc-ion batteries have attracted widespread attention in various energy storage systems due to their advantages such as low cost, high theoretical specific capacity, environmental friendliness, and good safety. However, for aqueous zinc-based batteries, numerous water-related side reactions severely affect the actual performance and cycle life of the battery. These side reactions mainly manifest as the formation of byproducts such as zinc dendrites and dead zinc on the negative electrode surface, irreversible consumption of zinc metal, and hydrogen evolution reactions caused by water decomposition on the electrode surface. To suppress these side reactions related to aqueous electrolytes, current research has employed organic molecules as electrolyte additives, while inorganic metal ion additives have also been proven to be an effective modification strategy.

[0003] For zinc-bromine batteries, common modification strategies on the cathode side mainly focus on the application of bromine complexing agents. Traditionally, quaternary ammonium compounds are often used as complexing agents to immobilize polybrominates, and some studies have also used ionic liquids to achieve similar functions, thereby effectively reducing the cross-diffusion of bromine species. In addition, some studies have constructed solid or quasi-solid bromine cathodes to suppress the spontaneous dissolution of bromine, further limiting the migration of bromine species in the electrolyte.

[0004] The aforementioned modification strategies have all achieved good results to some extent. However, for certain battery structures, especially membrane-free batteries, modifications targeting only one electrode are often insufficient. For example, in aqueous zinc-bromine membrane-free batteries, while eliminating the separator significantly reduces manufacturing costs, the lack of a separator also exacerbates the problem of cross-reactions between the positive and negative electrodes. In membrane-free zinc-bromine batteries, the cross-diffusion behavior of highly corrosive polybrominates and bromine species generated during cycling is more severe than in traditional zinc-bromine batteries. Furthermore, achieving an anode-free design in this type of battery presents greater challenges. The combined effect of diffusion of active materials at both electrodes and water-induced side reactions continuously consumes the active zinc deposited on the anode surface, leading to a significant decrease in battery cycle life and thus limiting its practical application.

[0005] Therefore, there is an urgent need to provide a membrane-free, anode-free zinc-bromine battery and its preparation method. Summary of the Invention

[0006] This invention provides a membrane-free, anode-free zinc-bromine battery and its preparation method, which can solve the problems of cross-reactions between the positive and negative electrodes in existing membrane-free zinc-bromine batteries and the short cycle life of the batteries.

[0007] In a first aspect, the present invention provides a membrane-free, anode-free zinc-bromine battery, comprising an open insulating container, a first graphite felt, and a second graphite felt; wherein the first graphite felt serves as a positive electrode current collector, and the second graphite felt serves as a negative electrode current collector, the first graphite felt and the second graphite felt are disposed separately and independently inside the container, and the first graphite felt and the second graphite felt are connected by a wire; the container contains an anolyte and a catholyte; the anolyte and the catholyte contain a bifunctional additive; the bifunctional additive can coexist in a first configuration and a second configuration in the electrolyte, and is used to suppress the cross-linking of bromine species between the positive and negative electrodes.

[0008] Preferably, the preparation method of the bifunctional additive is as follows: 2-aminobenzimidazole is added to water and stirred until homogeneous, and then an acidic reagent is added dropwise to carry out a protonation reaction to obtain the bifunctional additive.

[0009] Preferably, the acidic reagent is dilute sulfuric acid.

[0010] More preferably, the pH of the system after adding the acidic reagent is 4.0~4.5.

[0011] Preferably, the cathode electrolyte is obtained by stirring and mixing a bifunctional additive, a conductive agent, and an organic solvent.

[0012] Preferably, the conductive agent is Ketjen Black.

[0013] Preferably, in the cathode electrolyte, the concentration of the bifunctional additive is 45~55 mmol / L, and the concentration of the conductive agent is 8~12 g / L.

[0014] Preferably, the anolyte is obtained by mixing a composite electrolyte, a bifunctional additive, and water.

[0015] Preferably, the composite electrolyte is composed of zinc bromide and zinc sulfate.

[0016] Preferably, in the anolyte, the concentration of the bifunctional additive is 45-55 mmol / L, and the concentrations of zinc bromide and zinc sulfate are both 0.45-0.55 mol / L.

[0017] Preferably, the organic solvent is dichloromethane, carbon tetrachloride, or propylene carbonate.

[0018] More preferably, the organic solvent is propylene carbonate.

[0019] In a second aspect, the present invention also provides a method for preparing a membrane-free, anode-free zinc-bromine battery as described in any one of the first aspects above, the method comprising: (1) Add the composite electrolyte to water and mix well to obtain a blank electrolyte; add the bifunctional additive to the blank electrolyte and mix well to obtain an anolyte; (2) Add the conductive agent to the organic solvent and stir to mix well, then add the bifunctional additive and mix well to obtain the cathode electrolyte; (3) The anolyte and the cathode electrolyte are added to an open insulating container, and a first graphite felt and a second graphite felt are placed at both ends of the open insulating container as positive current collector and negative current collector, respectively. Then, the first graphite felt and the second graphite felt are connected by wires to obtain the membrane-free and anode-free zinc-bromine battery.

[0020] Preferably, in step (3), the wire is a titanium wire; the diameter of the titanium wire is 2~4mm.

[0021] Preferably, the conductor is covered with an insulating layer; the insulating layer is preferably Teflon tape.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects: In this invention, a bifunctional additive is prepared and simultaneously added to both the anolyte and the catholyte. This bifunctional additive has two proton-loving sites and can form two different 2-AB configurations in the electrolyte, with the first and second configurations coexisting. On the positive electrode side, it can achieve the attraction of bromine species (including Br2 and Br3). - and Br5 - The adsorption and complexation of bromine species effectively inhibits the cross-diffusion of bromine species to the negative electrode side. On the negative electrode side, this bifunctional additive can adsorb onto the negative electrode surface, improve the zinc deposition morphology, adjust the ratio of deposited zinc crystal faces, reduce the formation of zinc dendrites and dead zinc, and simultaneously inhibit the occurrence of water-induced side reactions. Furthermore, this bifunctional additive can increase the zinc affinity of the electrolyte and improve the wettability of the electrode material. Thanks to these multiple effects, the zinc-bromine battery of this invention successfully achieves an anode-free structure design without added zinc metal, based on a membrane-free battery. Only commercially available untreated carbon felt is used as the current collector on the positive and negative electrode sides. Spectroscopic characterization confirms that this bifunctional additive can effectively reduce the cross-diffusion of bromine species between the positive and negative electrodes, significantly extending the battery's cycle life. The membrane-free, anode-free zinc-bromine battery achieves a cycle life of 10 mA / cm². 2 It operates stably for 1451 cycles (approximately 740 hours) at current density, with an average coulombic efficiency of up to 99.97%. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is the UV-Vis spectrum of the electrolyte on the anode side of a membrane-free, anode-free zinc-bromine battery provided in Embodiment 1 and Comparative Example 1 of the present invention during uncharge-discharge cycles; where blank represents Comparative Example 1 and 2-AB represents Embodiment 1; Figure 2 This is the UV-Vis spectrum of the electrolyte on the anode side of a membrane-free, anode-free zinc-bromine battery provided in Embodiment 1 and Comparative Example 1 of the present invention after 100 charge-discharge cycles; Figure 3 The image shows the infrared spectrum (FT-IR) of the cathode-side electrolyte after 100 charge-discharge cycles of a membrane-free, anode-free zinc-bromine battery provided in Embodiment 1 and Comparative Example 1 of this invention. Figure 4 The image shows the infrared spectrum (FT-IR) of the cathode-side electrolyte after 100 charge-discharge cycles of a membrane-free, anode-free zinc-bromine battery provided in Embodiment 1 and Comparative Example 1 of this invention. Figure 5 These are Raman spectra of the anode-side electrolyte of a membrane-free, anode-free zinc-bromine battery provided in Embodiment 1 and Comparative Example 1 of the present invention, during uncharged and discharged cycling. Figure 6 This is the Raman spectrum of the anode-side electrolyte of a membrane-free, anode-free zinc-bromine battery provided in Embodiment 1 and Comparative Example 1 of the present invention after 100 charge-discharge cycles; Figure 7 This is the Raman spectrum of the cathode-side electrolyte after 100 charge-discharge cycles of a membrane-free, anode-free zinc-bromine battery provided in Embodiment 1 and Comparative Example 1 of the present invention; Figure 8 This is a scanning electron microscope image of the graphite felt current collector after 40 charge-discharge cycles of a membrane-free, anode-free zinc-bromine battery provided in Comparative Example 1 of this invention. Figure 9 This is a scanning electron microscope image of the graphite felt current collector after 40 charge-discharge cycles of a membrane-free, anode-free zinc-bromine battery provided in Embodiment 1 of the present invention; Figure 10 This is the XRD pattern of the graphite felt current collector after 40 charge-discharge cycles of a membrane-free, anode-free zinc-bromine battery provided in Embodiment 1 and Comparative Example 1 of the present invention. Figure 11 This is a membrane-free, anode-free zinc-bromine solution provided in Embodiment 1 of the present invention at 10 mA / cm. 2Time-voltage curves at current density; Figure 12 This is a membrane-free, anode-free zinc-bromine solution provided in Embodiment 1 of the present invention at 10 mA / cm. 2 Coulomb efficiency plot at current density; Figure 13 This invention provides a membrane-free, anode-free zinc-bromine solution at 10 mA / cm². 2 Time-voltage curves at current density; Figure 14 This invention provides a membrane-free, anode-free zinc-bromine solution at 10 mA / cm². 2 Coulomb efficiency plot at current density; Figure 15 This is a test diagram of a membrane-free, anode-free zinc-bromine electrolyte with starch-potassium iodide test paper added to the upper electrolyte layer of the anode after 200 charge-discharge cycles, as provided in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but 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.

[0026] This invention provides a membrane-free, anode-free zinc-bromine battery, comprising an open insulating container, a first graphite felt, and a second graphite felt; wherein the first graphite felt serves as the positive electrode current collector, and the second graphite felt serves as the negative electrode current collector, the first graphite felt and the second graphite felt are disposed separately and independently inside the container, and the first graphite felt and the second graphite felt are connected by a wire; the container contains an anolyte and a catholyte; the anolyte and the catholyte contain a bifunctional additive; the bifunctional additive can coexist in a first configuration and a second configuration in the electrolyte, and is used to suppress the cross-linking of bromine species between the positive and negative electrodes.

[0027] In this embodiment of the invention, a bifunctional additive is prepared and simultaneously added to both the anolyte and the catholyte. This bifunctional additive has two proton-loving sites and can form two different 2-AB configurations in the electrolyte, with the first and second configurations coexisting. On the positive electrode side, it can achieve the attraction of bromine species (including Br2 and Br3). - and Br5 -The adsorption and complexation of bromine species effectively inhibits the cross-diffusion of bromine species to the negative electrode side. On the negative electrode side, this bifunctional additive can adsorb onto the negative electrode surface, improve the zinc deposition morphology, adjust the ratio of deposited zinc crystal faces, reduce the formation of zinc dendrites and dead zinc, and simultaneously inhibit the occurrence of water-induced side reactions. Furthermore, this bifunctional additive can also increase the zinc affinity of the electrolyte and improve the wettability of the electrode material. Thanks to these multiple effects, the zinc-bromine battery of this invention successfully achieves an anode-free structure design without added zinc metal, based on a membrane-free battery. Only commercially available, untreated, clean carbon felt is used as the current collector on both the positive and negative electrode sides. Spectroscopic characterization confirms that this bifunctional additive can effectively reduce the cross-diffusion of bromine species between the positive and negative electrodes, significantly extending the battery's cycle life. The membrane-free, anode-free zinc-bromine battery achieves a cycle life of 10 mA / cm². 2 It operates stably for 1451 cycles (approximately 740 hours) at current density, with an average coulombic efficiency of up to 99.97%.

[0028] According to some preferred embodiments, the preparation method of the bifunctional additive is as follows: 2-aminobenzimidazole is added to water and stirred until homogeneous, and then an acidic reagent is added dropwise to carry out a protonation reaction to obtain the bifunctional additive; the acidic reagent is dilute sulfuric acid; the pH of the system after adding the acidic reagent is 4.0~4.5.

[0029] In this embodiment of the invention, during the preparation of the bifunctional additive, 2-aminobenzimidazole molecules are added to water and stirred, followed by slow dropwise addition of dilute sulfuric acid with a mass concentration of 5-30%. The pH of the solution is monitored in real time during the dropwise addition until the pH reaches 4.0-4.5. This allows the 2-aminobenzimidazole molecules to protonate under the aforementioned acidic conditions, generating 2-aminobenzimidazole cations (i.e., the 2-AB bifunctional additive), thereby enhancing its solubility in aqueous electrolytes. The resulting 2-AB molecules, utilizing the nitrogen-rich structure of their aminoimidazolium ring, can adsorb and complex bromine species, thus inhibiting the cross-linking of bromine species on the negative electrode side. Simultaneously, the 2-AB bifunctional additive molecules can also adsorb onto the negative electrode surface, improving zinc deposition morphology, reducing the formation of zinc dendrites and dead zinc, and inhibiting water-induced side reactions, thereby extending battery cycle life. Furthermore, contact angle testing confirms that the 2-AB bifunctional additive can also increase the zinc affinity of the electrolyte and improve electrode wettability. The bifunctional additive in this invention is not only applicable to membrane-free zinc-bromine batteries, but also enables an anode-free structure design without added zinc metal, effectively reducing the cross-linking of bromine species between the positive and negative electrodes and significantly extending the battery cycle life. At the same time, the additive can also effectively extend the cycle life of Zn / / Zn symmetric batteries and Zn / / Cu asymmetric batteries.

[0030] It should be noted that because 2-aminobenzimidazole undergoes a condensation reaction in a strongly acidic environment, the sulfuric acid concentration needs to be controlled to be less than 0.5 M. In addition, other inorganic acids may introduce foreign ions that are inconsistent with the original ions in the electrolyte. Therefore, dilute sulfuric acid is preferred to ensure that the introduced ions are consistent with the ions contained in the electrolyte itself.

[0031] According to some preferred embodiments, the cathode electrolyte is obtained by stirring and mixing a bifunctional additive, a conductive agent, and an organic solvent; the conductive agent is Ketjen Black; in the cathode electrolyte, the concentration of the bifunctional additive is 45~55 mmol / L (for example, it can be 45 mmol / L, 50 mmol / L, or 55 mmol / L), and the concentration of the conductive agent is 8~12 g / L (for example, it can be 8 g / L, 9 g / L, 10 g / L, 11 g / L, or 12 g / L).

[0032] In this embodiment of the invention, a conductive agent is first added to an organic solvent and stirred until homogeneous. Then, an appropriate amount of a bifunctional additive is added and mixed to form a cathode electrolyte. The bifunctional additive can adsorb onto the surface of the negative electrode, improving the zinc deposition morphology, reducing the formation of zinc dendrites and dead zinc, and inhibiting water-induced side reactions, thereby extending the battery cycle life and improving the battery's coulombic efficiency and cycle stability. If the concentration of the bifunctional additive is too high, it will increase the battery's internal resistance; if its concentration is too low, it will not be able to fully regulate the zinc deposition behavior. The addition of the conductive agent can form a continuous electron transport path inside the electrode, reducing the contact resistance between the electrode and the electrolyte. An appropriate amount of conductive agent is beneficial for building an efficient electron conduction network and reducing polarization losses; however, if its concentration is too high, it will increase the battery manufacturing cost and increase the fluid viscosity.

[0033] According to some preferred embodiments, the anolyte is obtained by stirring and mixing a composite electrolyte, a bifunctional additive, and water; the composite electrolyte is composed of zinc bromide and zinc sulfate.

[0034] According to some preferred embodiments, in the anolyte, the concentration of the bifunctional additive is 45~55 mmol / L (e.g., 45 mmol / L, 50 mmol / L or 55 mmol / L), and the concentrations of zinc bromide and zinc sulfate are both 0.45~0.55 mol / L (e.g., 0.45 mol / L, 0.50 mol / L or 0.55 mol / L).

[0035] In this embodiment of the invention, when preparing the anolyte, zinc bromide and zinc sulfate are first added to water and stirred until homogeneous. The zinc bromide and zinc sulfate in the electrolyte provide zinc and bromine sources, respectively, and reduce the solubility of water in the organic solvent through salting-out, thereby optimizing the electrolyte stability. Subsequently, a multifunctional additive is added, and finally, the two are mixed to obtain the anolyte. The multifunctional additive utilizes its nitrogen-rich structure of the aminoimidazolium ring to capture bromides diffusing from the positive electrode on the anode side, complexing and fixing them, slowing the migration of bromide species to the negative electrode side. Furthermore, it increases the zinc affinity of the electrolyte and improves the wettability of the electrode.

[0036] Furthermore, by optimizing the component concentrations, the anolyte in a membrane-free, anode-free zinc-bromine battery can both ensure the supply of active materials for the positive electrode reaction and effectively suppress cross-reactions and dendrite growth, thereby supporting the battery to achieve long cycle life and high coulombic efficiency. If the concentration of the multifunctional additive is too high, it will cause an increase in internal resistance and aggravated polarization, while if its concentration is too low, it will not be able to effectively complex bromine species, leading to an exacerbation of cross-reactions and a decrease in cycle stability.

[0037] According to some preferred embodiments, the organic solvent is dichloromethane, carbon tetrachloride, or propylene carbonate; preferably, the organic solvent is propylene carbonate.

[0038] In this embodiment of the invention, the organic solvents in the anolyte and catholyte are halogenated hydrocarbons or propylene carbonate. These solvents are immiscible with water, and the naturally formed liquid-liquid interface between them can replace the physical isolation function of a traditional membrane, thereby realizing the design of a membrane-free zinc-bromine battery. Furthermore, unlike traditional halogenated hydrocarbon solvents, which are mostly toxic, volatile, and difficult to degrade, this embodiment of the invention preferably uses propylene carbonate as the organic solvent to replace traditional halogenated hydrocarbons for preparing a membrane-free zinc-bromine battery. Compared to halogenated hydrocarbon solvents, propylene carbonate is less volatile (boiling point 240°C), easily degraded, has lower toxicity, and is less likely to cause environmental pollution. Simultaneously, it can synergistically work with the bifunctional additives prepared in this embodiment of the invention to effectively inhibit bromine species cross-reaction and significantly improve the side reactions on the negative electrode side. This allows this embodiment of the invention to successfully achieve an anode-free structure design without added zinc metal on the basis of a membrane-free battery, using only commercially available graphite felt without any special treatment as the current collector on the negative electrode side. The resulting battery system not only significantly reduces the cross-linking of bromine species between the positive and negative electrodes, but also significantly improves the battery's cycle life.

[0039] This invention also provides a method for preparing a membrane-free, anode-free zinc-bromine battery as described in any one of the above embodiments, the method comprising: (1) Add the composite electrolyte to water and mix well to obtain a blank electrolyte; add the bifunctional additive to the blank electrolyte and mix well to obtain an anolyte; (2) Add the conductive agent to the organic solvent and stir to mix well, then add the bifunctional additive and mix well to obtain the cathode electrolyte; (3) The anolyte and the cathode electrolyte are added to an open insulating container, and a first graphite felt and a second graphite felt are placed at both ends of the open insulating container as positive current collector and negative current collector, respectively. Then, the first graphite felt and the second graphite felt are connected by wires to obtain the membrane-free and anode-free zinc-bromine battery.

[0040] According to some preferred embodiments, in step (3), the wire is a titanium wire; the diameter of the titanium wire is 2~4mm (for example, it can be 2mm, 3mm or 4mm).

[0041] According to some preferred embodiments, the conductor is covered with an insulating layer; the insulating layer is preferably Teflon tape.

[0042] In this embodiment of the invention, the prepared anolyte and catholyte are added to an open insulating container (such as a glass container), and two graphite felts without any special treatment are placed at both ends as the anolyte and catholyte current collectors, respectively. Titanium wire is used as the conductor, and the outer layer is covered with Teflon tape, thereby preparing a membrane-free, anode-free zinc-bromine battery. Testing showed that at 10 mA / cm... 2 Under conditions of high current density and a discharge cutoff voltage of 1V, the battery operated stably for 1451 cycles (approximately 740 hours) and exhibited minimal efficiency fluctuations, with an average coulombic efficiency of 99.97%.

[0043] To more clearly illustrate the technical solution and advantages of the present invention, the following describes in detail a membrane-free, anode-free zinc-bromine battery and its preparation method through several embodiments.

[0044] Example 1: Preparation of bifunctional additive: 2-aminobenzimidazole was added to water and stirred until well mixed. Then, an acidic reagent (dilute sulfuric acid) was added dropwise until the pH of the reaction system was 4.0 to carry out a protonation reaction and obtain a bifunctional additive. (1) Add zinc bromide and zinc sulfate to 50 mL of deionized water and stir to obtain a blank electrolyte; wherein the concentration of zinc bromide and zinc sulfate is 0.5 mol / L; then add the prepared bifunctional additive and stir to obtain an anolyte; wherein the concentration of the bifunctional additive is 50 mmol / L. (2) Add the conductive agent (Ketjen Black) to 50 mL of organic solvent (propylene carbonate) and stir magnetically for 12 h to form a uniform and stable fluid. Then add the prepared bifunctional additive and stir to mix well to obtain the cathode electrolyte. The concentration of the conductive agent is 10 g / L and the concentration of the bifunctional additive is 50 mmol / L. (3) Add 14 mL of anolyte and 14 mL of catholyte to a 50 mL glass container, and place a first graphite felt (2 mm × 1 cm × 2 cm) and a second graphite felt (2 mm × 1 cm × 2 cm) at both ends of the glass container as positive current collector and negative current collector, respectively. Then, use titanium wire wrapped with Teflon tape as a wire to connect the first graphite felt and the second graphite felt to obtain a membrane-free and anode-free zinc-bromine battery.

[0045] Comparative Example 1 (1) Add zinc bromide and zinc sulfate to 50 mL of deionized water and stir to mix well to obtain a blank anolyte; wherein the concentration of zinc bromide and zinc sulfate is 0.5 mol / L. (2) Add the conductive agent (Ketjen Black) to 50 mL of organic solvent (propylene carbonate) and stir magnetically for 12 h to obtain the cathode electrolyte; wherein the concentration of the conductive agent is 10 g / L; (3) Slowly add 14 mL of anolyte and 14 mL of catholyte into a 50 mL glass container, and place a first graphite felt (2 mm × 1 cm × 2 cm) and a second graphite felt (2 mm × 1 cm × 2 cm) at both ends of the glass container as positive current collector and negative current collector, respectively. Then, use titanium wire wrapped with Teflon tape as a wire to connect the first graphite felt and the second graphite felt to obtain a membrane-free and anode-free zinc-bromine battery.

[0046] The membrane-free and anode-free zinc-bromine batteries obtained in Example 1 and Comparative Example 1 were subjected to performance testing, and the test results are as follows: Figures 1 to 10 As shown in Figure 1 and Table 1: Table 1 Sample Cycle number Average coulombic efficiency (%) Capacity retention rate after standing for 12h (%) Example 1 1451 99.97 93.2 Comparative Example 1 789 99.84 91.5 The present invention conducted a detailed analysis of the bromine complexation effect of the bifunctional additive in Example 1 during the actual operation of a membrane-free, anode-free zinc-bromine battery using various spectroscopic methods. First, the UV-Vis spectrum of the anolyte in Example 1 was analyzed. After the addition of the bifunctional additive, two absorption peaks appeared at 275 nm and 280 nm in the uncirculated electrolyte. The absorption rapidly decreased after 300 nm and returned to baseline levels. This was attributed to the E2 and B band absorptions of the aromatic ring. In contrast, no peaks were observed in the pure blank electrolyte of Comparative Example 1. Figure 1After performing 100 charge-discharge cycles on each of the two electrolyte groups, a characteristic peak of bromine species (at 265 nm) appeared in the electrolyte of Comparative Example 1, while no signal of bromine species was observed in Example 1. Figure 2 This demonstrates that bifunctional additives can effectively reduce cross-linking of bromine species on the anodic side after cycling.

[0047] Infrared spectroscopy of the cathode-side electrolyte ( Figure 3 Compared to Example 1, Comparative Example 1 showed C=C=C stretching vibration (2340 cm). - ¹), indicating that propylene carbonate (PC) is affected by polybrominated compounds (Br3). - Br5 - The bromine species were oxidized; compared with Comparative Example 1, the peak intensity associated with bromine species in Example 1 was also higher (400-550 cm⁻¹). - ¹), which confirms that the bromine species are effectively immobilized on the positive electrode side. Figure 4 ).

[0048] Raman spectroscopy of anolyte shows ( Figure 5 Compared with Comparative Example 1, Example 1 group was at 3500-4000 cm. -1 The peak intensity decreased significantly, indicating that the bifunctional additive reduced the activity of free water in the electrolyte. After 100 charge-discharge cycles, the peak intensity in Comparative Example 1 at 321 cm⁻¹ was significantly lower. -1 397 cm -1 and 452 cm -1 New peaks appeared at all locations, proving that bromine species crossover occurred on the anode side of Comparative Example 1, while it did not occur in Example 1 group. Figure 6 The Raman spectrum of the electrolyte on the negative electrode side after 100 cycles showed ( Figure 7 Compared with Example 1, Comparative Example 1 contained polybrominated compounds (Br3). - Br5 - The content was significantly higher (161cm). -1 ), and comparative example 1 at 450 cm -1 The peak intensity was lower than that of Example 1, indicating that the Br2 content in Comparative Example 1 was lower than that in Example 1. Raman spectroscopy confirmed that the bifunctional additive can effectively reduce the crossover of bromine species from the positive electrode side to the negative electrode side, while also reducing the conversion of polybrominates on the positive electrode side.

[0049] The morphology of the electrode sheets after different electrolyte cycles was analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Figures 8 to 9 The deposition morphology of graphite felt electrodes after 40 cycles in different electrolytes is shown. In Comparative Example 1, a large number of sharp dendrites adhere to the surface of the graphite felt electrode fibers after cycling in the electrolyte.Figure 8 In Example 1, the surface of the graphite felt current collector fiber after cycling in the electrolyte was smooth and free of dendrites. Figure 9 This is consistent with the results of three-dimensional optical profile scanning, which shows that on different substrate surfaces, bifunctional additive molecules can effectively promote smooth zinc metal deposition and inhibit the formation of zinc dendrites and dead zinc.

[0050] Figure 10 The XRD patterns of graphite felt immersed in the electrolytes of Example 1 and Comparative Example 1 for 30 days are shown. The XRD patterns of graphite felt electrodes after being cycled 40 times in the two groups of electrolytes show that the graphite felt in Example 1 group has a higher proportion of zinc deposition and contains less hydration byproducts, which proves that bifunctional additives can promote the effective deposition of zinc on carbon fiber surfaces.

[0051] like Figure 11 and Figure 12 As shown, at 10 mA / cm 2 At a current density of 1 V, the assembled membrane-free and anode-free zinc-bromine battery was operated with a discharge cutoff voltage of 1 V. The membrane-free battery in Example 1 operated stably for 1451 cycles (approximately 740 hours) and exhibited minimal efficiency fluctuations, with an average coulombic efficiency of 99.97%. In contrast, the battery in Comparative Example 1 only operated for 789 cycles (approximately 412 hours), less than two-thirds of the operating time of Example 1, and began to show drastic fluctuations in coulombic efficiency after 350 cycles. Figure 14 In the later stages of operation, the polarization voltage of the battery also increases continuously, and the battery stability deteriorates. Figure 13 It is speculated that the failure of the membrane-free and anode-free battery in Comparative Example 1 was caused by the oxidation of propylene carbonate due to the continuous generation of polybrominates on the positive electrode side, as well as the excessive formation of dead zinc on the surface of the current collector on the negative electrode side due to bromine cross-linking from the positive electrode side to the negative electrode side.

[0052] Due to the dual inhibitory effect of the bifunctional additive on the cross-linking of bromide species and the formation of dead zinc on the negative electrode surface in the membrane-free and anode-free battery, the self-discharge of the membrane-free and anode-free battery is also significantly suppressed. After 12 hours of rest, the capacity retention rate of the membrane-free and anode-free battery containing the bifunctional additive can still reach 93.2%, while that of the comparative example group is only 91.5%. Figure 15This paper compares the anode-side electrolytes of the membrane-free and anode-free zinc-bromine batteries of Example 1 and Comparative Example 1 after 200 cycles. The effectiveness of the bifunctional additive in suppressing polybromination cross-linking after long-term cycling was further verified using starch-potassium iodide test paper. As shown in the figure, after 200 cycles, the starch-potassium iodide test paper in the positive electrode electrolyte of Comparative Example 1 turned purple, confirming the presence of bromine species in the positive electrode electrolyte. In contrast, the positive electrode electrolyte of the membrane-free and anode-free zinc-bromine battery of Example 1 did not change color after the addition of starch-potassium iodide test paper. This further verifies the effective suppression of the cross-linking of bromine species from the positive electrode to the negative electrode by the bifunctional additive in the long-term cycling test of membrane-free and anode-free zinc-bromine batteries.

[0053] 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A membrane-free, anode-free zinc-bromine battery, characterized in that, Includes an open insulating container, a first graphite felt, and a second graphite felt; wherein, The first graphite felt serves as the positive electrode current collector, and the second graphite felt serves as the negative electrode current collector. The first graphite felt and the second graphite felt are disposed separately and independently inside the container, and are connected by a wire. The container contains an anolyte and a catholyte. The anolyte and the catholyte contain a bifunctional additive. The bifunctional additive can coexist in a first configuration and a second configuration in the electrolyte to inhibit the cross-linking of bromine species between the positive and negative electrodes.

2. The zinc-bromine battery according to claim 1, characterized in that, The preparation method of the bifunctional additive is as follows: 2-aminobenzimidazole is added to water and stirred until well mixed, and then an acidic reagent is added dropwise to carry out a protonation reaction to obtain the bifunctional additive. Preferably, the acidic reagent is dilute sulfuric acid; More preferably, the pH of the system after adding the acidic reagent is 4.0~4.

5.

3. The zinc-bromine battery according to claim 1, characterized in that, The cathode electrolyte is obtained by stirring and mixing a bifunctional additive, a conductive agent, and an organic solvent; and / or The conductive agent is Ketjen Black.

4. The zinc-bromine battery according to claim 3, characterized in that, In the cathode electrolyte, the concentration of the bifunctional additive is 45~55 mmol / L, and the concentration of the conductive agent is 8~12 g / L.

5. The zinc-bromine battery according to claim 1, characterized in that, The anolyte is obtained by mixing a composite electrolyte, a bifunctional additive, and water. The composite electrolyte is composed of zinc bromide and zinc sulfate.

6. The zinc-bromine battery according to claim 5, characterized in that, In the anolyte, the concentration of the bifunctional additive is 45-55 mmol / L, and the concentrations of zinc bromide and zinc sulfate are both 0.45-0.55 mol / L.

7. The zinc-bromine battery according to claim 3, characterized in that, The organic solvent is dichloromethane, carbon tetrachloride, or propylene carbonate; Preferably, the organic solvent is propylene carbonate.

8. A method for preparing a membrane-free, anode-free zinc-bromine battery according to any one of claims 1 to 7, characterized in that, The preparation method includes: (1) Add the composite electrolyte to water and mix well to obtain a blank electrolyte; add the bifunctional additive to the blank electrolyte and mix well to obtain an anolyte; (2) Add the conductive agent to the organic solvent and stir to mix well, then add the bifunctional additive and mix well to obtain the cathode electrolyte; (3) The anolyte and the cathode electrolyte are added to an open insulating container, and a first graphite felt and a second graphite felt are placed at both ends of the open insulating container as positive current collector and negative current collector, respectively. Then, the first graphite felt and the second graphite felt are connected by wires to obtain the membrane-free and anode-free zinc-bromine battery.

9. The preparation method according to claim 8, characterized in that, In step (3), the wire is a titanium wire; the diameter of the titanium wire is 2~4mm.

10. The preparation method according to claim 8, characterized in that, The conductor is covered with an insulating layer; the insulating layer is preferably Teflon tape.

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