Silk fibroin-based zinc-bromine flow battery separator material and preparation method and application thereof

Abstract

The application discloses a zinc-bromine flow battery diaphragm material based on silk fibroin and a preparation method and application thereof, and belongs to the technical field of electrochemical energy storage. Multiple synergistic optimization is realized through rich polar functional groups. The strong hydrophilicity improves the wettability of electrolyte, forms a uniform ion transmission interface, reduces the interface resistance and concentration polarization, and improves the energy efficiency. It can also form a coordination effect with bromine, inhibit bromine migration, and reduce self-discharge. The dense and flexible film can physically block zinc dendrite penetration, enhancing the safety of the diaphragm. At the same time, the molecular sponge structure of silk fibroin in the interface construction can guide the uniform distribution of zinc ions, promote the uniformization of current density, induce the smooth and dense deposition of zinc, reduce zinc dendrites and dead zinc, and improve the reversibility and utilization rate of the zinc negative electrode. In addition, it relieves bromine corrosion through physical barrier and chemical complexation, prolonging the service life of the diaphragm.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a zinc-bromine flow battery membrane material based on silk fibroin, its preparation method, and its application. Background Technology

[0002] Zinc-bromine flow batteries, as an important electrochemical energy storage technology, have broad application prospects in the field of large-scale energy storage due to their advantages such as high energy density, low cost, and long cycle life. However, their industrialization process has long been limited by the performance bottleneck of the separator material. As the core component of the battery, the separator needs to achieve ion conduction between the positive and negative electrodes while strictly blocking the cross-penetration of active materials. The separators in the existing technology are difficult to meet the stringent requirements of zinc-bromine battery system for high ion selectivity, high ion conductivity, and excellent mechanical and chemical stability at the same time. Specifically, they are as follows: (1) Insufficient bromine blocking ability and serious self-discharge problem: Commercial microporous separators (polypropylene, polyethylene separators) mainly rely on physical pore size sieving mechanism. However, the bromine element (Br2) and its complexed anions (such as Br3) generated during charging and discharging are not fully saturated. - (2) Due to their small size and high activity, they can easily penetrate the large pore structure of these separators and migrate from the positive electrode side to the negative electrode side. This will lead to two serious consequences: First, irreversible side reactions with the negative electrode zinc will occur, resulting in loss of active material and severe self-discharge, which will result in low battery coulombic efficiency (usually below 85%); Second, the shuttle of Br2 will continuously consume the negative electrode zinc, leading to rapid capacity decay and shortened cycle life; (3) During battery charging, zinc ions (Zn 2+ (3) The separator is exposed to a highly corrosive bromine (Br2) environment for a long time, which is the most severe challenge. The concentration of Br2 generated during charging increases, causing severe corrosion to the separator material. (4) Many separators have poor hydrophilicity, resulting in poor electrolyte wettability, high interfacial contact resistance, and slow ion transport. This will aggravate the concentration polarization of the battery and reduce voltage efficiency and power density. (5) The uneven distribution of the negative electrode electric field makes it easy for zinc to form dendrites when deposited, which can easily pierce the separator and cause battery short circuit, threatening safety and limiting cycle life (<500 times). Due to the above bottlenecks, zinc-bromine flow batteries have fallen into an industrialization dilemma.

[0003] To address these challenges, existing technologies have undergone some improvements. For example, ceramic membranes have been used to enhance bromine inhibition and thermal stability, but their inherent brittleness, high processing difficulty, and interfacial compatibility with electrolytes limit their application. Other studies have attempted to introduce materials such as metal-organic frameworks (MOFs) to improve bromine inhibition selectivity, but their mechanism of action remains primarily limited to physical sieving, and issues regarding the long-term chemical stability of these materials, their composite processing with the base membrane, and cost remain to be resolved.

[0004] Therefore, there is an urgent need to develop novel membrane materials that combine "high selectivity, high catalytic performance, high ion conductivity, and strong mechanical / chemical stability" to synergistically solve problems such as bromine shuttle, zinc dendrites, bromine corrosion, and interfacial transport. This is the key to breaking through the industrialization bottleneck of zinc-bromine flow batteries and is of great significance for improving the performance of zinc-bromine flow batteries and promoting their practical application. Summary of the Invention

[0005] To address the problems of traditional separators, such as poor bromine barrier capability leading to severe self-discharge and capacity decay, inability to suppress zinc dendrite growth posing short-circuit safety hazards, weak bromine corrosion resistance affecting cycle life, and poor hydrophilicity and low ionic conductivity resulting in high battery internal resistance and low energy efficiency, the main objective of this invention is to provide a zinc-bromine flow battery separator material based on silk fibroin, its preparation method, and its applications. This material achieves multiple synergistic optimizations through its abundant polar functional groups (-OH, -NH2, -COOH). Its strong hydrophilicity improves electrolyte wettability, forming a uniform ion transport interface, reducing interface resistance and concentration polarization, and improving energy efficiency. It can also form coordination with bromine, inhibiting bromine migration and reducing self-discharge. Its dense and flexible film can physically block zinc dendrite penetration, enhancing separator safety. Simultaneously, the "molecular sponge" structure constructed by silk fibroin at the interface can guide the uniform distribution of zinc ions, promoting uniform current density, inducing smooth and dense zinc deposition, reducing dendrite formation and the amount of "dead zinc," and improving the reversibility and utilization rate of the zinc anode. Furthermore, it mitigates bromine corrosion and extends membrane life through physical barrier and chemical complexation. Ultimately, it synergistically improves battery performance and cycle stability from multiple aspects, including wettability, conductivity, zinc dendrite inhibition, bromine inhibition, and corrosion resistance.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a zinc-bromine flow battery separator based on silk fibroin, comprising: Microporous membrane substrate; and silk fibroin functional layer; The silk fibroin functional layer is attached to the surface of the microporous membrane substrate and the inner wall of its pores; the silk fibroin functional layer contains silk fibroin molecules.

[0007] The silk fibroin molecules are derived from degummed silk, and their molecular chains are rich in at least one of the polar functional groups, including hydroxyl, amino, and carboxyl groups. The silk fibroin functional layer, through its polar functional groups, forms an interface layer on the negative electrode side of the composite membrane that can adsorb and homogenize the zinc ion flow, thereby inhibiting the growth of zinc dendrites. It also has the function of inducing uniform zinc deposition, thus doubly solving the two core problems of bromine shuttle and zinc dendrite formation.

[0008] The silk fibroin functional layer has zinc-loving properties, which are used to adsorb and homogenize the distribution of zinc ions.

[0009] Preferably, the mass of silk fibroin in the silk fibroin functional layer accounts for 0.5% to 5% of the total mass of the zinc-bromine flow battery separator. This ensures that the silk fibroin can fully modify the inner wall of the pores to form an effective functional layer, while avoiding excessive blockage of the micropores. This significantly improves the bromine barrier and dendrite suppression performance, while maximizing the maintenance of the separator's high ionic conductivity and avoiding a surge in battery internal resistance due to modification.

[0010] The silk fibroin functional layer has a β-sheet crystalline structure, which physically blocks the penetration of zinc dendrites. The β-sheet structure endows the functional layer with excellent mechanical strength and structural stability, ensuring its durability under long-term cycling and dendrite impact.

[0011] Preferably, the silk fibroin functional layer forms a continuous or semi-continuous impregnation-filling structure within the pores of the microporous membrane substrate. This impregnation-filling morphology, which is tightly bonded to the substrate, significantly increases the functional interface area, making the "chemical anchoring" and "ion regulation" effects more efficient and uniform, and avoiding the coating peeling or uneven coverage problems that may exist in simple surface coating.

[0012] This invention provides a method for preparing the above-mentioned zinc-bromine flow battery separator based on silk fibroin, comprising the following steps: The pretreated microporous membrane substrate was immersed in a silk fibroin solution; The impregnated microporous membrane substrate is dried to fix the silk fibroin onto the microporous membrane substrate, forming a silk fibroin functional layer.

[0013] The silk fibroin solution has a mass fraction of 2% to 10%.

[0014] Preferably, the solvent is water.

[0015] The soaking time is 2 hours to 6 hours.

[0016] The drying temperature is 40℃~60℃.

[0017] This invention provides the application of the above-mentioned zinc-bromine flow battery separator based on silk fibroin in the preparation of zinc-bromine flow batteries.

[0018] The present invention provides a zinc-bromine flow battery, comprising a positive electrode, a negative electrode, an electrolyte, and a zinc-bromine flow battery separator based on silk fibroin, wherein the separator is located between the positive electrode and the negative electrode.

[0019] Compared with the prior art, the present invention achieves the following technical effects: The zinc-bromine flow battery separator based on silk fibroin provided by this invention constructs a silk fibroin functional layer in situ on a microporous membrane substrate. This functional layer utilizes the polar functional groups (-OH, -NH2, -COOH) abundant in silk fibroin molecules to react with bromide ions (Br2) in the electrolyte. - ) and polybrominated complexes (such as Br3) - Specific chemical interactions (such as hydrogen bonding and coordination) occur, achieving chemical anchoring of bromine species. This fundamentally changes the traditional bromine-blocking mechanism of separators that relies on physical pore size sieving, achieving efficient and selective inhibition of bromine shuttle at the molecular level for the first time. Experimental data show that the coulombic efficiency of batteries using this composite separator is significantly improved from 91.2% in the comparative example (unmodified separator) to over 96%, effectively solving the core bottleneck problem of severe self-discharge and low coulombic efficiency caused by bromine permeation in zinc-bromine flow batteries, while maintaining good ionic conductivity.

[0020] Furthermore, the silk fibroin functional layer not only possesses chemical bromine barrier properties, but its strong hydrophilicity and abundant polar functional groups also enable the construction of a dynamic molecular sponge interface layer at the membrane interface facing the negative electrode. This interface layer can uniformly adsorb and redistribute the zinc ion flow, eliminating the ion concentration gradient and electric field "sharp effect" on the electrode surface, thereby guiding the uniform and smooth deposition of zinc ions from the nucleation source. This "chemically induced uniform deposition" mechanism, combined with the physical barrier toughness of the functional layer itself, forms a dual guarantee against zinc dendrite growth and puncture, greatly improving the cycle safety and lifespan of the battery.

[0021] The present invention provides a method for preparing a composite separator for zinc-bromine flow batteries. Through a simplified "immersion-drying" process, it achieves in-situ functionalization modification of the microporous separator substrate, ensuring the natural activity and suitable molecular weight of silk fibroin molecules, and optimizing their loading, penetration depth, and crystal morphology in the microporous substrate. This method is compatible with mainstream commercial separators such as PP, PE, and Celgard, without requiring modification to existing production lines. By controlling parameters such as solution concentration and soaking time, uniform adsorption and distribution of silk fibroin molecules within the pores are achieved. Compared to complex multilayer coating or composite processes, this method has fewer steps, lower energy consumption, and higher raw material utilization.

[0022] The application provided by this invention, using the composite separator described herein in zinc-bromine flow batteries, can simultaneously and synergistically solve multiple technical challenges such as bromine shuttle, zinc dendrite formation, high interfacial resistance, and bromine corrosion of the separator. The battery, integrating the above-mentioned technical effects, exhibits high coulombic efficiency, high energy efficiency, excellent cycle stability, and significantly improved safety. Its overall performance far surpasses that of zinc-bromine batteries using traditional separators, providing a highly promising high-performance battery solution for large-scale energy storage. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0024] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products. In this invention, unless otherwise specified, all experimental materials used are commercially available commodities well-known to those skilled in the art.

[0025] The microporous membrane substrate used in this invention was purchased from Shanghai Dinghao New Material Technology Co., Ltd., model Celgard®2400, with a thickness of 25μm.

[0026] This invention provides a zinc-bromine flow battery membrane material based on silk fibroin, and the specific preparation process is as follows: Step 1, Pretreatment of the microporous membrane Immerse the microporous membrane in ethanol or deionized water and place it in an ultrasonic cleaner. Clean it with 300W ultrasonic power for 15-30 minutes to remove impurities and contaminants from the surface. Remove the cleaned membrane, gently absorb excess liquid from the surface with filter paper, and then transfer it to a vacuum drying oven to dry at 40℃-60℃ for 12-24 hours for later use.

[0027] Step 2, prepare silk fibroin solution Weigh 10g of natural silk and place it in 500mL of 0.02mol / L sodium carbonate solution. Boil at 100℃ for 30 minutes, repeating the boiling process twice. Rinse the silk repeatedly with hot deionized water at 60℃-80℃ until the washing solution is clear. Dry the obtained pure silk fibroin fiber at 50℃ for 6-12 hours to obtain silk fibroin fiber. Cut the dried silk fibroin fiber into small pieces, and weigh 7g of silk fibroin fiber to dissolve in 60-65mL of 9.3mol / L lithium bromide aqueous solution. Stir magnetically in a water bath at 40-60℃ for 3-4 hours until the silk fibroin fibers are completely dissolved, forming a golden-yellow, viscous, transparent silk fibroin / lithium bromide solution. After cooling to room temperature, transfer the silk fibroin / lithium bromide solution into a dialysis bag (molecular weight cutoff 8-14 kDa) and dialyze against deionized water at 4℃. Change the deionized water every 6 hours and continue dialysis for at least 72 hours. Use silver nitrate solution to test the external dialysate until no white silver bromide precipitate forms, indicating that Br... - Ions have been completely removed; remove the dialysis bag from the water and place it in a dry container. Cover the bottom of the container and around the dialysis bag with polyethylene glycol powder of molecular weight 20,000. Let it stand at 4°C. The polyethylene glycol powder will absorb moisture. Replace the polyethylene glycol powder and shake the dialysis bag every 12 hours until the solution volume is reduced to 50 mL. Take a known weight of the concentrate and weigh its wet weight (W). wet After drying to constant weight, weigh the residue (W). dry The mass fraction (C) of silk fibroin is measured. The formula for calculating the mass fraction (C) of silk fibroin is: C(%) = (W / W) dry / W wet ()×100%. Based on the calculation results, the concentrate was precisely diluted with deionized water to prepare silk fibroin solutions with mass fractions of 2%, 4%, 6%, 8%, and 10%, respectively, with a total volume of 10 mL. These solutions were then sealed and stored at 4℃ for subsequent membrane modification.

[0028] Step 3: Preparation of silk fibroin-modified zinc-bromine flow battery membrane material The pretreated and dried microporous membrane from step 1 is slowly immersed in the silk fibroin solution from step 2, ensuring complete immersion and no air bubbles adhering to the surface. After standing and soaking at room temperature for 2-6 hours, the silk fibroin molecules are fully penetrated and physically adsorbed onto the inner wall and surface of the membrane pores. The immersed microporous membrane is then transferred to a vacuum drying oven and vacuum dried at 40-60℃ for 6-12 hours to completely remove residual solvent and water molecules, forming a zinc-bromine flow battery membrane based on silk fibroin.

[0029] The technical solution of the present invention will be described in detail below with reference to specific embodiments, and the conditions of the specific embodiments are shown in Table 1.

[0030] Table 1: Synthesis conditions of membrane materials in different embodiments

[0031] (I) Specific Examples of Zinc-Bromine Flow Battery Membrane Materials Based on Silk Fibroin Example 1 This embodiment provides a zinc-bromine flow battery membrane material based on silk fibroin, and the specific preparation process is as follows: Step 1, Pretreatment of the microporous membrane Take a commercial polypropylene microporous membrane (Celgard®2400), cut it to a size of 10 cm × 10 cm; immerse it in ethanol or deionized water and ultrasonically clean it at 300W for 30 min to remove impurities and contaminants from the surface, and then dry it in a vacuum drying oven at 50°C for 24 hours for later use.

[0032] Step 2, prepare silk fibroin solution Weigh 10g of natural silk and place it in 500mL of 0.02mol / L sodium carbonate solution. Boil at 100℃ for 30 minutes, repeating the boiling process twice. Rinse the silk repeatedly with hot deionized water at 60℃-80℃ until the washing solution is clear. Dry the obtained pure silk fibroin fibers. Cut the dried silk fibroin fibers into small pieces. Weigh 7g of silk fibroin fibers and dissolve them in 65mL of 9.3mol / L lithium bromide aqueous solution. Stir magnetically in a 40℃ water bath for 4 hours until the silk fibroin fibers are completely dissolved, forming a golden-yellow, viscous, transparent silk fibroin / lithium bromide solution. After cooling to room temperature, place the silk fibroin / lithium bromide solution into a dialysis bag (molecular weight cutoff 10kDa) and dialyze in deionized water at 4℃, changing the deionized water every 6 hours for 72 hours. Use silver nitrate solution to test the external dialysate until no white silver bromide precipitate forms, indicating that Br... - Ions have been completely removed; remove the dialysis bag from the water and place it in a dry container. Cover the bottom of the container and the dialysis bag with polyethylene glycol powder of molecular weight 20,000. Let it stand at 4°C. The polyethylene glycol powder absorbs moisture. Replace the polyethylene glycol powder and shake the dialysis bag every 12 hours until the solution volume is reduced to 50 mL. Take 5 mL of the concentrated solution, weigh it, and dry it. Weigh the residue again after drying and measure the mass fraction. Prepare a 10 mL silk fibroin solution with a mass fraction of 2% using deionized water. Store it in a sealed container at 4°C for subsequent dialysis membrane modification.

[0033] Step 3: Preparation of silk fibroin-modified zinc-bromine flow battery membrane material The pretreated and dried microporous membrane from step 1 was immersed in 10 mL of a 2% (w / w) silk fibroin solution at room temperature for 4 hours to allow the silk fibroin molecules to fully penetrate and physically adsorb onto the inner wall and surface of the membrane pores. The immersed microporous membrane was then transferred to a vacuum drying oven and dried at 40°C for 12 hours to obtain a zinc-bromine flow battery membrane material based on silk fibroin.

[0034] Example 2 This embodiment differs from Embodiment 1 in that the pretreated microporous membrane is immersed in a 10 mL solution of 4% silk fibroin for 4 hours, and then the immersed microporous membrane is placed in a vacuum drying oven and dried at 40°C for 12 hours to obtain a zinc-bromine flow battery membrane material based on silk fibroin.

[0035] Example 3 This embodiment differs from Embodiment 1 in that the pretreated microporous membrane is immersed in a 10 mL volume of a 6% silk fibroin solution for 4 hours, and then the immersed microporous membrane is placed in a vacuum drying oven and dried at 40°C for 12 hours to obtain a zinc-bromine flow battery membrane material based on silk fibroin.

[0036] Example 4 This embodiment differs from Embodiment 1 in that the pretreated microporous membrane is immersed in 10 mL of a silk fibroin solution with a mass fraction of 8% for 4 hours. The immersed microporous membrane is then placed in a vacuum drying oven and dried at 40°C for 12 hours to obtain a zinc-bromine flow battery membrane material based on silk fibroin.

[0037] Example 5 This embodiment differs from Embodiment 1 in that the pretreated microporous membrane is immersed in 10 mL of a 10% silk fibroin solution for 4 hours, and then the immersed microporous membrane is placed in a vacuum drying oven and dried at 40°C for 12 hours to obtain a zinc-bromine flow battery membrane material based on silk fibroin.

[0038] Example 6 This embodiment differs from Embodiment 1 in that the pretreated microporous membrane is immersed in 10 mL of a silk fibroin solution with a mass fraction of 8% for 2 hours. The immersed microporous membrane is then placed in a vacuum drying oven and dried at 40°C for 12 hours to obtain a zinc-bromine flow battery membrane material based on silk fibroin.

[0039] Example 7 This embodiment differs from Embodiment 1 in that the pretreated microporous membrane is immersed in 10 mL of a silk fibroin solution with a mass fraction of 8% for 6 hours. The immersed microporous membrane is then placed in a vacuum drying oven and dried at 40°C for 12 hours to obtain a zinc-bromine flow battery membrane material based on silk fibroin.

[0040] Example 8 This embodiment differs from Embodiment 1 in that the pretreated microporous membrane is immersed in 10 mL of a silk fibroin solution with a mass fraction of 8% for 6 hours. The immersed microporous membrane is then placed in a vacuum drying oven and dried at 50°C for 12 hours to obtain a zinc-bromine flow battery membrane material based on silk fibroin.

[0041] Example 9 This embodiment differs from Embodiment 1 in that the pretreated microporous membrane is immersed in 10 mL of a silk fibroin solution with a mass fraction of 8% for 6 hours. The immersed microporous membrane is then placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain a zinc-bromine flow battery membrane material based on silk fibroin.

[0042] (ii) Performance Testing Microporous membrane: Commercial polypropylene microporous membrane (Celgard® 2400), 25 μm thick. Battery testing system: Blue Battery testing system (CT2001A), with a self-made zinc-bromine flow battery single-cell fixture. Electrode materials: Both positive and negative electrodes are 3 mm thick graphite felt (5 cm × 5 cm area), ultrasonically cleaned and dried with acetone and deionized water before use. Electrolyte: Negative electrode electrolyte: 1.0 M ZnBr2 + 2.0 M KBr + 0.1 M KCl aqueous solution. Positive electrode electrolyte: Same composition as the negative electrode electrolyte, with the addition of a small amount of bromine complexing agent (such as N-ethyl-N-methylmorpholine bromide) to initially contain a small amount of Br2. Silk fibroin: Prepared and concentrated according to the method described in Example 1, for later use.

[0043] Comparative Example 1: A Celgard® 2400 separator of the same specifications was used, and the same pretreatment steps as in the examples were performed (ethanol washing, vacuum drying at 50°C for 24 hours), without silk fibroin modification, serving as a blank control. Battery performance tests were conducted using a microporous separator, with the membrane pretreatment consistent with the examples described above. The measured coulombic efficiency was 91.2%, voltage efficiency was 83.4%, and energy efficiency was 75.06%.

[0044] To test the performance of the zinc-bromine flow battery membrane materials in Examples 1-9 and Comparative Example 1, conventional electrode materials and electrolyte systems for zinc-bromine flow batteries were used, and the batteries were assembled in the order of "negative electrode graphite felt - separator - positive electrode graphite felt". Charge-discharge tests were performed on a battery testing system with a charge-discharge rate of 20 mA / cm². 2 The charging time was 2 hours, the test temperature was 25℃, and the coulombic efficiency (C) was [not specified]. E = (Discharge capacity / Charge capacity) × 100%; Voltage efficiency (V) E = (Average discharge voltage / Average charging voltage) × 100%; Energy efficiency (EE) = C E ×V E / 100%, the test results are shown in Table 2.

[0045] Table 2: Comparison of electrochemical performance of zinc-bromine flow batteries under different implementation conditions

[0046] As can be seen from Table 2, Examples 1-9 all showed better electrochemical performance data than Comparative Example 1, indicating that the silk fibroin-modified microporous membrane has better electrochemical performance than the unmodified microporous membrane when used as a membrane for zinc-bromine flow batteries. This shows that silk fibroin helps to improve the energy efficiency, coulombic efficiency, and voltage efficiency of zinc-bromine flow batteries, indicating that the silk fibroin-modified microporous membrane has a significant impact on improving bromine barrier capacity, reducing battery internal resistance, improving conductivity, reducing dead zinc, and inhibiting zinc dendrite formation.

[0047] Comparing Examples 1-5 and Comparative Example 1, when silk fibroin solutions of different mass fractions were used to modify the separator of zinc-bromine flow batteries, the batteries exhibited better electrochemical performance data. Among them, the energy efficiency, voltage efficiency, and coulombic efficiency of the batteries modified with silk fibroin solution were all higher than those of the unmodified batteries. Its mechanism of action can be summarized as follows: (1) Dual-effect synergistic bromine inhibition: Silk fibroin can inhibit the side effects of bromine at the positive electrode through dual-effect synergy. Through its rich polar functional groups (-OH, -NH2, -COOH), on the one hand, it reacts with bromide ions and complexes (Br3) - Br5 - (2) Inducing uniform zinc deposition: Silk fibroin constructs a layer of "molecular sponge" rich in zinc-loving sites at the separator-negative electrode interface. Its strong hydrophilicity and polar functional groups can uniformly adsorb and distribute zinc ions (Zn) 2+), avoiding local ion concentration from the source. This uniform ion distribution directly promotes the homogenization of current density on the electrode surface, further eliminating the "tip effect" that leads to dendrite growth, and guiding zinc ions to be uniformly reduced throughout the electrode surface, thereby fundamentally inhibiting the initial formation and growth of zinc dendrites, and greatly improving the safety and cycle stability of the battery. (3) Optimizing ion transport: The strong hydrophilicity of silk fibroin allows it to quickly and completely wet the electrolyte, eliminating "dry spots" and "cavitation" on the membrane and electrode surfaces, and greatly increasing the effective electrochemical contact area; at the same time, the hydrophilic layer forms a continuous ion transport network in the membrane channels, promoting rapid ion conduction and increasing the ion transport number. The combined effect of the two significantly reduces the overall internal resistance and concentration polarization of the battery, thereby directly improving the voltage efficiency and energy efficiency of the battery. (4) Enhanced mechanical protection: The β-sheet structure of silk fibroin itself endows the functional layer with excellent mechanical strength and flexibility, which can physically block the possible zinc dendrite puncture and prevent internal short circuit caused by membrane damage; at the same time, the zinc deposition layer induced by it has a flat and dense lamellar structure, which not only improves the reversibility of zinc deposition / dissolution reaction and reduces "dead zinc" that does not participate in the reaction, but also improves the utilization rate of zinc anode and battery energy density.

[0048] Compared with Examples 1-5, Example 4 showed better electrochemical performance, indicating that increasing the concentration of silk fibroin has a significant impact on the electrochemical performance data of the battery. However, when the concentration is too high, the silk fibroin solution is too viscous and difficult to penetrate into the internal pores of the separator. It is easy to form an excessively thick coating on the surface, which blocks the pores and leads to a decrease in ionic conductivity.

[0049] Compared with Examples 4 and 6-7, Example 7 showed better electrochemical performance, indicating that increasing the soaking time of the separator in the silk fibroin solution has a significant impact on the battery electrochemical performance data. Extending the soaking time allows the silk fibroin to be more fully and uniformly adsorbed and penetrated into the separator pores and surface, forming a denser and more stable functional coating, thereby improving its bromine barrier, dendrite inhibition and interface regulation performance.

[0050] Compared with Examples 7-9, Example 7 exhibits superior electrochemical performance, indicating that lowering the drying temperature of the silk fibroin-modified separator has a significant impact on the battery's electrochemical performance data. Lowering the drying temperature of the silk fibroin-modified separator can significantly regulate the crystallization kinetics of the silk fibroin molecular chains, allowing them more time for molecular rearrangement and self-assembly during the slow evaporation of moisture. This results in a functional coating with moderate β-sheet crystallinity, a more uniform structure, better flexibility, and stronger adhesion to the substrate. This structure avoids problems such as microcracks, interface desorption, and pore inlet blockage that are easily caused by high-temperature rapid drying, enabling the modified separator to exhibit superior overall electrochemical performance in the battery: on the one hand, the denser and more complete coating can effectively suppress bromine species shuttle, significantly improving coulombic efficiency; on the other hand, the uniform and pore-preserving coating structure can guide the uniform distribution of zinc ions and inhibit dendrite growth while achieving efficient ion transport, thereby significantly extending cycle life, improving rate performance, and keeping the increase in internal resistance at a low level.

[0051] This invention successfully prepared a series of high-performance zinc-bromine flow battery composite membranes by optimizing the concentration of silk fibroin solution, impregnation time, and drying temperature. Among them, the modified membrane prepared by soaking in an 8% (w / w) silk fibroin solution for 6 hours and then vacuum drying at 40°C for 12 hours (Example 7) exhibited the best overall performance, with an energy efficiency as high as 84.14%, which is more than 8 percentage points higher than that of the unmodified membrane (76.06%), significantly improving the energy storage efficiency and practicality of zinc-bromine flow batteries.

[0052] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A zinc-bromine flow battery separator based on silk fibroin, characterized in that, Including a microporous membrane substrate; and a silk fibroin functional layer; The silk fibroin functional layer is attached to the surface of the microporous membrane substrate and the inner wall of its pores; The silk fibroin functional layer contains silk fibroin molecules.

2. The zinc-bromine flow battery separator based on silk fibroin according to claim 1, characterized in that, The silk fibroin molecules are derived from degummed silk, and their molecular chains are rich in at least one of the polar functional groups, including hydroxyl, amino, and carboxyl groups.

3. The zinc-bromine flow battery separator based on silk fibroin according to claim 1, characterized in that, The silk fibroin functional layer has zinc-loving properties, which are used to adsorb and homogenize the distribution of zinc ions.

4. The zinc-bromine flow battery separator based on silk fibroin according to claim 1, characterized in that, The silk fibroin functional layer has a β-sheet crystalline structure.

5. A method for preparing a zinc-bromine flow battery separator based on silk fibroin according to any one of claims 1-4, characterized in that, Includes the following steps: The pretreated microporous membrane substrate was immersed in a silk fibroin solution; The impregnated microporous membrane substrate is dried to fix the silk fibroin onto the microporous membrane substrate, forming a silk fibroin functional layer.

6. The method for preparing a zinc-bromine flow battery separator based on silk fibroin according to claim 5, characterized in that, The silk fibroin solution has a mass fraction of 2% to 10%.

7. The method for preparing a zinc-bromine flow battery separator based on silk fibroin according to claim 5, characterized in that, The soaking time is 2 hours to 6 hours.

8. The method for preparing a zinc-bromine flow battery separator based on silk fibroin according to claim 5, characterized in that, The drying temperature is 40℃~60℃.

9. The application of the zinc-bromine flow battery separator based on silk fibroin as described in any one of claims 1-4 in the preparation of zinc-bromine flow batteries.

10. A zinc-bromine flow battery, characterized in that, The battery includes a positive electrode, a negative electrode, an electrolyte, and a zinc-bromine flow battery separator based on silk fibroin as described in any one of claims 1 to 4, wherein the separator is located between the positive electrode and the negative electrode.

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