Nano-silica modified porous membrane and preparation method and application in zinc-bromine flow battery

Abstract

The present invention discloses a nano-silica modified porous membrane, a preparation method and an application in a zinc-bromine flow battery, belonging to the technical field of battery separator materials. An organic alkoxysilane is mixed with an organic solvent, and then deionized water and an ammonia solution are added. After stirring and mixing, the solvent is removed and dried to obtain nano-silica; the nano-silica is then ultrasonically dispersed in a dispersant to obtain a nano-silica dispersion; the pretreated porous membrane is immersed in the nano-silica dispersion until the nano-silica is evenly loaded on the surface of the porous membrane, and after secondary vacuum drying, the nano-silica modified porous membrane is obtained. Nano-silica is synthesized by a sol-gel method and uniformly loaded on the surface of the porous membrane by ultrasonic dispersion and impregnation process to form a modified layer with size screening effect and surface negative charge characteristics. The diffusion of bromide ions is suppressed by electrostatic repulsion, self-discharge and side reactions are reduced, and coulomb efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery separator materials, and in particular relates to a nano-silica modified porous membrane, a preparation method thereof, and an application thereof in a zinc-bromine liquid flow battery. Background Art

[0002] Large-scale energy storage technology is crucial for ensuring a stable energy supply, improving energy efficiency, and promoting sustainable development. Zinc-bromine flow batteries, as a highly promising new energy storage technology, offer numerous significant advantages. Their relatively high energy density allows them to store more energy within a limited space, making them ideal for space-constrained energy storage scenarios. The abundant and low-cost raw materials of zinc and bromine ensure the economic viability of large-scale energy storage system construction. Their aqueous electrolyte system provides excellent safety, avoiding the safety hazards of organic electrolytes. Their long service life reduces the frequency of battery replacement and maintenance costs. Their environmentally friendly nature aligns with the development trend of green energy. Therefore, zinc-bromine flow batteries present broad application prospects in large-scale energy storage. In the structure of zinc-bromine flow batteries, the separator plays a core role in separating the positive and negative electrodes, preventing bromine diffusion, and facilitating ion transport. Its performance directly impacts the overall performance and service life of the battery. Developing high-performance separator materials is key to promoting the commercialization of zinc-bromine flow batteries.

[0003] To improve separator performance, researchers primarily use physical and chemical modification methods. For physical modification, polymer coatings on the separator surface are a common approach. For example, coating with polymers such as polyvinylidene fluoride (PVDF) can enhance the separator's mechanical properties, enabling it to withstand greater pressure and stress during battery assembly and operation, reducing the risk of breakage. Chemical modification focuses on altering the separator's surface chemical properties through chemical reactions. Adding inorganic particles to the separator is a typical approach. For example, inorganic particles such as silica and titanium dioxide utilize their large surface area and rich pore structure to increase ion transport channels, enhance ion migration rates, and enhance the separator's tolerance to electrolytes. However, these modification techniques still present numerous challenges. While polymer coatings can improve mechanical properties, they are ineffective in enhancing ion selectivity and suppressing zinc dendrite formation. Poor ion selectivity can lead to the migration of impurity ions, triggering side reactions within the battery, reducing charge / discharge and energy conversion efficiency. Furthermore, zinc dendrite growth cannot be effectively suppressed, and dendrites can pierce the separator, causing short circuits and threatening battery safety and lifespan. Furthermore, polymer coatings increase ion transport resistance, leading to increased internal resistance in the battery, increased heat generation, and reduced energy and coulombic efficiency. When inorganic particles are added to modify the separator, the inorganic particles have poor dispersion and tend to agglomerate within the separator matrix, forming particle clusters. This makes the separator pore structure uneven, increases ion transport resistance, reduces transport efficiency, affects battery current distribution, and accelerates aging. Furthermore, the inorganic particles lack sufficient bonding strength with the separator matrix, making them prone to falling off during long-term battery operation. They can deposit within the battery, blocking ion channels and even causing short circuits, severely impacting the stability and service life of the separator and hindering the commercialization of zinc-bromine flow batteries.

[0004] A Chinese patent application with publication number CN119153742A discloses a puncture-resistant zinc-bromine flow battery membrane, a preparation method, and its application. It uses two inorganic nanoparticles, a first nanoparticle and a second nanoparticle, as pore-forming agents, but does not clearly solve the problem of poor particle dispersibility. A Chinese patent application with publication number CN107170941B discloses a method for preparing a lithium-air battery nanocomposite membrane. For lithium-air batteries, it solves the problems of lithium negative electrode corrosion and positive-negative electrode interaction caused by moisture / oxygen penetration, and extends the cycle life by the chemical isolation function of the polyurethane coating and the filling of pores with nano-silica. A double-layer composite structure is adopted, and the polyurethane layer provides chemical isolation to block moisture / oxygen, but increases the interfacial impedance, increases the polarization voltage, and the charging voltage is as high as 4.8V. A high-concentration dispersion and multiple immersion-high-temperature drying are used, and the polyurethane coating needs to be repeated three times, which makes the process complicated.

[0005] In view of the problems of poor ion selectivity and limited zinc dendrite suppression ability of traditional zinc-bromine flow battery membranes, poor dispersion and weak bonding of inorganic particles in existing modification technologies, it is necessary to find a nano-silica modified porous membrane and its preparation method and application in zinc-bromine flow batteries to improve the overall performance and service life of zinc-bromine flow batteries. Summary of the Invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a nano-silica modified porous membrane and a preparation method and application in zinc-bromine liquid flow batteries, so as to solve the technical problems of poor ion selectivity of existing zinc-bromine liquid flow battery membranes, limited zinc dendrite inhibition ability, poor dispersion of inorganic particles in the membrane and weak binding.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention discloses a method for preparing a nano-silica modified porous membrane, comprising the following steps:

[0009] Mixing organic alkoxysilane with an organic solvent, then adding deionized water and an ammonia solution, stirring and mixing, removing the solvent and drying to obtain nano-silicon dioxide; then ultrasonically dispersing the nano-silicon dioxide in a dispersant to obtain a nano-silicon dioxide dispersion;

[0010] The pretreated porous membrane is immersed in a nano-silica dispersion until the nano-silica is evenly loaded on the surface of the porous membrane, and then vacuum-dried twice to obtain a nano-silica modified porous membrane;

[0011] Nano-silica modified porous membrane as separator material for zinc-bromine flow battery.

[0012] Preferably, the usage ratio of the organoalkoxysilane, the organic solvent, the deionized water and the ammonia solution is (8-10) g: (150-250) mL: (8-10) mL: (8-10) mL.

[0013] Preferably, the organic alkoxysilane includes ethyl orthosilicate or tetrapropoxysilane; the organic solvent includes methanol, ethanol, isopropanol or acetone; and the mass percentage of the ammonia solution is 25-28 wt %.

[0014] Preferably, the stirring and mixing reaction conditions are: stirring and mixing reaction at room temperature for 3 to 6 hours; and the drying conditions are: drying at 60 to 80° C. for 6 to 48 hours.

[0015] Preferably, the pretreatment conditions of the pretreated porous membrane include: ultrasonically cleaning the porous membrane with at least one of methanol, ethanol, isopropanol, acetone and deionized water, and then vacuum drying to obtain the pretreated porous membrane;

[0016] The ultrasonic cleaning time is 15~30min; the vacuum drying conditions are: vacuum drying at 40~60℃ for 12~24h.

[0017] Preferably, the ultrasonic dispersion conditions include: ultrasonic dispersion at an ultrasonic power of 300-400 W for 10-60 min;

[0018] The dispersant is at least one of ethanol and isopropanol;

[0019] The mass concentration of the nano-silica dispersion is 10~20 mg / mL.

[0020] Preferably, the porous membrane includes polyvinylidene fluoride, polypropylene, polyethylene, polyolefin composite membrane or glass fiber membrane; and the soaking time is 15 to 60 minutes.

[0021] Preferably, the secondary vacuum drying conditions are: vacuum drying at 60-80° C. for 6-12 hours.

[0022] The invention also discloses a nano-silicon dioxide modified porous membrane, which is prepared by adopting the above-mentioned preparation method of the nano-silicon dioxide modified porous membrane.

[0023] The present invention also discloses the use of the nano-silica modified porous membrane prepared by the preparation method of the nano-silica modified porous membrane in a zinc-bromine flow battery. The nano-silica modified porous membrane is used as a diaphragm material for the zinc-bromine flow battery. The zinc-bromine flow battery assembled from the nano-silica modified porous membrane has a coulombic efficiency of 95.4% to 97.2%; a voltage efficiency of 86.1% to 88.3%; and an energy efficiency of 82.6% to 85.4%.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention discloses a method for preparing a nano-silica-modified porous membrane. Nano-silica is synthesized by a sol-gel method, and ultrasonic dispersion and impregnation processes are used to achieve uniform loading of nano-silica particles in the porous membrane, avoiding the membrane structural heterogeneity caused by uneven dispersion in the prior art. Existing pore-forming agents, while containing regular pore structures, are not optimized for the size screening and charge characteristics of bromide ions. The present invention significantly reduces bromine permeability by leveraging the size screening effect and surface negative charge characteristics of nano-silica. This method addresses the problems of poor ion selectivity, high bromine permeability, zinc dendrite growth, and insufficient long-term cycling stability in zinc-bromine flow battery membranes. The size screening and surface negative charge characteristics of nano-silica achieve efficient bromide ion blocking and uniform zinc deposition. A single layer of nano-silica is used to modify the porous membrane, without the introduction of an additional polymer coating. The uniform loading of nanoparticles improves ion selectivity while maintaining low transmission resistance and keeping the polarization voltage essentially unchanged. Modifying the porous membrane with nano-silica improves the membrane's ion selectivity and reduces bromine diffusion while maintaining good ion transport properties, thereby enhancing the energy efficiency of zinc-bromine flow batteries. This enhanced membrane's ability to suppress zinc dendrite growth extends the cycle life of zinc-bromine flow batteries, improving their safety and stability. Furthermore, this method features a relatively simple and cost-effective preparation process, making it suitable for large-scale industrial production.

[0026] Furthermore, the ratio of organoalkoxysilane, organic solvent, deionized water, and aqueous ammonia solution is (8-10) g: (150-250) mL: (8-10) mL: (8-10) mL. This ratio, determined through extensive experimental exploration, is the optimal ratio and ensures sufficient hydrolysis and polycondensation of the organoalkoxysilane in the organic solvent. In the initial stages of the reaction, an appropriate amount of deionized water promotes the hydrolysis of the organoalkoxysilane, generating silanol monomers. The aqueous ammonia solution, acting as a catalyst and appropriately proportioned to the organoalkoxysilane, precisely regulates the rates of the hydrolysis and polycondensation reactions, ensuring a smooth and orderly reaction, avoiding agglomeration of the nanosilica particles due to an overly rapid reaction or reduced production efficiency due to an overly slow reaction. This specific ratio contributes to the formation of nanosilica particles with uniform particle size and good dispersion. Uniform particle size is crucial for subsequent loading in the porous membrane. It can ensure that the nanoparticles are evenly distributed on the membrane surface, give full play to the size screening effect, effectively block bromine molecules, and at the same time reduce the obstruction to zinc ion transmission, significantly improve the ion selectivity of the membrane, and thus improve the energy efficiency of the zinc-bromine flow battery.

[0027] Furthermore, tetraethyl orthosilicate or tetrapropoxysilane was selected as the organoalkoxysilane, both of which have unique chemical structures and reactivity. The silica generated by the hydrolysis of tetraethyl orthosilicate has a high specific surface area and good chemical stability, providing abundant active sites for the modified layer and enhancing its interaction with the porous membrane. Under specific conditions, tetrapropoxysilane can form nanosilica with a unique pore structure, which helps optimize the pore structure of the modified layer and further improve ion selectivity. Furthermore, these two raw materials are widely available and relatively low in cost, which helps reduce preparation costs and improve production efficiency. The selected organic solvent can fully dissolve the organoalkoxysilane, forming a homogeneous reaction system and is miscible with water, thus promoting the hydrolysis to form silica nanoparticles. It also provides a uniform medium environment for the reaction and promotes the polycondensation reaction. After the reaction, the solvent is easily evaporated and removed, leaving no impurities on the surface of the nanosilica particles, ensuring the purity and surface activity of the nanoparticles and, in turn, the excellent performance of the modified layer. Too high ammonia solution concentration may cause the reaction to be too violent, resulting in uneven particle size of the generated nano-silica particles; too low a concentration will slow down the reaction rate and extend the preparation cycle.

[0028] Furthermore, room temperature avoids side reactions that could occur at high temperatures, such as rapid volatilization of the organic solvent or agglomeration of the nanoparticles. A stirring time of 3–6 hours ensures complete hydrolysis and polycondensation of the organoalkoxysilane, forming a stable nanosilica sol system. During stirring, the raw materials are thoroughly mixed, allowing the reaction to proceed uniformly. The resulting nanoparticles possess a uniform particle size and good dispersion, paving the way for subsequent loading into the porous membrane and improving the separator's ion selectivity and ion transport properties. At temperatures between 60 and 80°C, the solvent evaporates slowly, allowing the nanoparticles to gradually and densely pack, forming a modified layer with sufficient mechanical strength. Furthermore, a drying time of 6–48 hours ensures complete solvent removal, preventing residual solvent from adversely affecting subsequent battery performance, such as increasing internal resistance or impairing ion transport.

[0029] Furthermore, a clean surface facilitates uniform loading of nano-silica particles, avoiding uneven particle distribution or unstable loading due to the presence of impurities, thereby improving the quality of the modified layer and the performance of the separator. A suitable dry state helps the nano-silica particles better adsorb onto the porous membrane surface, forming a uniform and stable modified layer, improving the separator's ion selectivity and chemical stability, and extending the cycle life of zinc-bromine flow batteries.

[0030] Furthermore, ultrasonic power of 300-400W provides sufficient energy to break up nanoparticle agglomerates, forming a uniformly dispersed suspension. Ultrasonic dispersion for 10-60 minutes ensures optimal nanoparticle dispersion, avoiding inadequate dispersion due to too short a dispersion time and excessive surface damage or the formation of new agglomerates due to too long a dispersion time. A uniformly dispersed nanosilica dispersion facilitates the formation of a uniform modified layer within the porous membrane, improving the membrane's ion selectivity and ion transport properties. At least one of ethanol and isopropanol is selected as the dispersant. These two solvents have excellent solubility and dispersibility, interacting well with the surface of the nanosilica particles to form a stable dispersion. Ethanol and isopropanol have moderate volatility, making them easy to remove during the subsequent drying process without leaving any impurities in the modified layer. Furthermore, their good compatibility with the porous membrane material facilitates better loading of the nanosilica particles onto the membrane, enhancing the bonding between the modified layer and the membrane, and enhancing the stability and durability of the membrane. Controlling the mass concentration of the nanosilica dispersion between 10 and 20 mg / mL ensures both good dispersion of the nanoparticles in the dispersion and sufficient loading in the porous membrane. A concentration that is too low may result in a thinner modified layer, failing to effectively block bromide ions and inhibit zinc dendrite growth. A concentration that is too high may increase the viscosity of the dispersion, leading to uneven loading of the nanoparticles in the porous membrane and even clogging the membrane pores, impairing ion transport.

[0031] Furthermore, polyvinylidene fluoride (PVDF) exhibits excellent chemical stability and mechanical strength, allowing it to withstand the various environmental changes during battery charging and discharging. Polypropylene and polyethylene are relatively low-cost and offer a certain degree of porosity and ionic conductivity. Glass fiber membranes offer high porosity and good thermal stability. Nylon and polyester offer excellent flexibility and processability. By selecting different types of porous membranes, flexible adjustments can be made to meet specific application scenarios and battery performance requirements, expanding the product's application range. The pore size of the porous membrane is limited to 10–200 nm, a range that matches the size of the nanosilica particles and the sizes of zinc and bromide ions. The smaller pore size effectively blocks the permeation of bromine molecules while allowing zinc ions to pass through, fully utilizing the size-sieving effect of the nanosilica. The appropriate pore size also ensures uniform loading of the nanosilica particles on the porous membrane surface, preventing particle clogging or shedding from the membrane surface. This improves the stability and ion selectivity of the modified layer, thereby enhancing the energy efficiency and cycle life of zinc-bromine flow batteries. If the immersion time is too short, the nano-silica particles may not be fully loaded into the porous membrane, resulting in insufficient modification layer thickness and affecting the performance of the membrane. If the immersion time is too long, the nano-silica particles may accumulate excessively on the membrane surface, causing pore blockage and increasing ion transport resistance. By properly controlling the immersion time, a uniform and stable nano-silica modified porous membrane can be obtained, achieving the optimal balance between ion selectivity and ion transport performance.

[0032] Furthermore, the temperature range of 60~80℃ can accelerate the volatilization of the solvent without damaging the structure of the nano-silica particles and the porous membrane. The vacuum environment further reduces the boiling point of the solvent, promotes the rapid removal of the solvent, and avoids the adverse effects of residual solvent on battery performance, such as increasing the internal resistance of the battery, affecting ion transport, or initiating side reactions. Appropriate drying temperature and time can form a tighter bond between the nano-silica particles and between the nano-silica particles and the porous membrane, thereby improving the mechanical strength and stability of the modified layer. During the drying process, the nano-silica particles gradually shrink and arrange tightly to form a structure with a certain strength, which can better withstand the stress changes during the battery's charge and discharge process, reduce the shedding and damage of the modified layer, extend the service life of the diaphragm, and thus improve the overall performance and reliability of the zinc-bromine flow battery.

[0033] The nano-silica modified porous membrane prepared by the above-mentioned preparation method disclosed in the present invention is obtained by a sol-gel method combined with ultrasonic dispersion and impregnation process, and the nano-silica particles are evenly dispersed and loaded on the surface of the porous membrane to form a dense and regular modified layer, avoiding the structural defects caused by particle agglomeration or uneven distribution in traditional processes. The evenly distributed nano-silica particles ensure the continuity of the modified layer in the porous membrane, significantly improve the stability of the size screening effect, while reducing local resistance and maintaining an efficient transmission channel for zinc ions. The particle size of the nano-silica particles and the pore size of the porous membrane work synergistically to construct a nanoscale pore structure that can effectively block the penetration of bromine molecules while allowing zinc ions to pass through. This selective screening effect greatly reduces the bromine permeability, while optimizing the pore structure, reducing ion transmission resistance, and improving ion selectivity. The surface of nano-silica is rich in silicon hydroxyl groups (Si-OH), which dissociate in the electrolyte to form a negative charge layer, which further inhibits the bromide ions (Br) through electrostatic repulsion. - ) diffusion. The negative charge layer and the size screening effect work synergistically to reduce the bromide ion diffusion coefficient, significantly reducing self-discharge and side reactions, and significantly improving Coulombic efficiency. The nano-silica modified layer regulates the local electric field distribution, promoting uniform zinc ion deposition and inhibiting zinc dendrite growth.

[0034] The present invention discloses the application of the nano-silica-modified porous membrane prepared by the above-mentioned preparation method in zinc-bromine flow batteries. The nano-silica-modified porous membrane is used as the diaphragm material of the zinc-bromine flow battery. The zinc-bromine flow battery assembled from the nano-silica-modified porous membrane has a coulombic efficiency of 95.4% to 97.2%; a voltage efficiency of 86.1% to 88.3%; and an energy efficiency of 82.6% to 85.4%. The modification of the porous membrane with nano-silica significantly improves the performance of the zinc-bromine flow battery. Its core mechanism is that the size screening effect of nano-silica effectively blocks the penetration of bromine molecules, while the negative charge characteristics of its surface further inhibit the diffusion of bromide ions through electrostatic repulsion, thereby significantly reducing self-discharge and side reactions and significantly improving the coulombic efficiency to as high as 97.2%. Furthermore, through a sol-gel method combined with ultrasonic dispersion and impregnation, nanosilica was uniformly loaded into the porous membrane, optimizing the pore structure. This not only maintains efficient zinc ion transport but also achieves high voltage efficiency, reaching a maximum of 88.3%. Energy efficiency was increased to 85.4%, representing improvements of approximately 15.0% and 6.6% compared to the 74.0% of conventional membranes and 79.8% of conventional modified membranes, respectively. This addresses the performance degradation issues inherent in existing technologies caused by severe bromine permeation or particle agglomeration, providing a membrane solution with high selectivity, low impedance, and stability for zinc-bromine flow batteries. High energy efficiency reduces energy loss during charging and discharging, significantly reducing system operating costs. For large-scale energy storage scenarios, such as grid peak shaving and renewable energy consumption, high energy efficiency improves overall system economics and extends the energy payback period in actual use. It also reduces heat generation caused by energy loss, reduces the load on the cooling system, and further optimizes system stability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a scanning electron microscope image of the nano-silica modified porous membrane disclosed in Example 4 of the present invention. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be described clearly and completely below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] In the present invention, unless otherwise specified, all the embodiments and preferred implementation methods mentioned herein can be combined with each other to form a new technical solution.

[0038] In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0039] In the present invention, unless otherwise specified, percentages (%) or parts refer to percentages by weight or parts by weight relative to the composition.

[0040] In the present invention, unless otherwise specified, the components involved or their preferred components can be combined with each other to form a new technical solution.

[0041] In this disclosure, 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 real numbers. For example, the numerical range "6-22" indicates that all real numbers between "6-22" are listed herein, and "6-22" is merely an abbreviation for these numerical combinations.

[0042] The "range" disclosed in the present invention is in the form of lower limit and upper limit, which can be one or more lower limits, and one or more upper limits respectively.

[0043] In the present invention, the term "and / or" used herein refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0044] In the present invention, unless otherwise specified, each reaction or operation step can be carried out sequentially or in accordance with the sequence. Preferably, the reaction method herein is carried out sequentially.

[0045] Unless otherwise indicated, the professional and scientific terms used herein are the same as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content can also be applied to the present invention.

[0046] The present invention provides a method for preparing a nano-silica modified porous membrane, comprising the following steps:

[0047] 1) Preparation of nano-silica

[0048] Mix 8-10g of organoalkoxysilane with 150-250mL of an organic solvent, then add 8-10mL of deionized water and 8-10mL of a 25-28wt% ammonia solution. Stir and react at room temperature for 3-6 hours, then remove the solvent and dry at 60-80°C for 6-48 hours to obtain nanosilica.

[0049] 2) Pretreatment of porous membrane

[0050] The porous membrane is cleaned by ultrasonic cleaning with a cleaning agent for 15 to 30 minutes to remove impurities and pollutants on the surface, and then dried in a vacuum drying oven at 40 to 60° C. for 12 to 24 hours to obtain a pretreated porous membrane.

[0051] 3) Preparation of nano-silica modified porous membrane

[0052] Disperse the nanosilica prepared in step 1) in a dispersant to form a nanosilica dispersion with a concentration of 10-20 mg / mL. Use ultrasonic dispersion at a power of 300-400 W for 10-60 minutes. Soak the pretreated porous membrane obtained in step 2) in the nanosilica dispersion for 15-60 minutes to ensure that the nanosilica is fully loaded on the surface of the porous membrane. Dry the soaked porous membrane in a vacuum drying oven at 60-80°C for 6-12 hours to produce a nanosilica-modified porous membrane.

[0053] In step 1), the organoalkoxysilane includes but is not limited to tetraethoxysilane (TEOS) or tetrapropoxysilane (TPOS). The organic solvent includes but is not limited to methanol, ethanol, isopropanol or acetone.

[0054] In step 2), the porous membrane is a thin film material with a microscopic pore structure, which is used to separate the positive and negative electrodes in the battery, allowing ion transmission while blocking the flow of electrons. The porous membrane includes polyvinylidene fluoride (PVDF), polypropylene (PP), polyethylene (PE), polyolefin composite membrane or glass fiber membrane. The pore size of the porous membrane in the zinc-bromine flow battery is generally 10~200 nm. It achieves ion selective separation through physical screening effect, while allowing zinc ions (Zn 2+ ) while effectively blocking larger bromine molecules and other impurities, reducing cross-contamination. The cleaning agent includes at least one of methanol, ethanol, isopropanol, acetone, and deionized water. The porous membrane has a pore size of 10-200 nm, a porosity of 50%-60%, and a thickness of 300-500 μm.

[0055] In step 3), the dispersant is at least one of ethanol and isopropanol.

[0056] The present invention synthesizes nano-silica by a sol-gel method, and utilizes ultrasonic dispersion and impregnation technology to uniformly load it on the surface of a porous membrane, forming a modified layer with size screening effect and surface negative charge characteristics, thereby significantly improving the bromide ion barrier capacity and ion selectivity of the diaphragm. From the process flow of nano-silica synthesis to porous membrane modification and post-treatment, in particular, by optimizing parameters such as dispersion concentration, ultrasonic time and drying temperature, the uniform distribution of nano-silica in the porous membrane is achieved, thereby greatly improving the energy efficiency of zinc-bromine flow batteries, effectively reducing energy loss, and improving the economy and practicality of the system. In addition, the preparation process of this method is relatively simple and cost-controllable, and it is suitable for large-scale industrial production applications. In addition, the present invention uses a low-concentration dispersion of 10~20mg / mL through ultrasonic dispersion and impregnation technology to achieve uniform distribution of nano-silica in the porous membrane, and the low drying temperature of 60~80℃ avoids the shedding of nano-silica particles.

[0057] The present invention also discloses a nano-silica modified porous membrane obtained by the above-mentioned preparation method. The nano-silica is uniformly loaded on the surface of the porous membrane to form a modified layer with a size screening effect and surface negative charge characteristics. The ion selectivity of the membrane is significantly improved. The size screening effect of the nano-silica effectively blocks the penetration of bromine molecules. The surface negative charge characteristics further inhibit the diffusion of bromide ions through electrostatic repulsion, significantly reducing the bromine permeability. Low transmission resistance is maintained, the polarization voltage remains basically unchanged, the pore structure is optimized, and the efficient transmission of zinc ions is maintained. The ability of the membrane to inhibit the growth of zinc dendrites is enhanced.

[0058] The present invention also discloses the use of the nano-silica-modified porous membrane prepared by the above-mentioned preparation method in a zinc-bromine flow battery. The zinc-bromine flow battery assembled with the nano-silica-modified porous membrane exhibits a coulombic efficiency of 95.4% to 97.2%, a voltage efficiency of 86.1% to 88.3%, and an energy efficiency of 82.6% to 85.4%. The energy efficiency is increased to 85.4%, representing improvements of approximately 15.0% and 6.6% compared to the 74.0% of a conventional diaphragm and 79.8% of a conventional modified diaphragm, respectively. Self-discharge and side reactions are significantly reduced, with a coulombic efficiency of up to 97.2%. The membrane also exhibits a high voltage efficiency of up to 88.3%. This extends the cycle life of the zinc-bromine flow battery, reduces heat generation caused by energy loss, reduces the load on the cooling system, and improves the overall stability and safety of the system. The high energy efficiency reduces energy loss during charging and discharging, significantly reducing system operating costs. It solves the performance degradation problem caused by severe bromine penetration or particle agglomeration in the existing technology, and provides a diaphragm solution with high selectivity, low impedance and stability for zinc-bromine flow batteries.

[0059] This invention synthesizes nanosilica via a sol-gel method and uniformly loads it onto the surface of a porous membrane using ultrasonic dispersion and impregnation techniques, forming a modified layer with a size-sieving effect and negative surface charge, significantly improving the membrane's bromide ion barrier and ion selectivity. The process flow, from nanosilica synthesis to porous membrane modification and post-treatment, specifically optimizes parameters such as dispersion concentration, ultrasonication time, and drying temperature to achieve uniform distribution of nanoparticles within the membrane, significantly improving the energy efficiency of zinc-bromine flow batteries, effectively reducing energy loss, and enhancing the system's economic and practicality.

[0060] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0061] Example 1

[0062] 1) Preparation of nano-silica

[0063] 8g of TEOS was mixed with 250mL of ethanol, and the solution was then added to 8mL of deionized water and 8mL of a 25wt% ammonia solution. The mixed solution was stirred at room temperature for 5 hours, and then the solvent was removed and the solution was dried at 80°C for 6 hours to obtain nanosilica.

[0064] 2) Pretreatment of porous membrane

[0065] The PVDF porous membrane was ultrasonically cleaned with ethanol for 20 minutes and dried in a vacuum drying oven at 50° C. for 18 hours to obtain a pretreated porous membrane.

[0066] 3) Preparation of nano-silica modified porous membrane

[0067] The prepared nanosilica was dispersed in ethanol to form a nanosilica dispersion with a concentration of 10 mg / mL. Ultrasonic power was set at 300 W for 30 minutes. The pretreated porous membrane was immersed in the nanosilica dispersion for 35 minutes. The immersed porous membrane was then placed in a vacuum drying oven and dried at 80°C for 8 hours to obtain a nanosilica-modified porous membrane.

[0068] Zinc-bromine flow battery assembly

[0069] The nano-silica modified porous membrane was cut to a 3cm×3cm stack size and sandwiched between a 3cm×3cm positive carbon felt electrode and a negative carbon felt electrode. The positive and negative electrolytes were both 60mL of a mixed solution consisting of 2 mol / L ZnBr2, 3 mol / L KCl, and 0.4 mol / L 1-Methyl-1-ethylpyrrolidinium bromide (MEP).

[0070] Zinc-bromine flow battery testing

[0071] The electrolyte is circulated in the liquid storage tank and the battery stack driven by a circulation pump. The flow rate of the positive and negative electrolytes is 50 mL / min. The battery is tested for constant current charge and discharge using a battery tester with a charging current of 20 mA / cm 2 (i.e. 180mA), charging time is 30min, and discharge current is 20mA / cm 2 , the discharge cut-off voltage is 0.5V, record the voltage change curve over time, and calculate the battery coulombic efficiency, voltage efficiency and energy efficiency according to the following formula.

[0072]

[0073]

[0074]

[0075] Among them, Q 放电 is the total capacity during the discharge process, in Ah; Q 充电 is the total capacity during the charging process, in Ah; V 放电 is the average voltage during the discharge process, in V; V 充电 is the average voltage during the charging process, in V; W 放电 is the total energy during the discharge process, in Wh; W 充电 It is the total energy during the charging process, in Wh.

[0076] Example 2

[0077] 1) Preparation of nano-silica

[0078] 10g of TPOS was mixed with 150mL of ethanol, and the solution was then added to 10mL of deionized water and 8mL of a 25wt% ammonia solution. The mixture was stirred at room temperature for 3 hours, and then the solvent was removed and the solution was dried at 60°C for 48 hours to obtain nanosilica.

[0079] 2) Pretreatment of porous membrane

[0080] The PE porous membrane was ultrasonically cleaned with methanol for 15 minutes and dried in a vacuum drying oven at 40° C. for 24 hours to obtain a pretreated porous membrane.

[0081] 3) Preparation of nano-silica modified porous membrane

[0082] The prepared nanosilica was dispersed in ethanol to form a nanosilica dispersion with a concentration of 15 mg / mL. Ultrasonic power was set at 300 W for 10 minutes. The pretreated porous membrane was immersed in the nanosilica dispersion for 15 minutes. The immersed porous membrane was placed in a vacuum drying oven at 60°C for 12 hours to obtain a nanosilica-modified porous membrane.

[0083] Zinc-bromine flow battery assembly: same as in Example 1.

[0084] Zinc-bromine flow battery test: same as Example 1.

[0085] Example 3

[0086] 1) Preparation of nano-silica

[0087] 9g of TPOS was mixed with 180mL of ethanol, and the solution was then added to 8mL of deionized water and 10mL of a 25wt% ammonia solution. The mixture was stirred at room temperature for 6 hours, after which the solvent was removed and the solution was dried at 70°C for 24 hours to produce nanosilica.

[0088] 2) Pretreatment of porous membrane

[0089] The PP porous membrane was ultrasonically cleaned with isopropyl alcohol for 30 minutes and dried in a vacuum drying oven at 50° C. for 12 hours to obtain a pretreated porous membrane.

[0090] 3) Preparation of nano-silica modified porous membrane

[0091] The prepared nanosilica was dispersed in ethanol to form a nanosilica dispersion with a concentration of 18 mg / mL. Ultrasonic power was set at 400 W for 10 minutes. The pretreated porous membrane was immersed in the nanosilica dispersion for 60 minutes. The immersed porous membrane was then placed in a vacuum drying oven and dried at 70°C for 10 hours to obtain a nanosilica-modified porous membrane.

[0092] Zinc-bromine flow battery assembly: same as in Example 1.

[0093] Zinc-bromine flow battery test: same as Example 1.

[0094] Example 4

[0095] 1) Preparation of nano-silica

[0096] 9g of TEOS was mixed with 250mL of ethanol, and the solution was then added to 10mL of deionized water and 10mL of a 25wt% ammonia solution. The mixture was stirred at room temperature for 6 hours, and then the solvent was removed and the solution was dried at 70°C for 18 hours to obtain nanosilica.

[0097] 2) Pretreatment of porous membrane

[0098] The PE porous membrane was ultrasonically cleaned with ethanol for 30 minutes and dried in a vacuum drying oven at 60° C. for 12 hours to obtain a pretreated porous membrane.

[0099] 3) Preparation of nano-silica modified porous membrane

[0100] The prepared nanosilica was dispersed in ethanol to form a nanosilica dispersion with a concentration of 20 mg / mL. Ultrasonic power was applied at 320 W for 60 minutes. The pretreated porous membrane was immersed in the nanosilica dispersion for 40 minutes. The immersed porous membrane was then dried in a vacuum drying oven at 80°C for 6 hours to obtain a nanosilica-modified porous membrane.

[0101] Zinc-bromine flow battery assembly: same as in Example 1.

[0102] Zinc-bromine flow battery test: same as Example 1.

[0103] Figure 1 This is a scanning electron microscope image of the nano-silica modified porous membrane prepared in Example 4 of the present invention. It can be seen from the figure that the nano-silica presents a nano-spherical morphology with a uniform size distribution. Its diameter is 400nm, forming a continuous and dense covering layer on the surface of the diaphragm without obvious agglomeration.

[0104] Example 5

[0105] 1) Preparation of nano-silica

[0106] 9g of ethyl orthosilicate was mixed with 200mL of isopropyl alcohol, and then the solution was added to 9mL of deionized water and 8.5mL of a 28wt% ammonia solution. The mixture was stirred at room temperature for 4 hours, and then the solvent was removed and the solution was dried at 65°C for 15 hours to obtain nanosilica.

[0107] 2) Pretreatment of porous membrane

[0108] The polyolefin composite porous membrane was ultrasonically cleaned with acetone for 25 minutes and dried in a vacuum drying oven at 55° C. for 20 hours to obtain a pretreated porous membrane.

[0109] 3) Preparation of nano-silica modified porous membrane

[0110] The prepared nanosilica was dispersed in isopropanol to form a nanosilica dispersion with a concentration of 15 mg / mL. The ultrasonic power was 350 W and the ultrasonic time was 20 minutes. The pretreated porous membrane was immersed in the nanosilica dispersion for 20 minutes. The immersed porous membrane was placed in a vacuum drying oven and dried at 60°C for 10 hours to obtain a nanosilica-modified porous membrane.

[0111] Zinc-bromine flow battery assembly: same as in Example 1.

[0112] Zinc-bromine flow battery test: same as Example 1.

[0113] Example 6

[0114] 1) Preparation of nano-silica

[0115] 8.5g of ethyl orthosilicate was mixed with 240mL of methanol, and the solution was then added to 8.5mL of deionized water and 9mL of a 26.5wt% ammonia solution. The mixture was stirred at room temperature for 4 hours, after which the solvent was removed and the solution was dried at 75°C for 20 hours to produce nanosilica.

[0116] 2) Pretreatment of porous membrane

[0117] The glass fiber porous membrane was ultrasonically cleaned with deionized water for 20 minutes and dried in a vacuum drying oven at 60° C. for 15 hours to obtain a pretreated porous membrane.

[0118] 3) Preparation of nano-silica modified porous membrane

[0119] The prepared nanosilica was dispersed in a mixture of ethanol and isopropanol (volume ratio of ethanol to isopropanol was 1:1) to form a nanosilica dispersion with a concentration of 16 mg / mL. Ultrasonication was performed at a power of 370 W for 40 minutes. The pretreated porous membrane was then immersed in the nanosilica dispersion for 25 minutes. The membrane was then dried in a vacuum drying oven at 65°C for 9 hours to obtain a nanosilica-modified porous membrane.

[0120] Zinc-bromine flow battery assembly: same as in Example 1.

[0121] Zinc-bromine flow battery test: same as Example 1.

[0122] Example 7

[0123] 1) Preparation of nano-silica

[0124] 9g of tetrapropoxysilane was mixed with 190mL of acetone, and the solution was then added to 9mL of deionized water and 9mL of a 27wt% ammonia solution. The mixture was stirred at room temperature for 5 hours, after which the solvent was removed and the solution was dried at 80°C for 24 hours to produce nanosilica.

[0125] 2) Pretreatment of porous membrane

[0126] The PE porous membrane was ultrasonically cleaned with a mixture of ethanol and deionized water in a volume ratio of 1:1 for 20 minutes, and dried in a vacuum drying oven at 45°C for 20 hours to obtain a pretreated porous membrane.

[0127] 3) Preparation of nano-silica modified porous membrane

[0128] The prepared nanosilica was dispersed in a mixture of ethanol and isopropanol (volume ratio of ethanol to isopropanol: 4:1) to form a nanosilica dispersion with a concentration of 12 mg / mL. Ultrasonication was performed at a power of 320 W for 45 minutes. The pretreated porous membrane was immersed in the nanosilica dispersion for 30 minutes. The membrane was then dried in a vacuum drying oven at 75°C for 6 hours to obtain a nanosilica-modified porous membrane.

[0129] Zinc-bromine flow battery assembly: same as in Example 1.

[0130] Zinc-bromine flow battery test: same as Example 1.

[0131] Comparative Example 1

[0132] Preparation of a porous membrane

[0133] The PE porous membrane was ultrasonically cleaned with ethanol for 30 min and dried in a vacuum drying oven at 60 °C for 12 h.

[0134] Zinc-bromine flow battery assembly: same as in Example 1.

[0135] Zinc-bromine flow battery test: same as Example 1.

[0136] Comparative Example 2

[0137] 1) Preparation of nano-silica

[0138] 9g of TPOS was mixed with 200mL of ethanol, and the solution was then added to 10mL of deionized water and 10mL of 25wt% ammonia solution. The mixture was stirred at room temperature for 6 hours, after which the solvent was removed and the solution was dried at 60°C to obtain the silica nanosphere template.

[0139] 2) Pretreatment of porous membrane

[0140] The PP porous membrane was ultrasonically cleaned with ethanol for 30 min and dried in a vacuum drying oven at 60 °C for 12 h.

[0141] 3) Preparation of nano-silica modified porous membrane

[0142] Disperse the prepared nanosilica in ethanol to form a 20 mg / mL nanosilica dispersion. Soak the pretreated porous membrane in this nanosilica dispersion for 30 minutes. Place the soaked porous membrane in a vacuum drying oven at 60°C for 6 hours.

[0143] Zinc-bromine flow battery assembly: same as in Example 1.

[0144] Zinc-bromine flow battery test: same as Example 1.

[0145] Table 1 Performance parameters of zinc-bromine flow batteries in Examples 1-7 and Comparative Examples 1-2

[0146]

[0147] Table 1 shows the performance parameters of the zinc-bromine flow batteries in Examples 1 to 7 and Comparative Examples 1 to 2, including coulombic efficiency, voltage efficiency, and energy efficiency. The performance of Comparative Example 2 is better than that of Comparative Example 1, mainly due to the use of a nano-silica modification process. The size screening effect and surface negative charge characteristics of nano-silica partially block the penetration of bromine, reducing the capacity loss caused by side reactions, thereby increasing the coulombic efficiency from 89.6% in Comparative Example 1 to 93.1%, and the energy efficiency is also increased from 74.0% to 79.8%. The overall performance of Examples 1 to 7 is better than that of Comparative Examples 1 to 2. The core lies in the uniform loading of nano-silica in the porous membrane (such as Figure 1 This uniform distribution not only more effectively inhibits bromine diffusion, achieving a Coulombic efficiency of 95.4% to 97.2%, but also avoids pore clogging caused by particle agglomeration or overfilling. This improves voltage efficiency to 86.1% to 88.3% and energy efficiency to 82.6% to 85.4% while maintaining ion transmission efficiency. Compared to Comparative Example 2, Examples 1 to 7 further optimize the dispersion uniformity and loading of the nanoparticles by precisely controlling parameters such as dispersion concentration, ultrasonication time, and drying temperature, balancing ion selectivity and transmission resistance, ultimately achieving a significant increase in Coulombic efficiency and comprehensive optimization of energy efficiency.

[0148] In summary, the nano-silica modified porous membrane, preparation method, and application in zinc-bromine flow batteries disclosed in the present invention address the problems of poor ion selectivity, limited zinc dendrite suppression ability, and poor dispersibility and weak binding of inorganic particles in existing modification technologies in traditional zinc-bromine flow battery membranes. Nano-silica is prepared by a sol-gel method, and ultrasonic dispersion and impregnation processes are combined to uniformly load the nano-silica on the surface of the porous membrane. The size screening effect and surface negative charge characteristics of the nanoparticles are utilized to significantly improve the bromide ion barrier capacity of the membrane and improve the coulombic efficiency. Experimental data show that the uniform distribution of nano-silica optimizes the pore structure, maintains ion transmission efficiency while reducing bromine penetration, maintains stable voltage efficiency, and increases energy efficiency to a maximum of 85.4%.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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. Application of a nano-silica modified porous membrane in a zinc-bromine flow battery, characterized in that: The method for preparing a nano-silica modified porous membrane specifically comprises the following steps: An organic alkoxysilane is mixed with an organic solvent, and then deionized water and an ammonia solution are added. After stirring and mixing, the mixture is reacted, the solvent is removed, and the mixture is dried to obtain nano-silica. The nano-silica is then ultrasonically dispersed in a dispersant to obtain a nano-silica dispersion. The amount ratio of the organic alkoxysilane, the organic solvent, the deionized water, and the ammonia solution is (8-10) g: (150-250) mL: (8-10) mL: (8-10) mL. The organic alkoxysilane includes ethyl orthosilicate or tetrapropoxysilane. The organic solvent includes methanol, ethanol, isopropanol, or acetone. The mass percentage of the ammonia solution is 25-28 wt%. The drying condition is: drying at 60-80° C. for 6-48 hours. The ultrasonic dispersion condition includes: ultrasonic dispersion at an ultrasonic power of 300-400 W for 10-60 minutes. The mass concentration of the nano-silica dispersion is 10-20 mg / mL. The pretreated porous membrane is immersed in a nano-silica dispersion until the nano-silica is evenly loaded on the surface of the porous membrane, and then vacuum-dried twice to obtain a nano-silica modified porous membrane; The nano-silica modified porous membrane is used as a diaphragm material for zinc-bromine flow batteries; The zinc-bromine flow battery assembled from nano-silica modified porous membrane has a coulombic efficiency of 95.4%~97.2%; a voltage efficiency of 86.1%~88.3%; and an energy efficiency of 82.6%~85.4%.

2. The use of the nano-silica modified porous membrane in a zinc-bromine flow battery according to claim 1, characterized in that: The stirring and mixing reaction conditions are: stirring and mixing at room temperature for 3 to 6 hours.

3. The use of the nano-silica modified porous membrane in a zinc-bromine flow battery according to claim 1, characterized in that: The pretreatment conditions of the pretreated porous membrane include: using at least one of methanol, ethanol, isopropanol, acetone and deionized water to ultrasonically clean the porous membrane, and then vacuum drying to obtain the pretreated porous membrane; The ultrasonic cleaning time is 15-30 minutes; the vacuum drying conditions are: vacuum drying at 40-60° C. for 12-24 hours.

4. The use of the nano-silica modified porous membrane in a zinc-bromine flow battery according to claim 1, characterized in that: The dispersant is at least one of ethanol and isopropanol.

5. The use of the nano-silica modified porous membrane in zinc-bromine flow battery according to claim 1, characterized in that: The porous membrane includes polyvinylidene fluoride, polypropylene, polyethylene, polyolefin composite membrane or glass fiber membrane; the soaking time is 15 to 60 minutes.

6. Use of the nano-silica modified porous membrane in zinc-bromine flow battery according to claim 1, characterized in that: The secondary vacuum drying conditions are: vacuum drying at 60-80° C. for 6-12 hours.

7. A nano-silica modified porous membrane, characterized in that: The nano-silica modified porous membrane is prepared by the preparation method according to any one of claims 1 to 6.

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