Cellulose / sodium alginate composite gel electrolyte membrane, preparation and aqueous zinc ion battery

Abstract

This invention relates to a biomass-based gel electrolyte membrane, its preparation method, and its application. The method includes preparing regenerated cellulose using a sol-gel method, adding sodium alginate and zinc chloride solution, and rapidly constructing a biomass-based composite gel electrolyte with a dual-network structure through metal ion coordination crosslinking. The biomass-based gel electrolyte membrane is obtained by adsorbing an aqueous electrolyte onto a gel membrane with a dual-network structure. This gel electrolyte membrane is then assembled with a zinc anode and a vanadium pentoxide cathode to obtain a zinc-ion battery. This invention features a simple method, readily available and inexpensive raw materials, easy product molding, convenient operation and control, and is conducive to industrial production. The prepared composite gel electrolyte membrane has a dual-network structure, exhibiting good stability, liquid retention capacity, and ionic conductivity, and demonstrates excellent cycle capacity and lifespan when applied to aqueous zinc-ion batteries.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of electrochemical energy storage and biomass materials, specifically involving a cellulose / sodium alginate composite gel electrolyte membrane, its preparation, and its application in aqueous zinc-ion batteries. Background Technology

[0002] With the increasing demand for clean energy, aqueous zinc-ion batteries (AZIBs) have attracted much attention as a promising energy storage solution. The separator, a crucial component of AZIBs, plays a key role. Currently, glass fiber, as the most traditional separator in AZIBs, has been the primary choice since the advent of AZIBs. However, the relatively low mechanical strength of glass fiber cannot prevent the growth and penetration of zinc dendrites, and its high production cost is not in line with the future development trend of separators, which has limited the commercialization of AZIBs to some extent. Therefore, developing high-performance, low-cost, and sustainable high-quality separator materials is of great significance.

[0003] Studies have shown that gel electrolyte membranes can replace separators and electrolytes, effectively isolating the positive and negative electrodes and providing ion transport channels. Furthermore, high-quality gel electrolyte membranes can reduce byproducts of internal battery reactions, inhibit dendrite growth and hydrogen evolution, and improve battery cycle performance and safety. Chinese patent CN114696037A discloses a polymer gel electrolyte separator. This separator is prepared by sequentially mixing a polymer matrix with acrylamide, a mixed electrolyte, N,N-methylenebisacrylamide, and K₂S₂O₈, and then solidifying the mixture on a base membrane. This effectively prevents the dissolution of vanadium / manganese-based positive electrode active materials and electrolyte leakage, significantly improving the lifespan of aqueous zinc-ion batteries. However, most commonly used polymer gel electrolyte membranes currently use toxic solvents or petroleum-based materials as raw materials, and their preparation processes are complex, with solvents difficult to recover, hindering sustainable manufacturing.

[0004] Biomass gel electrolytes are a novel type of gel electrolyte material formed by processing renewable biomass raw materials such as cellulose, sodium alginate, and chitosan through physical or chemical methods. They are characterized by abundant resources, biodegradability, and good biocompatibility, and are gradually becoming an ideal alternative to liquid electrolytes. With proper design, biomass gels can possess high ion transport performance, good mechanical strength, and excellent chemical stability, significantly improving the performance and safety of energy storage devices. Chinese Patent CN117457977A discloses a biomass-based polymer gel electrolyte membrane, its preparation method, and its applications. This method utilizes biomass materials with polyhydroxy groups and a crosslinking agent in a specific solvent for crosslinking and polymerization, followed by immersion in an electrolyte to obtain the biomass-based polymer gel electrolyte. The preparation method is simple, inexpensive, environmentally friendly, and exhibits high ionic conductivity, effectively improving the safety performance of secondary ion batteries.

[0005] Currently, research on biomass-based gel electrolyte membranes still needs further improvement, mainly focusing on material selection, network structure regulation, and optimization of preparation processes. By trying different types of biomass raw materials, regulating preparation conditions, and adding additives, the network structure and performance of the electrolyte membrane can be optimized. The goal is to develop a functional gel electrolyte that is simple to prepare, has excellent electrochemical performance, and is environmentally friendly, which is of great significance for promoting the large-scale development of aqueous zinc-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a low-carbon and low-cost biomass-based composite gel electrolyte, its preparation method, and its application as a separator and electrolyte material for zinc-ion batteries, so as to improve the safety, stability, coulombic efficiency, and cycle life of zinc-ion batteries.

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

[0008] In a first aspect, the present invention provides a composite gel electrolyte for zinc-ion batteries with a dual-network structure, the composite gel electrolyte being composed of regenerated cellulose, sodium alginate, and zinc ions. Cellulose and sodium alginate are sequentially added to a zinc chloride solution to obtain a mixture; the mixture is poured into a mold and aged until it becomes a non-flowing colloid; the mixed colloid is immersed in a coagulation bath solvent to regenerate a composite gel, which is then freeze-dried and immersed in an electrolyte to obtain a cellulose / sodium alginate composite gel electrolyte membrane with a dual-network structure.

[0009] Preferably, the cellulose is natural cellulose with a fiber diameter of 5-100 μm, a degree of polymerization ≥200, and a crystallinity of 50-90%.

[0010] Preferably, the sodium alginate is natural sodium alginate with a viscosity of 15-2500 mPa·s.

[0011] Preferably, the zinc chloride concentration is 65-75 wt%, and the temperature is 70-80°C.

[0012] Preferably, the sol-gel dissolution conditions are as follows: the mass ratio of cellulose to zinc chloride solution is (1.5-2):100, the stirring time is 0.5-2 h, and the stirring speed is 100-1000 rpm. In this process, the strong hydrogen bond donor [Zn(OH2)6][ZnCl4] formed in the molten salt hydrate interacts with the hydroxyl groups on cellulose, breaking the intermolecular and intramolecular hydrogen bonds of cellulose, dissolving it in the molten salt solution, and obtaining nanoscale regenerated cellulose after regeneration in the coagulation bath.

[0013] Preferably, the coordination crosslinking reaction conditions are: a mass ratio of sodium alginate to zinc chloride solution of (1.5-6):100, a stirring time of 0.5-2 h, and a stirring speed of 100-1000 rpm. During this process, the negatively charged carboxyl groups in sodium alginate interact electrostatically with the zinc ions in the zinc chloride solution, forming a stable crosslinking network through metal ion coordination.

[0014] Preferably, the gel regeneration reaction conditions are as follows: the mixed solution is poured into a mold, aged in air for 1-12 hours, and then placed in water and allowed to stand for 1-6 times, each time for 0.5-12 hours. This process strengthens the gel structure through aging, and then the coagulation bath solvent is used as a medium to promote the formation of hydrogen bonds, resulting in an interconnected double network structure.

[0015] Secondly, the present invention provides the application of the composite gel electrolyte membrane for zinc-ion batteries in zinc-ion batteries. The gel electrolyte membrane is composed of a cellulose / sodium alginate double crosslinked network and a filling electrolyte, and is an integration of a separator and an electrolyte.

[0016] The assembly method of the zinc-ion battery is as follows: taking a full battery as an example, using non-conductive tweezers, assemble the CR2032 button battery in the order of negative electrode shell, spring, steel sheet, negative electrode plate, electrolyte membrane, positive electrode plate, and positive electrode shell. Then, place the assembled battery on a hydraulic sealing machine, pressurize it to a certain pressure, and hold it for 5 seconds to seal the battery. The assembled batteries are placed for more than 1 hour before testing.

[0017] Preferably, the negative electrode is a zinc sheet with a purity of ≥99%, a diameter of 12-16 mm, and a thickness of 10-150 μm.

[0018] Preferably, the positive electrode uses vanadium pentoxide or manganese dioxide as the active material. The active material, SuperP, and sodium carboxymethyl cellulose are mixed in a mass ratio of 7:2:1, using deionized water as a solvent, and stirred to form a homogeneous slurry. This slurry is then uniformly coated onto the current collector to a thickness of 90-390 μm. After drying at 60°C for 8-24 hours, it is cut into round discs with a diameter of 12-16 mm, and the active material loading is 0.8-10 mg / cm³. 2 .

[0019] Preferably, the thickness of the gel electrolyte membrane is 25-800 μm, the porosity is ≥50%, and the average pore size is 10-200 nm.

[0020] Compared with the prior art, the gain effect of the present invention is mainly reflected in:

[0021] A high-performance gel electrolyte was prepared by using biomass as a raw material and introducing a dual-network structure design. This design utilizes the sol-gel method and metal ion coordination crosslinking to form a highly interwoven dual-network gel electrolyte, exhibiting superior cycle capacity and stability in batteries compared to commercially available glass fiber membranes. This invention prepares a cellulose / sodium alginate gel electrolyte (RC-SA) with a dual-network structure using environmentally friendly cellulose and sodium alginate as raw materials. By utilizing the dissolution and regeneration of cellulose through molten salt hydrates such as zinc chloride, lithium bromide, and ferric chloride, as well as the coordination mechanism between metal ions and polar groups, a dual-network structure is constructed simultaneously with the preparation of the gel film. Studies have shown that using zinc chloride solution yields the best results for its application in aqueous zinc-ion batteries. The abundant hydroxyl and carboxyl groups in the composite gel electrolyte accelerate the desolvation of hydrated zinc ions and promote rapid zinc ion migration; the uniform dual-network structure homogenizes the zinc ion flux, significantly mitigating the "spiking effect" and alleviating uneven zinc deposition. This invention opens up a new technological path for the application of biomass-based gel electrolyte membranes in energy storage devices, and promotes the commercialization and application of aqueous zinc-ion batteries.

[0022] Another objective of this invention is to provide a cellulose / sodium alginate composite gel electrolyte membrane prepared by the above preparation method. The prepared electrolyte membrane is a biomass-based composite membrane that is environmentally friendly and biodegradable.

[0023] This invention is mainly achieved through the following technical solutions:

[0024] A cellulose / sodium alginate composite gel electrolyte membrane mainly includes the following steps:

[0025] Cellulose and sodium alginate were added sequentially to a zinc chloride solution to obtain a mixture. The mixture was poured into a mold and aged until it became a non-flowing colloid. The mixed colloid was immersed in a coagulation bath solvent and washed to regenerate a composite gel. After freeze-drying, it was immersed in an electrolyte to obtain a cellulose / sodium alginate composite gel electrolyte membrane with a dual network structure.

[0026] Preferably, the zinc chloride solution has a concentration of 65-75 wt% and a temperature of 70-80°C.

[0027] Preferably, the mass ratio of cellulose to zinc chloride solution is (1.5-2):100, and the stirring time is 0.5-2h.

[0028] Preferably, the mass ratio of sodium alginate to zinc chloride solution is (1.5-6):100, and the stirring time is 0.5-2h.

[0029] Preferably, the aging time in air is 1-6 hours.

[0030] Preferably, the mold is made of one of the following materials: polytetrafluoroethylene, polyethylene, polypropylene, and borosilicate glass.

[0031] Preferably, the coagulation bath solvent is one or more of water and ethanol, with a mass ratio of ≥5 to the mixed solution, and the soaking is performed ≥1 time, with each soaking lasting ≥0.5 hours.

[0032] Preferably, the aqueous electrolyte for soaking is an aqueous solution of zinc sulfate with a concentration ≥1mol / L and a soaking time ≥0.1h.

[0033] A cellulose / sodium alginate composite gel electrolyte membrane prepared by the above method is a biomass-based gel electrolyte with a dual-network structure constructed in situ through sol-gel method and metal ion coordination crosslinking. The regenerated cellulose network skeleton formed by hydrogen bonding during the coagulation bath soaking process serves as the first network structure. After the cellulose is dissolved, the added sodium alginate crosslinks with zinc ions in the form of ionic bonds to form the second network structure. Thanks to the dual-network structure and abundant polar groups of the composite gel electrolyte, when applied to aqueous zinc-ion batteries, it promotes the uniform and rapid migration of zinc ions, effectively improving the cycle capacity and life of the battery.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] (1) The raw materials used in the preparation of the biomass-based composite gel electrolyte of the present invention are environmentally friendly and inexpensive. The preparation process is simple and the parameters are easy to control. Different types of gel electrolyte membranes can be prepared by controlling the conditions. The range of raw materials is wide and has the basis for large-scale preparation.

[0036] (2) The biomass-based composite gel electrolyte membrane of the present invention has a dual-network structure, which is constructed from biomass materials rich in polar groups. This dual-network structure can form a stable cross-linked network with zinc ions, improving the mechanical strength and stability of the gel electrolyte membrane and providing more channels for the transport of zinc ions in the gel. Compared with glass fiber membranes and other common polymer electrolyte membranes, the biomass-based composite gel electrolyte membrane of the present invention has advantages such as being environmentally friendly and sustainable, flexible and malleable, improving ion transport efficiency, and reducing costs.

[0037] (3) The gel electrolyte membrane prepared by this invention has excellent performance and good electrochemical performance. The in-situ constructed double network structure is uniformly distributed, which helps to homogenize the zinc ion flux and alleviate the dendrite growth problem. The abundant polar hydroxyl and carboxyl groups on the surface promote the desolvation of hydrated zinc ions, improve the zinc ion transport efficiency of the battery during charging and discharging, and greatly improve the cycle capacity and service life of aqueous zinc ion batteries. Attached Figure Description

[0038] Figure 1 (a) Surface SEM image of Comparative Example 1 of the present invention (magnification of 10,000x), (b) Surface SEM image of Comparative Example 2 of the present invention (magnification of 1,000x), (c) SEM image of Example 1 of the present invention (magnification of 10,000x).

[0039] Figure 2 Nyquist plots of Embodiments 1, 2 and Comparative Example 1 of the present invention.

[0040] Figure 3 Comparison of long-cycle performance of Zn / / V2O5 full cells assembled in Examples 1 and 2 of this invention.

[0041] Figure 4 Comparison of long-cycle performance of Zn / / V2O5 full cells assembled in Examples 2, 3, and 4 of this invention.

[0042] Figure 5 Comparison of the long-cycle performance of Zn / / V2O5 full cells assembled in Examples 3, 9, and 10 of this invention.

[0043] Figure 6 Comparison of long-cycle performance of Zn / / V2O5 full cells assembled in Examples 1 and 11-13 of this invention.

[0044] Figure 7 Comparison of the long-cycle performance of Zn / / V2O5 full cells assembled with glass fiber membranes in Examples 1-3 of this invention.

[0045] Figure 8 Comparative Example 1 of this invention assembles a Zn / / Zn symmetric cell at a current density of 1 mA / cm².2 The surface area capacity is 1mAh / cm². 2 The following is a long loop graph.

[0046] Figure 9 Example 2 of this invention assembles a Zn / / Zn symmetric cell at a current density of 1 mA / cm². 2 The surface area capacity is 1mAh / cm². 2 The following is a long loop graph. Detailed Implementation

[0047] The present invention will be further described in detail below with reference to embodiments, but the embodiments of the present invention are not limited thereto. The detection methods for gel electrolyte membranes in the embodiments are all battery separator standard detection methods.

[0048] Example 1

[0049] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h until a transparent and homogeneous solution is formed. Then, add 2.25g of sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain a pale yellow mixed solution. Take 35g of the mixed solution and pour it into a polystyrene circular mold with an inner diameter of 143mm. After aging in air for 4h, it becomes a non-flowing gel. Place it in a 350ml deionized water coagulation bath, let it stand for 1h, and wash it clean to obtain a cellulose / sodium alginate composite hydrogel. After freeze-drying to remove moisture, soak it in a 2mol / L zinc sulfate aqueous solution for 12h to obtain a cellulose / sodium alginate composite gel electrolyte membrane.

[0050] Comparative Example 1

[0051] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 2h until a transparent and homogeneous solution is formed. Take 35g of the solution and pour it into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in air for 4h, it becomes a non-flowing gel. Place it in a 350ml deionized water coagulation bath, let it stand for 1h, and wash it clean to obtain regenerated cellulose hydrogel. After freeze-drying to remove moisture, soak it in a 2mol / L zinc sulfate aqueous solution for 12h to obtain a regenerated cellulose gel electrolyte membrane.

[0052] Comparative Example 2

[0053] 2.25g of sodium alginate powder (viscosity 200±20mpa.s) was dissolved in 50g of deionized water at 75℃. The solution was stirred at 500rpm for 2h until a homogeneous solution was formed. 35g of the solution was poured into a polystyrene cylindrical mold with an inner diameter of 143mm. After freeze-drying to remove moisture, the solution was soaked in a 2mol / L zinc sulfate aqueous solution for 12h to obtain a sodium alginate gel electrolyte membrane.

[0054] Example 2

[0055] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h until a transparent and homogeneous solution is formed. Then, add 0.75g of sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain a pale yellow mixed solution. Take 35g of the mixed solution and pour it into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in air for 4h, it becomes a non-flowing gel. Place it in a 350ml deionized water coagulation bath, let it stand for 1h, and wash it clean to obtain a cellulose / sodium alginate composite hydrogel. After freeze-drying to remove moisture, soak it in a 2mol / L zinc sulfate aqueous solution for 12h to obtain a cellulose / sodium alginate composite gel electrolyte membrane.

[0056] Comparative Example 3

[0057] 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) was added to 50g of deionized water at 75℃ and stirred at 500rpm for 1h. Then, 0.75g of sodium alginate powder (viscosity 200±20mpa.s) was added to the solution and stirred at 500rpm for another 1h. 35g of the mixture was poured into a polystyrene cylindrical mold with an inner diameter of 143mm. After freeze-drying to remove moisture, the mixture was soaked in a 2mol / L zinc sulfate aqueous solution for 12h to obtain a cellulose / sodium alginate composite gel electrolyte membrane.

[0058] Comparative Example 4

[0059] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h until a transparent and homogeneous solution is formed. Then, add 0.25g of sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain a white mixed solution. Take 35g of the mixed solution and pour it into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in air for 4h, it becomes a non-flowing gel. Place it in a 350ml deionized water coagulation bath, let it stand for 1h, and wash it clean to obtain a cellulose / sodium alginate composite hydrogel. After freeze-drying to remove moisture, soak it in a 2mol / L zinc sulfate aqueous solution for 12h to obtain a cellulose / sodium alginate composite gel electrolyte membrane.

[0060] Comparative Example 5

[0061] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 3g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h. Then, add 1g of sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain a pale yellow mixed solution. Take 35g of the mixed solution and pour it into a polystyrene cylindrical mold with an inner diameter of 143mm. Due to the excessive amount of cellulose added, the mixture is very viscous and difficult to pour out to prepare a gel electrolyte membrane with a thickness of 25-800μm.

[0062] Comparative Example 6

[0063] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 0.25g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h until a transparent and homogeneous solution is formed. Then, add 1g of sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain a mixed solution. Take 35g of the mixed solution and pour it into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in air for 12h, it is still in a flowable state. Place it together with the mold into a 350ml deionized water coagulation bath. Due to insufficient regenerated cellulose and a fragile skeletal network, the mixture disperses into a paste in the coagulation bath and cannot be regenerated to form a gel film with sufficient strength.

[0064] Comparative Example 7

[0065] Prepare a 50g zinc chloride solution with a concentration of 50wt% and heat it to 75℃. Add 0.75g cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h. Then, add 0.75g sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain a mixed solution. Take 35g of the mixed solution and pour it into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in air for 12h, it is still in a flowable state. Place it together with the mold in a 350ml deionized water coagulation bath. Since the low concentration of zinc chloride solution cannot dissolve cellulose, the mixture disperses into a paste in the coagulation bath and cannot form a gel film with sufficient strength.

[0066] Comparative Example 8

[0067] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 0.75g of sodium alginate powder (viscosity 200±20mpa.s) to the zinc chloride solution and stir at 500rpm for 1h. Then, add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the solution and continue stirring at 500rpm for 1h to obtain a mixed solution. Pour 35g of the mixed solution into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in air for 12h, it is still in a flowable state. Then, place it together with the mold into a 350ml deionized water coagulation bath. Because the sodium alginate added earlier undergoes coordination crosslinking with some zinc ions, there are not enough strong hydrogen bond donors to react with cellulose molecules, and the cellulose cannot be completely dissolved. The mixture disperses into a paste in the coagulation bath and cannot form a gel film with sufficient strength.

[0068] Example 3

[0069] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h until a transparent and homogeneous solution is formed. Then, add 3g of sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain a pale yellow mixed solution. Take 35g of the mixed solution and pour it into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in air for 4h, it becomes a non-flowing gel. Place it in a 350ml deionized water coagulation bath, let it stand for 1h, and wash it clean to obtain a cellulose / sodium alginate composite hydrogel. After freeze-drying to remove moisture, soak it in a 2mol / L zinc sulfate aqueous solution for 12h to obtain a cellulose / sodium alginate composite gel electrolyte membrane.

[0070] Comparative Example 9

[0071] Prepare 50g of 65wt% zinc chloride solution and heat to 75℃. Add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) and 3g of sodium alginate powder (viscosity 200±20mpa.s) to the zinc chloride solution simultaneously. Stir at 500rpm for 2h to obtain a mixed solution. Pour 35g of the mixed solution into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in air for 4h, it becomes a non-flowing gel. Then, place the mold and the gel into a 350ml deionized water coagulation bath, let stand for 1h, and wash clean to obtain a cellulose / sodium alginate composite hydrogel. After freeze-drying to remove moisture, soak in a 2mol / L zinc sulfate aqueous solution for 12h to obtain a cellulose / sodium alginate composite gel electrolyte membrane.

[0072] Comparative Example 10

[0073] Prepare 50g of 65wt% zinc chloride solution and heat to 75℃. Add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h until a transparent and homogeneous solution is formed. Then, add 3g of sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain a pale yellow mixed solution. Take 35g of the mixed solution and pour it into a polystyrene cylindrical mold with an inner diameter of 143mm. Without aging, place the mold and the mixture directly into a 350ml deionized water coagulation bath and let stand for 1h. Then wash it clean to obtain a cellulose / sodium alginate composite hydrogel. After freeze-drying to remove moisture, soak it in a 2mol / L zinc sulfate aqueous solution for 12h to obtain a cellulose / sodium alginate composite gel electrolyte membrane.

[0074] Example 11

[0075] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h until a transparent and homogeneous solution is formed. Then, add 2.25g of sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain... The mixture was a pale yellow solution. 35g of the mixture was poured into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in the air for 4 hours, it became a non-flowing gel. The mixture, along with the mold, was then placed in a 350ml ethanol coagulation bath and allowed to stand for 1 hour. The mixture was then washed with deionized water to obtain a cellulose / sodium alginate composite hydrogel. After freeze-drying to remove moisture, the hydrogel was soaked in a 2mol / L zinc sulfate aqueous solution for 12 hours to obtain a cellulose / sodium alginate composite gel electrolyte membrane.

[0076] Comparative Example 12

[0077] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h until a transparent and homogeneous solution is formed. Then, add 2.25g of sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain the desired product. A pale yellow mixed solution was prepared. 35g of the mixed solution was poured into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in air for 4 hours, it became a non-flowing gel. The mixture, along with the mold, was then placed in a 350ml tert-butanol coagulation bath and allowed to stand for 1 hour. The mixture was then washed with deionized water to obtain a cellulose / sodium alginate composite hydrogel. After freeze-drying to remove moisture, the hydrogel was soaked in a 2mol / L zinc sulfate aqueous solution for 12 hours to obtain a cellulose / sodium alginate composite gel electrolyte membrane.

[0078] Comparative Example 13

[0079] Prepare 50g of a 65wt% zinc chloride solution and heat it to 75℃. Add 0.75g of cellulose (fiber diameter 10-50μm, degree of polymerization 6000-11000, crystallinity 60-75%) to the zinc chloride solution and stir at 500rpm for 1h until a transparent and homogeneous solution is formed. Then, add 2.25g of sodium alginate powder (viscosity 200±20mpa.s) to the solution and continue stirring at 500rpm for 1h to obtain the desired product. A pale yellow mixed solution was prepared. 35g of the mixed solution was poured into a polystyrene cylindrical mold with an inner diameter of 143mm. After aging in air for 4 hours, it became a non-flowing gel. The mixture, along with the mold, was then placed in a 350ml dimethyl sulfoxide coagulation bath and allowed to stand for 1 hour. The mixture was then washed with deionized water to obtain a cellulose / sodium alginate composite hydrogel. After freeze-drying to remove moisture, the hydrogel was soaked in a 2mol / L zinc sulfate aqueous solution for 12 hours to obtain a cellulose / sodium alginate composite gel electrolyte membrane.

[0080] The microstructure, thickness, ionic conductivity, and cycle performance of the assembled batteries in the above embodiments and comparative examples were tested and characterized.

[0081] Microscopic morphological characterization:

[0082] The surface microstructure of Comparative Example 1, Comparative Example 2, and Example 1 was characterized using scanning electron microscopy, and the results are shown below. Figure 1 .

[0083] from Figure 1As can be seen, the regenerated cellulose gel membrane (Comparative Example 1) is a single network structure composed of one material, with uneven pore distribution, relatively dense overall, and a porosity of <40%; the sodium alginate membrane (Comparative Example 2) has a sheet-like structure with no obvious pores; the cellulose / sodium alginate composite gel membrane (Example 1) exhibits a three-dimensional interpenetrating porous network structure with a porosity of over 60%, uniform pore size, and pore diameter mainly distributed in the range of 100-500 nm.

[0084] Film thickness measurement:

[0085] The thickness of different gel electrolyte membranes was measured using an electronic micrometer (accuracy 0.001 mm). Three points were randomly selected on the sample, and the average value was taken.

[0086] Ion conductivity test:

[0087] The gel electrolyte membrane was assembled into a steel sheet / separator / steel sheet symmetric cell, and EIS testing was performed using an electrochemical workstation. The ionic conductivity (σ) was obtained using the following formula:

[0088] σ=t / (R b ×S)

[0089] Where t is the thickness of the diaphragm, R b Let S be the resistance, and S be the overlap area between the diaphragm and the electrode.

[0090] Table 1 shows the test results of thickness and ionic conductivity for Comparative Example 1, Example 1, and Example 2. The Nyquist plot is shown in the figure. Figure 2 .

[0091] Table 1

[0092]

[0093] The thickness and ionic conductivity of the separator affect the ion transport rate inside the battery. Appropriate separator thickness and ionic conductivity can improve the battery's energy density and safety performance. Although Comparative Example 1 has a smaller thickness, its denser pores result in low ionic conductivity. Examples 1 and 2 have moderate thicknesses and higher ionic conductivity, allowing for faster charging and discharging, thus improving battery efficiency and safety.

[0094] Assembly and performance testing of aqueous zinc-ion batteries:

[0095] The electrolyte membranes and glass fiber separators (Whatman GF / D, 675 μm thick) prepared in Examples 1-3, Comparative Examples 1-4, and Comparative Examples 9-13 were assembled into Zn / / V₂O₅ full cells. These button cells (CR2032) used zinc foil as the negative electrode, vanadium pentoxide (V₂O₅) as the positive electrode, and a 2 mol / L zinc sulfate aqueous solution as the electrolyte. Assembly was completed in air. The charge-discharge performance of the obtained button cells was tested at room temperature using a Newway battery testing system (CT4008-5V 50mA), with a voltage range of 0.2-1.6V and a current density of 1 A / g. The results are shown below. Figure 3-7 .

[0096] The assembly method of the zinc-ion battery is as follows: taking a full battery as an example, using non-conductive tweezers, assemble the CR2032 button battery in the order of negative electrode shell, spring, steel sheet, negative electrode plate, electrolyte membrane, positive electrode plate, and positive electrode shell. Then, place the assembled battery on a hydraulic sealing machine, pressurize it to a certain pressure, and hold it for 5 seconds to seal the battery. The assembled batteries are placed for more than 1 hour before testing.

[0097] The negative electrode is a zinc sheet with a purity of ≥99%, a diameter of 15 mm, and a thickness of 100 μm.

[0098] The positive electrode uses vanadium pentoxide as the active material. The active material, SuperP, and sodium carboxymethyl cellulose are mixed in a mass ratio of 7:2:1, using deionized water as a solvent, and stirred to form a homogeneous slurry. This slurry is then uniformly coated onto a 316 stainless steel current collector to a thickness of 190 μm. After drying at 60°C for 24 hours, it is cut into 15 mm diameter discs. The active material loading is 1.5-2.5 mg / cm³. 2 .

[0099] The electrolyte membranes prepared in Comparative Example 1 and Example 2 were assembled into Zn / / Zn symmetric cells, respectively, using a 2 mol / L zinc sulfate aqueous solution as the electrolyte. These button cells (CR2032) were assembled in air using zinc foil as both the negative and positive electrodes. The resulting button cells were tested for cycle performance at room temperature using a Newway battery testing system (CT4008-5V 50mA) at a current density of 1 mA / cm². 2 The surface area capacity is 1mAh / cm². 2 The results are shown in Figure 8 , 9 .

[0100] from Figure 3As can be seen, due to its abundant pores and polar groups, Example 1 exhibits excellent cycle capacity and stability, with a reversible specific capacity still greater than 200 mAh / g after 500 cycles at a current density of 1 A / g. In contrast, the batteries assembled with electrolyte membranes containing only regenerated cellulose or sodium alginate (Comparative Examples 1 and 2) showed severe performance degradation, with the reversible specific capacity rapidly decreasing to below 100 mAh / g within 500 cycles (Comparative Example 1) or even failing (Comparative Example 2). This may be because a single network structure is difficult to form abundant ion channels, and the pore structure undergoes significant changes during cycling, leading to a sharp decline in battery capacity or even failure.

[0101] from Figure 4 It can be seen that after 500 cycles at a current density of 1 A / g, the reversible specific capacity of Example 2 is greater than 150 mAh / g. The cellulose / sodium alginate composite gel electrolyte (Comparative Example 3) that has not been regenerated by the sol-gel method has almost no capacity. This is because the natural cellulose is not dissolved and the pores between the cellulose fibers are filled and bound by sodium alginate, making it difficult to absorb and store electrolyte and provide ion channels. The low proportion of sodium alginate (Comparative Example 4) will lead to a decrease in electrochemical performance. Too much cellulose added (Comparative Example 5) will make the mixture too viscous and difficult to process further, while too little (Comparative Example 6) will prevent gel regeneration to form a sufficiently strong backbone network. Too low zinc chloride concentration (Comparative Example 7) or adding sodium alginate first to crosslink with zinc ions (Comparative Example 8) will both result in the failure of cellulose to dissolve, and the final mixture solution will not be able to regenerate a membrane.

[0102] from Figure 5 It can be seen that the reversible specific capacity of Example 3 is close to 200 mAh / g after 500 cycles at a current density of 1 A / g. The simultaneous addition of cellulose and sodium alginate during preparation (Comparative Example 9) will cause some fibers to fail to dissolve, resulting in an uneven electrolyte membrane. The assembled full battery is prone to failure during cycling. During the aging process, some interactions may occur between cellulose molecules, making the pore structure more stable. Although the lack of this process (Comparative Example 10) has a considerable reversible specific capacity, the mechanical strength is lower (<100 kPa) compared to Examples 1-3 (≥300 kPa) due to the unstable pore structure, making it difficult to meet the requirements of industrial production.

[0103] from Figure 6It can be seen that the polarity and properties of the solvent in the regeneration coagulation bath have a significant impact on the structure of the gel electrolyte membrane. The cellulose / sodium alginate composite gel electrolyte membranes regenerated using ethanol (Comparative Example 11), tert-butanol (Comparative Example 12), and dimethyl sulfoxide (Comparative Example 13) as coagulation bath solvents exhibited low reversible specific capacity in full cells, far lower than the effect when water was used as the coagulation bath solvent (Example 1). Furthermore, if the polarity and properties of a single solvent are mismatched, more than 10 wt% water can be added to the coagulation bath to improve the regeneration effect.

[0104] from Figure 7 It can be seen that Example 1 can stably cycle for more than 800 cycles at a current density of 1 A / g, with a capacity retention rate of 61.7% and a reversible specific capacity of more than 160 mAh / g, which is significantly higher than that of commercially available glass fiber membranes (52.8%, 113 mAh / g). Examples 2 and 3 also showed better cycling performance than glass fiber membranes.

[0105] from Figure 8-9 As can be seen, compared to Comparative Example 1 with a single network structure, Example 2 with a dual network structure has a longer cycle life at a current density of 1 mA / cm². 2 Area capacity 1mA / cm² 2 The battery can cycle stably for over 800 hours, indicating that the dual-network structure constructed in this invention can achieve more uniform zinc deposition during battery cycling, effectively improving the zinc dendrite growth problem. It also has advantages compared to the separator / gel electrolyte membranes reported in other patents shown in Table 2.

[0106] Table 2 compares Example 1 and Comparative Example 1 of this invention with the aqueous zinc-ion battery separator / gel electrolyte in a published invention patent.

[0107] Table 2

[0108]

[0109] The test and characterization results above show that the cellulose / sodium alginate composite gel electrolyte membrane prepared by the method of the present invention is a biomass-based gel electrolyte with a dual-network structure constructed in situ through sol-gel method and metal ion coordination crosslinking. The regenerated cellulose network skeleton formed by soaking in deionized water serves as the first network structure. After the cellulose is dissolved, sodium alginate is added and crosslinked with zinc ions in the form of ionic bonds to form a network as the second network structure. Thanks to the dual-network structure and abundant polar groups of the composite gel electrolyte, when it is applied to aqueous zinc-ion batteries, it promotes the uniform and rapid migration of zinc ions, effectively improving the cycle capacity and life of the battery.

[0110] The above embodiments are merely preferred embodiments of the present invention. The scope of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for producing a cellulose / sodium alginate composite gel electrolyte film, characterized by, The preparation process is as follows: cellulose is added to zinc chloride solution to form a transparent and homogeneous solution. Then, sodium alginate is added to the solution to obtain a mixture. The mixture is poured into a mold and aged until it becomes a non-flowing colloid. The mixed colloid is placed in a coagulation bath solvent and allowed to stand. The composite hydrogel is then regenerated and freeze-dried before being immersed in an electrolyte to obtain a cellulose / sodium alginate composite gel electrolyte membrane with a dual network structure. The zinc chloride solution has a concentration of 65-75 wt% and a temperature of 70-100℃.

2. The preparation method according to claim 1, characterized in that: The mass ratio of cellulose to zinc chloride solution is (0.75-5):100; The mass ratio of sodium alginate to zinc chloride solution is (0.75-10):

100.

3. The preparation method according to claim 1, characterized in that, The stirring time after adding cellulose to the zinc chloride solution is 0.5-6 hours, and the stirring speed is 50-2000 rpm. The stirring time after adding sodium alginate to the zinc chloride solution is 0.5-6 hours, and the stirring speed is 50-2000 rpm.

4. The preparation method according to claim 1, characterized in that: The mold is a container with a flat inner bottom. The aging process involves aging in air for 0.1-48 hours until the mixture forms a non-flowing colloid. The coagulation bath solvent is one or more of water, ethanol, acetone, tert-butanol, dimethyl sulfoxide and dimethylacetamide, the mass ratio of coagulation bath solvent to mixture is ≥1, the number of soaking times is ≥1, and the time for each soaking is ≥0.5h.

5. The preparation method according to claim 1, characterized in that: The aqueous electrolyte used for soaking includes one or more of zinc sulfate, zinc chloride, zinc bromide, zinc nitrate, and zinc trifluoromethanesulfonate, with a zinc salt concentration of 0.2-12 mol / L and a soaking time of ≥1 h.

6. A cellulose / sodium alginate composite gel electrolyte membrane prepared by the preparation method according to any one of claims 1-5.

7. The cellulose / sodium alginate composite gel electrolyte membrane according to claim 6, characterized in that, The cellulose / sodium alginate composite gel electrolyte has a regenerated cellulose network framework and a sodium alginate-zinc ion crosslinking network. The biomass-based gel electrolyte with a dual network structure is constructed in situ through sol-gel method and metal ion coordination crosslinking. The regenerated cellulose network framework formed during the coagulation bath soaking process serves as the first network structure. After the cellulose is dissolved, sodium alginate is added and crosslinked with zinc ions in the form of ionic bonds to form the second network structure.

8. An aqueous zinc-ion battery, characterized in that: The aqueous zinc-ion battery consists of a positive electrode, a separator, and a negative electrode, wherein the separator is the composite gel electrolyte membrane of claim 6 or 7.

9. The aqueous zinc-ion battery according to claim 8, characterized in that: The active material of the positive electrode includes one or more of vanadium pentoxide, manganese dioxide, Prussian blue, activated carbon, elemental iodine, elemental bromine, lithium manganate, and sodium vanadium phosphate. The active material of the negative electrode includes one or more of the following: zinc, lead, tin, zinc oxide, lead oxide, and tin oxide.

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