A high-temperature-resistant semiconductor nanowhisker-cellulose double-faced heterogeneous composite diaphragm, a preparation method and application thereof

Abstract

This invention discloses a high-temperature resistant semiconductor nanowhiskers-cellulose bifacial composite separator, its preparation method, and its application in zinc-ion batteries, belonging to the fields of nanomaterials and electrochemistry. One side of the composite separator is a pure cellulose membrane layer, and the other side is a semiconductor nanowhiskers-cellulose composite membrane layer. Preparation employs a vacuum filtration method, first filtering the pure cellulose dispersion, then filtering the semiconductor nanowhiskers-cellulose mixed dispersion, followed by forced-air drying. This invention suppresses polyiodide shuttle through the cascade trapping effect of semiconductor nanowhiskers, while simultaneously improving ionic conductivity, homogenizing the electrothermal field, guiding zinc ions to dendrite-free deposition, reducing side reactions, and significantly improving the electrochemical performance of zinc-iodine batteries under high-temperature and high-current conditions. The preparation process is simple, mild, green, and scalable. The resulting separator possesses high-temperature resistance, high mechanical strength, and excellent ion transport performance, making it suitable for energy storage systems such as aqueous zinc-iodine batteries.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and electrochemical energy storage technology, specifically relating to a high-temperature resistant semiconductor nanocrystal whisker-cellulose bifacial composite separator, its preparation method, and its application in zinc-iodine batteries. Background Technology

[0002] With the rapid development of portable electronic devices, biomedical equipment, and new energy vehicles, the demand for electrochemical energy storage is increasing. Currently, lithium-ion batteries dominate due to their high energy density and mature technology, but their scarcity of lithium resources and the flammability and high cost of organic electrolytes limit their further large-scale application. In contrast, aqueous zinc-ion batteries (AZIBs) have advantages such as intrinsic safety, low cost, and environmental friendliness. Among them, aqueous zinc-iodine batteries (Zn-I2) benefit from the fast redox kinetics of iodine and have a high theoretical capacity (211 mAh g⁻¹). -1 With its suitable redox potential (0.536 V vs. SHE) and abundant reserves in seawater, it is considered a very promising next-generation energy storage system.

[0003] However, the practical application of zinc-iodine batteries, especially their stability under high temperature (≥50 °C) and high current conditions, still faces severe challenges. Their failure mechanism mainly stems from the polyiodide shuttle on the positive electrode side and the zinc dendrite growth on the negative electrode side, and these two processes undergo drastic thermo-electrochemical coupling deterioration at high temperatures. On the one hand, polyiodide ions (I3... - , I5 - Iodine has extremely high solubility in aqueous electrolytes and easily diffuses through the membrane to the negative electrode, causing self-discharge. At high temperatures, the volatility of iodine increases significantly, leading to irreversible loss of active materials; simultaneously, the dissolution and diffusion kinetics of polyiodides accelerate, further exacerbating parasitic corrosion of the zinc negative electrode. On the other hand, the tiny protrusions on the surface of commercial zinc foil can accumulate a strong electric field due to the tip effect. At high temperatures, the formation of localized hot spots can lead to Zn... 2+ Localization of flux and kinetic mismatch between interfacial charge transfer and bulk diffusion induce loose, uneven zinc deposition and the growth of zinc dendrites, which can puncture the diaphragm and cause short circuits. Furthermore, high temperatures accelerate parasitic corrosion of zinc and hydrogen evolution reaction, leading to a sharp decline in coulombic efficiency.

[0004] As a key component of batteries, the separator plays a crucial role in preventing physical contact while simultaneously controlling ion transport, blocking polyiodides, and regulating the thermal field. Currently, commercially available glass fiber (GF) separators have large pore sizes, lack electrostatic shielding capabilities, cannot block polyiodide ion shuttles, and have low mechanical strength, making them susceptible to dendrite puncture. In recent years, to address these issues, various strategies have been explored to modify GF separators, including surface coatings and functionalization. For example, researchers such as Yao et al. modified commercial GF separators using carboxyl-functionalized metal-organic frameworks UiO-66-(COOH)2. This strategy utilizes the abundant polar carboxyl groups on the MOF surface to effectively block polyiodide shuttles and accelerate Zn transport through electrostatic repulsion. 2+ Desolvation effectively suppresses the shuttle effect and improves cycle stability; however, such organic or hybrid modified layers typically have low thermal conductivity, failing to effectively dissipate localized heat accumulation on the electrode surface under high-temperature conditions, thus limiting the application of batteries in harsh environments. Therefore, there is an urgent need to develop a high-temperature resistant semiconductor nanofiber composite separator that can achieve multi-iodide cascade trapping through defect engineering and utilize high thermal conductivity to achieve synergistic homogenization of electric and thermal fields, in order to overcome the performance bottleneck of high-temperature zinc-iodine batteries.

[0005] Cellulose, as a naturally abundant and environmentally friendly polymer, holds promise for solving the aforementioned problems. The abundant hydroxyl groups between cellulose molecules provide excellent wettability, while strong van der Waals forces and intramolecular hydrogen bonds enhance its mechanical properties. Therefore, cellulose can be used to prepare ultrathin, porous, functionalized membranes with excellent mechanical strength. However, due to the strong interactions within the protofibrils, pure cellulose membranes often have low porosity and lack specific adsorption sites for polyiodides, making it difficult to meet the requirements of high-performance batteries. Introducing semiconductor nanocrystals with high thermal conductivity and abundant defect sites into the cellulose matrix is ​​an effective strategy to overcome this bottleneck. Semiconductors possess excellent chemical stability and are not easily corroded in iodine electrolytes. More importantly, the stacking faults and carbon vacancy defects on the surface of silicon carbide whiskers can not only act as highly active sites for cascade capture and catalytic conversion of polyiodide ions, completely suppressing the shuttle effect; their excellent intrinsic thermal conductivity and semiconductor properties can also synergistically homogenize the thermal and electric fields at the electrode interface, eliminating local hot spots to inhibit zinc dendrite growth. Therefore, constructing a high-temperature resistant semiconductor nanocrystal / cellulose bifacial composite separator is an effective strategy to simultaneously regulate the chemistry of polyiodides and the physical field of zinc deposition, thereby significantly improving the electrochemical performance of zinc-iodine batteries under harsh conditions. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a high-temperature resistant semiconductor nanocrystal / cellulose bifacial composite membrane and its preparation method, which are in contrast to the above-mentioned prior art. The preparation method is simple, meets the requirements of green chemistry, and is easy to scale up. On this basis, the high-temperature resistant semiconductor nanocrystal / cellulose bifacial composite membrane also has excellent electrochemical performance.

[0007] To achieve the above objectives, the present invention provides a high-temperature resistant semiconductor nanocrystal whisker-cellulose biaxially oriented composite membrane. The composite membrane has a biaxially oriented layered structure, with one side being a pure cellulose membrane layer and the other side being a semiconductor nanocrystal whisker-cellulose composite membrane layer. In the composite membrane layer, the semiconductor nanocrystal whiskers and cellulose interweave to form a nanoporous structure.

[0008] Furthermore, the semiconductor nanocrystals are silicon carbide nanowires, silicon carbide nanocrystals, or modified silicon carbide nanomaterials; the cellulose is bacterial cellulose, carboxylated cellulose nanofibers, sulfonated cellulose nanocrystals, or microfibrillated cellulose.

[0009] Furthermore, the carboxylated cellulose nanofibers are derived from wood pulp or cotton.

[0010] Furthermore, in the composite separator layer, the mass ratio of semiconductor nanocrystals to cellulose is 1:1 to 1:3. Cellulose forms a strong three-dimensional network framework through intermolecular hydrogen bonds, providing fundamental mechanical support for the separator. If the proportion of semiconductor nanocrystals is higher than 1:1, the rigid whiskers will disrupt the continuous network of cellulose, causing the separator to become brittle and prone to cracking, and easily damaged during battery assembly and cycling. Simultaneously, an excessively high whisker ratio will result in overly dense pores or excessively large pore sizes, reducing the separator's physical barrier ability against polyiodides and potentially causing localized current concentration. If the ratio is lower than 1:3, the whisker content is too low, failing to form an effective through-and-through thermally conductive network, weakening its functionalization. Furthermore, an excessively low whisker ratio results in insufficient porosity, reduced electrolyte absorption, and reduced Zn content. 2+ Migration is hindered, increasing ion transport impedance.

[0011] This invention also provides a method for preparing the above-mentioned high-temperature resistant semiconductor nanocrystal-cellulose bifacial composite separator, characterized by comprising the following steps: 1) Preparation of high-temperature resistant semiconductor nanocrystals; 2) Disperse cellulose in deionized water to obtain dispersion A; 3) Add semiconductor nanocrystals and cellulose to deionized water and mix them using a homogenizer to obtain dispersion B; 4) First, vacuum filter the dispersion A obtained in step 2) onto a nylon filter membrane to obtain a pure cellulose membrane layer. Then, add the dispersion B obtained in step 3) and continue filtration to obtain a semiconductor nanocrystal whisker / cellulose composite membrane layer. 5) The obtained wet film is dried by blowing air to obtain a high-temperature resistant semiconductor nanocrystal whisker / cellulose bi-sided anisotropic composite membrane.

[0012] Furthermore, in step (5), the temperature of the blower drying is 60~80℃ and the drying time is 12~24h.

[0013] Furthermore, in step (3), the mass ratio of semiconductor nanocrystals to cellulose is 1:1 to 1:3.

[0014] The present invention also provides an application of the above-mentioned high-temperature resistant semiconductor nanocrystal-cellulose bifacial composite separator, characterized in that it is used as a separator material for zinc-ion batteries.

[0015] Furthermore, the zinc-ion battery is an aqueous zinc-iodine battery.

[0016] Furthermore, the composite separator is used to suppress the polyiodide shuttle effect and zinc dendrite growth in zinc-iodine batteries.

[0017] The beneficial effects of this invention are: Through extensive research, this invention has discovered that by selecting heat-resistant silicon carbide nanocrystals and combining them with different types of cellulose, and by controlling their mass ratio and microstructure, a high-temperature resistant semiconductor nanocrystal / cellulose bifacial composite membrane can be prepared using a simple vacuum filtration operation. Its mechanism of action is as follows: (1) The cellulose layer has abundant hydrophilic functional groups (hydroxyl groups), which not only endow the membrane with excellent electrolyte wettability, but also a large number of negatively charged oxygen-containing functional groups can form an electrostatic shielding layer, effectively repelling negatively charged polyiodide ions. At the same time, the strong hydrogen bond network between cellulose chains endows the membrane with excellent mechanical strength, constructing the first physical defense against zinc dendrite penetration. (2) Unlike ordinary materials, the defect-state silicon carbide semiconductor nanocrystals introduced in this invention are rich in stacking fault structures and positively charged carbon vacancies on their surface. These defect sites, as highly active centers, can effectively electrostatically adsorb and catalytically convert trace amounts of polyiodide ions that pass through the cellulose layer, thoroughly suppressing the shuttle effect of polyiodides from a chemical perspective and solving the problem of loss of positive electrode active material. (3) Silicon carbide, as a wide bandgap semiconductor, has unique dielectric properties. It can effectively regulate the ion flux at the interface, homogenize the micro electric field distribution, and significantly reduce the tip effect on the zinc anode surface, thereby inducing zinc ions to be deposited uniformly in a planar manner and suppressing uncontrollable dendrite growth. (4) Silicon carbide has excellent intrinsic thermal conductivity. Under high-temperature conditions, it can quickly dissipate the local heat accumulation on the electrode surface and eliminate local hot spots. This uniformity of the thermal field avoids the aggravation of zinc corrosion and malignant dendrite growth caused by local high temperature. Therefore, the use of this high-temperature resistant semiconductor nanofiber / cellulose biaxial anisotropic composite separator can significantly improve the cycle stability and coulombic efficiency of zinc-iodine batteries under high current density and high temperature harsh conditions, and has great application prospects.

[0018] The beneficial effects of this invention are as follows: Firstly, this invention primarily prepares a high-temperature resistant semiconductor nanofiber / cellulose bifacial composite separator using a simple and easy-to-implement vacuum filtration method. When used as a separator material for zinc-ion batteries, it exhibits long cycle life, good rate performance, and excellent cycle stability. Furthermore, by precisely controlling the mass ratio of semiconductor nanofibers to cellulose, an optimal balance is achieved between mechanical properties, ion transport performance, and functionalization synergistic effects. Secondly, the process of this invention is simple; a mixed dispersion of semiconductor nanofibers and cellulose can be obtained through simple mechanical mixing, followed by layered vacuum filtration to obtain the high-temperature resistant semiconductor nanofiber / cellulose bifacial composite separator. This method is highly feasible, easily scaled up, conforms to the characteristics of green chemistry, and is conducive to market promotion. Attached Figure Description

[0019] Figure 1 Scanning electron microscope image of silicon carbide nanocrystals; Figure 2Scanning electron microscope image of a silicon carbide nanocrystal / bacterial cellulose biaxial anisotropic composite membrane prepared by vacuum filtration; Figure 3 A Zn||Zn symmetric cell assembled using a silicon carbide nanocrystal / bacterial cellulose bifacial composite separator was tested at 0.5 mA / cm². 2 Cyclic performance at current density; Figure 4 A Zn||Zn symmetric cell assembled using a silicon carbide nanocrystal / bacterial cellulose bifacial composite separator was tested at 80 mA / cm². 2 Cyclic performance at current density; Figure 5 The graph shows the cycling performance of a Zn||Zn symmetric cell assembled using a silicon carbide nanocrystal / bacterial cellulose bifacial composite separator under high temperature conditions (50°C). Figure 6 The graph shows the long-cycle performance of a Zn||I2 full cell assembled using a silicon carbide nanocrystal / bacterial cellulose bifacial composite separator at a current density of 20 A / g. Figure 7 The graph shows the long-term cycling performance of a Zn||I2 full cell assembled using a silicon carbide nanocrystal / bacterial cellulose bifacial composite separator under high temperature conditions (50°C). Detailed Implementation

[0020] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0021] Example 1: A method for preparing a silicon carbide nanocrystal-bacterial cellulose bifacial composite membrane includes the following steps: 1) Prepare silicon carbide nanocrystal materials; 2) Disperse 15 mg of bacterial cellulose slurry in 30 g of deionized water and stir for 5 min to obtain a uniform bacterial cellulose dispersion (dispersion A). 3) Add 15 mg of bacterial cellulose slurry and 15 mg of silicon carbide nanocrystals to 30 g of deionized water and stir vigorously with a homogenizer for 1 h to obtain a uniform gray-green dispersion (dispersion B). 4) First, vacuum filter the dispersion A obtained in step 2) onto a nylon filter membrane, then add the dispersion B obtained in step 3), and continue filtration; 5) The obtained wet film was dried at 60℃ for 12 h to finally obtain a silicon carbide nanofiber / bacterial cellulose bi-sided anisotropic composite membrane.

[0022] Taking the silicon carbide nanocrystal / bacterial cellulose biaxially shaped composite membrane of the present invention as an example, the silicon carbide nanocrystal structure is determined by scanning electron microscopy. Figure 1 As shown, the synthesized silicon carbide nanocrystals exhibit high aspect ratio and specific surface area, with lengths reaching 5-10 μm and diameters of 80-120 nm. Figure 2 The image shows a SEM image of a silicon carbide nanocrystal / bacterial cellulose composite membrane. As can be seen from the image, the silicon carbide nanocrystals and bacterial cellulose are well interwoven to form a uniform nanoporous structure.

[0023] The application of the silicon carbide nanocrystal / bacterial cellulose biaxially shaped composite separator obtained in this embodiment as a separator material for zinc-ion batteries is as follows: The prepared silicon carbide nanocrystal / bacterial cellulose composite separator is used as the separator, zinc sheet is used as the negative electrode, I2 is used as the positive electrode, 2 M zinc sulfate aqueous solution is used as the electrolyte, and the battery shell is a CR2032 type stainless steel button battery shell.

[0024] Figure 3 A Zn||Zn symmetric cell assembled using a silicon carbide nanocrystal / bacterial cellulose bifacial composite separator was tested at 0.5 mA / cm². 2 Cyclic performance at current density. As shown in the figure, the symmetrical battery assembled using the separator prepared in this invention has a small polarization voltage and an ultra-long cycle life, and can be stably cycled for more than 6200 h.

[0025] Figure 4 A Zn||Zn symmetric cell assembled using a silicon carbide nanocrystal / bacterial cellulose bifacial composite separator was tested at 80 mA / cm². 2 Cyclic performance at current density. As shown in the figure, the symmetrical battery assembled using the separator prepared in this invention still has an ultra-long cycle life even at ultra-high current density, and can be stably cycled for more than 1000 h.

[0026] Figure 5 The figure shows the cycling performance of a Zn||Zn symmetric cell assembled using a silicon carbide nanocrystal / bacterial cellulose bifacial composite separator at high temperature (50°C). As can be seen from the figure, the symmetric cell assembled using the separator prepared in this invention exhibits excellent cycling performance even at high temperature (50°C) and 10 mA / cm². 2 Under current density conditions, it can still cycle stably for more than 600 hours.

[0027] Figure 6The figure shows the long-term cycling performance of a Zn||I2 full cell assembled using a silicon carbide nanocrystal / bacterial cellulose bifacial composite separator at a current density of 20 A / g. As can be seen from the figure, the Zn||I2 full cell assembled using the separator prepared in this invention achieves a discharge specific capacity of 152 mA h / g in the first cycle at a current density of 20 A / g, and still retains a discharge specific capacity of 161 mA h / g after 100,000 cycles, demonstrating excellent cycling stability.

[0028] Figure 7 The figure shows the long-term cycling performance of a Zn||I2 full cell assembled using a silicon carbide nanocrystal / bacterial cellulose bifacial composite separator under high-temperature conditions (50°C). As can be seen from the figure, even under harsh high-temperature conditions, the Zn||I2 full cell assembled using the separator prepared in this invention achieves a discharge specific capacity of 145 mAh / g in the first cycle at a current density of 10 A / g, and still retains a discharge specific capacity of 150 mA h / g after 15,000 cycles.

[0029] Example 2: A method for preparing a biaxially oriented composite membrane of silicon carbide nanocrystals and carboxylated cellulose nanofibers (wood pulp) includes the following steps: 1) The preparation process of silicon carbide nanocrystals is the same as in Example 1; 2) Disperse 15 mg of carboxylated cellulose nanofiber (wood pulp) in 30 g of deionized water and stir for 5 min to obtain a uniform cellulose aqueous dispersion (dispersion A). 3) Add 30 mg of carboxylated cellulose nanofiber (wood pulp) pulp and 15 mg of silicon carbide nanocrystals to 30 g of deionized water and stir vigorously with a homogenizer for 1 h to obtain a uniform gray-green dispersion (dispersion B). 4) First, vacuum filter the dispersion A obtained in step 2) onto a nylon filter membrane, then add the dispersion B obtained in step 3), and continue filtration; 5) The obtained wet film was dried at 60℃ for 24h to finally obtain a silicon carbide nanocrystal / carboxylated cellulose nanofiber (wood pulp) biaxial anisotropic composite membrane.

[0030] Taking the silicon carbide nanocrystal / carboxylated cellulose nanofiber (wood pulp) biaxially shaped composite membrane obtained in this embodiment as an example, at 80 mA / cm 2At high current density, the Zn||Zn symmetric cell assembled using the separator prepared by this invention can cycle stably for more than 820 h; at a high temperature of 50℃, the Zn||Zn symmetric cell assembled using the separator prepared by this invention can cycle stably for more than 510 h; at a current density of 10 A / g and a high temperature, the Zn||I2 full cell assembled using the separator prepared by this invention can achieve a discharge specific capacity of 145 mA h / g in the first cycle and 155 mA h / g after 13,000 cycles.

[0031] Example 3: A method for preparing a bifacial anisotropic composite membrane of silicon carbide nanocrystals and carboxylated cellulose nanofibers (cotton) includes the following steps: 1) The preparation process of silicon carbide nanocrystals is the same as in Example 1; 2) Disperse 15 mg of carboxylated cellulose nanofiber (cotton) slurry in 30 g of deionized water and stir for 5 min to obtain a uniform cellulose aqueous dispersion (dispersion A). 3) Add 45 mg of carboxylated cellulose nanofiber (cotton) slurry and 15 mg of silicon carbide nanocrystals to 30 g of deionized water and stir vigorously with a homogenizer for 1 h to obtain a uniform gray-green dispersion (dispersion B). 4) First, vacuum filter the dispersion A obtained in step 2) onto a nylon filter membrane, then add the dispersion B obtained in step 3), and continue filtration; 5) The obtained wet film was dried at 80℃ for 12 h to finally obtain a silicon carbide nanofiber / carboxylated cellulose nanofiber (cotton) bi-sided anisotropic composite membrane.

[0032] Taking the silicon carbide nanocrystal / carboxylated cellulose nanofiber (cotton) biaxially shaped composite membrane obtained in this embodiment as an example, at 80 mA / cm 2 At high current density, the Zn||Zn symmetric battery assembled using the separator prepared by this invention can cycle stably for more than 800 h; at a high temperature of 50℃, the Zn||Zn symmetric battery assembled using the separator prepared by this invention can cycle stably for more than 520 h; at a current density of 10 A / g and a high temperature, the Zn||I2 full cell assembled using the separator prepared by this invention can achieve a discharge specific capacity of 143 mA h / g in the first cycle and a discharge specific capacity of 150 mA h / g after 13,000 cycles.

[0033] Example 4: A method for preparing a biaxially shaped composite separator of silicon carbide nanocrystals and sulfonated cellulose nanocrystals includes the following steps: 1) The preparation process of silicon carbide nanocrystals is the same as in Example 1; 2) Disperse 15 mg of sulfonated cellulose nanocrystal slurry in 30 g of deionized water and stir for 5 min to obtain a uniform cellulose aqueous dispersion (dispersion A). 3) Add 15 mg of sulfonated cellulose nanofiber slurry and 15 mg of silicon carbide nanofiber to 30 g of deionized water and stir vigorously with a homogenizer for 1 h to obtain a uniform gray-green dispersion (dispersion B). 4) First, vacuum filter the dispersion A obtained in step 2) onto a nylon filter membrane, then add the dispersion B obtained in step 3), and continue filtration; 5) The obtained wet film was dried at 80℃ for 24 h to finally obtain a silicon carbide nanocrystal / sulfonated cellulose nanocrystal biaxial anisotropic composite membrane.

[0034] Taking the silicon carbide nanocrystal / sulfonated cellulose nanocrystal biaxially oriented composite membrane obtained in this embodiment as an example, at 80 mA / cm 2 At high current density, the Zn||Zn symmetric cell assembled using the separator prepared by this invention can cycle stably for more than 810 h; at a high temperature of 50℃, the Zn||Zn symmetric cell assembled using the separator prepared by this invention can cycle stably for more than 500 h; at a current density of 10 A / g and a high temperature, the Zn||I2 full cell assembled using the separator prepared by this invention can achieve a discharge specific capacity of 143 mA h / g in the first cycle and a discharge specific capacity of 152 mA h / g after 12,000 cycles.

[0035] Example 5: A method for preparing a silicon carbide nanocrystal-microfibrillated cellulose bifacial composite membrane includes the following steps: 1) The preparation process of silicon carbide nanocrystals is the same as in Example 1; 2) Disperse 15 mg of microfibrillated cellulose slurry in 30 g of deionized water and stir with a turbine for 5 min to obtain a uniform cellulose aqueous dispersion (dispersion A). 3) Add 15 mg of microfibrillated cellulose slurry and 15 mg of silicon carbide nanocrystals to 30 g of deionized water and stir vigorously with a homogenizer for 1 h to obtain a uniform gray-green dispersion (dispersion B). 4) First, vacuum filter the dispersion A obtained in step 2) onto a nylon filter membrane, then add the dispersion B obtained in step 3), and continue filtration; 5) The obtained wet film was dried at 60℃ for 12 h to finally obtain a silicon carbide nanocrystal whisker / microfibrillated cellulose bi-sided anisotropic composite membrane.

[0036] Taking the silicon carbide nanocrystal / microfibrillated cellulose biaxially shaped composite membrane obtained in this embodiment as an example, at 80 mA / cm 2At high current density, the Zn||Zn symmetric cell assembled using the separator prepared by this invention can cycle stably for more than 780 h; at a high temperature of 50 °C, the Zn||Zn symmetric cell assembled using the separator prepared by this invention can cycle stably for more than 480 h; at a current density of 10 A / g and a high temperature, the Zn||I2 full cell assembled using the separator prepared by this invention can achieve a discharge specific capacity of 140 mA h / g in the first cycle and 150 mA h / g after 14,000 cycles.

[0037] Example 6: A method for preparing a silicon carbide nanowire-bacterial cellulose bifacial composite membrane includes the following steps: 1) Silicon carbide nanowire materials were obtained using a hydrothermal method; 2) Disperse 15 mg of bacterial cellulose slurry in 30 g of deionized water and stir with a turbine for 5 min to obtain a uniform cellulose aqueous dispersion (dispersion A). 3) Add 15 mg of bacterial cellulose slurry and 15 mg of silicon carbide nanowires to 30 g of deionized water and stir vigorously with a homogenizer for 1 h to obtain a uniform dispersion (dispersion B). 4) First, vacuum filter the dispersion A obtained in step 5) onto a nylon filter membrane, then add the dispersion B obtained in step 3), and continue vacuum filtration; 5. The obtained wet membrane was dried at 60℃ for 12 h to finally obtain a silicon carbide nanowire / bacterial cellulose biaxial anisotropic composite membrane.

[0038] Taking the silicon carbide nanowire / bacterial cellulose biaxially shaped composite membrane obtained in this embodiment as an example, at 80 mA / cm 2 At high current density, the Zn||Zn symmetric battery assembled using the separator prepared by this invention can cycle stably for more than 750 h; at a high temperature of 50°C, the Zn||Zn symmetric battery assembled using the separator prepared by this invention can cycle stably for more than 550 h; at a current density of 10 A / g and a high temperature, the Zn||I2 full cell assembled using the separator prepared by this invention can achieve a discharge specific capacity of 141 mA h / g in the first cycle and 151 mA h / g after 12,000 cycles.

[0039] Example 7: A method for preparing a biaxially oriented composite membrane of silicon carbide nanowires and carboxylated cellulose nanofibers (wood pulp) includes the following steps: 1) The preparation process of silicon carbide nanowires is the same as in Example 6; 2) 15 mg of carboxylated cellulose nanofibers (wood pulp) were dispersed in 30 g of deionized water and stirred with a turbine for 5 min to obtain a uniform cellulose aqueous dispersion (dispersion A). 3) Add 30 mg of carboxylated cellulose nanofiber (wood pulp) pulp and 15 mg of silicon carbide nanowires to 30 g of deionized water and stir vigorously with a homogenizer for 1 h to obtain a uniform dispersion (dispersion B). 4) First, vacuum filter the dispersion A obtained in step 2) onto a nylon filter membrane, then add the dispersion B obtained in step 3), and continue filtration; 5) The obtained wet film was dried at 70℃ for 12 h to finally obtain a silicon carbide nanowire / carboxylated cellulose nanofiber (wood pulp) biaxial anisotropic composite membrane.

[0040] Taking the silicon carbide nanowire / carboxylated cellulose nanofiber (wood pulp) biaxially shaped composite membrane obtained in this embodiment as an example, at 80 mA / cm 2 At high current density, the Zn||Zn symmetric cell assembled using the separator prepared by this invention can cycle stably for more than 780 h; at a high temperature of 50℃, the Zn||Zn symmetric cell assembled using the separator prepared by this invention can cycle stably for more than 500 h; at a current density of 10 A / g and a high temperature, the Zn||I2 full cell assembled using the separator prepared by this invention can achieve a discharge specific capacity of 144 mA h / g in the first cycle and 153 mA h / g after 11,000 cycles.

[0041] Comparative Example 1: Compared to Example 1, 7.5 mg of bacterial cellulose slurry and 15 mg of silicon carbide nanocrystals were added to 30 g of deionized water (the mass ratio of nanocrystals to cellulose was 2:1), and everything else was the same as in Example 1. Due to the excessively high proportion of rigid whiskers, the continuous hydrogen bond network of cellulose was disrupted, leading to increased mechanical brittleness and excessively large pores in the resulting membrane. Taking the silicon carbide nanocrystal / bacterial cellulose biaxially oriented composite membrane obtained in this comparative example, at 80 mA / cm²... 2 At high current densities, the Zn||Zn symmetric cells assembled using this membrane fail short-circuit after less than 180 hours of cycling due to local current concentration and zinc dendrite piercing. At a high temperature of 50°C, the Zn||I2 full cells assembled using this membrane suffer from reduced physical barrier capacity and severe polyiodide shuttle, resulting in a specific capacity of only 95 mA h / g after 2000 cycles at a current density of 10 A / g.

[0042] Comparative Example 2: Compared to Example 1, 60 mg of bacterial cellulose slurry and 15 mg of silicon carbide nanocrystals were added to 30 g of deionized water, with everything else remaining the same as in Example 1 (the mass ratio of nanocrystals to cellulose was 1:4). Due to the low whisker content, an effective through-thermal conductive network could not be formed in the membrane, and the dense stacking of cellulose resulted in insufficient porosity. Taking the silicon carbide nanocrystal / bacterial cellulose biaxially oriented composite membrane obtained in this comparative example, at 80 mA / cm²... 2 At high current densities, the Zn||Zn symmetric cells assembled using this membrane exhibit significantly increased ion transport impedance and a substantial rise in polarization voltage, resulting in a cycle life of only 250 h. Under high-temperature conditions of 50 °C, due to the lack of sufficient active sites for cascade capture and catalytic conversion of polyiodides, the Zn||I2 full cells assembled using this membrane fail after only 1500 cycles, and exhibit poor rate performance.

[0043] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A high-temperature resistant semiconductor nanocrystal-cellulose biaxially shaped composite separator, characterized in that, The composite membrane has a biaxially oriented layered structure, with one side being a pure cellulose membrane layer and the other side being a semiconductor nanocrystal-cellulose composite membrane layer. In the composite membrane layer, the semiconductor nanocrystals and cellulose interweave to form a nanoporous structure.

2. The composite diaphragm according to claim 1, characterized in that, The semiconductor nanocrystals are silicon carbide nanowires, silicon carbide nanocrystals, or modified silicon carbide nanomaterials; the cellulose is bacterial cellulose, carboxylated cellulose nanofibers, sulfonated cellulose nanocrystals, or microfibrillated cellulose.

3. The composite diaphragm according to claim 2, characterized in that, The carboxylated cellulose nanofibers are derived from wood pulp or cotton.

4. The composite diaphragm according to claim 1, characterized in that, In the composite membrane layer, the mass ratio of semiconductor nanocrystals to cellulose is 1:1 to 1:

3.

5. A method for preparing a high-temperature resistant semiconductor nanocrystal-cellulose bifacial composite separator according to any one of claims 1 to 4, characterized in that, Includes the following steps: 1) Preparation of high-temperature resistant semiconductor nanocrystals; 2) Disperse cellulose in deionized water to obtain dispersion A; 3) Add semiconductor nanocrystals and cellulose to deionized water and mix them using a homogenizer to obtain dispersion B; 4) First, vacuum filter the dispersion A obtained in step 2) onto a nylon filter membrane to obtain a pure cellulose membrane layer. Then, add the dispersion B obtained in step 3) and continue filtration to obtain a semiconductor nanocrystal / cellulose composite membrane layer. 5) The obtained wet film is dried by blowing air to obtain a high-temperature resistant semiconductor nanocrystal whisker / cellulose bi-sided anisotropic composite membrane.

6. The preparation method according to claim 5, characterized in that, In step (5), the temperature of the blower drying is 60~80℃ and the drying time is 12~24h.

7. The preparation method according to claim 5, characterized in that, In step (3), the mass ratio of semiconductor nanocrystals to cellulose is 1:1 to 1:

3.

8. An application of the high-temperature resistant semiconductor nanocrystal whisker-cellulose biaxially shaped composite separator according to any one of claims 1 to 4, characterized in that, Used as a separator material in zinc-ion batteries.

9. The application according to claim 8, characterized in that, The zinc-ion battery is an aqueous zinc-iodine battery.

10. The application according to claim 8, characterized in that, The composite separator is used to suppress the polyiodide shuttle effect and zinc dendrite growth in zinc-iodine batteries.

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