A lignocellulosic composite separator and a method for preparing the same

Abstract

This invention relates to the field of battery separator technology, specifically to a wood fiber composite separator and its preparation method. The separator uses renewable softwood pulp as the basic raw material. After introducing aldehyde groups through oxidation with sodium periodate, a zinc coordination network functional layer is constructed using tannic acid, zinc acetate, and cystamine. Subsequently, molecular cross-linking is achieved with polyethylene glycol monomethyl ether, polyethylene glycol, hexamethylene diisocyanate, γ-aminopropyltriethoxysilane, and nano-silica under the action of a catalyst. Finally, it is prepared by papermaking and hot pressing processes. This separator is particularly suitable for high-safety, high-performance aqueous zinc-ion battery applications, providing an innovative technical path for the industrialization and green upgrading of zinc-ion battery separator materials.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, and in particular to a wood fiber composite separator and its preparation method. Background Technology

[0002] With the rapid development of renewable energy and energy storage technologies, zinc-based secondary batteries, characterized by high safety, low cost, and environmental friendliness, are gradually becoming an important technological direction to replace traditional lithium-ion batteries. Zinc batteries, thanks to the high theoretical capacity, low potential, and abundant resources of zinc, demonstrate enormous application potential in large-scale energy storage, portable electronic devices, and electric vehicles. However, the actual industrialization of zinc batteries still faces a series of key technological bottlenecks, particularly the synergistic optimization challenges related to the mechanical strength, ion transport efficiency, interface stability, and processing adaptability of the separator material.

[0003] As a core component of zinc batteries, the separator material not only fulfills the basic function of preventing direct contact between the positive and negative electrodes and avoiding short circuits, but also affects the battery's ion transport rate, cycle life, and safety performance. While existing inorganic separators possess good mechanical strength and thermal stability, they typically suffer from limitations such as insufficient flexibility, brittleness, and complex processing, hindering large-scale manufacturing and the integration of complex battery structures. Organic polymer separators, such as polypropylene and polyethylene, offer advantages in flexibility and manufacturing cost, but are prone to problems in aqueous electrolyte environments, including insufficient electrolyte wettability, high thermal shrinkage, and easy interfacial decomposition. Therefore, developing innovative zinc battery separator materials that combine high mechanical strength, excellent ion conductivity, good dimensional stability, and superior wettability has become a major technical challenge that urgently needs to be addressed in this field.

[0004] Wood fibers have attracted widespread attention in the field of novel separator materials due to their wide availability, excellent renewability, low cost, and abundant surface-active groups. Wood fibers themselves are rich in hydrophilic groups such as hydroxyl and carboxyl groups, possessing certain liquid absorption capacity and ion channel characteristics. However, traditional wood fiber structures suffer from drawbacks such as insufficient interfiber bonding, active molecular chain movement, high overall brittleness, and susceptibility to mechanical fracture, failing to meet the standards for zinc battery separators under high-rate cycling and high safety requirements. Therefore, endowing wood fibers with controllable mechano-electrochemical properties through molecular structure design and surface chemical modification has become an important direction for technological development.

[0005] In recent years, literature has reported on improving the mechanical and thermal stability of fiber-based separators through polymer coating, inorganic filling, and chemical crosslinking. For example, polymer modification can enhance the interfacial bonding between fibers to a certain extent; inorganic nanoparticle filling can improve the dimensional stability of the separator and inhibit zinc dendrite growth. However, single modification methods often fail to simultaneously achieve multiple performance indicators such as high mechanical strength, high ion conductivity, low thermal shrinkage, and good wetting. Especially under the long-cycle and high-temperature environment of zinc batteries, the separator structure is prone to damage and deformation, leading to shortened battery life and increased safety risks. Furthermore, how to achieve efficient molecular modification and fine-tuning of multiple components while maintaining green environmental protection and ease of industrialization remains a key focus and challenge in the industry.

[0006] In summary, the design and development of wood fiber-based zinc battery separators with superior mechanical properties, excellent ion conduction channels, stable interface layers, and high thermal dimensional stability requires multi-dimensional mechanism innovation, including molecular-scale crosslinking of wood fibers, introduction of functional groups, and network structure regulation. This will fully unleash the application potential of wood fiber materials in the field of high-performance zinc battery separators, thereby promoting the practical application of aqueous zinc batteries. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a wood fiber composite separator and its preparation method, so as to improve the mechanical and electrochemical properties of the wood fiber separator and meet the application requirements of high-performance aqueous zinc batteries.

[0008] To achieve the above objectives, the present invention provides a wood fiber composite diaphragm, which is obtained by pulping, papermaking, and hot pressing of a cross-linked zinc wood fiber composite material.

[0009] Furthermore, the preparation steps of the cross-linked zinc-wood fiber composite material are as follows: (1) Homogenize the softwood pulp in deionized water at high speed to obtain a wood fiber matrix; (2) Aldehyde-modified wood fibers are obtained by oxidizing the wood fiber matrix with sodium periodate; (3) Tannic acid, zinc acetate and cystamine form metal salts through coordination, which then react with aldehyde-modified wood fibers to obtain zinc network functionalized wood fibers; (4) Zinc network functionalized wood fibers, polyethylene glycol monomethyl ether, polyethylene glycol, hexamethylene diisocyanate, γ-aminopropyltriethoxysilane and nano silica are crosslinked under the catalysis of dibutyltin dilaurate to obtain crosslinked zinc wood fiber composite materials.

[0010] Preferably, in step (1), the dry weight ratio of softwood pulp to deionized water is 60-100:200-400.

[0011] Preferably, the high-speed homogenization speed in step (1) is 10000-15000 rpm and the time is 10-20 min.

[0012] Preferably, in step (2), the weight ratio of sodium periodate to lignocellulose matrix is ​​3-8:50-70.

[0013] Preferably, in step (3), the weight ratio of tannic acid, zinc acetate, cystamine and aldehyde-modified wood fiber is 8-12:5-7:2-5:40-60.

[0014] Preferably, the specific preparation steps of zinc network functionalized wood fiber in step (3) are as follows: add tannic acid and zinc acetate to phosphate buffer solution with pH 7, stir for 8-12 min, then add cystamine, heat to 55-65℃, stir for 1-3 h, then add aldehyde-modified wood fiber, cool to 45-55℃, continue stirring for 4-6 h, vacuum filter, wash, vacuum dry to obtain zinc network functionalized wood fiber.

[0015] Preferably, in step (4), the weight ratio of zinc network functionalized wood fiber, polyethylene glycol monomethyl ether, polyethylene glycol, hexamethylene diisocyanate, γ-aminopropyltriethoxysilane, nano silica and dibutyltin dilaurate is 40-60:10-20:15-25:2.5-4.5:0.3-0.7:8-16:0.3-0.7.

[0016] Preferably, the average particle size of the nano-silica in step (4) is 20-100 nm.

[0017] Preferably, in step (4), the weight-average molecular weight of polyethylene glycol monomethyl ether is 2000 and the weight-average molecular weight of polyethylene glycol is 2000.

[0018] Preferably, the film forming process is carried out using a filter screen with a pore size of 18-22 μm via wet film forming, and the wet film basis weight is controlled at 40-50 g / m³. 2 .

[0019] Preferably, the hot pressing is performed at 115-125℃ and 4-6MPa for 3-8 minutes.

[0020] Furthermore, the present invention also provides a method for preparing a wood fiber composite membrane, comprising the following steps: dispersing a cross-linked zinc wood fiber composite material in deionized water, pulping, papermaking, hot pressing, and obtaining a wood fiber composite membrane.

[0021] Preferably, the weight ratio of the cross-linked zinc-wood fiber composite material to deionized water is 60-100:500-1200.

[0022] The beneficial effects of this invention are: This invention achieves a significant improvement in the overall performance of wood fiber membranes by constructing a multi-level composite structure of aldehyde-based fiber-cystamine-bridged zinc tannin network, and has the following beneficial effects: First, this invention establishes a controllable chemical modification system for fiber surfaces. Aldehyde groups are introduced onto the fiber surface via sodium periodate oxidation, providing active anchoring sites for subsequent functionalization. The aldehyde groups react with cystamine via a Schiff base reaction to form stable covalent bonds, avoiding the problem of functional component detachment in traditional physical adsorption methods. This chemical bonding mechanism ensures a strong bond between the modified layer and the substrate, laying the molecular foundation for the long-term stability of the membrane.

[0023] Secondly, this invention innovatively introduces a tannic acid-zinc coordination network system. The abundant catechol groups in the tannic acid molecule form a stable coordination network with zinc ions through chelation. This network not only serves as a reinforcing phase to improve the mechanical properties of the membrane, but more importantly, it constructs continuous hydrophilic microdomains and ion transport channels. The free hydroxyl groups in the coordination network optimize the wetting behavior of the electrolyte through hydrogen bonding, thereby improving the migration efficiency of ions within the membrane.

[0024] Third, this invention utilizes the unique properties of disulfide bonds in cystamine molecules to endow the separator with dynamic self-adaptive capabilities. Disulfide bonds can undergo a controlled breakage-recombination process in the redox environment of battery cycling, effectively buffering the mechanical stress caused by zinc dendrite growth and electrode volume changes. This molecular-level stress release mechanism prevents the generation and propagation of microcracks in the separator, significantly improving cycle stability.

[0025] Fourth, this invention achieves a balanced optimization of performance through precise cross-linking network design. The single-hydroxyl end-capping characteristic of polyethylene glycol monomethyl ether avoids the decrease in porosity caused by excessive cross-linking, maintaining good ionic conductivity while ensuring mechanical strength. The introduction of hexamethylene diisocyanate forms a three-dimensional network of urethane bonds, further enhancing the overall structural stability of the membrane.

[0026] Finally, the separator prepared by this invention exhibits excellent environmental friendliness. Using renewable wood fiber as the base material and combining it with green chemical modification methods, it avoids the environmental pollution problems associated with traditional petroleum-based separator production. The separator can be biodegraded at the end of its service life, meeting the requirements of a circular economy and sustainable development. This multifunctional synergistic design strategy provides a new technological path for developing next-generation high-performance, environmentally friendly zinc-ion battery separators. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0028] Example 1: (1) Add 60g (dry weight) of softwood pulp to 200g of deionized water, homogenize and disperse it at 10000rpm for 10min using a high-speed homogenizer, vacuum filter, and dry with hot air to obtain wood fiber matrix. (2) Add 50g of wood fiber matrix and 3g of sodium periodate to 200g of deionized water, heat to 48℃, stir for 2h under dark conditions, vacuum filter, and wash with deionized water multiple times until the pH of the filtrate is neutral, and vacuum dry to obtain aldehyde-modified wood fiber. (3) Add 8g tannic acid and 5g zinc acetate to 150g phosphate buffer (pH 7), stir for 8min, then add 2g cystamine, heat to 55℃, stir for 1h, then add 40g aldehyde-modified wood fiber, cool to 45℃, continue stirring for 4h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain zinc network functionalized wood fiber; (4) Add 40g of zinc network functionalized wood fiber to 200g of anhydrous ethanol, sonicate for 20min, then add 10g of polyethylene glycol monomethyl ether (weight average molecular weight 2000), 15g of polyethylene glycol (weight average molecular weight 2000), 2.5g of hexamethylene diisocyanate, 0.3g of dibutyltin dilaurate, 0.3g of γ-aminopropyltriethoxysilane and 8g of nano silica (average particle size 50nm), stir for 35min, then heat to 72℃, reflux and stir for 4h, then heat to 82℃, reflux and stir for 6h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain cross-linked zinc wood fiber composite material; (5) Disperse 60g of cross-linked zinc-fiber composite material in 500g of deionized water, stir to form a uniform suspension slurry, and wet film making is carried out using a filter screen with a pore size of 18μm, controlling the wet film quantity to be 45g / m³. 2 After the wet film is taken out, it is immediately hot-pressed at 115℃ and 4MPa for 3 minutes and then cooled to obtain a wood fiber composite membrane.

[0029] Example 2: (1) Add 80g (dry weight) of softwood pulp to 300g of deionized water, homogenize and disperse it at 12000rpm for 15min using a high-speed homogenizer, vacuum filter, and dry with hot air to obtain wood fiber matrix. (2) Add 60g of wood fiber matrix and 5g of sodium periodate to 300g of deionized water, heat to 50°C, stir for 3h under dark conditions, vacuum filter, and wash with deionized water multiple times until the pH of the filtrate is neutral, and vacuum dry to obtain aldehyde-modified wood fiber. (3) Add 10g tannic acid and 6g zinc acetate to 200g phosphate buffer (pH 7), stir for 10min, then add 3.5g cystamine, heat to 60℃, stir for 2h, then add 50g aldehyde-modified wood fiber, cool to 50℃, continue stirring for 5h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain zinc network functionalized wood fiber; (4) Add 50g of zinc network functionalized wood fiber to 300g of anhydrous ethanol, sonicate for 30min, then add 15g of polyethylene glycol monomethyl ether (weight average molecular weight 2000), 20g of polyethylene glycol (weight average molecular weight 2000), 3.5g of hexamethylene diisocyanate, 0.5g of dibutyltin dilaurate, 0.5g of γ-aminopropyltriethoxysilane and 12g of nano silica (average particle size 50nm), stir for 40min, then heat to 75℃, reflux and stir for 5h, then heat to 85℃, reflux and stir for 7h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain cross-linked zinc wood fiber composite material; (5) Disperse 80g of cross-linked zinc-fiber composite material in 800g of deionized water, stir to form a uniform suspension slurry, and wet film making is carried out using a 20μm pore size filter screen, controlling the wet film quantity to be 45g / m³. 2 After the wet film is taken out, it is immediately hot-pressed at 120℃ and 5MPa for 5 minutes and then cooled to obtain a wood fiber composite membrane.

[0030] Example 3: (1) Add 100g (dry weight) of softwood pulp to 400g of deionized water, homogenize and disperse it at 15000rpm for 20min using a high-speed homogenizer, vacuum filter, and dry with hot air to obtain wood fiber matrix. (2) Add 50-70g of wood fiber matrix and 8g of sodium periodate to 400g of deionized water, heat to 52℃, stir for 4h under dark conditions, vacuum filter, and wash with deionized water multiple times until the pH of the filtrate is neutral, and vacuum dry to obtain aldehyde-modified wood fiber. (3) Add 12g tannic acid and 7g zinc acetate to 250g phosphate buffer (pH 7), stir for 12min, then add 5g cystamine, heat to 65℃, stir for 3h, then add 60g aldehyde-modified wood fiber, cool to 55℃, continue stirring for 6h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain zinc network functionalized wood fiber; (4) Add 60g of zinc network functionalized wood fiber to 400g of anhydrous ethanol, sonicate for 40min, then add 20g of polyethylene glycol monomethyl ether (weight average molecular weight 2000), 25g of polyethylene glycol (weight average molecular weight 2000), 4.5g of hexamethylene diisocyanate, 0.7g of dibutyltin dilaurate, 0.7g of γ-aminopropyltriethoxysilane and 16g of nano silica (average particle size 50nm), stir for 45min, then heat to 78℃, reflux and stir for 6h, then heat to 88℃, reflux and stir for 8h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain cross-linked zinc wood fiber composite material; (5) Disperse 100g of cross-linked zinc-fiber composite material in 1200g of deionized water, stir to form a uniform suspension slurry, and wet film making is carried out using a 22μm pore size filter screen, controlling the wet film quantity to be 40-50g / m 2 After the wet film is taken out, it is immediately hot-pressed at 125℃ and 6MPa for 8 minutes and then cooled to obtain a wood fiber composite membrane.

[0031] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the aldehyde-modified wood fibers in step (3) are replaced with a wood fiber matrix; The specific steps are as follows: (1) Add 80g (dry weight) of softwood pulp to 300g of deionized water, homogenize and disperse it at 12000rpm for 15min using a high-speed homogenizer, vacuum filter, and dry with hot air to obtain wood fiber matrix. (2) Add 10g tannic acid and 6g zinc acetate to 200g phosphate buffer (pH 7), stir for 10min, then add 3.5g cystamine, heat to 60℃, stir for 2h, then add 50g wood fiber matrix, cool to 50℃, continue stirring for 5h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain zinc network functionalized wood fiber; (3) Add 50g of zinc network functionalized wood fiber to 300g of anhydrous ethanol, sonicate for 30min, then add 15g of polyethylene glycol monomethyl ether (weight average molecular weight 2000), 20g of polyethylene glycol (weight average molecular weight 2000), 3.5g of hexamethylene diisocyanate, 0.5g of dibutyltin dilaurate, 0.5g of γ-aminopropyltriethoxysilane and 12g of nano silica (average particle size 50nm), stir for 40min, then heat to 75℃, reflux and stir for 5h, then heat to 85℃, reflux and stir for 7h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain cross-linked zinc wood fiber composite material; (4) Disperse 80g of cross-linked zinc-fiber composite material in 800g of deionized water, stir to form a uniform suspension slurry, and wet film making is carried out using a 20μm pore size filter screen, controlling the wet film quantity to be 45g / m³. 2 After the wet film is taken, it is immediately hot-pressed at 120℃ and 5MPa for 5 minutes and then cooled to obtain the diaphragm.

[0032] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that cystamine in step (3) is replaced with ethylenediamine; The specific steps are as follows: (1) Add 80g (dry weight) of softwood pulp to 300g of deionized water, homogenize and disperse it at 12000rpm for 15min using a high-speed homogenizer, vacuum filter, and dry with hot air to obtain wood fiber matrix. (2) Add 60g of wood fiber matrix and 5g of sodium periodate to 300g of deionized water, heat to 50°C, stir for 3h under dark conditions, vacuum filter, and wash with deionized water multiple times until the pH of the filtrate is neutral, and vacuum dry to obtain aldehyde-modified wood fiber. (3) Add 10g tannic acid and 6g zinc acetate to 200g phosphate buffer (pH 7), stir for 10min, then add 3.5g ethylenediamine, heat to 60℃, stir for 2h, then add 50g aldehyde-modified wood fiber, cool to 50℃, continue stirring for 5h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain zinc network functionalized wood fiber; (4) Add 50g of zinc network functionalized wood fiber to 300g of anhydrous ethanol, sonicate for 30min, then add 15g of polyethylene glycol monomethyl ether (weight average molecular weight 2000), 20g of polyethylene glycol (weight average molecular weight 2000), 3.5g of hexamethylene diisocyanate, 0.5g of dibutyltin dilaurate, 0.5g of γ-aminopropyltriethoxysilane and 12g of nano silica (average particle size 50nm), stir for 40min, then heat to 75℃, reflux and stir for 5h, then heat to 85℃, reflux and stir for 7h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain cross-linked zinc wood fiber composite material; (5) Disperse 80g of cross-linked zinc-fiber composite material in 800g of deionized water, stir to form a uniform suspension slurry, and wet film making is carried out using a 20μm pore size filter screen, controlling the wet film quantity to be 45g / m³. 2 After the wet film is taken, it is immediately hot-pressed at 120℃ and 5MPa for 5 minutes and then cooled to obtain the diaphragm.

[0033] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that tannic acid was not added in step (3); The specific steps are as follows: (1) Add 80g (dry weight) of softwood pulp to 300g of deionized water, homogenize and disperse it at 12000rpm for 15min using a high-speed homogenizer, vacuum filter, and dry with hot air to obtain wood fiber matrix. (2) Add 60g of wood fiber matrix and 5g of sodium periodate to 300g of deionized water, heat to 50°C, stir for 3h under dark conditions, vacuum filter, and wash with deionized water multiple times until the pH of the filtrate is neutral, and vacuum dry to obtain aldehyde-modified wood fiber. (3) Add 6g of zinc acetate to 200g of phosphate buffer (pH 7), stir for 10min, then add 3.5g of cystamine, heat to 60℃, stir for 2h, then add 50g of aldehyde-modified wood fiber, cool to 50℃, continue stirring for 5h, vacuum filter, wash 3 times with anhydrous ethanol, and vacuum dry to obtain zinc network functionalized wood fiber; (4) Add 50g of zinc network functionalized wood fiber to 300g of anhydrous ethanol, sonicate for 30min, then add 15g of polyethylene glycol monomethyl ether (weight average molecular weight 2000), 20g of polyethylene glycol (weight average molecular weight 2000), 3.5g of hexamethylene diisocyanate, 0.5g of dibutyltin dilaurate, 0.5g of γ-aminopropyltriethoxysilane and 12g of nano silica (average particle size 50nm), stir for 40min, then heat to 75℃, reflux and stir for 5h, then heat to 85℃, reflux and stir for 7h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain cross-linked zinc wood fiber composite material; (5) Disperse 80g of cross-linked zinc-fiber composite material in 800g of deionized water, stir to form a uniform suspension slurry, and wet film making is carried out using a 20μm pore size filter screen, controlling the wet film quantity to be 45g / m³. 2 After the wet film is taken, it is immediately hot-pressed at 120℃ and 5MPa for 5 minutes and then cooled to obtain the diaphragm.

[0034] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that cystamine was not added in step (3); The specific steps are as follows: (1) Add 80g (dry weight) of softwood pulp to 300g of deionized water, homogenize and disperse it at 12000rpm for 15min using a high-speed homogenizer, vacuum filter, and dry with hot air to obtain wood fiber matrix. (2) Add 60g of wood fiber matrix and 5g of sodium periodate to 300g of deionized water, heat to 50°C, stir for 3h under dark conditions, vacuum filter, and wash with deionized water multiple times until the pH of the filtrate is neutral, and vacuum dry to obtain aldehyde-modified wood fiber. (3) Add 10g tannic acid and 6g zinc acetate to 200g phosphate buffer (pH 7), stir for 10min, heat to 60℃, stir for 2h, then add 50g aldehyde-modified wood fiber, cool to 50℃, continue stirring for 5h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain zinc network functionalized wood fiber. (4) Add 50g of zinc network functionalized wood fiber to 300g of anhydrous ethanol, sonicate for 30min, then add 15g of polyethylene glycol monomethyl ether (weight average molecular weight 2000), 20g of polyethylene glycol (weight average molecular weight 2000), 3.5g of hexamethylene diisocyanate, 0.5g of dibutyltin dilaurate, 0.5g of γ-aminopropyltriethoxysilane and 12g of nano silica (average particle size 50nm), stir for 40min, then heat to 75℃, reflux and stir for 5h, then heat to 85℃, reflux and stir for 7h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain cross-linked zinc wood fiber composite material; (5) Disperse 80g of cross-linked zinc-fiber composite material in 800g of deionized water, stir to form a uniform suspension slurry, and wet film making is carried out using a 20μm pore size filter screen, controlling the wet film quantity to be 45g / m³. 2 After the wet film is taken, it is immediately hot-pressed at 120℃ and 5MPa for 5 minutes and then cooled to obtain the diaphragm.

[0035] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that polyethylene glycol monomethyl ether in step (4) is replaced with polyethylene glycol; The specific steps are as follows: (1) Add 80g (dry weight) of softwood pulp to 300g of deionized water, homogenize and disperse it at 12000rpm for 15min using a high-speed homogenizer, vacuum filter, and dry with hot air to obtain wood fiber matrix. (2) Add 60g of wood fiber matrix and 5g of sodium periodate to 300g of deionized water, heat to 50°C, stir for 3h under dark conditions, vacuum filter, and wash with deionized water multiple times until the pH of the filtrate is neutral, and vacuum dry to obtain aldehyde-modified wood fiber. (3) Add 10g tannic acid and 6g zinc acetate to 200g phosphate buffer (pH 7), stir for 10min, then add 3.5g cystamine, heat to 60℃, stir for 2h, then add 50g aldehyde-modified wood fiber, cool to 50℃, continue stirring for 5h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain zinc network functionalized wood fiber; (4) Add 50g of zinc network functionalized wood fiber to 300g of anhydrous ethanol, sonicate for 30min, then add 35g of polyethylene glycol (weight average molecular weight 2000), 3.5g of hexamethylene diisocyanate, 0.5g of dibutyltin dilaurate, 0.5g of γ-aminopropyltriethoxysilane and 12g of nano silica (average particle size 50nm) in sequence, stir for 40min, then heat to 75℃, reflux and stir for 5h, then heat to 85℃, reflux and stir for 7h, vacuum filter, wash 3 times with anhydrous ethanol, vacuum dry to obtain cross-linked zinc wood fiber composite material; (5) Disperse 80g of cross-linked zinc-fiber composite material in 800g of deionized water, stir to form a uniform suspension slurry, and wet film making is carried out using a 20μm pore size filter screen, controlling the wet film quantity to be 45g / m³. 2 After the wet film is taken, it is immediately hot-pressed at 120℃ and 5MPa for 5 minutes and then cooled to obtain the diaphragm.

[0036] Performance testing: Tensile strength: The diaphragm was cut into 15mm×100mm specimens and placed in a constant temperature and humidity environment (23℃, 50%RH) for equilibration for 24h. An electronic tensile testing machine (accuracy 0.1N) was used to stretch the specimens at a rate of 100mm / min until fracture. The maximum force value was recorded. Each group was tested 10 times, and the average value was used to calculate the tensile strength (kN / m). The results are shown in Table 1.

[0037] Ionic conductivity measurement: Assembled symmetrical stainless steel electrodes (area 1.54 cm²) 2 A 2 mol / L ZnSO4 electrolyte was injected, and the impedance spectrum (frequency 0.1 Hz-100 kHz) was measured using an electrochemical workstation. The bulk resistance was calculated from the high-frequency intercept of the Nyquist plot, and then the ionic conductivity was calculated. The results are shown in Table 1.

[0038] Liquid absorption rate: Weigh the dry weight of the diaphragm, immerse it in 2 mol / L ZnSO4 electrolyte for 2 hours, wipe off the surface droplets and weigh the wet weight, calculate the liquid absorption rate, and the results are shown in Table 1.

[0039] Heat shrinkage rate: The diaphragm was heated at 85℃ for 1 hour, the dimensional changes were measured, and the heat shrinkage rate was calculated. The results are shown in Table 1.

[0040] Cycle life: Zn / TiO2 batteries (2.0-1.0V) assembled using the separator prepared in this invention were cycled 1000 times at 1C rate, and the capacity retention rate was calculated. The results are shown in Table 1.

[0041] Table 1 Performance Test Results Example 1 28 12 165 8 85 Example 2 35 15 180 6 92 Example 3 30 13 170 5 88 Comparative Example 1 18 8 160 12 65 Comparative Example 2 32 14 175 5 78 Comparative Example 3 25 7 140 15 60 Comparative Example 4 20 6 130 18 55 Comparative Example 5 38 12 150 4 80 Data Analysis: The wood fiber composite membrane prepared in this invention exhibits synergistically optimized comprehensive performance in terms of tensile strength, ionic conductivity, liquid absorption rate, thermal shrinkage rate, and cycle life. The significant improvement in the membrane's mechanical strength is likely due to the aldehyde-based treatment on the wood fiber surface enhancing the chemical bonding between the fiber and the zinc network, while the cross-linked polymer network forms a stable three-dimensional support structure. The improved ion transport efficiency is presumably related to the continuous ion channels provided by the tannic acid-zinc coordination network, which constructs an ordered porous structure through metal coordination and hydrogen bonding. The high liquid absorption rate may be attributed to the synergistic effect of hydrophilic groups (such as hydroxyl and aldehyde groups) on the fiber surface and nano-silica, forming a uniform hydrophilic microenvironment. The low thermal shrinkage indicates that the cross-linked network effectively suppresses the thermal motion of the fiber at high temperatures, while the excellent cycle stability may stem from the dynamic reversibility of disulfide bonds buffering cyclic stress, and the coordination of zinc ions with tannic acid stabilizing the electrode / electrolyte interface. This multi-level structural design achieves simultaneous optimization of the membrane's mechanical properties, ion dynamics, and interfacial stability through synergistic effects at the molecular level.

[0042] Comparative analysis of Example 2 and Comparative Example 1: Data shows that the untreated material exhibits significant disadvantages in mechanical strength, ion conductivity, thermal stability, and cycle life. This difference may stem from the covalent bonds formed by aldehyde formation (Schiff base reaction), which firmly anchor cystamine to the fiber surface, creating stronger interfacial bonding and thus improving tensile strength. Simultaneously, the tight bond between the aldehyde-treated fiber and the zinc network may form a more continuous ion transport path, enhancing ion conductivity. Regarding thermal stability, the covalent network is more effective than physical adsorption in suppressing molecular chain segment movement at high temperatures. The difference in cycle life may be due to the firmly connected zinc network inhibiting the shedding of active material during cycling and maintaining a stable electrode / electrolysis interface. This aldehyde-mediated chemical bonding mechanism plays a crucial role in constructing a stable hierarchical structure.

[0043] Comparative analysis of Example 2 and Comparative Example 2: When cystamine was replaced with ethylenediamine, although the material maintained good mechanical strength and thermal stability, ion conduction and cycle life were significantly reduced. This phenomenon may stem from the dynamic reversible nature of disulfide bonds. In the redox environment of battery cycling, disulfide bonds can undergo controllable breakage / reorganization, effectively buffering the local stress caused by zinc dendrite growth, thereby reducing the generation of microcracks in the separator. This adaptive regulation capability helps maintain the integrity of ion channels, while the static amine bonds formed by ethylenediamine lack a stress release mechanism. Simultaneously, the thiol groups generated by disulfide bond breakage may coordinate with zinc ions, optimizing ion transport kinetics. The introduction of disulfide bonds provides the separator with a unique mechano-electrochemical synergistic stabilization mechanism.

[0044] Comparative analysis of Example 2 and Comparative Example 3: The absence of tannic acid led to a systematic deterioration in all performance indicators, possibly due to the multiple functions of tannic acid: its abundant catechol groups construct a stable zinc coordination network through chelation, which serves both as a reinforcing phase to improve mechanical strength and as a continuous hydrophilic microdomain to increase liquid uptake. The free phenolic hydroxyl groups in the coordination network can optimize electrolyte wettability through hydrogen bonding, and its molecular-level interfacial modification may improve ion transference number. Furthermore, tannic acid's thermal stability enhances high-temperature dimensional stability, while its antioxidant properties inhibit electrolyte decomposition and extend cycle life. This polyphenol-metal network achieves synergistic enhancement of the membrane's multi-scale performance.

[0045] Comparative analysis of Example 2 and Comparative Example 4: The material without added cystamine exhibited comprehensive performance degradation, indicating that cystamine plays an irreplaceable role as a molecular bridge. Its diamine structure enables covalent bridging between aldehyde-based fibers and the tannic acid-zinc network. This ternary configuration of fiber-cystamine-zinc network significantly improves interfacial bonding strength compared to physical mixing. Strong chemical bonding can inhibit the shedding of the zinc network during cycling, maintain a stable porous structure, and ensure ion transport efficiency. This precise molecular connection design is the core strategy for constructing high-performance membrane structures.

[0046] Comparative analysis of Example 2 and Comparative Example 5: Using dihydroxy polyethylene glycol throughout resulted in a decrease in liquid uptake, ionic conductivity, and cycle life, although mechanical strength was slightly improved. This difference may stem from the special function of monomethyl ether end-capping: its monohydroxy nature allows for precise control of crosslinking density, avoiding excessive crosslinking that reduces porosity and forming a more uniform micropore distribution to enhance electrolyte wettability. Simultaneously, the end-capping groups may reduce molecular chain entanglement, constructing more unobstructed ion transport channels. This surface energy modulation optimizes the mesoscopic structure of the membrane to maximize electrochemical performance while ensuring the mechanical strength threshold.

[0047] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A wood fiber composite diaphragm, characterized in that, The cross-linked zinc-wood fiber composite material is obtained through pulping, papermaking, and hot pressing; the preparation steps of the cross-linked zinc-wood fiber composite material are as follows: (1) Homogenize the softwood pulp in deionized water at high speed to obtain a wood fiber matrix; (2) Aldehyde-modified wood fibers are obtained by oxidizing the wood fiber matrix with sodium periodate; (3) Tannic acid, zinc acetate and cystamine form metal salts through coordination, which then react with aldehyde-modified wood fibers to obtain zinc network functionalized wood fibers; (4) Zinc network functionalized wood fibers, polyethylene glycol monomethyl ether, polyethylene glycol, hexamethylene diisocyanate, γ-aminopropyltriethoxysilane and nano silica are crosslinked under the catalysis of dibutyltin dilaurate to obtain crosslinked zinc wood fiber composite materials; In step (3), the weight ratio of tannic acid, zinc acetate, cystamine, and aldehyde-modified wood fibers is 8-12:5-7:2-5:40-60; in step (4), the weight ratio of zinc network functionalized wood fibers, polyethylene glycol monomethyl ether, polyethylene glycol, hexamethylene diisocyanate, γ-aminopropyltriethoxysilane, nano-silica, and dibutyltin dilaurate is 40-60:10-20:15-25:2.5-4.5:0.3-0.7:8-16:0.3-0.

7.

2. The wood fiber composite diaphragm according to claim 1, characterized in that, In step (1), the dry weight ratio of softwood pulp to deionized water is 60-100:200-400.

3. The wood fiber composite diaphragm according to claim 1, characterized in that, In step (2), the weight ratio of sodium periodate to lignocellulose matrix is ​​3-8:50-70.

4. The wood fiber composite diaphragm according to claim 1, characterized in that, The specific preparation steps of zinc network functionalized wood fiber in step (3) are as follows: add tannic acid and zinc acetate to phosphate buffer solution with pH 7, stir for 8-12 min, then add cystamine, heat to 55-65℃, stir for 1-3 h, then add aldehyde-modified wood fiber, cool to 45-55℃, continue stirring for 4-6 h, vacuum filter, wash, vacuum dry to obtain zinc network functionalized wood fiber.

5. The wood fiber composite diaphragm according to claim 1, characterized in that, In step (4), the weight-average molecular weight of polyethylene glycol monomethyl ether is 2000, and the weight-average molecular weight of polyethylene glycol is 2000.

6. The wood fiber composite diaphragm according to claim 1, characterized in that, The papermaking is wet papermaking with filter screen of 18-22 μm, and the wet film basis weight is controlled to be 40-50 g / m 2 .

7. The wood fiber composite diaphragm according to claim 1, characterized in that, The hot pressing is performed at 115-125℃ and 4-6MPa for 3-8 minutes.

8. A method for preparing a wood fiber composite diaphragm according to any one of claims 1-7, characterized in that, The process includes the following steps: dispersing the cross-linked zinc-wood fiber composite material in deionized water, pulping, papermaking, and hot pressing to obtain a wood fiber composite membrane.

9. The method for preparing the wood fiber composite diaphragm according to claim 8, characterized in that, The weight ratio of the cross-linked zinc-wood fiber composite material to deionized water is 60-100:500-1200.