Preparation method and application of polymer layer-nanocellulose composite diaphragm with compact nanopore structure

Abstract

The invention provides a preparation method and application of a polymer layer-nanocellulose composite diaphragm with a compact nanopore structure, and belongs to the technical field of new energy batteries. The preparation method comprises the following steps: S1, carrying out vacuum self-assembly to form a substrate; s2, bidirectional solution construction: S2.1, alkaline induction monomer ionization construction; s3, soaking; s4, carrying out self-assembly and dynamic cross-linking on heterogeneous molecules to form a film; and S5, carrying out annealing treatment. The diaphragm applied to the water-based zinc ion battery pack is prepared by adopting one of 2, 5-diaminobenzene sulfonic acid, o-phenylenediamine, p-toluenediamine, 2, 5-dimethyl-1, 4-phenylenediamine and 1, 4-cyclohexane diamine and 1, 3, 5-benzene triformyl chloride as raw materials, and the diaphragm applied to the water-based zinc ion battery pack is prepared by adopting one of 2, 5-diaminobenzene sulfonic acid, o-phenylenediamine, p-toluenediamine, 2, 5-dimethyl-1, 4-phenylenediamine and 1, 4-cyclohexane diamine as raw materials. According to the composite diaphragm disclosed by the invention, through the unique nanopore structure and functional group design, the performance of the water-based zinc ion battery is optimized from multiple aspects of inhibiting the growth of zinc dendrites, increasing the transference number of zinc ions, prolonging the cycle life of the battery and the like.

Description

Technical Field

[0001] The invention belongs to the field of new energy technology and relates to a preparation method and application of a polymer-nanocellulose composite diaphragm with a dense nanopore structure. Background Art

[0002] Aqueous zinc-ion batteries use zinc metal as the negative electrode and materials such as manganese dioxide and vanadium pentoxide as the positive electrode. Thanks to the high hydrogen evolution overpotential of the zinc negative electrode (–0.76Vvs SHE), zinc-ion batteries can directly use aqueous solutions as electrolytes, which greatly improves the safety of zinc-ion batteries. In addition, zinc metal negative electrodes have advantages that lithium metal negative electrodes cannot match, such as: high abundance of zinc resources in the earth's crust, low difficulty in zinc mining, low storage cost, and the production of aqueous zinc-ion batteries does not rely on a highly anhydrous and oxygen-free environment. These advantages make aqueous zinc-ion batteries far superior to lithium-ion batteries in terms of production cost and safety. However, there are many problems with the direct use of zinc metal negative electrodes, which hinder their large-scale application: 1. Uneven zinc ion deposition leads to dendrite growth: zinc ions tend to grow in a dendritic or mossy form during the electrodeposition process. This non-uniform deposition behavior will lead to the formation of zinc dendrites. The growth of zinc dendrites will pierce the battery separator and cause internal short circuits, which will not only seriously affect the cycle stability of the battery, but may also cause battery failure or cause safety problems. 2. Side reactions between aqueous electrolyte and zinc negative electrode: When water molecules in aqueous electrolyte come into contact with zinc negative electrode, hydrogen evolution reaction and corrosion reaction are likely to occur. These side reactions will not only consume the water in the electrolyte, but also reduce the energy efficiency of the battery, and may also cause hydrogen release, increasing the safety risk of the battery.

[0003] The above problems seriously restrict the practical application performance of aqueous zinc-ion batteries. Therefore, it is urgent to develop a diaphragm material that can inhibit the growth of zinc dendrites and prevent zinc negative electrode side reactions, so as to improve the cycle stability, energy efficiency and safety of aqueous zinc-ion batteries. Summary of the invention

[0004] The purpose of the present invention is to address the above-mentioned problems in the prior art and to propose a preparation method and application of a polymer layer-nanocellulose composite diaphragm with a dense nanopore structure.

[0005] The object of the present invention can be achieved by the following technical scheme: A method for preparing a polymer layer-nanocellulose composite membrane with a dense nanoporous structure, the method for preparing a polymer layer-nanocellulose composite membrane with a dense nanoporous structure comprises the following steps:

[0006] S1 Vacuum self-assembly forming substrate: nanocellulose is uniformly dispersed in pure water to obtain a nanocellulose solution, and the nanocellulose solution is vacuum filtered to obtain a composite diaphragm substrate;

[0007] The purposes of vacuum filtration are as follows: 1. Directed arrangement and dense structure construction of nanocellulose: Nanocellulose has the characteristics of high aspect ratio and surface hydroxyl enrichment, but it is easy to form disordered aggregation in aqueous solution due to hydrogen bonding. Shear force induced orientation: During the filtration process, nanocellulose is driven by shear force under negative pressure and is oriented along the surface of the filter membrane to form a layered stacking structure. Layer-by-layer densification: When water passes through the filter membrane, the nanocellulose particles are gradually compressed and self-assembled into a dense network through hydrogen bonding and van der Waals forces to reduce pore defects. Controllable porosity: By adjusting the filtration time, vacuum degree or solution concentration, the substrate porosity can be accurately controlled to provide a uniform interface for subsequent interfacial polymerization. 2. Efficient solvent removal and rapid film formation: Rapid water removal: Vacuum negative pressure accelerates the passage of water through the filter membrane to avoid redispersion or structural relaxation of nanocellulose caused by long-term natural drying. Inhibition of capillary shrinkage: Compared with natural drying, vacuum filtration drives liquid discharge through external force, reduces capillary stress during drying, and reduces the risk of substrate cracking or curling. 3. Balance laboratory research and industrial production: The vacuum filtration device is simple and low-cost, and can achieve large-area continuous preparation (such as roll-to-roll process) through porous filter membranes, which is suitable for industrial production. The core value of vacuum filtration in step S1 is: to achieve rapid directional self-assembly of nanocellulose through physical drive; to construct a uniform substrate with high porosity and high mechanical strength; to provide a chemically active surface and structural stability for subsequent interfacial reactions.

[0008] S2 Bidirectional solution construction: S2.1 Alkaline induced monomer ionization construction: After adding the polymer precursor into pure water and stirring evenly, the pH value is adjusted to 12-15 with an alkaline solution, and then the precursor liquid is dispersed to obtain a precursor liquid. S2.2: Acid chloride organic phase microenvironment dispersion: 1,3,5-benzenetricarboxylic acid chloride is added into an organic solvent, and an acid chloride dispersion operation is performed to obtain a 1,3,5-benzenetricarboxylic acid chloride dispersion;

[0009] The polymer precursor is one of 2,5-diaminobenzenesulfonic acid, o-phenylenediamine, p-xylylenediamine, 2,5-dimethyl-1,4-phenylenediamine and 1,4-cyclohexanediamine; the organic solvent is n-heptane or n-hexane;

[0010] S3 soaking: soaking the composite membrane substrate in the precursor liquid for soaking operation, and after the soaking operation is completed, performing interface liquid phase desorption regulation operation to obtain a nanocellulose heterogeneous interface substrate;

[0011] S4 Heterogeneous molecular self-assembly dynamic cross-linking film formation: 1,3,5-benzenetricarboxylic acid chloride dispersion is added dropwise to the upper surface of the nanocellulose heterogeneous interface substrate to carry out interfacial polymerization reaction. After the reaction is completed, the 1,3,5-benzenetricarboxylic acid chloride dispersion on the surface is removed to obtain an initial composite membrane;

[0012] S5 annealing treatment: the initial composite membrane is subjected to annealing treatment to obtain a polymer layer-nanocellulose composite membrane.

[0013] Alkaline activation mechanism: The alkaline environment induces the ionization of the polymer precursor, which gives the substrate surface charge characteristics and enhances the activity of subsequent interfacial polymerization reactions.

[0014] 1,3,5-Benzenetricarboxylic acid chloride and n-heptane / n-hexane were selected for the following reasons: Functional advantages of 1,3,5-Benzenetricarboxylic acid chloride: High crosslinking density: Three acyl chloride groups can react with multiple amino groups to form a three-dimensional crosslinking network, which significantly improves the mechanical strength and chemical stability of the polymer layer (better electrolyte corrosion resistance than linear polymers). Symmetrical structure: The triple symmetry of the benzene ring promotes uniform crosslinking, reduces stress concentration in the membrane, and avoids the generation of microcracks. Low hydrolysis rate: Compared with aliphatic acyl chlorides (such as oxalyl chloride), aromatic acyl chlorides have a lower hydrolysis rate in the organic phase, ensuring the full progress of the interfacial polymerization reaction. Characteristics of n-heptane / n-hexane: Low polarity forms a stable liquid-liquid interface with the aqueous phase (high polarity), limits the monomer diffusion area, and achieves a polymer layer of nanometer thickness; Solvent compatibility optimization: For example, the low surface tension of n-heptane promotes the spreading of acyl chloride monomers on the surface of the nanocellulose substrate to form a continuous liquid film, providing a uniform reaction interface for interfacial polymerization.

[0015] Synergistic effect: The alkaline aqueous phase and the organic phase form a pH gradient, and the local pH of the acyl chloride in the organic phase is close to neutral, which greatly reduces the side reaction of acyl chloride hydrolysis.

[0016] Soaking process: Soaking in alkaline precursor liquid causes the nanocellulose substrate to swell, exposing more hydroxyl groups to form hydrogen bonds with amino groups, thus enhancing the interfacial bonding strength;

[0017] Interfacial liquid phase desorption regulation operation: The purpose is to remove excess liquid on the substrate surface by physical means, thereby providing uniform reaction sites for subsequent interfacial polymerization.

[0018] The purpose of annealing treatment is as follows: Promote the densification of the polymer layer: In the initial composite membrane generated by the interfacial polymerization reaction (step S4), the polymer layer may have incompletely cross-linked areas or loosely arranged molecular chains. Annealing treatment promotes further cross-linking and rearrangement of polymer chains by thermally stimulating molecular chain movement, thereby forming a denser nanopore structure and reducing defects (such as pinholes or cracks). Eliminate internal stress and residual solvent: During interfacial polymerization, mechanical stress or trace organic solvents remain inside the material. Annealing treatment releases internal stress through thermal relaxation and accelerates solvent volatilization to avoid structural failure caused by solvent residues or stress concentration in subsequent applications. Enhance the interface bonding between the polymer layer and the substrate: There is physical adsorption or weak interaction (such as hydrogen bonding) at the interface between the nanocellulose substrate and the polymer layer. Annealing treatment promotes intermolecular interaction through thermal energy, strengthens the interface bonding between the two phases, and improves the mechanical strength and thermal stability of the composite membrane. Optimize nanopore structure and distribution: The porous structure of the nanocellulose substrate is partially covered or blocked during the interfacial polymerization process. Annealing adjusts the shrinkage behavior of the polymer layer through gentle heating, optimizes the pore distribution, and forms a uniform and well-connected nanopore network, thereby balancing ionic conductivity and mechanical strength. Improving the thermal stability of the diaphragm: Annealing can increase the glass transition temperature and thermal decomposition temperature of the polymer layer, so that the composite diaphragm maintains structural stability at the battery operating temperature and avoids deformation or shrinkage caused by high temperature. The core purpose of annealing is to regulate the microstructure of the composite diaphragm through thermal densification to achieve the following goals: enhance density (reduce defects); optimize pores and interfaces (improve ionic conductivity and mechanical strength); improve thermal stability (ensure battery application safety). This step is the key to the transformation of the composite diaphragm from the initial state to the functional state, ensuring that the final product meets the stringent performance requirements of high-energy-density batteries for diaphragms (anti-dendritic penetration, high ionic conductivity, and high temperature resistance).

[0019] Preferably, according to the weight ratio, the ratio of nanocellulose to pure water is 0.6:1000-3000, the ratio of polymer precursor to pure water is 1:50-100, and the ratio of 1,3,5-benzenetricarboxylic acid chloride to organic solvent is 2:90-100.

[0020] The reasons for the ratio of nanocellulose: pure water are as follows: Dispersibility and structural control: The concentration of nanocellulose directly affects its dispersion state in the solution. If the concentration is too high, it will agglomerate due to hydrogen bonding, resulting in uneven substrate pores formed by vacuum filtration; if the concentration is too low, it will be difficult to form a continuous nanofiber network, resulting in insufficient mechanical strength of the substrate. Film thickness and porosity: This ratio range can balance dispersibility and film-forming efficiency. At low concentrations, a uniform nanoporous structure is formed by self-assembly through vacuum filtration, providing a high specific surface area and interface binding sites for the subsequent polymer layer. At this ratio, the substrate pore size and mechanical properties are balanced, which is suitable for subsequent interfacial polymerization reactions.

[0021] Preferably, in step S2.1, the alkaline solution is a sodium hydroxide solution.

[0022] Preferably, in step S2.1, the precursor solution is dispersed by ultrasonic dispersion; and in step S2.2, the acyl chloride is dispersed by low-temperature ultrasonic-mechanical synergistic dispersion.

[0023] The precursor liquid dispersion operation adopts ultrasonic dispersion method to avoid nano-scale agglomeration;

[0024] Low-temperature ultrasonic-mechanical synergistic dispersion method: Ultrasonic-induced solvent micro-disturbance breaks up molecular clusters, and mechanical stirring maintains dynamic equilibrium to prevent sedimentation.

[0025] Preferably, in step S3, the soaking time of the soaking operation is 10-20 minutes; in the interfacial liquid phase desorption regulation operation, the filter paper is lightly pressed to adsorb excess liquid on the surface. The reasons for using filter paper to lightly press are as follows: No residue: The filter paper fibers do not chemically react with the reaction system to ensure a clean interface. Gentle operation: Lightly pressing the filter paper can avoid damaging the substrate structure and maintain the integrity of the nanopores. If nitrogen purging or centrifugation is used, mechanical stress may be introduced or the substrate morphology may be destroyed, while filter paper adsorption is more controllable and gentle. Industrial production: Using filter paper for adsorption is easy to operate and helps improve production efficiency.

[0026] Preferably, in step S4, the reaction time of the interfacial polymerization reaction is 1-5 minutes.

[0027] Preferably, in step S5, the annealing treatment parameters are as follows: the annealing temperature is 40-80°C; the annealing time is 10-20 minutes. 10-20 minutes is sufficient to complete the molecular chain rearrangement and pore structure closure, while avoiding the film embrittlement caused by long-term heat treatment.

[0028] The invention discloses an application of a polymer layer-nanocellulose composite diaphragm with a dense nanopore structure. The polymer layer-nanocellulose composite diaphragm with a dense nanopore structure is prepared by adopting the preparation method of the polymer layer-nanocellulose composite diaphragm with a dense nanopore structure. The polymer layer-nanocellulose composite diaphragm with a dense nanopore structure is applied in an aqueous zinc ion battery pack. In the assembly structure of the aqueous zinc ion battery pack, from top to bottom, there are a negative electrode shell, a spring, a gasket, a zinc negative electrode, a polymer layer-nanocellulose composite diaphragm, a glass fiber diaphragm, a polymer layer-nanocellulose composite diaphragm, a positive electrode and a positive electrode shell.

[0029] The core mechanism of the symmetrical double-layer composite diaphragm (zinc negative electrode → composite diaphragm → glass fiber → composite diaphragm → positive electrode) is as follows: the nanocellulose substrate provides good mechanical strength to inhibit the formation of zinc dendrites; the polymer layer helps zinc ions to be better desolvated before deposition on the negative electrode, increases the number of zinc ion migration, and effectively reduces the overpotential of the zinc negative electrode. At the same time, the porous skeleton can bring more active sites, which helps the uniform deposition of zinc ions and reduces the side reactions of the zinc negative electrode. The glass fiber layer acts as a buffer layer to absorb local stress, and the glass fiber has a high porosity to reduce the ion transmission resistance; interface consistency: the double-sided composite diaphragm ensures the symmetry of the positive and negative electrode interface reactions, and maintains a high coulomb efficiency after multiple cycles.

[0030] Preferably, the aqueous zinc ion battery is specifically a Zn-Zn symmetric battery or a Zn-V2O5 full battery.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. Significantly inhibit the growth of zinc dendrites and improve the battery cycle life: The composite diaphragm can promote the uniform deposition of zinc ions on the negative electrode surface and effectively inhibit the growth of zinc dendrites. 2 、0.5mAh / cm 2 At a current density of , the symmetrical battery using the separator of the present invention achieved an ultra-long cycle life of more than 3000 hours, which is much higher than the cycle performance of the traditional glass fiber separator. This shows that the separator of the present invention has significant advantages in solving the zinc dendrite problem.

[0033] 2. Improve the number of zinc ion migration and battery efficiency: The polymer layer promotes the desolvation process of zinc ions, optimizes the migration path of zinc ions in the electrolyte, and significantly improves the number of zinc ion migration. This improvement not only reduces the occurrence of side reactions, but also significantly improves the energy efficiency and coulomb efficiency of the battery.

[0034] 3. Excellent mechanical strength and battery stability: The nanocellulose layer provides the diaphragm with good mechanical strength and flexibility, ensuring that the diaphragm maintains structural stability during the battery cycle, effectively preventing the diaphragm from deforming or rupturing, thereby improving the safety and reliability of the battery.

[0035] 4. Excellent thermal and chemical stability: The synergistic effect of the polymer layer and the nanocellulose layer gives the separator excellent thermal and chemical stability, enabling it to exhibit good corrosion resistance and anti-degradation capabilities in aqueous electrolytes, thereby extending the overall service life of the battery.

[0036] 5. Precise pore size control to meet the needs of different electrochemical systems: By selecting organic monomers, the pore size of the covalent organic framework can be precisely controlled to meet the requirements of different electrochemical systems. This pore size control capability not only enhances the versatility of the diaphragm, but also enables it to adapt to the characteristics of different battery systems, further expanding its scope of application.

[0037] 6. Green, environmental protection and sustainability: Nanocellulose is a renewable material with abundant sources, and the polymer layer adopts a green preparation process. The entire diaphragm preparation process is environmentally friendly and sustainable, which is in line with the current trend of green development of energy storage devices.

[0038] In summary, the composite membrane of the present invention optimizes the performance of aqueous zinc ion batteries from multiple aspects, such as inhibiting zinc dendrite growth, increasing zinc ion migration number, and extending battery cycle life, through its unique nanopore structure and functional group design, and provides important technical support for the development of high-performance, high-safety and low-cost aqueous zinc ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is an electron microscope image of the polymer-cellulose composite diaphragm prepared in Example 1 of the present invention.

[0040] Figure 2 It is an electron microscope image of the polymer-glass fiber composite diaphragm prepared in Comparative Example 4 of the present invention.

[0041] Figure 3 This is a scanning electron microscope image of the zinc negative electrode surface of the zinc-zinc (Zn-Zn) symmetric battery assembled in Example 1 of the present invention after cycling for 60 hours.

[0042] Figure 4 This is a scanning electron microscope image of the zinc negative electrode surface of the zinc-zinc (Zn-Zn) symmetric battery assembled in Example 2 of the present invention after cycling for 60 hours.

[0043] Figure 5 This is a scanning electron microscope image of the zinc negative electrode surface of the zinc-zinc (Zn-Zn) symmetric battery assembled in Example 3 of the present invention after cycling for 60 hours.

[0044] Figure 6 It is a comparative diagram of the cycle performance analysis of zinc-zinc (Zn-Zn) symmetric batteries assembled in Examples 1, 2, 3 of the present invention and Comparative Examples 1, 2, 3.

[0045] Figure 7 This is a cycle performance analysis diagram of the zinc vanadium pentoxide full battery assembled in Example 1 of the present invention.

[0046] Figure 8 This is a scanning electron microscope image of the zinc negative electrode surface of the zinc-zinc (Zn-Zn) symmetrical battery assembled in Comparative Example 1 of the present invention after cycling for 60 hours. DETAILED DESCRIPTION

[0047] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0048] Embodiment 1:

[0049] A method for preparing a polymer layer-nanocellulose composite diaphragm with a dense nanoporous structure comprises the following steps:

[0050] S1 Vacuum self-assembly forming substrate: nanocellulose is uniformly dispersed in pure water to obtain a nanocellulose solution, and the nanocellulose solution is vacuum filtered to obtain a composite diaphragm substrate;

[0051] S2 Bidirectional solution construction: S2.1 Alkaline induced monomer ionization construction: After adding the polymer precursor into pure water and stirring evenly, the pH value is adjusted to 13 with an alkaline solution, and then the precursor liquid is dispersed to obtain a precursor liquid. S2.2 Acid chloride organic phase microenvironment dispersion: 1,3,5-benzenetricarboxylic acid chloride is added into an organic solvent, and an acid chloride dispersion operation is performed to obtain a 1,3,5-benzenetricarboxylic acid chloride dispersion; the alkaline solution is a sodium hydroxide solution;

[0052] The polymer precursor is 2,5-diaminobenzenesulfonic acid, and the organic solvent is n-heptane; the precursor liquid dispersion operation adopts the ultrasonic dispersion method; the acyl chloride dispersion operation adopts the low-temperature ultrasonic-mechanical coordinated dispersion method.

[0053] S3 immersion: immerse the composite diaphragm substrate in the precursor liquid for immersion operation. After the immersion operation is completed, the interface liquid phase desorption regulation operation is carried out to obtain a nanocellulose heterogeneous interface substrate. The immersion time of the immersion operation is 20 minutes. In the interface liquid phase desorption regulation operation, the filter paper is used to lightly press the method to adsorb the excess liquid on the surface.

[0054] S4 heterogeneous molecular self-assembly dynamic cross-linking film formation: 1,3,5-benzenetricarboxylic acid chloride dispersion is added dropwise to the upper surface of the nanocellulose heterogeneous interface substrate to carry out interfacial polymerization reaction. After the reaction is completed, excess 1,3,5-benzenetricarboxylic acid chloride dispersion is removed from the surface to obtain an initial composite membrane; the interfacial polymerization reaction time is 2 minutes.

[0055] S5 Annealing treatment: the initial composite membrane is subjected to an annealing treatment operation to obtain a polymer layer-nanocellulose composite membrane. The annealing treatment operation parameters are as follows: the annealing temperature is 60° C.; the annealing time is 10 minutes.

[0056] According to the weight ratio, nanocellulose: pure water is 0.6:1000, polymer precursor: pure water is 1:50, and 1,3,5-benzenetricarboxylic acid chloride: organic solvent is 2:98.

[0057] The polymer-nanocellulose composite separator with dense nanoporous structure prepared above was cut into a circle with a diameter of 15 mm and assembled into a zinc-zinc (Zn-Zn) symmetric battery and a zinc-vanadium pentoxide full battery using a 2032 battery shell.

[0058] In the zinc-zinc (Zn-Zn) symmetric battery assembly structure, from top to bottom, there are negative electrode shell, spring, gasket, zinc negative electrode, polymer layer-nanocellulose composite separator, glass fiber separator, polymer layer-nanocellulose composite separator, zinc positive electrode and positive electrode shell.

[0059] The assembly process of zinc-vanadium pentoxide full battery is as follows: negative electrode shell, spring, gasket, zinc negative electrode, polymer layer-nanocellulose composite diaphragm, glass fiber diaphragm, polymer layer-nanocellulose composite diaphragm, vanadium pentoxide (active material loading is 0.68 mg / cm 2 ), positive electrode shell.

[0060] Example 2

[0061] A method for preparing a polymer layer-nanocellulose composite diaphragm with a dense nanoporous structure comprises the following steps:

[0062] S1 Vacuum self-assembly forming substrate: nanocellulose is uniformly dispersed in pure water to obtain a nanocellulose solution, and the nanocellulose solution is vacuum filtered to obtain a composite diaphragm substrate;

[0063] S2 Bidirectional solution construction: S2.1 Alkaline induced monomer ionization construction: After adding the polymer precursor into pure water and stirring evenly, the pH value is adjusted to 13 with an alkaline solution, and then the precursor liquid is dispersed to obtain a precursor liquid. S2.2 Acid chloride organic phase microenvironment dispersion: 1,3,5-benzenetricarboxylic acid chloride is added into an organic solvent, and an acid chloride dispersion operation is performed to obtain a 1,3,5-benzenetricarboxylic acid chloride dispersion; the alkaline solution is a sodium hydroxide solution;

[0064] The polymer precursor is o-phenylenediamine, and the organic solvent is n-heptane; the precursor liquid dispersion operation adopts the ultrasonic dispersion method; the acyl chloride dispersion operation adopts the low-temperature ultrasonic-mechanical coordinated dispersion method.

[0065] S3 immersion: immerse the composite diaphragm substrate in the precursor liquid for immersion operation. After the immersion operation is completed, the interface liquid phase desorption regulation operation is carried out to obtain a nanocellulose heterogeneous interface substrate. The immersion time of the immersion operation is 20 minutes. In the interface liquid phase desorption regulation operation, the filter paper is used to lightly press the method to adsorb the excess liquid on the surface.

[0066] S4 Heterogeneous molecular self-assembly dynamic cross-linking film formation: 1,3,5-benzenetricarboxylic acid chloride dispersion is added dropwise to the upper surface of the nanocellulose heterogeneous interface substrate to carry out interfacial polymerization reaction. After the reaction is completed, excess 1,3,5-benzenetricarboxylic acid chloride dispersion is removed from the surface to obtain an initial composite membrane; the interfacial polymerization reaction time is 2 minutes.

[0067] S5 annealing treatment: the initial composite membrane is annealed to obtain a polymer layer-nanocellulose composite membrane.

[0068] According to the weight ratio, nanocellulose: pure water is 0.6:1000, polymer precursor: pure water is 1:50, and 1,3,5-benzenetricarboxylic acid chloride: organic solvent is 2:98.

[0069] The polymer-nanocellulose composite separator with dense nanoporous structure prepared above was cut into a circle with a diameter of 15 mm and assembled into a zinc-zinc (Zn-Zn) symmetrical battery using a 2032 battery shell.

[0070] In the zinc-zinc (Zn-Zn) symmetrical battery assembly structure, from top to bottom, there are negative electrode shell, spring, gasket, zinc negative electrode, polymer layer-nanocellulose composite diaphragm, glass fiber diaphragm, polymer layer-nanocellulose composite diaphragm, zinc positive electrode and positive electrode shell.

[0071] The assembled Zn-Zn symmetric battery was tested at 25°C and 1 mA / cm 2 (0.5mAh / cm 2 ) conditions, the symmetrical battery remained stable after 3000 hours of cycling.

[0072] Example 3

[0073] A method for preparing a polymer layer-nanocellulose composite diaphragm with a dense nanoporous structure comprises the following steps:

[0074] S1 Vacuum self-assembly forming substrate: nanocellulose is uniformly dispersed in pure water to obtain a nanocellulose solution, and the nanocellulose solution is vacuum filtered to obtain a composite diaphragm substrate;

[0075] S2 Bidirectional solution construction: S2.1 Alkaline induced monomer ionization construction: After adding the polymer precursor into pure water and stirring evenly, the pH value is adjusted to 13 with an alkaline solution, and then the precursor liquid is dispersed to obtain a precursor liquid. S2.2 Acid chloride organic phase microenvironment dispersion: 1,3,5-benzenetricarboxylic acid chloride is added into an organic solvent, and an acid chloride dispersion operation is performed to obtain a 1,3,5-benzenetricarboxylic acid chloride dispersion; the alkaline solution is a sodium hydroxide solution;

[0076] The polymer precursor is p-xylylenediamine, and the organic solvent is n-heptane; the precursor liquid dispersion operation adopts the ultrasonic dispersion method; the acyl chloride dispersion operation adopts the low-temperature ultrasonic-mechanical coordinated dispersion method.

[0077] S3 immersion: immerse the composite diaphragm substrate in the precursor liquid for immersion operation. After the immersion operation is completed, the interface liquid phase desorption regulation operation is carried out to obtain a nanocellulose heterogeneous interface substrate. The immersion time of the immersion operation is 20 minutes. In the interface liquid phase desorption regulation operation, the filter paper is used to lightly press the method to adsorb the excess liquid on the surface.

[0078] S4 Heterogeneous molecular self-assembly dynamic cross-linking film formation: 1,3,5-benzenetricarboxylic acid chloride dispersion is added dropwise to the upper surface of the nanocellulose heterogeneous interface substrate to carry out interfacial polymerization reaction. After the reaction is completed, excess 1,3,5-benzenetricarboxylic acid chloride dispersion is removed from the surface to obtain an initial composite membrane; the interfacial polymerization reaction time is 2 minutes.

[0079] S5 annealing treatment: the initial composite membrane is annealed to obtain a polymer layer-nanocellulose composite membrane.

[0080] According to the weight ratio, nanocellulose: pure water is 0.6:1000, polymer precursor: pure water is 1:50, and 1,3,5-benzenetricarboxylic acid chloride: organic solvent is 2:98.

[0081] The polymer-nanocellulose composite separator with a dense nanoporous structure prepared above was cut into a circle with a diameter of 15 mm and assembled into a zinc-zinc (Zn-Zn) symmetrical battery using a 2032 battery shell.

[0082] The assembly process of zinc-zinc (Zn-Zn) symmetric battery is as follows: negative electrode shell, spring, gasket, zinc negative electrode, polymer-nanocellulose composite diaphragm, glass fiber diaphragm, polymer-nanocellulose composite diaphragm, zinc positive electrode, and positive electrode shell.

[0083] Comparative Example 1

[0084] The glass fiber separator is directly used as the battery separator, and the 2032 battery shell is used to assemble a zinc-zinc (Zn-Zn) symmetrical battery. The zinc-zinc (Zn-Zn) symmetrical battery assembly structure consists of the negative electrode shell, shrapnel, gasket, zinc negative electrode, glass fiber separator, zinc positive electrode and positive electrode shell from top to bottom.

[0085] Comparative Example 2

[0086] A method for preparing a polymer layer-nanocellulose composite diaphragm with a dense nanoporous structure comprises the following steps:

[0087] S1 Vacuum self-assembly forming substrate: nanocellulose is uniformly dispersed in pure water to obtain a nanocellulose solution, and the nanocellulose solution is vacuum filtered to obtain a composite diaphragm substrate;

[0088] S2 Bidirectional solution construction: S2.1 Alkaline induced monomer ionization construction: After adding the polymer precursor into pure water and stirring evenly, the pH value is adjusted to 13 with an alkaline solution, and then the precursor liquid is dispersed to obtain a precursor liquid. S2.2 Acid chloride organic phase microenvironment dispersion: 1,3,5-benzenetricarboxylic acid chloride is added into an organic solvent, and an acid chloride dispersion operation is performed to obtain a 1,3,5-benzenetricarboxylic acid chloride dispersion; the alkaline solution is a sodium hydroxide solution;

[0089] The polymer precursor is p-phenylenediamine, and the organic solvent is n-heptane; the precursor liquid dispersion operation adopts the ultrasonic dispersion method; the acyl chloride dispersion operation adopts the low-temperature ultrasonic-mechanical coordinated dispersion method.

[0090] S3 immersion: immerse the composite diaphragm substrate in the precursor liquid for immersion operation. After the immersion operation is completed, the interface liquid phase desorption regulation operation is carried out to obtain a nanocellulose heterogeneous interface substrate. The immersion time of the immersion operation is 20 minutes. In the interface liquid phase desorption regulation operation, the filter paper is used to lightly press the method to adsorb the excess liquid on the surface.

[0091] S4 heterogeneous molecular self-assembly dynamic cross-linking film formation: 1,3,5-benzenetricarboxylic acid chloride dispersion is added dropwise to the upper surface of the nanocellulose heterogeneous interface substrate to carry out interfacial polymerization reaction. After the reaction is completed, excess 1,3,5-benzenetricarboxylic acid chloride dispersion is removed from the surface to obtain an initial composite membrane; the interfacial polymerization reaction time is 2 minutes.

[0092] S5 annealing treatment: the initial composite membrane is annealed to obtain a polymer layer-nanocellulose composite membrane.

[0093] According to the weight ratio, nanocellulose: pure water is 0.6:1000, polymer precursor: pure water is 1:50, and 1,3,5-benzenetricarboxylic acid chloride: organic solvent is 2:98.

[0094] The polymer-nanocellulose composite separator with a dense nanoporous structure prepared above was cut into a circle with a diameter of 15 mm and assembled into a zinc-zinc (Zn-Zn) symmetrical battery using a 2032 battery shell.

[0095] The assembly process of zinc-zinc (Zn-Zn) symmetric battery is as follows: negative electrode shell, spring, gasket, zinc negative electrode, polymer-nanocellulose composite diaphragm, glass fiber diaphragm, polymer-nanocellulose composite diaphragm, zinc positive electrode, and positive electrode shell.

[0096] Comparative Example 3

[0097] Nanocellulose was uniformly dispersed in pure water at a mass ratio of 0.6:1000, and a nanocellulose membrane was obtained by suction filtration. The nanocellulose membrane with a dense nanoporous structure prepared above was cut into a circle with a diameter of 15 mm, and assembled into a zinc-zinc (Zn-Zn) symmetrical battery using a 2032 battery shell.

[0098] The assembly process of zinc-zinc (Zn-Zn) symmetrical battery is as follows: negative electrode shell, spring, gasket, zinc negative electrode, nanocellulose diaphragm, glass fiber diaphragm, nanocellulose diaphragm, zinc positive electrode, and positive electrode shell.

[0099] Comparative Example 4

[0100] 2,5-diaminobenzenesulfonic acid was dispersed in pure water at a mass ratio of 1:50 and the pH value of the solution was adjusted to 13; 1,3,5-benzenetricarboxylic acid chloride was dispersed in n-heptane at a mass ratio of 2:98; the glass fiber diaphragm substrate was directly immersed in the 2,5-diaminobenzenesulfonic acid solution for 20 minutes, and then the 1,3,5-benzenetricarboxylic acid chloride solution was dropped on the surface of the diaphragm for interfacial polymerization reaction for 2 minutes; the obtained composite membrane was taken out from the n-heptane solution and annealed in an oven for 10 minutes to obtain a polymer-glass fiber composite diaphragm.

[0101] Performance testing and analysis:

[0102] like Figure 1 As shown, the polymer-nanocellulose composite membrane with a dense nanoporous structure prepared in Example 1 of the present invention is observed to have a flat, uniform and dense polymer layer, and there are multiple empty channels inside the nanocellulose that are beneficial to ion transmission. Figure 3 As shown, the assembled Zn-Zn symmetric battery is 2 (0.5mAh / cm 2 ) after 60 hours of circulation under the conditions of Figure 3 As shown in the figure, the protective layer is intact after the cycle, which indicates that the protective layer is conducive to the uniform deposition of zinc ions and effectively inhibits the formation of zinc dendrites. Figure 7 As shown, the initial discharge capacity of the zinc vanadium pentoxide full battery is as high as 240mAh / g. After more than 1000 cycles, the capacity retention reaches 90%, and the coulombic efficiency remains above 60%.

[0103] The polymer-nanocellulose composite membrane with dense nanoporous structure prepared in Examples 2 and 3 of the present invention, and the assembled zinc-zinc (Zn-Zn) symmetrical battery, at 25°C and 1 mA / cm 2 (0.5mAh / cm 2 ) conditions for 60 hours, respectively. Figure 4 and 5As shown, the protective layer is intact after the cycle, which indicates that the protective layer is conducive to the uniform deposition of zinc ions and effectively inhibits the formation of zinc dendrites.

[0104] like Figure 8 As shown, comparative example 1 was assembled into a zinc-zinc (Zn-Zn) symmetrical battery at 25°C and 1 mA / cm 2 (0.5mAh / cm 2 ) conditions, after 60 hours of cycling, it can be observed that zinc dendrites are formed in the Zn-Zn symmetric battery after only 60 hours of cycling. If the cycle continues, micron-sized dendrites will be formed, which can pierce the glass fiber separator and cause a short circuit in the battery.

[0105] like Figure 2 As shown, in Comparative Example 4, the interfacial polymerization reaction of 2,5-diaminobenzenesulfonic acid and 1,3,5-benzenetricarboxylic acid chloride was directly carried out on the surface of the glass fiber, and then directly observed by scanning electron microscopy, and no flat, uniform and dense polymer layer was observed, which indirectly illustrates that the interfacial polymerization reaction of the diamino monomer and 1,3,5-benzenetricarboxylic acid chloride requires nanocellulose as a substrate.

[0106] like Figure 6 As shown, the cycle performance of the zinc-zinc (Zn-Zn) symmetric batteries assembled in Examples 1, 2, 3 and Comparative Examples 1, 2, 3 were compared, and it was found that the batteries in Comparative Examples 1 and 2 were prone to short circuit during operation.

[0107] In summary, the diaphragm prepared by the present invention realizes desolvation of zinc ions through the polymer layer with dense nanopore structure and the pore structure of the porous skeleton, improves the zinc ion migration number, effectively reduces the overpotential of the zinc negative electrode, helps the uniform deposition of zinc ions, and reduces the side reactions of the zinc negative electrode. At the same time, the cellulose layer can provide good mechanical strength and inhibit the formation of zinc dendrites. The polymer with dense nanopore structure can be used in aqueous zinc ion batteries to improve the cycle life of the battery.

[0108] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways without departing from the spirit of the present invention or exceeding the defined scope.

Claims

1. A method for preparing a polymer layer-nanocellulose composite membrane having a dense nanoporous structure, characterized in that: The preparation method of the polymer layer-nanocellulose composite membrane comprises the following steps: S1 Vacuum self-assembly forming substrate: nanocellulose is uniformly dispersed in pure water to obtain a nanocellulose solution, and the nanocellulose solution is vacuum filtered to obtain a composite diaphragm substrate; S2 Bidirectional solution construction: S2.1 Alkaline induced monomer ionization construction: After adding the polymer precursor into pure water and stirring evenly, the pH value is adjusted to 12-15 with an alkaline solution, and then the precursor liquid is dispersed to obtain a precursor liquid. S2.2 Acid chloride organic phase microenvironment dispersion: 1,3,5-benzenetricarboxylic acid chloride is added into an organic solvent, and the acid chloride dispersion is performed to obtain a 1,3,5-benzenetricarboxylic acid chloride dispersion; The polymer precursor is one of 2,5-diaminobenzenesulfonic acid, o-phenylenediamine, p-xylylenediamine, 2,5-dimethyl-1,4-phenylenediamine and 1,4-cyclohexanediamine; the organic solvent is n-heptane or n-hexane; S3 soaking: soaking the composite membrane substrate in the precursor liquid for soaking operation, and after the soaking operation is completed, performing interface liquid phase desorption regulation operation to obtain a nanocellulose heterogeneous interface substrate; S4 Heterogeneous molecular self-assembly dynamic cross-linking film formation: 1,3,5-benzenetricarboxylic acid chloride dispersion is added dropwise to the upper surface of the nanocellulose heterogeneous interface substrate to carry out interfacial polymerization reaction. After the reaction is completed, excess liquid on the surface is removed to obtain an initial composite membrane; S5 annealing treatment: the initial composite membrane is subjected to annealing treatment to obtain a polymer layer-nanocellulose composite membrane.

2. The method for preparing the polymer layer-nanocellulose composite diaphragm having a dense nanoporous structure according to claim 1, characterized in that: According to the weight ratio, the ratio of nanocellulose to pure water is 0.6:1000-3000, the ratio of polymer precursor to pure water is 1:50-100, and the ratio of 1,3,5-benzenetricarboxylic acid chloride to organic solvent is 2:90-100.

3. The method for preparing the polymer layer-nanocellulose composite diaphragm having a dense nanoporous structure according to claim 1, characterized in that: In step S2.1, the alkaline solution is a sodium hydroxide solution.

4. The method for preparing the polymer layer-nanocellulose composite diaphragm having a dense nanoporous structure according to claim 1, characterized in that: In step S2.1, the precursor solution is dispersed by ultrasonic dispersion; in step S2.2, the acyl chloride is dispersed by low-temperature ultrasonic-mechanical synergistic dispersion.

5. The method for preparing the polymer layer-nanocellulose composite diaphragm having a dense nanoporous structure according to claim 1, characterized in that: In step S3, the soaking time of the soaking operation is 10-20 minutes; in the interface liquid phase desorption control operation, the filter paper is used to gently press the excess liquid on the surface.

6. The method for preparing the polymer layer-nanocellulose composite diaphragm having a dense nanoporous structure according to claim 1, characterized in that: In step S4, the reaction time of the interfacial polymerization reaction is 1-5 minutes.

7. The method for preparing the polymer layer-nanocellulose composite diaphragm having a dense nanoporous structure according to claim 1, characterized in that: In step S5, the annealing process parameters are as follows: the annealing temperature is 40-80° C.; the annealing time is 10-20 minutes.

8. Application of a polymer layer-nanocellulose composite membrane with a dense nanoporous structure, wherein the polymer layer-nanocellulose composite membrane with a dense nanoporous structure is prepared by the preparation method of the polymer layer-nanocellulose composite membrane with a dense nanoporous structure according to claims 1-7, characterized in that: Application of polymer layer-nanocellulose composite separator with dense nanoporous structure in aqueous zinc-ion battery pack.

9. The use of the polymer layer-nanocellulose composite membrane with dense nanoporous structure as claimed in claim 8, characterized in that: In the assembly structure of the aqueous zinc ion battery pack, from top to bottom are the negative electrode shell, spring, gasket, zinc negative electrode, polymer layer-nanocellulose composite separator, glass fiber separator, polymer layer-nanocellulose composite separator, positive electrode and positive electrode shell.

10. The use of the polymer layer-nanocellulose composite membrane with dense nanoporous structure as claimed in claim 8, characterized in that: The aqueous zinc ion battery is specifically a Zn-Zn symmetric battery or a Zn-V2O5 full battery.

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