Preparation and application of multifunctional group mixed cellulose zinc negative electrode protective layer

Abstract

The present application relates to the technical field of aqueous zinc-ion battery, and particularly relates to preparation and application of multifunctional group mixed cellulose zinc negative electrode protective layer, which is formed by mixing diacetate cellulose and nitrate cellulose according to a mass ratio, and in-situ forming a three-dimensional nanofiber network structure on the surface of zinc negative electrode through electrospinning. The symmetric battery assembled by the zinc negative electrode with the protective layer can be stably cycled for more than 5800 hours under a current density of 1 mA cm-2 and a surface capacity of 1 mAh cm-2. The half-cell assembled by the zinc negative electrode with the protective layer can be stably cycled for more than 7000 hours under a current density of 5 mA cm-2 and a surface capacity of 1 mAh cm-2, and the coulombic efficiency still remains at 99.9%, which significantly improves the cycle stability and service life of the aqueous zinc-ion battery.

Description

Technical Field

[0001] This invention relates to the technical field of aqueous zinc-ion batteries, and in particular to the preparation and application of a multifunctional mixed cellulose zinc anode protective layer. Background Technology

[0002] Aqueous zinc-ion batteries have become a research hotspot in large-scale energy storage in recent years due to their high safety, low cost, and environmental friendliness. Compared with traditional organic electrolyte systems, aqueous electrolytes have higher ionic conductivity and non-flammability, significantly reducing the risk of thermal runaway. However, zinc metal anodes are prone to dendrite growth, hydrogen evolution reaction, and surface passivation during cycling, leading to battery capacity decay and shortened cycle life. Especially under high current density and deep charge-discharge conditions, the uneven deposition / dissolution behavior of zinc anodes accelerates battery failure, which has become a key bottleneck restricting the practical application of this technology.

[0003] Zinc dendrite formation is influenced by various factors, such as the current density during cycling, deposition capacity, uniformity of current distribution, and electrolyte concentration. Zinc dendrites first appear in alkaline electrolytes, primarily because metallic zinc is thermodynamically unstable in alkaline electrolytes. During charge and discharge, significant concentration polarization forms on the electrode surface, leading to prolonged irregular two-dimensional diffusion of Zn²⁺ on the negative electrode surface. To reduce surface energy, Zn²⁺ accumulates at preferential nucleation sites, forming initial protrusions, which then continue to adsorb Zn²⁺, gradually forming dendrites during repeated charge and discharge cycles. Further dendrite growth can puncture the separator, causing internal battery malfunctions. Furthermore, during cycling, some dendrites have very loose contact with the negative electrode, easily detaching to form "dead zinc," thus reducing the negative electrode capacity and the battery's cycle life. Although dendrite growth can be relatively mitigated in neutral or weakly acidic ZnSO₄ electrolytes, dendrite formation still occurs during long-term cycling, and its impact on the battery cannot be ignored.

[0004] The corrosion in aqueous zinc-ion batteries is mainly due to self-corrosion and electrochemical corrosion. Metallic zinc inevitably reacts in neutral or weakly acidic ZnSO4 solutions. Because zinc has a lower electronegativity than hydrogen, it readily reacts with water, resulting in hydrogen evolution, which corrodes the zinc metal surface and affects battery performance. Furthermore, the hydrogen evolution reaction consumes a large amount of H⁺ in the water, increasing the concentration of OH⁻, which further accumulates near the interface between the zinc anode and the electrolyte. These ions combine with Zn²⁺ and electrolyte components to form basic zinc hydroxysulfate hydrate byproducts.

[0005] Passivation of the zinc anode is mainly caused by free water molecules and active water during the desolvation process. During discharge, sparingly soluble substances Zn(OH)2 and ZnO are generated on the surface of metallic zinc in the electrolyte. As the cycle continues, these sparingly soluble substances are deposited on the surface of the zinc anode to form a passivation layer. The continuous increase of the passivation layer will affect the normal dissolution of zinc and inhibit the activity of the zinc anode, thereby reducing the utilization rate and practicality of the zinc anode and causing the battery performance to deteriorate.

[0006] Researchers have proposed solutions to address the aforementioned problems with zinc anodes, including surface modification, electrolyte optimization, structural design, and diaphragm modification. Surface modification, a common method, involves creating an artificial solid-state electrolyte interface on the anode surface to prevent direct contact between the zinc anode and the electrolyte, thereby reducing corrosion. Its purpose is to regulate the deposition behavior of zinc ions, restricting their two-dimensional diffusion through physical confinement or electrostatic interactions. Generally, suitable protective layer criteria include: first, the protective layer should be hydrophilic, with its components chemically stable in aqueous electrolytes, insoluble in the electrolyte, and not reacting with it; second, the protective layer should be dense to prevent direct contact between the electrolyte and the zinc anode; and third, the protective layer should possess sufficient strength and toughness to withstand volume changes during cycling.

[0007] Cellulose-based materials have attracted widespread attention in the field of zinc batteries due to their wide availability, low cost, biodegradability, and richness in polar functional groups such as hydroxyl groups. In terms of membrane applications, Chinese patent CN202010465547 discloses the application of a mixed cellulose ester membrane in an aqueous zinc-ion battery. This mixed cellulose ester membrane, with a pore size of 0.22–10 μm and a thickness of 50–200 μm, maintains a capacity retention of 91.8% after 4000 cycles at a high current density of 5 A g⁻¹. Furthermore, literature reports the use of mixed cellulose ester membranes as ion redistributors to stabilize the zinc anode. Their dense and uniform pore structure physically diverts ion diffusion, while the polar oxygen-containing functional groups in the mixed cellulose ester promote and regulate ion diffusion through coordination. The synergistic effect of physical pores and chemical ion guidance suppresses dendrite formation. A Zn / Zn symmetric battery using this membrane exhibits a cycle life exceeding 1250 hours at 0.5 mA cm⁻². However, the above-mentioned technical solutions all use mixed cellulose esters as separators, which are at a certain distance from the zinc anode surface and cannot directly act on the anode interface. This makes it difficult to fundamentally solve the side reaction problems such as hydrogen evolution and corrosion on the zinc anode surface. Furthermore, existing technologies mainly focus on their ion transport regulation role as separators, without deeply exploring the direct regulation mechanism of their functional groups at the zinc anode interface.

[0008] The application of cellulose-based materials in zinc anode surface coatings has also been extensively studied. Numerous studies have reported on the construction of zinc anode coatings using single cellulose esters. For example, some studies have used a composite coating of cellulose acetate and zinc salts, utilizing the complexation of the polar ester groups in cellulose acetate with the zinc salts to enhance the hydrophilicity of the zinc anode, reduce interfacial resistance, and achieve rapid diffusion and uniform deposition of zinc ions. Symmetrical cells using this coating can achieve reversible plating / stripping cycles exceeding 2800 hours. Other studies have used nitrocellulose to construct an interfacial protective layer, utilizing the strong coordination ability of nitro functional groups to bind with Zn²⁺. Simultaneously, its negatively charged surface can repel SO₄²⁻ anions, inhibiting corrosion reactions on the zinc anode surface. Symmetrical cells using this interfacial layer can achieve stable cycling exceeding 5100 hours at 1 mA cm⁻². However, single cellulose esters contain a limited number of functional groups, making it impossible to simultaneously meet multiple requirements such as electrolyte affinity, chemical inertness, and hydrogen evolution inhibition. For example, although cellulose acetate has good film-forming properties and a certain zinc ion complexing ability, its chemical inertness is insufficient, making it susceptible to electrolyte corrosion during long-term cycling. On the other hand, although cellulose nitrate has good chemical stability, its zinc affinity and electrolyte affinity need to be improved.

[0009] To overcome the performance limitations of single cellulose esters, current technologies often employ composites of cellulose with other materials to construct zinc anode protective layers. For example, some studies have used sulfonated cellulose acetate nanofiber membranes as zinc anode protective layers. By introducing sulfonic acid groups into the cellulose acetate molecular chain, a synergistic regulation of zinc affinity and hydrophobicity is achieved. Simultaneously, the negative charge of the sulfonic acid groups repels polyiodides, making it suitable for zinc-iodine battery systems. Other studies have used composites of cellulose acetate and zinc tin oxide nanoparticles to construct hybrid coatings. The film-forming properties of cellulose acetate and the synergistic effect of the ester functional groups with the zinc affinity of zinc tin oxide create a synergistic effect. Ion flux is regulated through Lewis acid-base interactions, achieving uniform zinc ion deposition. Furthermore, there are schemes using hydroxypropyl cellulose and zinc trifluoromethanesulfonate composites to construct protective layers. The multi-hydroxyl structure forms a hydrogen bond network to suppress hydrogen evolution reactions, while ether bonds act as zinc-affinity sites to enhance ion conduction. However, the above-mentioned composite solutions are mostly physical mixtures of cellulose with inorganic materials or zinc salts, which have problems such as poor compatibility and weak interfacial bonding. Moreover, they mostly rely on the addition of zinc salts or inorganic fillers to achieve functional enhancement, and fail to make full use of the unique functional group characteristics of different types of cellulose esters to achieve synergistic effects.

[0010] In the application of various cellulose blends, some studies have used a mixture of sodium alginate and sodium carboxymethyl cellulose to construct a gel coating. This utilizes the ionic association between the carboxyl groups and Zn²⁺, as well as the strong adsorption effect of the hydroxyl groups, to form a flexible gel coating with a porous structure in situ on the zinc electrode surface, reducing side reactions such as hydrogen evolution and corrosion at the interface. However, this approach uses a mixture of two natural polysaccharide cellulose derivatives, whose functional groups are mainly carboxyl and hydroxyl groups, lacking diversity and complementarity of functional groups. Furthermore, the spin-coating method limits the control of the coating structure and porosity.

[0011] In summary, the application of cellulose-based materials in zinc anode protection still suffers from the following shortcomings in existing technologies: First, the functional groups of a single cellulose ester are limited, failing to simultaneously meet the performance requirements of the zinc anode protective layer in terms of zinc affinity, hydrophobicity, chemical stability, and mechanical strength. Second, existing composite solutions are mostly simple physical mixtures of cellulose with inorganic materials or zinc salts, lacking a systematic design of the synergistic mechanism of different types of cellulose ester functional groups, making it difficult to achieve a synergistic effect of "1+1>2". Third, existing cellulose-based zinc anode protective layers are mostly applied by spin coating, coating, or direct use of commercial films, resulting in limited control over the coating structure and porosity, making it difficult to form a uniform three-dimensional nanofiber network structure to effectively guide zinc ion deposition. Therefore, there is an urgent need to develop a zinc anode protective layer based on a specific cellulose ester combination with synergistic effects of multifunctional groups. Through precise complementarity and synergistic effects of different functional groups, this layer can simultaneously achieve multiple effects such as inhibiting zinc dendrite growth, mitigating hydrogen release side reactions, and enhancing corrosion resistance, further improving the cycle stability and practical application of aqueous zinc-ion batteries. Summary of the Invention

[0012] The purpose of this invention is to provide a preparation and application of a multifunctional mixed cellulose zinc anode protective layer, in order to solve the problems mentioned in the background art, such as the inability of a single cellulose ester functional group to simultaneously meet multiple performance requirements, poor compatibility between cellulose and inorganic materials and lack of synergistic design of functional groups, and the difficulty of forming a uniform three-dimensional nanofiber network structure by traditional coating methods.

[0013] To achieve the above objectives, this invention selects cellulose diacetate (containing hydroxyl and carboxyl groups) and cellulose nitrate (containing hydroxyl and nitro groups) as raw materials, and constructs a three-dimensional nanofiber network protective layer in situ on the zinc anode surface using electrospinning technology. The carboxyl groups in cellulose diacetate and the nitro groups in cellulose nitrate synergistically regulate the formation of a uniform porous framework structure in the nanofibers, effectively homogenizing the interfacial zinc ion flow and reducing local current density, guiding uniform zinc ion deposition, and inhibiting the formation and growth of zinc dendrites. The hydroxyl groups shared by the two cellulose esters, along with the ester and nitro groups, synergistically construct a polar-rich surface, anchoring free water molecules in the electrolyte through strong hydrogen bonding, increasing the hydrogen ion reduction barrier, significantly enhancing the hydrogen evolution overpotential, and mitigating the hydrogen evolution side reaction through a chemical passivation pathway. Simultaneously, the carboxyl groups of cellulose diacetate impart good electrolyte affinity to the coating, reducing interfacial impedance, while the nitro groups of cellulose nitrate enhance the chemical inertness of the fiber framework, improving the structural stability of the coating during long-term cycling. Together, they inhibit electrolyte decomposition and zinc anode corrosion through both physical barrier and chemical passivation pathways.

[0014] This invention provides the following technical solution: a multifunctional mixed-group cellulose zinc anode protective layer, which is formed by electrospinning a mixture of cellulose diacetate and cellulose nitrate to form a three-dimensional nanofiber network structure; the cellulose diacetate is rich in hydroxyl and carboxyl groups, and the cellulose nitrate is rich in hydroxyl and nitro groups. The synergistic effect of carboxyl, nitro and hydroxyl groups regulates the uniform deposition of zinc ions and inhibits the hydrogen evolution side reaction. The mass ratio of cellulose diacetate to cellulose nitrate is (5-9):(5-1).

[0015] Furthermore, the mass ratio of cellulose diacetate to cellulose nitrate is 5:5, 6:4, 7:3, 8:2, or 9:1; and the thickness of the protective layer is 90 μm.

[0016] The preparation method of the above-mentioned multifunctional group mixed cellulose zinc anode protective layer includes the following steps:

[0017] 1) Dissolve cellulose diacetate and cellulose nitrate in N,N-dimethylformamide to obtain a mixed cellulose dispersion, and mix the mixed cellulose dispersion with acetone to obtain an electrospinning precursor solution;

[0018] 2) Electrospinning the electrospinning precursor solution directly onto the surface of the zinc sheet to obtain a zinc sheet with mixed cellulose ester nanofibers attached.

[0019] 3) The zinc sheet with the attached mixed cellulose ester nanofibers is dried to form a multifunctional mixed cellulose zinc anode protective layer in situ on the zinc anode surface.

[0020] Further, in step 1), the concentration of the mixed cellulose dispersion is 8 wt%, and the volume ratio of N,N-dimethylformamide to acetone is 7:3. In step 2), the electrospinning conditions are a voltage of 20 kV, a feed speed of 0.0008 mm / s, and the use of a No. 21 needle. In step 3), the drying conditions are drying at 60°C for 12 h.

[0021] Furthermore, the preparation method of the cellulose diacetate includes: swelling wood pulp cellulose with glacial acetic acid, reacting it with excess acetic anhydride under sulfuric acid catalysis to generate cellulose triacetate, then adding dilute acetic acid aqueous solution and hydrolyzing it at 50-70°C until the degree of substitution is 2-2.5, and obtaining cellulose diacetate by precipitation, washing and drying.

[0022] Further, the method for preparing nitrocellulose includes: soaking dried cotton fibers in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:6, reacting at 20-30°C for 20-60 minutes, stopping the reaction in ice water, washing with water until neutral, boiling in water to remove acid, and drying at a low temperature below 40°C to obtain nitrocellulose.

[0023] The present invention also provides an aqueous zinc battery negative electrode, comprising a zinc negative electrode sheet, wherein the surface of the zinc negative electrode sheet is in situ modified with the above-mentioned multifunctional group mixed cellulose zinc negative electrode protective layer; the protective layer is directly formed on the surface of the zinc negative electrode by electrospinning and is tightly bonded to the zinc negative electrode.

[0024] Furthermore, the multifunctional group mixed cellulose zinc anode protective layer is prepared by the above preparation method.

[0025] The present invention also provides the application of the above-mentioned multifunctional group mixed cellulose zinc anode protective layer in aqueous zinc-ion batteries.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. This invention overcomes the limitation of single functional groups in cellulose esters by mixing cellulose diacetate and cellulose nitrate in a specific ratio, achieving precise complementarity of multiple functional groups, including carboxyl, nitro, and hydroxyl groups. The carboxyl groups provide excellent electrolyte affinity and zinc ion complexation ability, the nitro groups enhance the chemical inertness of the framework and anion repulsion, and the hydroxyl groups anchor water molecules through hydrogen bonds to inhibit hydrogen evolution. The synergistic effect of these three groups achieves a "1+1>2" effect, simultaneously meeting the multiple performance requirements of the zinc anode protective layer for zinc affinity, chemical stability, and hydrogen evolution inhibition.

[0028] 2. This invention uses electrospinning technology to construct a protective layer in situ on the surface of the zinc anode, forming a uniform and continuous three-dimensional nanofiber network structure. Compared with traditional spin coating, coating or direct lamination of commercial films, it has a higher specific surface area and controllable porosity, which can effectively homogenize the interfacial current distribution. Moreover, the fiber network has good flexibility, which can adapt to the volume change of the zinc anode during cycling and maintain the integrity of the coating structure.

[0029] 3. Through in-situ electrospinning, the protective layer is tightly bonded to the zinc anode surface, eliminating the interfacial gap problem encountered in commercial membrane bonding. It can directly act on the zinc anode / electrolyte interface, fundamentally suppressing interfacial side reactions such as hydrogen evolution and corrosion. This is different from existing technologies that use mixed cellulose esters as separators and cannot directly control the anode interface.

[0030] 4. Good material compatibility: The present invention uses two cellulose esters as raw materials, both of which are cellulose derivatives. They have good compatibility and film-forming properties, avoiding problems such as weak interfacial bonding and uneven dispersion that exist when cellulose is combined with inorganic materials or zinc salts. Furthermore, it can achieve excellent protective effects without relying on the addition of zinc salts or inorganic fillers.

[0031] 5. Symmetrical cells assembled with zinc anodes using the protective layer of this invention can achieve stable cycling for more than 5800 hours at a current density of 1 mA cm⁻² and a deposition capacity of 1 mAh cm⁻². Half-cells assembled with zinc anodes can be stably cycled for more than 7000 hours at a current density of 5 mA cm⁻² and a areal capacity of 1 mAh cm⁻², and their coulombic efficiency remains at 99.9%, which is significantly better than bare zinc electrodes and electrodes modified with a single cellulose acetate or cellulose nitrate coating, demonstrating excellent long-term cycling stability.

[0032] 6. This invention uses electrospinning technology, which is simple to operate, has controllable parameters, and uses widely available and inexpensive raw materials, making it suitable for large-scale preparation and promising for industrial application. Attached Figure Description

[0033] Figure 1 This is a surface appearance image of the aqueous zinc battery negative electrode modified with a mixed cellulose ester coating prepared in Example 1 of the present invention;

[0034] Figure 2 The scanning electron microscope images show the surface and cross-sectional morphology of the aqueous zinc battery negative electrode modified with a mixed cellulose ester coating prepared in Example 1 of this invention.

[0035] Figure 3 The images show a comparison of the surface morphology of the negative electrode after 100 cycles under the conditions of 1 mA cm⁻² current density and 1 mAh cm⁻² deposition capacity of Example 1 and Comparative Example 1 of the present invention, respectively.

[0036] Figure 4 The infrared spectrum curves of cellulose diacetate, cellulose nitrate and mixed cellulose esters in Example 1 of the present invention are shown.

[0037] Figure 5 This is a comparison chart of the wettability contact angle test results of the negative electrode and 2M zinc sulfate electrolyte in Example 1 and Comparative Example 1 of the present invention.

[0038] Figure 6 This is a comparison of in-situ observations of zinc dendrite growth at different times in Example 1 and Comparative Example 1 of the present invention under the conditions of 2M zinc sulfate electrolyte, 5mA cm⁻² current density, and 2mAh cm⁻² deposition capacity.

[0039] Figure 7 The graph shows the cycling performance of the symmetrical coin cell with negative electrode assembly prepared in Example 1 of the present invention at a current density of 1 mA cm⁻² and a deposition capacity of 1 mAh cm⁻².

[0040] Figure 8 The cycling performance of the symmetrical button cell assembled with the negative electrode prepared in Example 2 of the present invention is shown in the figure at a current density of 1 mA cm⁻² and a deposition capacity of 1 mAh cm⁻².

[0041] Figure 9 The cycling performance of the symmetrical coin cell assembled with the negative electrode prepared in Example 3 of the present invention is shown in the figure at a current density of 1 mA cm⁻² and a deposition capacity of 1 mAh cm⁻².

[0042] Figure 10 The cycling performance of the symmetrical coin cell with negative electrode assembly prepared in Example 4 of the present invention is shown at a current density of 1 mA cm⁻² and a deposition capacity of 1 mAh cm⁻².

[0043] Figure 11 The cycling performance of the symmetrical button cell assembled with the negative electrode prepared in Example 5 of the present invention is shown in the figure at a current density of 1 mA cm⁻² and a deposition capacity of 1 mAh cm⁻².

[0044] Figure 12 This is a comparison chart of the cycle performance of the symmetrical button cells assembled in Example 1 and Comparative Examples 1-3 of the present invention at a current density of 1 mA cm⁻² and a deposition capacity of 1 mAh cm⁻².

[0045] Figure 13 The graph shows a comparison of the cycle performance of the symmetrical button cells assembled in Example 1 and Comparative Examples 1-3 of this invention at a current density of 0.5 mA cm⁻² and a deposition capacity of 0.5 mAh cm⁻².

[0046] Figure 14The graph shows a comparison of the cycle performance of the symmetrical button cells assembled in Example 1 and Comparative Examples 1-3 of the present invention at a current density of 10 mA cm⁻² and a deposition capacity of 1 mAh cm⁻².

[0047] Figure 15 This is a comparison chart of the rate performance of symmetrical button batteries assembled with negative electrodes in Embodiment 1 and Comparative Example 1 of the present invention.

[0048] Figure 16 A comparison chart of the coulombic efficiency tests of zinc-copper half-cells assembled with negative electrodes in Example 1 and Comparative Example 1 of this invention.

[0049] Figure 17 This is a comparison diagram of the negative electrodes of Embodiment 1 and Comparative Example 1 of the present invention undergoing Tafel testing and linear sweep voltammetry testing in a three-electrode system.

[0050] Figure 18 The graph shows a comparison of the electrochemical impedance spectroscopy and time-current curves of the symmetrical button cells assembled with negative electrodes in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available conventional products, and all methods described herein are conventional methods in the field unless otherwise specified.

[0053] The zinc foil used in the example has a thickness of 100μm. Before use, it is polished with 800-grit and 2000-grit sandpaper to remove the surface oxide layer, ultrasonically cleaned with anhydrous ethanol for 10 minutes, and then air-dried at room temperature for later use.

[0054] The 2M zinc sulfate electrolyte used in the examples was prepared by dissolving zinc sulfate in deionized water.

[0055] The preparation method of cellulose diacetate according to the present invention is as follows: wood pulp cellulose is swollen with glacial acetic acid at room temperature for 2 hours to obtain a pre-prepared sample; under sulfuric acid catalysis, the pre-prepared sample is reacted with excess acetic anhydride at 30°C for 2 hours to generate cellulose triacetate with a degree of substitution of about 3; a 10% (w / w) dilute acetic acid aqueous solution is added to the reaction system, and the temperature is raised to 50-70°C for hydrolysis for 4-6 hours until the degree of substitution drops to 2-2.5 to obtain a pre-prepared solution; the pre-prepared solution is slowly poured into deionized water to precipitate a white solid, which is repeatedly washed with deionized water until neutral, and then vacuum dried at 60°C for 12 hours to obtain cellulose diacetate.

[0056] The preparation method of nitrocellulose according to the present invention is as follows: Defatted cotton is vacuum dried at 40°C for 12 hours to obtain dried cotton fibers; the dried cotton fibers are soaked in a mixed acid pre-cooled to 0-5°C, wherein the mixed acid is prepared by mixing concentrated nitric acid and concentrated sulfuric acid at a volume ratio of 1:6; the temperature is raised to 20-30°C and reacted for 20-60 minutes; after the reaction is completed, the product is immediately poured into a large amount of ice water to terminate the reaction, and the product is repeatedly washed with deionized water until the filtrate is neutral, and then boiled in boiling water for 30 minutes to remove residual acid, obtaining a pre-prepared sample; the pre-prepared sample is vacuum dried at below 40°C for 24 hours to obtain white flocculent nitrocellulose.

[0057] Example 1

[0058] This embodiment provides a method for preparing a multifunctional mixed-group cellulose zinc anode protective layer, the specific steps of which are as follows:

[0059] (1) Preparation of electrospinning precursor solution: Weigh cellulose diacetate and cellulose nitrate prepared by the above method at a mass ratio of 7:3, with a total mass of 0.8g. Dissolve them in 7mL of N,N-dimethylformamide and stir magnetically at room temperature for 6 hours until completely dissolved. Then add 3mL of acetone and continue stirring for 2 hours to mix evenly to obtain a uniform and transparent electrospinning precursor solution with a concentration of 8wt%, wherein the volume ratio of N,N-dimethylformamide to acetone is 7:3.

[0060] (2) Electrospinning: The above-mentioned precursor liquid is drawn into a 10mL syringe, a No. 21 stainless steel needle is installed, and the electrospinning parameters are set as follows: voltage 20kV, feed speed 0.0008mm / s, receiving distance 15cm. The pretreated zinc foil is fixed on the receiving roller and rotated at 100rpm. Electrospinning is carried out at room temperature and relative humidity of 30-40%. The spinning time is controlled to make the coating thickness reach 90μm.

[0061] (3) Post-processing: After spinning, the zinc sheet with mixed cellulose ester nanofibers attached is placed in a vacuum oven and dried at 60°C for 12 hours to remove residual solvent, and a zinc anode with a multifunctional mixed cellulose zinc anode protective layer on the surface is obtained, which is denoted as Zn@MCE-7 / 3.

[0062] The surface appearance of the Zn@MCE-7 / 3 anode prepared in this embodiment is as follows: Figure 1 As shown, the zinc foil surface is covered with a uniform white fibrous film, and the surface is flat and without defects.

[0063] Figure 2 The image shows the scanning electron microscope morphology of the Zn@MCE-7 / 3 negative electrode prepared in this embodiment. As can be seen from the image, the mixed cellulose ester nanofibers interweave to form a three-dimensional network structure with uniform fiber diameter and interconnected porous structure between fibers. The cross-sectional image shows that the coating thickness is about 90 μm, which is tightly bonded to the zinc foil substrate and there is no obvious delamination.

[0064] Figure 4 The figures show the infrared spectra of cellulose diacetate, cellulose nitrate, and the mixed cellulose ester of this embodiment. As can be seen from the figures, cellulose diacetate exhibits a C=O stretching vibration peak at 1740 cm⁻¹, while cellulose nitrate exhibits asymmetric and symmetric stretching vibration peaks at 1650 cm⁻¹ and 1280 cm⁻¹. The mixed cellulose ester exhibits the above characteristic peaks simultaneously, indicating that the two cellulose esters were successfully mixed and have a stable chemical structure.

[0065] Example 2

[0066] This embodiment is basically the same as Embodiment 1, except that the mass ratio of cellulose diacetate to cellulose nitrate is 5:5, that is, 0.5g of cellulose diacetate and 0.5g of cellulose nitrate are weighed. The remaining steps and parameters are the same as in Embodiment 1. The obtained zinc negative electrode is denoted as Zn@MCE-5 / 5.

[0067] Example 3

[0068] This embodiment is basically the same as Embodiment 1, except that the mass ratio of cellulose diacetate to cellulose nitrate is 6:4, that is, 0.6g of cellulose diacetate and 0.4g of cellulose nitrate are weighed. The remaining steps and parameters are the same as in Embodiment 1. The obtained zinc negative electrode is denoted as Zn@MCE-6 / 4.

[0069] Example 4

[0070] This embodiment is basically the same as Embodiment 1, except that the mass ratio of cellulose diacetate to cellulose nitrate is 8:2, that is, 0.8g of cellulose diacetate and 0.2g of cellulose nitrate are weighed. The remaining steps and parameters are the same as in Embodiment 1. The obtained zinc negative electrode is denoted as Zn@MCE-8 / 2.

[0071] Example 5

[0072] This embodiment is basically the same as Embodiment 1, except that the mass ratio of cellulose diacetate to cellulose nitrate is 9:1, that is, 0.9g of cellulose diacetate and 0.1g of cellulose nitrate are weighed. The remaining steps and parameters are the same as in Embodiment 1. The obtained zinc negative electrode is denoted as Zn@MCE-9 / 1.

[0073] Comparative Example 1

[0074] This comparative example uses a bare zinc negative electrode. The zinc foil is simply sanded, cleaned with anhydrous ethanol, and dried before use. No coating or modification is applied. This is denoted as Bare Zn.

[0075] Comparative Example 2

[0076] This comparative example is basically the same as Example 1, except that only cellulose diacetate is used and cellulose nitrate is not added. That is, 0.8g of cellulose diacetate is weighed and dissolved in a mixed solvent of 7mL N,N-dimethylformamide and 3mL acetone. The remaining electrospinning and post-treatment steps and parameters are the same as in Example 1, and a zinc anode modified with pure cellulose diacetate coating is obtained, denoted as Zn@CA.

[0077] Comparative Example 3

[0078] This comparative example is basically the same as Example 1, except that only nitrocellulose is used and no diacetate is added. That is, 0.8g of nitrocellulose is weighed and dissolved in a mixed solvent of 7mL N,N-dimethylformamide and 3mL acetone. The remaining electrospinning and post-treatment steps and parameters are the same as in Example 1, and a zinc anode modified with pure nitrocellulose coating is obtained, denoted as Zn@NC.

[0079] Performance testing

[0080] The zinc anodes prepared in Examples 1-5 and Comparative Examples 1-3 were assembled into CR2032 coin cells for electrochemical performance testing. Cell assembly was conducted in air, using glass fiber as the separator and 2M ZnSO4 aqueous solution as the electrolyte. Symmetrical cells used two identical zinc electrodes as the working and counter electrodes; zinc-copper half-cells used copper foil as the counter electrode and zinc foil as the reference electrode.

[0081] Figure 5 The figure shows the electrolyte contact angle test results of the Zn@MCE-7 / 3 negative electrode of Example 1 and the bare zinc negative electrode of Comparative Example 1. As can be seen from the figure, the contact angle of the bare zinc surface is larger, indicating poor electrolyte wettability; while the contact angle of the Zn@MCE-7 / 3 surface is significantly reduced, indicating that the mixed cellulose ester coating significantly improves the electrolyte wettability of the zinc negative electrode surface, which is beneficial to the uniform wetting of the electrolyte and rapid ion transport.

[0082] Figure 6 The figures show in-situ optical microscopy observations of zinc dendrite growth at different deposition times under a current density of 5 mA cm⁻² and a deposition capacity of 2 mAh cm⁻² for Examples 1 and Comparative Example 1. As can be seen from the figures, obvious protrusions and dendrites appear on the bare zinc surface after a short deposition time, and the dendrites continue to grow as the deposition time increases. In contrast, the Zn@MCE-7 / 3 surface remains flat throughout the deposition process, with no obvious dendrite formation. This indicates that the protective layer of the present invention can effectively guide the uniform deposition of zinc and inhibit dendrite growth.

[0083] Figure 3 The images show the scanning electron microscope (SEM) morphology of the negative electrode surfaces of Examples 1 and Comparative Example 1 after 100 cycles at 1 mA cm⁻² and 1 mAh cm⁻². As can be seen from the images, the surface of the bare zinc electrode after cycling is uneven, with a large number of moss-like dendrites and corrosion pits. In contrast, the surface of Zn@MCE-7 / 3 still maintains a smooth and dense deposition morphology, without obvious dendrites and corrosion products. This indicates that the protective layer of the present invention can still effectively protect the zinc negative electrode after long-term cycling.

[0084] Figures 7-11 The figures show the long-term cycling performance of symmetrical cells assembled with zinc anodes prepared in Examples 1-5 at a current density of 1 mA cm⁻² and a deposition capacity of 1 mAh cm⁻². The test results show that Zn@MCE-7 / 3 (Example 1) can cycle stably for over 5800 hours with stable overpotential, making it the best among the five examples. The cycle life of the mixed cellulose ester coating modified electrodes with the other proportions is better than that of the bare zinc electrode, but shorter than that of Example 1. This indicates that when the mass ratio of cellulose diacetate to cellulose nitrate is 7:3, the synergistic effect is optimal, and the cycling stability is the best.

[0085] Figure 12 The graph shows a comparison of the symmetrical battery cycle performance of Example 1 and Comparative Examples 1-3 under the conditions of 1 mA cm⁻² and 1 mAh cm⁻². The test results show that bare zinc (Comparative Example 1) short-circuited after a short cycle time, with drastic fluctuations in overpotential; the cycle life of Zn@CA (Comparative Example 2) and Zn@NC (Comparative Example 3) was longer than that of bare zinc, but both were significantly shorter than that of Zn@MCE-7 / 3 (Example 1), proving that the mixture of cellulose diacetate and cellulose nitrate produced a significant synergistic effect, which was better than that of a single-component coating.

[0086] Figure 13 This is a comparison of the cycling performance of symmetrical batteries in Example 1 and Comparative Examples 1-3 at low current densities of 0.5 mA cm⁻² and 0.5 mAh cm⁻². The test results show that Zn@MCE-7 / 3 still exhibits the best cycling stability at low current densities, with low and stable overpotential, significantly better than the comparative examples.

[0087] Figure 14 The graph shows a comparison of the cycle performance of symmetrical batteries in Example 1 and Comparative Examples 1-3 at high current densities of 10 mA cm⁻² and 1 mAh cm⁻². The test results show that at high current densities, bare zinc quickly fails, and the cycle life of the single-component coating is also significantly shortened. However, Zn@MCE-7 / 3 can still maintain stable cycling for a long time, indicating that the protective layer of this invention can effectively protect the zinc anode even at high current densities.

[0088] Figure 15 The graph shows a comparison of the rate performance of the symmetrical batteries in Example 1 and Comparative Example 1. The test current densities were 0.5, 1, 2, 5, 10, and 20 mA cm⁻², respectively, with each current density cycled for 10 times before returning to 0.5 mA cm⁻². As can be seen from the graph, with increasing current density, the overpotential of bare zinc increases sharply and exhibits significant fluctuations; while Zn@MCE-7 / 3 maintains a stable overpotential at all current densities, and the overpotential recovers to its initial value after returning to a lower current density. This indicates that the protective layer of the present invention has excellent rate performance and interface stability.

[0089] Figure 16 The graphs show the coulombic efficiency test results of zinc-copper half-cells in Example 1 and Comparative Example 1, with test conditions of 1 mA cm⁻² and 1 mAh cm⁻². As can be seen from the graphs, the coulombic efficiency of bare zinc begins to fluctuate drastically after a short number of cycles, resulting in a low average coulombic efficiency. In contrast, Zn@MCE-7 / 3 can be stably cycled for hundreds of cycles, maintaining an average coulombic efficiency above 99%, indicating that the protective layer of this invention significantly improves the reversibility of zinc deposition / dissolution.

[0090] Figure 17 The Tafel curves and linear sweep voltammetry curves for Example 1 and Comparative Example 1 are shown. The Tafel test results indicate that the corrosion current density of Zn@MCE-7 / 3 is significantly lower than that of bare zinc, and the corrosion potential shifts positively, indicating that the protective layer of the present invention effectively suppresses the corrosion reaction of the zinc anode. The linear sweep voltammetry results indicate that the hydrogen evolution onset potential of Zn@MCE-7 / 3 is significantly negatively shifted compared to bare zinc, and the hydrogen evolution overpotential is significantly increased, indicating that the protective layer of the present invention effectively suppresses the hydrogen evolution side reaction.

[0091] Figure 18 The electrochemical impedance spectroscopy and time-current curves for Example 1 and Comparative Example 1 are shown. The impedance test results indicate that the interfacial charge transfer resistance of Zn@MCE-7 / 3 is significantly lower than that of bare zinc, indicating that the protective layer of this invention reduces the interfacial impedance, which is beneficial for the rapid transport of zinc ions. The time-current curve test results show that the current of bare zinc continuously increases under constant potential, indicating that zinc ions undergo two-dimensional diffusion and lead to dendrite growth; while the current of Zn@MCE-7 / 3 rapidly stabilizes after an initial brief increase, indicating that zinc ions achieve uniform three-dimensional diffusion within the protective layer, effectively suppressing dendrite growth.

[0092] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A multifunctional mixed-group cellulose zinc anode protective layer, disposed on the surface of the zinc anode to suppress zinc dendrite growth and hydrogen evolution side reaction, characterized in that, A three-dimensional nanofiber network structure is formed by electrospinning a mixture of cellulose diacetate and cellulose nitrate. The cellulose diacetate is rich in hydroxyl and carboxyl groups, and the cellulose nitrate is rich in hydroxyl and nitro groups. The uniform deposition of zinc ions and the hydrogen evolution side reaction are regulated by the synergistic effect of carboxyl, nitro and hydroxyl groups. The mass ratio of cellulose diacetate to cellulose nitrate is (5-9):(5-1).

2. The multifunctional group-mixed cellulose zinc anode protective layer according to claim 1, characterized in that, The mass ratio of cellulose diacetate to cellulose nitrate is 5:5, 6:4, 7:3, 8:2, or 9:1; the thickness of the protective layer is 90 μm.

3. A method for preparing a multifunctional mixed cellulose zinc anode protective layer as described in claim 1, characterized in that, Includes the following steps: 1) Dissolve cellulose diacetate and cellulose nitrate in N,N-dimethylformamide to obtain a mixed cellulose dispersion, and mix the mixed cellulose dispersion with acetone to obtain an electrospinning precursor solution; 2) Electrospinning the electrospinning precursor solution directly onto the surface of the zinc sheet to obtain a zinc sheet with mixed cellulose ester nanofibers attached. 3) The zinc sheet with the attached mixed cellulose ester nanofibers is dried to form a multifunctional mixed cellulose zinc anode protective layer in situ on the zinc anode surface.

4. The method for preparing the multifunctional group-mixed cellulose zinc anode protective layer according to claim 3, characterized in that, In step 1), the concentration of the mixed cellulose dispersion is 8 wt%, and the volume ratio of N,N-dimethylformamide to acetone is 7:3; in step 2), the electrospinning conditions are a voltage of 20 kV, a feed speed of 0.0008 mm / s, and the use of a No. 21 needle; in step 3), the drying conditions are drying at 60°C for 12 h.

5. The method for preparing the multifunctional group-mixed cellulose zinc anode protective layer according to claim 3, characterized in that, The method for preparing cellulose diacetate includes: swelling wood pulp cellulose with glacial acetic acid, reacting it with excess acetic anhydride under sulfuric acid catalysis to generate cellulose triacetate, then adding dilute acetic acid aqueous solution and hydrolyzing it at 50-70°C until the degree of substitution is 2-2.5, and obtaining cellulose diacetate by precipitation, washing and drying.

6. The method for preparing the multifunctional group-mixed cellulose zinc anode protective layer according to claim 3, characterized in that, The method for preparing nitrocellulose includes: soaking dried cotton fibers in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:6, reacting at 20-30°C for 20-60 minutes, stopping the reaction in ice water, washing with water until neutral, boiling in water to remove acid, and drying at a low temperature below 40°C to obtain nitrocellulose.

7. A water-based zinc battery negative electrode, comprising a zinc negative electrode sheet, characterized in that, The zinc anode sheet is in situ modified with a multifunctional group mixed cellulose zinc anode protective layer as described in claim 1; the protective layer is formed directly on the zinc anode surface by electrospinning and is tightly bonded to the zinc anode.

8. The aqueous zinc battery negative electrode according to claim 7, characterized in that, The multifunctional group mixed cellulose zinc anode protective layer is prepared by the preparation method described in any one of claims 3 to 6.

9. The application of the multifunctional group mixed cellulose zinc anode protective layer as described in claim 1 in an aqueous zinc-ion battery.

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