Preparation method of gradient asymmetric hydrogel electrolyte

Abstract

The invention belongs to the field of new energy storage materials, and particularly discloses a preparation method of a gradient asymmetric hydrogel electrolyte, which is characterized in that the gradient asymmetric hydrogel electrolyte is prepared by regulating the concentration of electrolyte salt as a main time factor and cooperating with the fine adjustment effect of a nano inorganic filler and the space factor of gravity settling. And rapidly preparing the organic-inorganic composite hydrogel electrolyte with a gradient structure at room temperature. The method has universality, can be adapted to various inorganic fillers, and finally forms a gradient structure of negative electrode side filler enrichment layer-middle transition layer-positive electrode side polymer network layer by adjusting the salt concentration to match the sedimentation behaviors of different fillers. The electrolyte can simultaneously realize negative electrode interface stability, positive electrode ion rapid transmission and mechanical property enhancement, and shows excellent cycling stability and capacity retention ratio in a symmetric battery and a total battery. The preparation method is simple, low in energy consumption, high in controllability and suitable for large-scale energy storage and flexible electronic equipment.

Description

Technical Field

[0001] This invention belongs to the field of energy storage material preparation, specifically relating to a method for preparing a gradient asymmetric hydrogel electrolyte. Background Technology

[0002] Guided by the "dual carbon" goals, new energy storage technologies have become a strategic engine for energy transformation. Among them, aqueous zinc-ion batteries (AZIBs) stand out due to their high theoretical specific capacity (820 mAh g). -1 With its advantages such as low redox potential (-0.76 V vs. SHE), environmental friendliness, abundant resources, and low cost, AZIBs have become one of the core candidates for next-generation electrochemical energy storage systems. However, the practical application of AZIBs still faces severe challenges. The core bottleneck lies in the inherent contradiction between the functional requirements of the positive and negative electrodes for the electrolyte, leading to electrolyte-electrode interface mismatch, specifically manifested in the following two aspects: On the one hand, the requirements of the positive and negative electrodes for gel network content and water activity are conflicting. The zinc negative electrode side requires a high-density gel network to reduce free water content, suppress side reactions such as hydrogen evolution reaction (HER), corrosion, and dendrite growth, and guide Zn... 2+ Uniform deposition; however, the positive electrode side (such as V-based, Mn-based oxides and organic positive electrodes) relies on sufficient water activity to ensure H + / Zn 2+ Rapid intercalation and deintercalation of two ions; excessively high gel network content can enhance the interaction between functional groups and water, Zn. 2+ The interaction between these two factors hinders ion transport and limits the release of the positive electrode capacity. Traditional homogeneous hydrogel electrolytes require a compromise between these two factors, making it difficult to fully realize the overall performance of the battery.

[0003] On the other hand, the positive and negative electrodes are related to H + The required concentration varies significantly. High H+ + The content of certain substances accelerates the chemical corrosion of the zinc anode, damaging the stability of the electrode structure; while many cathode materials (such as NaV3O8, MnO2, etc.) possess H... + / Zn 2+ Dual ion storage mechanism, sufficient H + The supply and strong hydrogen bond network structure are key to improving the energy storage capacity of the cathode. How to precisely control the H+ in the positive and negative electrode regions through electrolyte structure design is crucial. + Concentration and water activity have become the core scientific issues for solving the performance bottlenecks of AZIBs.

[0004] To overcome these challenges, researchers both domestically and internationally have proposed the design concept of asymmetric hydrogel electrolytes, achieving some progress by adapting the differential structure of the two interfaces to meet the requirements of positive and negative electrodes. For example, Academician Jiang Lei's team at the Institute of Physics and Chemistry, Chinese Academy of Sciences, used an epitaxial polymerization strategy to construct a covalently fixed gradient hydrogel network, accelerating the reaction of Zn by leveraging the asymmetric distribution of negatively charged functional groups. 2+Selective transport; Professor Zhi Chunyi's team at City University of Hong Kong designed a bilayer structure combining an inorganic solid electrolyte and a hydrogel to meet the requirements of dendrite-free deposition at the negative electrode and rapid ion transport at the positive electrode, respectively; Researcher Yang Weishen's team at the Dalian Institute of Chemical Physics prepared Janus hydrogels through a gradient distribution of hydrophilic and hydrophobic monomers, precisely controlling the activity of water molecules at the positive and negative electrode interfaces. These studies fully demonstrate the effectiveness of asymmetric structure design, but current technologies still have many limitations: 1. Insufficient research on organic-inorganic composite systems: Existing asymmetric hydrogels are mostly based on pure organic networks. Most schemes rely on the gradient distribution of hydrophilic and hydrophobic monomers, functional group modification, or special molds to induce asymmetric structures. They fail to synergistically design inorganic materials (such as inorganic frameworks and nanomaterials) with polymer networks. Inorganic materials are insufficient for enhancing mechanical properties and regulating Zn content. 2+ The unique advantages of organic-inorganic composite asymmetric systems in terms of desolvation and uniform deposition have not been fully utilized, and systematic research on the preparation and performance regulation of organic-inorganic composite asymmetric systems is still lacking.

[0005] 2. Significant interfacial dynamics issues: Existing technologies mostly employ stepwise bilayer structures, and prolonged heating and gelation can easily lead to surface moisture evaporation. Stacking of different network layers can easily generate interfacial impedance, limiting the release of high-rate performance. Furthermore, some processes rely on UV light sources, special initiators, or harsh reaction conditions, further increasing the difficulty of application.

[0006] 3. Insufficient functional integration: Existing gradient gels mostly only achieve bilateral differences in water content or mechanical strength, failing to integrate the positive electrode H. + Enabling, negative electrode H + While it possesses multiple functions such as capture and interface adhesion adjustment, its effect on improving battery performance is limited.

[0007] 4. Inefficient and poorly versatile preparation strategies: Existing methods suffer from problems such as cumbersome steps, long processing time, and narrow applicability. They lack novel, efficient, and practical preparation technologies, making it difficult to meet the needs of large-scale applications.

[0008] In summary, the core bottleneck of existing technologies lies in the fact that the process of constructing gradient structures typically fails to effectively coordinate and regulate two key dimensions: the kinetics of gel network formation and the final spatial arrangement of functional fillers or polymer segments. Therefore, developing a novel preparation strategy that can integrate and regulate these two dimensions under mild reaction conditions to rapidly construct continuous gradient structures in situ is a crucial way to overcome the current predicament. This requires the new strategy to focus on solving the following technical problems: how to simplify the process to achieve rapid and low-energy preparation; how to ensure the continuity and stability of the formed gradient structure and the precise controllability of the distribution of inorganic fillers; and how to establish universal preparation principles to adapt to a wide range of filler and positive / negative electrode material systems.

[0009] Based on this, this invention proposes a "spatiotemporal+" regulation strategy, using a controllable accelerated polymerization mechanism as a time regulation factor, which works synergistically with a spatial regulation factor to construct an organic-inorganic composite gradient asymmetric hydrogel electrolyte. This strategy enables precise control of the gelation process, avoids interfacial impedance problems, and integrates multiple functions to synergistically optimize the performance of both positive and negative electrodes, providing a new path for the development of high-performance AZIBs. Summary of the Invention

[0010] This invention addresses the shortcomings of existing technologies by providing a method for preparing gradient asymmetric hydrogel electrolytes. Through the synergistic regulation of time and space factors, an organic-inorganic composite gradient structure is constructed, which can synergistically optimize the stability of the zinc anode interface and the ion transport efficiency of the cathode, thus resolving the contradiction between the electrolyte requirements of positive and negative electrodes in AZIBs. This method is suitable for high-performance aqueous zinc-ion batteries (AZIBs) and promotes the application of AZIBs in large-scale energy storage, flexible electronic devices, and other fields.

[0011] The technical concept of this invention is as follows: The core innovation of this invention lies in proposing a "spatiotemporal+" synergistic regulation strategy, with the controllable accelerated polymerization (CAP) mechanism as the core, to achieve rapid and controllable preparation of gradient asymmetric hydrogel electrolytes. The specific idea is as follows: 1. Time-factor regulation mechanism: Zn 2+ Hydrolysis produces H + (System pH 2.5-4.5), promotes the decomposition of the initiator to generate SO4• - Free radicals accelerate monomer polymerization; high concentration of Zn 2+ It inhibits free radical decay and maintains high polymerization efficiency. If it is an electronegative filler (such as sodium-type ZSM-5), its framework oxygen atoms carry a negative charge and preferentially adsorb H₂. + Increasing the pH of the system by 0.5-1 unit slows down the polymerization time. Non-electronegative fillers affect the microenvironment of the system through their own physical properties, which can also fine-tune the polymerization time. Finally, the gelation time (1-20 min) can be precisely controlled by "main adjustment of salt concentration + fine adjustment of filler".

[0012] 2. Spatial factor regulation mechanism: There is a density difference between the inorganic filler and the polymer precursor. During the gelation process, the filler settles towards the negative electrode side under gravity. The polymer network is formed simultaneously and locks the settling state. The presence of the transition layer eliminates the interfacial impedance of the traditional double-layer structure, ensuring the continuity of ion transport and forming a gradient structure of "zinc negative electrode side filler enrichment layer - intermediate transition layer - positive electrode side polymer network layer".

[0013] 3. Multifunctional synergistic mechanism: The negative electrode side filler enrichment layer adsorbs H... +Water molecules (electronegative filler) and physical confinement (non-electronegative filler) inhibit side reactions and dendrite growth; the polymer network on the positive electrode side (containing an acidic layer) maintains high water activity and sufficient H₂. + , ensure H + / Zn 2+ Rapid transmission; the organic-inorganic composite structure combines high tensile strength, elongation at break, and interfacial adhesion, making it suitable for flexible battery requirements.

[0014] 4. Scalable acidic layer design principle: The acidic layer monomers can be flexibly selected. Conventional unsaturated monomers (amides, carboxyl groups, hydroxyl groups) can be used with acids (sulfuric acid, hydrochloric acid, concentration 0.5-2 mol / L) to modulate the layer. Alternatively, acidic monomers (such as 2-acrylamido-2-methylpropanesulfonic acid) can be used directly, with precise pH adjustment (0.5-3.0) to match the positive electrode H₂. + Demand, while avoiding H + Excessive diffusion corrodes the zinc anode.

[0015] 5. Principle of Universality: The strategy is not limited to specific fillers; the core lies in coordinating gel kinetics with the physical properties of the filler. Gel kinetics are controlled by adjusting the electrolyte salt concentration to obtain a suitable time window for gravity sedimentation. For example, changing the ZnSO4 concentration (1.5 M to 3 M) can result in drastically different distributions of ZSM-5, from complete sedimentation to uniform dispersion, demonstrating that different sedimentation behaviors can be adapted by adjusting the gelation time. For fillers with higher density or larger particle size (faster sedimentation) (such as hydrotalcite-like materials with a density of approximately 2.4-2.6 g / cm³), this approach is also applicable. -3 For fillers with particle sizes of 50-100 nm, higher salt concentrations (shorter gel times) can be used to limit excessive sedimentation and maintain gradient integrity; conversely, for lighter or smaller fillers (such as nanocellulose with a density of approximately 1.1-1.3 g / cm³), lower salt concentrations (shorter gel times) are preferable. -3 (5-20 nm in diameter), can use lower salt concentrations (longer gelation time) to allow sufficient sedimentation to form a gradient layer, and is compatible with a variety of inorganic fillers such as molecular sieves, SiO2, TiO2, and montmorillonite.

[0016] Based on the above concept, the specific technical solution of this application is as follows: A method for preparing a gradient asymmetric hydrogel electrolyte, the specific steps of which are as follows: (1) Preparation of dispersion A: The nano-inorganic filler was dispersed in an electrolyte salt solution, stirred and sonicated to obtain dispersion A; The aforementioned nano-inorganic filler is one or more selected from molecular sieves, montmorillonite, hydrotalcite-like materials, halloysite, nanocellulose, and titanate nanotubes; the aforementioned nano-inorganic filler is a zero-dimensional, one-dimensional, or two-dimensional nanomaterial, further specifying that the zero-dimensional material has a size of 1-100 nm; the one-dimensional material has a diameter of 1-100 nm and a length greater than 1 μm; and the two-dimensional layered material has an average crystallite thickness of less than 25 nm, with different densities (1.0-5.0 g / cm³) selectable according to actual needs. -3 The particle size of the filler; the mass fraction of the nano-inorganic filler in dispersion A is 5-50 mg / mL. -1 ; Electrolyte salt concentration is 1-5 mol / L -1 The electrolyte salt is selected from one or a mixture of two of zinc sulfate (ZnSO4) and zinc trifluoromethanesulfonate (Zn(CF3SO3)2); The ultrasonic parameters are strictly controlled at power 100-300 W, frequency 20-100 KHz, and time 0.1-5 h to ensure uniform dispersion of the nano-inorganic filler and avoid agglomeration.

[0017] (2) Preparation of solution B: Dissolve the unsaturated monomer containing double bonds in the above dispersion A and stir until completely dissolved to obtain solution B; The unsaturated monomers mentioned above are amide, carboxyl, and hydroxyl monomers, accounting for 3-25 wt% of the total mass of solution B; The amide monomers are selected from one or more of sodium 2-acrylamido-2-methylpropanesulfonate, acrylamide, N-2-(hydroxyethyl)-acrylamide, and N,N-dimethylacrylamide; the carboxyl monomers are selected from one or more of acrylic acid, methacrylic acid, and sodium acrylate; and the hydroxyl monomers are selected from one or more of N-hydroxymethylacrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide. Single or mixed monomers can be selected according to the application scenario.

[0018] (3) Gradient gel preparation: Add crosslinking agent and initiator to solution B prepared in step (2) in sequence. After vortex mixing for 10-30 s, pour into a horizontal mold and let stand at room temperature for 1-20 min. The nano-inorganic filler settles to the bottom of the mold under the action of gravity. Finally, the side corresponding to the bottom of the mold is the zinc negative electrode side (filler enrichment layer), and the side corresponding to the top of the mold is the positive electrode side (polymer network layer). Gradient asymmetric hydrogel electrolyte is formed through the synergistic effect of "spacetime+".

[0019] The crosslinking agent is selected from one or more of N,N-methylenebisacrylamide and divinylbenzene; the initiator is selected from one or more of potassium persulfate, sodium persulfate, and ammonium persulfate; the amount of initiator is 0.1-0.6 wt% of the total monomer mass, and the amount of crosslinking agent is 0.01-0.2 wt% of the total monomer mass. This dosage range can ensure that the gel structure is stable and flexible.

[0020] The aforementioned "spatiotemporal+" synergistic effect can be explained as follows: adjusting the gelation time (principal time factor) by regulating the electrolyte salt concentration, and utilizing nano-inorganic fillers to enhance H... + By adjusting the adsorption effect (if the filler is electronegative) or its own physical properties, the polymerization time can be finely adjusted. Simultaneously, a gradient distribution (space factor) can be achieved through gravity sedimentation of the nano-inorganic filler, forming a structure of "zinc negative electrode side filler enrichment layer - intermediate transition layer - positive electrode side polymer network layer." By adjusting the salt concentration to adapt to inorganic fillers of different densities and particle sizes—for example, changing the ZnSO4 concentration (1.5-3 M) can result in drastically different distributions of ZSM-5, from complete sedimentation to uniform dispersion—it is demonstrated that different sedimentation behaviors can be adapted by adjusting the gelation time. For fillers with higher density or larger particle size (faster sedimentation) (such as hydrotalcite-like materials with a density of approximately 2.4-2.6 g / cm³), the effect is further enhanced. -3 For fillers with particle sizes of 50-100 nm, higher salt concentrations (shorter gel times) can be used to limit excessive sedimentation and maintain gradient integrity; conversely, for lighter or smaller fillers (such as nanocellulose with a density of approximately 1.1-1.3 g / cm³), lower salt concentrations (shorter gel times) are preferable. -3 (5-20 nm in diameter) can be used with lower salt concentrations (longer gelation time) to allow sufficient sedimentation to form a gradient layer. It is compatible with a variety of inorganic fillers such as molecular sieves, SiO2, TiO2, and montmorillonite, and has versatility.

[0021] (4) Optional acidic layer construction on the positive electrode side: Acidic gel precursor solution is coated on the positive electrode side of the gradient asymmetric hydrogel electrolyte (i.e., the polymer network layer side at the top of the mold determined in step (3)), and in-situ polymerization is carried out at room temperature for 3-10 min. The thickness of the acidic layer is 10-50 μm and the pH value is 0.5-3.0. The acidic gel precursor solution includes monomers, crosslinking agents, and initiators. The monomers are selected from the same amide, carboxyl, and hydroxyl unsaturated monomers as in step (2), or acidic unsaturated monomers. The acidic unsaturated monomers are selected from one or more of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, methacrylic acid, itaconic acid, and styrene sulfonic acid. The crosslinking agent is selected from one or more of N,N-methylenebisacrylamide and divinylbenzene. The initiator is selected from one or more of potassium persulfate, sodium persulfate, and ammonium persulfate. The amount of initiator is 0.1-0.6 wt% of the total monomer mass, and the amount of crosslinking agent is 0.01-0.2 wt% of the total monomer mass.

[0022] When the monomer is an amide, carboxyl, or hydroxyl unsaturated monomer, acid addition is required. The acid is selected from one or two of sulfuric acid and hydrochloric acid, with a concentration of 0.5-2 mol / L. -1 The pH of the acidic layer is adjusted to 0.5-3.0 by adjusting the acid concentration.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) The “spatiotemporal+” control strategy proposed in this invention simplifies the preparation conditions of asymmetric hydrogel electrolytes from the traditional high temperature heating of 50-90℃ for tens of minutes to 1-20 minutes at room temperature. Furthermore, the gelation time can be flexibly controlled by adjusting the electrolyte salt concentration, monomer content, system temperature and filler characteristics to adapt to different structural requirements. The preparation process does not require additional energy consumption and has significant advantages in saving resources, reducing costs, and being environmentally friendly and economical.

[0024] (2) Compared with traditional thermally initiated or stepwise asymmetric gels, the present invention locks the gradient distribution state of inorganic fillers through a rapid gelation process, effectively avoiding the structural inhomogeneity caused by filler agglomeration and sedimentation during long-term transformation. At the same time, the gradient transition layer design eliminates the interfacial impedance of the bilayer structure, significantly optimizes ion transport dynamics, improves electrode-electrolyte interface compatibility, and thus improves the high-rate performance of the battery.

[0025] (3) The asymmetric structure of the present invention achieves precise adaptation and multifunctional integration of positive and negative electrode functional requirements. In step (1), specific nano-inorganic fillers with specific properties (electronegativity / non-electronegativity, specific density / particle size) are selected, and in step (3), a negative electrode enrichment layer is formed by gravity sedimentation. H2 is adsorbed. + By interacting with water molecules or through physical confinement, hydrogen evolution, corrosion, and dendrite growth are inhibited at the zinc anode; the highly active polymer network on the positive electrode side formed in step (3) (or combined with the acidic layer constructed in step (4)) further replenishes H. + Supply), core guarantee positive electrode H + / Zn 2+Dual-ion rapid transport; through the construction of the organic-inorganic composite system in step (1) (synergistic interaction between nano-inorganic filler and polymer matrix) and the stable network structure regulated by the crosslinking agent in step (3), the core takes into account the mechanical strength, interfacial adhesion and environmental tolerance of the electrolyte, comprehensively solves the performance bottleneck caused by the compromise of positive and negative electrode requirements of traditional gel electrolyte, and significantly improves the cycle stability and energy density of aqueous zinc-ion batteries.

[0026] (4) The preparation strategy of the present invention has strong versatility and is not limited to specific filler or monomer system. By adjusting the time and space control factors, it can be adapted to inorganic fillers of different densities and particle sizes and various cathode systems (Mn-based, V-based, organic cathode, etc.), breaking the application limitations of existing asymmetric gel electrolytes and providing a flexible and feasible solution for the diversified design and large-scale application of aqueous zinc-ion batteries. Attached Figure Description

[0027] Figure 1 The image shows the linear relationship between ZnSO4 concentration and gelation time (with / without ZSM-5) in Example 1, as well as optical micrographs of different ZSM-5 distributions in the cross-section of the hydrogel membrane. The left vertical axis represents gelation time, and the horizontal axis represents ZnSO4 concentration, clearly showing the rule that the higher the concentration, the shorter the gelation time. The addition of ZSM-5 also prolongs the gelation time. The optical image on the right visually shows the differences in ZSM-5 distribution at different concentrations, with a clear gradient structure formed in the 2.5 M ZnSO4 system.

[0028] Figure 2 a represents the pH value of the hydrogel electrolytes with different compositions in Example 1. It can be observed that the pH value of the system after adding ZSM-5 is significantly higher than that of the pure ZnSO4 system. Figure 2 b is Example 1 ZSM-5-H + and H2O-H + The binding energy comparison proves that ZSM-5 binds to H + The stronger adsorption capacity explains the core reason for the increase in pH value.

[0029] Figure 3 The contact angles are those of the ZSM-5 depleted side and the ZSM-5 enriched side of the GHE in Example 1. The contact angle of the ZSM-5 enriched side (negative electrode side) is 56.0°. o The value on the depleted side (positive electrode side) is 45.2. o This clearly confirms the successful construction of the asymmetric structure.

[0030] Figure 4 The tensile stress-strain curve of the hydrogel in Example 1 ( Figure 4 a) and compressive stress-strain curve ( Figure 4b); Comparing GHE, UHE (uniform hydrogel) and pure PAM gel, it can be seen that the tensile strength and compressive strength of GHE are significantly better than those of the control group, proving that the gradient distribution of ZSM-5 and the polymer network synergistically improve the mechanical properties.

[0031] Figure 5 The image shows the long-cycle performance test results of the Zn / / Zn battery assembled by gradient gel prepared in Example 1 of this invention. The cycle life of the symmetric battery assembled by GHE exceeds 5800 h, which is far superior to that of UHE and pure PAM gel systems, verifying the high stability of the negative electrode interface.

[0032] Figure 6 This is a long-cycle performance test image of the Zn / / NaV3O81.5H2O battery assembled with gradient gel prepared in Example 1 of this invention, 3 A g. -1 At current density, the GHE system retains 93.7% capacity after 3300 cycles, which is significantly higher than UHE (80.3%) and pure PAM (53.1%), demonstrating the synergistic optimization of positive and negative electrode performance.

[0033] Figure 7 Zn / / NaV6O gel assembled as described in Example 2 of this invention 16 The long-cycle performance test chart of 3H2O battery shows that the discharge specific capacity of the S+GHE system containing the acidic S layer is significantly higher than that of the single GHE system, proving the enhancing effect of the acidic layer on the proton supply of the positive electrode.

[0034] Figure 8 This is a comparison diagram of hydrogen evolution and oxygen absorption of the gel prepared in Example 2 of the present invention. Figure 8 a represents the hydrogen evolution reaction (HER) test curve. Figure 8 b shows the oxygen evolution reaction (OER) test curve; it can be seen that the stable potential window of S+GHE is similar to that of GHE and pure PAM gel, and wider than that of the system containing only the S layer, confirming that the GHE layer can effectively bind H. + This inhibits the hydrogen evolution reaction at the negative electrode. Detailed Implementation

[0035] The invention will be further illustrated below with specific implementation examples. These examples are only intended to provide a complete and clear explanation of the invention, and are not intended to represent all possible implementations. All other implementations created based on this invention are within the scope of protection of this invention.

[0036] Example 1: A method for preparing a gradient asymmetric hydrogel electrolyte, the specific steps of which are as follows: Prepare a 2.5 mol L solution using a volumetric flask. -1Accurately weigh 0.4 g of sodium-type ZSM-5 molecular sieve (density 2.0-2.2 g / cm³) into a ZnSO₄ electrolyte salt solution. -3 (Particles with a diameter of 10-20 nm) were added to 25 mL of 2.5 mol L⁻¹ -1 In the ZnSO4 electrolyte salt, ZSM-5 and ZnSO4 were stirred at room temperature for 2 h to ensure uniform mixing. Subsequently, the ZSM-5 and ZnSO4 dispersion was sonicated at 100 W power and 50 kHz frequency for 60 min to exfoliate and further disperse ZSM-5.

[0037] ZSM-5 is an aluminosilicate crystal, whose framework contains Al. 3+ Ion-substituted Si 4+ The presence of ions results in oxygen atoms carrying a negative charge, and the 0.536 nm microporous structure effectively blocks the complete solvation of [Zn(H₂O)₆]. 2+ The complex (0.86 nm in diameter) allows for the desolvation of Zn. 2+ Ions (0.148 nm) permeate, thus limiting the Zn content at the negative electrode. 2+ The surrounding solvated water.

[0038] Take 2 mL of the sonicated dispersion into a centrifuge tube and add 0.3 g of acrylamide, stirring for 2 h. Then, add 20 μL of 2 wt% N,N-methyleneacrylamide solution, vortex for a few seconds, and then add 20 μL of 3 wt% potassium persulfate solution, vortex for a few seconds, and transfer a portion of the solution into a custom mold. Let it stand at room temperature for 5 min to obtain the gel electrolyte. In this gel electrolyte, the bottom of the mold (ZSM-5 enriched side) is the zinc negative electrode side, and the top of the mold (PAM dominant network side) is the positive electrode side (ZSM-5 depleted side).

[0039] Different ZnSO4 concentrations have a significant effect on the distribution of ZSM-5. Figure 1 The 2 M ZnSO4 system, due to its excessively long gelation time (7.2 min), resulted in complete sedimentation and stratification of ZSM-5, leading to poor adhesion and mechanical strength in the resulting ZSM-5 layer due to a lack of sufficient polymer network. The 3 M ZnSO4 system, with its excessively rapid gelation process (2.8 min), exhibited insufficient ZSM-5 sedimentation, resulting in a macroscopically uniform structure with no significant gradient differences. Only the 2.5 M ZnSO4 system achieved a precise match between gelation time and ZSM-5 sedimentation rate, enabling a stable gradient distribution of ZSM-5 within the gel. The negative electrode side consisted of a ZSM-5-rich layer, while the positive electrode side was dominated by a PAM network, with contact angles of 56.0° on both sides. o and 45.2 o ( Figure 3 ).

[0040] The introduction of ZSM-5 has a significant effect on the pH value of the system. Figure 2 a) The pH of the 2.5 M ZnSO4 pure electrolyte system was approximately 3.2. After adding ZSM-5, the pH rose to 4.6. This is due to the electronegative framework of ZSM-5 affecting H+. + Its adsorption capacity is stronger than that of water molecules ( Figure 2 b), thereby reducing the free H in the system + Concentration. Furthermore, ZSM-5 can interact with the polymer network through hydrogen bonds, further stabilizing the three-dimensional structure of the gel. Compared to pure PAM gel without ZSM-5, this composite gel exhibits significantly improved mechanical strength and adhesion. Figure 4 Its tensile strength can reach 0.68 MPa, which meets the mechanical requirements of battery assembly and cycling.

[0041] Example 2: A method for preparing a gradient asymmetric hydrogel electrolyte, the specific steps of which are as follows: Prepare a 1.0 mol L solution using a volumetric flask. -1 Accurately weigh 0.3 g of titanate nanotubes (density approximately 2.3-2.5 g cm⁻¹) into a Zn(CF₃SO₃)₂ electrolyte salt solution. -3 Titanate nanotubes (10-50 nm in diameter, with hydroxyl groups (-OH) on their walls and a negatively charged surface) were added to 25 mL of the above solution and stirred at room temperature for 3 h to ensure that the titanate nanotubes and Zn(CF3SO3)2 were fully mixed. Then, the mixture was sonicated at 150 W power and 40 kHz frequency for 45 min to ensure that the titanate nanotubes were uniformly dispersed and free from agglomeration.

[0042] Take 3 mL of the ultrasonically dispersed solution into a centrifuge tube, add 0.4 g of acrylamide monomer, stir for 1 h until completely dissolved, then add 15 μL of 2 wt% N,N-methyleneacrylamide solution and 25 μL of 3 wt% ammonium persulfate solution in sequence, vortex mix for 15 s, and then pour the mixture into a horizontally placed custom mold and let it stand at room temperature for 10 min (time factor and space factor are adapted). The bottom of the mold is the titanate nanotube enrichment side (negative electrode side), and the top is the polymer network side (positive electrode side). Utilizing the density difference between titanate nanotubes and PAM precursor solution, an asymmetric structure of "titanate nanotube enriched functional layer - pure PAM support layer" is formed by gravity self-settling.

[0043] This electrolyte replicates the softness of skin with a flexible PAM matrix, closely adhering to the electrode and alleviating interfacial stress caused by volume changes. Through the dynamic adaptation and protective capabilities of biomimetic skin with an asymmetric structure, it synergistically achieves the suppression of negative electrode side reactions and the protection of positive electrode ion transport.

[0044] Example 3: A method for preparing a gradient asymmetric hydrogel electrolyte, the specific steps of which are as follows: Prepare 3 mol / L solution using a volumetric flask. -1 A ZnSO4 electrolyte salt solution. Accurately weigh 0.20 g of hydrotalcite-like substances (LDHs) and add them to 10 mL of 3 mol / L solution. -1 The LDHs and ZnSO4 electrolyte salt were stirred at room temperature for 2 h to ensure uniform mixing. Subsequently, the LDHs-ZnSO4 dispersion was sonicated at 300 W power and 40 kHz frequency for 180 min to further disperse the LDHs.

[0045] Take 2 mL of the sonicated dispersion into a centrifuge tube and add 0.4 g of sodium acrylate and 0.1 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide. Stir for 3 h. Then add 25 μL of 2 wt% N,N-methyleneacrylamide solution, vortex for a few seconds, and then add 20 μL of 3 wt% ammonium persulfate. Vortex for a few seconds and then transfer a portion of the solution into a custom mold. Let it stand at room temperature for 5 min to obtain the gradient gel electrolyte. The bottom of the mold is the LDHs enrichment side (negative electrode side), and the top is the polymer network side (positive electrode side).

[0046] The density of hydrotalcite-like materials (LDHs) is approximately 2.4-2.6 g / cm³. -3 With a particle size of 50-100 nm, it belongs to the category of fillers with relatively high density and coarse particle size, resulting in a faster settling rate. Experiments have shown that if 2.5 mol L... -1 In a low-concentration ZnSO4 system, the gelation time reaches 5.5 min. LDHs, due to excessively rapid sedimentation, tend to aggregate excessively at the bottom, forming a layered structure with extremely poor mechanical strength. However, using a 3 mol L... -1 With a higher salt concentration, the gelation time is shortened to 2.7 min, which perfectly matches the sedimentation rate of LDHs, effectively preventing excessive sedimentation and ultimately forming a uniform gradient distribution. The negative electrode side is an LDHs enrichment layer and the positive electrode side is a polymer network layer, which fully verifies the design logic that "higher density or coarser particle size fillers and higher salt concentration (shorter gelation time) can prevent excessive sedimentation".

[0047] As can be seen from the above three embodiments, for fillers with higher density or larger particle size (faster settling) (such as hydrotalcite-like materials, with a density of approximately 2.4-2.6 g / cm³), -3 For fillers with particle sizes of 50-100 nm, higher salt concentrations (shorter gel times) can be used to limit excessive sedimentation and maintain gradient integrity; conversely, for lighter or smaller fillers (such as nanocellulose, with a density of approximately 1.1-1.3 g / cm³), lower salt concentrations can be used. -3The material has a diameter of 5-20 nm and can be packed with a lower salt concentration (with a longer gelation time) to allow for sufficient sedimentation and the formation of a gradient layer. It is compatible with various inorganic fillers such as molecular sieves, SiO2, TiO2, and montmorillonite. To further verify the above scheme, the inventors conducted the verification in Example 4.

[0048] Example 4: A method for preparing a gradient asymmetric hydrogel electrolyte, the specific steps of which are as follows: Prepare 1.5, 2, 2.5, and 3 mol L using volumetric flasks. -1 ZnSO4 electrolyte salt solution. Accurately weigh 0.15 g of halloysite (HNTs) and add it to 10 mL of ZnSO4 electrolyte salts of different concentrations. Stir at room temperature for 2 h to ensure homogeneous mixing of HNTs and ZnSO4. Then, sonicate the HNTs-ZnSO4 dispersion at 200 W power and 25 kHz to exfoliate and further disperse the HNTs.

[0049] Two mL of ultrasonically dispersed solutions of different concentrations were added to centrifuge tubes, and 0.3 g of acrylamide was added and stirred for 3 h. Then, 10 μL of 2 wt% N,N-methyleneacrylamide solution was added sequentially, and the mixture was vortexed for several seconds. Afterward, 25 μL of 3 wt% sodium persulfate was added, and the mixture was vortexed for several seconds. A portion of the solution was then transferred to a custom mold and allowed to stand at room temperature for different times to obtain gel electrolytes (HNTs-PAM). The bottom of the mold is the HNTs enrichment side (negative electrode side), and the top is the polymer network side (positive electrode side). The gelation times of different concentrations of ZnSO4 electrolyte salts in this example are shown in Table 1.

[0050] Table 1 Effect of electrolyte salt concentration on gelation time Table 1 shows that the gelation time gradually shortens with increasing electrolyte salt concentration. The halloysite used is a tubular nanostructure (outer diameter 50-100 nm, length several hundred nanometers) with a density of approximately 1.9-2.1 g / cm³. -3 Compared to hydrotalcite-like materials (density 2.4-2.6 g / cm³), -3With its lower density and tubular structure leading to greater fluid resistance and slower settling rate, HNTs belong to the "lighter and slower settling" filler type. Therefore, in the 3 M and 2.5 M ZnSO4 systems, due to the short gelation time (1.5 min, 3.1 min), HNTs did not settle sufficiently, exhibiting a macroscopically uniform structure with no obvious gradient differences; in the 1.5 M ZnSO4 system, the gelation process was too long (9.8 min), causing HNTs to settle completely and stratify, resulting in HNT layers with poor adhesion and mechanical strength due to the lack of sufficient polymer network; only the 2 M ZnSO4 system (lower salt concentration) provided a longer gelation time of 5.9 min, allowing HNTs to settle sufficiently without excessive aggregation, achieving a precise match between gelation time and HNT settling rate, ultimately forming a stable gradient distribution, verifying the design logic that "for lighter or smaller fillers, lower salt concentration (longer gelation time) allows them to settle sufficiently and form an enriched layer."

[0051] Example 5: Based on the gradient asymmetric hydrogel electrolyte (GHE) prepared in Example 1, an acidic gel layer (S layer) was further constructed on the positive electrode side (the PAM-dominant network side at the top of the mold determined in Example 1) to achieve a functionalized internal partitioning design of the electrolyte. The specific steps are as follows: First, an acidic gel precursor solution was prepared by sequentially adding 0.123 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 1.63 mL of sodium 2-acrylamido-2-methylpropanesulfonate (AMPSNa), and 0.127 g of acrylamide (AM) to 4 mL of a 2.5 M zinc sulfate aqueous solution and stirring until the solid was completely dissolved. Then, 0.15 wt% of N,N-methylenebisacrylamide crosslinking agent and 0.3 wt% of potassium persulfate initiator were added, and stirring was continued until completely dissolved to obtain an acidic precursor solution with a pH of approximately 1.0.

[0052] 150 μL of the precursor solution was dropped onto a polytetrafluoroethylene plate. Due to the strong acidity of the system, the rate of free radical generation from the decomposition of potassium persulfate was significantly accelerated, thus shortening the polymerization time considerably. After standing at room temperature for about 3 minutes until the system reached a slightly stringy state (i.e., the gel network had initially formed but remained viscous), the positive electrode side of the ZSM-5-containing GHE prepared in Example 1 was then rapidly applied to the surface of the acidic gel layer. After standing at room temperature for 10 minutes, the two gel layers were further integrated and cross-linked. This stepwise sequential polymerization strategy ensured a strong bond between the two layers and, through interface regulation of the initial gel state of the S layer, suppressed excessive diffusion of small molecules, forming a functional partitioned structure with a progressive interface: the S layer on the positive electrode side, with its abundant sulfonic acid groups, provides a stable acidic environment and proton source, satisfying the requirements of the positive electrode H... + Demand; ZSM-5 in the GHE layer on the negative electrode side adsorbs H+ With water molecules, regulating Zn 2+ The solvation structure effectively stabilizes the zinc anode interface.

[0053] Example 6: Based on the gradient asymmetric hydrogel electrolyte (GHE) prepared in Example 1, an acidic gel layer (S' layer) was further constructed on the positive electrode side (the PAM-dominant network side at the top of the mold determined in Example 1) to achieve a functionalized internal partitioning design of the electrolyte. The specific steps are as follows: Based on the gradient asymmetric hydrogel electrolyte (GHE) prepared in Example 1, an acidic layer modulated by acid was constructed on the positive electrode side (the PAM-dominated network side at the top of the mold), as follows: Preparation of acidic precursor solution (acid-modified solution): Dissolve 0.3 g acrylamide in 2 mL of 2.5 M zinc sulfate solution, add 0.2 wt% N,N-methylenebisacrylamide crosslinking agent and 0.4 wt% ammonium persulfate initiator, stir well, and add 10 wt% H2SO4 to adjust the pH to 2.0. Coating polymerization: The above-mentioned acidic precursor solution is uniformly coated on the positive electrode side surface of GHE, with the thickness controlled at 30-50 μm. After standing at room temperature for 5 min, the acidic layer construction is completed (denoted as S'+GHE).

[0054] Experimental Example 1 Using conventional methods, aqueous zinc-ion batteries (Zn / GHE / Zn and Zn / GHE / NaV3O81.5H2O, respectively) were assembled using the gradient asymmetric gel electrolyte (GHE) prepared in Example 1, and their electrochemical performance was tested. Simultaneously, as a comparison, a uniformly structured hydrogel electrolyte (UHE) was obtained by polymerization at room temperature using the same total ZSM-5 content and ZnSO4 concentration as the gradient hydrogel electrolyte (GHE); a gel electrolyte (PAM) without the inorganic nanomaterial ZSM-5 was prepared using the same ZnSO4 concentration, and aqueous zinc-ion batteries were assembled using the same method.

[0055] The preparation method of UHE is as follows: 0.4 g of ZSM-5 molecular sieve, 0.3 g of acrylamide, 20 μL of 2wt% N,N-methyleneacrylamide solution, and 20 μL of 3wt% potassium persulfate were added sequentially to 2 mL of 2.5 mol / L ZnSO4 solution. The mixture was stirred at high speed (1000 rpm) for 5 min until the system reached a viscous flow state. The mixture was immediately poured into a mold and allowed to stand at room temperature for 5 min for polymerization. This process ensured that ZSM-5 was uniformly dispersed without sedimentation, resulting in a homogeneous hydrogel electrolyte (UHE).

[0056] The preparation method of PAM gel is as follows: 0.3 g of acrylamide, 20 μL of 2 wt% N,N-methyleneacrylamide solution, and 20 μL of 3 wt% potassium persulfate were added to 2 mL of 2.5 mol / L ZnSO4 solution and polymerized at room temperature to obtain pure PAM gel electrolyte.

[0057] During battery use, battery life is an important parameter for evaluating battery performance. The Zn / GHE / Zn symmetric battery prepared using Example 1 of this application achieves a lifespan of 1 mA cm⁻¹. -2 and 1 mAh cm -2 It achieved excellent cycling stability of over 5800 hours under the given conditions: such as Figure 5 As shown, the horizontal axis represents cycle time (h) and the vertical axis represents voltage (V). The voltage curve of the GHE system remained stable for 5800 h without significant fluctuations or decay, while the UHE system experienced a sudden voltage drop and short circuit at about 2200 h, and the PAM system failed at about 750 h. This fully demonstrates the stabilizing effect of GHE on the negative electrode interface.

[0058] The Zn / GHE / NaV3O81.5H2O full cell at 3 A g -1 After 3300 cycles, the capacity retention rate was 93.7%. Figure 6 The horizontal axis represents the number of cycles, and the vertical axis on the left represents the discharge specific capacity (mAh g). -1 The right-hand vertical axis represents the capacity retention rate (%). The capacity stability of the GHE system in Example 1 of this application is much higher than that of UHE (80.3%) and PAM (53.1%). After 3300 cycles, it can still maintain a capacity retention rate of 93.7%, which confirms that the gradient structure of GHE achieves synergistic optimization of the positive and negative electrode performance.

[0059] Experimental Example 2 Using the integrated partitioned gel electrolyte (S+GHE) with an acidic S layer and a ZSM-5-reinforced G layer prepared in Example 5, an aqueous zinc-ion battery (Zn / S+GHE / Na2V6O) was assembled. 16 (3H2O full cell) and its electrochemical behavior were systematically evaluated. Compared with the single GHE structure in Experimental Example 1, this partitioned design, while maintaining the stability of the negative electrode interface, focuses on providing a continuous and rapid proton supply through the abundant sulfonic acid groups on the positive electrode side, thereby significantly enhancing the ion transport and capacity utilization of the positive electrode.

[0060] With Na2V6O 16 3H2O was used as the positive electrode to assemble a full cell for testing. Figure 7 ), in 2 Ag -1At the specified current density, the full cell using S+GHE achieves a discharge specific capacity of 326.61 mAh g⁻¹. -1 Compared to a single GHE battery (278.36 mAh g), -1 The improvement is significant. This is attributed to the locally high proton concentration environment created by the acidic S layer, which effectively promotes the H+ in the cathode material. + / Zn 2+ The co-intercalation reaction kinetics allow for the release of higher capacity.

[0061] A battery was assembled using a zinc sheet as the negative electrode and a stainless steel sheet as the positive electrode. The electrochemical windows of the hydrogen evolution reaction (HER) on the zinc negative electrode side and the oxygen evolution reaction (OER) on the positive electrode side were evaluated using linear sweep voltammetry (LSV). Figure 8 The stable potential window of S+GHE is similar to that of GHE without an acidic layer and pure PAM gel, but significantly wider than that of the system containing only an S layer. This result confirms that the negative electrode enrichment layer composed of ZSM-5 molecular sieves in GHE can effectively bind H₂ diffusing from the positive electrode acidic layer. + This inhibits the hydrogen evolution reaction that is exacerbated by the enrichment of hydrogen at the negative electrode interface, thereby maintaining the high stability of the overall electrolyte.

[0062] The above results demonstrate that by constructing an acidic functional layer on the positive electrode side and integrating it with the ZSM-5 enhanced gel on the negative electrode side, this invention not only comprehensively improves the cycle life of the battery but also specifically enhances the capacity output of the positive electrode, providing an effective strategy for resolving the contradiction between the positive and negative electrode requirements of aqueous zinc-ion batteries.

[0063] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The description of the above embodiments can help understand the principles and methods of the present invention. However, the above embodiments are not unique and should not be construed as limiting the present invention. At the same time, those skilled in the art can make flexible changes to the specific implementation methods and application scope based on the principles and methods of the present invention.

Claims

1. A method for preparing a gradient asymmetric hydrogel electrolyte, characterized in that, The specific steps are as follows: (1) Preparation of dispersion A: The nano-inorganic filler was dispersed in an electrolyte salt solution, stirred and sonicated to obtain dispersion A; the mass fraction of the nano-inorganic filler in dispersion A was 5-50 mg / mL. -1 The electrolyte salt concentration is 1-5 mol / L. -1 ; (2) Dissolve the unsaturated monomer containing double bonds in the dispersion A prepared in step (1) to obtain solution B; the unsaturated monomer containing double bonds is an amide, carboxyl, or hydroxyl monomer, which accounts for 3-25 wt% of the total mass of solution B. (3) Add crosslinking agent and initiator to solution B prepared in step (2) in sequence, mix for 10-30 s and pour into a horizontal mold and let stand at room temperature for 1-20 min. The nano-inorganic filler settles to the bottom of the mold under the action of gravity. Finally, the side corresponding to the bottom of the mold is the zinc negative electrode side and the side corresponding to the top of the mold is the positive electrode side, forming a gradient asymmetric hydrogel electrolyte.

2. The method for preparing the gradient asymmetric hydrogel electrolyte according to claim 1, characterized in that, It also includes step (4) construction of the acidic layer on the positive electrode side: the acidic gel precursor solution is coated on the positive electrode side of the gradient asymmetric hydrogel electrolyte obtained in step (3), and in-situ polymerization is carried out at room temperature for 3-10 min. The thickness of the acidic layer is 10-50 μm and the pH value is 0.5-3.

0. The acidic gel precursor solution includes monomers, crosslinking agents and initiators, wherein the monomers are selected from amide, carboxyl, hydroxyl unsaturated monomers or acidic unsaturated monomers.

3. The method for preparing the gradient asymmetric hydrogel electrolyte according to claim 1, characterized in that, The nano-inorganic filler mentioned in step (1) is one or more of molecular sieves, montmorillonite, hydrotalcite-like material, halloysite, nanocellulose, and titanate nanotubes; the above-mentioned nano-inorganic filler is a zero-dimensional, one-dimensional or two-dimensional nanomaterial, wherein the zero-dimensional material has a size of 1-100 nm; the one-dimensional material has a diameter of 1-100 nm and a length greater than 1 μm; and the two-dimensional layered material has an average wafer thickness of less than 25 nm.

4. The method for preparing the gradient asymmetric hydrogel electrolyte according to claim 1, characterized in that, In step (1), the electrolyte salt is selected from one or a mixture of two of zinc sulfate and zinc trifluoromethanesulfonate; the ultrasonic parameters are power 100-300W, frequency 20-100 KHz, and time 0.1-5 h.

5. The method for preparing the gradient asymmetric hydrogel electrolyte according to claim 1, characterized in that, In step (2), the amide monomers are selected from one or more of sodium 2-acrylamido-2-methylpropanesulfonate, acrylamide, N-2-(hydroxyethyl)-acrylamide, and N,N-dimethylacrylamide; the carboxyl monomers are selected from one or more of acrylic acid, methacrylic acid, and sodium acrylate; and the hydroxyl monomers are selected from one or more of N-hydroxymethylacrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide.

6. The method for preparing the gradient asymmetric hydrogel electrolyte according to claim 1, characterized in that, In step (3), the crosslinking agent is selected from one or more of N,N-methylenebisacrylamide and divinylbenzene; the initiator is selected from one or more of potassium persulfate, sodium persulfate and ammonium persulfate; the amount of initiator accounts for 0.1-0.6 wt% of the total mass of monomers, and the amount of crosslinking agent accounts for 0.01-0.2 wt% of the total mass of monomers.

7. The method for preparing the gradient asymmetric hydrogel electrolyte according to claim 2, characterized in that, In step (4), the amide monomers in the acidic gel precursor solution are selected from one or more of sodium 2-acrylamido-2-methylpropanesulfonate, acrylamide, N-2-(hydroxyethyl)-acrylamide, and N,N-dimethylacrylamide; the carboxyl monomers are selected from one or more of acrylic acid, methacrylic acid, and sodium acrylate; and the hydroxyl monomers are selected from one or more of N-hydroxymethylacrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide.

8. The method for preparing the gradient asymmetric hydrogel electrolyte according to claim 7, characterized in that, When the monomers of the acidic gel precursor solution in step (4) are amide, carboxyl, or hydroxyl unsaturated monomers, acid preparation is required. The acid is selected from one or two of sulfuric acid and hydrochloric acid, with a concentration of 0.5-2 mol / L. -1 The pH of the acidic layer is adjusted to 0.5-3.0 by adjusting the acid concentration.

9. The method for preparing the gradient asymmetric hydrogel electrolyte according to claim 2, characterized in that, The acidic unsaturated monomer in the acidic gel precursor solution in step (4) is selected from one or more of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, methacrylic acid, itaconic acid, and styrene sulfonic acid.

10. The method for preparing the gradient asymmetric hydrogel electrolyte according to claim 2, characterized in that, The crosslinking agent mentioned in step (4) is selected from one or more of N,N-methylenebisacrylamide and divinylbenzene; the initiator is selected from one or more of potassium persulfate, sodium persulfate and ammonium persulfate; the amount of initiator accounts for 0.1-0.6 wt% of the total mass of monomers, and the amount of crosslinking agent accounts for 0.01-0.2 wt% of the total mass of monomers.

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