Process for the preparation of surface-modified silica and its use in zinc-based structural energy storage composites in propylene carbonate electrolyte systems

Abstract

The application relates to a method for preparing a surface-modified silicon dioxide and application of the surface-modified silicon dioxide in a zinc-based structural energy storage composite material in a propylene carbonate electrolyte system, and relates to a method for preparing an electrolyte of a zinc-based structural energy storage composite material, and aims to solve the technical problem that the liquid phase component of an existing propylene carbonate electrolyte system is prone to loss in a structural energy storage composite material. The method comprises the following steps: preparing an epoxy group-modified silicon dioxide, and then introducing the epoxy group-modified silicon dioxide into a zinc-based structural energy storage composite material with propylene carbonate as a main solvent of an electrolyte; the surface-modified silicon dioxide enables the propylene carbonate to stably exist on the surface of a structural electrolyte layer, at an air / structural electrolyte interface and at an electrode / structural electrolyte interface, reduces the exposure degree of free liquid propylene carbonate, and inhibits the volatilization loss of the propylene carbonate; and the specific capacity of the zinc-based structural energy storage composite material reaches 312.8 mAh g ‑1 , and the zinc-based structural energy storage composite material can be stably cycled for more than 400 h; and can be applied to the field of energy storage materials.

Description

Technical Field

[0001] This invention belongs to the field of composite functional materials and electrochemical energy storage technology, specifically relating to a zinc-based structural energy storage composite material based on a propylene carbonate electrolyte system and its preparation method. Background Technology

[0002] As electrochemical energy storage devices develop towards lighter weight, higher integration, and multifunctionality, material systems are gradually evolving from single-function to a synergistic integration of structure and function. Structural energy storage materials, by coupling mechanical load-bearing functions with electrochemical energy storage functions in the same material or component, achieve the integration of structural support and energy storage, and have become an important development direction for highly integrated energy devices.

[0003] Among various structural energy storage systems, zinc-based structural energy storage materials have advantages in application due to their high specific energy, low cost, and good safety. Existing systems mostly use ionic liquids, zinc salts, and resin matrices to construct the structural electrolyte. While ionic liquid electrolytes have low volatility, they generally suffer from high viscosity, large mass transfer resistance, and limited ionic conductivity, making it difficult to balance high-rate performance with good processability. In contrast, propylene carbonate organic solvent systems have advantages such as high ionic conductivity, low cost, and adjustable composition, which are beneficial for improving zinc ion transport performance. However, the application of propylene carbonate electrolyte systems in structural energy storage composite materials still faces certain challenges: during wetting, curing, and service, the liquid phase component in the system is prone to free liquid exposure and volatilization, leading to electrolyte loss and adversely affecting electrochemical performance and long-term service performance. Therefore, while replacing ionic liquids with propylene carbonate electrolytes can improve the ion transport performance and processability of the system to some extent, it is still difficult to fully guarantee the stable retention of propylene carbonate on the surface of the structural electrolyte and at the multiphase interface. Summary of the Invention

[0004] This invention addresses the technical problem of easy loss of the liquid phase component in existing propylene carbonate electrolyte systems used in structural energy storage composites. It provides a method for preparing surface-modified silica and its application in zinc-based structural energy storage composites using propylene carbonate electrolyte systems. The propylene carbonate used in this invention, as the main electrolyte solvent, improves zinc ion transport performance and processing wettability. Simultaneously, by introducing surface-modified silica filler, it can stably exist on the surface of the structural electrolyte layer, at the air / structural electrolyte interface, and at the electrode / structural electrolyte interface, reducing the exposure of propylene carbonate to free liquid and suppressing its volatilization loss. This results in a synergistic improvement in electrochemical performance, interfacial stability, and cycle life.

[0005] The method for preparing surface-modified silica according to the present invention is carried out according to the following steps:

[0006] 1. Disperse silica in a mixed solvent, add dilute nitric acid solution to adjust the pH of the system to 3.5~4.0 to carry out the surface hydroxyl activation reaction, centrifuge, wash and dry to obtain silica with surface hydroxyl activation;

[0007] 2. Surface-activated silica with hydroxyl groups is dispersed in ethanol, and the pH is adjusted to 8-9 with dilute ammonia. Then, γ-aminopropyltriethoxysilane is added to carry out an amination modification reaction to obtain an amination intermediate. The amination intermediate is dispersed in ethanol, and the pH is adjusted to 4.5-5.0 with dilute acetic acid. Then, γ-glycidoxypropyltrimethoxysilane is added to carry out a bifunctional modification reaction to obtain epoxy-modified silica.

[0008] 3. The epoxy-modified silica and solvent are added to the reaction vessel for solvothermal treatment to improve crosslinking stability. After washing and drying, surface-modified silica is obtained.

[0009] Furthermore, the silica mentioned in step one is one or more of nano-silica, mesoporous silica, or fumed silica; the particle size of the silica is 10 to 100 nm.

[0010] Furthermore, the mixed solvent mentioned in step one is a mixture of anhydrous ethanol and deionized water in a volume ratio of 5:1.

[0011] Furthermore, the surface hydroxyl activation reaction described in step one is carried out under reflux at a temperature of 60°C for 3 hours.

[0012] Furthermore, the amination modification reaction described in step two is carried out under reflux at a temperature of 70°C for 4 hours.

[0013] Furthermore, the bifunctional modification reaction described in step two is carried out under reflux at 65°C for 5 h.

[0014] Furthermore, in step two, the mass ratio of hydroxyl-activated silica to the volume ratio of γ-aminopropyltriethoxysilane is 1 g: (0.15~0.2) mL; the volume ratio of the aminated intermediate to γ-glycidoxypropyltrimethoxysilane is 1 g: (0.25~0.35) mL.

[0015] Furthermore, the solvothermal treatment described in step three is carried out at a temperature of 135°C for 6 hours.

[0016] The application of the surface-modified silica prepared by the above method is to use it in zinc-based structural energy storage composite materials based on propylene carbonate electrolyte system.

[0017] Furthermore, a zinc-based structural energy storage composite material based on a propylene carbonate electrolyte system includes a composite positive electrode, a composite negative electrode, and a structural electrolyte layer located between the composite positive electrode and the composite negative electrode, wherein: the composite positive electrode includes a supporting substrate and a positive electrode active material layer loaded on its surface; the composite negative electrode includes a conductive substrate and a metallic zinc negative electrode layer loaded on its surface; and the structural electrolyte layer is a multiphase composite structure composed of a propylene carbonate electrolyte system, zinc salt, polymer matrix, and surface-modified silica.

[0018] Furthermore, the preparation method of zinc-based structural energy storage composite material based on propylene carbonate electrolyte system is carried out according to the following steps:

[0019] I. Using propylene carbonate as the main electrolyte, zinc salt is added to form an electrolyte system with ion conductivity; wherein the concentration of zinc salt is 0.5-2.0 mol / L, which gives the system high ionic conductivity and good fluidity;

[0020] 2. A curable polymer is used as a structural support phase and mixed with the propylene carbonate electrolyte system to form a stable composite precursor system; wherein the mass fraction of the curable polymer in the composite precursor system is 10% to 30%.

[0021] 3. Surface-modified silica is added to the composite precursor system to obtain a modified composite precursor system. The amphiphilic properties of the amino and epoxy bifunctional groups of surface-modified silica are utilized to enrich the interface between the polymer and propylene carbonate. During curing, the epoxy groups are covalently cross-linked with the polymer to achieve anchoring, while the amino groups specifically adsorb the polar carbonyl groups of propylene carbonate molecules through hydrogen bonds, binding the free propylene carbonate on the surface to the interfacial network, thereby inhibiting the volatilization of propylene carbonate and stabilizing the interfacial structure.

[0022] IV. Using a conductive substrate as a support framework, a positive electrode active material layer is constructed on the surface of the conductive substrate to obtain a composite positive electrode; a metallic zinc negative electrode layer is constructed on the surface of the conductive substrate to obtain a composite negative electrode.

[0023] 5. The modified composite precursor system is introduced into the electrode structure composed of composite positive and composite negative electrodes, so that the modified composite precursor system wets the electrode interface area and the internal pores of the supporting skeleton, realizing the synergistic distribution of the electrolyte phase and the structural skeleton; the wetted electrode structure system is subjected to static, pre-curing and thermal curing treatments to allow the polymer to gradually cross-link and cure, and form a stable and continuous structure inside the system, thereby obtaining a zinc-based structural energy storage composite material based on the propylene carbonate electrolyte system.

[0024] Furthermore, the zinc salt mentioned in step one is one or more of Zn(TFSI)2, Zn(FSI)2 or Zn(OTf)2, and the concentration of the zinc salt in the electrolyte system is 0.8 to 1.5 mol / L.

[0025] Furthermore, the curable polymer described in step two consists of a polymer and its curing agent; wherein the polymer is one or more of epoxy resin, acrylate resin, polyurethane, or polyether. The polymer and the corresponding curing agent together constitute a crosslinkable curable system. By controlling the compatibility between the electrolyte phase and the polymer, the electrolyte phase is uniformly dispersed in the polymer matrix.

[0026] Furthermore, the surface-modified silica content in the modified composite precursor system described in step three is 0.1% to 5% by mass.

[0027] Furthermore, the conductive substrate mentioned in step four is carbon fiber.

[0028] Furthermore, the positive electrode active material mentioned in step four is NH4V4O 10 Positive electrode active material NH4V4O 10 The substrate is loaded onto the surface of the support substrate by solution reaction, in-situ growth or coating.

[0029] Furthermore, the zinc anode layer described in step four is formed by electrodeposition, wherein the electrodeposition current density is 0.5–5 mA / cm². 2 The deposition time is 5–30 min.

[0030] Furthermore, the method for introducing the modified composite precursor system into the electrode structure composed of the composite positive electrode and the composite negative electrode in step five is impregnation, drop coating or vacuum impregnation; the modified composite precursor system is introduced between the composite positive electrode and the composite negative electrode, and during the standing process, sufficient wetting of the interface between the structural electrolyte layer and the composite positive electrode and the interface between the structural electrolyte layer and the composite negative electrode is achieved, as well as the uniform distribution of the electrolyte phase inside the support skeleton.

[0031] Furthermore, the pre-curing temperature in step five is 40–60°C, and the time is 10–30 min.

[0032] Furthermore, the thermosetting temperature in step five is 60–120°C, and the time is 30–120 min. During the curing process, the modified silica is distributed on the surface of the structural electrolyte layer and in the interface regions between the structural electrolyte layer and the composite positive electrode, and between the structural electrolyte layer and the composite negative electrode. The modified silica filler interacts with the polymer matrix through surface functional groups, improving the dispersibility of silica in the composite precursor system and enhancing the bonding stability between the structural electrolyte layer and the electrode interface.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] First, the present invention uses a propylene carbonate electrolyte system to construct a zinc-based energy storage material, which has advantages such as high ionic conductivity, low viscosity and adjustable composition compared with traditional ionic liquid systems, and is conducive to improving the electrochemical performance and processing performance of the material.

[0035] Second, this invention achieves a stable distribution of the electrolyte phase and the structural support phase in the system through the synergistic design of the propylene carbonate electrolyte system and the polymer matrix, thereby contributing to the synergistic optimization of electrochemical performance and cycle life.

[0036] Third, the modified silica introduced in this invention is used as an auxiliary functional component. The amino and epoxy bifunctional groups on its surface play an interfacial bridging role: one end forms covalent crosslinks with the polymer matrix to enhance structural stability, and the other end adsorbs and anchors the liquid phase component of propylene carbonate through secondary bonds, thereby effectively binding the free liquid of volatile propylene carbonate on the surface of the material and reducing the adverse effects of organic component loss on the system performance.

[0037] Fourth, this invention helps maintain the distribution stability of the electrolyte phase in the polymer matrix within the composite system, and maintains the stability of the interfacial wetting state between the structural electrolyte layer and the composite positive and negative electrodes, thereby improving the interfacial consistency and cycle stability of the material.

[0038] Fifth, this invention achieves a synergistic improvement in both high ion transport performance and structural stability of organic systems, resulting in a specific capacity of 312.8 mAh g for zinc-based energy storage materials. -1 It can be stably cycled for more than 400 hours; it can be used in the field of structural energy storage materials. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the overall configuration of the zinc-based structural energy storage material prepared in Example 2;

[0040] Figure 2 This is a schematic diagram showing the tensile properties test results of the zinc-based structural energy storage composite material prepared in Example 2;

[0041] Figure 3 The graph shows the charge-discharge curves of the zinc-based energy storage composite material prepared in Example 2 under different rate conditions.

[0042] Figure 4 This is a comparison diagram of the precursor solution with modified silica and the precursor solution without modified silica in Comparative Example 1.

[0043] Figure 5This is a comparison of the cycling curves of the precursor solutions with and without modified silica in Comparative Example 1 in an open zinc-zinc symmetric cell.

[0044] Figure 6 The electrochemical impedance spectroscopy (EIS) of different electrolyte systems in Comparative Example 2 is shown in the figure.

[0045] Figure 7 This is a comparison chart of the ionic conductivity of different electrolyte systems in Comparative Example 2.

[0046] Figure 8 This is a comparison of the cycling performance of the propylene carbonate electrolyte system with modified silica added in Comparative Example 3 and the ionic liquid electrolyte system. Detailed Implementation

[0047] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments. All equivalent substitutions, equivalent transformations or improvements made within the spirit and principles of the present invention should fall within the protection scope of the present invention.

[0048] Example 1: The preparation method of surface-modified silica in this example is carried out according to the following steps:

[0049] 1. 10.0 g of nano silica powder was added to a mixed solvent of 250 mL anhydrous ethanol and 50 mL deionized water and ultrasonically dispersed for 20 min. The pH of the system was adjusted to 3.5 by adding 0.5 mol / L dilute nitric acid solution dropwise. The surface hydroxyl activation reaction was carried out by reflux at 60°C for 3 h. After centrifugation, the silica powder was washed with deionized water until neutral, then washed with anhydrous ethanol, and then vacuum dried in a vacuum drying oven at 80°C for 12 h to obtain surface hydroxyl activated silica.

[0050] 2. 8.0 g of surface-hydroxyl-activated silica was dispersed in 150 mL of anhydrous ethanol, and the pH was adjusted to 8 with 2.0 mol / L dilute ammonia. Then, 1.5 mL of γ-aminopropyltriethoxysilane was added, and the mixture was refluxed at 70°C for 4 h to carry out an amination modification reaction, yielding an amination intermediate. 6.0 g of the amination intermediate was dispersed in 120 mL of anhydrous ethanol, and the pH was adjusted to 4.5 with 0.1 mol / L dilute acetic acid. Then, 1.8 mL of γ-glycidoxypropyltrimethoxysilane was added, and the mixture was refluxed at 65°C for 5 h to carry out a bifunctional modification reaction, yielding a mixture containing epoxy-modified silica.

[0051] 3. The mixture containing epoxy-modified silica was transferred to a reaction vessel and subjected to solvothermal treatment at 135°C for 6 h to improve crosslinking stability. After natural cooling, it was centrifuged, thoroughly washed with anhydrous ethanol and acetone, and vacuum dried to obtain surface-modified silica. The product was a white, loose powder with a yield of approximately 93% and an organic grafting amount of approximately 12 wt%.

[0052] Example 2: A zinc-based energy storage composite material based on a propylene carbonate electrolyte system was prepared using the surface-modified silica from Example 1. The specific preparation method is as follows:

[0053] 1. Using propylene carbonate as the electrolyte solvent, add Zn(TFSI)2 at a concentration of 1.0 mol / L and stir for 30 min at room temperature to form the electrolyte system;

[0054] 2. The curable polymer is added to the electrolyte system at a mass fraction of 20%, and mixed evenly under stirring to form a stable composite precursor system; wherein the curable polymer is bisphenol A methacrylate diester monomer and curing initiator 2,2-azobisisobutyronitrile, and the mass of 2,2-azobisisobutyronitrile is 1.5% of the mass of bisphenol A methacrylate diester monomer;

[0055] 3. Surface-modified silica is added to the composite precursor system. First, it is mechanically stirred for 30 min, then ultrasonically dispersed for 15 min to ensure uniform dispersion of the modified silica. Then, it is vacuum degassed for 15 min to obtain the modified composite precursor system. The mass percentage of surface-modified silica in the modified composite precursor system is 2%. The amphiphilic properties of the amino and epoxy bifunctional groups of surface-modified silica are utilized to enrich it at the interface between the polymer and propylene carbonate. During curing, the epoxy groups are covalently cross-linked with the polymer to achieve anchoring, while the amino groups specifically adsorb the polar carbonyl groups of propylene carbonate molecules through hydrogen bonds, binding the free propylene carbonate on the surface within the interfacial network, thereby inhibiting the volatilization of propylene carbonate and stabilizing the interfacial structure.

[0056] IV. First, prepare a composite cathode;

[0057] (1) A carbon fiber cloth with a length × width × thickness of 20 mm × 20 mm × 0.3 mm was used as a conductive substrate. After being cleaned with anhydrous ethanol and deionized water respectively, it was dried at a temperature of 60℃ for 2 h to remove surface impurities and improve the surface activity of the carbon fiber cloth.

[0058] (2) Weigh 1.2822 g of ammonium metavanadate and 1.6565 g of oxalic acid and add them to 160 mL of deionized water; and use ammonium chloride as the ammonium source to adjust the pH of the reaction system to 3, so that the system is suitable for the positive electrode active material NH4V4O 10 The precursor solution containing vanadium source and ammonium salt is generated;

[0059] (3) The treated carbon fibers were arranged in a precursor solution containing vanadium source and ammonium salt, transferred to a closed reactor, and reacted at 160℃ for 8 h to allow NH4V4O 10 In-situ growth of carbon fiber surface to form a uniform load structure;

[0060] (4): Take out the sample, wash it repeatedly with deionized water and ethanol, and dry it at 70℃ for 2 hours to obtain carbon fiber cloth loaded with NH4V4O. 10 Composite cathode;

[0061] Re-preparation of composite anode:

[0062] (1) A carbon fiber cloth with a length × width × thickness of 20 mm × 20 mm × 0.3 mm was used as a conductive substrate. After being cleaned with anhydrous ethanol and deionized water in sequence, it was dried at a temperature of 60℃ for 2 h to remove surface impurities and improve the surface activity of the carbon fiber cloth.

[0063] (2) Add ZnSO4 to water with a concentration of 1.5 mol / L and stir at room temperature for 30 min to obtain a uniform and transparent electrodeposition electrolyte;

[0064] (3) A three-electrode electrodeposition system was constructed using carbon fiber cloth as the working electrode, zinc sheet as the counter electrode, and Hg / HgSO4 electrode as the reference electrode. Constant current deposition was carried out for 20 min under a current density of 3 mA / cm² to deposit metallic zinc on the surface of carbon fiber, forming a zinc negative electrode layer.

[0065] (4) After electrodeposition, the sample is taken out and cleaned with deionized water and ethanol to remove residual electrolyte on the surface. Then it is dried at 40°C for 1 h to obtain a composite negative electrode; it is a zinc-loaded carbon fiber.

[0066] 5. An electrode structure consisting of a composite positive electrode and a composite negative electrode is formed. A modified composite precursor system is then introduced into the electrode structure through impregnation. 0.5 mL of the modified composite precursor system is added between each positive and negative electrode and kept wetting for 20 min. The modified composite precursor system wets the electrode interface area and the internal pores of the supporting skeleton, achieving a synergistic distribution of the electrolyte phase and the structural skeleton. The impregnated system is allowed to stand at room temperature for 30 min to enhance interface wetting and system uniformity. Then, it is heated in an environment at 60℃ for 20 min to gradually increase the viscosity of the system and form a preliminary structural fixation. Finally, it is heated at 100℃ for 100 min to crosslink the polymer matrix and form a continuous structure, thereby obtaining a zinc-based structural energy storage composite material based on a propylene carbonate electrolyte system.

[0067] A schematic diagram of the overall configuration of the zinc-based structural energy storage composite material based on the propylene carbonate electrolyte system prepared in Example 2 is shown below. Figure 1 As shown, from Figure 1 It can be seen that the zinc-based structural energy storage composite material can support a weight of 1150 g without exhibiting significant cracking or delamination during the load-bearing process, indicating that the material has good structural stability and load-bearing capacity. This result demonstrates that the composite material obtained in this embodiment can not only be used as an energy storage unit but also provide structural support under certain load conditions.

[0068] The zinc-based structural energy storage composite material based on the propylene carbonate electrolyte system prepared in Example 2 was cut into strips with dimensions of 30 mm × 10 mm. Tensile properties were tested using a universal testing machine. During the test, both ends of the sample were clamped, and uniaxial tension was applied at a loading rate of 1 mm / min. The stress-strain curves of the samples during the tensile process were recorded, and their tensile properties were analyzed. A schematic diagram of the obtained tensile property test results is shown below. Figure 2 As shown, from Figure 2 It can be seen that the stress of the zinc-based structural energy storage composite material gradually increases with strain during tensile loading, and reaches a maximum tensile strength of about 40 MPa under high strain conditions, indicating that it has good tensile bearing capacity and certain deformation adaptability.

[0069] The zinc-based structural energy storage composite material based on the propylene carbonate electrolyte system prepared in Example 2 was cut into test samples with dimensions of 20 mm × 20 mm. Conductive connection ends of 5 mm length were reserved on both sides of the composite positive and negative electrodes, and connected to external test leads using conductive silver paste, copper foil, or nickel strip to form a complete structural battery test unit. The structural battery test unit was placed at room temperature for 4 h to ensure the stability of the electrolyte distribution within the system; then it was connected to an electrochemical workstation with a test voltage range of 0.2–1.6 V. Constant current charge-discharge tests were performed under different rate conditions, with test current densities set to 10, 20, 50, 100, and 200 mA g, respectively. -1 The charge-discharge curves and corresponding specific capacities were recorded, and the changes in charge-discharge plateaus and specific capacity retention under different current densities were compared to evaluate the rate performance and ion transport capability of the zinc-based energy storage composite material. Example 2 shows the charge-discharge curves of the zinc-based energy storage composite material under different rate conditions. Figure 3 As shown, Figure 3 This indicates that at 10, 20, 50, 100, and 200 mA g... -1 Under different rate conditions, the structural energy storage composite material exhibits stable charge-discharge curves. It shows a high specific capacity at low rates and maintains a certain capacity output at high rates, indicating that the material has good rate adaptability.

[0070] Comparative Example 1: Photos of the composite precursor system prepared in step two of Example 2 (without modified silica) and the modified composite precursor system prepared in step three of Example 2 are shown below. Figure 4 As shown in the figure. The composite precursor system prepared in step two of Example 2 and the modified composite precursor system prepared in step three of Example 2 were used as electrolyte systems to construct open-type zinc-zinc symmetric batteries. Specifically, two zinc sheets of the same size (10 mm × 10 mm, 0.2 mm thick) were selected as positive and negative electrodes. A glass fiber membrane (12 mm × 12 mm) was placed between the two zinc sheets. 80 μL of the electrolyte precursor system was added to the membrane to fully wet it before battery assembly. The battery adopted an open structure to simulate the potential volatilization of organic components in the system under actual environmental conditions. The assembled zinc-zinc symmetric battery was subjected to constant current charge-discharge cycle testing under the same environmental conditions. The test current density was 0.5 mA / cm², and the single deposition / stripping time was 0.5 h. The voltage changes and charge-discharge curves during the cycle were recorded. A comparison of the cycle curves of the zinc-zinc symmetric battery is shown in the figure. Figure 5As shown, the electrolyte system with modified silica exhibits a more stable charge-discharge curve and smaller voltage fluctuations during open-circuit cycling. In contrast, the system without modified silica shows significantly increased voltage fluctuations and poorer stability. These results indicate that the introduction of modified silica helps improve system stability and, to some extent, reduces the adverse effects of changes in organic components on performance.

[0071] Comparative Example 2: This comparative example describes the preparation of an ionic liquid electrolyte system. The specific preparation method is as follows: 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (EMIM-TFSI) was used as the electrolyte solvent. Zn(TFSI)2 was weighed out according to a zinc salt concentration of 1.0 mol / L and added to EMIM-TFSI. The mixture was stirred for 30 min to form an ionic liquid zinc salt electrolyte system. A curable polymer, consisting of an acrylate resin and a curing system, was added to the electrolyte system at a mass fraction of 20%. The curable polymer was mixed uniformly under stirring to form a stable composite precursor system.

[0072] The ionic liquid electrolyte system prepared in Comparative Example 2, the composite precursor system prepared in step two of Example 2 (without modified silica), and the modified composite precursor system prepared in step three of Example 2 (with modified silica) were used as electrolytes to assemble test cells for comparison. The test cells were assembled using a coin cell structure. Two stainless steel sheets with a diameter of 16.2 mm were selected as blocking electrodes. A glass fiber membrane with a thickness of 0.2 mm was placed between the two stainless steel sheets, and 80 μL of electrolyte was added. After fully wetting the membrane, it was sealed to form a stainless steel / electrolyte / stainless steel structure test cell. The cell was connected to an electrochemical workstation at a frequency range of 10... -2 ~10 5 AC impedance testing was performed under Hz conditions, with the disturbance voltage amplitude preferably between 5 and 10 mV. The electrochemical impedance spectra of each electrolyte system were recorded as follows: Figure 6 As shown in the figure, the resistance values ​​of each electrolyte system were determined using the AC impedance method, and their ionic conductivity was calculated using the formula σ=L / (R×S), where L is the electrode spacing, S is the electrode area, and R is the measured resistance. A comparison of the ionic conductivity of different electrolyte systems is shown in the figure. Figure 7 As shown, from Figure 6 and Figure 7 It can be seen that ① the propylene carbonate electrolyte system with modified silica exhibits a smaller impedance semicircle diameter and lower interfacial charge transport impedance, while its ionic conductivity is approximately 1.02 mS·cm. -1 ② The propylene carbonate electrolyte system without modified silica has a relatively high impedance, with an ionic conductivity of approximately 0.81 mS·cm. -1③ The ionic liquid electrolyte system has the highest impedance, and its ionic conductivity is approximately 0.16 mS·cm. -1 The above results indicate that replacing ionic liquids with propylene carbonate can improve the ion transport capacity of the system, while the introduction of modified silica helps to further reduce interfacial impedance and increase ionic conductivity, thereby improving the electrochemical performance of the electrolyte system.

[0073] Comparative Example 3: Assembling a zinc-based energy storage battery using an ionic liquid electrolyte system, the specific method is as follows:

[0074] 1. Prepare the ionic liquid electrolyte system. This step is the same as the preparation method in Comparative Example 2.

[0075] II. Preparation of composite positive and composite negative electrodes, this step is the same as step four of Example 2;

[0076] 3. An electrode structure consisting of a composite positive electrode and a composite negative electrode is formed. An ionic liquid electrolyte system is then introduced into the electrode structure through impregnation. 0.5 mL of the modified composite precursor system is added between each positive and negative electrode and kept wet for 20 min. The impregnated system is allowed to stand at room temperature for 30 min, and then heated in an environment at 60℃ for 20 min to gradually increase the viscosity of the system and form a preliminary fixed structure. Finally, it is heated at 100℃ for 100 min to crosslink the polymer and form a continuous structure, thereby obtaining a zinc-based energy storage composite material based on an ionic liquid electrolyte system.

[0077] The zinc-based structural energy storage composite material based on the ionic liquid electrolyte system prepared in Comparative Example 3 was cut into test samples with dimensions of 20 mm × 20 mm. Conductive connection ends of 5 mm length were reserved on both sides of the composite positive and negative electrodes, and connected to external test wires using conductive silver paste, copper foil, or nickel strip to form a complete structural battery test unit. The structural battery test unit was placed at room temperature for 4 h to ensure the stability of the electrolyte distribution within the system. The structural battery test unit prepared in Example 2 and the structural battery test unit prepared in Comparative Example 3 were simultaneously subjected to a current density of 10–100 mA g. -1 Under constant current density conditions, charge-discharge cycle tests were conducted, and the specific capacity change and coulombic efficiency were recorded during the cycle. The resulting cycle performance comparison graph is shown below. Figure 8 As shown, from Figure 8 It can be seen that the propylene carbonate electrolyte system with modified silica exhibits a high specific capacity and a relatively stable cycling curve during the cycling process, with a specific capacity reaching 312.8 mAh g. -1The system can cycle stably for 400 hours. In contrast, the ionic liquid electrolyte system has lower capacity and relatively poorer cycle stability. These results indicate that the propylene carbonate electrolyte system has superior electrochemical performance compared to the ionic liquid electrolyte system, and the introduction of modified silica helps to further improve the system's cycle stability and capacity retention.

[0078] This invention utilizes modified silica to reduce its free exposure in the interface region, suppressing the changes in electrolyte composition and performance degradation caused by the volatilization of propylene carbonate-based electrolyte. At the same time, modified silica can be stably enriched or anchored in the interface region, and improve interface consistency and overall material stability through interface regulation, thereby achieving a balance between high electrochemical performance and long service life of the material.

Claims

1. A method for preparing surface-modified silica, characterized in that, This method is performed in the following steps:

1. Disperse silica in a mixed solvent, add dilute nitric acid solution to adjust the pH of the system to 3.5~4.0 to carry out the surface hydroxyl activation reaction, centrifuge, wash and dry to obtain silica with surface hydroxyl activation; 2. Surface-activated silica with hydroxyl groups is dispersed in ethanol, and the pH is adjusted to 8-9 with dilute ammonia. Then, γ-aminopropyltriethoxysilane is added to carry out an amination modification reaction to obtain an amination intermediate. The amination intermediate is dispersed in ethanol, and the pH is adjusted to 4.5-5.0 with dilute acetic acid. Then, γ-glycidoxypropyltrimethoxysilane is added to carry out a bifunctional modification reaction to obtain epoxy-modified silica.

3. The epoxy-modified silica and solvent are added to the reaction vessel for solvothermal treatment to improve crosslinking stability. After washing and drying, surface-modified silica is obtained.

2. The method for preparing surface-modified silica according to claim 1, characterized in that, The silica mentioned in step one is one or more of nano silica, mesoporous silica, or fumed silica; the particle size of the silica is 10 to 100 nm.

3. The method for preparing surface-modified silica according to claim 1 or 2, characterized in that, The mixed solvent mentioned in step one is anhydrous ethanol and deionized water mixed in a volume ratio of 5:

1.

4. The method for preparing surface-modified silica according to claim 1 or 2, characterized in that, The surface hydroxyl activation reaction described in step one was carried out under reflux at 60°C for 3 h; the amination modification reaction described in step two was carried out under reflux at 70°C for 4 h; and the bifunctional modification reaction described in step two was carried out under reflux at 65°C for 5 h.

5. The method for preparing surface-modified silica according to claim 1 or 2, characterized in that, In step two, the mass ratio of hydroxyl-activated silica to the volume ratio of γ-aminopropyltriethoxysilane is 1 g: (0.15~0.2) mL; the volume ratio of the aminated intermediate to γ-glycidoxypropyltrimethoxysilane is 1 g: (0.25~0.35) mL.

6. The application of the surface-modified silica prepared by the method of claim 1, characterized in that, This application involves using surface-modified silica in zinc-based structural energy storage composites based on a propylene carbonate electrolyte system.

7. The application of surface-modified silica according to claim 6, characterized in that, A zinc-based structural energy storage composite material based on a propylene carbonate electrolyte system includes a composite positive electrode, a composite negative electrode, and a structural electrolyte layer located between the composite positive electrode and the composite negative electrode. The composite positive electrode includes a supporting substrate and a positive electrode active material layer loaded on its surface. The composite negative electrode includes a conductive substrate and a metallic zinc negative electrode layer loaded on its surface. The structural electrolyte layer is a multiphase composite structure composed of a propylene carbonate electrolyte system, a zinc salt, a polymer matrix, and surface-modified silica.

8. The application of the surface-modified silica according to claim 6, characterized in that, The preparation method of zinc-based structural energy storage composite material based on propylene carbonate electrolyte system is carried out according to the following steps: I. Using propylene carbonate as the main electrolyte, zinc salt is added to form an electrolyte system with ion conductivity; wherein the concentration of zinc salt is 0.5-2.0 mol / L, which gives the system high ionic conductivity and good fluidity; 2. A curable polymer is used as a structural support phase and mixed with the propylene carbonate electrolyte system to form a stable composite precursor system; wherein the mass fraction of the curable polymer in the composite precursor system is 10% to 30%.

3. Surface-modified silica is added to the composite precursor system to obtain the modified composite precursor system; IV. Using a conductive substrate as a support framework, a positive electrode active material layer is constructed on the surface of the conductive substrate to obtain a composite positive electrode; a metallic zinc negative electrode layer is constructed on the surface of the conductive substrate to obtain a composite negative electrode.

5. The modified composite precursor system is introduced into the electrode structure composed of composite positive and composite negative electrodes, so that the modified composite precursor system wets the electrode interface area and the internal pores of the supporting skeleton, realizing the synergistic distribution of the electrolyte phase and the structural skeleton; the wetted electrode structure system is subjected to static, pre-curing and thermal curing treatments to allow the polymer to gradually cross-link and cure, and form a stable and continuous structure inside the system, thereby obtaining a zinc-based structural energy storage composite material based on the propylene carbonate electrolyte system.

9. The application of surface-modified silica according to claim 8, characterized in that, The zinc salt mentioned in step one is one or more of Zn(TFSI)2, Zn(FSI)2 or Zn(OTf)2, and the concentration of the zinc salt in the electrolyte system is 0.8 to 1.5 mol / L.

10. The application of surface-modified silica according to claim 8 or 9, characterized in that, The curable polymer described in step two consists of a polymer and its curing agent; wherein the polymer is one or more of epoxy resin, acrylate resin, polyurethane or polyether.

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