A pom-based solid-state polymer electrolyte and a method for preparing the same

Abstract

The application relates to the technical field of solid electrolyte materials, in particular to a POM-based solid-state polymer electrolyte and a preparation method thereof, which comprises the following steps: dispersing bacterial cellulose raw materials in an aqueous solution to form a precursor solution, vacuum-filtering and drying to obtain a bacterial cellulose film; adding a Lewis acid initiator into an organic solvent, stirring and mixing to form coating slurry; immersing the bacterial cellulose film into the coating slurry, air-drying at room temperature and heat-drying to obtain an initiator-modified bacterial cellulose film; adding a lithium salt and a cyclic ether monomer into an ether solvent to obtain POM-based solid electrolyte slurry, coating the POM-based solid electrolyte slurry on the initiator-modified bacterial cellulose film, and drying to obtain the POM-based solid-state polymer electrolyte. The POM and the Lewis acid initiator-modified bacterial cellulose support layer are used to improve ionic conductivity, and an ultrathin, high-mechanical-strength and high-ionic-conductivity POM-based solid electrolyte is prepared.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte materials technology, and in particular to a POM-based solid polymer electrolyte and its preparation method. Background Technology

[0002] With the global energy structure transitioning towards cleaner and lower-carbon energy, new energy storage technology has become a key component supporting the large-scale application of renewable energy. Lithium metal batteries, thanks to the extremely high theoretical capacity of lithium metal anodes (3860 mAh g / g),... -1 With its extremely low reduction potential (-3.04V vs. SHE), it has become the core development direction for breaking through the energy density bottleneck of traditional lithium-ion batteries, showing broad application prospects in the field of new energy storage.

[0003] However, the liquid electrolyte system used in traditional lithium metal batteries has many serious safety hazards, which greatly limits its industrialization. On the one hand, liquid electrolytes are prone to leakage, leading to internal corrosion problems in the battery; on the other hand, under high-temperature environments, liquid electrolytes may burn or even explode, posing a significant safety risk. Furthermore, lithium metal anodes are prone to dendrite growth during battery cycling. These lithium dendrites can not only puncture the battery separator, causing a short circuit, but also exacerbate side reactions between the electrode and the electrolyte, significantly shortening the battery's lifespan.

[0004] Solid-state electrolytes, as the core component of all-solid-state lithium metal batteries, can fundamentally solve the safety issues associated with liquid electrolytes. Furthermore, by optimizing the interfacial contact between the electrode and the electrolyte, solid-state electrolytes can effectively improve the cycle stability and energy density of the battery, thus becoming a key research focus in the field of lithium metal batteries. Among various solid-state electrolytes, polymer solid-state electrolytes have become a current research hotspot due to their outstanding advantages such as good flexibility, excellent electrode interface compatibility, low cost, and ease of large-scale processing. Specifically, polyoxymethylene (POM)-based solid-state electrolytes, through in-situ polymerization of monomers, can effectively eliminate interfacial voids between the electrolyte and the electrode, reducing interfacial impedance; and the regular ether-oxygen structure of the POM molecular chain theoretically facilitates lithium-ion conduction, demonstrating good application potential.

[0005] Despite the significant advantages of POM-based solid electrolytes, their development still faces several technical bottlenecks that restrict their practical application: First, insufficient mechanical strength: Pure POM electrolytes have extremely poor mechanical strength, exhibiting brittleness or insufficient flexibility at room temperature, making them unable to withstand the volume changes generated during lithium metal deposition / stripping, easily leading to cracking and ultimately battery failure; Second, low room temperature ionic conductivity: typically below 10. -5 Scm -1The main reasons for the limitations of POM are: firstly, it cannot meet the high-rate charging and discharging requirements of batteries at room temperature; secondly, the high crystallinity of POM molecular chains obstructs the diffusion path of lithium ions between molecular chain segments; thirdly, the lithium ion transference number is limited, typically less than 0.3, and the migration of a large number of anions can lead to concentration polarization at the electrode interface, thereby exacerbating lithium dendrite growth and affecting battery performance and lifespan; and fourthly, the preparation process has defects: in the existing preparation process, the polymerization of POM often relies on high temperature or strong light stimulation, which not only consumes a lot of energy but may also trigger side reactions of monomers, affecting the purity and electrochemical stability of the electrolyte.

[0006] To address the aforementioned issues, existing technologies often employ the addition of inorganic fillers (such as Al2O3 and TiO2 nanoparticles) or blending with other polymers (such as PEO and PVDF) to enhance the mechanical strength of POM-based solid electrolytes. However, the practical application results are not ideal. When adding inorganic fillers, the fillers are prone to agglomeration, leading to defects within the electrolyte and consequently reducing ion conduction efficiency. Polymer blends, on the other hand, may experience phase separation within the electrolyte due to compatibility issues between different polymers, disrupting the continuous lithium-ion conduction pathway. Furthermore, while increasing the lithium salt concentration can improve ionic conductivity to some extent, excessively high salt concentrations can reduce electrolyte flexibility and may exacerbate the corrosion of the lithium metal anode.

[0007] Therefore, developing a POM-based solid electrolyte that combines ultra-thin structure, high mechanical strength, high room temperature ionic conductivity, high lithium-ion transference number, and simple and controllable preparation process has become a key technological breakthrough for promoting the industrialization of all-solid-state lithium metal batteries and is of great significance to the progress of the new energy storage field. Summary of the Invention

[0008] The purpose of this invention is to provide a POM-based solid polymer electrolyte and its preparation method. By utilizing POM and a bacterial cellulose support layer modified with Lewis acid initiators to improve ionic conductivity, an ultrathin POM-based solid electrolyte with high mechanical strength and high ionic conductivity is prepared.

[0009] To achieve the above objectives, the present invention provides a method for preparing a POM-based solid polymer electrolyte, comprising the following steps: S1. The bacterial cellulose raw material is uniformly dispersed in an aqueous solution to form a precursor solution; S2. The precursor solution of S1 is vacuum filtered and then dried to obtain a bacterial cellulose membrane. S3. Add Lewis acid initiators to organic solvents, stir and mix to form a uniform coating slurry; S4. Immerse the bacterial cellulose membrane of S2 in the coating slurry of S3, and after air drying and heat drying at room temperature, obtain the initiator-modified bacterial cellulose membrane. S5. Lithium salt and cyclic ether monomers are added to an ether solvent to undergo cationic ring-opening polymerization, resulting in POM-based solid electrolyte slurry. S6. Coat the POM-based solid electrolyte slurry obtained in S5 onto the bacterial cellulose membrane modified by the initiator in S4, and dry it to obtain the POM-based solid polymer electrolyte.

[0010] Preferably, in S1, the bacterial cellulose raw material is dispersed in an aqueous solution using an ultrasonic blender; the power of the ultrasonic blender is 800W; and the dispersion time is 30-60 minutes.

[0011] Preferably, in S2, the drying temperature is 90-110℃ and the drying time is 10-14h.

[0012] Preferably, in S3, the Lewis acid initiator is Al(CF3SO3)3, and the organic solvent is N,N-dimethylformamide.

[0013] Preferably, in S3, the mass-to-volume ratio of Lewis acid initiator to organic solvent is 40-60 mg: 15-25 mL.

[0014] Preferably, in S3, the stirring time is 10-14 hours, and the stirring method is vigorous stirring.

[0015] Preferably, in S4, the bacterial cellulose membrane is immersed in the coating slurry for 4-6 minutes, air-dried at room temperature for 2-4 hours, and the heat-drying temperature is 70-90℃ for 46-50 hours.

[0016] Preferably, in S5, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide, the cyclic ether monomer is trioxane, and the ether solvent is diethylene glycol dimethyl ether, wherein the concentration of the lithium salt in the ether solvent is 1.0 M, and the mass ratio of trioxane to the ether solvent is 1:2.3.

[0017] Preferably, in S6, the drying is performed by vacuum drying at 50-70°C for 10-14 hours, and the thickness of the POM-based solid electrolyte membrane is 20-25 μm.

[0018] The present invention also provides a POM-based solid polymer electrolyte, which is prepared by the above-described method for preparing a POM-based solid polymer electrolyte.

[0019] Mechanism of the present invention This invention uses bacterial cellulose (BC) as a supporting framework, whose natural three-dimensional interwoven fiber network provides a stable mechanical support for the electrolyte; simultaneously, the surface of bacterial cellulose is rich in hydroxyl groups, which react with metal cations (such as Al) in Lewis acid initiators. 3+This forms a coordination effect, significantly improving the bonding stability between the initiator and the support layer, thereby enhancing the interfacial compatibility between the POM matrix formed by subsequent polymerization and the BC support layer, avoiding interlayer delamination, and laying the structural foundation for the high mechanical strength of the electrolyte.

[0020] Lewis acid initiators (such as Al(CF3SO3)3) are selected, which can efficiently trigger the cationic ring-opening polymerization of cyclic ether monomers (such as trioxane) through Lewis acid catalysis. This simplifies the preparation process, reduces energy consumption, and reduces the occurrence of monomer side reactions, ensuring the purity and electrochemical stability of the POM matrix. During the polymerization process, POM molecular chains grow uniformly on the surface and inside the BC support layer, forming a dense and continuous electrolyte matrix, eliminating the interfacial voids between the electrode and the electrolyte.

[0021] Metal cations in Lewis acid initiators (such as Al) 3+ On the one hand, it reacts with the anions of lithium salts (such as lithium bis(trifluoromethanesulfonyl)imide) in the electrolyte (such as TFSI). - This forms a strong coordination interaction, effectively fixing anions, reducing concentration polarization caused by anion migration, and promoting Li + The lithium cations dissociate and migrate freely from the lithium salt; on the other hand, the metal cations interact weakly with the ether oxygen atoms in the POM molecular chain, weakening the Li... + The binding force with the POM molecular chain reduces the diffusion resistance of lithium ions between molecular chain segments. At the same time, the regular ether-oxygen structure of the POM molecular chain provides a continuous channel for lithium ion conduction, synergistically improving the ionic conductivity and lithium ion transference number of the electrolyte.

[0022] Therefore, the present invention employs the above-mentioned POM-based solid polymer electrolyte and its preparation method, which has the following beneficial effects: (1) The POM-based solid polymer electrolyte membrane prepared by this invention, utilizing the supporting effect of the three-dimensional bacterial cellulose fiber network and the interfacial strengthening effect of the initiator, exhibits excellent mechanical properties. Its thickness is only 20-25 μm, belonging to an ultrathin structure, which can significantly reduce the battery volume ratio; simultaneously, the tensile strength is ≥23 MPa, and the fracture energy is ≥0.9 MJ·m. -3 It can effectively withstand volume changes during lithium metal deposition and stripping, avoid electrolyte rupture, and ensure the structural integrity of the battery during cycling.

[0023] (2) Through the synergistic effect of the optimized ion conduction mechanism, the electrochemical performance of the electrolyte in this invention is significantly superior to that of traditional POM-based electrolytes. At 30°C, the ionic conductivity reaches 1.8 × 10⁻⁶. -4 S·cm -1 It is far higher than that of traditional POM-based electrolytes (typically below 10). -5 S·cm -1It meets the high-rate charge and discharge requirements of batteries at room temperature; the lithium-ion transference number is increased to 0.78, which is significantly higher than the conventional value (usually <0.3), effectively suppressing concentration polarization at the electrode interface and lithium dendrite growth, and improving the cycle stability of the battery.

[0024] (3) The present invention adopts a room temperature cationic ring-opening polymerization process; no harmful by-products are generated during the polymerization process, and the selected bacterial cellulose is a natural renewable material, and the organic solvent can be recycled, which is in line with the green and environmentally friendly industrial development trend; at the same time, the process steps are simple and controllable, which is convenient for large-scale production.

[0025] (4) The all-solid-state lithium metal battery assembled based on this electrolyte exhibits excellent rate performance and long cycle life due to the good interfacial compatibility between the electrolyte and the electrode, high ion conduction efficiency, and stable mechanical structure. It can be stably charged and discharged at a rate of 0.1-5C, and the capacity retention rate is still at a high level after 1000 cycles. Moreover, there are no safety hazards such as electrolyte leakage or combustion. This provides key technical support for the industrial application of all-solid-state lithium metal batteries and helps to achieve the unity of high energy density and high safety in batteries.

[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0027] Figure 1 This is a SEM cross-sectional view of the POM-based solid polymer electrolyte of Example 1 of the present invention; Figure 2 This is a top SEM view of the POM-based solid polymer electrolyte of Example 1 of the present invention; Figure 3 The stress-strain curves of the bacterial cellulose membrane prepared in S1 of Example 1 of the present invention, the bacterial cellulose membrane modified with an initiator in S4, the POM-based solid polymer electrolyte prepared in S6, and the POM-based solid polymer electrolyte prepared in Comparative Example 2 are compared. Figure 4 This is a comparison chart of the ionic conductivity of the POM-based solid polymer electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. Figure 5 A comparison chart of the critical current densities of the POM-based solid polymer electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention; Figure 6 This is a graph showing the lithium-ion transference number variation of the POM-based solid polymer electrolytes prepared in Example 1 and Comparative Example 1 of the present invention. Figure 7 This is a comparison of the long-cycle curves of batteries composed of POM-based solid polymer electrolyte lithium prepared in Example 1 and Comparative Examples 1-2 of the present invention. Figure 8 This is a comparison chart of the rate curves of the POM-based solid polymer electrolytes prepared in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0029] A method for preparing a POM-based solid polymer electrolyte includes the following steps: S1. The bacterial cellulose raw material is uniformly dispersed in an aqueous solution to form a precursor solution; S2. The precursor solution of S1 is vacuum filtered and then dried to obtain a bacterial cellulose membrane. S3. Add Lewis acid initiators to organic solvents, stir and mix to form a uniform coating slurry; S4. Immerse the bacterial cellulose membrane of S2 in the coating slurry of S3, and after air drying and heat drying at room temperature, obtain the initiator-modified bacterial cellulose membrane. S5. Lithium salt and cyclic ether monomers are added to an ether solvent to undergo cationic ring-opening polymerization, resulting in POM-based solid electrolyte slurry. S6. Coat the POM-based solid electrolyte slurry obtained in S5 onto the bacterial cellulose membrane modified by the initiator in S4, and dry it to obtain the POM-based solid polymer electrolyte.

[0030] Preferably, in S1, the bacterial cellulose raw material is dispersed in an aqueous solution using an ultrasonic blender; the power of the ultrasonic blender is 800W; and the dispersion time is 30-60 minutes.

[0031] In this invention, bacterial cellulose (BC) in S1 is a natural polymer material with a unique three-dimensional interwoven nanofiber network structure. Its surface is rich in hydroxyl groups, exhibiting excellent hydrophilicity and dispersibility. The bacterial cellulose raw material is dispersed in an aqueous solution using an ultrasonic cell disruptor, which breaks down the aggregated structure of the raw material, causing the fiber bundles to untangle and disperse, forming a uniform and stable aqueous precursor solution. Precise control of the ultrasonic power and dispersion time (30-60 min) ensures sufficient fiber dispersion while avoiding excessive ultrasonication that could damage the fiber structure, thus ensuring the mechanical properties of the subsequent support membrane.

[0032] The present invention provides a uniform precursor solution prepared by ultrasonic dispersion, which lays the foundation for the subsequent formation of a bacterial cellulose membrane with a dense structure and excellent mechanical properties. The aqueous solution is used as a dispersion medium, which is green, environmentally friendly, and inexpensive, and can retain the natural structural advantages of bacterial cellulose to the greatest extent and avoid damage to the fiber structure by organic solvents.

[0033] Preferably, in S2, the drying temperature is 90-110℃ and the drying time is 10-14h.

[0034] In step S2 of this invention, vacuum filtration utilizes negative pressure to rapidly remove moisture from the precursor solution, causing the dispersed bacterial cellulose nanofibers to accumulate in an orderly manner, forming a continuous fiber network structure. Subsequent drying at 90-110℃ for 10-14 hours further removes residual moisture from the membrane, enhances hydrogen bonding between fibers, and improves the membrane's density and mechanical strength. The optimized range of drying temperature and time ensures sufficient moisture removal while avoiding thermal degradation of the fibers due to prolonged high-temperature processing.

[0035] The bacterial cellulose membrane prepared by this invention has a three-dimensional interwoven fiber network structure, providing a stable mechanical support framework for the electrolyte; the membrane has high density and controllable porosity, which can effectively carry subsequent electrolyte slurry, avoid electrolyte leakage, and provide a continuous channel for lithium-ion conduction.

[0036] Preferably, in S3, the Lewis acid initiator is Al(CF3SO3)3, and the organic solvent is N,N-dimethylformamide.

[0037] Preferably, in S3, the mass-to-volume ratio of Lewis acid initiator to organic solvent is 40-60 mg: 15-25 mL.

[0038] Preferably, in S3, the stirring time is 10-14 hours, and the stirring method is vigorous stirring.

[0039] In this invention, the Lewis acid initiator (such as Al(CF3SO3)3) in S3 serves as a key catalyst for subsequent cationic ring-opening polymerization and must be uniformly dispersed in an organic solvent to exert its efficient catalytic effect. Mixing 40-60 mg of the Lewis acid initiator with 15-25 mL of organic solvent at a specific mass-to-volume ratio, followed by vigorous stirring for 10-14 hours, ensures complete dissolution and uniform dispersion of the initiator, forming a stable coating slurry. Vigorous stirring breaks down the intermolecular aggregation forces of the initiator, ensuring uniform dispersion in the organic solvent and preventing excessively high or low local concentrations from affecting subsequent modification effects and polymerization efficiency.

[0040] The uniform coating slurry of this invention can ensure uniform loading of the initiator on the surface and inside of the bacterial cellulose membrane, providing uniform catalytic active sites for the subsequent in-situ polymerization of monomers; the selected organic solvent (such as DMF) has good solubility for the initiator and good compatibility with the bacterial cellulose membrane, and will not damage the fiber network structure of the membrane.

[0041] Preferably, in S4, the bacterial cellulose membrane is immersed in the coating slurry for 4-6 minutes, air-dried at room temperature for 2-4 hours, and the heat-drying temperature is 70-90℃ for 46-50 hours.

[0042] In step S4 of this invention, the bacterial cellulose membrane is immersed in the coating slurry for 4-6 minutes. Utilizing capillary action and the adsorption of hydroxyl groups on the fiber surface, the initiator molecules adhere to the fiber surface and penetrate into the membrane's internal pores. Air drying at room temperature for 3-4 hours slowly removes some of the organic solvent, initially fixing the initiator molecules. Heat drying at 70-90℃ for 46-50 hours completely removes residual organic solvent and simultaneously promotes the formation of coordination bonds or hydrogen bonds between the initiator and the hydroxyl groups on the bacterial cellulose surface, achieving robust modification of the initiator. Precise control of the heat drying temperature and time ensures stable fixation of the initiator while preventing initiator deactivation due to high temperatures.

[0043] The bacterial cellulose membrane modified with the initiator of this invention has both mechanical support and catalytic functions. On the one hand, it retains the high mechanical strength advantage of the bacterial cellulose membrane, and on the other hand, through the uniform loading of the initiator, it provides sufficient and uniform active sites for subsequent cationic ring-opening polymerization, promoting the efficient progress of the polymerization reaction. The strong bond between the initiator and the fiber surface can prevent the initiator from being lost during the polymerization process and improve the stability of the electrolyte.

[0044] Preferably, in S5, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide, the cyclic ether monomer is trioxane, and the ether solvent is diethylene glycol dimethyl ether, wherein the concentration of the lithium salt in the ether solvent is 1.0 M. The mass ratio of trioxane to the ether solvent is 1:2.3.

[0045] In S5 of this invention, lithium salts (such as LiTFSI) are dissolved in ether solvents to form an ion-conducting system. Cyclic ether monomers (TXE) undergo cationic ring-opening polymerization under the catalysis of Lewis acid initiators to form polyoxymethylene (POM) molecular chains. The POM molecular chains have a regular ether oxygen structure, which can coordinate with lithium ions, providing a channel for lithium ion conduction. The optimized lithium salt concentration of 1.0 M ensures a sufficient source of lithium ions while avoiding ion aggregation caused by excessively high salt concentrations, thus ensuring ion conduction efficiency.

[0046] The cationic ring-opening polymerization reaction of this invention can be carried out efficiently, reducing monomer side reactions; the prepared POM-based solid electrolyte slurry has good fluidity and coatability, and can be tightly bonded to the modified bacterial cellulose membrane; the regular structure of the POM molecular chain is conducive to lithium-ion conduction, laying the foundation for the high ionic conductivity of the electrolyte.

[0047] Preferably, in S6, the drying is performed by vacuum drying at 50-70°C for 10-14 hours, and the thickness of the POM-based solid electrolyte membrane is 20-25 μm.

[0048] In step S6 of this invention, a POM-based solid electrolyte slurry is coated onto an initiator-modified bacterial cellulose membrane. The slurry can penetrate into the pores of the membrane through capillary action and tightly bond with the fiber network. Vacuum drying at 50-70°C for 10-14 hours slowly removes residual solvent from the slurry, promoting further cross-linking and solidification of the POM molecular chains to form a dense electrolyte membrane. The vacuum environment accelerates solvent evaporation, preventing the formation of bubbles or pore defects inside the membrane. Optimization of drying temperature and time ensures complete solvent removal while preventing thermal degradation of the POM molecular chains, ultimately forming an ultrathin electrolyte membrane with a thickness of 20-25 μm.

[0049] The POM-based solid polymer electrolyte membrane prepared by this invention has a thickness of only 20-25 μm, which significantly reduces the battery volume ratio and helps to realize high energy density batteries. The electrolyte membrane is tightly bonded to the bacterial cellulose support layer, with good interfacial compatibility and no interlayer delamination. The dense membrane structure can effectively inhibit lithium dendrite growth, avoid battery short circuits, and improve battery safety.

[0050] The present invention also provides a POM-based solid polymer electrolyte, which is prepared by the above-described method for preparing a POM-based solid polymer electrolyte.

[0051] Example 1 This invention provides a POM-based solid polymer electrolyte, the preparation method of which includes the following steps: S1. Add the bacterial cellulose raw material to the aqueous solution and disperse it for 30 minutes using an 800W ultrasonic blender to form a uniform precursor solution.

[0052] S2. The precursor solution of S1 is vacuum filtered and then dried at 100°C for 12 hours to obtain a bacterial cellulose membrane.

[0053] S3. Add 50 mg Al(CF3SO3)3 to 20 mL N,N-dimethylformamide and stir vigorously for 12 h to form a uniform coating slurry.

[0054] S4. Immerse the bacterial cellulose membrane from S2 in the coating slurry from S3 for 5 minutes, air dry at room temperature for 3 hours, and then heat dry at 80°C for 48 hours to obtain the initiator-modified bacterial cellulose membrane.

[0055] S5. Lithium bis(trifluoromethanesulfonyl)imide (concentration 1.0M) and trioxane (trioxane to diethylene glycol dimethyl ether mass ratio of 1:2.3) are added to diethylene glycol dimethyl ether to undergo cationic ring-opening polymerization to obtain POM-based solid electrolyte slurry.

[0056] S6. The POM-based solid electrolyte slurry obtained in S5 is uniformly coated onto the bacterial cellulose membrane modified by the initiator in S4, and vacuum dried at 60°C for 12 h to obtain a POM-based solid polymer electrolyte with a thickness of 23 μm, denoted as ABC-POM.

[0057] Example 2 This invention provides a POM-based solid polymer electrolyte, the preparation method of which includes the following steps: S1. Add the bacterial cellulose raw material to the aqueous solution and disperse it for 45 minutes using an 800W ultrasonic wall-breaking machine to form a uniform precursor solution.

[0058] S2. The precursor solution of S1 is vacuum filtered and then dried at 95°C for 13 hours to obtain a bacterial cellulose membrane.

[0059] S3. Add 45 mg Al(CF3SO3)3 to 18 mL N,N-dimethylformamide and stir vigorously for 11 h to form a uniform coating slurry.

[0060] S4. Immerse the bacterial cellulose membrane from S2 in the coating slurry from S3 for 4 minutes, air dry at room temperature for 2.5 hours, and then heat dry at 75°C for 47 hours to obtain the initiator-modified bacterial cellulose membrane.

[0061] S5. Lithium bis(trifluoromethanesulfonyl)imide (concentration 1.0M) and trioxane (trioxane to diethylene glycol dimethyl ether mass ratio of 1:2.3) are added to diethylene glycol dimethyl ether to undergo cationic ring-opening polymerization to obtain POM-based solid electrolyte slurry.

[0062] S6. The POM-based solid electrolyte slurry obtained in S5 is uniformly coated onto the bacterial cellulose membrane modified by the initiator in S4, and vacuum dried at 55°C for 11 h to obtain a POM-based solid polymer electrolyte with a thickness of 21 μm.

[0063] Example 3 This invention provides a POM-based solid polymer electrolyte, the preparation method of which includes the following steps: S1. Add the bacterial cellulose raw material to the aqueous solution and disperse it for 60 minutes using an 800W ultrasonic wall-breaking machine to form a uniform precursor solution.

[0064] S2. The precursor solution of S1 is vacuum filtered and then dried at 110°C for 10 hours to obtain a bacterial cellulose membrane.

[0065] S3. Add 60 mg Al(CF3SO3)3 to 25 mL N,N-dimethylformamide and stir vigorously for 14 h to form a uniform coating slurry.

[0066] S4. Immerse the bacterial cellulose membrane from S2 in the coating slurry from S3 for 6 minutes, air dry at room temperature for 4 hours, and then heat dry at 90°C for 50 hours to obtain the initiator-modified bacterial cellulose membrane.

[0067] S5. Lithium bis(trifluoromethanesulfonyl)imide (concentration 1.0M) and trioxane (trioxane to diethylene glycol dimethyl ether mass ratio of 1:2.3) are added to diethylene glycol dimethyl ether to undergo cationic ring-opening polymerization to obtain POM-based solid electrolyte slurry.

[0068] S6. The POM-based solid electrolyte slurry obtained in S5 is uniformly coated onto the bacterial cellulose membrane modified by the initiator in S4, and vacuum dried at 70°C for 14 hours to obtain a POM-based solid polymer electrolyte with a thickness of 25 μm.

[0069] Comparative Example 1 A method for preparing a POM-based solid polymer electrolyte differs from Example 1 in that steps S3 and S4 are omitted; instead, the POM-based solid electrolyte slurry from step S5 is directly coated onto the unmodified bacterial cellulose membrane from step S2. The remaining steps are the same as in Example 1. A POM-based solid polymer electrolyte with a thickness of 24 μm, denoted as BC-POM, is finally obtained.

[0070] Comparative Example 2 A method for preparing a POM-based solid polymer electrolyte differs from Example 1 in that steps S1 to S4 are omitted, while step S5 is the same as in Example 1. The POM-based solid electrolyte slurry from step S5 is directly poured into a polytetrafluoroethylene mold, i.e., bacterial cellulose membrane is not used as a support layer. The mixture is then vacuum dried at 60°C for 12 hours to obtain a POM-based solid polymer electrolyte with a thickness of 23 μm, denoted as POM.

[0071] Performance testing The POM-based solid polymer electrolyte prepared in Example 1 was characterized using scanning electron microscopy (SEM). Figures 1 to 2As shown, the POM-based solid polymer electrolyte prepared in Example 1 has a thickness of approximately 23 μm, which is an ultrathin structure and can significantly reduce the battery volume ratio.

[0072] Stress-strain tests were conducted on the POM-based solid polymer electrolytes prepared in Example 1 and Comparative Example 2, the bacterial cellulose membrane (BC) prepared in S1 of Example 1, and the initiator-modified bacterial cellulose membrane (ABC) prepared in S4. Figure 3 As shown, the peak value and enclosed area of ​​the curve in Example 1 (ABC-POM) are significantly larger than those in Comparative Example 2 (POM). The tensile strength (23.31 MPa) and fracture energy (0.93 MJ·m) of Example 1 of this invention are also significantly higher. -3 The mechanical properties of the POM-based solid polymer electrolyte membrane, significantly improved compared to the comparative example, are due to the superior mechanical properties achieved by utilizing the supporting effect of the three-dimensional bacterial cellulose fiber network and the interfacial strengthening effect of the initiator. This membrane effectively withstands volume changes during lithium metal deposition and stripping, preventing electrolyte rupture and ensuring structural integrity during battery cycling.

[0073] The POM-based solid polymer electrolytes prepared in Example 1 and Comparative Examples 1-2 were subjected to ionic conductivity (EIS) testing. Figure 4 As shown, the ionic conductivity of ABC-POM (Example 1) is significantly higher than that of BC-POM (Comparative Example 1) and pure POM (Comparative Example 2) across the entire temperature range (25℃-80℃), especially at low temperatures (25℃). At 25℃, the ionic conductivity of ABC-POM (σ = 5 × 10⁻⁶) is significantly higher than that of BC-POM (Comparative Example 1). -4 S·cm -1 The magnitude of the difference is much higher than that of BC-POM (σ = 1.38 × 10⁻⁶). -4 S·cm -1 ) and pure POM (σ is 3.72×10 -5 S·cm -1 This demonstrates that the ABC-POM electrolyte of the present invention exhibits superior ion conductivity over a wide temperature range. This is because the metal cations in the Lewis acid initiator (such as Al) 3+ On the one hand, it reacts with the anions of lithium salts (such as lithium bis(trifluoromethanesulfonyl)imide) in the electrolyte (such as TFSI). - This forms a strong coordination interaction, effectively fixing anions, reducing concentration polarization caused by anion migration, and promoting Li + The electrolyte dissociates from lithium salts and migrates freely. This demonstrates that the electrochemical performance of the electrolyte is significantly superior to that of traditional POM-based electrolytes through the synergistic effect of the ion conduction optimization mechanism.

[0074] The POM-based solid polymer electrolytes prepared in Example 1 and Comparative Examples 1-2 were subjected to critical current density (CCD) testing. Figure 5 As shown, Example 1 exhibits a higher critical current density and lower overpotential compared to Comparative Examples 1 and 2. Example 1 demonstrates the best overall performance, which is attributed to the mechanical reinforcement effect of the bacterial cellulose (BC) framework: BC provides strong mechanical support, physically blocking the penetration of lithium dendrites and preventing their growth; simultaneously, Al... 3+ The ions coordinate with TFSI anions in the electrolyte and ether oxygen in POM, promoting the dissociation of lithium salt and increasing the free L... + The concentration of charge carriers, thereby accelerating the Li + The transport of [material / material] demonstrates that these synergistic effects enable the ABC-POM electrolyte to not only possess excellent mechanical strength but also enhance ionic conductivity and Li [material / material]. + The migration number is increased, thus maintaining stable lithium deposition / stripping at higher current densities, effectively suppressing dendrite formation, and thereby achieving higher CCD.

[0075] The POM-based solid polymer electrolytes prepared in Example 1 and Comparative Example 1 were subjected to lithium-ion transference number (it) tests. Figure 6 As shown, Example 1 exhibits a higher lithium-ion transference number (0.78). This is because the metal cation interacts weakly with the ether oxygen atoms in the POM molecular chain, weakening the Li-ion transference number. + The binding force with the POM molecular chain reduces the diffusion resistance of lithium ions between molecular chain segments. At the same time, the regular ether-oxygen structure of the POM molecular chain provides a continuous channel for lithium ion conduction, synergistically improving the ionic conductivity and lithium ion transference number of the electrolyte. This demonstrates that the electrochemical performance of the electrolyte is significantly better than that of traditional POM-based electrolytes through the synergistic effect of the ion conduction optimization mechanism.

[0076] The POM-based solid polymer electrolytes prepared in Example 1 and Comparative Examples 1-2 were assembled into symmetrical cells and full cells (NMC811 positive electrode and lithium metal negative electrode) for chemical performance testing, such as... Figures 7 to 8 As shown, Example 1 exhibits better cycling and rate performance due to the optimized ionic conductivity and mechanochemical stability of ABC-POM, which benefits from the in-situ polymerization of POM on the ABC framework. This demonstrates that this modular design establishes a competitive Al... 3+ Coordination environment to achieve efficient Li + Diffusion, while mechanically stabilizing the electrode-electrolyte interface.

[0077] Therefore, the present invention uses the above-mentioned POM-based solid polymer electrolyte and its preparation method. The prepared POM-based solid polymer electrolyte has excellent mechanical properties, ionic conductivity, ion transport number and critical current density. The assembled battery has better cycle performance and rate performance. This electrolyte membrane is beneficial to achieving high energy density of all-solid-state lithium batteries.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a POM-based solid polymer electrolyte, characterized in that: Includes the following steps: S1. The bacterial cellulose raw material is uniformly dispersed in an aqueous solution to form a precursor solution; S2. The precursor solution of S1 is vacuum filtered and then dried to obtain a bacterial cellulose membrane. S3. Add Lewis acid initiators to organic solvents, stir and mix to form a uniform coating slurry; S4. Immerse the bacterial cellulose membrane of S2 in the coating slurry of S3, and after air drying and heat drying at room temperature, obtain the initiator-modified bacterial cellulose membrane. S5. Lithium salt and cyclic ether monomers are added to an ether solvent to undergo cationic ring-opening polymerization, resulting in POM-based solid electrolyte slurry. S6. Coat the POM-based solid electrolyte slurry obtained in S5 onto the bacterial cellulose membrane modified by the initiator in S4, and dry it to obtain the POM-based solid polymer electrolyte.

2. The method for preparing a POM-based solid polymer electrolyte according to claim 1, characterized in that: In S1, bacterial cellulose raw materials are dispersed in an aqueous solution using an ultrasonic blender with a power of 800W and a dispersion time of 30-60 minutes.

3. The method for preparing a POM-based solid polymer electrolyte according to claim 1, characterized in that: In S2, the drying temperature is 90-110℃ and the drying time is 10-14h.

4. The method for preparing a POM-based solid polymer electrolyte according to claim 1, characterized in that: In S3, the Lewis acid initiator is Al(CF3SO3)3, and the organic solvent is N,N-dimethylformamide.

5. The method for preparing a POM-based solid polymer electrolyte according to claim 1, characterized in that: In S3, the mass-to-volume ratio of Lewis acid initiator to organic solvent is 40-60 mg: 15-25 mL.

6. The method for preparing a POM-based solid polymer electrolyte according to claim 1, characterized in that: In S3, the stirring time is 10-14 hours, and the stirring method is vigorous stirring.

7. The method for preparing a POM-based solid polymer electrolyte according to claim 1, characterized in that: In S4, the bacterial cellulose membrane is immersed in the coating slurry for 4-6 minutes, air-dried at room temperature for 2-4 hours, and then dried at 70-90℃ for 46-50 hours.

8. The method for preparing a POM-based solid polymer electrolyte according to claim 1, characterized in that: In S5, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide, the cyclic ether monomer is trioxane, and the ether solvent is diethylene glycol dimethyl ether. The concentration of the lithium salt in the ether solvent is 1.0 M, and the mass ratio of trioxane to the ether solvent is 1:2.

3.

9. The method for preparing a POM-based solid polymer electrolyte according to claim 1, characterized in that: In S6, drying is performed under vacuum at 50-70℃ for 10-14 hours, and the thickness of the POM-based solid electrolyte membrane is 20-25 μm.

10. A POM-based solid polymer electrolyte, characterized in that: It is prepared by the method for preparing a POM-based solid polymer electrolyte according to any one of claims 1-9.

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