A method for preparing a silicone polyurethane blended polyvinylidene fluoride polymer electrolyte

Abstract

The application discloses a preparation method of a siloxane polyurethane blended polyvinylidene fluoride polymer electrolyte, and belongs to the field of lithium-sulfur solid electrolyte materials. The method successfully prepares a composite solid-state polymer electrolyte of siloxane modified polyurethane (PU) and polyvinylidene fluoride (PVDF) through molecular structure design, aiming at solving the core problems of slow ion transmission, poor interface stability and low sulfur utilization rate in traditional solid-state lithium-sulfur batteries. The high-binding-energy groups (-NH-C=O, -CH2-CH2-O-) in the prepared polymer electrolyte form a dense multi-point coordination network with Li+, and the low-binding-energy -Si-O-Si- segment constructs a "low-resistance channel" for Li+ migration, realizing an elastic "jump" transmission mechanism independent of the large-scale movement of polymer segments, so that the electrolyte ion conductivity is as high as 6.01*10 ‑4 S*cm-1, and the lithium ion migration number is increased to 0.8. The application shows that the blending modification strategy of siloxane polyurethane and polyvinylidene fluoride can realize the synergistic optimization of electrolyte molecular structure, ion transmission mechanism and interface characteristics, and the prepared electrolyte has a good practical application prospect in the field of high-energy-density lithium-sulfur solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of polymer electrolyte technology for solid-state lithium-sulfur batteries, and specifically to a method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte. Background Technology

[0002] Solid-state polymer electrolyte (SPE)-based lithium-sulfur (Li-S) batteries have become a research hotspot in the energy storage field due to their high theoretical energy density and excellent safety performance. However, this system still faces key technical bottlenecks such as slow lithium-ion transport and insufficient sulfur utilization efficiency. Specifically, slow lithium-ion transport leads to blockage of the cathode-solid-state polymer electrolyte interface by electrochemically inactive lithium polysulfides (LiPS), which is the core failure mechanism causing performance degradation in SPE-based Li-sulfur batteries. These problems create a slow and irreversible electrochemical environment inside the battery, severely hindering the sulfur redox reaction process and ultimately limiting the practical industrial application of high-energy-density solid-state lithium-sulfur batteries (SSLSBs). To address these challenges, controlling the ion transport characteristics of polymer electrolytes through molecular structure design has become an effective solution. Utilizing different functional groups in polymers such as polyurethane (PU) and Li⁺ to construct elastic "jumping" ion transport channels, this design does not rely on large-scale movement of polymer chains and can significantly improve the ionic conductivity and lithium-ion transference number of the electrolyte. Simultaneously, a high-strength N–H···F hydrogen bond network is constructed by utilizing the hydrogen bonding between the -NH groups in the PU molecule and the -CF groups in polyvinylidene fluoride (PVDF). This hydrogen bond network not only effectively immobilizes the bis(trifluoromethanesulfonyl)imide (TFSI⁻) anion and suppresses interfacial side reactions between the electrolyte and the electrode, but more importantly, it reconstructs the interfacial potential distribution within the electrolyte, significantly reducing local interfacial polarization and Li⁺ migration barrier fluctuations. This, in turn, promotes the dissociation of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), increases the concentration of free Li⁺ in the system, and improves the continuity of ion transport channels, fundamentally optimizing the ion transport kinetics of the electrolyte. Summary of the Invention

[0003] The main objective of this invention is to provide a method for preparing a polyvinylidene fluoride polymer electrolyte with siloxane polyurethane blend, in order to overcome the problem of poor sulfur utilization caused by slow lithium-ion transport in existing solid-state lithium-sulfur batteries.

[0004] To address the aforementioned technical problems, the present invention provides the following technical solutions:

[0005] I. Preparation of Siloxane Polyurethane

[0006] Polytetrahydrofuran (PTMEG, Mn ≈ 2000 g·mol⁻¹) and hexamethylene diisocyanate (HDI) were dissolved in anhydrous dichloromethane (DCM) and stirred magnetically until a homogeneous and transparent solution was formed. A catalyst was then added to the system, and stirring continued for prepolymerization. When the reaction solution gradually became viscous, dihydroxy-terminated polydimethylsiloxane (PDMS-OH, Mn ≈ 1000 g·mol⁻¹) was added, and the reaction continued at the same temperature to obtain the target polymer solution. To ensure the processability of the system, anhydrous N,N-dimethylformamide (DMF) was used as a diluent to adjust the solution viscosity during the reaction, and DMF was added as needed. The resulting solution was cast onto a glass plate and dried in a vacuum oven. The resulting polymer film was named SiPu.

[0007] II. Preparation of Siloxane Polyurethane Blend PVDF Polymer Electrolyte Precursor

[0008] Weigh PVDF and dissolve it in anhydrous DMF, stirring magnetically until a homogeneous and transparent solution is formed; then add LiTFSI and continue stirring to ensure complete dissolution and uniform dispersion; on this basis, add SiPU to the solution and continue stirring for 10-14 hours to obtain a polymer precursor solution.

[0009] III. Preparation of Polymer Electrolytes

[0010] The resulting solution was poured into a PTFE mold using a casting method to obtain a polymer electrolyte membrane, which was then vacuum dried for 12-16 hours to prepare a polymer electrolyte membrane with a thickness of approximately 100-140 μm. This membrane was named SiPu / PVDF / LiTFSI polymer electrolyte (SPLE). Simultaneously, as a comparative experiment, a PVDF / LiTFSI electrolyte membrane (PLE) was prepared using the same method, with a ratio of 0.5 g PVDF to 0.4 g LiTFSI.

[0011] IV. Preparation of Solid-State Lithium-Sulfur Battery Electrodes

[0012] Elemental sulfur and porous carbon material were mixed in a ratio of 7:3 (wt:wt) and ground in a ball mill for 3 hours; then the resulting material was heated in an oven at 155 °C for 12 hours to obtain elemental sulfur-supported porous carbon material, named S / NPC.

[0013] V. Preparation of Solid-State Lithium-Sulfur Batteries

[0014] The polymer electrolyte prepared in step three is assembled with the positive electrode, lithium sheet, pad, and spring sheet prepared in step four in an argon-filled glove box to form a solid lithium-sulfur battery.

[0015] Furthermore, the molar ratio of polytetrahydrofuran (PTMEG, Mn ≈ 2000 g·mol⁻¹) to hexamethylene diisocyanate (HD) in step one is 1:1.5-1:2.0; if the mixing ratio is too low, the polymerization of polyurethane will be incomplete, and if the ratio is too high, the proportion of hard segments in polyurethane will be high, resulting in a decrease in the elasticity of the polymer electrolyte.

[0016] Furthermore, the stirring temperature under magnetic stirring described in step one is 30℃-50℃; if the temperature is too high or too low, it will lead to uneven polymerization.

[0017] Furthermore, the catalyst added to the above system in step one is one or more of dibutyltin diacetate (DBTA), tetrabutyltin (TBT), and dibutyltin dilaurate (DBTDL).

[0018] Furthermore, the prepolymerization time mentioned in step one is 20-40 min; if the prepolymerization time is too long, PTMEG and HDI will react excessively, the active end groups of the prepolymer will be consumed in large quantities, the subsequent chain extender will not be able to participate in the reaction effectively, and the chain extension modification will fail.

[0019] Furthermore, the amount of dihydroxy-terminated polydimethylsiloxane (PDMS-OH, Mn ≈ 1000 g·mol⁻¹) mentioned in step one is 0.00015-0.00018 mol; if PDMS-OH is in excess, it will lead to uncontrolled chain growth of the polymer and deterioration of the overall electrolyte performance.

[0020] Furthermore, the time interval for adding DMF during the reaction process described in step one is 0.5-1.5 hours; if the time interval for adding DMF is too long, the polymer will harden and fail.

[0021] Furthermore, the mass ratio of LiTFSI to PVDF added in step two is 0.7:1 to 0.9:1; if the mass ratio of LiTFSI to PVDF is too low, it will result in a lack of ion transport sites, which will directly lead to a significant decrease in the electrolyte ionic conductivity.

[0022] Furthermore, the SiPU addition ratio in step two is between 10% and 30% of the total PVDF mass. A low SiPU mass ratio will result in insufficient -NH groups in the system capable of participating in the construction of the N–H···F hydrogen bond network, leading to poor hydrogen bond network density and ineffective fixation of TFSI. - .

[0023] Furthermore, the vacuum drying temperature described in step three is 60-100 ℃; if the drying temperature is insufficient, the solvent and small molecule residues in the electrolyte membrane cannot be fully removed, leading to an increase in side reactions at the battery interface.

[0024] Based on the above technical solution, the following beneficial effects are achieved:

[0025] This invention proposes a method for preparing a siloxane-modified polyurethane blended with polyvinylidene fluoride (PVDF) polymer electrolyte. The method involves blending siloxane-modified polyurethane with PVDF to achieve high-performance solid-state lithium-sulfur batteries. The benefits are as follows: First, this invention successfully prepares a siloxane-modified polyether polyurethane polymer using polydimethylsiloxane as a chain extender. The high-binding-energy groups such as -NH-C=O and -CH2-CH2-O- in this polyurethane form a dense multi-point coordination network with Li⁺, while the low-binding-energy groups -Si-O-Si- construct low-resistance channels for Li⁺ migration, providing an elastic "jump" transport path for Li⁺ independent of large-scale polymer chain movement, thereby increasing the electrolyte ionic conductivity to 6.01 × 10⁻⁶. -4 With a lithium-ion transference number as high as 0.8 (S·cm⁻¹), this invention achieves efficient and selective Li⁺ transport, breaking through the ion transport bottleneck of traditional polymer electrolytes at the molecular level. Secondly, this invention utilizes the N–H···F strong hydrogen bond network formed by the -NH groups of polyurethane and the -CF groups of polyvinylidene fluoride to effectively reconstruct the interfacial potential distribution within the electrolyte, significantly reducing local interfacial polarization and Li⁺ transport. + The migration barrier fluctuations significantly reduce the apparent activation energy of Li⁺ migration. Simultaneously, this hydrogen-bonded network efficiently immobilizes TFSI⁻ anions, promoting the full dissociation of LiTFSI lithium salt, increasing the concentration of free Li⁺ within the system, improving the continuity of ion transport channels, and effectively suppressing interfacial side reactions between the electrolyte and electrode. Finally, this invention achieves highly efficient Li⁺ transport performance and uniform ion flux, optimizing the Li⁺ transport path from the polymer electrolyte to the sulfur cathode, effectively alleviating the internal ion transport bottleneck of the battery, promoting uniform distribution of Li⁺ and balanced redox reactions at the sulfur cathode, completely solving the problem of low sulfur utilization caused by slow and uneven lithium-ion transport, significantly improving the utilization rate of active materials in the sulfur cathode, and improving the overall electrochemical performance of the battery. Furthermore, the cycle stability time of the lithium symmetric battery is significantly improved to over 700 hours, solving the key problems of severe interfacial polarization and interfacial failure during cycling in traditional solid-state lithium-sulfur batteries. Attached Figure Description

[0026] To more clearly illustrate the modified results of the embodiments of the present invention, the accompanying drawings used in the description of the comparative examples and embodiments will be briefly introduced below.

[0027] Figure 1This is a schematic diagram illustrating the mechanism of polymer electrolyte preparation in the examples;

[0028] Figure 2 Scanning electron microscope (SEM) image of the polymer electrolyte prepared for the example;

[0029] Figure 3 Scanning electron microscope image of the polymer electrolyte prepared for comparison;

[0030] Figure 4 Stress-strain curves of the polymer electrolytes prepared in Examples and Comparative Example 1;

[0031] Figure 5 Thermogravimetric analysis of the polymer electrolyte prepared for the examples;

[0032] Figure 6 Infrared spectra of the siloxane polyurethane prepared for the example;

[0033] Figure 7 Infrared spectra of the polymer electrolytes prepared in Examples and Comparative Example 1;

[0034] Figure 8 Impedance diagrams of the polymer electrolytes prepared in Examples and Comparative Example 1;

[0035] Figure 9 Linear sweep voltammetry curves of the polymer electrolytes prepared in Examples and Comparative Example 1;

[0036] Figure 10 Arrhenius curves of the polymer electrolytes prepared for Examples and Comparative Example 1;

[0037] Figure 11 The migration number test curve of the polymer electrolyte prepared for the example;

[0038] Figure 12 Impedance diagrams of different polymer solid-state lithium-sulfur batteries assembled for Examples and Comparative Example 1;

[0039] Figure 13 Tafel curves of polymer electrolytes prepared for Examples and Comparative Example 1;

[0040] Figure 14 The constant current polarization curves of the polymer electrolytes prepared for Examples and Comparative Example 1 are shown.

[0041] Figure 15 Critical current density diagram of the polymer electrolyte prepared for the example;

[0042] Figure 16 Cyclic voltammetry curves of solid-state lithium-sulfur batteries prepared and assembled for Examples and Comparative Example 1;

[0043] Figure 17Rate performance graphs of solid-state lithium-sulfur batteries prepared and assembled for examples and comparative examples;

[0044] Figure 18 The graph shows the cycle performance of the lithium-sulfur batteries assembled in Examples 1 and Comparative Example 1 at 0.2 rate.

[0045] Figure 19 The graph shows the calculated adsorption energy of lithium ions for different functional groups in the siloxane polyurethane in the examples.

[0046] Figure 20 This is a calculation diagram of hydrogen bonds in the polymer electrolyte of the examples; Detailed Implementation

[0051] The following embodiments further illustrate the above-mentioned content of the present invention in detail. However, the subject matter of the present invention is not limited to the following embodiments, and all technologies implemented based on the above-mentioned content of the present invention fall within the scope of the present invention.

[0052] The reagents used in the experiment are shown in Table 1, and the instruments used in the experiment are shown in Table 2.

[0053] Experimental drugs

[0054] Drug Name Chemical abbreviation Specification factory polyvinylidene fluoride PVDF Battery level Taiyuan Lizhiyuan Technology Co., Ltd. elemental sulfur S Chemically pure Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd. Lithium bis(trifluoromethanesulfonylimide) LiTFSI Analytical Pure Shanghai Chengjie Chemical Co., Ltd. N,N-dimethylformamide DMF Analytical Pure Tianjin Tianli Chemical Reagent Co., Ltd. Acetylene black AB Battery level Pengxiang Yunda Machinery Technology Co., Ltd. Hexamethylene diisocyanate HDI ≥99.0％ Aladdin Reagents (Shanghai) Co., Ltd. Dihydroxy-terminated polydimethylsiloxane PDMS-OH ≥99.0％ Aladdin Reagents (Shanghai) Co., Ltd. Polytetrahydrofuran PTMEG ≥99.0％ Aladdin Reagents (Shanghai) Co., Ltd.

[0055] Experimental equipment

[0056] Instrument Name model factory Analytical balance FC-204 Shanghai Jingke Balance Magnetic stirrer CL-200 Gongyi Yuhua Instrument Co., Ltd. Vacuum drying oven ZK-82BB Shanghai Experimental Instrument Factory Co., Ltd. Button battery sealing machine MSK-110 Shenzhen Kejing Zhida Technology Co., Ltd. Electrode punching machine MSK-T10 Shenzhen Kejing Zhida Technology Co., Ltd. LAND Battery Testing System CT2001A Wuhan Jinno Electronics Co., Ltd. Electrochemical workstation CHI760E Shanghai Chenhua Instrument Co., Ltd. Scanning electron microscope FEI sirion200 FEI Company Vacuum glove box ZKX Nanjing University Instrument Factory Tubular furnace SK-3-9K Harbin Longjiang Electric Furnace Factory Planetary ball mill MK-3 Shanghai Zhuo's Instrument Factory

[0057] The preparation process steps of the following examples are further described in conjunction with the accompanying drawings and comparative examples, but the scope of protection of the present invention is not limited to the following examples.

[0058] Example: The preparation method of a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte in this example is carried out according to the following steps:

[0059] I. Preparation of Siloxane Polyurethane

[0060] 0.48 g of polytetrahydrofuran (PTMEG, Mn ≈ 2000 g·mol⁻¹, 0.00024 mol) and 0.0706 g of hexamethylene diisocyanate (HDI, 0.00042 mol) were dissolved in 1.5 mL of anhydrous dichloromethane (DCM), and stirred magnetically at 40 °C until a homogeneous and transparent solution was formed. Then, 0.005 g of dibutyltin dilaurate (DBTDL) was added to the above system as a catalyst for polyurethane synthesis, and prepolymerization was continued with stirring. When the reaction solution gradually became viscous, 0.16 g of dihydroxy-terminated polydimethylsiloxane (PDMS-OH, Mn ≈ 1000 g·mol⁻¹) was added. -1 The reaction was continued at the same temperature for 12 h to obtain the target polymer solution. To ensure the processability of the system, anhydrous N,N-dimethylformamide (DMF) was used as a diluent to adjust the solution viscosity during the reaction, and 0.5 mL of DMF was added every 1 h during the reaction. The resulting solution was cast onto a glass plate and placed in a vacuum oven to dry at 80 °C for 12 h, resulting in a SiPu polymer film.

[0061] II. Preparation of Siloxane Polyurethane Blend PVDF Polymer Electrolyte Precursor

[0062] Weigh 0.5 g of PVDF and dissolve it in anhydrous DMF. Stir magnetically until a homogeneous and transparent solution is formed. Then add 0.4 g of LiTFSI and continue stirring to ensure complete dissolution and uniform dispersion. On this basis, add 20% SiPU to the solution and continue stirring for 12 hours to obtain a polymer precursor solution.

[0063] III. Preparation of Polymer Electrolytes

[0064] The resulting solution was poured into a PTFE mold using a casting method to obtain a polymer electrolyte membrane, which was then vacuum dried at 80 °C for 14 hours to prepare a polymer electrolyte membrane with a thickness of approximately 100-140 μm. This membrane was named SiPu / PVDF / LiTFSI polymer electrolyte (SPLE).

[0065] IV. Preparation of Solid-State Lithium-Sulfur Battery Electrodes

[0066] Elemental sulfur and porous carbon material were mixed in a ratio of 7:3 (wt:wt) and ground in a ball mill for 3 hours; then the resulting material was heated in an oven at 155 °C for 12 hours to obtain elemental sulfur-supported porous carbon material, named S / NPC.

[0067] V. Preparation of Solid-State Lithium-Sulfur Batteries

[0068] The polymer electrolyte prepared in step three, along with the positive electrode, lithium sheet, gasket, and spring sheet prepared in step four, are assembled into a solid-state lithium-sulfur battery in an argon-filled glove box.

[0069] Comparative Example 1

[0070] Unlike the above embodiments, 0.5 g of PVDF was weighed and dissolved in anhydrous DMF, and magnetically stirred until a homogeneous and transparent solution was formed; then 0.4 g of LiTFSI was added, and stirring was continued to ensure complete dissolution and uniform dispersion; the resulting solution was poured into a PTFE mold by casting to obtain a polymer electrolyte membrane, and vacuum dried at 80 ℃ for 14 hours to prepare a polymer electrolyte membrane with a thickness of approximately 100-140 μm, which was named PVDF / LiTFSI polymer electrolyte (PLE).

[0071] Comparative Example 2

[0072] Unlike the above embodiments, 0.5 g of PVDF was weighed and dissolved in anhydrous DMF, and magnetically stirred until a homogeneous and transparent solution was formed; then 0.4 g of LiTFSI was added, and stirring was continued to ensure full dissolution and uniform dispersion; on this basis, 5% SiPU was added to the solution, and stirring was continued for 12 hours to obtain a polymer precursor solution.

[0073] Comparative Example 3

[0074] Unlike the above embodiments, 0.5 g of PVDF was weighed and dissolved in anhydrous DMF, and magnetically stirred until a homogeneous and transparent solution was formed; then 0.4 g of LiTFSI was added, and stirring was continued to ensure full dissolution and uniform dispersion; on this basis, 10% SiPU was added to the solution, and stirring was continued for 12 hours to obtain a polymer precursor solution.

[0075] Comparative Example 4

[0076] Unlike the above embodiments, 0.5 g of PVDF was weighed and dissolved in anhydrous DMF, and magnetically stirred until a homogeneous and transparent solution was formed; then 0.4 g of LiTFSI was added, and stirring was continued to ensure full dissolution and uniform dispersion; on this basis, 15% SiPU was added to the solution, and stirring was continued for 12 hours to obtain a polymer precursor solution.

[0077] Comparative Example 5

[0078] Unlike the above embodiments, 0.5 g of PVDF was weighed and dissolved in anhydrous DMF, and magnetically stirred until a homogeneous and transparent solution was formed; then 0.4 g of LiTFSI was added, and stirring was continued to ensure complete dissolution and uniform dispersion; on this basis, 25% SiPU was added to the solution, and stirring was continued for 12 hours to obtain a polymer precursor solution.

[0079] The drying method for the polymer electrolyte is exactly the same as that in Comparative Example 1.

[0080] Performance characterization was performed on the above embodiments and comparative examples.

[0081] Figure 1 This is a schematic diagram illustrating the mechanism of polymer electrolyte preparation in this example. A dense multi-point coordination network is formed between C=O and other groups and Li⁺, providing an elastic "jumping" channel for Li⁺ without relying on large-scale polymer chain movement. Furthermore, hydrogen bonds are formed between SiPu and PVDF chains to immobilize the TFSI anion. Simultaneously, the interaction between PU and PVDF chains reconstructs the interfacial potential distribution of the electrolyte, effectively reducing local interfacial polarization and energy barrier fluctuations, thereby reducing the Li⁺ concentration. + Apparent activation energy of migration (E) a This enables selective Li⁺ transport. It optimizes the lithium-ion transport path from the polymer electrolyte to the sulfur cathode, alleviating internal transport bottlenecks, promoting uniform lithium-ion flux and balanced redox reactions, and solving the problem of low sulfur utilization caused by slow and uneven lithium-ion transport and distribution in polymer solid-state lithium-sulfur batteries.

[0082] Figure 2 The image shows a scanning electron microscope (SEM) image of the polymer electrolyte prepared for Comparative Example 1. The polymer electrolyte surface has large cracks, which disrupt the originally continuous Li⁺ transport pathways within the electrolyte, further reducing the lithium-ion transport number.

[0083] Figure 3 The image shows a scanning electron microscope (SEM) image of the polymer electrolyte prepared for this example. The introduction of polyurethane makes the polymer electrolyte surface denser and reduces the pore size, indicating a tighter contact with the electrode. This lays the structural foundation for subsequent ion transport and interfacial stability.

[0084] Figure 4 The stress-strain curves of the polymer electrolytes prepared in Examples and Comparative Example 1 are shown. The PVDF / LiFSI electrolyte of the Comparative Example has a tensile strength of approximately 2.4 MPa and an elongation at break of approximately 60%. The SiPU / PVDF / LiFSI electrolyte of Examples 1 has a tensile strength increased to 2.51 MPa and an elongation at break significantly increased to approximately 90%.

[0085] Figure 5Thermogravimetric analysis of the polymer electrolyte prepared for the examples was performed. The solvent loss of the example electrolyte was only 6% in the temperature range of 100 °C–200 °C, indicating a low liquid content, which proves that the low liquid content of the example electrolyte is closer to the characteristics of a solid electrolyte.

[0086] Figure 6 The infrared spectrum of the siloxane polyurethane prepared for the example. A strong tensile vibration peak of COC (1102 cm⁻¹) is present in the SiPu sample. −1 After polymerization, polyurethane groups (-NH, 3325 cm⁻¹) can be clearly observed. −1 C=O, 1719 cm −1 This confirms the successful polymerization of polyurethane. Furthermore, the SiPu sample also exhibited a characteristic absorption band of 1256 cm⁻¹ belonging to PDMS. −1 1010 cm −1 and 793cm −1 All of them appeared in the spectrum of SiPu, indicating that polysiloxane has been introduced into SiPu. Furthermore, compared to the raw material, the -NCO groups in HDI showed a higher concentration at 2270 cm⁻¹. -1 The complete disappearance of the characteristic absorption frequency band indicates that the polyurethane polymerization is complete.

[0087] Figure 7 The infrared spectra of the polymer electrolytes prepared in Examples and Comparative Example 1 are shown. The hydrogen bonding between SiPu and PVDF was confirmed by FTIR spectroscopy. Infrared measurements were performed on the SiPu / PVDF / LiTFSI and PVDF / LiTFSI polymer electrolytes, respectively. Notably, the absorption peak at 1188 cm⁻¹ is attributed to the stretching vibration of the –CF group. With the introduction of SiPu, this peak position shifted slightly, indicating that the –NH group in SiPu forms NH···F hydrogen bonds with the CF group in the polymer.

[0088] Figure 8 Impedance plots of the polymer electrolytes prepared in Examples and Comparative Example 1 are shown. It can be seen from the plots that the polymer electrolyte membrane of the Examples has a lower impedance value of 11.34 Ω. The ionic conductivity of the polymer electrolyte membrane of the Examples is calculated to be 6.01 × 10⁻⁶ using the ionic conductivity calculation formula. -4 S cm -1 The ionic conductivity of the comparative polymer electrolyte membrane was 4.21 × 10⁻⁶. -5 S cm -1 .

[0089] Figure 9Linear sweep voltammetry curves of the polymer electrolytes prepared in Examples 1 and Comparative Example 1 are shown. In Examples 1, the polymer electrolyte showed a change in current when the applied voltage reached 4.83 V. In Comparative Example 1, the polymer electrolyte showed a change in current when the applied voltage reached 4.65 V.

[0090] Figure 10 Arrhenius curves of the polymer electrolytes prepared in Examples and Comparative Example 1; the activation energies of the polymer electrolytes in Examples and Comparative Example 1 are 11.04 kJ / mol. -1 and 16.3 KJ mol -1 .

[0091] Figure 11 The migration number test curves for the polymer electrolyte prepared in this example are shown. The migration number of the polymer electrolyte in this example is 0.80. The introduction of SiPu enables preferential and directional transport of Li⁺, significantly reducing concentration polarization caused by anion migration.

[0092] Figure 12 Impedance diagrams are shown for the different polymer solid-state lithium-sulfur batteries assembled in Examples and Comparative Example 1. The impedances of the solid-state lithium-sulfur batteries assembled in Examples and Comparative Example 1 are 650 Ω and 329 Ω, respectively.

[0093] Figure 13 Tafel curves for the polymer electrolytes prepared in Examples and Comparative Example 1 are shown. The exchange current densities of the lithium-symmetric batteries assembled with the polymer electrolyte membranes in Examples and Comparative Example 1 are 0.0020 A / cm², respectively. -2 and 0.0015 A cm -2 The interface of the illustrated embodiment is better.

[0094] Figure 14 The constant current polarization curves of the polymer electrolytes prepared in Examples 1 and Comparative Example 1 are shown. The constant current polarization times of the lithium symmetric batteries assembled with the polymer electrolyte membranes of Examples 1 and Comparative Example 1 were 700 h and 408 h, respectively. This result intuitively and strongly demonstrates that the interfacial compatibility, interfacial stability, and resistance to lithium dendrite growth between the electrolytes and lithium metal electrodes of the Examples 1 were significantly improved.

[0095] Figure 15 The critical current density diagrams for the polymer electrolytes prepared in Examples 1 and Comparative Example 1 are shown. The critical current density that the polymer electrolyte membrane in Example 1 can withstand is 0.75 mA cm⁻¹. -2 A higher critical current density means that the electrolyte membrane can support the battery to operate at larger charge and discharge currents, making it possible to develop high-rate, high-energy-density solid-state lithium-sulfur batteries.

[0096] Figure 16Cyclic voltammetry curves of the solid-state lithium-sulfur batteries prepared and assembled for Examples 1 and Comparative Example 1 are shown. The cyclic voltammetry curves of the solid-state lithium-sulfur battery assembled with the polymer electrolyte membrane in Examples 1 show a lower polarization voltage.

[0097] Figure 17 The rate performance diagrams show the solid-state lithium-sulfur batteries prepared and assembled in Examples 1 and Comparative Example 1. The highest discharge capacities of the lithium-sulfur batteries assembled in Examples 1 at rates of 0.1, 0.2, 0.5, 1, and 2 are 895.7, 683.1, 581.6, 462.6, and 380.1 mAh g, respectively. -1 When restored to a 0.5x rate, it can recover 587.8 mAh g. -1 It has high capacity and excellent reversibility.

[0098] Figure 18 The graph shows the cycling performance of the lithium-sulfur batteries assembled in Examples 1 and Comparative Example 1 at 0.2 rate. The initial discharge specific capacity of the lithium-sulfur batteries assembled in Examples 1 and Comparative Example 1 at 0.2 rate is 707.7 mAh g⁻¹. -1 and 454.2 mAhg -1 Furthermore, the capacity retention rates of the lithium-sulfur batteries assembled in the examples and the assembly after 200 cycles were 59.3% and 34.0%, respectively. This indicates that the lithium-sulfur batteries assembled in the examples exhibit higher sulfur utilization during cycling.

[0099] Figure 19 The diagram shows the calculated adsorption energies of different functional groups for lithium ions in the siloxane polyurethane in the examples; it illustrates the binding energy (ΔG) of Li⁺ with characteristic functional groups in the polymer segments under three different coordination conditions. The ΔG for the Li⁺ ether oxygen bond (COC) is -37.9 kcal mol. -1 ΔG for the Li⁺ ether oxygen bond (-Si(CH₃)₂O⁻) is -31.9 kcal / mol. -1 ΔG for the Li⁺ ether oxygen bond (-NH-COO-) is -55.0 kcal mol. -1 .

[0100] Figure 20 The diagram shows the calculated hydrogen bond number of the polymer electrolyte in the examples. It can be seen that the number of hydrogen bonds in PVDF-SiPu is consistently significantly higher than that in SiPu-SiPu, indicating that the intermolecular hydrogen bonds between PVDF and SiPu in the electrolyte are much stronger than the aggregation effect of SiPu itself. This proves that a stable and dense hydrogen bond network is formed between SiPU and PVDF, ensuring the structural homogeneity of the electrolyte.

Claims

1. A method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte, characterized in that, A method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte is carried out according to the following steps: I. Preparation of Siloxane Polyurethane Polytetrahydrofuran (PTMEG, Mn ≈ 2000 g·mol⁻¹) -1 Hexamethylene diisocyanate (HDI) and dichloromethane (DCM) were dissolved in anhydrous dichloromethane and stirred magnetically until a homogeneous, transparent solution was formed. A catalyst was then added to the system, and stirring continued during prepolymerization. When the reaction solution gradually became viscous, dihydroxy-terminated polydimethylsiloxane (PDMS-OH, Mn ≈ 1000 g·mol⁻¹) was added. -1 The reaction was continued at the same temperature to obtain the target polymer solution. To ensure the processability of the system, anhydrous N,N-dimethylformamide (DMF) was used as a diluent to adjust the solution viscosity during the reaction, and DMF was added during the reaction. The resulting solution was cast onto a glass plate and dried in a vacuum oven. The resulting polymer film was named SiPu. II. Preparation of Siloxane Polyurethane Blend PVDF Polymer Electrolyte Precursor Weigh PVDF and dissolve it in anhydrous DMF, stirring magnetically until a homogeneous and transparent solution is formed; then add LiTFSI and continue stirring to ensure complete dissolution and uniform dispersion; on this basis, add SiPU to the solution and continue stirring for 10-14 hours to obtain a polymer precursor solution; III. Preparation of Polymer Electrolytes The resulting solution was poured into a PTFE mold using a casting method to obtain a polymer electrolyte membrane, which was then vacuum dried for 12-16 hours to prepare a polymer electrolyte membrane with a thickness of approximately 100-140 μm. This membrane was named SiPu / PVDF / LiTFSI polymer electrolyte (SPLE). Simultaneously, as a comparative experiment, a PVDF / LiTFSI electrolyte membrane (PLE) was prepared using the same method, with a ratio of 0.5 g PVDF to 0.4 g LiTFSI. IV. Preparation of Solid-State Lithium-Sulfur Battery Electrodes Elemental sulfur and porous carbon material were mixed in a ratio of 7:3 (wt:wt) and ground in a ball mill for 3 hours; then the resulting material was heated in an oven at 155 °C for 12 hours to obtain elemental sulfur-supported porous carbon material, named S / NPC. V. Preparation of Solid-State Lithium-Sulfur Batteries The polymer electrolyte prepared in step three, along with the positive electrode, lithium sheet, gasket, and spring sheet prepared in step four, are assembled into a solid-state lithium-sulfur battery in an argon-filled glove box.

2. The method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte according to claim 1, characterized in that, The polytetrahydrofuran (PTMEG, Mn ≈ 2000 g·mol) mentioned in step one -1 The molar ratio of hexamethylene diisocyanate (HDI) to HDI is 1:1.5-1:2.

0.

3. The method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte according to claim 1, characterized in that, The stirring temperature under magnetic stirring described in step one is 30 ℃-50 ℃.

4. The method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte according to claim 1, characterized in that, The catalyst added to the above system in step one is one or more of dibutyltin diacetate (DBTA), tetrabutyltin (TBT), and dibutyltin dilaurate (DBTDL).

5. The method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte according to claim 1, characterized in that, The prepolymerization time mentioned in step one is 20-40 min.

6. The method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte according to claim 1, characterized in that, The dihydroxy-terminated polydimethylsiloxane (PDMS-OH, Mn ≈ 1000 g·mol) mentioned in step one -1 The amount of substance is 0.00015-0.00018 mol.

7. The method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte according to claim 1, characterized in that, The time interval for adding DMF during the reaction process described in step one is 0.5-1.5 hours.

8. The method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte according to claim 1, characterized in that, The mass ratio of LiTFSI to PVDF added in step two is 0.7:1 to 0.9:

1.

9. The method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte according to claim 1, characterized in that, The SiPU addition ratio mentioned in step two is between 10% and 30% of the total PVDF mass.

10. The method for preparing a siloxane-polyurethane blended polyvinylidene fluoride polymer electrolyte according to claim 1, characterized in that, The vacuum drying temperature described in step three is 60-100 ℃.

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