A polymer solid-state electrolyte, a preparation method thereof and application thereof in a solid-state lithium-sulfur battery

Abstract

This invention relates to the field of new energy materials technology, specifically to a polymer solid electrolyte, its preparation method, and its application in solid-state lithium-sulfur batteries. The solid electrolyte is composed of polyethylene oxide, a selenium-containing substance, and a lithium salt. First, polyethylene oxide and the selenium-containing substance are mixed and heat-treated to obtain a composite product. Then, the composite product and the lithium salt are dissolved in a solvent, stirred, and mixed to obtain a mixed solution. The mixed solution is transferred to a separator and vacuum-dried to obtain the polymer solid electrolyte. This invention uses a heat treatment process to composite polyethylene oxide and the selenium-containing substance, forming a rapid lithium-ion transport channel within the electrolyte. This solid electrolyte exhibits high ionic conductivity, effectively promotes the reaction kinetics of the sulfur cathode material, and stabilizes the lithium anode. Solid-state lithium-sulfur batteries using the solid electrolyte prepared according to this invention exhibit high capacity utilization and stable cycle characteristics.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, specifically to a polymer solid electrolyte, its preparation method, and its application in solid-state lithium-sulfur batteries. Background Technology

[0002] Lithium-sulfur (Li-S) batteries are known for their extremely high theoretical energy density (2600 Wh kg⁻¹). -1 Lithium-sulfur batteries, with their low cost and high specific energy content, are considered a promising next-generation high-energy-density energy storage system. However, traditional liquid lithium-sulfur batteries face serious "shuttle effect" and safety hazards caused by dendrite growth in the lithium metal anode. Assembling all-solid-state lithium-sulfur batteries using polymer solid-state electrolytes (SPEs) promises to fundamentally solve leakage and safety issues and has become a current research hotspot.

[0003] Among various polymer matrices, polyethylene oxide (PEO) is widely used due to its excellent dissociation ability for lithium salts and good processing flexibility. However, applying PEO-based solid electrolytes to high-energy-density solid-state lithium-sulfur battery systems still faces severe technical bottlenecks. First, PEO segments tend to form crystalline regions through regular arrangement, which severely hinders the migration of lithium ions between polymer segments, resulting in an electrolyte ionic conductivity that fails to meet the requirements of high-performance batteries, thus limiting its application in practical scenarios. Second, sulfur and organic sulfur materials are inherently electron / ion insulators. In an all-solid-state environment, the lack of dissolution and mediation by liquid electrolytes leads to fewer electrochemical reaction active sites and extremely slow redox kinetics, resulting in low utilization of active materials, high polarization, and rapid capacity decay. Furthermore, during long-term cycling, the interface between PEO and the lithium metal anode is easily corroded, and uneven lithium ion flow can induce lithium dendrite growth, piercing the electrolyte membrane and causing short circuits.

[0004] Existing modification strategies mainly focus on adding inert ceramic fillers (such as SiO2) or active ceramic fillers (such as LLZO) to reduce crystallinity and improve polymer molecular chain motion. While these methods can improve ionic conductivity to some extent, they often cannot simultaneously achieve the catalytic / promoting effect on the redox reaction of sulfur cathode. Simple physical blending is insufficient to address the slow kinetics of sulfur cathode in a solid-state environment. Therefore, there is an urgent need to develop a novel polymer composite electrolyte that can effectively promote the conversion reaction kinetics of sulfur cathode while improving ionic conductivity and stabilizing the lithium metal anode interface, thereby constructing a high-performance all-solid-state lithium-sulfur battery. Summary of the Invention

[0005] The purpose of this invention is to provide a polymer solid electrolyte, its preparation method, and its application in solid-state lithium-sulfur batteries. By combining polyethylene oxide with selenium-containing materials, a rapid lithium-ion transport channel is formed within the electrolyte, significantly improving ionic conductivity. This electrolyte also promotes the reaction kinetics of the sulfur cathode, effectively stabilizing the lithium anode, thus enabling solid-state lithium-sulfur batteries to exhibit high capacity utilization and excellent cycle characteristics.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a polymer solid electrolyte includes the following steps: (1) Polyethylene oxide is mixed with selenium-containing substances and subjected to heat treatment to obtain a composite product; (2) Dissolve the composite product obtained in step (1) and the lithium salt in a solvent, stir and mix to obtain a mixed solution; (3) Transfer the mixed solution obtained in step (2) onto the diaphragm and dry it under vacuum to obtain the polymer solid electrolyte.

[0007] Further, in step (1), the mass ratio of the polyethylene oxide to the selenium-containing substance is 100:(1-10); the molecular weight of the polyethylene oxide is 600,000 to 7,000,000; the selenium-containing substance is one or more of elemental selenium or selenium-containing compounds; the selenium-containing compounds include, but are not limited to, selenium disulfide, selenium dioxide, selenomethionine and dimethyl diselenoether.

[0008] The heat treatment temperature is 100-200℃, and the heat treatment time is 2-6 hours.

[0009] Further, in step (2), the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium hexafluorophosphate, lithium nitrate, lithium tetrafluoroborate and lithium difluorooxalate borate. The solvent is one or more of acetonitrile, chloroform and acetone; The mass of the lithium salt is 5wt%-40wt% of the total mass of the composite product and the lithium salt.

[0010] The concentration of the composite product in the mixed solution is 5wt%-20wt%.

[0011] The mixing time is 12-48 hours.

[0012] Further, in step (3), the mixed solution transfer process is as follows: the polyethylene diaphragm is laid flat in the polytetrafluoroethylene mold, and the mixed solution is uniformly poured onto the polyethylene diaphragm; the vacuum drying temperature is 40-60℃, the vacuum drying time is 12-60 hours, the vacuum degree is ≤0.1Mpa; the polymer solid electrolyte is composed of the diaphragm and the coating formed after the mixed solution on the diaphragm is dried.

[0013] A polymer solid electrolyte, wherein the polymer solid electrolyte is prepared by the method described above.

[0014] The polymer solid electrolyte has a thickness of 50-150 μm; the membrane thickness is 5-10 μm.

[0015] An application of a polymer solid electrolyte, wherein the polymer solid electrolyte is used as an electrolyte in a solid lithium-sulfur battery.

[0016] In this solid-state lithium-sulfur battery, the positive electrode is a sulfur-based positive electrode, including but not limited to elemental sulfur and organic sulfur compounds; the organic sulfur compounds are benzoquinone-based polytetrasulfide propane, sulfurized polyacrylonitrile, sulfur-1,3-diisopropene-phenylene copolymer or tetrasulfide dipentamethylene thiuram.

[0017] The principle of this invention is as follows: A PEO-selenium-containing composite material was prepared by mixing polyethylene oxide (PEO) with a selenium-containing substance and then subjecting the mixture to heat treatment. This process significantly improves the ionic conductivity of the PEO-based solid electrolyte, enabling the assembled solid-state lithium-sulfur battery to achieve excellent electrochemical performance.

[0018] Furthermore, the introduction of selenium-containing substances has a dual effect of promoting the rapid conversion of sulfur-based cathode materials and stabilizing lithium metal anodes. In summary, the solid electrolyte prepared using PEO-selenium-containing composite materials exhibits excellent reaction kinetics, high discharge specific capacity, and stable long-cycle characteristics.

[0019] Advantages and beneficial effects of the present invention: 1. Significantly Enhanced Cathode Reaction Kinetics: This invention utilizes a combination of selenium-containing materials and PEO. The introduction of selenium species effectively promotes the redox reaction kinetics of the sulfur / organosulfur cathode, accelerating the reaction rate. This enhanced kinetics significantly reduces battery polarization, improves the utilization rate of the cathode active material, and thus enhances the actual capacity of the battery.

[0020] 2. Significantly improved ionic conductivity: After PEO is combined with selenium-containing substances, a rapid lithium-ion transport channel is formed inside the electrolyte, which makes the polymer solid electrolyte exhibit high ionic conductivity.

[0021] 3. Excellent negative electrode stability: PEO-selenium-based polymer solid electrolyte can effectively stabilize the lithium metal negative electrode. This electrolyte promotes uniform lithium ion deposition, inhibits lithium dendrite formation, and prevents electrolyte puncture, thereby significantly extending the battery's cycle life.

[0022] 4. Simple process and easy to scale up: The preparation method of the present invention has a simple process flow, widely available raw materials, low cost, and good process reproducibility, making it suitable for large-scale industrial production.

[0023] 5. This invention uses a heat treatment process to composite polyethylene oxide with selenium-containing materials, forming a rapid lithium-ion transport channel within the electrolyte. This solid-state electrolyte exhibits high ionic conductivity, effectively promoting the reaction kinetics of the sulfur cathode material and stabilizing the lithium anode. Solid-state lithium-sulfur batteries using the solid-state electrolyte prepared according to this invention demonstrate high capacity utilization and stable cycle characteristics. The preparation process of this invention is simple, effectively improving battery performance and providing broad prospects for the application of solid-state lithium-sulfur batteries. Attached Figure Description

[0024] Figure 1 The process flow diagram is shown for the PEO-selenium-containing polymer solid electrolyte prepared according to the present invention.

[0025] Figure 2 Comparison chart of ionic conductivity tests of polymer solid electrolytes prepared in Examples 1, 3, 1, and 3.

[0026] Figure 3 Comparative graphs show the cyclic voltammetry test results of the solid lithium-sulfur batteries prepared in Example 2, Comparative Example 2, and Comparative Example 4.

[0027] Figure 4 Images showing the deposition morphology of the polymer solid electrolytes prepared in Examples 1, 1, and 3 after lithium deposition. In the figures: a represents Example 1; b represents Comparative Example 1; c represents Comparative Example 3.

[0028] Figure 5 The graph shows a comparison of the long-cycle performance of lithium-lithium symmetric batteries prepared by polymer solid electrolytes in Example 1, Comparative Example 1, and Comparative Example 3. In the graph: a represents Example 1; b represents Comparative Example 1; c represents Comparative Example 3.

[0029] Figure 6 The graph shows a comparison of charge-discharge curves of solid lithium-sulfur batteries prepared in Example 2, Comparative Example 2, and Comparative Example 4 at different rates. In the graph: a represents Example 2; b represents Comparative Example 2; c represents Comparative Example 4.

[0030] Figure 7 Comparative graphs show the long-cycle tests of solid-state lithium-sulfur batteries prepared in Example 2, Comparative Example 2, and Comparative Example 4. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, examples, and comparative examples.

[0032] Example 1 This embodiment describes the preparation of a polymer solid electrolyte using selenium disulfide (SeS2) as the selenium-containing species. The process is as follows: 1g of PEO (molecular weight 600,000) and 50mg of SeS2 were ball-milled for 20 minutes until the components were homogeneous. The mixture was then heated in a sealed container at 200°C for 4 hours, followed by cooling to room temperature in air to obtain the PEO-SeS2 complex. Figure 1 As shown, the PEO-SeS2 composite and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) were dissolved in acetonitrile and stirred for 24 h to obtain a homogeneous solution. The concentration of PEO-SeS2 in the solution was approximately 15 wt.%, and the mass of LiTFSI accounted for 30% of the total mass of LiTFSI and PEO-SeS2. Subsequently, a polyethylene diaphragm was laid flat in a polytetrafluoroethylene mold, and the solution was uniformly poured onto the polyethylene diaphragm. After drying under vacuum (0.1 MPa) at 40 °C for 48 hours, the electrolyte membrane (containing the polyethylene diaphragm, with a thickness of 5 μm) was removed from the polytetrafluoroethylene mold, with a thickness of approximately 70 μm, thus obtaining the PEO-SeS2-based polymer solid electrolyte.

[0033] Example 2 This embodiment describes the preparation of a high-performance all-solid-state lithium-sulfur battery, and the process is as follows: First, a mixed electrolyte slurry was prepared using the same method as the homogeneous solution preparation method in Example 1. The obtained mixed electrolyte slurry was mixed uniformly with an organic sulfur polymer and conductive carbon black in a PEO-SeS2 ratio (4:5:1 mass ratio of organic sulfur polymer (benzoquinone-based polytetrasulfide propane) to conductive carbon black) in an appropriate amount of NMP to obtain a composite cathode slurry. The mass ratio of benzoquinone-based polytetrasulfide propane to NMP was 0.07:(0.5-1.5). This cathode slurry was then coated onto the carbon-coated side of a single-sided carbon-coated aluminum foil, which was purchased from Shandong Xinxin Electronic Materials Co., Ltd. After vacuum drying at 60°C to remove acetonitrile and NMP, a composite cathode was obtained. The resulting composite cathode material coating consists of an organic sulfur polymer, conductive carbon black, and a polymer solid electrolyte.

[0034] The obtained composite positive electrode was cut into a circular sheet with a diameter of 10 mm to serve as the composite positive electrode sheet, with a sulfur loading of 0.6-0.8 mg. A lithium sheet (12 mm in diameter and 0.45 mm in thickness) was used as the negative electrode. The polymer membrane (electrolyte membrane) from Example 1 was cut into a circular sheet with a diameter of 16 mm and sandwiched between the composite positive and negative electrode sheets as the electrolyte. The mixture was then placed into a 2025 battery case to assemble a button cell.

[0035] Example 3 This embodiment describes the preparation of a polymer solid electrolyte using selenium powder (Se) as a selenium-containing species. The process is as follows: 1g of PEO (molecular weight 600,000) and 50mg of Se powder were ball-milled for 20 minutes until the components were homogeneous. The mixture was then heated in a sealed container at 200°C for 4 hours, followed by cooling to room temperature in air to obtain the PEO-Se complex. Figure 1 As shown, the PEO-Se composite and LiTFSI were dissolved in acetonitrile and stirred for 24 hours to obtain a homogeneous solution. The concentration of PEO-Se in the solution was approximately 15 wt.%, and the weight of LiTFSI accounted for 30% of the total mass of LiTFSI and PEO-Se. Subsequently, a polyethylene diaphragm was laid flat in a polytetrafluoroethylene (PTFE) mold, and the solution was uniformly transferred onto the PTFE diaphragm. After vacuum drying at 40°C for 48 hours, the electrolyte membrane was removed from the PTFE mold; its thickness was approximately 70 μm. This yielded the PEO-Se-based polymer solid electrolyte.

[0036] Comparative Example 1 This embodiment describes the preparation of a polymer solid electrolyte, and the process is as follows: 1g of PEO with a molecular weight of 600,000 was heated in a sealed container at 200°C for 4 hours, then cooled to room temperature in air to obtain the PEO-ht product (a high-temperature treated polyoxyethylene product). The PEO-ht product and LiTFSI were dissolved in acetonitrile and stirred for 24 hours to obtain a homogeneous solution. The concentration of PEO-ht in the solution was approximately 15 wt.%, and the weight of LiTFSI accounted for 30% of the total mass of LiTFSI and PEO-ht. Subsequently, a polyethylene diaphragm was laid flat in a polytetrafluoroethylene (PTFE) mold, and the solution was uniformly transferred onto the PTFE diaphragm. After vacuum drying at 40°C for 48 hours, the electrolyte membrane was removed from the PTFE mold; its thickness was approximately 70 μm. This yielded the PEO-ht-based polymer solid electrolyte.

[0037] Comparative Example 2 This comparative example demonstrates the fabrication of an all-solid-state lithium-sulfur battery, and the process is as follows: First, a mixed electrolyte slurry is prepared using the same method as the homogeneous solution in Comparative Example 1. The obtained mixed electrolyte slurry is then mixed uniformly with an organic sulfur polymer and conductive carbon black in a PEO-HT ratio of 4:5:1 (mass ratio of organic sulfur polymer to conductive carbon black) in an appropriate amount of NMP to obtain a composite cathode slurry. This cathode slurry is then coated onto the carbon-coated side of a single-sided carbon-coated aluminum foil. After vacuum drying at 60°C to remove acetonitrile and NMP, a composite cathode is obtained. The resulting composite cathode material coating consists of an organic sulfur polymer, conductive carbon black, and a polymer solid electrolyte.

[0038] The obtained composite positive electrode was cut into a circular sheet with a diameter of 10 mm to serve as the composite positive electrode. The positive electrode had a sulfur loading of 0.6-0.8 mg, and a lithium sheet (12 mm in diameter and 0.45 mm thick) was used as the negative electrode. The polymer film from Comparative Example 1 was cut into a circular sheet with a diameter of 16 mm and sandwiched between the above positive and negative electrode sheets. The sheets were then placed into a 2025 battery case to assemble a button cell.

[0039] Comparative Example 3 This embodiment describes the preparation of a polymer solid electrolyte, and the process is as follows: 1 g of PEO (molecular weight 600,000) and LiTFSI were dissolved in acetonitrile and stirred for 24 h to obtain a homogeneous solution. The concentration of PEO in the solution was approximately 15 wt.%, and the weight of LiTFSI accounted for 30% of the total mass of LiTFSI and PEO. Subsequently, a polyethylene diaphragm was laid flat in a polytetrafluoroethylene (PTFE) mold, and the solution was uniformly transferred onto the PTFE diaphragm. After vacuum drying at 40 °C for 48 hours, the electrolyte membrane was removed from the PTFE mold; its thickness was approximately 70 μm. This yielded the PEO-based polymer solid electrolyte.

[0040] Comparative Example 4 This comparative example demonstrates the preparation of a solid-state lithium-sulfur battery, and the process is as follows: First, a mixed electrolyte slurry is prepared using the same method as the homogeneous solution in Comparative Example 3. The obtained mixed electrolyte slurry is then mixed uniformly with an organic sulfur polymer and conductive carbon black in NMP at a PEO to organic sulfur polymer mass ratio of 4:5:1 to obtain a composite positive electrode slurry. This positive electrode slurry is then coated onto the carbon-coated side of a single-sided carbon-coated aluminum foil. After vacuum drying at 60°C to remove acetonitrile and NMP, a composite positive electrode is obtained. The resulting composite positive electrode material coating consists of an organic sulfur polymer, conductive carbon black, and a polymer solid electrolyte.

[0041] The obtained composite positive electrode was cut into a circular sheet with a diameter of 10 mm to serve as the composite positive electrode sheet, with a sulfur loading of 0.6-0.8 mg. A lithium sheet (12 mm in diameter and 0.45 mm thick) was used as the negative electrode. The polymer film from Comparative Example 3 was cut into a circular sheet with a diameter of 16 mm and sandwiched between the above composite positive and negative electrode sheets. The sheets were then placed into a 2025 battery case to assemble a button cell.

[0042] The following are the performance tests of the samples prepared in each embodiment: 1. Ionic conductivity test: The samples prepared in Examples 1, 3, 1, and 3 were tested. The polymer films prepared in Examples 1, 3, 1, and 3 were dried and then die-cut into polymer film discs using a die-cutting machine. The thickness of these discs was found to be 70 micrometers, and the diameter was 19 millimeters. The conductivity of the samples was tested using the following method: the sample was sandwiched between two stainless steel sheets and then placed into a 2032 battery casing. A constant pressure (2 MPa) was applied to ensure good contact, forming a battery for testing. The stainless steel sheets had a diameter of 16 mm and a thickness of 1 mm. The test frequency range was 0.1 Hz to 10 MHz. The impedance diagram of the sample at 50°C is shown below. Figure 2 The ionic conductivity of the sample was calculated based on parameters such as electrochemical impedance, sample thickness, and electrode area. In Example 1, the ionic conductivity of the sample measured at 50°C was 1.41 × 10⁻⁶. -4 S / cm; The ionic conductivity of the sample in Example 3, measured at 50°C, was 0.95 × 10⁻⁶. -4 S / cm; The ionic conductivity of the sample in Comparative Example 1, measured at 50℃, was 0.5 × 10⁻⁶. -4 S / cm; The ionic conductivity of the sample in Comparative Example 3, measured at 50℃, was 0.2 × 10⁻⁶. -4 S / cm. Therefore, the polymer electrolytes prepared using Examples 1 and 3 exhibit high ionic conductivity at 50°C.

[0043] 2. Positive electrode reaction kinetics test: The solid-state lithium-sulfur batteries prepared in Example 2, Comparative Example 2, and Comparative Example 4 were subjected to cyclic voltammetry (CV) tests at 50°C. The charging cutoff voltage was 3.0V, and the discharging cutoff voltage was 1.5V. The scan rate was 0.1mV / s. Figure 3The figure shows the cyclic voltammetry curves of the all-solid-state batteries prepared according to Example 2, Comparative Example 2, and Comparative Example 4 at 50°C. As can be seen from the figure, the solid-state lithium-sulfur battery containing the PEO-SeS2-based polymer solid electrolyte exhibits the highest redox current and the lowest polarization at 50°C. Therefore, this type of polymer solid electrolyte can promote the reaction kinetics of the organic sulfur polymer cathode, accelerate the reaction rate, and improve the utilization rate of the cathode active material.

[0044] 3. Morphological observation of lithium anode: Lithium deposition of the same capacity was performed on samples from Example 1, Comparative Example 1, and Comparative Example 3. The specific procedure was as follows: The polymer solid electrolytes prepared in Examples 1, 1, and 3 were stamped into polymer solid electrolyte wafers using a stamping machine. The electrolyte wafers were all 16 mm in diameter and 70 μm thick. Copper foil with a thickness of 13 μm was cut into 14 mm diameter circles to serve as the working electrode. A lithium sheet (16 mm in diameter, 0.45 mm thick) was used as the negative electrode. The polymer solid electrolyte wafers from Examples 1, 1, and 3 were sandwiched between the positive and negative electrode sheets and assembled into three types of coin cells using a 2025 battery case. A discharge current of 0.1 mA was applied to each of the three types of batteries at 50°C for 1 hour, and then stopped. The three copper foil wafers with a deposited capacity of 0.1 mAh were removed and transferred to a scanning electron microscope for morphological observation. Figure 4 As shown, the lithium deposition morphology on the copper foil surface of the battery prepared in Example 1 is uniform and densely spherical, with no lithium dendrites forming within the field of view. This morphology contributes to the stability of the lithium anode, reduces side reactions, and delays the failure behavior of the lithium anode. The lithium deposition morphology on the copper foil surface of the battery prepared in Comparative Example 1 is spherical, relatively loose, and uneven, and its stabilizing effect on the lithium anode is not as good as that of the PEO-SeS2-based polymer solid electrolyte. The lithium deposition morphology on the copper foil surface of the battery prepared in Comparative Example 3 is dendritic and even looser, making the battery prone to short circuits and detrimental to stable cycling. Therefore, the PEO-SeS2-based polymer solid electrolyte can effectively stabilize the lithium anode of solid lithium-sulfur batteries, promote uniform lithium-ion deposition, and extend battery life.

[0045] 4. Electrochemical testing of the cycling stability of lithium anode: The lithium-ion migration overpotential of the samples from Example 1, Comparative Example 1, and Comparative Example 3 was tested. The specific testing method was as follows: the polymer solid electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 3 were stamped into polymer solid electrolyte wafers using a stamping machine. The wafers had a diameter of 16 mm and a thickness of 70 μm. The samples were sandwiched between two lithium wafers (16 mm in diameter and 0.45 mm in thickness) and placed in a 2025 battery case to form a lithium-lithium symmetric battery. Long-cycle charge-discharge testing was conducted at a temperature of 50°C and a charge-discharge current of 0.2 mA. Figure 5 As shown, the lithium-lithium symmetric battery using the PEO-SeS2-based polymer solid electrolyte prepared in Example 1 had an initial lithium-ion migration overpotential of only 9 mV and could cycle stably for 1600 hours. The lithium-lithium symmetric battery using the PEO-ht-based polymer solid electrolyte prepared in Comparative Example 1 had an initial lithium-ion migration overpotential of 23 mV and failed after 620 hours of cycling. The lithium-lithium symmetric battery using the PEO-based polymer solid electrolyte prepared in Comparative Example 3 had an initial lithium-ion migration overpotential of 26 mV and failed after 411 hours of cycling. Therefore, the PEO-SeS2-based polymer solid electrolyte prepared in Example 1 can effectively guide uniform lithium deposition and stripping in solid-state lithium-sulfur batteries, showing a significant advantage in improving the cycle life of the lithium anode.

[0046] 5. Electrochemical performance testing: The solid-state lithium-sulfur battery prepared in Example 2 was tested at 50°C. The charging cutoff voltage was 3.0V, and the discharging cutoff voltage was 1.5V. The charging and discharging currents were set to 0.1C, 0.2C, 0.5C, and 1C. Figure 6 Figure a shows the charge-discharge curves of the solid-state lithium-sulfur battery prepared according to Example 2 at 50°C and 0.1C, 0.2C, 0.5C, and 1C, with electrochemical capacities of 1371.0 mAh / g, 1145.0 mAh / g, 1009.8 mAh / g, and 1007.1 mAh / g, respectively. Therefore, the PEO-SeS2-based solid-state lithium-sulfur battery exhibits high charge-discharge capability.

[0047] The all-solid-state battery prepared in Comparative Example 2 was tested at 50°C. The charging cutoff voltage was 3.0V, and the discharging cutoff voltage was 1.5V. The charging and discharging currents were set to 0.1C, 0.2C, 0.5C, and 1C. Figure 6Figure b shows the charge-discharge curves of the solid-state lithium-sulfur battery prepared according to Comparative Example 2 at 50°C and 0.1C, 0.2C, 0.5C, and 1C, with electrochemical capacities of 968.3 mAh / g, 572.0 mAh / g, 579.6 mAh / g, and 455.7 mAh / g, respectively. Therefore, the actual capacity of the PEO-HT-based solid-state lithium-sulfur battery is lower than that of the solid-state lithium-sulfur battery prepared in Example 2, and it exhibits greater polarization.

[0048] The all-solid-state battery prepared in Comparative Example 4 was tested at 50°C. The charging cutoff voltage was 3.0V, and the discharging cutoff voltage was 1.5V. The charging and discharging currents were set to 0.1C, 0.2C, 0.5C, and 1C. Figure 6 Figure c shows the charge-discharge curves of the solid-state lithium-sulfur battery prepared according to Comparative Example 4 at 50°C and 0.1C, 0.2C, 0.5C, and 1C, with electrochemical capacities of 620.9 mAh / g, 466.9 mAh / g, 238.6 mAh / g, and 206.5 mAh / g, respectively. Therefore, the actual capacity of the PEO-based solid-state lithium-sulfur battery is lower than that of the solid-state lithium-sulfur batteries prepared in Example 2 and Comparative Example 2, and it exhibits the highest degree of polarization.

[0049] The all-solid-state batteries prepared in Example 2, Comparative Example 2, and Comparative Example 4 were subjected to long-term cycling tests at 50°C. The charging cutoff voltage was 3.0V, and the discharging cutoff voltage was 1.5V. The charge / discharge current was set to 0.2C. Figure 7 As shown, the PEO-SeS2-based solid-state lithium-sulfur battery prepared according to Example 2 exhibits good cycle stability and considerable capacity, maintaining a specific capacity of 900.9 mAh / g after 120 cycles with an average capacity decay rate of 0.19% per cycle. The PEO-HT-based solid-state lithium-sulfur battery maintained a specific capacity of 607.3 mAh / g after 120 cycles with an average capacity decay rate of 0.45% per cycle, while the PEO-based solid-state lithium-sulfur battery maintained a specific capacity of 458.9 mAh / g after 120 cycles with an average capacity decay rate of 0.39% per cycle. This demonstrates that the PEO-SeS2 polymer solid-state electrolyte can significantly improve the cycle performance of solid-state lithium-sulfur batteries.

[0050] Therefore, based on the above description, this invention provides a polymer solid-state electrolyte, its preparation method, and its applications. This effectively improves the ionic conductivity of the solid-state electrolyte, enhances the reaction kinetics of the organic sulfur cathode, and stabilizes the lithium anode. The resulting solid-state lithium-sulfur battery assembled with this polymer solid-state electrolyte exhibits high capacity utilization and good cycle performance. This is beneficial for the widespread production and application of all-solid-state batteries and has significant practical application prospects.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that the above embodiments are exemplary and should not be construed as limiting the present invention. Several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing a polymer solid-state electrolyte, characterized by, Includes the following steps: (1) Polyethylene oxide is mixed with selenium-containing substances and subjected to heat treatment to obtain a composite product; (2) Dissolve the composite product obtained in step (1) and the lithium salt in a solvent, stir and mix to obtain a mixed solution; (3) Transfer the mixed solution obtained in step (2) onto the diaphragm and dry it under vacuum to obtain the polymer solid electrolyte.

2. The method for producing a polymer solid electrolyte according to claim 1, characterized by: In step (1), the mass ratio of the polyethylene oxide to the selenium-containing substance is 100:(1-10); the molecular weight of the polyethylene oxide is 600,000 to 7,000,000; the selenium-containing substance is one or more of elemental selenium or selenium-containing compounds; the selenium-containing compounds include, but are not limited to, selenium disulfide, selenium dioxide, selenomethionine and dimethyl diselenoether.

3. The method of claim 1, wherein the method is characterized by: In step (1), the heat treatment temperature is 100-200℃ and the heat treatment time is 2-6 hours.

4. The method of claim 1, wherein the method is characterized by: In step (2), the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium hexafluorophosphate, lithium nitrate, lithium tetrafluoroborate and lithium difluorooxalate borate. The solvent is one or more of acetonitrile, chloroform and acetone; The mass of the lithium salt is 5wt%-40wt% of the total mass of the composite product and the lithium salt; The concentration of the composite product in the mixed solution is 5wt%-20wt%.

5. The method for preparing the polymer solid electrolyte according to claim 1, characterized in that: In step (2), the mixing time is 12-48 hours.

6. The method for preparing the polymer solid electrolyte according to claim 1, characterized in that: In step (3), the mixed solution transfer process is as follows: the polyethylene diaphragm is laid flat in the polytetrafluoroethylene mold, and the mixed solution is poured evenly onto the polyethylene diaphragm; the vacuum drying temperature is 40-60℃, the vacuum drying time is 12-60 hours, the vacuum degree is ≤0.1Mpa; the polymer solid electrolyte is composed of the diaphragm and the coating formed after the mixed solution on the diaphragm is dried.

7. A polymer solid electrolyte, characterized in that: The polymer solid electrolyte is prepared by the method described in any one of claims 1-6.

8. The polymer solid electrolyte according to claim 7, characterized in that: The thickness of the polymer solid electrolyte is 50-150 μm; The thickness of the diaphragm is 5-10 μm.

9. An application of the polymer solid electrolyte according to claim 7, characterized in that: The polymer solid electrolyte is used as an electrolyte in solid lithium-sulfur batteries.

10. The application of the polymer solid electrolyte according to claim 9, characterized in that: In the solid-state lithium-sulfur battery, the positive electrode is a sulfur-based positive electrode, including but not limited to elemental sulfur and organic sulfur compounds; the organic sulfur compounds are benzoquinone-based polytetrasulfide propane, sulfurized polyacrylonitrile, sulfur-1,3-diisopropene-phenylene copolymer or tetrasulfide dipentamethylene thiuram.

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