A method for dual interface modification of lithium-sulfur battery polymer electrolyte

Abstract

The application relates to a method for double interface modification of a lithium-sulfur battery polymer electrolyte, and relates to a preparation method of a polymer electrolyte positive electrode and negative electrode side interface modification for improving the performance of a lithium-sulfur battery. The application mainly solves the problems of uneven solid-solid contact between an electrode and an electrolyte and serious side reactions between interfaces in a cycle process. The method is as follows: 1. preparation of an ultrathin carbon sheet material; 2. preparation of a single-side coating polymer electrolyte; 3. preparation of a double-side coating polymer electrolyte; and 4. assembly of a solid-state lithium-sulfur battery. The lithium-sulfur battery assembled by using the polymer electrolyte with double interface modification in the application obtains excellent electrochemical performance at room temperature, and meets the actual production application. The application is applied to the field of lithium-sulfur batteries.

Description

Technical Field

[0001] This invention relates to a method for modifying the interface between the positive and negative electrodes of a polymer electrolyte to improve the performance of lithium-sulfur batteries. Background Technology

[0002] With the widespread adoption of electric vehicles and portable electronic devices, the demand for energy storage devices with long lifespans and high energy density is growing stronger. Lithium-sulfur batteries have attracted much attention in electrochemical energy storage devices due to their high theoretical specific capacity. However, there are still many obstacles on the road to the commercialization and practical application of lithium-sulfur batteries. These obstacles mainly include: 1) volume expansion caused by complex electrochemical reaction processes, which shortens electrode life; 2) poor conductivity of active sulfur and its reaction products, resulting in large electrochemical polarization; and 3) severe shuttle effect, which reduces the utilization rate of sulfur.

[0003] Therefore, from both a safety and energy density perspective, developing polymer electrolytes to prepare lithium-sulfur batteries represents the ultimate form of lithium-sulfur batteries. While polymer electrolytes can fundamentally solve the shuttle effect problem, the polymer matrix exhibits some compatibility with polysulfides during charge and discharge. Furthermore, during cycling, the uneven solid-solid contact between the lithium metal battery anode and electrolyte exacerbates dendrite growth. Simultaneously, severe interfacial side reactions make it difficult to form a stable SEI film conducive to lithium-ion migration, leading to increased polarization during cycling. Therefore, interfacial modification of the polymer electrolyte on both the positive and negative electrode sides can effectively improve the stability of the anode-electrolyte interface while providing redox reaction active sites for deactivated sulfur / lithium sulfide on the positive electrode surface. This fundamentally solves the problems existing in lithium-sulfur batteries and meets the requirements for commercial production of lithium-sulfur batteries. Summary of the Invention

[0004] This invention addresses the problems of uneven solid-solid contact between electrodes and electrolytes and severe interfacial side reactions during cycling in existing lithium-sulfur batteries by proposing a method for dual interfacial modification of polymer electrolytes in lithium-sulfur batteries.

[0005] Ultrathin carbon sheets were prepared using sodium citrate as a raw material to serve as interfacial modification layers between the polymer electrolyte and both the positive and negative electrodes. For the positive electrode-electrolyte interface, an ultrathin carbon sheet coating was prepared on the positive electrode side of the electrolyte membrane to prevent the compatibility of polysulfides with the polymer matrix. Simultaneously, the highly conductive ultrathin carbon sheet acted as a second current collector, providing redox reaction active sites for deactivated sulfur / lithium sulfide on the positive electrode surface. For the negative electrode-electrolyte interface, the ultrathin carbon sheet was blended into the polymer electrolyte slurry to prepare an interfacial layer on the negative electrode side of the electrolyte membrane. This improved the stability of the negative electrode-electrolyte interface, mitigated side reactions, induced the formation of a stable SEI film, thereby improving the compatibility of the negative electrode-electrolyte interface, and increased the uniformity of charge density distribution, thus mitigating dendrite growth. The lithium-sulfur battery assembled with the double-sided coated polymer electrolyte prepared using the above method exhibited excellent electrochemical performance at room temperature.

[0006] 1. The objective of this invention can be achieved through the following method: a method for dual interface modification of a lithium-sulfur battery polymer electrolyte, characterized in that the method for dual interface modification of a lithium-sulfur battery polymer electrolyte is carried out according to the following steps:

[0007] I. Preparation of Ultrathin Carbon Sheet Materials

[0008] Take 1-4g of sodium citrate and grind it in a mortar for 20-40 minutes, then ball mill it in a ball mill. Transfer the powder sample to a tube furnace and anneal it in a nitrogen atmosphere to obtain black carbon powder. Then, soak the obtained black carbon powder in hydrochloric acid solution and ultrasonically clean it until there are no bubbles. Let it stand for 10-14 hours. Then, wash it repeatedly with deionized water and anhydrous ethanol until the filtrate is neutral. Finally, transfer the black carbon powder to a vacuum drying oven and dry it at 40-80℃ for 12-24 hours to obtain ultrathin carbon sheet material.

[0009] II. Preparation of Single-sided Coated Polymer Electrolytes

[0010] Ultrathin carbon sheet material, polyvinylidene fluoride, and lithium bis(trifluoromethanesulfonyl)imide were uniformly dispersed in N-methylpyrrolidone and stirred at room temperature for 12 hours. The mixture was then uniformly coated onto aluminum foil and vacuum dried at 100–300°C for 1–3 hours to obtain an ultrathin carbon sheet material coating. Subsequently, a polymer electrolyte slurry was cast onto the coating surface and dried in a vacuum drying oven for 1–3 hours to obtain a single-sided coated polymer electrolyte with interface modification of the ultrathin carbon sheet material.

[0011] III. Preparation of Double-sided Coated Polymer Electrolytes

[0012] Take 0.2-0.6g of polyvinylidene fluoride-hexafluoropropylene and 0.06-0.08g of polyethylene oxide-polypropylene oxide-polyethylene oxide and dissolve them in 2-5mL of N,N-dimethylformamide. Stir at room temperature for 10-12h, add 0.2-0.6g of lithium trifluoromethanesulfonylimide and continue stirring to obtain a uniform slurry. Add ultrathin carbon sheet material and continue stirring for 4-8h to obtain an interface layer precursor slurry. Coat the interface layer slurry onto a clean glass plate and vacuum dry at 100-300℃ for 1-3h to obtain a new interface layer. Cover this interface layer with the single-sided coated polymer electrolyte membrane prepared in step two, with the polymer electrolyte directly contacting the new interface layer. Vacuum dry at 100-300℃ for 1-3h to obtain a double-sided coated polymer electrolyte with dual interface modification.

[0013] IV. Assembly of Solid-State Lithium-Sulfur Batteries

[0014] Lithium-sulfur cathode material, acetylene black, and binder are mixed and stirred at room temperature for 10–14 h to obtain a black slurry. The black slurry is coated onto aluminum foil and vacuum dried at 40–80 °C for 12–24 h to obtain a cathode sheet for later use. No organic electrolyte is added during the assembly of the coin-type lithium-sulfur battery. The battery is assembled in a glove box filled with argon gas, where the water and oxygen contents are both less than 0.1 ppm. One side of the ultrathin carbon sheet material layer is brought into contact with the cathode. The assembly sequence is as follows: 2025 coin-type battery cathode shell, lithium-sulfur battery cathode sheet, 1–4 μL ionic liquid, the prepared polymer electrolyte with double interface modification and double-sided coating, lithium sheet, gasket, spring sheet, and 2025 coin-type battery anode shell are assembled in that order. The coin-type battery is then sealed with a sealing machine to complete the battery assembly and obtain a lithium-sulfur battery.

[0015] Furthermore, the ball milling time in the ball mill described in step one is 10 to 12 hours.

[0016] Furthermore, the annealing time for transferring the powder sample to a tube furnace in a nitrogen atmosphere as described in step one is 1 to 3 hours.

[0017] Furthermore, in step one, the powder sample is transferred to a tube furnace and annealed in a nitrogen atmosphere at a temperature of 650–750°C.

[0018] Furthermore, the concentration of the hydrochloric acid solution used to soak the black toner in step one is 10% to 30%.

[0019] Furthermore, the ultrathin carbon sheet material, polyvinylidene fluoride, and lithium trifluoromethanesulfonylimide mentioned in step two are in a mass ratio of (6-10):1:1.

[0020] Furthermore, in step two, after casting the polymer electrolyte slurry onto the coating surface, the drying temperature in the vacuum drying oven is 100–300°C.

[0021] Furthermore, the mass of the ultrathin carbon sheet material added in step three is 0.1 to 0.3 g.

[0022] Furthermore, the mass ratio of the lithium-sulfur cathode composite material, acetylene black, and binder in step four is 5:2:(2-6).

[0023] Furthermore, the ionic liquid mentioned in step four is 1-butyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide.

[0024] The gain effect of the present invention:

[0025] First, this invention uses sodium citrate as a raw material and synthesizes an ultrathin carbon sheet material by annealing in a tube furnace and controlling different annealing times and temperatures. Under the action of surface free energy, the ultrathin carbon sheet material undergoes a certain degree of bending. The sodium citrate material undergoes a three-stage decomposition process in the tube furnace: sodium citrate decomposes at 230–260°C, and carbonization occurs when the temperature rises to 380–500°C, with the main component being C@Na2CO3. As the temperature continues to rise, the structure of C@Na2CO3 is partially destroyed, which is attributed to the activation and decomposition of Na2CO3 (Carbon., 2017, 111:419e427). The inorganic products formed in this process are easily removed after acid washing, and a microporous structure is formed on the carbon sheet surface during acid washing, and the porosity can play a certain adsorption role. At the positive electrode-electrolyte interface, the ultrathin carbon sheet coating material, acting as a second current collector, provides a uniform reaction environment between the positive electrode and the coating interface. Higher conductivity facilitates carrier transfer at the electrode-electrolyte interface, and faster reaction kinetics help reduce interfacial impedance and improve battery performance (J. Mater. Chem. A., 2019, 7: 13679-1368). It provides redox reaction active sites for deactivated sulfur / lithium sulfide on the cathode surface; the thickness of the ultrathin carbon sheet has a certain influence on the migration ability of lithium ions, with thinner carbon sheets being more conducive to lithium ion migration.

[0026] For the negative electrode-electrolyte interface, blending ultrathin carbon sheet material into the polymer electrolyte slurry to prepare an interfacial layer on the negative electrode side of the electrolyte membrane can induce the formation of a stable SEI film, thereby improving the compatibility of the negative electrode-electrolyte interface. The interaction between the ultrathin carbon sheet material and the polymer electrolyte promotes the formation of SEIs containing Li3N, Li2CO3, and LiF. LiN(SO2CF3)2+ne - +nLi + →LiF + Li3N + Li2S2O4 + C2F X Li y(J. Phys. Chem. C., 2018, 122(18):9835-9834).

[0027] Secondly, compared to graphite coatings, ultrathin carbon sheet coatings maintain a uniformly dispersed stacking. This morphology, while suppressing the compatibility of polysulfides with the polymer matrix, does not hinder lithium-ion migration during charging and discharging. In contrast, graphite coatings exhibit large agglomerates and numerous cracks; these large agglomerates severely impede lithium-ion migration during charging and discharging. Furthermore, compared to graphite coatings, ultrathin carbon sheet coatings, due to their smaller size and extremely thinness, are advantageous in reducing the energy barrier that lithium-ion transitions must overcome.

[0028] Finally, in this invention, lithium-sulfur cathode composite material, conductive agent acetylene black, and binder are mixed in a mass ratio of 5:2:3 and stirred at room temperature for 12 hours to obtain a black slurry. The black slurry is coated onto clean aluminum foil and vacuum dried at 60°C for 24 hours to obtain a cathode sheet. The battery is assembled in an argon-filled glove box with H2O and O2 contents both less than 0.1 ppm. The side modified with an ultrathin carbon layer is brought into contact with the cathode. The assembly sequence is as follows: 2025 coin cell cathode shell, lithium-sulfur battery cathode sheet, 2 μL ionic liquid, the prepared polymer electrolyte membrane with dual interface modification, lithium sheet, gasket, spring sheet, and 2025 coin cell anode shell are assembled in that order to form a coin cell. After sealing with a sealing machine, the battery assembly is complete, resulting in a solid-state lithium-sulfur battery. The preparation process of this invention is safe, the battery performance is excellent, and it is suitable for large-scale commercial production. Attached Figure Description

[0029] To more clearly illustrate the modification results of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. The ultrathin carbon sheet is named UCS; the polymer electrolyte (LNPP) with interface modification on the positive electrode side of the ultrathin carbon sheet is named UCS-LNPP; the polymer electrolyte with interface modification on the commercial graphite side is named Graphite-LNPP; the polymer electrolyte with interface modification on the negative electrode side is named CPE / UCS; and the polymer electrolyte with dual interface modification is named UCS-LNPP-CPE / UCS. Ultrathin carbon sheets with different carbonization temperatures are named UCS-600, UCS-700, and UCS-800, respectively.

[0030] Figure 1 This is a SEM image of UCS-600 in Comparative Example 1 of the present invention;

[0031] Figure 2 This is a SEM image of the UCS-700 in Embodiment 1 of the present invention;

[0032] Figure 3 Here is a SEM image of UCS-800 in Comparative Example 2 of this invention;

[0033] Figure 4 (a) TEM image of UCS-600 and (b) thickness of UCS-600 material in Comparative Example 1 of the present invention;

[0034] Figure 5 (a) TEM image of UCS-700 and (b) thickness of UCS-700 material in Embodiment 1 of the present invention;

[0035] Figure 6 (a) TEM image of UCS-800 and (b) thickness of UCS-800 material in Comparative Example 2 of the present invention;

[0036] Figure 7 The XRD patterns of UCS materials at different carbonization temperatures according to the present invention are shown below.

[0037] Figure 8 This is a planar SEM image of the UCS-LNPP polymer electrolyte in Example 1 of the present invention;

[0038] Figure 9 This is a cross-sectional SEM image of the UCS-LNPP polymer electrolyte in Example 1 of the present invention;

[0039] Figure 10 This is a planar SEM image of the Graphite-LNPP polymer electrolyte in Comparative Example 3 of the present invention;

[0040] Figure 11 This is a cross-sectional SEM image of the Graphite-LNPP polymer electrolyte in Comparative Example 3 of this invention;

[0041] Figure 12 The curves showing the change in ionic conductivity of UCS-LNPP and Graphite-LNPP polymer electrolytes with temperature in Example 1 and Comparative Example 3 of this invention;

[0042] Figure 13 The lithium-ion transference number of the UCS-LNPP polymer electrolyte in Example 1 of this invention;

[0043] Figure 14 This refers to the lithium-ion transference number of the Graphite-LNPP polymer electrolyte in Comparative Example 3 of this invention;

[0044] Figure 15 The constant current polarization curves of Graphite-LNPP and UCS-LNPP in Comparative Example 3 and Example 1 of this invention are shown.

[0045] Figure 16 The charge-discharge curves of the lithium-sulfur batteries assembled with polymer electrolytes in Example 1 and Comparative Example 3 of this invention are shown at room temperature.

[0046] Figure 17 XPS of the S element at the negative electrode-electrolyte interface after cycling of the UCS-LNPP polymer electrolyte in Example 1 of this invention;

[0047] Figure 18 The following are cross-sectional SEM images and surface distribution diagrams of different elements of the UCS-LNPP-CPE / UCS polymer electrolyte in Example 1 of this invention: (a) C element; (c) O element; (d) S element; (e) F element;

[0048] Figure 19 The lithium-ion transference number of the UCS-LNPP-CPE / UCS polymer electrolyte in Example 1 of this invention;

[0049] Figure 20 Constant current polarization test of UCS-LNPP and UCS-LNPP-CPE / UCS in Embodiment 1 of the present invention;

[0050] Figure 21 The charge-discharge curves of the lithium-sulfur battery before and after dual interface modification in Example 1 of the present invention are shown.

[0051] Figure 22 The rate performance curves of the lithium-sulfur battery before and after dual interface modification in Example 1 of the present invention are shown.

[0052] Figure 23 XPS spectra of the negative electrode-electrolyte interface after cycling in the UCS-LNPP-CPE / UCS lithium-sulfur battery of Example 1 of the present invention: (a) N 1s; (b) C 1s; (c) F 1s;

[0053] Figure 24 This is a SEM image of dendrite growth on the surface of the lithium anode after cycling in the UCS-LNPP lithium-sulfur battery of Example 1 of the present invention.

[0054] Figure 25 This is a SEM image of dendrite growth on the surface of the lithium anode after cycling in Example 1 of the present invention, using the UCS-LNPP-CPE / UCS lithium-sulfur battery.

[0055] Figure 26 This is a schematic diagram of the dual interface modification mechanism of the lithium-sulfur battery of the present invention. Detailed Implementation

[0056] The following embodiments further illustrate the above-described 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-described content of the present invention fall within the scope of the present invention. The table below shows the experimental reagents and equipment.

[0057] Experimental drugs

[0058]

[0059]

[0060] Experimental equipment

[0061]

[0062] Specific Implementation Method 1: This implementation method describes a method for preparing a dual-interface modification of a polymer electrolyte for lithium-sulfur batteries, which is carried out according to the following steps:

[0063] I. Preparation of Ultrathin Carbon Sheet Materials

[0064] Take 1-4g of sodium citrate and grind it in a mortar for 20-40 minutes, then ball mill it in a ball mill. Transfer the powder sample to a tube furnace and anneal it in a nitrogen atmosphere to obtain black carbon powder. Then, soak the obtained black carbon powder in hydrochloric acid solution and ultrasonically clean it until there are no bubbles. Let it stand for 10-14 hours. Then, wash it repeatedly with deionized water and anhydrous ethanol until the filtrate is neutral. Finally, transfer the black carbon powder to a vacuum drying oven and dry it at 40-80℃ for 12-24 hours to obtain ultrathin carbon sheet material.

[0065] II. Preparation of Single-sided Coated Polymer Electrolytes

[0066] Ultrathin carbon sheet material, polyvinylidene fluoride, and lithium bis(trifluoromethanesulfonyl)imide were uniformly dispersed in N-methylpyrrolidone and stirred at room temperature for 12 hours. The mixture was then uniformly coated onto aluminum foil and vacuum dried at 100–300°C for 1–3 hours to obtain an ultrathin carbon sheet material coating. Subsequently, a polymer electrolyte slurry was cast onto the coating surface and dried in a vacuum drying oven for 1–3 hours to obtain a single-sided coated polymer electrolyte with interface modification of the ultrathin carbon sheet material.

[0067] III. Preparation of Double-sided Coated Polymer Electrolytes

[0068] Take 0.2-0.6g of polyvinylidene fluoride-hexafluoropropylene and 0.06-0.08g of polyethylene oxide-polypropylene oxide-polyethylene oxide and dissolve them in 2-5mL of N,N-dimethylformamide. Stir at room temperature for 10-12h, add 0.2-0.6g of lithium trifluoromethanesulfonylimide and continue stirring to obtain a uniform slurry. Add ultrathin carbon sheet material and continue stirring for 4-8h to obtain an interface layer precursor slurry. Coat the interface layer slurry onto a clean glass plate and vacuum dry at 100-300℃ for 1-3h to obtain a new interface layer. Cover this interface layer with the single-sided coated polymer electrolyte membrane prepared in step two, with the polymer electrolyte directly contacting the new interface layer. Vacuum dry at 100-300℃ for 1-3h to obtain a double-sided coated polymer electrolyte with dual interface modification.

[0069] IV. Assembly of Solid-State Lithium-Sulfur Batteries

[0070] Lithium-sulfur cathode material, acetylene black, and binder are mixed and stirred at room temperature for 10–14 h to obtain a black slurry. The black slurry is coated onto aluminum foil and vacuum dried at 40–80 °C for 12–24 h to obtain a cathode sheet for later use. No organic electrolyte is added during the assembly of the coin-type lithium-sulfur battery. The battery is assembled in a glove box filled with argon gas, where the water and oxygen contents are both less than 0.1 ppm. One side of the ultrathin carbon sheet material layer is brought into contact with the cathode. The assembly sequence is as follows: 2025 coin-type battery cathode shell, lithium-sulfur battery cathode sheet, 1–4 μL ionic liquid, the prepared polymer electrolyte with double interface modification and double-sided coating, lithium sheet, gasket, spring sheet, and 2025 coin-type battery anode shell are assembled in that order. The coin-type battery is then sealed with a sealing machine to complete the battery assembly and obtain a lithium-sulfur battery.

[0071] First, this invention uses sodium citrate as a raw material and synthesizes an ultrathin carbon sheet material by annealing in a tube furnace and controlling different annealing times and temperatures. Under the action of surface free energy, the ultrathin carbon sheet material undergoes a certain degree of bending. The sodium citrate material undergoes a three-stage decomposition process in the tube furnace: sodium citrate decomposes at 230–260°C, and carbonization occurs when the temperature rises to 380–500°C, with the main component being C@Na2CO3. As the temperature continues to rise, the structure of C@Na2CO3 is partially destroyed, attributed to the activation and decomposition of Na2CO3. The inorganic products formed during this process are easily removed after acid washing, and a microporous structure is formed on the carbon sheet surface during acid washing, which can play a certain adsorption role. At the positive electrode-electrolyte interface, the ultrathin carbon sheet coating material, acting as a second current collector, provides a uniform reaction environment between the positive electrode and the coating interface. The stronger the conductivity, the more favorable it is for the transfer of charge carriers between the electrode and electrolyte interface; faster reaction kinetics help reduce interfacial impedance and improve battery performance. It provides redox reaction active sites for deactivated sulfur / lithium sulfide on the cathode surface; the thickness of the ultrathin carbon sheet has a certain influence on the migration ability of lithium ions, and a thin carbon sheet is conducive to the migration of lithium ions.

[0072] For the negative electrode-electrolyte interface, blending ultrathin carbon sheet material into the polymer electrolyte slurry to prepare an interfacial layer on the negative electrode side of the electrolyte membrane can induce the formation of a stable SEI film, thereby improving the compatibility of the negative electrode-electrolyte interface. The interaction between the ultrathin carbon sheet material and the polymer electrolyte promotes the formation of SEIs containing Li3N, Li2CO3, and LiF. LiN(SO2CF3)2+ne - +nLi + →LiF + Li3N + Li2S2O4 + C2F X Li y .

[0073] Secondly, compared to graphite coatings, ultrathin carbon sheet coatings maintain a uniformly dispersed stacking. This morphology, while suppressing the compatibility of polysulfides with the polymer matrix, does not hinder lithium-ion migration during charging and discharging. In contrast, graphite coatings exhibit large agglomerates and numerous cracks; these large agglomerates severely impede lithium-ion migration during charging and discharging. Furthermore, compared to graphite coatings, ultrathin carbon sheet coatings, due to their smaller size and extremely thinness, are advantageous in reducing the energy barrier that lithium-ion transitions must overcome.

[0074] Finally, in this invention, lithium-sulfur cathode composite material, conductive agent acetylene black, and binder are mixed in a mass ratio of 5:2:3 and stirred at room temperature for 12 hours to obtain a black slurry. The black slurry is coated onto clean aluminum foil and vacuum dried at 60°C for 24 hours to obtain a cathode sheet. The battery is assembled in an argon-filled glove box with H2O and O2 contents both less than 0.1 ppm. The side modified with an ultrathin carbon layer is brought into contact with the cathode. The assembly sequence is as follows: 2025 coin cell cathode shell, lithium-sulfur battery cathode sheet, 2 μL ionic liquid, the prepared polymer electrolyte membrane with dual interface modification, lithium sheet, gasket, spring sheet, and 2025 coin cell anode shell are assembled in that order to form a coin cell. After sealing with a sealing machine, the battery assembly is complete, resulting in a solid-state lithium-sulfur battery. The preparation process of this invention is safe, the battery performance is excellent, and it is suitable for large-scale commercial production.

[0075] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the ball milling time in step one is 10-12 hours. Everything else is the same as in Specific Implementation Method One.

[0076] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the annealing time for transferring the powder sample to a tube furnace in a nitrogen atmosphere in step one is 1–3 hours. Everything else is the same as in Specific Implementation Method One or Two.

[0077] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the annealing temperature in step one, where the powder sample is transferred to a tube furnace and annealed in a nitrogen atmosphere, is 650–750°C. Everything else is the same as in Specific Implementation Methods One to Three.

[0078] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the concentration of the hydrochloric acid solution used to soak the black toner in step one is 10% to 30%. Everything else is the same as in Specific Implementation Methods One to Four.

[0079] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the ultrathin carbon sheet material, polyvinylidene fluoride, and lithium trifluoromethanesulfonylimide described in step two are in a mass ratio of (6-10):1:1. Everything else is the same as in Specific Implementation Methods One to Five.

[0080] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: after casting the polymer electrolyte slurry onto the coating surface in step two, the drying temperature in a vacuum drying oven is 100–300°C. Everything else is the same as in Specific Implementation Methods One to Six.

[0081] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the mass of the ultrathin carbon sheet added in step three is 0.1–0.3 g. Everything else is the same as in Specific Implementation Methods One to Seven.

[0082] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the mass ratio of the lithium-sulfur cathode composite material, acetylene black, and binder in step four is 5:2:(2-6). Everything else is the same as in Specific Implementation Methods One to Eight.

[0083] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the ionic liquid described in step four is 1-butyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide. Everything else is the same as in Specific Implementation Methods One to Nine.

[0084] Example 1

[0085] The beneficial effects of the present invention were verified through the following experiments:

[0086] The method for dual interface modification of polymer electrolytes for lithium-sulfur batteries in this experiment is carried out according to the following steps:

[0087] I. Preparation of Ultrathin Carbon Sheet Materials

[0088] 2g of sodium citrate was ground in a mortar for 30 minutes, then ball-milled for 12 hours. The powder sample was transferred to a tube furnace and annealed in a nitrogen atmosphere for 3 hours at 700℃ to obtain black carbon powder. The black carbon powder was then immersed in a 10% hydrochloric acid solution and ultrasonically cleaned until no bubbles were present. It was then allowed to stand for 12 hours. The powder was repeatedly washed with deionized water and anhydrous ethanol until the filtrate was neutral. Finally, the black carbon powder was transferred to a vacuum drying oven and dried at 60℃ for 24 hours to obtain ultrathin carbon sheets.

[0089] II. Preparation of Single-sided Coated Polymer Electrolytes

[0090] Ultrathin carbon sheet material, polyvinylidene fluoride, and lithium bis(trifluoromethanesulfonyl)imide were uniformly dispersed in N-methylpyrrolidone at a mass ratio of 8:1:1 and stirred at room temperature for 12 hours. The mixture was then uniformly coated onto aluminum foil and vacuum dried at 100°C for 2 hours to obtain an ultrathin carbon sheet coating. Subsequently, a polymer electrolyte slurry was cast onto the coating surface and dried in a vacuum drying oven at 100°C for 2 hours to obtain a single-sided coated polymer electrolyte with ultrathin carbon sheet interface modification.

[0091] III. Preparation of Double-sided Coated Polymer Electrolytes

[0092] 0.4 g of polyvinylidene fluoride-hexafluoropropylene and 0.08 g of polyethylene oxide-polypropylene oxide-polyethylene oxide were dissolved in 3 mL of N,N-dimethylformamide and stirred at room temperature for 12 h. 0.4 g of lithium trifluoromethanesulfonylimide was added and stirring was continued to obtain a uniform slurry. 0.2 g of ultrathin carbon sheet was added and stirring was continued for 6 h to obtain an interface layer precursor slurry. The interface layer slurry was coated onto a clean glass plate and vacuum dried at 100 °C for 2 h to obtain a new interface layer. The single-sided coated polymer electrolyte membrane prepared in step two was covered on this interface layer and vacuum dried at 100 °C for 1 h to obtain a double-interface modified polymer electrolyte.

[0093] IV. Assembly of Solid-State Lithium-Sulfur Batteries

[0094] Lithium-sulfur cathode material, acetylene black, and binder were mixed in a certain mass ratio and stirred at room temperature for 12 hours to obtain a black slurry. The black slurry was coated onto aluminum foil and vacuum dried at 60°C for 24 hours to obtain a cathode sheet for later use. No organic electrolyte was added during the assembly of the coin-type lithium-sulfur battery. The battery was assembled in a glove box filled with argon gas, where the water and oxygen contents were both less than 0.1 ppm. The side modified with the ultrathin carbon sheet layer was brought into contact with the cathode. The assembly sequence was as follows: 2025 coin-type battery cathode shell, lithium-sulfur battery cathode sheet, 2 μL ionic liquid, the prepared polymer electrolyte membrane with dual interface modification, lithium sheet, gasket, spring sheet, and 2025 coin-type battery anode shell. The coin-type battery was then sealed with a sealing machine to complete the battery assembly and obtain the lithium-sulfur battery.

[0095] Comparative Example 1

[0096] The difference between this comparative example and Example 1 is that the annealing time in step one is 600°C, while the other steps are the same as in Example 1, resulting in an ultrathin carbon sheet annealed at 600°C.

[0097] Comparative Example 2

[0098] The difference between this comparative example and Example 1 is that the annealing time in step one is 800°C, while the other steps are the same as in Example 1, resulting in an ultrathin carbon sheet annealed at 800°C.

[0099] Comparative Example 3

[0100] The difference between this comparative example and Example 1 is that the same method was used, but the ultrathin carbon sheet was replaced with commercial graphite. The other steps were the same as in Example 1 to obtain a single-sided coated polymer electrolyte with commercial graphite interface modification.

[0101] Performance characterization was performed on the above comparative examples and embodiments.

[0102] 1) X-ray diffraction analysis (XRD). The phase composition of the material was determined using XRD. This paper uses the X'Pert PRO measuring instrument from Malvern Panaco GmbH, Netherlands, with a scanning range of 10-90° and a scanning speed of 5°·min. -1 Sample preparation: Place the powder sample or thin film sample evenly in the groove of the glass slide, and then insert the glass slide into the retaining seat of the XRD tester.

[0103] 2) Scanning Electron Microscopy (SEM). SEM was used to observe the morphology of the cathode material, electrolyte membrane, and cycled lithium sheet. A FEI Sirion 200 scanning electron microscope (SEM) was used, with an accelerating voltage of 0.2–30 kV and a resolution of 20 kV. Sample preparation: Dried powder samples, thin film samples, or lithium sheet samples were adhered to an aluminum sample holder using conductive adhesive. Gold was then sprayed onto the sample, and the samples were tested. Each gold spraying session lasted 10 seconds, with a 60-second interval, for a total of 10 sprayings.

[0104] 3) X-ray photoelectron spectroscopy (XPS). XPS was used to analyze the elemental composition and valence state of the samples. A Thermo Scientific ESCALAB 250Xi instrument was used for the tests. The results were charge-corrected to the C1s standard peak of 285.0 eV and fitted using XPSPEAK41. Sample preparation: The powder samples and polymer electrolyte membranes were dried before testing.

[0105] 4) Constant Current Charge-Discharge Test. The assembled batteries were tested using the Blue Battery Testing System (CT2001A) and the Newwell Battery Testing System (CT4008T). The constant current charge-discharge test involves charging and discharging the assembled batteries under a constant current and a specific voltage range. Simultaneously, multiple parameters are recorded and analyzed, including current, voltage, time, capacity, rate performance, voltage plateau, coulombic efficiency, and differential capacity curves. Specific capacity is measured in mAh·g. -1 .

[0106] Figure 1 This is a SEM image of the UCS-600 in Comparative Example 1 of this invention. Figure 1It can be seen that UCS-600 has an ultrathin carbon sheet stacked structure. The sheet structure is beneficial to improve conductivity and facilitates the transfer of charge carriers between the electrode and electrolyte interface. The faster reaction kinetics are beneficial to reduce interfacial impedance.

[0107] Figure 2 This is a SEM image of the UCS-700 in Embodiment 1 of the present invention. Figure 2 It is known that UCS-700 has an ultrathin carbon sheet stacked structure. By comparison, UCS-700 material has the thinnest thickness. The extremely thin thickness of UCS is conducive to lithium ion migration, and the smaller size can increase the contact between the electrode and electrolyte interface, forming a second current collector and providing reaction sites for deactivated sulfur / lithium sulfide on the positive electrode surface.

[0108] Figure 3 This is a SEM image of the UCS-800 in Comparative Example 2 of this invention. Figure 3 It can be seen that UCS-800 has an ultra-thin carbon sheet stacking structure.

[0109] Figure 4 The images show (a) a TEM image of UCS-600 and (b) the thickness of the UCS-600 material in Comparative Example 1 of this invention. Figure 4 As can be seen, the test results are consistent with those of SEM. In Figure (a), the ultrathin carbon sheet exhibits a rolled-up and stacked morphology. In Figure (b), the thickness of UCS-600 is 9.65 nm.

[0110] Figure 5 The images show (a) a TEM image of UCS-700 and (b) the thickness of the UCS-700 material in Embodiment 1 of the present invention. Figure 5 As can be seen, the test results are consistent with SEM. In Figure (a), the ultrathin carbon sheet exhibits a rolled-up and stacked morphology. In Figure (b), the thickness of UCS-700 is 5.02 nm.

[0111] Figure 6 The images show (a) a TEM image of UCS-800 and (b) the thickness of the UCS-800 material in Comparative Example 2 of this invention. Figure 6 As can be seen, the test results in Figure (a) are consistent with those in SEM, and the ultrathin carbon sheet exhibits a rolled-up and stacked morphology. The thickness of UCS-800 in Figure (b) is 5.75 nm.

[0112] Figure 7 The images show the XRD patterns of the UCS materials at different carbonization temperatures according to this invention. Figure 7As shown, at a carbonization temperature of 600℃, the peak intensity of the "bun" peak located at 21°–25° is relatively weak, while at carbonization temperatures of 700℃ and 800℃, the peak intensity is closer. The higher the degree of graphitization, the better the conductivity of the material, and the better it provides an electron transfer channel for surface sulfur / lithium sulfide as a secondary current collector. Based on the XRD test results and the material thickness, the optimal carbonization temperature is 700℃.

[0113] Figure 8 This is a planar SEM image of the UCS-LNPP polymer electrolyte in Example 1 of the present invention. Figure 8 As shown, UCS-LNPP maintains a uniformly dispersed stacking. This morphology, while inhibiting the compatibility of polysulfides with the polymer matrix, does not hinder the migration of lithium ions during charging and discharging.

[0114] Figure 9 This is a cross-sectional SEM image of the UCS-LNPP polymer electrolyte in Example 1 of the present invention. Figure 9 As shown in the cross-sectional SEM image of UCS-LNPP, the coating thickness is approximately 4.35–4.96 μm. Corresponding to the planar SEM results, UCS-LNPP exhibits a uniformly dispersed densely packed morphology.

[0115] Figure 10 This is a planar SEM image of the Graphite-LNPP polymer electrolyte in Comparative Example 3 of this invention. Figure 10 As shown, the graphite coating of the Graphite-LNPP film exhibits large agglomerates and numerous cracks. Such large agglomerates severely hinder lithium-ion migration during charging and discharging.

[0116] Figure 11 This is a cross-sectional SEM image of the Graphite-LNPP polymer electrolyte in Comparative Example 3 of this invention. Figure 11 As shown, the cross-section of the Graphite-LNPP membrane exhibits a scattered and loose mass accumulation, with a thickness of approximately 8.26–9.35 μm.

[0117] Figure 12 The figures show the curves of ionic conductivity versus temperature for the UCS-LNPP and Graphite-LNPP polymer electrolytes in Example 1 and Comparative Example 3 of this invention. Figure 12 As shown in the figure, the ionic conductivity of two polymer electrolytes was tested at 25℃, 45℃, 65℃, 85℃, and 105℃. The figure shows that the ionic conductivity of both polymer electrolytes increases with increasing temperature, exhibiting a linear relationship overall. The conductivity follows the Arrhenius equation. Calculations yielded that the intrinsic activation energies of the polymer electrolytes are Ea = 33.92 kJ·mol⁻¹. -1 Ea = 43.37 kJ·mol -1Compared to graphite coatings, UCS coatings, due to their smaller size and extremely thinner thickness, help to lower the energy barrier that lithium ions need to overcome for transitions, thus facilitating lithium ion migration.

[0118] Figure 13 This refers to the lithium-ion transference number of the UCS-LNPP polymer electrolyte in Example 1 of this invention. Figure 13 As shown, the lithium-ion transference number of the UCS-LNPP polymer electrolyte is calculated to be 0.36.

[0119] Figure 14 This represents the lithium-ion transference number of the Graphite-LNPP polymer electrolyte in Comparative Example 3 of this invention. For example... Figure 14 As shown, the lithium-ion transference number of the Graphite-LNPP polymer electrolyte is calculated to be 0.11.

[0120] Figure 15 The constant current polarization curves of Graphite-LNPP and UCS-LNPP in Comparative Example 3 and Example 1 of this invention are shown. Figure 15 As shown, after adding the graphite coating, Graphite-LNPP exhibits a large polarization voltage. This is because the graphite coating severely hinders the transport of lithium ions at the electrode-electrolyte interface. The transition process requires overcoming an extremely high energy barrier, preventing lithium ions from combining with electrons in a timely manner. This results in a large accumulation of electrons at the electrode interface, leading to significant polarization. In contrast, for UCS-LNPP, the polarization voltage is stable at approximately 0.03V, consistent with the aforementioned activation energy and transference number test results.

[0121] Figure 16 The figures show the charge-discharge curves of the lithium-sulfur batteries assembled with polymer electrolytes in Example 1 and Comparative Example 3 of this invention at room temperature. Figure 16 The charge-discharge curves of the assembled lithium-sulfur battery at 0.1C are shown. The initial discharge specific capacity of the Graphite-LNPP battery is 815.2 mAh·g. -1 The initial discharge specific capacity of the UCS-LNPP battery is 1166.2 mAh·g. -1 .

[0122] Figure 17 XPS analysis of sulfur (S) at the negative electrode-electrolyte interface after cycling of the UCS-LNPP polymer electrolyte in Example 1 of this invention. Peak separation analysis of the S 2p orbital was performed. The double peaks located around 170 eV and 169 eV represent TFSI. - The peaks at 165.55 eV and 164.37 eV (Δ = 1.18 eV) produced by S in the anion are attributed to S. bridgingThe peaks at 2p1 / 2 and 2p3 / 2, 164.83 eV and 163.65 eV (Δ = 1.18 eV), are assigned to S. terminal The 2p 1 / 2 and 2p 3 / 2 pF values ​​were observed. XPS values ​​at the negative electrode-electrolyte interface of the UCS-LNPP lithium-sulfur battery after cycling were also observed. After adding the coating to modify the electrolyte, the shuttle effect was completely prevented; therefore, no characteristic peaks of polysulfides were observed at the negative electrode-electrolyte interface after cycling. The UCS coating does not hinder lithium-ion migration at the electrode-electrolyte interface, making it more suitable for interface modification of the positive electrode-electrolyte in solid-state lithium-sulfur batteries.

[0123] Figure 18 The images show the cross-sectional SEM image and surface distribution diagram of different elements of the UCS-LNPP-CPE / UCS polymer electrolyte in Example 1 of this invention: (a) C element; (c) O element; (d) S element; (e) F element. Figure 18 As shown, the UCS coating, serving as a polysulfide barrier layer, and the CPE / UCS coating, serving as a stable lithium anode interface, are located on both sides of the membrane, forming a sandwich-structured polymer electrolyte. Figures (b), (c), (d), and (e) show the surface distribution diagrams of C, O, S, and F elements, respectively. The elemental distributions indicate that the UCS coating and the CPE / UCS coating are densely and uniformly distributed on both sides of the polymer electrolyte.

[0124] Figure 19 This refers to the lithium-ion transference number of the UCS-LNPP-CPE / UCS polymer electrolyte in Example 1 of this invention. Figure 19 As shown, t is calculated to be... Li+ =0.57. After adding the CPE / UCS coating, lithium ion migration was improved, which is because the CPE / UCS interface layer also has good ion transfer ability.

[0125] Figure 20 This refers to the constant current polarization test of UCS-LNPP and UCS-LNPP-CPE / UCS in Embodiment 1 of the present invention. Figure 20 As shown, the constant current polarization test further illustrates the interface conditions during the deposition and stripping of lithium ions on the lithium metal surface. At room temperature, the current density is 0.1 mA·cm⁻¹. -2 The following tests were conducted. As shown in the figure, the polarization voltage was further reduced after adding the CPE / UCS interface layer. At the same time, the polarization voltage remained almost unchanged throughout the entire cycle, indicating that the CPE / UCS interface layer can effectively stabilize the lithium metal interface, suppress the side reactions between lithium metal and polymer electrolyte, and enable lithium ions to be uniformly deposited and stripped on the lithium metal anode surface, thereby reducing electrochemical polarization.

[0126] Figure 21The images show the charge-discharge curves of the lithium-sulfur battery before and after dual interface modification in Example 1 of this invention. Figure 21 As shown, Figure 21 Charge-discharge curves of a solid-state lithium-sulfur battery assembled with two polymer electrolytes at 0.2C and room temperature. The initial discharge specific capacity of the UCS-LNPP solid-state lithium-sulfur battery at 0.2C is 751.2 mAh·g. -1 After 100 cycles, the discharge specific capacity is 158.8 mAh·g. -1 The capacity retention rate was 21.03%. The UCS-LNPP-CPE / UCS solid-state lithium-sulfur battery had an initial discharge specific capacity of 1050.4 mAh·g at 0.2C. -1 After 100 cycles, the discharge specific capacity is 298.0 mAh·g. -1 The capacity retention rate reached 28.4%.

[0127] Figure 22 The figures show the rate performance curves of the lithium-sulfur battery before and after dual interface modification in Example 1 of this invention. Figure 22 As shown, at room temperature, the discharge specific capacity of the UCS-LNPP lithium-sulfur battery at 0.1C, 0.2C, and 0.5C is 966.2 mAh·g⁻¹. -1 716.8mAh·g -1 and 276.8mAh·g -1 When the current density recovered to 0.1C, the discharge specific capacity recovered to 574.0 mAh·g. -1 .

[0128] Figure 23 XPS spectra of the negative electrode-electrolyte interface after cycling in the UCS-LNPP-CPE / UCS lithium-sulfur battery of Example 1 of this invention: (a) N 1s; (b) C 1s; (c) F 1s. Figure 23 As shown in Figure (a), the XPS spectrum of the N1s interface after cycling is displayed. The peak at 399.6 eV corresponds to TFSI. -The peak at 398.6 eV represents the Li-N bond in the anion, indicating that Li3N is a component of the SEI film during cycling. It is very stable for lithium metal and is commonly used for the protection of lithium metal anodes and solid electrolytes. (b) shows the C1s binding energy. The peak at 285.0 eV represents the C-C and CH bonds, originating from the polymer electrolyte matrix material. The peaks at 287.0 eV and 288.7 eV represent the CO and C=O bonds, respectively, demonstrating that the addition of ultrathin carbon sheets increases the Li2CO3 content in the SEI film. The presence of Li2CO3 is beneficial for passivating the activity of the lithium anode and inhibiting side reactions. The peak at 293.2 eV represents the C1s binding energy of CF, corresponding to the F1s peak in Figure (c). The peak at 688.8 eV represents the TFSI. - The F1s binding energy of CF3 is shown, with the peak at 684.3 eV representing the F1s binding energy of Li-F. XPS analysis results indicate that the SEI film contains Li3N, Li2CO3, and LiF.

[0129] Figure 24 This is a SEM image of dendrite growth on the lithium anode surface after cycling in the UCS-LNPP lithium-sulfur battery of Example 1 of the present invention. Figure 24 As shown, only the solid-state battery with the UCS-LNPP interface layer exhibits relatively uniform blocky and dendritic lithium on the lithium sheet surface after cycling. This morphology means that a large number of dead lithium cannot participate in subsequent charge-discharge migration.

[0130] Therefore, the capacity decreased sharply.

[0131] Figure 25 This is a SEM image of dendrite growth on the lithium anode surface after cycling in the UCS-LNPP-CPE / UCS lithium-sulfur battery of Example 1 of the present invention. Figure 25 As is known, after adding the CPE / UCS interface layer, there is almost no dendrite growth on the lithium sheet surface. CPE / UCS has the ability to conduct both electrons and ions, which effectively enhances the uniform distribution of charge density between the interfaces, enabling lithium ions to be deposited and stripped uniformly.

[0132] Figure 26 This is a schematic diagram illustrating the dual interface modification mechanism of the lithium-sulfur battery of the present invention. Figure 26As shown, through the above characterization and research, the lithium-sulfur battery with dual interface modification achieved good electrochemical performance. For the unmodified solid electrolyte, lithium ions migrate rapidly within the electrolyte, but this does not restrict the compatibility between polysulfides and the polymer matrix. The Graphite coating restricts polysulfides but inhibits lithium ion migration. The UCS coating, however, restricts polysulfides while ensuring unimpeded lithium ion migration. For the solid electrolyte with the added CPE / UCS interface layer, the interface modification between the negative electrode and electrolyte forms a mixed ion / electron conduction intermediate layer, effectively mitigating the concentration gradient difference of lithium ions at the interface and balancing the non-uniform charge distribution to regulate the ion and electron distribution at the electrode-electrolyte interface. This results in the formation of a stable SEI film at the interface, promoting uniform lithium ion deposition / stripping and inhibiting lithium dendrite growth.

Claims

1. A method for dual interface modification of polymer electrolytes for lithium-sulfur batteries, characterized in that... A method for dual interface modification of polymer electrolytes for lithium-sulfur batteries is carried out according to the following steps: Preparation of ultrathin carbon sheet materials Take 1-4 g of sodium citrate and grind it in a mortar for 20-40 min, then ball mill it in a ball mill. Transfer the powder sample to a tube furnace and anneal it in a nitrogen atmosphere to obtain black carbon powder. Then, soak the obtained black carbon powder in hydrochloric acid solution and ultrasonically clean it until no bubbles are present. Let it stand for 10-14 h. Then, wash it repeatedly with deionized water and anhydrous ethanol until the filtrate is neutral. Finally, transfer the black carbon powder to a vacuum drying oven and dry it at 40-80 ℃ for 12-24 h to obtain ultrathin carbon sheet material. Preparation of single-sided coated polymer electrolyte Ultrathin carbon sheet material, polyvinylidene fluoride, and lithium bis(trifluoromethanesulfonyl)imide were uniformly dispersed in N-methylpyrrolidone and stirred at room temperature for 12 h. The mixture was then uniformly coated onto aluminum foil and vacuum dried at 100-300 °C for 1-3 h to obtain an ultrathin carbon sheet material coating. Subsequently, a polymer electrolyte slurry was cast onto the coating surface and dried in a vacuum drying oven for 1-3 h to obtain a single-sided coated polymer electrolyte with interface modification of the ultrathin carbon sheet material. Preparation of double-sided coated polymer electrolyte Dissolve 0.2–0.6 g of polyvinylidene fluoride-hexafluoropropylene and 0.06–0.08 g of polyethylene oxide-polypropylene oxide-polyethylene oxide in 2–5 mL of N,N-dimethylformamide and stir at room temperature for 10–12 h. Add 0.2–0.6 g of lithium bis(trifluoromethanesulfonyl)imide and continue stirring to obtain a homogeneous slurry. Add ultrathin carbon sheet material and continue stirring for 4–8 h to obtain an interface layer precursor slurry. Coat the interface layer slurry onto a clean glass plate and vacuum dry at 100–300 °C for 1–3 h to obtain a new interface layer. Cover this interface layer with the single-sided coated polymer electrolyte membrane prepared in step two, with the polymer electrolyte directly contacting the new interface layer. Vacuum dry at 100–300 °C for 1–3 h to obtain a double-sided coated polymer electrolyte with dual interface modification. Assembly of solid-state lithium-sulfur batteries Lithium-sulfur cathode material, acetylene black, and binder are mixed and stirred at room temperature for 10–14 h to obtain a black slurry. The black slurry is coated onto aluminum foil and vacuum dried at 40–80 °C for 12–24 h to obtain a cathode sheet for later use. No organic electrolyte is added during the assembly of the coin-type lithium-sulfur battery. The battery is assembled in a glove box filled with argon gas, where the water and oxygen contents are both less than 0.1 ppm. One side of the ultrathin carbon sheet material layer is brought into contact with the cathode. The assembly sequence is as follows: 2025 coin-type battery cathode shell, lithium-sulfur battery cathode sheet, 1–4 μL ionic liquid, the prepared polymer electrolyte with double interface modification and double-sided coating, lithium sheet, gasket, spring sheet, and 2025 coin-type battery anode shell are assembled in that order. The coin-type battery is then sealed with a sealing machine to complete the battery assembly and obtain the lithium-sulfur battery.

2. The method for dual interface modification of polymer electrolytes for lithium-sulfur batteries according to claim 1, characterized in that... The ball milling time in the ball mill described in step one is 10-12 hours.

3. The method for dual interface modification of polymer electrolytes for lithium-sulfur batteries according to claim 1, characterized in that... The powder sample described in step one is transferred to a tube furnace and annealed in a nitrogen atmosphere for 1 to 3 hours.

4. The method for dual interface modification of polymer electrolytes for lithium-sulfur batteries according to claim 1, characterized in that... The powder sample described in step one is transferred to a tube furnace and annealed in a nitrogen atmosphere at a temperature of 650~750 °C.

5. The method for dual interface modification of polymer electrolytes for lithium-sulfur batteries according to claim 1, characterized in that... The concentration of the hydrochloric acid solution used to soak the black toner in step one is 10% to 30%.

6. The method for dual interface modification of polymer electrolytes for lithium-sulfur batteries according to claim 1, characterized in that... The mass ratio of the ultrathin carbon sheet material, polyvinylidene fluoride, and lithium bis(trifluoromethanesulfonylimide) mentioned in step two is (6~10):1:

1.

7. The method for dual interface modification of polymer electrolytes for lithium-sulfur batteries according to claim 1, characterized in that... In step two, after casting the polymer electrolyte slurry onto the coating surface, it is dried in a vacuum drying oven at a temperature of 100~300 ℃.

8. The method for dual interface modification of polymer electrolytes for lithium-sulfur batteries according to claim 1, characterized in that... The mass of the ultrathin carbon sheet material added in step three is 0.1~0.3 g.

9. The method for dual interface modification of polymer electrolytes for lithium-sulfur batteries according to claim 1, characterized in that... The mass ratio of the lithium-sulfur cathode composite material, acetylene black, and binder mentioned in step four is 5:2:(2~6).

10. A method for dual interface modification of a lithium-sulfur battery polymer electrolyte according to claim 1, characterized in that... The ionic liquid mentioned in step four is 1-butyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide.

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