Preparation method of monolithic high-entropy MXene / carbon fiber composite difunctional interlayer and application of interlayer in lithium-sulfur battery

Abstract

The invention discloses a preparation method of a monolithic high-entropy MXene / carbon fiber composite difunctional interlayer and application of the interlayer in a lithium-sulfur battery, and belongs to the technical field of rechargeable high-specific-energy secondary batteries. The invention aims to solve the problems of slow lithium polysulfide conversion kinetics and serious lithium dendrite growth in the existing lithium-sulfur battery. The method comprises the following steps: 1, preparing a high-entropy MAX precursor; 2, preparing a single sheet type high-entropy MXene; and 3, preparing the monolithic high-entropy MXene / carbon fiber composite difunctional intermediate layer. The monolithic high-entropy MXene / carbon fiber composite difunctional intermediate layer is used as an intermediate layer in a lithium-sulfur battery and is respectively arranged between a positive electrode and a diaphragm and between a negative electrode and the diaphragm, so that electron conduction can be enhanced, polysulfide adsorption can be optimized, catalytic activity can be remarkably improved, and a high-configuration entropy generated by a solid solution structure of the intermediate layer can stabilize a material phase structure and also can improve catalytic activity. And mechanical strain can be induced to promote uniform deposition of lithium, so that the comprehensive performance of the Li-S battery is comprehensively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of rechargeable high-energy-density secondary batteries, and specifically relates to a method for preparing a monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer and its application in lithium-sulfur batteries. Background Art

[0002] Lithium-sulfur (Li-S) batteries are considered promising candidates for next-generation electrochemical energy storage systems due to their ultra-high energy density, abundant sulfur resources, and excellent cost-effectiveness. However, their commercialization remains hampered by several key challenges: poor conductivity of sulfur and lithium sulfide, shuttle effects caused by lithium polysulfide dissolution, slow sulfur conversion kinetics, and uncontrollable lithium dendrite growth on the lithium anode. These factors collectively lead to persistent capacity degradation and pose safety risks. To address these challenges, the research community has explored various approaches, including sulfur carrier design, electrolyte regulation, and separator / interlayer modification. Introducing a functionalized interlayer between the sulfur cathode / lithium anode and commercial separators has proven to be a straightforward and effective strategy. This design not only suppresses the shuttle effect of polysulfides but also regulates lithium dendrite growth. To optimize sulfur cathodes, researchers have developed a variety of interlayer materials, including carbon materials, polar compounds, single metal atoms, and conductive polymers, which immobilize polysulfides through physical confinement or chemical adsorption. However, when polar active sites are saturated with polysulfides or covered by insulating Li2S during cycling, the shuttle effect remains difficult to completely avoid. Furthermore, while materials with lithiophilic properties and high lithium ion flux have been applied to interlayers, effectively alleviating lithium volume expansion stress and completely suppressing lithium dendrite formation remain pressing challenges. Two-dimensional transition metal carbides / nitrides (MXenes) exhibit great potential for improving the performance of Li-S batteries due to their unique layered structure, high conductivity, polar surface, and lithiophilic properties. However, conventional MXene materials are limited in their adsorption capacity for long-chain polysulfides due to the insufficient spacing between polar sites composed of single metal atoms. Furthermore, the d-band center of their single metal centers often deviates from the Fermi level, resulting in insufficient catalytic activity for polysulfide conversion. These limitations have prompted researchers to strategically design MXenes at the atomic scale to comprehensively enhance their ability to suppress the shuttle effect, optimize reaction kinetics, and control lithium deposition. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems of slow lithium polysulfide conversion kinetics and severe lithium dendrite growth in existing lithium-sulfur batteries, and to provide a method for preparing a monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer and its application in lithium-sulfur batteries.

[0004] The present invention addresses the key issues of slow lithium polysulfide conversion kinetics and severe lithium dendrite growth in lithium-sulfur batteries, and proposes an innovative solution using a single high-entropy MXene / carbon fiber composite dual-functional intermediate layer. This design achieves performance breakthroughs through the synergistic effects of the following five aspects: (1) The high-entropy MXene material prepared by the present invention achieves quasi-atomic uniform doping, effectively overcoming the inherent defects of poor stability and single active site of traditional MXene; (2) The unique atomic-level relay catalytic effect of high-entropy MXene significantly improves the conversion kinetics of sulfur positive electrodes; (3) The synergistic effect of the high-entropy-MXene multi-active centers prepared by the present invention produces optimized d-band centers and ideal adsorption energy, achieving efficient capture and conversion of lithium polysulfides, simultaneously suppressing the shuttle effect and improving cycle stability; (4) The high-entropy MXene prepared by the present invention significantly reduces the Gibbs free energy barrier of the lithium polysulfide conversion process, promoting the efficient conversion of Li2S2 / Li2S; (5) The high-entropy MXene promotes the uniform distribution of electric field and lithium ion flux, guiding the uniform nucleation and deposition of lithium, while the gradient ion channels formed by its lattice distortion achieve dendrite-free lithium deposition. The monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer prepared by the present invention enables the energy density of lithium-sulfur soft-pack batteries to exceed 450Wh / kg and the cycle life to be increased by 300%, laying the foundation for commercial applications.

[0005] A method for preparing a monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer is specifically completed by the following steps: 1. Preparation of high entropy MAX precursor: ①, titanium powder, vanadium powder, niobium powder, molybdenum powder, chromium powder, tantalum powder, and tungsten powder, aluminum powder, and carbon powder were placed in a mortar and thoroughly mixed at a molar ratio of 0.6:0.6:0.6:0.6:0.6:1.2:2 to obtain a mixed powder; ②. Under an argon atmosphere, the mixed powder is heated to 1400°C~1600°C and kept warm for a period of time to obtain a reaction product; the reaction product is ground, then immersed in hydrochloric acid for washing, vacuum filtered, and the solid reaction product is vacuum dried to obtain a high-entropy MAX precursor powder; 2. Preparation of monolithic high-entropy MXene: ① Add high entropy MAX precursor powder to hydrofluoric acid, stir for a while, then repeatedly wash with deionized water until neutral, and vacuum dry to obtain multilayer MXene powder; ② Disperse the multilayer MXene powder in deionized water, add tetramethylammonium hydroxide solution, stir for a period of time for intercalation treatment, and then use deionized water as a cleaning agent to wash by multiple centrifugation until neutrality to obtain a precipitate; ③ Disperse the precipitate in deionized water, perform water bath ultrasonic treatment, and then centrifuge at a centrifugal speed of 3500 rpm to 5000 rpm to collect the supernatant, which is the monolithic high-entropy MXene solution; 3. Preparation of a monolithic high-entropy MXene / carbon fiber composite dual-functional interlayer: ① The monolithic high-entropy MXene solution was subjected to high-speed centrifugation to replace the solvent, the aqueous phase was replaced with N,N-dimethylformamide, and the concentration of the monolithic high-entropy MXene solution was adjusted to 40 mg / mL~60 mg / mL to obtain a concentrated monolithic high-entropy MXene solution; ② Add polyacrylonitrile to the concentrated monolithic high-entropy MXene solution and stir for a period of time to obtain an electrospinning precursor solution; ③. Electrospin the electrospinning precursor solution to obtain a fiber membrane; in an air atmosphere, pre-oxidize the fiber membrane at 260℃~300℃ for a period of time, then introduce argon gas, raise the temperature from 260℃~300℃ to 800℃~1000℃ in an argon atmosphere, and keep it at 800℃~1000℃ for a period of time to obtain a self-supporting monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer.

[0006] A monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer is used as an intermediate layer in lithium-sulfur batteries, placed between the positive electrode and the separator, and between the negative electrode and the separator.

[0007] Principle of the present invention: The high-entropy MXenes in the monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer prepared by the present invention provide a new platform for the precise control of electronic structure and electrochemical properties by integrating five or more size-matched transition metals in the M layer; compared with traditional single-metal MXenes, high-entropy MXenes have three significant advantages: (1) the "cocktail effect" produced by the synergistic production of multiple metal sites can achieve the synergistic control of electronic structure and d-band center; (2) the atomic-level elastic lattice configuration gives the material excellent mechanical properties; (3) compared with other high-entropy materials (such as high-entropy alloys), its intrinsic conductivity and surface functionalization properties are more conducive to the improvement of catalytic performance; these properties enable high-entropy MXenes to be used as intermediate layer materials, not only to enhance electronic conduction and optimize polysulfide adsorption, but also to significantly improve catalytic activity; more importantly, the high configurational entropy generated by its solid solution structure can not only stabilize the material phase structure, but also induce mechanical strain to promote uniform lithium deposition, thereby comprehensively improving the comprehensive performance of Li-S batteries.

[0008] The monolithic high-entropy MXene / carbon fiber composite dual-functional interlayer of the present invention will be applied to lithium-sulfur batteries, including the following beneficial effects: 1. The high-entropy MXene material in the monolithic high-entropy MXene / carbon fiber composite dual-functional interlayer prepared by the present invention is uniformly doped at the quasi-atomic level with five transition metal elements to construct a high-entropy stable crystal structure. This unique atomic arrangement significantly improves the thermodynamic stability of the material and creates a rich distribution of active sites, effectively solving the problems of easy oxidation deactivation and single catalytic site of traditional MXene materials; 2. In the monolithic high-entropy MXene / carbon fiber composite bifunctional interlayer of the present invention, different metal atoms of the high-entropy MXene material form a relay catalytic network through electron orbital coupling, exhibiting a stepwise electron transfer characteristic during the sulfur reduction reaction. This atomic-level division of labor and cooperation mechanism significantly improves the conversion reaction kinetics efficiency of the sulfur cathode; 3. The multi-metal active centers of the high-entropy MXene material in the monolithic high-entropy MXene / carbon fiber composite dual-functional interlayer of the present invention synergistically produce an optimized electronic structure and ideal adsorption characteristics, which can efficiently capture lithium polysulfides and promote their rapid conversion, while effectively inhibiting the shuttle effect of polysulfides, significantly improving the cycle stability of the battery; 4. The high-entropy MXene material in the monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer of the present invention reduces the reaction energy barrier during the lithium polysulfide conversion process by regulating the surface electronic state, especially promoting the key conversion step of Li2S2 to Li2S, making the sulfur conversion reaction process more efficient; 5. The unique electronic structure and lattice distortion characteristics of the high-entropy MXene material in the monolithic high-entropy MXene / carbon fiber composite bifunctional interlayer of the present invention can evenly distribute the electric field and lithium ion flux, guiding the uniform nucleation and deposition of lithium ions. At the same time, the gradient ion channel formed by it effectively inhibits the growth of lithium dendrites and realizes a stable lithium metal negative electrode interface; 6. The application of the present invention's single-piece high-entropy MXene / carbon fiber composite dual-functional intermediate layer can make the energy density of a 5Ah lithium-sulfur soft-pack battery reach 450Whkg -1 , Coulombic efficiency exceeds 99% and cycle life reaches 200 times, which is significantly better than lithium-sulfur batteries using low-entropy MXene interlayers; 7. The preparation method of the present invention has been verified by multiple experiments and has good reproducibility and stability, which can ensure the consistency of product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a flow chart for preparing a monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer in Example 1; Figure 2 X-ray diffraction images of high-entropy MAX and high-entropy MXene prepared in Example 1; Figure 3Transmission electron microscopy and atomic force microscopy characterization images of the single-sheet high-entropy MXene prepared in step 2③ of Example 1; Figure 4 a, b and c are the crystal orbital Hamiltonian populations between Li2S6, Li2S4, Li2S and different metal atoms in high-entropy MXene, respectively; d is a schematic diagram of high-entropy MXene cascade catalytic polysulfide conversion; Figure 5 In-situ X-ray diffraction images of lithium-sulfur batteries assembled using the intermediate layers of the comparative example and Example 1; Figure 6 In figure a, the cycle performance of lithium-lithium symmetrical batteries assembled using the intermediate layers of the comparative example and Example 1 is shown; in figure b, the effect of the intermediate layers of the comparative example and Example 1 on the lithium deposition morphology in the lithium-lithium symmetrical batteries assembled using the intermediate layers of the comparative example and Example 1 is observed using an in-situ optical microscope. The scale bar is 20 μm. Figure 7 The figure shows the cycle performance of lithium-sulfur soft-pack batteries assembled using the intermediate layers of the comparative example and embodiment 1. DETAILED DESCRIPTION

[0010] Specific embodiment 1: This embodiment is a method for preparing a monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer, which is specifically completed by the following steps: 1. Preparation of high entropy MAX precursor: ①, titanium powder, vanadium powder, niobium powder, molybdenum powder, chromium powder, tantalum powder, and tungsten powder, aluminum powder, and carbon powder were placed in a mortar and thoroughly mixed at a molar ratio of 0.6:0.6:0.6:0.6:0.6:1.2:2 to obtain a mixed powder; ②. Under an argon atmosphere, the mixed powder is heated to 1400°C~1600°C and kept warm for a period of time to obtain a reaction product; the reaction product is ground, then immersed in hydrochloric acid for washing, vacuum filtered, and the solid reaction product is vacuum dried to obtain a high-entropy MAX precursor powder; 2. Preparation of monolithic high-entropy MXene: ① Add high entropy MAX precursor powder to hydrofluoric acid, stir for a while, then repeatedly wash with deionized water until neutral, and vacuum dry to obtain multilayer MXene powder; ② Disperse the multilayer MXene powder in deionized water, add tetramethylammonium hydroxide solution, stir for a period of time for intercalation treatment, and then use deionized water as a cleaning agent to wash by multiple centrifugation until neutrality to obtain a precipitate; ③ Disperse the precipitate in deionized water, perform water bath ultrasonic treatment, and then centrifuge at a centrifugal speed of 3500 rpm to 5000 rpm to collect the supernatant, which is the monolithic high-entropy MXene solution; 3. Preparation of a monolithic high-entropy MXene / carbon fiber composite dual-functional interlayer: ① The monolithic high-entropy MXene solution was subjected to high-speed centrifugation to replace the solvent, the aqueous phase was replaced with N,N-dimethylformamide, and the concentration of the monolithic high-entropy MXene solution was adjusted to 40 mg / mL~60 mg / mL to obtain a concentrated monolithic high-entropy MXene solution; ② Add polyacrylonitrile to the concentrated monolithic high-entropy MXene solution and stir for a period of time to obtain an electrospinning precursor solution; ③. Electrospin the electrospinning precursor solution to obtain a fiber membrane; in an air atmosphere, pre-oxidize the fiber membrane at 260℃~300℃ for a period of time, then introduce argon gas, raise the temperature from 260℃~300℃ to 800℃~1000℃ in an argon atmosphere, and keep it at 800℃~1000℃ for a period of time to obtain a self-supporting monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer.

[0011] Compared with the prior art, this embodiment has the following advantages and outstanding effects: This embodiment constructs a high-entropy stable crystal structure through quasi-atomic uniform doping of five transition metal elements, significantly improving the material's thermodynamic stability and antioxidant capacity, and solving the problem of easy oxidation and deactivation of traditional MXene. The electronic orbital coupling between different metal atoms forms a relay catalytic network, achieving gradual electron transfer in the sulfur reduction reaction, significantly improving the kinetic efficiency of the sulfur conversion reaction. The synergistic effect of multi-metal active centers optimizes the electronic structure and adsorption characteristics, efficiently captures lithium polysulfide and promotes its rapid conversion, while suppressing the polysulfide shuttle effect and enhancing cyclic stability. The regulation of the surface electronic state reduces the energy barrier for lithium polysulfide conversion, especially accelerating the key step of Li2S2 to Li2S. The unique electronic structure and lattice distortion characteristics evenly distribute the electric field and lithium ion flux, guiding the uniform nucleation and deposition of lithium ions, inhibiting the growth of lithium dendrites, and achieving a stable lithium metal negative electrode interface, thereby simultaneously improving the positive and negative electrode performance of lithium-sulfur batteries and breaking through the single-function limitations of traditional intermediate layers. The use of this intermediate layer can significantly improve the cycling performance of lithium-sulfur batteries.

[0012] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the heating rate in step 1 (2) is 3°C / min to 5°C / min; the holding time in step 1 (2) is 2 hours to 4 hours; and the reaction product is ground to 400-600 mesh in step 1 (2). Other steps are the same as those in specific embodiment 1.

[0013] Specific embodiment 3: This embodiment differs from either specific embodiment 1 or 2 in that the volume ratio of the reaction product to hydrochloric acid in step 1 (2) is 1 g:10 mL, and the mass fraction of the hydrochloric acid is 38%. The vacuum drying temperature in step 1 (2) is 60°C to 80°C, and the vacuum drying time is 12 to 15 hours. Other steps are the same as those in specific embodiments 1 or 2.

[0014] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the mass fraction of hydrofluoric acid in step 2 (1) is 40% to 49%; and the volume ratio of the high-entropy MAX precursor powder to hydrofluoric acid in step 2 (1) is 1 g:10 mL. The other steps are the same as specific embodiments 1 to 3.

[0015] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that: the stirring temperature in step 2 (1) is 40°C to 50°C, the stirring speed is 400 rpm to 600 rpm, and the stirring time is 80 hours to 100 hours; the vacuum drying temperature in step 2 (1) is 60°C to 80°C, and the vacuum drying time is 12 hours to 15 hours. The other steps are the same as specific embodiments 1 to 4.

[0016] Specific embodiment 6: This embodiment differs from Specific embodiments 1 to 5 in that the mass-to-volume ratio of the multilayer MXene powder, deionized water, and tetramethylammonium hydroxide solution in step 2 (2) is 1 g:20 mL:(2 mL to 5 mL); and the mass fraction of the tetramethylammonium hydroxide solution in step 2 (2) is 25% to 30%. Other steps are the same as Specific embodiments 1 to 5.

[0017] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the stirring speed in step 2 (2) is 200-300 rpm and the stirring time is 12-18 hours; the centrifugal washing speed in step 2 (2) is 12,000 rpm and the centrifugal washing time is 30-40 minutes. The other steps are the same as specific embodiments 1 to 6.

[0018] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that: the mass ratio of the multilayer MXene powder described in step 2 (2) to the volume ratio of deionized water in step 2 (3) is 1g:40mL; the temperature of the water bath ultrasonic treatment described in step 2 (2) is 30°C to 40°C, and the water bath ultrasonic treatment time is 30min to 40min; the centrifugation time at a centrifugal speed of 3500rpm to 5000rpm in step 2 (2) is 30min to 40min; the volume ratio of the polyacrylonitrile described in step 3 (2) to the concentrated monolithic high-entropy MXene solution is 10g:10mL; the stirring speed described in step 3 (2) is 100r / min to 150r / min, and the stirring time is 8h to 12h. The other steps are the same as specific embodiments 1 to 7.

[0019] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that: The temperature of the electrospinning described in step 3③ is 30℃~40℃, the humidity is 30%~35%, the voltage of the electrospinning is 14kV~18kV, and the distance between the nozzle and the receiver is set to 15cm~20cm; in step 3③, the fiber membrane is pre-oxidized at 260℃~300℃ for 2h~4h under an air atmosphere; the heating rate described in step 3③ is 5℃ / min~10℃ / min; the insulation time at 800℃~1000℃ in step 3③ is 2h~4h.

[0020] The other steps are the same as those in Specific Embodiments 1 to 8.

[0021] Specific embodiment ten: This embodiment is a monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer used as an intermediate layer in a lithium-sulfur battery and placed between the positive electrode and the separator, and between the negative electrode and the separator.

[0022] The following examples are used to verify the beneficial effects of the present invention: Example 1: A method for preparing a monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer, characterized in that the preparation method is specifically completed according to the following steps: 1. Preparation of high entropy MAX precursor: ①, titanium powder, vanadium powder, niobium powder, chromium powder, molybdenum powder, aluminum powder, and carbon powder were placed in a mortar and thoroughly mixed at a molar ratio of 0.6:0.6:0.6:0.6:0.6:1.2:2 to obtain a mixed powder; ②. Under an argon atmosphere, the mixed powder was heated from room temperature to 1400°C and kept warm for 2 hours to obtain a reaction product; the reaction product was ground to 400 mesh, then immersed in hydrochloric acid and washed three times to remove excess aluminum, vacuum filtered, and the solid reaction product was vacuum dried at 60°C for 12 hours to obtain a high-entropy MAX precursor powder; The heating rate in step 1 (2) is 3°C / min; The mass ratio of the reaction product described in step 1② to the volume of hydrochloric acid is 1g:10mL, and the mass fraction of the hydrochloric acid is 38%; 2. Preparation of monolithic high-entropy MXene: ① Add 1g of high-entropy MAX precursor powder to 10mL of hydrofluoric acid, stir at 400rpm at 40℃ for 96h, then wash repeatedly with deionized water until neutral (pH=7), and then vacuum dry at 60℃ for 12h to obtain multilayer MXene powder; The mass fraction of the hydrofluoric acid described in step 2① is 49%; ② Disperse 1 g of multilayer MXene powder in 20 mL of deionized water, add 2 mL of tetramethylammonium hydroxide solution, and stir at a stirring speed of 200 r / min for 12 h for intercalation treatment. Then, use deionized water as a cleaning agent and wash by multiple centrifugation until neutral to obtain a precipitate; The mass fraction of the tetramethylammonium hydroxide solution described in step 2② is 25%; In step 2②, the speed of each centrifugal washing is 12000 rpm, and the centrifugal washing time is 30 min; ③ Disperse the precipitate in 40 mL of deionized water, ultrasonicate it in a water bath for 30 min, and then centrifuge it at 3500 rpm for 30 min. Collect the supernatant, which is the monolithic high-entropy MXene solution. The temperature of the water bath ultrasonic treatment described in step 2② is 35°C; 3. Preparation of a monolithic high-entropy MXene / carbon fiber composite dual-functional interlayer: ① The monolithic high-entropy MXene solution was subjected to high-speed centrifugation to replace the solvent, the aqueous phase was replaced with N,N-dimethylformamide, and the concentration of the monolithic high-entropy MXene solution was adjusted to 40 mg / mL to obtain a concentrated monolithic high-entropy MXene solution; ② Add 10 g of polyacrylonitrile to 10 mL of concentrated monolithic high-entropy MXene solution and stir for a while to obtain an electrospinning precursor solution; The stirring speed in step 3② is 100 r / min and the stirring time is 8 h; ③. Electrospinning the electrospinning precursor solution to obtain a fiber membrane; pre-oxidizing the fiber membrane at 260°C for 2 hours in an air atmosphere, then introducing argon, heating the membrane from 260°C to 800°C in an argon atmosphere, and maintaining the temperature at 800°C for 2 hours to obtain a self-supporting monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer; The electrospinning temperature in step 3 (3) was 40°C, the humidity was 30%, the electrospinning voltage was 14 kV, and the distance between the nozzle and the receiver was set to 15 cm; The heating rate described in step 3 ③ is 10°C / min.

[0023] Comparative Example: The preparation method of the Ti3C2 / carbon fiber intermediate layer is specifically completed according to the following steps: 1. Preparation of low-entropy MAX materials: ① Titanium powder, aluminum powder, and carbon powder were placed in a mortar and thoroughly mixed at a molar ratio of 3:1.2:2 to obtain a mixed powder; ②. Under an argon atmosphere, the mixed powder was heated from room temperature to 1400°C and kept at this temperature for 2 hours to obtain a reaction product; the reaction product was ground to 400 mesh, then immersed in hydrochloric acid and washed three times to remove excess aluminum, vacuum filtered, and the solid reaction product was vacuum dried at 60°C for 12 hours to obtain a low-entropy MAX material; The heating rate in step 1 (2) is 3°C / min; The mass ratio of the reaction product described in step 1② to the volume of hydrochloric acid is 1g:10mL, and the mass fraction of the hydrochloric acid is 38%; 2. Preparation of monolithic low-entropy MXene: ① Add 1g of low-entropy MAX material to 10mL of hydrofluoric acid, stir at 400rpm at 40℃ for 96h, then repeatedly wash with deionized water until neutral (pH=7), and then vacuum dry at 60℃ for 12h to obtain multilayer low-entropy MXene powder; The mass fraction of the hydrofluoric acid described in step 2① is 49%; ② Disperse 1 g of multilayer low-entropy MXene powder in 20 mL of deionized water, add 2 mL of tetramethylammonium hydroxide solution, stir at a stirring speed of 200 r / min for 12 h for intercalation treatment, and then use deionized water as a cleaning agent to wash by multiple centrifugation until neutrality to obtain a precipitate; The mass fraction of the tetramethylammonium hydroxide solution described in step 2② is 25%; In step 2②, the speed of each centrifugal washing is 12000 rpm, and the centrifugal washing time is 30 min; ③ Disperse the precipitate in 40 mL of deionized water, ultrasonicate it in a water bath for 30 min, and then centrifuge it at 3500 rpm for 30 min. Collect the supernatant, which is the monolithic low-entropy MXene solution. The temperature of the water bath ultrasonic treatment described in step 2② is 35°C; 3. Preparation of a monolithic high-entropy MXene / carbon fiber composite dual-functional interlayer: ① The monolithic low-entropy MXene solution was subjected to high-speed centrifugation to replace the solvent, the aqueous phase was replaced with N,N-dimethylformamide, and the concentration of the monolithic high-entropy MXene was adjusted to 40 mg / mL to obtain a concentrated monolithic low-entropy MXene solution; ② Add 10 g of polyacrylonitrile to 10 mL of concentrated monolithic low-entropy MXene solution and stir for a while to obtain an electrospinning precursor solution; The stirring speed in step 3② is 100 r / min and the stirring time is 8 h; ③. Electrospinning the electrospinning precursor solution to obtain a fiber membrane; pre-oxidizing the fiber membrane at 260°C for 2 hours, then heating it from room temperature to 800°C in an argon atmosphere, and keeping it at 800°C for 2 hours to obtain a Ti3C2 / carbon fiber intermediate layer; The electrospinning temperature in step 3 (3) was 40°C, the humidity was 30%, the electrospinning voltage was 14 kV, and the distance between the nozzle and the receiver was set to 15 cm; The heating rate described in step 3 ③ is 10°C / min.

[0024] The effects of the monolithic high-entropy MXene / carbon fiber composite bifunctional interlayer prepared in Example 1 and the Ti3C2 / carbon fiber interlayer prepared in the comparative example on the lithium polysulfide conversion kinetics and lithium deposition behavior were tested by the following electrochemical tests.

[0025] The electrochemical tests were performed using the LANDCT3001A battery testing system produced by Wuhan Landian Electronics Co., Ltd.

[0026] Assembly and testing of lithium-lithium symmetric batteries: Commercial lithium metal sheets were used as working and counter electrodes, an ether electrolyte (1M LiTFSI dissolved in a DOL / DME mixed solvent with a volume ratio of 1:1, and 2wt% LiNO3 was added as an electrolyte additive) was used as the electrolyte for lithium-sulfur batteries, Celgard 2400 was used as the separator, and the intermediate layers prepared in Example 1 and the comparative example were used as the intermediate intercalation layers (the intermediate intercalation layers were placed between the separator and the working electrode and between the separator and the counter electrode, respectively), and assembled into CR-2032 button cells. At 1 mA cm -2 , 1mAhcm -2 Repeated lithium deposition / stripping tests were carried out under the conditions of , and the relationship between the cycle time and polarization was observed.

[0027] Assembly and testing of lithium-sulfur soft pack batteries: Commercial carbon-sulfur composite electrode sheets (purchased from Shenzhen Kejing Co., Ltd., with a sulfur content of 68 wt% and an active material surface loading of 5.5 mg cm -2) as the positive electrode. A lithium-sulfur battery used an ether electrolyte (1M LiTFSI dissolved in a 1:1 volume ratio of DOL / DME mixed solvent, with 2wt% LiNO3 added as an electrolyte additive) as the electrolyte, Celgard 2400 as the separator, and the intermediate layers prepared in Example 1 and the comparative example as the intermediate intercalation layers (the intermediate intercalation layers were placed between the separator and the carbon-sulfur composite electrode and between the separator and the lithium negative electrode, respectively). A soft-pack battery was assembled with a liquid-sulfur ratio of 2.5mL / g. Constant-current charge and discharge tests were performed on the assembled full cell at a current density of 0.1C and a voltage window of 1.7-2.6V.

[0028] Figure 2 X-ray diffraction images of high-entropy MAX and high-entropy MXene prepared in Example 1; Figure 2 The efficient synthesis of high-entropy MXene nanosheets from their corresponding high-entropy MAX phases was successfully demonstrated.

[0029] Figure 3 Transmission electron microscopy and atomic force microscopy characterization images of the single-sheet high-entropy MXene prepared in step 2③ of Example 1; Figure 3 It was further confirmed that the prepared high-entropy MXene was an ultrathin nanosheet structure with a thickness of about 2.4 nm.

[0030] Figure 4 a, b and c are the crystal orbital Hamiltonian populations between Li2S6, Li2S4, Li2S and different metal atoms in high-entropy MXene, respectively; d is a schematic diagram of high-entropy MXene cascade catalytic polysulfide conversion; Based on the results of first-principles calculations Figure 4 The differentiated bonding between different metal sites in high-entropy MXene and lithium polysulfides (Li2S6, Li2S4, Li2S) was revealed, confirming that the material has cascade catalytic properties.

[0031] Figure 5 In-situ X-ray diffraction images of lithium-sulfur batteries assembled using the intermediate layers of the comparative example and Example 1; Figure 5 It shows that the lithium-sulfur battery using the intermediate layer of Example 1 can significantly promote the conversion of S8 to Li2S and the reoxidation process of Li2S.

[0032] Figure 6 In figure a, the cycle performance of lithium-lithium symmetrical batteries assembled using the intermediate layers of the comparative example and Example 1 is shown; in figure b, the effect of the intermediate layers of the comparative example and Example 1 on the lithium deposition morphology in the lithium-lithium symmetrical batteries assembled using the intermediate layers of the comparative example and Example 1 is observed using an in-situ optical microscope. The scale bar is 20 μm. Lithium symmetric battery testing combined with in situ optical microscopy observation ( Figure 6 ) confirmed that the intermediate layer can effectively inhibit the growth of lithium dendrites and significantly extend the cycle stability of the metallic lithium negative electrode; the single-piece high-entropy MXene / carbon fiber composite bifunctional intermediate layer prepared in Example 1 can enable the lithium-lithium symmetric battery to stably cycle for more than 5300h, which is higher than the 3800h of the comparative example.

[0033] Figure 7 The figure shows the cycle performance of lithium-sulfur soft-pack batteries assembled using the intermediate layers of the comparative example and embodiment 1.

[0034] like Figure 7 As shown, the use of the single-piece high-entropy MXene / carbon fiber composite dual-functional intermediate layer prepared in Example 1 can make the cycle life of the lithium-sulfur soft-pack battery reach 200 cycles, which is more than five times the cycle life of the control battery, while maintaining a high coulombic efficiency.

Claims

1. A method for preparing a monolithic high entropy MXene / carbon fiber composite dual-functional intermediate layer, characterized in that The preparation method is specifically completed according to the following steps:

1. Preparation of high entropy MAX precursor: ①, titanium powder, vanadium powder, niobium powder, molybdenum powder, chromium powder, tantalum powder, and tungsten powder, aluminum powder, and carbon powder were placed in a mortar and thoroughly mixed at a molar ratio of 0.6:0.6:0.6:0.6:0.6:1.2:2 to obtain a mixed powder; ②. Under an argon atmosphere, the mixed powder is heated to 1400°C~1600°C and kept warm for a period of time to obtain a reaction product; the reaction product is ground, then immersed in hydrochloric acid for washing, vacuum filtered, and the solid reaction product is vacuum dried to obtain a high-entropy MAX precursor powder; 2. Preparation of monolithic high-entropy MXene: ① Add high entropy MAX precursor powder to hydrofluoric acid, stir for a while, then repeatedly wash with deionized water until neutral, and vacuum dry to obtain multilayer MXene powder; ② Disperse the multilayer MXene powder in deionized water, add tetramethylammonium hydroxide solution, stir for a period of time for intercalation treatment, and then use deionized water as a cleaning agent to wash by multiple centrifugation until neutrality to obtain a precipitate; ③ Disperse the precipitate in deionized water, perform water bath ultrasonic treatment, and then centrifuge at a centrifugal speed of 3500 rpm to 5000 rpm to collect the supernatant, which is the monolithic high-entropy MXene solution; 3. Preparation of a monolithic high-entropy MXene / carbon fiber composite dual-functional interlayer: ① The monolithic high-entropy MXene solution was subjected to high-speed centrifugation to replace the solvent, the aqueous phase was replaced with N,N-dimethylformamide, and the concentration of the monolithic high-entropy MXene solution was adjusted to 40 mg / mL~60 mg / mL to obtain a concentrated monolithic high-entropy MXene solution; ② Add polyacrylonitrile to the concentrated monolithic high-entropy MXene solution and stir for a period of time to obtain an electrospinning precursor solution; ③, electrospinning the electrospinning precursor solution to obtain a fiber membrane; In an air atmosphere, the fiber membrane is pre-oxidized at 260℃~300℃ for a period of time, then argon is introduced, and the temperature is raised from 260℃~300℃ to 800℃~1000℃ in an argon atmosphere, and then kept at 800℃~1000℃ for a period of time to obtain a self-supporting monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer.

2. The method for preparing a monolithic high entropy MXene / carbon fiber composite dual-functional intermediate layer according to claim 1, characterized in that The heating rate in step 1 ② is 3°C / min~5°C / min; the holding time in step 1 ② is 2h~4h; and the reaction product in step 1 ② is ground to 400 mesh~600 mesh.

3. The method for preparing a monolithic high entropy MXene / carbon fiber composite dual-functional intermediate layer according to claim 1, characterized in that The mass ratio of the reaction product described in step 1 ② to hydrochloric acid is 1g:10mL, and the mass fraction of the hydrochloric acid is 38%; the vacuum drying temperature described in step 1 ② is 60°C~80°C, and the vacuum drying time is 12h~15h.

4. The method for preparing a monolithic high entropy MXene / carbon fiber composite dual-functional intermediate layer according to claim 1, characterized in that The mass fraction of the hydrofluoric acid described in step 2① is 40%~49%; the volume ratio of the mass of the high entropy MAX precursor powder described in step 2① to the hydrofluoric acid is 1g:10mL.

5. The method for preparing a monolithic high entropy MXene / carbon fiber composite dual-functional intermediate layer according to claim 1, characterized in that The stirring temperature in step 2① is 40°C~50°C, the stirring speed is 400rpm~600rpm, and the stirring time is 80h~100h; the vacuum drying temperature in step 2① is 60°C~80°C, and the vacuum drying time is 12h~15h.

6. The method for preparing a monolithic high entropy MXene / carbon fiber composite dual-functional intermediate layer according to claim 1, characterized in that The mass volume ratio of the multilayer MXene powder, deionized water and tetramethylammonium hydroxide solution described in step 2② is 1g:20mL:(2mL~5mL); the mass fraction of the tetramethylammonium hydroxide solution described in step 2② is 25%~30%.

7. The method for preparing a monolithic high entropy MXene / carbon fiber composite dual-functional intermediate layer according to claim 1, characterized in that The stirring speed in step 2② is 200r / min~300r / min, and the stirring time is 12h~18h; the speed of each centrifugal washing in step 2② is 12000rpm, and the centrifugal washing time is 30min~40min.

8. The method for preparing a monolithic high entropy MXene / carbon fiber composite dual-functional intermediate layer according to claim 1, characterized in that The mass ratio of the multilayer MXene powder described in step 2② to the volume ratio of the deionized water in step 2③ is 1g:40mL; the temperature of the water bath ultrasonic treatment described in step 2② is 30℃~40℃, and the time of the water bath ultrasonic treatment is 30min~40min; the time of centrifugation at a centrifugal speed of 3500rpm~5000rpm in step 2② is 30min~40min; the mass ratio of the polyacrylonitrile described in step 3② to the volume ratio of the concentrated monolithic high-entropy MXene solution is 10g:10mL; the stirring speed described in step 3② is 100r / min~150r / min, and the stirring time is 8h~12h.

9. The method for preparing a monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer according to claim 1, characterized in that The temperature of the electrospinning described in step 3③ is 30℃~40℃, the humidity is 30%~35%, the voltage of the electrospinning is 14kV~18kV, and the distance between the nozzle and the receiver is set to 15cm~20cm; in step 3③, the fiber membrane is pre-oxidized at 260℃~300℃ for 2h~4h under an air atmosphere; the heating rate described in step 3③ is 5℃ / min~10℃ / min; the insulation time at 800℃~1000℃ in step 3③ is 2h~4h.

10. Application of a monolithic high entropy MXene / carbon fiber composite dual-functional intermediate layer prepared by the preparation method according to claim 1, characterized in that A monolithic high-entropy MXene / carbon fiber composite dual-functional intermediate layer is used as an intermediate layer in lithium-sulfur batteries, placed between the positive electrode and the separator, and between the negative electrode and the separator.

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