A nitrogen-doped graphene-intercalated MoS2 heterostructure, its preparation method, and its application.

Abstract

The application belongs to the technical field of lithium-sulfur batteries, and relates to a nitrogen-doped graphite-like intercalated MoS2 heterostructure and a preparation method and application thereof. The preparation method is as follows: after molybdenum salt and thiourea are completely dissolved in deionized water or ultrapure water, polyethylene imine is added, and the mixture is stirred to obtain a mixed solution; the mixed solution is subjected to a hydrothermal reaction to obtain a precipitate; the precipitate is washed, centrifuged and dried for multiple times to obtain a MoS2 / PEI composite material; the MoS2 / PEI composite material is subjected to annealing treatment at 550 DEG C to 850 DEG C for 2 h to 10 h under the protection of argon to obtain a MoS2 / g-CM heterostructure. The application successfully constructs and systematically verifies that the nitrogen-doped graphite-like single-layer carbon inserted into the interlayer of MoS2 forms a heterostructure as a multifunctional catalyst and interface regulation material for high-performance lithium-sulfur batteries. On the premise of ensuring excellent catalytic properties, the conductivity is improved, and the defects of active site scarcity and easy collapse of the layered structure are overcome.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery technology, and specifically relates to a nitrogen-doped graphene-intercalated MoS2 heterostructure, its preparation method, and its application. Background Technology

[0002] Against the backdrop of continuous social development and soaring energy demand, traditional lithium-ion batteries can no longer meet today's energy storage needs. Lithium-sulfur batteries (LSBs), with their extremely high theoretical energy density (2600Wh / kg), offer a solution. -1 Excellent theoretical specific capacity (1675mAh g) -1 Lithium-sulfur batteries, with their abundant sulfur resources, low-cost advantages, and good environmental compatibility, have become highly promising candidate technologies for next-generation energy storage systems. They show broad application prospects in areas such as long-endurance drones, long-range electric vehicle operation, and grid energy storage. Currently, practically deployed lithium-sulfur batteries have achieved capacities exceeding 600Wh / kg. -1 The energy density of lithium-sulfur batteries is 2-3 times higher than that of traditional lithium-ion batteries, further highlighting their transformative technological value. However, the commercialization of lithium-sulfur batteries is still severely constrained by many key challenges, the most critical of which is the shuttle effect and slow redox reaction kinetics of lithium polysulfides (LiPSs, Li2Sx, 4≤x≤8). Sulfur itself has insulating properties, and its reaction process requires a complex phase transition from solid sulfur to liquid lithium polysulfides, and then to solid Li2S2 / Li2S. The high activation energy barrier between lithium polysulfides and insoluble Li2S2 / Li2S not only leads to slow reaction kinetics but also causes lithium polysulfides to accumulate in the electrolyte. These accumulated lithium polysulfides easily migrate and diffuse between the positive and negative electrodes, triggering the shuttle effect, which in turn leads to rapid capacity decay, reduced coulombic efficiency, and seriously affects the cycle stability of the battery. To solve this problem, many researchers have focused on the synergistic effect of chemisorption-catalysis, using electrocatalysts to anchor LiPSs and accelerate their conversion, thereby suppressing shuttle and extending cycle life.

[0003] To address the significant limitations on the commercialization of lithium polysulfides (LiPSs) due to their shuttle effect and slow redox reaction kinetics, molybdenum disulfide (MoS2) was introduced. MoS2, a typical two-dimensional transition metal chalcogenide (TMD), exhibits broad application prospects in electrocatalysis and energy storage fields such as lithium-sulfur batteries and lithium-ion batteries due to its unique layered crystal structure and excellent catalytic properties. However, inherent defects in MoS2 severely restrict the full realization of its electrochemical performance, specifically its poor intrinsic conductivity, leading to sluggish electron transport kinetics. Ordinary molybdenum disulfide (MoS2) has scarce catalytic active sites; only the edge regions possess strong metal-S bonds with catalytic activity, while the basal surface, which constitutes the bulk of the material, is catalytically inert. Figure 1 a). Furthermore, molybdenum disulfide (MoS2) readily undergoes a phase transition from crystalline MoS2 to metallic Mo nanoparticles and crystalline lithium sulfide (Li2S) during deep conversion reactions such as lithiation / delithiation. During delithiation, Li2S does not reconstruct MoS2 but decomposes into polysulfides. In the initial lithiation process, Li... + Extensive insertion and formation with Li2S lead to the disintegration of the MoS2 interlayer structure, resulting in the collapse of the layered structure and a decline in the material's cycle stability. Therefore, there is an urgent need for a MoS2 heterostructure that can provide key material support and technical reference for the development of high-performance lithium-sulfur batteries through synergistic optimization of structural design and performance. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, the present invention aims to provide a nitrogen-doped graphene-like intercalated MoS2 heterostructure, its preparation method, and its application. The present invention successfully constructed and systematically verified a nitrogen-doped graphene-like monolayer carbon embedded in the MoS2 interlayer (MoS2 / g-CM) as a high-performance lithium-sulfur battery multifunctional catalyst and interface regulation material. While ensuring its excellent catalytic properties, the invention improves conductivity, overcomes the defects of scarce active sites and easy collapse of layered structures, and further reduces the probability of the material's cycling stability deteriorating.

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a nitrogen-doped graphene-intercalated MoS2 heterostructure, comprising the following steps: After completely dissolving molybdenum salt and thiourea in deionized water or ultrapure water, polyethyleneimine is added and mixed and stirred to obtain a mixture. After the mixture was subjected to hydrothermal reaction at 150℃~300℃ for 10h~20h, a precipitate was obtained. The precipitate was washed with deionized water and alcohol multiple times, and then centrifuged and dried to obtain the MoS2 / PEI composite material. The MoS2 / PEI composite material was annealed at 550℃~850℃ for 2h~10h under argon protection to obtain a MoS2 / g-CM heterostructure, wherein the molybdenum salt is one of ammonium molybdate, molybdenum trioxide or sodium molybdate.

[0006] Preferably, the mass ratio of molybdenum ions in the molybdenum salt to 99% pure polyethyleneimine is 0.11~8.15:1. Specifically, when the molybdenum salt is ammonium heptamolybdate tetrahydrate, the concentration of ammonium heptamolybdate tetrahydrate in the mixture is 0.03 g / mL~0.15 g / mL; the concentration of 99.5 wt% thiourea in the mixture is 0.05 g / mL~0.15 g / mL; and the concentration of 99% pure polyethyleneimine in the mixture is 0.01 g / mL~0.15 g / mL.

[0007] This invention preferentially uses ammonium heptamolybdate as the molybdenum source. Too low a concentration leads to insufficient MoS2 nucleation and poor crystallinity, while too high a concentration causes aggregation. Thiourea is used as the sulfur source and reducing agent; too low a concentration results in incomplete MoS2 conversion and residual molybdenum oxide impurities, while too high a concentration exacerbates side reactions and introduces sulfur vacancy defects. Polyethyleneimine is used as the nitrogen source and structure directing agent; too low a concentration fails to achieve effective nitrogen doping, while too high a concentration coats the MoS2 surface and reduces product purity. Controlling the concentrations of these three sources within the aforementioned preferred ranges allows for an optimal balance between the molybdenum, sulfur, and nitrogen sources, simultaneously achieving high-crystallinity MoS2 growth, uniform nitrogen doping, and effective graphene intercalation.

[0008] The method for preparing the nitrogen-doped graphene-intercalated MoS2 heterostructure provided in this invention yields a MoS2 / g-CM heterostructure.

[0009] This invention provides a MoS2 / g-CM modified membrane, comprising a MoS2 / g-CM heterostructure.

[0010] A method for preparing a MoS2 / g-CM modified membrane includes the following steps: MoS2 / g-CM heterostructure, hydroxylated multi-walled carbon nanotubes and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a homogeneous slurry. The obtained uniform slurry was coated onto a polypropylene separator to obtain a functionalized separator. This functionalized separator was pre-dried at 50℃~70℃ for 0.5h~2h, and then dried under vacuum at 50℃~100℃ for 2h~24h to obtain a MoS2 / g-CM modified separator. The mass percentages of the MoS2 / g-CM heterostructure, hydroxylated multi-walled carbon nanotubes, and polyvinylidene fluoride in 1-methyl-2-pyrrolidone were 60%~80%:15%~25%:5%~15%, with a sum of 100%.

[0011] This invention discloses the application of a MoS2 / g-CM modified separator in lithium-sulfur batteries.

[0012] Preferably, the lithium-sulfur battery includes a sulfur / carbon composite positive electrode, a lithium negative electrode, a MoS2 / g-CM modified separator, and an electrolyte.

[0013] Preferably, the sulfur / carbon composite cathode is prepared as follows: Sublimed sulfur and CNT powder were ground into homogeneous materials to obtain the reactants. The reactants were placed in an argon atmosphere and heated at 150℃~155℃ for 10h~24h to make sulfur uniformly distributed in CNTs, thus obtaining sulfur / carbon composite materials. Sulfur / carbon composite material, conductive carbon black, and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a uniform slurry. The uniform slurry was then coated onto carbon-coated aluminum foil to obtain a sulfur / carbon composite cathode. Sublimed sulfur and CNT powder were mixed in a mass ratio of 1.2 to 4:1. The mass percentages of sulfur / carbon composite material, conductive carbon black, and polyvinylidene fluoride in 1-methyl-2-pyrrolidone were 70%–90%: 5%–15%: 5%–15%, with the sum of the three being 100%.

[0014] Preferably, the electrolyte is prepared by dissolving 1.0 mol of lithium bis(trifluoromethanesulfonyl)imide and 2 g of lithium nitrate in 1 L of solvent, wherein the solvent is a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1.

[0015] Preferably, the lithium-sulfur battery exhibits excellent capacity retention at rates ranging from 0.1C to 5C, with a discharge capacity of 734 mAh g⁻¹ remaining after 500 cycles at 1C. -1 The capacity decay rate per cycle is only 0.077%, even at high rates of 5C and 5mg / cm³. -2 It maintains stable cycle performance even under high sulfur loading.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention presents a method for successfully constructing and systematically validating a nitrogen-doped graphene-like monolayer carbon-intercalated heterostructure (MoS2 / g-CM) as a high-performance multifunctional catalyst and interface control material for lithium-sulfur batteries. Nitrogen doping enables Mo-N and Mo-C bonds to synergistically immobilize Mo atoms between carbon monolayers, restricting the disordered migration of Mo and S atoms during lithiation / delithiation. Even when MoS2 is deeply transformed into Mo and Li2S, the relative atomic positions remain stable, laying the foundation for the re-bonding of Mo and S and the reversible reconstruction of the intercalated structure after delithiation. Stable intercalation of g-CM significantly expands the MoS2 interlayer spacing from 0.63 nm to 1.02 nm, while simultaneously constructing a continuous three-dimensional conductive network, synergistically solving the core problems of poor conductivity, limited active sites, and structural instability inherent in traditional MoS2. This overcomes the defects of scarce active sites and the easy collapse of the layered structure, further reducing the probability of material degradation during cycling. Electrochemical results show that the MoS2 / g-CM composite material exhibits excellent ion transport properties (ionic conductivity of 1.92 mS cm⁻¹, lithium-ion transference number of 0.603) and a significantly reduced reaction energy barrier (ion migration activation energy of 2.44 kJ mol⁻¹). -1 The activation energy for polysulfide conversion is 31.21 kJ / mol. -1 Through a triple synergistic mechanism of physical confinement, chemisorption, and electrocatalytic conversion, this material effectively suppresses the shuttle effect of polysulfides and significantly accelerates the liquid-solid conversion kinetics. When applied to lithium-sulfur battery systems, this material exhibits high specific capacity, low polarization, and excellent cycle stability over a wide rate range (0.1C–5C), especially at high rates of 5C and 5 mg / cm³. -2 Stable electrochemical performance can be maintained even under high sulfur loading conditions. This work not only elucidates the mechanism by which interlayer engineering and interfacial catalysis synergistically enhance the performance of lithium-sulfur batteries at the atomic scale, but also provides innovative material design ideas and reliable technical pathways for developing next-generation lithium-sulfur batteries that combine high energy density, long cycle life, and good practicality. Attached Figure Description

[0017] Figure 1 The figures show the synthesis and morphological characterization of the materials, where (a) is a schematic diagram of the structure of molybdenum disulfide (MoS2), (b) is a schematic diagram of the structure of MoS2 / g-CM (graphitized carbon material), (c) is a schematic diagram of the preparation process of the MoS2 / g-CM catalyst, (d) is a scanning electron microscope (SEM) image of MoS2 / g-CM and MoS2, and (e) is an X-ray diffraction (XRD) pattern of MoS2 / g-CM and MoS2.

[0018] Figure 2The following are electrochemical characterization diagrams of the separators, where (a) is the ionic conductivity of various separators in the electrolyte; (b) is the Arrhenius plot; and (c) is the chronocurrent curve of lithium / lithium symmetric batteries using different separators. Figure 3 The figures show the characterization of the catalytic performance of the materials, where (a) shows the adsorption test and corresponding UV-Vis spectra of MoS2 / g-CM, MoS2 and Li2S6; and (b) shows the XRD patterns of MoS2 / g-CM and MoS2.

[0019] Figure 4 Cyclic voltammetry (CV) curves of a diaphragm-assembled battery.

[0020] Figure 5 Comparison of battery cycle performance with separator assembly. Detailed Implementation

[0021] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0022] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in Examples 1 to 9, preferred embodiments are described in this invention to avoid redundancy. However, this invention is not limited to these, but can be implemented in other ways within the scope of the technical solutions defined in the appended claims. All raw materials, reagents, instruments, and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0023] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] Sublimed sulfur (99.5 wt%), ammonium molybdate tetrahydrate (NH4)6Mo7O 24• 4H2O was purchased from Shanghai Test & Inspection Group SCR. N-methyl-2-pyrrolidone (NMP, 99.5wt%), polyethyleneimine (PEI, 99wt%), and thiourea (CS(NH2)2, 99.5wt%) were purchased from Aladdin. Conductive carbon black and polyvinylidene fluoride (PVDF 900, 99.5wt%) were purchased from KELOD. Sulfur (99.5wt%) was purchased from Alfa Aesar. Hydroxylated multi-walled carbon nanotubes (CNTs), 1,3-dioxolane (DOL, 99.8wt%), and dimethyl ethylene glycol ether (DME, 99wt%) were purchased from Maclean's. Lithium-sulfur electrolyte was purchased from Duoduo Chemical Reagent Network. Lithium metal discs (Li) were purchased from Tianjin Zhongneng Lithium Industry. Battery-grade aluminum foil (Al) and copper foil (Cu) were purchased from Shenzhen Honghai Battery Materials. The battery separator Celgard 2400 was purchased from Celgard Corporation, USA.

[0025] The TEM used in this invention is a Talos F200S from the USA, equipped with elemental energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) measurements were performed using a Smartlab SE (3kW fixed target, Cu target) from Japan, with a measurement range of 2θ = 5°~70° and a scanning speed of 2°min. –1 The fine morphology of the material surface was observed using a scanning electron microscope (SEM, S-4800) made in Japan. Ultraviolet-visible spectroscopy analysis was performed using a UV-2700I ultraviolet-visible spectrophotometer.

[0026] The molybdenum salt can be one of ammonium molybdate, molybdenum trioxide, or sodium molybdate, all of which can be used as precursors for the preparation of molybdenum disulfide (MoS2). The following examples preferably use ammonium heptamolybdate tetrahydrate.

[0027] Example 1 A method for preparing a nitrogen-doped graphene-intercalated MoS2 heterostructure includes the following steps: 1.45g ammonium heptamolybdate tetrahydrate and 2.81g thiourea were completely dissolved in 42mL of ultrapure water, and then 2.1g polyethyleneimine was added. The mixture was stirred for 1 hour to obtain a mixed solution. The mixture was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and hydrothermally reacted at 220°C for 18 hours to obtain a precipitate. The precipitate was washed with deionized water and alcohol multiple times and then centrifuged at 10,000 rpm. The centrifuged product was vacuum dried at 60°C for 12 hours to obtain the MoS2 / PEI composite material. The MoS2 / PEI composite material was annealed at 600℃ for 6 hours under argon protection to obtain the MoS2 / g-CM heterostructure.

[0028] Example 2 A method for preparing a nitrogen-doped graphene-intercalated MoS2 heterostructure includes the following steps: 1.26 g of ammonium heptamolybdate tetrahydrate and 2.11 g of thiourea were completely dissolved in 42 mL of ultrapure water, and then 0.42 g of polyethyleneimine was added. The mixture was stirred for 1 h to obtain a mixed solution. The mixture was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After hydrothermal reaction at 150°C for 20 hours, a precipitate was obtained. The precipitate was washed with deionized water and alcohol multiple times, and then centrifuged at 10,000 rpm. The centrifuged product was vacuum dried at 60°C for 12 hours to obtain the MoS2 / PEI composite material. The MoS2 / PEI composite material was annealed at 550℃ for 10 h under argon protection to obtain a MoS2 / g-CM heterostructure.

[0029] Example 3 A method for preparing a nitrogen-doped graphene-intercalated MoS2 heterostructure includes the following steps: 6.3g ammonium heptamolybdate tetrahydrate and 6.33g thiourea were completely dissolved in 42mL of ultrapure water, and then 6.36g polyethyleneimine was added. The mixture was stirred for 1 hour to obtain a mixed solution. The mixture was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After hydrothermal reaction at 300°C for 10 hours, a precipitate was obtained. The precipitate was washed with deionized water and alcohol multiple times, and then centrifuged at 10,000 rpm. The centrifuged product was vacuum dried at 60°C for 12 hours to obtain the MoS2 / PEI composite material. The MoS2 / PEI composite material was annealed at 850℃ for 2 hours under argon protection to obtain the MoS2 / g-CM heterostructure.

[0030] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that polyethyleneimine was not added, and the hydrothermal reaction product was not annealed.

[0031] A method for preparing molybdenum disulfide (MoS2) includes the following steps: 1.45 g of ammonium heptamolybdate tetrahydrate and 2.81 g of thiourea were completely dissolved in 42 mL of ultrapure water. The solution was then transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After hydrothermal reaction at 220 °C for 18 h, a precipitate was obtained. The precipitate was washed repeatedly with deionized water and alcohol, and then centrifuged at 10,000 rpm. The centrifuged product was vacuum dried at 60 °C for 12 h to obtain MoS2. The above Examples 1 to 3 all successfully prepared MoS2 / g-CM heterostructures. Now, the performance of the MoS2 / g-CM heterostructure prepared in Example 1 and the MoS2 prepared in Comparative Example 1 are verified and the structure is confirmed.

[0032] Experimental results (a) Structural confirmation The nitrogen-doped graphene-like monolayer carbon (g-CM) constructed in this invention, embedded in the interlayer of MoS2 to form a MoS2 / g-CM heterostructure, can specifically overcome the bottleneck of ordinary molybdenum disulfide (MoS2). As a stable intercalating phase, g-CM extends the interlayer spacing of the (002) crystal plane from 0.63 nm to 1.02 nm, effectively expanding the interlayer spacing of MoS2 to ensure unobstructed lithium-ion transport channels, and constructing a continuous conductive network to improve the overall conductivity of the material, thus solving the problem of insufficient intrinsic conductivity of MoS2. Simultaneously, the carbon monolayer formed by this invention, confined to a two-dimensional atomic scale space, can further enhance the exposure of active edge sites in MoS2 and activate the originally inert basal planes, promoting the formation of stable S-Li bonds and metal-S bonds between MoS2 and lithium polysulfides (LiPSs). This significantly optimizes the adsorption and catalytic conversion kinetics of LiPSs, breaking through the bottleneck of catalytic activity being limited by doping concentration in traditional chemical doping strategies.

[0033] More importantly, nitrogen atoms form Mo-N bonds with Mo atoms in MoS2, and together with the Mo-C bonds formed by carbon atoms, firmly fix the Mo atoms in the two-dimensional space between the carbon monolayers. This chemical bonding restricts the disordered migration of Mo and S atoms during the lithiation / delithiation process. Even in the deep conversion reaction of MoS2 to Mo and Li2S, the relative spatial positions of the atoms remain stable, providing a prerequisite for the rebonding of Mo and S and the reversible reconstruction of the intercalation structure during delithiation. This enables the reversible reconstruction of MoS2, which can withstand the drastic phase transition and volume expansion during the charging and discharging of lithium-sulfur batteries, effectively suppressing the collapse of the layered structure and solving the key problem of the degradation of cycle stability of two-dimensional layered intercalation materials in the deep conversion reaction of lithium-sulfur batteries. Figure 1 (b) Benefiting from the synergistic effect of the above-mentioned structural and performance advantages, the MoS2 / g-CM separator can effectively regulate the internal reaction process of lithium-sulfur batteries. During the lithium insertion / extraction process, the second phase can provide sufficient structural support and interfacial active sites. By inhibiting Mo agglomeration and reducing the Mo-S bond reconstruction energy barrier, it can significantly improve the rate performance and long-term cycle stability of the battery, providing an important material basis and technical support for its practical application in the field of lithium-sulfur batteries.

[0034] The preparation method of molybdenum disulfide (MoS2) given in Comparative Example 1 is basically the same as the preparation method of nitrogen-doped graphene-intercalated molybdenum disulfide (MoS2 / g-CM) given in Example 1. However, the preparation of MoS2 / g-CM given in Example 1 requires further annealing of the MoS2 / PEI composite material under argon protection to obtain the final MoS2 / g-CM. Figure 1 (As shown in c). After the MoS2 and MoS2 / g-CM materials were prepared, their morphologies were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Figure 1 As shown in d, the molybdenum disulfide material exhibits a uniform nanoflower structure with thinner edges and loose aggregation, making adsorption sites easily covered. The MoS2 / g-CM obtained after PEI intercalation and annealing exhibits a regular spherical / quasi-spherical porous structure. While the surface still has wrinkles, the aggregates are denser, providing more adsorption sites. Simultaneously, the polar sites of MoS2 form strong chemisorption with LiPSs, achieving both physical and chemical anchoring, which significantly reduces LiPSs diffusion.

[0035] Figure 1 The image shows the X-ray diffraction (XRD) patterns of the original MoS2 and MoS2 / g-CM. Compared with the original MoS2, the (002) peak of MoS2 / g-CM is significantly shifted to the left, which corresponds to an interlayer spacing of about 1.02 nm, which is larger than that of the original MoS2 (about 6.3 nm).

[0036] (II) Performance Analysis (1) Visual adsorption and diffusion experiments of Li2S6 by MoS2 / g-CM The experimental steps are as follows: First, prepare a Li2S6 solution, which is prepared by the following reaction equation.

[0037] 5S + Li₂S → Li₂S₆ Sulfur powder and Li2S were dissolved in a 5:1 ratio in a 1:1 volume ratio of 1,3-dioxolane DOL and ethylene glycol dimethyl ether DME, and stirred at 60°C for 24 h to obtain a 0.2 M Li2S6 solution.

[0038] Then, 20 mg of MoS2 / g-CM and 20 mg of MoS2 powder were placed into 2 mM Li2S6 solution and allowed to stand for different times to complete the visualization adsorption experiment.

[0039] like Figure 3As shown in Figure a, the degree of color change at different times was observed to indicate the adsorption effect on polysulfides. Initially, all three solutions exhibited the characteristic brownish-yellow color of Li₂S₆. With prolonged time, the color of the blank group showed no significant change, indicating that the polysulfides remained relatively stable without the material's action. The pure MoS₂ group began to lighten in color after 2 hours, and the fading was more pronounced by 12 hours, indicating that it possesses a certain adsorption or catalytic conversion ability for polysulfides. The MoS₂ group showed a much more significant fading effect than pure MoS₂ at 2 hours, and the solution became almost colorless by 12 hours, indicating that it had the highest adsorption / conversion efficiency and the fastest kinetics for polysulfides. Visual adsorption tests showed that the catalyst exhibited strong adsorption kinetic performance, effectively capturing all Li₂S₆ in the solution within a short time, indicating its strong adsorption capacity for lithium polysulfides (LiPSs). We used UV-Vis absorption spectroscopy to test the adsorption capacity of MoS₂ and MoS₂ / g-CM catalysts in Li₂S₆ solution. Figure 3 (as shown in a). After 12 hours of adsorption, the remaining S6 2⁻ The strength of MoS2 / g-CM is less than that of MoS2, which is consistent with the visual observation results, further confirming that MoS2 / g-CM has an enhanced ability to capture soluble lithium polysulfides.

[0040] (2) Kinetic performance of polysulfide conversion by MoS2 / g-CM The Li₂S₆ symmetric cell was used to evaluate the kinetic performance of the material for polysulfide conversion. The electrode of the Li₂S₆ symmetric cell was obtained by loading MoS₂ / g-CM and MoS₂ onto carbon paper (using carbon paper (CP) as the current collector, and stamping the CP into a circular sheet with a diameter of 10 mm). MoS₂ / g-CM and MoS₂ were dispersed separately in ethanol and then dropped onto the 10 mm circular sheet, controlling the areal loading to be approximately 3.0 mg cm⁻¹. -2 The positive electrode was made using this method; the negative electrode was lithium foil; a Celgard 2400 separator was used to assemble the CR2025 coin cell; the electrolyte was a 0.2M Li₂S₆ solution (prepared by dissolving 1 M LiTFSI in a 1:1 volume ratio of DOL and DME). A symmetrical cell was assembled into the CR2025 coin cell using the above electrodes as the working and counter electrodes, along with 40 μL of Li₂S₆ solution. Figure 3As shown in b, cyclic voltammetry (CV) tests were performed on a CHI760E electrochemical workstation within a voltage window of -0.8V to 0.8V at a scan rate of 10mV / s. 25μL of positive electrode electrolyte (0.2M Li₂S₈ solution (dissolved in 1M LiTFSI DOL / DME = 1 / 1, v / v)) was added to the positive electrode side, and 25μL of Li₂S₈-free electrolyte (1M LiTFSI DOL / DME = 1 / 1, v / v) was added to the lithium negative electrode side. The CR2025 coin cell was first constant-current discharged at 0.134mA to 2.09V, and then held at a constant voltage of 2.08V until the current dropped below 0.01mA. The nucleation rate and specific capacity of lithium sulfide (Li₂S) deposition were evaluated using Faraday's law.

[0041] Example 4 A method for preparing a MoS2 / g-CM modified membrane includes the following steps: MoS2 / g-CM heterostructure, hydroxylated multi-walled carbon nanotubes and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a homogeneous slurry. The obtained uniform slurry was coated onto a Celgard 2400 polypropylene membrane to obtain a functionalized membrane. The functionalized membrane was pre-dried at 50°C for 1 hour and then dried under vacuum at 60°C for 6 hours to obtain a MoS2 / g-CM modified membrane. The mass percentages of the MoS2 / g-CM heterostructure, hydroxylated multi-walled carbon nanotubes, and polyvinylidene fluoride in 1-methyl-2-pyrrolidone were 70%:20%:10%.

[0042] Example 5 A method for preparing a MoS2 / g-CM modified membrane includes the following steps: MoS2 / g-CM heterostructure, hydroxylated multi-walled carbon nanotubes and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a homogeneous slurry. The obtained uniform slurry was coated onto a Celgard 2400 polypropylene membrane to obtain a functionalized membrane. The functionalized membrane was pre-dried at 70°C for 0.5 h and then dried under vacuum at 50°C for 24 h to obtain a MoS2 / g-CM modified membrane. The mass percentages of the MoS2 / g-CM heterostructure, hydroxylated multi-walled carbon nanotubes, and polyvinylidene fluoride in 1-methyl-2-pyrrolidone were 60%:25%:15%.

[0043] Example 6 A method for preparing a MoS2 / g-CM modified membrane includes the following steps: MoS2 / g-CM heterostructure, hydroxylated multi-walled carbon nanotubes and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a homogeneous slurry. The obtained uniform slurry was coated onto a Celgard 2400 polypropylene membrane to obtain a functionalized membrane. The functionalized membrane was pre-dried at 60°C for 2 hours and then dried under vacuum at 100°C for 2 hours to obtain a MoS2 / g-CM modified membrane. The mass percentages of the MoS2 / g-CM heterostructure, hydroxylated multi-walled carbon nanotubes, and polyvinylidene fluoride in 1-methyl-2-pyrrolidone were 80%:15%:5%.

[0044] Comparative Example 2 A method for preparing a MoS2 modified membrane includes the following steps: MoS2, hydroxylated multi-walled carbon nanotubes and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a homogeneous slurry. The obtained uniform slurry was coated onto a Celgard 2400 polypropylene membrane to obtain a functionalized membrane. The functionalized membrane was pre-dried at 60°C for 2 hours and then dried under vacuum at 60°C for 6 hours to obtain a MoS2 modified membrane. The mass percentages of MoS2, hydroxylated multi-walled carbon nanotubes and polyvinylidene fluoride in 1-methyl-2-pyrrolidone were 70%:20%:10%.

[0045] Examples 4 to 6 all successfully prepared MoS2 / g-CM modified separators. The MoS2 / g-CM modified separator prepared in Example 4 and the MoS2 modified separator prepared in Comparative Example 2 are preferred as battery separators for assembling stainless steel / electrolyte / lithium (SS / electrolyte / Li) half-cells.

[0046] Experimental Analysis (III) Performance Analysis of Lithium-Sulfur Batteries The ionic conductivity of the electrolyte in two lithium-sulfur batteries, one with a MoS2-modified separator and the other with a MoS2 / g-CM-modified separator, was tested by AC impedance spectroscopy.

[0047] The specific steps for electrochemical impedance spectroscopy are as follows: In a glove box, a barrier cell is formed by sandwiching the separator between two stainless steel sheets (SS) (SS / separator / SS). After standing for 12 hours, the cell impedance is measured. A perturbation voltage of 10mV is applied using a Chenhua 660e electrochemical workstation, with a frequency range of 1Hz to 100,000Hz. The intercept of the measured curve with the X-axis corresponds to the bulk resistance (Rb) of the electrolyte. The ionic conductivity at different temperatures can be calculated using the following formula:

[0048] Where σ is the conductivity (S cm–1), l is the electrolyte thickness (cm), and A is the effective contact area (cm2).

[0049] Figure 2 As shown in Figure a, at room temperature (25℃), the intrinsic resistances of MoS2 / g-CM and pure MoS2 are 1.17Ω and 1.53Ω, respectively. Calculations show that MoS2 / g-CM exhibits a higher ionic conductivity (1.92 mS / cm). -1 Compared to pure MoS2 (1.48 mS / cm), -1 The performance was improved by approximately 29.7%, a significant enhancement primarily attributed to the introduction of g-CM, which constructed a continuous, highly conductive network. This network not only effectively promoted rapid interfacial charge transport but also optimized the electrical connections between MoS2 nanosheets, thereby reducing overall ion migration resistance. The Arenius curve was obtained by fitting the dependence of ionic conductivity on temperature. Figure 2 As shown in Figure b), the ion conduction behavior of MoS2 / g-CM and pure MoS2 in the temperature range of 25℃ to 85℃ was analyzed based on the Arrhenius diagram. The activation energy (Ea) of MoS2 / g-CM was 2.44 kJ mol. -1 It is significantly lower than the activation energy (Ea) of pure MoS2, which is 2.89 kJ / mol. -1 This indicates that its ion transport barrier is lower, and ion migration is easier in MoS2 / g-CM, which is beneficial to the cycling performance of the full cell.

[0050] The lithium-ion transport number is calculated using the static current method. The specific steps involve assembling a stainless steel / separator / Li battery in a glove box, allowing it to stand for 12 hours, and then testing it using an electrochemical workstation. First, the AC impedance Ro is measured under conditions of a 10mV step potential (ΔE) within a frequency range of 1kHz to 100kHz. Then, a chronoflowmetry method is used for 1000s (step potential ΔE = 10mV). Finally, another AC impedance measurement is performed to obtain the polarized impedance Rs. The lithium-ion transport number (tLi) is then calculated. +） It can be obtained from the following formula:

[0051] in, and The initial steady-state currents, measured in mA, are obtained before and after 1000s chronocurrent polarization; the step potential (ΔV) is 10mV. R0 and RS are the AC impedances of the battery before and after polarization, respectively, in Ω.

[0052] The lithium-ion transport number is calculated using the chrono-flow rate method, such as... Figure 2As shown in c, the lithium-ion transference number of MoS2 / g-CM (0.603) is higher than that of MoS2 (0.511), indicating that lithium ions can shuttle between the electrode and the electrolyte more efficiently, reducing the "ion congestion" phenomenon in the charge transport process and providing sufficient ion supply for the battery electrochemical reaction.

[0053] Example 7 A lithium-sulfur battery includes a sulfur / carbon composite positive electrode, a lithium negative electrode, a MoS2 / g-CM modified separator, and an electrolyte.

[0054] The preparation method of the sulfur / carbon composite cathode is as follows: Sublimed sulfur and CNT powder were ground into homogeneous materials to obtain the reactants. After placing the reactants in an argon atmosphere for 30 minutes, the mixture was heated at 155°C for 24 hours to ensure that sulfur was uniformly distributed in the CNTs, thus obtaining a sulfur / carbon composite material. Sulfur / carbon composite material, conductive carbon black, and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a uniform slurry. The uniform slurry was then coated onto carbon-coated aluminum foil to obtain a sulfur / carbon composite cathode. Sublimed sulfur and CNT powder were mixed in a mass ratio of 1.6:1. The mass percentages of sulfur / carbon composite material, conductive carbon black, and polyvinylidene fluoride in 1-methyl-2-pyrrolidone were 80%:10%:10%.

[0055] The electrolyte was prepared by dissolving 1.0 mol of lithium bis(trifluoromethanesulfonyl)imide and 2 g of lithium nitrate in 1 L of solvent, wherein the solvent was a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1.

[0056] Example 8 A lithium-sulfur battery includes a sulfur / carbon composite positive electrode, a lithium negative electrode, a MoS2 / g-CM modified separator, and an electrolyte.

[0057] The preparation method of the sulfur / carbon composite cathode is as follows: Sublimed sulfur and CNT powder were ground into homogeneous materials to obtain the reactants. After placing the reactants in an argon atmosphere for 30 minutes, the mixture was heated at 150°C for 10 hours to ensure that sulfur was uniformly distributed in the CNTs, thus obtaining a sulfur / carbon composite material. Sulfur / carbon composite material, conductive carbon black, and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a uniform slurry. The uniform slurry was then coated onto carbon-coated aluminum foil to obtain a sulfur / carbon composite cathode. Sublimed sulfur and CNT powder were mixed in a mass ratio of 1.2:1. The mass percentages of sulfur / carbon composite material, conductive carbon black, and polyvinylidene fluoride in 1-methyl-2-pyrrolidone were 70%:15%:15%.

[0058] The electrolyte was prepared by dissolving 1.0 mol of lithium bis(trifluoromethanesulfonyl)imide and 2 g of lithium nitrate in 1 L of solvent, wherein the solvent was a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1.

[0059] Example 9 A lithium-sulfur battery includes a sulfur / carbon composite positive electrode, a lithium negative electrode, a MoS2 / g-CM modified separator, and an electrolyte.

[0060] The preparation method of the sulfur / carbon composite cathode is as follows: Sublimed sulfur and CNT powder were ground into homogeneous materials to obtain the reactants. After placing the reactants in an argon atmosphere for 30 minutes, the mixture was heated at 152°C for 15 hours to ensure that sulfur was uniformly distributed in the CNTs, thus obtaining a sulfur / carbon composite material. Sulfur / carbon composite material, conductive carbon black, and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a uniform slurry. The uniform slurry was then coated onto carbon-coated aluminum foil to obtain a sulfur / carbon composite cathode. Sublimed sulfur and CNT powder were mixed in a certain mass ratio. The mass percentage of sulfur / carbon composite material, conductive carbon black, and polyvinylidene fluoride in 1-methyl-2-pyrrolidone was 90%:5%:5%.

[0061] The electrolyte was prepared by dissolving 1.0 mol of lithium bis(trifluoromethanesulfonyl)imide and 2 g of lithium nitrate in 1 L of solvent, wherein the solvent was a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1.

[0062] Comparative Example 3 The only difference between Comparative Example 3 and Example 7 is that the MoS2 / g-CM modified membrane was replaced with a MoS2 modified membrane.

[0063] The performance of the lithium-sulfur battery prepared in Example 7 and the lithium-sulfur battery prepared in Comparative Example 3 were analyzed.

[0064] The lithium-sulfur battery prepared in Example 7 and the lithium-sulfur battery prepared in Comparative Example 3 were both button-type lithium-sulfur batteries (CR2025), and both were assembled in a glove box filled with argon gas and subjected to electrochemical tests.

[0065] For low and high sulfur loading, the electrolyte-to-sulfur ratio is approximately 20 μL mg. -1 and 10 μL mg -1 Constant current charge-discharge tests were performed between 1.7V and 2.8V using a Blue Electric CT3002A battery testing instrument. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests were performed using a CHI760E electrochemical workstation.

[0066] Experimental Analysis (III) Performance Analysis of Lithium-Sulfur Batteries The comparison of CV curves further confirms that MoS2 / g-CM has excellent catalytic ability. Figure 4 The paper presents the cyclic voltammetry (CV) curves of lithium-sulfur batteries (LSBs) evaluated using two catalysts. The tests were conducted over a voltage range of 1.7 V to 2.8 V at a frequency of 0.1 mV s⁻¹. −1 The scan rate was used. Figure 4 In the cyclic voltammetry (CV) curve of the membrane-assembled battery, the peaks PeakC and PeakC correspond to the gradual reduction of S8 to long-chain soluble lithium polysulfides (LiPSs), and then to insoluble Li2S2 / Li2S, respectively. The anodic peak of Peak A indicates that Li2S2 / Li2S undergoes an oxidation reaction, converting back to Li2S. x And finally, S8 is generated.

[0067] Next, we will verify the cycle stability of different catalysts in focused lithium-sulfur batteries (LSBs), such as... Figure 5 As shown, the charge-discharge long-cycle performance was evaluated under 1C conditions, and its capacity and cycle stability were further assessed. Under 1C test conditions, the initial capacity of the MoS2 / g-CM-based battery was 1200 mAh g. -1 After 500 cycles, it maintained 734 mA hg. -1 The discharge capacity of the [specific cell name] was [specific value], with a capacity decay rate of 0.077% per cycle. In contrast, the battery based on the original MoS2 catalyst maintained 468 mA hg after 500 cycles. -1 The discharge capacity was high, with a capacity decay rate of 0.113% per cycle. This highlights that the MoS2 / g-CM catalyst effectively mitigates the shuttle effect of lithium polysulfides (LiPSs) and improves cycle performance due to its rapid sulfur redox kinetics.

[0068] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a nitrogen-doped graphene-intercalated MoS2 heterostructure, characterized in that, Includes the following steps: After completely dissolving molybdenum salt and thiourea in deionized water or ultrapure water, polyethyleneimine is added and mixed and stirred to obtain a mixture. After the mixture was subjected to hydrothermal reaction at 150℃~300℃ for 10h~20h, a precipitate was obtained. The precipitate was washed with deionized water and alcohol multiple times, and then centrifuged and dried to obtain the MoS2 / PEI composite material. The MoS2 / PEI composite material was annealed at 550℃~850℃ for 2h~10h under argon protection to obtain the MoS2 / g-CM heterostructure.

2. The method for preparing nitrogen-doped graphene-intercalated MoS2 heterostructures according to claim 1, characterized in that, The mass ratio of molybdenum ions in the molybdenum salt to 99% pure polyethylene ether is 0.11 to 8.15:

1.

3. The method for preparing nitrogen-doped graphene intercalated MoS2 heterostructure according to any one of claims 1 to 2 yields a MoS2 / g-CM heterostructure.

4. A MoS2 / g-CM modified separator, characterized in that, Including the MoS2 / g-CM heterostructure as described in claim 3.

5. The method for preparing the MoS2 / g-CM modified membrane according to claim 4, characterized in that, Includes the following steps: MoS2 / g-CM heterostructure, hydroxylated multi-walled carbon nanotubes and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a homogeneous slurry. The obtained uniform slurry was coated onto a polypropylene membrane to obtain a functionalized membrane. The functionalized membrane was pre-dried at 50℃~70℃ for 0.5h~2h, and then dried in a vacuum environment at 50℃~100℃ for 2h~24h to obtain a MoS2 / g-CM modified membrane. The mass percentages of the MoS2 / g-CM heterostructure, hydroxylated multi-walled carbon nanotubes, and polyvinylidene fluoride in 1-methyl-2-pyrrolidone were 60%~80%:15%~25%:5%~15%, and the sum of the three was 100%.

6. The application of the MoS2 / g-CM modified separator according to claim 4 in lithium-sulfur batteries.

7. The application according to claim 6, characterized in that, The lithium-sulfur battery includes a sulfur / carbon composite positive electrode, a lithium negative electrode, a MoS2 / g-CM modified separator, and an electrolyte.

8. The application according to claim 6, characterized in that, The method for preparing the sulfur / carbon composite cathode is as follows: Sublimed sulfur and CNT powder were ground into homogeneous materials to obtain the reactants. The reactants were placed in an argon atmosphere and heated at 150℃~155℃ for 10h~24h to make sulfur uniformly distributed in CNTs, thus obtaining sulfur / carbon composite materials. Sulfur / carbon composite material, conductive carbon black, and polyvinylidene fluoride were mixed in 1-methyl-2-pyrrolidone solvent and stirred to obtain a uniform slurry. The uniform slurry was then coated onto carbon-coated aluminum foil to obtain a sulfur / carbon composite cathode. Sublimed sulfur and CNT powder were mixed in a mass ratio of 1.2 to 4:

1. The mass percentages of sulfur / carbon composite material, conductive carbon black, and polyvinylidene fluoride in 1-methyl-2-pyrrolidone were 70%–90%: 5%–15%: 5%–15%, with the sum of the three being 100%.

9. The application according to claim 6, characterized in that, The electrolyte is prepared by dissolving 1.0 mol of lithium bis(trifluoromethanesulfonyl)imide and 2 g of lithium nitrate in 1 L of solvent, wherein the solvent is a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:

1.

10. The application according to claim 6, characterized in that, The lithium-sulfur battery exhibited excellent capacity retention at rates ranging from 0.1C to 5C, with a discharge capacity of 734 mAh g⁻¹ remaining after 500 cycles at 1C. -1 The capacity decay rate per cycle is only 0.077%, even at high rates of 5C and 5mg / cm³. -2 It maintains stable cycle performance even with high sulfur loading.

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