Lithium-sulfur battery catalyst, preparation method thereof and lithium-sulfur battery

Abstract

The invention relates to the technical field of battery materials, and discloses a lithium-sulfur battery catalyst, a preparation method thereof and a lithium-sulfur battery. According to the lithium-sulfur battery catalyst, particles of the catalyst comprise an MXTiO base material and alpha-Fe2O3 deposited on the surface of the MXTiO base material; the MXTiO base material comprises an MXene nanosheet and a titanium oxide layer covering the surface of the MXene nanosheet; the metal element in the MXene nanosheet is Ti. The preparation method comprises the following steps: carrying out hydrothermal reaction on MXene to generate titanium oxide on the surface of MXene to obtain an MXTiO material; preparing a mixed dispersion liquid, wherein iron ions are dissolved in the mixed dispersion liquid, and an MXTiO material is dispersed in the mixed dispersion liquid; alkali liquor is added into the mixed dispersion liquid, ferric hydroxide is precipitated on the surfaces of particles of the MXTiO material, then a reaction product is calcined, and the MXTiO / alpha-Fe2O3 heterostructure material is obtained. The catalyst shows excellent electro-catalytic performance in the lithium-sulfur battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a lithium-sulfur battery catalyst and a preparation method thereof, and a lithium-sulfur battery. Background Art

[0002] Lithium-sulfur batteries have become the leader in post-lithium-ion energy storage technologies, not only with unparalleled theoretical energy density (about 2,600Whkg -1 ), also boasting advantages such as abundant natural sulfur, economic feasibility, and ecological sustainability. However, their commercialization faces significant hurdles, including sluggish sulfur cathode redox kinetics, irreversible lithium anode degradation, and, in particular, the parasitic shuttling effect, whereby mobile polysulfide intermediates (Li2Sn, 4≤n≤8) diffuse between electrodes, resulting in active material loss and metal anode corrosion. Notably, the delayed polysulfide conversion kinetics is a key factor exacerbating these challenges, perpetuating the shuttle-driven capacity fade and cycling instability.

[0003] Recent advances have demonstrated that targeted catalytic strategies can simultaneously accelerate the dynamic transformation of polysulfides and disrupt the shuttling pathway, offering a dual solution to these interrelated limitations. Previous research has explored metal oxides, sulfides, phosphides, nitrides, and monodisperse metal atoms or clusters as catalysts. Metal oxides possess polar surfaces and possess strong chemisorption capacity for lithium polysulfides, effectively mitigating the shuttling effect by anchoring soluble intermediates. Furthermore, they exhibit exceptional thermal and chemical stability, which is crucial for long-term cycling under harsh operating conditions. However, most transition metal oxides are non-conductive, resulting in sluggish charge transfer kinetics. Fortunately, MXenes have garnered significant attention in the lithium-sulfur battery field due to their inherent metallic conductivity and unique surface properties, including ultrahigh surface area and tunable surface termination. This unique combination makes MXenes ideal conductive scaffolds, preventing nanoparticle aggregation within metal oxide composites, thereby synergistically improving polysulfide capture efficiency and redox conversion kinetics. Therefore, heterogeneous catalysts combining MXenes with metal oxides can achieve optimal performance through interfacial synergistic effects that are not present in homogeneous systems, as their distinct physicochemical properties can yield complementary functional advantages. The MXene / metal oxide interface can enhance electron extraction between the metallic MXene metal compensator and the insulating metal oxide through interfacial charge redistribution, reflecting a "1+1>2" effect, whereby both conductivity and adsorption are optimized simultaneously.

[0004] In addition, when elucidating the mechanism of adsorption catalysis, a comprehensive study of the electronic structure of the catalyst under physical fields, including band configuration, surface state density, and atomic-level orbital interactions, can provide more substantial insights than simple material screening. This fundamental analysis reveals how electronic structure effects directly regulate reaction energy barriers and intermediate adsorption strengths. This atomistic perspective is indispensable for the rational design of next-generation catalysts. For example, Zhang and his collaborators found that an external magnetic field can modulate the spin state of cobalt sulfide from a low-spin state to a high-spin polarization state, thereby increasing the orbital hybridization between Co3d and S3p and lowering the energy barrier of the electrochemical reaction. Zhou et al. developed a high-entropy ceramic catalyst (La0.15Nd0.15Sm0.4Eu0.15Gd0.15)2Zr2O7 for lithium-sulfur electrochemistry. They found that a synergistic dual field (electric and crystal fields) modulated the electronic structure of Zr, thereby enhancing its adsorption to Li2S4. Furthermore, the highly localized electron density originating from f orbitals promoted the emergence of an interfacial electronic buffer band, mediating charge transfer between the upper and lower Hubbard bands (UHB / LHB), significantly improving catalytic activity. Strategic design of heterostructured catalysts is one of the most effective approaches to precisely tune the electronic structure of catalysts, as interfacial charge transfer spontaneously generates a built-in electric field (BIEF), fundamentally altering the electronic band configuration. However, current research has primarily focused on composition and junction types (e.g., p-n, p-p, Schottky junctions), while significantly neglecting how these interfacial charge redistribution phenomena directly reshape the surface electronic states of active sites. This is a major scientific gap with urgent implications: without understanding how interfacial charge transfer alters the surface electronic structure, the rational design of next-generation heterostructure catalysts for lithium-sulfur batteries will be fundamentally constrained by empirical trial-and-error approaches.

[0005] In view of this, this application is hereby filed. Summary of the Invention

[0006] The object of the present invention is to provide a lithium-sulfur battery catalyst and a preparation method thereof, and a lithium-sulfur battery, aiming to improve at least one problem mentioned in the background art.

[0007] The present invention is achieved in that: In a first aspect, the present invention provides a method for preparing a lithium-sulfur battery catalyst, comprising: Providing MXene materials, wherein the metal element in the MXene materials is Ti; The MXene material is placed in water for a hydrothermal reaction to generate titanium oxide on the surface of the MXene material to obtain the MXTiO material; preparing a mixed dispersion, wherein the mixed dispersion contains dissolved iron ions and dispersed MXTiO material; Alkali solution is added to the mixed dispersion to react the iron ions into iron hydroxide, which is deposited on the surface of the MXTiO material particles. After sufficient reaction, the solid is extracted from the reaction system to obtain an intermediate product. The intermediate product is calcined under an inert atmosphere to convert iron hydroxide into iron oxide, thereby obtaining a MXTiO / α-Fe2O3 heterostructure material.

[0008] In an optional embodiment, the method for preparing MXene material comprises: The MAlX nanopowder composed of the elements Ti, Al, and X reacts with an etching solution, so that the Al element in the MAlX dissolves in the etching solution and forms active sites on the surface of the powder particles to obtain MXene material; The X element is at least one of C and N.

[0009] In an optional embodiment, the solute in the etching solution includes LiF and HCl, the concentration of LiF in the etching solution is 0.5-2M, and the concentration of HCl is 0.1-12M.

[0010] In an optional embodiment, the Al element in MAlX is dissolved in an etching solution to form active sites on the surface of the powder particles, and the method for obtaining the MXene material includes: The MAlX nanopowder and the etching solution are evenly mixed to obtain a mixed solution, and then the mixed solution is heated to 30-40° C. and kept warm for 40-60 hours, followed by solid-liquid separation and washing the obtained solid product with water.

[0011] In an optional embodiment, the mass ratio of iron ions to MXTiO material in the mixed dispersion is 20.66-103.3:100.

[0012] In an optional embodiment, the mixed dispersion is obtained by mixing FeCl3, MXTiO material and water; Optionally, the concentration of iron ions in the mixed dispersion is 0.6-1.8 g / L.

[0013] In an optional embodiment, at least one of the following features (1) to (4) is also included: (1) Ways to fully respond include: After adding alkali solution to the mixed dispersion, stir at 70-80°C for 8-12 minutes, and then keep it at 80-110°C for 36-60 hours; (2) Methods for extracting solids from the reaction system to obtain intermediates include: After the reaction is completed, solid-liquid separation is performed, followed by washing with water and ethanol and drying; (3) The method of calcining the intermediate product under an inert atmosphere to convert iron hydroxide into iron oxide includes: Calcining at 430-470℃ under argon atmosphere for 1.5-2.5h; (4) The MXene material is placed in water to perform a hydrothermal reaction, so that titanium oxide is generated on the surface of the MXene material, and a MXTiO material is obtained. The MXene material is placed in water, heated in a water bath or oil bath at 60-120℃ for 1.5-2.5h, and then solid-liquid separation is performed, and the solid product is freeze-dried.

[0014] In an optional embodiment, the alkali solution is a potassium hydroxide solution. Optionally, the concentration of the potassium hydroxide solution is 0.8-1.2M.

[0015] In a second aspect, the present application provides a lithium-sulfur battery catalyst prepared by the preparation method of any one of the preceding embodiments.

[0016] In a third aspect, the present application provides a lithium-sulfur battery comprising the lithium-sulfur battery catalyst of the preceding embodiments.

[0017] The present application has the following beneficial effects: The lithium-sulfur battery catalyst prepared by the preparation method of the present application uses MXTiO material as an electron acceptor, steals part of the electrons from α-Fe2O3 through an interface asymmetric Ti-O-Fe bridge, and induces spontaneous charge redistribution; the electron transfer through the interface Ti-O-Fe channel forms an electron-deficient Fe site on the surface, which not only reduces the antibonding orbital electron occupancy (relative to isolated α-Fe2O3), thereby strengthening the d-p orbital hybridization between the surface Fe and polysulfides, providing strong sulfur affinity, but also weakens the S-S bond, thereby accelerating the cleavage and enhancing the catalytic performance on the lithium-sulfur battery. The lithium-sulfur battery catalyst (MXTiO / α-Fe2O3 heterostructure material) provided in the embodiments of the present application exhibits excellent electrocatalytic performance in lithium-sulfur batteries, which makes the capacity of the battery high, the cycle performance good, and the capacity decay rate extremely low, and can enhance the cycle performance of the lithium-sulfur battery under high sulfur load and poor electrolyte conditions. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0019] Figure 1 SEM image of the MXene nanosheet prepared in Example 1; Figure 2This is a SEM image of the MXTiO / α-Fe2O3 heterostructure composite material prepared in Example 1; Figure 3 HAADF image and EDS composition map of the MXTiO / α-Fe2O3 heterostructure prepared in Example 1; Figure 4 X-ray diffraction patterns of α-Fe2O3 and MXTiO / α-Fe2O3; Figure 5 Raman spectra of MXene nanosheets (represented by MX), α-Fe2O3, and MXTiO / α-Fe2O3; Figure 6 To add various catalysts to Li2S6 solution, the solution state diagram was observed after a period of reaction; Figure 7 The enlarged GCD curve at 0.1C; Figure 8 is the rate performance at different current densities; Figure 9 is the cycle performance at a current density of 0.1C; Figure 10 is the cycle performance at a current density of 5C; Figure 11 The cycling performance of lithium-sulfur batteries with MXTiO / α-Fe2O3 catalyst under high sulfur loading and poor electrolyte conditions. DETAILED DESCRIPTION

[0020] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0021] In response to the problems existing in the existing technology, this application makes the following design: Using modified MXene (MXTiO material) and readily available α-Fe2O3 heterostructure (MXTiO / α-Fe2O3) as model catalysts, a fundamental study is conducted on how interfacial charge redistribution affects the surface electronic structure. Systematic experimental studies and in-depth theoretical calculations reveal that the BIEF at the heterointerface promotes the directional transfer of electrons from α-Fe2O3 to MXene through an asymmetric Ti-O-Fe charge transfer channel, thereby forming an electron-deficient α-Fe2O3 phase. First-principle electronic structure analysis shows that this electronic defect reduces the out-of-plane Fe-3d (d z^2 ,d xz ,d yz) / S-3p hybrid orbital, thereby optimizing the adsorption energy of polysulfides. In addition, the electron-deficient iron site weakens the SS bonds within the sulfur species by shifting the antibonding center downward, thereby promoting their cleavage.

[0022] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0023] An embodiment of the present invention provides a method for preparing a lithium-sulfur battery catalyst, comprising: Providing MXene materials, wherein the metal element in the MXene materials is Ti; The MXene material is placed in water for a hydrothermal reaction to generate titanium oxide on the surface of the MXene material to obtain the MXTiO material; preparing a mixed dispersion, wherein the mixed dispersion contains dissolved iron ions and dispersed MXTiO material; Alkali solution is added to the mixed dispersion to react the iron ions into iron hydroxide, which is deposited on the surface of the MXTiO material particles. After sufficient reaction, the solid is extracted from the reaction system to obtain an intermediate product. The intermediate product is calcined under an inert atmosphere to convert iron hydroxide into iron oxide, thereby obtaining a MXTiO / α-Fe2O3 heterostructure material.

[0024] The preparation method provided in an embodiment of the present invention modifies a MXene material by a hydrothermal reaction to obtain an MXTiO material, and then loads α-Fe2O3 on the MXTiO material to obtain an MXTiO / α-Fe2O3 heterostructure material. This material is used as a lithium-sulfur battery catalyst, using the MXTiO material as an electron acceptor to steal some electrons from α-Fe2O3 through an asymmetric Ti-O-Fe bridge bond at the interface, inducing spontaneous charge redistribution; electron transfer through the interfacial Ti-O-Fe channel forms electron-deficient Fe sites on the surface, which not only reduces the antibonding orbital electron occupancy (relative to isolated α-Fe2O3), thereby strengthening the dp orbital hybridization between the surface Fe and polysulfides, providing strong sulfur affinity, but also weakens the SS bond, thereby accelerating the cracking and enhancing its catalytic performance in lithium-sulfur batteries. The lithium-sulfur battery catalyst (MXTiO / α-Fe2O3 heterostructure material) provided by the embodiment of the present invention exhibits excellent electrocatalytic performance in lithium-sulfur batteries, which enables the battery to have high capacity, good cycle performance, and extremely low capacity decay rate, and can enhance the cycle performance of lithium-sulfur batteries under high sulfur load and poor electrolyte conditions.

[0025] Specifically, the preparation method includes: S1. Preparation of MXene nanosheet materials MAlX nanopowder composed of the elements Ti (titanium), Al (aluminum) and X is reacted with an etching solution, so that the Al element in MAlX dissolves in the etching solution and forms active sites on the surface of the powder particles to obtain MXene material; the X element is at least one of C (carbon) and N (nitrogen).

[0026] It should be noted that MXene nanosheet material is a two-dimensional material, which belongs to the prior art. In addition to the MXene nanosheet material prepared by the preparation method mentioned in this application, the MXene nanosheet material used to implement the present invention can also be directly purchased from commercially available MXene nanosheet materials to implement this application.

[0027] To prepare Ti3C2T x For example (T represents an active site, such as oxygen, fluorine or free radical, etc.): (1) Preparation of etching solution An appropriate amount of LiF powder is dissolved in a 0.1-12M (e.g., 0.1M, 0.5M, 1M, 5M, 8M, or 12M) HCl solution to obtain an etching solution, wherein the concentration of LiF in the etching solution is 0.5-2M (e.g., 0.5M, 1M, or 2M).

[0028] (2) Etching reaction MAlX nanopowder is slowly added to the etching solution and stirred for about 30 minutes. The mixture is then heated to 30~40°C (for example, 30°C, 35°C or 40°C) and kept warm for 40~60h (for example, 40h, 50h or 60h). It is then centrifuged and washed with deionized water at 3500r until the pH value reaches 6. The solid is separated to obtain MXene nanosheet material.

[0029] Optionally, the ratio of the amount of MAlX nanopowder to the etching solution is 1g: 10-50mL (e.g., 10mL, 30mL, or 50mL). It should be noted that there is no strict requirement for the ratio of the amount of the two, and generally, it is sufficient to completely etch the Al in the MAlX nanopowder.

[0030] Specifically, the X element is at least one of C and N.

[0031] S2. Preparation of MXTiO The MXene nanosheet material is placed in deionized water and heated in a water bath or oil bath at 60-120°C (e.g., 60°C, 80°C, 100°C, or 120°C) for 1.5-2.5 hours (e.g., 1.5 hours, 2 hours, or 2.5 hours), followed by solid-liquid separation and freeze-drying the solid product.

[0032] Optionally, the solid-liquid separation method is centrifugal separation.

[0033] S3, α-Fe2O3 deposition (1) Preparation of mixed dispersion Add trivalent iron salt (e.g., FeCl3•6H2O) and the MXTiO nanosheets prepared in the previous step into deionized water to fully dissolve the iron salt and evenly disperse the MXTiO nanosheets to obtain a mixed dispersion.

[0034] Optionally, the mass ratio of iron ions to MXTiO material in the mixed dispersion is 20.66-103.3:100.

[0035] Optionally, the concentration of the trivalent iron ions in the mixed dispersion is 0.6-1.8 g / L (eg, 0.6 g / L, 1 g / L, 1.2 g / L, or 1.8 g / L).

[0036] (2) Precipitation reaction Add alkali solution dropwise to the mixed dispersion at 70~80℃ (70℃, 75℃ or 80℃), stir at 70~80℃ (70℃, 75℃ or 80℃) for 8~12min (for example, 8min, 10min or 12min), and then place at 80~110℃ (for example, 80℃, 100℃ or 110℃) for 36~60h (for example, 36h, 40h, 45h, 50h or 60h).

[0037] Optionally, the alkali solution is a potassium hydroxide solution; further, the concentration of the potassium hydroxide solution is 0.8 to 1.2 M (e.g., 0.8 M, 1 M, or 1.2 M). The amount of potassium hydroxide solution added can be calculated based on the amount of ferric ions to be precipitated. To ensure sufficient precipitation of the ferric ions, a slight excess of potassium hydroxide solution may be used.

[0038] S3. Intermediate product extraction After the product obtained in the previous step is cooled to room temperature, the red product is separated by centrifugation, and then washed with water and ethanol at least three times, and then dried at 65-75°C (e.g., 65°C, 70°C or 75°C) overnight.

[0039] S4. Calcination The MXTiO / α-Fe2O3 heterostructure material is prepared by calcining the MXTiO / α-Fe2O3 heterostructure material at 430-470°C (e.g., 430°C, 450°C, or 470°C) for 1.5-2.5h (e.g., 1.5h, 2h, or 2.5h) under an argon environment.

[0040] The lithium-sulfur battery catalyst provided by the embodiment of the present invention is prepared using the preparation method provided by the embodiment of the present invention.

[0041] Optionally, the mass ratio of α-Fe2O3 to MXTiO substrate in the lithium-sulfur battery catalyst is 0.29~1.48:1.0 (the optimal ratio is 0.89:1).

[0042] The lithium-sulfur battery provided by the embodiment of the application comprises the lithium-sulfur battery catalyst provided by the embodiment of the application.

[0043] Embodiment 1 Preparation of MXene nanosheet material: Dissolve 0.8 g of LiF powder in 30 mL of 9M HCl solution and stir for 20 min to obtain an etching solution, then slowly add 1 g of Ti3AlC2 powder to the etching solution and stir for 30 min. Heat the mixed solution to 35℃ and keep for 48 h, then centrifugal wash with deionized water at 3500 r to obtain a solid until the pH value reaches 6, and then extract the solid to obtain the MXene nanosheet material.

[0044] Preparation of MXTiO: Add 120 mg of the MXene nanosheet material powder prepared in the previous step to 30 ml of deionized water, heat in a water bath at 90℃ for 2 h to form a titanium oxide layer on the surface of the MXene nanosheet. Centrifugal collect the obtained product and freeze-dry to obtain MXTiO.

[0045] Preparation of MXTiO / α-Fe2O3: First, add 0.3 g of FeCl3•6H2O and 100 mg of MXTiO nanosheet to 50 mL of deionized water.

[0046] Then, add 50 mL of KOH solution (1M) dropwise to the mixture, and continue to stir at 75℃ for 10 min. Then keep in a preheated furnace at 100℃ for 2 days. After natural cooling to room temperature, centrifugal the red product, wash with deionized water and ethanol three times, and dry at 70℃ overnight.

[0047] Finally, calcine at 450℃ for 2 h in an argon environment to successfully prepare the MXTiO / α-Fe2O3 composite material.

[0048] Embodiment 2 Preparation of MXene nanosheet material: This step is the same as Embodiment 1.

[0049] Preparation of MXTiO: Add 120 mg of the MXene nanosheet material powder prepared in the previous step to 30 ml of deionized water, heat in a water bath at 60℃ for 2.5 h to form a titanium oxide layer on the surface of the MXene nanosheet. Centrifugal collect the obtained product and freeze-dry to obtain MXTiO.

[0050] Preparation of MXTiO / α-Fe2O3: First, 0.5 g FeCl3·6H2O and 100 mg MXTiO nanosheets were added to 50 mL deionized water.

[0051] Then, 50 mL of 1 M KOH solution was added dropwise to the mixture, and stirring was continued at 70°C for 12 minutes. The mixture was then kept in a preheated oven at 80°C for 60 hours. After cooling naturally to room temperature, the red product was centrifuged, washed three times with deionized water and ethanol, and dried at 65°C overnight.

[0052] Finally, the MXTiO / α-Fe2O3 composite material was successfully prepared by calcining at 430℃ for 2.5h in an argon environment.

[0053] Example 3 Preparation of MXene nanosheet materials: This step is the same as Example 1.

[0054] Preparation of MXTiO: 120 mg of the MXene nanosheet powder prepared in the previous step was added to 30 ml of deionized water and heated in a 120°C water bath for 1.5 h to form a titanium oxide layer on the surface of the MXene nanosheets. The resulting product was collected by centrifugation and freeze-dried to obtain MXTiO.

[0055] Preparation of MXTiO / α-Fe2O3: First, 0.1 g FeCl3•6H2O and 100 mg MXTiO nanosheets were added to 50 mL deionized water.

[0056] Then, 50 mL of 1 M KOH solution was added dropwise to the mixture, and stirring was continued at 80°C for 8 minutes. The mixture was then kept in a preheated oven at 110°C for 36 hours. After cooling naturally to room temperature, the red product was centrifuged, washed three times with deionized water and ethanol, and dried at 75°C overnight.

[0057] Finally, the MXTiO / α-Fe2O3 composite material was successfully prepared by calcining at 470℃ for 1.5h in an argon environment.

[0058] Comparative Example This comparative example is basically the same as Example 1, except that: the MXene nanosheet material is not subjected to a hydrothermal reaction treatment, and α-Fe2O3 is directly deposited on the MXene nanosheet material.

[0059] Experimental Example 1 (1) Take SEM images of the MXene nanosheets obtained in the first step of Example 1 and the final MXTiO / α-Fe2O3 heterostructure product. Figure 1 and Figure 2As shown in the figure, it can be seen that Ti3C2T x The MXTiO / α-Fe2O3 heterostructures exhibited a stacked nanosheet structure with large lateral dimensions, while the MXTiO / α-Fe2O3 heterostructures showed a thin-layer microstructure with uniformly dispersed α-Fe2O3 nanoparticles.

[0060] (2) The HAADF image and EDS composition map of the MXTiO / α-Fe2O3 heterostructure prepared in Example 1 are as follows: Figure 3 As shown in the figure, it can be seen that its elemental composition includes carbon, iron, oxygen and titanium.

[0061] (3) Prepare X-ray diffraction patterns of α-Fe2O3 and MXTiO / α-Fe2O3, such as Figure 4 As shown in the figure, it can be seen that MXTiO / α-Fe2O3 has the component α-Fe2O3.

[0062] (4) Prepare Raman spectra of MXene nanosheets (represented by MX), α-Fe2O3 and MXTiO / α-Fe2O3, such as Figure 5 As shown in the figure, it can be seen that the 215cm -1 The scattering peak centered on the MXene nanosheets corresponds to the Ti and C atoms (A 1g ) out-of-plane vibration mode. In the MXTiO / α-Fe2O3 heterostructure, this vibration mode disappears due to the deep oxidation. Located at 232 and 292 cm -1 The vibration peak can be attributed to the A 1g and E 1g Vibration mode. MXTiO / α-Fe2O3 heterostructure at 174cm - ¹(E g ) exhibits a sharp phonon mode at 401 cm -1 (B 1g ) and 622cm -1 (E g ) exhibit broad modes at the α-axis, which can be attributed to the vibrational signals of titanium oxide, indicating that a large surface oxide layer has formed on the MXene nanosheets during the water bath and hydrothermal process. These signals are also detected in MXene due to the slight oxidation in the atmospheric environment.

[0063] (5) Visual adsorption experiment of Li2S6 solution: Various catalysts were added to the Li2S6 solution and the solution state was observed after a period of reaction. Figure 6 shown.

[0064] Figure 6Figure 1 represents a blank control (Li2S6 solution without catalyst). Figures 2 to 6 show the state of the solution after adding equal masses of MXene nanosheets prepared in Example 1, MXTiO prepared in Example 1, α-Fe2O3, the MX / α-Fe2O3 composite material prepared in the comparative example, and the MXTiO / α-Fe2O3 heterostructure material prepared in Example 1 to the Li2S6 solution for a period of time. The figures show that the addition of the MXTiO / α-Fe2O3 heterostructure material exhibits excellent polysulfide anchoring ability.

[0065] (6) Lithium-sulfur batteries were prepared using α-Fe2O3, MX / α-Fe2O3 and MXTiO / α-Fe2O3 as catalysts, and their electrochemical performance was tested.

[0066] Preparation method of lithium-sulfur battery: Membrane Synthesis: 10 mg of the MXTiO / α-Fe2O3 composite was added to 20 mL of isopropanol and sonicated for 30 minutes. Then, 0.2 mL of a binder solution (PVDF dissolved in NMP, 2.5% by mass) was added and sonicated for 30 minutes. The mixed solution was filtered through a Celgard 2400 membrane using a vacuum filtration apparatus and dried under vacuum at 60°C for 8 hours. MX / α-Fe2O3 / PP and α-Fe2O3 / PP were prepared using the same method.

[0067] Fabrication of the S cathode: Typically, S powder and Ketjen Black (8:2 weight ratio) were mixed and sealed in an argon-filled Teflon container, then heated to 155°C in an oven for 12 hours. S / KB and a water-based binder (LA132) were mixed in a 9:1 weight ratio, crushed, coated on aluminum foil, and dried in a vacuum at 60°C for 12 hours. The bulk electrode was a 1×1 cm carbon fiber cloth coated with the active material.

[0068] Preparation of Li2S6 and Li2S8 solutions: Li2S6 and Li2S8 were selected as prototypes of LiPS. Sulfur and Li2S (weight ratio of 5:1) were mixed in a mixed solvent of 1,3-dioxolane (DOL) and dimethoxymethane (DME) (1:1, v / v), and then stirred at 60°C for 24 hours to prepare a 0.5M Li2S6 solution. 0.3M Li2S8 was also prepared according to the above method, but the solvent was changed to diethylene glycol dimethyl ether.

[0069] LiPS adsorption test: 10 mg of different samples were added to 5 mL of 3 mmol Li2S6 for adsorption experiments.

[0070] Symmetrical cell assembly and testing: 5 mg of active material was dissolved in 10 mL of ethanol, sonicated for 30 minutes, and the corresponding solution was measured with a pipette and dropped onto carbon paper to prepare the electrode material. 20 μL of Li₂S₆ (0.5 M) was added to both sides of the separator to assemble a symmetrical cell for electrochemical testing within a voltage window of -1 to 1 V.

[0071] CR2032 coin cells were assembled and sealed in a glove box filled with high-purity argon. A 15.6 mm lithium foil served as the anode, and a S@C electrode served as the cathode. The electrolyte was prepared by dissolving 1 M LiTFSI and 2.0 wt% LiNO₃ in a 1:1 v / v mixture of dimethyl ether and 1,3-dioxolane (DOL). The electrolyte volume used in standard cells was 40 μL.

[0072] The battery with high sulfur loading and poor electrolyte is mainly due to the increase in the amount of material coating during the preparation of the S cathode, which achieves a negative electrode material loading of 9.34 mg / cm 2 , and reduce the amount of electrolyte added: 20μL.

[0073] Current static charge and discharge tests were performed on a LAND battery tester with a voltage range of 1.7-2.8 V. CV and EIS measurements (0.01-105 kHz) were performed on a CHI-760E electrochemical workstation. The test results were recorded in Figures 7 to 11 .

[0074] Figure 7 The enlarged GCD curve at 0.1C shows that the polarization potentials of the α-Fe2O3 system are 36.7 mV (precipitation) and 101.2 mV (dissolution), respectively, indicating significant kinetic limitations in the Li2S phase transition. Notably, the introduction of an asymmetric Ti-O-Fe bridge in the BIEF configuration significantly reduces these barriers to 15.7 mV and 35.6 mV, respectively. Compared to the reference system, this reduction is approximately 50% (relative to MX / α-Fe2O3) and 60% (relative to α-Fe2O3) due to enhanced interfacial charge transfer. Figure 8 The figure shows the rate performance at different current densities. It can be seen from the figure that MXTiO / α-Fe2O3 has better rate performance than α-Fe2O3 and MX / α-Fe2O3 as catalysts for lithium-sulfur batteries at different current densities. Figure 9The lithium-sulfur battery prepared by using the MXTiO / α-Fe2O3 heterostructure material prepared in Example 1 as a catalyst has a cycle performance at a current density of 0.1C, and it can be seen from the figure that, compared with α-Fe2O3 and MX / α-Fe2O3, the MXTiO / α-Fe2O3 can make the battery have better cycle performance at a low current density. The 0.1C capacity and cycle performance data of each example are recorded in Table 1.

[0075] Table 1: Capacity and cycle performance data of each example

[0076] As can be seen from Table 1, the initial capacity of the battery prepared in Example 1 can reach 1633mAhg -1 , and the capacity decay rate is extremely low, only 0.049% per cycle. The batteries prepared in Examples 2 and 3 both exhibit high initial capacity and cycle performance, reaching 1401mAhg -1 (single cycle decay rate: 0.061%) and 1011mAhg -1 (single cycle decay rate: 0.089%) respectively.

[0077] Figure 10 The cycle performance at a current density of 5C, and it can be seen from the figure that, compared with α-Fe2O3 and MX / α-Fe2O3, the MXTiO / α-Fe2O3 can make the battery have better cycle performance at a high current density, and can cycle for 1000 times at 5C; Figure 11 The cycle performance of the lithium-sulfur battery with the catalyst MXTiO / α-Fe2O3 under high sulfur loading and poor electrolyte conditions (on the basis of the specific preparation method of the lithium-sulfur battery, the coating amount of the material is increased during the preparation process of the S cathode, the negative material loading is 9.34mg / cm 2 , and the amount of electrolyte added is reduced: 20μL, and the MXTiO / α-Fe2O3 heterostructure material prepared in Example 1 is used as a catalyst to prepare a new test battery), and it can be seen from the figure that, even under a high sulfur loading of 10.1mg•cm -2 , the system can still maintain a high surface density of 13.1mAh•cm -2 at 0.01C, showing its potential for practical application.

[0078] The experimental results show that the MXTiO / α-Fe2O3 heterostructure material provided by the present application exhibits excellent electrocatalytic performance in a lithium-sulfur battery, can cycle for 1000 times at 5C, and the initial capacity reaches 1633mAhg -1, and the capacity decay rate is extremely low, only 0.049% per cycle. This excellent performance is due to the synergistic effect between the optimized surface electronic configuration and the interface BIEF. -2 Even with a high sulfur loading of 1.5 wt %, the system can still maintain 13.1 mAh cm at 0.01 °C. -2 The high areal density shows its potential for practical applications.

[0079] In summary, the sulfur battery catalyst provided by the present invention uses the MXTiO material as an electron acceptor, stealing some electrons from α-Fe2O3 through the interfacial asymmetric Ti-O-Fe bridge bond, inducing spontaneous charge redistribution. Electron transfer through the interfacial Ti-O-Fe channel forms electron-deficient Fe sites on the surface. This not only reduces the antibonding orbital electron occupancy (relative to isolated α-Fe2O3), thereby enhancing the dp orbital hybridization between the surface Fe and polysulfides, providing strong sulfur affinity, but also weakens the SS bond, thereby accelerating the cleavage and enhancing its catalytic performance in lithium-sulfur batteries. The lithium-sulfur battery catalyst (MXTiO / α-Fe2O3 heterostructure material) provided by the embodiments of the present invention exhibits excellent electrocatalytic performance in lithium-sulfur batteries, resulting in high battery capacity, good cycle performance, and extremely low capacity decay rate, and can enhance the cycling performance of lithium-sulfur batteries under high sulfur loading and electrolyte-poor conditions.

[0080] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-sulfur battery catalyst, characterized in that: include: Providing a MXene material, wherein the metal element in the MXene material is Ti; Placing the MXene material in water for a hydrothermal reaction to generate titanium oxide on the surface of the MXene material to obtain a MXTiO material; preparing a mixed dispersion in which iron ions are dissolved and the MXTiO material is dispersed; adding an alkaline solution to the mixed dispersion to react the iron ions into iron hydroxide and deposit it on the particle surface of the MXTiO material; extracting a solid from the reaction system after sufficient reaction to obtain an intermediate product; The intermediate product is calcined under an inert atmosphere to convert the iron hydroxide into iron oxide, thereby obtaining a MXTiO / α-Fe2O3 heterostructure material.

2. The preparation method according to claim 1, characterized in that The preparation method of the MXene material comprises: reacting MAlX nanopowder composed of elements Ti, Al, and X with an etching solution, so that the Al element in the MAlX dissolves in the etching solution and forms active sites on the surface of the powder particles, thereby obtaining the MXene material; The X element is at least one of C and N.

3. The preparation method according to claim 2, characterized in that The solutes in the etching solution include LiF and HCl. The concentration of LiF in the etching solution is 0.5-2M, and the concentration of HCl is 0.1-12M.

4. The preparation method according to claim 3, characterized in that The method of dissolving the Al element in the MAlX in the etching solution and forming active sites on the surface of the powder particles to obtain the MXeneMXene material includes: The MAlX nanopowder and the etching solution are uniformly mixed to obtain a mixed solution, and then the mixed solution is heated to 30-40° C. and kept warm for 40-60 hours, followed by solid-liquid separation and washing the obtained solid product with water.

5. The preparation method according to claim 1, characterized in that The mass ratio of iron ions to the MXTiO material in the mixed dispersion is 20.66-103.3:

100.

6. The preparation method according to claim 5, characterized in that The mixed dispersion is obtained by mixing FeCl3, the MXTiO material and water; Optionally, the concentration of iron ions in the mixed dispersion is 0.6-1.8 g / L.

7. The preparation method according to claim 1, characterized in that Also includes at least one of the following features (1) to (4): (1) Ways to fully respond include: After adding alkali solution to the mixed dispersion, stirring at 70-80° C. for 8-12 minutes, and then maintaining at 80-110° C. for 36-60 hours; (2) Methods for extracting solids from the reaction system to obtain intermediates include: After the reaction is completed, solid-liquid separation is performed, followed by washing with water and ethanol and drying; (3) The method of calcining the intermediate product under an inert atmosphere to convert iron hydroxide into iron oxide includes: Calcinate at 430-470 °C for 1.5-2.5 h under argon atmosphere; (4) Placing the MXene material in water for a hydrothermal reaction to generate titanium oxide on the surface of the MXene material. Methods for obtaining the MXTiO material include: The MXene material is placed in water and heated in a water bath or oil bath at 60-120° C. for 1.5-2.5 hours, followed by solid-liquid separation and freeze-drying of the solid product.

8. The preparation method according to claim 1, characterized in that The alkali solution is potassium hydroxide solution; Optionally, the concentration of the potassium hydroxide solution is 0.8~1.2M.

9. A lithium-sulfur battery catalyst, characterized in that The method is as described in any one of claims 1 to 8.

10. A lithium-sulfur battery, characterized in that: The invention comprises the lithium-sulfur battery catalyst as claimed in claim 9.

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