Preparation method and application of transition metal phosphorus sulfide with two-dimensional nano layered structure

Abstract

The invention relates to a preparation method of a two-dimensional nano layered transition metal phosphorus sulfide, which comprises the following steps: mechanically and uniformly mixing a transition metal precursor and P2S5 in an inert atmosphere, heating for melting and calcining, adding a crude product into an alcohol-water solution, heating and stirring, centrifugally separating, washing a precipitate, and drying to obtain the two-dimensional nano layered transition metal phosphorus sulfide. The two-dimensional nanometer layered transition metal phosphorus sulfide is obtained; the transverse size of the two-dimensional nano layered transition metal phosphorus sulfide is 1-20 microns, and the thickness of the nanosheet is 5-30 nm. Through simple process steps, the two-dimensional nano layered transition metal phosphorus sulfide which is difficult to obtain by a conventional method can be obtained, the special morphology has abundant active sites exposed on the surface, and the reaction kinetics of the Li-O2 battery is accelerated; and meanwhile, the nanosheet structure can provide more geometric spaces and improve the charge-discharge specific capacity of the battery, so that the Li-O2 battery positive electrode catalyst can show excellent performances of high specific capacity, low overpotential and long cycle life.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium air batteries, and particularly relates to a preparation method of a two-dimensional nano layered transition metal phosphorus sulfide and application thereof. BACKGROUND

[0002] With the rapid development of global economy, the environmental problems such as greenhouse effect caused by overuse of fossil fuels are increasingly prominent, and people's demand for clean energy is particularly urgent. Under the background of global implementation of "energy saving and emission reduction", the market of new energy vehicles and their supporting energy storage industry develops very rapidly. The essential conditions of vehicle power supply are: high power, high energy density, high safety, strong environmental adaptability. The traditional lead-acid battery has the disadvantages of large mass and small specific energy (<50 Wh / kg); fuel cells not only have high cost, but also have great safety hazards; the existing lithium ion battery is widely used in mobile electronic devices and power batteries, but its energy density is still small (<300 Wh / kg), which cannot meet the further demand of power equipment for energy. Therefore, metal air batteries emerge as the times require, among which lithium air batteries have an energy density close to that of gasoline (energy density is about 11400 Wh / kg), and stand out among metal air batteries and are considered as a battery system with great potential.

[0003] Although lithium air batteries have ultra-high theoretical specific capacity and energy density, the overpotential in the charging and discharging process seriously affects the cycle stability and energy efficiency of the battery, which greatly limits its practical process. Numerous research results show that loading catalysts in the positive electrode material of lithium air batteries can greatly improve the electrochemical performance of Li-O2 batteries. It is found that loading noble metal catalysts such as Pt, Pd, Ru and RuO2 in the positive electrode of lithium air batteries can improve the performance of lithium air batteries, but it is still difficult to meet the requirements of practical application, and the high cost of such metal catalysts also limits their large-scale production and application. Functionalized carbon materials (such as graphene, carbon nanotubes, mesoporous carbon, etc.) are less expensive than noble metals, but they do not have excellent catalytic performance and the production process is complex, which is difficult to realize large-scale production and application. Based on the above problems, the team designed to use transition metal precursors and phosphorus sulfide as raw materials to obtain active materials with excellent catalytic activity and high catalytic stability through one-step solid-state reaction.

[0004] Two-dimensional transition metal phosphorus sulfides (MPS3) are a large class of layered compounds, which have open space structure and good electrocatalytic activity, and have been widely used in electrochemical energy storage and conversion. At present, the preparation methods of phosphorus sulfides mainly include high temperature vacuum calcination and chemical vapor phase conversion, but these two preparation methods have obvious shortcomings. For example, the preparation environment is high, the preparation steps are complex, it is not easy to prepare in batches, and the crystallinity of the prepared samples is high, and in most cases, the samples exist in the form of bulk phase, which is difficult to further process.

[0005] CN116856079A discloses a method for preparing transition metal phosphorus sulfide fibers by melt-blowing spinning process, comprising the following steps: (1) a certain amount of phosphorus P, sulfur S, and one or more transition metal ultrafine powder (Me = V, Fe, Co, Ni, Cu, Zn, Cr, Mn, Al) mixture is placed in a high-temperature-resistant (> 700℃) metal barrel, and the number of metal powder types is 1 to 5; (2) the multiple instruments used for melt-blowing spinning, including gas heating air blower, metal barrel, fiber collecting device, etc., are placed in a closed inert gas environment, the gas heating air blower provides high-speed and high-pressure dry gas flow, and the fiber collecting device can be a mesh collector and a roller collector; (3) the tail end of the metal barrel is connected and inert gas (argon or nitrogen, gas path A) is introduced, and the front end is connected with a steel needle, and the gas outlet (gas path B) of the gas heating air blower is aligned with the needle from the side; (4) the metal barrel is heated, and the heating temperature is controlled at a temperature about 100℃ higher than the melting point of the lower metal or non-metal, the molten metal liquid wraps part of the un-melted metal ultrafine powder, and the gas pressure of gas path A is slightly higher than atmospheric pressure to ensure that the gas generated when P and S are heated does not backflow; (5) after the barrel temperature reaches the above-mentioned temperature for 1h, the gas pressure of gas path A is increased, the molten metal liquid is pushed out from the needle hole, is stretched into fibers under the influence of high-speed and high-temperature dry gas flow (gas path B), and the height of the needle hole should be at the same horizontal height as the center of the fiber collecting device; (6) when the fiber volume reaches the target requirement, the heating device is turned off and the fiber is naturally cooled, and after cooling to room temperature, it can be taken out, and the fiber material is a transition metal phosphorus sulfide fiber.CN114763620A discloses a preparation method of transition metal phosphorus sulfide catalyst for hydrogen evolution by water electrolysis, which uses a mixture of transition metal phosphate and thiourea as precursor, and prepares transition metal phosphorus sulfide by programmed temperature reduction method in hydrogen atmosphere; the transition metal in the transition metal phosphorus sulfide is W or Mo or Ni or Co; the active phase of the transition metal phosphorus sulfide is sulfur-containing WP or MoP or Ni2P or Co2P; the transition metal phosphate is prepared by co-precipitation method; the mixture of the transition metal phosphate and thiourea is a mechanical mixture of the two, and the mass ratio of transition metal phosphate / thiourea is 1-3; the reducing gas of the programmed temperature reduction is hydrogen, the pressure is normal pressure to 10MPa, the reduction temperature is 300-800℃, and the reduction time is 6-12 hours.CN113908858A discloses a transition metal sulfur phosphide and a preparation method thereof, comprising the following steps: a soluble nickel source, red phosphorus, a soluble sulfur source and water are mixed, the pH value is adjusted, and the obtained alkaline raw material liquid is subjected to hydrothermal reaction to obtain the transition metal sulfur phosphide.CN112877712A discloses a transition metal phosphorus sulfide and a preparation method thereof, comprising the following steps: mixing nickel nitrate, cobalt nitrate, urea and ammonium fluoride, and preparing a solution to obtain a precursor solution; adding foamed nickel into the precursor solution for hydrothermal reaction to obtain a precursor; placing the precursor in a sulfur hydride sodium and sodium hypophosphite containing environment for calcination treatment under a protective atmosphere to obtain the transition metal phosphorus sulfide.

[0006] However, the above-mentioned patent obtains a bulk phase of transition metal phosphorus sulfide. To obtain a two-dimensional transition metal phosphorus sulfide, a complex exfoliation step is still needed, and the yield is low and unstable.

[0007] CN119038507A discloses a metal phosphorus sulfide nanowire and a preparation method thereof. A mixture containing NPS3 powder and an alkali metal salt solution is reacted for a period of time.

[0008] CN119263231A discloses a transition metal phosphorus sulfide and a preparation method thereof, comprising the following steps: ball-milling a transition metal, phosphorus and sulfur to obtain a mixture; and high-temperature, long-time vacuum sintering the mixture to obtain the transition metal phosphorus sulfide. The transition metal phosphorus sulfide obtained by the patent has a layered structure. However, the transition metal phosphorus sulfide obtained by the patent is still a bulk phase in a microscopic view. As can be seen from the SEM image, it is not a two-dimensional nanometer layered structure, but a micron-level layered structure. When the bulk phase sample is used as a catalyst, its surface area is small, the active site exposure rate is low, and most of the active sites are covered by the stacking between the layers, which is not conducive to the improvement of the catalytic performance related to the surface / interface. The main idea of the patent is to mix transition metal, phosphorus and sulfur and then vacuum calcine to prepare transition metal phosphorus sulfide. This method is complicated to operate and requires high equipment. During the mixing process, vacuum sealing tube technology is needed to heat seal the glass tube while vacuumizing. On the other hand, this technology is difficult to scale up. The volume of the vacuum glass tube is limited, and the amount of weak sulfur and phosphorus is too much. At high temperatures, the gasification of sulfur and phosphorus may cause an explosion risk. If the volume of the glass tube is increased to increase the yield, a very large volume is needed to achieve this, and the glass tube is a disposable product, which will greatly increase the cost. In addition, the high-temperature reaction time in this technology is very long. If the synthesis is shortened, there will be problems such as incomplete reaction or generation of solid impurities, and the product cannot be separated and purified. Therefore, compared with the present patent, this technology is suitable for preparing a small amount of bulk phase structure sample, and has no advantages in other aspects.

[0009] Science (2020, 370, 596) and Energy Environ. Mater. (2022, 5, 899) reported that transition metal phosphorus sulfide two-dimensional nanometer layered structure is prepared by ultrasonic exfoliation method. First, the transition metal raw material is mixed with sulfur source and phosphorus source, and then bulk crystal is prepared by long time, high temperature vacuum sealing tube calcination. Then, the two-dimensional nanometer layered structure is obtained by exfoliating the bulk material in the ultrasonic environment. The preparation process is complex, the efficiency is low, and it is not suitable for industrial large-scale production. SUMMARY

[0010] In order to solve the defects of the prior art of preparing two-dimensional nanometer layered structure of transition metal phosphorus sulfide, the process is complex, the cost is high, and the efficiency is low. The present application can realize rapid preparation of two-dimensional phosphorus sulfide nanometer layered material by reaction of transition metal precursor with phosphorus sulfide, which shows good electrocatalytic activity and stability as a positive electrode catalyst of Li-O2 battery. Among them, the FePS3 electrode has a discharge specific capacity as high as 12500mAh g -1 , and when the current density is 500mAg -1 , the specific capacity is limited to 500mAh g -1 , and it can be stably cycled for about 545 cycles, which is expected to become a kind of cheap and efficient Li-O2 battery positive electrode catalyst. It provides a new idea and method for efficient lithium air battery solid electrolyte.

[0011] Specifically, the present application provides the following technical solutions to solve the above technical problems:

[0012] A preparation method of two-dimensional nanometer layered transition metal phosphorus sulfide, comprising the following steps: uniformly mixing transition metal precursor and P2S5 in an inert atmosphere, then heating and melting calcining, adding the crude product into an alcohol-water solution, heating and stirring, centrifugal separation, washing the precipitate, and drying to obtain two-dimensional nanometer layered transition metal phosphorus sulfide; the lateral size of the two-dimensional nanometer layered transition metal phosphorus sulfide is 1-20μm, and the thickness of the nanometer sheet is 5-30nm.

[0013] Further, the transition metal precursor is selected from at least one of oxalate, hydroxide, oxide, halide (chloride, bromide, iodide), sulfate, nitrate, acetate, metal element, sulfide, nitride, carbide, and organic metal salt of transition metal M, and metal M is selected from at least one of Fe, Cu, Co, Ti, Sc, V, Cr, Cd, Ni, Mn, Zn, Hg, Ca, In, Sn, and Lu.

[0014] Further, the transition metal precursor is selected from Fe(OH)2, FeO, CuO, MgO,

[0015] Further, the transition metal precursor and P2S5 are used in an amount that the molar ratio of metal M and P2S5 is 1:3-20, preferably 1:3-10, more preferably 1:3-5.

[0016] Further, the inert atmosphere is nitrogen and / or argon.

[0017] Further, the mechanical mixing uniformity is not particularly limited, such as grinding, ball milling, ultrasonic, mechanical stirring.

[0018] Before calcination, the pretreatment step of mechanically mixing the transition metal precursor and P2S5 uniformly in an inert atmosphere is crucial, which directly affects whether the two-dimensional nanometer layered structure product can be successfully obtained. P2S5 is sensitive to water and oxygen, and is prone to deterioration, forming hydrogen sulfide and phosphate, etc., resulting in loss of sulfur and phosphorus sources, and the transition metal phosphorus sulfide product cannot be obtained. At the same time, P2S5 is a highly toxic product; grinding in an argon atmosphere glove box can ensure that P2S5 and metal source are stably and uniformly mixed, avoiding direct contact with air, water and experimental personnel.

[0019] Further, the temperature is raised to 400-600℃ at a rate of 1-20℃ / min, preferably 5-10℃ / min, and the calcination dimension is 400-480℃. The calcination time is 2-5h.

[0020] Further, the alcohol aqueous solution is a mixed solvent of water and C1-4 alcohol in a volume ratio of 1-3:1-3. The C1-4 alcohol is selected from at least one of methanol, ethanol, propanol, butanol, butanediol and propylene glycol. Preferably, the alcohol aqueous solution is a mixed solvent of water and ethanol in a volume ratio of 1-2:1-2. The temperature is raised to 50-90℃, preferably 60-70℃. The purpose of using hot alcohol aqueous solution treatment is to remove unreacted P2S5 and by-products.

[0021] Further, the washing is washed with anhydrous ethanol for 1-5 times, such as 3-4 times. The drying is vacuum drying.

[0022] Further, the two-dimensional nanometer layered transition metal phosphorus sulfide has a lateral size of 1-20μm, preferably 2-10μm, such as 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm; and a nanosheet thickness of 5-30nm, preferably 10-20nm.

[0023] The second object of the present application is to provide the use of the two-dimensional nanometer layered transition metal phosphorus sulfide as a Li-O2 battery positive electrode catalyst.

[0024] Lithium-air battery reaction is a complex reaction involving gas-solid-liquid three-phase interface, two-dimensional nanostructure not only inherits the characteristics of bulk materials, but also has a high proportion of exposed metal atoms on the surface, and these exposed atoms are sites with dangling bonds, which play an important role in the electrocatalytic conversion of small molecules such as oxygen. At the same time, with the reduction of dimension, the nano material also has good electrical conductivity, two-dimensional nano material can promote the rapid transfer of electrons and fast mass transfer, ensure the close contact of the catalyst and the electrolyte, provide more three-phase reaction sites, and promote the charging and discharging reaction of Li-O2 battery.

[0025] By simple process steps, the two-dimensional nano layered transition metal phosphorus sulfide which is difficult to obtain by conventional method can be obtained, compared with the bulk phase transition metal phosphorus sulfide, the two-dimensional nano layered morphology of the present application can be simply and effectively obtained by mixing the transition metal precursor and P2S5 under inert atmosphere and then calcining. The traditional bulk phase structure: the traditional synthesis method is mainly synthesized by gas phase conversion, in the gaseous state, the atoms can grow in three-dimensional direction at high temperature, with the extension of time, larger bulk phase structure is generated. The reaction of the present application is carried out in the molten state, the overall reaction system has large viscosity, the growth speed of MPS3 material along the layer direction is slightly smaller, and for the vertical layer direction, the growth rate is greatly limited due to the weak van der Waals force between layers, therefore, the overall presents the ultra-thin two-dimensional nano structure. This special morphology has rich surface exposed active sites, which can provide more effective adsorption sites for the electrochemical process of O2, capture the reaction intermediates, promote the nucleation and growth of the reaction intermediates on the surface of the catalyst, avoid the occurrence of side reactions, and accelerate the reaction kinetics of Li-O2 battery; at the same time, the nanosheet structure can provide more geometric space for storing solid reaction products, so as to improve the charge-discharge specific capacity of the battery, therefore, as the positive catalyst of Li-O2 battery, the two-dimensional nano layered transition metal phosphorus sulfide can exhibit excellent performance of high specific capacity, low overpotential and long cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is the XRD pattern of the two-dimensional nano layered transition metal phosphorus sulfide prepared in example 1 to example 6

[0027] Figure 2 is the XPS full spectrum of FePS3 prepared in example 2 and CdPS3 prepared in example 5.

[0028] Figure 3 is the SEM image (a), TEM image (b), HRTEM image (c), high resolution transmission electron microscope image (d) and element distribution map (e) of FePS3 prepared in example 2.

[0029] Figure 4(a) charge-discharge curve (b, c) cycle stability test results of the FePS3 electrode of Example 3 in a Li-O2 battery. DETAILED DESCRIPTION

[0030] The following specific examples further explain the technical solutions of the present application.

[0031] Example 1

[0032] 10 mmol of MnC2O4 and 30 mmol of P2S5 were weighed and placed in a glove box under high-purity argon protection (O2 and H2O content ≤ 20 ppm) for mechanical grinding and mixing. The grinding speed was 200 rpm, and the grinding time was 10 minutes. After grinding, the mixture was passed through a 100-mesh sieve to remove larger-sized raw materials. The uniformly mixed raw materials were transferred to a covered corundum crucible, which was placed in a tube furnace and protected by argon. The temperature was raised to 450°C at a rate of 5°C / min and maintained for 2 h. After natural cooling, the crude MnPS3 product was obtained. The crude product was placed in a water / ethanol mixed solution with a volume ratio of 1:1, and stirred at 70°C for 1 h to dissolve and remove the unreacted P2S5 byproduct. After centrifugal separation (8000 rpm, 10 min), the precipitate was collected, washed with anhydrous ethanol three times, and finally dried in a vacuum drying box at 60°C for 1 h to obtain high-purity two-dimensional nanometer layered MnPS3 material.

[0033] Example 2

[0034] 10 mmol of Fe(OH)2 and 30 mmol of P2S5 were weighed and placed in a glove box under high-purity argon protection (O2 and H2O content ≤ 20 ppm) for mechanical grinding and mixing. The uniformly mixed raw materials were transferred to a covered corundum crucible, which was placed in a tube furnace and protected by argon. The temperature was raised to 420°C at a rate of 5°C / min and maintained for 2 h. After natural cooling, the crude FePS3 product was obtained. The crude product was placed in a water / ethanol mixed solution with a volume ratio of 1:1, and stirred at 70°C for 1 h to dissolve and remove the unreacted P2S5 byproduct. After centrifugal separation (8000 rpm, 10 min), the precipitate was collected, washed with anhydrous ethanol three times, and finally dried in a vacuum drying box at 60°C for 1 h to obtain high-purity two-dimensional nanometer layered FePS3 material.

[0035] Example 3

[0036] 10 mmol of Co3O4 and 30 mmol of P2S5 were weighed and mechanically ground in a glove box under high-purity argon protection (O2 and H2O content ≤20 ppm) at 200 rpm for 10 minutes. After grinding, the mixture was passed through a 100-mesh sieve to remove larger pieces. The homogeneous mixture was transferred to a covered corundum crucible and placed in a tube furnace under argon protection. The temperature was increased to 460℃ at 5℃ / min and maintained for 2 hours. After natural cooling, crude CoPS3 product was obtained. The crude product was placed in a 1:1 water / ethanol mixture and stirred at 70℃ for 1 hour to dissolve and remove unreacted P2S5 byproducts. The precipitate was collected by centrifugation (8000 rpm, 10 minutes), washed three times with anhydrous ethanol, and finally dried in a vacuum drying oven at 60℃ for 1 hour to obtain high-purity two-dimensional nanolayered CoPS3 material.

[0037] Example 4

[0038] 10 mmol Ni(CH3COO)2 and 30 mmol P2S5 were weighed and mechanically ground in a glove box under high-purity argon protection (O2 and H2O content ≤20 ppm) at 200 rpm for 10 minutes. After grinding, the mixture was passed through a 100-mesh sieve to remove larger pieces. The homogeneous mixture was transferred to a covered corundum crucible and placed in a tube furnace under argon protection. The temperature was increased to 450℃ at 5℃ / min and maintained for 2 hours. After natural cooling, crude NiPS3 was obtained. The crude product was placed in a 1:1 water / ethanol mixture and stirred at 70℃ for 1 hour to dissolve and remove unreacted P2S5 byproducts. The precipitate was collected by centrifugation (8000 rpm, 10 minutes), washed three times with anhydrous ethanol, and finally dried in a vacuum drying oven at 60℃ for 1 hour to obtain high-purity two-dimensional nanolayered NiPS3 material.

[0039] Example 5

[0040] 10 mmol of CdCl2 and 30 mmol of P2S5 were weighed and mechanically ground in a glove box under high-purity argon protection (O2 and H2O content ≤20 ppm) at 200 rpm for 10 minutes. After grinding, the mixture was passed through a 100-mesh sieve to remove larger pieces. The homogeneous mixture was transferred to a covered corundum crucible and placed in a tube furnace under argon protection. The temperature was increased to 460℃ at 5℃ / min and maintained for 2 hours. After natural cooling, crude NiPS3 was obtained. The crude product was placed in a 1:1 water / ethanol mixture and stirred at 70℃ for 1 hour to dissolve and remove unreacted P2S5 byproducts. The precipitate was collected by centrifugation (8000 rpm, 10 minutes), washed three times with anhydrous ethanol, and finally dried in a vacuum drying oven at 60℃ for 1 hour to obtain high-purity two-dimensional nanolayered CdPS3 material.

[0041] Example 6

[0042] 10 mmol Zn(C5H7O2)2 and 30 mmol P2S5 were weighed and mechanically ground in a glove box under high-purity argon protection (O2 and H2O content ≤20 ppm) at 200 rpm for 10 minutes. After grinding, the mixture was passed through a 100-mesh sieve to remove larger pieces. The homogeneous mixture was transferred to a covered corundum crucible and placed in a tube furnace under argon protection. The temperature was increased to 480℃ at 5℃ / min and maintained for 2 hours. After natural cooling, crude NiPS3 was obtained. The crude product was placed in a 1:1 water / ethanol mixture and stirred at 70℃ for 1 hour to dissolve and remove unreacted P2S5 byproducts. The precipitate was collected by centrifugation (8000 rpm, 10 minutes), washed three times with anhydrous ethanol, and finally dried in a vacuum drying oven at 60℃ for 1 hour to obtain high-purity two-dimensional nanolayered ZnPS3 material.

[0043] Comparative Example 1

[0044] FePS3 was prepared according to the method described in Example 2 of patent CN119263231A, but the resulting product was not a two-dimensional nanolayer, but a bulk phase. The specific steps are as follows: 50g of elemental iron, 27.68g of elemental phosphorus, and 85.71g of elemental sulfur were mixed and placed in a ball mill. The mixture was ball-milled at 600 rpm for 30 minutes to obtain a mixture. The mixture was then placed in a quartz tube with burnished indentations, vacuum-sealed, and then kept at 700°C for 60 hours. After the reaction was completed, the mixture was cooled to room temperature, and the vacuum-sintered product was taken out and ground again in a ball mill for 20 minutes to obtain a bulk transition metal phosphorus sulfide.

[0045] Comparative Example 2

[0046] CdPS3 was prepared according to the chemical vapor transport method described in Science (2020, 370, 596), but the resulting product was a bulk structure and required further ultrasonic exfoliation to obtain a nanosheet structure. The specific steps are as follows: 938 mg of cadmium powder, 259 mg of red phosphorus blocks, 803 mg of sulfur tablets, and 40 mg of iodine were mixed and vacuum-sealed in a quartz ampoule (13 cm long and 16 mm in diameter); the sealed ampoule was placed in the middle of a tube furnace and kept at 700 °C for 5 days. After the ampoule cooled to room temperature, the product was collected at the cold end and washed with ethanol to remove residual iodine, finally obtaining CdPS3 crystals; 500 mg of CdPS3 crystals were weighed and treated in 40 mL of deionized water for 2 hours by ultrasonic exfoliation. The resulting dispersion was then centrifuged at 2000 rpm for 5 minutes to remove thicker flakes. The supernatant was filtered through a polyethersulfone membrane under vacuum and dried at 50 °C for 24 hours to obtain the original CdPS3 nanosheet membrane.

[0047] Figure 1 These are XRD patterns of the two-dimensional nanolayered transition metal phosphorus sulfides prepared in Examples 1 to 6. They include MnPS3, CdPS3, CoPS3, FePS3, NiPS3, and ZnPS3. The FePS3 sample is used as an example here for illustration. Figure 1 The d-value is the XRD pattern of FePS3. The sample exhibits a series of strong diffraction peaks at 13.86°, 27.84°, 30.48°, 35.52°, and 53.40°, which correspond to the (001), (002), (130), (-202), and (060) crystal planes in the standard card PDF No. 74-1501. This indicates that the sample synthesized by this method is a pure phase. Furthermore, information from the standard PDF card indicates that the sample belongs to the monoclinic crystal system, space group C2 / m(12). The overall XRD pattern results demonstrate that the series of samples synthesized by this method possess high purity and excellent crystal structure, verifying the effectiveness and reliability of this method.

[0048] Figure 2 These are the XPS full spectra of FePS3 prepared in Example 2 and CdPS3 prepared in Example 5. X-ray photoelectron spectroscopy was used to analyze the valence states of each element present on the surface of the synthesized samples. Figure 2 The image 'a' is the XPS full spectrum of CdPS3, which shows that the sample is mainly composed of Cd, P, and S. Figure 2 Figure b is the FePS3 spectrum, which shows that the sample is mainly composed of Fe, P, and S. XPS test results indicate that a series of transition metal phosphorus sulfides were successfully synthesized using this method.

[0049] Figure 3These are SEM images (a), TEM images (b), HRTEM images (c), high-resolution transmission electron microscope images (d), and elemental distribution maps (e) of FePS3 prepared in Example 2. Figure 3 As can be seen from a, FePS3 is a typical two-dimensional nanolayer structure, with the lateral size of its nanosheets distributed in the range of 5 μm. Figure 3 b represents the atomic force microscopy test results of the sample, which shows that the sample thickness is approximately 18.7 nm, indicating an ultrathin two-dimensional nanosheet structure. Figure 3 c is a transmission electron microscope image of the sample. The image shows obvious wrinkles and low contrast, which indicates that the sample synthesized by this method is thin, consistent with the results of atomic force microscopy. Figure 3 Image d is a high-resolution transmission electron microscope image, which shows clear lattice fringes with a spacing of 0.292 nm on the sample, corresponding to the (130) crystal plane of FePS3. This is consistent with the XRD analysis results, indicating that the sample has good crystallinity. At the same time, it can be seen from the inset that the lattice fringes are discontinuous, which indicates that there are defects in the synthesized sample. Figure 3 The 'e' diagram shows the elemental distribution of the sample, with iron, phosphorus, and sulfur evenly distributed throughout. In summary, the FePS3 synthesized using this method exhibits the ultrathin structure of a two-dimensional material, good crystallinity, and is rich in metal vacancies. Other samples synthesized using this method show similar structural characteristics and features.

[0050] Application examples

[0051] The two-dimensional nanolayered transition metal phosphorus sulfide prepared in the examples was used as a positive electrode catalyst to assemble a Li-O2 battery. The specific steps are as follows: 9 mg of Ketjen black and 1 mg of carbon nanotubes were added to 1 mL of N-methylpyrrolidone and dispersed evenly, and then 10 mg of [unclear text] was added. FePS3 nanosheets and 222.2 mg of 1% polyvinylidene fluoride solution were stirred evenly to obtain a mixed slurry. The mixed slurry was then coated onto the surface of carbon paper and dried under vacuum at 110°C (wherein, the 1% polyvinylidene fluoride solution refers to a solution with polyvinylidene fluoride as the solute, N-methylpyrrolidone as the solvent, and a polyvinylidene fluoride mass fraction of 1%). Using the above electrode as the positive electrode, a lithium sheet as the negative electrode, and a 1 mol / L LiTFSI-TEGDME (lithium bis(trifluoromethanesulfonyl)imide-tetraethylene glycol dimethyl ether) solution as the electrolyte, the Li-O2 battery was assembled in a glove box in the following order: negative electrode shell - gasket - lithium sheet - separator (injected electrolyte) - positive electrode sheet - positive electrode shell, forming a Li-O2 battery (wherein the positive electrode shell is a sieve structure that can be connected to the external gas).

[0052] The assembled Li-O2 batteries were subjected to constant current charge-discharge tests in a high-purity oxygen atmosphere. All current densities and specific capacities were calculated based on the mass of the loaded materials. The test system pressure was 1 atmosphere, the test system temperature was room temperature, the test system was a Newwell tester, and the constant current charge-discharge voltage range was 2.0-4.5V. Both the unrestricted charge-discharge test and the limited-capacity cycle test were performed at 500 mAg. -1 The experiment was conducted at a current density of [value missing].

[0053] Figure 4 These are the (a) charge-discharge curves and (b, c) cycle stability test results of the FePS3 electrode in a Li-O2 battery according to Example 2. The FePS3 electrode exhibits a very high discharge specific capacity, approaching 12500 mAh g⁻¹. -1 Generally, the median voltage can be used to represent the average voltage at each stage, and the round-trip efficiency of the battery can be further calculated. For the FePS3 electrode, the median discharge voltage and median charge voltage are 2.60V and 4.05V, respectively, and the overpotentials for charge and discharge reactions are 1.09V and 0.36V, respectively, exhibiting good activity in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The above results fully demonstrate that the FePS3 sample prepared by this method can serve as a highly efficient bifunctional electrocatalyst for catalyzing ORR and OER reactions in lithium-oxygen batteries. Typically, for battery stability testing, multiple constant-current charge-discharge cycles need to be performed under limited capacity. Figure 4 (b) shows the battery cycle performance when the FePS3 electrode is used as the Li-O2 electrode, and (c) shows the corresponding change in coulombic efficiency cycle number. As can be seen from the figures, the battery assembled with the FePS3 electrode has a limited discharge specific capacity of 500 mAh g in a high-purity oxygen system. -1 Under these conditions, it can run stably for 545 cycles, and the coulomb efficiency can still be maintained at 100% at 545 cycles, showing excellent cycle performance.

[0054] The electrical performance data of Li-O2 batteries using two-dimensional nanolayered transition metal phosphorus sulfides as cathode catalysts in different embodiments are listed in Table 1 below.

[0055] Cyclic stability testing is limited to a discharge specific capacity of 500 mAh g. -1 Under these conditions, the discharge specific capacity and coulombic efficiency remain at 100% and can operate stably for a certain number of cycles.

[0056] Table 1 Electrical performance data of Li-O2 batteries

[0057] Positive electrode catalyst Material Discharge specific capacity (mAh g -1 ) Overpotential (V) Cycle stability number of cycles Example 1 MnPS3 9000 1.50 250 Example 2 FePS3 12500 1.45 545 Example 3 CoPS3 10000 1.50 300 Example 4 [NiPS3] 7000 1.48 230 Example 5 [CdPS3] 6600 1.60 190 Example 6 ZnPS3 5000 1.75 170 Comparative Example 1 FePS3 4000 1.80 50 Comparative Example 2 [CdPS3] 3600 1.90 40

[0058] In summary, the FePS3 electrode not only exhibits excellent performance in discharge capacity and charge / discharge overpotential, but also demonstrates superior stability in long-term cycling tests. The FePS3 sample prepared using this method shows potential as a highly efficient bifunctional electrocatalyst, capable of effectively catalyzing the ORR and OER reactions in lithium-oxygen batteries, making it a strong candidate for future cathode catalysts in lithium-oxygen battery electrode materials.

Claims

1. A method for preparing two-dimensional nanolayered transition metal phosphorus sulfides, characterized in that, The process includes the following steps: under an inert atmosphere, a transition metal precursor and P2S5 are mechanically mixed uniformly, then heated for melting and calcination. The crude product is added to an alcohol-water solution, heated and stirred, centrifuged, the precipitate is washed and dried to obtain a two-dimensional nanolayered transition metal phosphorus sulfide. The two-dimensional nanolayered transition metal phosphorus sulfide has a lateral dimension of 1-20 μm and a nanosheet thickness of 5-30 nm.

2. The preparation method according to claim 1, characterized in that, The transition metal precursor is selected from at least one of the following: oxalate, hydroxide, oxide, halide (chloride, bromide, iodide), sulfate, nitrate, acetate, elemental metal, sulfide, nitride, carbide, organometallic salt of transition metal M; and metal M is selected from at least one of Fe, Cu, Co, Ti, Sc, V, Cr, Cd, Ni, Mn, Zn, Hg, Ca, In, Sn, and Lu.

3. The preparation method according to claim 1, characterized in that, The transition metal precursor is selected from Fe(OH)2, FeO, CuO, and MgO.

4. The preparation method according to claim 1, characterized in that, The amounts of transition metal precursor and P2S5 satisfy the molar ratio of metal M to P2S5 as 1:3-20.

5. The preparation method according to claim 1, characterized in that, The inert atmosphere is nitrogen and / or argon; there are no particular limitations on the method of mechanical mixing, such as grinding, ball milling, ultrasonication, or mechanical stirring; grinding is preferred.

6. The preparation method according to claim 1, characterized in that, The melting and calcining process involves heating the temperature at a rate of 1-20℃ / min to 400-600℃, preferably at a rate of 5-10℃ / min, with a calcination temperature of 400-480℃. The calcination time is 2-5 hours.

7. The preparation method according to claim 1, characterized in that, The alcohol-water solution is a mixed solvent of water and C1-4 alcohol in a volume ratio of 1-3:1-3; the C1-4 alcohol is selected from at least one of methanol, ethanol, propanol, butanol, butanediol, and propylene glycol; preferably, the alcohol-water solution is a mixed solvent of water and ethanol in a volume ratio of 1-2:1-2; the heating and stirring are carried out at 50-90°C, preferably 60-70°C.

8. The preparation method according to claim 1, characterized in that, The lateral dimensions of the two-dimensional nanolayered transition metal phosphorus sulfides are 2-10 μm, and the thickness of the nanosheets is 10-20 nm.

9. A two-dimensional nanolayered transition metal phosphorus sulfide, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. The use of the two-dimensional nanolayered transition metal phosphorus sulfide prepared by the preparation method according to any one of claims 1-8 as a positive electrode catalyst for Li-O2 batteries.

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