As-prepared ultrathin carbon-coated metal sulfide nanodot material, preparation and application thereof

Abstract

The application belongs to the field of electrode materials, and particularly relates to a raw-state ultra-thin carbon-coated metal sulfide nanodot material, which comprises metal sulfide nanodots and a nanoscale-thickness carbon layer uniformly coated on the surface of the metal sulfide nanodots. The application also provides a preparation method and application of the material. Different from conventional metal sulfide@carbon materials, the nanomaterial disclosed by the application is formed synchronously with metal sulfide and carbon materials, and the metal sulfide particles are smaller (nanodots), and the surface is uniformly coated with ultra-thin carbon material reaching atomic level nanoscale. Research finds that the material has better stability and better electrochemical performance in alkali metal secondary batteries.

Description

Technical Field

[0001] This invention belongs to the field of electrode material preparation technology, specifically relating to the field of negative electrode materials. Background Technology

[0002] In recent years, lithium-ion rechargeable batteries have been successfully applied in transportation, information, aerospace, and other fields. However, traditional graphite electrodes exhibit relatively small capacities, especially when used as anodes in sodium-ion batteries, failing to meet the growing demands of modern life. Transition sulfides, another major anode material in lithium-ion rechargeable battery research, have attracted widespread attention due to their wide availability and high theoretical specific capacity. However, the significant volume expansion during cycling directly leads to pulverization, ultimately resulting in significant detachment from the current collector, causing a decline in electrochemical performance and potential safety malfunctions. Simultaneously, their low conductivity also limits their practical application in battery materials.

[0003] To further enhance the electrochemical performance of materials, structural design, carbon-based composites, and interfacial valence bond construction are frequently employed in the design and synthesis of materials. Due to their unique volume and surface effects, the interactions between atoms, and the wave-like nature of electrons within the material, nanomaterials exhibit special interfacial characteristics and surface structures, resulting in their unique electrochemical properties. Numerous studies have shown that nanomaterials demonstrate excellent performance in increasing energy density, mitigating volume expansion, reducing capacity decay, and improving cycling stability. Simultaneously, encapsulating metal-based materials within carbon-based materials can effectively mitigate the volume expansion caused by ion intercalation stress, which is significant for improving electrochemical stability, reducing material shedding and capacity loss during charge-discharge cycles, and improving material conductivity.

[0004] However, existing methods for preparing carbon-coated transition metal sulfides mainly involve pre-forming a metal sulfide, then coating the solid surface of the metal sulfide with an exogenous carbon source (mainly polymers such as polydopamine, PVP, and phenolic resins), followed by high-temperature treatment to carbonize the polymer and form a carbon coating layer on the solid surface. These methods suffer from drawbacks such as complex synthesis processes, high costs, and difficulty in industrialization. Furthermore, the exogenous composite between the carbon and core in the coating layer formed by these methods results in poor interfacial bonding, leading to unsatisfactory material stability and electrochemical performance. In addition, existing methods present significant challenges in controlling material properties, and the targeted optimization effect on electrochemical performance is not obvious.

[0005] For example, CN201710650566.2 discloses a NiS@C nanocomposite material for battery anodes and its preparation method. Using nickel chloride hexahydrate and thiourea as reactants, NiS is generated via a solvothermal method, followed by a hydrothermal glucose reaction to coat the NiS surface with carbon, and then high-temperature annealing to obtain the NiS@C nanocomposite material. Theoretically, coating the surface of nickel sulfide with carbon in this composite material can effectively compensate for the poor cycling performance and stability of sulfides, improving the material's cycling performance and stability. Although this material exhibits a high initial capacity when used as a lithium-ion battery anode material, it demonstrates poor cycling stability; at a low charge-discharge current of 34 mA / g, the capacity decays to 78 mAh / g after only 109 cycles. Furthermore, the sulfur and carbon sources are introduced into the material in two steps, a cumbersome process that limits its industrialization potential.

[0006] For example, CN201710198130.4 discloses a carbon-coated NiS hierarchical microsphere electrode material, its preparation method, and its application. Nickel sulfide is first obtained hydrothermally, and then, using nickel sulfide as a substrate, phenolic resin is coated onto it via surface polymerization of phenol and formaldehyde. Subsequently, carbonization is performed to obtain coated carbon. This invention significantly improves the material's capacity and cycle stability; however, the four-step process of solvothermal reaction-coating-calcination-etching is cumbersome, the raw materials are complex, and industrialization is challenging. Summary of the Invention:

[0007] To address the technical problems of unsatisfactory performance and difficulty in property control of existing carbon-coated metal sulfide materials, the primary objective of this invention is to provide a pristine ultrathin carbon-coated metal sulfide nanodot material.

[0008] The second objective of this invention is to provide a method for preparing the original ultrathin carbon-coated metal sulfide nanodot material, which aims to provide a method for preparing ultrathin carbon-coated metal sulfide nanodot material based on a novel preparation idea and mechanism.

[0009] The third objective of this invention is to provide an application of the aforementioned original ultrathin carbon-coated metal sulfide nanodot material as a negative electrode material for alkali metal-based secondary batteries such as lithium, sodium, and potassium batteries.

[0010] To improve the energy density, alleviate volume expansion, reduce capacity decay, and enhance the cycle stability of alkali metal-based secondary battery anode materials, this invention provides a pristine ultrathin carbon-coated metal sulfide nanodot material, comprising metal sulfide nanodots and a carbon layer uniformly coated on their surface; wherein the thickness of the carbon layer is less than or equal to 30 nm.

[0011] Unlike conventional metal sulfide@carbon materials, the nanomaterials described in this invention involve the simultaneous formation of metal sulfides and carbon materials. Furthermore, the metal sulfide particles are smaller (nanodots), and their surfaces are uniformly coated with ultrathin carbon materials at the atomic and nanoscale levels. Studies have found that this material exhibits superior stability and electrochemical performance in alkali metal-based secondary batteries.

[0012] In this invention, the metal sulfide is a sulfide of metal M, wherein metal M is at least one of transition metals, Group IV metals, and Group V metals;

[0013] Preferably, the metal M is at least one selected from copper, zinc, cobalt, nickel, iron, manganese, silver, antimony, tin, and gold;

[0014] Preferably, the metal sulfide is Co. 1-x S, Cu 7.2 S4.Ni 0.96 At least one of S and layered wurtzite-10H.

[0015] In this invention, the metal sulfide and carbon layer are formed simultaneously through a one-step heat treatment of the xanthate of metal M. The carbon layer and metal sulfide nanodots exhibit MSC bonds and a small number of COM bonds. Unlike conventional exogenous carbon-coated materials, the native material of this invention exhibits a chemical interaction between the carbon layer and the metal sulfide, resulting in more uniform bonding and a thinner thickness. This helps improve the crystal phase purity of the metal sulfide, prevents agglomeration, and further improves the material's stability and electrochemical performance.

[0016] Preferably, the thickness of the carbon layer is 3-10 nm.

[0017] The structure is a nano-dot structure, with a carbon layer firmly coating the outside of the nano-sulfide, having a uniform thickness and no obvious gaps.

[0018] This invention also provides a method for preparing the original ultrathin carbon-coated metal sulfide nanodot material, wherein M(ROSS)n and molten salt are mixed and calcined in a protective atmosphere; the calcination temperature is 450-750℃.

[0019] M is at least one of a transition metal, a Group IV metal, and a Group V metal; n is the valence of metal M;

[0020] The R mentioned is C3~C 15 alkane group, C5-C 10 Cyclic hydrocarbon groups, C5-C 10Heterocyclic aryl or phenyl groups; the alkane group, cyclic alkyl group, phenyl group, and heterocyclic aryl group are allowed to have substituents, and the substituents are preferably at least one of C4-C6 alkane group, C4-C6 alkoxy group, halogen, and phenyl group.

[0021] Existing approaches to carbon coating of metal sulfides mostly involve first forming a metal sulfide substrate, then coating its surface with a carbon source (mainly polymerized carbon), and finally calcining it. This approach results in materials with thick carbon layers, uneven coating, interfacial gaps, hindered ion transport, easy agglomeration, and low crystal phase purity, among other drawbacks. To address these technical problems, this invention provides a novel carbon coating approach: using a xanthic acid compound to capture the metal M ions, forming a small-molecule metal coordination compound, followed by calcination. This achieves simultaneous intramolecular endogenous carbon in-situ chemical deposition during sulfide preparation. Research has shown that the preparation method described in this invention effectively improves the bonding state between the carbon layer and the metal sulfide, improves the crystal phase purity of the metal sulfide, reduces material agglomeration, and also improves the material morphology, forming ultrathin or even atomically thin carbon layers. Research has also found that the materials prepared by the method described in this invention exhibit superior morphology, stability, and electrochemical performance.

[0022] This invention innovatively utilizes the trapping effect of the compound of Formula 1 on metal M ions and innovatively calcines it using a molten salt method. This allows for the complete formation of the sulfide crystal phase within the molecule, simultaneous carbon deposition, and in-situ construction of interfacial valence bonds, thereby obtaining the material described above. In this invention, the interaction between the -OCSS- group and the metal, as well as the calcination under molten salt conditions, are prerequisites for achieving good preparation results.

[0023] Preferably, the M(ROSS)n can be prepared by existing methods, and in this invention, it is preferred to be prepared by M n+ Source and ROSS - The source reaction yields;

[0024] The aforementioned ROSS - The source is energy ionization to produce ROSS - At least one of the following: acid, sodium salt, potassium salt, and ammonium salt;

[0025] The study found that controlling the R substituents helps to further control particle size, defects, and carbon layer thickness, thereby further affecting the cycling stability and capacity of the material.

[0026] In this invention, in R, C3 to C 15 The alkane group can be a straight-chain or branched alkane group. (C5~C5) 10 The cyclic hydrocarbon group can be a saturated or partially unsaturated cycloalkyl group. The C5-C6 group... 10The heterocyclic aryl group can be a five- or six-membered heterocyclic aryl group, such as a furan ring, a pyran ring, or a pyridine ring. Furthermore, the alkane group, cycloalkyl group, heterocyclic aryl group, and benzene ring may or may not have substituents, but are also permitted to have substituents. The substituents are preferably at least one of a C1-C6 alkane group, a C1-C6 alkoxy group, or a halogen.

[0027] Preferably, R is a C3-C6 straight-chain or branched alkane group; preferably ethyl, isopropyl, propyl, isobutyl, butyl, isopentyl, pentyl, neopentyl, isohexyl or hexyl.

[0028] Preferably, the metal M is at least one selected from copper, zinc, cobalt, nickel, iron, manganese, silver, antimony, tin, and gold; preferably, the M n+ Source is M n+ Water-soluble salts; for example, chlorides, sulfates, acetates, citrates, etc.

[0029] For example, the M mentioned n+ The source includes at least one of copper salts, zinc salts, cobalt salts, nickel salts, iron salts, manganese salts, silver salts, and tin salts. In this invention, the transition metal salt is preferably a water-soluble salt of at least one element selected from copper, zinc, cobalt, nickel, iron, manganese, silver, and tin; for example, it may be a chloride salt, nitrate salt, acetate salt, sulfate salt, etc.

[0030] In this invention, the valence state of metal M is preferably the valence state present at its temperature; for example, copper, zinc, cobalt, nickel, and manganese are preferably divalent. Silver is monovalent.

[0031] As a preferred option, the ROSS - The amount of source used is not less than the theoretical amount required to completely react the transition metal salt, preferably 1 to 6 times the theoretical reaction amount; more preferably 1 to 3 times.

[0032] In this invention, the solvent for the reaction is water or a mixture of water and an organic solvent, wherein the organic solvent is a solvent that is miscible with water;

[0033] Preferably, the reaction temperature is 1.0–40°C, more preferably 20–35°C;

[0034] The preferred time is 0.1h to 20h, and more preferably 1 to 10h.

[0035] In this invention, M n+ Source and ROSS - After the source reaction, solid-liquid separation was performed to obtain the M(ROSS)n product.

[0036] In this invention, the solid-liquid separation method can be a conventional method in the industry, such as vacuum filtration, centrifugation, etc.

[0037] In this invention, the product obtained from solid-liquid separation is dried, then mixed with molten salt, and subsequently calcined to obtain the product. The drying process can be a conventional method used in the industry, preferably vacuum drying, forced-air drying, freeze drying, etc.

[0038] Preferably, the protective atmosphere is an oxygen-free atmosphere; preferably, it is nitrogen or an inert gas; more preferably, the argon or nitrogen is high-purity argon or high-purity nitrogen with a purity ≥ 99.99%.

[0039] The melting point of the molten salt is 500–1200℃, preferably 800–1000℃;

[0040] Preferably, the molten salt is at least one of sodium chloride, potassium chloride, calcium chloride, sodium sulfite, sodium sulfate, potassium sulfate, and potassium sulfite;

[0041] Preferably, the weight ratio of M(ROSS)n to molten salt is 1:2 to 10.

[0042] Preferably, the ratio of the calcination temperature to the melting point temperature of the molten salt is 0.5 to 1:1, more preferably 0.5 to 0.75:1. This invention has found that controlling this ratio allows for calcination under micro-melting of the surface, which unexpectedly further improves the electrochemical properties of the resulting product.

[0043] Preferably, the calcination temperature is 500-600℃. Studies have found that the electrochemical properties of the prepared material can be further synergistically improved at the molten salt and calcination temperature.

[0044] Preferably, the heating rate during the calcination stage is 1-10℃ / min, more preferably 3-8℃ / min;

[0045] Preferably, the roasting time is 1 to 4 hours.

[0046] The present invention also includes the original ultrathin carbon-coated metal sulfide nanodot material prepared by the preparation method described above.

[0047] This invention also provides an application of the aforementioned pristine ultrathin carbon-coated metal sulfide nanodot material: using it as an electrode material; preferably as a negative electrode active material; more preferably, using it as a negative electrode active material for preparing a battery and its negative electrode. The battery is at least one of an alkali metal battery and an alkali metal ion battery. Preferably, the alkali metal is at least one of lithium, sodium, and potassium.

[0048] This invention also provides an alkali metal-based secondary battery anode material comprising the aforementioned pristine ultrathin carbon-coated metal sulfide nanodot material. Preferably, it further comprises a conductive agent and a binder. The conductive agent and binder can be components known in the industry, and their content and preparation methods can also be known. The alkali metal is at least one selected from lithium, sodium, and potassium.

[0049] The present invention also provides an alkali metal-based secondary battery, comprising the aforementioned alkali metal-based secondary battery negative electrode material. The alkali metal-based secondary battery is, for example, an alkali metal battery or an alkali metal-ion battery.

[0050] Principles and advantages

[0051] 1. A novel approach to preparing metal sulfide carbon-coated materials is provided;

[0052] The technical solution of this invention changes the industry's approach of pre-preparing metal sulfides, coating polymeric carbon precursors, and then carbonizing them. For the first time in the industry, it provides a method for simultaneously optimizing the phase of metal sulfides and depositing in-situ carbon based on the coordination effect of xanthic acid and metal, and based on the molten salt micro-dissolution calcination of the coordination compound, thereby realizing the preparation of the material.

[0053] 2. Preparation mechanism:

[0054] Based on the fundamental principle of the interaction between xanthates and metal ions, xanthates form metal sulfide seed crystals with metal ions through the S atom in the C-S single bond, with the metal sulfide quantum dots located in the inner layer of the product. The original nonpolar carbon atoms in xanthic acid exist in the form of C-C bonds, while the hydrocarbon groups in the xanthic acid molecule form a hydrophobically associated micelle layer through van der Waals forces. The formation of the micelle layer constructs a uniform organic carbon protective layer outside the metal sulfide quantum dots, effectively restricting their growth.

[0055] During the molten salt roasting process, the sulfide crystal phase is further refined and optimized, and the hydrocarbon chain structure transforms into amorphous carbon containing heteroatoms and abundant pores. In the presence of molten salt, CSM and COM bonds form at the interface between the carbon layer and the metal sulfide. Furthermore, the obtained material exhibits characteristics such as small carbon layer thickness (<10 nm), high graphitization degree, large specific surface area, and well-developed pore structure, with CSM and COM bonds present at the interface. These properties endow the material with a high lithium-ion diffusion coefficient, a large contribution rate to pseudocapacitive behavior, and ideal electrochemical reversibility, thus significantly improving lithium storage capacity, rate performance, and cycle stability.

[0056] This invention ingeniously utilizes the ease with which divalent sulfur atoms (thiol groups) in xanthates can form stable sulfides with valuable metals, and the tunable and controllable organic carbon chains in xanthates, to develop a novel method for preparing nano-carbon-based sulfide materials. Furthermore, by controlling the raw material ratio and the type of xanthate, the morphology, particle size, phase composition, defect composition, and carbon layer thickness can be controlled. The developed material, when used as a battery material, exhibits high capacity, good stability, excellent rate performance, and long cycle life. Simultaneously, the raw material cost is low, the production process is simple, and the product yield is high, making large-scale industrial production a promising possibility.

[0057] 3. This invention provides a material prepared using a novel approach and mechanism. Research has revealed that this material possesses an ultrafine core and ultrathin, atomically scaled carbon layers, with the core and carbon layers forming synchronously, and enabling in-situ construction of interfacial valence bonds. The material described in this invention exhibits superior crystal structure, excellent morphology, and enhanced stability and electrochemical performance.

[0058] 4. Research has found that the material prepared by the above method can be used as a negative electrode material for ion batteries, which can effectively improve the electrochemical performance of ion batteries. Attached Figure Description

[0059] Figure 1 Infrared spectrum of zinc xanthate precursor prepared in Example 1.

[0060] Figure 2 Transmission electron microscopy image of the zinc xanthate precursor prepared in Example 1.

[0061] Figure 3 XRD (a) and Raman spectroscopy (b) of the zinc xanthate precursor prepared in Example 1.

[0062] Figure 4 XRD pattern of the carbon-coated nano-dot zinc sulfide finally prepared in Example 1.

[0063] Figure 5 The TGA curve of the carbon-coated nano-dot zinc sulfide finally prepared in Example 1.

[0064] Figure 6 Raman spectra of the carbon-coated nano-dot zinc sulfide finally prepared in Example 1.

[0065] Figure 7 Example 1: Nitrogen adsorption-desorption curve (a) and pore size distribution diagram (b) of carbon-coated nano-dot zinc sulfide.

[0066] Figure 8 SEM image (a) and EDS spectrum (b) of the carbon-coated nano-dot zinc sulfide finally prepared in Example 1.

[0067] Figure 9 Transmission electron microscopy image of the carbon-coated nanodot zinc sulfide finally prepared in Example 1.

[0068] Figure 10 XPS spectra of the carbon-coated nano-dot zinc sulfide finally prepared in Example 1, including (a) the full spectrum, (b) Zn 2p, (c) S 2p, (d) C 1s, and (e) O 1s high-resolution spectra.

[0069] Figure 11 Example 1: The carbon-coated nanoparticle zinc sulfide finally prepared at 0.1 A g -1 Constant current charge-discharge cycle curves at current density.

[0070] Figure 12 Example 1: The carbon-coated nano-dot zinc sulfide finally prepared at 5.0 A g -1 Long-cycle performance curves at current density.

[0071] Figure 13 Example 1: The carbon-coated nano-dot zinc sulfide finally prepared at 5.0 A g -1 Constant current charge-discharge cycle curves at current density.

[0072] Figure 14 Example 2: XRD pattern of the final coated nano-dot copper sulfide.

[0073] Figure 15 Example 2: Raman spectrum of the final coating of nano-dot copper sulfide.

[0074] Figure 16 Transmission electron microscopy image of the final coated nano-dot copper sulfide in Example 2.

[0075] Figure 17 XPS spectra of the final coated nano-dot copper sulfide in Example 2.

[0076] Figure 18 Example 2: The final coating of nano-dot copper sulfide was 0.1 A g. -1 Constant current charge-discharge cycle curves at current density.

[0077] Figure 19 Example 3: XRD pattern of carbon-coated nano-dot cobalt sulfide.

[0078] Figure 20 Example 3: Transmission electron microscopy and high-resolution transmission electron microscopy images of carbon-coated nano-dot cobalt sulfide.

[0079] Figure 21 XPS spectra of carbon-coated nano-dot cobalt sulfide in Example 3.

[0080] Figure 22Example 3: The final carbon-coated nanoparticle cobalt sulfide was 0.1 A g. -1 Cyclic performance curves at current density.

[0081] Figure 23 Transmission electron microscopy image of carbon composite wurtzite prepared in Example 4.

[0082] Figure 24 Example 4 shows the preparation of carbon-composite wurtzite at 0.1 A g. -1 Cyclic performance curves at current density.

[0083] Figure 25 Transmission electron microscopy image of carbon composite wurtzite prepared in Example 5.

[0084] Figure 26 Example 5 shows the preparation of carbon-composite wurtzite at 0.1 A g. -1 Cyclic performance curves at current density.

[0085] Figure 27 Example 6 shows the material prepared at 10A g. -1 Cyclic performance curves at current density.

[0086] Figure 28 Example 7 shows the material prepared at 0.1 A g. -1 Cyclic performance curves at current density.

[0087] Figure 29 Example 8 yielded a material at 0.2 A g -1 Cyclic performance curves at current density.

[0088] Figure 30 Transmission electron microscopy image of the material prepared in Comparative Example 2. Detailed Implementation

[0089] In the following examples, the reaction between xanthates and metals is carried out at room temperature, for example, 15–35°C.

[0090] Example 1

[0091] Step (1):

[0092] At 20°C, 0.01M sodium isobutylxanate (xanthate) and 0.02M zinc sulfate (metal source) solution were mixed at a volume ratio of 4:1. The mixture was stirred continuously at 500 rpm for 10 min to ensure thorough mixing. The mixture was then centrifuged at 3000 rpm for 5 min to separate the solid and liquid phases. The resulting complex was freeze-dried for 12 h to obtain the precursor. Figure 1 Infrared spectroscopy confirmed that the complex was zinc xanthate (precursor). Figure 2Transmission electron microscopy images show the presence of quantum dots in the zinc xanthate complex. Figure 3 The XRD pattern and Raman spectrum confirm that the quantum dots are ZnS (JCPDs:89-2205), indicating that xanthate and ZnS react at room temperature. 2+ The process simultaneously achieved the formation of ZnS quantum dots and the coating of organic hydrocarbon chains on the ZnS quantum dots.

[0093] Step (2):

[0094] The complex (the aforementioned precursor) was mixed with NaCl at a mass ratio of 1:5 until homogeneous. The mixture was then heated to 500℃ at a rate of 5℃ / min under a nitrogen atmosphere and calcined at 500℃ for 2 hours to obtain carbon-coated nano-dot zinc sulfide. XRD, TGA, Raman spectroscopy, pore size analysis, SEM, TEM, and XPS measurements were performed, as shown below. Figures 4 to 10 .

[0095] Figure 4 The XRD pattern of carbon-coated nano-dot zinc sulfide proves that ZnS quantum dots are transformed into layered 10H-type wurtzite during the modification process. The layered structure is more conducive to ion diffusion and improves reaction kinetics.

[0096] Figure 5 The TGA curves of carbon-coated nano-dot zinc sulfide confirm the presence of carbon in the composite material. Figure 6 This indicates the presence of amorphous carbon and graphite microcrystals in the material. The IG / ID value is 1.39, indicating a high degree of graphitization, which will significantly improve the material's conductivity.

[0097] Figure 7 The nitrogen adsorption-desorption curves and the pore size distribution diagram of the BJH model indicate that the composite material obtained by the method of this invention has a higher pore size structure than commonly used polymers with ectopic carbon inclusions. Furthermore, the pore size is mainly mesoporous, which is conducive to ion diffusion, further improving the electrochemical reaction kinetics of the material. Scanning electron microscopy and transmission electron microscopy images of the modified carbon-composite 10H wurtzite show that the material morphology is nano-dot-like, with wurtzite particle diameters of approximately 14-23 nm. Highly graphitized amorphous carbon is uniformly coated on the outer side of the particles, with a carbon layer thickness of only 3-5 nm. In addition, the interface between the carbon layer and the internal wurtzite is blurred, indicating that there is a chemical bond between the carbon layer and the ZnS interface.

[0098] Figure 10 XPS analysis further confirmed the existence of valence bonds at the CSM-COM interface. Furthermore, high-resolution C1s spectra demonstrated the presence of O / S heteroatoms in the carbon layer, and high-resolution O spectra confirmed the existence of the Zn-O heterostructure. These material properties will significantly improve the lithium storage performance of nano-sulfides.

[0099] The lithium-ion battery anode composite material (carbon-coated nano-dot zinc sulfide) prepared in this embodiment was mixed with carboxymethyl cellulose (CMC) and conductive carbon black at a mass ratio of 70:15:15. A suitable amount of deionized water was added to form a slurry, which was then coated onto copper foil. After the water evaporated, the mixture was dried in a vacuum drying oven at 80°C for 12 hours. The copper foil coated with the active material was then cut into 12mm diameter discs. Using these 12mm diameter discs as the working electrode, lithium metal as the counter electrode, and a Celgard 2400 composite membrane as the separator, coin cells were assembled in an inert gas glove box. Electrochemical performance tests revealed that the synthesized material exhibited excellent performance. Due to the material's nanoscale particle size, ultrathin carbon layer structure, interfacial CXM bonds, and O and S doping, lithium ions diffuse through the material via a short path and have a high migration rate. The material also possesses a large pseudocapacitive contribution rate, thus demonstrating a lithium storage specific capacity higher than the theoretical value. Figure 11 This indicates that the electrode made from the carbon-coated nano-dot zinc sulfide anode material has a performance of 0.1 A·g -1 At the specified current density, the initial charge and discharge specific capacities were 1052.8 and 1480.9 mAh·g, respectively. -1 After 100 cycles, the reversible specific capacity remained at 927.2 mAh·g. -1 The coulombic efficiency is close to 100%, which shows high capacity. This is due to the small particle size of the material, suitable defects, and high degree of graphitization. Figure 12 This indicates that at 5A·g -1 At a current density of 500 mAh·g, the reversible specific capacity remained at 500 mAh·g after 4000 cycles. -1 The ideal electrochemical behavior at high current densities is attributed to strong interfacial bonds, the enhancement of conductivity due to defects and high graphitization, and the improvement of ion diffusion kinetics due to suitable pore structure and small particle size. The long cycle life is attributed to the increased structural stability of the material due to small particle size and suitable carbon layer structure.

[0100] Example 2

[0101] Compared with Example 1, the main difference is that copper chloride is used instead of zinc chloride as the metal source, while the other preparation steps are the same as in Example 1.

[0102] For example, the distinguishing steps are as follows: at 20°C, 0.01M sodium isobutylxanthate and 0.02M copper chloride solution are mixed at a volume ratio of 4:1 to prepare carbon-coated nano-dot copper sulfide based on the experimental conditions of Example 1. XRD, Raman, TEM, and XPS measurements are then performed, as shown in the figures below. Figures 14-17 .

[0103] Figure 14XRD pattern of carbon-copper sulfide indicates that the material is Cu. 7.2 A mixture of S4 and Cu2S, Cu 7.2 S4 is a non-stoichiometric copper sulfide that can improve the conductivity of materials and enhance their rate performance.

[0104] Figure 16 This is a transmission electron microscope (TEM) image of modified copper sulfide. As shown in the image, the material contains two types of particles: nanospheres and nanorods. These correspond to the two structures in the SEM image. The nanospheres have a diameter of 50-200 nm, while the nanorods have a width of approximately 20 nm and a length of 61-88 nm. The nanorods have lattice fringes with a spacing of 0.274 nm, which corresponds to the (103) crystal plane of Cu2S in the XRD results. The nanospheres have lattice fringes with a spacing of 0.198 nm, which is consistent with the (202) crystal plane parameters of Cu7.2S4 in the XRD.

[0105] Figure 17 This indicates the presence of a large number of O and S heteroatoms in the modified copper sulfide, which will significantly increase the lithium storage specific capacity of the pseudocapacitive reaction within the carbon layer and improve the material's conductivity. Furthermore, the signal peaks of CO-Cu and CS-Cu indicate the existence of chemical bridging bonds between the internal copper sulfide and the outer amorphous carbon layer. This provides active sites and will significantly enhance the migration rate of lithium ions at the interface.

[0106] The lithium-ion battery is assembled using the method described in Example 1 of this embodiment. Figure 18 It is 487.6, 640.6mAh g -1 At 0.1A g -1 At the specified current density, after 100 charge-discharge cycles, the discharge specific capacity still reaches 508.6 mAh g. -1 It is far higher than its theoretical value (337mAh g). -1 Mechanistic analysis results indicate that the large capacitance behavior is the main reason for the high lithium storage capacity of the modified copper sulfide composite material, which is attributed to the material's suitable defect composition, large specific surface area, and abundant heteroatom structure.

[0107] Example 3

[0108] Compared with Example 1, the only difference is that cobalt chloride is used in an equimolar amount to replace zinc chloride as the metal source, while other operations and processes are the same as in Example 1.

[0109] The distinguishing steps are as follows: At 30°C, 0.01M sodium isobutylxanthate and 0.02M cobalt chloride solution are mixed at a volume ratio of 4:1 to prepare carbon-coated nanoparticle cobalt sulfide under the experimental conditions of Example 1. XRD, TEM, and XPS measurements are then performed, as shown in the figures below. Figures 19-21 .

[0110] Figure 19 The XRD pattern shows that the diffraction peaks at 2θ = 30.16°, 35.18°, 46.76°, and 54.27° correspond to Co, respectively. 1-x The (100), (101), (102), and (110) crystal planes of S (JCPDS No. 42-0826) are observed. A sharp peak also appears near 2θ = 20.88°, which corresponds to the (001) crystal plane of CoO2 (JCPDS No. 89-8398), indicating that some Co and O have combined during the inert high-temperature modification process of PCoIBX. Figure 20 The images show transmission electron microscopy (TEM) and high-resolution TEM images of the derived material. The cobalt sulfide particles are approximately 15-25 nm in size, and the carbon layer is approximately 10 nm thick. The smaller nanoscale size helps increase the contact area between lithium ions and the material, reducing ion diffusion paths and mitigating material pulverization caused by volume expansion. The carbon is tightly bound to the internal particles without significant gaps, indicating the existence of chemical bonds between the carbon layer and the internal material. The images are obtained from HRTEM images in high-resolution mode. Figure 20 It can be seen that the composite material contains two types of lattice fringes with spacings of 0.425 nm and 0.194 nm, which correspond to the (001) crystal plane of CoO2 (JCPDS No. 89-8398) and Co, respectively. 1-x The (002) crystal plane of S (JCPDS No: 42-0826) is consistent with the XRD results. CoO2 and Co 1-x The absence of a clear boundary at the S interface indicates a highly stable bond between the two substances. According to the mechanism of lithium-sulfur batteries, a small amount of oxide helps suppress the sulfur shuttle effect. This is due to the nanoscale particle size, the carbon layer, and the internal CoO2 / Co... 1-x S is firmly bonded and there may be chemical bonds at the interface, lithium ions at the interface and CoO2 / Co 1-x The migration rate within S will be improved. Figure 21 XPS results showed that Co sulfides and oxides existed in the composite material after in-situ modification, and the carbon layer contained CoO2 and Co. 1-X The presence of CS-Co and CO-Co bonds in S enhances the bonding between the carbon layer and the internal materials, increasing the migration rate of lithium ions at the interface. The presence of O and S elements in the carbon layer will increase the active sites for lithium storage and improve the specific capacity of the material.

[0111] The lithium-ion battery is assembled using the method described in Embodiment 1. Figure 22 It is 0.1 A·g -1 The cycling performance curve at the specified current density shows a reversible specific capacity of up to 1002.5 mAh·g after 100 cycles. -1The high capacitance of cobalt composite materials is mainly due to the nanoscale size of the material, the in-situ generated ultrathin carbon layer, the abundance of heteroatoms, the strong interfacial CXM bonds, and the large specific surface area.

[0112] Example 4

[0113] The method of Example 1 is used, except that sodium isopentyl xanthate is used as the xanthate salt; all other operations and parameters are the same as in Example 1. TEM images of the final product are shown below. Figure 23 The battery was assembled and measured using the method described in Example 1.

[0114] Figure 23 This is a transmission electron microscope image of the final material. The wurtzite particle size is smaller than that of the zinc isobutyl xanthate derivative. Figure 24 The prepared electrode material is at 0.1 A·g -1 At a current density of [value missing], the reversible specific capacity after 100 cycles is only 702.3 mAh·g. -1 It is 104.45% of the discharge specific capacity in the second week, showing excellent performance and good cycle performance, but the capacity is slightly lower than that of Example 1.

[0115] Example 5

[0116] The method of Example 1 was used, except that sodium n-butylxanthate was used as the xanthate salt; all other operations and parameters were the same as in Example 1. Battery assembly and testing were performed using the method of Example 1.

[0117] Figure 25 The image shows a transmission electron microscope (TEM) image of the final material. The wurtzite particle size is smaller than that of the isobutyl and isopentyl xanthate zinc derivatives, indicating that the branching helps to increase the thickness of the carbon layer. Figure 26 The prepared electrode material is at 0.1 A·g -1 The cycling performance curve at the specified current density shows a charge-discharge specific capacity of 642.2 mAh·g after 100 cycles. -1 The capacity is slightly lower because the particle size is slightly larger, resulting in a longer ion diffusion path.

[0118] Example 6

[0119] Compared to Example 1, the only difference is that the ratio of xanthic acid to the metal source is changed. The difference lies in the following steps:

[0120] Following the method of Example 1, 0.01 M sodium isobutylxanthate and 0.01 M zinc sulfate solution were mixed at a volume ratio of 6:1; subsequent operations and parameters were the same as in Example 1, yielding the final product, labeled SZnIBX-2. A coin cell was then assembled. The prepared electrode material was tested at 0.1 A·g... -1At a current density of [value missing], the reversible specific capacity after 100 cycles is only 756.3 mAh·g. -1 The increased use of sodium isopentyl xanthate resulted in a slight decrease in capacity, but improved cycle stability.

[0121] Figure 27 The material is at 10A g -1 The high current density charge-discharge cycle curves were obtained, and after activation with a small current, the current was increased to 10 Ag. -1 The initial charge / discharge specific capacity is 377.6 mAh g. -1 As the number of cycles increases, the specific capacity increases slightly. After 1000 cycles, the specific capacity decreases slightly. When the number of charge-discharge cycles reaches 2800, the charge-discharge specific capacity of SZnIBX-2 is still as high as 374.9 mAh g. -1 It has a capacity retention rate as high as 99.27%.

[0122] Example 7

[0123] Using the method in Example 1, the only difference is changing the ratio of xanthic acid to the metal source. The steps that differ are:

[0124] Sodium isobutyl xanthate (0.01 M) and ferric chloride (0.01 M) solution were mixed at a volume ratio of 3:1, with other processes and operations the same as in Example 1. The electrode material was assembled using the method of Example 1 and electrochemical measurements were performed. The prepared electrode material was measured at 0.1 A·g -1 The charge-discharge cycle performance curves at current densities are shown in the figure. Figure 28 It has a high lithium storage capacity and good cycle stability. However, after 100 cycles, the reversible specific capacity is only 915.3 mAh·g. -1 .

[0125] Example 8

[0126] Following the method of Example 8, the only difference is that 0.01 M sodium isobutylxanthate and 0.01 M ferric chloride solution were mixed at a volume ratio of 3:1, and the mixture was modified at 600 °C to prepare the electrode material. A coin cell was then assembled. The prepared electrode material showed a yield of 0.2 A·g -1 The cycling performance curves at current densities are shown below. Figure 29 After 100 cycles, the reversible specific capacity is 806 mAh·g. -1 The high lithium storage capacity and good cycle stability indicate that the modification temperature of 600℃ is suitable.

[0127] Example 9

[0128] The method described in Example 7 is used, except that sodium sulfite is used as the molten salt to prepare the electrode material, and then a coin cell is assembled. The prepared electrode material is available in 0.2 A·g -1 After 100 cycles at a current density, the reversible specific capacity is 901.2 mAh·g. -1 The good cycle stability indicates that sodium sulfite is a suitable molten salt.

[0129] Example 10

[0130] The method described in Example 7 is used, except that potassium sulfate is used as the molten salt to prepare the electrode material, and then a coin cell is assembled. The prepared electrode material is available in 0.2 A·g -1 The reversible specific capacity after 100 cycles at a current density is 886 mAh·g. -1 The good cycle stability indicates that potassium sulfate is a suitable molten salt.

[0131] Comparative Example 1

[0132] Compared to Example 1, the only difference is that in step (1), an equimolar amount of sodium methyl xanthate was used to replace the sodium isobutyl xanthate. Precipitation could not be successfully obtained.

[0133] Comparative Example 2

[0134] Compared with Example 1, the only difference is that in step (1), sodium ethyl xanthate is used to replace sodium isobutyl xanthate in an equimolar amount.

[0135] The transmission electron microscope images of the prepared electrode materials are shown below. Figure 30 Compared to Examples 1, 4, and 5, the material has a larger particle size, numerous planar defect structures, and an indistinct carbon layer structure. At 0.1 A·g -1 After 70 cycles at a current density, the reversible specific capacity remains reduced to 398 mAh·g. -1 The cycle stability and lithium storage capacity of the sample were lower than those of Examples 1, 4 and 5. This was because the hydrocarbon carbon chain length in the precursor xanthate was too short, resulting in larger wurtzite particles, longer transport paths, and poorer electrochemical reaction kinetics. In addition, the numerous surface defects and the lack of carbon layers were not conducive to maintaining the structural stability of the active material during charge and discharge.

[0136] Comparative Example 3

[0137] All other conditions were the same as in Example 1, except that an equimolar amount of sodium hexadecyl xanthate was used instead of the butyl xanthate. The prepared electrode material was prepared at 0.1 A·g -1 At the specified current density, the reversible specific capacity remained at 503.1 mAh·g after 100 cycles. -1 This indicates that if the carbon layer is too thick, the capacity will decrease.

[0138] Comparative Example 4

[0139] All other conditions were the same as in Examples 1 and 2, except that the molar ratio of sodium isobutylxanthate to Zn²⁺ was changed to 1:2. Compared to Examples 1 and 2, the carbon layer structure of the material was thinner, and XPS results showed that the heteroatom content of the material was much lower than that in Examples 1 and 2. At 5 A·g -1 At a current density of 0, the lithium storage capacity is close to 0 after 100 cycles, indicating that the xanthate ratio in the reactants is too low, which is not conducive to maintaining the cycling stability of the material at high current densities.

[0140] Comparative Example 5

[0141] Compared to Example 1, the only difference is that calcination was performed directly instead of using the sodium chloride molten salt method. Due to the absence of interfacial bonds, ion transport between interfaces is hindered, 0.1 A·g -1 At current density, after 100 cycles, the lithium storage capacity is 455 mAh g. -1 5A·g -1 At current density, after 1000 cycles, the lithium storage capacity is only 263 mAh g. -1 This indicates that the presence or absence of interfacial bonds affects the electrochemical reaction kinetics, leading to a decrease in the material's lithium storage capacity.

[0142] Comparative Example 6

[0143] Compared to Example 1, the only difference was that the temperature was increased to 800°C at a rate of 5°C / min under a nitrogen atmosphere, and then calcined at 800°C for 2 hours. The prepared electrode material was [value missing - likely related to a specific material or process]. -1 At high current densities, the material's capacity is still less than 50 mAh·g after 10 cycles. -1 Excessive temperature causes metallic elements to precipitate, damaging the material's structure.

[0144] Comparative Example 7

[0145] All other conditions were the same as in Example 1, except that the temperature was increased to 400℃ at a rate of 5℃ / min under a nitrogen atmosphere, and then calcined at 400℃ for 2 hours. The prepared electrode material was [value missing - likely a specific material or process]. -1 At current densities, the capacity is less than 100 mAh·g -1 .

Claims

1. A method for preparing a pristine ultrathin carbon-coated metal sulfide nanodot material, characterized in that: M(ROSS)n and the molten salt are mixed and calcined in a protective atmosphere; The M(ROSS)n is obtained by reacting M n+ source and ROSS - source reaction; wherein, ROSS - is xanthate; The M n+ source is a water soluble salt of M n+ ; M is iron; n is 3; The ROSS - The source is at least one of an acid, a sodium salt, a potassium salt, an ammonium salt that can ionize the ROSS - acid R is isopropyl, propyl, isobutyl, butyl, isoamyl, amyl, neopentyl, iso-hexyl or hexyl; The molten salt is at least one of sodium chloride, potassium chloride, calcium chloride, sodium sulfite, sodium sulfate, potassium sulfate, and potassium sulfite; The calcination temperature is 500-600℃; The ROSS - The source is 1 times the theoretical reaction molar amount.

2. The method of claim 1, wherein the as-prepared ultrathin carbon-coated metal sulfide nanodot material is prepared by the following steps: The solvent for the reaction is water or a mixed solvent of water and an organic solvent that is miscible with water.

3. The method of claim 1, wherein the as-prepared ultrathin carbon-coated metal sulfide nanodot material is prepared by the following steps: The reaction temperature is 1.0-40℃.

4. The method for preparing the original ultrathin carbon-coated metal sulfide nanodot material as described in claim 1, characterized in that: The reaction time is 0.1 h-20 h.

5. The method for preparing the original ultrathin carbon-coated metal sulfide nanodot material as described in claim 1, characterized in that: The molten salt is at least one of sodium sulfite, sodium sulfate, potassium sulfate, and potassium sulfite.

6. The method for preparing the original ultrathin carbon-coated metal sulfide nanodot material as described in claim 1, characterized in that: The weight ratio of M(ROSS)n to the molten salt is 1:2-10.

7. The method for preparing pristine ultrathin carbon-coated metal sulfide nanodot materials as described in claim 1, characterized in that: The protective atmosphere is an oxygen-free atmosphere.

8. The method for preparing the original ultrathin carbon-coated metal sulfide nanodot material as described in claim 1, characterized in that: The temperature rising rate in the calcination stage is 1-10℃ / min.

9. The method for preparing the original ultrathin carbon-coated metal sulfide nanodot material as described in claim 1, characterized in that: The calcination time is 1-4 h.

10. A material of as-prepared ultra-thin carbon-coated metal sulfide nanodots prepared by the preparation method of any one of claims 1-9.

11. The use of the as-prepared ultrathin carbon-coated metal sulfide nanodot material prepared by the method of any one of claims 1-9, characterized in that: It is used as an electrode active material.

12. The use according to claim 11, characterized in that: It is used as a negative electrode active material.

13. The use according to claim 11, wherein: It is used as a negative electrode active material, and is used for preparing a battery and a negative electrode thereof.

14. The use of claim 11, wherein: The battery is an alkali metal ion battery. The alkali metal is at least one of lithium, sodium, and potassium.

15. An alkali metal-based secondary battery negative electrode material, characterized in that, It comprises the material of as-prepared ultra-thin carbon-coated metal sulfide nanodots prepared by the preparation method of any one of claims 1-9.

16. The alkali metal-based secondary battery anode material of claim 15, wherein, It further comprises a conductive agent and a binder. The alkali metal is at least one of lithium, sodium, and potassium.

17. An alkali metal-based secondary battery, characterized by comprising: It comprises the alkali metal-based secondary battery negative electrode material of claim 16.

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