Crystalline metal polysulfides and methods of making, composites with sandwich structure, methods of making and uses thereof

Abstract

The application discloses a kind of crystalline metal polysulfides, crystalline metal polysulfides [Mn (phen) 2]S8 is synthesized using hydrothermal method, and it is used as precursor, and through high-temperature carbonization one-step reaction, composite material of MnS nanoparticle and nitrogen-doped carbon nanosheet sandwich structure is prepared.The composite material prepared in the application can be used as negative electrode material to prepare secondary lithium ion battery.The method of the application synthesizes a manganese-based crystalline metal sulfide [Mn (phen) 2]S8 with novel polysulfide structure; and using it as precursor, the sandwich structure of MnS nanosphere and N-doped carbon nanosheet is prepared, which effectively improves the conductivity of MnS as negative electrode material, thereby improving the electrochemical stability of MnS material; the lithium battery prepared by using the sandwich structure as lithium battery negative electrode material has excellent cycle stability and rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to the synthesis of a novel crystalline compound [Mn(phen)2]S8 with a MnS8 ring structure and its preparation method as a precursor for a composite nano sandwich structure, as well as the application of this composite material with N-doped carbon nanosheets and metal sulfides as a negative electrode material in lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used in mobile electronic devices, electric vehicles, and hybrid vehicles due to their advantages such as high energy density, low self-discharge, good rate performance, and environmental friendliness. Currently, much research is focused on developing novel lithium-ion battery anode materials to achieve low-cost, high-energy-density, and well-developed lithium-ion batteries. Transition metal oxides are being considered as a potential candidate for graphene (372 mA h) due to their high theoretical capacity. -1 It has been widely studied as an alternative to lithium-ion batteries. However, its low conductivity has become a major bottleneck in its application in lithium-ion batteries.

[0003] Metal sulfides have attracted widespread attention due to their metallic properties, rich redox properties, and good thermal stability. However, during charge and discharge, the insertion and extraction of lithium ions often cause significant volume expansion in metal sulfides, leading to structural breakage of the electrode material and contact losses in the current collector. Furthermore, the poor conductivity of metal sulfides, when used as negative electrode materials, delays the electrochemical reaction and reduces rate performance. These drawbacks limit the practical application of metal sulfides in lithium-ion batteries. To address these issues, reducing the size of MnS to the nanoscale and compositing it with carbon nanosheets is considered an effective method to improve battery structural stability and conductivity. The main method for preparing composite materials involves preparing precursors followed by high-temperature calcination.

[0004] Patent CN 115133000 A discloses a method for preparing and applying an amorphous CoS NDs / NSCN composite material. The preparation method involves uniformly mixing a cobalt source, a sulfur source, a carbon source, and a salt template in a specific ratio, followed by high-temperature pyrolysis and subsequent water washing to remove the template, ultimately obtaining the amorphous CoS NDs / NSCN composite material. The main drawback of this patent is that the precursor is prepared by physically mixing various raw materials, resulting in generally uneven dispersion between the substances. This makes it difficult to achieve uniform dispersion of metal sulfides and nanosheets in the prepared composite material, leading to limited improvement in cycle performance.

[0005] Patent CN 114094078 A discloses a nitrogen-doped carbon-coated metal sulfide heterostructure p-MoS2 / n-Bi2S3@NC composite electrode material prepared from bismuth, molybdenum, and sulfur sources via hydrothermal reaction and calcination. The built-in electric field of the heterojunction effectively enhances the diffusion kinetics and electronic conductivity of metal ions, thereby improving battery rate performance. The carbon coating significantly improves the structural stability of the material. While this patent utilizes a hydrothermal method to prepare a precursor, the specific structure and composition of the precursor are unclear, making it difficult to control the content of the subsequent calcined product. This is detrimental to the specific capacity of the metal sulfide and easily leads to excessive doping of nanosheet materials. Furthermore, this invention suffers from uneven dispersion of the metal sulfide and nanosheets, which is detrimental to the electrochemical performance of the metal sulfide.

[0006] In addition, patent CN 107681139 A also discloses a method of first preparing a precursor using a solvent method, and then preparing a nitrogen-carbon-coated metal sulfide nanocomposite material by calcination. However, the precursor prepared at present has problems such as indeterminate structure and unclear purity. When preparing composite materials, it is easy to have uneven distribution of active materials and nanosheets, which will reduce the specific capacity of active materials. At the same time, uneven structural dispersion may affect the electrochemical cycling stability of the material.

[0007] Regarding research on MnS materials, a paper from Nanjing University of Technology, titled "MnS nanoparticles embedded in N,Sco-doped carbon nanosheets for superior lithium ion storage," describes a composite material of MnS nanoparticles and N / S-doped carbon nanosheets. The main method involves preparing Mn3O4 nanosheets on carbon fiber cloth via a three-electrode electrolysis process, followed by a reaction in dopamine hydrochloride to prepare Mn3O4@PDA / CFC. This is then followed by a carbothermic reduction reaction to prepare MnO@CN / CFC, and finally, high-temperature calcination under a sulfur source to obtain the composite material of MnS nanoparticles and N / S-doped carbon nanosheets. The preparation process in this paper is relatively complex, and the excessive amount of material introduced at the end results in poor specific capacity utilization of the MnS material, affecting the capacity improvement. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention aims to synthesize a zero-dimensional manganese-based crystalline metal sulfide [Mn(phen)2]S8 with a novel structure containing sulfur via a hydrothermal method, and use it as a precursor to prepare a sandwich structure composite material (MnS@NC) of MnS nanoparticles and nitrogen-doped carbon nanosheets through a one-step reaction by high-temperature carbonization.

[0009] Another object of the present invention is to provide such a composite material with a sandwich structure and its application as a negative electrode material for lithium-ion secondary batteries and lithium batteries.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0011] A crystalline metal chalcogenide, the molecular formula of which is [Mn(phen)2]S8, has a structure in which one manganese atom and eight S atoms are connected end-to-end to form a zero-dimensional MnS8 ring, and two phenanthroline molecules are connected to the Mn atom through N-Mn coordination.

[0012] On the other hand, the aforementioned method for preparing crystalline metal disulfides includes the step of reacting manganese acetate or manganese chloride, tin disulfide, sulfur powder, o-phenanthroline and deionized water in a reaction vessel to obtain the crystalline metal disulfides.

[0013] In one specific embodiment, the molar ratio of manganese acetate or manganese chloride, tin disulfide, sulfur powder, o-phenanthroline and deionized water is 1:0.2-1:1:1:20-100; preferably, the reaction temperature is 150-160℃ and the reaction time is 5-7 days.

[0014] On the other hand, a composite material with a sandwich structure is a composite material (MnS@NC) in which MnS nanospheres are uniformly distributed between nitrogen-doped carbon nanosheets to form a sandwich structure, wherein the composite material is prepared by using the aforementioned crystalline metal chalcogenide as a precursor.

[0015] In one specific implementation, the aforementioned crystalline metal dichalcogenide is prepared by high-temperature calcination under an inert gas atmosphere, using it as a precursor.

[0016] In one specific implementation, the inert gas is selected from at least one of nitrogen, helium, and argon.

[0017] In one specific implementation, the high-temperature calcination temperature is 400-500℃ and the calcination time is 3.5-5h; preferably, the high-temperature calcination heating method is uniform heating, with a heating rate of 6-15℃ / minute.

[0018] In another aspect, a negative electrode material comprises the following components in weight percentage:

[0019] MnS@NC: 60%-80%;

[0020] Adhesive: 8%-15%;

[0021] Electronic conductive agent: 12-32%;

[0022] Wherein, MnS@NC is the composite material MnS@NC with a sandwich structure prepared by the aforementioned method or the aforementioned method.

[0023] In one specific embodiment, the binder is at least one of polyvinylidene fluoride (PVDF), hydrogenated nitrile butadiene rubber (HNBR), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), and polyacrylic acid (PAA), and the electronic conductive agent is at least one of acetylene black, hard carbon, and graphite.

[0024] On the other hand, a secondary lithium-ion battery includes a negative electrode made of the aforementioned negative electrode material.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention utilizes a simple hydrothermal method to synthesize a manganese-based crystalline metal sulfide, [Mn(phen)2]S8, with a sulfide-linked structure (S8 ring). This novel precursor offers advantages such as simple preparation method, environmental friendliness, and low energy consumption. Using this precursor, and leveraging the multi-carbon properties of o-phenanthroline, a sandwich structure of MnS nanoparticles and N-doped carbon nanosheets is prepared through high-temperature calcination. The increased contact area between the nitrogen-doped carbon nanosheets and MnS nanospheres effectively enhances the conductivity of MnS as an anode material. This sandwich structure provides an ion pathway for lithium-ion conduction while also acting as a structural support, thereby improving the electrochemical stability of the MnS material.

[0027] The synthesis process of the crystalline metal dichalcogenide compound and the preparation process of the sandwich structure of the present invention are relatively simple, safe and low cost. The lithium battery prepared by using this sandwich structure composite material as the negative electrode material of lithium battery has excellent cycle stability, which expands the application scenarios of crystalline metal dichalcogenide compounds in lithium-ion batteries.

[0028] The MnS@NC prepared by the method of this invention exhibits excellent electrochemical performance. In research on using MnS@NC as a negative electrode material for lithium-ion batteries, the composite material formed by MnS@NC showed good performance at a current density of 500 mA g. -1 and 1000mAg -1 In the cyclic performance test, when the current density was 500 mA g -1 After 200 cycles of constant current charge and discharge, its lithium storage capacity is 878.2 mA hg. -1 At a higher current density of 1000 mAg -1 In long-term cycling tests, it still had 753 mAh g after 500 cycles. -1The reversible capacity. Compared to pure MnS powder as the anode material, the low capacity retention (30%) and initial specific capacity (285 mAh g) are significant advantages. -1 Using a crystalline metal sulfide with a specific structure as a precursor, the MnS@NC composite material prepared as a lithium-ion battery anode material exhibits excellent electrochemical stability and specific capacity. Furthermore, the electrode demonstrates good electrochemical reversibility due to its approximately 100% coulombic efficiency during cycling at both current densities. Therefore, the self-designed synthesis of novel crystalline metal sulfide structures as precursors to prepare composite materials with specific metal sulfide morphologies is of significant importance for improving the cycling stability of metal sulfides as anode materials. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the morphology of the MnS@NC composite material with a sandwich structure according to the present invention.

[0030] Figure 2 The structure diagram is shown for the crystalline metal dichalcogenide [Mn(phen)2]S8 prepared in Example 1 of this invention.

[0031] Figure 3 The electron microscope image shows the morphology of the sandwich-structured composite material MnS@NC prepared in Example 1 of this invention.

[0032] Figure 4 The image shows the EDS spectrum of the composite material with a sandwich structure prepared in Example 1 of this invention.

[0033] Figure 5 The MnS@NC composite material prepared in Example 1 of this invention is used as the negative electrode material in a lithium battery at 500 mAg. -1 Cyclic performance diagram at current density.

[0034] Figure 6 The MnS@NC composite material prepared in Example 1 of this invention is used as the negative electrode material in a lithium battery at 500 mAg. -1 The charge-discharge curves for different cycles at the given current density are shown.

[0035] Figure 7 The composite material MnS@NC prepared in Example 1 of this invention is used as the negative electrode material in lithium batteries manufactured at 1000 mAg. -1 Cyclic performance diagram at current density.

[0036] Figure 8 The MnS composite material powder prepared in Example 1 of this invention was used as the negative electrode material in the manufacture of a lithium battery with a capacitance of 1000 mAg. -1 Cyclic performance diagram at current density. Detailed Implementation

[0037] To better understand the technical solution of the present invention, the following embodiments will further illustrate the method provided by the present invention. However, the present invention is not limited to the listed embodiments, but should also include any other known modifications within the scope of the claims of the present invention.

[0038] The overall technical concept of this invention is as follows: a manganese-based crystalline metal sulfide [Mn(phen)2]S8 containing sulfur is synthesized by hydrothermal method as a precursor, and then calcined at a certain high temperature as a precursor to finally prepare a composite material (MnS@NC) of MnS nanoparticles and nitrogen-doped carbon nanosheets with a sandwich structure; and then the composite material is used as a negative electrode material for lithium-ion batteries to prepare lithium-ion batteries.

[0039] The prepared crystalline metal chalcogenide [Mn(phen)2]S8 has a structure in which one manganese atom and eight sulfur atoms are connected end-to-end to form a zero-dimensional MnS8 ring. Two phenanthroline molecules are connected to the Mn atom through N-Mn coordination. Zero-dimensional refers to a structure that exists alone and does not grow in other directions. For example, a single molecule is zero-dimensional; molecules connected and growing in one direction are one-dimensional; growing in two directions is two-dimensional; and growing in three directions is three-dimensional. The crystalline metal chalcogenide of this invention has a single, zero-dimensional structure.

[0040] Among them, the hydrothermal method is used to prepare crystalline metal disulfide [Mn(phen)2]S8, which is prepared by placing manganese acetate or manganese chloride, tin disulfide, sulfur powder, o-phenanthroline and deionized water in a reaction vessel in a certain proportion and reacting them at a certain reaction temperature for a period of time.

[0041] Specifically, taking manganese acetate as an example, the addition amounts of each raw material in the hydrothermal method are as follows: the molar ratio of manganese acetate, tin disulfide, sulfur powder, o-phenanthroline, and deionized water is 1:0.2-1:1:1:20-100; for example, including but not limited to 1:1:1:1:20, 1:0.2:1:1:100, 1:0.5:1:1:50, and 1:0.8:1:1:80. The reaction temperature in the hydrothermal method is 150℃-160℃, such as 150℃, 155℃, and 160℃, and the reaction time is 5-7 days, such as 5 days, 6 days, and 7 days. The hydrothermal reaction is carried out in a hydrothermal reactor, and there are no particular restrictions on the reaction pressure; for example, a hydrothermal reaction at atmospheric pressure is sufficient.

[0042] The crystalline metal sulfide [Mn(phen)2]S8 prepared by the above method can be used to prepare composite materials with sandwich structures. Specifically, the composite material MnS@NC with sandwich structure is prepared by high-temperature calcination. It is obtained by grinding the precursor crystalline metal sulfide [Mn(phen)2]S8 into powder and then calcining it at 400-500℃ for 3.5-5 hours under inert gas conditions.

[0043] The inert gas used in the high-temperature calcination of the powder is selected from at least one of nitrogen, helium, and argon, for example, an argon atmosphere. The high-temperature calcination temperature is, for example, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, etc.; the high-temperature calcination time is 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc.; the preferred method for high-temperature calcination is uniform heating, with a heating rate of, for example, 6-15℃ / minute, such as 6℃ / minute, 7℃ / minute, 8℃ / minute, 9℃ / minute, 10℃ / minute, 11℃ / minute, 12℃ / minute, 13℃ / minute, 14℃ / minute, 15℃ / minute, etc.

[0044] The sandwich composite material (MnS@NC) prepared by this invention is as follows: Figure 1 As shown, MnS nanospheres are uniformly distributed between nitrogen-doped carbon nanosheets to form a sandwich structure. This sandwich structure provides more contact surfaces between the nitrogen-doped carbon nanosheets and MnS nanospheres, effectively improving the conductivity of MnS as a negative electrode material. Its sandwich structure can provide an ion pathway for lithium-ion conduction while also serving as a supporting structure, thereby improving the electrochemical stability of MnS materials.

[0045] In this invention, the sandwich-structured composite material MnS@NC can be used as the negative electrode material for lithium-ion batteries. Specifically, the lithium-ion battery consists of a positive electrode material, a negative electrode material, and an electrolyte. The positive electrode material is, for example, metallic lithium, and the electrolyte consists of an electrolyte and a solvent, wherein the electrolyte is, for example, LiPF6; the solvent is ethylene carbonate (EC), dimethyl carbonate (DEC), or methyl carbonate (EMC) (volume ratio of v(EC):v(DMC):v(EMC) = 1:1:1), and the concentration of the electrolyte is, for example, a 1 mol / L solute solution.

[0046] The components and their weight percentages of the negative electrode material are as follows:

[0047] MnS@NC: 60%-80%;

[0048] Adhesive: 8%-15%;

[0049] Electronic conductive agent: 12-32%;

[0050] The binder is at least one of polyvinylidene fluoride (PVDF), hydrogenated nitrile butadiene rubber (HNBR), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), and polyacrylic acid (PAA), and the electronic conductive agent is at least one of acetylene black, hard carbon, and graphite.

[0051] The present invention will be further explained and illustrated below through more specific embodiments, but these do not constitute any limitation.

[0052] The main sources of raw materials for the examples and comparative examples are as follows:

[0053] Tin disulfide was obtained from high-purity tin disulfide powder purchased from Aladdin, CAS No.: 1315-01-1;

[0054] The o-phenanthroline is derived from raw materials purchased from Hubei Benofu Chemical, CAS No.: 5144-89-8;

[0055] Acetylene black was sourced from Yirui Stone products purchased from suppliers.

[0056] The PVDF is sourced from Solvay's 5130 product.

[0057] The source of manganese sulfide (MnS) is the purchase of products from Thermo Fisher Scientific.

[0058] The electrical performance testing methods for precursors and cathode materials are as follows:

[0059] Electron microscopy and EDS testing: Morphological characterization and energy dispersive spectroscopy analysis were performed under a scanning electron microscope;

[0060] For red bulk crystals, Mo-K α radiation Single-crystal X-ray diffraction (SCXRD) data were acquired using a Bruker APEX-II CCD diffractometer as the radiation source. The direct method was used to solve the problem using SHELX-2016 software, and the results were obtained at F... 2 The above was refined using the full matrix least squares method, and finally, the structure was drawn using Diamond software, resulting in a detailed structure as shown below. Figure 2 As shown in Table 1, the specific crystallographic data are listed.

[0061] The assembled battery was subjected to charge-discharge cycles at currents of 500mA / g and 1000mA / g using the Blue Electric testing system to test its cycle performance.

[0062] Example 1

[0063] 1) Synthesis of crystalline metal dichalcogenide [Mn(phen)2]S8

[0064] Weigh out 1 mmol of manganese acetate, 1 mmol of tin disulfide, 1 mmol of sulfur powder, and 1 mmol of o-phenanthroline, mix them thoroughly, and then place the mixed powder in a suitable reaction vessel. Add 28 mmol of deionized water, seal the vessel with a metal casing, and place it in an oven at 160°C for 5 days. Remove the reaction vessel, cool it to room temperature in air, and wash the product repeatedly with alcohol and water to obtain red blocky crystals.

[0065] 2) Crystal analysis

[0066] For red bulk crystals, Mo-K was used. α radiation Single-crystal X-ray diffraction (SCXRD) data were acquired using a Bruker APEX-II CCD diffractometer as the radiation source. The direct method was used to solve the problem using SHELX-2016 software, and the results were obtained at F... 2 The above was refined using the full matrix least squares method, and finally, the structure was drawn using Diamond software, resulting in a detailed structure as shown below. Figure 2 As shown in Table 1, the specific crystallographic data are listed.

[0067] Table 1 shows the crystallographic data obtained after crystal analysis.

[0068]

[0069]

[0070] b wR2=[Σw(F o 2 -F c 2 ) 2 / Σw(F o 2 ) 2 ] 1 / 2

[0071] 3) Preparation of MnS@NC composite material with sandwich structure

[0072] Take 10g of [Mn(phen)2]S8 crystals and place them in a mortar. Grind them into powder, then place the powder in a porcelain boat and heat it in a tube furnace under a nitrogen atmosphere at 6℃ for 1 minute. -1 The temperature was increased to 500°C at a heating rate and held at that temperature for 4 hours. After cooling to room temperature, a brownish-red powder was obtained.

[0073] Example 2

[0074] 1) Synthesis of crystalline metal dichalcogenide [Mn(phen)2]S8

[0075] Weigh out 2 mmol of manganese chloride, 2 mmol of tin disulfide, 2 mmol of sulfur powder, and 2 mmol of o-phenanthroline, mix them thoroughly, and then place the mixed powder in a suitable reaction vessel. Add 75 mmol of deionized water, seal the vessel with a metal casing, and place it in an oven at 150°C for 7 days. Remove the reaction vessel, cool it to room temperature in air, and wash the product repeatedly with alcohol and water to obtain red blocky crystals.

[0076] 2) Crystal analysis

[0077] Crystal analysis was performed according to the crystal analysis method in Example 1, and the crystallographic data and structure obtained were consistent with those in Example 1.

[0078] 3) Preparation of MnS@NC composite material with sandwich structure

[0079] Take 10g of [Mn(phen)2]S8 crystals and place them in a mortar. Grind them into powder, then place the powder in a porcelain boat and heat it in a tube furnace under a helium atmosphere at 8℃ for 1 minute. -1 The temperature was increased to 450°C at a certain rate and held at that temperature for 3.5 hours. After cooling to room temperature, a brownish-red powder was obtained.

[0080] Example 3

[0081] 1) Synthesis of crystalline metal dichalcogenide [Mn(phen)2]S8

[0082] Weigh out 2 mmol of manganese acetate, 1 mmol of tin disulfide, 2 mmol of sulfur powder, and 2 mmol of o-phenanthroline, mix them thoroughly, and then place the mixed powder in a suitable reaction vessel. Add 200 mmol of deionized water, seal the vessel with a metal casing, and place it in an oven at 150°C for 5 days. Remove the reaction vessel, cool it to room temperature in air, and wash the product repeatedly with alcohol and water to obtain red blocky crystals with a higher yield.

[0083] 2) Crystal analysis

[0084] Crystal analysis was performed according to the crystal analysis method in Example 1, and the crystallographic data and structure obtained were consistent with those in Example 1.

[0085] 3) Preparation of MnS@NC composite material with sandwich structure

[0086] Take 10g of [Mn(phen)2]S8 crystals and place them in a mortar. Grind them into powder, then place the powder in a porcelain boat and heat it in a tube furnace under an argon atmosphere at 10℃ for 1 minute. -1The temperature was increased to 500°C at a certain rate and held at that temperature for 4 hours. After cooling to room temperature, a brownish-red powder was obtained.

[0087] Example 4

[0088] 1) Synthesis of crystalline metal dichalcogenide [Mn(phen)2]S8

[0089] Weigh out 2 mmol of manganese acetate, 0.5 mmol of tin disulfide, 2 mmol of sulfur powder, and 2 mmol of o-phenanthroline, mix them thoroughly, and then place the mixed powder in a suitable reaction vessel. Add 100 mmol of deionized water, seal the vessel with a metal casing, and place it in an oven at 150°C for 6 days. Remove the reaction vessel, cool it to room temperature in air, and wash the product repeatedly with alcohol and water. Finally, a higher yield of red blocky crystals was obtained compared to Example 3.

[0090] 2) Crystal analysis

[0091] Crystal analysis was performed according to the crystal analysis method in Example 1, and the crystallographic data and structure obtained were consistent with those in Example 1.

[0092] 3) Preparation of MnS@NC composite material with sandwich structure

[0093] Take 10g of [Mn(phen)2]S8 crystals and place them in a mortar. Grind them into powder, then place the powder in a porcelain boat and heat it in a tube furnace under a nitrogen atmosphere at 15°C for 1 minute. -1 The temperature was increased to 500°C at a certain rate and held at that temperature for 5 hours. After cooling to room temperature, a brownish-red powder was obtained.

[0094] The powders obtained in each embodiment were characterized by morphology and subjected to energy dispersive spectroscopy (EDS) analysis.

[0095] The product obtained after high-temperature calcination was characterized by SEM morphology, and the morphology of the composite material obtained after high-temperature calcination conforms to the schematic diagram. Figure 1 The morphology of the product mainly consists of two types of morphologies: spherical granular products and two-dimensional layered products. Furthermore, these two structures, along with the distribution of small spheres between the layers, form a sandwich structure of sheets and spheres. Figure 3 It can be seen that this layered compound is a relatively thin two-dimensional nanomaterial, and the spheres are extremely small nanospheres, which are uniformly distributed between the layers and on the surface of the two-dimensional nanospheres. Energy dispersive spectroscopy (EDS) was then performed on it. Figure 4 As shown, the nanosheets mainly contain N and C elements, while the nanospheres mainly contain Mn and S elements, further verifying that the composite material is a sandwich structure of N-doped C nanosheets and MnS nanospheres.

[0096] The composite materials obtained in each embodiment are used as negative electrode materials in the fabrication of the negative electrode:

[0097] The composite materials MnS@NC, acetylene black, and polyvinylidene fluoride were weighed out in a ratio of 70mg:10mg:20mg. The weighed substances were mixed and ground in a mortar for 10 minutes until homogeneous. The mixture was then transferred to a magnetic volumetric flask, and 100g of NMP was added as a dispersant. The mixture was stirred on a magnetic stirring table for 12 hours. After the slurry was homogeneous, it was coated onto copper foil to form an electrode. The coated electrode was then dried in a conventional oven at 60℃ for 1 hour, followed by vacuum drying in a vacuum oven at 60℃ for 12 hours to prepare the negative electrode sheet.

[0098] Preparation of MnS anode material as a control

[0099] Weigh out MnS powder, acetylene black, and polyvinylidene fluoride in a ratio of 70mg:10mg:20mg. Mix the weighed substances and grind them in a mortar for 10 minutes until homogeneous. Then transfer the mixture to a magnetic volumetric flask, add 100g of NMP as a dispersant, and stir on a magnetic stirring table for 12 hours. After the slurry is homogeneous, coat it onto copper foil to form an electrode. Dry the coated electrode sheet in a 60℃ ordinary oven for 1 hour, then transfer it to a 60℃ vacuum oven for vacuum drying for 12 hours to prepare the negative electrode sheet.

[0100] Battery assembly and testing

[0101] The electrode sheet to be used was placed in a glove box under an argon atmosphere, with a lithium sheet as the positive reference electrode, and a Celgard 2400 diaphragm and 1 mol L... -1 A battery is assembled using LiPF6 / ethylene carbonate (EC), dimethyl carbonate (DEC), and methyl carbonate (EMC) electrolytes (volume ratio of v(EC):v(DMC):v(EMC) = 1:1:1) and negative electrode sheets.

[0102] Using the LAND CT2001A system, the test was conducted within a voltage range of 0.05-3V at a speed of 500mAg. -1 Cycling at a current density for 200 cycles, the results are as follows: Figure 5 As shown, the initial charge / discharge capacity of the MnS@NC composite material reached 830 mAh g. -1 and 1338.8mAh g -1 Furthermore, its specific capacity hardly decayed during subsequent cycles, and after 200 cycles at this current density, the battery's reversible capacity was 878.2 mAh g. -1Compared to the second cycle, its capacity decreased by only 3%, indicating that the MnS@NC nanocomposite material synthesized by the method of this invention has excellent cycle stability as a lithium battery anode material. During cycling, its approximately 100% coulombic efficiency demonstrates that the material possesses excellent electrochemical reversibility and structural stability.

[0103] Cyclic performance was tested using the LAND CT2001A system within a voltage range of 0.05–3V. At 500mA g -1 Charge-discharge curves for different cycles were obtained at different current densities, such as... Figure 6 As shown, the trend and plateau of the charge-discharge curves remained unchanged with increasing charge-discharge cycles, indicating that the redox reactions occurring in different cycles were consistent. This further confirms that the composite material of the present invention possesses excellent structural stability and electrochemical reversibility.

[0104] High-current cycling performance was tested using the LAND CT2001A system within a voltage range of 0.05-3V. At 1000mA g... -1 Long-term cyclic stability tests were conducted at the specified current density, and the results are shown in [Figure number missing]. Figure 7 and Figure 8 When cycled 500 times, the battery using the MnS@NC composite material of this invention as the negative electrode material can provide a reversible capacity of 753 mAh g. -1 Compared to the initial capacity, there was almost no decrease, and it still maintained a high coulombic efficiency. When pure MnS powder was used as the anode material, its specific capacity was 85.3 mAh g⁻¹ after 500 cycles. -1 Compared to the 285mA hg in the first lap -1 The capacity retention rate is only 30%.

[0105] Comparative test results show that the MnS@NC composite nanomaterials prepared by high-temperature calcination using the crystalline metal sulfide [Mn(phen)2]S8 synthesized in this invention as a precursor have significantly improved initial specific capacity and capacity retention compared to pure MnS powder at higher current densities.

[0106] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A composite material having a sandwich structure, characterized by, The composite material is a composite material (MnS@N-C) in which MnS nanospheres are uniformly distributed between nitrogen-doped carbon nanosheet interlayers to form a sandwich structure, wherein the composite material is prepared from a crystalline metal polysulfide as a precursor; The crystalline metal polysulfide has a molecular formula of [Mn(phen)2]S8, and a structure in which one manganese atom and eight S atoms are connected end to end to form a zero-dimensional MnS8 ring, and two o-phenanthroline molecules (phen) are connected to the Mn atom by N-Mn coordination.

2. The composite material having a sandwich structure according to claim 1, characterized by, The preparation method of the crystalline metal polysulfide comprises the step of reacting manganese acetate or manganese chloride, tin disulfide, sulfur powder, o-phenanthroline, and deionized water in a reaction kettle to obtain the crystalline metal polysulfide.

3. The composite material having a sandwich structure according to claim 2, characterized by, The molar ratio of the manganese acetate or manganese chloride, tin disulfide, sulfur powder, o-phenanthroline, and deionized water is 1:0.2-1:1:1:20-100.

4. The composite material having a sandwich structure according to claim 3, characterized by, The reaction temperature is 150-160°C, and the reaction time is 5-7 days.

5. Process for the production of a composite material having a sandwich structure according to any one of claims 1 to 4, characterized in that The crystalline metal polysulfide is used as a precursor to prepare the composite material by high-temperature calcination in an inert gas atmosphere.

6. The production method according to claim 5, wherein The inert gas is at least one selected from nitrogen, helium, and argon.

7. The preparation method according to claim 5, characterized in that, The high-temperature calcination temperature is 400-500°C, and the calcination time is 3.5-5h.

8. The preparation method according to claim 7, characterized in that, The high-temperature calcination temperature is 400-500°C, and the calcination time is 3.5-5h.

9. A negative electrode material, characterized by, The high-temperature calcination temperature is 400-500°C, and the calcination time is 3.5-5h. The negative electrode material comprises the following components in weight percentage: MnS@N-C: 60%-80%; Binder: 8%-15%; Electronic conductive agent: 12-32%; 10. The negative electrode material according to claim 9, characterized in that, The MnS@N-C is the composite material with a sandwich structure according to any one of claims 1-4 or the composite material with a sandwich structure prepared by the method according to any one of claims 5-8.

11. A secondary lithium-ion battery, characterized by The binder is at least one selected from polyvinylidene fluoride (PVDF), hydrogenated nitrile rubber (HNBR), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), and polyacrylic acid (PAA), and the electronic conductive agent is at least one selected from acetylene black, hard carbon, and graphite. The negative electrode comprises the negative electrode material according to claim 9 or 10.

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