Trimetallic sulfide core-shell composite materials, their preparation methods, and their applications in lithium-ion batteries.

Abstract

This invention belongs to the field of lithium-ion battery technology, specifically relating to lithium-ion battery anode materials, and more specifically to trimetallic sulfide core-shell structure composite materials, their preparation methods, and their applications in lithium-ion batteries. Under inert atmosphere conditions, a metal-organic framework (ZnCoFe-ZIF) precursor is prepared by a one-pot method using zinc salt, divalent cobalt salt, ferrous salt, and 2-methylimidazole. PDA is then coated onto the surface of the ZnCoFe-ZIF precursor via surface polymerization. Under inert atmosphere conditions, the PDA-coated ZnCoFe-ZIF precursor is calcined and sulfided with sublimed sulfur powder to obtain the final product. The trimetallic sulfide core-shell structure composite material provided by this invention has a simple, economical, and efficient preparation method, exhibiting excellent electrochemical performance, high specific capacity, and good cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to lithium-ion battery anode materials, specifically trimetallic sulfide core-shell structure composite materials, their preparation methods, and their applications in lithium-ion batteries. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] The most commonly used negative electrode material for lithium-ion batteries (LIBs) is graphite, but its theoretical capacity (372 mA hg) is limited. -1 The inherent low conductivity of TMS makes it difficult to meet demanding market requirements. Transition metal sulfides (TMS) possess higher theoretical capacities, and due to the low electronegativity of sulfur and weaker metal-S bonds, TMS exhibits higher electron transfer capabilities, thus holding significant research value. However, due to their inherently low conductivity, TMS struggles to consistently provide high capacity during cycling. Furthermore, the significant volume changes and severe pulverization issues hinder the achievement of superior electrochemical performance.

[0004] The hollow structure of materials can not only reduce density and increase specific surface area, but also expose more active sites and improve reaction mass transfer and diffusion rates. However, synthesizing hollow structure materials with controllable structures (especially complex structures) and certain compositions in a safe, efficient, and controllable manner remains a challenging task. Currently, the most commonly used method is the hard template method, but the synthesis and removal of the template are not only cumbersome but also increase costs. Furthermore, according to the inventors' research, existing studies on TMS mostly focus on single-metal or bimetallic sulfides, and their electrochemical performance still needs improvement. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a trimetallic sulfide core-shell structured composite material, its preparation method, and its application in lithium-ion batteries. The trimetallic sulfide core-shell structured composite material provided by the present invention has a simple, economical, and efficient preparation method, and features excellent electrochemical performance, high specific capacity, and good cycle stability.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] On one hand, a method for preparing a trimetallic sulfide core-shell composite material involves preparing a metal-organic framework ZnCoFe-ZIF precursor by one-pot reaction of zinc salt, divalent cobalt salt, ferrous salt, and 2-methylimidazole under an inert atmosphere; coating the surface of the ZnCoFe-ZIF precursor with PDA (polydopamine) by surface polymerization; and then calcining and vulcanizing the PDA-coated ZnCoFe-ZIF precursor with sublimed sulfur powder under an inert atmosphere to obtain the final product.

[0008] The molar ratio of zinc salt, divalent cobalt salt, and ferrous salt, calculated by zinc, cobalt, and iron elements, is 10:0.9~1.1:0.2~0.4; the calcination and sulfidation treatment temperatures are 550~650℃.

[0009] ZIF-8, a metal-organic framework material formed by the coordination of zinc ions and 2-methylimidazole, has a dodecahedral structure. After coating its surface with PDA, calcining, and sulfurizing, the 2-methylimidazole in ZIF-8 is removed, forming a sulfide. The pyrolysis of PDA forms a nitrogen-doped carbon shell on the sulfide surface, improving the overall electrical conductivity of the material. During the calcination and sulfurization process, because the occupancy of sulfur (S) is significantly smaller than that of 2-methylimidazole, the core volume shrinks as S replaces 2-methylimidazole. Simultaneously, when the PDA coating on the surface pyrolyzes into a nitrogen-doped carbon shell, the difference in materials between the core and shell causes a difference in the degree of core volume shrinkage compared to the shell, creating voids between them. These voids provide pore size to accommodate the volume expansion during charge-discharge cycles, thus avoiding large volume changes and severe pulverization. Furthermore, after calcination, the material's microstructure retains its dodecahedral structure, ensuring structural stability and guaranteeing excellent electrochemical performance.

[0010] To further improve the electrochemical performance of the material as a negative electrode for lithium-ion batteries, this invention also employs doping with other metals. However, doping with other metals makes it difficult to guarantee the formation of a dodecahedral metal-organic framework structure, and it is also difficult to regulate the formation of voids between the core and shell. Further research revealed that the molar ratio of zinc, cobalt, and iron has a regulatory effect on the formation of the metal-organic framework structure. This invention uses a molar ratio of zinc salt, divalent cobalt salt, and ferrous salt of 10:0.9–1.1:0.2–0.4, which can guarantee the formation of a dodecahedral metal-organic framework structure. This allows voids to be formed between the core and shell according to the aforementioned mechanism, ensuring that the final morphology of the material still maintains the dodecahedral structure. Based on this research, it is shown that although iron and cobalt are both iron-based elements, compared with ZIF-8 doped iron or cobalt, the trimetallic sulfide core-shell structure composite material formed by ZIF-8 doped iron and cobalt has a higher specific capacity as a lithium-ion battery anode material. This indicates that there is a synergistic effect between zinc, cobalt and iron in the trimetallic sulfide core-shell structure composite material formed in this invention, thereby improving electrochemical performance, increasing the lithium storage capacity, and being more conducive to electrochemical reactions.

[0011] On the other hand, a trimetallic sulfide core-shell composite material is obtained by the above-described preparation method. The Zn-Co-Fe-S@NC prepared by this invention exhibits good structural stability and a large specific surface area, which can improve the transfer and diffusion of electrons and ions in lithium-ion batteries and provide greater capacity. It also demonstrates good electrochemical performance such as cycle stability, rate performance, and lithium storage performance. These characteristics are mainly attributed to the unique core-shell structure, nitrogen-doped carbon matrix, and the synergistic effect of multiple metals.

[0012] Thirdly, the application of the aforementioned trimetallic sulfide core-shell structure composite material in lithium-ion batteries, particularly in the negative electrode of lithium-ion batteries.

[0013] Fourthly, a lithium-ion battery negative electrode includes an active material, a conductive agent, a binder, and a current collector, wherein the active material is a nanocomposite material with a trimetallic sulfide core-shell structure as described above.

[0014] Fifthly, a lithium-ion battery includes the aforementioned lithium-ion battery negative electrode, positive electrode, separator, and electrolyte.

[0015] The beneficial effects of this invention are as follows:

[0016] 1. This invention uses a one-pot method to synthesize zinc, cobalt and iron trimetallic ZIF precursors, which are then coated with dopamine and carbonized directly with sulfur powder, greatly simplifying the synthesis process and making it highly operable.

[0017] 2. The trimetallic sulfide core-shell nanocomposite material of the present invention contains zinc, cobalt and iron transition metal sulfides. Due to the multiple oxidation states of each metal and the synergistic effect between the multiple metals, the electrochemical reactivity is improved, which is more conducive to the electrochemical reaction.

[0018] 3. The trimetallic sulfide core-shell structured nanocomposite material prepared by this invention can shorten the diffusion path of ions, and the gap between the shell and the core can effectively buffer volume expansion, thereby promoting the electrochemical reaction.

[0019] 4. The trimetallic sulfide core-shell nanocomposite material provided by this invention contains nitrogen-doped carbon, which not only improves electron transport dynamics but also enhances the structural stability of the material.

[0020] 5. The trimetallic sulfide core-shell nanocomposite material provided by the present invention forms a porous structure due to the removal of organic ligands during the calcination and carbonization process, which is conducive to ion transport and promotes the electrochemical reaction.

[0021] 6. When the trimetallic sulfide core-shell structured nanocomposite material provided by this invention is used as a lithium-ion battery anode material, it exhibits good rate performance and cycle stability in electrochemical tests. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 The XRD spectra of the materials prepared in Examples 1-3 of this invention are shown below. a is the XRD spectrum of ZnCoFe-ZIF, ZnCo-ZIF and ZnFe-ZIF, b is the XRD spectrum of ZnCoFe-ZIF@PDA, ZnCo-ZIF@PDA and ZnFe-ZIF@PDA, and c is a comparison of the characteristic peaks of XRD of Zn-Co-Fe-S@NC, Zn-Co-S@NC and Zn-Fe-S@NC.

[0024] Figure 2 The above are FESEM images of the precursors prepared in Examples 1-3 of this invention, where a is ZnCoFe-ZIF, b is ZnFe-ZIF, and c is ZnCo-ZIF.

[0025] Figure 3 The above are FESEM images of Zn-Co-Fe-S@NC prepared in Example 1 of this invention. a is high resolution and b is low resolution.

[0026] Figure 4These are TEM images of the materials used in the preparation process of Example 1 of this invention. a is ZnCoFe-ZIF, b is ZnCoFe-ZIF@PDA, and c is Zn-Co-Fe-S@NC.

[0027] Figure 5 The full spectrum of Zn-Co-Fe-S@NC XPS prepared in Example 1 of this invention;

[0028] Figure 6 The XPS energy spectrum of Zn-Co-Fe-S@NC prepared in Example 1 of this invention is shown. a represents Zn 2p, b represents Co 2p, c represents Fe 2p, d represents C1s, e represents N1s, and f represents S 2p.

[0029] Figure 7 The Nyquist curves are for the composite materials prepared in Examples 1-3 of this invention.

[0030] Figure 8 The discharge-charge curve of the Zn-Co-Fe-S@NC composite material prepared in Example 1 of this invention is shown, where a is 100 mA g. -1 Discharge-charge curves at current density, b represents charge-discharge curves at different current densities;

[0031] Figure 9 The graph shows the cycling performance and coulombic efficiency of the Zn-Co-Fe-S@NC composite material prepared in Example 1 of this invention. a represents 100 mA g. -1 Current density, b is 500mA g -1 Current density;

[0032] Figure 10 The graphs show the electrochemical performance results of the composite materials prepared in Examples 1-3 of this invention. Figure a shows the rate performance of Zn-Co-Fe-S@NC, Zn-Co-S@NC, and Zn-Fe-S@NC; figure b shows the rate performance of Zn-Co-Fe-S@NC, Zn-Co-S@NC, and Zn-Fe-S@NC at 2000 mA g. -1 Cyclic performance and coulombic efficiency at current density. Detailed Implementation

[0033] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0035] Given the drawbacks of existing transition metal sulfide materials, such as complex preparation, simple composition and structure, low capacity and poor cycle stability, this invention proposes a trimetallic sulfide core-shell composite material, its preparation method, and its application in lithium-ion batteries.

[0036] A typical embodiment of the present invention provides a method for preparing a trimetallic sulfide core-shell composite material. Under inert atmosphere conditions, a one-pot method is used to prepare a metal-organic framework ZnCoFe-ZIF precursor by reacting zinc salt, divalent cobalt salt, ferrous salt, and 2-methylimidazole. PDA is then coated onto the surface of the ZnCoFe-ZIF precursor using surface polymerization. Under inert atmosphere conditions, the PDA-coated ZnCoFe-ZIF precursor is calcined and vulcanized with sublimed sulfur powder to obtain the final product.

[0037] The molar ratio of zinc salt, divalent cobalt salt, and ferrous salt, calculated by zinc, cobalt, and iron elements, is 10:0.9~1.1:0.2~0.4; the calcination and sulfidation treatment temperatures are 550~650℃.

[0038] The zinc salts described in this invention are compounds containing zinc ions, such as zinc chloride, zinc nitrate, and zinc acetate.

[0039] The divalent cobalt salts described in this invention are compounds containing divalent cobalt ions, such as cobalt chloride, cobalt nitrate, and cobalt acetate.

[0040] The ferrous salts described in this invention are compounds containing ferrous ions, such as ferrous chloride, ferrous nitrate, and ferrous acetate.

[0041] The metal-organic framework ZnCoFe-ZIF precursor is prepared under an inert atmosphere to ensure the reaction proceeds in an oxygen-free environment, thus guaranteeing a higher success rate in obtaining dodecahedrons. In some embodiments, zinc salt and divalent cobalt salt are mixed uniformly under an inert atmosphere, followed by the addition of ferrous salt and mixing uniformly, and then 2-methylimidazole is added to react and prepare the metal-organic framework ZnCoFe-ZIF precursor. The purpose of adding ferrous salt later is: 1. to reduce the amount of ferrous salt added and shorten the mixing time; 2. to remove oxygen through pre-stirring and avoid ferrous oxidation.

[0042] In some embodiments, the molar ratio of zinc salt, divalent cobalt salt, and ferrous salt, calculated based on zinc, cobalt, and iron elements, is 10:0.99-1.01:0.25-0.35.

[0043] In some embodiments, the surface polymerization process is as follows: the ZnCoFe-ZIF precursor is added to a buffer solution containing tris(hydroxymethyl)aminomethane (Tris), then dopamine hydrochloride is added, and the mixture is stirred to react, thus obtaining the product.

[0044] In one or more embodiments, the mass ratio of ZnCoFe-ZIF precursor to dopamine hydrochloride is 3.5 to 4.5:1.

[0045] In one or more embodiments, the buffer solution is an ethanol solution of tris(hydroxymethyl)aminomethane.

[0046] In one or more embodiments, the concentration of tris(hydroxymethyl)aminomethane in the buffer solution is 5–15 mmol / L.

[0047] In some embodiments, the mass ratio of the ZnCoFe-ZIF precursor coated with PDA to the sublimated sulfur powder is 1:1.5 to 2.5.

[0048] In some embodiments, the calcination and vulcanization treatment employs a programmed temperature rise. The heating rate is 1–5 °C / min, preferably 2.5–3.5 °C / min. The calcination and vulcanization treatment time is 1–3 h.

[0049] Another embodiment of the present invention provides a trimetallic sulfide core-shell structured composite material, obtained by the above preparation method.

[0050] A third embodiment of the present invention provides an application of the above-mentioned trimetallic sulfide core-shell structure composite material in lithium-ion batteries, particularly in the negative electrode of lithium-ion batteries.

[0051] A fourth embodiment of the present invention provides a lithium-ion battery negative electrode, comprising an active material, a conductive agent, a binder, and a current collector, wherein the active component is the aforementioned trimetallic sulfide core-shell structure composite material.

[0052] In some embodiments, the preparation method is as follows: the trimetallic sulfide core-shell structure composite material is mixed evenly with an adhesive and a conductive agent, a solvent is added, and the mixture is mixed evenly to form a gel. The gel is then rolled onto a current collector.

[0053] A fifth embodiment of the present invention provides a lithium-ion battery, comprising the above-described lithium-ion battery negative electrode, positive electrode, separator, and electrolyte.

[0054] In some embodiments, the positive electrode is a lithium sheet.

[0055] In some embodiments, the diaphragm is a high-strength, thin-film polyolefin porous membrane.

[0056] In some embodiments, the secondary electrolyte used is LB-002, wherein the electrolyte is lithium hexafluorophosphate, and the solvent is a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (volume ratio of 1:1:1).

[0057] The lithium-ion battery is a CR2032 button cell.

[0058] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0059] Example 1

[0060] Preparation of trimetallic sulfide core-shell structured Zn-Co-Fe-S@NC dodecahedral composite material.

[0061] (1) Preparation of the precursor ZnCoFe-ZIF:

[0062] ① Dissolve 10 mmol Zn(NO3)2·6H2O and 1 mmol Co(NO3)2·6H2O in 100 mL methanol and stir for 30 min under inert gas protection.

[0063] ② Add 0.3 mmol FeSO4·7H2O to the solution obtained in step ① and stir for 30 min.

[0064] ③ Add 40 mmol of 2-methylimidazole to 100 mL of methanol, stir for 30 min under an inert gas atmosphere, and quickly pour it into the solution obtained in step ② above, and stir for 12 h under an inert gas atmosphere.

[0065] ④ Collect the precipitate by centrifugation, wash it several times with methanol, and dry it in a vacuum drying oven at 60℃ for 12 hours.

[0066] (2) Preparation of ZnCoFe-ZIF@PDA:

[0067] ① Dissolve 1 mmol of tris(hydroxymethyl)aminomethane (Tris) in 100 mL of anhydrous ethanol to obtain a buffer solution.

[0068] ② Add 80 mg ZnCoFe-ZIF@PDA to the buffer solution obtained in step ① and sonicate for 30 min.

[0069] ③ Add 20 mg of dopamine hydrochloride to the solution obtained in step ② and stir for 3-4 hours.

[0070] ④ The solution obtained in ③ is washed by centrifugation with ethanol and dried in a vacuum drying oven at 60℃ for 12 hours.

[0071] (3) Preparation of trimetallic sulfide core-shell structure Zn-Co-Fe-S@NC dodecahedral composite material.

[0072] ZnCoFe-ZIF@PDA and excess sulfur powder (mass ratio 1:2) were placed in the same calcining boat and calcined at 600℃ in an argon atmosphere to obtain a trimetallic sulfide core-shell structure Zn-Co-Fe-S@NC dodecahedral composite material. The heating rate was 2℃ / min and the holding time was 2h.

[0073] Example 2

[0074] Preparation of bimetallic sulfide core-shell structured Zn-Fe-S@NC dodecahedral composite material.

[0075] (1) Preparation of the precursor ZnFe-ZIF:

[0076] ① Dissolve 10 mmol Zn(NO3)2·6H2O and 0.3 mmol FeSO4·7H2O in 100 mL methanol and stir for 30 min under inert gas protection.

[0077] ② Add 40 mmol of 2-methylimidazole to 100 mL of methanol, stir for 30 min under an inert gas atmosphere, and quickly pour it into the solution obtained in step ① above, and stir for 12 h under an inert gas atmosphere.

[0078] ③ Collect the precipitate by centrifugation, wash it several times with methanol, and dry it in a vacuum drying oven at 60℃ for 12 hours.

[0079] The preparation of ZnFe-ZIF@PDA is the same as step (2) in Example 1.

[0080] The preparation of the bimetallic sulfide core-shell structure Zn-Fe-S@NC dodecahedral composite material is the same as step (3) in Example 1.

[0081] Example 3

[0082] Preparation of bimetallic sulfide core-shell structured Zn-Co-S@NC dodecahedral composite material.

[0083] (1) Preparation of the precursor ZnCo-ZIF:

[0084] ① Dissolve 10 mmol Zn(NO3)2·6H2O and 1 mmol Co(NO3)2·6H2O in 100 mL methanol and stir for 30 min under inert gas protection.

[0085] ② Add 40 mmol of 2-methylimidazole to 100 mL of methanol, stir for 30 min under an inert gas atmosphere, and quickly pour it into the solution obtained in step ① above, and stir for 12 h under an inert gas atmosphere.

[0086] ③ Collect the precipitate by centrifugation, wash it several times with methanol, and dry it in a vacuum drying oven at 60℃ for 12 hours.

[0087] The preparation of ZnCo-ZIF@PDA is the same as step (2) in Example 1.

[0088] The preparation of the bimetallic sulfide core-shell structure Zn-Co-S@NC dodecahedral composite material is the same as step (3) in Example 1.

[0089] Example 4

[0090] The trimetallic sulfide core-shell structure Zn-Co-Fe-S@NC composite material prepared in Example 1 was used to fabricate a button cell.

[0091] The prepared trimetallic sulfide core-shell structure Zn-Co-Fe-S@NC composite material was added to deionized water at a mass ratio of 7:2:1 and mixed evenly. The mixture was then coated onto copper foil and vacuum dried to obtain the negative electrode. The positive electrode was a lithium sheet. The separator used was a high-strength thin-film polyolefin porous membrane. The secondary electrolyte was LB-002, in which lithium hexafluorophosphate was the electrolyte and a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (volume ratio of 1:1:1) was used as the solvent. A lithium-ion battery was then assembled.

[0092] The bimetallic sulfide core-shell composite materials prepared in Examples 2 and 3 were used to fabricate button batteries, as described in Example 4.

[0093] Figure 1 a shows that the diffraction peaks of ZnCoFe-ZIF prepared in Example 1, ZnCo-ZIF prepared in Example 2, and ZnFe-ZIF prepared in Example 3 can be well matched with the diffraction peaks of ZIF-8, confirming the doping properties of Fe and Co and indicating the success of crystallization. Figure 1 b represents the XRD patterns of ZnCoFe-ZIF@PDA, ZnCo-ZIF@PDA, and ZnFe-ZIF@PDA after PDA coating. The diffraction peaks do not show significant changes compared to the diffraction peaks of the precursor. Figure 1c shows the XRD patterns of ZnCoFe-ZIF@PDA, ZnCo-ZIF@PDA, and ZnFe-ZIF@PDA after high-temperature carbonization with sulfur powder under N2 atmosphere to obtain Zn-Co-Fe-S@NC, Zn-Co-S@NC, and Zn-Fe-S@NC. The diffraction peaks of Zn-Co-Fe-S@NC, Zn-Co-S@NC, and Zn-Fe-S@NC at 28.5°, 47.5°, 56.2°, 69.5°, and 76.8° correspond one-to-one with the (111), (220), (311), (400), and (331) crystal planes of ZnS (JCPDS:05-0566) standard card, further demonstrating the successful doping of Co and Fe.

[0094] from Figures 2-3 As can be seen, the precursors prepared in Examples 1-3 are all dodecahedrons with smooth surfaces, uniform size, and identical shapes, indicating successful crystallization and successful doping with Co and Fe. During calcination, the surface of the dodecahedrons becomes rough and wrinkled, but they still maintain their dodecahedral shape, indicating that the dodecahedrons can be preserved during calcination and carbonization.

[0095] To better observe the internal structure of the material, TEM analysis was performed, such as... Figure 4 As shown. Figure 4 As can be seen, the precursor ZnCoFe-ZIF has a uniform solid structure inside and a relatively smooth surface. Figure 4 Figure b shows that the surface of ZnCoFe-ZIF@PDA is relatively rough, indicating that dopamine was successfully coated on the outer layer of the precursor ZnCoFe-ZIF, while the internal structure remains solid. From Figure 4 Figure c clearly shows the outer shell and the inner core, indicating that the core-shell structure was successfully prepared, and there is a gap between the outer shell and the inner core.

[0096] Figure 5 This indicates the presence of Zn, Co, Fe, C, N, and S elements in Zn-Co-Fe-S@NC. Moreover, the total spectrum clearly shows the presence of Zn 2p, Co 2p, Fe 2p, C 1s, N 1s, and S 2p signal peaks in the prepared Zn-Co-Fe-S@NC sample. Figure 6 a is the energy spectrum of Zn 2p, and the characteristic peak at 1021.78 eV corresponds to Zn 2+ Zn 2p 3 / 2 The characteristic peak at 1044.82 eV corresponds to Zn orbital. 2+ Zn 2p 1 / 2 Orbital. The energy spectrum of Co 2p is as follows: Figure 6 As shown in b, Co 3+ 2p 3 / 2and 2p 1 / 2 The spin-orbit double peaks are located at 779.89 and 794.58 eV, respectively. 2+ 2p 3 / 2 and 2p 1 / 2 The spin orbital double peaks are located at 781.5 and 797.05 eV, respectively, while the peaks at 785.22, 789.57, 800.67 and 805.74 eV are satellite peaks. Figure 6 c represents the energy spectrum of Fe2p, where the characteristic peaks at 709.06 and 722.42 eV correspond to Fe2p. 2+ 2p 3 / 2 and 2p 1 / 2 The characteristic peaks at 711.97 and 725.05 eV of the orbital correspond to Fe. 3+ 2p 3 / 2 and 2p 1 / 2 The orbital characteristics at 715.28 and 718.78 eV are satellite peaks. The XPS spectrum of C 1s is shown below. Figure 6 As shown in d, the characteristic peaks located at 284.8, 286.12, and 288.56 eV correspond to sp, respectively. 2 - Hydrogenated carbon, CN bonds, and OC=O bonds. The presence of CN bonds further confirms nitrogen doping in the carbon matrix. The presence of OC=O bonds is mainly due to surface adsorption. Nitrogen doping not only improves the electronic conductivity of the carbon matrix but also generates more defects for Li. + The insertion provides more active sites, which is beneficial for improving the electrochemical performance of the electrode. For example... Figure 6 As shown in Figure e, the high-resolution XPS spectrum of N 1s shows two peaks at 398.78 and 400.56 eV, which is consistent with the release of pyridine N and pyrrole N in N-doped carbon materials. Figure 6 f shows the XPS spectrum of S 2p, with two peaks at 161.51 and 162.69 eV, belonging to the Zn-S bond and the Co-S bond, respectively, in the S 2p region. 3 / 2 and S 2p 1 / 2 The track indicates the success of sulfidation during the high-temperature carbonization process.

[0097] Electrochemical impedance spectroscopy (EIS) measurements were performed on the electrodes, and an equivalent circuit diagram was fitted, such as... Figure 7 As shown. From Figure 7 In the diagram, a semicircle in the high-frequency region on the left and a diagonal line in the low-frequency region on the right can be observed. They correspond to the charge transfer resistance (R) in the equivalent circuit, respectively. ct ) and Warburg impedance (W0).

[0098] The high-frequency region radius of Zn-Co-Fe-S@NC is smaller than that of Zn-Co-S@NC and Zn-Fe-S@NC. Through equivalent circuit diagram fitting, the equivalent resistance of Zn-Co-Fe-S@NC is calculated to be approximately 67Ω, while the equivalent resistances of Zn-Co-S@NC and Zn-Fe-S@NC are approximately 75Ω and 126Ω, respectively.

[0099] The excellent electrochemical performance of the Zn-Co-Fe-S@NC composite material is mainly attributed to the porous core-shell structure of the nitrogen-doped carbon matrix and the synergistic effect of multiple metals, which not only provides sufficient contact area between the electrolyte and the active material, but also shortens the diffusion distance and accelerates the migration rate of Li ions.

[0100] Figure 8 a is Zn-Co-Fe-S@NC at 100mA g -1 Discharge-charge curves at different current densities and for different numbers of cycles. During the first charge-discharge cycle, the discharge capacity and charge capacity are 1201.65 and 889.64 mA hg, respectively. -1 The coulombic efficiency was 74.03%. The discharge plateau was approximately 0.75V. As the reaction progressed, the discharge plateau shifted to approximately 0.9V, primarily due to the formation of the SEI layer. In subsequent cycles, the charge-discharge curves showed high overlap, indicating that the trimetallic core-shell structure of the Zn-Co-Fe-S@NC dodecahedron exhibits excellent cycling performance. Figure 8 b represents the charge-discharge curves of Zn-Co-Fe-S@NC at different current densities. The curves are shown for current densities of 100, 200, 500, 1000, and 2000 mA. -1 At that time, the specific capacities were 971.60, 907.96, 767.44, 759.72, and 732.47 mA hg, respectively. -1 Even at 2000mA g -1 Maintaining a high specific capacity even at high current densities indicates that the core-shell structure and the synergistic effect between the metals contribute to improved electrochemical performance. Simultaneously, the unique core-shell structure of Zn-Co-Fe-S@NC can buffer volume expansion, provide more active sites, and promote electrochemical reactions, thereby enhancing the electrochemical performance of the anode material.

[0101] Figure 9 a is Zn-Co-Fe-S@NC at 100mA g -1 Cyclic performance and coulombic efficiency at current density show that the specific capacity gradually increases during cycling, mainly because the electrode material is gradually activated as cycling progresses. Figure 9b represents Zn-Co-Fe-S@NC and Zn-Fe-S@NC at 500 mA g -1 Cyclic performance and coulombic efficiency at current density. Figure 9 In step b, it can be clearly observed that the specific capacity of Zn-Co-Fe-S@NC is consistently higher than that of Zn-Fe-S@NC. After 100 cycles, the specific capacity of Zn-Co-Fe-S@NC still reaches 708.6 mA hg. -1 The specific capacity of Zn-Fe-S@NC is only 633.1 mA hg. -1 This demonstrates the superiority of multi-metal core-shell structures.

[0102] The rate performance results of the three anode materials are as follows: Figure 10 As shown in figure a, the specific capacity of Zn-Co-Fe-S@NC is significantly higher than that of Zn-Co-S@NC and Zn-Fe-S@NC. At a current density of 2000 mA g -1 At this time, the specific capacity of Zn-Co-Fe-S@NC can reach 666.5 mA hg. -1 As the current density decreases, the specific capacitance of Zn-Co-Fe-S@NC gradually increases, until the current density recovers to 100 mA g. -1 At that time, the specific capacity reached 925.8 mA hg -1 The results show that Zn-Co-Fe-S@NC exhibits good rate performance. In contrast, Zn-Fe-S@NC and Zn-Co-S@NC have poor rate performance at a current density of 2000 mA g. -1 The specific capacities were 316.7 and 255.1 mA g, respectively. -1 However, Zn-Fe-S@NC and Zn-Co-S@NC also exhibit good rate performance. This demonstrates the significant advantages of Zn-Co-Fe-S@NC in terms of composition and structure. Figure 10 b shows the Zn-Co-Fe-S@NC, Zn-Co-S@NC, and Zn-Fe-S@NC at 2000 mA g. -1 Cyclic performance and coulombic efficiency at current density. The initial discharge capacity of Zn-Co-Fe-S@NC is 1201.65 mA hg. -1 The initial coulombic efficiency was 74.03%, and after 200 cycles, the coulombic efficiency reached 99.71%, demonstrating excellent electrochemical performance. Figure 10 In sample b, it can be observed that the specific capacity of Zn-Co-S@NC and Zn-Fe-S@NC is significantly lower than that of Zn-Co-Fe-S@NC at 2000 mA g. -1At the given current density, after 200 cycles, the specific capacitances were only 221.05 and 320.2 mA hg, respectively. -1 This demonstrates the advantages of multi-metal synergy. Among them, Zn-Co-Fe-S@NC, Zn-Co-S@NC, and Zn-Fe-S@NC all exhibited good cycling stability, indicating that the core-shell structure has a greater advantage in terms of stability. This is mainly related to the fact that the core-shell structure can effectively mitigate volume changes.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a trimetallic sulfide core-shell structured composite material, characterized in that, in Under inert atmosphere conditions, zinc salt, divalent cobalt salt, ferrous salt and 2-methylimidazole were used in a one-pot process to prepare a metal-organic framework ZnCoFe-ZIF precursor; PDA was then coated on the surface of the ZnCoFe-ZIF precursor by surface polymerization. Under inert atmosphere conditions, the ZnCoFe-ZIF precursor with PDA coating on its surface is calcined and sulfided with sublimed sulfur powder to create a void between the core and the shell, thus obtaining the product. The molar ratio of zinc salt, divalent cobalt salt, and ferrous salt, calculated by zinc, cobalt, and iron elements, is 10:0.99~1.01:0.25~0.35; the calcination and sulfidation treatment temperatures are 550~650 ℃; the calcination and sulfidation treatments employ programmed temperature increases; and the heating rate is 1~5 ℃ / min. The synthesis sequence of the metal-organic framework ZnCoFe-ZIF precursor is as follows: zinc salt and divalent cobalt salt are mixed evenly under an inert atmosphere, ferrous salt is added and mixed evenly, and then 2-methylimidazole is added and reacted to prepare the metal-organic framework ZnCoFe-ZIF precursor.

2. The method for preparing the trimetallic sulfide core-shell composite material as described in claim 1, characterized in that, The surface polymerization process is as follows: ZnCoFe-ZIF precursor is added to a buffer solution containing tris(hydroxymethyl)aminomethane, then dopamine hydrochloride is added, and the mixture is stirred to react, thus obtaining the product.

3. The method for preparing the trimetallic sulfide core-shell composite material as described in claim 2, characterized in that, The mass ratio of the ZnCoFe-ZIF precursor to dopamine hydrochloride is 3.5~4.5:

1.

4. The method for preparing the trimetallic sulfide core-shell composite material as described in claim 2, characterized in that, The buffer solution is an ethanol solution of tris(hydroxymethyl)aminomethane.

5. The method for preparing the trimetallic sulfide core-shell composite material as described in claim 2, characterized in that, The concentration of tris(hydroxymethyl)aminomethane in the buffer solution is 5–15 mmol / L.

6. The method for preparing the trimetallic sulfide core-shell composite material as described in claim 1, characterized in that, The mass ratio of the ZnCoFe-ZIF precursor coated with PDA to sublimated sulfur powder is 1:1.5~2.

5.

7. The method for preparing the trimetallic sulfide core-shell composite material as described in claim 1, characterized in that, The calcination and sulfidation treatment time is 1~3 hours.

8. The method for preparing the trimetallic sulfide core-shell composite material as described in claim 1, characterized in that, The heating rate is 2.5~3.5 ℃ / min.

9. A trimetallic sulfide core-shell structured composite material, characterized in that, Obtained by the preparation method described in any one of claims 1 to 8.

10. The application of the trimetallic sulfide core-shell structure composite material of claim 9 in lithium-ion batteries.

11. A lithium-ion battery negative electrode, characterized in that, It includes an active material, a conductive agent, a binder, and a current collector, wherein the active material is a trimetallic sulfide core-shell structured nanocomposite material as described in claim 9.

12. A lithium-ion battery, characterized in that, Includes the lithium-ion battery negative electrode, positive electrode, separator, and electrolyte as described in claim 11.

Images