Preparation method of nickel disulfide / copper sulfide / carbon composite hollow sphere and application thereof

Abstract

This invention relates to the field of batteries and discloses a method for preparing nickel disulfide / copper sulfide / carbon composite hollow spheres and their applications. The invention uses hollow spherical Ni-MOF as a precursor, combined with subsequent ion exchange, PDA coating, glucose coating, carbonization, and sulfidation to prepare nickel disulfide / copper sulfide / carbon composite hollow spheres. This material inherits the porous hollow structure of Ni-MOF, providing a high-speed and efficient transport channel for ion diffusion in electrode materials, while mitigating volume change effects and improving the cycle life of sodium-ion batteries. Furthermore, the controllable introduction of appropriate amounts of copper ions through ion exchange to form a nickel-copper bimetallic sulfide heterostructure can accelerate ion diffusion kinetics, reduce the ion diffusion barrier, and enhance structural stability. Finally, the nitrogen-doped carbon derived from polydopamine carbonization in the middle layer improves the conductivity of the composite material and increases sodium storage active sites, while the outermost carbon layer derived from glucose carbonization further enhances the structural stability of the composite material.

Description

Technical Field

[0001] This invention belongs to the field of batteries, and more specifically relates to a method for preparing nickel disulfide / copper disulfide / carbon composite hollow spheres and their applications. Background Technology

[0002] Sodium-ion batteries are considered a candidate for next-generation large-scale energy storage devices due to the advantages of abundant sodium resources, low cost, and high safety. The electrochemical performance of sodium-ion batteries largely depends on the choice of electrode materials. For the negative electrode side, because Na... + Sodium storage anode materials have a large ionic radius and cannot be effectively embedded in commercial lithium battery anode materials such as graphite. Therefore, there is an urgent need to develop sodium storage anode materials with high specific capacity, high rate capability and long cycle life.

[0003] Nickel disulfide is due to its high theoretical specific capacity (870 mAh g). -1 Nickel disulfide (NiDIS) possesses characteristics such as low electronic conductivity and a relatively low voltage plateau, making it a highly promising anode material for sodium-ion batteries. However, problems such as its low electronic conductivity, easy agglomeration during preparation, and significant volume changes during electrochemical processes hinder its further development and application in sodium-ion batteries.

[0004] To address the above problems, researchers mainly adopted the following strategies for improvement: (1) nanomaterial design (such as quantum dots, nanowires, nanosheets, etc.); (2) compositing with materials with good conductivity (such as graphene, carbon nanotubes, etc.); (3) constructing bimetallic sulfide heterojunctions. Among these, constructing heterostructures is a strategy with outstanding advantages. Heterostructures composed of different materials not only combine the energy storage advantages of two or more materials, but also form abundant defects at the heterostructure interface, which is beneficial for increasing Na+ energy storage capacity. + Storage sites. Furthermore, the built-in electric field spontaneously generated at the heterostructure interface also plays a positive role in enhancing the sodium storage reaction kinetics. While rationally designed and fabricated heterostructures can maximize the advantages of different component materials, the fabrication methods for heterostructures are often very complex and difficult to control.

[0005] The existing invention patent CN116588974A discloses a NiS2 / MoS2 / C composite negative electrode material for sodium-ion batteries. The preparation method of the composite material includes: (1) mixing nickel salt with a complexing agent and preparing a carbon framework composite material by a hard template method; (2) mixing the carbon framework composite material, ammonium heptamolybdate, and thiourea, and preparing carbon-supported MoS2 by hydrothermal reaction. x Nanosheet composite materials; (3) under the action of a vulcanizing agent, carbon-supported MoS xThe nanosheet composite material was calcined to prepare a carbon-supported MoS2 nanosheet and NiS2 nanocrystal composite material. The resulting composite material has a layered structure, which effectively buffers the volume expansion of the negative electrode material during the sodium storage reaction and promotes rapid electron / ion transfer. However, this method is relatively complex to prepare and cannot precisely control the ratio of the two metal ions; moreover, molybdenum, as a rare metal, results in high raw material costs. Summary of the Invention

[0006] To address the shortcomings and problems of existing technologies, this invention provides a method for preparing nickel disulfide / copper sulfide / carbon composite hollow spheres and their applications. This invention uses hollow spherical Ni-MOF synthesized by a simple solvothermal method as a precursor, and combines ion exchange, dopamine hydrochloride (PDA) and glucose bilayer coating, carbonization, and sulfidation to prepare nickel disulfide / copper sulfide / carbon composite hollow spheres. The prepared nickel disulfide / copper sulfide / carbon composite hollow sphere material inherits the porous hollow structure of Ni-MOF and can be used as a substrate for Na+ in electrode materials. + Ion diffusion provides a high-speed and efficient transport channel while mitigating volume expansion and contraction, thus improving the cycle life of sodium-ion batteries. Furthermore, the controllable introduction of appropriate amounts of copper ions through ion exchange to form a nickel-copper bimetallic sulfide heterostructure accelerates ion diffusion kinetics, lowers the ion diffusion barrier, and enhances structural stability. Finally, the nitrogen-doped carbon derived from polydopamine carbonization in the middle layer improves the conductivity of the composite material and increases sodium storage active sites, while the outermost carbon layer derived from glucose carbonization further enhances the structural stability of the composite material.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: a method for preparing nickel disulfide / copper sulfide / carbon composite hollow spheres, comprising the following steps:

[0008] (1) Nickel salt, organic ligand pyromellitic acid and surfactant are mixed and dissolved in a solvent, stirred and then transferred to a reaction vessel for solvothermal reaction to obtain Ni-MOF hollow spheres.

[0009] (2) Mix and disperse Ni-MOF hollow spheres and copper salt in a solvent, stir, and centrifuge to obtain CuNi-MOF.

[0010] (3) Disperse CuNi-MOF in buffer solution, then add dopamine hydrochloride, stir at room temperature, and centrifuge to obtain CuNi-MOF / PDA.

[0011] (4) Disperse CuNi-MOF / PDA in a solvent, then add glucose, stir, and transfer to a reaction vessel. Obtain CuNi-MOF / PDA / C6H through a solvothermal reaction. 12 O6.

[0012] (5) Put CuNi-MOF / PDA / C6H 12 O6 was calcined under an inert gas atmosphere to obtain CuNi / NC / C hollow spheres.

[0013] (6) Gas-phase sulfidation of CuNi / NC / C hollow spheres yields nickel disulfide / copper sulfide / carbon composite hollow spheres.

[0014] In the above preparation process, this invention first uses hollow spherical Ni-MOF synthesized by a simple solvothermal method as a precursor, and then combines ion exchange, dopamine hydrochloride and glucose bilayer coating, carbonization and sulfidation to prepare nickel disulfide / copper sulfide / carbon composite hollow spheres. The nickel disulfide / copper sulfide / carbon composite hollow sphere composite material prepared by this method inherits the porous hollow structure of Ni-MOF, and can be used as a substrate for Na+ in electrode materials. + Ion diffusion provides a high-speed and efficient transport channel while mitigating volume expansion and contraction, thus improving the cycle life of sodium-ion batteries. Furthermore, the controllable introduction of appropriate amounts of copper ions through ion exchange to form a nickel-copper bimetallic sulfide heterostructure accelerates ion diffusion kinetics, lowers the ion diffusion barrier, and enhances structural stability. Finally, the nitrogen-doped carbon derived from polydopamine in the middle layer improves the conductivity of the composite material and increases sodium storage active sites, while the outermost carbon layer derived from glucose further enhances the structural stability of the composite material. The greatest advantage of polydopamine coating is its ability to self-aggregate on almost any material surface, making it suitable for uniform coating of CuNi-MOFs. However, the coating environment must be weakly alkaline; therefore, glucose coating must follow polydopamine coating to avoid the influence of the weakly alkaline environment on glucose.

[0015] Preferably, in step (2), the mass ratio of the Ni-MOF hollow spheres to the copper salt is 1:(2-7).

[0016] This invention reveals that the mass ratio of Ni-MOF hollow spheres to copper salts is crucial to the performance of the final product. During ion exchange, excessively high Cu ion concentrations can lead to overly vigorous ion exchange, thereby damaging the Ni-MOF structure; conversely, excessively low Cu ion concentrations result in fewer introduced Cu ions, and the constructed heterostructure offers negligible performance improvement to the material.

[0017] Preferably, in step (3), the mass ratio of CuNi-MOF to dopamine hydrochloride is 1:(5-10).

[0018] This invention reveals that the mass ratio of CuNi-MOF to dopamine hydrochloride is crucial to the performance of the final product. Excessive dopamine hydrochloride leads to an overly thick carbon layer, negatively impacting the material's electrochemical performance. This is because while a thicker inner carbon layer can better mitigate volume expansion, its increased density reduces sodium ion transport performance. Conversely, insufficient dopamine hydrochloride results in uneven carbon coating.

[0019] Preferably, in step (4), the mass ratio of CuNi-MOF / PDA to glucose is 1:(10-30).

[0020] This invention reveals that the quality of CuNi-MOF / PDA and glucose is crucial to the performance of the final product. Excessive glucose content can lead to agglomeration of some glucose molecules, resulting in an excessively high carbon content in the composite material and consequently reducing its capacity. Conversely, insufficient glucose content can lead to uneven carbon coating.

[0021] Preferably, in step (1), the mass ratio of the nickel salt, organic ligand, and surfactant is 1:(0.3-0.5):(2-6).

[0022] Preferably, the surfactant is polyvinylpyrrolidone; the nickel salt is nickel nitrate hexahydrate, nickel sulfate heptahydrate, or nickel chloride.

[0023] Preferably, in step (1), the solvent is a mixed solution of water / anhydrous ethanol / N,N-dimethylformamide with a volume ratio of 1:(0.8~1.2):(0.8~1.2).

[0024] Preferably, in step (1), the solvothermal conditions are: reacting at a temperature of 130–170°C for 10–16 h.

[0025] Preferably, in step (2), the copper salt is copper sulfate pentahydrate, copper nitrate trihydrate, or copper chloride.

[0026] Preferably, in step (2), the solvent is methanol, anhydrous ethanol, or N,N-dimethylformamide.

[0027] Preferably, in step (3), the solvent is ethylene glycol or N,N-dimethylformamide.

[0028] Preferably, in step (3), the solvothermal conditions are: reacting at a temperature of 130–170°C for 5–10 h.

[0029] Preferably, in step (4), the calcination conditions are: calcination at 400-600°C for 1-3 hours under a nitrogen or argon atmosphere at a heating rate of 2-5°C / min.

[0030] Preferably, in step (6), the conditions for gas-phase sulfidation are: the mass ratio of CuNi / NC / C hollow spheres to sulfur powder is 1:(3-6), the sulfidation temperature is 300-500℃, and the heating rate is 2-5℃.

[0031] This invention also provides the application of the nickel disulfide / copper sulfide / carbon composite hollow spheres obtained by the above preparation method as a negative electrode material for sodium-ion batteries.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] (1) The present invention obtains hollow spherical Ni-MOF by a simple solvothermal method. The preparation method is simple, the reaction conditions are mild, and the morphology and size are controllable.

[0034] (2) The nickel disulfide / copper sulfide / carbon composite hollow spheres prepared by the present invention retain the unique hollow spherical structure of the precursor, which can alleviate the volume change of the electrode material during charging and discharging.

[0035] (3) The present invention introduces an appropriate amount of copper ions through ion exchange to form a nickel-copper bimetallic sulfide heterostructure. A uniform heterostructure interface is formed between the two phase components, which can accelerate ion diffusion kinetics, reduce ion diffusion barrier and significantly improve electrochemical performance.

[0036] (4) The nickel disulfide / copper sulfide / carbon composite hollow spheres prepared by this invention contain a double-layer carbon material. The middle layer, nitrogen-doped carbon derived from polydopamine carbonization, can improve the conductivity of the composite material and increase sodium storage active sites, while the outermost layer, carbon derived from glucose carbonization, can further enhance the structural stability of the composite material.

[0037] (5) This invention combines multiple methods to alleviate the volume effect of metal sulfides during charging and discharging and improve their conductivity, so that the composite material has good electrochemical performance as a negative electrode material for sodium-ion batteries. Attached Figure Description

[0038] Figure 1 This is a scanning electron microscope image of the Ni-MOF in Example 1 of the present invention;

[0039] Figure 2 This is the X-ray powder diffraction pattern of Ni-MOF in Example 1 of the present invention;

[0040] Figure 3 This is the X-ray powder diffraction pattern of the nickel disulfide / copper disulfide / carbon composite hollow sphere in Example 1 of the present invention;

[0041] Figure 4 This is a scanning electron microscope image of the nickel disulfide / copper sulfide / carbon composite hollow sphere in Example 1 of the present invention;

[0042] Figure 5 This is a scanning electron microscope image of the nickel disulfide / copper sulfide / carbon composite hollow sphere in Example 2 of the present invention;

[0043] Figure 6 This is a scanning electron microscope image of the nickel disulfide / copper sulfide / carbon composite hollow sphere in Example 3 of the present invention;

[0044] Figure 7 The sample in Example 1 of this invention is in 1Ag -1 The following is a graph showing the cyclic performance. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to the embodiments, and the technical content and effects thereof are not limited thereto.

[0046] Example 1

[0047] (1) Dissolve 864 mg of nickel sulfate, 300 mg of organic ligand (trispicoic acid) and 3 g of polyvinylpyrrolidone K-30 in 60 mL of mixed solvent (deionized water: anhydrous ethanol: N,N-dimethylformamide = 1:1:1, V / V / V) and stir magnetically for 60 min. Transfer to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 16 h. Cool to room temperature, centrifuge the product, wash with N,N-dimethylformamide and anhydrous ethanol and vacuum dry to obtain hollow spherical Ni-MOF.

[0048] (2) Disperse and dissolve the hollow spherical Ni-MOF obtained in step 1 and 1 mmol of copper salt (copper chloride) in methanol, stir for 4 h, and then centrifuge and dry to obtain CuNi-MOF.

[0049] (3) Disperse the CuNi-MOF obtained in step 2 in 100ml buffer solution, then add 1g dopamine hydrochloride, stir at room temperature for 6h, and centrifuge to obtain CuNi-MOF / PDA.

[0050] (4) The CuNi-MOF / PDA obtained in step 3 and 1g of glucose were dispersed and dissolved in N,N-dimethylformamide, then transferred to a reaction vessel and kept at 160℃ for 10h to obtain CuNi-MOF / PDA / C6H 12 O6.

[0051] (5) The CuNi-MOF / PDA / C6H obtained in step 3 12 O6 was heated to 600℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and held at this temperature for 2h to obtain CuNi / NC / C hollow spheres.

[0052] (6) The CuNi / NC / C hollow spheres and sulfur powder obtained in step 4 are placed on both sides of the quartz boat at a mass ratio of 1:4 and sealed with aluminum foil. Under nitrogen atmosphere, the temperature is raised to 500℃ at a heating rate of 2℃ / min and held for 2h to finally obtain nickel disulfide / copper sulfide / carbon composite hollow spheres.

[0053] Example 2

[0054] (1) Dissolve 864 mg of nickel sulfate, 300 mg of organic ligand (trispicoic acid) and 3 g of polyvinylpyrrolidone K-30 in 60 mL of mixed solvent (deionized water: anhydrous ethanol: N,N-dimethylformamide = 1:1:1, V / V / V) and stir magnetically for 60 min. Transfer to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 16 h. Cool to room temperature, centrifuge the product, wash with N,N-dimethylformamide and anhydrous ethanol and vacuum dry to obtain hollow spherical Ni-MOF.

[0055] (2) Disperse and dissolve the hollow spherical Ni-MOF obtained in step 1 and 2 mmol of copper salt (copper nitrate trihydrate) in methanol, stir for 4 h, and obtain CuNi-MOF by centrifugation and drying.

[0056] (3) Disperse the CuNi-MOF obtained in step 2 in 100ml buffer solution, then add 1g dopamine hydrochloride, stir at room temperature for 6h, and centrifuge to obtain CuNi-MOF / PDA.

[0057] (4) The CuNi-MOF / PDA obtained in step 3 and 1g of glucose were dispersed and dissolved in N,N-dimethylformamide, then transferred to a reaction vessel and kept at 160℃ for 10h to obtain CuNi-MOF / PDA / C6H 12 O6.

[0058] (5) The CuNi-MOF / PDA / C6H obtained in step 3 12 O6 was heated to 600℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and held at this temperature for 2h to obtain CuNi / NC / C hollow spheres.

[0059] (6) The CuNi / NC / C hollow spheres and sulfur powder obtained in step 4 are placed on both sides of the quartz boat at a mass ratio of 1:4 and sealed with aluminum foil. Under nitrogen atmosphere, the temperature is raised to 500℃ at a heating rate of 2℃ / min and held for 2h to finally obtain nickel disulfide / copper sulfide / carbon composite hollow spheres.

[0060] Example 3

[0061] (1) Dissolve 864 mg of nickel sulfate, 300 mg of organic ligand (trispicoic acid) and 3 g of polyvinylpyrrolidone K-30 in 60 mL of mixed solvent (deionized water: anhydrous ethanol: N,N-dimethylformamide = 1:1:1, V / V / V) and stir magnetically for 60 min. Transfer to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 16 h. Cool to room temperature, centrifuge the product, wash with N,N-dimethylformamide and anhydrous ethanol and vacuum dry to obtain hollow spherical Ni-MOF.

[0062] (2) Disperse and dissolve the hollow spherical Ni-MOF obtained in step 1 and 1 mmol of copper salt (copper sulfate pentahydrate) in methanol, stir for 4 h, and obtain CuNi-MOF by centrifugation and drying.

[0063] (3) Disperse the CuNi-MOF obtained in step 2 in 100ml buffer solution, then add 1g dopamine hydrochloride, stir at room temperature for 6h, and centrifuge to obtain CuNi-MOF / PDA.

[0064] (4) The CuNi-MOF / PDA obtained in step 3 and 2g of glucose were dispersed and dissolved in N,N-dimethylformamide, then transferred to a reaction vessel and kept at 160℃ for 10h to obtain CuNi-MOF / PDA / C6H 12 O6.

[0065] (5) The CuNi-MOF / PDA / C6H obtained in step 3 12 O6 was heated to 600℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and held at this temperature for 2h to obtain CuNi / NC / C hollow spheres.

[0066] (6) The CuNi / NC / C hollow spheres and sulfur powder obtained in step 4 are placed on both sides of the quartz boat at a mass ratio of 1:4 and sealed with aluminum foil. Under nitrogen atmosphere, the temperature is raised to 500℃ at a heating rate of 2℃ / min and held for 2h to finally obtain nickel disulfide / copper sulfide / carbon composite hollow spheres.

[0067] Comparative Example 1

[0068] (1) Dissolve 864 mg of nickel sulfate, 300 mg of organic ligand (trispicoic acid) and 3 g of polyvinylpyrrolidone K-30 in 60 mL of mixed solvent (deionized water: anhydrous ethanol: N,N-dimethylformamide = 1:1:1, V / V / V) and stir magnetically for 60 min. Transfer to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 16 h. Cool to room temperature, centrifuge the product, wash with N,N-dimethylformamide and anhydrous ethanol and vacuum dry to obtain hollow spherical Ni-MOF.

[0069] (2) The Ni-MOF obtained in step 1 is heated to 600℃ at a heating rate of 2℃ / min under a nitrogen atmosphere and held at this temperature for 2h to obtain Ni hollow spheres.

[0070] (3) The Ni / C hollow spheres and sulfur powder obtained in step 2 are placed on both sides of the quartz boat at a mass ratio of 1:4 and sealed with aluminum foil. Under nitrogen atmosphere, the temperature is raised to 500℃ at a heating rate of 2℃ / min and held for 2h to finally obtain nickel disulfide hollow spheres.

[0071] Comparative Example 2

[0072] (1) Dissolve 864 mg of nickel sulfate, 300 mg of organic ligand (trispicoic acid) and 3 g of polyvinylpyrrolidone K-30 in 60 mL of mixed solvent (deionized water: anhydrous ethanol: N,N-dimethylformamide = 1:1:1, V / V / V) and stir magnetically for 60 min. Transfer to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 16 h. Cool to room temperature, centrifuge the product, wash with N,N-dimethylformamide and anhydrous ethanol and vacuum dry to obtain hollow spherical Ni-MOF.

[0073] (2) Disperse the Ni-MOF obtained in step 1 in 100ml buffer solution, then add 1g dopamine hydrochloride, stir at room temperature for 6h, and centrifuge to obtain Ni-MOF / PDA.

[0074] (3) The Ni-MOF / PDA obtained in step 2 and 1g of glucose were dispersed and dissolved in N,N-dimethylformamide, then transferred to a reaction vessel and kept at 160℃ for 10h to obtain Ni-MOF / PDA / C6H 12 O6.

[0075] (4) The Ni-MOF / PDA / C6H obtained in step 3 12 O6 was heated to 600℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and held at this temperature for 2h to obtain Ni / NC / C hollow spheres.

[0076] (5) The Ni / NC / C hollow spheres and sulfur powder obtained in step 4 are placed on both sides of the quartz boat at a mass ratio of 1:4 and sealed with aluminum foil. Under nitrogen atmosphere, the temperature is raised to 500℃ at a heating rate of 2℃ / min and held for 2h to finally obtain nickel disulfide / carbon composite hollow spheres.

[0077] Comparative Example 3

[0078] (1) Disperse 1 mmol of copper salt (copper chloride) in 100 ml of buffer solution, then add 1 g of dopamine hydrochloride, stir at room temperature for 6 h, finally add 1 g of glucose, transfer to a reaction vessel, and keep warm at 160 °C for 10 h to obtain the precursor.

[0079] (2) The precursor obtained in step 1 is heated to 600°C at a heating rate of 2°C / min under a nitrogen atmosphere and held at this temperature for 2h to obtain Cu / NC / .

[0080] (3) The Cu / NC / C and sulfur powder obtained in step 2 are placed on both sides of the quartz boat at a mass ratio of 1:4 and sealed with aluminum foil. Under nitrogen atmosphere, the temperature is raised to 500℃ at a heating rate of 2℃ / min and held for 2h to finally obtain copper sulfide / carbon composite material.

[0081] Comparative Example 4

[0082] (1) Dissolve 864 mg of nickel sulfate, 300 mg of organic ligand (trispicoic acid) and 3 g of polyvinylpyrrolidone K-30 in 60 mL of mixed solvent (deionized water: anhydrous ethanol: N,N-dimethylformamide = 1:1:1, V / V / V) and stir magnetically for 60 min. Transfer to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 16 h. Cool to room temperature, centrifuge the product, wash with N,N-dimethylformamide and anhydrous ethanol and vacuum dry to obtain hollow spherical Ni-MOF.

[0083] (2) Disperse and dissolve the hollow spherical Ni-MOF obtained in step 1 and 1 mmol of copper salt (copper chloride) in methanol, stir for 4 h, and then centrifuge and dry to obtain CuNi-MOF.

[0084] (3) The CuNi-MOF obtained in step 2 and 1g of glucose were dispersed and dissolved in N,N-dimethylformamide, then transferred to a reaction vessel and kept at 160℃ for 10h to obtain CuNi-MOF / C6H 12 O6.

[0085] (4) The CuNi-MOF / C6H obtained in step 3 12 O6 was heated to 600℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and held at this temperature for 2h to obtain CuNi / C hollow spheres.

[0086] (5) The CuNi / C hollow spheres and sulfur powder obtained in step 4 are placed on both sides of the quartz boat at a mass ratio of 1:4 and sealed with aluminum foil. Under nitrogen atmosphere, the temperature is raised to 500℃ at a heating rate of 2℃ / min and held for 2h to finally obtain nickel disulfide / copper sulfide / carbon composite hollow spheres.

[0087] Comparative Example 5

[0088] (1) Dissolve 864 mg of nickel sulfate, 300 mg of organic ligand (trispicoic acid) and 3 g of polyvinylpyrrolidone K-30 in 60 mL of mixed solvent (deionized water: anhydrous ethanol: N,N-dimethylformamide = 1:1:1, V / V / V) and stir magnetically for 60 min. Transfer to a high-pressure reactor with a polytetrafluoroethylene liner and react at 160 °C for 16 h. Cool to room temperature, centrifuge the product, wash with N,N-dimethylformamide and anhydrous ethanol and vacuum dry to obtain hollow spherical Ni-MOF.

[0089] (2) Disperse and dissolve the hollow spherical Ni-MOF obtained in step 1 and 1 mmol of copper salt (copper nitrate trihydrate) in methanol, stir for 4 h, and obtain CuNi-MOF by centrifugation and drying.

[0090] (3) Disperse the CuNi-MOF obtained in step 2 in 100ml buffer solution, then add 1g dopamine hydrochloride, stir at room temperature for 6h, and centrifuge to obtain CuNi-MOF / PDA.

[0091] (4) The CuNi-MOF / PDA obtained in step 3 is heated to 600℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and held at this temperature for 2h to obtain CuNi / NC hollow spheres.

[0092] (5) The CuNi / NC hollow spheres and sulfur powder obtained in step 4 were placed on both sides of a quartz boat at a mass ratio of 1:4, and sealed with aluminum foil. Under a nitrogen atmosphere, the temperature was raised to 500℃ at a heating rate of 2℃ / min and held for 2h to obtain nickel disulfide / copper sulfide / carbon composite hollow spheres.

[0093] Performance testing

[0094] The final products obtained in Examples 1-3 and Comparative Examples 1-5 were mixed with conductive agent Super P and binder polyvinylidene fluoride in a mass ratio of 7:2:1 and solvent N-methylpyrrolidone to form a homogeneous slurry. This slurry was coated onto a copper current collector and dried. After drying, it was cut into discs with a diameter of 12 mm to serve as the negative electrode, with metallic sodium as the counter electrode. 1M sodium hexafluorophosphate (NaPF6) dissolved in diethylene glycol dimethyl ether was used as the electrolyte, and glass fiber was used as the separator. The CR2025 button cell was assembled in a glove box filled with argon atmosphere and with water and oxygen values ​​of less than 0.01 ppm. After being left to stand for 24 hours, a constant current charge-discharge test was performed in the range of 0.01-3V using a Newway tester.

[0095] Figure 1 The images show SEM images of the Ni-MOFs prepared in Examples 1-3. It can be seen that the prepared Ni-MOFs are regular hollow sphere structures with a size of about 3 μm.

[0096] Figure 2 The XRD patterns are those of the Ni-MOFs prepared in Examples 1-3.

[0097] Figure 3 The image shows the X-ray powder diffraction pattern of the nickel disulfide / copper disulfide / carbon composite hollow sphere in Example 1. Figure 3 It can be seen that the nickel disulfide / copper disulfide / carbon composite hollow spheres prepared in Example 1 exhibit characteristic peaks of NiS2 and CuS.

[0098] Figure 4 The image shows the SEM image of the nickel disulfide / copper sulfide / carbon composite hollow sphere in Example 1. It can be seen that the composite material has a regular hollow sphere structure with a size of about 3 μm.

[0099] Figure 5 The image shows the SEM image of the nickel disulfide / copper disulfide / carbon composite hollow spheres in Example 2. It can be seen that the hollow sphere structure is mostly destroyed, which may be due to the excessively high concentration of copper ions during the ion exchange process and the overly intense ion exchange leading to the destruction of the Ni-MOF structure.

[0100] Figure 6 The image shows the SEM image of the nickel disulfide / copper sulfide / carbon composite hollow sphere in Example 3. It can be seen that many irregular blocky substances are agglomerated together. This may be because there is too much glucose, and some of the glucose agglomerated together. After carbonization, many irregularly shaped carbon blocks are generated.

[0101] Figure 7 The circuit performance graph for Example 1 shows that the sodium-ion battery operates at 1Ag... -1 After cycling 100 times at a current density, the capacity remained at 810 mAh g. -1 The capacity retention rate was 100.1%, indicating that the composite material has excellent cycle stability.

[0102] The products obtained in Examples 1-3 and Comparative Examples 1-5 were used as anode materials for sodium-ion batteries and assembled into sodium ion cells. After assembly, the sodium ion cell temperature was 1 A·g -1 The specific capacity and retention rate after 100 cycles at the specified current density are shown in Table 1.

[0103] Table 1

[0104]

[0105] As shown in Table 1, and combining the data from Examples 1-3 and Comparative Examples 1-5, it can be seen that the controllable introduction of an appropriate amount of copper ions through ion exchange to construct a nickel-copper bimetallic sulfide heterostructure and additional double-layer carbon coating can effectively improve the reversible capacity and cycle stability of the material. Combining Examples 1 and 2, it can be seen that excessive ion exchange will destroy the original hollow spherical morphology, thus affecting its sodium storage performance. Combining Examples 1 and 3, it can be seen that excessive glucose will lead to an excessively high carbon content in the composite material, thus affecting its sodium storage performance. Combining Examples 1 and Comparative Examples 4-5, it can be seen that compared to single-layer carbon coating, double-layer carbon coating can better improve the conductivity and structural stability of the material, thereby improving its cycle performance.

[0106] The above embodiments of the present invention are merely illustrative examples and are not intended to limit the implementation of the invention. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a nickel disulfide / copper sulfide / carbon composite hollow sphere, characterized in that... Includes the following steps: (1) Nickel salt, organic ligand pyromellitic acid, and surfactant are mixed and dissolved in a solvent and subjected to a solvothermal reaction to obtain Ni-MOF hollow spheres; (2) Ni-MOF hollow spheres and copper salt are mixed and dispersed in a solvent, stirred and reacted, and centrifuged to obtain CuNi-MOF; the mass ratio of Ni-MOF hollow spheres to copper salt is 1:(2~7). (3) Disperse CuNi-MOF in buffer solution, add dopamine hydrochloride (PDA), stir to react, centrifuge to obtain CuNi-MOF / PDA; the mass ratio of CuNi-MOF to dopamine hydrochloride is 1: (5~10). (4) Disperse CuNi-MOF / PDA in a solvent, add glucose, stir, and then carry out a solvothermal reaction to obtain CuNi-MOF / PDA / C6H 12 O6; The mass ratio of CuNi-MOF / PDA to glucose is 1:(10~30); (5) Combine CuNi-MOF / PDA / C6H 12 O6 is calcined in a nitrogen or argon atmosphere, and heated to 400-600 ℃ for 1-3 h at a heating rate of 2-5 ℃ / min to obtain CuNi / NC / C hollow spheres; (6) Gas-phase sulfidation of CuNi / NC / C hollow spheres to obtain nickel disulfide / copper sulfide / carbon composite hollow spheres; the gas-phase sulfidation conditions are: the mass ratio of CuNi / NC / C hollow spheres to sulfur powder is 1:(3~6), the sulfidation temperature is 300~500 ℃, and the heating rate is 2~5 ℃.

2. The preparation method according to claim 1, characterized in that, In step (1), The mass ratio of the nickel salt, organic ligand, and surfactant is 1:(0.3~0.5):(2~6); The surfactant is polyvinylpyrrolidone; The nickel salt is nickel nitrate hexahydrate, nickel chloride, or nickel sulfate heptahydrate.

3. The preparation method according to claim 1, characterized in that, In step (1), the solvent is water, anhydrous ethanol, and [other solvents] in a volume ratio of 1:(0.8~1.2):(0.8~1.2). N,N A mixed solution of dimethylformamide.

4. The preparation method according to claim 1, characterized in that, In step (1), the conditions for the solvothermal reaction are: reacting at 130~170 °C for 10~16 h.

5. The preparation method according to claim 1, characterized in that, In step (2), The copper salt is copper sulfate pentahydrate, copper nitrate trihydrate, or copper chloride; The solvent is methanol, anhydrous ethanol, or... N,N -Dimethylformamide.

6. The preparation method according to claim 1, characterized in that, In step (4), the solvent is ethylene glycol or... N,N -Dimethylformamide.

7. The preparation method according to claim 1, characterized in that, In step (4), the conditions for the solvothermal reaction are: reacting at 130~170 °C for 5~10 h.

8. The application of a nickel disulfide / copper sulfide / carbon composite hollow sphere prepared by any one of claims 1 to 7 as a negative electrode material for sodium-ion batteries.

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