Preparation Of Metal Sulfides Composites As Anode Materials For High Performance Lithium/Sodium Ion Batteries

With the increasing consumption of fossil energy and the environmental pollution caused by it,the development of clean energy has received more and more attention.However,new energy sources such as wind and solar energy cannot be continuously and stably powered by time and geographical restrictions.Therefore,the development of high-performance energy storage technology has become one of the future research directions.Limited by anode materials,lithium/sodium ion battery can not meet the high demand for energy density in the future.As anode material for redox mechanism,metal sulfides are ideal anode materials for new generation of lithium/sodium ion battery due to its higher theoretical specific capacity and initial-coulomb efficiency.However,large volume fluctuations and poor conductivity during cycling limit the development of metal sulfide anode materials.In this paper,the lithium/sodium storage properties of metal sulfides are improved by preparing specific micro-nano structures and compounding with carbon materials.The details are as follows:?1?The fractional flower-like MoS₂/C composites were successfully prepared by one-step hydrothermal method.The ultra-thin MoS₂ is uniformly and vertically distributed on the surface of the carbon nanospheres.In this structure,the MoS₂ nanosheet has a large specific surface area,which can ensure enough contact between the electrode material and the electrolyte,provide more active sites,and reduce the diffusion path of lithium ions.In addition,the gap between the sheets can accommodate the volume deformation of the MoS₂ during cycles,maintaining a good cycle stability.As a growth substrate for MoS₂nanosheets in the synthesis of materials,carbon nanospheres can not only improve the conductivity of materials,but also prevent aggregation during the synthesis of layered MoS₂.Based on the above advantages,the reversible capacity of MoS₂/C composties,as anode material for lithium ion battery,was maintained at 650 mAh g^-1 after 300 cycles at a current density of 1 A g^-1.In addition,the capacity can reach 477 mAh g^-1 even at a high current density of 4 A g^-1.Compared with bare MoS₂,the electrochemical performance has been significantly improved.?2?The precursor SnS₂ nanosheets were firstly distributed on the surface of the carbon microspheres by hydrothermal method,and then flower-like C/SnS@C nanocomposites were obtained after carbon annealing.The SnS@C nanosheets were vertically anchored on the carbon microspheres.The addition of carbon material improves the conductivity of the material.The carbon microspheres as a matrix can also avoid the aggregation of the SnS₂ nanosheet during the synthesis process.The presence of the carbon layer can prevent the polymerization of the SnS nanosheet during the cycles.The void space between the SnS@C nanosheets reduces the volume fluctuation of the material during cycles.In addition,the S,N co-doped carbon shell can provide more active sites and increase the adsorption capacity of Li⁺/Na⁺.As anode material for lithium ion battery,the sample obtained a reversible specific capacity of 740 mAh g^-1 after 1000 cycles at 1 A g^-1.The C/SnS@C nanocomposite also showed good sodium storage performance,and the reversible specific capacity of485 mAh g^-1 was obtained after 400 cycles at 500 mA g^-1.After diffusion kinetic analysis,it is found that there are pseudocapacitance behaviors of the flower-like C/SnS@C nanocomposite as the anode material of lithium/sodium ion battery,which is beneficial for the cycle life of the material.?3?In this chapter,CoS₂ nanoparticles?²0 nm?were uniformly dispersed on a sponge-like carbon substrate by freeze-drying and hydrothermal sulfuration to obtain a sponge-like CoS₂/C.The presence of the carbon layer in the composite material can improve the conductivity of the material,and the porous structure not only provides a feasible transmission route for ions,but also provides space for the volume deformation of CoS₂ during the cycle.As anode material of lithium ion battery,the sample was circulated for 120 cycles at a current density of 500mA g^-1 to obtain a high specific capacity of 610 mAh g^-1.For sodium ion batteries,the sample provided a reversible specific capacity of 330 mAh g^-1 at 500 mA g^-1.In addition,the freeze-drying/hydrothermal process developed in this work can be used to construct other high-capacity metal sulfide composites as anode materials for lithium/sodium ion batteries.?4?Based on the hydrolysis reaction of thioacetamide in alkaline environment,Co₉S₈@C nanospheres with 5 nm thick carbon shell and a 50nm diameter Co₉S₈ core were synthesized by one-step hydrothermal method combined with annealing process.The extremely small size of the nanosphere not only shortens the diffusion free path of sodium ions,but also resists the strain of the material during the cycle.In addition,the presence of the carbon layer can improve the conductivity of Co₉S₈ and the rate performance of the material.The results show that the Co₉S₈@C nanospheres have excellent cycle performance and rate performance.A high specific capacity of 305 mAh g^-1 was obtained after 1000 cycles at a current density of 5 A g^-1,and a reversible specific capacity of 405 mAh g^-1 was obtained at a current density of 500 mA g^-1.After diffusion kinetic analysis,the extremely long cycle life benefits from the pseudocapacitance behavior at the end of the cycle.?5?Based on the complexation of nitrilotriacetic acid,Fe³⁺was used as an electron acceptor in the solution to obtain one-dimensional nanowire composed of metal organic structure.In order to maintain the structure of presuror during the sulfuration process,glucose was used as carbon source to wrap the precursor by hydrothermal method.Finally,the Fe₇S₈nanoparticles were uniformly dispersed in the carbon material by sulfuration process,and the overall nanowire structure was also maintained.Such a structure can provide the necessary void space for the active material to alleviate the volume expansion of cycles.In addition,the coating of carbon materials provides a convenient transport path for electron/ion transfer.In a lithium ion battery,the sample obtained a high specific capacity of 730.9 mAh g^-1 after 350 cycles at a current density of2 A g^-1.As a negative electrode material for sodium ion batteries,the sample provided a reversible specific capacity of 546.8 mAh g^-1 under 200mA g^-1.In addition,the complexation reaction in this work can be used to construct other high capacity metal sulfide composites as anode materials for lithium/sodium ion batteries.