Preparation Of M_xS_y(M=Mo,Fe,V)/C Composites And Its Application In Lithium/Sodium Ion Batteries

Transition metal sulfide(TMS)was considered to be a potential next-generation lithium-ion battery(LIBs)and sodium-ion battery(SIBs)commercial anode material due to its resource,price advantage and theoretical capacity much higher than that of traditional anode materials.However,the shortcomings of TMS limits its actual market application.First,the poor conductivity of TMS leads to slow electrochemical reaction kinetics.Secondly,the volume expansion effect will destroy the original structure of the material,resulting in cycle capacity loss and poor cycle stability,which will greatly limit the application of TMS in LIBs and SIBs anode materials.In view of these shortcomings,the current main solution was to prepare special morphology and composite high-conductivity materials.Therefore,this article combines TMS with carbon materials and prepares composite materials with special morphologies,so that the structure has strong impact resistance,it can effectively alleviate the volume expansion effect,shorten the charge/ion diffusion path,improving the rate parameters and kinetics of the electrode in the reaction process,and the electrochemical performance of the material will be improved.The main research contents and results are as follows:(1)A high-temperature sintering method was used to synthesize a special mosaic structure composite material with Mo S₂ embedded in the wrinkled carbon layer in one step.When the Mo S₂/C composite material was used as the negative electrode material of LIBs/SIBs,the composite material shows an excellent cycle stability,high specific capacity and long cycle life.In LIBs,after 50 cycles at 0.1 A g^-1,the specific capacity of Mo S₂/C composite material can show 760 mAh g^-1,even after 1000 cycles at a current density of 4 A g^-1,the material can also show a high stable specific capacity of350 mAh g^-1;In SIBs,after 50 charge-discharge cycles at 0.1 A g^-1,the remaining specific capacity shows 480 mAh g^-1,when the current was increased to 2 A g^-1,the specific capacity of Mo S₂/C after 500 charge-discharge cycles still shows 355 mAh g^-1.The improvement of the electrochemical performance of Mo S₂/C composite can be attributed to the combination of Mo S₂ and carbon material.The carbon coating in the composite material can stabilize the structure,buffer the volume expansion and improve the charge mobility.(2)Using in situ solid-phase method to prepare ionic liquid-derived thin-layer carbon-covered nano-sized Fe S composite material.When Fe S/C composite material was used as a negative electrode material for LIBs/SIBs,it exhibits high specific capacity,stable cycle capacity and long cycle life.In LIBs,at a current of 0.1 A g^-1,the specific capacity of Fe S/C can show 788 mAh g^-1 after 100 cycles.When the current increases to 0.5 A g^-1,the reversible lithium storage capacity of Fe S/C can retain 453mAh g^-1 after 70 cycles.In the high-rate current test,the material was charged and discharged 500 times at 4 A g^-1,and the specific capacity was as high as 305 mAh g^-1;In SIBs,the reversible capacity after 100 cycles at 0.1 A g^-1 was 404.7 mAh g^-1,and the capacity after 100 cycles at 0.5 A g^-1 reaches 304.8 mAh g^-1,and the current increases to 4 A g^-1,the composite material can retain a capacity of 178.8 mAh g^-1 after1000 cycles.The excellent electrochemical performance can be attributed to the corrugated thin carbon layer on the surface of Fe S,which enhances the impact resistance of the structure,it can alleviate the volume expansion of Fe S during the cycle,increase the conductivity,and improve the charge mobility.(3)The vanadium-containing group was compounded with reduced graphene oxide by a hydrothermal method,and then thiourea was used as a sulfur source,and a solid-phase heat treatment method was used for the vulcanization process,and finally a composite structure of rGO uniformly encapsulating V₃S₄ nanorods was obtained.When the composite material was used as LIBs/SIBs anode material,the unique structure ensures its high-strength impact resistance,it effectively improves the stability of cycle and rate performance,and obtains excellent electrochemical performance.In LIBs,when the current was 0.1 A g^-1,the specific capacity of V₃S₄/rGO was 733.1 mAh g^-1 after 200 cycles.When the current was increased to 2 A g^-1,the V₃S₄/rGO can still show a specific capacity of 312.5 mAh g^-1 after 1000 cycles;In SIBs,when the current was 0.1 A g^-1,the specific capacity of V₃S₄/rGO nanorods can reach to 537.3 mAh g^-1 after 200 cycles,when the long-cycle performance was test at2 A g^-1,the high specific capacity of the composite was shown to be 232.8 mAh g^-1after 2000 cycles.The unique composite structure of V₃S₄/rGO and the special morphology can effectively alleviate the volume expansion of V₃S₄ during charge and discharge,it can avoid structural collapse,and the presence of carbon can also increase the charge transfer rate and accelerate the electrochemical reaction kinetics.