Synthesis And Electrochemical Energy Storage Of Transition Metal Sulfides

With the further development of science and society,people put forward higher requirements for portable electronic products,new energy vehicles and energy storage equipment.However,the anode of commercial lithium-ion batteries is graphite.Its low theoretical capacity(372 mAh g^-1),poor rate performance and short cycle life seriously restrict the further development of lithium-ion batteries.Therefore,it is urgent to develop a new generation of anode materials.In recent years,transition metal sulfides?TMS?,such as Co₉S₈,FeS,NiS,have attracted much attention because they have the advantages of high capacity,good conductivity,thermal stability,low price and a wide range of sources compared with corresponding oxides as anode materials for lithium-ion batteries.They have become one of the new anode materials which are most likely to replace graphite materials.However,the transition metal sulfides have low first Coulomb efficiency,low lithium ion diffusion kinetics and large volume effect of lithium intercalation/deintercalation in the process of charge and discharge,which lead to the material being easily comminuted and destroyed so that the cycle stability is poor.It is found that the electrochemical stability can be effectively improved by carbon recombination,doping and morphology control.In this paper,double-layer N,S-codoped porous carbon nanotubes protected MnS nanoparticles composites and phosphorus-doped cobalt sulfide yolk–shell structure nanospheres were prepared by hydrothermal reaction.The composites were characterized by XRD?SEM?TEM etc.And as a anode for energy storage research,The main contents are as follows:1.A MnS nanoparticles/N,S-codoping carbon nanotubes?MnS@N,S-C NTs?with double-layer carbon have been synthesized,and its demonstrated excellent electrochemical performance as anode material for lithium ion battery.The MnS@N,S-C-NTs electrode has a high reversible specific capacity(796 mAh g^-11 after 200 cycles at 1 A g^-1).Excellent high-rate performance and cycle stability?with a specific capacity of 400 mAh g^-11 at a high current density of 10 A g^-11 after 3500 cycles?.This excellent electrochemical performance can be attributed to the high conductivity and protection of the double-layer N,S-codoped porous carbon and its unique one-dimensional porous structure which can effectively accommodate the volume change of MnS during the cycling process.2.A phosphorus-doped cobalt sulfide yolk–shell structure sphere composite was synthesized and used as anode material to investigate its lithium storage performance.Due to its unique yolk–shell structure,the specific capacity of phosphorus-doped cobalt sulfide remained at 838 mAh g^-11 after 100 cycles.The capacity of phosphorus-doped cobalt sulfide electrode kept at 543 mAh g^-11 after 4000 cycles at high current density of 5 A g^-1,indicating that the phosphorus-doped cobalt sulfide electrode has good electrochemical performance.