Synthesis And Properties Of Carbon/FeS Lithium-Ion Battery Anode Materials

Transition metal sulfides with electrochemical activity have been considered as promising anode materials.FeS has attracted extensive attention because of its high theoretical specific capacity(609 mAh/g),good electrochemical properties,abundant natural storage and low cost.However,the volume expansion,low conductivity and cycling stability of FeS during lithiation still limits its charge/discharge performance.Many efforts have been devoted to overcome above-mentioned problems by forming FeS composite materials with carbon-based materials.In this thesis,we use modified carbon-based materials to form composite materials with FeS to enhance the electrochemical properties of FeS material.The research methods are as follows:(1)In the first part of the work,we adopted two-step in-situ immersion/calcination method synthesis of FeS/PC composite materials by the reaction of iron salt in porous carbon and sulfur powder.The specific synthesis steps are as follows:The first,porous carbon materials with different specific surface areas were prepared by controlling the concentration of ZnCl2 solution.Then,the obtained porous carbon material was soaked with ferric nitrate solution,and then the PC/FeS composite materials were obtained by vacuum vulcanization.The optimized LIBs with the FeS@PC anode demonstrate an initial charge/discharge capacity as high as 854.8 and 1397.3 mAh/g,and 591.9 mAh/g after 65 cycles at a current density of 0.1 C.The porous carbon structure will provide more active sites for FeS loading and can solve the issues of volume expansion during charge and discharge of the FeS@PC composites.(2)FeS nanosheets encapsulated into hollow B/N-co doped carbon were synthesized by a one-step pyrolysis following with vulcanization using ferrocene,thiourea,boric acid and PEG-4000 as reactants.The different B/N doping ratio will lead to the change of its doping position in the carbon material,which can affect the structure and electrical conductivity of the composite materials.The LIBs with the 1-4-NBC/FeS anode demonstrate 500 mAh/g after 100 cycles at a current density of 1C.Appropriate B/N doping ratio can optimize the structure of the composite materials and improve the lithium storage performance of the composite material.The high electrochemical properties mainly resulted from the special microstructures and B/N-codoped carbon,which could alleviate the volume expansion and enhance the conductivity.