Synthesis And Application Of Metal Sulfides Lithium/Sodium Battery Anodes

Graphite is difficult to meet the requirement of next generation lithium ion batteries due to its low charge-discharge potential and low theoretical capacity?372 mAh/g?.On the other hand,due to the larger ionic radius of Na⁺?1.02 A?than Li⁺?0.76 A?,commercialized graphite anode of LIBs can not be applied in Na-battery system because of its limited interlayer distance.Development of high-performance anode materials is the key point of LIBs/SIBs.Transition metal sulfides are considered as potential anode materials owing to its abundant natural reserves and high theoretical capacity.However,it suffers from poor cycling stability due to its volume expansion during charge-discharge processes.This thesis aims to retain high performance metal sulphides for LIBs/SIBs anode materials by a facile and controllable synthesis method and provide ideas for its practical applications.Severe lattice distorted MoS₂ nanosheets with a flower-like morphology were prepared with PEG400 as additive,which acts not only as surfactant but importantly,also as reactant.Notably,in the existence of a carbon-related incorporation/decoration,it demonstrates superior electrochemical performance with a high reversible capacity,a good cycling stability,and an excellent rate capability,originated from the advantages of synthesized MoS₂ including enlarged interlayer spacing,1T-like metallic behavior,and coupling of Mo-O-C?and Mo-O?hetero-bonds.A facile oxygen plasma engineering approach was used to modify MoS₂ nanosheets,fabricated via a PEG-assisted hydrothermal method.An oxygen plasma treatment not only generates vacancies/defects but also incorporates heteroatom doping to form Mo-O-C bonds.The presence of defects and Mo–O–C bonds after plasma treatment facilitates additional active sites for Li⁺intercalation and stabilizes the structural change during cycling and thus result in superior electrochemical properties.The electrode maintains a reversible capacity over 900 mAh/g for 1000 cycles at a current density of 1 A/g and delivers a value of 473 mAh/g under a current density of 10 A/g during the rate tests.FeS₂/C composites were prepared by high-energy ball grinding,forming a mulbery-like structure with strong chemical binding force between the free?electrons of CNTs and metal Fe.There exists sufficient void space between adjacent FeS₂ nanoparticles for accommodate the large volume changes in this structure.Besides,the conductivity of the whole material could be improved owing to the existence of CNTs.Therefore,the prepared FeS₂@CNTs composite exhibites excellent sodium storage performance.The electrode maintains a reversible capacity over 403 mAh/g for 250 cycles at a current density of 1 A/g with a coulombic efficiency of 99%.In addition,the electrode demenstrates good capacity retention with increasing current densities.