Synthesis And Electrochemical Properties Of Molybdenum (Iron) Sulfide/Carbon Composites

Lithium ion batteries (LIBs) are widely used in portable electronic devicesbecause of their high energy density, long service life, and friendly-environment.Graphite has been commercially used as LIBs anode material due to its excellentperformance such as good electrical conductivity, high cycle efficiency and safety.However, it can’t meet the requirement of high performance of lithium ion batterywith only372mAh g-1theoretical specific capacity. It is therefore desirable todevelop anode materials with high lithium storage capacity.Molybdenum sulfide and iron sulfide with layered structure have hightheoretical specific capacity (lithium storage capacity of MoS2is800mAh g-1, FeSand FeS2are609mAh g-1,894mAh g-1respectively). Therefore they are reversibleintercalation/delithiation lithium material. In recent years, the study of compositesconsisting of molybdenum sulfide or iron sulfide as electrode materials has attractedmore and more attention. In this dissertation, MoS2/C and FeS/C composite weresuccessfully synthesized by solvothermal method. The composition and structure ofproducts were characterized by XRD, FT-IR, TG-DTA, SEM, TEM, and theinfluence of the synthesis conditions on products were investigated. Constant currentcharge/discharge tests were performed to evaluate the electrochemical lithiumstorage performance.MoS2/C composite were synthesized by solvothermal method usingmolybdenum carbonyl as molybdenum source, sulfur powder as sulfur source anddifferent carbon source in organic solvent. It was found that the products synthesizedin benzene and acetone are irregular nanoparticles and homogeneously dispersednanospheres respectively. The nanospheres are of core-shell structure withamorphous carbon spheres coated by molybdenum sulfide layer. The size of thenanospheres can be adjusted in the range of70~150nm by changing solvent or theamount of added glucose. The prepared MoS2/C nanospheres were used as anode materials for LIBs. The constant current charge/discharge tests carried out tocharacterize its lithium storage performance indicated that MoS2/C anode materialexhibited reversible discharge capacity up to819.5mAh g-1, and the capacity canstill reach601.7mAh g-1after50cycles, much higher than the capacity of bulkmolybdenum sulfide.FeS/C composite were synthesized by solvothermal method using ferrocene asiron source and sulfur powder as sulfur source in benzene solvent. The products withflower-sheet microspheres consist of various iron and sulfur atom ratio. Thesynthesis conditions (such as raw material proportion, reaction time, reactionpressure) have significant effect on the morphology and phase of product. FeS/Ccomposite were used as anode materials for LIBs. The constant currentcharge/discharge tests carried out to characterize its lithium storage performanceshowed that the first discharge capacity of material is920.5mAh g-1and the initialirreversible capacity of material is up to373.1mAh g-1, However, after100cycles,the capacity reduced to394.8mAh g-1.