Study On Transition Metal Sulfide As Anode Materials For Lithium Ion Batteries

As a major contributor to the capacity,the quality of the anode materials directly affects the electrochemical performance of the entire battery.Due to higher theoretical specific capacities and rich redox reactions,transition metal sulfides(TMSs)used as anode materials of LIBs has attracted more and more attention.However,TMSs will undergo large volume expansion during the lithiation process,which results in poor cycling stability of the corresponding LIBs.A properly design of composite nanostructure of TMSs and conductive carbon support/matrix can effectively enhance its lithium storage performance.Based on the strategy that designing different structures and introducing a carbon matrix,Fe1-xS nanoparticles wrapped by reduced graphene oxide(Fe1-xS@rGO),hollow CuCo2S4@C with zeolite imidazole skeleton structure derived from ZIF-67,and core-shell CoIn2S4 microsphercs and polyacrylonitrile(Coln2S4@CPAN)composites were prepared,which all show better performance than the corresponding pure phase materials.The introduced carbon matrix can not only act as a structural buffer,effectively alleviating the volume changes during cycling,but also act as a conductive agent,which can significantly improve the conductivity of the resulting nanocomposites.The designed layered nanostructures also help promote rapid ion/electron transfer,reduce charge transfer resistance,and improve electrochemical performance.The main research contents of this the thesis are as follows:(1)A simple in-situ hydrothermal method was used to synthesize a composite material of iron sulfide nanoparticles and reduced graphene oxide(Fe1-xS@rGO).After wrapped by rGO,the morphology of Fe1-xS particles changes from hexagonal flakes to irregular particles with much smaller sizes.Fe1-xS@rGO exhibits excellent reversible performance when used as an anode electrode material,it can deliver an initial discharge capacity of 1575.5 mA h/g at a current density of 0.1 A/g.After 200 cycles,it can maintain a reversible capacity of 907.8 mAh/g,and the Coulomb efficiency is close to 100%.The improved electrochemical performance can be attributed to the addition of the rGO matrix,which effectively relieves the volume change of Fe1-xS,improves the electrical conductivity of the composite material,and increases the Li+transmission channel.(2)The zeolite imidazole ester structure of CuCo2S4@C materials were synthesized by futher sulfiding the ZIF-67/Cu-Co double hydroxide derived from ZIF-67 via solvothermal-annealing method.At a constant current density of 0.1 A/g,CuCo2S4@C delivers an initial discharge capacity of 1715.0 mAh/g,and after 200 cycles,the reversible capacity of 1100.8 mAh/g,which is much better than the pure phase CuCo2S4 nanoparticles(646.9 mAh/g)Due to its material structure,CuCo2S4@C show good electrochemical performance.The high electrochemical activity and fast electrochemical reaction kinetics of the materials are caused by the hollow structure and thin shell(3)The CoIn2S4 microspheres with core-shell structure were prepared by a simple self-template hydrothermal.Then the mixture of obtained core-shell CoIn2S4 microspheres and PAN were calcined at high temperature under the protection of N2 to obtain CoIn2S4@CAPN composite.Limited by the unique core-shell structure of CoIn2S4 microspheres and the N-containing carbon ring structure in the carbonized PAN,the prepared composites exhibit excellent cycling performance and rate performance when used as an anode material for LIBs.At a constant current density of 0.1 A/g,it delivers an initial discharge capacity of 1214.2 mAh/g,and the Coulomb efficiency after the first circle remains at about 98.5%.After 250 cycles,the reversible specific capacity is 779.8 mAh/g.In addition,even if the current density increases to 5 A/g,it still retains 50%of the capacity at 0.1 A/g.The structure-performance relationship of CoIn2S4@CAPN electrode is also discussed.