Preparation And Lithium-ion Storage Performances Of Composite Materials Based On Molybdenum And Cobalt Sulfides

The innovation of electrode materials plays an important role in the development and promotion of lithium-ion batteries.However,they still suffer from the sluggish charge/discharge rate and insufficient specific capacity.Therefore,it has become the priority to improve the rate performance and specific capacity of electrode materials in the research of lithium-ion batteries.Transition metal sulfides are a kind of compounds with high theoretical specific capacity,low lithium intercalation potential and good safety performance.However,they also face the drawbacks of serious volume change and poor electrical conductivity during the charging and discharging processes.In this thesis,the cobalt and molybdenum sulfide based composites were synthesized in different ways,and the lithium-ion storage performances of the products were investigated.The main contents of this thesis are as follows:A layer of Mo S₂ nanosheets was grown on the carbon coated MXene nanosheets by hydrothermal method.The best electrochemical performances were obtained for the composite with 10%content of MXene.The resultant composite achieves high specific capacity(1097m Ah g^-1 at 0.1 A g^-1)and great rate capability(710 m Ah g^-1 at 10 A g^-1)as well as remarkable long-term cycling stability(1260 m Ah g^-1 after 160 cycles at 0.5 A g^-1).The coin-type full battery fabricated with Li Fe PO₄ cathode shows specific capacity of 95.6 and 56.8 m Ah g^-1under the current densities of 0.1 and 10.0 A g^-1,respectively.Based on the synthetic process of ZIF-67,ZIFs with different zinc ratios were synthesized by replacing partial cobalt with zinc.After combining with MXene nanosheets,the composite was prepared by solvothermal sulfidation.The composite exhibits reversible specific capacity of 528 m Ah g^-1 at 0.1 A g^-1 and maintain 243 m Ah g^-1 even at 10.0 A g^-1.Moreover,it shows high reversible capacity of 633 m Ah g^-1 after 200 cycles at 0.5 A g^-1 with capacity retention ratio of 127.1%.The Co-MOF nanoflakes were delaminated in Li Cl/KCl molten salts under nitrogen atmosphere.Cobalt sulfide nanoparticles supported on ultrathin carbon nanosheets were prepared by vulcanization.The composites show high specific capacity of 983 m Ah g^-1 at a current density of 0.1 A g^-1 and 483 m Ah g^-1 at 10 A g^-1 with capacity retention ratio of 142.5%after 200 cycles at 0.5 A g^-1.