Synthesis And Electrochemical Energy Storage Properties Of Molybdenum Disulfide/carbon Nanocomposites

Rechargeable lithium-ion batteries?LIBs?have been regarded as one of the most promising power technologies in the applications of energy storage stations,electric vehicles,and so on.High energy and power density,excellent security,and long cycling performance are key features for the development of LIBs.Nowadays,commercially used carbon-based anode materials are limited by their intrinsically low theoretical capacity value of 372 m Ah g-1.Layered MoS₂ has promising applications in lithium ion batteries due to its advantages such as high specific capacity?ca.670 m Ah g-1?and environment-friendliness.Nevertheless,its inferior rate capability and cycling life are restricted by the low electronic conductivity,low lithium ion diffusion coefficient,and large volume changes during the charge-discharge process.In our work,the Roselike MoS₂/nitrogen-containing carbon/graphene?MoS₂/NC/G?hybrids,Carbon encapsulated nanosheet-assembled MoS₂?C@MoS₂?nanospheres and MoS₂@C hollow nanospheres with widened interlayer spacing are successfully synthesized to improve their slow electronic conductivity,low lithium ion diffusion coefficient,and accommodate large volume changes during the discharge and charge cycles.Electrochemical energy storage performances demonstrate that the above MoS₂-based nanocomposites exhibit high specific capacity,excellent rate capability,and good cycling stability.The main results are as follows:?1?Roselike MoS₂/nitrogen-containing carbon/graphene?MoS₂/NC/G?hybrids: Roselike MoS₂/NC/G hybrids have been successfully synthesized via a facile polypyrrole?PPy?-assisted hydrothermal approach in combination with hightemperature calcination.The obtained MoS₂/NC/G hybrids manifest roselike MoS₂ composed of nanosheets coupled uniformly on NC/G nanosheets due to the strong interaction between MoS₂ and the abundant nitrogen-containing functional groups of PPy.The MoS₂/NC/G hybrids possess a high specific surface area of 30.43 m2 g–1 with meso-and micro-pores.The NC/G nanosheets have distinctively boosted the electronic conductivity of the MoS₂/NC/G hybrids and facilitate the efficient and fast transfer of electrons and Li+ ions.When used as an anode materials for lithium ion batteries,the MoS₂/NC/G hybrids exhibit enhanced electrochemical energy storage performances compared to the bare MoS₂ nanosheets,including high specific capacity?1570.6 mAh g–1 at 0.1 A g-1?,excellent rate capability?704.8 mAh g–1 at 5 A g-1?and good cycling stability?96.4% capacity retention after 100 cycles at 0.2 A g-1?.The enhanced lithium storage properties of the MoS₂/NC/G hybrids can be ascribed to the boosted electronic conductivity arising from the novel hybrids nanostructures of MoS₂/NC/G.?2?Carbon encapsulated nanosheet-assembled MoS₂?C@MoS₂?nanospheres: C@MoS₂ nanospheres have been synthesized using poly?vinylpyrrolidone??PVP?as sufactant and carbon source via hydrothermal approach in combination with hightemperature calcination process.PVP plays an important role in the formation of nanosheet-assembled Mo S₂ nanospheres,which can be in-situ converted into amorphous carbon to encapsulate MoS₂.The as-prepared 3D radially oriented MoS₂ nanospheres have a specific surface area of 23.63 m2 g–1 with mesoporous structures.The 3D structures with the few layer will significantly improve the diffusion efficiency of Li+ ions,provide large contact area between the electrode and electrolyte and provides free space for buffering strains during the discharge-charge process.When evaluated for electrochemical lithium storage properties,the C@MoS₂ nanospheres exhibit enhanced electrochemical energy storage performances compared to the bare MoS₂ nanosheets,including high specific capacity?1135.8 mAh g-1 at 0.1 A g-1?,excellent rate capability?384.4 mAh g-1 at 8 A g-1 and 330.5 mAh g-1 at 10 A g-1?,and good cycling stability?97.03% capacity retention after 100 cycles at 0.5 A g-1?.The enhanced lithium storage performances of the C@MoS₂ nanospheres can be ascribed to the boosted electronic conductivity arising from PVP derived carbon,and the facilitated lithium ion transport due to the shorter diffusion length of MoS₂ nanosheet-assembled structures.?3?MoS₂@C hollow nanospheres with widened interlayer spacing: MoS₂@C hollow nanospheres with widened interlayer spacing have been synthesized by in situ vapor phase sulfurization of the polypyrrole-polyoxometalate?PPy-PMo12?precursor,in which MoS₂ layers and amorphous carbon are generated synchronically.The vapor phase sulfurization process can retain the spherical morphology of the precursor,and facilitate the formation of the hollow MoS₂ structures.When evaluated as a anode for lithium ion batteries,the MoS₂@C hollow nanospheres exhibit enhanced electrochemical energy storage performances compared to the bulk MoS₂,including high specific capacity?1511.7 mAh g–1 at 0.1 A g–1?,excellent rate capability?492 mAh g–1 at 8 A g–1and 406 mAh g–1 at 10 A g–1?,and good cycling stability?94.28% capacity retention after 500 cycles at 1 A g-1?.The hollow structures of MoS₂ could provide more active sites and buffer the volume changes for the electrochemical reactions.Moreover,the interoverlapped architectures between MoS₂ layer and carbon can greatly improve the electronic conductivity and electrochemistry stability,thus leading to enhanced lithium storage performances.