Synthesis Of Hierarchically Architectural MoS₂ Materials And Their Application In Sodium-ion Batteries

In recent years,as a result of the energy crisis and increasing people's environmental awareness,the sodium-ion batteries?SIBs?have gradually become a research hotspot.Compared to lithium,the storage of sodium is more abundant and the cost of sodium is lower.Therefore,SIBs are expected to replace lithium-ion batteries as the next generation of energy storage system.As a typical layered transition metal sulfide,molybdenum sulfide?MoS₂?has a similar structure to that of graphene,which is comsisted of three atom layers?S-Mo-S?stacked together through van der Waals interactions,the layer spacing is 0.62 nm.When evaluated as an anode material for SIBs,the large spacing of 0.62 nm can facilitate the reversible sodium-ion insertion and extraction.However,due to the tremendous volume change associated with Na-ion insertion/extraction,the cycle performance of MoS₂ is poor.In the present work,we synthesized a series of new three-dimension hierarchical architectures and carbon-based MoS₂ composite materials via a simple hydrothermal method and investigated the influences of reaction time and the ratio of reactants on the structure and morphology of MoS₂.Furthermore,these materials were used as the anode materials for SIBs,and their electrochemical properties were also investigated.The main contents and results are as following:?1?Hierarchical MoS₂?H-MoS₂?were synthesized using ammonium molybdate,thiourea and hydrazine hydrate as raw materials and PVP as a template via a hydrothermal method.After annealed,the H-MoS₂ were successfully obtained.When used as anode material for SIBs,the H-MoS₂ exhibited good reversible capacity and excellent cycling stability.The excellent electrochemical performance could be attributed to the porous structure which shortened the sodium-ion insertion/extraction pathways,promoted electrolyte diffusion and lessened the volume change.?2?The hierarchical MoS₂@RGO nanosheets,where ultrathin MoS₂ nanosheets were perpendicularly anchored on both sides of RGO were prepared by hydrothermal route using MoO₃-EDA,L-cysteine and graphene oxide as raw materials.Such hybrid structures not only improved the conductivity of the hybrid structure and effectively prevented the aggregation of MoS₂ nanosheets,but also maximized the MoS₂ loading in the electrode for over 92%.When evaluated as an anode material for SIBs,the hierarchical MoS₂@RGO nanosheets delivered a high specific capacity of 420 mA h g-1 at 0.1 A g-1 after 160 cycles.?3?The hierarchical MoS₂/C@RGO nanosheets,where MoS₂/carbon hybrid nanosheets perpendicularly anchored on both sides of RGO were prepared by hydrothermal route using MoO₃-EDA,L-cysteine,glucose and graphene oxide as raw materials.When compared to MoS₂@RGO,the MoS₂/C@RGO exhibited more excellent cycling stability and rate capacity.At a current density of 1 A g-1,the hierarchical MoS₂/C@RGO nanosheets showed a capacity of 257 mAh g-1 after 200 cycles.