Synthesis And Property Modification Of MoS₂ Anode Material For Lithium-/Sodium-ion Batteries

MoS2 owns a layered graphene-like structure.When used as an anode material for lithium/sodium ion batteries(LIBs/SIBs),MoS2 shows an excellent electrochemical performance owing to its large specific surface area and interlayer spacing,rich electrochemical active sites and fast ion and electron transport properties.However,it also suffers from some shortcomings in the practical application,such as poor rate performance caused by the low electrical conductivity of the material,poor structural stability resulted from the large volume variation upon cycling,and even serious pulverization and shedding.To solve these issues,we have performed some modification researches on MoS2 anode materials via varies strategies,such as the conductive materials composting,morphology controlling,phase engineering,etc.,obtaining some MoS2-based materials with excellent electrochemical performance.The main content of this thesis is as follows:(1)The performance of MoS2 electrode material was effectively improved through a highly conductive Co metal element composting method.MoS2/Co composite material delivers a high initial capacity of 1130 mAh g-1 at 100 mA g-1 and the capacity can reach 1340 mA g-1 after 50 cycles.Moreover,even at 2 A g-1,the capacity can reach a high value of 766 mAh g-1.The excellent electrochemical performance of the MoS2/Co composite is a synthetic effect of the high-conductivity Co compositing and the ultrathin MoS2 nanosheet structure with fast ion transport.(2)The cycling stability and rate performance of MoS2 material were optimized by preparing a carbon-coated V4C3-MXene/MoS2/C nanohybrid with V4C3-MXene and few-layer MoS2 nanosheet.The capacity of V4C3-MXene/MoS2/C nanohybrid can deliver 600 mAh g-1 after 450 cycles at 1 A g-1.Even at 10 A g-1,a high capacity of 500 mAh g-1can still be maintained.In the nanohybrid,the V4C3-MXene serves as a substrate,which can significantly enhance the structural stability and electrical conductivity of the nanohybrid.The few-layer MoS2 nanosheet structure can effectively enlarge the specific surface area and shorten the diffusion path of lithium ions in the nanohybrid.In addition,the carbon coating can further improve the electrical conductivity and structural stability of the nanohybrid.(3)The high-performance carbon-coated MoS2-PVP@NC nanosphere composite was prepared using the PVP-assisted hydrothermal method.MoS2-PVP@NC composite can deliver a capacity of about 600 mAh g-1 after 300 cycles at 1 A g-1 and the capacity can still be maintained to about 360 mAh g-1 at 10 A g-1,showing an excellent lithium storage performance;For the anode material in SIBs,the capacity maintains 400 mAh g-1 at 1 A g-1 after 200 cycles.Even at 10 A g-1,the capacity can still retain 350 mAh g-1,indicating a superior sodium storage performance.The excellent electrochemical performance of the nanohybrid can be attributed to its hierarchical structure.The yarn ball-like MoS2 nanosphere structure can effectively alleviate the volume change during lithium/sodium ions intercalating or de-intercalating processes,enhancing the structural stability of the material.The carbon coating layer can further strengthen the structural stability and electrical conductivity of the material.(4)The carbon coated 1T-MoS2 was synthesized via glucose assisted one-step hydrothermal method.The 1T-MoS2/C hybrid has a high initial discharge capacity of 920.6 mAh g-1 at 1 A g-1 and the capacity is still as high as 870 mAh g-1 after 300 cycles when used as an anode material of LIBs.The capacity can still keep 600 mAh g-1 under 10 A g-1.The superior property of the hybrid can be attributed to the following three factors:Firstly,the higher conductivity of 1T-MoS2 can accelerate the transfer of ions or electrons.Secondly,its larger interlayer distance of 0.94 nm can effectively relieve the volume change during the intercalation or deintercalation of lithium ions.Thirdly,the few-layer nanosheet structure and its carbon coating layer can effectively increase the specific surface area of the hybrid,reduce the diffusion path of lithium ions in the hybrid,and accelerate the reaction kinetics.(5)The MoSe2/MoS2 nanocomposite heterostructure was obtained through two-step hydrothermal method.From the structural and morphological characterization,the ultrasmall MoSe2 nanosheets are embedded between spherical MoS2 nanoflowers.MoSe2/MoS2 nanocomposite exhibits a high specific capacity of 462.3 mAh g-1 after 120 cycles at 1 A g-1,and it still shows a specific capacity of 300.2 mAh g-1 at 10 A g-1.The excellent sodium storage performance is due to the special MoSe2/MoS2 heterostructure,which can effectively relieve the volume change caused by the intercalation or deintercalation of sodium ions,enhancing the structural stability of the nanocomposite.In addition,the heterostructure material also owns a high electrical conductivity,expediting charge transfer in the material during the electrochemical reaction process.