Solvent-thermal Synthesis Of Hierarchical MoO₂-C Composites And Their Electrochemical Properties

Environmentally-friendly technology is the focus of the society,developing renewable green energy has become the world’s common goals.Lithium-ion batteries(LIBs)as the source of clean energy were favored by society.However,commercialization of graphite negative electrode materials,energy density and power density is relatively low,cannot meet the needs of next-generation high-performance lithium-ion batteries.Designing high-performance anode material for lithium-ion batteries has become a very urgent task.Molybdenum dioxide(MoO2)has good conductivity,good mechanical properties and advantages of theoretical capacity,is currently the research one of the hottest material of lithium ion battery cathode materials.In this dissertation,a series of MoO2 have been synthesized and characterized,they were applied as anodes for lithium ion batteries,and then their electrochemical performances were also investigated in detail.These results will enrich molybdenum oxide materials,and will provide new ideas for designing and synthesizing novlty anode materials in LIBs.The main contents are as follows:(1)The MoO2-C composites were synthesized by a simple solvothermal method and then were characterized by XRD,TG,SEM and TEM measurements.It was found that the MoO2-C-2d sample possess the hierarchical hollow structure and the carbon coating structure.This material was used as an anode for LIBs and found that MoO2-C-2d showed excellent electrochemical properties.For example,a large reversible capacity of 763 mAh g-1 can be reached at current density of 0.2 A g-1 after 50 cycles.Moreover,a large reversible capacity of 573 mAh g-1 can also be remained at the current density as high as 2 A g-1.Such excellent performance can be attributed to the unique hierarchical architecture.(2)In situ carbon compositing is an efficient way to improve the electrochemical performance of molybdenum dioxide.Glucose and graphene oxide were used as carbon source to react with sodium molybdate to form a precursor via a solvothermal methode.The MoOC microspheres and hierarchical MoO2@RGO composite were obtained after the precursor at a H2 atmosphere.It can be found that the electrochemical performance of Mo02@RGO was better than that of MoOC.MoO2@RGO exhibited a high reversible discharge capacity of 708 mAh g-1 at 500 mA g-1 after 50 cycles.(3)The MoO2-C nanoparticle was obtained through a simple ionic liquid route,then this material used as an anode material for lithium-ion batteries and found that it has good electrochemical performance.For instance,a large discharge capacity of 715 mAh g-1 can be reached at 0.1 A g－1 after 50 cycles with a capacity retention of 84%.Moreover,the material delivered a reversible capacity of 569 mAh g-1 at 1 A g-1 after 50 cycles.These great electrochemical properties might be arise from the small particle size of M0O2-C nanoparticle(20nm),which can provide short path for Li＋diffusion.Moreover,the carbon matrix around MoO2 nanoparticles provided fast electron transport route.