Synthesis And Electrochemical Properties Of MoO_3-x Anode Materials

Lithium ion batteries?LIBs?,as one of the most promising power sources,have attracted tremendous attention owing to their distinctive advantages,such as high energy density,low self-discharge and long cycle life.Nowadays,higher energy density LIBs are required for applications in electric vehicles and smart grids.However,commercialized anode graphite can't satisfy these requirements because of its limited theoretical specific capacity(372mAh g^-1).Recently,a variety of new anode materials have been developed to meet the demand,like iron oxide,lithium titanate,vanadium nitride,cobaltosic oxide,tin dioxide and molybdenum oxide.Molybdenum trioxide?MoO3?is a suitable candidate for anodes due to its superior theoretical specific capacity(1117mAh g^-1),environmental benignity and affordable cost.Nevertheless,its practical utilizations in LIBs have been hindered severely by the poor intrinsically lithium ion/electron conductivity and drastic structural degradation upon conversion reaction.Hence,lots of strategies have been adopted to mitigate these issues including preparation of nanosized electrodes,design of composites with high conductive materials and construction of morphology controlled anodes.In this work,assembled-sheets like MoO3 has been successfully synthesized via hydrothermal-heat treatment process,during which the crystalline type of MoO3 could be transferred from hexagonal to orthorhombic structure.Also,MoO_3-x has been prepared with addition of glocuse or citic acid.The outer layer of MoO_3-x has been partially reduced to MoO2.As a consequence,the conductivity of MoO_3-x has been enhanced.?1?Assembled-sheets like ?-MoO3 has been prepared by hydrothermal-heat treatment method.During heat treatment process,the crystalline type of MoO3 has been transferred from hexagonal into orthorhombic structure.Besides,the morphology of products has been changed from microrods to microplates.Furthermore,a porous-interwaved structure of ?-MoO3^-100 has been obtained after this ?-MoO3 is cycled several times.The discharge capacity of MoO3 is maintained at 889mAh g^-1 at 0.1 C current density over 100 cycles,with capacity retention of ¹00%.Meanwhile,?-MoO3 delivers enhanced rate capability(567mAh g^-1 at 2 C).The excellent cycle stability and better rate performan ce of ?-MoO3 are associated with a porous-interweaved structure obtained after several cycles.?2?MoO_3-x nanoplates have been prepared using low-temperature solid-state method modified with glocuse.With the limitted reducibility of glocuse,MoO2 has been produced at the surface of MoO3 within a depth of 5^-10 nm.As a result,the conductivity of MoO_3-x has been improved with the help of MoO2 greatly.For the sample 550-MoO_3-x synthesized at 550 oC,the charge transfer resistance value R ct is remained at 100 ? after cycling.The discharge capacity of 550-MoO_3-x is 850mAh g^-1.Also,550-MoO_3-x has a capacity of 284mAh g^-1 at a higher current rate of 2000 m A g^-1.?3?MoO_3-x nanorods have been successfully obtained by hydrothermal process,using citric acid as the reducing agent.The outlayer of MoO_3-x is MoO2 surroundings ascribed from oxygen vacancy.The Mo element chemical states at the surface of nanorods are +5 and +4 mostly.Capacitance process as well as diffusion-controlled process is attributed to the capacity of C-MoO3 with the addition of CA.Consequently,the conductivity of C-MoO3 has been enhanced evidently.A discharge capacity of 787mAh g^-1 could be maintained after 100 cycles for C-MoO3 at 0.1 m A g^-1,with capacity retention of 90.1%.Notably,C-MoO3 has exhibited a high capacity of 536mAh g^-1 even at 5 A g^-1.