Preparation Of Mo-based Electrode Materials For Sodium Ion Batteries

Sodium ion batteries(SIBs)are considered as the most promising substitutes to lithium ion batteries because of high reserves abundance,wide distribution and relatively low price of sodium salt.However,the radius of sodium ion and relative atomic mass is larger than Li ion,which hinder its insertion/extraction in the current commercial graphite electrode materials,leading to unsatisfactory electrochemistry performance.Hence,it is of great importance to develop novel electrode materials for SIBs and create rapid diffusion path for electron and ion.Mo-based compounds are regarded as ideal electrode materials due to their unique physical and chemical properties including favorable thermal stability and chemical stability.In this work,we report hydrogen molybdenum bronze(HMB)and molybdenum dioxide(MoO2)as new electrodes for SIBs.With the help of carbon hybridization,nanostructuring and surface modification,we rationally design three-dimensional porous core-shell nanosheet arrays to explore and improve sodium storage performance.The main research contents and results are as follows:(1)We propose a facile successive electrodeposition method to sandwich HMB into vertical graphene(VG)bottom backbone and top poly(3,4-ethylenedioxythiophene)(PEDOT)shell forming self-supported VG/HMB/PEDOT core/shell composite arrays.The three materials are fully compatible.The VG prepared by microwave plasma enhanced chemical vapor deposition method has many advantages such as high surface to volume ratio,excellent electrical conductivity and large open three-dimensional network configuration,which can promote the fast transfer of ions/electrons and consequently improve electrochemical performance.In addition,the PEDOT shell can also improve the conductivity and structural stability of the electrode.At a current density of200 mA g'1,the specific capacity reaches to 511.9 mA h g-1.After 500 cycles,the electrode still maintains a capacity of 320 mA h g-1 and nearly 100%coulomb efficiency.(2)Two-layer VG/MoO2 core/shell nanosheet arrays are fabricated via combined electrochemical deposition method and annealing approach.The two materials are fully compatible and the wrinkled MoO2 is uniformly coated on the surface of the VG.The 3D structures of vertical nanosheet arrays are also maintained.At a current density of 200 mA g-1,the specific capacity reaches to 511.9 mA h g-1.After 500 cycles,the electrode still maintains a capacity of 320 mA h g-1.