Controllable Fabricate And Lithium/Sodium Storage Properties Of Molybdenum Oxide/Nitrogen Doped Carbon Composite

With the progress and development of human society,the demand for high-power battery energy storage systems has become stronger.The most effective way to meet the application conditions is to develop a new high-energy electrode to improve the secondary energy storage battery.Molybdenum-based materials such as MoO2,M0S2,MoSe2,and MoO3 are considered to be ideal electrode materials for secondary energy storage batteries because of their high valence state,high specific energy,wide source,and low price.However,when it is used as an electrode material,the disadvantages are also obvious.Such as severely volume expansion during charging and discharging,poor cycle stability and other shortcomings.In view of the shortcomings of molybdenum-based electrode materials,this research topic is based on the controllability of its morphology and structure,element doping and compounding with carbon materials.The MoO2 and MoSe2 electrode materials were designed and prepared,and their electrochemical performance as a lithium/sodium ion battery anode was studied.The main research work is as follows.1.Strongly surface-bonded MoO2@carbon nanocomposites are obtained through in-situ nitrogen-doping of MoO2@carbon and evaluated as the anode material of Li-ion batteries.Nitrogen,derived from polydopamine,is in-situ doped into both MoO2 core and carbon shell.Strong Mo-N bonding is validated from X-ray photoelectron spectra and Fourier transform infrared spectra.The in-situ nitrogen-doping process can generate a strong interfacial interaction between MoO2 and carbon,facilitating the transport of electron and Li+across the interface of heterophases.The nitrogen-doping feature of MoO2 can improve the electrochemical reactivity and kinetics for Li-storage.2.Supramolecule precursors exhibit unique superiority in preparing functional nanocomposites comprising of ultrasmall active nanoparticles uniformly embedded in carbon.By virtue of the self-assembly of supramolecule Moo42--polydopamine(Mo-PDA)on the surface of sulfonated polystyrene microspheres,hierarchical hollow MoO2/nitrogen-doped carbon(H-MoO2/NC)microspheres,which are assembled from ultrathin nanosheets comprising of ultrasmall nanoislands-like MoO2 embedded in nitrogen-doped carbon,are obtained.During the preparation of H-MoO2/NC,the confining effect of the surrounding carbon effectively inhibits the growth of MoO2 nanoparticles and results in the formation of ultrasmall nanoislands-like MoO2.In addition,the nanoislands-like MoO2 is strongly embedded in the nitrogen-doped carbon as indicated by the presence of strong Mo-N bond.The strong coupling between MoO2 nanocrystallites and nitrogen-doped carbon results in an enhanced synergistic effect for the purpose of application in Li-ion batteries.As the anode material of LIBs,H-MoO2/NC manifests high capacity of 1191 mAh g-1 after 100 cycles at 0.2 C,and excellent rate capability with a capacity of 697 mAh g-1 at 20 C.3.The supramolecular precursor is formed by the perfect fusion of metal ions and organic units,and the super-molecular nanostructured MoSe2 and MoO2 particles are uniformly embedded in the nitrogen-doped carbon network to form nanosheets,finally a hollow structure of molybdenum diselide/molybdenum dioxide/nitrogen doped carbon composite material(H-MoSe2/MoO2/NC)was constructed.This heterostructure composite is more conducive to the transfer of sodium ions and electronic.Moreover,it can significantly alleviate the violent volume expansion during charging and discharging.In this heterostructure,MoO2 can increase the conductivity of the overall material because of its ultra-high conductivity(1.0×104S cm-1).MoSe2 can provide a wider channel to transfer of sodium ions.The nitrogen-doped carbon network can not only change the inherent conductivity of the material itself,shorten the transmission route of sodium ions and electrons,but also prevent the electrode destruction of MoO2/MoSe2 during long-term cycling.The hollow multi-stage heterostructure formed by the synergy of the three creates more active sites for sodium ions,which makes the prepared H-MoSe2/MoO2/NC have ultra-high capacity,good cycle stability and good rate performance.