Preparation Of Transitional Metal Compounds/Carbon Composites And Their Research On Lithium/Sodium Ion Batteries

Lithium-ion batteries?LIBs?have been regarded as a technology of choice for hybrid electric vehicles and smart power grids due to their high energy densities,long lifespan,and environmental friendliness.Recently,sodium-ion batteries?SIBs?have attracted great interest owing to the natural abundance of sodium resource in comparison to LIBs.Nevertheless,fundamental problems still remain that severely impede its practical application in LIBs and SIBs,including poor kinetics of ion/electron diffusion and pulverization and aggregation of the electrode caused by volume change during the Li⁺/Na⁺insertion/extraction process.Hence,it is more challenging and urgent to develop efficient anode materials with higher discharge/charge capacities and better cycling behavior for application in LIBs and SIBs.Among a variety of new anode materials,transition metal compounds has great application prospect due to the abundant,high safety,simple preparation and high theoretical specific capacity.Therefore,in this paper,we synthesized a series of transition metal compounds or transition metal compounds-carbon hybrid materials with different components by adjusting the corresponding composition,morphology and structure.The merits of each component make the electrode stable enough to maintain its structural integrity,which significantly improve the electrochemical performance of transition metal compounds.The major contents of the paper are as follows:?1?Various self-assembled hollow mesoporous metal oxides with different detailed structures?Fe₂O₃ nanorods,Co₃O₄ nanoparticles and NiO nanosheets?were successfully fabricated by a novel facile strategy to fabricate using sulfonated polystyrene?SPS?microspheres as hard templates.When tested as the anode materials in half and full cells,the as-prepared metal oxide hollow microspheres show remarkable electrochemical performance.Then,we demonstrate a facile approach to directly grow ultrathin NiO nanosheets on the surface of hollow carbon?HC?microspheres by using PS microspheres as a template.And the electrochemical performance of the as-prepared core-shell HC@NiO composite as an anode material for LIBs and SIBs were also studied.?2?CoFe₂O₄ nanoclusters/graphene aerogels?CoFe₂O₄/GAs?composite was successfully synthesized by a simple solvothermal method.SEM and TEM results confirm that CoFe₂O₄ nanoclusters are well wrapped by the graphene.As an anode material for LIBs,CoFe₂O₄/GAs composite displays a stable cycling performance with a reversible capacity(1070 mAh g^-1)of after 100 discharge/charge cycles at the current density of 0.1 A g^-1,much higher than that of CoFe₂O₄ nanoclusters(473 mAh g^-1).Most important of all,a new CoFe₂O₄/GAs//LiCoO₂ full cell was successfully assembled,and exhibited excellent electrochemical performance.The superior electrochemical performance of the CoFe₂O₄/GAs composite in half and full cells can be attributed to the synergistic interaction between the uniform CoFe₂O₄ nanoclusters and GAs,the high electrical conductivity,and three-dimensional hierarchically porous structure.?3?A novel architecture of Mo₂C/graphene?Mo₂C/GR?was synthesized through a simple and environmentally friendly carburization process.The unique and special structural features of the Mo₂C/GR hybrids including good structural robustness,small particle size and porous structure permit easy access for electrons and ions to the electrode/electrolyte.Electrochemical tests indicate that Mo₂C/GR hybrids displays a high reversible capacity(813 mAh g^-1)after 100 discharge/charge cycles at the current density of 0.1 A g^-1,much higher than that of pure GR and bulk Mo₂C electrodes(443 mAh g^-1 and110 mAh g^-1).The enhanced electrochemical properties of the Mo₂C/GR hybrids are mainly ascribed to the synergetic effects between Mo₂C nanoparticles and the highly conductive GR support.?4?Core shell MoS₂/C nanospheres embedded in foam-like interconnected macroporous carbon sheets composite were successfully fabricated by a facile glucose carbonization process.SEM and TEM results confirm that the interconnected void nanospheres produced by Si O₂ nanopsheres homogeneously surround the core shell MoS₂/C nanospheres.When evaluated an anode material for sodium-ion batteries,the as-synthesized porous carbon sheets supported core shell MoS₂/C composite displays a discharge capacity of 523 mAh g^-1 after 100 discharge/charge cycles at the current density of 0.1 A g^-1.The superior electrochemical performance can be attributed to the synergetic effects between MoS₂nanospheres,coating carbon shell and supporting carbon sheets with an interconnected macroporous structure.?5?One-dimensional iron compound?Fe₂O₃,FeS and FeSe₂?nanoparticles encapsulated in carbon?denoted as Fe₂O₃@C,FeS@C and FeSe₂@C?hybrid nanofibers was synthesized by a simple and general process.The 1D porous nanoarchitecture effectively alleviates the pulverization or aggregation induced by huge volume changes during cycling as well as provides a short electron/ion diffusion length in the crystal.Furthermore,the external nanosized carbon wall and the internal porous carbon keep the mechanical stability of the electrode.When evaluated as anodes for SIBs,the as-synthesized iron compound?Fe₂O₃,FeS and FeSe₂?@carbon hybrid nanofibers show high specific capacities,robust cycling stability and desirable rate capabilities.As anodes for NIBs,FeSe₂@C show good Na storage properties due to its low charge transfer resistance and fast Na⁺kinetics.