Design And Synthesis Of Metal Oxide/Carbon Composites With Various Morphologies For Li-ion Batteries

A promising family of metal oxides(MOs)with high theoretical capacity and reliable safety has attracted increasing research interest worldwide.Benefiting from their remarkable electrochemical properties,MOs play significant roles on low-cost and environmental friendly energy storage technologies in Li-ion secondary batteries.Unfortunately,the reversible charging/discharging processes of MO based electrode involve tremendous volume variation and dramatic mechanical stress,which lead to electrode disintegration and rapid capacity fading.In order to improve the cycle life of MOs,one successful practicable is the combination of MOs with carbon materials,which could be considered as the conductive and elastic matrix to prevent the exfoliation and agglomeration of MOs during rechargeable cycling as well as increase the electrical conductivity of electrode.Thereby it is urgent need but it is still a significant challenge to rationally design and delicately tailor the MOs/carbon electrodes for advanced LIBs.In this work,various metal oxides/carbon composites with different structures,morphologies,and functional carbonaceous materials were prepared for improving their capacity and cyclic stability.The role and function of structure,morphology,and functionalized carbon layer of active material in the electrochemical reaction was systematically investiated.The main contents and results are as following.(1)Through the introduction of well-distributed tin oxide nanoparticles on the surface of self-made TiO2 nanotubes and followed by carbon coating,a novel TiO2/SnO2-C double-shells nanotube has been synthesized.Resorcinol-formaldehyde was used as raw carbon material and deposited on the TiO2-SnO2 composite and followed by thermal treatment to form a continuous carbon layer.Due to the synergetic effect of a unique combination of TiO2,SnO2,and carbon layer,the DSNTs electrode exhibits a greatly enhanced reversible capacity(256 m Ah?g-1 after 710 cycles at 1 A?g-1).(2)A novel Mn-Co/N-CNT composite was readily synthesized by in situ banding Mn-Co nanoparticles on nitrogen doped carbon nanotubes(N-CNT)through solvothermal method and followed by high temperature pyrolysis.The as-made Mn-Co/N-CNT as LIBs anode material exhibits excellent rechargeable capability,i.e.1028 m Ah?g-1 at 200 m A?g-1.Doped nitrogen on CNT effectively increase the conductivity of the complex and the binding energy between Mn-Co nanoparticles and CNT,which lead to more stable and higher conductive complex during charge/discharge cycling process.(3)N-doped graphene/MnOOH/Mn3O4 composites with controllable structure,morphology,and composition were prepared by a facile hydrothermal process.When the weight ratio of Mn SO4/KMnO4 is 36/500 and the reaction time is 2 h,the obtained material has the best electrochemical performance.The discharge capacity of NG-36 electrode after 140 cycles is 588 m Ah?g-1 at a current density of 1 A?g-1.