Design And Synthesis Of Porous Transition Metal Oxides And Carbon Materials For Lithium-ion Battery Applications

Owing to advantages of high theory capacity,abundant and eco-friendly,transition metal oxides are next generation cathode materials to replace commercial graphite.However,the practical applications have been limited by problems of poor electrical conductivity,low efficiency in the first charge/discharge process and obvious volume change in lithium ion embedded and removal process.Although natural carbon material with abundance and no pollution can also be regarded as an ideal anode material to replace graphite,the limitation of poor conductivity and low theoretical capacity restrict its application.In this paper,to improve electrode material conductivity and optimize structure,various methods including bake-in-salt method,complex thermal decomposition,biological template method,solvothermal method and natural products functionalization were used to prepare series of anode nanomaterials and electrochemical performance were further studied respectively.The main contents and results are as follows:（1）The synthesis of porous Mn₃O₄@C、MoO₃@C nanocomposites with bake-in-salt method.The porous Mn₃O₄@C nanocomposites were prepared by thermal decomposition of manganese acetylacetonate in air with advantages of high specific heat capacity and thermal stability of sodium chloride which was regarded as protective layer and hard template.The prepared porous Mn₃O₄@C nanocomposites with excellent electrochemical performance could deliver capacity of 754.4 m A hg^-1 after 950 cycles at current density of 1 Ag^-1.MoO₃@C nanocomposites also were prepared by this method.The capacity could maintain at 411.1 m A hg^-1 after 500 cycles at current density of 4 Ag^-1,even under higher current density of 10 Ag^-1,the capacity still reach 291.8 m A hg^-1.（2）The synthesis of oxygen defect porous α-Fe₂O₃-δ nanostructures with biological template method.Natural coconut shell was used as template,the Fe（OH）3 gel adsorbed on surface of coconut shell by physical adsorption.And then after thermal decomposition,in situ carbon thermal reaction,oxygen defect porous α-Fe₂O₃-δ nanostructure was obtained.The introduction of oxygen defect improves effectively electrical conductivity of α-Fe₂O₃.The specific capacity could maintain at 1062.6 m Ahg^-1 after 900 cycles at current density of 1 Ag^-1.（3）The synthesis of flower like NiCo₂O₄ nanostructures.To relieve problem of capacity fading fast,flower like NiCo₂O₄ nanostructure was synthesized for increasing structural stability of anode materials with solvothermal method.The final product was prepared by thermal decomposition of flower like Ni-Co precursor which was synthesized by controlled of solvothermal reaction time.The capacity can still maintain at 1128 m A hg^-1 after 330 cycles at current density of 1 Ag^-1,even at high current density of 5 Ag^-1,the capacity could reach 948.1 m A hg^-1.（4）The synthesis of porous Mn₃O₄@C nanomaterials with thermal decomposition of bis（1-aminoundecane）tetrachloromanganate.1-Aminoundecane and Mn Cl2·4H2O were respectively used as ligand and manganese source to synthesize precursor bis（1-aminoundecane）tetrachloromanganate.And then porous Mn₃O₄@C nanomaterial was obtained by thermal decomposition of above precursor.The prepared porous Mn₃O₄@C nanomaterial shows excellent electrochemical performance,which deliver capacity of 934.1 m A hg^-1 after 2000 cycles at current density of 2 Ag^-1.（5）The synthesis of N/S co-doped carbon porous nanosheets with natural products functionalization.Natural Poplar Fluff was used as raw material,N/S co-doped carbon porous nanosheet was obtained by in-situ hydrothermal carbonization method with thiourea assisted.This method promotes enhancement of electrochemical properties of carbon materials by ways of utilizing layer structure of natural catkin and improving electrical conductivity by N/S doped.