Preparation Of Spinel-type ZnGa₂O₄ Nanomaterials And Their Carbon Nanocomposites And Corresponding Lithium Storage Properties

Fossil fuels?coal,oil,etc.?,followed by the advances of science and technology,has initiated a serious energy crisis and environmental pollution.Therefore,development of efficient and sustainable utilization of the new energy has gained numerous intrests of research experts at home and abroad.As a kind of energy storing device,lithium ion batteries?LIBs?play a significant role due to their high gravimetric and volumetric energy,high energy density,long cycle life and low self-discharge property.Hence,the employment of LIBs in portable electronic devices?smart mobile phone,laptops,etc.?is a big achievement.In order to meet the increasing energy density of electric vehicles,hybrid vehicles as well as smart grids and other large energy storage systems,the exploration and development of novel LIBs materials with high capacity and long cycle stability is on the high agenda.Transition metal oxides?TMOs?have proved to be suitble next generation anode alternatives for LIBs owing to their low cost,low toxicity and high theoretical capacity(as high as 600^-1000 mAh g^-1),which is about 2-3 times higher than that of graphite.Two intrinsic problems exist,however,for TMOs-based anodes,such as low electrical conductivity and large volume changes during battery cycling,which lead to low coulombic efficiency and cyclability.Controlling the morphology of spinel TMOs and build composite materials can effectively improve the electrochemical properties of LIBs.This thesis mainly starts with the elaborate construction of micro/nano materials?spinel structure of ZnGa₂O₄ nanocubes and yolk-shell ZnGa₂O₄@C nanospheres?.When applied as LIBs anode materials,the materials showed excellent electrochemical performance.?1?With Zn?CH₃COO?₂·2H₂O,Ga?NO₃?₃·xH₂O and urea as raw materials,ZnGa₂O₄ nanocubes were successfully synthesized through a simple one step hydrothermal method.The phase and morphology of ZnGa₂O₄ nanocubes were characterized in detail.When used for LIBs anode materials,ZnGa₂O₄ nanocubes exhibited good electrochemical cycle stability.At the current density of 100 mA g^-1,the capacity of 720 mAh g^-1 can be maintained even after 160 cycles,which was better than that of ZnGa₂O₄ nanospheres and ZnO/Ga₂O₃ mechanical mixture samples.?2?Yolk-shell ZnGa₂O₄@C nanospheres were fabricated via a hydrolysis polymerization method.As LIBs anode materials,ZnGa₂O₄@C nanospheres exhibited high specific capacity and rate performance during charge and discharge.The large specific surface area of ZnGa₂O₄@C nanospheres increased the contact area between the electrode and electrolyte,shortened the Li⁺ diffusion path,improving the electrode kinetics.The amorphous carbon materials effectively boosted the electrical conductivity of the electrode materials.The cavity between the outer shell and the inner core were beneficial to buffer the volume change during cycling.