Study On The Fabrication And Lithium (Sodium) Storage Performances Of Hard Carbon Anode Materials

Hard carbon is a kind of carbon which is difficult to be graphitized.Hard carbon precursors are divided into three categories:fossil fuels?such as coal tar pitch?,polymer materials?such as polyacrylonitrile and other organic polymers?,biomass?such as sucrose,starch,humic acid?.Different morphologies and microstructure of hard carbon materials were studied in this paper.We fabricated different biomass-derived and pitch-based hard carbons and optimized parameters of oxidative stabilization.The impact of the microstructure,morphology,and sodium?lithium?storage characteristics were explored in detail and the energy storage mechanisms of lithium/sodium ions in hard carbon materials were studied.Humic acid-based carbon nanofibers were prepared by electrospinning methods together with heat treatment process.By comparing lithium insertion behaviors under various carbonization conditions,we prove the intercalation mechanisms at high potential sloping region are between graphene layers and at low potential plateau region are insertion into nanopores.Adding humic acid in the polyacrylonitrile solution introduces defects and pore structures into the system,which could increase the sodium storage capacity and improve the electrochemical behaviors.The anode obtained at 1300 ^oC with 30 wt%humic acid exhibits a high reversible capacity of 261.3 mAh g^-1 with an initial efficiency of 69.6%,high rate capability(81.7 mAh g^-1 at 1 A g^-1,respectively)and excellent cycle stability(248 mAh g^-1 reversible capacity at 0.1 A g^-1 over 100cycles).In this dissertation,petroleum asphalt were used as a raw material to produce hard carbon materials by pre-oxidation and carbonization processes.Thermogravimetric analysis,FT-IR and scanning electron microscope were performed to characterize the properties of two materials in different processes.The extension of pre-oxidation has little effect on the improvement of reversible capacity.