Porous Iron Oxides Structure Regulation And Studies Of Electrochemical-performance

Currently, the anode materials used in the commercial lithium-ion batteries arecarbonaceous materials. However, the relatively low specific capacity (theoreticalvalue372mAh.g^-1) hinders their further application in high energy-densitylithium-ion batteries. α-Fe₂O₃is one of the promising candidates as anode materials inhigh energy-density lithium-ion batteries, because of its high specific capacity (1004mAh.g^-1), low cost and environmental affinity. However, the Li+insertion/desertion inα-Fe₂O₃cause a big volume change, resulting in low cycling stability. In thisdissertation, porous α-Fe₂O₃particles with tunable pore size and quantity werefabricated using hydrothermal process with purpose to enhance cycling stability ofα-Fe₂O₃. The electrochemical properties of the porous α-Fe₂O₃were studied.XRD, SEM, TEM and N2absorption were employed to investigate morphology,size, microstructure and pore size distribution of the porous α-Fe₂O₃particles, whichindicate that the pore quantity and pore size distribution could be tuned by adjustingdensity of Cl-and F-in the precursor solution.Cyclic voltammetry and charg/discharge measurement were employed to studyelectrochemical properties of the porous α-Fe₂O₃particles as anode materials. Effectsof pore quantity and pore size distribution on the electrochemical properties of theporous α-Fe₂O₃particles were discussed. The nano-sized α-Fe₂O₃particles exhibitgood cycling properties at low current density condition.When the current density is500mAh.g^-1, the reversible capacity of the mesoporous α-Fe₂O₃particles with averagesize of262.35nm is as high as600mAh.g^-1at the100thcycle with capacity retentionof55.68%. The mcro-sized α-Fe₂O₃particles with mesoporous and macroporousstructure exhibit good cycling properties at low current density condition. Even at1Crate, their reversible capacity is as high as520mA.g^-1at the100thcycle with capacityretention of63.25%. The good rate capacity of the porous α-Fe₂O₃particles could beascribed to their unique porous structure and monocrystallinity, which makes porousα-Fe₂O₃particles the promising candidate as anode materials in high energy-densitylithium-ion batteries.