Research On Preparation And Modification Of Cathode Material LiFePO₄for Lithium Ion Battery

Energy crisis and environment pollution force main countries to develop clean andrenewable energy.Chemical power source is one of the new energy to extensiveresearch. Lithium ion battery becomes secondary electrical power supply which offervery high development and utilization value because of its low cost andEnvironment-friendly. Lithium iron phosphate, LiFePO₄, has recently attractedsignificant interest becsuse of its low cost, high safety, environmentally friendly andelectrochemical performance and so on.LiFePO₄is produced through the mixed precipitation method. The influence ofthe concentration of Fe2+, reaction time-span and reaction temperature to the LiFePO₄,in terms of crystallization and the particle shape were studied in this paper. The resultsshow that the yield of Li3PO4and Fe3（PO4）2is dropping with a good pH. The sphericalLiFePO₄with a particle size of0.5¹.0μm is produced when concentration of FeSO4is0.01mol/L, pH control6.0, mixing speed is200rpm,17h reaction at roomtemperature. Which first Charge capacity is111.7mAh/g, and Discharge Capacity is110.8mAh/g at0.2C.LiFePO₄is produced through the hydrothermal method with FeSO4·7H2O、LiOH·H2O and H3PO4as the reactants. The results show that pure-phase a LiFePO₄isproduced to select proper hydrothermal process and Li/Fe. LiFePO₄with highercrystallinity and better morphology is produced when reaction temperature is160℃,reaction time is6h and pH is8.0. Particle morphology and dispersion can obviouslyimprove when Ethanol/water as reaction medium. The spindle apparatus LiFePO₄firstCharge capacity is86.7mAh/g, and Discharge Capacity is86.5mAh/g at0.2C.The spindle, flky and spherical LiFePO₄is produced through the hydrothermalmethod and CTAB, CMC, TWEEN80, Trolamine as the surfactant. The CarbonCoated LiFePO₄Cathode with smaller particle size and more better charge and discharge performance. LiFePO₄/C which has most high first charge and dischargewhen glucose as carbon source and respectively135.5mAh/g and134.5mAh/g. ThePEG molecular weight and doping amount of glucose had not effect to First charge anddischarge performance.The LiF1-xNixPO4and LiFe1-xMnxPO4are produced with NiSO4and MnSO4as dopant. The results show that after ion dopan LiFePO₄has more better chargeand discharge performance, the charge and discharge performance of LiFe0.9Mn0.1PO4respectly143.5mAh/g and143mAh/g. correspondingly, the charge and discharge performance of LiFe0.95Ni0.05PO4respectly132mAh/g and131mAh/g.The materials of composite doping with Ni2+、Mn2+and carbon coated have bettercharge and discharge performance than separate doping, the LiFe0.8Ni0.1Mn0.1PO4/Cfirst charge and discharge performance is154.1mAh/g and152.8mAh/g when,Compared with no doping, enhance respectively75.3%and120.8%. Its shows thatdoping with carbon coated is a feasible method to enhance electrochemical performanceof cathode material LiFePO₄.