Study Of Iron Phosphate Prepared By Fast Precipitation And Its Application In Synthesis And Modification Of LiFePO₄/C

Olive-type LiFePO4which has many advantages such as excellent safety performance,thermostability and cycle performance,low self-discharge and environmentally friendly has been seen the most promising cathode material for power battery and energy storage system. Low electronic and ionic conductivity, which result in poor rate performance, affect its practical application. Therefore, we adopt measures to improve the material performance through controlling particle size, coating the particles with conducting carbon and doping metallic cations.The initial precipitation pH values of FePO4-2H2O and Fe(OH)3at diffirent concentration of reactants are calculated according to the solubility product principle. The initial precipation pH values of other elements such as Mg, Mn, Ti, Al are also calculated. The result show that all of Ti and part of Al can precipitate into FePO4, but Mn and Mg cannot precipitate.Submicro amorphous FePO4·2H2O is prepared by fast precipitation method using FeSO4·7H2O, NH4H2PO4and H2O2as starting materials. Submicro amorphous FePO4·2H2O synthesized with solution concentration of0.2mol/L and reaction temperature at50℃has uniform particle size distribution, and its ratio of Fe and P is1.00. We conducted the scale up test under the optimized condition, and cost estimation shows that the process is promising for industrialization.LiFePO4/C composites was synthesized by FePO4/2H2O prepared, Li2CO3and glucose. The effect of sintering temperature on performance of LiFePO4was studied, LiFePO4/C prepared at650℃show a discharge specific capacity of136.3mAh/g and capacity retention of99.4%at1C-rate after20cycles. Iron phosphate precursor doped Nb and Ti was prepared by fast precipitation method. LiFe1-xNbxPO4and LiFe1-xTixPO4synthesized through it have fine uniform grain size, complete conductive carbon coating. LiFe1-xNbxPO4and LiFe1-xTixPO4show a discharge capacity of145.3and145.5mAh/g and capacity retention145.7and144.5mAh/g at1C-rate after50cycles,and capacity retention of100%and99.0%at1C-rate after50cycles.