The Doping Modification Of LiFePO₄Cathode Materials And Batch Prepatation

Olive-type LiFePO4as cathode material of Li-ion batteries has attracted the eyes from both academe and industry Circles because of its long cyclic life and calendar life, high safety and low cost. However, the problems such as bad low temperature performance, low energy density and processing performance have largey limited its Factory practical applications.LiFe0.98M0.02PO4doped cathode materials were synthesized by two step solid state reation using the acetate of Co, Mn, Ni and Zn as doping soureces with aim to research the performance of LiFePO4at low temperature. The electrochemical measurements show that the Co-doped sample show the best performance at-20℃. This is attributed the fact that Co occupies the corresponding Fe site and weakenes the olivine structure, and that makes lithium ion esay access.To in situ synthesize carbon nanofibers coated LiMno.6Feo.4PO4of high energy density, first, the precursor was prepared by ball-milling iron phosphate, manganese acetate, lithium hydroxide and ammonium dihydrate phosphate followed by spray-drying, then the precursor was subjected to chemical vapor deposition (CVD) reactions at450℃in N2/C2H2and solid phase reactions at various temperatures. The results show that the sample prepared at600℃exhibits the best cycling performance among the other samples. After being cycled at1C for200times, a high specific capacity of98.1mAh/g can still be maintained.Our work mainly attempts to improve the poor processing performance of LiOH system sources through synthesizing the doped samples on5kg scale with Li2CO3as lithium source, which were prepared through high-energy ball-milling, spray drying and solid state reaction at700℃in rocking furnace. It shows that the doped samples synthesized by this process have good crystalline and homogeneous particle size distribution. The electrochemical measurements reveal that the sample doped with F(LFP-F) exhibits the best electrochemical performance when compared with the other two samples(LFP-F,Mg and LFP). the initial discharge capacity reaches145.1mAh/g, after50cycles at1C, the capacity still maintains120.4mAh/g, which reflects the good cycling performance.