Study On The Preparation And Modification Of LiFePO₄/Cathode Materials

LiFePO4 as a cathode material for lithium ion batteries has arouse much interest because of its excellent properties such as higher specific capacity,better cyclic stability and much cheaper cost comparing with other cathode materials. With the purpose of studying the techniques on the sample preparations and improving the electrochemical properties, researches in the following aspects were done for different samples by using high temperature solid state methodFeC2O4·2H2O as raw materials for Fe source to prepare LiFePO4 is much better than FeCl2, from which the LiFePO4 sample showed higher degree of crystallinity, better high rate ability and electrochemical stability than that from FeCl2. Meanwhile, the sample got smaller cell volume and higher discharge capacity while it prepared on the condition with ball-to-weight ratio at 10:1 and with the sintering temperature at 660℃. It keeps 87.5 mAh·g-1 of discharge capacity even after 400 cycles at 10 C.In the study of Mn-doped LiFePO4/C, the doped sample show better performances when the doped amount is 6mol%, which showed better cyclic ability and high rate ability, with discharge capacity 135mAh·g-1 at 0.2 C and 100 mAh·g-1 at 3C. The discharge capacities of the 6mol% Mn doped LiFePO4 material with 22 sintering hours are 140, 134, 105mAh·g-1 at 0.1 C,0.2 C,3 C, respectively.The materials got improvement in electrochemical properties and without much change in crystal structure while using Na and Ni partial substituted Li and Fe of LiFePO4/C,respectively. Material prepared with NaCMC showed excellent electrochemical properties, especially in impedance and high rate ability. For Ni doped LiFePO4/C study, the material with 138.15 mAh·g-1 of discharge capacity,8.1×10-3 mA·cm-2 of exchange current density when doped amount is 9mol%.The material which doped by Na and Ni could cover the shortage of poor high rate ability in only Na doped and worse cyclic ability in only Ni doped.In the study of Zr doped LiFePO4, ZrO were found in 6mol% and 9mol% samples as the amount of Zr could doped into LiFePO4 is limited. Among all doped materials,6mol% showed best electrochemical properties as its highest discharge capacity and best cyclic stability.While using Al to modified the LiFePO4, we found that discharge capacity decrease with the increase of Al amount. FePO4were found in the A15wt% and7.5wt% samples, which was bad for Li+ insertion/extraction during the reaction process.The diffusion rate of Li+ increase while the discharge capacity decrease Zr doped LiFePO4 material when modifield byAl...