Hybrid Coating Of LiMnPO₄ Cathode Material And Preparation Of LiFe_xMn_1-xPO₄ By Hydrothermal Method

The olivine structure Li MnPO₄ is intensively studied nowadays and becomes one of the most promising new generation cathode materials for rechargeable lithium batteries owing to its low cost,environmental-friendliness,high theoretical discharge capacity and superior potential energy density.However,it suffers from intrinsically low ionic and electronic conductivity which hinder its further application,we try to solve this problem by hybrid coating layers of C&AlPO₄ and C&ZrO₂.We attempt to synthesize the Li Fe_xMn_1-xPO₄ solid solution which combines the both advantages of LiMnPO₄ and Li FePO₄.The LiMnPO₄/C and LiMnPO₄/?C&AlPO4?composite cathode materials with different AlPO₄ content?0.25wt.%,0.5wt.%,1wt.%?are attained by hydrothermal method followed by wet ball-milling.The initial discharge capacity of the above four samples is 144.9?148.7?153.9?146.4 mAhg^-1 respectively at 0.1C rate,the discharge of the 50^th cycle is 131.9?140.3?148.7?135.7 mAhg^-1,with capacity retention of 91.0%?94.1%?96.6%?92.7%respectively.Besides,the initial discharge capacity of ZrO₂?0.5wt.%?-LiMnPO₄/C,synthesized by the same method as LiMnPO₄/?C&AlPO₄?is 151.9 mAhg^-1,the capacity retention after 50 cycles at 0.1C rate is 97.7%,exhibiting a superior electrochemical performance compared with LiMnPO₄/C.Li Fe_0.85Mn_0.15PO₄/C composite is prepared by hydrothermal method,and the optimum condition is obtained by discussing the effects of the molar ratio of water and DEG,the hydrothermal time,the calcination temperature and the calcination time on the morphology and the electrochemical performance of LiFe_0.85Mn_0.15PO₄/C composite.Then the LiFe_xMn_1-xPO₄/C solid solution with different manganese content?1-x=0.10,0.15,0.20,0.25?is obtained under the above optimal condition.The results show that the nanoscale Li Fe_0.85Mn_0.15PO₄/C composite with the molar ratio of 3,the hydrothermal time of 24h,the calcination temperature of 550?and the calcination time of 3h has the best electrochemical performance.The Li Fe_0.85Mn_0.15PO₄/C synthesized under the optimum condition delivers the highest initial discharge capacity of 155.5mAhg^-1.