| LiMnPO4 and LiCoPO4 with olivine structure,which is similar to LiFePO4,are considered to be the promising next generation of power lithium ion battery cathode materials for higher potential and energy density than that of LiFePO4.But,their poor electrochemical performances attributed to their extremely low electronic conductivity and Li+ diffusion coefficient limit the commerialization.In this paper,LiMn1-xFexPO4?0?x?0.5?cathode materials were synthesizd by microwave solvothermal method,which were coated with carbon to form LiMn1-xFexPO4/C?0?x?0.5?.The crystal structure,morphology,crystal size,electrochemical properties,Li+diffusion coefficient of LiMn1-xFexPO4/C cathode materials with different Fe contents were investigated.The results indicated that the as-prepared LiMn1-xFexPO4 were solid solutions of LiMnPO4 and LiFePO4 with the sizes about 50-100 nm.Electrochemical tests showed that Fe substitution could significantly increase the initial specific capacity,cycle performance and rate capability,which attributed to the enhanced of Li+ diffusions.LiMn0.8Fe0.2PO4/C exhibited the highest reversible specific discharge energy,LiMn0.5Fe0.5PO4/C showed the best cycle performance with retention of 99.9%after 50 cycles at 0.5C.In chapter 4,LiCo1-xFexPO4/C?0?x?0.5?cathode materials were synthesizd by microwave solvothermal method.The influence of reaction time,the ratios of Li:P,calcination atmosphere and Fe contents on the crystal structure,electrochemical properties,Li+ diffusion coefficient of LiCo1-xFexPO4/C?0?x?0.5?have been investigated.The results indicated that the optimal reaction temperature is 200?,time is 20min,n?Li?:n?P?=3:1,calcination atmosphere is N2.Electrochemical tests showed that Fe substitution could significantly increase the initial specific capacity,coulombic efficiency,cycle performance and rate capability,which attributed to the enhanced of Li+ diffusions.LiCo0.6Fe0.4PO4/C exhibited the highest reversible specific discharge energy. |
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