| Recently, olive LiFePO4has been a research focus of cathode materials due to its low cost, environmental benignity, high-safety, long cycle life and high theoretical capacity. However, the major drawback of LiFePO4is its poor high-rate capability mainly caused by its intrinsic low electronic conductivity and lithium-ion diffusion. In this work, LiFePO4has been successfully synthesized by solid-state reaction and hydrothermal technique. The effect of surface modification or doping on electrochemical performances was systematically investigated, especially at high current density and elevated temperature.The experimental results reveal that the single-phase LiFePO4crystals were obtained without any impurity via hydrothermal process and the particles have small sized and distributed uniformly. The rate performances of LiFePO4are remarkably improved with incorporation of Si nanoparticles at elevated temperature and (LiFePO4)98(Si)2exhibits best reversible capacity (145mAhg-1at0.2C) and capacity retention (95.2%at60℃).LiFe1-xMxPO4/C (M=Mn, Ni) composites as a function of M content are prepared by solid state reaction. It is found that LiFe0.98Mn0.02PO4/C composite shows the highest reversible capacity of165mAh·g-1at0.2C rate. In the case of Ni-doping, the cell parameters of Ni2+-doped LiFePO4/C decreases with the increase of Ni2+content. The other phase forms in LiFe1-xNixPO4/C composites at high Ni2+content, resulting in the deterioration of electrochemical performances. LiFe0.9Ni0.1PO4/C demonstrates the best rate performance and reversible capacity (160mAh·g-1at0.2C).LiFePO4/(Sn+C) composites were successfully prepared by chemical plating procedure. The results indicated that the tin and carbon co-coating on LiFePO4surface can improve the electrode conductivity, resulting in enhancing rate performances and cycle stability of LiFePO4in a wide operation temperature range. Keywords:Lithium ion battery; LiFePO4; Solid-state reaction; Hydrothermal; Doping; Surface modification... |
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