| Summary: | 博士 === 大同大學 === 材料工程學系(所) === 101 === To promote the cathode material performances of lithium ion batteries, V-substituted LiFePO4 (LiFe1-xVxPO4, 0≤x≤0.10 and LiFe1-3y/2VyPO4, 0≤y≤0.05), Fe-substituted Li3V2(PO4)3 (Li3V2-yFey(PO4)3, 0≤y≤0.06), and LFVP/LVFP (LiFe0.97V0.02PO4/Li3V1.95Fe0.05(PO4)3) composite have been synthesized via a solution route in this study. These materials are characterized by ICP-OES, XRD and Rietveld methods. The oxidation states of the doped ions are examined by XAS. The morphology and the microstructure of the as-prepared powders are investigated by FE-SEM and FE-TEM. The electrochemical properties of powders are evaluated for both coin-type and pouch-type cells.
The results indicate V-substituted LiFePO4 system, the LiFe0.97V0.02PO4 (149 mAh g-1) not only reveals a higher capacity than that of LiFe0.95V0.05PO4 (148 mAh g-1) at initial cycle, but also a better rate performance at 1000 mAh g-1. For Fe-substituted Li3V2(PO4)3 system, Li3V1.95Fe0.05(PO4)3 cathode also demonstrates a better rate capability than that of the intrinsic Li3V2(PO4)3 and Li3V1.86Fe0.21(PO4)3. The LiFe0.97V0.02PO4 and Li3V1.95Fe0.05(PO4)3 materials with best performances are selected to prepare the composite system to optimize the capacities of Li ion battery. The ratio of 3 to 1 for LiFe0.97V0.02PO4 and Li3V1.95Fe0.05(PO4)3 shows not only the highest initial specific discharge capacity of 155.2mAh g-1 and lowest polarization at 100 mA g-1 in coin cell study, but also 98.3% capacity retention when comprised of MCMB cycling at current density of 100 mA g-1 after 50 cycles.
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