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The defense date of the thesis is 2013-08-29
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URN etd-0829113-003920 Statistics This thesis had been viewed 2509 times. Download 0 times. Author Mao-Sung Chen Author's Email Address email@example.com Department Materials Engineering Year 2012 Semester 2 Degree Ph.D. Type of Document Doctoral Dissertation Language English Page Count 193 Title Preparation and Characterization of Composite LiFePO4/Li3V2(PO4)3 cathode materials Keyword discharge capacity cathode material lithium ion battery V-substituted LiFePO4 Fe-substituted Li3V2(PO4)3 composite materials composite materials Fe-substituted Li3V2(PO4)3 V-substituted LiFePO4 lithium ion battery cathode material discharge capacity Abstract 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.
Advisor Committee She-huang Wu - advisor
Jeng-Yu Lin - co-chair
Nae-Lih Wu - co-chair
Ru-Shi Liu - co-chair
Yi Hu - co-chair
Files Date of Defense 2013-07-31 Date of Submission 2013-08-29