| Summary: | 碩士 === 國立雲林科技大學 === 環境與安全衛生工程系 === 105 === In order to improve the performance of lithium-ion battery, lithium iron phosphate (LiFePO4) cathode materials were modified with doped metal ion and coated carbon by co-precipitation method. We assessed the influence of adding cupric ions and magnesium ions as well as different doping ways on the electrochemical performance of LiFePO4 cathode material. The results of electrochemical characterization indicated that doping cupric ions and magnesium ions could enhance the charge/discharge capacity of LiFePO4 cathode material and showed no decay after cycle test. Its capacity retention rations were remained above 99 % after 100 cycle test. The LiFePO4 doped cupric ions showed better electrochemical performance than doped magnesium ions. The discharge capacities of LF0.99PMg0.01/C and LFPCu0.01/C sample at 10 C were 74 and 107 mAh/g, respectively. The cyclic voltammetry results showed that both LF0.99PMg0.01/C and LFPCu0.01/C obtained symmetrical redox curves. It indicated that Li+ in both samples had a great reversibility. Moreover, the X-Ray Diffraction spectra indicated that the crystal structure was still the same after coated carbon and doped ion. The particle morphology of LiFePO4 doped ions was analyzed by Scanning Electron Microscope and Transmission Electron Microscopy. The results showed that the LiFePO4 doped metal ions contained small interlinked-particle, and was also covered by carbon layer. The carbon content which was verified by Elemental Analysis of all samples was around 4.1 wt.% with the addition of glucose. Therefore, it could be confirmed that the excellent electrochemical performance was indeed caused by the doping metal ions as well as doping ways. The results confirmed that LiFePO4 composite cathode material obtained an excellent electrochemical performance.
|
|---|
