| LiFePO4has high theoretical capacity (170mAh/g), stable voltage (about3.4V vs. Li/Li+),good cycling performance, which signs that a new age of the lithium battery is coming. Because of the inherent limitation, LiFePO4has lower electronic conductivity and lithium ion diffusivity than some other lithium batteries, so LiFePO4has not been widely used in our life. How to improve the electronic conductivity and lithium ion diffusivity now becomes the research hotspot of Chemical power sources industry. There are two ways to improve the performance of LiFePO4.The first way is to coat LiFePO4with electronically conductive materials, such as carbon or some metals; the second way is to substitute Li or Fe by other metal ions to improve the electrochemical performance. The main contents of this thesis are followed:1LiFe0.8Mn0.2PO4was obtained by liquid co-precipitation reaction. XRD results confirmed that LiFe0.8Mn0.2PO4was Single-phase; SEM results showed that the particles of LiFe0.8Mn0.2PO4were uniform ellipsoid; DSC results combined with electrochemical performance analysis:the first discharge capacity of LiFe0.8Mn0.2PO4was122mAh/g, which was sintered at750℃, but the sample sintered at450"C had a considerably low first discharge capacity with a bad cycling performance indicated that the optimal calcination temperature was750℃.2With PEG as the carbon source, we prepared LiFe0.8Mn0.2PO4/C by liquid co-precipitation reaction. We found that when n(PEG):n(LFP)=0.5:1, LiFe0.8Mn0.2PO4/C had good electrochemical performance, and with the increase of molecular weight of PEG, LiFe0.8Mn0.2PO4/C also showed better electronic conductivity and lithium ion diffusivity.3We got LiFe0.6Mn0.4PO4by liquid co-precipitation reaction with the olivine orthogonal crystal structure. We studied that the impact of doping different content of Mn2+on the electrochemical performance of LiFe0.6Mn0.4PO4and also compared LiFe0.8Mn0.2PO4with LiFe0.6Mn0.4PO4on the structure, the morphology and the electrochemical performance. |
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