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This study investigates a root cause of the improved rate performance of after metal doping to Fesites. This is because the metal doped /C maintains its initial capacity at higher C-rates than undoped one. Using /C and doped /C (M=, , ), which are synthesized by a mechanochemical process followed by one-step heat treatment, the Li content before an...
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... pro- files showed pure phases with an ordered olivine structure and the secondary phases such as Fe 2 p and Li 3 PO 4 were not detected. The lattice parameter obtained from the samples showed slightly changed (Table 1), which indicated that Fe ion might be substituted by M ion (M=Al, Cr, Zr). ...
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... 14,15 Although many publications report the feasibility of aliovalent doping (e.g. Mo 6+ , Ti 4+ , Al 3+ , Zr 4+ ) and its beneficial role on the electrochemical properties of LiFePO 4 , [16][17][18][19][20] this issue is still under debate due to conflicting results. [21][22][23] Some authors observed that the improved electronic conductivity after metal doping may arise from carbon contamination 24 or phosphides formation. ...
A series of Li1-xFe1-xVxPO4/C (with 0≤x≤0.1) samples have been synthesized using a wet chemistry method and characterized via Rietveld structure refinement of powder X-ray diffraction data. The amount of impurities is negligible up to x = 0.07, whereas for higher V content also Li3V2(PO4)3 phase is formed in minor quantities. The unit cell parameters of the olivine phase undergo anisotropic variations that cause an overall decrease of the unit cell volume with increasing Vanadium content. Structural data suggest that V enters the olivine lattice substituting for Fe. Compared with those of pure LiFePO4, V doped compounds have higher specific capacities especially at high rates delivering about 100 mAhg−1 at 10C rate. Local geometry and oxidation state of Fe and V in cycled electrodes was determined by X-ray absorption spectroscopy at the Fe and V K-edge. The data demonstrate that V is trivalent in both the oxidized and reduced electrodes meaning that V does not participate to the redox process. However, with increasing the vanadium content in the LiFePO4 lattice, the amount of Fe that reversibly oxidizes and reduces during battery cycling increases with an enhancement of the electrochemical performances.
The new ZnAl2O4-coated LiFePO4 (LFP) electrode was prepared via polypropylene glycol-assisted sol-gel method and investigated as a cathode material in Li-ion batteries. The pure LFP and ZnAl2O4-coated LFP electrodes were characterized using XRD, HRTEM, FESEM/EDS/mapping and XPS techniques. XRD data affirmed the creation of LFP phase with good crystallinity. TEM revealed that the pure LFP and ZnAl2O4-coated LFP electrodes crystallized with spherical-like shape. However, the ZnAl2O4-coated LFP electrode offered greater crystallite size than that of pure LFP electrode. The typical atomic state of these electrodes was examined through XPS. Additionally, EDS analysis provided an actual evidence for the visualization mapping of each element, signifying the success of coating process on the surface of LFP electrodes. Furthermore, the ZnAl2O4@LFP electrode demonstrated higher charge and discharge capacities ~ 122 and 95 mAhg⁻¹, respectively. The coulombic efficiency of ZnAl2O4@LFP electrode was significantly enhanced from 80% in the 1st cycle to 99.8% in the 8th cycle, indicating excellent stability over the following cycles. Accordingly, the ZnAl2O4 layer played a vital role for improving the structural stability and electrochemical performance of a LFP cathode. Combined with the admirable electrochemical performance of ZnAl2O4@LFP, this will attract the interest for the future development of potential cathode materials.
We synthesized Nb-doped LiFePO4 /C nano composite cathode materials by mechanochemical activation followed by a single step calcination. The starting chemicals of Li2 CO3 , FeC2 O4 .2H2O, NH4 H2 .PO4 and C6 H8 O7 as lithium, iron, phosphate, and carbon sources are mixed in a high energy ball mill 250 rpm, 5h and calcined at 650 °C and 10 hours. The resultant materials are structurally XRD, SEM, TEM and electrochemically characterized and high purity LiFePO4 with high electrochemical performance is obtained. Voltage vs. specific capacity, discharge capacity vs. cycle number in manufactured battery is presented. An initial specific discharge capacity of 153 mAhg−1 and a specific discharge capacity of 128.4 mAhg−1 after the 8th charge/discharge cycling at 1C is recorded.
