Nonstoichiometric Lithium Iron Phosphate Synthesized by Hydrothermal Route
Lithium iron phosphate with varied Fe/P molar ratio was synthesized from LiOH, FeSO4, and H3PO4 by hydrothermal route at 180°C for 6 h. The samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), chemical analysis, and constant current charge-discharge cycling test. It was found that at the same pH value of reaction, the Fe/P ratio had a major effect on the content of impurity phase, crystal structure and electrochemical performance of the samples. However, it had a minor effect on the morphology of the samples. A single phase structure was obtained for the samples with the Fe/P ratio of 0.97-1.02. The sample with the Fe/P ratio of 0.97 exhibited the best electrochemical behaviors, whose specific discharge capacities could reach 152.7, 144.8 and 133.2mAhg-1 at 0.2C, 1C and 5C rate, respectively, with the capacity retention rate close to 100% after 50 cycles at 5C. It is believed that the excellent electrochemical performance of specific discharge capacity, rate capability and cycling stability is attributed to the nonstoichiometry of LiFePO4, which results in the Li-rich defective crystal structure and the decrease of cell parameters, thus facilitating the discharge behaviors at high rates.
Jinsheng Liang and Lijuan Wang
X. Q. Ou et al., "Nonstoichiometric Lithium Iron Phosphate Synthesized by Hydrothermal Route", Advanced Materials Research, Vol. 178, pp. 118-123, 2011