| 초록 |
In a number of Li intercalation compounds in which an ordered array of Li is usually maintained, the control of point defects including cation disordering is of major significance for application to electrodes in rechargeable cells. Furthermore, as the chemically different environment induced by point defects leads to breaking of the ordered arrangement of atoms in crystals with a complex structure, mass and charge transport behaviors are also considerably affected by the presence of the defects. A variety of investigations on Li vacancies and cation intermixing have been reported for layered oxides. In contrast, few experimental details revealing the atomic-scale point defects in olivine-type lithium metal phosphates, LiMPO4 (where M = Fe, Mn, Ni, Co), available in the literature, while these phosphates have attracted a great deal of attention as alternative cathode materials in Li-ion cells over the past decade. Proper control and direct identification of their distribution in the lattice on the basis of crystal chemistry will be crucial steps toward enhancement of effective Li mobility during the intercalation reaction in olivine phosphates. In this presentation, the observations of a variety of lattice defects in ordered olivine LiFePO4 crystals after rapid phase transformation during crystallization are presented, showing notable distribution behaviors of the defects. For this direct observation, in siu and ex situ HREM and HAADF-STEM is utilized. This analysis suggests that the lattice defects in LiFePO4 can be adjusted for improved Li ion transport. |
