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exhibits various crystal systems, such as orthorhombic , tetragonal , and monoclinic , among which synthesized at is commercially used as a cathode material of the lithium ion battery. The battery performances depended on the structure of , and the synthesized at exhibited an excellent cycling performance with a large discharge capacity of . The structural variations of during electrochemical reaction were examined. The in situ synchrotron radiation-X-ray diffraction (XRD) measurement indicated that - and maintain their original crystal lattices, accompanying a small change in the cell volume even after the Li intercalation. The in situ X-ray absorption fine structure (XAFS) analysis of - and revealed that the continuous variation from to took place during the intercalation process. A significant rearrangement of the Nb–O octahedra accompanied by the change of Nb–O and Nb–Nb interactions occurred in both structures with Li intercalation. XRD and XAFS data suggests that the two-dimensional layer structure of seems to be more flexible regarding the Li intercalation compared with the three-dimensional structure of . This may account for the better cyclic performance of the former material as the electrode material.
Kodama et al. (Sun,) studied this question.