Local structure of dilute gallium ions in LiNi0.908Co0.085Ga0.003O2 cathode material -: In situ X-ray absorption study

We have utilized in situ'' X-ray absorption spectroscopy (XAS) to study the local atomic structure of dilute Ga dopants in LiNi0.908Co0.085Ga0.003O2 cathode material. We find that in the as-prepared material Ga3+ ions occupy Ni-type sites in the host lattice, as expected. On delithiation (charging), Ga migrates from octahedral Ni-type sites to interstitial tetrahedral sites. The high site preference of Ga3+ ions for tetrahedral sites leads to the stabilization of the Ga ions in these sites. We speculate that this migration of the Ga3+ ions suppresses the transfer of Ni to Li-type sites and also helps to maintain a single hexagonal phase by acting as pillaring ions during high states of charge. We suggest that the high stability of Ga in tetrahedral sites is at the origin of the significant improvement of the cycling and structural properties of Ga-doped cathode materials reported earlier by others. (C) 2002 The Electrochemical Society.