We examined the oxidation state and atomic structures of Ni and Co in LiNi0.3Co0.7O2 and compared them with those of LiNiO2 and LiCoO2. The X-ray absorption near-edge structure and extended X-ray absorption fine structure results show that Ni (primarily ) and Co are present with an oxidation state of +3. Ni (III) in LiNiO2 has a distorted octahedral coordination due to an active Jahn-Teller effect as shown previously. However, Ni (III) in LiNi0.3Co0.7O2 has a regular octahedral coordination with six oxygen atoms at a distance of 1.913 angstrom and, hence, the Jahn-Teller effect is inactive. The oxidation state and local atomic structure of Co in LiNi0.3Co0.7O2 are similar to those of LiCoO2. (c) 2005 The Electrochemical Society.