LiMO sub(2) (M = Ni, Co) thin film cathode materials: a correlation between the valence state of transition metals and the electrochemical properties

The electronic properties of the LiMO sub(2) (M = Ni, Co) thin film cathode materials grown by RF sputtering/co-sputtering are in situstudied by X-ray photoelectron spectroscopy (XPS). Stoichiometric Li sub(1.0)Co sub(1.0)O sub(2) thin films deposited on a heated substrate at T= 500-550 degree C reveal the Co super(3+) (t sub(2g) super(6)e sub( g) super(0)) ground state configuration in the low spin (LS) state. Stoichiometry of the Li sub(x)(Ni,Co)O sub(2) films and the valence and spin states of the Ni ions depend strongly on the growth conditions. The electronic configuration of stoichiometric Li sub(1.0)Ni sub(0.5)Co sub(0.5)O sub(2) is described as the Ni super(3+) (t sub(2g) super(6)e sub( g) super(1)) LS and Co super(3+) (t sub(2g) super(6)e sub( g) super(0)) LS states. The Li-deficient Li sub(x)