Lithium diffusion in LixCoO2 (0.45 < x < 0.7) intercalation cathodes

Mass transport and thermodynamic properties of LixCoO2 were studied by the potentiostatic intermittent titration technique (PITT). We determined the chemical diffusion coefficient ((D) over tilde (Li)) and the thermodynamic factor (Theta) of Li in the region 0.45 < x < 0.7, where LixCoO2 exists as a single phase having either a rhombohedral or a monoclinic structure. Solid-state thin-film batteries were used in order to ensure a well-defined diffusion geometry. Both (D) over tilde (Li) and Theta have minima at the phase boundaries of the Li vacancy ordered phase Li0.5CoO2. The self-diffusion coefficient of Li (D-Li) has a minimum at x = 0.5 associated with the Li vacancy ordering. As the degree of ordering increases, nonmonotonic variations of (D) over tilde (Li), Theta, and D-Li become more pronounced when approaching x = 0.5 in LixCoO2. (C) 2001 The Electrochemical Society.