Li Diffusion and High-Voltage Cycling Behavior of Thin-Film LiCoO2 Cathodes

Mass transport and thermodynamic properties of Li(sub x)CoO(sub 2) were studied by the potentiostatic intermittent titration technique (PITT) using solid-state thin-film batteries that provide a well-defined diffusion geometry. Both the chemical diffusion coefficient and the thermodynamic factor have minima at the phase boundaries of the Li/vacancy ordered phase ''Li(sub 0.5)CoO(sub 2)''. The self-diffusion coefficient of Li has a minimum at x= 0.5 associated with the Li/vacancy ordering. As the degree of ordering increases, the nonmonotonic variations become more pronounced when approaching x= 0.5 in Li(sub x)CoO(sub 2). We also show that thin-film LiCoO(sub 2) cathodes having grains of sub-micrometer size combined with the Li upon electrolyte exhibit excellent capacity retention when charged up to 4.5 V