Analysis of thin-film lithium batteries with cathodes of 50 nm to 4 μm thick LiCoO2

Discharge properties of more than 40 Li–LiCoO2 solid-state thin-film batteries with cathode film thickness from 50 nm to 4 μm have been examined with respect to the lithium diffusion in the cathode. For all but the thinnest cathodes or very low current densities, the discharge capacity from 4.2 to 3.0 V is limited by the lithium diffusivity in LixCoO2 and the ultimate formation of a resistive layer at the interface as x approaches 1.0. Measurements of the equilibrium open circuit potential and ac impedance upon deep discharge support this model. Promoting a higher diffusion for the 0.96