Transition from ideal statistics to interactions by host distortion in the intercalation thermodynamics of Li into amorphous WO3 films of varying thickness

We studied the effect of the intercalant–host interaction in homogeneous a-LixWO3 by electrochemical experiments in films of different thickness (100–400 nm) prepared by electron beam evaporation. The intercalation thermodynamics was derived from the analysis of the chemical capacitance (proportional to the derivative of the composition x with respect of the chemical potential, ∂x/∂μ). It was found that thinner films can be modeled by the ideal statistics of a dilute solution (non-interacting lattice gas), while host–guest interactions are the determining factor for the electrode performance in case of thicker films (> 200 nm).