Stress and Electrochromism Induced by Li Insertion in Crystalline and Amorphous V2O5 Thin Film Electrodes.

Vanadium pentoxide thin films produced by reactive dc magnetron sputtering have different and peculiar electrochemical behavior in LiClO4-propylene carbonate solutions depending on the sputtering conditions which determine the film crystal structure. Deep charge-discharge cycles have been performed under constant current density and the thin film electrode potential, the mechanical stress and the optical transmittance have been followed in situ simultaneously. Close correlation has been noticed between the stress changes in the crystalline film and the electrode potential steps which are typical of the lithium insertion mechanisms in V2O5 cathode materials used in secondary lithium batteries. The irreversibility of the electrochemical processes and the amorphisation of the as-grown crystalline films have been described in comparison with the behavior of the V2O5 film electrodes which are amorphous from growth.