Structural, morphological and electrochemical properties of nanocrystalline V_2O_5 thin films deposited by means of radiofrequency magnetron sputtering

摘要

Due to easiness of preparation and high energy density, V_2O_5 nanocrystalline thin films are particularly attractive as cathode materials for all-solid-state rechargeable lithium microbatteries. However, their electrochemical performances are strictly related to the film microstructure, which, in turn, is related to the nature and parameters of the deposition technique. For this reason, the preparation of thin films with reproducible electrochemical properties is still an open problem. Here, we report on the deposition of V_2O_5 crystalline thin films by means of reactive radiofrequency (r.f.) magnetron sputtering, using vanadium metal as the target. Different deposition times and substrate temperatures were adopted. X-ray powder diffraction (XRD) and atomic force microscopy were used to investigate the structural and morphological features of the films. In particular, XRD analysis revealed that the deposition parameters affect the crystallographic orientation of the films. A h00 orientation is observed in case of thin samples (about 100 nm) prepared at 300 C, whereas a 110 preferential growth is obtained for thicker films. Films deposited at 500 C display a 00 1 orientation irrespective on the deposition time. Reversible Li intercalation/deintercalation processes and high specific capacity are observed for the h 0 0-oriented V_2O_5 thinner films, with the ab plane arranged perpendicular to the substrate. In this case, the cycling behaviour is very promising, and a stable capacity higher than 300 mAh g~(-1) was delivered in the potential range 3.8-1.5 V at 1C rate over at least 70 cycles.