Surface film morphology (AFM) and chemical features (XPS) of cycled V2O5 thin films in lithium microbatteries

Sputtered vanadium pentoxide thin films have been used as positive electrode in lithium microbatteries and extensively studied after cycling over the 31st galvanostatic cycles by two complementary techniques, especially well-adapted for thin films analysis: X-ray photoelectron spectroscopy and atomic force microscopy. This study is mainly focussed on the characterization of the surface film (solid electrolyte interface-type) which is formed during subsequent discharges and charges and especially on its composition and its morphology that are changing during cycling. First, the growth of a surface layer between the positive electrode and the liquid electrolyte has been evidenced upon the discharge as well as its partial dissolution upon the charge. Secondly, the chemical and topographic changes of this interfacial layer at various stages of cycling are discussed in correlation with the evolution of the discharge capacity over cycles. (C) 2008 Elsevier B.V. All rights reserved.