Distribution of intercalated lithium in V2O5 thin films determined by SIMS depth profiling

The distribution of Li in the V2O5 films was determined before and after intercalation/deintercalation electrochemical cycles by time of flight secondary ion mass spectroscopy (ToF-SIMS) depth profiling. On deintercalation most of the inserted Li is removed except in the vicinity of the interface with the fluorine-substituted tin oxide, used as a conducting substrate. More surprisingly, Li was also found in the interface region of the part of the film that has not been immersed in the electrolyte and that had thus not been electrochemically controlled. This finding suggests that Li diffuses through the interface, in the plane of the electrode surface, during intercalation of the main body of the film. The SIMS results have been confirmed by proton beam analysis using the nuclear reaction between H and Li to produce characteristic alpha particles that reveal the distribution of Li, both inside and outside the electrochemically treated area of the electrode. The energy loss of the alpha particles on their way through the sample to the detector also reveals the Li concentration distribution inside the V2O5 films. Copyright (C) 2006 John Wiley & Sons, Ltd.