Influences of treatment temperature and water content on capacity and rechargeability of V2O5 xerogel films

V2O5 xerogel films prepared with spray deposition have been investigated for their lithium battery applications. The influences of spray deposition and postannealing temperatures on the water content, structure, and electrochemical performance of the films have been studied. Water contents of the V2O5.nH(2)O films depend on the deposition and postannealing temperatures. One film sprayed at 150degreesC and annealed at 190degreesC exhibited a large discharge capacity and the longest cycling life. By contrast, the films sprayed or annealed at high temperatures (>250degreesC) showed poor electrochemical performance. The film deposited at a substrate temperature of 420degreesC demonstrated structural features and electrochemical behavior of orthorhombic V2O5. X-ray diffraction patterns of the films treated at different temperatures reveal that removal of too much water at high temperatures results in crystallization or a small interlayer spacing, which may restrict the diffusion of lithium ions inside V2O5.nH(2)O films. V-51 solid-state nuclear magnetic resonance spectra show that the films annealed at low temperatures (i.e., 120degreesC or room temperature) have broad peaks and significant downfield isotropic chemical shifts, suggesting that the interlayered water produces a distorted square-pyramidal ligand field that may favor lithium intercalation and electron transfer within the matrix of the films. (C) 2003 The Electrochemical Society.