Electrochemical lithium insertion in sol-gel crystalline vanadium pentoxide thin films

The electrochemical lithium insertion into sol-gel crystalline vanadium pentoxide thin films has been investigated. An appropriate heat-treatment of the viscous V2O5 gel spread on platinum yields the formation of thin crystalline V2O5 films (1-3 mu m thick). Up to 1.8 Li ions can enter the oxide lattice at a 2 V cut-off voltage. The electrochemical performances (capacity, reversibility, kinetics) of the crystalline film compare well with that known for a composite electrode including oxide powder, carbon and a binder. However, preliminary cycling tests show the structural changes occurring during the Li insertion-extraction for 0 < x < 1 have a detrimental effect on the cycle life, probably due to a loss of adherence of the film to the substrate. The kinetics of the Li insertion reaction is studied by ac impedance spectroscopy for 0 < x less than or equal to 0.7. The chemical diffusion coefficient of lithium D-Li varies in the range 6 x 10(-10)-2 x 10(-11) cm(2) s(-1). The dependence of D-Li on the composition of the LixV2O5 film is discussed in relation with XRD data obtained on electrochemically inserted films. (C) 1998 Elsevier Science Ltd. All rights reserved.