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

Abstract

The electrochemical lithium insertion into sol-gel crystalline vanadium pentoxide thin films has been investigated. An appropriate heat-treatment of the viscous V 2O 5 gel spread on platinum yields the formation of thin crystalline V 2O 5 films (1–3 μm 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≤0.7. The chemical diffusion coefficient of lithium D Li varies in the range 6×10 −10–2×10 −11 cm 2 s −1. The dependence of D Li on the composition of the Li x V 2O 5 film is discussed in relation with XRD data obtained on electrochemically inserted films.