Role of lithium intercalation in fluorine-doped tin oxide thin films: Ab initio calculations and experiment

Using a combination of experimental techniques and density functional theory (DFT) calculations, the influence of lithium insertion on the electronic and electrochemical properties of fluorine-doped SnO₂ (FTO) is assessed. For this purpose, we investigate the electrochromic behavior of a commercial FTO electrode embedded in a solution of lithium perclorate (LiClO₄). The electrochromic properties are evaluated by UV-vis spectroscopy, cyclic voltammetry, and chronoamperometry. These tests show that FTO exhibits electrochromism with a respectable coloration efficiency (η = 47.9 cm²/C at 637 nm). DFT study indicates that lithium remains ionized in the lattice, raising the Fermi level about 0.7 eV deep into the conduction band. X-ray photoelectron spectroscopy (XPS) is used to study chemical bonding and oxidation states. XPS analysis of the Sn 3d core levels reveals that lithium insertion in FTO induces a shift of 350 meV in the Sn 3d states, suggesting that lithium is incorporated into the SnO₂ lattice.