Li ions segregated on anatase powders: Surface excess and ionic conductivity in the natural adsorbed water

The exploration of doped titanium dioxide (TiO₂) materials presents significant potential for advancing technologies in energy storage, catalysis, and electronics. Among various dopants, lithium (Li) ions have attracted considerable interest due to their role in lithium-ion batteries. However, the understanding of lithium-ion distribution within the bulk and at the interfaces (surface and grain boundaries) of anatase TiO₂ nanoparticles remains limited and poorly understood. The lithium concentrations examined in this study were 0.0, 0.7, 3.2, 6.5, and 16.7 mol%. The specific surface area increased notably for lithium concentrations above 3.2 mol%, indicating the segregation of lithium ions on the TiO₂ surface. This segregation was demonstrated using several techniques, including x-ray photoelectron spectroscopy, nuclear magnetic resonance (NMR), and diffuse reflectance infrared Fourier transform spectroscopy (FTIR-DRIFT). NMR, in particular, provided novel insights into the proportions of lithium segregated on the surface and at grain boundaries. Impedance spectroscopy measurements revealed that overall electrical conductivity increases proportionally with the excess of lithium ions on the surface, whereas it decreases in dry atmospheres. This suggests that the segregated lithium ions dissolve in the naturally adsorbed water layer on the nanoparticle surfaces, contributing to ionic conductivity. This study offers valuable insights into the effects of lithium distribution in the nanostructure of TiO₂.