From Dense to Nanostructured Thin Film Anodes: Boosting Li-Ion Accessibility in TiO2 Thin Film Electrodes

Abstract

Dense TiO2 thin-film electrodes suffer from limited electrolyte penetration and restricted Li-ion transport, making the electrode architecture a critical parameter for efficient charge storage. Herein, glancing-angle deposition (GLAD) combined with reactive magnetron sputtering is used to engineer ion-accessible TiO2 nanocolumnar architectures without compositional modification or postprocessing. Kinetic Monte Carlo simulations guided the selection of substrate tilt and azimuthal rotation conditions to control the column orientation, intercolumnar spacing, and open porosity. The predicted morphologies were subsequently validated by electron microscopy for the experimentally deposited thin films. Electrochemical measurements show that GLAD-engineered electrodes deliver up to approximately 4-fold higher areal capacitance than dense TiO2 films. ToF-SIMS depth profiling further reveals that Li species remain largely concentrated near the surface of dense films. In contrast, the GLAD-engineered nanocolumnar architecture allows for a more uniform Li distribution throughout the electrode depth. These results establish morphology-controlled ion accessibility as the primary origin of the enhanced electrochemical response.