Amorphization as a Pathway to Fast Charging Kinetics in Atomic Layer Deposition-Derived Titania Films for Lithium Ion Batteries

Safe, reliable materials with fast charging kinetics are required to increase the power density of batteries in electric vehicles. One potential avenue for improving kinetics involves disturbing the electrode crystalline structure to alter diffusion properties. However, it remains controversial whether amorphization universally benefits intercalation kinetics, and the specific enhancement mechanisms with respect to the crystalline counterpart are often unclear. In this work, we systematically explore the effects of amorphization on Li+ intercalation kinetics using variable-thickness TiO2 films derived from atomic layer deposition. The amorphous films exhibit an order-of-magnitude faster Li+ diffusivity and >0.3 eV reduction in the effective Li+ migration barrier with respect to the crystalline anatase phase, resulting in superior high-rate capacity. To investigate the origin of this improvement, we perform a energy landscape, migration barriers, and diffusion rates in validated models of amorphous TiO2 using multiscale simulations. The range of site energies produced by the intrinsic structural disorder of amorphous TiO2 is found to generate low-barrier pathways for Li+ migration that penetrate some distance into the material, resulting in defined regions with faster diffusion behavior. We propose that the formation of these fast ion transport "highways" improves accessibility to interior sites, leading to significantly improved overall rate performance in the amorphous films. In addition to confirming the viability of amorphous TiO2 films as an alternative to crystalline layered materials for high-rate-performance energy storage, this work outlines a strategy for determining the conditions under which such performance might be realized in other similar materials.