Thin, uniform, and conformal coatings on the active electrode materials are gaining more importance to mitigate degradation mechanisms in lithium-ion batteries. To avoid polarization of the electrode, mixed conductors are of crucial importance. Atomic layer deposition (ALD) is employed in this work to provide superior uniformity, conformality, and the ability to precisely control the stoichiometry and thickness of the desired coating materials. We provide experimental and computational guidelines for the need of mixed electronic and ionic conducting coating materials, especially in the case where highly uniform and conformal coatings are achieved. We report promising results for ALD-deposited protective films achieved by doping fluorine (F) into a lithium vanadate coating. The F-doped lithium vanadate coating at the optimal doping level exhibits an electrical conductivity of 1.2 × 10-5 S·cm-1. Density functional theory calculations corroborate enhanced mixed electronic and ionic conduction in F-doped lithium vanadate through band structure analysis and climbing-image nudge elastic band (CI-NEB) calculations. It has been demonstrated that the experimentally determined optimal doping concentration aligns well with that predicted by density functional theory calculations. CI-NEB calculations have shown that the activation energy for lithium-ion transport was the lowest for optimally doped lithium vanadate.
Keywords: cathode materials; fluorine-doping; functional coatings; lithium batteries; mixed ionic and electronic conductors.