Atomic Layer Deposition of Al–W–Fluoride on LiCoO2 Cathodes: Comparison of Particle- and Electrode-Level Coatings

Atomic layer deposition (ALD) of the well-known Al 2 O 3 on a LiCoO 2 system is compared with that of a newly developed AlW x F y material. ALD coatings (∼1 nm thick) of both materials are shown to be effective in improving cycle life through mitigation of surface-induced capacity losses. However, the behaviors of Al 2 O 3 and AlW x F y are shown to be significantly different when coated directly on cathode particles versus deposition on a composite electrode composed of active materials, carbons, and binders. Electrochemical impedance spectroscopy, galvanostatic intermittent titration techniques, and four-point measurements suggest that electron transport is more limited in LiCoO 2 particles coated with Al 2 O 3 compared with that in particles coated with AlW x F y . The results show that proper design/choice of coating materials (e.g., AlW x F y ) can improve capacity retention without sacrificing electron transport and suggest new avenues for engineering electrode-electrolyte interfaces to enable high-voltage operation of lithium-ion batteries.