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 Al₂O₃ on a LiCoO₂ system is compared with that of a newly developed AlW_<i>x</i>F_<i>y</i> 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 Al₂O₃ and AlW_<i>x</i>F_<i>y</i> 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 LiCoO₂ particles coated with Al₂O₃ compared with that in particles coated with AlW_<i>x</i>F_<i>y</i>. The results show that proper design/choice of coating materials (e.g., AlW_<i>x</i>F_<i>y</i>) 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