First-principles investigation of Al₂O₃ cathode coatings on Co and Ni-rich cathodes

We investigate the characteristics of atomic layer deposited (ALD) Al₂O₃ on LiCoO₂ cathode surfaces (LCO) using density functional theory and ab initio molecular dynamics (AIMD). The cathode+coating+electrolyte interfaces are simulated with varied Co-rich cathode orientations, lithiation, and the thickness of the coating. Organic electrolytes were explicitly modeled, composed of ethylene carbonate (EC)/dimethyl carbonate (DMC) (1:1), while LiBF₄ was included as a salt. We observe a more pronounced decomposition of electrolyte molecules on delithiated systems relative to lithiated surfaces and the initial signs of the formation of cathode-electrolyte interphase. Molecular O₂ had more propensity to evolve from the exposed cathode (012) surface, while it was more uniform for coated surfaces. Dehydrogenation of electrolyte molecules close to the exposed surface was more prevalent. O₂ formation within the cathode-coating interface was observed for the (012) surface. Charge analysis using the DDEC6 method revealed that the coating of the cathode consistently preserves the charge of surface Co atoms closer to the charge of bulk Co, otherwise significantly different on the exposed side. We also report on the mechanisms of ALD deposition of Al₂O₃ on Ni-rich cathodes. Our work highlights the applicability of combining AIMD and DFT approaches to guide the design of innovative cathode coatings.