First-principles study on the thermal stability of LiNiO₂ materials coated by amorphous Al₂O₃ with atomic layer thickness

Using first-principles calculations, we study how to enhance thermal stability of high Ni compositional cathodes in Li-ion battery application. Using the archetype material LiNiO₂ (LNO), we identify that ultrathin coating of Al₂O₃ (0001) on LNO(012) surface, which is the Li de-/intercalation channel, substantially improves the instability problem. Density functional theory calculations indicate that the Al₂O₃ deposits show phase transition from the corundum-type crystalline (c-Al₂O₃) to amorphous (a-Al₂O₃) structures as the number of coating layers reaches three. Ab initio molecular dynamic simulations on the LNO(012) surface coated by a-Al₂O₃ (about 0.88 nm) with three atomic layers oxygen gas evolution is strongly suppressed at T = 400 K. We find that the underlying mechanism is the strong contacting force at the interface between LNO(012) and Al₂O₃ deposits, which, in turn, originated from highly ionic chemical bonding of Al and O at the interface. Furthermore, we identify that thermodynamic stability of the a-Al₂O₃ is even more enhanced with Li in the layer, implying that the protection for the LNO(012) surface by the coating layer is meaningful over the charging process. Our approach contributes to the design of innovative cathode materials with not only high-energy capacity but also long-term thermal and electrochemical stability applicable for a variety of electrochemical energy devices including Li-ion batteries.