Bifunctional Al₂O₃-Based Artificial Layers on LiNiO₂ Cathodes for High-Energy-Density Aqueous Li-Ion Batteries

Passivation films, commonly referred to as solid–electrolyte interphase and cathode–electrolyte interphase (CEI), are essential for the operation of rechargeable batteries due to their positive impact on electrochemical performances. This paper reports a bifunctional Al 2 O 3 artificial layer on a LiNiO 2 (LNO) cathode for high-energy-density aqueous Li-ion batteries (ALIBs). As determined by first-principles density functional theory calculations, Al 2 O 3 has a relatively high adsorption energy with H 2 O molecules at the surface, which is expected to effectively block their direct contact with the LNO surface. The electrochemical characteristics of LNO cathodes can be improved by coating an Al 2 O 3 layer, especially cyclability (capacity retention of ∼77.8% after 50 cycles), forming an effective CEI layer and providing stability to the LNO bulk structure. Particularly, the Al 2 O 3 layer undergoes an in situ modification to the more stable Al(OH) 3 in the aqueous electrolyte, which has an important role in producing a more effective CEI layer and suppressing the interfacial side reactions. This paper presents a promising approach for LNO-based cathodes for high-energy-density ALIBs, with a crucial methodology to enhance their electrochemical properties, even in conventional aqueous solutions.