Implications of Aqueous Processing for High Energy Density Cathode Materials: Part II. Water-Induced Surface Species on LiNi_0.8Co_0.15Al_0.05O₂

Aqueous electrode manufacturing of nickel-rich layered oxide cathode materials poses a significant challenge due to their high water sensitivity. LiNi_0.8Co_0.15Al_0.05O₂(NCA) has been shown to be particularly sensitive not only to water during processing, but also ambient air. In an effort to further clarify the processes that occur when NCA is in contact with water, the active material was investigated after different durations of water exposure. The results show that a differentiation has to been made between the surface impurities already present on NCA in the pristine state, water-induced surface species and water-induced leached species. The results demonstrate that the water-induced surface species can be mainly attributed to chemisorbed CO₂, nickel carbonate and NiOOH-like species but also smaller amounts of newly-formed aluminum and cobalt compounds. The water-induced leached species were assigned to lithium and aluminum-containing species. Water-induced surface species lead to a severe deterioration of the cells due to the resistive nature of these moieties and their involvement in side reactions during cycling. It is essential to find ways to suppress the formation of these species for the successful implementation of aqueous processing for NCA and likely nickel-rich cathode materials in general.