Enabling Ambient Stability of LiNiO₂ Lithium-Ion Battery Cathode Materials via Graphene–Cellulose Composite Coatings

Abstract

Nickel-rich layered oxides are widely used as cathode materials for energy-dense lithium-ion batteries. These chemistries, based on the parent compound LiNiO2 (LNO), are highly sensitive to ambient environments and are known to readily react with moisture and carbon dioxide. As a result, impurities such as lithium hydroxides and lithium carbonates are formed at the LNO surface, compromising electrochemical behavior. Here, we address this issue by coating LNO cathode particles with a hydrophobic barrier layer composed of graphene and ethyl cellulose (GrEC). This coating limits contact between atmospheric moisture and the LNO surface, which minimizes the generation of lithium impurities. This scheme is evaluated by exposing coated LNO to humidified CO2 for 24 h as an accelerated ambient degradation test. Subsequent spectroscopy, microscopy, and electrochemical characterization show no detectable signatures of carbonates on the LNO surface, thus verifying that the GrEC coating prevents ambient degradation. By demonstrating this methodology for the ultimate nickel-rich chemistry, this approach can likely be generalized to a wide range of ambient-sensitive battery materials.