Self-Terminated Artificial SEI Layer for Nickel-Rich Layered Cathode Material via Mixed Gas Chemical Vapor Deposition

Because of the higher specific capacity, nickel-rich layered cathode material has received much attention from the lithium-ion battery community. However, its cycle life is desired to improve further for practical applications, and unstable interface with electrolyte is one of the main capacity fading mechanisms. Here, we report a facile chemical vapor deposition process involving mixed gases of CO<sub>2</sub> and CH<sub>4</sub>, which yields thin and conformal artificial solid-electrolyte-interphase (SEI) layer consisting of alkyl lithium carbonate (LiCO<sub>3</sub>R) and lithium carbonate (Li<sub>2</sub>CO<sub>3</sub>) on nickel-rich active cathode powder. The coating layer protects from side reactions and improves the cycle life and efficiency significantly. Remarkably, the coating process is self-terminated after the thickness reaches ∼10 nm, leading to the coating layer to account for only 0.48 wt %, because of the growing binding energy between the gas mixture and the surface products. The self-termination is characterized by various analytical tools and is well-explained by density functional theory calculations. The current gas phase coating process should be applicable to other battery materials that suffer from continuous side reactions with electrolyte.