Effect of washing on nickel-rich NCMs: methodology to quantify the lithium/proton-exchange kinetics, the inserted protons, and the structural changes

Abstract

The washing of cathode active materials (CAMs) for lithium-ion batteries (LIBs) to remove unwanted contaminants is of high importance in industrial CAM manufacturing. Nickel-rich NCMs (LiMO₂, M = Ni, Co, Mn), a family of commercial high-energy CAMs, are known for their detrimental reactivity with liquid/gaseous water; yet, insights on the kinetics of the occurring lithium/proton (Li⁺/H⁺) exchange are still lacking. To assess the Li⁺/H⁺ exchange, a set of five independent techniques is developed and employed to quantify its extent for a nickel-rich NCM (LiNi_0.83Co_0.12Mn_0.05O₂) as a function of the washing parameters. Using titration, prompt-gamma activation analysis, thermogravimetric analysis, temperature-dependent X-ray diffraction, and X-ray photoelectron spectroscopy, the proton content of washed NCM samples is determined, exploring the impact of washing time and water-to-CAM mass ratio. Furthermore, a highly protonated NCM (H_0.25Li_0.75Ni_0.83Co_0.12Mn_0.05O₂) is used to investigate the bulk properties, e.g., the change of lattice parameters and the spatial proton distribution, as well as the thermal decomposition of the protonated phase. The gained knowledge on the mechanism and the kinetics of the Li⁺/H⁺ exchange as well as on the decomposition mechanism of the protonated NCM phase is essential for the successful aqueous processing of nickel-rich CAMs, advancing the sustainable production of LIBs.