Investigation of Aluminum Environments in Li-Ion Cathode NCA and Al-Doped NMC Via 27al MAS NMR Spectroscopy

Abstract

Application of aluminum based coatings and partial aluminum substitution for transition metals (doping) are commonly used in lithium ion batteries to improve electrochemical performance and chemical stability of the cathode systems by modifying the surface of cathode materials, increasing the operating voltages, enhancing thermal stability of the material, and reducing metal dissolution. However understanding the nature of surface and lattice aluminum environments or understanding possible aluminum diffusion in to the interphase have been a challenge for aluminum bearing Li-ion battery materials such as LiNi1-y-zCoyAlzO2 (NCA), aluminum doped LiNixMnyCozO2 (NMC) and coated layered metal oxides. 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is one of the few structural probes currently available that can qualitatively and quantitatively characterize lattice and non-lattice (i.e. surface, coatings, segregation, secondary phase etc.) aluminum coordinations. In the present study, we use NMR to gain new insights into transition metal (TM)-O-Al coordiations and evolution of lattice aluminum sites upon cycling. In each case, aluminum coordination of paramagnetic (lattice) and diamagnetic (non-lattice) nature have been investigated and their respective evolutions upon cycling reported.