Identifying the Distribution of Al³⁺ in LiNi_0.8Co_0.15Al_0.05O₂

The doping of Al into layered Li transition metal (TM) oxide cathode materials, LiTMO 2, is known to improve the structural and thermal stability, although the origin of the enhanced properties is not well understood. The effect of aluminum doping on layer stabilization has been investigated using a combination of techniques to measure the aluminum distribution in layered LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) over multiple length scales with 27 Al and 7 Li MAS NMR, local electrode atom probe (APT) tomography, X-ray and neutron diffraction, DFT, and SQUID magnetic susceptibility measurements. APT ion maps show a homogeneous distribution of Ni, Co, Al, and O 2 throughout the structure at the single particle level in agreement with the high-temperature phase diagram. 7 Li and 27 Al NMR indicates that the Ni 3+ ions undergo a dynamic Jahn–Teller (JT) distortion. 27 Al NMR spectra indicate that the Al reduces the strain associated with the JT distortion, by preferential electronic ordering of the JT lengthened bonds directed toward the Al 3+ ion. The ability to understand the complex atomic and orbital ordering around Al 3+ demonstrated in the current method will be useful for studying the local environment of Al 3+ in a range of transition metal oxide battery materials.