Structure Solution of Metal-Oxide Li Battery Cathodes from Simulated Annealing and Lithium NMR Spectroscopy

Discerning the arrangement of transition metal atoms in Li­[Ni x Mn y Co z ]­O2 cathode materials has remained an open problem for many years despite the commercial importance of some stoichiometries and the even more promising characteristics of others. We present a method for structural determination in this class of cathode materials. A simple definition of the total energy, based on the chemical principle of electroneutrality, is used in combination with a simulated annealing algorithm to generate model structures. The method reproduces the well-known structure of Li­[Li1/3Mn2/3]­O2 and produces structures of the disordered Li­[Ni x Mn x Co1–2x ]­O2 phases (where x = 0.02, 0.1, 0.33) that are verified by detailed 7Li NMR spectra. For each Li­[Ni x Mn x Co1–2x ]­O2 phase, the solution is found to be heavily disordered, yet retaining significant ion pairing. Since the underlying notion of favoring charge-neutral regions is generic, we anticipate its utility in a much broader family of materials.