Stoichiometrically driven disorder and local diffusion in NMC cathodes

Major structural differences in lithium nickel manganese cobalt oxides (NMC) prepared under identical conditions have been uncovered using neutron powder diffraction. Sample NMC-622 was obtained as a single R 3&cmb.macr; m crystal structure with little defects, whereas NMC-811 showed significant Li deficiency and NMC-433 formed three distinct phases; ordered R 3&cmb.macr; m , disordered R 3&cmb.macr; m and a C 2/ m phase. Local diffusion behaviour was also studied by muon spin relaxation (μSR). It was observed that single phase R 3&cmb.macr; m NMC-622 showed a higher lithium diffusion coefficient (4.4 × 10 −11 cm 2 s −1 ) compared to lithium deficient NMC-811 (2.9 × 10 −11 cm 2 s −1 ), or the highly disordered NMC-433 (3.4 × 10 −11 cm 2 s −1 ). Furthermore, activation energies for the Li diffusion process were estimated to be 58 meV, 61 meV and 28 meV for NMC-811, NMC-622 and NMC-433, respectively. Neutron powder diffraction has uncovered major stoichiometry-driven structural differences in NMC cathodes otherwise obscured in lab-based X-ray powder diffraction. The atomic scale Li diffusion has also been probed by muon spin relaxation.