Stoichiometrically driven disorder and local diffusion in NMC cathodes

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2021-04, Vol.9 (16), p.1477-1486
• Main Authors: Ashton, Thomas E, Baker, Peter J, Sotelo-Vazquez, Carlos, Footer, Charles J. M, Kojima, Kenji. M, Matsukawa, Takeshi, Kamiyama, Takashi, Darr, Jawwad A
• Format: Article
• Language: English
• Subjects: Cathodes; Cobalt; Cobalt oxides; Crystal defects; Crystal structure; Diffusion; Diffusion coefficient; Lithium; Manganese; Muon spin relaxation; Neutron diffraction; Nickel
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d1ta01639c

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.