Surface Structure, Morphology, and Stability of Li(Ni1/3Mn1/3Co1/3)O2 Cathode Material

Layered Li(Ni_1-x-yMn_xCo_y)O₂ (NMC) oxides are promising cathode materials capable of addressing some of the challenges associated with next-generation energy storage devices. In particular, improved energy densities, longer cycle-life, and improved safety characteristics with respect to current technologies are needed. However, sufficient knowledge on the atomic-scale processes governing these metrics in working cells is still lacking. Herein, Density Functional Theory (DFT) is employed to predict the stability of several low-index surfaces of Li(Ni_1/3Mn_1/3Co_1/3)O₂ (NMC111) as a function of Li and O chemical potentials. Predicted particle shapes are compared with those of single crystal NMCs synthesized under different conditions. The most stable surfaces for stoichiometric NMC111 are predicted to be the non-polar (104), the polar (012) and (001), and the reconstructed, polar (110) surfaces. Results indicate that intermediate spin Co³⁺ ions lower the (104) surface energy. Furthermore, it was found that removing oxygen from the (012) surface was easier than from the (104) surface, suggesting a facet dependence on surface-oxygen vacancy formation. In conclusion, these results give important insights into design criteria for the rational control of synthesis parameters as well as establish a foundation on which future, mechanistic studies of NMC surface instabilities can be developed.