Theoretical insights on alleviating lattice-oxygen evolution by sulfur substitution in Li1.2Ni0.6Mn0.2O2 cathode material

Abstract

Here, we demonstrate that the lattice oxygen release on the high-capacity cathode, Li1.2Ni0.6Mn0.2O2 (LNMO) surface can be successfully suppressed through S-anion-substitution using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The oxygen evolution mechanisms on pristine and sulfur (S)-substituted LNMO (003) surfaces in the presence of an electrolyte mixture are compared. Over-oxidation of O2− anions during delithiation in the pristine surface results in oxygen evolution and subsequent structural deformation. Whereas, in the S-substituted LNMO, S2− anions primarily participate in charge compensation and further inhibit oxygen evolution and O vacancy formation at high degrees of delithiation. Furthermore, the S-substitution effectively prevents the formation of Ni3+ ions and Jahn-Teller distortion, retaining the layered structure during delithiation. Our findings provide insight into improving the structural stability of the LNMO (003) surface, paving the way for developing Li-rich LNMO cathode materials for next-generation LIBs.