Highly structural stability from small-sized Li2MnO3-like domains in Co-free Li-rich layered oxide cathodes

Li-rich layered oxides (LLOs) are attractive cathode materials for high-energy-density lithium-ion batteries. However, the aggregation of Li2MnO3-like domains causes critical issues such as capacity/voltage fading and structural transformation. Here, we design the Co-free Li-rich Li-Fe-Ni-Mn-O system with dispersed Li2MnO3-like domains (D-LFNMO) and aggregated Li2MnO3-like domains (A-LFNMO) to investigate the effect of Li2MnO3-like domain sizes on structures and oxidation process using density function theory (DFT) calculations. Structural stability is finished through calculating oxygen release energies and migration energies of Mn4+ ions. The oxidation mechanism of oxygen was explored. Uniquely, in the Li-rich Li-Fe-Ni-Mn-O system, O ions in the linear Fe-O-Li configuration are activated to participate into charge compensation. The Fe-doping and especially dispersed Li2MnO3-like domains trigger more lattice oxygen ions to avoid the peroxidation of lattice oxygen and suppress the oxygen release. The climbing image nudged elastic band (CI-NEB) calculations find that dispersed Li2MnO3-like domains hinder the migration of Mn4+ ions to Li-vacancies to form irreversible structures. Consequently, LLOs with dispersed Li2MnO3-like domains would possess highly reversible oxygen redox and excellent structural stability, and exhibit superior cycling stability of high capacity. The findings provide new perspectives and concepts for designing high-energy Li-rich cathodes.