Lithium and oxygen dimer diffusion in solid-state oxygen-redox cathode materials: insights from neural network molecular dynamics

In conventional Li‐ion battery cathodes, redox activity is centered on transition metals; by contrast, lithium‐rich oxides in which lattice oxygen participates in the redox process have attracted widespread interest in recent years, not only because of their high‐capacity characteristics but also for the unique mechanistic insights they offer into oxygen redox. In this work, we target the prototypical oxygen‐redox cathode Li1.2-xTi0.4Mn0.4O2 and carry out large‐scale molecular dynamics simulations employing a neural network potential (NNP). We systematically analyze Li‐ion diffusion, O – O dimer formation, and the evolution of oxygen diffusion behavior during charge. Our results reveal that, as Li extraction progresses, oxygen dimers form selectively in the vicinity of remaining Li to locally avoid the higher‐valent Mn and Ti centers. Furthermore, dimerized oxygen exhibits markedly enhanced mobility (with an activation energy of < 0.57 eV) relative to non‐dimerized oxygen, undergoing repeated cycles of dimer formation and dissociation as it migrates through the lattice at ×≥ 0.6. Extrapolation to room temperature yields an oxygen diffusion coefficient on the order of 10−13 cm2 s−1 at × = 0.6, implying that bulk oxygen diffusion to the particle surface could initiate side reactions with the electrolyte and trigger thermal runaway. These findings underscore that, in designing oxygen‐redox cathode materials, crystal structures must be engineered to suppress oxygen dimer formation.