Charge Transfer Effect in Layered Cathodes Through MEMS-Based In Situ TEM Studies

The irreversible lattice oxygen release is the primary issue in layered oxide cathodes which is generally attributed to a consecutive phase transition with less lattice oxygen content. Herein, an anomalous metal segregation pathway is observed in oxygen vacancy defective layered cathodes, which happens far before the onset of phase transitions. The correlation of electron energy loss spectroscopy indicates that an early charge transfer from oxygen 2p to Mn 3d orbital is responsible. It further reveals a specific local vacancy heterogeneity that significantly lowers the migration barrier of Mn. This is further supported by the density functional theory simulations. In fact, the oxygen release is always initiated from the defective crystal, which alters the general degradation pathway initiated from the perfect crystal. This work shed light on the critical role of the local oxygen vacancy heterogeneity in the phase degradation of layered cathodes.