Origin of Electrochemical Activation Leading to Enhanced Cycling Stability of Li‐ and Mn‐Rich Cathodes

ABSTRACT Electrochemical activation is a critical step for optimal functioning of Li‐ and Mn‐rich (LMR) cathodes, yet the underlying mechanism for such activation remains elusive. Here, by using scanning/transmission electron microscopy (S/TEM) combined with the associated energy‐dispersive x‐ray spectroscopy (EDS) and electron energy‐loss spectroscopy (EELS), we decipher the origin of the activation enhanced electrochemical properties. We reveal that activation induces the formation of a spinel‐like phase within the C2/m domains of the LMR cathode, where the transition‐metal ions partially occupy both the tetrahedral (8a) and octahedral (16c) sites of the Fd m spinel lattice, distinguishing the spinel‐like phase from the conventional high‐voltage spinel. Systematic varying the cycling voltage reveals a critical activation voltage above which this spinel‐like phase forms, while lower voltages preserve the layered bulk structure. As the spinel‐like phase is a stable structure for electrochemical cycling, the present findings provide direct mechanistic insight into the voltage‐dependent activation process and explain how the C2/m to spinel‐like transformation upon activation contributes to the electrochemical performance of LMR cathodes, providing guidance for the rational design of Li‐rich cathodes with enhanced cycling durability.