Localizing Oxygen Lattice Evolutions Eliminates Oxygen Release and Voltage Decay in All‐Mn‐Based Li‐Rich Cathodes

All‐Mn‐based Li‐rich cathodes Li2MnO3 have attracted extensive attention because of their cost advantage and ultrahigh theoretical capacity. However, the unstable anionic redox reaction (ARR), which involves irreversible oxygen releases, causes declines in cycling capacity and intercalation potential, thus hindering their practical applications. Here, it is proposed that introducing stacking‐fault defects into the Li2MnO3 can localize oxygen lattice evolutions and stabilize the ARR, eliminating oxygen releases. The thus‐made cathode has a highly reversible capacity (320 mA h g−1) and achieves excellent cycling stability. After 100 cycles, the capacity retention rate is 86% and the voltage decay is practically eliminated at 0.19 mV per cycle. Attributing to the stable ARR, samples show reduced stress–strain and phase transitions. Neutron pair distribution function (nPDF) measurements indicate that there is a structure response of localized oxygen lattice distortion to the ARR and the average oxygen lattice framework is well‐preserved which is a prerequisite for the high cycle reversibility.