Dual Honeycomb‐Superlattice Enables Double‐High Activity and Reversibility of Anion Redox for Sodium‐Ion Battery Layered Cathodes

Anion redox contributes to the anomalous capacity exceeding the theoretical limit of layered oxides. However, double-high activity and reversibility is challenging due to the structural rearrangement and potential oxygen loss. Here, we propose a strategy for constructing a dual honeycomb-superlattice structure in Na2/3 Li1/7 Mn5/14 Mg1/7 Mn5/14 O2 to simultaneously realize high activity and reversibility of lattice O redox. Theoretical simulation and electrochemical tests show that Li1/7 Mn5/14 superlattice units remarkably trigger the anion redox activity and enable the delivery of a record capacity of 285.9 mA g-1 in layered sodium-ion battery cathodes. Nuclear magnetic resonance and in situ X-ray diffraction reveal that Mg1/7 Mn5/14 superlattice units are beneficial to the structure and anion redox reversibility, where Li+ reversibly shuttles between Na layers and transition-metal slabs in contrast to the absence of Mg1/7 Mn5/14 units. Our findings underline the importance of multifunctional units and provide a path to advanced battery materials.