Transition Metal Slab Gliding: One Key Process for Activating Anionic Redox Reaction in P2‐Type Transition Metal Oxide Cathodes

Anionic redox chemistry is crucial for determining the capacity and stability of layered oxide cathodes for Na-ion batteries. However, the driving forces of anionic redox remain elusive. Na-O-A (A = alkali metal, alkaline earth metal, or vacancy) configurations have been identified as key to activating anionic redox reactions in transition metal (TM)-deficient oxide materials. However, reversible oxygen redox reactions are also observed in TM-stoichiometric oxide materials, although the Na-O-A configurations cannot be established in these systems. A TM-stoichiometric P2-type Na_2/3Cu_1/3Mn_2/3O₂ cathode and its Ti⁴⁺-substituted analogue (Na_2/3Cu_1/3Mn_1/2Ti_1/6O₂) are herein studied for deciphering the underlying mechanism. The incorporation of Ti⁴⁺ disrupts the ordered arrangement of TM layers, accelerates TM slab gliding, and facilitates TM migration, thus affording new Na-O-vacancy configurations and activating the reversible oxygen redox reaction. Consequently, Na_2/3Cu_1/3Mn_1/2Ti_1/6O₂ exhibits an initial discharge capacity of 153 mAh g^-1 and a capacity retention of 80% after 300 cycles at 2 C rate. This work provides plausible routes for reversible anionic redox reactions and increasing the energy density of SIBs.