Ligand‐to‐Metal Charge Transfer Motivated the Whole‐Voltage‐Range Anionic Redox in P2‐Type Layered Oxide Cathodes

Abstract

AbstractAnionic redox in layered transition metal oxides (TMOs) cathodes presents significant opportunities for achieving high energy density batteries. However, the O 2p non‐bonding state can only undergo redox at high voltages and is often accompanied by severe structural distortion. In this study, the whole‐voltage‐range anionic redox has successfully been achieved in Metal‐organic frameworks (MOF) derived chemically homogeneous P2‐Na0.67Ni0.2Mg0.2Mn0.6O2 (NNMMO). Through a systematic analysis of the orbital combinations of TMs and O, it is found that the Mg‐induced O 2p non‐bonding state as an electron donor, forming strong π‐type interactions between Ni 3d spin‐down t2g orbitals. The resulting π‐configurational oxygen occupies an anti‐bonding state just below the Fermi level, exhibiting high oxidation activity and stability. Additionally, the high covalency between Mn and O increases the strength of the Mn–O bond, mitigating the structural aberration of NNMMO. As a result, NNMMO demonstrates a high capacity of 216 mAh g−1 at 0.1 C and stable battery performance, with a capacity retention of ≈90% after 500 cycles at 2 C. This π‐type anionic redox and intrinsic competition mechanism present an alternative strategy for achieving advanced cathode materials for sodium‐ion batteries.