Role of Ligand-to-Metal Charge Transfer in Anionic Redox Activity of the Layered Oxide Cathode for Na-Ion Batteries

Here, we introduce a P2-type layered oxide cathode material, Na_0·67Ni_0·33Mn_0·51Ru_0·16O₂, which demonstrates exceptional electrochemical performance through a robust dual cationic–anionic redox mechanism. This material delivers a high discharge capacity of 175.6 mAh g⁻¹ at an average voltage of 3.6 V and maintains remarkable cycling stability with ∼93% capacity retention after 1000 cycles.

A key to this performance is the strategic Ru doping, which plays a pivotal role in electronically stabilizing the oxidized oxygen states. By mediating the reversible formation of oxygen holes and preventing oxygen undercoordination, the Ru dopant stabilizes the anionic redox process. Unlike Na-rich layered oxides, this ligand-to-metal charge-transfer mechanism effectively suppresses detrimental oxygen evolution and preserves the structural integrity of the layered Na-deficient P2-type framework.