Enhancing the Electrochemical Performance of P2‐Na _0.66 Mg _0.1 Cu _0.1 Mn _0.8 O ₂ Layered Oxide Cathode Through Ru Substitution

In this work, Ru substitution at the Mn sites of P2‐Na 0.66 Mg 0.1 Cu 0.1 Mn 0.8 O 2 is explored as an effective strategy to enhance the electrochemical performance, and its effects are systematically analyzed through experimental and theoretical studies. Ru incorporation enhances the specific capacity, and the optimized composition, Na 0.66 Mg 0.1 Cu 0.1 Mn 0.55 Ru 0.2 O 2 , delivers 94.0% capacity retention over 300 cycles at 2 C. Density functional theory results indicate that Ru substitution promotes preferential occupation of Na + at the energetically favorable Na e sites during Na + intercalation/deintercalation, whereas Na + occupies both Na e and Na f sites in the undoped material. Galvanostatic intermittent titration technique studies reveal that Ru substitution increased the Na + diffusion coefficient, thereby enhancing Na + diffusion kinetics and the rate capability. Ex situ X‐ray photoelectron spectroscopy analysis confirms that Ru incorporation enables reversible anionic redox activity and shows that oxygen redox occurs prior to the complete oxidation of Ru 4+ to Ru 5+ and Mn 3+ to Mn 4+ . Ex situ X‐ray diffraction analysis of the NMCMR‐0.2 cathode shows that the P2 phase is maintained during cycling. The results demonstrate that Ru substitution enhances Na + diffusion kinetics, improves capacity retention, and preserves structural stability in P2‐type cathode materials.