Dual‐Site Doping in Transition Metal Oxide Cathode Enables High‐Voltage Stability of Na‐Ion Batteries

Abstract Designing cathode materials that effectively enhancing structural stability under high voltage is paramount for rationally enhancing energy density and safety of Na‐ion batteries. This study introduces a novel P2‐Na 0.73 K 0.03 Ni 0.23 Li 0.1 Mn 0.67 O 2 (KLi‐NaNMO) cathode through dual‐site synergistic doping of K and Li in Na and transition metal (TM) layers. Combining theoretical and experimental studies, this study discovers that Li doping significantly strengthens the orbital overlap of Ni (3d) and O (2p) near the Fermi level, thereby regulates the phase transition and charge compensation processes with synchronized Ni and O redox. The introduction of K further adjusts the ratio of Na e and Na f sites at Na layer with enhanced structural stability and extended lattice space distance, enabling the suppression of TM dissolution, achieving a single‐phase transition reaction even at a high voltage of 4.4 V, and improving reaction kinetics. Consequently, KLi‐NaNMO exhibits a high capacity (105 and 120 mAh g −1 in the voltage of 2–4.2 V and 2–4.4 V at 0.1 C, respectively) and outstanding cycling performance over 300 cycles under 4.2 and 4.4 V. This work provides a dual‐site doping strategy to employ synchronized TM and O redox with improved capacity and high structural stability via electronic and crystal structure modulation.