Boosting the Energy Density of Potassium‐Based Layered Oxide Cathodes by Anionic Redox Chemistry

Despite extensive efforts to develop high‐energy cathode materials for potassium‐ion batteries (PIBs), achieving enhanced energy density remains challenging due to the inherent limitations in capacity and average voltage of conventional materials. Herein, a strategy is proposed to boost the energy density of PIBs by activating anionic redox (ARR) reactions in P3‐K 0.67 Ni 0.33 Mn 0.67 O 2 (KNMO). The ARR is activated by the formation of unique K‐O‐□ TM and □ K ‐O‐□ TM configurations, which are induced by the migration of Ni ions from the transition metal layer to the alkali metal layer during the charging process. Therefore, KNMO exhibits the high initial discharge capacity of 101.66 mAh g −1 with an improved voltage of ≈4.15 V, achieving the ultrahigh energy density of >421 Wh kg −1 . In addition, the irreversible phase transformation, oxygen release, and sluggish electrochemical reaction kinetics at high voltages are identified as key factors contributing to the rapid capacity degradation of KNMO. This work underscores the pivotal role of anionic redox reactions in enhancing the energy density of PIBs and provides valuable guidance for the future development of anionic redox chemistry.