In Situ Electrochemical K‐Doping Assists Li and F Multisite Doping for Long‐Life Sodium‐Ion Batteries

Abstract P2‐type layered oxide materials have been widely applied in sodium‐ion batteries (SIBs), yet they confront challenges such as phase transitions, irreversible oxygen release, and Na + /vacancy ordering, resulting in low cycle life. Herein, an in situ K─Na 0.67 Ni 0.25 Li 0.08 Mn 0.67 O 1.93 F 0.07 (IsK─NaNLMF) material through a combination of traditional sol–gel method and advanced in situ electrochemical doping is synthesized. The doped F at O sites widens the interlayer spacing of the Na layer and enhances the reversibility of lattice oxygen redox reactions. The doped Li at Ni sites inhibits the formation of the Na + /vacancy ordering and phase transitions at high voltage. Especially, precisely introducing K into Na sites through in situ electrochemical doping stabilizes the structure, provides wide Na + channels, and inhibits the irreversible stripping of Li during cycling. The designed IsK─NaNLMF realizes higher capacity retention of 80.74% compared to Na 0.67 Ni 0.33 Mn 0.67 O 2 (39.08%) after 200 cycles at 1 C, and it retains a capacity of 80.90% after 500 cycles and 70% even after 1000 cycles at 5 C. This work provides an advanced method of in situ electrochemical doping for the precise control of doping sites and improves the electrochemical performance of layered oxide materials through the synergistic effect of multisite‐doped ions, hoping to promote the development of long‐life SIBs.