Redox Decoupling Modulates Multi‐Electron Reaction in Mn‐Rich NASICON Cathode for High‐Energy Sodium‐Ion Batteries

ABSTRACT

Coupled redox reactions caused by voltage hysteresis limit the application of Mn‐rich NASICON cathodes for sodium‐ion batteries. Herein, this work fabricates a Na _3.6 Mn _1.25 Ti _0.7 Ni _0.05 (PO ₄ ) ₃ (NM1.25TP‐Ni) cathode material achieving redox decoupling of Mn/Ti. Specifically, the introduction of an appropriate amount of Ni effectively facilitates the redox reaction of Mn ^{2 +} /Mn ^{3 +} and significantly accelerates its reaction kinetics, thereby achieving effective separation of the electrochemical active regions of Mn and Ti. Crucially, the in situ electrochemical impedance spectra based on distribution relaxation time shows that the redox decoupling effect achieves kinetic decoupling of Mn/Ti by stabilizing the local coordination environment and specifically accelerating the charge transfer process of Mn ²⁺ /Mn ³⁺ . Furthermore, the enhanced kinetics effectively suppress voltage hysteresis in the high‐voltage region, ensuring the full occurrence of the Mn ³⁺ /Mn ⁴⁺ redox reaction. Consequently, NM1.25TP‐Ni exhibits an excellent capacity output (166.3 mAh g ⁻¹ ) and a high practical energy density (467.6 Wh kg ⁻¹ ). This work establishes that redox decoupling as an effective paradigm for overcoming the kinetic barriers in Mn‐rich NASICON cathodes with multi‐electron reactions provides a new approach for the design of high energy density materials for sodium‐ion batteries.