Inert Al Doping Into Mn‐Rich NASICON Cathode to Effectively Suppress Voltage Hysteresis in Sodium‐Ion Batteries

Mn‐rich sodium superionic conductor (NASICON) Na 3.4 Mn 1.2 Ti 0.8 (PO 4 ) 3 (MT) is a promising cathode material for sodium‐ion batteries (SIBs), thanks to multiple redox couples, cost‐effectiveness and environmental friendliness. However, Jahn–Teller distortion and voltage hysteresis hinder its practical application. To address these challenges, herein, trace doping of inert Al into MT to form Na 3.45 Mn 1.2 Ti 0.75 Al 0.05 (PO 4 ) 3 (MTA) is proposed to stabilize the lattice structure and modulate the electronic structure of MnO 6 octahedra. Electrochemical analysis reveals that voltage hysteresis is remarkably mitigated owing to increased activity ofMn, electron‐rich distribution around Mn/Ti atoms and low sodium‐ion migration barrier. In situ X‐ray diffraction confirms a two‐phase reaction mechanism during the charge–discharge process, which is same as that of MT. In a practical full‐cell configuration, hard carbon (HC)||MTA achieves a high capacity of 138 mAh g −1 and energy density of 419 Wh kg −1 at 0.2C, distinctly surpassing HC||MT (114 mAh g −1 and 337 Wh kg −1 ). After 100 cycles, MTA still retains 90% of the initial capacity, much higher than MT (72%). These results underscore the efficacy of Al doping in activating redox couples while stabilizing lattice structure of Mn‐rich NASICON cathodes, paving a way for high‐performance SIBs.