Enhancing Mn(II)/Mn(IV) Redox Activity and Reducing Polarization of NASICON‐Type Na ₃ MnTi(PO ₄ ) ₃  Through Al‐Doping

ABSTRACT NASICON‐type cathode materials have garnered significant interest for their stable structure and favorable Na + diffusion pathways. However, Na 3 MnTi(PO 4 ) 3 (NMTP) often suffers from substantial voltage hysteresis and limited capacity, primarily attributed to intrinsic anti‐site defects. To address this challenge, we propose an Al‐doping strategy to simultaneously reduce the polarization and enhance the electrochemical activity. A series of Na 3+ x MnTi 1‐ x Al x (PO 4 ) 3 ( x = 0, 0.05, 0.1) compounds are synthesized, with Na 3.05 MnTi 0.95 Al 0.05 (PO 4 ) 3 (NMTAP‐0.05) demonstrating an optimal specific capacity and ideal cyclability. In situ XRD reveals the coexistence of solid‐solution and biphasic reactions, while ex situ XAS analyses confirm highly reversible Mn 2+ /Mn 4+ redox behavior. When paired with hard carbon (HC) in full‐cell, NMTAP‐0.05//HC delivers a high capacity, highlighting its practical potential. This work provides new insights into designing high‐performance phosphate‐based cathodes for sodium‐ion batteries.