V Doping in NASICON‐Structured Na 3 MnTi(PO 4 ) 3 Enables High‐Energy and Stable Sodium Storage

NASICON‐structured Na 3 MnTi(PO 4 ) 3 represents an appealing cathode for sodium storage. However, the low potential from Ti 3+ / 4+ redox pair (≈2.1 V versus Na + /Na), undesirable rate capability, and unfavorable cyclability have inhibited its practical application. Herein, this study designs a Na 3.1 MnTi 0.9 V 0.1 (PO 4 ) 3 (NMTVP) cathode material by doping V into the Na 3 MnTi(PO 4 ) 3 . The V substitution not only increases the medium discharge voltage, but also increases the capacity. The as‐prepared NMTVP demonstrates a four‐step redox reaction from the redox couples of V 5+/4+ (≈4.1 V), Mn 4+/3+ (≈4.0 V), Mn 3+/2+ (≈3.6 V), and V 4+/3+ (3.4 V). The NMTVP delivers a high capacity (118.5 mAh g −1 at 0.1 C), a high medium discharge voltage (3.53 V), a decent energy density (422 Wh kg −1 ), and an ideal cyclability (86% retention after 4500 cycles at 5 C). In situ X‐ray diffraction (XRD) uncovers the reversible structural evolution between Na 3.1 MnTi 0.9 V 0.1 (PO 4 ) 3 and Na 0.9 MnTi 0.9 V 0.1 (PO 4 ) 3 phases. The assembled NMTVP//hard carbon (HC) full cell also delivers a high capacity, a high operating voltage, and a good cyclability. This contribution offers new insights into the design of high‐energy NASICON‐structured cathode materials.