V Doping in NASICON‐Structured Na3MnTi(PO4)3 Enables High‐Energy and Stable Sodium Storage.

NASICON‐structured Na3MnTi(PO4)3 represents an appealing cathode for sodium storage. However, the low potential from Ti3+/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 Na3.1MnTi0.9V0.1(PO4)3 (NMTVP) cathode material by doping V into the Na3MnTi(PO4)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 V5+/4+ (≈4.1 V), Mn4+/3+ (≈4.0 V), Mn3+/2+ (≈3.6 V), and V4+/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 Na3.1MnTi0.9V0.1(PO4)3 and Na0.9MnTi0.9V0.1(PO4)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. [ABSTRACT FROM AUTHOR]