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

Abstract NASICON‐structured Na₃MnTi(PO₄)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_3.1MnTi_0.9V_0.1(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 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_3.1MnTi_0.9V_0.1(PO₄)₃ and Na_0.9MnTi_0.9V_0.1(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.