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 (approximate to 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+ (approximate to 4.1 V), Mn4+/3+ (approximate to 4.0 V), Mn3+/2+ (approximate to 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.

Automated summary

This study designs a V-doped Na3.1MnTi0.9V0.1(PO4)(3) (NMTVP) cathode material, which increases the medium discharge voltage and capacity. The NMTVP exhibits a high capacity, high medium discharge voltage, decent energy density, and ideal cyclability.