Fe-Doped NaVPO₄F/C Compounds for Sodium-Ion Battery Cathodes: Electrochemical Performance and Analysis of Kinetic Properties

NASICON-type NaVPO4F (NVPF) has received much attention from researchers due to its open three-dimensional framework and high theoretical capacity. However, the limited internal electronic conductivity and energy density hinder the widespread commercialization of NVPF. Herein, a series of NaV1–xFexPO4F/C (x = 0, 0.04, 0.06, and 0.08) was constructed via a sol–gel method by introducing a partial amount of Fe3+ into NVPF. The introduction of Fe3+ doping effectively enhanced the structural stability of the material, thereby facilitating rapid Na+ intercalation/deintercalation and leading to improved electrochemical properties. The results show that NVPF–Fe0.06 has excellent electrochemical performance, with a discharge specific capacity of 133.8 mAh g–1 at 0.2 C and a capacity retention of 94.5% after 100 charge/discharge cycles. Even after 1000 cycles at 5 C, it still has a high capacity retention of 86.2%. Additionally, the de-embedding mechanism of the NVPF–Fe0.06 electrode material is revealed by ex situ X-ray diffraction and in situ electrochemical impedance spectroscopy results. More importantly, the specific discharge capacity of assembled HC//NVPF–Fe0.06 full cell reached 112.1 mAh g–1 at 5 C. This work explores a new avenue to facilitate the commercialization of polyanionic cathode materials.