Na₃V₂(PO₄)₃/Porous Carbon Skeleton Embellished with ZIF-67 for Sodium-Ion Storage

Sodium super ionic conductor (NASICON) Na₃V₂(PO₄)₃ (NVP) is a type of promising cathode material for sodium-ion batteries (SIBs) with superior structural integrity, high energy density, and fast diffusion of sodium ions. However, NVP suffers from intrinsically low electrical conductivity, which results in poor rate performance. Herein, we report on the outstanding cathode performance of Na₃V₂(PO₄)₃ (NVP@C-ZIF67) wrapped by the ZIF-67-derived carbon, which was prepared by sol-gel method and solid-phase method. Electrochemical measurements show an initial discharge-specific capacity of 135 mA h g^-1 at 1 C, and the discharge capacity maintains 82 mA h g^-1 after 1000 cycles at 10 C. The results indicate the improvement in electrical conductivity and electrochemical performance due to the Co doping from ZIF-67. Moreover, we calculate the diffusion coefficient of sodium ions by the cyclic voltammetry (CV, D_Na = 1.521 × 10^-11 and 2.3484 × 10^-11 cm² s^-1 for charging and discharging, respectively) and the galvanostatic intermittent titration technique (GITT, D_Na ranges from 10^-11-10^-15 cm² s^-1). The exceptional performance is ascribed to the excellent structural stability and outstanding electrical conductivity of NVP modified by porous carbon skeleton and ZIF-67-derived carbon.