Improved electrode kinetics of a modified Na₃V₂(PO₄)₃ cathode through Zr substitution and nitrogen-doped carbon coating towards robust electrochemical performance at low temperature

Na₃V₂(PO4)₃ (NVP) with a unique NASICON-type framework, possessing superior qualities in terms of structural stability, rate capability, and long cycling life, has been deemed to be a promising cathode material for sodium-ion batteries, especially for applications at low temperatures. Nevertheless, the inferior conductivity and severe volumetric shrinkage seriously hinder the applications of NVP. Herein, Zr substitution and simultaneous hybridization with nitrogen-doped carbon (NC) were employed for the NVP cathode, realizing enlarged lattice distance, improved electronic conductivity, and fast ionic diffusion, which contribute to the remarkable modification of electrode kinetics and significant enhancement of electrochemical performance. Consequently, the optimized Na₃V_1.9Zr_0.1(PO₄)₃/NC (0.1Zr-NVP/NC) demonstrates a reversible capacity of 109.8 mA h g⁻¹ up to 100 cycles at 0.1 A g⁻¹, along with a superior capacity retention of 84.4% after 3000 cycles at 10 A g⁻¹. Furthermore, a reversible capacity of 103.7 mA h g⁻¹ can still be achieved after 100 cycles at 0.1 A g⁻¹ at −20 °C. The kinetics investigations based on cyclic voltammetry, galvanostatic intermittent titration technique, and electrochemical impedance spectra, combined with the structural evolution of 0.1Zr-NVP/NC monitored by X-ray diffraction, reveal its dramatically improved ionic kinetics, excellent structural stability, and electrochemical reversibility.