Insights into Reversible Sodium Intercalation in a Novel Sodium‐Deficient NASICON‐Type Structure:Na3.40□0.60Co0.5Fe0.5V(PO4)3

Abstract

AbstractThe rational design of novel high‐performance cathode materials for sodium‐ion batteries is a challenge for the development of the renewable energy sector. Here, a new sodium‐deficient NASICON phosphate, namely Na3.40□0.60Co0.5Fe0.5V(PO4)3, demonstrating the excellent electrochemical performance is reported. The presence of Co allows a third Na+ to participate in the reaction thus exhibiting a high reversible capacity of ≈155 mAh g−1 in the voltage range of 2.0–4.0 V versus Na+/Na with a reversible single‐phase mechanism and a small volume shrinkage of ≈5.97% at 4.0 V. 23Na solid‐state nuclear magnetic resonance (NMR) combined with ex situ X‐ray diffraction (XRD) refinements provide evidence for a preferential Na+ insertion within the Na2 site. Furthermore, the enhanced sodium kinetics ascribed to Co‐substitution is also confirmed in combination with electrochemical impedance spectroscopy (EIS), galvanostatic intermittent titration technique (GITT), and theoretical calculation.