Improved electrochemical performance of NASICON type Na$_{3}$V$_{2-x}$Co$_x$(PO$_{4}$)$_{3}$/C ($x=$ 0--0.15) cathode for high rate and stable sodium-ion batteries

TL;DR

This study enhances sodium-ion battery cathodes by Co doping in NASICON structures, achieving high capacity, excellent rate performance, and long-term stability through structural and electrochemical optimization.

Contribution

It demonstrates that Co substitution at V sites significantly improves the electrochemical performance and cycling stability of NASICON-type Na$_{3}$V$_{2-x}$Co$_x$(PO$_{4}$)$_{3}$/C cathodes.

Findings

Achieved 105 mAh g$^{-1}$ capacity at 0.1 C for x=0.05.

Maintained 80 mAh g$^{-1}$ at 10 C with 92 ext% retention after 500 cycles.

Structural stability confirmed after 500 cycles at high rate.

Abstract

In recent years, the Na-ion SuperIonic CONductor (NASICON) based polyanionics are considered the pertinent cathode materials in sodium-ion batteries due to their 3D open framework, which can accommodate a wide range of Na content and can offer high ionic conductivity with great structural stability. However, owing to the inferior electronic conductivity, these materials suffer from unappealing rate capability and cyclic stability for practical applications. Therefore, in this work we investigate the effect of Co substitution at V site on the electrochemical performance and diffusion kinetics of Na$_{3}$V$_{2-x}$Co$_x$(PO$_{4}$)$_{3}$/C ($x=$ 0--0.15) cathodes. All the samples are characterized through Rietveld refinement of the x-ray diffraction patterns, Raman spectroscopy, transmission electron microscopy, etc. We demonstrate improved electrochemical performance for the $x=$ 0.05 electrode with reversible capacity of 105 mAh g$^{-1}$ at 0.1 C. Interestingly, the specific capacity of 80 mAh g$^{-1}$ is achieved at 10 C with retention of about 92\% after 500 cycles and 79.5\% after 1500 cycles and having nearly 100\% Coulombic efficiency. The extracted diffusion coefficient values through galvanostatic intermittent titration technique and cyclic voltammetry are found to be in the range of 10$^{-9}$--10$^{-11}$ cm$^{2}$ s$^{-1}$. The postmortem studies show the excellent structural and morphological stability after testing for 500 cycles at 10 C. Our study reveals the role of optimal dopant of Co$^{3+}$ ions at V site to improve the cyclic stability at high current rate.