Electrochemical Analysis of Na$_{0.74}$Co$_{1-x}$Nb$_x$O$_2$ ($x=$ 0, 0.05) as Cathode Materials in Sodium-ion Batteries

TL;DR

This study investigates the electrochemical properties of Na$_{0.74}$Co$_{1-x}$Nb$_x$O$_2$ cathodes for sodium-ion batteries, highlighting improved capacity with Nb doping and analyzing ion diffusion characteristics.

Contribution

It provides new insights into Nb doping effects on Na$_{0.74}$CoO$_2$'s electrochemical performance and characterizes the diffusion coefficient of sodium ions.

Findings

Na$_{0.74}$Co$_{0.95}$Nb$_{0.05}$O$_2$ shows higher capacity (91 mAhg$^{-1}$) than undoped Na$_{0.74}$CoO$_2$ (70 mAhg$^{-1}$).

The diffusion coefficient of Na$^+$ ions is approximately 10$^{-10}$ cm$^2$s$^{-1}$.

Hexagonal crystal structure confirmed by X-ray diffraction.

Abstract

Sodium-ion batteries (SIBs) have received significant attention as promising alternative for energy storage applications owing to the large availability and low cost of sodium. In this paper we study the electrochemical behavior of Na$_{0.74}$Co$_{1-x}$Nb$_x$O$_2$ ($x=$ 0 and 0.05 samples), synthesized via solid-state reaction. The Rietveld refinement of x-ray diffraction patterns reveals the hexagonal crystal symmetry with P63/mmc space group. The Na$_{0.74}$Co$_{0.95}$Nb$_{0.05}$O$_2$ cathode exhibits a specific capacity of about 91 mAhg$^{-1}$ at a current density of 6 mAg$^{-1}$, whereas Na$_{0.74}$CoO$_2$ exhibits comparatively low specific capacity (70 mAhg$^{-1}$ at a current density of 6 mAg$^{-1}$). The cyclic voltammetry (CV) and electron impedance spectroscopy (EIS) were performed to determine the diffusion coefficient of Na, which found to be in the range of 10$^{-10}$ cm$^2$s$^{-1}$.