Physical properties and electrochemical performance of Zn-substituted Na$_{0.44}$Mn$_{1-x}$Zn$_x$O$_2$ nanostructures as cathode in Na-ion batteries

TL;DR

This study explores Zn substitution in Na$_{0.44}$MnO$_2$ nanostructures, revealing improved electrochemical stability and capacity at low Zn levels, with detailed analysis of physical and electrochemical properties relevant for Na-ion battery cathodes.

Contribution

It introduces Zn substitution in Na$_{0.44}$MnO$_2$ nanostructures and analyzes its effects on structure, electrical, and electrochemical performance, highlighting optimal doping levels.

Findings

Zn substitution stabilizes orthorhombic structure.

Low Zn doping improves cycle life and capacity.

Resistivity increases with Zn, but defect levels rise.

Abstract

We report the synthesis, physical properties and electrochemical performance of Zn substituted Na$_{0.44}$Mn$_{1-x}$Zn$_x$O$_2$ ($x=$ 0 -- 0.02) nanostructures as cathode in Na-ion batteries for energy storage applications. These samples stabilize in the orthorhombic structure and the morphology is found to be slab like with 100 -- 200~nm width and few micrometer of length. The resistivity measurements show highly insulating nature for all the samples, where the activation energy decreases with increasing Zn concentration indicating more defect levels in the band gap. The cyclic voltammogram (CV) shows reversible oxidation and reduction peaks, which clearly shift towards higher/lower potentials with increasing Zn concentration up to 2\%. We observed the specific capacity of about 100~mAh/g at current density of 4 mA/g and improved cycle life for Zn substituted $x=$ 0.005 sample. However, with further increasing the Zn concentration ($x=$ 0.02), the specific capacity decreases, which can be a manifestation of the decreased number of reduction peaks in the CV data.