  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.
