Lithium
Storage Properties of Pristine and (Mg, Cu)
Codoped ZnFe<sub>2</sub>O<sub>4</sub> Nanoparticles
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Abstract
ZnFe<sub>2</sub>O<sub>4</sub> and Mg<sub><i>x</i></sub>Cu<sub>0.2</sub>Zn<sub>0.82–<i>x</i></sub>Fe<sub>1.98</sub>O<sub>4</sub> (where <i>x</i> = 0.20, 0.25, 0.30,
0.35, and 0.40) nanoparticles were synthesized by sol–gel assisted
combustion method. X-ray diffraction (XRD), FTIR spectroscopy, Raman
spectroscopy, scanning electron microscopy (SEM), transmission electron
microscopy (TEM), and Brunauer–Emmett–Teller (BET) surface
area studies were used to characterize the synthesized compounds.
ZnFe<sub>2</sub>O<sub>4</sub> and the doped compounds crystallize
in <i>Fd</i>3<i>m</i> space group. The lattice
parameter of ZnFe<sub>2</sub>O<sub>4</sub> is calculated to be <i>a</i> = 8.448(3) Å, while the doped compounds show a slight
decrease in the lattice parameter with an increase in the Mg content.
The particle size of all the compositions are in the range of ∼50–80
nm, and the surface area of the compounds are in the range of 11–12
m<sup>2</sup> g<sup>–1</sup>. Cyclic voltammetry (CV), galvanostatic
cycling, and electrochemical impedance spectroscopy (EIS) studies
were used to investigate the electrochemical properties of the different
compositions. The as-synthesized samples at 600 °C show large-capacity
fading, while the samples reheated at 800 °C show better cycling
stability. ZnFe<sub>2</sub>O<sub>4</sub> exhibits a high reversible
capacity of 575 mAh g<sup>–1</sup> after 60 cycles at a current
density of 100 mA g<sup>–1</sup>. Mg<sub>0.2</sub>Cu<sub>0.2</sub>Zn<sub>0.62</sub>Fe<sub>1.98</sub>O<sub>4</sub> shows a similar capacity
of 576 mAh g<sup>–1</sup> after 60 cycles with better capacity
retention