Electrochemical energy storage systems are critical in
several
ways for a smooth transition from nonrenewable to renewable energy
sources. Zn-based batteries are one of the promising alternatives
to the existing state-of-the-art Li-ion battery technology, since
Li-ion batteries pose significant drawbacks in terms of safety and
cost-effectiveness. Zn (with a reduction potential of −0.76
V vs SHE) has a significantly higher theoretical volumetric capacity
(5851 mAh/cm3) than Li (2061 mAh/cm3), and it
is certainly far less expensive, safer, and more earth-abundant. The
formation of dendrites, hydrogen evolution, and the formation of a
ZnO passivation layer on the Zn anode are the primary challenges in
the development and deployment of rechargeable zinc batteries. In
this work, we examine the role of imidazole as an electrolyte additive
in 2 M ZnCl2 to prevent dendrite formation during zinc
electrodeposition via experimental (kinetics and imaging) and theoretical
density functional theory (DFT) studies. To characterize the efficacy
and to identify the appropriate concentration of imidazole, linear
sweep voltammetry (LSV) and chronoamperometry (CA) are performed with
in situ monitoring of the electrodeposited zinc. The addition of 0.025
wt % imidazole to 2 M ZnCl2 increases the cycle life of
Zn-symmetric cells cycled at 1 mA/cm2 for 60 min of plating
and stripping dramatically from 90 to 240 h. A higher value of the
nucleation overpotential is noted in the presence of imidazole, which
suggests that imidazole is adsorbed at a competitively faster rate
on the surface of zinc, thereby suppressing the zinc electrodeposition
kinetics and the formation. X-ray tomography reveals that a short
circuit caused by dendrite formation is the main plausible failure
mechanism of Zn symmetric cells. It is observed that the electrodeposition
of zinc is more homogeneous in the presence of imidazole, and its
presence in the electrolyte also inhibits the production of a passivating
coating (ZnO) on the Zn surface, thereby preventing corrosion. DFT
calculations conform well with the stated experimental observations.
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