Control of Growth Front Evolution by Bi Additives during ZnAu Electrodeposition

The
performance of many electrochemical energy storage systems
can be compromised by the formation of metal dendrites during charging.
Additives in the electrolyte represent a useful strategy to mitigate
dendrite formation, but understanding the mechanisms involved requires
knowledge of the nanoscale effects of additives during electrochemical
deposition. Here we quantify the effects of an inorganic additive
on the morphology of an evolving electrochemical growth front, using
liquid cell electron microscopy to provide the necessary spatial and
temporal resolution. We examine deposition of ZnAu on Au in the presence
of Bi additive, and show that low concentrations of Bi delay but do
not prevent the formation of growth front instabilities. We describe
a model in which Bi segregates at the growth front and promotes the
surface diffusion and relaxation of Zn, allowing better coverage of
the initial Au electrode surface. A more precise knowledge of the
mechanism of inorganic additive effects may help in designing electrolyte
chemistry for battery and other applications where morphology control
is essential.