Rechargeable zinc-nickel flow-assisted batteries are attractive in applications like frequency regulations, UPS inverters and hybrid electrical vehicles, etc[1] due to their advantages, such as, being cheap, capable of rapid charging and discharging and high energy density. However, the challenge that rechargeable zinc-anode batteries are facing is short lifespan time due to non-uniform morphology of zinc deposition during charging, hydrogen evolution that compromises energy efficiency and zinc corrosion during battery resting, which leads to further capacity loss[2].

We developed an indicator that monitors the transition of zinc morphology during battery charging[3]. Zincate concentration in the electrolyte, flow velocity and current density were varied over a wide range in the experiments. The results from SEM and 3D X-ray computer tomography (figure 1) show that the ratio between the effective current density and the limiting current density (current density ratio), which is directly related to the zincate concentration at the electrode surface, determines the zinc morphology. 

Furthermore, we investigated the causes of transition of zinc morphology. Compact zinc deposits are found to have a fine-grained, bright finish and the highest anodic efficiency (figure 2)[4]. Electrochemical impedance spectroscopy (EIS) proves that compact zinc corresponds to the minimum in the half-cell resistance, indicating it is kinetically preferred for compact zinc to form. Preferred crystal orientations of compact zinc depositions make good agreement with the EIS results.

Anode substrate is a parameter that also influences the zinc morphology. We studied the effects of various novel metal substrates on zinc morphology over battery cycling. Results from electrochemical techniques, chemical characterization and cell cycling showed that Cu and Bi are promising anode substrates.

In order to alleviate the corrosion rate and increase the lifespan of zinc-anode batteries, we investigated the impacts of additives on zinc morphology and cell performance. Lab-scale cells have demonstrated more than 2000 cycles and large-scale cells (113Ah) have demonstrated more than 200 cycles (figure 4 and figure 5). The results indicate that the morphologies of zinc deposition with the presence of additives are finer and the battery performance is improved as well.

References:

[1]       D.E. Turney, M. Shmukler, K. Galloway, M. Klein, Y. Ito, T. Sholklapper, J.W. Gallaway, M. Nyce, S. Banerjee, J. Power Sources 264 (2014) 49–58.

[2]       Y. Ito, M. Nyce, R. Plivelich, M. Klein, D. Steingart, S. Banerjee, J. Power Sources 196 (2011) 2340–2345.

[3]       Y. Ito, X. Wei, D. Desai, D. Steingart, S. Banerjee, J. Power Sources 211 (2012) 119–128.

[4]       D. Desai, X. Wei, D.A. Steingart, S. Banerjee, J. Power Sources 256 (2014) 145–152.