Electrodeposition of Zinc for Redox Flow Batteries

The redox flow batteries (RFBs) have received great attention due to their attractive features for large-scale energy storage applications. A RFB is a type of flow-based energy storage device capable of providing reversible conversion between electrical and chemical energy through two redox half-cell reactions. Nowadays the most common RFBs exploit the vanadium chemistry, followed by the zinc-bromine chemistries. Though RFB technology has advantage for energy storage and has successful demonstration of systems up to MWh levels, they have not enjoyed broad market penetration. Some of the reasons are relatively high capital and life-cycle costs. New applications are envisaged for RFBs, including the electric mobility which is becoming increasingly important. Zinc based redox flow batteries (Zn-RFBs) based on new chemistries with respect to the chlorine and bromine ones can be the answer to new market success devices, not only in the large storage field but also in the medium and mobility sector. In this presentation, the electrodeposition of zinc will be discussed in light of its exploitation in the new generation of zinc based RFBs. Alkaline and acidic baths will be presented in combination with proper chemistries for the other half cells. The role of additives and pulse plating will be discussed in terms of nucleation and growth of the metallic layer and its dissolution during charging/discharging cycles. A zinc-iron RFB with low cost and high energy density will be presented. In particular, inorganic electrolytes based on high soluble salts have been developed, achieving a charge density of 30-70 Wh/l. Moreover, in order to enhance the capacity of Zn-Fe flow battery, the use of slurry dispersed electrodes to decuple capacity from the power rating have been studied. As another example, zinc electrodeposition and its optimization will be introduced in combination with the iodine chemistry for high energy efficiency Zn-I RFBs, in the order of 70% at 20 mA cm-2, with high energy density ranging from 25 to 60 Wh/l.