Effect of additives and binders on the electrochemical performance of Zinc anodes in Zinc – Air Batteries

Summary:

In the race for ever higher capacity battery technologies that are also safe and environmentally benign the group of secondary Metal-Air batteries have received considerable attention. Of these, Zinc-Air batteries (ZABs) are the most mature and closest to being commercially viable. The intrinsic safety characteristics of systems using aqueous electrolytes, the high theoretical specific energy of ZABs and the natural abundance as well as the environmentally benign nature of the active material all make this a very attractive technology. While primary ZABs have been successfully commercialized in niche applications such as, for instance, hearing aids, their use as secondary batteries is hampered by several factors, including anodic passivation by Zinc oxide formation and dendrite formation during charging. Our research and results being presented here address these issues.
For our investigations, the binders and ion-exchange additives were used to prepare slurries that also contain Zinc particles and carbon black. These slurries were then coated onto copper meshes. These anodes were tested in a three-electrode-setup in cells with either stagnant or flowing electrolyte. After an initial discharge the cells are either charged using a continuous or pulsed sequence.
The nature and the amount of the ion-exchange resin added to the anode slurry have a clear influence on the electrochemical performance of the ZABs, with a modest amount of a sulfonic acid decorated resin resulting in a much greater capacity being accessible during the initial discharging of the cell. Similarly, substitution of the reference PVdF binder by either Polyurethane or Nitril-Butyl-Rubber binders results in better discharge behavior.
Our research shows that the components of the anode have a clear influence on the performance of ZABs. The possible coordination of the generated Zincate ions by the functional groups of the ion-exchange resins or the nitrogen atoms in the binder polymers might well explain the observed improvements in the performance of the ZABs. For comparison, the use of surfactants and soluble polymers as electrolyte additives have been shown to have a positive effect on the electrochemistry of ZABs.