Optimization of Zinc Electrodeposition for Mild-Acid Aqueous Batteries Applications

Energy harvesting from renewable sources must be integrated with efficient energy storage systems to enable their massive integration into the grid and to support the shift from fossil fuels to clean energy. Rechargeable batteries are currently the most promising technology for this purpose. Indeed, they are characterized by unparalleled energy densities and lifespans and they can be easily designed according to any specific application, from grid-scale to home backup systems. However, their application on large scales is often hindered by the costs related to their manufacturing process and by the toxicity of most of their components. For these reasons, notable efforts have been devoted to the development of cost-effective, environmentally compatible aqueous batteries since the early 2000s.
Among these, rechargeable aqueous zinc-ion batteries are known to be the most promising system because of the low redox potential and high capacity of the zinc-based electrodes. In addition, zinc is cheap, non-toxic, easily recyclable and widely available worldwide. However, the plating/stripping mechanism of zinc in aqueous media is severely affected by the concomitant evolution of gaseous hydrogen and dendrite growth. This often leads to internal short-circuits, dangerous pressure build-ups, irreversible zinc losses and to the alkalinization of the aqueous electrolyte.
This dissertation reports the employment of porous electrodes pasted with metallic substrates that kinetically favor the zinc electrodeposition over the hydrogen reduction reaction. When the composition of these substrates is optimized, the hydrogen evolution is strongly suppressed and the zinc electrodeposition is characterized by high efficiencies and smooth deposits. Also, the use of optimized substrates is proved to be cost-effective compared to a standard zinc-based electrode. The electrodeposition performances of zinc on these substrates are then evaluated using different mass loadings and plating currents, in order to assess the limits of the optimized substrates. Finally, in the last sections of this dissertation, zinc-based electrodes employing these substrates are tested in realistic setups in combination with several cathode materials. According to these cells’ performances, the soluble species originating from the positive electrode can have serious consequences on the electrodeposition performances of zinc and therefore on the battery lifespan. Nevertheless, when this can be inhibited (e.g., by using concentrated electrolytes) or even avoided (e.g., by using suitable active materials), the cycling performances of the full cell are limited only by the positive electrode’s performances.