Approaches Towards Improving Zinc-Nickel Batteries Performance

Abstract

The zinc/nickel electrochemical system has long been proposed as a good candidate of secondary alkaline batteries due to its excellent performance versus other aqueous batteries, such as high practical specific energy, excellent specific power, high open circuit voltage, low cost and low toxicity [1,2]. These advantages make it suitable for replacing lead-acid and nickel-cadmium batteries [3]. However, the high solubility of zinc in concentrated alkaline electrolytes is still a significant problem that induces two main failure mechanisms: a shape-change of the zinc electrode and a redistribution of the zinc active material due to its dissolution/redeposition during cycling. Dendritic growth can occur as a consequence of zinc dissolution/redeposition, and if severe, may lead to separators’ perforation and internal electrical short-circuits [4]. These drawbacks reduce the cell's capacity and lifetime, especially compared to traditional competing systems [5]. In addition, since the hydrogen evolution reaction (HER) is thermodynamically possible (especially during charging), the coulombic efficiency of the zinc electrode can be lowered by this parasite reaction [6]. The undesirable HER consumes water and some of the active material, yielding zinc hydroxide which in turn can generate a passivation layer that lowers the usability of the zinc anode materials [7]. There are different approaches to overcome these problems, such as the integration of additives in the active material formulation and/or in the electrolyte.In this contribution, we will show how regeneration of the active material can be obtained via appropriate steps of rest submitted to the active material and without the need for additional energy input. The so-called “self-healing” of the active material allows to recover a substantial part of the electrochemical performance. The concept was deeply studied and monitored by scanning electron microscopy coupled with elemental mapping by X-ray energy dispersive spectrometry, and operando tomography. An increase in the coulombic efficiency has been demonstrated making this discovery very promising for the future of zinc-based alkaline batteries. Keywords: Zinc-nickel batteries, additives, self-healing