Systematic cycle life assessment of a secondary zinc–air battery as a function of the alkaline electrolyte composition

Abstract

Development of secondary zinc-air batteries goes through a proper specification of the electrolyte formulation adapted to extend the cycle life of the battery. However, defining an optimal formulation is not a trivial work due to the specific requirements for each electrode. At half-cell level it has been determined that ZnO-saturated 4 M KOH with 2 M KF and 2 M K2CO3 (4s-2) is the most suitable formulation to increase the cycle life of secondary zinc electrode whereas additive-free 8 M KOH (8-0) formulation is more beneficial for the bifunctional air electrode (BAE). Through this systematic cycle life assessment, it has been found that the most suitable electrolyte formulation for the full cell system is a compendium for both electrodes requirements. It has determined an optimal electrolyte formulation for the full system consisting of ZnO-saturated 7 M KOH with 1.4 M KF and 1.4 M K2CO3 (7s-1.4). This electrolyte composition increases at least 2.5 times the reversibility of the secondary zinc-air battery in comparison to that employing the traditional formulation for primary zinc-air batteries (additive free 8 M KOH). In addition, the development of a proper cell design or separator is also necessary to further enhance the secondary zinc-air cycle life.