Abstract
The commercialization of rechargeable alkaline zinc–air batteries (ZAB) requires advanced approaches to improve secondary zinc anode performance, which is hindered by the high corrosion and dissolution rate of zinc in this medium. Modified (with additives) alkaline electrolyte has been one of the most investigated options to reduce the high solubility of zinc. However, this strategy alone has not been fully successful in enhancing the cycle life of the battery. The combination of mitigation strategies into one joint approach, by using additives (ZnO, KF, K2CO3) in the base alkaline electrolyte and simultaneously preparing zinc electrodes that are based on ionomer (Nafion®)-coated zinc particles, was implemented and evaluated. The joint use of electrolyte additives and ionomer coating was intended to regulate the exposition of Zn, deal with zincate solubility, minimize the shape change and dendrite formation, as well as reduce the hydrogen evolution rate. This strategy provided a beneficial joint protective efficiency of 87% thanks to decreasing the corrosion rate from 10.4 (blank) to 1.3 mgZn cm−1·s−1 for coated Zn in the modified electrolyte. Although the rate capability and capacity are limited, the ionomer-coated Zn particles extended the ZAB cycle life by about 50%, providing battery roundtrip efficiency above 55% after 270 h operation.
Highlights
Energy storage systems that are based on secondary zinc electrodes are potential candidates to fulfill the need for light-weight and high discharge rate applications
As the ionomer content increases, an apparent dark rough surface when compared to the clean surface of Ionomer-Coated Zinc Particles (ICZP)-0 (Figure 1a) appears
In the same 4s-2 electrolyte, the coated ICZP-5 sample has an Ecorr = −1.484 VHg/HgO. These results suggest that the electrolyte and electrode additives lead to a cathodic shift of the corrosion potential with respect to the blank electrolyte, suggesting that zinc corrosion is mainly inhibited by suppressing the cathodic reaction, namely the hydrogen evolution reaction
Summary
Energy storage systems that are based on secondary zinc electrodes are potential candidates to fulfill the need for light-weight and high discharge rate applications. In general, one can consider that the zinc electrode still suffers from a limited cycle life [3]. This long-term limitation is usually assigned to zinc corrosion [4] (associated to the evolution of hydrogen), high dissolution rate of zinc [5] in the traditional aqueous alkaline electrolytes Limitations arise from the stability and performance of the bifunctional air electrode, which needs to support significant cell voltage changes during the cycle life due to its large overpotential towards both the reduction and evolution of oxygen [1]
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