Design Strategy for Zinc Anodes with Enhanced Utilization and Retention: Electrodeposited Zinc Oxide on Carbon Mesh Protected by lonomeric Layers

Abstract

In order to establish secondary zinc oxygen batteries as sustainable and cost-efficient future energy storage technology, the cycle life of zinc anodes must be further improved. We show that using a three-dimensional carbon mesh as a host structure for the active material zinc oxide and then coating it homogeneously with an ionomeric, hydroxide conductive confinement layer yields unprecedented cycling stability. Long-term stable charge/discharge of the zinc anode can only be achieved by using this order of compounds: oxidized zincate species that would otherwise leech into the bulk electrolyte are directly confined at the electron conductive host structure by the applied ionomeric coating. We confirm with operando X-ray diffraction measurements that the defined layer of electrodeposited active material (zinc oxide) can be converted efficiently into zinc during charge and reversed then back to zinc oxide during discharge directly on the carbon host. We evidence high utilization of the active material (up to 93% based on initial amount of zinc oxide) and enhanced capacity retention (4 times higher compared to uncoated anodes after 30 cycles), tested for coin-type cell batteries with optimal amount of ionomeric coating. Analyses by means of scanning electron microscopy and cyclic voltammetry are used to prove that the polymer applied is chemically and electrochemically stable. In addition, permeability measurements prove low permeation rates for zincate ions for the tested ionomeric membranes, and zinc oxygen cells without zincate species in the bulk electrolyte indicate the confinement of zincate ions during cycling keeping them near the electrochemical active surface area where they are needed.