Polymer and Chaotropic Anion: A dual-additive strategy enables stable Zn Anode and high energy efficiency for Zn-Air/Iodide hybrid batteries

Abstract

The severe Zn dendrite growth and low energy efficiency inhibit the application of Zn-air batteries (ZABs) in energy storage. Electrolyte additives are promising to resolve these issues and improve battery performance. Polyacrylamide (PAM) additive with abundant polar functional groups can theoretically induce a uniform Zn deposition and interacts with water molecules to lower the water activity but suffer from limited effect in practice due to low solubility. Concurrently, chaotropic anion I^- with a lower oxidation potential is also introduced to substitute the sluggish oxygen evolution reaction (OER) with a faster iodide oxidation reaction (IOR) during charging, contributing to a Zn-air/iodide hybrid battery with enhanced energy efficiency. However, the I^- has no effect on Zn dendrite issues. Herein, we develop a dual-additive strategy employing polymer and chaotropic anion simultaneously to take both their advantages but also avoid the drawbacks. I^- can facilitate the dissolution and untangling of PAM chains, which enables more functional groups to interact with Zn and water molecules. Thanks to the synergetic effect of PAM and I^-, the hybrid ZAB delivers a long cycle life of 240 h with a high energy efficiency of 74.6 % and obtains a stable Zn anode with alleviated dendrite growth and improved utilization rate. Moreover, the rapid IOR process enables stable battery operation at -20 °C, further broadening the application scenarios of ZABs.