Precipitated iodine cathode enabled by trifluoromethanesulfonate oxidation for cathode/electrolyte mutualistic aqueous Zn−I batteries

Abstract Aqueous Zn − I batteries hold great potential for high-safety and sustainable energy storage. However, the iodide shuttling effect and the hydrogen evolution reaction that occur in the aqueous electrolyte remain the main obstacles for their further development. Herein, we present the design of a cathode/electrolyte mutualistic aqueous (CEMA) Zn − I battery based on the inherent oxidation ability of trifluoromethanesulfonate ([OTf]−) based aqueous electrolyte towards triiodide species. This results in the formation of iodine sediment particles assembled by fine iodine nanocrystals (approximately 10 nm). An iodine host cathode with high areal iodine loading was realized via a spontaneous absorption process that enriched redox-active iodine and iodide species from aqueous electrolyte onto nanoporous carbon based current collector. By tuning iodide redox process and suppressing competitive hydrogen evolution reaction, the assembled CEMA Zn − I batteries demonstrated a remarkable capacity retention of 76.9% over 1000 cycles, retaining a capacity ranging from 141 to 112 mAh g− 1 at a current density of 0.5 mA cm− 2. Moreover, they exhibited a notable rate capability, with a capacity retention of 74.6% when the current density was increased from 0.5 to 5.0 mA cm− 2, resulting in a capacity retention range of 130 to 97 mAh g− 1. This study demonstrates the feasibility of using the oxidation effect to repel redox-active species from the electrolyte to the cathode, paving a new avenue for high-performance aqueous Zn − I batteries.