Amino acid-based functional additive enables fast polyiodide conversion kinetics for durable Zn-I2 batteries

Abstract

The applications of Zn-I2 batteries are plagued by severe side reactions, including the polyiodide shuttle on the cathode and parasitic by-products on the zinc anode. Herein, we introduce an amino acid derivative, D-penicillamine (DPL), as a molecular-level mediator to simultaneously resolve these challenges. Its functional groups effectively anchor iodine species and catalyze polyiodide conversion, thus suppressing the shuttle effect for highly reversible iodine redox. Concurrently, its preferential adsorption and favorable electronic structure enable the protection on the zinc anode, which inhibits dendrite growth and gas evolution reaction. Consequently, the DPL-containing electrolyte enables exceptional long-term stability: a symmetric Zn||Zn cell operates stably for over 1500 h at 5 mA cm-2 and 1 mAh cm-2, while a full Zn-I2 cell endures an unprecedented 12000 cycles at 10 A g-1 with 87.6% capacity retention. Especially at high I2 loading of 14.7 mg cm-2, the corresponding pouch cell exhibits impressive reversible capacity of 160 mA h g-1 and considerable retention ratio of 95.2% after 100 cycles at low current density of 0.5 A g-1. This paper demonstrates that employing molecular mediators is a powerful strategy to design and develop high-performance Zn-I2 batteries.