Lotus seedpod-inspired electrocatalytic interlayer synthesized via ultrafast Joule heat treatment: overcoming polyiodide shuttle and enhancing redox kinetics in high-areal-capacity aqueous zinc-iodine batteries

Abstract

Aqueous zinc-iodine (Zn-I2) batteries are gaining attention as cost-effective and safe energy storage solutions with high energy density. However, their practical performance is hindered by issues such as polyiodide dissolution, the shuttle effect, and slow iodine redox kinetics, which restrict reversible areal capacity and cycling stability. Herein, we develop a biomimetic electrocatalytic interlayer (Fe-Ni@ACC) for advanced Zn-I2 batteries using Joule heat ultrafast high-temperature (UHT) treatment. This bio-inspired structure resembles a lotus seedpod, where ultrafine Fe-Ni alloy nanoparticles (lotus seed) are embedded within activated carbon fibers (lotus seedpod), ensuring strong binding strength and efficient electron transfer. Additionally, the UHT process also induces the spontaneous formation of abundant nanocavities, effectively accommodating iodine species. Comprehensive in situ characterizations and theoretical calculations demonstrate that Fe-Ni alloy nanoparticles, with the unique electronic structure inside nanocavities, significantly accelerates polyiodide conversion through efficient d-p orbital hybridization. Consequently, these lotus seedpod-like reaction chambers effectively anchor polyiodide and enhance iodine redox kinetics, enabling Zn-I2 batteries to achieve a high areal capacity of 4.05 mAh cm-2 and an ultralong lifespan exceeding 12,000 cycles. This work provides a facile and scalable methodological platform for synthesizing electrocatalytic interlayers, advancing the practical implementation of Zn-I2 batteries.