Bifunctional electrolyte inducing uniform Zn deposition and suppressing polyiodide shuttle for long life zinc-iodine batteries with low-temperature applicability

Abstract

Aqueous zinc‑iodine (Zn//I₂) batteries hold substantial promise for large-scale electrochemical energy storage systems due to their intrinsic safety, cost-effectiveness, and high energy density. However, their practical implementation is hindered by the well-known dendrite formation and adverse reactions at the Zn anode, along with the polyiodide shuttle effect from the I₂ cathode. Herein, a bifunctional gel electrolyte composed of eco-friendly cellulose and chitosan is developed to simultaneously address these challenges. The gel electrolyte can regulate the homogeneity of electric and Zn²⁺ concentration fields at the Zn anode and induce Zn (002) oriented deposition, thus achieving uniform Zn deposition. In addition, water activity can be also restricted by the gel electrolyte, which suppresses corrosion and hydrogen evolution reactions and improves frost resistance ability. The gel electrolyte can also effectively block the migration of polyiodide species, minimizing active material loss and enhancing cathode stability. Consequently, Zn//Zn cell with the gel electrolyte achieves an ultra-stable lifespan for over 2300 h at 5 mA cm⁻²/2.5 mAh cm⁻², and Zn//Cu cell exhibits outstanding Coulombic efficiency of 99.2 %. Zn//I₂ full cell based on this gel electrolyte demonstrates superior cycling performance, retaining 93.1 % of its capacity at 0.5 A g⁻¹. This work presents an effective strategy for developing high-performance, durable, and anti-freezing Zn//I₂ batteries.