A novel water-reducer-based hydrogel electrolyte for robust and flexible Zn-I2 battery

Abstract

Aqueous zinc-iodine (Zn-I₂) batteries are becoming increasingly attractive due to their considerable capacity, inherent safety and economic viability. However, the key issues remain unsolved including the shuttling of polyiodides in the I₂ cathode and the severe corrosion and dendrite growth in the zinc anode. This work propose a novel water reducer-based gel electrolyte, PC-PVA/Zn(CF₃SO₃)₂, to concurrently handle with Zn anode and I₂ cathode. Specifically, the hydrogen evolution corrosion for the Zn anode is effectively inhibited by forming hydrogen bonds to lock free H₂O molecules and the dendrite growth of the Zn anode could be hindered by adjusting the electric filed to realize the homogenous Zn²⁺ deposition. Simultaneously, the abundant polar oxygen-containing group in PC-PVA gel can capture polyiodide and mitigate the “shuttle effect”, thereby enhancing the I₂/I⁻ redox kinetics. This hydrogel electrolyte with excellent mechanical properties also gives rise to the electrode's high stability. As a result, such a PC-PVA/Zn(CF₃SO₃)₂ electrolyte enables Zn anode with an excellent lifespan over 4000 cycles and at 1 mA cm⁻², 1 mAh cm⁻², and the average coulombic efficiency could attain 99.4%. And the resulting Zn||I₂ full cells also demonstrate excellent performances, which the reversible capacity could maintain at 155.2 mAh g⁻¹ after 5000 cycles at 1 A g⁻¹, and the capacity decay rate is only 0.0015% per cycle. This cost-effective and readily available gel electrolyte provides a viable strategy for commercializing Zn-I₂ batteries.