High-iodine-loading quasi-solid-state zinc–iodine batteries enabled by a continuous ion-transport network

Abstract

Zinc–iodine (Zn–I₂) batteries are promising candidates for next-generation large-scale energy storage systems due to their inherent safety, environmental sustainability, and potential cost-effectiveness compared to lithium-ion batteries. Their applications, however, have been limited by the sluggish Zn²⁺ transfer kinetics, severe polyiodide shuttling, and relatively low mass loading of iodine cathodes. Herein, we report a design strategy for a quasi-solid-state Zn–I₂ battery with a continuous 3D ion-transport network by integrating a thick iodine cathode and a bacterial cellulose hydrogel electrolyte. The polar bacterial cellulose fibers formed an interconnected network that provided abundant ion pathways for inward Zn²⁺ transport and also limited iodine species dissolution. The continuous 3D ion-transport networks were formed throughout the entire thick iodine cathode, resulting in a 10-times higher Zn-ion conductivity compared with the conventional-structured cathode. The quasi-solid-state Zn–I₂ battery based on the Zn anode and an integrated cathode delivered a reversible capacity of 176.6 mA h g⁻¹ and achieved long-term cycling for 900 cycles at 1C under an iodine loading of 20.0 mg cm⁻². The iodine loading can be further increased to 39.3 mg cm⁻² by adjusting the thickness of the cathode. Under a practical condition of low negative/positive ratio (N/P) of 2.1, an energy density of 56.4 Wh kg⁻¹ is achieved. This integrated electrode design provides guidelines for fabricating high-energy quasi-solid-state Zn ion batteries.