A Biphasic Membraneless Zinc‐Iodine Battery with High Volumetric Capacity

Abstract As one of the latest research directions, membraneless batteries provide an economical solution to redox flow batteries. Advances in electrolyte and device design have promoted membraneless batteries from microfluidic demonstration to systems with stimulated modes and considerable electrochemical properties. However, the achieved cycling volumetric capacity is typically limited. Herein, a biphasic membraneless zinc‐iodine battery (Z|T‐I) is proposed, through optimized Zn growth, the Z|T‐I battery achieved a volumetric capacity of 8.93 Ah L −1 for 100 cycles with an average Coulombic efficiency (CE) of 98.49% (2300 h), the deep cycling exhibited a volumetric capacity of 21.7 Ah L −1 (50.43 Wh L −1 based on typical membraneless battery calculation, 1200 h); both values are the highest among single/biphasic membraneless batteries using liquid active materials with/out stimulations (<6.6 Ah L −1 ) reported so far based on the total electrolyte volume. A thorough analysis of Zn growth in Zn‐Br 2 /I 2 electrolytes with various testing conditions provided direct evidence of the contrasting Zn electrodeposition morphologies at both macro and micro scales. The biphasic ZnI 2 battery design strategy gives insights into optimizing material crossover/spatial utilization and electrolyte interfacial stability to realize a scalable membraneless energy storage system with a reduced cost.