Toward Practical Zn‐Ion Batteries Through Separator/Electrolyte Co‐Design

ABSTRACT While substantial research effort has been paid to address short‐circuits and parasitic hydrogen evolution reactions (HER) in Zn‐ion batteries (ZIBs), a remaining challenge that is often overlooked is ZIB separators. Currently, thick glass fiber (GF) separators are used, which unnecessarily reduce the volumetric cell performance and lead to non‐uniform Zn plating/stripping. Unfortunately, separators optimized for Li‐ion batteries are intrinsically hydrophobic and therefore incompatible with aqueous ZIB systems. Here, we propose using a hybrid organic‐aqueous electrolyte which is compatible with thin polypropylene (PP) separators developed for Li‐ion batteries. The hybrid electrolyte, together with the PP separator, enables uniform Zn plating and suppresses HER. Combined, these effects allow for stable cycling for 4360 h at 1 mA cm −2 and 3 mAh cm −2 in a Zn symmetrical cell. Further, replacing the currently used 350 µm‐thick GF separator with our proposed 23 µm PP separator can increase the energy densities of multi‐layer pouch cells by over 2.5‐fold. Finally, Zn//NVO full cells using our hybrid electrolyte and separator demonstrate stable cycling performance for over 200 cycles at a high areal capacity of 4.4 mAh cm −2 , demonstrating that electrolyte/separator co‐design is an overlooked strategy toward practical ZIBs.