All‐Climate Energy‐Dense Cascade Aqueous Zn‐I <sub>2</sub> Batteries Enabled by a Polycationic Hydrogel Electrolyte
Yangyang Liu, Longhai Zhang, Ling Liu, Quanwei Ma, Rui Wang, Peng Xiong, Hongbao Li, Shilin Zhang, Junnan Hao, Chaofeng Zhang
Abstract
Abstract The practical development of aqueous zinc‐iodine (Zn‐I 2 ) batteries is greatly hindered by the low energy density resulting from conventional I 0 /I − conversion and the limited temperature tolerance. Here, a temperature‐insensitive polycationic hydrogel electrolyte borax‐bacterial cellulose / p (AM‐ co ‐VBIMBr) (denoted as BAVBr) for achieving an energy‐dense cascade aqueous Zn‐I 2 battery over a wide temperature range from −50 to 50 °C is designed. A comprehensive investigation, combining advanced spectroscopic investigation and DFT calculations, has revealed that the presence of Br species in the gel electrolyte facilitates the conversion reaction of Br 0 /Br − . Simultaneously, it activates the high voltage I + /I 0 redox reaction through interhalogen formation. Consequently, sequential and highly reversible redox reactions involving I 0 /I − , I + /I 0 , and Br 0 /Br − are achieved with the assistance of −NR 3 + units in BAVBr, effectively suppressing interhalogen hydrolysis in aqueous electrolyte. The cascade reactions lead to a high area capacity of 0.76 mAh cm −2 at a low I 2 loading of 1 mg cm −2 or 760 mAh g −1 based on the mass of iodine, demonstrating exceptional long‐term cycling stability over a wide temperature range from −50 to 50 °C. This study offers valuable insights into the rational design of electrolytes for high‐energy aqueous batteries, specifically tailored for wide‐temperature operation.