Low‐Concentration Hydrogel Polyelectrolyte with In Situ Formed Interphases Enables 2.7 V Aqueous Pouch Cell
Tianfeng Qin, Kaiwen Li, Yingjun Liu, Zhen Xu, Chao Gao
Abstract
Abstract To maximize energy output, aqueous zinc‐based batteries are pushed to extreme potentials far beyond thermodynamic stability limit of aqueous electrolytes. Interphases at interfaces of electrodes/electrolytes are needed to make aqueous batteries stable and reversible kinetically. The absence of interphases at interfaces of hydrogel/electrodes severely impedes aqueous batteries operating in extreme potentials, although low‐concentration hydrogels are regarded as promising polyelectrolytes. Herein, a type of initiator system as cross‐linking agent is developed that makes hydrogel polyelectrolyte spontaneously in situ form interphases at 25 °C and darkness. This widens the electrochemical stability window of hydrogel polyelectrolyte to above 3.5 V. Also, the initiator system makes the designed hydrogel become a single ion conductor, increasing ionic conductivity to ≈280 mS cm −1 . This hydrogel pushes a zinc//LiMn 2 O 4 pouch cell to operate stably in a voltage window of 0.2 to 2.7 V and deliver high energy densities (e.g., 471 Wh kg LiMn2O4 −1 at 2.2 mg LiMn2O4 cm −2 ; 203 Wh kg LiMn2O4 −1 , 7.1 mg LiMn2O4 cm −2 ) and excellent rate capabilities (e.g., 410 mAh g −1 at 0.11 C, 50 mAh g −1 at 57 C, 2.2 mg LiMn2O4 cm −2 ; 175 mAh g −1 at 0.7 C, 70 mAh g −1 at 7.5 C, and 7.1 mg LiMn2O4 cm −2 ).