Engineering\nSelf-Adhesive Polyzwitterionic Hydrogel\nElectrolytes for Flexible Zinc-Ion Hybrid Capacitors with Superior\nLow-Temperature Adaptability

Abstract

Flexible zinc-ion hybrid capacitors\n(ZIHCs) based on hydrogel electrolytes\nare an up-and-coming and highly promising candidate for potential\nlarge-scale energy storage due to their combined complementary advantages\nof zinc batteries and capacitors. However, the freezing induces a\nsharp drop in conductivity and mechanical property with tremendous\ncompromise of the interfacial adhesion, thereby severely impeding\nthe low-temperature application of such flexible ZIHCs. To achieve\nthe flexible ZIHCs with excellent low-temperature adaptability, an\nantifreezing and self-adhesive polyzwitterionic hydrogel electrolyte\n(PZHE) is engineered <i>via</i> a self-catalytic nano-reinforced\nstrategy, affording unparalleled conductivity and robust interfacial\nadhesion, together with superhigh mechanical strength over a broad\ntemperature ranging from 25 to −60 °C. Meanwhile, the\nwater-in-salt-type PZHE filled with ZnCl₂ can provide ion\nmigration channels to enhance the reversibility of Zn metal electrodes,\nthus greatly reducing side reactions and extending the cycling life.\nWith distinctive integrated merits of the water-in-salt type PZHE,\nthe as-built ZIHCs deliver a high-level energy density of 80.5 Wh\nkg^–1, a desired specific capacity of 81.5 mAh g^–1, along with a long-duration cycling lifespan (100\n000 cycles) with 84.6% capacity retention at −40 °C, even\noutperforming the state-of-the-art ZIHCs at room temperature. More\nencouragingly, the extraordinary temperature-adaptability for both\nelectrochemical and mechanical performance under severe mechanical\nchallenges is achieved for the flexible ZIHCs at extremely low temperature.\nNoticeably, the ZIHC is also capable of operating in an ice–water\nbath and vacuum. It is believed that this strategy makes contributions\nto inspire the design and application of high-performance PZHEs in\nfields of flexible and wearable electronics that can work in extremely\ncold environments.