Dendrite-free zinc anode enabled by zwitterionic organic hydrogel electrolytes for high-voltage zinc-ion hybrid capacitors

Aqueous zinc-ion hybrid supercapacitors (ZIHC) have been widely researched due to their inherent high safety, low cost, and high power. However, the low operating voltage of aqueous electrolytes, H2O-induced side reactions, and intractable dendrites severely compromise the energy output and durability of ZIHC. Herein, a freeze-tolerant zwitterionic organic hydrogel electrolyte (PSAMOHE) was constructed for high-voltage flexible ZIHC. The hydrogen bonding between ethylene glycol and water inhibited the formation of ice crystals, preventing the electrolyte from freezing at −40 °C. Concurrently, the hydrophilic PSAMOHE mitigated harmful side reactions and achieved a wide electrochemical stability window (2.2 V) by anchoring water molecules. In addition to exhibiting exceptional interface adhesion and mechanical adaptability, PSAMOHE with charged functional groups effectively facilitated ion migration, diminished the desolvation energy barrier of hydrated Zn2+, and induced uniform Zn deposition. By combining these advantages, the assembled flexible ZIHC exhibited a battery-level specific capacity of 269.1 mAh/g (at 0.5 A/g), impressive environmental adaptability, and excellent mechanical adaptability. Impressively, the ZIHC maintained 89.5 % of the initial capacity and obtained a dendrite-free Zn anode after 14,000 cycles of charge and discharge. This study provides valuable insights into the exploration of hydrogel electrolyte engineering for high-performance zinc-based flexible energy storage devices.