Biological Zwitterion Betaine‐Assisted Wide Voltage Window and Freeze‐Resistance Hydrogel Electrolyte for Flexible Supercapacitor

ABSTRACT Flexible supercapacitors based on hydrogels have developed rapidly, although they still face issues such as low voltage window and easy freezing of gel at low temperatures. Herein, the biological zwitterionic betaine is utilized to lock water molecular for widening the voltage window and improving anti‐freezing performances of PAM/PEG/CS/Betaine‐composited hydrogels (named as PPCBx, x denotes the amount of betaine). By optimizing the betaine contents, the PPCB 0.03 hydrogel reaches the stress limit of 102.04 KPa at the tensile strain limit of 400%, with a high ionic conductivity of 2.87 S m −1 . The ionic conductivity remains at 0.45 and 0.15 S m −1 even at −30 and −50°C. The assembled supercapacitor can endow a high voltage window reaching 2.4 V. The specific area capacity of the device is 585.45 mF cm −2 at the current density of 2 mA cm −2 and maintains 82% after 9000 cycles. The specific capacity can still remain 191.24 mF cm −2 even at −50°C, demonstrating its remarkable anti‐freezing feature. Assembled with solar cells, the device can be successfully utilized for energy harvesting.