Freeze-tolerant gel electrolyte membrane for flexible Zn-ion hybrid supercapacitor

At low temperatures, the working capability of Zn-ion energy storage devices at low temperatures is becoming a huge challenge in the field of electrochemical energy storage. This is primarily due to the slow kinetic process of ions along with the failure of hydrogel electrolytes under subzero temperatures. Herein, a flexible anti-freezing Zn-ion hybrid supercapacitor is developed with the use of freeze-tolerant polyacrylamide‑sodium alginate (PAM-SA) gel electrolyte membrane combined with graphene cathode and Zn foil anode. The freeze-tolerant PAM-SA gel electrolyte membrane is synthesized by a simple solvent displacement process and it shows an excellent ionic conductivity of ∼15.29 mS cm−1 at room-temperature (RT) with an anti-freezing ability of 4.17 mS cm−1 at −25 °C. Also, the prepared electrolyte membrane demonstrates an outstanding long-term stability over 900 h without the formation of Zn dendrites. The anti-freezing Zn-ion hybrid supercapacitor displays a sound electrochemical performance with an excellent capacity of 210.6 F g−1 in conjunction with the capacitance retention of 65 % even after charge-discharge cycling for 40,000 times at RT. Also, the device possesses an excellent anti-freezing performance. It can still deliver a capacity of 79.60 F g−1 and the capacitance retention of 80 % after cycling for 15,000 times even at a low temperature of −25 °C. These results indicate that the present work may offer a feasible way of constructing Zn-ion energy storage devices applicable in a subzero temperature environment.