Low-temperature and high-voltage planar micro-supercapacitors based on anti-freezing hybrid gel electrolyte

By introducing ethylene glycol into aqueous LiCl solution, high-voltage and anti-freezing electrolyte with low cost and high ionic conductivity is developed for aqueous planar micro-supercapacitors, with high voltage, enhanced energy density and excellent low-temperature stability. Micro-supercapacitors (MSCs) are considered as highly competitive power sources for miniaturized electronics. However, narrow voltage window and poor anti-freezing properties of MSCs in conventional aqueous electrolytes lead to low energy density and limited environmental adaption. Herein, we report the construction of low-temperature and high-energy-density MSCs based on anti-freezing hybrid gel electrolytes (HGE) through introducing ethylene glycol (EG) additives into aqueous LiCl electrolyte. Since EG partially destroys hydrogen bond network among water molecules, the HGE exhibits maximum electrochemical stability window of 2.7 V and superior anti-freezing features with a glass transition temperature of −62.8 °C. Further, the optimized MSCs using activated carbon microelectrodes possess impressive volumetric capacitance of 28.9 F cm −3 and energy density of 10.3 mWh cm −3 in the voltage of 1.6 V, 2.6 times higher than MSCs tested in 1.2 V. Importantly, the MSCs display 68.3% capacitance retention even at −30 °C compared to the value at 25 °C, and ultra-long cyclability with 85.7% of initial capacitance after 15,000 times, indicating extraordinary low-temperature performance. Besides, our devices offer favorable flexibility and modular integration. Therefore, this work provides a general strategy of realizing flexible, safe and anti-freezing microscale power sources, holding great potential towards subzero-temperature microelectronic applications.