Stretchable supercapacitor based on a hierarchical PPy/CNT electrode and hybrid hydrogel electrolyte with a wide operating temperature

Hydrogel is frequently used as a solid electrolyte for all solid-state supercapacitors (SCs) because of its liquid-like ion-transport property and high conformability. However, due to the higher water content, the hydrogel electrolyte undergoes inevitable freezing and/or dehydration with climate change. Herein, polypyrrole/carbon all-solid-state SCs (PCSCs) were developed based on a hierarchical polypyrrole/carbon nanotube electrode and a highly stretchable double-network polymer hydrogel electrolyte with LiCl/ethylene glycol as a mixed solvent. The PCSCs showed excellent electrochemical performance and cycle stability with a wide operating temperature. The specific capacitances could reach 202.2 and 112.3 mF cm⁻² at current densities of 0.5 and 3.0 mA cm⁻², respectively. Meanwhile, the PCSCs showed outstanding mechanical properties in maintaining a high areal capacitance under deformations of bending and tension. The excellent water retention of the device also ensured the stable electrochemical performance of PCSCs in a wide temperature range (30–80°C), which could potentially represent a reliable application in various harsh environments.