Hydrogel electrolyte based on sodium polyacrylate/KOH hydrogel reinforced with bacterial cellulose aerogel for flexible supercapacitors

• The BC aerogel reinforced PANa/KOH hydrogel was prepared through a simple free radical polymerization. • The terminal groups and inorganic ion on PANa/BC/KOH endow hydrogel electrolyte good antifreeze property. • The BC aerogel was introduced to improve the tensile strength and ionic conductivity of hydrogel electrolyte observably. • The SC-PANa/BC/KOH showed a notable electrochemical performance and exhibited excellent flexibility and safety. Hydrogels are particularly promising electrolyte materials for constructing flexible and safe quasi-solid state supercapacitor due to their good flexibility, ionic conductivity and intrinsic safety. However, it remains a challenge to simultaneously obtain excellent mechanical robustness, high ionic conductivity and outstanding flexibility, particularly in sub-zero temperatures. Hence, we introduced a novel bacterial cellulose (BC) aerogel reinforced sodium polyacrylate/potassium hydroxide (PANa/KOH) hydrogel as a hydrogel electrolyte for flexible alkaline supercapacitor. The PANa/BC/KOH hydrogel electrolyte showed outstanding mechanical property (stress of 1.1 MPa), excellent anti-swelling performance and high ionic conductivity of 1.91 S m -1 at 25 ℃, 1.35 S m -1 at -25 ℃, exhibiting a superior anti-freezing performance. Benefiting from these intriguing integrated characteristics, the asymmetric supercapacitor (SC-PANa/BC/KOH) assembled PANa/BC/KOH hydrogel electrolyte and CoNi LDH@CC//AC@CC electrodes delivered a superior energy density of 25.63 W h kg -1 at a power density of 1200 W kg -1 and maintained a good retention of 92.05% after 10000 cycles. Meanwhile, the SC-PANa/BC/KOH exhibited excellent flexibility and safety, which is well adapted to various extreme conditions, such as weight-loading, bending and hammering. This work provided new sights into design of strong, anti-freezing, anti-swelling and high ionic conductive hydrogel electrolyte, paving the way for developing extremely safe wearable storage devices.