MXene-based film electrode and all-round hydrogel electrolyte for flexible all-solid supercapacitor with extremely low working temperature

The fabrication of a flexible all-solid supercapacitor able to work under various deformations, even under extreme conditions, remains challenging because of the rigidity of electrodes, the freezing of gel electrolytes, and interfacial contact problems. Here, we report a flexible supercapacitor with excellent mechanical deformation and ultra-low temperature tolerance assembled by using the designed MXene/carboxymethyl cellulose film electrode and all-round polyvinyl alcohol/LiCl (PVA/LiCl) hydrogel electrolyte. The supercapacitor combines mechanically flexible (12.7 MPa at 5.9% strain) and highly conductive (267 S/cm) electrodes with the PVA/LiCl hydrogel electrolyte with high ion conductivity, excellent mechanical properties, self-adhesion, and antifreezing ability. As a result, the assembled supercapacitor exhibits a high specific capacitance (113.13 mF cm−2) with a retention of ∼95% under mechanical deformations, and more importantly, the electrochemical stability can be maintained even at −40°C when subjected to severe deformations. This work offers an option to design flexible supercapacitors as environment-adaptable energy-storage devices.