A mechanically robust all-solid-state supercapacitor based on a highly conductive double-network hydrogel electrolyte and Ti3C2Tx MXene electrode with anti-freezing property

Abstract

Hydrogels are peculiarly attractive electrolyte materials for constructing flexible and secure all-solid-state supercapacitors due to their mechanical flexibility, ionic conductivity and noninflammability. However, upon severe mechanical stresses, hydrogel electrolyte-based supercapacitors will undergo irreversible structural damage, which results in dramatically fluctuant energy output. Additionally, invalid mechanical flexibility and serious capacitance degradation at subzero temperature are also urgent issues to be addressed. Herein, a mechanically reliable, exceptional-performance and anti-freezing all-solid-state supercapacitor is constructed from a highly ionic conductive double-network (DN) hydrogel electrolyte, intrinsically powerful Ti₃C₂T_x MXene film electrode and carbon nanotube film current collector. The DN hydrogel possesses impressive ionic conductivities of 4.8 and 3.6 S m⁻¹ at room temperature and −20 °C, respectively, together with an effective energy-dissipation mechanism and freezing tolerance (<−40 °C). The distinct combination endows the assembled supercapacitor with low internal resistance and eminent stress dissipation, which results in extraordinary capacitive performance (capacitance of 297.1 mF cm⁻² and energy density of 14.76 μW h cm⁻²), remarkable structural reliability and electrochemical stability under multiple severe damages. Even upon consecutive 3 d of trampling, the supercapacitor still delivers an unimpaired capacitance. Significantly, superior freezing tolerance enables the supercapacitor to well maintain high areal capacitance (150.0 mF cm⁻² at 1.0 mA cm⁻²) at −20 °C and excellent capacitive stability upon external stresses. Furthermore, a self-powered sensing device is successfully integrated from the hydrogel-based supercapacitor and sensor to accurately detect various human motions. This study will pave a way to develop ultrahigh-performance and freezing-tolerant supercapacitors for wearable power sources against severe mechanical damage.