Extraordinary Areal and Volumetric Performance of Flexible Solid‐State Micro‐Supercapacitors Based on Highly Conductive Freestanding Ti₃C₂T_x Films

Abstract Approaching state‐of‐the‐art areal and volumetric capacitances while maintaining high‐power characteristic is a big challenge that promotes practical application of flexible solid‐state micro‐supercapacitors (MSCs), which have recently attracted great attention with the rapid development of flexible microelectronics. Herein, it is reported that freestanding extrahigh conductive Ti₃C₂T_x (MXene) films with excellent flexibility and effectively controlled thickness ranging from 1–21 µm performed as excellently scalable and flexible solid‐state MSCs owing to their ultrahigh underlying electrical conductivity (up to 1.25 × 10⁵ S m⁻¹) and self‐functionalized surfaces (O, OH, and F terminations). Amazingly, freestanding conductive Ti₃C₂T_x based flexible solid‐state MSCs with interdigital electrodes and polyvinyl alcohol/sulfuric acid (PVA/H₂SO₄) gel electrolyte display outstanding areal capacitances of 340 mF cm⁻² at 0.25 mA cm⁻² based on the two working electrodes. Moreover, the maximum corresponding volumetric capacitance and energy density of flexible solid‐state MSCs reach up to 183 F cm⁻³ and 12.4 mWh cm⁻³, which is on the topmost level among all the unconventional supercapacitors to date. Compared with materials currently used in MSCs, this freestanding conductive Ti₃C₂T_x shows potential and scalability in increasing overall micro‐supercapacitor performance, which evidently sheds light on promising application of freestanding conductive MXenes for next‐generation flexible, portable, and integrated MSCs.