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

Abstract

as well as light-weight, remarkable flexibility, and security. [1][2][3][4][5] During last 5-7 years, we witnessed the rapid improvement of unconventional supercapacitors including high-performance (especially the areal and volumetric properties) supercapacitors, [6][7][8][9] novel structured micro-supercapacitors, [10][11][12] ultrathin and transparent devices, [13,14] flexible all-solid-state supercapacitors, [15][16][17][18][19] and on-chip and large-scale integrated micro-supercapacitors. [20][21][22] Although these breakthroughs were made, development of MSCs is still in its infancy. And lots of importance and challenges such as 3D architecture design, highconductive leakage-free electrolytes, low self-discharge effect, large-scale on-chip integration at microscale, high mechanical reliability, and outstanding performances in areal and volumetric need to be further addressed. Similar to conventional supercapacitors with inflexibility and liquid electrolytes, the intrinsic properties of the electrode materials, which are critical to high-performance supercapacitors and the method of electrode fabrication, evidently play the most important role in developing state-of-the-art MSCs. In this respect, it is the key to find one material that possesses both outstanding mechanical flexibility and electrochemical performance.MXenes, one kind of novel 2D materials, are promising candidates for developing state-of-the-art MSCs because of their outstanding electrical conductivity, superior areal and 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 Ti 3 C 2 T 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 × 10 5 S m −1 ) and self-functionalized surfaces (O, OH, and F terminations). Amazingly, freestanding conductive Ti 3 C 2 T x based flexible solid-state MSCs with interdigital electrodes and polyvinyl alcohol/sulfuric acid (PVA/H 2 SO 4 ) 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 Ti 3 C 2 T x shows potential and scalability in increasing overall

Highly Stretchable and Self‐Healable MXene/Polyvinyl Alcohol Hydrogel Electrode for Wearable Capacitive Electronic Skin

“…The MXene was obtained via an improved etching procedure previously reported . The dark‐green few‐layer Ti 3 C 2 T x MXene exhibits good dispersion in aqueous solutions, with a long stability (Figure b) confirmed by the Tyndall effect . The well‐dispersed MXene is in favor of preparing the homogeneous mixed solution.…”

Enhancing Capacitance Performance of Ti3C2Tx MXene as Electrode Materials of Supercapacitor: From Controlled Preparation to Composite Structure Construction

“…This defect is particularly significant in the hydrothermal method [32]. In order to control those situations, many works have focused on the modification of Ti 3 C 2 T x [33][34][35]. Figure 1 shows the common methods of enhancing the capacitance of Ti 3 C 2 T x as electrode materials of supercapacitors [21,[36][37][38][39][40][41].…”

Recent developments of advanced micro-supercapacitors: design, fabrication and applications

“…It is worth mentioning that, as a new class of 2D metal compounds in the field of electrochemistry, MXene has attracted wide attention in planar MSCs because its 2D open structure can offer high surface area, good electron mobility, as well as excellent electrolyte permeability [107][108][109][110] . However, like graphene, 2D MXene sheets also endure severe re-stacking in practical application 111,112 . Therefore, it is necessary to take steps avoiding its restacking prior to real use.…”