Flexible Ti₃C₂T_x@Al electrodes with Ultrahigh Areal Capacitance: In Situ Regulation of Interlayer Conductivity and Spacing

Abstract

Although Ti 3 C 2 MXene has shown great potential in energy storage field, poor conductivity and restacking between MXene flakes seriously hinders the maximization of its capacitance. Herein, a new strategy to solve the problems is developed. Gallery Al atoms in Ti 3 AlC 2 are partially removed by simple hydrothermal etching to get Ti 3 C 2 T x reserving appropriate Al interlayers (Ti 3 C 2 T x @Al). Ti 3 C 2 T x @Al keeps stable layered structure rather than isolated Ti 3 C 2 T x flakes, which avoids flake restacking. The removal of partial Al frees up space for easy electrolyte infiltration while the reserved Al as "electron bridges" ensures high interlayer conductivity. As a result, the areal capacitance reaches up to 1087 mF cm −2 at 1 mA cm −2 and over 95% capacitance is maintained after 6000 cycles. The all-solid-state supercapacitor (ASSS) based on Ti 3 C 2 T x @Al delivers a high capacitance of 242.3 mF cm −2 at 1 mV s −1 and exhibits stable performance at different bending states. Two ASSSs in tandem can light up a light-emitting diode under the planar or wrapping around an arm. The established strategy provides a new avenue to improve capacitance performances of MXenes.

A MXene‐Coated Activated Carbon Cloth for Flexible Solid‐State Supercapacitor

“…The prepared gel electrolyte above was coated on one side of two HHK‐CC@Ti 3 C 2 T X ‐3, with the same shape and size. The two electrodes were gently pressed together face‐to‐face to assemble a symmetric SSC …”

Two‐Dimensional Transition Metal Carbides and Nitrides (MXenes): Synthesis, Properties, and Electrochemical Energy Storage Applications

“…Previous reports indicate that Al has to be completely removed from the MAX phase. Recently, Guo et al partially removed gallery Al layers in Ti 3 AlC 2 to obtain Ti 3 C 2 T x with appropriate Al interlayers (Ti 3 C 2 T x @Al), which demonstrated excellent areal capacitances. In another report, hexagonal WO 3 was deposited on Ti 3 C 2 to enhance the electrical conductivity and surface area .…”

“…Another typical example on engineering the electrode configuration is the partial removal of the Al layer from the Ti 3 AlC 2 phase, leading to Ti 3 C 2 T x MXene with a stable layered structure and minimized flake restacking . The removal of Al freed up space for easy electrolyte infiltration while the preserved Al as “electron bridges” ensured high out‐of‐plane conductivity (Figure b) . Very recently, Li et al .…”

“…b) Schematic demonstration of the synthesis process for Ti 3 C 2 T x @Al (together with corresponding HRTEM images) and transfer of electrons and ions in it. Reproduced with permission from ref . Copyright 2018, John Wiley & Sons.…”

Low‐Temperature Reduction Strategy Synthesized Si/Ti3C2 MXene Composite Anodes for High‐Performance Li‐Ion Batteries

“…In this regard, 2D Ti 3 C 2 MXene is an ideal alternative due to its high diffusion mobility of Li + ions (≈10 −10 –10 −9 cm 2 s −1 ) with lower Li + diffusion barrier (0.07 eV) than that of graphene (0.3 eV) . Ti 3 C 2 MXene also has been an attractive candidate for electrode materials of supercapacitors and anodes of LIBs due to the abundant surface redox reaction, which enables Ti 3 C 2 display significant contribution to the capacity rather than only work as conductive matrix. For instance, black phosphorus quantum dot (BPQD)/Ti 3 C 2 MXene nanosheet composites synthesized by an interfacial assembly strategy present a high reversible capacity of 1124 mAh g −1 at 50 mA g −1 when used as anodes of LIBs, which is attributed to the excellent conductivity of Ti 3 C 2 MXene and indispensable synergies of BPQD and Ti 3 C 2 MXene in capacity contribution .…”