Reassembly of MXene Hydrogels into Flexible Films towards Compact and Ultrafast Supercapacitors

Abstract

The freestanding MXene films are promising for compact energy storage ascribing to their high pseudocapacitance and density, yet the sluggish ion transport caused by the most densely packed structure severely hinders their rate capability. Here, a reassembly strategy for constructing freestanding and flexible MXene-based film electrodes with a tunable porous structure is proposed, where the Ti 3 C 2 T x microgels disassembled from 3D structured hydrogel are reassembled together with individual Ti 3 C 2 T x nanosheets in different mass ratios to form a densely packed 3D network in microscale and a film morphology in macroscale. The space utilization of produced film can be maximized by a good balance of the density and porosity, resulting in a high volumetric capacitance of 736 F cm −3 at an ultrahigh scan rate of 2000 mV s −1 . The fabricated supercapacitor yields a superior energy density of 40 Wh L −1 at a power density of 0.83 kW L −1 , and an energy density of 21 Wh L −1 can be still maintained even when the power density reaches 41.5 kW L −1 , which are the highest values reported to date for symmetric supercapacitors in aqueous electrolytes. More promisingly, the reassembled films can be used as electrodes of flexible supercapacitors, showing excellent flexibility and integrability.

Manipulating the Interlayer Spacing of 3D MXenes with Improved Stability and Zinc‐Ion Storage Capability

“…In regard to electrochemical energy storage, MXenebased materials still suffer from the intrinsic restacking tendency, reduced accessibility of electrochemical surface area, and limited ion transport. [16,17] MXene-based hybrid materials can be further developed to obtain an architecture that can empower access to nanospaces and promote ion transfer. [18][19][20][21] Thus, it is highly desired to engineer the interlayer spacing of MXenes to improve their electrolyte-accessible surface area and enhance the charge-transport properties to achieve their full chargestorage capability.…”

Bridging sheet size controls densification of MXene films for robust electromagnetic interference shielding

“…Particularly, as shown in Figure 1 B, when the sheet size of bridging GO decreased from 14.04 to 0.35 μm, the interlayer distance gradually decreases, verifying that the MXene-GO films became more compact. In fact, during the forming process of MXene films, the MXene sheets are mainly affected by the capillary force and the electrostatic repulsion force as schematically shown in Figure 1 C ( Wu et al., 2021 ). Among them, the capillary force tends to make the stacking of MXene sheets denser, while the electrostatic repulsive force tends to make the stacking of MXene sheets looser.…”

Three‐Dimensional MXenes for Supercapacitors: A Review

“…As MXene nanosheets are negatively charged, the interlayer repulsion makes them to form stable aqueous dispersions. Therefore, through adding suitable crosslinking agents [76][77][78] or weakening the repulsion, [79,80] the assembly into 3D structures can be achieved by breaking the dispersion balance.…”

“…Recently, Yang et al reported a reassembly strategy for producing a flexible MXene-based electrode with tunable porous structure by disassembling MXene microgels from 3D hydrogel and then reassembling with individual MXene nanosheets. [76] The layered arrangement of individual MXene nanosheets formed a densely packed texture, and the well-dispersed MXene microgels introduced pores for ion transport. By controlling the ratio of MXene microgels and individual nanosheets, the density and porosity of the MXene film could be balanced, leading to considerable volumetric capacitance under ultrahigh rate.…”