Modified MXene/Holey Graphene Films for Advanced Supercapacitor Electrodes with Superior Energy Storage

Abstract

MXene films are attractive for advanced supercapacitor electrodes requiring high volumetric energy density due to their high redox capacitance combined with extremely high packing density. However, the self‐restacking of MXene flakes unavoidably decreases the volumetric performance, mass loading, and rate capability. Herein, a simple strategy is developed to prepare a flexible and free‐standing modified MXene/holey graphene film by filtration of the alkalized MXene and holey graphene oxide dispersions, followed by a mild annealing treatment. After terminal groups (—F/—OH) are removed, the increased proportion of Ti atoms enables more pseudocapacitive reaction. Meanwhile, the embedded holey graphene effectively prevents the self‐restacking of MXene and forms a high nanopore connectivity network, which is able to immensely accelerate the ion transport and shorten transport pathways for both ion and electron. When applied as electrode materials for supercapacitors, it can deliver an ultrahigh volumetric capacitance (1445 F cm−3) at 2 mV s−1, excellent rate capability, and high mass loading. In addition, the assembled symmetric supercapacitor demonstrates a fantastic volumetric energy density (38.6 Wh L−1), which is the highest value reported for MXene‐based electrodes in aqueous electrolytes. This work opens a new avenue for the further exploration of MXene materials in energy storage devices.

Hydrous RuO2‐Decorated MXene Coordinating with Silver Nanowire Inks Enabling Fully Printed Micro‐Supercapacitors with Extraordinary Volumetric Performance

“…As shown in Figure 5d, the Nyquist plots of the different inks all exhibit similar curves, including a squashed semicircle in the high frequency region, and an approximately vertical line in the low-frequency region. [19] The improved ion transport behavior in inks with AgNWs is attributed largely in part to the embedded nanowires, which can provide more electrolyte permeable active sites. [63] In addition, the slopes of the plots in the low-frequency regions of M-A MSC, R-M-A MSC, and R@M-A 0.75:1 MSC are significantly greater than that of the MXene MSC, indicating their lower diffusion resistances.…”

“…[6,19] Following the ultrasonic treatment, 1.0 g Ti 3 AlC 2 powder was slowly added into the aforementioned solution and magnetically stirred for 24 h at 35 °C. [6,19] Following the ultrasonic treatment, 1.0 g Ti 3 AlC 2 powder was slowly added into the aforementioned solution and magnetically stirred for 24 h at 35 °C.…”

“…[15,16] Although over 20 different MXene materials have been successfully realized to date, Ti 3 C 2 T x is the most commonly studied for electrochemical capacitor applications due to its high metallic conductivity (up to 6500 S cm −1 ) for high current charge. [19] To mitigate this issue in efforts to enhance the electrochemical performance of the MXene-based supercapacitors, techniques must be developed to restrain selfrestacking to keep the MXene nanosheets separated within the electrodes. [17] Due to the existence of surface functional terminations, the delaminated negatively charged Ti 3 C 2 T x nanosheets are highly hydrophilic, which enables Ti 3 C 2 T x to form a stable, viscous, and aqueous colloidal suspension or ink without the need for additional surfactant or polymer additives.…”

The Development of Pseudocapacitor Electrodes and Devices with High Active Mass Loading

“…A great deal of research has been done to improve performance of MXenes by the formation of composites, containing graphene and other carbon materials. [ 269,270 ] Ti 3 C 2 T x materials were decorated with Ag nanoparticles and used for the fabrication of flexible electrodes and asymmetric devices. [ 271 ] A hydrothermal etching of Al from the Ti 3 AlC 2 structure facilitated electrolyte transfer, which resulted in enhanced conductivity and high areal capacitance.…”

All Hierarchical Core–Shell Heterostructures as Novel Binder‐Free Electrode Materials for Ultrahigh‐Energy‐Density Wearable Asymmetric Supercapacitors

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Supercapacitors (SCs), especially fiber-shaped supercapacitors (FSCs) with their tiny volume, remarkable flexibility, and excellent stitchability as well as fast charge-discharge capability, a high power density, and a long cycle life, are promising energy storage and supply devices. [25,[28][29][30][31][32] Additionally, low specific capacitance of fiber-shaped asymmetric supercapacitors (FASCs) has limited further improvements in the energy density of these devices. [25,[28][29][30][31][32] Additionally, low specific capacitance of fiber-shaped asymmetric supercapacitors (FASCs) has limited further improvements in the energy density of these devices.…”