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Abstract: Flexible fiber‐based supercapacitor (FSC) with excellent electrochemical performance and high tensile strength and modulus is strongly desired for some special circumstances, such as load‐bearing, abrasion resistant, and anticutting fabrics. Here, a series of ultrahigh‐strength fiber electrodes are prepared for flexible FSCs based on ultrahigh molecular weight polyethylene fibers, on which the polydopamine, Ag, and poly (3,4‐ethylene dioxythiophene): poly(styrenesulfonate) are deposited in sequence. The modified fiber‐based electrode exhibits superhigh strength up to 3.72 GPa, which is the highest among fiber‐based electrodes reported to date. In addition, FSCs fabricated with the optimized fiber electrode shows a specific areal capacity as high as 563 mF cm−2 at 0.17 mA cm−2, which corresponds to a high areal energy density of ≈50.1 µWh cm−2 at a power density of ≈124 µW cm−2. The specific areal capacity only decrease 8% after 1000 times bending test, indicating the outstanding bending performance of this composite fiber electrode. Furthermore, several FSCs can be connected in series or in parallel to get higher working voltage or higher capacity respectively, which demonstrates its potential for broad applications in flexible devices. [ABSTRACT FROM AUTHOR]

Advanced 2D materials have spurred great interest as a new paradigm in pursuing improved energy storage performance. Herein, for the first time, antimonene is utilized as an effective active component for constructing highly deformable and editable freestanding film electrodes, as the basis of a supercapacitor with record‐breaking electrode performance. The insertion of antimonene is able to improve the environmental stability of the antimonene/MXene composite electrode and remarkably enhance the energy storage capability in both protic and neutral electrolytes. Notably, an ultrahigh specific volumetric capacitance of 4255 F cm−3 is achieved by the electrode tested in a1 m H2SO4 electrolyte, which represents the state‐of‐the‐art value reported to date for supercapacitor electrodes based on MXenes. The flexible supercapacitors constructed by the composite electrode, also demonstrate highly competitive energy and power densities: 459.75 mWh cm−3 and 3.12 W cm−3 for the asymmetrical one with a much widened potential window of 2 V in neutral electrolyte; 112.52 mWh cm−3 and 1 W cm−3 for the symmetrical configuration with an outstanding capacitance of 1265 F cm−3 in acidic media. This work sheds new light on the fabrication of high‐performance supercapacitor electrodes with functionalities in different electrolyte media and various device configurations. [ABSTRACT FROM AUTHOR]

The precise design and fabrication of electrode materials is important for the development of high-performance flexible supercapacitors. Cu 2 O/MXene film electrodes with an interconnected conductive network structure are prepared in this work by in situ growth of Cu 2 O nanoparticles in a Ti 3 C 2 Tx dispersion, followed by alkali induction and vacuum filtration. The interconnected crimpled Ti 3 C 2 Tx structure produced by alkali induction not only works as the self-supported conductive network of the thin film electrode but also demonstrates sufficient open pores and high surface area, which can promote electrolyte penetration and increase active sites for energy storage. The synergy between Cu 2 O nanoparticles and the crimpled Ti 3 C 2 Tx framework leads to good structural stability and electrochemical performance. The results show that the Cu 2 O/MXene electrode exhibits a high specific area capacitance of 1518 mF cm−2 in 1 M LiCl electrolyte. In addition, the all-solid-state flexible supercapacitor fabricated with the Cu 2 O/MXene electrode exhibits excellent cyclic stability and flexibility; the capacity retains 94.3% after 10,000 charge and discharge cycles, and the energy storage performance remains stable after 50 mechanical bending cycles. • In situ growing Cu 2 O in Ti 3 C 2 Tx dispersion helps achieve higher energy density. • The interconnected network structure benefits charge transfer. • The interaction between Cu 2 O and MXene improve the energy storage performance. [ABSTRACT FROM AUTHOR]

• Borophene is applied to flexible supercapacitors for the first time. • The insertion of borophene into MXene film increases its energy storage performance. • The flexible electrode shows a high capacitance of 1328 mF cm−2 at 0.5 mA cm−2. As a unique elemental metallic Dirac material, borophene, which is predicted to have ever-increasing mechanical and electronic characters, attracts fast-grown attention in electronics. In fact, it is theoretically addressed and experimentally confirmed that borophene works well for energy storage. However, limited by the current synthesis techniques, until now, there is no attempt that has been made to explore borophene's application in the prospective flexible electrodes. This fact keeps us pondering. In this work, we offers a reliable way to overcome the adversity by randomly stacking MXene and borophene flakes to form macroscopic flexible film. It is proved that the insertion of borophene into the hybrid film can remarkably enhance the energy storage capability and energy output. The optimized hybrid film electrode shows an outstanding specific areal capacitance of 1328 mF cm−2 at a current density of 0.5 mA cm−2 in 1 M LiCl aqueous electrolyte, which is highly comparable with, or in most cases much higher than previously reported MXene-based flexible electrodes tested in neutral electrolyte. Additionally, the high specific capacitance can be well preserved with a capacitance retention of more than 98.5% even after charging-discharging for 10,000 cycles. Besides, the borophene hybrid film based flexible supercapacitor maintains stable capacitive performance when subjected to bending of up to 180° for 100 cycles, suggesting great feasibility for applying borophene in future flexible and portable electronics. [ABSTRACT FROM AUTHOR]

• 1T-MoS 2 was applied as a flexible and functional "spacer" to hybridize with Ti 3 C 2 T X MXene, forming flexible capacitive freestanding films. • The insertion of electrically neutral pseudocapacitive could mitigate the restacking of Ti 3 C 2 T X MXene layers and improves the capacity of the composite paper. • The supercapacitor fabricated with acidic gel electrolyte and composite electrode with randomly stacked MXene and 1T-MoS 2 in a mass ratio of 6:1 demonstrated optimal performance. In the case of increasing shortage of non-renewable resources, developing high-efficiency and high-capacity energy storage devices is critical. Supercapacitors have the potential of high-efficiency and high-capacity. MXene and 1T-MoS 2 are two kinds of high performance pseudocapacitive materials. However, the stacking and aggregation of MXene nanosheets greatly reduce its capacity. The poor conductivity of 1T-MoS 2 also limits the full expression of its excellent pseudocapacitive performance. A flexible MXene/1T-MoS 2 composite paper electrode is designed and prepared in this work where the restacking of MXene can be relieved and the whole electrode maintains the conductivity. The interior stacking structure of MXene and 1T-MoS 2 in the composite paper, as well as the gel electrolyte type are explored. The device constructed with the electrode composed of randomly stacked MXene and 1T-MoS 2 (mass ratio 6:1) and acidic electrolyte (PVA/H 2 SO 4 gel electrolyte) demonstrates the optimal performance. The specific areal and volumetric capacitances reach 561.2 mF cm−2 and 1268.17 F cm−3 at the current density of 0.8 mA cm−2 respectively, outperforming most of the previously reported values for MXene based supercapacitors tested in gel electrolyte. The supercapacitor has excellent deformation durability and long cycle stability, demonstrating promising prospect in future flexible electronics. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The protective hydrothermal treatment maintains the conductivity of MXene layers. • The in-situ generated TiO 2 worked as spacer and electrochemical active additive. • N doping enlarges inter layer distance and improve energy storage performance. • The supercapacitor displays excellent flexibility and stability. In terms of enhancing the energy storage performance of flexible MXene electrode, both heteroatom doping and introducing electroactive "spacers" are proved to be effective strategies. In this work, a facial protective hydrothermal method is explored to synthesis nitrogen doped porous MXene/TiO 2 heterostructure in one pot, which enables a well preserved conductivity of porous N-doped MXene and controlled in-situ generation of uniformly dispersed electroactive TiO 2 spacers. This unique hybridized structure provides a chance to integrate several physical and chemical advantages in a complementary easy way. As a result, the assembled freestanding film electrode based on the N-doped porous MXene/TiO 2 heterogeneous layers demonstrates excellent energy storage performance with an outstanding specific capacitance value of 2194.33 mF cm−2 (918.69 F g−1), which outperforms most of the heteroatom-doped MXene electrodes reported previously. Besides, the film electrode delivers excellent cycling performance with a 74.39% capacitance retention after 10,000 cycles and the as fabricated flexible supercapacitor displays almost no changes on capacitive performance when subjected to mechanical deformations, indicating its excellent flexibility and stability. This work presents a simple way of modifying MXene with N doping and inserting "spacer" for enhancing the electrochemical performance, and builds up an exciting potential for applying to highly flexible and integrated energy storage devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tyvek paper substrate applied in the supercapacitors for the first time. • High flexibility and excellent tear resistance of the supercapacitors. • Higher power density and energy density compared with CNTs-related and PEDOT:PSS-based supercapacitors. The current information era has witnessed the fast development of flexible high-performance energy storage devices for portable and wearable smart electronics. Here, tough supercapacitor with high flexibility and tear resistance based on Ag-coated Tyvek/PEDOT:PSS/carbon nanotubes (Tyvek/Ag/PCNTs) composite electrodes has been well designed and fabricated for the first time via a facile and scalable method. In the supercapacitor, Ag-coated Tyvek substrate roles as the current collector through a polymer-assisted metal deposition method while the treatment of sulfuric acid on the electrode contributes to the removal of insulating PSS part and the increase of the crystallinity of the active materials. Due to the tough and flexible substrate and the increased conductivity of the electrodes, the supercapacitor exhibits excellent stability and rate capacity as well as brilliant mechanical strength and flexibility. The prepared supercapacitor can exhibit large specific mass capacitance (138.7 F/g) and specific volume capacitance (544.2 F/cm3) at the scan rate of 50 mV/s. As far as we can concern, the Tyvek/Ag/PCNTs-based supercapacitor owns higher energy density or power density than any other CNTs-based or PEDOT-related supercapacitors. In addition, after 1000 bending cycles, the capacitance of the supercapacitor can still reach to 91.2% of the initial value. This work will help to enlarge the study in the Tyvek-based supercapacitors for the flexible and tough energy storage devices. [ABSTRACT FROM AUTHOR]

• The porous structure provides a convenient transmission path for electrons and ions. • Co-Fe oxides provide enhanced pseudo-capacitance by the changes of complex valence state. • The composite film successfully combined the advantages of different components. • The film has excellent electrochemical performance and flexibility. • The capacitance performance maintains well after repeated mechanical bending. In this work, a MOF-derived Co-Fe oxide porous nanorod is introduced into the freestanding MXene film to produce a high-performance flexible electrode with excellent deformability and editability. The as-prepared composite film electrode demonstrates several advantages: MXene layer functions as a binder and conductive additive to coat Co-Fe oxide, which can effectively facilitate charge transfer and maintain the excellent flexibility of the film electrode. In the meantime, Co-Fe oxide can work as a spacer, thereby expanding the interlayer distance, improving the ion transmission path in the electrode. As a result, the optimal Co-Fe oxide/Ti 3 C 2 T X composite paper manifests a remarkable volumetric capacitance of 2467.6 F cm−3 in 1 M LiCl electrolyte. When assembled into a flexible symmetrical supercapacitor, an outstanding specific areal capacitance of 356.4 mF cm−2 can be obtained. Meanwhile, the flexible supercapacitor demonstrates excellent cycling performance with a high capacitance retention of 88.2% after 10 000 charge/discharge cycles, as well as stable electrochemical energy storage stability after 100 cycles of mechanical bending, indicating its great application potential in future flexible and portable energy storage equipment. [ABSTRACT FROM AUTHOR]

• A 2D MXene wrapped Ni-Fe oxide nanocube based flexible electrode was synthesized. • The composite film functioned like a mixed analogous heterostructure. • The film successfully combined the advantages of different components. • The film demonstrated satisfied electrochemical performance and flexibility. In this work, we addresses the fabrication of a flexible film electrode based on 2D MXene wrapped 3D Ni-Fe oxide nanocube mixed analogous heterostructure. The resulted composite film electrode successfully inherits the merit of different building blocks: MXene layers works as binders and conductive additives that can connect cubic Ni-Fe oxide nanoparticals, facilitate the charge transfer and avoid a significant conductivity decrease in the resulting electrode. While cubic Ni-Fe oxide serves as an active spacer inside the adjacent MXene layers to increase the interlayer space, facilitate the electrolyte diffusion and enhance the electrochemical activity of the composite film. As a result, the optimized composite film manifests excellent specific capacitance of 1038.43 mF cm−2 at current density 0.5 mA cm−2. Meanwhile by assembling into all-solid-state flexible supercapacitor, an excellent specific areal capacitance of 328.35 mF cm−2 at 0.2 mA cm−2 was achieved. Additionally, the excellent energy storage performance is well maintained with a capacitance retention of 90.9% during 10,000 charging-discharging long cycles. Furthermore, a high mechanical robustness with 88.9% capacitance remained after subjected to bending at 90° for 50 cycles, suggesting great potentials for the applications in future flexible and wearable devices. [ABSTRACT FROM AUTHOR]