Wet-spun poly(ionic liquid)-graphene hybrid fibers for high performance all-solid-state flexible supercapacitors

It is crucial to develop flexible and wearable electronic devices that have attracted tremendous interest due to their merits on compactness,flexibility and high capacitive properties.Herein we report the continuously ordered macroscopic poly(ionic liquid)-graphene fibers by wet spinning method via liquid crystal assembly for supercapacitor application.The fabricated all-solid-state supercapacitors exhibited a high areal capacitance(268.2 mF cm 2)and volumetric capacitance(204.6 F cm 3)with an outstanding areal energy density(9.31μWh cm-2)and volumetric energy density(8.28 mWh cm-3).The fiber supercapacitors demonstrated exceptional cycle life for straight electrodes of about 10,000 cycles(94.2%capacitance retention)and flexibility at different angles(0°,45°,90°,180°)along with a good flexible cycling stability after 6000 cycles(92.7%capacitance retention).To date,such a novel poly(ionic liquid)-graphene fiber supercapacitors would be a new platform in real-time flexible electronics.

All-solid-state flexible asymmetric supercapacitors with high energy and power densities based on NiCo_2S_4@MnS and active carbon

Electrode material based on a novel core–shell structure consisting of NiCoS（NCS） solid fiber core and Mn S（MS） sheet shell（NCS@MS） in situ grown on carbon cloth（CC） has been successfully prepared by a simple sulfurization-assisted hydrothermal method for high performance supercapacitor. The synthesized NiCoS@Mn S/CC electrode shows high capacitance of 1908.3 F gat a current density of 0.5 A gwhich is higher than those of NiCoSand Mn S at the same current density. A flexible all-solid-state asymmetric supercapacitor（ASC） is constructed by using NiCoS@Mn S/CC as positive electrode, active carbon/CC as negative electrode and KOH/poly（vinyl alcohol）(PVA) as electrolyte. The optimized ASC shows a maximum energy density of 23.3 Wh kgat 1 A g, a maximum power density of about7.5 kw kgat 10 A gand remarkable cycling stability. After 9000 cycles, the ASC still exhibited67.8% retention rate and largely unchanged charge/discharge curves. The excellent electrochemical properties are resulted from the novel core–shell structure of the NiCoS@Mn S/CC electrode, which possesses both high surface area for Faraday redox reaction and superior kinetics of charge transport. The NiCoS@Mn S/CC electrode shows a promising potential for energy storage applications in the future.

Ultrathin ZnS nanosheet/carbon nanotube hybrid electrode for high-performance flexible all-solid-state supercapacitor

Flexible and easily reconfigurable supercapacitors show great promise for application in wearable electronics. In this study, multiwall C nanotubes （CNTs） decorated with hierarchical ultrathin zinc sulfide （ZnS） nanosheets （ZnS@CNT） are synthesized via a facile method. The resulting ZnS@CNT electrode, which delivers a high specific capacitance of 347.3 F·g^-1 and an excellent cycling stability, can function as a high-performance electrode for a flexible all-solid-state supercapacitor using a polymer gel electrolyte. Our device exhibits a remarkable specific capacitance of 159.6 F·g^-1, a high energy density of 22.3 W·h·kg^-1, and a power density of 5 kW·kg^-1 It also has high electrochemical performance even under bending or twisting. The all-solid-state supercapacitors can be easily integrated in series to power different commercial light-emitting diodes without an external bias voltage.

Activated carbon felts with exfoliated graphene nanosheets for flexible all-solid-state supercapacitors

The recent development of portable electronics promotes the growing demand for flexible energy storage devices. Supercapacitors are promising candidates due to their high power density. Therefore, flexible supercapacitors are desired. Here, the porous activated carbon felts(ACFs) with exfoliated graphene nanosheets and rich oxygen-containing groups were fabricated by a facile thermal treatment strategy.Such ACFs can act as the flexible electrodes of all-solid-state supercapacitors directly without the use of binder and conductive materials. They exhibit excellent electrochemical properties, such as high specific areal capacitance, superior rate ability and long-term cycling stability. Moreover, the fabricated flexible all-solid-state supercapacitors based on ACFs deliver stable electrochemical performance under different bending states.

In-Situ Annealed Ti_(3)C_(2)T_(x) MXene Based All-Solid-State Flexible Zn-Ion Hybrid Micro Supercapacitor Array with Enhanced Stability

Zn-ion hybrid supercapacitors(SCs)are considered as promising energy storage owing to their high energy density compared to traditional SCs.How to realize the miniaturization,patterning,and flexibility of the Zn-ion SCs without affecting the electrochemical performances has special meanings for expanding their applications in wearable integrated electronics.Ti_(3)C_(2)T_(x) cathode with outstanding conductivity,unique lamellar structure and good mechanical flexibility has been demonstrated tremen-dous potential in the design of Zn-ion SCs,but achieving long cycling stability and high rate stability is still big challenges.Here,we proposed a facile laser writing approach to fabricate patterned Ti_(3)C_(2)T_(x)-based Zn-ion micro-supercapacitors(MSCs),followed by the in-situ anneal treatment of the assembled MSCs to improve the long-term stability,which exhibits 80%of the capacitance retention even after 50,000 charge/discharge cycles and superior rate stability.The influence of the cathode thickness on the electrochemical performance of the MSCs is also studied.When the thickness reaches 0.851μm the maximum areal capacitance of 72.02 mF cm^(−2)at scan rate of 10 mV s^(−1),which is 1.77 times higher than that with a thickness of 0.329μm(35.6 mF cm^(−2)).Moreover,the fab-ricated Ti_(3)C_(2)T_(x) based Zn-ion MSCs have excellent flexibility,a digital timer can be driven by the single device even under bending state,a flexible LED displayer of“TiC”logo also can be easily lighted by the MSC arrays under twisting,crimping,and winding conditions,demonstrating the scalable fabrication and application of the fabricated MSCs in portable electronics.

Carbon-Based Flexible and All-Solid-State Micro-supercapacitors Fabricated by Inkjet Printing with Enhanced Performance

By means of inkjet printing technique, flexible and all-solid-state micro-supercapacitors(MSCs) were fabricated with carbon-based hybrid ink composed of graphene oxide(GO,98.0vol.%) ink and commercial pen ink(2.0vol.%). A small amount of commercial pen ink was added to effectively reduce the agglomeration of theGO sheets during solvent evaporation and the following reduction processes in which the presence of graphite carbon nanoparticles served as nano-spacer to separate GO sheets. The printed device fabricated using the hybrid ink,combined with the binder-free microelectrodes and interdigital microelectrode configuration, exhibits nearly 780%enhancement in areal capacitance compared with that of pure GO ink. It also shows excellent flexibility and cycling stability with nearly 100% retention of the areal capacitance after 10,000 cycles. The all-solid-state device can be optionally connected in series or in parallel to meet the voltage and capacity requirements for a given application.This work demonstrates a promising future of the carbonbased hybrid ink for directly large-scale inkjet printing MSCs for disposable energy storage devices.

Peripheral octamethyl-substituted nickel(Ⅱ)-phthalocyanine-decorated carbon-nanotube electrodes for high-performance all-solid-state flexible symmetric supercapacitors

Construction of advanced electrode materials with unique performance for supercapacitors(SCs)is essential to achieving high implementation in the commercial market.Here,we report a novel peripheral octamethyl-substituted nickel(Ⅱ)phthalocyanine(Ni Me_(2)Pc)-based nanocomposite as the electrode material of all-solid-state SCs.The highly redox-active NiMe_(2)Pc/carboxylated carbon nanotube(CNTCOOH)dendritic nanocomposite provides rapid electron/electrolyte ion-transport pathways and exhibits excellent structural stability,resulting in high-capacity activity and impressive cycling stability.The composite prepared with the optimized weight ratio of Ni Me_(2)Pc:CNT-COOH(6:10)showed the highest specific capacitance of 330.5 F g^(-1)at 0.25 A g^(-1).The constructed NiMe_(2)Pc/CNT-COOH-based all-solid-state symmetric SC device showed excellent performance with a maximum energy density of 22.8 Wh kg^(-1)and outstanding cycling stability(111.6%retained after 35,000 cycles).Moreover,flexible carbon cloth significantly enhanced the energy density of the NiMe_(2)Pc/CNT-COOH all-solid-state symmetric device to 52.1 Wh kg^(-1)with 95.4%capacitance retention after 35,000 cycles,and it could be applied to highperformance flexible electronics applications.These findings provide a novel strategy to design phthalocyanine-based electrode materials for next-generation flexible SC devices.

Mechanical reliable,NIR light-induced rapid self-healing hydrogel electrolyte towards flexible zinc-ion hybrid supercapacitors with low-temperature adaptability and long service life

Hydrogel electrolytes hold great potential in flexible zinc ion supercapacitors(ZICs)due to their high conductivity,good safety,and flexibility.However,freezing of electrolytes at low temperature(subzero)leads to drastic reduction in ionic conductivity and mechanical properties that deteriorates the performance of flexible ZICs.Besides,the mechanical fracture during arbitrary deformations significantly prunes out the lifespan of the flexible device.Herein,a Zn^(2+)and Li^(+)co-doped,polypyrrole-dopamine decorated Sb_(2)S_(3)incorporated,and polyvinyl alcohol/poly(N-(2-hydroxyethyl)acrylamide)double-network hydrogel electrolyte is constructed with favorable mechanical reliability,anti-freezing,and self-healing ability.In addition,it delivers ultra-high ionic conductivity of 8.6 and 3.7 S m^(-1)at 20 and−30°C,respectively,and displays excellent mechanical properties to withstand tensile stress of 1.85 MPa with tensile elongation of 760%,together with fracture energy of 5.14 MJ m^(-3).Notably,the fractured hydrogel electrolyte can recover itself after only 90 s of infrared illumination,while regaining 83%of its tensile strain and almost 100%of its ionic conductivity during−30–60°C.Moreover,ZICs coupled with this hydrogel electrolyte not only show a wide voltage window(up to 2 V),but also provide high energy density of 230 Wh kg^(-1)at power density of 500 W kg^(-1)with a capacity retention of 86.7%after 20,000 cycles under 20°C.Furthermore,the ZICs are able to retain excellent capacity even under various mechanical deformation at−30°C.This contribution will open up new insights into design of advanced wearable flexible electronics with environmental adaptability and long-life span.

Preparation by Wet-spinning and Properties Polyaniline-Polyethersulfone Fibers for Flexible Supercapacitor Electrodes

Flexible PANI-Polyethersulfone (PES) fibers were fabricated using the wet-spinning technique.PANI particles were uniformly distributed within the matrix and micropores formed by the phase separation of PES,which prevented PANI particles aggregation and facilitated the formation of continuous ion transport channels.The experimental results reveals that the electrochemical performance of the fiber electrode material is optimal when the concentration of PES in the spinning solution is 15wt%.The assembled supercapacitor exhibits a commendable specific area capacitance of 162.75 mF·cm^(-2) at a current density of 0.5 mA·cm^(-2) and achieves an energy density of 14.47 mWh·cm^(-2) at a power density of 321.69 mW·cm^(-2).The capacitor retains 98.1% of its capacitance after 1 000 bending cycles.Therefore,the prepared fibers have good electrochemical properties and flexibility,and this simple and efficient preparation method is promising for the scalable production of flexible electrodes.

Balancing loading mass and gravimetric capacitance of NiCo-layered double hydroxides to achieve ultrahigh areal performance for flexible supercapacitors

Delivering high areal capacitance(CA)at high rates is crucial but challenging for flexible supercapacitors.CA is the product of areal loading mass(MA)and gravimetric capacitance(CW).Finding and understanding the balance between MA and CW of supercapacitor materials is significant for designing high-CA electrodes.Herein,we have systematically studied the correlation between MA and CW of the nanosheet arrays of NiCo-layered double hydroxide(NiCo-LDH),which were electrodeposited on carbon cloth with different heights to adjust the MA,accompanied by the interlayer distance regulation to improve the CW.The optimal CW performance is achieved at the best charge transfer kinetics for each of MA series.The NiCo-LDH electrode with the suitable MA(2.58 mg cm^(-2))and the relatively high CW(1918 F g^(-1) at 5 A g^(-1) and 400 F g^(-1) at 150 A g^(-1))present a high CA of 4948 mF cm^(-2) at 12.9 mA cm^(-2) and a record-high 1032 mF cm^(-2) among LDHs-based flexible electrodes at an ultrahigh current density of 387 mA cm^(-2).The corresponding flexible supercapacitor coupled with activated carbon delivers a high energy density of 0.28 mWh cm^(-2) at an ultrahigh power density of 712 mW cm^(-2),showing great potential applications.

High rate and ultralong life flexible all-solid-state zinc ion battery based on electron density modulated NiCo_(2)O_(4) nanosheets

The development of zinc ion batteries (ZIBs) with large capacity,high rate,and durable cathode material is a crucial and urgent task.Ni Co_(2)O_(4)(NCO) has received ever-growing interest as a potential cathode material for ZIBs,owing to the high theoretical capacity,rich source,cost-effective,and versatile redox nature.However,due to the slow dynamics of the NCO electrodes,its practical application in highperformance systems is severely limited.Herein,we report an electron density modulated NCO nanosheets (N-NCO NSs) with high-kinetics Zn^(2+)-storage capability as an additive-free cathode for flexible all-solid-state (ASS) ZIBs.By virtue of the enhanced electronic conductivity,improved reaction kinetics,and increased active sites,the optimized N-NCO NSs electrode delivers a high capacity of 357.7 m Ah g^(-1)at 1.0 A g^(-1)and a superior rate capacity of 201.4 m Ah g^(-1)at 20 A g^(-1).More importantly,a flexible ASS ZIBs device is manufactured using a solid polymer electrolyte of a poly (vinylidene fluoride hexafluoropropylene)(PVDF-HFP) film.The flexible ASS ZIBs device shows superb durability with 80.2%capacity retention after 20,000 cycles and works well in the range of-20–70℃.Furthermore,the flexible ASS ZIBs achieves an impressive energy density as high as 578.1 W h kg^(-1)with a peak power density of 33.6 k W kg^(-1),substantially outperforming those latest ZIBs.This work could provide valuable insights for constructing high-kinetics and high-capability cathodes with long-term stability for flexible ASS ZIBs.

Flexible free-standing graphene-like film electrode for supercapacitors by electrophoretic deposition and electrochemical reduction

Electrophoretic deposition in conjunction with electrochemical reduction was used to make flexible free-standing graphene-like films. Firstly, graphene oxide （GO） film was deposited on graphite substrate by electrophoretic deposition method, and then reduced by subsequent electrochemical reduction of GO to obtain reduced GO （ERGO） film with high electrochemical performance. The morphology, structure and electrochemical performance of the prepared graphene-like film were confirmed by SEM, XRD and FT-IR. These unique materials were found to provide high specific capacitance and good cycling stability. The high specific capacitance of 254 F/g was obtained from cyclic voltammetry measurement at a scan rate of 10 mV/s. When the current density increased to 83.3 A/g, the specific capacitance values still remained 132 F/g. Meanwhile, the high powder density of 39.1 kW/kg was measured at energy density of 11.8 W-h/kg in 1 mol/L H2SO4 solution. Furthermore, at a constant scan rate of 50 mV/s, 97.02% of its capacitance was retained for 1000 cycles. These promising results were attributed to the unique assembly structure of graphene film and low contact resistance, which indicated their potential application to electrochemical capacitors.

A flexible solid-state supercapacitor based on graphene/polyaniline paper electrodes

The direct coating of graphene sheets obtained by electrochemical exfoliation on commercial paper renders the preparation of highly conductive flexible paper substrate for subsequent deposition of polyaniline (PANi) nanorods via electrochemical polymerization. The deposit ion of PANi can be well-controlled by adjusting the electrochemical polymerization time, leading to the formation of PANi coated graphene paper (PANi-GP). The as-prepared electrode exhibited high areal capacitance of 176 mF cm^-2 in three-electrode system at a current density of 0.2 mA cm^-2 which is around 10 times larger than that of pris-tine graphene paper due to the pseudocapacitive behavior of PANi. In-situ Raman test was used to determine the molecular changes during redox process of PANi. More importantly, all-solid-state symmetric capacitor assembled with two PANi-GP electrodes in a polymer electrolyte delivered an areal capacitanee of 123 mF cm^-2, corresponding to an areal energy density of 17.1 μWh cm^-2 and an areal power density of 0.25 mW cm^-2. The symmetric capacitor held a capacitive retention of 74.8% after 500 bending tests from 0 to 120°, suggesting the good flexibility and mechanical stability. These results showed the great promising application in flexible energy-storage devices.

High-Performance Flexible Asymmetric Supercapacitor Based on CoAl-LDH and rGO Electrodes

A flexible asymmetric supercapacitor(ASC)based on a Co Al-layered double hydroxide(Co Al-LDH)electrode and a reduced graphene oxide(r GO) electrode was successfully fabricated. The Co Al-LDH electrode as a positive electrode was synthesized by directly growing Co Al-LDH nanosheet arrays on a carbon cloth(CC)through a facile hydrothermal method, and it delivered a specific capacitance of 616.9 F g^(-1)at a current density of1 A g^(-1). The r GO electrode as a negative electrode was synthesized by coating r GO on the CC via a simple dipcoating method and revealed a specific capacitance of110.0 F g^(-1)at a current density of 2 A g^(-1). Ultimately,the advanced ASC offered a broad voltage window(1.7 V)and exhibited a high superficial capacitance of1.77 F cm^(-2)at 2 m A cm^(-2)and a high energy density of0.71 m Wh cm^(-2)at a power density of 17.05 m W cm^(-2),along with an excellent cycle stability(92.9% capacitance retention over 8000 charge–discharge cycles).

Activated carbon fibers with manganese dioxide coating for flexible fiber supercapacitors with high capacitive performance

Fiber supercapacitor(FSC)is a promising power source for wearable/stretchable electronics and high capacitive performance of FSCs is highly desirable for practice flexible applications.Here,we report a composite of manganese dioxide(Mn O_2)and activated carbon fibers(ACFs)with high MnO_2mass loading and microporous structure(abbreviated as Mn O_2@ACF),which is used as a fiber electrode to produce a FSC with a high capacitive performance and a good flexibility.The MnO_2@ACF composite electrode in FSCs delivers an ultrahigh specific capacitance of 410 mF/cm^2at 0.1 mA/cm^2,corresponding to a high energy density of 36μWh/cm^2and high power density of 726μW/cm^2.Such high capacitive performance and simple fabrication method indicates that the Mn O_2@ACF composite is a very promising electrode material for flexible fiber supercapacitors.

Electrodeposited NiSe2 on carbon fiber cloth as a flexible electrode for high-performance supercapacitors

A flexible electrode of nickel diselenide/carbon fiber cloth(NiSe/CFC) is fabricated at room temperature by a simple and efficient electrodeposition method. Owing to NiSecharacter of nanostructure and high conductivity, the as-synthesized electrodes possess perfect pseudocapacitive property with high specific capacitance and excellent rate capability. In three-electrode system, the electrode specific capacitance of the NiSe/CFC electrode varies from 1058 F gto 996.3 F gat 2 A gto 10 A grespectively, which shows great rate capability. Moreover, the NiSeelectrode is assembled with an active carbon(AC) electrode to form an asymmetric supercapacitor with an extended potential window of 1.6 V. The asymmetric supercapacitor possesses an excellent energy density 32.7 Wh kgwith a power density 800 W kgat the current density of 1 A g. The nanosheet array on carbon fiber cloth with high flexibility, specific capacitance and rate capacitance render the NiSeto be regarded as the promising material for the high performance superconductor.

Flexible quasi-solid-state dual-ion asymmetric supercapacitor based on Ni（OH）2 and Nb2O5 nanosheet arrays

Increasing the energy density, power density as well as widening the operation voltage are essential to electrochemical capacitors to meet the practical energy demands. Herein, a novel flexible quasi-solid-state dual-ion asymmetric supercapacitor(ASC) with Ni(OH)2 and Nb2O5 nanosheets directly grown on stainless steel mesh is developed. In the dual-ion ASC, Nb2O5 negative and Ni(OH)2 positive electrodes react with Li+ and OH- respectively in alkaline gel electrolyte to store energy, which is quite different from conventional alkali metal ion SCs and alkaline SCs. The as-assembled flexible device has an extended working voltage of 1.7 V and delivers a capacity of 5.37 mAh cm-2, a maximum energy density and power density of 0.52 mWh cm-3 and 170 mW cm-3 , respectively. The device maintains around 60% capacity retention after long cycling up to 1000 cycles. Moreover, our device can light up a LED light efficiently upon fast charging. The proposed quasi-solid-state dual-ion ASC has potential applications in future portable electronics and flexible energy storage devices.

MXene-coated silk-derived carbon cloth toward flexible electrode for supercapacitor application

Flexible supercapacitors are promising energy storage devices in wearable smart electronics. Exploring cost-efficient electrodes with high capacitance would promote the wide-scale application of such capacitors. Herein, in order to explore a methodology for preparing low cost, flexible, tough, and up-scalable supercapacitor electrodes, silk textile is directly carbonized to make a conductive free-standing textile substrate. Through mildly baking the surfactant-free TiCTflakes suspension loaded on the carbonized silk cloth, a uniform and adhesive coating consisting of nanometer-thick TiCTflakes is well established on the conductive fabric support, forming a MXene-coated flexible textile electrode. The fabricated electrode exhibits a high areal capacitance of 362 m F/cm~2 with excellent cyclability and flexibility. Moreover,capacitance changes neglegibly under the bending deformation mode. This study elucidates the feasibility of using silk-derived carbon cloth from biomss for MXene-based flexible supercapacitor.

Recent progress in 2D materials for flexible supercapacitors

High performance supercapacitors coupled with mechanical flexibility are needed to drive flexible and wearable electronics that have anesthetic appeal and multi-functionality. Two dimensional（2D） materials have attracted attention owing to their unique physicochemical and electrochemical properties, in addition to their ability to form hetero-structures with other nanomaterials further improving mechanical and electrochemical properties. After a brief introduction of supercapacitors and 2D materials, recent progress on flexible supercapacitors using 2D materials is reviewed. Here we provide insights into the structure–property relationships of flexible electrodes, in particular free-standing films. We also present our perspectives on the development of flexible supercapacitors.

Ni3S2 nanorods growing directly on Ni foam for all-solid-state asymmetric supercapacitor and efficient overall water splitting

Transition metal compounds are attractive for their significant applications in supercapacitors and as non-noble metal catalysts for electrochemical water splitting.Herein,we develop Ni3 S2 nanorods growing directly on Ni foam,which act as multifunctional additive-free Ni3 S2@Ni electrode for supercapacitor and overall water splitting.Based on PVA-KOH gel electrolyte,the assembled all-solid-state Ni3 S2@Ni//AC asymmetric supercapacitor delivers a high areal energy density of 0.52 mWh cm^-2 at an areal power density of 9.02 MW cm^-2,and exhibits an excellent cycling stability with a capacitance retention ratio of 89%after 10000 GCD cycles at a current density of 30 mA cm^-2.For hydrogen evolution reaction and oxygen evolution reaction in 1 M KOH,Ni3 S2@Ni electrode achieves a benchmark of 10 mA cm^-2at overpotentials of 82 mV and 310 mV,respectively.Furthermore,the assembled Ni3 S2@Ni‖Ni3 S2@Ni electrolyzer for overall water splitting attains a current density of 10 mA cm^-2 at 1.61 V.The in-situ synthesis of Ni3 S2@Ni electrode enriches the applications of additive-free transition metal compounds in high-performance energy storage devices and efficient electrocatalysis.