Flexible Symmetric Supercapacitor Research Articles

Time-dependent synthesis of tungsten disulfide for flexible supercapacitors

Tungsten disulfide (WS2) with various nanostructures was synthesized for times ranging from 6 to 72 h, using a simple and easy hydrothermal technique, for high-performance supercapacitor applications. The synthesized WS2 for 24 h (WS2–24), among other synthesized WS2, exhibited flower-like structures, composed of numerous nanosheets, demonstrating superior electrochemical properties in terms of electrochemical surface area, charge transfer resistance, specific capacitance, and rate capability. In addition, WS2–24 was coated on a flexible activated carbon cloth substrate to make flexible electrodes and assemble a flexible symmetric supercapacitor with a gel electrolyte. The flexible supercapacitor exhibited a specific capacitance of 262.5 F g−1 at 1 A g−1 with an energy density of 23.6 Wh kg−1 and a power density of 802 W kg−1. It also showed excellent capacitance retention of 94.5 % and a Coulombic efficiency of 86.4 % after 5000 cycles. The remarkable electrochemical properties of the synthesized WS2 materials highlight them as highly effective active materials for high-performance supercapacitor electrodes.

Fabrication of highly flexible, wearable, free-standing symmetric supercapacitors with high voltage operation enabled by hierarchical graphene/cerium oxide/polypyrrole hybrid films

Flexible, free-standing supercapacitors play a significant role in the development of future wearable energy storage devices. Herein, we successfully fabricated the highly flexible and free-standing graphene/cerium oxide/polypyrrole hybrid films by thermal reduction of graphene oxide (GO) followed by the sol–gel synthesis of CeO2 and then the addition of PPy. By regulating oxygen functional groups in GO, the electronic conductivity and electroactive sites of the hybrid films are significantly controlled, leading to enhanced energy storage capability. Finally, a symmetric flexible supercapacitor (FSC) device was developed using the prepared films as electrodes. Resulting, the integrated symmetric GO-400/CeO2/PPy FSC manifests excellent areal capacitance of 49.0 mF cm−2 at 1 mA cm−2, with a durability of 83.1 % over 10,000 cycles. Specifically, the FSC exhibited capacitance retention of 77.2 % after 10,000 cycles under bending state with exceptional rate ability. Meanwhile, an impressive energy density of 19.69 µW h cm−2 was attained at a power density of 0.85 mW cm−2. Evidently, the synergistic interactions between GO and PPy nanosheets, along with CeO2 favour the rapid electron movement of electrode material for next-generation wearable, portable electronics.

Polyaniline nanoarrays grown on holey graphene constructed by frozen interfacial polymerization as binder−free and flexible gel electrode for high−performance supercapacitor

Compared with disordered structures, electrode materials with nanoarray structures can effectively improve the energy storage capacity of supercapacitors. Therefore, the construction of nanoarrays structures is an important research direction. Here, one kind of frozen interfacial polymerization was used to create a polyaniline (PANI) nanoarrays grown on holey graphene (HG). Long polyaniline nanoarrays were constructed with the promotion of ice crystal growth and the abundant pores of the HG. It is demonstrated that the formation of PANI array and hierarchical nanofiber structures is not only conducive to shorten charge transport, but also can effectively alleviate interfacial side reactions. Moreover, benefiting from the abundant active sites and hierarchical porous structure of the HG, highly oriented growth of PANI arrays, efficient charge diffusion and electrolyte infiltration can be achieved. As a result, specific capacitance, reversibility and cycling stability could be significantly improved. Especially, the PANI/HG−10 exhibited the maximum specific capacitance of 793.7 F g−1 at a current density of 1 A g−1. The all−solid−state flexible symmetric supercapacitor assembled by gel electrode possesses the energy density of 32.5 Wh kg–1 at a power density of 326.5 W kg–1, and maintained an excellent cycle retention approaching 90.5 % after 5000 cycles. This work expands the ideas for array structure construction and electrode fabrication.

Self-healable PVA-Borax-K2SO4 hydrogel electrolyte for flexible symmetric supercapacitors

The self-healing hydrogel materials are formed from the reaction between polyvinyl alcohol (PVA) and sodium tetraborate (Borax). The O-B-C vibration peak from the FT-IR spectrum is used to confirm the formation of the self-healing hydrogel structure. With 0.5 M concentration K2SO4, the resistivity of PVA-Borax-K2SO4 material is evaluated by Bode cure and obtained at 4.13 Ω.cm. With the improvement in hybrid structure, the flexible supercapacitor (FSS) devices were fabricated from two carbon fiber fabrics as symmetric electrodes with a self-healing hydrogel material (PVA-Borax-K2SO4) as electrolyte and separator. The electrochemical performances of flexible symmetric supercapacitor (FSS) devices are measured by cyclic voltammetric, charge/discharge, and impedance tests. The specific capacitance of FSS obtained 1.725 mF/cm2 at 0.05 mA/cm2 discharge current. Moreover, the stability of the FSS device attained confirmation by the comparison of the specific capacitance at 2 and 50 cycles.

Pseudocapacitive Kinetics in Synergistically Coupled MoS2-Mo2N Nanowires with Enhanced Interfaces toward All-Solid-State Flexible Supercapacitors.

Pseudocapacitive kinetics in rationally engineered nanostructures can deliver higher energy and power densities simultaneously. The present report reveals a high-performance all-solid-state flexible symmetric supercapacitor (FSSC) based on MoS2-Mo2N nanowires deposited directly on stainless steel mesh (MoS2-Mo2N/SSM) employing DC reactive magnetron co-sputtering technology. The abundance of synergistically coupled interfaces and junctions between MoS2 nanosheets and Mo2N nanostructures across the nanocomposite results in greater porosity, increased ionic conductivity, and superior electrical conductivity. Consequently, the FSSC device utilizing poly(vinyl alcohol)-sodium sulfate (PVA-Na2SO4) hydrogel electrolyte renders an outstanding cell capacitance of 252.09 F·g-1 (44.12 mF·cm-2) at 0.25 mA·cm-2 and high rate performance within a wide 1.3 V window. Dunn's and b-value analysis reveals significant energy storage by surface-controlled capacitive and pseudocapacitive mechanisms. Remarkably, the symmetric device boosts tremendous energy density ∼10.36 μWh·cm-2 (59.17 Wh·kg-1), superb power density ∼6.5 mW·cm-2 (37.14 kW·kg-1), ultrastable long cyclability (∼93.7% after 10,000 galvanostatic charge-discharge cycles), and impressive mechanical flexibility at 60°, 90°, and 120° bending angles.

Cross-Linked Polyacrylic-Based Hydrogel Polymer Electrolytes for Flexible Supercapacitors.

Hydrogel polymer electrolytes (GPEs), as an important component of flexible energy storage devices, have gradually received wide attention compared with traditional liquid electrolytes due to their advantages of good mechanical, bending, and safety properties. In this paper, two cross-linked GPEs of poly(acrylic acid-co-acrylamide) or poly(acrylic acid-co-N-methylolacrylamide) with NaNO3 aqueous solution (P(AA-co-AM)/NaNO3 or P(AA-co-HAM)/NaNO3) were successfully prepared using radical polymerization, respectively, using acrylic acid (AA) as the monomer, N-methylolacrylamide (HAM) or acrylamide (AM) as the comonomer, and N, N-methylenebisacrylamide (MBAA) as the cross-linking agent. We investigated the morphology, glass transition temperature (Tg), ionic conductivities, mechanical properties, and thermal stabilities of the two GPEs. By comparison, P(AA-co-HAM)/NaNO3 GPE exhibits a higher ionic conductivity of 2.00 × 10-2 S/cm, lower Tg of 152 °C, and appropriate mechanical properties, which are attributed to the hydrogen bonding between the -COOH and -OH, and moderate cross-linking. The flexible symmetrical supercapacitors were assembled with the two GPEs and two identical activated carbon electrodes, respectively. The results show that the flexible supercapacitor with P(AA-co-HAM)/NaNO3 GPE shows good electrochemical performance with a specific capacitance of 63.9 F g-1 at a current density of 0.2 A g-1 and a capacitance retention of 89.4% after 3000 charge-discharge cycles. Our results provide a simple and practical design strategy of GPEs for flexible supercapacitors with wide application prospects.

Superior energy storage and stability realized in flexible carbon nanotube aerogel-metal organic framework based supercapacitor via interface engineering

Our present study unveils a new carbon nanotube aerogel-metal organic framework free-standing electrode, showcasing exceptional dual functionality as an electrode and current collector. In the prepared electrode, an interface engineering between functionalized carbon nanotubes (FCNT) and metal-organic frameworks (MOF) leads to the excellent electrochemical performance of the supercapacitor. The carbon nanotube aerogel with its exceptional surface area and electrical conductivity, lays the foundation for lightning-fast charge transfer. Meanwhile, the metal-organic frameworks present at the interface, grant ions unbridled storage space contributing to efficient charge storage. The ulta-light-in-weight FCNT-MOF free-standing electrode exhibited an excellent specific capacitance of 465 F g−1 (116 mF cm−2) at 2 A g−1 with outstanding cyclic stability of 92 % after 6000 cycles. The flexible FCNT-MOF symmetric supercapacitor demonstrated a high energy density of 40.5 W h kg−1 at a power density of 1600 W kg−1. The simplified fabrication process, reduced active material requirements (0.25 mg cm−2), and enhanced performance make it an attractive option for supercapacitor application. Furthermore, the integration of this electrode design into supercapacitors holds great promise for portable electronics, electric vehicles, and renewable energy systems.

Mechanically Robust and Highly Conductive Poly(ionic liquid)/Polyacrylamide Double-Network Hydrogel Electrolytes for Flexible Symmetric Supercapacitors with a Wide Operating Voltage Range.

Flexible electronic devices, such as supercapacitors (SCs), place high demands on the mechanical properties, ionic conductivity, and electrochemical stability of electrolytes. Hydrogels, which combine flexibility and the advantages of both solid and liquid electrolytes, will meet the demand. Here, we report the synthesis of novel poly(ionic liquid)/polyacrylamide double-network (DN) (PIL/PAM DN) hydrogel electrolytes containing different metal salts via a two-step γ-radiation method. The resultant Li2SO4-1.0/PIL/PAM DN hydrogel electrolyte possesses excellent mechanical properties (tensile strength of 3.64 MPa, elongation at break of 446%) and high ionic conductivity (24.1 mS·cm-1). The corresponding flexible SC based on the Li2SO4-1.0/PIL/PAM DN hydrogel electrolyte (SC-Li2SO4) presents improved ion diffusion, ideal electrochemical double-layer capacitor behavior, good rate capability, and excellent cyclic stability. Moreover, symmetric SC-Li2SO4 achieves a wide operating voltage range of up to 1.5 V, with a maximum energy density of 26.0 W h·kg-1 and a capacitance retention of 94.1% after 10,000 galvanostatic charge-discharge cycles, owing to the deactivation of free water molecules by the synergistic effect of PIL, PAM, and SO42-. Above all, the capacitance of SC-Li2SO4 is well-maintained after overcharge, overdischarge, short circuit, extreme temperature, compression, and bending tests, indicating its high security and flexibility. This work reveals the enormous application potential of PIL-based conductive hydrogel electrolytes for flexible electronic devices.

Exploration of Charge Storage in an Anion-Exchanged Synthesized Sn–Co–Se Nanorod-Based Flexible Symmetric Supercapacitor

Exploration of Charge Storage in an Anion-Exchanged Synthesized Sn–Co–Se Nanorod-Based Flexible Symmetric Supercapacitor

Synthesis of MXene-based nanocomposite electrode supported by PEDOT:PSS-modified cotton fabric for high-performance wearable supercapacitor

The rapid development of wearable and portable electronic devices prompts the ever-growing demand for wearable, flexible, and light-weight power sources. In this work, a MXene/GNS/PPy@PEDOT/Cotton nanocomposite electrode with excellent electrochemical performances was fabricated using cotton fabric as a substrate. Poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) was coated on the cotton fabric to obtain a conductive substrate through a controllable dip-drying coating process, while a nanocomposite consisting of MXene, Graphene nanoscroll (GNS), and polypyrrole (PPy) was directly synthesized and deposited on the PEDOT:PSS-modified cotton fabric via a one-step in situ polymerization method. The resultant MXene/GNS/PPy@PEDOT/Cotton electrode delivers excellent electrochemical performances including an ultra-high areal capacitance of 4877.2 mF·cm−2 and stable cycling stability with 90 % capacitance retention after 3000 cycles. Moreover, the flexible symmetrical supercapacitor (FSC) assembled with the MXene/GNS/PPy@PEDOT/Cotton electrodes demonstrates a prominent areal capacitance (2685.28 mF·cm−2 at a current density of 1 mA·cm−2) and a high energy density (322.15 μWh·cm−2 at a power density of 0.46 mW·cm−2). In addition, the application of the FSC for wearable electronic devices was demonstrated.

First report on binder-free boehmite (AlOOH) based prototype, flexible, high-energy and high-power density solid-state symmetric supercapacitor

Supercapacitor has potential to accomplish the world-wide growing demand for clean and sustainable energy. It has virtue of both the battery and the conventional capacitor. The proper selection of electrode material is one of the deterministic factors for the excellent performance of supercapacitor. This work presents the first report on the boehmite phase of a polymorph of earth abundant and inexpensive aluminum based oxy hydroxide for energy storage application. The binder-free synthesis of AlOOH electrode has been carried out by the simple, user-friendly, and low-cost successive ionic layer adsorption and reaction (SILAR) technique at 300 K. The X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy characterizations are performed for the knowledge of crystal structure, chemical bonds, oxidation states, morphology and elements present in the sample, respectively. The electrochemical activities of electrode as well as fabricated solid-state symmetric device are disclosed by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The maximum specific capacitance of 726.5 F g−1 @ 5 mV s−1 has been achieved for AlOOH electrode with ~67 % cyclic stability for 6500 cycles. The assembled device exhibits an excellent specific capacitance of 314 F g−1 @ 5 mV s−1, energy density of 242 Wh Kg−1 and power density of 4701 W Kg−1 with ~80 % stability up to 6500 cycles. The device has ability to glow red, green, blue and white coloured light emitting diodes (LEDs) for 50, 52, 27 and 21 min respectively. Also, the fabricated device is successful for glowing a panel ‘MNNIT’ made up by 56 red coloured LEDs. These results indicate that this work can be beneficial for fulfilling the energy demand of future generation.

Protective hydrothermal treatment to improve ion pathway in Ti3C2Tx MXene for high-performance flexible supercapacitors

The strong re-stacking of Ti3C2Tx MXene nanosheets severely blocks ion transport pathway and sacrifices electrochemical performance. Here, a protective hydrothermal treatment is used to improve ion pathway in Ti3C2Tx MXene. The protective hydrothermal treatment is simply conducted in the hydrothermal kettle (filled with N2 atmosphere) placed in vacuum oven. The optimal Ti3C2Tx is achieved by the hydrothermal treatment of 150 °C for 12h, and recorded as h-Ti3C2Tx@150 °C/12h. The h-Ti3C2Tx@150 °C/12h film electrode achieves significantly improved ion transport pathways and enhanced ion accessibility with more pseudocapacitive active sites due to the increased interlayer spacing and pores as well as decreased flake size. According to DFT calculations, a small number of oxides (TiO2 nanoparticles) produced during the hydrothermal treatment also facilitate to increase the capacitive performance of h-Ti3C2Tx@150 °C/12h. Therefore, the h-Ti3C2Tx@150 °C/12h film electrode achieves significantly increased capacitance and rate performance. The h-Ti3C2Tx@150 °C/12h film electrode exhibits excellent capacitance (498.3 F g−1 and 1911 F cm−3 at 1 A g−1) and rate performance (63 % retention from 1 to 20 A g−1) with high cycling stability (98.2 % retention after 20 000 cycles), which are among the best electrochemical performances of undoped Ti3C2Tx based film electrodes reported so far. Thick h-Ti3C2Tx@150 °C/12h film electrode of 33.1 μm thickness exhibits an ultra-high areal capacitance of 3.23 F cm−2 at 1 A g−1. Moreover, the h-Ti3C2Tx@150 °C/12h-based flexible symmetric supercapacitor device exhibits excellent energy storage performance (117 F g−1 at 0.5 A g−1 and 23.4 Wh kg−1 at 299.8 W kg−1) with high cycling stability (84 % retention after 3000 cycles) and bending stability, outperforming most of previously reported Ti3C2Tx-based flexible supercapacitors. The impressive results indicate the great application potential of the h-Ti3C2Tx@150 °C/12h film in flexible energy storage devices.

(Digital Presentation) Electrospun N-Doped CNFs Embedded Metal Oxides with Improved Graphitization for Superior Pseudocapacitive Energy Storage

One-dimensional carbon nanofibers (CNFs) based pseudocapacitive hybrid electrodes are the next step forward in achieving highly efficient supercapacitor(SCs) electrodes. However, it is still a paramount challenge to develop rationally designed CNFs with sufficient pseudocapacitive surface functionalities, and adequate porosity via a facile synthesis for better practical applicability. Herein, we are reporting a single-step electrospinning methodology followed by carbonization to generate a unique spatial 1D structure with metal oxide (MO) particles embedded in CNFs (M-CNFs). By optimizing the polymer ratio with that of MO, it was possible to obtain an in-situ N-enriched porous CNF network generating a predominant pseudocapacitive charge-storing mechanism. The resulting material is a synergistic combination of MOs, and surface-enriched N-CNFs with good electrical properties and high surface area, suitable to be employed as electrodes for SCs. A deep investigation of the M-CNFs properties has been performed to understand the physical characteristics of the hybrid MO/CNFs material. Further, a flexible symmetric SC device exploiting the polymeric gel-based (PVA+ H2SO4) electrolyte was assembled delivering a maximum energy density of up to 50 Wh Kg-1 and capacitance retention of 90% with a coulombic efficiency of 95%, enabling both electric double-layer and pseudo-capacitance behaviors. The resulting performances of the here-proposed material allow the prediction of the enormous potentialities of these flexible energy-storage devices for industrial-scale application. Keywords: surface N enrichment, electrospinning, hybrid CNFs, flexible symmetric supercapacitors.

Pseudocapacitive Storage in Molybdenum Oxynitride Nanostructures Reactively Sputtered on Stainless-Steel Mesh Towards an All-Solid-State Flexible Supercapacitor.

Exploiting pseudocapacitance in rationally engineered nanomaterials offers greater energy storage capacities at faster rates. The present research reports a high-performance Molybdenum Oxynitride (MoON) nanostructured material deposited directly over stainless-steel mesh (SSM) via reactive magnetron sputtering technique for flexible symmetric supercapacitor (FSSC) application. The MoON/SSM flexible electrode manifests remarkable Na+-ion pseudocapacitive kinetics, delivering exceptional ≈881.83Fg-1 capacitance, thanks to the synergistically coupled interfaces and junctions between nanostructures of Mo2N, MoO2, and MoO3 co-existing phases, resulting in enhanced specific surface area, increased electroactive sites, improved ionic and electronic conductivity. Employing 3D Bode plots, b-value, and Dunn's analysis, a comprehensive insight into the charge-storage mechanism has been presented, revealing the superiority of surface-controlled capacitive and pseudocapacitive kinetics. Utilizing PVA-Na2SO4 gel electrolyte, the assembled all-solid-state FSSC (MoON/SSM||MoON/SSM) exhibits impressive cell capacitance of 30.7mFcm-2 (438.59Fg-1) at 0.125mAcm-2. Moreover, the FSSC device outputs a superior energy density of 4.26µWhcm-2 (60.92Whkg-1) and high power density of 2.5mWcm-2 (35.71kWkg-1). The device manifests remarkable flexibility and excellent electrochemical cyclability of ≈91.94% over 10,000 continuous charge-discharge cycles. These intriguing pseudocapacitive performances combined with lightweight, cost-effective, industry-feasible, and environmentally sustainable attributes make the present MoON-based FSSC a potential candidate for energy-storage applications in flexible electronics.

Nanocellulose/carbon nanotube/manganese dioxide composite electrodes with high mass loadings for flexible supercapacitors

The increasing commercialization of flexible electronic products has sparked a rising interest in flexible wearable energy storage devices. Supercapacitors are positioned as one of the systems with the most potential due to their distinctive advantages: high power density, rapid charge and discharge rates, and long cycle life. However, electrode materials face challenges in providing excellent mechanical strength while ensuring sufficient energy density. This study presents a method for constructing a flexible composite electrode material with high capacitance and mechanical performance by electrochemically depositing high-quality manganese dioxide (MnO2) onto the surface of a nanocellulose (CNF) and carbon nanotube (CNT) conductive film. In this electrode material, the CNF/CNT composite film serves as a flexible conductive substrate, offering excellent mechanical properties (modulus of 3.3 GPa), conductivity (55 S/cm), and numerous active sites. Furthermore, at the interface between MnO2 and the CNF/CNT substrate, C-O-Mn bonds are formed, promoting a tight connection between the composite materials. The assembled symmetric flexible supercapacitor (FSC) demonstrates impressive performance, with an areal specific capacitance of 934 mF/cm2, an energy density of 43.10 Wh/kg, a power density of 166.67 W/kg and a long cycle life (85 % Capacitance retention after 10,000 cycles), suggesting that they hold promise for FSC applications.

Performance of solid-state symmetric supercapacitors based on Dy2S3 electrodes

Rare earth metal sulfides show good capacitance retention and better charge discharge performance. Dysprosium based materials could be a promising candidate for the utilization in supercapacitors due to it's multiple transition states. The dysprosium sulfide (Dy2S3) thin films were deposited on stainless steel (SS) substrate using facile successive ionic layer adsorption and reaction (SILAR) method. The films exhibits orthorhombic crystal structure and spherical nanoparticles morphology. The electrochemical supercapacitive performance of Dy2S3 film showed maximum specific capacitance (Cs) of 273 F g−1 at a scan rate of 5 mV s−1 with excellent (83 %) cycling performance over 2000 cycles in 1 M Na2SO4 electrolyte. The industrial application of SILAR deposited Dy2S3 thin film was examined by fabricating flexible solid-state symmetric supercapacitor (FSS-SSC) device with configuration Dy2S3/PVA-Na2SO4/Dy2S3. It exhibited Cs of 26 F g−1 with specific energy of 17 Wh kg−1 and specific power of 520 W kg−1. A good cyclic stability was observed with capacitive retention of 79 % at the scan rate of 100 mV s−1 after 5000 cyclic voltammetry (CV) cycles. This study highlights the potential application of Dy2S3 for supercapacitor application.

A mild one-step synthesis of sodium pre-intercalated δ-MnO2@CC for flexible high-performance supercapacitors with ultralong cycle life

Cation ion intercalated δ-MnO2 has been considered as a promising candidate for flexible energy storage devices. Herein, we fabricated Na ion pre-intercalated δ-MnO2 immobilized on flexible carbon cloth (CC) for symmetric supercapacitors via a mild one-step cyclic voltammetry (CV) electrodeposition method. Compared to that of NaxMnO2–32 without NH4+additive, NaxMnO2–32-N with NH4+ additive obtained a larger Cs (1208 mF·cm−2) with a 40 % increase and a maintained Cm (208 F·g−1 at 1 mA·cm−2). In addition, NaxMnO2–32-N exhibited more remarkable capacitive behavior and better rate capability. Based on the XPS, BET, TEM and SEM results, the increase of specific surface area, Na+ ion pre-embedded content and deposition mass were deduced to be the dominant role in optimizing electrochemical properties of δ-MnO2. A flexible symmetric supercapacitor was assembled by NaxMnO2–32-N electrodes to evaluate its applications and demonstrated a high energy density of 117.74 μW·h·cm−2 (at a power density of 225 μW·cm−2) and power density of 3375 μW·cm−2 (at an energy density of 12.35 μW·h·cm−2) with good flexibility. Furthermore, it showed excellent capacity retention rate (97 %) and coulomb efficiency (105 %) after 80,000 long-term charging/recharging cycles.

Graphene nanoflake-self stabilized dispersion polymerized PANI hybrids as efficient, binder-free electrode materials for high-performance flexible symmetric supercapacitors

In this study, we prepared hybrid electrodes of self-stabilized dispersion polymerized (SSDP) polyaniline (PANI) and graphene nanoflakes by a facile solution intercalation approach. Unlike the conventional electrode preparation methods, the SSDP PANI dispersion was prepared by adopting the secondary doping method. The preparation of hybrid electrodes by a unique combination of these methods eliminates the use of binders and imparts excellent electrochemical properties to these electrodes due to synergistic effects. The optimized electrode (PG 2:1) demonstrates a specific capacitance of 454.9 F g−1 at a current density of 0.5 A g–1 and the symmetric supercapacitor using this electrode, achieved an energy density of 33.2 Wh kg−1 at a power density of 1 kW kg−1. Furthermore, even at a high-power density of 10 kW kg−1, the device delivers an energy density of 25.4 Wh kg−1. Interestingly, the symmetric supercapacitor retains 89.2 % of its initial capacitance even after 10,000 continuous charge–discharge cycles at a current density of 5 A g–1. The performance of these devices was also tested for different bending angles and was found to exhibit excellent stability. The superior performance of this hybrid electrode offers significant potential for the development of efficient binder-free flexible supercapacitors for portable and wearable devices.

Biomass-based porous carbon from trachycarpus fortunei silk with the hierarchical oxygen-enriched structure for high performance flexible all-solid-state supercapacitor

Hierarchical porous carbons with diverse pore scales are commonly chosen as electrode materials for high-performance supercapacitors due to their excellent electrochemical properties. Herein, a novel synthetic method, dilute H2SO4 pretreatment coupling with subsequent KOH activation, is adopted to prepare hierarchical oxygen-enriched porous carbon using trachycarpus fortunei silk (TFSPC) waste as the raw material. The optimized TFSPC2 possesses a 2049 m2 g−1 specific surface area, 1.58 cm3 g−1 total pore volume, and 22.54 at% oxygen-containing doping. Benefiting from such characteristics, the TFSPC2 electrode exhibits an excellent specific capacitance of 469 F g−1 at 0.5 A g−1 and remarkable cycling stability of only 4.94% capacitance decay even after 20000 uninterrupted cycles in a 6 M KOH electrolyte. Furthermore, the assembled flexible symmetric supercapacitor device TFSPC2//TFSPC2 achieves a high energy density of 14.60 Wh kg−1 in a potential range of 0–1.3 V when the power density is 320 W kg−1. More importantly, the TFSPC2//TFSPC2 device demonstrates superior mechanical flexibility and maintains 88.70% capacity retention even through 2000 cycles (90°) of reduplicative bending/recovering. The research provides a low-cost, green, and renewable strategy for the synthesis of hierarchical porous carbons for supercapacitors.

In Situ Construction of the Fe-Cu Hydroxide Interlocking Structure with Solution-Derived Cu/Ag Current Collectors for Flexible Symmetric Supercapacitors.

The current collector serves as a crucial element in supercapacitors, acting as a medium between the electrode material and the substrate. Due to its excellent conductivity, a metal collector is typically favored. Enhancing the binding strength between the collector and the substrate as well as between the collector and the electrode material has emerged as a critical factor for enhancing the capacitance performance. In this study, a Ag film with a grass root-like structure was initially grown on a PI substrate through the surface modification and ion exchange (SMIE) process. This Ag interlocking structure contributes to strong binding between the PI substrate and Ag without compromising the mechanical properties of the Ag film. To further enhance the electrochemical properties at low scan rates, electroless-plated Cu was subsequently deposited on the Ag film to form the Cu/Ag current collector. Moreover, the Cu within the Cu/Ag current collector served as a precursor for the growth of FeOOH-Cu(OH)2 via a two-step in situ method. The resulting FeOOH-Cu(OH)2/Cu/Ag structure as a whole is binder-free. Supercapacitors employing symmetric FeOOH-Cu(OH)2/Cu/Ag structures were assembled, and their energy storage properties were investigated. The solution-based low-temperature process used in this study offers the potential for cost-effective and large-scale applications.