High-performance Flexible Energy Storage Devices Research Articles

High-Conductivity and Ultrastretchable Self-Healing Hydrogels for Flexible Zinc-Ion Batteries.

Aqueous zinc-ion batteries are promising candidates for flexible energy storage devices due to their safety, economic efficiency, and environmental friendliness. However, the uncontrollable dendrite growth and side reactions at the zinc anode hinder their commercial application. Herein, we designed and synthesized a dual network self-healing hydrogel electrolyte with zwitterionic groups (PAM-PAAS-QCS), which can be used for the large deformations of flexible devices due to its excellent stretchability (ε = 5100%). The incorporation of zwitterionic groups into the PAM-PAAS-QCS hydrogel electrolyte endows it with high ionic conductivity (33.61 mS/cm), a wide electrochemical stability window, and the ability to suppress zinc dendrite formation and side reactions. Besides, the Zn//Zn symmetric cell with PAM-PAAS-QCS can stably plate and strip zinc for 1500 h at 0.5 mA/cm2, and the Zn//Polyaniline full cell retains 82.4% of its capacity after 1500 cycles at 1 A/g. Additionally, flexible batteries based on both the original and self-healed PAM-PAAS-QCS hydrogel electrolytes demonstrate good cycling stability and stable charge-discharge performance under various bending conditions. This self-healing hydrogel electrolyte with excellent stretchability and high ionic conductivity is expected to pave the way for the development of high-performance flexible energy storage and wearable devices.

Facile assembly of flexible, stretchable and attachable symmetric microsupercapacitors with wide working voltage windows and favorable durability

With the increasing development of intelligent robots and wearable electronics, the demand for high-performance flexible energy storage devices is drastically increasing. In this study, flexible symmetric microsupercapacitors (MSCs) that could operate in a wide working voltage window were developed by combining laser-direct-writing graphene (LG) electrodes with a phosphoric acid-nonionic surfactant liquid crystal (PA-NI LC) gel electrolyte. To increase the flexibility and enhance the conformal ability of the MSC devices to anisotropic surfaces, after the interdigitated LG formed on the polyimide (PI) film surface, the devices were further transferred onto a flexible, stretchable and transparent polydimethylsiloxane (PDMS) substrate; this substrate displayed favorable flexibility and mechanical characteristics in the bending test. Furthermore, the electrochemical performances of the symmetric MSCs with various electrode widths (300, 400, 500 and 600 μm) were evaluated. The findings revealed that symmetric MSC devices could operate in a large voltage range (0–1.5 V); additionally, the device with a 300 μm electrode width (MSC-300) exhibited the largest areal capacitance of 2.3 mF cm−2 at 0.07 mA cm−2 and an areal (volumetric) energy density of 0.72 μWh cm−2 (0.36 mWh cm−3) at 55.07 μW cm−2 (27.54 mW cm−3), along with favorable mechanical and cycling stability. After charging for ~20 s, two MSC-300 devices connected in series could supply energy to a calculator to operate for ~130 s, showing its practical application potential as an energy storage device. Moreover, the device displayed favorable reversibility, stability and durability. After 12 months of aging in air at room temperature, its electrochemical performance was not altered, and after charging-discharging measurements for 5000 cycles at 0.07 mA cm−2, ~93.6% of the areal capacitance was still retained; these results demonstrated its practical long-term application potential as an energy storage device.

Polymethylene trisulfide/reduced graphene oxide nanocomposite electrodes: Deciphering microstructure/electrochemistry relationship

Flexible polysulfide electrodes can play a crucial role in the future development of wearable energy storage devices. Understanding the electrochemical energy storage mechanism in these electrodes can guide the engineering of polysulfides and their composites to design high-performance flexible energy storage devices. Polymethylene trisulfide (PMTS) and PMTS/reduced graphene oxide (rGO) nanocomposites, synthesized via in-situ interfacial polymerization, are introduced as active materials for developing high-performance electrodes. The fundamental scientific objective of this study is to uncover the correlation between the microstructural properties of linear polysulfides and the electrochemical behavior of low molecular weight intermediate polysulfide species. Based on microstructural studies, Coulomb interactions between rGO and PMTS macromolecules dictate PMTS chain confinements. Such molecular confinements affect the glass transition temperature and the crystallinity of PMTS, hence controlling the electrochemistry of electrodes. A high specific capacity of 366 mAh/g (5 μA) is reached using the flexible PMTS/0.5 wt% rGO nanocomposite electrode in Li-PMTS cells. The suggested mechanism for the anodic and cathodic polarizations in Li-PMTS cells is based on the formation of low molecular weight sulfide polymeric species. Therefore, the crystallinity and moveability of polymeric chains are introduced as structural features of polysulfide electrodes that can be utilized to improve the performance of energy storage systems based on these active materials.

Conformal Engineering of Both Electrodes Toward High-Performance Flexible Quasi-Solid-State Zn-Ion Micro-Supercapacitors.

The severe Zn-dendrite growth and insufficient carbon-based cathode performance are two critical issues that hinder the practical applications of flexible Zn-ion micro-ssupercapacitors (FZCs). Herein, a self-adaptive electrode design concept of the synchronous improvement on both the cathode and anode is proposed to enhance the overall performance of FZCs. Polypyrrole doped with anti-expansion graphene oxide and acrylamide (PPy/GO-AM) on the cathode side can exhibit remarkable electrochemical performance, including decent capacitance and cycling stability, as well as exceptional mechanical properties. Meanwhile, a robust protective polymeric layer containing reduced graphene oxide and polyacrylamide is self-assembled onto the Zn surface (rGO/PAM@Zn) at the anode side, by which the "tip effect" of Zn small protuberance can be effectively alleviated, the Zn-ion distribution homogenized, and dendrite growth restricted. Benefiting from these advantages, the FZCs deliver an excellent specific capacitance of 125mFcm-2 (125Fcm-3) at 1mAcm-2, along with a maximum energy density of 44.4µWhcm-2, and outstanding long-term durability with 90.3% capacitance remained after 5000 cycles. This conformal electrode design strategy is believed to enlighten the practical design of high-performance in-plane flexible Zn-based electrochemical energy storage devices (EESDs) by simultaneously tackling the challenges faced by Zn anodes and capacitance-type cathodes.

Dendrite-free zinc anode enabled by zwitterionic organic hydrogel electrolytes for high-voltage zinc-ion hybrid capacitors

Aqueous zinc-ion hybrid supercapacitors (ZIHC) have been widely researched due to their inherent high safety, low cost, and high power. However, the low operating voltage of aqueous electrolytes, H2O-induced side reactions, and intractable dendrites severely compromise the energy output and durability of ZIHC. Herein, a freeze-tolerant zwitterionic organic hydrogel electrolyte (PSAMOHE) was constructed for high-voltage flexible ZIHC. The hydrogen bonding between ethylene glycol and water inhibited the formation of ice crystals, preventing the electrolyte from freezing at −40 °C. Concurrently, the hydrophilic PSAMOHE mitigated harmful side reactions and achieved a wide electrochemical stability window (2.2 V) by anchoring water molecules. In addition to exhibiting exceptional interface adhesion and mechanical adaptability, PSAMOHE with charged functional groups effectively facilitated ion migration, diminished the desolvation energy barrier of hydrated Zn2+, and induced uniform Zn deposition. By combining these advantages, the assembled flexible ZIHC exhibited a battery-level specific capacity of 269.1 mAh/g (at 0.5 A/g), impressive environmental adaptability, and excellent mechanical adaptability. Impressively, the ZIHC maintained 89.5 % of the initial capacity and obtained a dendrite-free Zn anode after 14,000 cycles of charge and discharge. This study provides valuable insights into the exploration of hydrogel electrolyte engineering for high-performance zinc-based flexible energy storage devices.

Improving the capacitance of hydrogel-based supercapacitors by pre-depositing a zwitterionic 3,4-ethylenedioxythiophene

Polymer hydrogel electrolytes show great advantages in the flexible electronic applications of supercapacitors, but the poor interfaces between electrode and electrolyte are limiting their energy and power densities. In this work, by taking the well-developed pair of poly(vinyl alcohol)/H2SO4 gel electrolyte and graphene film electrode as a prototype, after electrochemically depositing a functional monomer of zwitterionic 3,4-ethylenedioxythiophene (EDOTSB) onto the graphene film electrodes, the specific capacitance of supercapacitors receives a 2.5-fold increase up to 248 mF cm−2 (346 F g−1). By comparing with other pendent groups on EDOT, the decisive role of the zwitterionic group is demonstrated. Attributed to the strong hydration ability of the zwitterion group, the deposition of EDOTSB effectively improves the hydrophilicity of graphene film electrodes, so that the interfacial affinity between the electrode and hydrogel electrolyte is greatly promoted. On the one hand, the EIS measurements certify that the charge-transfer resistance is largely reduced. On the other hand, tests with electrochemical quartz crystal microbalance demonstrate that the interior of graphene film is highly accessible for EDOTSB, thereby enlarging the accessible surface area on the electrode and accelerating the electrolyte infilling process. Furthermore, the general comparison with the liquid electrolyte counterpart is also discussed. This developed method is highly universalizable and can find applications in different electrode/electrolyte supercapacitors and other high-performance flexible energy storage devices.

A flexible supercapacitor with high energy density and wide range of temperature tolerance using a high-concentration aqueous gel electrolyte

As the demand for a wide range of wearable devices increases, extensive effort is devoted to developing high-performance flexible energy storage devices such as batteries and supercapacitors. Of particular interest, flexible supercapacitors using aqueous electrolytes have high application potential owing to their many advantages including low cost, harmlessness to the human, and environmental safety compared to others using electrolytes such as ionic liquids and organic electrolytes. However, poor temperature tolerance and narrow operation voltage window have hindered the practical application of aqueous supercapacitors. In this study, we report on a wide temperature-tolerant flexible aqueous supercapacitor featuring high electrochemical performance designed by a deliberate selection of electrode materials and electrolytes. As a flexible electrode, three-dimensional microporous graphene foam coated with conducting polymer Polypyrrole (PPy) is used to enhance capacitance up -to 90.0 F/g by increasing the surface area and inducing the pseudo-capacitance of PPy. As a gel-type electrolyte, a high-concentration NaClO4 is mixed with Polyvinyl alcohol to enlarge the voltage window to 1.8 V and a stable temperature range from -25 to 80°C, even under repetitive bending deformation. The fabricated supercapacitor exhibits a superior energy density of 37.4 Wh kg−1 and maintains 92.0% of initial capacitance at room temperature after three repeated cycles of cooling/heating across a wide temperature range over 100°C. This work suggests a high potential application of the fabricated supercapacitor as an eco-friendly and stable energy storage system for powering diverse wearable devices under various conditions.

Scalable fabrication of textile-based planar-structured supercapacitors with excellent capacitive performance

The researchers have been engaged in the development of textile-based high-performance flexible energy storage devices. The conventional fabrics are transformed into electrode composites by uniformly depositing polypyrrole (PPy) coating onto them using a simple interfacial solution polymerization method. The traditional textiles encompass cellulose fabrics such as cotton and ramie, protein fabrics like silk and wool, as well as chemical fiber fabric including polyester, polyamide, and acrylon. The PPy can be effectively coated onto the surface of cellulose fibers and penetrate into their interior, resulting in significantly higher loading capacity on cotton and ramie fabrics compared to other types of fibers. The two fabric electrodes (cotton@PPy and ramie@PPy) have better capacitive properties, especially the areal capacitance of ramie@PPy reaches 2836 mF cm−2. The PPy-coated fabric is precisely divided into standardized interdigital electrodes of consistent dimensions through the utilization of laser cutting techniques. The fabrication of a planar supercapacitor can be achieved through the straightforward assembly of two interdigital electrodes. The planar supercapacitor based on ramie@PPy shows a maximum energy density of 8.21 μWh cm−2 at power density of 0.20 mW cm−2. After undergoing 5000 cycles, the device demonstrates a remarkable ability to retain 90 % of its initial capacitance. The assembled supercapacitors exhibit exceptional flexibility and practicality, enabling power supply to electronic devices when connected in series. The fabric-based flexible supercapacitor can be easily mass-produced, making it a promising candidate for flexible energy storage devices.

Boosting the Lithium Storage Properties of a Flexible Li4Ti5O12/Graphene Fiber Anode via a 3D Printing Assembly Strategy

Traditional lithium-ion batteries cannot meet the high flexibility and bendability requirements of modern flexible electronic devices due to the limitations of the electrode material. Therefore, the development of high-performance flexible energy storage devices is of great significance for promoting flexible electronics. In recent years, one-dimensional flexible fiber lithium-ion batteries have been rapidly developed due to their advantages of high flexibility and bendability. However, it remains highly challenging to realize 1D flexible fiber lithium-ion batteries with excellent electrochemical properties and good mechanical performance. In this work, a reduced graphene oxide-based printing ink is proposed for the fabrication of flexible Li4Ti5O12/graphene fiber electrodes using a 3D printing assembly strategy. It is noteworthy that the green reducing agent vitamin C was used to reduce the graphene oxide in one step, which improved the conductivity of the fiber electrode. Furthermore, a 3D conductive network was constructed inside the fiber electrodes due to the high specific surface area of the reduced graphene oxide, which enhanced the electronic conductivity and ion mobility. The fiber electrode not only exhibits good mechanical performance, but also has excellent electrochemical properties. Equally importantly, the method is simple and efficient, and the working environment is flexible. It can precisely control the shape, size and structure of the one-dimensional fiber flexible electrode, which is of great significance for the development of future flexible electronic devices.

Rational designed Cu-MOF@1D carbon nanofibers as free-standing and flexible electrode for robust electrochemical energy storage

The present study reported the performance of free-standing carbon nanofibers decorated with copper-metal-organic frameworks (Cu-MOFs). A green electrospinning technique was utilized to obtain nanofiber sheets that were carbonized and activated to produce activated carbon nanofiber sheets (ACNFs). These ACNFs consist of inherent oxygen functionalities of the lignin that can aid the growth of MOF structure on it in a single step, which motivated us to do this work. Cu-MOF particles were in-situ grown over the surface of ACNFs using a hydrothermal-assisted technique. The developed materials were characterized using FESEM, Raman Spectroscopy and BET analysis in order to identify morphological, porosity, and surface area transformations. Along with these, Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and Galvanostatic Charge-Discharge (GCD) studies were performed to compare the electrochemical performance of the Cu-MOF, ACNF, and Cu-MOF@ACNF as electrode materials for supercapacitors. Among three electrodes, the Cu-MOF@ACNF sheet reveals a higher specific capacitance of 303.2 F/g compared to ACNF (203.3 F/g) and Cu-MOF (68.2 F/g) at the same current density of 1 A/g. Based on the higher performance of Cu-MOF@ACNF two types of symmetrical devices, i.e., aqueous (using electrolyte-impregnated filter paper) and solid-state devices (using a polymeric gel electrolyte), were fabricated. The all-solid-state supercapacitor device was found to feature high flexibility, stand-alone characteristics, and excellent performance as an electrode with a working potential window of 0–2.0 V. The device demonstrates a high energy density of 78.71 Wh/kg and a power density of 1050.0 W/kg, along with high coulombic efficiency (99.8 %) after 10,000 cycles. The achieved performance is superior to many published reports, revealing that the developed composite materials hold prospect for applications in green and high-performance flexible energy storage devices.

Aestivum-inspired photothermal 3D-MXene-unity membrane-aerogel for flexible supercapacitor with solar enhanced performance

Designing high gravimetric capacitance, flexible, and functional structural electrodes based on 2D nanomaterials is crucial for wearable electronics, however, it is still limited by serious restacking problems and uncontrollable assembly processes. Herein, inspired by a specialized network of rigidity-flexible integration in aestivum, an effective half-dry 2D-1D-2D pre-assembly combined with an “ice templating” strategy was proposed to construct a novel 3D-MXene-unity membrane-aerogel for the desirable supercapacitor substrate with energy harvesting capacity, addressing the incompatible contradiction between electrochemical properties and desirable mechanical strength. With cellulose nanofiber serving as a 1D structural modifier as well as black-phosphorus nanosheets applied as a 2D restacking reliever and electron-conductive network jointer, the multi-leveled mimicked topology facilitated the configured complexity of the membrane-aerogel can be achieved to be utilized in multifunctional composite electrodes. The resulting super-flexible and net-shaped 3D-MXene-unity membrane-aerogel showed low-tortuosity topology, superior electron-conductive network (870 S/cm), outstanding mechanical strength (53.2 MPa), and favorable electrochemical property (215 F/g), hardly achieved in a single system. Because of the synergistic photo-thermal capability from MXene and BP, assembled supercapacitors can harvest energy from sunlight and result in a 196% enhancement in capacitance. This work would lay a significant foundation for the construction of high-performance flexible energy storage devices.

FeV LDH Coated on Sandpaper as an Electrode Material for High-Performance Flexible Energy Storage Devices

Recently, considerable research efforts to achieve advanced design of promising electroactive materials as well as unique structures in supercapacitor electrodes have been explored for high-performance energy storage systems. We suggest the development of novel electroactive materials with an enlarged surface area for sandpaper materials. Based on the inherent micro-structured morphologies of the sandpaper substrate, nano-structured Fe-V electroactive material can be coated on it by facile electrochemical deposition technique. A hierarchically designed electroactive surface is covered with FeV-layered double hydroxide (LDH) nano-flakes on Ni-sputtered sandpaper as a unique structural and compositional material. The successful growth of FeV-LDH is clearly revealed by surface analysis techniques. Further, electrochemical studies of the suggested electrodes are carried out to optimize the Fe-V composition as well as the grit number of the sandpaper substrate. Herein, optimized Fe0.75V0.25 LDHs coated on #15000 grit Ni-sputtered sandpaper are developed as advanced battery-type electrodes. Finally, along with the negative electrode of activated carbon and the FeV-LDH electrode, it is utilized for hybrid supercapacitor (HSC) assembly. The fabricated flexible HSC device indicates high energy and power density by showing excellent rate capability. This study is a remarkable approach to improving the electrochemical performance of energy storage devices using facile synthesis.

High-Performance Flexible Energy Storage Devices Based on Graphene Decorated with Flower-Shaped MoS2 Heterostructures

MoS2, owing to its advantages of having a sheet-like structure, high electrical conductivity, and benign environmental nature, has emerged as a candidate of choice for electrodes of next-generation supercapacitors. Its widespread use is offset, however, by its low energy density and poor durability. In this study, to overcome these limitations, flower-shaped MoS2/graphene heterostructures have been deployed as electrode materials on flexible substrates. Three-electrode measurements yielded an exceptional capacitance of 853 F g-1 at 1.0 A g-1, while device measurements on an asymmetric supercapacitor yielded 208 F g-1 at 0.5 A g-1 and long-term cyclic durability. Nearly 86.5% of the electrochemical capacitance was retained after 10,000 cycles at 0.5 A g-1. Moreover, a remarkable energy density of 65 Wh kg-1 at a power density of 0.33 kW kg-1 was obtained. Our MoS2/Gr heterostructure composites have great potential for the development of advanced energy storage devices.

COF-Based Electrodes with Vertically Supported Tentacle Array for Ultrahigh Stability Flexible Energy Storage

As an emerging porous crystal polymer, covalent organic frameworks (COFs) possess unique characteristics, such as high porosity, excellent stability, diverse topologies, designable open channels, and functional tunability. However, limited by the solid powder form, most COFs display low active site utilization and weak binding force with the current collector. In this pioneering research, we integrate redox-active COFs onto carbon fiber surfaces (AC-COFs) via strong covalent bridging. The 2,6-diaminoanthraquinone (DAAQ) pillars embedded on the carbon fiber surface are the key to precisely controlling the growth direction of COFs. The obtained tentacle-like array vertically supported on the surface of the carbon fiber can effectively induce charge transfer and prevent COFs from aggregating/collapsing. The strong covalent coupling and increase of accessible active sites contributed to the high specific capacitance of AC-COFs electrode (1034 mF cm-2). In addition, the COF-based flexible electrode retains an initial capacitance of 98% after 20000 charge-discharge cycles. The flexible all-solid-state symmetric supercapacitor is assembled by PVA/H2SO4 gel electrolyte with an areal capacitance of 715 mF cm-2. Besides, a red LED can be easily powered by three-bending AC-COFs//AC-COFs devices. The innovative synthesis strategy opens up new opportunities to develop high-performance flexible energy storage devices based on COFs.

Data-driven design of carbon-based materials for high-performance flexible energy storage devices

With the rise of flexible electronics, the demand for advanced power sources has grown. Developing high-performance energy storage devices requires comprehensive consideration of various factors such as electrodes, electrolytes, and service conditions. Herein, a data-driven research framework is proposed to optimize the electrode-electrolyte system in supercapacitors. With the help of machine learning, we reveal the key factors affecting the capacitance performance of carbon-based materials. According to the algorithm analysis, a kind of 3D carbon network is prepared with controlled composition and structure, which is incorporated with a high-safety ionic liquid to obtain a supercapacitor device. This device with high energy density and impressive flexibility can maintain operational stability under extreme conditions such as humidity, shock, and localized damage. Overall, this work presents a typical pipeline for accelerating the design of energy-related devices.

Hybrid carbon nanofiller/polymer composites as self-healable current collector electrodes for use in high-performance flexible metal-free supercapacitors

Supercapacitors with multiple features, such as high capacitance, high-rate capability, high flexibility, and self-healing properties, are regarded as good candidates for powering portable and wearable electronics. Herein, a symmetric supercapacitor with multiple functions is fabricated by sandwiching a highly conductive self-healable composite current collector electrode with an active material, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/multiwalled carbon nanotubes (PEDOT:PSS/MWNTs), and a poly(vinyl alcohol)/ phosphoric acid (PVA/H3PO4) electrolyte. The novelty of this work lies in the synergy arising from the combination of two conducting carbon nanofillers, referred to as hybrid carbon nanofiller (HCF), coupled with healable polymer matrices (HCF/HPU) to fabricate self-healing high-conductivity composite current collector electrodes. These can be used in flexible metal-free supercapacitors, which have not been specifically considered previously. The use of two geometrically varied nanofillers with proper selection of the nanofiller content ratio can induce the formation of an effectively conductive co-supporting network, which drastically enhances the electrical properties and mechanical strength of the composite current collector compared to that of single nanofillers. More importantly, the supercapacitor assembled by the HCF/HPU composite current collector delivers high specific capacitance and energy density. In addition, noticeable cycling stability with only ∼ 10 % capacitance loss was observed after 20,000 consecutive charge/discharge cycles at a high current density of 10 mA cm–2. Furthermore, at a medium temperature of 60 °C, supercapacitors with this HCF/HPU composite current collector restore at least 96.2 % of their capacitance properties even after 5 cycles of severing/healing. The capacitive retention rate after 2000 bending cycles was 97.4 % at a bending radius of 4.0 mm. These properties indicate this HCF/HPU composite current collector is a promising candidate for use in high-performance flexible energy storage devices.

Metal-organic framework-derived NiS@Cobalt-Molybdenum layered double hydroxides shell@core as cathode and CoFe2O4-nanoparticles@MXene shell@core as anode materials for ultra-high energy-density flexible asymmetric supercapacitor

Modern electronics industries-based on portable and wearable devices, urgently needed the design and fabrication of high-performance flexible electrochemical supercapacitors. However, the low specific capacitance and deprived rate-capability of cathode and anode electrode materials are two prominent hurdles in obtaining the optimal electrochemical performance of flexible asymmetric supercapacitors (ASCs) devices. Herein, for the first time, metal-organic framework-derived shell@core and MXene-supported shell@core strategies are reported to fabricate high-performance cathode and anode electrode materials, respectively for sustainable flexible asymmetric supercapacitor. The NiS@Co–Mo–LDHs shell@core as cathode and Co–Fe–O–nanoparticles@MXene as anode electrodes demonstrate high areal capacities of 1.43 and 0.949 mA h cm−2, respectively at a current density of 1 mA cm−2. Benefiting from the commendable individual electrochemical performances of the cathode and anode electrode materials, the as-assembled NiS@Co–Mo–LDHs//Co–Fe–O@MXene flexible all-solid-state asymmetric supercapacitor (FSS-ASC) device exhibits an excellent energy density of 90.2 W h Kg−1 with superior capacitance retention up-to 90.6 % after 10,000 cycles. Furthermore, after flexibility testing, the NiS@Co–Mo–LDHs//Co–Fe–O@MXene FSS-ASC device also retains excellent electrochemical properties. These electrochemical findings reveal that the NiS@Co–Mo–LDHs shell@core and Co–Fe–O@MXene shell@core electrode materials are the appropriate candidates for the development of high-performance flexible energy storage devices.

Fabrication and Performance Test of Flexible Supercapacitors Based on Three-Dimensional Graphene Hydrogel

Flexible supercapacitors have attracted more and more attention and research because they can be used as energy storage devices for future flexible electronic devices. In the existing research, graphene has been used to make supercapacitor electrodes, but usually these electrodes have very low specific capacitance or flexibility. Here, a three-dimensional graphene hydrogel for the fabrication of flexible supercapacitors was presented, and the preparation of flexible supercapacitors based on three-dimensional graphene hydrogels was given. Through the research, we find that the prepared flexible supercapacitor has excellent capacitance characteristics, such as high specific capacitance of 168F/g and excellent mechanical flexibility. This study shows that the three-dimensional graphene macro structure has great potential in the preparation of high-performance flexible energy storage devices.

Highly flexible, freestanding supercapacitor electrodes based on hollow hierarchical porous carbon nanofibers bridged by carbon nanotubes

Supercapacitors are considered to be the next generation of wearable energy storage devices because of reliable safety, high power density, and long cycle life, but the flexibility and energy density limit their practical applications. Herein, the flexible hollow hierarchical porous carbon nanofibers bridged by carbon nanotubes (HPCNFs@CNTs) are designed and constructed, followed by polyaniline (PANI) decorating to fabricate PANI@HPCNFs@CNTs. The synergistic effect of the hollow structure, hierarchical pores, in-situ nitrogen doping, and the bridging structure endows the HPCNFs@CNTs with a high specific capacitance of 461.0F g−1 (207.4 mF cm−2) while maintaining glorious flexibility under various deformation states. Besides, PANI@HPCNFs@CNTs possesses a high specific capacitance of 629.1F g−1 (405.2 mF cm−2) and remarkable cycle stability with 88.5 % capacitance retention after 5000 charging-discharging cycles. The device assembled by PANI@HPCNFs@CNTs renders an ultra-high energy density of 23.3 Wh kg−1 at a power density of 202.7 W kg−1. Furthermore, the device provides remarkable cycle stability and high-rate capability with a capacity retention of 91.3 % after 5000 cycles at 5 A g−1 and 76.7 % at 10 A g−1, respectively, demonstrating a tremendous potential to construct high-performance flexible energy storage devices.

Data-Driven Design of Carbon-Based Materials for High-Performance Flexible Energy Storage Devices

Data-Driven Design of Carbon-Based Materials for High-Performance Flexible Energy Storage Devices