Electrode Materials For Flexible Supercapacitors Research Articles

Evaluation of nitrogen- and sulfur-doped porous carbon textiles as electrode materials for flexible supercapacitors

With an objective to increase an electrochemical performance, simple and effective modifications of activated carbon fiber textiles (ACT) were carried out prior to their testing as supercapacitors. The modifications included a high-temperature treatment of the textile impregnated with N- and S-containing species (i.e. dicyandiamide, urea and thiourea). This led to an improvement in an electrical conductivity and in an enhanced mechanical strength with a preserved porosity. Compared to the performance of the initial unmodified carbon textile, a urea-functionalized material showed an enhancement in the electrochemical capacitance. An increase from 177 to 209 F g−1 at a scan rate 10 mV s−1 in an alkaline electrolyte was recorded (3-cell CV measurements) and from 138 to 166 F g−1 at 0.10 A g−1 (2-cell galvanostatic charge-discharge). The results suggested that mechanically stable, flexible and conductive ACT have a potential to be used in textile-based flexible supercapacitors. Benefits coming from the applied modification routes can be also adapted for the fabrication of other types of carbon-based composite electrode materials.

Thermally Activated Multilayered Carbon Cloth as Flexible Supercapacitor Electrode Material with Significantly Enhanced Areal Energy Density

AbstractCarbon cloth, an inexpensive and conductive textile, holds great promise as substrate for constructing electrical double‐layer capacitors due to its mechanical and electrochemical superiority. However, its widespread application is significantly hampered by the intrinsic low specific capacity. In this work, we demonstrate that the areal capacitance of commercial carbon cloth is raised for 800‐folds by a direct thermal activation strategy. When evaluated as the symmetric supercapacitor electrodes, thermally activated carbon cloth (TACC) displays the outstanding performance with areal capacitance up to 3291 mF cm−2 and the energy density of 740 μW h cm−2 at a power density of 9000 μW cm−2. In addition, the TACC‐based electrode reserves 95.2 % capacitance after 10,000 charge‐discharge cycles in a neutral NaBF4 electrolyte, showing outstanding cycle durability of the material. This work offers a foolproof and scalable method to prepare flexible electrode materials for wearable energy storage devices.

Rylene Diimide-Based Alternate and Random Copolymers for Flexible Supercapacitor Electrode Materials with Exceptional Stability and High Power Density

Donor–acceptor pi-conjugated polymers are emerging as interesting electrode materials for supercapacitor device applications. They offer an exciting possibility of charge storage in both positive a...

NaTi2(PO4)3/C‖carbon package asymmetric flexible supercapacitors with the positive material recycled from spent Zn‒Mn dry batteries

Spent Zn‒Mn batteries (ZMBs) pose a serious threat on eco-system and human health because of the toxic heavy metal ions released from ZMBs into the environment. In this report, carbon package is recycled from spent ZMBs and used as a positive electrode material for flexible supercapacitors. In a three-electrode system using 1 mol L−1 Na2SO4 as the electrolyte, the recycled carbon package (RCP) can deliver a specific capacitance of 100 F g−1 at 1 A g−1. After 5000 cycles at 1 A g−1, a specific capacitance of 86 F g−1 is retained with nearly 100% coulombic efficiency. Nanocomposite of NaTi2(PO4)3 with nitrogen-doped carbon layer (NTP/C) is prepared through a simple co-precipitation plus annealing method. NTP/C can deliver specific capacity of 320 and 273 F g−1 at 1 and 10 A g−1, using 1 mol L−1 Na2SO4 as the electrolyte. The high rate capability of NTP/C is attributed to the high specific surface area and nitrogen-doped carbon layer. Flexible asymmetric supercapacitors are assembled in configuration of NTP/C‖RCP, using 1 mol L−1 Na2SO4 as the electrolyte and stainless steel foil as the current collector. At 0.5 A g−1, the typical flexible supercapacitor cell can deliver a specific energy of 17.8 W h kg−1 with corresponding specific power of 503 W kg−1, and retain 15 W h kg−1 after 2000 cycles.

Fabrication of stretchable multi-element composite for flexible solid-state electrochemical capacitor application

The rapid development of various portable and wearable electronics proposes a great demand on flexible supercapacitors. It is critical to develop highly flexible electrode materials for flexible supercapacitors. In this paper, we present the development of stretchable polyvinyl alcohol (PVA)/carbon nanomaterials(CNM)/polyaniline (PANI) composite with the elongation at break as high as 365% by incorporating stretchability of PVA, electrical conductivity and double-layer capacitance of CNM (CNT and carbon black), and pseudocapacitance of PANI. Based on PVA/CNM/PANI film, a flexible solid-state supercapacitor is fabricated. Supercapacitor not only delivers an outstanding specific capacitance of 284.6 mF cm−2, but also displays high cycle life. Importantly, a stretchable supercapacitor can also be assembled by two PVA/CNM/PANI film without using carbon cloth and shows no significant energy storage capacity change at different stretching shapes and even repeated stretching/bending cycles. The results from this study can contribute to the development and fabrication of high stretchable composite and stretchable energy-storage devices.

Layer-opened graphene paper with carbon nanotubes as support in a flexible electrode material for supercapacitors

Graphene paper is a promising electrode material for use in flexible supercapacitors due to its good electronic conductivity and excellent mechanical characteristics. However, layers of graphene paper have a strong tendency to restack, resulting in a seriously reduced specific surface area and limited electrochemical performance. In this paper, restacked layers of graphene paper are reopened by a vacuum-assisted method, and carbon nanotubes (CNTs) are directly deposited on the enlarged space between the opened graphene layers. Consequently, an ordered carbon composite structure with alternately arranged graphene sheets and CNTs is constructed and exhibits increased specific surface area and a 3D conductive network. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and N2 adsorption/desorption measurements. The electrochemical performance was tested by galvanostatic charge-discharge test (GDC), electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV). The obtained graphene/CNT paper exhibits a remarkably improved capacity of 170.8 F g−1, which is nearly two times higher than that obtained for a regular graphene paper.

Reduced graphene oxide/polymer dots-based flexible symmetric supercapacitors delivering an output potential of 1.7 V with electrochemical charge injection

Electrochemical charge injection (ECI) is proved a powerful technique to maximize the available widen potential range of aqueous electrolyte. In this report, reduced graphene oxide/polymer dots (rGO/PDs) nanocomposites are prepared and tested as electrode materials for flexible supercapacitors. The weight ratio of GO/PDs plays an important role in the electrochemical performance of rGO/PDs nanocomposites. Through the ECI technique, a 1.7-V output potential can be delivered by rGO/PDs-based flexible supercapacitors operating with 1 mol L−1 Na2SO4 aqueous electrolyte. A specific energy of 7.1 W h kg−1 with corresponding specific power of 85 W kg−1 can be achieved for a typical flexible supercapacitor, which exhibits a capacitance retention of 90.6% after 5000 cycles at 0.5 A g−1.

A novel MnO2/Ti3C2Tx MXene nanocomposite as high performance electrode materials for flexible supercapacitors

MnO2 is considered as one of the most promising electrode materials for flexible supercapacitors but it often suffer in poor conductivity, which limits practical applications according to industry needs. To enhance the performance, forming MnO2-based hybrid structures with conductive materials is a promising implement approach. Ti3C2Tx MXene sheets, a new kind of 2D transition metal carbides with metallic conductivity and hydrophilic nature, are promising candidate to couple with MnO2. According to the complementary principle, we design a novel structure MnO2/Ti3C2Tx hybrid nanocomposite by synergistically coupling one-dimensional (1D) MnO2 nanoneedles with two-dimensional (2D) Ti3C2Tx MXene sheet for flexible supercapacitor. XPS investigations suggest the obvious charge transfer from Ti3C2Tx sheets to MnO2 nanoneedles, where Ti3C2Tx sheets serve as a remarkable 2D conductive substrate to facilitate the electrons transfer in the nanocomposites. This strong synergistic effect between Ti3C2Tx and MnO2 resulting from the chemical interaction greatly enhance the electrical conductivity, specific capacitance, rate stability and structural stability of the MnO2/Ti3C2Tx nanocomposite. To show the potential application in energy storage, a symmetrical flexible supercapacitor device with good electrochemical performance, high flexibility and super cycling ability is fabricated by utilizing MnO2/Ti3C2Tx nanocomposites as electrode materials. This work has proposed a new approach of developing advanced nanocomposites from a MnO2-based electrode for high performance flexible electronics.

Micro-/mesoporous carbon nanofibers embedded with ordered carbon for flexible supercapacitors

Currently carbon nanofibers are attracting myriad interest for supercapacitors due to their high specific capacitance and low cost. However, their poor electrical conductivity and microporous structure restrict their wide applications. Here, flexible micro-/mesoporous carbon nanofibers embedded with ordered carbon (MCNF) were prepared by coaxial electrospinning and subsequent corrosion. Field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray diffraction spectroscopy and nitrogen adsorption-desorption isotherm were used to characterize their morphology, structure and specific surface area. Electrochemical tests of cyclic voltammetry and electrochemical impedance spectroscopy show that the specific capacitance of MCNF can reach 272 F g−1 at 1 A g−1, much higher than that of carbon nanofibers (216 F g−1) which is obtained by single axial electrospinning. The flexible symmetrical supercapacitor based on MCNF electrodes exhibits an excellent electrochemical performance, with a capacitance retention of 96.7% after 3000 charge-discharge cycles and a high energy density of 11.1 Wh kg−1 when the power density is 0.25 kW kg−1. More interestingly, its specific capacitance almost does not change even when it is bent to 135°. The results show that MCNF is a promising electrode material for flexible supercapacitors.

Design and synthesis of carbon nanotubes/carbon fiber/reduced graphene oxide/MnO2 flexible electrode material for supercapacitors

We present an easy method to use the carbon nanotubes (CNT)/carbon fiber (CF) membrane as a collector to load reduced graphene oxide (RGO)/MnO2 nanocomposites. The CNT/CF has a good flexibility and mechanical strength with the good pliable, mechanical strength and large porosity. RGO can provide high surface area for the deposition of MnO2, also as an effective dispersant and adhesive for MnO2, which can improve the connection effect among CNT/CF and MnO2 particles. The highly porous MnO2 nanospheres have provided high specific capacitance for the CNT/CF/RGO/MnO2 (CCRM) composite. The flexible CCRM composite film with excellent structural and electrochemical performance was obtained. Under the current density of 0.5 A/g, the CCRM flexible electrode has exhibited high specific capacitance of 356 F/g, the CCRM has showed good overall specific capacitance of 30.28 F/g (the areal capacitance is 131.72 F/cm) and excellent cycle performance, after 1000 cycles the specific capacitance has no obvious attenuation.

A high-performance flexible supercapacitor electrode material based on nano-flowers-like FeS2/NSG hybrid nanocomposites

Novel FeS2/nitrogen-sulfur double doped graphene (NSG) flexible hybrids electrode materials have been successfully prepared via a rapid microwave method followed by tube furnace heating process. Small size nano-flower-like structure of FeS2 uniformly supported on multi-fold NSG, which promote electron transport and electrochemical reaction. The material shows good electrochemical performance in a three-electrode system, such as high specific capacitance (528.7 F g−1 at the current density of 1 A g−1), excellent charge/discharge stability and long-term cycling life (89% of capacitance retention after 10,000 cycles at 10 A g−1). These results demonstrate great potential of FeS2/NSG flexible hybrid nanocomposites for supercapacitor application.

NiCo2O4 grown on Co/C hybrid nanofiber film with excellent electrochemical performance for flexible supercapacitor electrodes

A flexible film electrode of NiCo2O4 grown on Co/C hybrid nanofibers (NCCNF) was synthesized through electrospinning combining with carbonization and hydrothermal reaction. X-ray diffraction, Raman spectroscopy, scanning electron microscopy and N2 adsorption/desorption measurement were employed to characterize the composition, microstructure and morphology. The as-prepared flexible NCCNF film was used as a binder-free working electrode in three-electrode system and its electrochemical performance was evaluated by cyclic voltammetry, galvanostatic charge and discharge test and electrochemical impedance spectroscopy. The resulting flexible film shows excellent electrochemical performance with a high specific capacitance of up to 1710 F g−1 at 5 mV s−1, making it a potentially practical electrode material for flexible supercapacitors.

Ultrafine MnO2 nanowires grown on RGO-coated carbon cloth as a binder-free and flexible supercapacitor electrode with high performance.

Reduced graphene oxide coated carbon cloth has been used as a substrate for the growth of ultrafine MnO2 nanowires (CC/RGO/MnO2), forming binder-free and flexible supercapacitor electrode materials. The experimental results indicate that a maximum area-specific capacitance of 506.8 mF cm−2 was gained from the CC/RGO/MnO2 electrode at the current density of 0.128 mA cm−2. Furthermore, the electrode exhibits excellent cycling stability (98.6% specific capacitance was still retained after 10 000 galvanostatic charge–discharge (GCD) tests when the current density was 1.28 mA cm−2). What's more, the area-specific capacitance of the CC/RGO/MnO2 electrode was hardly changed, when the electrode was operated under bending mechanical conditions. In addition, the charge storage performance and mechanism of the MnO2 nanostructures was discussed.

Synthesis of NiCo2O4 onto carbon current collector films as the flexible electrode material for supercapacitors

NiCo2O4 is one of the well-known pseudocapacitive material with higher specific capacitance. In this work, carbon nanotubes (CNT) integrated carbon fibers (CF) are used as the flexible substrate for the growth of NiCo2O4 nanoneedle arrays by an in-situ hydrothermal approach to obtain NiCo2O4/CC flexible electrode for supercapacitors application. The NiCo2O4 nanoneedles with diameters of 40–50 nm were formed on the hydroxyl-functionalized CC. This hybrid electrode NiCo2O4/CC not only exhibits a high specific capacitance of 249.69 F g−1, but also shows a favourable cycling stability of 63.3% retention after 1000 cycles at high mass loading. In addition, the proposed method provides a simple and effective strategy for preparing flexible electrode materials for supercapacitor and enables the perfect combination of pseudocapacitance and double layer capacitance.

Soft and wrinkled carbon membranes derived from petals for flexible supercapacitors

Biomass materials are promising precursors for the production of carbonaceous materials due to their abundance, low cost and renewability. Here, a freestanding wrinkled carbon membrane (WCM) electrode material for flexible supercapacitors (SCs) was obtained from flower petal. The carbon membrane was fabricated by a simple thermal pyrolysis process and further activated by heating the sample in air. As a binder and current collector-free electrode, the activated wrinkled carbon membrane (AWCM) exhibited a high specific capacitance of 332.7 F/g and excellent cycling performance with 92.3% capacitance retention over 10000 cycles. Moreover, a flexible all-solid supercapacitor with AWCM electrode was fabricated and showed a maximum specific capacitance of 154 F/g and great bending stability. The development of this flower petal based carbon membrane provides a promising cost-effective and environmental benign electrode material for flexible energy storage.

Nitrogen-Enriched Porous Carbon Nanofiber Mat as Efficient Flexible Electrode Material for Supercapacitors

Freestanding nitrogen-doped porous carbon nanofiber (NCNF) mats were prepared by electrospinning polyacrylonitrile/poly(m-aminophenol) (PAN/PmAP) precursor blends with different polymeric compositions followed by thermal stabilization and carbonization. The morphology, pore structure, and surface elemental compositions of as-prepared NCNFs were characterized by different techniques such as scanning electron microscopy, transmission electron microscopy, N2 adsorption, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The charge-storage capability of the fabricated NCNFs was investigated in KOH electrolyte. The electrochemical performances of NCNFs were evaluated by varying the PmAP loading in the blend compositions. The highest specific capacitance of 347.5 F g–1 at 0.5 mA cm–2 together with a capacitance retention of 173.2 F g–1 at 20 mA cm–2 was achieved for the PAN:PmAP (85:15 w/w) NCNFs (NCNF85:15). The volumetric capacitance of 200.8 F cm–3 at 0.5 mA cm–2 was recorded for NC...

Facile synthesis of α-MnO2 nanorod/graphene nanocomposite paper electrodes using a 3D precursor for supercapacitors and sensing platform to detect 4-nitrophenol

Manganese dioxide (α-MnO2)/reduced graphene oxide (RGO) nanocomposite paper was synthesized using a 3D precursor manganese benzoate dihydrazinate for supercapacitor and sensor applications. The new 3D precursor and residue-free synthesis are the advantages of this method. Transmission electron microscopy showed that MnO2 nanorods with a mean diameter of <10nm were decorated densely over the RGO surface. Owing to the paper’s freestanding structure, the composite was used directly as a binder-free electrode in the electrochemical experiments. The composite exhibited a higher capacitance of 360Fg−1 at a current density of 2.5Ag−1 as well as a long cycle life with 7.0% capacitance loss after 10,000 cycles. The specific capacitance reached 228Fg−1 at a current density of 25Ag−1. In addition, the developed electrochemical sensor showed a linear relationship with the 4-nitrophenol (4-NP) concentration from 1 to 100μM with a detection limit of 0.017μM. The sensor was used to determine the level of 4-NP in tap water and river water samples with good recovery, highlighting the sensor’s feasibility for industrial applications. Overall, this composite paper is a promising electrode material for flexible supercapacitors and sensors.

Fabrication of Polyaniline/Graphene/Polyester Textile Electrode Materials for Flexible Supercapacitors with High Capacitance and Cycling Stability.

Vertical polyaniline (PANI) nanowire arrays on graphene-sheet-coated polyester cloth (RGO/PETC) were fabricated by the in situ chemical polymerization of aniline. The 3D conductive network that was formed by the graphene sheets greatly enhanced the conductivity of PANI/RGO/PETC and improved its mechanical stability. PANI nanowire arrays increased the active surface area of PANI, whilst the hierarchically porous structure of the PANI/RGO/PETC electrode facilitated the diffusion of the electrolyte ions. Electrochemical measurements showed that the composite electrode exhibited a maximum specific capacitance of 1293 F g(-1) at a current density of 1 A g(-1) . Capacitance retention was greater than 95 %, even after 3000 cycles, which indicated that the electrode material has excellent cycling stability. Moreover, the electrode structure endowed the PANI/RGO/PETC electrode with a stable electrochemical performance under mechanical bending and stretching.

Hydrothermal synthesis and electrochemical performance of MnO2/graphene/polyester composite electrode materials for flexible supercapacitors

Textile-based electrode materials have attracted intensive attention for flexible supercapacitors. However, the low electrochemical capacitance hinders their further application. In this study, MnO2 with high theoretical capacitance was successfully deposited on the conductive graphene/polyester composite fabric using a hydrothermal method. The MnO2 morphology can be controlled by adjusting the reaction time. The effects of MnO2 morphology, electrode structure, mechanical bending and stretching on the electrochemical performance of MnO2/graphene/polyester composite electrode materials were studied in detail. When a MnO2 sheet layer deposited on the graphene/polyester composite fabric, the resulted composite electrode material exhibited a specific capacitance of 332Fg−1 at a scan rate of 2mVs−1 and excellent cycling stability. The electrochemical performances of MnO2/graphene/polyester composite electrode material and its corresponding solid-state supercapacitor device were stable under mechanical bending and stretching conditions.

Electrochemical activation of carbon cloth in aqueous inorganic salt solution for superior capacitive performance.

Carbon cloth (CC) is an inexpensive and highly conductive textile with excellent mechanical flexibility and strength; it holds great promise as an electrode material for flexible supercapacitors. However, pristine CC has such a low surface area and poor electrochemical activity that the energy storage capability is usually very poor. Herein, we report a green method, two-step electrochemical activation in an aqueous solution of inorganic salts, to significantly enhance the capacitance of CC for supercapacitor application. Micro-cracks, exfoliated carbon fiber shells, and oxygen-containing functional groups (OFGs) were introduced onto the surface of the carbon filament. This resulted in an enhancement of over two orders of magnitude in capacitance compared to that of the bare CC electrode, reaching up to a maximum areal capacitance of 505.5 mF cm(-2) at the current density of 6 mA cm(-2) in aqueous H2SO4 electrolyte. Electrochemical reduction of CC electrodes led to the removal of most electrochemically unstable surface OFGs, resulting in superior charging/discharging rate capability and excellent cycling stability. Although the activated CC electrode contained a high-level of surface oxygen functional groups (∼15 at%), it still exhibited a remarkable charging-discharging rate capability, retaining ∼88% of the capacitance when the charging rate increased from 6 to 48 mA cm(-2). Moreover, the activated CC electrode exhibited excellent cycling stability with ∼97% capacitance remaining after 10 000 cycles at a current density of 24 mA cm(-2). A symmetrical supercapacitor based on the activated CC exhibited an ideal capacitive behavior and fast charge-discharge properties. Such a simple, environment-friendly, and cost-effective strategy to activate CC shows great potential in the fabrication of high-performance flexible supercapacitors.