Structural Supercapacitors Research Articles

Comparison of Nanoarchitecture to Porous Media Diffusion Models in Reduced Graphene Oxide/Aramid Nanofiber Electrodes for Supercapacitors.

Structural electrodes made of reduced graphene oxide (rGO) and aramid nanofiber (ANF) are promising candidates for future structural supercapacitors. In this study, the influence of nanoarchitecture on the effective ionic diffusivity, porosity, and tortuosity in rGO/ANF structural electrodes is investigated through multiphysics computational modeling. Two specific nanoarchitectures, namely, "house of cards" and "layered" structures, are evaluated. The results obtained from nanoarchitecture computational modeling are compared to the porous media approach and show that the widely used porous electrode theories, such as Bruggeman or Millington-Quirk relations, overestimate the effective diffusion coefficient. Also, the results from nanoarchitecture modeling are validated with experimental measurements obtained from electrochemical impedance spectroscopy and cyclic voltammetry. The effective diffusion coefficients obtained from nanoarchitectural modeling show better agreement with experimental measurements. Evaluation of microscopic properties such as porosity, tortuosity, and effective diffusivity through both experiment and simulation is essential to understand the material behavior and to improve its performance.

Multifunctional Structural Supercapacitor Based on Urea-Activated Graphene Nanoflakes Directly Grown on Carbon Fiber Electrodes

Structural energy storage systems offer both load bearing and electrochemical energy storage capabilities in a single multifunctional platform. They are emerging technologies for modern air and gro...

Damage-tolerant, laminated structural supercapacitor composites enabled by integration of carbon nanotube fibres

A natural embodiment for multifunctional materials combining energy-storing capabilities and structural mechanical properties are layered structures, similar to both laminate structural composites and electrochemical energy-storage devices. A structural composite with integrated electric double layer capacitive storage is produced by resin infusion of a lay up including woven glass fabric used as mechanical reinforcement, carbon nanotube non-woven fabrics as electrodes/current collectors and a polymer electrolyte. The energy-storing layer is patterned with holes, which after integration form resin plugs for mechanical interconnection between layers, similar to rivets. Finite element modelling is used to optimise rivet shape and areal density on interlaminar shear properties. Galvanostatic charge-discharge tests during three-point bending show no degradation of properties after large deflections or repeated load/unload cycling at 3.5 V. This mechanical tolerance is a consequence of the elimination of metallic current collectors and the effective integration of multifunctional materials, as observed by electron microscopy and x-ray computed tomography. In contrast, control samples with metallic current collectors, analogous to embedded devices, rapidly degrade upon repeated bending.

A large areal capacitance structural supercapacitor with a 3D rGO@MnO2 foam electrode and polyacrylic acid–Portland cement–KOH electrolyte

The fabrication process of an asymmetric structural supercapacitor (SSC) with structural electrodes and structural electrolytes.

A 3D-printed stretchable structural supercapacitor with active stretchability/flexibility and remarkable volumetric capacitance

3D-printed stretchable negative Poisson's ratio structural CoNi2S4/NiCo-LDHs-based supercapacitor with active stretchability/flexibility and remarkable volumetric capacitance are built.

Pore forming with hemp fiber for magnesium phosphate structural supercapacitor

For multifunctional structural supercapacitor, pore structure can store lots of aqueous electrolyte in the matrix and interconnected pore structure can offer numerous channels for ion movement during charge-discharge. This paper first investigates the effects of pore forming with hemp fiber on the performance of structural supercapacitor. Various contents of hemp fiber were employed to alter the pore structure of the magnesium phosphate electrolyte containing 2 M KOH. Plenty of macropores causing by adding large content of fiber are normally bad for mechanical properties, yet they are beneficial to change the pore structure of structural electrolyte. The results show that porosity and pore connectivity of the structural electrolyte are gradually increasing from 8.3% to 18.6% and from 5.6% to 15.5% with the content of hemp fiber increasing within a certain range, respectively. Thus the specific capacitance of structural supercapacitor gradually increases by 46.8%. The results of multifunctionality of structural supercapacitor show that the sample with the most developed pore structure appears for an optimum balance between mechanical and electrochemical performance.

Structural composite supercapacitor using carbon nanotube mat electrodes with interspersed metallic iron nanoparticles

A carbon nanotube (CNT) mat interspersed with metallic iron nanoparticles is investigated as a structural supercapacitor electrode material that could be incorporated into fiber-reinforced composites. Both ionic liquid and aqueous potassium hydroxide electrolytes are trialed to examine pseudocapacitive mechanisms and the long-term electrochemical stability of the CNT mat in symmetrical supercapacitors. High-resolution transmission electron microscopy showed the high level of interconnection of the CNTs and evenly distributed metallic iron nanoparticles, which enhances the structural and electrical performance of the electrode. Raman and X-ray photoelectron spectroscopies combined with thermogravimetric and surface area analyses are used to characterize the physico-chemical properties of the CNT mat and identify the different electrochemical mechanisms contributing to the supercapacitive behavior. Three electrode experiments demonstrated the relative contributions of the cathode and anode processes to the total capacitance. Symmetrical supercapacitor coin-cell trials used a structural glass-fiber separator and showed the ionic liquid electrolyte facilitated stable pseudocapacitance with the available iron nanoparticles, leading to specific energy and power as high as 18.3 Wh.kg−1 at 0.15 kW kg−1 and 5.6 Wh.kg−1 at 2.4 kW kg−1 after 5000 cycles. It is envisioned these materials can readily be incorporated into composite materials for structural energy storage technology.

Development of structural supercapacitors with epoxy based adhesive polymer electrolyte

Abstract Epoxy based adhesive polymer electrolyte was prepared using polyvinylidene fluoride, lithium triflate, and epoxy. The effect of the composition of the adhesive polymer electrolyte on the ionic conductivity, viscosity, and tension strength was investigated. The ionic conductivity of an adhesive polymer electrolyte could reach the order of magnitude of 10−2 S cm−1. Structural supercapacitors with epoxy based adhesive polymer electrolyte were fabricated using a vacuum bagging method. The structural supercapacitors showed excellent electrochemical performance and acceptable mechanical strength simultaneously. The maximum specific energy was 2.64 Wh kg−1 and the ultimate tensile strength was 80 MPa. The capacitance retention of the structural SC was 84% and the columbic efficiency was above 95% after 5000 cycles. The response of electrochemical performance of the structural supercapacitors to in-plane tensile stress was studied. Before fracture, both the specific power and the specific energy increased slightly with increasing the stress level.

Mechanical and physical performance of carbon aerogel reinforced carbon fibre hierarchical composites

Carbon aerogel (CAG) is a potential hierarchical reinforcement to improve the matrix-dominated mechanical properties of continuous carbon fibre reinforced polymer (CFRP) composites in both multifunctional and purely structural applications. When using CAG to reinforce a polyethylene glycol diglycidyl ether (PEGDGE) matrix, the interlaminar shear strength, compressive modulus and strength increased approximately four-fold, whilst the out-of-plane electrical conductivity increased by 118%. These mechanical and electrical performance enhancements significantly improve the multifunctional efficiency of composite structural supercapacitors, which can offer weight savings in transport and other applications. However, CAG also has the potential to reinforce conventional continuous CF composites in purely structural contexts. Here, CAG reinforcement of structural epoxy resin composites marginally increased compressive (1.4%) and tensile (2.7%) moduli respectively, but considerably reduced compressive, tensile and interlaminar shear strengths. Fractographic analysis shows that the reduced performance can be attributed to poor interfacial adhesion; in the future, alternative processing routes may resolve these issues to achieve advances in both moduli and strengths over conventional structural CFRPs.

Bicontinuously crosslinked polymer electrolyte membranes with high ion conductivity and mechanical strength

Recently, safety has become an important issue for energy storage devices due to explosion and leakage of conventional liquid electrolytes. Traditional polymer electrolytes also have a strong dependence on the tradeoff relationship and do not exhibit sufficient ionic conductivity as a solid; thus, they are often used as a gel. We report the preparation of a highly ion-conductive, mechanically strong solid electrolyte membranes based on bicontinuously crosslinked polymer electrolytes for solid-state supercapacitors. The solid electrolyte membranes are synthesized in situ via facile ring-opening polymerization in the presence of a conductive ionic liquid without any solvents. The crosslinking structure is based on the reaction of the amines of the polyethylenimine oligomer with the epoxy groups of hydrophilic poly(ethylene glycol) diglycidyl ether and hydrophobic bisphenol A diglycidyl ether at 50 °C for 3 h. This unique structure endows the solid electrolyte membranes with high tensile strength as well as high ion conductivity (2.41 × 10−3 S cm−1 at 25 °C). All the membranes have good thermal stability and an amorphous phase in which the ionic species are uniformly distributed in the matrix. Upon application to solid-state supercapacitors based on carbon electrodes, a capacitance of 19.8 F g−1 at 2 mV s−1 is obtained, with an excellent capacitance retention and a coulombic efficiency close to 100% for 10,000 cycles. The solid electrolyte membrane has potential applications in structural supercapacitors and batteries, which require high mechanical strength.

3D Structural Strengthening Urchin‐Like Cu(OH)2‐Based Symmetric Supercapacitors with Adjustable Capacitance

AbstractDeveloping advanced three‐dimensional (3D) structural supercapacitors with both high capacity and good mechanical strength remains challenging. Herein, a novel road is reported for fabricating 3D structural strengthening supercapacitors with adjustable capacitance based on urchin‐like Cu(OH)2 lattice electrodes by bridging 3D printing technology with a facile electroless plating and electro‐oxidation method. As revealed by the results, the 3D‐printed octet‐truss lattice electrode features a high volumetric capacitance of 8.46 F cm−3 at 5 mA cm−3 and superior retention capacity of 68% at 1 A cm−3. The assembled symmetric supercapacitor with a 70.2% capacitance retention after 5000 cycles possesses a 12.8 Wh kg−1 energy density at a power density of 2110.2 W kg−1. Additionally, the resulting 3D structural strengthening electrodes can achieve both high compressive strength and toughness of 30 MPa and 264.7 kJ m−3, respectively, demonstrating high mechanical strength and excellent antideformation capacity. With the proposed strategy, the electrochemical and mechanical properties of these novel 3D structural strengthened supercapacitors can be easily tuned by a simple spatial framework design, fulfilling the increasing demand of highly customized power sources in the space‐constrained microelectronics and astronautic electronics industries.

Cover Feature: Interfacial Engineering of Reduced Graphene Oxide for Aramid Nanofiber‐Enabled Structural Supercapacitors (Batteries & Supercaps 5/2019)

Cover Feature: Interfacial Engineering of Reduced Graphene Oxide for Aramid Nanofiber‐Enabled Structural Supercapacitors (Batteries & Supercaps 5/2019)

Interfacial Engineering of Reduced Graphene Oxide for Aramid Nanofiber‐Enabled Structural Supercapacitors

AbstractStructural energy storage systems can simultaneously store energy and bear mechanical loads and are emerging technologies for electric vehicles, aircrafts, and satellites since they offer significant mass and volume savings. However, many of the materials used in energy storage applications are not mechanically robust or, on the other hand, mechanically stiff materials are not necessarily electrochemically active. One solution is to combine reduced graphene oxide (rGO) sheets and aramid nanofibers (ANFs). Here we hypothesize that engineering the interfacial interactions between rGO sheets and the ANFs will lead to enhanced mechanical properties, as noncovalent interactions offer multiple sites for load transfer. rGO sheets are functionalized with carboxylic acid (−COOH) and amine (−NH2) groups, and the effect on the mechanical and electrochemical performance of nanocomposite supercapacitor electrodes is investigated. Notably, the −NH2 functionalization and the addition of ANFs leads to a dramatic 200 % improvement of the strength of the electrodes without significantly compromising the electrochemical performance. Furthermore, it is demonstrated that these electrodes’ multifunctionality is superior to other state‐of‐the‐art structural electrodes and may pose possible replacements for steel or epoxy. These findings provide critical knowledge for the design of next‐generation multifunctional electrodes in that we highlight the importance of interfacial engineering.

A structural supercapacitor based on activated carbon fabric and a solid electrolyte

ABSTRACTThis paper presents investigations to create a structural supercapacitor with activated carbon fabric electrodes and a solid composite electrolyte, consisting of organic liquid electrolyte 1 M TEABF4 in propylene carbonate and an epoxy matrix where different compositions were considered of 1:2, 1:1 and 2:1 w/w epoxy:liquid electrolyte. Vacuum-assisted resin transfer moulding was used for the impregnation of the electrolyte mixture into the electrochemical double layer capacitor (EDLC) assembly. The best electrochemical performance was exhibited by the 1:2 w/w epoxy: liquid electrolyte ratio, with a cell equivalent-in-series resistance of 160 Ω cm2 and a maximum electrode-specific capacitance of 101.6 mF g−1 while the flexural modulus and strength were 0.3 GPa and 29.1 MPa, respectively, indicating a solid EDLC device.

Investigation of Mechanical and Electrochemical Performance of Multifunctional Carbon-Fiber Reinforced Polymer Composites for Electrical Energy Storage Applications

Concept of structural supercapacitors, based on carbon fiber reinforced polymer composites, has been introduced that can act as a structural load bearing component as well as an electrical energy storing device simultaneously. This multifunctional carbon fiber reinforced structural supercapacitors are fabricated by using carbon fiber and glass fiber/filter paper as reinforcements and cross-linked polymer electrolyte as a matrix. Carbon fiber mats also simultaneously serve the role of electrodes in addition to reinforcements whereas the glass fiber mat/filter paper also acts as an insulator to avoid the short-circuiting of the carbon fiber electrodes. A polymer epoxy matrix is modified by introducing ions within the cross-linked structure in order to develop an optimized polymer electrolyte. Flexural tests of structural supercapacitor are conducted to evaluate the structural performance while charge/discharge tests are conducted to evaluate the electrochemical performance. Multifunctional structural supercapacitors are tested mechanically as well as electrochemically. A structural supercapacitor is fabricated showing simultaneously an energy density of 0.11 mWh m-3, a specific capacitance of 0.8 mF.cm-3 and a flexural modulus of 26.6 GPa simultaneously.

Micromechanics modeling of the elastic moduli of rGO/ANF nanocomposites

Energy storage materials that also provide structural integrity are needed to decrease the weight of electrically powered ground and air vehicles. Toward this end, structural supercapacitor electrodes consisting of aramid nanofiber (ANF) and reduced graphene oxide (rGO) were reported in our previous work. Surprisingly, the experimentally measured tensile moduli of these rGO/ANF nanocomposites were not bounded by the experimentally measured moduli of the ANF and rGO materials and were an order of magnitude lower than those of Kevlar fibers and graphene sheets. The purpose of the present work is to develop a micromechanics model for elastic moduli to support the development of rGO/ANF multifunctional composite electrodes. Both the ANF and the rGO are transversely isotropic, wavy and randomly oriented, and no traditional isotropic polymeric matrix is present. We are aware of no existing micromechanics model that is applicable to such a composite. The Mori–Tanaka model is used three times, to model the rGO and ANF separately, and then the rGO/ANF composite films. The model predictions of elastic moduli were compared with experimental results. Waviness was found to be the main factor controlling the effective composite moduli, due to the extreme anisotropy of the rGO. This implies that the effective elastic moduli of rGO/ANF composites can be considerably increased by developing processing methods that reduce waviness. The experimentally observed unbounded moduli were attributed to the relationship between waviness and the volume fraction of the ANF.

Multifunctional structural supercapacitors based on graphene nanoplatelets/carbon aerogel composite coated carbon fiber electrodes

Multifunctional structural energy storage composites have gained an increasing interest as they offer volume and weight savings in different military and civilian applications. Current engineering approach is to develop structural energy storage materials having ability to perform energy storage and load bearing functions simultaneously. Energy storage composites have ability to simultaneously store electrical energy and bear mechanical loads. We have successfully fabricated structural fiber reinforced polymer composites that can simultaneously store electrochemical energy and withstand structural loads. Structural supercapacitors are fabricated by using graphene nanoplatelets (GNPs)/aerogel composite modified carbon fibers as electrodes and reinforcement, filter paper as a separator and multifunctional epoxy resin as an electrolyte and matrix. The structural supercapacitors were prepared by using resin infusion under flexible tooling (RIFT) method. The increasing concentrations of graphene nanoplatelets in carbon aerogels boost the electrochemical and shear performance of structural supercapacitors. A structural supercapacitor with an energy density of 0.8 Wh. kg−1, power density of 108 W.kg−1 and a normalized shear modulus of 2.6 GPa has been displayed in the current study.

Improving the multifunctionality of structural supercapacitors by interleaving graphene nanoplatelets between carbon fibers and solid polymer electrolyte

Novel structural supercapacitors, containing graphene nanoplatelets incorporated carbon fiber mats as electrodes, crosslinked diglycidylether of bisphenol-A epoxy polymer electrolyte and filter paper separator, have been manufactured for the first time by vacuum-assisted resin transfer molding process. These supercapacitors can bear structural loads and store electrochemical energy at the same time. Loading of high surface area graphene nanoplatelets on carbon fiber mats is an effective process to improve the charge storage capacity of the electrodes. Electrochemical and structural properties of the structural supercapacitors are explored through in-plane shear testing, dynamic mechanical thermal analysis, chronoamperometry and impedance spectroscopy, respectively. As graphene nanoplatelet loadings on carbon fiber mat electrodes increase from 0 to 10 wt.%, the structural supercapacitors exhibit significant improvements in specific capacitance (8.9–118.7 mF·cm−3), energy density (19.7–263.8 Wh·m−3) and normalized in-plane shear modulus (1.7–3.1 GPa). Thus, this study has revealed that using the graphene nanoplatelet loaded carbon fiber mats as structural supercapacitor electrodes is a relatively novel and easy approach to enhance the multifunctionality of structural supercapacitors.

Bimetallic copper cobalt selenide nanowire-anchored woven carbon fiber-based structural supercapacitors

Structural supercapacitors provide a variety of opportunities for woven carbon fibers in portable electronics, hybrid automobiles and aerospace applications. We describe herein the synthesis of bimetallic Cu-Co selenide nanowires based on woven carbon fibers, and their use as electrodes in supercapacitors. Woven Kevlar fiber is used as separator for the electrodes and a polyester resin with an ionic liquid and lithium salt is used as solid polymer electrolyte. The supercapacitors exhibit efficient energy storage and significant enhancements in mechanical strength (89.38%) and modulus (70.41%) over those of bare woven carbon fiber base supercapacitors. The specific capacitance of these supercapacitors increases from 0.197 F g−1 to 28.63 F g−1 after the growth of nanowires, with accordingly high energy density (191.64 mW h kg−1) and power density (36.65 W kg−1). In situ mechano-electrochemical tests of these supercapacitors yield excellent capacitance retention (77.3%) at the mechanical failure point (481.29 MPa).

Multifunctional structural supercapacitor based on graphene and magnesium phosphate cement

A novel structural supercapacitor is assembled with graphene electrodes and the magnesium phosphate cement separator. Magnesium phosphate cement acts as separator material for the first time due to its high strength and relatively high porosity. Magnesium phosphate cement is synthesized by acid-based reaction between phosphate and magnesia. Effects of processing parameters of magnesium phosphate cement, including M/P ratio and the curing time, on the electrochemical and mechanical properties are investigated. The maximum specific capacitance is as high as 46.38 F g−1 with M/P ratio of 3 at the curing time of 1 day. Moreover, the structural supercapacitor exhibits a specific capacitance of 40.92 F g−1 and simultaneously a compressive strength of 24.59 MPa with the M/P ratio of 3 at the curing time of 28 days. Thus, the optimal M/P ratio is 3 regarding the multifunctionality of structural supercapacitor.