Electric Double Layer Capacitors Research Articles

High Volumetric Energy Density Supercapacitor of Additive-Free Quantum Dot Hierarchical Nanopore Structure.

The high surface-area-to-volume ratio of colloidal quantum dots (QDs) positions them as promising materials for high-performance supercapacitor electrodes. However, the challenge lies in achieving a highly accessible surface area, while maintaining good electrical conductivity. An efficient supercapacitor demands a dense yet highly porous structure that facilitates efficient ion-surface interactions and supports fast charge mobility. Here we demonstrate the successful development of additive-free ultrahigh energy density electric double-layer capacitors based on quantum dot hierarchical nanopore (QDHN) structures. Lead sulfide QDs are assembled into QDHN structures that strike a balance between electrical conductivity and efficient ion diffusion by employing meticulous control over inter-QD distances without any additives. Using ionic liquid as the electrolyte, the high-voltage ultrathin-film microsupercapacitors achieve a remarkable combination of volumetric energy density (95.6 mWh cm-3) and power density (13.5 W cm-3). This achievement is attributed to the intrinsic capability of QDHN structures to accumulate charge carriers efficiently. These findings introduce innovative concepts for leveraging colloidal nanomaterials in the advancement of high-performance energy storage devices.

Metal oxide-based nanocomposites as advanced electrode materials for enhancing electrochemical performance of Supercapacitors: A comprehensive review

In recent years, the escalating use of nonrenewable fossil fuels has emerged as a significant threat to global sustainability, prompting the need for renewable, cost-effective, and eco-friendly energy storage solutions. Supercapacitors (SCs) are notable for their high power density (PD), cycle stability, and swift charge/discharge rates, although they fall short in energy density (ED) compared to traditional batteries. The performance of SCs is greatly influenced by the electrode materials used, highlighting the importance of material innovation in tackling the challenges posed by increasing fossil fuel consumption. Transition metal oxides (TMOs), known for their redox activity in energy storage, have been thoroughly investigated for their exceptional specific capacitance, which ranges from 100 to 2000F g−1, surpassing that of electrical double-layer capacitors (EDLCs). TMOs such as ruthenium oxide (RuO2), manganese oxide (MnO2), nickel oxide (NiO), cobalt oxide (Co3O4), tin oxide (SnO2), zinc oxide (ZnO), tungsten oxide (WO3), and vanadium pentoxide (V2O5) are widely researched for their high theoretical capacitance, affordability, and longevity. This review emphasizes the groundbreaking potential of metal oxide nanocomposites (NCs) formed by combining them with graphene, carbon nanotubes (CNTs), and polymers, leading to synergistic enhancements in electrical conductivity, surface area, and charge storage capacity. This thorough review not only presents an in-depth analysis of current research but also sheds light on potential future developments, contributing to the ongoing progress in the field of advanced electrode materials for energy storage.

Novel approach: Simultaneous application of ionic liquid doped polymer electrolyte in supercapacitor and dye-sensitized solar cells

The present study reports the synthesis, characterization, and application as energy devices of an ionic liquid blended polymer electrolyte film in which the host polymer polyvinyl alcohol (PVA) is mixed with low viscosity ionic liquid (IL) 1-ethyl-3-methylimidazolium thiocyanate. Various characterization tools have been used further to elaborate electrical, structural, and photoelectrochemical properties. X-ray diffraction (XRD) and polarized optical microscope (POM) affirm the reduction of crystallinity of polymer, while Fourier transform infrared spectroscopy (FTIR) shows complexation and composite nature. Electrochemical impedance spectroscopy shows an enhancement in ionic conductivity by IL doping, where the highest conductivity is achieved at 60 wt% of IL concentration with a conductivity value of 6.21 × 10⁻⁴ S/cm. The ionic transference number (tion) and electrochemical stability measurement show the film's predominantly ionic nature and a reasonable stability window. Using maximum conducting film sandwiched between electrodes, we have successfully fabricated two devices, i.e., an electrical double-layer capacitor (EDLC) and a dye-sensitized solar cell (DSSC). The fabricated EDLC capacitor shows a specific capacitance of 125 F/g, while DSSC shows an efficiency of 1.1 % at one sun condition.

Holistic Processing of Sawdust to Enable Sustainable Hybrid Li-Ion Capacitors

AbstractActivated carbon has long been recognized as a promising electrode material for energy storage devices. The extraordinarily high specific area makes it challenging to replace in supercapacitors since electrical double-layer capacitors need such surfaces but also porous networks to enable electrolyte penetration. As a raw material for synthesizing activated carbon, sawdust offers key benefits, such as its renewability, abundance, favorable physical attributes for energy storage, and a more environmentally friendly synthesis process compared to mined alternative sources. In this work, electrochemical characterization is carried out which highlights the critical role of pelletization in enhancing the capacitive performance of sawdust-derived activated carbon, in addition to the implicit handling and logistical benefits. Subsequently, a Li-ion capacitor is assembled with an organic solvent-based electrolyte, sawdust-derived activated carbon serving as the positive electrode, and an Al-based foil negative electrode, potentially combining high energy and power density materials into a hybrid device. Despite commendable electrochemical performance and the use of a sustainable waste-derived positive electrode with a commoditized negative electrode, challenges remain regarding the ability to mitigate the role of surface functional groups that are stabilized by bio-carbon thermal treatments. Nevertheless, this distinctive architecture holds promise as an alternative high-power energy storage technology for a future filled with renewable energy, electric vehicles, and portable electronic devices.

The NaClO4-water eutectic electrolyte for environmentally friendly electrical double-layer capacitors operating at low temperature

Herein, owing to its remarkable ionic conductivity, the 8.84 mol kg−1 NaClO4 water-in-salt (WIS) eutectic electrolyte is suggested for the low temperature operation of electrical double-layer capacitors down to -35 °C. Molecular dynamic simulations reveal that the local structure of the solution remains relatively stable from RT to -35 °C, with distinct channel-like domains formed by hydrogen-bonded water molecules, which facilitate the ionic diffusion within the bulk of the electrolyte. Interestingly, on activated carbon (AC) electrodes, the electrolyte demonstrates an electrochemical stability window (ESW) increasing from 1.8 V to 2.1 V as temperature decreases from 25 °C to -35 °C. The high ESW of this electrolyte is due to i) pH close to neutrality enabling high overpotential of water reduction on porous AC electrodes; ii) WIS characteristics with a reduced amount of free water in the Stern layer under positive polarization of AC; iii) higher oxidation potential at low temperature ascribed to the enhanced immobilization of the ClO4− anions in the Stern layer as well as reduced diffusion of water molecules in the AC electrode porosity. The electrochemical investigations on laminate AC//AC cells in the NaClO4-water electrolyte demonstrate low values of their resistive components down to -30 °C, while the devices can operate with rated voltage of 2.0 V and 1.7 V at -30 °C and RT, respectively. At -30 °C and under discharge power as high as 10 kW kg−1, the AC//AC capacitor in the NaClO4-water electrolyte outperforms the specific output energy of a traditional AC//AC cell in the 1 M TEABF4/ACN electrolyte. Hence, for sub-ambient temperatures, the presented environmentally friendly EDLC holds promise to compete with traditional devices implementing an organic electrolyte.

Preparation of polyimide-based activated carbon fibers and their application as the electrode materials of electric double-layer capacitors

Preparation of polyimide-based activated carbon fibers and their application as the electrode materials of electric double-layer capacitors

Dynamic Effect of Overscreening on Electrochemical and Thermal Properties of EDLC Electrodes during Charging/Discharging Cycles

Overscreening was commonly observed during charging/discharging cycles of electric double layer capacitors(EDLCs). This study presented a two-dimensional continuum electrochemical thermal model with a distribution function for concentration considering overscreening to investigate how overscreening affected the dynamic formation of electric double layer (EDL) near electrodes in macroscale. The results indicated that ion distribution was co-affected by EDL formation and overscreening near the electrode. Correspondingly, layered space charge density distribution resulted in a thicker diffuse layer, whose thickness was determined by the sum of co-ion and counter-ion diameters. Additionally, the diffuse layer capacitance was proportional to the reciprocal of counter-ion diameter, while the total capacitance was proportional to a linear combination of counter-ion and the larger ion diameters. Moreover, the shift from endothermic to exothermic for the total heat generation rate was dominated by heat of mixing, and was caused by the local ion mixing due to overscreening, resulting in local entropy increase. The results of this study can be used to further investigate the effect of overscreening on ion transient transport dynamic and heat generation rates.

Lotus Root Type Nickel Oxide-Carbon Nanofibers: A Hybrid Supercapacitor Electrode Material

In this study, we investigate the electrochemical properties of a nickel oxide-carbon (NiO/C) material, synthesized in the form of highly porous carbon nanofibers through the electrospinning of polymers such as polyacrylonitrile (PAN) and polystyrene (PS) followed by a carbonization process. The primary focus of this work is to determine the optimal mixing ratio for the hybrid material composed of NiO and carbon. While it is widely acknowledged that supercapacitor materials benefit from having a high specific surface area, our findings reveal that hybrid carbon nanofibers with a 45% specific carbon-to-nickel oxide ratio exhibit significantly enhanced capacitance (39.9 F g−1). This outcome suggests the promising potential of our materials as an energy storage material for hybrid supercapacitors, combining the advantages of electric double-layer capacitors (EDLC) and Pseudo capacitors (Pseudo).

State of Charge and State of Health Coestimation for Lithium-Ion Capacitor Based on Multi-innovation Filters

The lithium-ion capacitor (LIC) is a new type of hybrid energy storage device, which combines the advantages of lithium-ion battery and electric double layer capacitor. To achieve efficient and reliable application of LIC in practical scenarios, accurate model and state estimation method are needed. In this work, the electrical behavior of LIC is studied, which is then described by the Thevenin model. A multi-innovation filter- (MIF-) based coestimation method is proposed, in which the multi-innovation linear Kalman filter (MI-LKF) is used for model parameter identification, the multi-innovation cubature Kalman filter (MI-CKF) is used for state of charge estimation, and the multi-innovation extended Kalman filter (MI-EKF) is used for state of health estimation. Compared to traditional methods, this method can significantly improve estimation accuracy by only expanding the innovation used to update the state from a single moment to multiple moments. The experimental results indicate that the estimation errors of SOC and SOH can be constrained within ±0.5%. In addition, the proposed method has good robustness and can achieve high-precision state estimation even in the face of noise interference, uncertain initial values of the algorithm, and uncertain starting operating points.

Microgrid-Patterned Ni Foams as Current Collectors for Ultrafast Energy Storage Devices

Current research is focused on developing active materials through surface functionalization, porosity, composites, and doping for ultrafast electric double layer capacitors (EDLCs). In this study, deviating from existing strategies focused on active materials, we designed tunable 3D microgrid-patterned (MP) surface morphologies on Ni foams used as current collectors using SUS meshes as rigid stamps during roll pressing. The surface geometries of the MP-Ni foams were controlled to standard mesh scales of 24, 40, and 60 (denoted as 24MP-Ni, 40MP-Ni, and 60MP-Ni, respectively). The three MP-Ni samples with different microgrid sizes presented different surface geometries, such as root-mean-square roughness (Rrms), skewness roughness (Rsk), and width/depth scales of the microgrid patterns. Consequently, 40MP-Ni demonstrated an optimized surface geometry with high Rrms (35.4 μm) and Rsk (−0.19) values, which facilitated deep slurry infiltration and increased its contact area with the active material. Surface optimization of the MP-Ni enabled ultrafast and reversible charge transport kinetics owing to its relaxed electron transfer resistance and robust adhesion to the active material compared with bare Ni foam. EDLC electrodes with 40MP-Ni achieved an ultrafast-rate capability (96.0 F/g at 20 A/g) and ultrafast longevity (101.9% capacity retention after 5000 cycles at 5 A/g) without specific modification of active material.

Enhanced Performance of Electrical Double-Layer Capacitor by Controlling the Specific Surface Area and Pore Structure of ZIF-67

Enhanced Performance of Electrical Double-Layer Capacitor by Controlling the Specific Surface Area and Pore Structure of ZIF-67

A Cross-linked n-Type Conjugated Polymer with Polar Side Chains Enables Ultrafast Pseudocapacitive Energy Storage.

Pseudocapacitors bridge the performance gap between batteries and electric double-layer capacitors by storing energy via a combination of fast surface/near-surface Faradaic redox processes and electrical double-layer capacitance. Organic semiconductors are an emerging class of pseudocapacitive materials that benefit from facile synthetic tunability and mixed ionic-electronic conduction. Reported examples are mostly limited to p-type (electron-donating) conjugated polymers, while n-type (electron-accepting) examples remain comparatively underexplored. This work introduces a new cross-linked n-type conjugated polymer, spiro-NDI-N, strategically designed with polar tertiary amine side chains. This molecular design aims to synergistically increase the electroactive surface area and boost ion transport for efficient ionic-electronic coupling. Spiro-NDI-N demonstrates excellent pseudocapacitive energy storage performance in pH-neutral aqueous electrolytes, with specific capacitance values of up to 532 F g-1 at 5 A g-1 and stable cycling over 5000 cycles. Moreover, it maintains a rate capability of 307 F g-1 at 350 A g-1 . The superior pseudocapacitive performance of spiro-NDI-N, compared to strategically designed structural analogues lacking either the cross-linked backbone or polar side chains, validates the essential role of its molecular design elements. More broadly, the design and performance of spiro-NDI-N provide a novel strategy for developing high-performance organic pseudocapacitors.

Synthesis and assessment of novel Na2S dispersed high performance nanocomposite gel polymer electrolyte intended for sodium batteries and electric double layer capacitors

Sodium sulphide (Na2S) nanoparticles are synthesized by hydrothermal method and utilized for electrochemical application for the first time. A series of sodium-ion conducting nanocomposite gel polymer electrolytes (NCGPEs) incorporating poly (methyl methacrylate) i.e., (PMMA) as the polymer backbone, sodium tetrafluoro-borate (NaBF4) as the salt, tetraethylene glycol dimethyl ether (TEGDME) as the plasticizer, and Na2S as the active fillers, are fabricated and studied. The optimized electrolyte having PMMA/NaBF4/TEGDME matrix incorporated with 2.5 wt% Na2S nanoparticles exhibits a high ionic conductivity of 3.0 × 10−4 S cm−1, low activation energy of 0.13 eV and operating voltage range of ~2.8 V at ambient temperature. Thermal studies reveal that the fabricated NCGPEs have the ability to retain the gel phase up to 473 K. The X-ray diffraction (XRD) and Fourier transform Infra-red (FTIR) spectroscopy indicate changes in structure and the ion–filler–polymer interactions inside the synthesized NCGPEs. A proto-type sodium cell with an optimized NCGPE has an open circuit voltage of 2.3 V and a first discharge capacity of 205 mAh g−1. The electric double layer capacitor (EDLC) designed with optimized electrolyte has a specific capacitance of 58 F g−1 and is stable up to 2000 charge-discharge cycles.

Two-dimensional (2D) materials for 3D printed micro-supercapacitors and micro-batteries

Two-dimensional (2D) materials display a unique set of physical/chemical properties and are considered potential building blocks for the manufacturing of microstructured materials for a number of applications. Prominent applications range from advanced electronics to miniaturized electrochemical energy storage devices (EESDs). Herein, we present a comprehensive and critical review of the recent developments in design and microfabrication of 2D-driven microscale electrodes for three-dimensional (3D)-printed micro-supercapacitors and micro-batteries. Firstly, we systematically discuss the advantages and disadvantages associated with various microfabrication techniques such as stereolithography, fused deposition modeling, inkjet printing, and direct ink writing. Next, key parameters disclosing the relationship between the characteristics of 2D-based materials and extrusion-driven 3D printing process for the development of versatile and sustainable EESDs are highlighted. 2D materials utilized for the construction of microelectrodes for supercapacitors (e.g., electric double layer capacitors (EDLCs), pseudocapacitors, and hybrid capacitors) and batteries (e.g., Li-based systems and next-generation systems, e.g., sodium-ion batteries and zinc-ion batteries) along with their prominent electrochemical contributions in relation to obtained 3D-printed architectures are discussed in detail. To promote the development of 2D materials-driven high-performance microscale EESDs, the relevant challenges and future research opportunities are also addressed.

Exploring optical and electrochemical studies on thulium selenite (TmSeO3)

Abstract Thulium selenite (TmSeO3) has been synthesized by precipitation method. It shows interesting smooth surface with nearly non-symmetric texture similar to water droplets spreading on hydrophobic surface. TmSeO3 is found to be monoclinic structure with lattice parameters a = 5.919±0.01 Å, b = 12.422±0.01 Å, c = 8.717±0.01 Å, α = γ = 90°, β = 106.01° and V = 616.1 Å3. Fourier transform infrared spectroscopy confirms the presence of Tm–Se bonding. X-ray photo emission spectrum confirmed the presence of thulium, selenium and oxygen in the samples in oxide form. Magnetic study between 300 and 20 K, shows decrease of magnetic moment with temperature, then reaches saturation and aligns all thulium spins. This results cooperative interaction of thulium spins. M–H curve at 300 K confirms the paramagnetic nature of sample. Cyclic voltammogram of three electrode system, manifests electric double layer capacitance with a potential window of 0.55 V. Specific capacitance is 102 F/g. Chronopotentiometry analysis shows 75 F/g specific capacitance, 11 Wh kg−1 energy density, and 275 W kg−1 power density. Impedance analysis confirms electric double layer capacitor behavior. Hence, TmSeO3 electrode based symmetric supercapacitor device was successfully fabricated and tested by two electrode configuration in aqueous electrolyte of KOH. A specific capacitance of 64.60 F/g at 1 A/g within a potential window of 1.85 V was achieved. Impedance analysis also confirms electric double layer capacitor nature with low series resistance of 0.2596 Ω and charge transfer resistance of 1.6352 Ω. The improved cycling performance after 4000 cycles is 51.5 % specific capacitance retention. Thus, symmetric supercapacitor electrodes based TmSeO3 materials are expected to have good electrochemical properties and good stability for energy storage and conversion applications. Furthur, optical parameters 5.28 eV energy gap, 0.4924 eV Urbach energy value and 1.959 refractive index are determined.

From Molecular Simulations to Experiments: The Recent Development of Room Temperature Ionic Liquid-Based Electrolytes in Electric Double-Layer Capacitors.

Due to the unique properties of room temperature ionic liquids (RTILs), most researchers' interest in RTIL-based electrolytes in electric double-layer capacitors (EDLCs) stems from molecular simulations, which are different from experimental scientific research fields. The knowledge of RTIL-based electrolytes in EDLCs began with a supposition obtained from the results of molecular simulations of molten salts. Furthermore, experiments and simulations were promoted and developed rapidly on this topic. In some instances, the achievements of molecular simulations are ahead of even those obtained from experiments in quantity and quality. Molecular simulations offer more information on the impacts of overscreening, quasicrowding, crowding, and underscreening for RTIL-based electrolytes than experimental studies, which can be helpful in understanding the mechanisms of EDLCs. With the advancement of experimental technology, these effects have been verified by experiments. The simulation prediction of the capacitance curve was in good agreement with the experiment for pure RTILs. For complex systems, such as RTIL-solvent mixtures and RTIL mixture systems, both molecular simulations and experiments have reported that the change in capacitance curves is not monotonous with RTIL concentrations. In addition, there are some phenomena that are difficult to explain in experiments and can be well explained through molecular simulations. Finally, experiments and molecular simulations have maintained synchronous developments in recent years, and this paper discusses their relationship and reflects on their application.

All-functionalized-graphene ribbon films for flexible asymmetric supercapacitors with ultrahigh energy and power densities

Asymmetric (hybrid) supercapacitors (ASCs) based on different positive and negative pseudocapacitance materials can deliver more energy density than electric double layer capacitors (EDLCs). Yet, few pseudocapacitive materials can provide high energy and power density, simultaneously, due to their poor conductivity and unfavorable reaction kinetics under fast charge/discharge rates. Here, we graft sulphur- and oxygen- functionalized into interconnected graphene ribbons to improve the accessibility of ion and enhance redox-active sites. The prepared sulphur- and oxygen- functionalized interconnected graphene ribbon (S-IGR and O-IGR) films as positive electrode and negative electrode, respectively, for high energy density flexible ASCs. Benefiting from the more “active sites” for the graphene ribbons, the S-IGR and O-IGR films connect more sulphur and oxygen groups. As a result, the S-IGR and O-IGR films exhibit ultra-high specific capacitance of 1660 F g−1 (1.66 F cm−2) and 428 F g−1 (0.43 F cm−2), respectively. More importantly, the assembled O-IGR//S-IGR ASCs based on aqueous and gel electrolytes exhibit ultra-high energy densities of 106.6 Wh kg−1 and 35.6 Wh kg−1, respectively. With the ultrafast charging and discharging capability, the ASCs based on aqueous electrolytes can be charge/discharged within 0.53 s to deliver high energy density of 15.0 Wh kg−1 and ultrahigh-power density of 101.4 kW kg−1. Thus, this strategy could possibly be used as designing and fabricating new generation of all grphene-based ASCs with high energy and power densities.

One-step generation of hollow graphitic carbon nanospheres with suitable oxygenated structures as conductive additives for water-soluble binder in highly stable supercapacitor electrodes

Although the weight ratio of electron conductive additives and the binder to porous carbons in the electrode component of electric double-layer capacitors (EDLC) is minimal, however, without them the electrochemical performances of EDLC would decay quickly. In this work, we present a one-step approach for manufacturing a unique conductive carbon material that shows highly connecting hollow structures as well as approximate oxygenated surface groups to create a synergy effect with aqueous binder and the main component, porous carbon. The as-prepared carbon nanospheres (HCNs) were generated from a typical carbon black-PC20 in air (denoted as PC20HT) at mild temperatures ranging from 400 to 700 °C for 2–4 h at a massive scale of approximate 1 kg h−1. The as-prepared PC20HT displays a high specific surface area of 657 m2 g−1 (the pristine PC20 has 112 m2 g−1) with a pore volume of 0.71 cm3 g−1, and an oxygen content of 14.10 wt%. Interestingly, a premixing of PC20HT and porous carbon is required before making the electrode pastes. The well-premixed carbon materials and a water-soluble binder-polyacrylic acid are composed into highly-stable components as EDLC electrodes in an organic electrolyte. As consequently, the PC20HT-assisted electrodes demonstrate highly stable life cycles (charge-discharge behaviors), with a retention rate 82.13 % over 50,000 cycles at a narrow voltage window of 2.5–2.7 V at 0.5 A g−1 when compared to two conventional conductive carbons, BP2000 (68.45 %) and Super P (67.46 %). Thermal annealing at 900 °C in Ar reduces the oxygen content of PC20HT to 4.25 wt% (referred to as TPC20HT), increasing the retention rate of life cycle to 88.89 % after the same cycles. TPC20HT-assisted EDLC electrodes exhibit a superior energy density of 34.76 Wh kg−1, which is higher than CB-BP2000 and Super P-assisted EDLC electrodes. The transforming of structural morphologies as well as the surface oxygenated and graphitic structures of the as-prepared HCS, PC20HT, and TPC20HT were also described before and after long-term cycling. This simple route for producing conductive carbons is applicable in an aqueous binder system for preparing EDLC electrodes with a cost-effective and environmentally friendly approach.

Low-grade heat recycling of vertical thermoelectric cells based on thermal-induced electric double layer

Employing electric double-layer (EDL) capacitors to harvest low-grade heat (LGH) is a novel technique in the high-efficiency energy absorption field. This work reports the fabrication of a vertical thermoelectric cell, based on a nanoporous graphene electrode immersed in low-concentration saline solution, for use as thermo-charging supercapacitors to convert LGH to electricity via thermally induced voltage. Because of a large specific area and a large number of micropores of nanoporous graphene films, the effective thermoelectric coefficient of the thermoelectric cell containing 0.01 M KCl solution can reach as high as 4.73 mV/°C. However, many factors, such as electrode materials, electrolyte solutions, and energy conversion device components, determine the efficiency of a thermoelectric conversion device. In summary, the device has a lower internal resistance and higher output voltage when the concentration of KCl solution is 0.05 M, and demonstrates higher thermoelectric conversion efficiency. Moreover, improving the conductivity of the electrolyte solution without affecting the device output voltage is also a way to reduce the internal power consumption of the device. The specific power and thermoelectric conversion efficiency of the device are increased by several orders of magnitude when uniformly dispersed silver nanoparticles are added to the potassium chloride solution to enhance the conductivity of the solution. The specific power underwent an increase from 0.50 mW g−1 to 42.37 mW g−1, and the thermoelectric conversion efficiency also increased from 0.0022% to 0.1358%.

Utilizing bioprinting for hydrogel-based electric double-layer capacitor fabrication

Utilizing bioprinting for hydrogel-based electric double-layer capacitor fabrication