Ultrahigh Capacitance Research Articles

Ultrahigh Capacitive Energy Storage in a Heterogeneous Nanolayered Composite

AbstractFerroelectric polymers with robust electrical polarization have been extensively investigated for capacitive energy storage. However, their inherent ferroelectric hysteresis loss limits the discharged energy density and compromises energy efficiency. Here, a heterogeneous nanolayered composite of ferroelectric polymer poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) and Al2O3 is presented, which effectively mitigates ferroelectric hysteresis loss while maintaining high polarization and enhanced breakdown strength. Phase‐field simulations indicate that the polarization behaviors of the heterogeneous layered structure are jointly influenced by the thickness and dielectric constant of each component, which balances the electrical energy and Landau energy within the heterogeneous system. Guided by the theoretical simulations, optimized polarization behaviors are achieved with a significant reduction in remnant polarization and ferroelectric loss in the P(VDF‐TrFE)/Al2O3 composites through careful control of P(VDF‐TrFE) thickness at nanometer scale. Moreover, the presence of multiple interfaces in the layered composites leads to a remarkable enhancement in polarization and breakdown strength. Consequently, an ultrahigh energy density of about 108 J cm−3 is achieved with a high charge–discharge efficiency of exceeding 80%. This work not only presents a straightforward approach to modify the polarization behaviors of ferroelectric polymers but also demonstrates a promising strategy for developing high‐energy‐density polymer nanocomposites.

Regulating Composition and Structure of Coal-based Graphene and Its Electrochemical Characteristics

Abstract Coal, a carbon-rich mineral with plentiful reserves, serves not only as a fuel but also as a raw material, presenting lower pollution emissions in the latter use. From a materials chemistry standpoint, coal is a viable raw material for graphene production. This study develops a promising and sustainable method to convert coal into graphene, leveraging its unique macromolecular aromatic structure and high carbon content. The investigation includes an analysis of the lateral size, morphology, and chemical composition of coal-derived graphene using techniques such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and optical microscopy. Results confirm that coal can effectively replace natural graphite flakes in graphene production, with the derived graphene featuring 3-6 exfoliated layers and an oxygen content below 5.5%. While the graphene from coal shares a similar morphology to that derived from graphite, it exhibits more structural defects. Interestingly, the macroscopic size of the coal does not influence the microscopic composition and structure of the graphene. However, the thermal reduction method for oxidized graphene proves more effective at repairing structural defects than chemical reduction. Employing coal-derived graphene as a supercapacitor electrode demonstrates excellent cycling stability and ultra-high capacitance storage capacity. The H-CG-325 shows the highest discharge area-specific capacitance across various current densities. At an increased current density of 10 A/g, the H-CG-325 maintains 80.6% of its initial capacitance of 79 F/g observed at 1 A/g. Electrochemical tests reveal that coal-based graphene holds significant potential as a supercapacitor material, indicating promising applications in energy storage and conversion.

Acidic "Water-in-Salt" Electrolyte Enables a High-Energy Symmetric Supercapacitor Based on Titanium Carbide MXene.

Titanium carbide MXene, Ti3C2Tx, exhibits ultrahigh capacitance in acidic electrolytes at negative potentials yet poor stability at positive potentials, resulting in low-energy densities for Ti3C2Tx-based symmetric supercapacitors. Utilizing "water-in-salt" electrolytes has successfully expanded the stable operation potential window of MXenes. However, this advancement comes at the cost of sacrificing their high capacitance in acidic electrolytes. In this work, we report an acidic "water-in-salt" (AWIS) electrolyte composed of sulfuric acid and saturated lithium halide, which effectively doubled the energy density of the Ti3C2Tx-based symmetric supercapacitor compared to those with bare acidic electrolytes. Specifically, the AWIS electrolyte successfully expanded the voltage window of the symmetric device to 1.1 V. A high specific capacitance of 112.34 F g-1 (at 10 mV s-1) was obtained due to the presence of proton redox. As a result, the symmetric device achieved a high-energy density of 19.1 Wh kg-1 and a high capacitance retention of 96.3% after 10,000 cycles. This work demonstrates the importance of designing stable and redox-active electrolytes for high-energy MXene-based symmetric supercapacitors.

NiO nanolayer electrodeposited with Cobalt and Phosphide as a novel supercapacitor with high areal capacitance

In the present work, a novel supercapacitor electrode is fabricated via a two-step synthesis procedure. A NiO nanolayer was initially fabricated on a nickel foam electrode using hydrothermal synthesis to obtain a substrate with a high electrocatalytic area and good adhesive properties. Subsequently, the NiO-decorated nickel foam (NF) was employed as a substrate for the electrodeposition of cobalt and phosphorous. Morphological, structural, and surface characterization, along with various electrochemical tests, were conducted to gain insight into structure-property relationships. The as-prepared electrode (CoP@NF) exhibited excellent electrochemical behavior with an ultra-high areal capacitance of 3340 mF cm−2 at 5 mA cm−2 and high capacitance values even at high current densities. The exceptional electrochemical behavior can be attributed to the morphological and electronic modifications induced by aliovalent doping and the synergetic effect between the different electrode counterparts.

Microporous tungsten oxide spheres coupled with Ti3C2Txnanosheets for high-volumetric capacitance supercapacitors.

In the contemporary landscape of technological advancements, the burgeoning demand for portable electronics and flexible wearable devices has necessitated the development of energy storage systems with superior volumetric performance. Tungsten oxide (WO3), known for its high density and theoretical capacitance, is a promising electrode material for supercapacitors. However, low conductivity and poor cycling stability are still the key bottlenecks for its application. Herein, a novel composite comprising hollow porous WO3 spheres (HPWS) derived by template method was electrostatic self-assembled on the surface of the Ti3C2Tx nanosheets. The resulting electrodes exhibited ultra-high volumetric capacitance of 1930 F cm-3 at 1 A g-1 and rate capability of 46% at 50 A g-1, attributed to enhanced ion accessibility from microporous structure and electron transport from conductive network of Ti3C2Tx even at a high packing density of 3.86 g cm-3. Utilizing HPWS/Ti3C2Tx as the negative electrode and porous carbon as the positive electrode, the assembled asymmetric supercapacitor achieved an energy density of 31 Wh kg-1 at a power density of 650 W kg-1 with over 107% capacitance retention after 5000 cycles. This work provides a promising approach for developing next-generation supercapacitors with ultra-high volumetric capacitance.

Theoretical and experimental studies on 2D β-NiS battery-type electrodes for high-performance supercapacitor

Recently, quirky features and eccentric structures of transition metal sulfides have grasped great attention to remove roadblocks and unwrap fresh avenues for electrodes in energy storage devices. Herein, we developed a 2D beta phase nickel sulfide nanosheets (2D β-NiS NSs) electrode with remarkable enhancement in charge storage properties. When served as active electrodes for electrochemical tests, 2D NiS NSs exhibited ultra-high capacitance of 2693 Fg−1 at 1 mVs−1 and specific capacity of 219 mAhg−1 at 1 Ag−1. The symmetric battery type solid-state supercapacitor device comprising 2D β-NiS NSs electrodes exhibits specific capacity of 83.43 mAhg−1at 2 Ag−1 over broad potential range of 0.7V with good cycling performance, and energy and power density of 28.9 Whkg−1 (@ 2 Ag−1) and 21 kWkg−1 (@ 6 Ag−1) respectively. Complementary first-principles density functional theory (DFT) calculations accomplished to explore the electrolyte ion interactions with nickel sulfide nanostructures defining 2D NiS NSs as a potential candidate for real-time applications.

Oxygen-rich 3D hierarchical porous MXene prepared by Zn powder reduction for flexible supercapacitors

Ti3C2Tx MXene is highly compelling as an energy storage material, but 2D MXene sheets experience significant stacking due to hydrogen bonding and van der Waals forces. This blocks active sites and impedes fast electrolyte ion transport. The pseudocapacitance of MXene materials is highly reliant on their terminal groups. Therefore, an effective strategy was designed herein to prepare an oxygen-rich 3D hierarchical porous MXene (P-OR-Ti3C2Tx). First, Zn powder was used as a template to construct three-dimensional hierarchical porous structures that spanned the microporous, mesoporous, and macroporous scales. Second, Zn powder was used as a metal reducing agent in a reaction at 500 °C to eliminate most −F terminal groups on the MXene. Then, a subsequent acid washing step was used to introduce numerous −O terminal groups. The energy storage process of the prepared MXene was investigated by in situ Raman. More redox active sites (−O terminal groups) are exposed by the constructed oxygen-rich 3D hierarchical porous MXene structure, which also provides a shorter pathway for electrolyte ion transport. P-OR-Ti3C2Tx displays superb rate performance (88.19 % retention at 100Ag−1) and ultra-high capacitance (676.7F/g at 2 mV/s and 698.7Fg−1 at 1 Ag−1) when used as a supercapacitor electrode. Moreover, a symmetric flexible supercapacitor device prepared using P-OR-Ti3C2Tx and carbon cloth achieves a superb energy density of 32.8Whkg−1 at a power density of 236.5Wkg−1. This study offers insight into the design of MXenes that exhibit both high capacity and excellent rate performance.

Controlled N-doped Fe3O4@C arrays: Achieving enhanced donor density and capacity for hybrid supercapacitors

Carbon modified nitrogen-doped Fe3O4(N–Fe3O4@C) nanorod array directly grown on carbon cloth was fabricated. Nitrogen-doping and carbon shell effectively decrease the potential barrier of ion migration of the oxides and improve the electrochemical performance. An enhanced donor density of N-Fe2O3 (7.6 × 1015 cm−3) is achieved with optimized doping temperature. Following with carbon coated, the optimized N–Fe3O4@C electrode showed ultrahigh capacitance over an extended potential window and remarkable cycling performance. A new quasi-solid-state supercapacitor with N–Fe3O4@C and NiCoP@Ni(OH)2 achieved high voltage to 2.0 V and high energy density (72.37 Wh kg−1, 2.36 mWh cm−3).

Efficient Fabrication of Disordered Graphene with Improved Ion Accessibility, Ion Conductivity, and Density for High-Performance Compact Capacitive Energy Storage.

High-performance compact capacitive energy storage is vital for many modern application fields, including grid power buffers, electric vehicles, and portable electronics. However, achieving exceptional volumetric performance in supercapacitors is still challenging and requires effective fabrication of electrode films with high ion-accessible surface area and fast ion diffusion capability while simultaneously maintaining high density. Herein, a facile, efficient, and scalable method is developed for the fabrication of dense, porous, and disordered graphene through spark-induced disorderly opening of graphene stacks combined with mechanical compression. The obtained disordered graphene achieves a high density of 1.18gcm-3, sixfold enhanced ion conductivity compared to common laminar graphene, and an ultrahigh volumetric capacitance of 297Fcm-3 in ionic liquid electrolyte. The fabricated stack cells deliver a volumetric energy density of 94.2WhL-1 and a power density of 13.7kWL-1, representing a critical breakthrough in capacitive energy storage. Moreover, the proposed disordered graphene electrodes are assembled into ionogel-based all-solid-state pouch cells with high mechanical stability and multiple optional outputs, demonstrating great potential for flexible energy storage in practical applications.

Ultra-sensitive humidity sensing based on Coherent perfect absorber-lasing system

Abstract As a singularity in non-Hermitian physics, coherent perfect absorber-lasing (CPAL) point theoretically has an infinite quality factor and can detect small perturbations, so it has potential applications in ultra-sensitive sensors. However, in the radio frequency field, due to deviations in actual components, the system will deviate from the CPAL point and the performance will degrade significantly (the output coefficient amplitude is only 30 dB). At the same time, actual sensing research is also very lacking. Based on these, we demonstrate a CPAL-based sensor system that increases its output coefficient amplitude to 60dB. When using the lasing state as the sensing mode, it has a capacitance detection accuracy of 10 fF. Then a high-frequency capacitive humidity sensor based on polyaniline/graphene oxide/titanium dioxide film is designed. The heterojunction formed between these materials increases the number of active sites for adsorbing water molecules. With the ultra-high capacitance detection accuracy of the CPAL sensor system, it is finally able to distinguish a 1% relative humidity change at 20%RH (corresponding to a 20 fF capacitance change, or a 1.63 dB output coefficient change), showing potential sensing application prospects.

Direct Fabrication of 3D Electrodes Based on Graphene and Conducting Polymers for Supercapacitor Applications

AbstractThe development of commercially viable composite conducting polymer electrodes for energy storage is limited by the requirement of multiple and complex fabrication steps, low energy density, and poor cycling stability. In this work, a straightforward, economical, single‐step method is developed for creating densely packed nanostructured PEDOT/graphene composite material demonstrating its application as an electrode for supercapacitors. The electrode achieved the highest mass loading reported so far in the literature for composite vapor phase polymerized PEDOT/rGO using aqueous FeCl3 (25.2 mg cm−2), and displayed an ultrahigh areal capacitance of 4628.3 mF cm−2 at 0.5 mA cm−2. The symmetric two‐electrode setup displayed an energy density of 169.3 µWh cm−2 and a 70% capacitance retention after 70 000 cycles, showcasing its exceptional performance and durability.

Flexible zinc-ion hybrid micro-supercapacitors with polymeric current collector for integrated energy storage in wearable devices

The ubiquity of conventional micro-fabrication techniques has encountered impediments in constructing cost-effective micro-devices, thereby constraining their broad deployment. Concurrently, the suboptimal energy density inherent to supercapacitors exacerbates this challenge. This study presents a straightforward assembly methodology for the fabrication of a mechano-electrochemically efficient micro-zinc ion hybrid supercapacitor (M−ZSC), alongside the introduction of an innovative polymeric current collector. The M−ZSC is fabricated through a process involving masked spray deposition of a novel adhesive current collector and the electrode materials, and electroplating of zinc nanosheets onto the anode finger, creating an electrochemically performant and mechanically robust device. The resulting M−ZSC exhibits a notable areal capacitance of 52.2 mF/cm2 and an energy density of 18.5 µWh/cm2 for the normal mass-loading of 3.6 mg/cm2, which is amongst the highest reported values for energy storage. The masked spray deposition/hot pressing technique enabled us to fabricate free-standing thick electrodes with a loading density of up to 56.1 mg/cm2, facilitating the achievement of an ultrahigh areal capacitance of 227 mF/cm2 and an energy density of 80.5 µWh/cm2. Furthermore, the M−ZSC exhibits a robust retention of 95 % capacitance at 1 mA/cm2. Critical to its flexibility, the device is constructed using purely additive deposition methods on flexible substrates and is therefore well-tailored for deployment in flexible electronics and on-chip applications. These micro-devices are well-poised for seamless integration within a singular electronics package or chip architecture.

Boosting the Capacitor Performance of the Metal Organic Frameworks Derived V2O5 Nanoflower by Cu Doping.

Due to its ultrahigh theoretical capacitance, vanadium pentoxide (V2O5) is considered to be a valid candidate for advanced supercapacitors. However, because of the low electron/electrolyte transfer rate, the capacitive performance still remains to be improved. In this report, Cu doping is adopted to improve the capacitive performance by a two-steps strategy consisting of microwave-assisted solvothermal and postannealing treatments. The electrochemical results indicate that the Cu doping was beneficial for improving the specific capacitance, extending the potential window, and improving the rate ability and long-term stability of V2O5. Furthermore, the mechanism for the performance improvement is explained in detail by combining theoretical calculation and experiments. The results indicated that, compared with that of undoped V2O5, the larger interplanar spacing, better electrical conductivity, a larger proportion of V3+/V4+, and more abundant oxygen vacancies result in an improved capacitive performance. Our proposed Cu-doped V2O5 (Cu-V2O5) can be used as both a positive electrode and a negative electrode for the assembly of the symmetric supercapacitor, which can be used as an energy storage device for light emitting diode lamps.

Synthesis of Microscopic 3D Graphene for High-Performance Supercapacitors with Ultra-High Areal Capacitance.

Despite graphene being considered an ideal supercapacitor electrode material, its use in commercial devices is limited because few methods exist to produce high-quality graphene at a large scale and low cost. A simple method is reported to synthesize 3D graphene by graphenization of coal tar pitch with a K2CO3 catalyst. This produces 3D graphenes with high specific surface areas up to 2113 m2 g-1 and exceptional crystallinity (Raman ID/IG as low as ≈0.15). The material has an outstanding specific capacitance of 182.6 F g-1 at a current density of 1.0 A g-1. This occurs at a mass loading of 30mg cm-2 which is 3 times higher than commercial requirements, yielding an ultra-high areal capacitance of 5.48 F cm-2. The K2CO3 is recycled and reused over 10 cycles with material quality and electrocapacitive performance of 3D graphene retained and verified after each cycle. The synthesis method and resulting electrocapacitive performance properties create new opportunities for using 3D graphene more broadly in practical supercapacitor devices.

Tuning the electrochemical properties of ZnO through chromium doping and its suitability for supercapacitor application

ZnO nanoparticles doped with chromium (Cr) were synthesized through a simple sol gel route. The successful Cr doping into the ZnO lattice has been evidenced via several characterisation techniques i.e., XRD and XPS. A high oxygen vacancies (OV) density has been located through Photoluminescence (PL) and EPR studies for the Cr doped ZnO (1 %) (ZnCr1) sample. The high density of OV defects induced from Cr doping in ZnO lattice was considered at the origin of the improved electrochemical performances by promoting efficient electron transfer ability with intercalation process of the electrolyte's ions during charge-discharge mechanism. The ZnOCr1 electrode displays an important capacitance value (367 F.g−1), ultrahigh capacitance retention (86 %) while changing the current from 1 to 20 A·g−1, and marvellous stability of 84 % during 4000 cycles. An asymmetric supercapacitor based ZnOCr1 electrode achieves significant potential window up to 1.6 V with encouraging specific energy density. The device showcases a satisfactory specific energy of 27.1 Wh·Kg−1 at specific power of 480 W·Kg−1 and a great retention of 17 % decay after 4000 cycles at current density of 10 A g−1. This opens door to the developed ZnO-Cr1 material for its application in future supercapacitor devices.

Heteroatoms-doped hierarchically porous graphene as electrode material for supercapacitors with ultra-high capacitance

In this work, a dual-templating pyrolysis strategy is successfully developed to synthesize a highly crumpled graphene (N-TRPG-800). The achievement of the graphene is based on the carbonization of the d(+)-glucosamine hydrochloride and the spatial confinement effect of the graphitic carbon nitride (g-C3N4) in the presence of zinc nanoparticles (Zn NPs). During the pyrolysis process, the d(+)-glucosamine hydrochloride first polymerizes into the layers of g-C3N4, which is derived from melamine. Afterwards, a further increase in pyrolysis temperature leads to the decomposition of g-C3N4 and the generation of reducing NH3 gas, which eventually resulting in the formation of 2D ultrathin structure and high heteroatoms doping degree. Simultaneously, the volatilization of the Zn NPs also plays a key role in the pore formation and the hierarchical structure generation. As a result, the as-synthesized graphene sheets simultaneously possesses hierarchical porous structure, high heteroatoms-doped degree, and large specific surface area (506 m2 g−1). Electrochemical measurements show that the N-TRPG-800 exhibits an ultrahigh supercapacitance of 471 F g−1 at 0.2 A g−1 in a three-electrode mode, approaching the theoretical capacitance of 550 F g−1 of graphene, which is superior to that of the state-of-the-art heteroatom-doped porous carbons in literature.

The production of electrodes for microsupercapacitors based on MoS2-modified reduced graphene aerogels by 3D printing

Micro-supercapacitors (MSCs) are of interest because of their high power density and excellent cycling performance, offering a broad array of potential applications. However, preparing electrodes for the MSCs with an extremely high areal capacitance and energy density remains a challenge. We constructed MSC electrodes with an ultra-high area capacitance and a high energy density, using reduced graphene oxide aerogel (GA) and MoS2 as the active materials, combined with 3D printing and surface modification. Using 3D printing, we obtained electrodes with a stable macrostructure and a GA-crosslinked micropore structure. We also used a solution method to load the surface of the printed electrode with molybdenum disulfide nanosheets, further improving the electrochemical performance. The surface capacitance of the electrode reached 3.99 F cm−2, the power density was 194 W cm−2, and the energy density was 1 997 mWh cm−2, confirming its excellent electrochemical performance and cycling stability. This work provides a simple and efficient method for preparing MSC electrodes with a high areal capacitance and energy density, making them ideal for portable electronic devices.

A cleaner lignin-induced 3D porous MXenes hybrid electrode with enlarged voltage and high capacitance retention

Conventional supercapacitors face narrow voltage and an inevitable reduction in capacitance retention during operation, significantly preventing its further commercial application. So, biomass-derived composite materials have attracted intensive attention, especially for pseudocapacitive supercapacitors. Herein, a high-end utilization strategy of lignin to induce a 3D porous layered MXenes/graphene oxide hybrid electrode (LGM2-80) and homologous gel electrolytes with low interface resistance for lignin-derived supercapacitors is demonstrated by a simple hydrothermal method. A more uniform distribution and smaller nanospheres ≈<10 nm of lignin prevent the restacking and increase the interlayer spacing of graphene oxide, also play an adhesive role between graphene oxide and MXene, guaranteeing the maximization of the pseudocapacitance effect between lignin and MXene. Consequently, the LGM2-80 electrode showed a wide operating potential (−0.7∼1.0 V), breaking through the bottleneck of MXene-derived devices with limited working voltage (typically≤0.6 V). Furthermore, the lignin-derived symmetric quasi-solid-state supercapacitor (LGM2-80//lignin gel//LGM2-80) possesses an excellent capacitance retention rate of 149 % at 5,000 cycles, which is far exceeding the current reported supercapacitors. This innovative use of lignin opens up new perspectives for ultra-voltage and ultra-high capacitance retention of advanced supercapacitors.

Soluble starch-derived porous carbon microspheres with interconnected and hierarchical structure by a low dosage KOH activation for ultrahigh rate supercapacitors

The developed porous structure and high density are essential to enhance the bulk performance of carbon-based supercapacitors. Nevertheless, it remains a significant challenge to optimize the balance between the porous structure and the density of carbon materials to realize superior gravimetric and areal electrochemical performance. The soluble starch-derived interconnected hierarchical porous carbon microspheres were prepared through a simple hydrothermal treatment succeeded by chemical activation with a low dosage of KOH. Due to the formation of interconnected spherical morphology, hierarchical porous structure, reasonable mesopore volume (0.33 cm3 g−1) and specific surface area (1162 m2 g−1), the prepared carbon microsphere has an ultrahigh capacitance of 394 F g−1 @ 1 A g−1 and a high capacitance retention of 62.7 % @ 80 A g−1. The assembled two-electrode device displays good cycle stability after 20,000 cycles and an ultra-high energy density of 11.6 Wh kg−1 @ 250 W kg−1. Moreover, the sample still exhibits a specific capacitance of 165 F g−1 @ 1 A g−1 at a high mass loading of 10 mg cm−2, resulting in a high areal capacitance of 1.65 F cm−2. The strategy proposed in this study, via a low-dose KOH activation process, provides the way for the synthesis of high-performance porous carbon materials.

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

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