Rate Supercapacitors Research Articles

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.

Solvent-free, deep eutectic system-assisted synthesis of nanoarchitectonics of hierarchical porous carbons for high rate supercapacitors

Solvent-free, deep eutectic system-assisted synthesis of hierarchical porous carbons for high rate and high energy density supercapacitors.

Self-standing porous MXene film via in situ formed microgel induced by 2- methylimidazole for high rate supercapacitor

Ti3C2Tx MXene has been considered a potential supercapacitor electrode material on account of its fast electron transfer performance, large volume pseudocapacitance, excellent hydrophilicity and mechanical properties. However, the serious stacking of MXene nanosheets reduced the exposed active sites and hindered diffusion of ions, leading to bad electrochemical property. Here, we report a strategy to transform MXene nanosheets into 3D MXene microgels induced by 2-methylimidazole. Benefitting from the existence of microgels, it facilitates the rapid vacuum filtration to prepare the porous MXene film, thus enhancing the ion transfer efficiency. Furthermore, 2-methylimidazole can also act as an intercalated agent to increase the layer spacing of MXene nanosheets. Therefore, the as-prepared porous MXene film demonstrates a superior rate capacity, and its capacitance reaches 223.4 F g−1 at the scan rates of 1000 mV s−1. Moreover, the assembled MXene//AC asymmetrical supercapacitor displays a 16.88 Wh kg−1 at a power density of 799 W kg−1, and maintains 13.11 Wh kg−1 at a power density of 8 kW kg−1. This work develops a simple way to prepare the porous MXene film for supercapacitors with excellent electrochemical performance.

Ce3+ ion regulated CoNi-hydroxides for ultrahigh charge rate supercapacitors

α-form Ce3+:CoNi-LDH//AC supercapacitors exhibited an energy density of 30 W h kg−1 at a power density of 10 kW kg−1 thanks the unique crystal and electronic structures of Ce3+:CoNi-LDH.

Flexible and cross-linked carbon nanofibers based on coal liquefaction residue for high rate supercapacitors

Free-standing electrospun carbon nanofibers nonwovens (CNF) with an outstanding cross-linked architecture can be successfully achieved via a simple and practicable strategy by combining electrospinning, stabilization and carbonization. In this study, the hybrids of asphaltene extracted from coal residue liquefaction, polyacrylonitril and terephthalic acid are used as precursors. Due to the synergistic effect of efficient cross-linked structures and short charge transfer channels, flexible cross-linked asphaltene-based CNF (CLACF), as the binder-free supercapacitor electrode, exhibits a high capacity of 225 F g−1 at 0.2 A g−1 and an outstanding rate capability of 148 F g−1 at 100 A g−1. The developed symmetrical supercapacitor based on CLACF has a maximum energy density of 4.20 Wh kg−1 with a power density of 1.22 kW kg−1. It also has excellent cyclic stability with 97.3% capacitance retention after 10,000 cycles at 2 A g−1.

A dual‐activation strategy to tailor the hierarchical porous structure of biomass‐derived carbon for ultrahigh rate supercapacitor

Suffering from the competitive relationship between the abundant electrochemically active sites and the fast ion transfer channel, it still faces tremendous challenges in simultaneously designing and preparing biomass-derived carbons with excellent capacitive and rate performance. Herein, a dual-activation strategy of KOH and KMnO4 is used to prepare cotton stalks-derived porous carbon with large specific surface area (SSA) (1634 m2 g−1), interconnected network structure, as well as rational mesopores and micropore ratio. Consequently, the obtained sample exhibits an ultrahigh specific capacitance of 318 F g−1 at 1 A g−1, 71% capacitance retention at current density up to 50 A g−1, and only 2% capacitance dissipation in a two-electrode system in 6 M KOH after 10 000 cycles. Importantly, the obtained sample also shows a high areal capacitance of 3.8 F cm−2 under a high mass loading of 16 mg cm−2. Moreover, the obtained sample also delivers a high energy density of 19.9 Wh kg−1 at 397 W kg−1 in the symmetric two-electrode system using 1 M Na2SO4 aqueous electrolyte. This work provides an alternative avenue for the facile and scaled-up conversion of earth-abundant agricultural wastes into advanced carbon materials for supercapacitors application.

Covalent modified reduced graphene oxide: Facile fabrication and high rate supercapacitor performances

Covalent modified graphene (denoted as DMFrGO180) was facilely fabricated by one-step solvothermal process with graphene oxide (GO) and N, N-dimethylformamide (DMF) as the raw materials. DMF serves as not only the solvent but also reactants to generate a reductive amination environment. Solvothermal treatment at 180 °C promotes the reductive amination and produces DMFrGO180 with covalent bonded dimethylamine groups, spit-ball like morphologies, and hierarchical micro- and mesoporous structure. The abundant covalent acidamide bonds render DMFrGO180 plenty of seamless ohmic contact to provide more electron transfer paths. The excellent electrical conductivity enhances and accelerates the redox reversibility of oxygen-containing functional groups to provide more pseudocapacitance. The hierarchical porous structure also accelerates the electrolyte transportation. These features bestow DMFrGO180 excellent rate capability. In three-electrode tests, DMFrGO180 exhibits high gravimetric specific capacitance of 287 F g−1 at 1 A g−1 and 192 F g−1 at 100 A g−1. Quasi-solid-state symmetrical two-electrode supercapacitors by using PVA/KOH gel as electrolyte also shows excellent supercapacitive properties with 193.5 F g−1 and 86.9 F g−1 at 1 A g−1 and 50 A g−1. Especially, it achieves high energy density 11.35 W h kg−1 at a power density of 649.7 W kg−1 and 5.09 W h kg−1 at power density of 32.4 KW kg−1. The present results may open a door of graphene oxide for applications in energy storage and conversion fields via a green and energy-efficient process.

3D Carbon Frameworks for Ultrafast Charge/Discharge Rate Supercapacitors with High Energy-Power Density

Highlights3D carbon frameworks (3DCFs) constructed by interconnected nanocages show a high specific surface area, hierarchical porosity, and conductive network.The deoxidization process removed most of surface oxygen-containing groups in 3DCFs that leads to fast ion diffusion kinetics, good electric conductivity, and limited side reactions.The deoxidized 3DCFs exhibit an ultrafast charge/discharge rate as electrodes for SCs with high energy-power density in both aqueous and ionic liquids electrolytes.

Ultrahigh Rate Supercapacitor based on Self-Standing Carbon Nanotubes Supported Vertically Aligned MoS2 Sheets

Abstract Recently, two-dimensional layered structures, especially MoS2 has come out as the most investigated electrode material for batteries and supercapacitors, possessing well preserved in-plane covalent bonding, leading to extraordinary mechanical elasticity within the layers as well as outstanding firmness along the c-axis. The present work is aimed to fabricate vertically aligned edge exposed molybdenum disulfide nanoflakes on the surface of the self-standing hydrophilic carbon nanotubes, using a two-step process involving a chemical route and magnetron sputtering techniques for flexible supercapacitor application. These hybrid heterostructures have been characterized using XRD, FESEM, and cyclic voltammetry. In the aqueous electrolyte of 1M Li2SO4, the symmetric device revealed very high areal capacitance of 182.5 mF/cm2 and 155 mF/cm2, at scan rates of 2 and 5 mV/s, respectively. The device shows high energy density of 365 mWh/cm2.

MnO2 nanospheres electrode composed of low crystalline ultra-thin nanosheets for high performance and high rate supercapacitors

In this work, we report an alternative approach to self-assemble low crystalline ultra-thinMnO2nano-sheets into MnO2nano-spheres by a cost-effective, one-potandinstant ultrasonic synthesis without the assistance of acid or template within an hour for high performance and high rate supercapacitors.The MnO2nano-spheres are demonstrated to be excellent working electrodes in a three-electrode cell revealing remarkable specific capacitance of 309 F g−1at the current density of 1.0 A g−1and good cyclic stability with capacitance retention of 90% after 5000 cycles in 1 M Na2SO4electrolyte aqueous solution. Further, an aqueous asymmetrical supercapacitor (MnO2//AC) device was constructed whose maximum workable potential window for the MnO2//AC device reached 0–2.0 V.MnO2//AC illustrated an energy density of 40 Wh kg−1with a maximum power density of 19000 W kg−1. Besides, this device sustained a long cycle life with 85% capacitance retention after 5000 cycles.

3D Printing Engineered Multi-porous Cu Microelectrodes with In Situ Electro-Oxidation Growth of CuO Nanosheets for Long Cycle, High Capacity and Large Rate Supercapacitors

Developing excellent pseudocapacitive electrodes with long cycle, high areal capacity and large rate has been challenged. 3D printing is an additive manufacture technique that has been explored to construct microelectrodes of arbitrary geometries for high-energy–density supercapacitors. In comparison with conventional electrodes with uncontrollable geometries and architectures, 3D-printed electrodes possess unique advantage in geometrical shape, mechanical properties, surface area, especially in ion transport and charge transfer. Thus, a desirable 3D electrode with ordered porous structures can be elaborately designed by 3D printing technology for improving electrochemical capacitance and rate capability. In this work, a designed, monolithic and ordered multi-porous 3D Cu conductive skeleton was manufactured through 3D direct ink writing technique and coated with CuO nanosheet arrays by an in situ electro-oxidation treatment. Benefiting from the highly ordered multi-porous nature, the 3D-structured skeleton can effectively enlarge the surface area, enhance the penetration of electrolyte and facilitate fast electron and ion transport. As a result, the 3D-printed Cu deposited with electro-oxidation-generated CuO (3DP Cu@CuO) electrodes demonstrates an ultrahigh areal capacitance of 1.690 F cm−2 (38.79 F cm−3) at a large current density of 30 mA cm−2 (688.59 mA cm−3), excellent lifespan of 88.20% capacitance retention after 10,000 cycles at 30 mA cm−2 and superior rate capability (94.31% retention, 2-30 mA cm−2). This design concept of 3D printing multi-porous current collector with hierarchical active materials provides a novel way to build high-performance 3D microelectrodes.

Nitrogen-doped porous carbon composite with three-dimensional conducting network for high rate supercapacitors

Nitrogen-doped porous carbon materials are widely used as electrode materials for supercapacitors. However, the electrodes based on these materials generally suffer from poor conductivity due to point-to-point contact of granular materials, especially at high charging/discharging rates. Herein, nitrogen-doped porous carbon composite (N-PC/CNT) with three-dimensional (3D) conducting network is prepared by carbonizing carbon nanotube (CNT) thread zeolitic imidazolate framework-8 (ZIF-8) composite. In this construction, the carbonized ZIF-8 with rich pore structure serves as a “reservoir” to provide storage space for electrolyte ions, while CNTs act as “wires” to form internal 3D conducting network for rapid electron transfer. As a result, the obtained N-PC/CNT exhibits a high specific capacitance of 334.5 F g−1 at 1 A g−1, excellent rate capability (195.5 F g−1 at 100 A g−1, capacitance retention of 58%), remarkable cycling stability (almost 100% capacitance retention after 20000 cycles) and outstanding frequency response with an ultrahigh rate up to 3 V s−1 in 6 M KOH electrolyte. These prominent performances result from the synergy of high nitrogen doping content (12.1 at.%), large specific surface area (980.2 m2 g−1), suitable pore size distribution and excellent conductivity. The assembled N-PC/CNT//N-PC/CNT symmetric supercapacitor exhibits a maximal energy density of 17 Wh kg−1 at a power density of 533 W kg−1 in 1 M Na2SO4 electrolyte. Evidently, the nitrogen-doped porous carbon composite has a great development potential for advanced supercapacitors or other electrochemical energy storage devices.

Defect-rich honeycomb-like nickel cobalt sulfides on graphene through rapid microwave-induced synthesis for ultrahigh rate supercapacitors

Nickel cobalt sulfides (NCS) are regarded as potential energy storage materials due to the versatile valent states and rich electrochemical activity, but their sluggish synthesis process and inferior rate performance hinder them from large-scale application. Herein, microwave-induced strategy has been employed for efficient synthesis of honeycomb-like NCS/graphene composites, which are explored as ultrahigh rate battery-type electrodes for supercapacitors. Due to the internal heat mechanism, the synthesis time of NCS by microwave could be shortened from hours to minutes. Density functional theory was simulated to uncover the interfacial effect between NCS and graphene, and the resulted Schottky barrier is in favor of enhancing redox activity and capacity. Ultimately, the obtained defect-rich nickel cobalt sulfides/graphene with thermal treatment (NCS/G-H) could exhibit a high specific capacitance of 1186 F g−1 at 1 A g−1 and sustain 89.8% capacity even after the increase of current density over 20 times, which is much superior to bare NCS and NCS/graphene. Furthermore, the assembled NCS/G-H hybrid supercapacitor delivers supreme energy density of 46.4 Wh kg−1, and retains outstanding long-term stability of 89.2% after 10 k cycles. These results indicate that the synthesized NCS/G-H by time-saving microwave-induced liquid process could be served as high rate materials for supercapacitors.

Interconnected and hierarchical porous carbon derived from soybean root for ultrahigh rate supercapacitors

Abstract Suffering from the stable intrinsic structure and strong cross-linking between cellulose, hemicellulose, and lignin, the strategy of directional editing of biomass pore structure is rare. Here, we develop a simple hydrothermal strategy to reconstruct the macroporous biomass precursor to obtain interconnected and hierarchical porous carbon. Benefiting from its interconnected and hierarchical micro/meso/macroporous structure, high mesopore ratio of 74%, large surface area of 2690 m2 g−1, and abundant surface heteroatom (O, N, S), the resulting carbon performs an ultrahigh capacitance of 328 F g−1 at 1 A g−1, outstanding rate performance with a high capacitance retention of 60% at 100 A g−1, as well as good cycle stability in two-electrode system in 6 M KOH. Importantly, the resulting carbon also exhibits high areal capacitance of 4.1 F cm−2 at 1 A g−1 under a high mass loading of 20 mg cm−2 due to the robust ion-transfer kinetics. Furthermore, superior energy densities of 46.7 Wh kg−1 at 622 W kg−1 and 25.8 Wh kg−1 at 27.3 kW kg−1 are achieved in neat EMIM BF4.

Graphene Quantum Dot Reinforced Electrospun Carbon Nanofiber Fabrics with High Surface Area for Ultrahigh Rate Supercapacitors.

High surface area, good conductivity, and high mechanical strength are important for carbon nanofiber fabrics (CNFs) as high-performance supercapacitor electrodes. However, it remains a big challenge because of the trade-off between the strong and continuous conductive network and a well-developed porous structure. Herein, we report a simple strategy to integrate these properties into the electrospun CNFs by adding graphene quantum dots (GQDs). The uniformly embedded GQDs play a crucial bifunctional role in constructing an entire reinforcing phase and conductive network. Compared with the pure CNF, the GQD-reinforced activated CNF exhibits a greatly enlarged surface area from 140 to 2032 m2 g-1 as well as a significantly improved conductivity and strength of 5.5 and 2.5 times, respectively. The mechanism of the robust reinforcing effect is deeply investigated. As a freestanding supercapacitor electrode, the fabric performs a high capacitance of 335 F g-1 at 1 A g-1 and extremely high capacitance retentions of 77% at 100 A g-1 and 45% at 500 A g-1. Importantly, the symmetric device can be charged to 80% capacitance within only 2.2 s, showing great potential for high-power startup supplies.

An ultrafast supercapacitor built by Co3O4 with tertiary hierarchical architecture

The fast charge/discharge ability is very important for electric energy storage devices. Here, Co3O4 electrode with flower-wire-nanoparticle tertiary hierarchical architecture for ultrafast charge/discharge rate supercapacitor is developed via a facile and scalable hydrothermal method and subsequent sintering treatment. The as-prepared Co3O4 electrode exhibits an outstanding rate performance of 95.6% capability at 80 times current density from 0.5 A g−1 to 40 A g−1 and a good cycling stability of 98.5% retention after 2000 charge/discharge cycles at the current density of 2 A g−1. The Co3O4//AC asymmetric supercapacitor reveals an energy density of 16.25 Wh kg−1 at a power density of 7500 W kg−1. These impressive electrochemical behaviors suggest that such Co3O4 tertiary hierarchical architecture holds great promise for high-rate energy storage devices.

Micelle-induced assembly of graphene quantum dots into conductive porous carbon for high rate supercapacitor electrodes at high mass loadings

Achieving high rate capability of porous carbon at high mass loading is important for developing advanced supercapacitors. But it still remains a big challenge because thick electrode causes severely reduced electric conductivity and blocked ion migration channels. Herein, we develop a micelle-induced assembly method to prepare conductive porous carbon through puzzling flexible graphene quantum dots (GQDs). The unique sp2 hybridized GQDs ensure the product with a two times higher electric conductivity than the commercial activated carbon. The interconnected mesoporous structure promotes robust ion transport kinetics especially at high mass loadings. As supercapacitor electrode, it shows high capacitances of 315 and 170 F g−1 at 1 and 100 A g−1, respectively. Importantly, at a very high mass loading of 20 mg cm−2, it shows a remarkably high areal capacitances of 2.8 F cm−2 at 10 A g−1, which is much better than other reported carbon materials. The symmetric supercapacitors show maximum energy densities of 9.21 and 6.45 Wh kg−1 at the mass loadings of 2 mg cm−2 and 20 mg cm−2, respectively, revealing the structural advantage of GQD-puzzled porous carbon for practical applications.

Hierarchical bimetallic hydroxide/chalcogenide core-sheath microarrays for freestanding ultrahigh rate supercapacitors.

Transition metal compounds (TMCs) either crystalline or amorphous exhibit specific advantages in electrochemical energy storage. To integrate their merits into one electrode, we have herein developed hierarchical bimetallic hydroxide/chalcogenide core-sheath microarrays on nickel foam (NF) for freestanding high-efficiency supercapacitors, wherein interior crystalline metal chalcogenides serve as highly conductive pivots and exterior amorphous bimetallic hydroxides provide rich ion diffusion channels. With the synergic effect of the unique structure and bimetallic composition, the as-prepared Ni(OH)2-Co(OH)2/NiSe-Ni3S2/NF electrode displays an ultrahigh areal specific capacitance of 19.01 F cm-2 at 15 mA cm-2, which can be retained as 6.01 F cm-2 even at 125 mA cm-2. To the best of our knowledge, such excellent tolerance of ultrafast ion insertion/extraction at high current density is rare among NF-based free-standing electrodes. The asymmetric supercapacitor by assembling with activated carbon as the negative electrode delivers a volumetric capacitance of 3.93 F cm-3 at 30 mA cm-2, corresponding to an energy density of 13.9 mW h cm-3 at a power density of 200 mW cm-3. A capacitance retention of 82.5% was observed after 4000 cycles, together with an average 97% coulombic efficiency. This work may provide a facile strategy to construct hierarchical microarrays for efficient energy storage devices.

Two-dimensional layered magnesium\u2013cobalt hydroxide crochet structure for high rate and long stable supercapacitor application

Pseudocapacitors with nickel/cobalt hydroxide-based electrodes show promises energy storage devices, because they are economical and safe, but cycle stability and high current rate capability have not been achieved. We shed light on how magnesium in double-layered hydroxides serves as a supercapacitor electrode in optimal environments. Here we show the high rate capability and long-term stability of layered magnesium–cobalt double hydroxide (L-MCH) electrodes, which is superior to existing electrodes. The pseudocapacitor made with Mg2+ and Co2+ double hydroxide as active materials, does not have an intricate fabrication process. The L-MCH pseudocapacitor has a specific capacitance comparable to most double hydroxide-based materials and capacity retention greater than 107% over 10,000 cycles, which is in line with commercial devices. Our proposed method also offers a much faster and reliable route for electrode fabrication, which could result in the development of a new generation of supercapacitors, batteries and hybrid devices.

Jahn-Teller distortions in molybdenum oxides: An achievement in exploring high rate supercapacitor applications and robust photocatalytic potential

Although transition-metal oxides offer the potential for intimate coupling of energy storage application and environmental sustainability, how to find the suitable relationship between materials structures and properties is still a problem to explore further applications. In this work, Jahn-Teller effects proved by Crystal Field Theory (CFT) and Density Functional Theory (DFT) are used to predict the electronic structures of MoO3 and MoO2 reasonably, such results guided us to design two more reasonable applications. On account of the metallicity tendency of MoO2 with a stronger electron mobility from band structure, MoO2/rGO/g-C3N4 composite was performed as a high-performance electrode in asymmetric supercapacitors (SCs). MoO2 with the assistance of mesoporous graphitic carbon nitride and high conductivity graphene shows an enhanced capacity at 1700 F g−1 at 1 A g−1 and cycling retention at 84% retention after 3000 cycles for supercapacitors, the corresponding assemble asymmetric devices shows a maximum power density of 6.25 kW kg−1 at an energy density of 16.0 W h kg−1. Furthermore, the proper band structure of MoO3 predicted by DFT calculation has guided MoO3/rGO composite as a photocatalyst to degrade tetracycline, which shows a high elimination efficiency of 90.6% within 2 h illumination of simulated solar light.