Showing papers on "Supercapacitor published in 2015"

Graphene, related two-dimensional crystals, and hybrid systems for energy conversion and storage

Abstract: Graphene and related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging energy needs, in particular for the ever growing market of portable and wearable energy conversion and storage devices. Graphene's flexibility, large surface area, and chemical stability, combined with its excellent electrical and thermal conductivity, make it promising as a catalyst in fuel and dye-sensitized solar cells. Chemically functionalized graphene can also improve storage and diffusion of ionic species and electric charge in batteries and supercapacitors. Two-dimensional crystals provide optoelectronic and photocatalytic properties complementing those of graphene, enabling the realization of ultrathin-film photovoltaic devices or systems for hydrogen production. Here, we review the use of graphene and related materials for energy conversion and storage, outlining the roadmap for future applications.

Metallic 1T phase MoS2 nanosheets as supercapacitor electrode materials

Abstract: The 1T metallic phase of MoS2 shows high volumetric capacitance and electrochemical properties that are attractive for supercapacitor applications. Efficient intercalation of ions in layered materials forms the basis of electrochemical energy storage devices such as batteries and capacitors1,2,3,4,5,6. Recent research has focused on the exfoliation of layered materials and then restacking the two-dimensional exfoliated nanosheets to form electrodes with enhanced electrochemical response7,8,9,10,11. Here, we show that chemically exfoliated nanosheets of MoS2 containing a high concentration of the metallic 1T phase can electrochemically intercalate ions such as H+, Li+, Na+ and K+ with extraordinary efficiency and achieve capacitance values ranging from ∼400 to ∼700 F cm−3 in a variety of aqueous electrolytes. We also demonstrate that this material is suitable for high-voltage (3.5 V) operation in non-aqueous organic electrolytes, showing prime volumetric energy and power density values, coulombic efficiencies in excess of 95%, and stability over 5,000 cycles. As we show by X-ray diffraction analysis, these favourable electrochemical properties of 1T MoS2 layers are mainly a result of their hydrophilicity and high electrical conductivity, as well as the ability of the exfoliated layers to dynamically expand and intercalate the various ions.

Supercapacitor electrode materials: nanostructures from 0 to 3 dimensions

Abstract: Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.

Nitrogen-doped mesoporous carbon of extraordinary capacitance for electrochemical energy storage

Abstract: Carbon-based supercapacitors can provide high electrical power, but they do not have sufficient energy density to directly compete with batteries. We found that a nitrogen-doped ordered mesoporous few-layer carbon has a capacitance of 855 farads per gram in aqueous electrolytes and can be bipolarly charged or discharged at a fast, carbon-like speed. The improvement mostly stems from robust redox reactions at nitrogen-associated defects that transform inert graphene-like layered carbon into an electrochemically active substance without affecting its electric conductivity. These bipolar aqueous-electrolyte electrochemical cells offer power densities and lifetimes similar to those of carbon-based supercapacitors and can store a specific energy of 41 watt-hours per kilogram (19.5 watt-hours per liter).

Hybrid energy storage: the merging of battery and supercapacitor chemistries

Abstract: The hybrid approach allows for a reinforcing combination of properties of dissimilar components in synergic combinations. From hybrid materials to hybrid devices the approach offers opportunities to tackle much needed improvements in the performance of energy storage devices. This paper reviews the different approaches and scales of hybrids, materials, electrodes and devices striving to advance along the diagonal of Ragone plots, providing enhanced energy and power densities by combining battery and supercapacitor materials and storage mechanisms. Furthermore, some theoretical aspects are considered regarding the possible hybrid combinations and tactics for the fabrication of optimized final devices. All of it aiming at enhancing the electrochemical performance of energy storage systems.

Hierarchical Porous Nitrogen-Doped Carbon Nanosheets Derived from Silk for Ultrahigh-Capacity Battery Anodes and Supercapacitors

Abstract: Hierarchical porous nitrogen-doped carbon (HPNC) nanosheets (NS) have been prepared via simultaneous activation and graphitization of biomass-derived natural silk. The as-obtained HPNC-NS show favorable features for electrochemical energy storage such as high specific surface area (SBET: 2494 m2/g), high volume of hierarchical pores (2.28 cm3/g), nanosheet structures, rich N-doping (4.7%), and defects. With respect to the multiple synergistic effects of these features, a lithium-ion battery anode and a two-electrode-based supercapacitor have been prepared. A reversible lithium storage capacity of 1865 mA h/g has been reported, which is the highest for N-doped carbon anode materials to the best of our knowledge. The HPNC-NS supercapacitor’s electrode in ionic liquid electrolytes exhibit a capacitance of 242 F/g and energy density of 102 W h/kg (48 W h/L), with high cycling life stability (9% loss after 10 000 cycles). Thus, a high-performance Li-ion battery and supercapacitors were successfully assembled f...

Sulfur Cathodes Based on Conductive MXene Nanosheets for High-Performance Lithium–Sulfur Batteries

Abstract: Lithium–sulfur batteries are amongst the most promising candidates to satisfy emerging energy-storage demands. Suppression of the polysulfide shuttle while maintaining high sulfur content is the main challenge that faces their practical development. Here, we report that 2D early-transition-metal carbide conductive MXene phases—reported to be impressive supercapacitor materials—also perform as excellent sulfur battery hosts owing to their inherently high underlying metallic conductivity and self-functionalized surfaces. We show that 70 wt % S/Ti2C composites exhibit stable long-term cycling performance because of strong interaction of the polysulfide species with the surface Ti atoms, demonstrated by X-ray photoelectron spectroscopy studies. The cathodes show excellent cycling performance with specific capacity close to 1200 mA h g−1 at a five-hour charge/discharge (C/5) current rate. Capacity retention of 80 % is achieved over 400 cycles at a two-hour charge/discharge (C/2) current rate.

Formation of nickel cobalt sulfide ball-in-ball hollow spheres with enhanced electrochemical pseudocapacitive properties

Abstract: While the synthesis of hollow structures of transition metal oxides is well established, it is extremely challenging to fabricate complex hollow structures for mixed transition metal sulfides. Here we report an anion exchange method to synthesize a complex ternary metal sulfides hollow structure, namely nickel cobalt sulfide ball-in-ball hollow spheres. Uniform nickel cobalt glycerate solid spheres are first synthesized as the precursor and subsequently chemically transformed into nickel cobalt sulfide ball-in-ball hollow spheres. When used as electrode materials for electrochemical capacitors, these nickel cobalt sulfide hollow spheres deliver a specific capacitance of 1,036 F g(-1) at a current density of 1.0 A g(-1). An asymmetric supercapacitor based on these ball-in-ball structures shows long-term cycling performance with a high energy density of 42.3 Wh kg(-1) at a power density of 476 W kg(-1), suggesting their potential application in high-performance electrochemical capacitors.

Asymmetric Supercapacitors Using 3D Nanoporous Carbon and Cobalt Oxide Electrodes Synthesized from a Single Metal-Organic Framework.

Abstract: Nanoporous carbon and nanoporous cobalt oxide (Co3O4) materials have been selectively prepared from a single metal–organic framework (MOF) (zeolitic imidazolate framework, ZIF-67) by optimizing the annealing conditions. The resulting ZIF-derived carbon possesses highly graphitic walls and a high specific surface area of 350 m2·g–1, while the resulting ZIF-derived nanoporous Co3O4 possesses a high specific surface area of 148 m2·g–1 with much less carbon content (1.7 at%). When nanoporous carbon and nanoporous Co3O4 were tested as electrode materials for supercapacitor application, they showed high capacitance values (272 and 504 F·g–1, respectively, at a scan rate of 5 mV·s–1). To further demonstrate the advantages of our ZIF-derived nanoporous materials, symmetric (SSCs) and asymmetric supercapacitors (ASCs) were also fabricated using nanoporous carbon and nanoporous Co3O4 electrodes. Improved capacitance performance was successfully realized for the ASC (Co3O4//carbon), better than those of the SSCs bas...

Flexible Solid-State Supercapacitor Based on a Metal–Organic Framework Interwoven by Electrochemically-Deposited PANI

Abstract: Metal–organic frameworks (MOFs) have received increasing attention as promising electrode materials in supercapacitors (SCs). Yet poor conductivity in most MOFs largely thwarts their capacitance and/or rate performance. In this work, an effective strategy was developed to reduce the bulk electric resistance of MOFs by interweaving MOF crystals with polyaniline (PANI) chains that are electrochemically deposited on MOFs. Specifically we synthesized cobalt-based MOF crystals (ZIF-67) onto carbon cloth (CC) and further electrically deposited PANI to give a flexible conductive porous electrode (noted as PANI-ZIF-67-CC) without altering the underlying structure of the MOF. Electrochemical studies showed that the PANI-ZIF-67-CC exhibits an extraordinary areal capacitance of 2146 mF cm–2 at 10 mV s–1. A symmetric flexible solid-state supercapacitor was also assembled and tested. This strategy may shed light on designing new MOF-based supercapacitors and other electrochemical devices.

NiCo2S4 Nanosheets Grown on Nitrogen‐Doped Carbon Foams as an Advanced Electrode for Supercapacitors

Abstract: To push the energy density limit of supercapacitors, a new class of electrode materials with favorable architectures is strongly needed. Binary metal sulfides hold great promise as an electrode material for high-performance energy storage devices because they offer higher electrochemical activity and higher capacity than mono-metal sulfides. Here, the rational design and fabrication of NiCo2S4 nanosheets supported on nitrogen-doped carbon foams (NCF) is presented as a novel flexible electrode for supercapacitors. A facile two-step method is developed for growth of NiCo2S4 nanosheets on NCF with robust adhesion, involving the growth of Ni-Co precursor and subsequent conversion into NiCo2S4 nanosheets through sulfidation process. Benefiting from the compositional features and 3D electrode architectures, the NiCo2S4/NCF electrode exhibits greatly improved electrochemical performance with ultrahigh capacitance (877 F g−1 at 20 A g−1) and excellent cycling stability. Moreover, a binder-free asymmetric supercapacitor device is also fabricated by using NiCo2S4/NCF as the positive electrode and ordered mesoporous carbon (OMC)/NCF as the negative electrode; this demonstrates high energy density (≈45.5 Wh kg−1 at 512 W kg−1).

Nanostructured Mn-based oxides for electrochemical energy storage and conversion

Abstract: Batteries and supercapacitors as electrochemical energy storage and conversion devices are continuously serving for human life. The electrochemical performance of batteries and supercapacitors depends in large part on the active materials in electrodes. As an important family, Mn-based oxides have shown versatile applications in primary batteries, secondary batteries, metal-air batteries, and pseudocapacitors due to their high activity, high abundance, low price, and environmental friendliness. In order to meet future market demand, it is essential and urgent to make further improvements in energy and power densities of Mn-based electrode materials with the consideration of multiple electron reaction and low molecular weight of the active materials. Meanwhile, nanomaterials are favourable to achieve high performance by means of shortening the ionic diffusion length and providing large surface areas for electrode reactions. This article reviews the recent efforts made to apply nanostructured Mn-based oxides for batteries and pseudocapacitors. The influence of structure, morphology, and composition on electrochemical performance has been systematically summarized. Compared to bulk materials and notable metal catalysts, nanostructured Mn-based oxides can promote the thermodynamics and kinetics of the electrochemical reactions occurring at the solid-liquid or the solid-liquid-gas interface. In particular, nanostructured Mn-based oxides such as one-dimensional MnO2 nanostructures, MnO2-conductive matrix nanocomposites, concentration-gradient structured layered Li-rich Mn-based oxides, porous LiNi0.5Mn1.5O4 nanorods, core-shell structured LiMnSiO4@C nanocomposites, spinel-type Co-Mn-O nanoparticles, and perovskite-type CaMnO3 with micro-nano structures all display superior electrochemical performance. This review should shed light on the sustainable development of advanced batteries and pseudocapacitors with nanostructured Mn-based oxides.

Growth of Polypyrrole Ultrathin Films on MoS2 Monolayers as High-Performance Supercapacitor Electrodes

Abstract: A scalable solution-based approach is developed to controllably grow PPy ultrathin films on 2D MoS2 monolayers. When these sandwiched nanocomposites are utilized as supercapacitor electrodes, a record high specific capacitance, remarkable rate capability, and improved cycling stability are achieved, offering a feasible solution to create the next generation of energy-storage device with superior power density and energy density.

All-Solid-State Symmetric Supercapacitor Based on Co3O4 Nanoparticles on Vertically Aligned Graphene

Abstract: We have synthesized the hybrid supercapacitor electrode of Co3O4 nanoparticles on vertically aligned graphene nanosheets (VAGNs) supported by carbon fabric. The VAGN served as an excellent backbone together with the carbon fabric, enhancing composites to a high specific capacitance of 3480 F/g, approaching the theoretical value (3560 F/g). A highly flexible all-solid-state symmetric supercapacitor device was fabricated by two pieces of our Co3O4/VAGN/carbon fabric hybrid electrode. The device is suitable for different bending angles and delivers a high capacitance (580 F/g), good cycling ability (86.2% capacitance retention after 20 000 cycles), high energy density (80 Wh/kg), and high power density (20 kW/kg at 27 Wh/kg). These excellent electrochemical performances, as a result of the particular structure of VAGN and the flexibility of the carbon fabric, suggest that these composites have an enormous potential in energy application.

Wearable energy-dense and power-dense supercapacitor yarns enabled by scalable graphene–metallic textile composite electrodes

Abstract: One-dimensional flexible supercapacitor yarns are of considerable interest for future wearable electronics. The bottleneck in this field is how to develop devices of high energy and power density, by using economically viable materials and scalable fabrication technologies. Here we report a hierarchical graphene-metallic textile composite electrode concept to address this challenge. The hierarchical composite electrodes consist of low-cost graphene sheets immobilized on the surface of Ni-coated cotton yarns, which are fabricated by highly scalable electroless deposition of Ni and electrochemical deposition of graphene on commercial cotton yarns. Remarkably, the volumetric energy density and power density of the all solid-state supercapacitor yarn made of one pair of these composite electrodes are 6.1 mWh cm(-3) and 1,400 mW cm(-3), respectively. In addition, this SC yarn is lightweight, highly flexible, strong, durable in life cycle and bending fatigue tests, and integratable into various wearable electronic devices.

Nanostructured Mo-based electrode materials for electrochemical energy storage

Abstract: The development of advanced energy storage devices is at the forefront of research geared towards a sustainable future. Nanostructured materials are advantageous in offering huge surface to volume ratios, favorable transport features, and attractive physicochemical properties. They have been extensively explored in various fields of energy storage and conversion. This review is focused largely on the recent progress in nanostructured Mo-based electrode materials including molybdenum oxides (MoOx, 2 ≤ x ≤ 3), dichalconides (MoX2, X = S, Se), and oxysalts for rechargeable lithium/sodium-ion batteries, Mg batteries, and supercapacitors. Mo-based compounds including MoO2, MoO3, MoO3−y (0 < y < 1), MMoxOy (M = Fe, Co, Ni, Ca, Mn, Zn, Mg, or Cd; x = 1, y = 4; x = 3, y = 8), MoS2, MoSe2, (MoO2)2P2O7, LiMoO2, Li2MoO3, etc. possess multiple valence states and exhibit rich chemistry. They are very attractive candidates for efficient electrochemical energy storage systems because of their unique physicochemical properties, such as conductivity, mechanical and thermal stability, and cyclability. In this review, we aim to provide a systematic summary of the synthesis, modification, and electrochemical performance of nanostructured Mo-based compounds, as well as their energy storage applications in lithium/sodium-ion batteries, Mg batteries, and pseudocapacitors. The relationship between nanoarchitectures and electrochemical performances as well as the related charge-storage mechanism is discussed. Moreover, remarks on the challenges and perspectives of Mo-containing compounds for further development in electrochemical energy storage applications are proposed. This review sheds light on the sustainable development of advanced rechargeable batteries and supercapacitors with nanostructured Mo-based electrode materials.

Controlled Growth of NiMoO4 Nanosheet and Nanorod Arrays on Various Conductive Substrates as Advanced Electrodes for Asymmetric Supercapacitors

Abstract: Hierarchical NiMoO4 architectures assembled from well-aligned uniform nanosheets or nanorods are successfully grown on various conductive substrates using a facile and effective general approach. Importantly, the nanostructures of NiMoO4 can be easily controlled to be nanosheets or nanorods by using different solvents. By virtue of their intriguing structure features, NiMoO4 nanosheets as integrated additive-free electrodes for supercapacitors manifest higher Faradaic capacitance than NiMoO4 nanorods. Moreover, an asymmetric supercapacitor (ASC) is constructed using the as-prepared NiMoO4 nanosheets as the positive electrode and activated carbon (AC) as the negative electrode. The optimized ASC with an extended operating voltage range of 0–1.7 V displays excellent electrochemical performance with a high energy density of 60.9 Wh kg−1 at a power density of 850 W kg−1 in addition to superior rate capability. Furthermore, the NiMoO4//AC ASC device exhibits remarkable cycling stability with 85.7% specific capacitance retention after 10 000 cycles. The results show that these NiMoO4-based nanostructures are promising for high-energy supercapacitors.

Ultrahigh volumetric capacitance and cyclic stability of fluorine and nitrogen co-doped carbon microspheres

Abstract: Highly porous nanostructures with large surface areas are typically employed for electrical double-layer capacitors to improve gravimetric energy storage capacity; however, high surface area carbon-based electrodes result in poor volumetric capacitance because of the low packing density of porous materials. Here, we demonstrate ultrahigh volumetric capacitance of 521 F cm−3 in aqueous electrolytes for non-porous carbon microsphere electrodes co-doped with fluorine and nitrogen synthesized by low-temperature solvothermal route, rivaling expensive RuO2 or MnO2 pseudo-capacitors. The new electrodes also exhibit excellent cyclic stability without capacitance loss after 10,000 cycles in both acidic and basic electrolytes at a high charge current of 5 A g−1. This work provides a new approach for designing high-performance electrodes with exceptional volumetric capacitance with high mass loadings and charge rates for long-lived electrochemical energy storage systems. Carbon-based supercapacitors often suffer from poor volumetric capacitance due to the low packing density which arises from attempts to increase the electrode surface area. Here, in contrast, the authors fabricate N and F co-doped non-porous solid carbon spheres and achieve exceptional performances.

Engineering three-dimensional hybrid supercapacitors and microsupercapacitors for high-performance integrated energy storage

Abstract: Supercapacitors now play an important role in the progress of hybrid and electric vehicles, consumer electronics, and military and space applications. There is a growing demand in developing hybrid supercapacitor systems to overcome the energy density limitations of the current generation of carbon-based supercapacitors. Here, we demonstrate 3D high-performance hybrid supercapacitors and microsupercapacitors based on graphene and MnO2 by rationally designing the electrode microstructure and combining active materials with electrolytes that operate at high voltages. This results in hybrid electrodes with ultrahigh volumetric capacitance of over 1,100 F/cm3. This corresponds to a specific capacitance of the constituent MnO2 of 1,145 F/g, which is close to the theoretical value of 1,380 F/g. The energy density of the full device varies between 22 and 42 Wh/l depending on the device configuration, which is superior to those of commercially available double-layer supercapacitors, pseudocapacitors, lithium-ion capacitors, and hybrid supercapacitors tested under the same conditions and is comparable to that of lead acid batteries. These hybrid supercapacitors use aqueous electrolytes and are assembled in air without the need for expensive “dry rooms” required for building today’s supercapacitors. Furthermore, we demonstrate a simple technique for the fabrication of supercapacitor arrays for high-voltage applications. These arrays can be integrated with solar cells for efficient energy harvesting and storage systems.

Conducting polymer-based flexible supercapacitor

Abstract: Flexible supercapacitors, a state-of-the-art material, have emerged with the potential to enable major advances in for cutting-edge electronic applications. Flexible supercapacitors are governed by the fundamentals standard for the conventional capacitors but provide high flexibility, high charge storage and low resistance of electro active materials to achieve high capacitance performance. Conducting polymers (CPs) are among the most potential pseudocapacitor materials for the foundation of flexible supercapacitors, motivating the existing energy storage devices toward the future advanced flexible electronic applications due to their high redox active-specific capacitance and inherent elastic polymeric nature. This review focuses on different types of CPs-based supercapacitor, the relevant fabrication methods and designing concepts. It describes recent developments and remaining challenges in this field, and its impact on the future direction of flexible supercapacitor materials and relevant device fabrications.

Probing the Mechanism of High Capacitance in 2D Titanium Carbide Using In Situ X-Ray Absorption Spectroscopy

Abstract: The field of supercapacitors (electrochemical capacitors) is constantly evolving. The global motivation is to create devices that possess a significant energy density without compromising the power density. To achieve this goal, new materials must be discovered and complex electrode architectures developed.

Hydrous Ruthenium Oxide Nanoparticles Anchored to Graphene and Carbon Nanotube Hybrid Foam for Supercapacitors

Abstract: In real life applications, supercapacitors (SCs) often can only be used as part of a hybrid system together with other high energy storage devices due to their relatively lower energy density in comparison to other types of energy storage devices such as batteries and fuel cells. Increasing the energy density of SCs will have a huge impact on the development of future energy storage devices by broadening the area of application for SCs. Here, we report a simple and scalable way of preparing a three-dimensional (3D) sub-5 nm hydrous ruthenium oxide (RuO2) anchored graphene and CNT hybrid foam (RGM) architecture for high-performance supercapacitor electrodes. This RGM architecture demonstrates a novel graphene foam conformally covered with hybrid networks of RuO2 nanoparticles and anchored CNTs. SCs based on RGM show superior gravimetric and per-area capacitive performance (specific capacitance: 502.78 F g−1, areal capacitance: 1.11 F cm−2) which leads to an exceptionally high energy density of 39.28 Wh kg−1 and power density of 128.01 kW kg−1. The electrochemical stability, excellent capacitive performance, and the ease of preparation suggest this RGM system is promising for future energy storage applications.

Carbon-Stabilized High-Capacity Ferroferric Oxide Nanorod Array for Flexible Solid-State Alkaline Battery–Supercapacitor Hybrid Device with High Environmental Suitability

Abstract: Iron oxides are promising to be utilized in rechargeable alkaline battery with high capacity upon complete redox reaction (Fe3+ Fe0). However, their practical application has been hampered by the poor structural stability during cycling, presenting a challenge that is particularly huge when binder-free electrode is employed. This paper proposes a “carbon shell-protection” solution and reports on a ferroferric oxide–carbon (Fe3O4–C) binder-free nanorod array anode exhibiting much improved cyclic stability (from only hundreds of times to >5000 times), excellent rate performance, and a high capacity of ≈7776.36 C cm−3 (≈0.4278 C cm−2; 247.5 mAh g−1, 71.4% of the theoretical value) in alkaline electrolyte. Furthermore, by pairing with a capacitive carbon nanotubes (CNTs) film cathode, a unique flexible solid-state rechargeable alkaline battery-supercapacitor hybrid device (≈360 μm thickness) is assembled. It delivers high energy and power densities (1.56 mWh cm−3; 0.48 W cm−3/≈4.8 s charging), surpassing many recently reported flexible supercapacitors. The highest energy density value even approaches that of Li thin-film batteries and is about several times that of the commercial 5.5 V/100 mF supercapacitor. In particular, the hybrid device still maintains good electrochemical attributes in cases of substantially bending, high mechanical pressure, and elevated temperature (up to 80 °C), demonstrating high environmental suitability.

Self-Assembled Three-Dimensional Graphene Macrostructures: Synthesis and Applications in Supercapacitors

Abstract: ConspectusGraphene and its derivatives are versatile building blocks for bottom-up assembly of advanced functional materials. In particular, with exceptionally large specific surface area, excellent electrical conductivity, and superior chemical/electrochemical stability, graphene represents the ideal material for various electrochemical energy storage devices including supercapacitors. However, due to the strong π–π interaction between graphene sheets, the graphene flakes tend to restack to form graphite-like powders when they are processed into practical electrode materials, which can greatly reduce the specific surface area and lead to inefficient utilization of the graphene layers for electrochemical energy storage. The self-assembly of two-dimensional graphene sheets into three-dimensional (3D) framework structures can largely retain the unique properties of individual graphene sheets and has recently garnered intense interest for fundamental investigations and potential applications in diverse techn...

Iron Oxide-Decorated Carbon for Supercapacitor Anodes with Ultrahigh Energy Density and Outstanding Cycling Stability

Abstract: Supercapacitor with ultrahigh energy density (e.g., comparable with those of rechargeable batteries) and long cycling ability (>50000 cycles) is attractive for the next-generation energy storage devices. The energy density of carbonaceous material electrodes can be effectively improved by combining with certain metal oxides/hydroxides, but many at the expenses of power density and long-time cycling stability. To achieve an optimized overall electrochemical performance, rationally designed electrode structures with proper control in metal oxide/carbon are highly desirable. Here we have successfully realized an ultrahigh-energy and long-life supercapacitor anode by developing a hierarchical graphite foam–carbon nanotube framework and coating the surface with a thin layer of iron oxide (GF–CNT@Fe2O3). The full cell of anode based on this structure gives rise to a high energy of ∼74.7 Wh/kg at a power of ∼1400 W/kg, and ∼95.4% of the capacitance can be retained after 50000 cycles of charge–discharge. These pe...

Facile Synthesis of Hematite Quantum-Dot/Functionalized Graphene-Sheet Composites as Advanced Anode Materials for Asymmetric Supercapacitors

Abstract: For building high-energy density asymmetric supercapacitors, developing anode materials with large specific capacitance remains a great challenge. Although Fe2O3 has been considered as a promising anode material for asymmetric supercapacitors, the specific capacitance of the Fe2O3-based anodes is still low and cannot match that of cathodes in the full cells. In this work, a composite material with well dispersed Fe2O3 quantum dots (QDs, ≈2 nm) decorated on functionalized graphene-sheets (FGS) is prepared by a facile and scalable method. The Fe2O3 QDs/FGS composites exhibit a large specific capacitance up to 347 F g−1 in 1 m Na2SO4 between –1 and 0 V versus Ag/AgCl. An asymmetric supercapacitor operating at 2 V is fabricated using Fe2O3/FGS as anode and MnO2/FGS as cathode in 1 m Na2SO4 aqueous electrolyte. The Fe2O3/FGS//MnO2/FGS asymmetric supercapacitor shows a high energy density of 50.7 Wh kg−1 at a power density of 100 W kg−1 as well as excellent cycling stability and power capability. The facile synthesis method and superior supercapacitive performance of the Fe2O3 QDs/FGS composites make them promising as anode materials for high-performance asymmetric supercapacitors.

Facile self-templating large scale preparation of biomass-derived 3D hierarchical porous carbon for advanced supercapacitors

Abstract: Corn husk, a renewable biomass, has been successfully explored as a low-cost crude carbon source to prepare advanced higher-value 3D HPCs by means of KOH pre-treatment and direct pyrolysis, the synthesis route is simple, self-templating and easy to scale-up for industrialization. The CHHPCs present many advantages for supercapacitor applications, including higher surface area (928 m2 g−1), hierarchical porosity consisting of macro, meso, and micropores, a turbostratic carbon structure, uniform pore size, 3D architecture and rich O-doping (17.1 wt%). The supercapacitor performance of CHHPCs was evaluated in a 6 M KOH electrolyte and 1 M Na2SO4 electrolyte. The CHHPCs exhibit a high specific capacitance of 356 F g−1 and 300 F g−1 at 1 A g−1, 20 A g−1, respectively, ultra-high rate capability with 88% retention rate from 1 to 10 A g−1 and outstanding cycling stability with 95% capacitance retention after 2500 cycles. The CHHPCs symmetric supercapacitor display a high energy density of 21 W h kg−1 at a power density of 875 W kg−1 and retains as high as 11 W h kg−1 at 5600 W kg−1 in 1 M Na2SO4 electrolyte. The facile, efficient and template-free synthesis strategy for novel 3D-HPCs from biomass sources may promote commercial application of 3D-HPCs in the fields of supercapacitors, lithium ion batteries, fuel cells and sorbents.