Electrochemical Double Layer Supercapacitors Research Articles

Cross-linked and pillared graphene with nonconventional redox benzidine dimethyl ether for high-performance supercapacitors

To hinder Van der Waals-induced agglomeration between graphene sheets to increase specific surface area, and to supplement pseudocapacitance, graphene processing with active molecules is highly effective. Redox polymers and quinones, instead of aromatic ethers, were popular candidates. They were universally blended with graphene sheets through noncovalent modes, leading to issues of electrochemical stability and rate capability, etc. Herein, we broke through stereotype to develop aromatic ethers–benzidine with two remote methoxyls (i.e. 3,3′–dimethoxybenzidine, DMeOBD)–to covalently functionalize graphene, obtaining the cross-linked and pillared graphene electrode material (DMeOBD-rGO). It exhibited redox activity and featured a combination of electrochemical double layer supercapacitor and pseudocapacitor, thus yielded an enhanced specific capacitance of 363 F g−1. When assembled into two-electrode solid-state supercapacitors, the whole devices also delivered an impressive specific capacitance of 263 F g−1, and a high energy density of 13.2 Wh kg−1, along with excellent rate capability and cycling stability.

Guide for the development and evaluation of supercapacitors with the proposal of a novel design to improve their performance

Supercapacitors, as an energy storage device, have shown great potential as a tool to help solve today's energy problems. There are currently three types of supercapacitors: electrochemical double layer, pseudocapacitors and hybrid supercapacitors. They have aroused great interest due to their high-power density, fast charging and discharging and good cyclic behaviour, and nowadays, it is necessary to continue their study in order to extend their capabilities. This work proposes a design and fabrication method for supercapacitors with a materials guide that, firstly, guides researchers in the development of supercapacitors and, secondly, proposes an improvement of the current supercapacitor design to ensure parallelism of the collectors, avoid corrosive processes of the collectors using graphite and avoid pad breakage. All this is carried out with 3D design and additive manufacturing or 3D printing technologies, which means a reproducible solution with low available resources. In addition, the model proposed here avoids the breakage of the pads that act as electrodes by designing an intermediate body that prevents the Swagelok® cell thread from being consumed.

A Historical Review of Electrode Materials and Electrolytes for Electrochemical Double Layer Supercapacitors and Pseudocapacitors

The supercapacitor is one of the most promising alternatives to other popular energy storage solutions, viz., rechargeablebatteries and capacitors. They are considered the bridge between batteries (high energy density) and capacitors (high powerdensity) because of their fast charge/discharge capacity, high specific power/energy, and good service-life, which makethem the most promising candidate for future energy storage/redistribution systems as well as hybrid electric vehicles. In thepast, much progress has occurred in electrode materials, electrode architecture, electrolytes, separators, and deviceconfiguration. This review article discusse the basics of electrochemical super capacitors, storage principal, deviceconfiguration, electrode materials, and electrolytes, including the coverage of the comprehensive literature account of theadvancements in the area; and, finally, the discussion on technological challenges in the development of commerciallyviable next-gen supercapacitor devices.

Charging a electrochemical double layer supercapacitor exhibiting a distribution of relaxation times

A charging electrochemical double layer supercapacitor can usually be described by a single capacitance and a single resistance in parallel, wherein the latter represents the ohmic losses. Such an ideal behavior may occur if the supercapacitor consists of self-similar porous carbon micro- and nanostructures. However, if the electrochemical double layer supercapacitor consists of a sequence of slices with different relaxation times, a strong deviation from ideal charging curves may occur. Here, it is demonstrated how such charging curves can be interpreted in terms of a distribution of relaxation times. It is found that in the presence of a broad distribution of charge transfer resistances, the voltage initially appears to increase faster than normal during galvanostatic charging. Care should be taken to avoid misinterpretation of the capacitance under such circumstances.

Biopolymer Based Materials as Alternative Greener Binders for Sustainable Electrochemical Energy Storage Applications

AbstractIn this study, we address the most recent innovations in the field of sustainable and environment friendlier binders for electrochemical energy storage devices such as, supercapacitors and batteries accompanied by the explanation, how they could reduce the impacts of environment and cost and enhance the efficiency of the energy equipment. Hitherto, the number of sustainable and environment friendlier binders are categorized according to their chemical composition, processability and natural availability. Different electrochemical devices are being employed to investigate their wide‐ranging advantages. Among them the most commonly employed devices are lithium‐ion batteries (LIBs) and electrochemical double layer supercapacitors (ECDSs). A detailed insight into the anodic half as well as cathodic half has been presented. The Si derived anodes exhibit enhanced capacitive performance as a result of increased cycling ability. This feature owes from the greater interactions between the functionalities and surface of the active particles of the anode material for example, polysaccharides such as carboxymethyl cellulose (CMC)/nanocellulose (NC). On the other hands the transition to water‐processable cathodes is more complicated compared to anodes. Among various polysaccharides, the NC has gained considerable attention as a sustainable and environment friendlier class of greener materials. Herein, we have discussed the role of NC based electrode materials with applications in supercapacitors and batteries. Finally, a comprehensive overview based on the documented work and current views for the further development of NC based aqueous electrodes in the field of electrochemical energy storage devices are discussed.

Few-Layer Graphene As an Electrode, Electrode Additive and an Interfacial Layer in Aqueous Supercapacitors

The intermittent nature of many renewable energy sources such as wind and solar, coupled with fluctuations in energy demand, creates a pressing need for efficient, low-cost energy storage technologies. Supercapacitors are promising candidates to play a role in next-generation energy storage systems. They have a higher power density and better cycle life (although lower energy density) than batteries making them ideal for rapid energy storage and deployment [1]. Activated carbon is a favoured electrode material due to high surface area, although low conductivity requires use of a conductive additive (often carbon black), reducing available surface area for charge storage. In contrast, the high conductivity and specific surface area of graphene has made it a promising material for electrochemical double layer supercapacitors (EDLCs) [2], however, performance is limited by restacking of the graphene sheets, reducing available surface area.In this work, high-shear exfoliated few layer graphene (FLG) [3] is investigated both as an electrode material and as a conductive additive/interfacial layer for EDLCs. FLG suspensions were produced under a variety of exfoliation conditions, with platelet thickness and linear dimension determined from Raman spectroscopy based on metrics developed by Backes et al. [4] and through scanning electron microscopy (SEM).The FLG suspensions were used in three ways: i) to create thin ‘graphene paper’ electrodes; ii) as a conductive additive, mixed into the activated carbon electrode material; iii) deposited onto the back of (and diffused within) activated carbon electrodes. These electrodes were investigated by Raman spectroscopy and Scanning Electron Microscopy, before being assembled into symmetric two-terminal aqueous cells then evaluated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS), and their electrochemical performance related to structure and composition.As expected, pure FLG electrodes often showed excellent low series resistance values, however specific capacitance was low, due to restacking. Directly mixing 5% FLG into activated carbon as a conventional conductive additive led to a specific capacitance of 63 F/g (from CV at 10 mV/s), and a series resistance of 19 W (from GCD at 1 A/g) - markedly inferior to those with 5% carbon black as a conductive additive (95 F/g and 2 Ohm) and inferior even to electrodes with no conductive additive (87 F/g and 10 Ohm).However, post fabrication deposition/infusion of FLG offers comparable performance to carbon black (90 F/g and 1 Ohm) at 7% FLG by weight. As the quantity of FLG is increased the specific capacitance decreases sharply. This behaviour is attributed to FLG restacking on the rear of the electrode, so adding mass whilst providing limited additional capacitance, and compression of the electrode.Adding high-shear exfoliated FLG to activated carbon electrodes shows promise for obtaining the benefits of both materials. At present, FLG/activated carbon electrodes can match the performance of those produced from activated carbon with a carbon black conductive additive and, with further optimization, we expect will be able to exceed them.Figure: a) Cross sectional SEM image of activated carbon electrode with graphene interfacial layer; b) magnified cross sectional SEM image of graphene interfacial layer; c) cyclic voltammograms at 10 mV/s of the different electrodes mentioned in the abstract.

An electrochemical route to exfoliate vein graphite into graphene with black tea

The study is focused on exfoliating vein graphite into graphene using an unsophisticated and low-cost process through a non-oxidative production route. High-quality graphene production with low-cost methods that give high yields and suitable for large-scale production, using vein graphite is a challenge to address, though there are many methods for graphene production. Vein graphite directly received from the mining site was electrochemically exfoliated to small particles which were further exfoliated by ultrasonic vibration. In addition, commonly used highly toxic, expensive solvents were substituted by inexpensive and nontoxic aqueous black tea solution, in the exfoliation by ultrasonic vibration process. Four different tea types were used to compare the quality and quantity of yields. Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and Raman spectroscopy were utilized for the characterization, and the study uncovers a low-cost, nontoxic, promising and nonoxidative route to exfoliate vein graphite into either single or double-layer graphene. The study uncovers that the four different tea types tested can be used to successfully exfoliate graphite. The suitability of the exfoliated graphene for applications was checked by utilizing them to prepare electrochemical double layer supercapacitors (EDLC). Electrochemical properties of fabricated EDLC were investigated by cyclic voltammetry (CV) and Galvanostatic charge-discharge curves (GCD). Graphene based EDLC exhibited energy density of 0.385 W h kg−1 and a power density of 17.3 W kg−1 for the 0.01 V s−1 scan rate.

Gel electrolytes and aerogel electrodes from ILs-based emulsions for supercapacitor applications

Electrochemical double-layer supercapacitors as advanced energy storage devices have the properties of portability and stable performance. Electrode materials and functional electrolytes as important components of supercapacitors have become the most research filed. Here, we strategically established an oil-in-water (O/W) emulsion, which was synergistically stabilized by a cationic polymerizable ionic liquids ([VCnIm]Br) and similarly charged upconversion nanoparticles (UCNPs). The O/W emulsion was used as template to prepare emulsion gel by polymerizing monomers of [VCnIm]Br (n = 4 and 12) in the continuous phase. When using monomer, [VC4Im]Br, the emulsion gels can be acted as electrolytes, showing considerably high ionic conductivity (8.42 mS cm−1), excellent mechanical strength, superior thermal stability and freezing resistance. While monomer, [VC12Im]Br, was used, the hierarchically porous aerogels were obtained after the emulsion gel being freeze-dried. The all-solid-state supercapacitors were fabricated by assembling the emulsion gels as electrolytes and the aerogels as electrode materials. UCNPs not only served as the stabilizer to synergistically stabilize the O/W emulsion, but also can act as a photovoltaic converter achieving photoelectric conversion performance. The supercapacitor presents large energy density, power density, and promising stability.

Potassium Hydroxide Doped With (Poly(Methyl Methacrylate) (PMMA) Polymer as Electrolyte for Electrolytic Double layer Supercapacitor (EDLC) Application

The prime objective of the present paper is to develop polymer electrolyte doped with salt. A solution cast technique was adopted to develop a solid polymer electrolyte of polymer (Poly (methyl methacrylate) (PMMA) as host polymer and salt potassium hydroxide, KOH as dopant. Incorporation of salt increases the amophosity and homogeneity, decreases the surface roughness. Moreover, doping of salt (KOH) increases the overall conductivity of polymer electrolyte film. Electrochemical impedance spectroscopy (EIS) reveals the enhancement in conductivity (4 orders of magnitude) by salt doping. FTIR shows the complexation and composite nature of films. Polarized optical microscopy (POM) shows reduction in crystallinity which is further confirmed by Differential scanning calorimetry (DSC). Fabricated electrochemical double-layer supercapacitor using maximum conducting polymer salt electrolyte and symmetric carbon nanotubes electrodes shows specific capacitance of 21.86.
 Keywords: Polymer electrolyte; conductivity; DSC; FTIR

Stable Electrodes Fabricated from Carbon Fibers for Electrochemical Double Layer Supercapacitors, Pseudocapacitors and Zn-Air Batteries

The ever-increasing demand for sustainable energy has led to the development of inexpensive energy storage devices. The electrode material is one of the most important parts of an energy storage device; the electrode material has a major impact on the device’s price, sustainability, environmental friendliness, performance and lifetime.Asphaltene, as a high carbon content by-product of the oil sands industry, currently has a higher supply than demand. Furthermore, asphaltene can be used to prepare low-cost carbon fibers (CFs) as the electrode material in energy storage devices. Electrochemical double layer supercapacitors (EDLCs), pseudocapacitors and the air-electrode in Zn-air batteries (ZABs) were prepared in this study by using asphaltene based CF.Activated carbon fibers (ACFs) were prepared by chemically activating the CF derived from asphaltene produced in Alberta, Canada. ACFs were used to prepare stable, high performance and flexible EDLC and birnessite MnO2 type pseudocapacitors. CFs were also used as a conductive base layer for spinel type MnCo2O4, which is an efficient electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). MnCo2O4 coated CFs were used to prepare stable and high efficiency homemade air electrodes for ZAB.ACFs, that were used as the active material in an aqueous EDLC, had a specific surface area of 2290 m2 g-1 and total porosity (pore volume) of 1.27 cm3 g-1, which includes 0.88 cm3 g-1 of micropores (pore width < 2 nm) and 0.29 cm3 g-1 of mesopores (2 nm < pore width < 50 nm). The maximum specific capacitance (Cs) reached was 311 F g-1 at a specific current (is) of 0.04 A g-1; this was reduced to 248 F g-1 at a specific current of 1 A g-1. Capacitance retention of this EDLC was 91% after 10,000 cycles. This material was later used in an EDLC device with an ionic liquid electrolyte (EMIMBF4, 1-ethyl-3-methylimidazolium tetrafluoroborate); ionic liquid electrolytes provide wider voltage windows. As a result, a specific energy (Es) of 35.7 Wh kg-1 was achieved at a power density (Ps) of 525.4 W kg-1. These values are comparable to energy and power values delivered by some batteries.Birnessite-type MnO2 (δ-MnO2) is a promising material for charge storage devices like pseudocapacitors (slower charge/discharge compared with EDLCs but faster charge/discharge compared with batteries). However, the insulating nature of δ-MnO2 limits its electrochemical performance. Because of the high performance and high conductivity of ACF used in EDLC devices, this material was chosen to fabricate ACF/δ-MnO2 composite electrodes to enhance capacitive performance of δ-MnO2. δ-MnO2 was coated onto ACFs through a hydrothermal process. The crystal structure of δ-MnO2 was subsequently thermally modified to reduce its crystallinity by introducing oxygen deficient defects. These defects acted as active sites to enhance electrolyte ion adsorption/desorption, which improved the capacitive performance. The maximum Cs reached for the composite electrode was 327 F g-1 at a specific current of 0.04 A g-1, which was significantly improved compared to the δ-MnO2 powder (not coated on ACF, 195 F g-1 at 0.04 A g-1). Capacitance retention for the composite electrode was 93% (initial capacitance of 298 F g-1 and final capacitance of 279 F g-1 at 1 A g-1), while the retention for the δ-MnO2 powder was 64% (from 154 F g-1 to 98 F g-1) after 10,000 cycles.CFs were utilized to prepare homemade gas diffusion layers (GDLs) for use in air electrodes in ZABs. Air electrodes were prepared with CF carbonized at three different temperatures, i.e., 500 oC, 800 oC and 1500 oC. the ORR and OER activity of the homemade air-electrodes, as well as commercially purchased electrodes, were tested in 1 M KOH. All homemade electrodes showed much better OER activity than the purchased ones. ORR activity was similar for both commercial electrodes and homemade electrodes prepared with CF at 1500 oC (CF-1500). CF-1500 was coated with spinel type MnCo2O4 via a facile sonication procedure. MnCo2O4 coated CF-1500 had excellent catalytic activity towards both ORR and OER, outperforming the bench mark Pt-RuO2 catalyst. The cycling behavior of CF-100 was very stable with initial and final efficiencies of ~63% and ~58%, respectively, after 200 cycles (100 h) of charge and discharge at 10 mA cm-2.

Fabrication and Supercapacitor Applications of Multiwall Carbon Nanotube Thin Films

Multiwalled carbon nanotubes (MWCNTs) are a one-dimensional nanomaterial with several desirable material properties, including high mechanical tensile modulus and strength, high electrical conductivity, and good thermal conductivity. A wide variety of techniques have been optimized to synthesize MWCNTs and to fabricate thin films of MWCNTs. These synthesis and fabrication methods vary based on precursor materials, process parameters, and physical and chemical principals, and have a strong influence on the properties of the nanotubes and films. Thus, the fabrication methods determine the performance of devices that can exploit the advantageous material properties of MWCNTs. Techniques for the fabrication of carbon nanotubes and carbon nanotube thin films are reviewed, followed by a discussion of the use of MWCNTs as an electrode material for electrochemical double-layer supercapacitors (EDLCs). EDLCs feature high power density, excellent reversibility and lifetime, and improved energy density over electrolytic capacitors. Beyond surveying fabrication techniques previously explored for MWCNT electrodes, an alternative approach based on inkjet printing capable of depositing a small amount of active material is discussed. Such an approach allows for a high degree of control over electrode properties and can potentially reduce cost and active material waste, which are essential components to the gradual conversion to green energy.

Waste coffee grounds derived nanoporous carbon incorporated with carbon nanotubes composites for electrochemical double-layer capacitors in organic electrolyte

Carbon nanotube (CNT)-incorporated nanoporous carbon (NPC) derived from the waste coffee ground composite was proposed as a potential electrode material for electrochemical double layer supercapacitors with an organic electrolyte. CNT-incorporated NPC pastes with different CNT contents were fabricated via a simple ball-milling method and then coated on a carbon nanofiber paper using a doctor blade technique. According to structural characterization data, the 3%CNT/NPC material offered a high specific surface area of 1157.8 m2 g−1 with a small average pore diameter of 1.42 nm owing to the intercalation of CNT structures between the NPC flakes. From electrochemical measurements, a coin cell using 3%CNT/NPC in 1 M TEABF4/ACN exhibited a high specific capacitance of 132 Fg−1 and a high specific energy of 37.7 Wh kg−1 at 0.5 Ag−1, which are considerably higher than those using NPC (74 Fg−1 and 20.1 Wh kg−1) and CNT (48 Fg−1 and 14.7 Wh kg−1). In addition, the composite possessed higher rate capability, better cycling stability, and lower self-discharge rate compared with NPC and CNT electrodes. Hence, the 3%CNT/NPC composite was promising as an active material for producing advanced supercapacitors.

Flax-Derived Carbon: A Highly Durable Electrode Material for Electrochemical Double-Layer Supercapacitors.

Owing to their low cost, good performance, and high lifetime stability, activated carbons (ACs) with a large surface area rank among the most popular materials deployed in commercially available electrochemical double-layer (EDLC) capacitors. Here, we report a simple two-step synthetic procedure for the preparation of activated carbon from natural flax. Such ACs possess a very high specific surface area (1649 m2 g–1) accompanied by a microporous structure with the size of pores below 2 nm. These features are behind the extraordinary electrochemical performance of flax-derived ACs in terms of their high values of specific capacitance (500 F g–1 at a current density of 0.25 A g–1 in the three-electrode setup and 189 F g–1 at a current density of 0.5 A g–1 in two-electrode setup.), high-rate stability, and outstanding lifetime capability (85% retention after 150,000 charging/discharging cycles recorded at the high current density of 5 A g–1). These findings demonstrate that flax-based ACs have more than competitive potential compared to standard and commercially available activated carbons.

Jute Sticks Derived and Commercially Available Activated Carbons for Symmetric Supercapacitors with Bio‐electrolyte: A Comparative Study

The fabrication of eco-benign, low cost, and high-performance supercapacitors comprising hierarchical porous electrodes and superior electrolytes are crucial for effective energy storage. In this study, a comparison of electrochemical performances between jute sticks derived activated carbon (JC) and commercially available activated carbon (AC) based symmetric supercapacitors was carried out. We developed highly effective porous activated hierarchical carbon nanosheets through the pyrolysis of abundantly available jute sticks. Electrochemical double-layer supercapacitor devices were assembled utilizing JC and AC based electrodes with glycerol-based bio-electrolyte. The developed JC-based supercapacitor exhibit a negligible IR drop compared to the AC-based supercapacitor, attributed to low charge transfer resistance in the prepared JC. The results showed that the JC-based supercapacitor provides higher specific capacitance (150 F/g) than the AC-based supercapacitor (29 F/g) at a scan rate of 10 mV/sec. The JC-based supercapacitor illustrates a specific energy density of 20 Wh/kg at a specific power density of 500 W/kg with fabulous performance after 10,000 charge/discharge cycles. The series and parallel connection tests demonstrate a stable behavior and indicate that the specific capacitance and operating potential windows of the JC-based supercapacitor can be tuned. In addition, the fabricated JC-based supercapacitor shows mechanical robustness at different bending positions. Our findings confirm that the processed bio-waste shows promise as energy storage materials.

Fabrication of Rambutan-like Activated Carbon Sphere/Carbon Nanotubes and Their Application as Supercapacitors

Developing advanced electrochemical double-layer supercapacitors (EDLCs) with high energy density and capacitance can be realized by exploring the electrodes possessing large specific surface area ...

Green synthesis of high-performance supercapacitor electrode materials from agricultural corncob waste by mild potassium hydroxide soaking and a one-step carbonization

Porous carbons derived from waste biomass are distinguished active materials for developing high performance, low-cost and environmental-friendly electrochemical double layer supercapacitors. However, efficient control over the microstructure of biomass activated carbons to achieve high capacitor performance still remains a challenge. Herein, agricultural waste biomass corncobs that were simply chopped were demonstrated to be effectively activated via facile KOH solution soaking at room temperature prior to a one-step carbonization process. The electrode material showed a high capacity of 394.9 F g−1, at a current density of 1 A g−1 in a three-electrode system in a 6 M KOH aqueous electrolyte solution. Corncobs, carbonized at 750 °C, were further assembled into coin-type symmetrical devices, and displayed a high energy density of 8.9 W h kg−1, achieving outstanding cycling stability (99 % life time retention after 10,000 cycles). Through this green and energy-efficient process, the natural hierarchical nature of the corncob was fully utilized and partly preserved, and the obtained porous carbon has high degree of graphitization and effective specific surface area with improved electrochemical performance. These porous carbons are expected to become ideal active materials for high-performance supercapacitors. The mild KOH soaking coupled with the one-step carbonization method developed herein is considered as a facile way to up-scale production of functional carbon materials from waste biomass.

Electrochemical characterization of RuO2 and activated carbon (AC) electrodes using multivalent Ni(NO3)2 electrolyte for charge storage applications

Among various transition metal oxides, Ruthenium oxide (RuO2) has been widely studied for its high ionic conductivity, excellent electrochemical reversibility and superior pseudocapacitive properties. However, it is significantly expensive from the practical applications point of view. On the other hand, activated carbon (AC) has been an attractive choice for electrochemical double layer supercapacitors due to its tailorable porosity and surface area, high electronic conductivity and low cost. In the current study, we examined the electrochemical behavior of nanocrystalline RuO2 against AC in an asymmetric configuration using a multivalent aqueous Ni(NO3)2 electrolyte with a purpose to understand the applicability of a multivalent and inexpensive Ni based electrolyte for charge storage in RuO2 electrodes. The electrochemical characterization of asymmetric RuO2/AC cells in 1M aqueous Ni(NO3)2 electrolyte revealed a maximum specific capacitance of 248 Fg−1 for RuO2 electrodes with a retention of 93.9% of its initial capacitance over one thousand cycles. These results demonstrated the viability of charge storage in RuO2 and AC electrodes using multivalent Ni2+ ion/electrolyte while shedding the light on possible changes in the crystallinity and surface chemistry of RuO2 electrode.

Superior Performance of Electrochemical Double Layer Supercapacitor Made with Asphaltene Derived Activated Carbon Fibers

High energy and power values are obtained from fabricated electrochemical double layer supercapacitor (EDLS) cells derived from asphaltene precursors, which are a solid by‐product of bitumen extraction in pentane solvents. Chemical activation, using dry KOH, is used to activate carbon fibers. Chemical activation introduces high specific surface areas (SSAs) into the fiber microstructure by partially etching the carbon. The electrodes are prepared by mixing activated fibers, polytetrafluoroethylene (PTFE), and acetylene black to form flexible electrode films. The unique bimodal pore size distribution with large micropore and mesopore volumes (micropore volume as high as 0.88 cm3 g−1), from chemical activation, generate high‐performance EDLS symmetric cells with capacitance values exceeding 310 F g−1 in aqueous electrolytes and 210 F g−1 in ionic liquid electrolytes (at a specific current of 40 mA g−1). A specific energy of 36 Wh kg−1 at a specific power of 525 W kg−1 is reached in ionic liquid electrolytes.

Advanced Battery‐Type Anode Materials for High‐Performance Sodium‐Ion Capacitors

AbstractHigh‐efficiency energy storage technologies and devices have gained numerous attention because of their ever‐increasing requirement. Sodium‐ion capacitors (SICs), as a burgeoning electrochemical energy storage device, combine virtues of rechargeable batteries and electrochemical double layer supercapacitors, delivering both high energy–power density and long cycling life. In the past decades, great efforts have been made to find suitable anode material to conquer the kinetic imbalance between the battery‐type anode with sluggish bulk redox reaction and the capacitor‐type cathode with fast ion absorption/desorption process. By exploring high‐rate performance anode materials, the great reaction kinetic gap between cathodes and anodes can be narrowed down, which directly affects the energy–power densities of SICs. In this article, an overview of advanced battery‐type anode materials is offered for high‐performance SICs with an emphasis on anode structural design and improved energy–power density, including carbonaceous materials, metallic compounds, MXene, organic polymers, and so on. Furthermore, the implementation of presodiation for the sake of optimizing the SICs is also illustrated. Finally, the challenges faced and the perspectives for future developing trends of SICs are discussed.

Activated Carbons From Winemaking Biowastes for Electrochemical Double-Layer Capacitors.

Revalorizing organic biowaste is critical to achieve a full circular economy, where waste is transformed into resources. One of the main strategies is to produce activated carbons and use them as functional materials for electrochemical energy storage. In this study, winemaking wastes, bagasse (BAG), and cluster stalks (CS) were recovered and used in the preparation of activated carbons by a hydrothermal process. Then, they were chemically activated using KOH and investigated for electrochemical capacitor applications. The activation treatment resulted in microporous structures, characterized by a type I isotherm for low partial pressures (P/P0), and a type IV for higher pressures, as observed by Brunauer–Emmett–Teller surface analysis, with specific surfaces of 1,861 and 2,662 m2·g−1 for BAG and CS, respectively. These microporous structures were also investigated by means of scanning electron microscopy, revealing a high porous degree. Micro-Raman spectroscopy and X-ray photoelectron spectroscopy measurements displayed bands associated to disorder of the structure of the carbonaceous material. The electrochemical performance of the resulting materials was investigated for electrochemical energy storage applications, as supercapacitor electrode, in 1 M KOH aqueous electrolyte. These biowaste-derived materials displayed electrochemical double-layer capacitance, with 129 F·g−1 at 10 A·g−1 in the 0.1 to −1.0 V vs. saturated calomel electrode. For that reason, they are pin-pointed as potential negative electrodes for electrochemical double-layer supercapacitors and hybrid or asymmetric supercapacitors.