Supercapacitors In Organic Electrolyte Research Articles

Synthesis of porous carbon with low oxygen content from fulvic acid for high voltage organic supercapacitors

The operating voltage of over 3.0 V is a severe challenge for commercial supercapacitors in organic electrolyte, which raises rigorous requirements for the structure and composition characteristics of porous carbon. There are few reports regarding the construction of ultra-high voltage withstanding porous carbon derived from cheap biomass carbon sources. Herein, using cheap and renewable fulvic acid (FA) and graphene oxide (GO) as carbon precursors, the ultra-high withstanding voltage 2D porous carbon nanosheets are synthesized through KOH activation and annealing treatment, assisted by the π-π conjugation and hydrogen bonding. The incorporation of GO plays an important role in modulating the 2D nanosheet morphology of FA derived porous carbon, enhancing the e-conductivity and reducing the OFGs of porous carbons, which makes significant contribution to improving the structural stability and electrochemical performance of material. The obtained FG1% C/C composite simultaneously exhibits high specific surface area (2593 m2/g) and desirable e-conductivity (101 S m−1). More critically, it possesses highly stable surface chemical microenvironment with very-low surface oxygen content of 2.7 at.%, mainly existing as stable ether and quinone bonds. Thus, FG1% exerts ultra-high withstanding voltage up to 3.3 V in commercial TEABF4/PC electrolyte with the maximum energy density of 68.6 Wh kg−1, superior to most of the literatures, also it shows excellent stability throughout its lifespan, maintaining improved capacity retention rate (88.9%) at 2.5 A/g over 10,000 cycles. This work pares the way for the architecture design of high withstanding voltage porous carbon.

Study on the Application of Nitrogen-Doped Holey Graphene in Supercapacitors with Organic Electrolyte.

We present a facile low-cost method to produce nitrogen-doped holey graphene (N-HGE) and its application to supercapacitors. A composite of N-HGE and activated carbon (AC) was used as the electrode active material in organic-electrolyte supercapacitors, and the performances were evaluated. Melamine was mixed into graphite oxide (GO) as the N source, and an ultra-rapid heating method was used to create numerous holes during the reduction process of GO. X-ray photoelectron spectra confirmed the successful doping with 2.9-4.5 at.% of nitrogen on all samples. Scanning electron micrographs and Raman spectra revealed that a higher heating rate resulted in more holes and defects on the reduced graphene sheets. An extra annealing step at 1000 °C for 1 h was carried out to further eliminate residual oxygen functional groups, which are undesirable in the organic electrolyte system. Compared to the low-heating-rate counterpart (N-GE-15), N-HGE boosted the specific capacity of the supercapacitor by 42 and 22% at current densities of 0.5 and 20 A/g, respectively. The effects of annealing time (0.5, 1, and 2 h) at 1000 °C were also studied. Longer annealing time resulted in higher capacitance values at all current densities due to the minimized oxygen content. Volumetric specific capacitances of 49 and 24 F/cm3 were achieved at current densities of 0.5 and 20 A/g, respectively. For the high-power-density operation at 31,000 W/kg (or 10,000 W/L), an energy density as high as 11 Wh/kg (or 3.5 Wh/L) was achieved. The results indicated that N-HGE not only improved the conductivity of the composite supercapacitors but also accelerated ion transport by way of shortened diffusion paths through the numerous holes all over the graphene sheets.

In-situ electrochemical and operando Raman techniques to investigate the effect of porosity in different carbon electrodes in organic electrolyte supercapacitors

The analyzes of micro-, meso‑ and macro-porous carbon electrodes in a symmetrical supercapacitor filled with a 1.0 M TEABF4 EC-DMC electrolyte were reported in this work. The activated carbon (AC), multi-walled carbon nanotubes, and graphite materials were studied. The results indicate AC is the best electrode material for the application with high specific capacitance and energy. The Raman operando analyzes of AC show that the D- and G- bands shift their positions and intensities. The cause of this phenomenon is the electrostatic ionic adsorption inside very narrow pores, affecting the vibrational mode and the work function of the material, resulting in the shift of the Fermi level of the material. For mesoporous carbon, this phenomenon is much less pronounced. In principle, graphite has enough specific capacitance for competitive application. However, its overall surface area is reduced. Graphite's Raman operando analyzes revealed the BF4−insertion into graphene layers. The G-band splits while the in-situ electrochemical data support a capacitance with three orders of magnitude higher than expected for a purely electrostatic adsorption process on graphite. Overall, this fundamental study evidences that in-situ electrochemistry and Raman spectroscopy combined could offer important information on the energy storage process for supercapacitors.

Ultrafast pore-tailoring of dense microporous carbon for high volumetric performance supercapacitors in organic electrolyte

Preparing activated carbon with high volumetric performance in organic electrolyte is crucial for developing high-energy and miniaturized supercapacitors, but still challenging because high surface area and large pore size are required to effectively store large-sized organic electrolyte ions, which usually result in the low density. Herein, an ultrafast strategy is proposed to tailor the interconnected porous structure of activated carbon through introducing CO2 at the end of homogeneous activation. The uniformly distributed potassium components in carbon matrix promote a robust catalytic etching by CO2, leading to precise tailoring of the ultramicropores (0.50–0.72 nm) to large micropores (0.81–1.14 nm) within only 2 min. The optimized sample with both high surface area and compaction density (2147 m2 g−1, 0.68 g cm−3) shows high gravimetric and volumetric capacitances (155 F g−1 and 106 F cm−3 at 1 A g−1) as well as good rate performance (102 F g−1 and 70 F cm−3 at 20 A g−1) in organic electrolyte. The symmetric supercapacitor achieves high energy densities of 35 Wh kg−1 and 24 Wh L−1 at 573 W kg−1 and 395 W L−1, respectively, indicating great potential of the ultrafast tailoring strategy for practical application.

Nitrogen Doped Superactivated Carbons Prepared at Mild Conditions as Electrodes for Supercapacitors in Organic Electrolyte

Nitrogen functionalization of a highly microporous activated carbon (SBET > 3000 m2/g), to be used as electrode of electric double layer capacitor (EDLC), was carried out by different methods based on organic chemistry protocols at low temperature and selective thermal post-treatments under inert atmosphere. The combination of both methods allowed the production of carbon materials with very similar surface area (2400–3000 m2/g) and different surface chemistry. The nitrogen functionalization by chemical methods produce the attachment of 4 at. % N (XPS) by consumption of oxygen functional groups. The thermal treatments rearrange the surface chemistry by decreasing and converting both nitrogen and oxygen moieties. The effect of surface chemistry on the performance of these materials as electrodes for symmetric supercapacitors was analyzed in organic electrolyte (1M TEMABF4/propylene carbonate). The devices showed high gravimetric capacitance (37–40 F/g) and gravimetric energy density (31–37 Wh/kg). The electrochemical stability of the EDLC was evaluated by a floating test under severe conditions of voltage and temperature. The results evidence an improvement of the durability of nitrogen-doped activated carbons modified by chemical treatments due to the decrease of detrimental oxygen functionalities and the generation of nitrogen groups with higher electrochemical stability.

Can polyoxometalates enhance the capacitance and energy density of activated carbon in organic electrolyte supercapacitors?

Polyoxometalates (POMs) have been shown to work as faradaic additivesto activated carbon (AC) in acidic aqueous electrolytes. Yet, their use in organic media allows not only for added capacity but also higher voltage. Here we show that the tetraethylammonium derivative of phosphotungstate [PW12O40]3− (PW12) can be homogeneously distributed throughout the pores of activated carbon (AC) in organic solvents such as N,N’-dimethylformamide (DMF) and demonstrate the use of this hybrid electrode material in an organic electrolyte (1 M TEABF4 in acetonitrile) supercapacitor. Our results show the efficient electroactivity of the PW12 cluster even in the absence of protons, providing a higher voltage than aqueous electrolytes and fast and reversible redox activity. The hybrid material shows a combination of double-layer (AC) and redox (PW12) capacities leading to an increase (36%) in volumetric capacitance with respect to pristine AC in the same organic electrolyte (1 M TEABF4 in acetonitrile). Remarkably, we were able to quantify this increase as coming predominantly from non-diffusion-limited processes thanks to the utterly dispersed nature of POMs. Moreover, the hybrid material delivers a good rate capability and excellent cycle stability (93% retention of the initial capacitance after 10,000 cycles). This study has a profound significance on improving capacitance of carbon-based materials in organic electrolytes.

Hybrid nanospheres with metastable silica-nanonetwork and confined phenyl for simple fabrication of high-surface-area microporous carbon materials

How to successfully achieve the effective construction and precisely control the pore structure of porous carbon materials based on advanced precursors, is still challenging. Herein, a kind of precise organic-inorganic hybrid nanospheres have been designed to synthesize activation-free and high-surface-area microporous carbon materials (MCMs), in which metastable silica-nanonetwork and confined phenyl are formed by the emulsion polymerization of phenyltriethoxysilane. Within this strategy, it is successful to realize the efficient formation of carbon framework, benefiting from the self-crosslinking of confined phenyl and the dual roles of metastable silica-nanonetwork. It is surprising that the silica-nanonetwork can act as the role of template, as well as cross-linker, making the obtained MCMs with high surface area (up to 2614 m2 g−1). Thus, as-prepared MCMs exhibit excellent performance as the electrode materials of supercapacitors in organic electrolyte, i.e. an energy density of 15.36 W h kg−1 at a power density of 27 kW kg−1.

Cotton fabrics-derived flexible nitrogen-doped activated carbon cloth for high-performance supercapacitors in organic electrolyte

Activated carbon cloth, due to its excellent flexibility, good conductivity, and high surface area, is featured as a kind of promising material for energy storage devices. However, the non-optimized pore structures limit its application as electrode material in supercapacitors with organic electrolytes, which can provide both high energy density and power density due to the high applied cell voltage. In this paper, nitrogen-doped activated carbon cloth with hollow tubular fiber units, high surface area, controllable hierarchical porous structure, and beneficial surface functional groups, is synthesized via a simple ammonia treatment of commercial cotton fabrics. The resulting organic-electrolyte supercapacitors based on this hierarchical porous hollow carbon cloth exhibit a high specific capacitance (up to 215.9 F g−1 at 1 A g−1), extremely high rate capability (89% from 1 A g−1 to 200 A g−1), small IR drop (0.23 V at 100 A g−1), outstanding cycling stability (98% capacitance retention over 20 000 cycles), as well as good flexibility. This N-doped activated carbon cloth thus overcomes the drawbacks of presently available carbon cloths and opens up a new horizon toward energy storage devices with high energy density at high power density.

Hierarchical Nanosheets/Walls Structured Carbon-Coated Porous Vanadium Nitride Anodes Enable Wide-Voltage-Window Aqueous Asymmetric Supercapacitors with High Energy Density.

The energy density of aqueous asymmetric supercapacitors (ASCs) is usually limited by low potential windows and capacitances of both anode and cathode. Herein, a facile strategy to fabricate hierarchical carbon‐coated porous vanadium nitride nanosheet arrays on vertically aligned carbon walls (CC/CW/p‐VN@C) as anode for aqueous ASCs is reported. The potential window of CC/CW/p‐VN@C electrode can be stably extended to –1.3 to 0 V (vs Ag/AgCl) with greatly improved specific capacitance (604.8 F g−1 at 1 A g−1), excellent rate capability (368 F g−1 at 60 A g−1), and remarkable electrochemical stability. To construct ASCs, a Birnessite Na0.5MnO2 nanosheet arrays (CC/CW/Na0.5MnO2) cathode is similarly built. Benefiting from the matchable potential windows and high specific capacitances of the rationally designed anode and cathode, aqueous CC/CW/p‐VN@C||CC/CW/Na0.5MnO2 ASCs with a wide voltage window of 2.6 V are fabricated. Moreover, the ASCs showcase an ultrahigh energy density up to 96.7 W h kg−1 at a high power density of 1294 W kg−1, and excellent cycling stability (92.5% retention after 10 000 cycles), outperforming most of previously reported ASCs and even comparable to that of organic electrolyte supercapacitors (SCs). This efficient strategy for fabricating 2.6 V aqueous ASCs suggests a promising research system for high energy density SCs.

Highly mesoporous carbon flakes derived from a tubular biomass for high power electrochemical energy storage in organic electrolyte

Abstract Carbon flakes with a specific surface area of 3010 m2 g−1, a pore volume of 2.756 cm3 g−1 and an ultrahigh mesoporous volumetric ratio of 97.6% were prepared from tubular kapok fibers through a simple low-temperature pre-carbonization and KOH activation process. The low-temperature pre-carbonization in air was effectively dewaxed the biomass and the thus obtained thin precursor was adequately wetted and etched by KOH, both of which might have resulted in the much improved textural properties. When used as electrode materials of symmetric supercapacitors in organic electrolyte, the carbon flakes displayed high energy density at high power density, e.g. 24 Wh kg−1 at 24,029 W kg−1, which was among the best values reported so far on biomass-derived porous carbon electrodes. The results reported in this work indicated that both the selection of bio-resources and pre-carbonization treatment were important for preparation of carbonaceous electrode materials with tailored texture properties and enhanced electrochemical energy storage performance.

Facile one-step synthesis of three-dimensional freestanding hierarchical porous carbon for high energy density supercapacitors in organic electrolyte

Three-dimensional freestanding hierarchical porous carbon materials with high specific surface areas (up to 1688 m2 g−1) were prepared by the one-step carbonization of sucrose and zinc chloride (ZnCl2), defined as SCs for simplicity. Herein, ZnO particles served as the etchant and template to produce micropores and mesopores. The formation mechanism, morphology and structure were investigated by a series of techniques. The SCs exhibited highly enhanced electrochemical performances as supercapacitors, and the one synthesized at 800 °C (SC-800) showed high specific capacitances of 130 F g−1 and 124 F g−1 at the current densities of 1 and 20 A g−1 in 1 M TEABF4/AN, respectively. This device delivered the high energy density of 55 Wh kg−1 to afford the power density of 2.5 kW kg−1 (voltage range of 3 V) and good cycling stability (85% capacitance retention after 10,000 cycles).

High-performance organic electrolyte supercapacitors based on intrinsically powdery carbon aerogels

A novel class of powdery carbon aerogels (PCAs) has been developed by the union of microemulsion polymerization and hypercrosslinking, followed by carbonization. The resulting aerogels are in a microscale powdery form, demonstrate a well-defined 3D interconnected nanonetwork with hierarchical pores derived from numerous interstitial nanopores and intraparticle micropores, and exhibit high surface area (up to 1969m2/g). Benefiting from these structural features, PCAs show impressive capacitive performances when utilized as electrodes for organic electrolyte supercapacitors, including large capacitances of up to 152F/g, high energy densities of 37-15 Wh/kg at power densities of 34–6750W/kg, and robust cycling stability.

A smart bottom-up strategy for the fabrication of porous carbon nanosheets containing rGO for high-rate supercapacitors in organic electrolyte

Exploration of various porous carbon materials with enhanced electrochemical performance is critical for the development of long-term sustainable energy storage and production systems. Herein, we have designed a smart bottom-up strategy to transformation of pitch into porous carbon nanosheets containing rGO (reduced graphene oxides) (PCSG) through a soft solution process coupling with KOH activation. This efficient solution process without involving hard templates or harmful solvents, which is clearly different from all the previously reported process, opening a new route towards porous carbons for energy storage applications. Notably, the as-obtained PCSG-60 sample (synthesized from 60mg of GO) presents an optimum integration of a large specific surface area of 2217m2/g, uniform micropore size (∼1.5nm), and sheet-like morphologies. When evaluated as electrode materials for supercapacitor in 1M TEABF4/AN electrolyte, the PCSG-60 exhibits excellent capacitive performance including large specific capacitances of 221F/g (at 1A/g), considerable rate capability (71.9% capacitance retention from 1A/g to 50A/g), smaller IR drop (0.637V at 50A/g), good cycling stability (91.8% of the initial capacitance after 3000 cycles at 10A/g) and an energy density up to 38.2 Wh/kg even at an ultrahigh power density of 40500W/kg, which puts the PCSG-60 among the best electrochemical performance in the reported pitch-derived carbon electrodes for supercapacitors. The outstanding capacitive electrochemical performance combined with the low-cost and readily accessible precursors enable the PCSG-60 is a promising electrode material for supercapacitor and other electrochemical energy storage system applications.

Unconventional mesopore carbon nanomesh prepared through explosion–assisted activation approach: A robust electrode material for ultrafast organic electrolyte supercapacitors

This work presented an unconventional mesopore carbon nanomesh (MCNM), featured with numerous evenly distributed in–plane micro/mesopores, which was obtained by a novel explosion–assisted activation process employing carboxymethylcellulose sodium (CMCS) as the carbon precursor while potassium nitrate (KNO3) acts as both an explosive and activating reagent. This work opens a new route toward nanocarbon materials for high–performance electrochemical energy storage devices, which is totally different from the previously reported approaches. Considering the mesopore carbon nanomesh structures combined with the presence of abundant in–plane micro/mesopores as well as large specific surface area, the application of the MCNM materials in high–performance symmetric supercapacitors in organic electrolyte was investigated. The supercapacitor device exhibited competitive performance, including high specific capacitance (up to 149 F/g at 1 A/g), extremely high rate capability (84.6% from 1 A/g to 50 A/g), small IR drop (0.37 V at 50 A/g), outstanding cycling stability (99% capacity retention over 5000 cycles), and reasonable energy densities of 28.7 Wh/kg at an ultrahigh power density of 54000 W/kg. The facile, low–cost and scalable synthesis strategy together with excellent electrochemical performance makes it suitable for applications in electrochemical energy storage devices such as supercapacitors.

From Trash to Treasure: Direct Transformation of Onion Husks into Three-Dimensional Interconnected Porous Carbon Frameworks for High-Performance Supercapacitors in Organic Electrolyte

Onion husks (Allium cepa L.), an abundant biomass, has been tentatively explored as a renewable carbon source to prepare value-added three-dimensional interconnected porous carbon frameworks (OHCFs) by means of direct carbonization & activation process, and the synthetic procedure is quite simple as easy to be scaled up for industrial applications. The two-electrode symmetric supercapacitor based on the OHCF-2 sample (synthesized from 2MK2CO3 solution) exhibits excellent electrochemical performance with large specific capacitance (up to 188F/g at 1A/g), good cycling stability (92.5% capacity retention after 2000 cycles), small IR drop (0.48V at 30A/g), outstanding rate capability (74.9% from 1A/g to 30A/g), and unusually high energy densities of 35.4-47.6 Wh/kg at power densities of 675–20250W/kg in organic electrolyte. This facile, efficient and template-free synthesis strategy holds great promise for preparing novel porous carbons from renewable biomass resources for application in state-of-art energy storage devices.

Performance evaluation of conductive additives for activated carbon supercapacitors in organic electrolyte

In this study, we investigate two different activated carbons and four conductive additive materials, all produced in industrial scale from commercial suppliers. The two activated carbons differed in porosity: one with a narrow microporous pore size distribution, the other showed a broader micro-mesoporous pore structure. Electrochemical benchmarking was done in one molar tetraethylammonium tetrafluoroborate in acetonitrile. Comprehensive structural, chemical, and electrical characterization was carried out by varied techniques. This way, we correlate the electrochemical performance with composite electrode properties, such as surface area, pore volume, electrical conductivity, and mass loading for different admixtures of conductive additives to activated carbon. The electrochemical rate handling (from 0.1 Ag−1 to 10 Ag−1) and long-time stability testing via voltage floating (100h at 2.7V cell voltage) show the influence of functional surface groups on carbon materials and the role of percolation of additive particles.

Fabrication of porous carbon monoliths with a graphitic framework

Macro/mesoporous carbon monoliths with a graphitic framework were synthesized by carbonizing polymeric monoliths of poly(benzoxazine-co-resol). The overall synthesis process consists of the following steps: (a) the preparation of polymeric monoliths by co-polymerization of resorcinol and formaldehyde with a polyamine (tetraethylenepentamine), (b) doping the polymer with a metallic salt of Fe, Ni or Co, (c) carbonization and (d) the removal of inorganic nanoparticles. The metal nanoparticles (Fe, Ni or Co) formed during the carbonization step catalyse the conversion of a fraction of amorphous carbon into graphitic domains. The resulting carbon monoliths contain >50wt.% of graphitic carbon, which considerably improves their electrical conductivity. The use of tetraethylenepentamine in the synthesis results in a nitrogen-containing framework. Textural characterization of these materials shows that they have a dual porosity made up of macropores and mesopores (∼2–10nm), with a BET surface area in the 280–400m2g−1 range. We tested these materials as electrodes in organic electrolyte supercapacitors and found that no conductive additive is needed due to their high electrical conductivity. In addition, they show a specific capacitance of up to 35Fg−1, excellent rate and cycling performance, delivering up to 10kWkg−1 at high current densities.

An advanced carbonaceous porous network for high-performance organic electrolyte supercapacitors

A new class of advanced porous network structured carbon materials exhibits very attractive capacitive properties when utilized as electrodes for organic electrolyte supercapacitors, including large capacitances up to 210 F g−1, unusually high energy densities of 21.4–41.8 W h kg−1 at power densities of 67.5–10 800 W kg−1, and excellent cycling stability.

Electrochemical Insight into Cycle Stability of Organic Electrolyte Supercapacitors

Two types of activated carbons were produced by chemical activation respectively with and without pre-carbonization procedure, and were used in organic electrolyte supercapacitors. Galvanostatic charge and discharge results show that voltage upper limit and activated carbon type obviously influence the cycle stability of the capacitors. And cyclic voltammograms reveal the better capacitive behavior and cycle stability of the activated carbon produced with carbonization procedure implying the correlation between these two factors. While Nyquist plots disclose the tendency of equivalent circuit component parameters and electrode processes with cycling.

Manganese dioxide-coated activated mesocarbon microbeads for supercapacitors in organic electrolyte

MnO 2 nanostructures are successfully coated onto activated mesocarbon microbeads (a-MCMB) by a simple chemical coprecipitation method. The structure and morphology of the as-prepared a-MCMB/MnO 2 composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the nano-MnO 2 is of short fiber-like structures with about 200 nm in length and 60 nm in width. A growing mechanism was also proposed for the nano-MnO 2 on the surface of a-MCMB. This novel composite was used as an electrode material for supercapacitors. Electrochemical measurements showed that the composite electrode has a maximum specific capacitance of 183 F g −1 in 1 M LiPF 6 (EC + DMC) organic electrolyte with an operating voltage up to 3.0 V. The specific capacitance base on the MnO 2 is estimated to be as high as 475 F g −1, corresponding to a considerable energy density of 106 wh kg −1.