Use of KCl Aqueous Electrolyte for 2 V Manganese Oxide/Activated Carbon Hybrid Capacitor
TL;DR: In this paper, a hybrid capacitor in neutral KCl aqueous electrolyte, which consists of amorphous manganese oxide (a-MnO 2.nH 2 O) as a cathode and activated carbon as an anode, was reported.
Abstract: This study reports a hybrid capacitor in neutral KCI aqueous electrolyte, which consists of amorphous manganese oxide (a-MnO 2 .nH 2 O) as a cathode and activated carbon as an anode. The electrochemical performance of the hybrid capacitor is characterized by cyclic voltammetry and a dc charge/discharge test. The hybrid capacitor shows ideal capacitor behavior with an extended operating voltage of 2 V. The extended operating voltage is preferentially attributed to having asymmetric electrodes with different stable voltage windows and good electrochemical stability in neutral KCl aqueous electrolyte. According to the extended operating voltage, the energy density of the hybrid capacitor at a current density of 0.25 A/g, was found to be 28.8 Wh/kg which is comparable to that of an amorphous ruthenium oxide capacitor (26.7 Wh/kg). The hybrid capacitor also shows no degradation of capacitance during 100 cycles except an initial loss of 7% within a few cycles.
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TL;DR: This work has shown that combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries.
Abstract: Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.
14,213 citations
TL;DR: Electrochemical capacitors enable rapid storage and efficient delivery of electrical energy in heavy-duty applications and are being enabled by electrochemical capacitor technology.
Abstract: Rapid storage and efficient delivery of electrical energy in heavy-duty applications are being enabled by electrochemical capacitors.
4,177 citations
TL;DR: The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature, and challenges in producing high-performing electrolytes are analyzed.
Abstract: Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).
2,480 citations
TL;DR: This review discusses the basic principles of the electrical double-layer (EDL), especially regarding the correlation between ion size/ion solvation and the pore size of porous carbon electrodes, and summarizes the key aspects of various carbon materials synthesized for use in supercapacitors.
Abstract: Electrical energy storage (EES) is one of the most critical areas of technological research around the world. Storing and efficiently using electricity generated by intermittent sources and the transition of our transportation fleet to electric drive depend fundamentally on the development of EES systems with high energy and power densities. Supercapacitors are promising devices for highly efficient energy storage and power management, yet they still suffer from moderate energy densities compared to batteries. To establish a detailed understanding of the science and technology of carbon/carbon supercapacitors, this review discusses the basic principles of the electrical double-layer (EDL), especially regarding the correlation between ion size/ion solvation and the pore size of porous carbon electrodes. We summarize the key aspects of various carbon materials synthesized for use in supercapacitors. With the objective of improving the energy density, the last two sections are dedicated to strategies to increase the capacitance by either introducing pseudocapacitive materials or by using novel electrolytes that allow to increasing the cell voltage. In particular, advances in ionic liquids, but also in the field of organic electrolytes, are discussed and electrode mass balancing is expanded because of its importance to create higher performance asymmetric electrochemical capacitors.
2,140 citations
TL;DR: This review looks at the essential energy-storage mechanisms and performance evaluation criteria for asymmetric supercapacitors to understand the wide-ranging research conducted in this area and highlights several key scientific challenges.
Abstract: Ongoing technological advances in diverse fields including portable electronics, transportation, and green energy are often hindered by the insufficient capability of energy-storage devices By taking advantage of two different electrode materials, asymmetric supercapacitors can extend their operating voltage window beyond the thermodynamic decomposition voltage of electrolytes while enabling a solution to the energy storage limitations of symmetric supercapacitors This review provides comprehensive knowledge to this field We first look at the essential energy-storage mechanisms and performance evaluation criteria for asymmetric supercapacitors to understand the wide-ranging research conducted in this area Then we move to the recent progress made for the design and fabrication of electrode materials and the overall structure of asymmetric supercapacitors in different categories We also highlight several key scientific challenges and present our perspectives on enhancing the electrochemical performance of future asymmetric supercapacitors
2,030 citations
References
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TL;DR: In this paper, the performance of thin films of manganese dioxide on nickel foils was studied by cyclic voltammetry in the range 0.0-0.9 V (SCE) and by chronopotentiometry in unbuffered solution.
Abstract: Thin films of manganese dioxide were formed on nickel foils by electrodeposition and by both dip‐coating and drop‐coating with manganese dioxide suspensions (sols) and their subsequent gelation and calcination. The performance of these films as ultracapacitors was studied by cyclic voltammetry in the range 0.0–0.9 V (SCE) and by chronopotentiometry in unbuffered solution. The cyclic voltammograms of ultrathin, dip‐coated sol‐gel‐derived films indicated better capacitive behavior and gave differential specific capacitance values as high as 698 F/g compared to values half to two‐thirds as great for the electrodeposited films. Multilayer drop‐coated sol‐gel films were prepared to attain film thicknesses comparable to the electrodeposited films, and these were found to provide charge‐storage capacity as high as , more than three times greater than that of the electrodeposited films. All films, except electrodeposited films that were not thermally cured, exhibited good cycling stability, losing not much more than 10% of capacity after 1500 cycles. © 2000 The Electrochemical Society. All rights reserved.
1,014 citations
TL;DR: Amorphous MnO2·nH2O in a mild 2 M KCl aqueous electrolyte proves to be an excellent electrode for a faradaic electrochemical capacitor cycled between −0.2 and +1.0 V versus SCE.
1,006 citations
TL;DR: The hydrous form of ruthenium oxide (RuO[sub 2][center dot]xH [sub 2]O) has been demonstrated to be an excellent electrode material for electrochemical capacitors as discussed by the authors.
Abstract: The hydrous form of ruthenium oxide (RuO[sub 2][center dot]xH[sub 2]O) has been demonstrated to be an excellent electrode material for electrochemical capacitors. This material, as prepared by a sol-gel process at low temperatures, is amorphous and electrically conductive. The specific capacitance is over 720 F/g. This value is at least two times higher than the highest value ever reported for such materials. The charge storage mechanism is believed to involve bulk electrochemical protonation of the oxide. This discovery opens a new avenue of research in the field of high energy density electrochemical capacitors.
694 citations
TL;DR: In this paper, NiO/Ni composite films have been found to perform as superior electrodes in electrochemical capacitor applications, which can provide a specific capacitance of 50 to 64 F/g.
Abstract: Nano-sized NiO/Ni composite films have been found to perform as superior electrodes in electrochemical capacitor applications. These films can provide a specific capacitance of 50 to 64 F/g. The specific energy and specific power of these films were 25 to 40 kJ/kg and 4 to 17 kW/kg, respectively. These specific quantities are dependent on the microstructure of the films. Superior performance can be obtained from samples having rough surfaces and consisting of larger secondary particles (ca. 100 to 120 nm in diam).
530 citations
TL;DR: In this paper, high-surface-area carbons were prepared by carbonization of cotton cloth at elevated temperatures (up to 1050°C), followed by activation at 900°C by oxidation with CO 2 during different time periods.
Abstract: We characterized activated carbon electrodes for electrical double-layer capacitor (EDLC) systems. High-surface-area carbons were prepared by carbonization of cotton cloth at elevated temperatures (up to 1050°C), followed by activation at 900°C by oxidation with CO 2 during different time periods. Specific surface areas and characteristic pore sizes obtained from gas adsorption isotherms were correlated with those obtained from ion electroadsorption at the electrical double layer. Electrolytes studied included aqueous LiCI, NaCI, and KCl solutions and nonaqueous propylene carbonate solutions with LiBF 4 and (C 2 H 5 ) 4 NBF 4 salts. We found clear evidence that the porous carbons thus formed exhibit ion sieving properties, and that increasing activation time systematically increases the average pore sizes of these carbons. The electric double layer (EDL) capacity of these samples (calculated from voltammetric measurements) depends strongly on the adsorption interaction of the ions in the pores, and hence the relationship between the average pore size and the effective ion size determines the specific EDL capacitance of these samples. The following order of dimension of adsorbed species was found, based on the ion sieving of the various synthesized carbons of different average pore size N 2 ; Na + (aq); Cl - (3.6 A) < BF 4 - < TEA + (PC) < Li + (PC).
525 citations