High-power Electrochemical Capacitors Research Articles

Iso-Oriented NaTi2(PO4)3 Mesocrystals as Anode Material for High-Energy and Long-Durability Sodium-Ion Capacitor.

Sodium-ion capacitors (SIC) combine the merits of both high-energy batteries and high-power electrochemical capacitors as well as the low cost and high safety. However, they are also known to suffer from the severe deficiency of suitable electrode materials with high initial Coulombic efficiency (ICE) and kinetic balance between both electrodes. Herein, we report a facile solvothermal synthesis of NaTi2(PO4)3 nanocages constructed by iso-oriented tiny nanocrystals with a mesoporous architecture. It is notable that the NaTi2(PO4)3 mesocrystals exhibit a large ICE of 94%, outstanding rate capability (98 mA h g-1 at 10 C), and long cycling life (over 77% capacity retention after 10 000 cycles) in half cells, all of which are in favor to be utilized into a full cell. When assembled with commercial activated carbon to an SIC, the system delivers an energy density of 56 Wh kg-1 at a power density of 39 W kg-1. Even at a high current rate of 5 A g-1 (corresponds to finish a full charge/discharge process in 2 min), the SIC still works well after 20 000 cycles without obvious capacity degradation. With the merits of impressive energy/power densities and longevity, the obtained hybrid capacitor should be a promising device for highly efficient energy storage systems.

Rational construction the composite of graphene and hierarchical structure assembled by Fe2O3 nanosheets for lithium storage

Taking the advantage of hierarchical nanostructures into consideration, herein a facile and template free approach to achieve hierarchical microspheres assembled from the α-Fe2O3 nanosheet was formulated. The followed freeze-drying treatment is employed to realize the construction of nanostructured Fe2O3/graphene composite. The unique hierarchical structure of α-Fe2O3 combined with the flexible graphene layer not only effectively buffer the volume expansion during the cycling process, but also promote the transport of lithium ion and electron through three-dimensional networks when being assessed for lithium ion battery. The as-obtained composite exhibits significantly enhanced cycling stability (1850mAhg−1 after 190 cycles at the current of 300mAg−1) and superior rate performance (around 520mAhg−1 for the current of 5000mAg−1). The obtained-results illustrate that the rational designing of the nanostructured composite can result in the fast lithium insertion/de-insertion in lithium ion batteries which mimic merits seen in high-power electrochemical capacitors.

Constructing Hierarchical Spheres from Large Ultrathin Anatase TiO2 Nanosheets with Nearly 100% Exposed (001) Facets for Fast Reversible Lithium Storage

Synthesis of nanocrystals with exposed high-energy facets is a well-known challenge in many fields of science and technology. The higher reactivity of these facets simultaneously makes them desirable catalysts for sluggish chemical reactions and leads to their small populations in an equilibrated crystal. Using anatase TiO(2) as an example, we demonstrate a facile approach for creating high-surface-area stable nanosheets comprising nearly 100% exposed (001) facets. Our approach relies on spontaneous assembly of the nanosheets into three-dimensional hierarchical spheres, which stabilizes them from collapse. We show that the high surface density of exposed TiO(2) (001) facets leads to fast lithium insertion/deinsertion processes in batteries that mimic features seen in high-power electrochemical capacitors.

Electrical Double-Layer Capacitance of Zeolite-Templated Carbon in Organic Electrolyte

Porous carbon materials have been prepared using chemical vapor deposition of ethylene and acetonitrile on zeolite Y templates with the subsequent removal of the template. The use of zeolite templates enabled tuning of the carbon chemistry, microstructure, and specific surface area while maintaining ordered pores and similar pore-size distribution. Evaluation of the performance of the templated carbons in electrochemical capacitors with tetraethylammonium tetrafluoroborate salt solution in acetonitrile showed a high gravimetric capacitance of up to and a short time constant of up to , indicating fast charge/discharge capability. Nitrogen doping limited the capacitor performance at high current densities without enhancing the energy-storage characteristics at low current densities. Specific capacitance at a constant pore size was found to linearly depend on the surface area, suggesting a potential for further improvements. Carbons produced by zeolite-templating method are promising for use in high-energy, high-power electrochemical capacitors employing organic electrolytes.

Modeling and Sizing of Supercapacitors

Abstract —Faced with numerous challenges raised by the requirements of the modern industries for higher power and higher energy, supercapacitors study started playing an important role in offering viable solutions for some of these requirements. This paper presents the surface redox reactions based modeling in order to study the origin of high capacity of EDLC (electrical double-layer capacitor) for better understanding the working principles of supercapacitors. Some application-dependent sizing methods are also presented since proper sizing can increase the efficiency and the life cycle of the supercapacitor based systems. Index Terms—electrochemical capacitor, modeling, sizing, pseudo-capacitance I. INTRODUCTION Electrochemical capacitors have achieved substantial acceptance in the electronics industry, replacing backup batteries in many CMOS memory applications. Many of the first commercially available el ectrochemical capacitors were directed toward such applications and, consequently, were of limited size and power performance. As will be shown in the next sections, these limitations are not inherent in the technology, so larger, higher-voltage capacitors with greatly enhanced power performance have been available for several years from some suppliers and currently are being developed by others [18]. Different names like “double layer capacitors”, “supercapacitors” , “ultracapacitors” , “power capacitors” , “gold capacitors”, “power cache” were used to indicate different types of capacitors displaying high values of capacity, but the first mention of a double-layer electrochemical capacitor realizati on is made just in 1957, in a patent application of General Electric (Becker). [ 4] In 1966, SOHIO (Standard Oil Company, Cleveland, Ohio) patented a similar device having porous carbon electrode but with a higher energy density than that of General Electric. Further patents described improved SOHIO developed solutions in the following years, but their licenses are transferred to NEC which produced for the first time commercial devices under the name “supercapacitor”. The first high power electrochemical capacitors were produced in the years 1980 by Pinnacle Research Institute (PRI) for military applications like laser weapon and guided missiles with ruthenium/tantalum oxide electrodes under the name “PRI ultracapacitor”. [4] Nowadays, electrical double-la yer capacitors (EDLC) are gaining more attention due to their practical potential in applications areas with increasing power demands. Due to reversible electrochemical energy storage these capacitors can be recharged very quickly with best long cycle life. Energy storage is by means of st atic charge rather than of an electro-chemical process (inherent to common battery). New applications are emerging in fields like automotive engineering

Polypyrrole/carbon composite electrode for high-power electrochemical capacitors

Nano-thin polypyrrole (PPy) layers with thickness from ∼5 nm to several 10s nm were deposited on vapor grown carbon fibers (VGCF) by an in situ chemical polymerization. Using different concentrations of the pyrrole could control the thicknesses of deposited PPy layers. Surface morphology and thickness of the deposited PPy layers were confirmed by means of scanning electron microscopy and scanning transmission emission microscopy. Pseudo-capacitive behavior of the deposited PPy layers on VGCF investigated by means of cyclic voltammetry. Then, the PPy/VGCF composites were mixed with activated carbons (AC) at various mixing ratios. For the PPy/VGCF/AC composite electrodes, characteristics of specific capacitance and power capability were examined by half-cell tests. As results of this study, it was investigated that nano-thin PPy layer below ∼10 nm deposited on VGCF had high pseudo-capacitance and fast reversibility. Its specific capacitance per averaged weight of active material (PPy) was obtained as ∼588 F g −1 at 30 mV s −1 and maintained as ∼550 F g −1 at 200 mV s −1 of scan rate. Also, from the mixing 60 wt.% of the PPy/VGCF with 25 wt.% of AC, the PPy/VGCF/AC composite electrode exhibited higher power capability maintaining the specific capacitance per active materials of PPy and AC as ∼300 F g −1 at 200 mV s −1 in 6 M KOH.

Proton and Electron Conductivity in Hydrous Ruthenium Oxides Evaluated by Electrochemical Impedance Spectroscopy: The Origin of Large Capacitance

Electrochemical impedance spectroscopy was conducted on a series of hydrous ruthenium oxides, RuO(2).xH(2)O, (x = 0.5, 0.3, 0) and a layered ruthenic acid hydrate (H(0.2)RuO(2.1).nH(2)O) in order to evaluate their protonic and electronic conduction. The capacitor response frequency was observed at lower frequency for RuO(2).xH(2)O with higher water content, which was suggested to be due to electrolyte exhaustion within the film and/or utilization of hydrated interparticle micropores that have high ionic resistance. Analysis of the impedance data indicated that the charge-transfer resistance through the film is not significantly affected by the water content in RuO(2).xH(2)O, and the capacitor frequency response is dominated by the protonic conduction. The capacitor response frequency of layered H(0.2)RuO(2.1).nH(2)O was comparable to RuO(2).0.5H(2)O. The high specific capacitance at low frequency for layered H(0.2)RuO(2.1).nH(2)O is attributed to the utilization of the expandable hydrous interlayer, which accounts for the ionic conduction. The present results demonstrate the importance of hydrous regions (either interparticle or interlayer) to allow appreciable protonic conduction for high energy and high power electrochemical capacitors.