Synthesis, properties, and performance of nanostructured metal oxides for supercapacitors

Abstract

Beyond activated carbon and other forms of high-surface area carbon operating solely as double layer storage materials in capacitors of high capacitance commonly somewhat imprecisely called supercapacitors other electrode materials storing electric charge by reversible and fast superficial redox processes are studied as active masses. The resulting devices combining double layer and Faradaic process-based charge storage -commonly called hybrid ones -show significantly higher capacitances at only marginally diminished power capability. Among the suggested materials metal oxides feature most prominently. Their formation, characterization and properties together with the performance of prepared devices are reviewed here.Electric energy cannot be stored directly in amounts large enough to gain commercial viability. Systems employing e.g., superconductors or dielectric capacitors are either too large or too expensive in order to be of any wide importance (for examples and a brief review see [1]). Thus, basically two modes of rather direct storage employing chemical, more specifically physico-chemical, and electrochemical principles remain: Storage based on charge separation in the electrochemical double layer (i.e., capacitors) or storage based on the reversible conversion of electrical into chemical energy and vice versa A+ B C+ D: the accumulator (see Fig. 1).For various reasons the former mode has for a long time been associated with high power mostly because of the inherently fast processes leaving out any interfacial electrochemical reaction limited by the inherent constraints of interfacial processes and the latter with high energy because of the much larger amounts of energy which could be stored based on associated chemical conversion reactions. This is also the inherent reason of the lower power of the latter devices, interfacial reactions mostly associated with phase transformations and extended transport of matter tend to be slow. The energy density of the former devices tends to be low because of the limited amount of interfacial surface area available in any given device. This is illustrated in a Ragone plot showing some examples of storage devices (see Fig. 2).As indicated devices based on traditional electrolytic capacitor technologies (as in aluminum foil-or tantalum-pentoxide-based ones) show highest power density. Although these devices are based only on the movement and separation of electric charges without any chemical reaction being involved a short characterization of salient features may be helpful to settle the current confusion about these various devices.

Improved Electrochemical Behavior of Amorphous Carbon-Coated Copper/CNT Composites as Negative Electrode Material and Their Energy Storage Mechanism

“…We have prepared a composite of copper nanograins grown on the surface of CNTs by a redox reaction between Cu(Ac) 2 and EG. The composite material consists of metallic copper, CNTs and carbon coating.…”

Scaling from Single Molecule to Macroscopic Adhesion at Polymer/Metal Interfaces

“…37) Wie diese Materialbeispiele zeigen, verschwimmt die Grenze zwischen Batterie-und Kondensatormaterialien, Abbildung 5 zeigt dies am Beispiel Nickeloxid. [38][39][40][41][42][43] Die Arbeiten mit Metallchalkogeniden und weiteren komplexen Metallverbindungen (siehe dazu Lit. [44][45][46][47][48]…”

Preparation of Co-Ni Oxide/Vertically Aligned Carbon Nanotube and Their Electrochemical Performance in Supercapacitors

“…Electrical double layer capacitors (EDLCs) and pseudocapacitors are two main types of supercapacitors with different charge storage mechanisms [2,3]. EDLCs recently have extensively been investigated as energy storage devices that store charge electrostatically within the electrode-electrolyte interface [1,4].…”