An Era of Powerful Supercapacitors: Materials Science and Engineering toward the System-Level Design of Ionic Supercapacitor Electrode and Electrolyte

Perspective

Ann J Materials Sci Eng. 2014;1(1): 3.

An Era of Powerful Supercapacitors: Materials Science and Engineering toward the System-Level Design of Ionic Supercapacitor Electrode and Electrolyte

Chen Kunfeng and Xue Dongfeng*

State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, China

*Corresponding author: Xue Dongfeng, State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Renmin Street, No. 5625, Changchun 130022, China

Received: May 02, 2014; Accepted: May 05, 2014; Published: May 06, 2014

Perspective

Electrochemical energy storage technologies are the most promising for solving the demand for energy and the concerns of environmental pollution, but to meet the needs of different applications in terms of energy, power, cycle life, safety, and cost, different systems, such as lithium ion batteries, redox flow batteries, and supercapacitors, need be considered [1]. Electrochemical capacitors, also called supercapacitors, are highly desirable energy storage devices because they can deliver high levels of electrical power and offer long operating lifetime, which have had an important role in complementing or replacing battery [2,3]. Supercapacitors have been developed for more than fifty years. First patent of supercapacitors date back to 1957 where a capacitor based on high surface area carbon was described by Becker [4]. Later in 1969 first attempts to market such devices were undertaken by SOHIO [5]. Only in the nineties electrochemical capacitors became famous in the context of hybrid electric vehicles [6]. Today many companies in electrochemical capacitors are developing [7]. However, the main bottleneck thathinders the practical application of supercapacitors is their low energy density. The charge is confined to the material surface, so the energy density of electrochemical double layer capacitors is less than batteries [8]. In the 1970s, Conway et al. recognized that reversible redox reaction can occur at or near the surface of an appropriate electrode material [3], which can result in much greater charge storage. Due to the progress of nanotechnology, nanostructured electrode materials have been developed to enhance the energy density of supercapacitors [9]. However, the application of nanostructured materials certainly does not automatically lead to the enhancement in energy density.

System–level planning of theoretical and experimental efforts is increasingly important for the development of modern materials science [10]. Nowhere has this become more obvious than in the area of energy storage and conversion, where it seems clear there is atrend towards an emerging new field of integrated systems materials engineering [10]. Based on the system– and ion–level design, for the first time, we reported the proof–of–principle of a new concept of ionic supercapacitor systems [11,12]. These systems include the transition metal salt electrode and an alkaline electrolyte operating at room temperature, which can show ultrahigh specific capacitance and energy density [13–16]. For example, CuCl2 electrodes deliver a very high specific pseudocapacitance ˜5442 F⁄g, which exceeds the one–electron transfer theoretical capacitance of ˜5061 F⁄g [12]. YbCl3 pseudocapacitor can show the specific capacitance of 2210 F⁄g, which also exceeds one–electron redox theoretical capacitance of ~1358 F⁄g [15]. These new alkaline ionic supercapacitor systems are launching an era of powerful supercapacitors by the system–level design of ionic supercapacitor electrode and electrolyte.

The capacitive behavior of inorganic pseudocapacitor is associated primarily with the redox reactions of the cations or changes in oxidation states of the cations in electrode materials during operation [3]. In order to increase the energy density of pseudocapacitors, redox–active metal cations in these electrode materials must be fully utilized in Faradaic reaction. Figure 1 shows the charge storage mechanisms of new ionic pseudocapacitors systems and traditional pseudocapacitors. In ionic pseudocapacitor system, highly active ionic state colloids were designed as electrode material, which can facilely cooperate with electrolyte. Thus, the Faradaic redox reaction of Cu2+, Co2+, Ce3+, Yb3+, Sn4+ cations can occur in the whole colloids; thus high cations utilization can lead to high energy density. In addition, this specific structure can shorten the transport paths for ions and electrons, which can maintain high power density. The efficient manipulation of active cations is a powerful way for developing high performance pseudocapacitors.

Citation: Kunfeng C, Dongfeng X. An Era of Powerful Supercapacitors: Materials Science and Engineering toward the System-Level Design of Ionic Supercapacitor Electrode and Electrolyte. Ann J Materials Sci Eng. 2014;1(1): 3. ISSN:2471-0245