Li‐Ion‐Based Hybrid Supercapacitors in Organic Medium

Abstract

Environment protection and sustainable energy development have recently become a growing industry, in which energy storage devices are such important components that they play crucial roles. Energy storage devices include batteries, for example, lithium-ion batteries, nickel-metal hydride batteries, and lead-acid batteries, which have high energy densities. The batteries are under vigorous study for further increasing their energy density so that they can power electric vehicles. On the other hand, electric double-layer capacitors (EDLCs), which are high-power energy storage devices capable of effectively utilizing energy, have been also studied and are practically used in tracks, buses, elevators, and in heavy-duty construction and railway usage such as forklifts, yard cranes, and bullet trains [1].However, since EDLCs generally have low energy densities, their uses are limited and they cannot fully meet the various performance demands of the recent markets as shown in Figure 7.1. Particularly in the field of automobiles, new energy devices are strongly desired to have hybrid characteristics between lithium-ion batteries and EDLCs, and, thereby, can be suitably employed in idle reduction systems. Accordingly, it is expected for them to form a large market [2]. In order to satisfy the performance demands, it is often suggested that the energy density of EDLCs be enhanced to 20-30 Wh l −1 , which is approximately twice or more that of the present EDLCs, namely 5-10 Wh l −1 . To realize this high energy density, hybrid capacitor systems comprising nonaqueous redox materials are being dynamically researched and developed in recent years [3][4][5][6][7][8][9][10][11]. This chapter deals with the recent contributions to get this high energy density by focusing on two major hybridized cell configurations in organic media. Voltage Limitation of Conventional EDLCsAs described, increasing the energy density is one of the most crucial matters. For conventional EDLC systems, designed with two symmetrical activated carbon

A Review of Metal Oxide Composite Electrode Materials for Electrochemical Capacitors

“…69 In addition, conducting polymer-based electrochemical capacitors exhibit lower cycle life due to volume change or swelling as a result of the doping (intercalation)/de-doping (de-intercalation) of ions. 67 The conductivity of conducting polymer was rst reported in 1963 by McNeill and co-workers. 65 They exhibit the pseudocapacitive and conductive behavior via electron delocalization in conjugated chemical bond system along the polymer backbone.…”

“…It is suggested that the adsorption-desorption of anions from electrolytes occurs on the AC electrode while lithium intercalation-deintercalation occurs in the graphite electrode. 67 Similarly, Sivakkumar and Pandolfo have fabricated a lithium-ion capacitor assembled with pre-lithiated graphite anode and AC cathode, exhibiting energy density of 100 Wh/kg. 125 However, the study reveals that the instability of pre-doped graphite during the cycling is the main root cause of the capacity deterioration.…”

“…Cost continues existing as a major challenge to the mass production of EC particularly for high-performance applications. In view of this, the recent development of cost-e®ective electrode materials is underway by a 67 The use of these lithium metal oxides in hybrid capacitor results in excellent cyclability and rate capability, o®ering alternatives for the lifespan limitations associated with batteries as well as unsatisfactory energy density of capacitors. 114 Amatucci et al¯rst proposed the Li 4 Ti 5 O 12 /AC hybrid energy storage system which is able to achieve more than 10 Wh/kg in acetonitrile solution.…”

“…69 66 With these reasons, three main approaches are proposed: (i) replacing electrode material with higher capacitance nanostructured carbon or pseudocapacitive materials, (ii) changing electrolyte by durable new electrolytes and (iii) developing hybrid cell con¯gurations. 67 In particular, exploring new hybrid energy storage systems have received a great deal of attention. The possible hybrid cell con¯guration is the combination of EDLCs and pseudocapacitive materials which o®ers synergetic e®ect in capacitive performance.…”

“…124 Very recently, Naoi's group has identi¯ed that the conventional lithium metal oxides have the greatest drawback of low power characteristics as a result of poor Li þ di®usion coe±cient and poor electronic conductivity. 67 To overcome these problems, further development on composite electrode materials which couple lithium metal oxide powder with other electrocondcutive material may become a versatile solution. With regards to this, the research group has developed lithium-ion capacitors comprise AC cathode and conductive graphite/AC anode pre-doped with lithium ions.…”