High-energy-density hybrid electrochemical capacitor using graphitizable carbon activated with KOH for positive electrode

Aida, Taira; Murayama, Ichiro; Yamada, Kôji; Morita, Masayuki

doi:10.1016/j.jpowsour.2007.01.037

Cited by 64 publications

(34 citation statements)

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“…69 Aida et al has proposed an advanced hybrid electrochemical capacitor (HEC) using KOHactivated soft carbon for the positive electrode combined with a hard carbon negative electrode. 10 It showed high specific energy of 134 Wh L ¹1 as well as high power density (14 kW L ¹1 ). 10 In spite of relatively larger particle size (ca.…”

Section: ¹1mentioning

confidence: 99%

“…10 It showed high specific energy of 134 Wh L ¹1 as well as high power density (14 kW L ¹1 ). 10 In spite of relatively larger particle size (ca. 12 µm) and smaller surface area (46 m 2 g ¹1 ), the specific capacitance of the soft carbon significantly increases by the first charging process, so-called electrochemical activation, and the specific capacitance of the resulting HEC exceeds those of conventional EDLCs using AC.…”

Section: ¹1mentioning

confidence: 99%

“…Typically, the ASC material was considered to be a positive electrode of HEC, because the electrochemical activation is effectively taken place accompanied by electrochemical insertion of anions. 8,10 However, the electrochemical activation also occurs by the cathodic polarization accompanying cation-insertion, 11 which suggests that ASC can be used as a negative electrode in a HEC system. Thus, model capacitor cells have been constructed using ACF as the counter (positive or negative) electrode.…”

Section: ¹1mentioning

confidence: 99%

“…10,11 The ACF made from petroleum pitch was received from Kureha Chemical, Japan. The SEM images of ASC and ACF electrode materials are shown in Fig.…”

Section: ¹1mentioning

confidence: 99%

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Combination of Alkali-Treated Soft Carbon and Activated Carbon Fiber Electrodes for Asymmetric Electric Double-Layer Capacitor

et al. 2012

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An asymmetric combination of alkali-treated soft carbon (ASC) with activated carbon fiber (ACF) electrodes has been utilized to develop a novel electric double-layer capacitor (EDLC). The capacitance of ASC electrode was significantly increased after electrochemical activation at the first high potential cycling. Electrochemical measurements were carried out by charge-discharge polarization and ac impedance methods using a 3-electrode cell with propylene carbonate (PC) dissolving 1.0 M tetrafluorobrate (BF 4 − ) salt of tetraethylammonium (TEA + ) or lithium (Li + ). The charge-discharge performance of the cell that consists of ASC as the negative and ACF as the positive electrodes with TEABF 4 electrolyte, denoted as ASC(−)/TEABF 4 (PC)/ACF(+), showed higher specific capacitance than other systems for the cycling in the voltage range of 0.0-3.0 V. The cell using LiBF 4 electrolyte, ASC(−)/LiBF 4 (PC)/ACF(+), gave poor capacitance behavior probably due to undesirable electrolyte decomposition at the positive electrode. The ACF(−)/ASC(+) cell using TEABF 4 /PC also showed high capacitance, high coulombic efficiency and good cycle stability. The optimized cell with TEABF 4 /PC electrolyte had over 100 Wh kg −1 of energy density for the cycling in 0.0-3.5 V range.

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confidence: 99%

Section: ¹1mentioning

confidence: 99%

Section: ¹1mentioning

confidence: 99%

“…10,11 The ACF made from petroleum pitch was received from Kureha Chemical, Japan. The SEM images of ASC and ACF electrode materials are shown in Fig.…”

Section: ¹1mentioning

confidence: 99%

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Combination of Alkali-Treated Soft Carbon and Activated Carbon Fiber Electrodes for Asymmetric Electric Double-Layer Capacitor

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“…z E-mail: staser@ohio.edu of the two electrodes is different, the device is known as an asymmetric capacitor. [8][9][10][11][12][13][14][15][16][17][18][30][31][32][33][34][35] In this paper, we will use the term "hybrid asymmetric capacitor" to indicate that one electrode behaves like a capacitor and the other electrode like a battery material (i.e., faradaic reactions).Srinivasan and Weidner developed analytical solutions for symmetric capacitors with porous electrodes to demonstrate the tradeoff between energy and power density upon varying the physical properties (i.e., the thickness) of the porous electrode.6 Lin, et al developed similar models based on finite difference solutions of the capacitor equations that showed that energy density increased with decreasing pore size, with little effect of pore size on power density.7 Recently, Kang, et al have developed equivalent circuit models for double-layer electrochemical capacitors using electrochemical impedance spectroscopy experiments. 36 They were able to correlate the resistance of the electrolyte with the capacitor performance during charge/discharge cycles.…”

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Mathematical Modeling of Hybrid Asymmetric Electrochemical Capacitors

Weidner

2014

J. Electrochem. Soc.

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Electrochemical capacitors may be ideal energy storage devices for applications ranging from renewable energy storage to transportation. Electrochemical capacitors are characterized by high power density and cycle life, and can be classified based on the properties of their electrodes. Symmetric capacitors have two electrodes that exhibit the same behavior, while asymmetric capacitors have two electrodes that exhibit different behavior. A hybrid asymmetric capacitor is a device that has two electrodes that behave differently because of different processes occurring in them. In this paper, we present a mathematical model of hybrid asymmetric capacitors made up of a redox couple electrode and a double-layer electrode. We show that, because of the different behavior of each electrode, the hybrid asymmetric capacitor possesses higher energy and power density than the symmetric capacitor. Our model is generic and can be extended to any device so long as the properties of the electrodes are known. Electrochemical energy storage systems like electrochemical capacitors may be ideal to meet the needs of renewable energy storage and electric vehicles.1-3 Electrochemical capacitors are characterized by high power density and high cycle life. In the simplest terms, electrochemical capacitors store energy in the double layer at the interface of an electrically conductive material and the electrolyte. No faradaic reaction occurs. Double layer capacitance is low, usually between 10 and 40 μF cm −2 of electrode surface area. Therefore, high surface area materials are used (e.g., porous carbon electrodes) to significantly increase the capacitance of the device. 4 Because the voltage across a double layer is proportional to the charge stored, the voltage of a device decreases linearly with time during an entire constant-current discharge. In contrast, the voltage across a device where a faradaic reaction occurs across the electrode/electrolyte interface (i.e., a battery) is determined by the activity of the reactants and products. Therefore, its constant-current discharge curve is sigmoidal in shape, and hence the voltage is fairly constant over a significant portion of the discharge. Finally, pseudocapacitance is a term used to describe storage of charge via faradaic reactions where the activities of reactants and products are such that the discharge curve of a device more closely resembles a capacitor than it does a battery. Although pseudocapacitor response is much like a double-layer capacitor, they have considerably higher capacitance, and hence energy.Regardless of the type of device (i.e., double-layer capacitor or pseudocapacitor), the term "capacitor" is valid when the electrodes behave like a capacitor. Major efforts related to double-layer capacitors have focused on understanding the effect of electrode thickness and pore structure on the energy density and device capacity. 5-7Efforts toward developing pseudocapacitors have mostly focused on creating different electrode materials with most emphasis given to metal oxide...

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2017

Supercapacitors Based on Carbon or Pseudocapacitive Materials

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High-energy-density hybrid electrochemical capacitor using graphitizable carbon activated with KOH for positive electrode

Cited by 64 publications

References 19 publications

Combination of Alkali-Treated Soft Carbon and Activated Carbon Fiber Electrodes for Asymmetric Electric Double-Layer Capacitor

Combination of Alkali-Treated Soft Carbon and Activated Carbon Fiber Electrodes for Asymmetric Electric Double-Layer Capacitor

Mathematical Modeling of Hybrid Asymmetric Electrochemical Capacitors

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