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    28 October 2017, Volume 23 Issue 5
    Table of Contents
    Table of Contents-2017,Vol 23(5)
    2017, 23(5):  0. 
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    Special Issue on Supercapacitors(Editor: Prof. ZHANG Xiao-gang)
    Special Issue on Supercapacitors
    ZHANG Xiao-gang
    2017, 23(5):  495-496.  doi:10.13208/j.electrochem.170340
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    Supercapacitors (SCs) have become a new bright spot in electrochemical power source due to their high power density, long cycling life and wide operation temperature. As the high-power density energy storage devices, SCs have been widely applied in electric vehicle, modern communication, aerospace, defense, and many other emerging fields. The markets for SCs are continuously increasing. However, the commercialization of SCs suffers from a lower energy density and higher cost. Thus, one great challenge for the supercapacitor (SC) technology is to improve the energy density without sacrificing the power density and cycle life. To address this critical issue, the worldwide SC researchers have focused on design of electrode materials, developments in new-type electrolyte and assemble method of device. Many significant breakthroughs in theoretical studies and engineering applications have been achieved. In this special issue, we collect eight submissions including review and research articles from the leading research groups in SCs. The recent progresses, future trends and new challenges in the field of SCs researches have been presented and highlighted. We hope that this special issue may attract more attention from researchers to focus their studies on this booming field, and to promote the research and development of SCs in China. We would like to take this opportunity to thank all the authors, reviewers, and editorial staffs of Journal of Electrochemistry for their excellent and professional contributions to this special issue.
    Electrochemical Capacitors Based on Anion-Graphite Intercalation Compounds
    WANG Hong-yu, FAN Hui, WANG Xiao-hong, Qi Li
    2017, 23(5):  497-506.  doi:10.13208/j.electrochem.170343
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    Anions can be electrochemically intercalated into a graphite electrode with a reversible capacity as high as 120 mAh·g-1 at the high potential near 5 V vs. Li/Li+. Besides, graphite is environmentally benign, economic and abundant in China. Therefore, graphite is a very promising positive electrode material for asymmetric capacitors using non-aqueous electrolytes. However, the performance of graphite positive electrode is quite sensitive to various affecting factors, such as the compositions of electrolyte solutions, graphite type and ambient temperature, and so on. In the platform of activated carbon/graphite capacitors, the electrochemical behavior of anion-graphite intercalation compounds can be systematically studied by a series of in situ electrochemical techniques. Future development in this type of electrode materials has been anticipated in terms of new electric energy storage devices under different circumstances.
    Strategies to Enhance Energy Density for Supercapacitors
    LANG Jun-wei, ZHANG Xu, WANG Ru-tao, YAN Xing-bin
    2017, 23(5):  507-532.  doi:10.13208/j.electrochem.170348
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    The biggest advantage of supercapacitor lies in not only the excellent pulse and fast charging-discharging performance, but also the characteristics of long cycle life and wide operating temperature window with no pollution. However, the energy density of supercapacitor is low. In this paper, the working principle, the development status, defects and improvement method of supercapacitors are introduced. Based on the research workes of the supercapacitors with high energy density in our group, combined with the literature reports in recent years, the strategies to promote the energy density of supercarpacitors will be focused. The strategies for the enhancement of energy density include: 1) to increase the specific capacitance of the electrode by reducing the existing materials to nano sizes or to develop new materials with high capacity; 2) to increase the voltage window of the supercapacitor by developing ionic liquid electrolyte with high voltage window or to adopt asymmetric supercapacitors in which one electrode is pseudocapacitive, while the other utilizes double layer capacitance; 3) to build lithium ion hybrid supercapacitors with both high energy density and high power density by “internal cross” the supercapacitor and lithium ion battery. Finally, the prospects in the future development of supercapacitors will be provided.
    Attempts to Improve the Energy Capacity of Capacitive Electrochemical Energy Storage Devices
    YU Lin-po, CHEN George Z.
    2017, 23(5):  533-547.  doi:10.13208/j.electrochem.170347
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    This article reviews selected literatures from the authors’ research group on the development of capacitive electrochemical energy storage (EES) devices, focusing on supercapacitors and supercapatteries at both the electrode material level and device level. Electronically conducting polymers (ECPs) and transition metal oxides (TMOs) composited with carbon nanotubes (CNTs) were found to be able to improve the capacitance performance as capacitive faradaic storage electrode. Carbon materials, like activated carbon (Act-C) and carbon black, were used to fabricate non-faradaic capacitive storage electrode. It was found that the electrode capacitance balance can effectively extend the maximum charging voltage (MCV) of the supercapacitor, and hence, to enhance the energy capacity of this capacitive EES device. The MCV of this kind of device can also be multiplied by bipolarly stacking the supercapacitors to meet the high voltage demand from the power device. Supercapatteries that take advantages of both capacitive and faradaic charge storage mechanisms have been proposed and demonstrated to achieve the high power capability of supercapacitors and the large storage capacity of batteries.
    Porous Carbon Materials Produced by KOH Activation for Supercapacitor Electrodes
    YE Jiang-lin, ZHU Yan-wu
    2017, 23(5):  548-559.  doi:10.13208/j.electrochem.170341
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    Porous carbon materials with high specific surface area and excellent conductivity have wide applications in supercapacitor electrodes. Much effort has been made to synthesize and tailor the microstructures of porous carbon materials via various activation procedures (physical and chemical activations). In particular, the chemical activation using potassium hydroxide (KOH) as an activating reagent is promising because of the well-defined micropore size distribution and ultrahigh specific surface area up to 3000 m2·g-1 of the resulting porous carbons. Based mainly on the previous works taken by the authors and collaborators in the field, we have summarized the activation mechanism of KOH, the conversion of the carbon resources to porous carbons and the performance of the resulting porous carbons in supercapacitor electrodes. We hope that this review will be helpful to promote the development of high-performance porous carbon materials as supercapacitor electrodes.
    Recent Advances on Carbon and Transition Metallic Compound Electrodes for High-Performance Supercapacitors
    LIN Dun, ZHANG Xi-yue, ZENG Yin-xiang, YU Ming-hao, LU Xi-hong,TONG Ye-xiang
    2017, 23(5):  560-580.  doi:10.13208/j.electrochem.170342
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    Supercapacitors (SCs) have stimulated intensive interests for their promising applications in electric vehicles and portable electronics, etc. Electrode material is the most important key component of SCs, which vastly determines the performance of SCs. Carbon and transition metallic compound materials have attracted considerable attention and been widely explored as electrode materials. However, the insufficient capacitance of carbon materials and unsatisfactory conductivity and cyclic stability of transition metallic compounds severely limit their implementation as robust SC electrodes. Herein, we highlight our recent efforts to boost the capacitive performance of carbon and metal oxide/nitride electrodes by rationally structural and componential design. The relationships between structures and performances,  as well as the mechanisms are discussed. Finally, we also present our personal perspectives on the further research of these electrodes.

    An Aqueous Zn-Ion Capacitor
    ZHAO Jing-wen,LI Jia-jia,HAN Peng-xian,CUI Guang-lei
    2017, 23(5):  581-585.  doi:10.13208/j.electrochem.170344
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    We first present a new aqueous zinc-ion (Zn-ion) capacitor based on vanadium pentoxide ( V2O5) cathode, activated carbon (AC) anode, and 2 mol·L-1 zinc trifluoromethanesulfonate (Zn(TfO)2) electrolyte. The Zn-ion capacitor possesses a wide electrochemical window of 1.4 V, good rate capability and cycling stability. The XRD data demonstrates that the Zn2+ ion serving as the charge carrier could be reversibly intercalated into the V2O5. This capacitor delivered a power density of 181 W·kg-1 and an energy density of 4.5 Wh·kg-1 at 1000 mA·g-1. This work may open up new opportunities for developing multivalent ion-based electrochemical capacitors.
    Lithium Ion Hybrid Capacitor with High Energy Density
    SUN Xian-zhong, ZHANG Xiong, WANG Kai, MA Yan-wei
    2017, 23(5):  586-603.  doi:10.13208/j.electrochem.170346
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    Lithium ion hybrid capacitors are electrochemical energy storage devices combining the advantages of both Li-ion battery and electrochemical capacitor. They can be extensively used in many fields. However, the commercialization of lithium ion hybrid capacitor has been encountered several problems, e.g., the device structure design, the screening of materials, the pre-lithiation process, and the interface between electrolyte and electrode, etc. This review summarizes the recent research advances in lithium ion hybrid capacitor with high energy density, including the selection of the active materials in cathode/anode and the separator, the pre-lithiation method using the three-electrode structure, the high- and low-temperature performances, the capacity fading behaviors, the charge storage mechanisms and the device fabrication of lithium ion hybrid capacitor (including lithium ion capacitor and lithium battery-type supercapacitor). Finally, the perspectives and future developments of lithium ion hybrid capacitor are highlighted.

    Template Induced Fabrication of Nitrogen Doped Carbon Sheets as Electrode Materials in Supercapacitors
    HUANG Tao, TAO Guang-zhi, YANG Chong-qing, LU Deng, MA Lie, WU Dong-qing
    2017, 23(5):  604-609.  doi:10.13208/j.electrochem.170345
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    Due to the good electrical conductivity, high specific surface area, and excellent chemical/mechanical stability, carbon nanomaterials with two-dimensional morphology have gradually become the hot topic of the research on supercapacitors. Herein, we report for the first time the fabrication of nitrogen doped carbon sheets (NCSs). In our approach, the sheet-like magnisum aluminum (MgAl) layered double hydroxide was used as the hard template, which was mixed with o-phenylene diamine and iron chloride. The following thermal treatment could render the polymerization and carbonization of o-phenylene diamine. The NCSs with ordered hexagonal architectures were formed by final etching process of the thermally treated mixture. The morphology, structure, graphitic degree, nitrogen content and surface area of the as-prepared NCSs could be adjusted by the temperatures of the thermal treatment. More importantly, the NCSs exhibited outstanding electrochemical performances as the electrode materials in supercapacitors. Among the NCSs, the sample obtained from 600 oC (NCS-600) achieved a capacity of 290.0  F·g-1 at a current density of 0.5 A·g-1. After 10,000 cycles at 1 A·g-1, the NCS-600 still retained 83% of its initial capacity, indicating high cycling stability.
    Articles
    Preparation and Characterization of Cellulose Acetate-based Separator for Lithium-ion batteries
    LUO Hua-feng, QIAO Yuan-dong
    2017, 23(5):  610-616.  doi:10.13208/j.electrochem.160723
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    To improve the electrolyte wettability and thermal resistance of separators used for lithium-ion battery, a novel cellulose acetate (CA)-based separator is facilely prepared by non-solvent induced phase separation (NIPS) wet-process and investigated in lithium-ion batteries. Systematical investigations including morphological characterization, electrolyte wettability and thermal resistance testing were carried out. The results demonstrated that the CA-based separator exhibited well developed three-dimensional porous structures with porosity up to 65%, which is 1.5 times higher than that of PE separator. The CA separator also showed excellent electrolyte uptake (285%) and thermal stability at 150 oC for 30 min. Compared with the commercial PE separator, the CA separator exhibited better electrochemical performances, achieving superior discharge C-rate capability and cycling performance.