Electrode and electrolyte materials for electrochemical capacitors

Among different electric energy storage technologies electrochemical capacitors are used for energy storage applications when high power delivery or uptake is needed. Their energy and power densities, durability and efficiency are influenced by electrode and electrolyte materials however due to a high cost/performance ratio; their widespread use in energy storage systems has not been attained yet.Thanks to their properties such as high surface area, controllable pore size, low electrical resistance, good polarizability and inertness; activated carbons derived from polymeric precursors are the most used electrode materials in electrochemical capacitors at present. Other electrode materials such as shaped nano-carbons or metal oxides are also investigated as electrode materials in electrochemical capacitors, but only as useful research tools.Most commercially used electrochemical capacitors employ organic electrolytes when offering concomitant high energy and high power densities. The use of aqueous based electrolytes in electrochemical capacitor applications is mainly limited to research purposes as a result of their narrow operating voltage. Recent studies on room temperature ionic liquids to be employed as electrolyte for electrochemical capacitor applications are focused on fine tuning their physical and transport properties in order to bring the energy density of the device closer to that of batteries without compromising the power densities.In this paper a performance analysis, recent progress and the direction of future developments of various types of materials used in the fabrication of electrodes for electrochemical capacitors are presented. The influence of different types of electrolytes on the performance of electrochemical capacitors such as their output voltage and energy/power densities is also discussed.     

Synthesis of engineered graphene nanocomposites coated with NiCo metal-organic frameworks as electrodes for high-quality supercapacitor

Metal-organic frameworks (MOF) are a novel generation of promising electrodes for supercapacitors. The synthesis of glucose modified, high-quality graphene (HQG) as a platform for the nucleation and growth of bimetallic MOF nanosheets (NiCo-MOF) is reported. The –COOH and –OH groups formed on the surface, thus enhance the interaction between the HQG and NiCo-MOF. This heterostructure is used as an electrode in the preparation of asymmetric supercapacitors with a capacity of 244 F/g and an energy density of 76.3 W h/g. The nanocomposite also exhibits a high specific capacitance of 4077.3 F/g at a current density of 2.5 A/g. Therefore, new approaches have been introduced for the fabrication of efficient supercapacitors, and a step forward has been taken for the development of other electrical applications, including batteries, fuel cells, catalysts, and types of sensors.     

Metal-organic frameworks as highly efficient electrodes for long cycling stability supercapacitors

Among a large variety of energy storage technologies, supercapacitors possess special advantages such as rapid charge/discharge, high power density, safety, and environmental friendliness to meet the requirement of specific applications. The common electrode materials of supercapacitors, including porous carbon, conductive polymers, and metal oxides/hydroxides, have their own benefits and drawbacks in energy density and stability. Owing to the big surface area and controllable porosity, the metal-organic frameworks (MOFs) have been explored as important candidates for supercapacitor applications. This mini-review focuses on the recent advances of MOF-based materials including pristine MOFs, MOFs composite materials, and MOF-derived materials in the development of long cycling life supercapacitors. The devices discussed here mean those with capacitive retention rates of more than 90% after 10,000 cycles and high energy density. In addition, we also describe the fundamental knowledge of supercapacitors, highlight the stabilization mechanism of MOFs, and propose the strategies to enhance the stability of MOF-based supercapacitor electrodes.     

Graphene‐based materials for flexible electrochemical energy storage

Sustainable development of renewable energy sources is one of the most important themes that humanity faces in this century. Wide use of renewable energy sources will require a drastically increased ability to store electrical energy. Electrochemical energy storage devices are expected to play a key role. With the increased demand in flexible energy resource for wearable electronic devices, great efforts have been devoted to developing high‐quality flexible electrodes for advanced energy storage and conversion systems. Because of its high specific surface area, good chemical stability, high mechanical flexibility, and outstanding electrical properties, graphene, a special allotrope of carbon with two‐dimensional mono‐layered network of sp² hybridized carbon, have been showing great potential in next‐generation energy conversion and storage devices. This review presents the latest advances on the flexible graphene‐based materials for the most vigorous electrochemical energy storage devices, that is, supercapacitors and lithium‐ion batteries. Copyright © 2014 John Wiley & Sons, Ltd.     

Research progress of metal oxides as anode materials for lithium ion capacitors

锂离子电容器是一种介于超级电容器和锂离子电池之间的新型储能器件,具有高能量密度、高功率密度以及长循环寿命等优点,在电动汽车、轨道交通、智能电网、可移动电子设备等领域具有非常广泛的应用前景。金属氧化物具有脱/嵌锂能力优异,理论比容量普遍较高,而且自然资源丰富、环境友好的优点,是一类理想的锂离子电容器负极材料,但电子导电率不高,脱/嵌锂过程中不可逆体积畸变较大,影响了其商业化的应用。本文综述了金属氧化物负极材料的制备方法,并分析了其作为锂离子电容器负极材料的电化学性能与优缺点,最后展望了金属氧化物负极材料未来的发展方向。     

生物炭应用于超级电容器电极的研究进展

生物质资源储量丰富,可通过热化学等方法转化制备性能优良的生物炭.生物炭材料具有较大的比表面积、较高的孔隙率、丰富多样的孔道结构以及优良的导电率,将其作为超级电容器电极材料有利于提高双电层超级电容器的电化学性能,应用前景良好.通过介绍两种超级电容器工作原理,总结了生物炭作为电极材料的制备和改性方法,论述了生物炭的比表面积...     

Graphene/single-walled carbon nanotube hybrids and applications in supercapacitors

双电层超级电容器作为新型清洁能源储能器件,具有安全、高功率密度和长寿命的优点。目前发展新电极材料与提高工作电压窗口是提高电容器能量密度的重要方向。本工作利用化学气相沉积法制备了石墨烯-碳纳米管杂化物,具有导电性优良、孔径可调、化学稳定性高、比表面积大（1200～1800 m2/g）的优点,同时避免了单独石墨烯或者碳纳米管电极制备过程中堆叠的缺点。并且系统研究了石墨烯-碳纳米管杂化物在水系、有机电解液和离子液体中的电容性质,考察了以活性炭为主体电极材料,石墨烯-碳纳米管为添加剂的软包电容器的性质,为开发高能量密度和高功率密度的超级电容器提供了基础。     

Rational design of hierarchical core-shell structured CoMoO4@CoS composites on reduced graphene oxide for supercapacitors with enhanced electrochemical performance

Engineering multicomponent active materials as an advanced electrode with the rational designed core-shell structure is an effective way to enhance the electrochemical performances for supercapacitors. Herein, three-dimensional self-supported hierarchical CoMoO₄@CoS core-shell heterostructures supported on reduced graphene oxide/Ni foam have been rationally designed and prepared via a facile approach. The unique structure and the synergistic effects between two different materials, as well as excellent electronic conductivity of the reduced graphene oxide, contribute to the increased electrochemically active site and enhanced capacitance. The core-shell CoMoO₄@CoS composite displays the superior specific capacitance of 3380.3 F g⁻¹ (1 A g⁻¹) in the three-electrode system and 81.1% retention of the initial capacitance even after 6000 cycles. Moreover, an asymmetric device was successfully prepared using CoMoO₄@CoS and activated carbon as positive/negative electrodes. It is worth mentioning that the device delivered the high energy density of 59.2 W h kg⁻¹ at the power density of 799.8 W kg⁻¹ and the excellent cycle performance (about 91.5% capacitance retention over 6000 cycles). These results indicate that the core-shell CoMoO₄@CoS composites offers the novelty strategy for preparation of electrodes for energy conversion and storage devices.     

Analyses of international patents on DII based supercapacitors

超级电容器作为一种新型储能装置越来越受到世界各国的重视。因此，本文基于德温特创新索引国际专利数据库（DⅡ），利用Thomson Data Analyzer（TDA）、智慧芽数据库（Patsnap）等专业分析工具和平台，对超级电容器专利技术进行深入分析，以期全面系统揭示超级电容器技术的研发现状、研发热点、技术方向布局及竞争格局等。研究结果表明，从2009年开始，超级电容器技术专利申请量快速增长，目前仍在快速增长期；其主要技术方向为超级电容电极材料及其制备方法、电解质及其制备方法；研究热点主要为双层电容、电容器电极、电解液等；专利申请排名前三位的国家分别为中国、日本和美国；专利申请排名前三位的机构依次为松下电器、日本贵弥功株式会社、明电舍株式会社。     

Graphene-conducting polymer nanocomposite as novel electrode for supercapacitors

A novel graphene-polyaniline nanocomposite material synthesized using chemical precipitation technique is reported as an electrode for supercapacitors. The graphene (G)-polyaniline (PANI) nanocomposite film was dissolved in N-Methyl-2-pyrrolidone (NMP) and characterized using Raman, FTIR, Scanning Electron Microscopy, Transmission Electron Microscopy, and cyclic voltammetry (CV) techniques. The interesting composite structure could be observed using different ratios of graphene and aniline monomer. The supercapacitor is fabricated using G-PANI in N-Methyl-2-pyrrolidone (NMP) and G-PANI-Nafion films on graphite electrodes. A specific capacitance of 300-500 F g⁻¹ at a current density of 0.1 A g⁻¹ is observed over graphene-PANI nanocomposite materials. The aim of this study is to tailor the properties of the capacitors through the optimization of their components, and packaging towards a qualification for portable systems applications. Based on experimental data shown in this work, conducting polymer nanocomposite capacitor technology could be viable, and could also surpass existing technologies when such a novel approach is used.     

Carbon nanotubes: A potential material for energy conversion and storage

Carbon nanotube-based materials are gaining considerable attention as novel materials for renewable energy conversion and storage. The novel optoelectronic properties of CNTs (e.g., exceptionally high surface area, thermal conductivity, electron mobility, and mechanical strength) can be advantageous for applications toward energy conversion and storage. Although many nanomaterials are well known for the unique structure-property relations, such relations have been sought most intensively from CNTs due to their extreme diversity and richness in structures. For the development of energy-related devices (like photovoltaic cells, supercapacitors, and lithium ion batteries), it is critical to conduct pre-evaluation of their design, operation, and performance in terms of cost, life time, performance, and environmental impact. This critical review was organized to address the recent developments in the use of CNT-based materials as working/counter electrodes and electrolytes in photovoltaic devices and as building blocks in next-generation flexible energy storage devices. The most promising research in the applications of CNTs toward energy conversion and storage is highlighted based on both computational and experimental studies along with the challenges for developing breakthrough products.     

The choice of noble electrolyte for symmetric polyurethane-graphene composite supercapacitors

Simple, low cost, highly conducting, flexible, lightweight and porous electrodes are prepared using reduced graphene oxide (rGO) for energy storage device applications. Graphene oxide (GO) slurry is prepared using graphite powder through oxidation followed by solvothermal reduction. A simple dip and dry method to fabricate flexible electrodes by depositing GO on the skeleton of foams is reported. These electrodes are chemically reduced to enhance the conductivity and are used as an electrode material to facilitate large surface area and fast ionic diffusion. The state of the art of present work is all the devices studied under open air condition. The electrochemical studies demonstrate that the constructed supercapacitors exhibit a high specific capacitance of 69 F/g in 1 M NaOH electrolyte at 2 mVs⁻¹ scan rate which is significantly high. Also, the devices showed encouraging performance when constructed with different electrolytes, which helps to understand the electrolytic effect and to choose the best electrolyte for the high performance of supercapacitors.     

Advances in supercapacitors: From electrodes materials to energy storage devices

随着绿色储能器件的快速发展,超级电容器作为兼具高比能量与高比功率的优点,在储能领域具有重要发展潜力的新型储能器件,本综述从超级电容器的电极材料出发,详细概括了超级电容器电极材料的发展,包括双电层电容材料、赝电容材料以及双电层/赝电容复合材料;在此基础上,基于固态电解质,深入讨论了近年来全固态超级电容器的典型构型,针对性地总结了提高储能器件储能容量的关键问题。最后,基于电极材料与电解液的研究焦点,对超级电容器的研究提出了未来发展方向。     

Graphene-based electrocatalysts: Hydrogen evolution reactions and overall water splitting

Recently, carbon-based materials (e.g., graphene, carbon nanotubes, carbon quantum dots) have been used as electrocatalysts to catalyze the reactions such as hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Among them, graphene has attracted attention as an electrocatalyst, and its electrocatalytic performances have been improved by doping with metals and non-metals, surface and defect engineering, and hybrid development. In this perspective, the present paper reviewed the recent advances (2018 onwards) on the progress of graphene-based electrocatalysts for HER and overall water splitting (OWS). It is emphasizing strategies for optimizing electrocatalytic properties followed by challenges and future outlook. This review will provide the essential ideas and strategies that can help design graphene-based electrocatalysts of high performance that can be implemented for sustainable energy application.     

Recent progress in the application of carbon materials to supercapacitors and lead-carbon batteries

新型炭材料是电化学储能领域中非常重要的一类储能材料,目前广泛应用于各种电化学储能器件.本文综述了具有电容特性的高比表面积炭材料在超级电容器与铅炭电池中的应用.采用不同的方法合成具有高比表面积的新型炭材料作为超级电容器电极材料,能够得到较高的比容量.适量高比表面积的炭材料应用于铅酸电池负极,形成铅炭电池,极大地提高了电池的储能特性.论文最后探讨了新型炭材料在超电容以及铅炭电池中应用的发展方向.     

Solvothermal synthesis of flower-like structure Cu-Mn bimetallic sulfide on Ni-foam for high-performance symmetric supercapacitors

Although transition metal sulfides have gotten extensive attention due to their high electrical conductivity, fast charge transfer kinetics, outstanding mechanical stability, the performances of them applied separately to supercapacitors are not satisfactory, and one solution is to hybridize with other metal sulfide materials. Therefore, in the study, the flower-like structure Cu-Mn bimetallic sulfide on Ni-foam (CuS/MnS@NF) was firstly synthesized by a hierarchical two-step solvothermal reaction to our knowledge, which was directly utilized as electrodes without binders or conductive agents. The CuS/MnS@NF electrode possesses flower-like morphology, superior electrical conductivity, and there are the synergistic effect and intense interaction between CuS and MnS. They can display higher specific capacitance of 1517.07 F g⁻¹ at 1 A g⁻¹ and excellent cyclic stability with specific capacity retention of 115.6% at 10 A g⁻¹ after 3000 cycles, which is more admirable than their individual metal sulfide electrodes (CuS@NF and MnS@NF) and other recently reported metal-based electrodes. In short, the CuS/MnS@NF electrodes are promising candidate when used in battery-type supercapacitors.     

Carbon nanotubes for flexible energy storage devices--A review

碳纳米管具有本征sp²共价结构所带来的优异导电,导热及力学性能,并在锂电池,超级电容器等储能体系中具有广泛的应用前景.本文回顾了碳纳米管柔性储能的背景,介绍了碳纳米管优异的性能,独特的结构.这种一维的管状结构既可以作为柔性电极中的支撑骨架,也可以构建优越的长程导电网络,提供能源存储活性位点,进而提高柔性器件的性能.本文详细评述近年来碳纳米管在柔性超级电容器,锂离子电池,锂硫电池等能源存储元件应用中的一些最新进展和研究热点,其中柔性超级电容器,锂离子电池方面研究比较成熟,而锂硫电池尚在起步阶段,预期会取得快速进步.文章介绍了电极构建途径及性能评估方法,展示了碳纳米管基柔性储能器件的进展,并展望了其未来发展方向.     

Research progress on capacitive lithium-ion battery

锂离子电池具有高的能量密度,而超级电容器则以高功率密度和长循环寿命为突出优势。电容型锂离子电池是在锂离子电池的正极中加入部分电容炭材料,在不显著降低能量密度的情况下,大幅度改善锂离子电池的功率特性和循环寿命,从而实现电容与电池技术的融合。本文综述了国内外近年来在电容型锂离子电池领域的最新研究进展,介绍了主要的电容型锂离子电池体系及其性能特点,并对其未来发展方向进行了展望。     

Pt/3D-graphene/FTO electrodes: Electrochemical preparation and their enhanced electrocatalytic activity

We report a facile, low-cost and green route to fabricate platinum nanoparticle (Pt NP) decorated three-dimensional (3D) graphene assembled on fluorine-doped tin oxide (FTO) electrodes (Pt/3D-G/FTO) with enhanced electrocatalytic activity. The fabrication process was accomplished by preparation of 3D graphene (3D-G/FTO) electrodes through electrochemical reduction of a graphene oxide suspension followed by electrodeposition of Pt NPs onto them. The Pt/3D-G/FTO electrode exhibits much higher catalytic activity and better stability for methanol oxidation compared with the electrodes prepared by electrodeposition of Pt NPs onto two-dimensional graphene sheets substrate (Pt/G/FTO) or bare FTO (Pt/FTO) under the same condition. These enhancements can be attributed to the high surface area, large void volume and high electrical conductivity as well as smaller size of Pt NPs in the hollows of the 3D architecture and a large amount of ridges on it.     

Analysis of electrodes matching for asymmetric electrochemical capacitor

Asymmetric electrochemical capacitor was categorized into two types: a battery-type electrode|capacitor-type electrode capacitor and a capacitor-type electrode|capacitor-type electrode capacitor. When designing asymmetric electrochemical capacitor, the influences of both current density and the electrode's potential window were taken into account. This article analyzed how the mass ratio between two electrodes influenced the electrochemical performances of asymmetric electrochemical capacitor. The formulas describing capacitor performance parameters (work voltage, specific capacitance, energy density and power density) were derived and applied to two types of asymmetric electrochemical capacitors. Therefore, the concrete relationships between mass ratio of electrodes and capacitor parameters were obtained. The influence of current density on mass ratio was investigated with organic LiMn₂O₄/AC system and others.