Electrolytic Double-Layer Supercapacitors Based on Sodium-Ion Systems,with Activated-Carbon Electrodes

1 M solutions of NaClO₄ mixed with ethylene carbonate, dimethyl carbonate, and fluoroethylene carbonate were studied as electrolytes for a double-layer supercapacitor with electrodes made of Norit DLC Supra 30 activated carbon. It was shown that the specific capacity of activated carbon depends on the electrolyte composition, range of cycling voltages, and current density. The maximum specific capacitance of 40 F g^–1 was obtained in 1 M NaClO₄ mixed with ethylene carbonate: dimethyl carbonate: fluoroethylene carbonate (4: 5: 1) at a current density of 36 mA g^–1 in the range 10–2300 mV. The minimum specific capacitance was obtained under the same cycling conditions in the electrolyte with 1 M NaClO₄ + ethylene carbonate: dimethyl carbonate (1: 1). The variation of the specific capacitance with the electrolyte composition and range of cycling voltages is accounted for by the existence of a pseudocapacitance caused by the occurrence of side processes on the surface of activated carbon. The impedance spectroscopy was used to find that the introduction of fluoroethylene carbonate into the electrolyte positively affects the charge-transfer resistance and favors an increase in the specific capacitance of activated carbon.     

Preparation and electrochemical performance of activated carbon thin films with polyethylene oxide-salt addition for electrochemical capacitor applications

The effect of polymer–salt addition in the activated carbon electrode for electric double-layer capacitor (EDLC) has been investigated. A series of composite thin film electrode consisting of activated carbon, carbon black, polytetrafluoroethylene and polymer–salt complex (polyethyleneoxide–LiClO₄) with an appropriate weight ratio were prepared and examined their performance for EDLCs using 1 mol L⁻¹ LiClO₄ in ethylene carbonate:diethylcarbonate electrolyte solution. The electrochemical capacitance performances of these electrodes with different compositions were characterized by cyclic voltammetry, galvanostatic charge–discharge cycling, and AC impedance measurements. By comparison, the best results were obtained with a composite electrode rich in polymer–salt additive (132 F g⁻¹ at 100 mA g⁻¹ of galvanostatic experiment). In general, the polymer–salt-containing electrode had shown improved performance over activated carbon electrodes without polymer–salt at high current density.     

Effect of surface oxygen functionalities on capacitance of activated carbon in non-aqueous electrolyte

Electric double-layer capacitors (EDLCs) are composed of two activated carbon (AC) electrodes and an electrolyte/separator, in which the ACs contain numbers of surface oxygen functionalities (SOFs). In this work, the effect of SOFs on the EDLC’s capacitance in non-aqueous electrolytes is studied by using a 1.0 m (molality) LiPF₆ 3:7 (wt.) ethylene carbonate-ethyl methyl carbonate electrolyte and a commercial activated carbon. Results show that the SOFs on one hand contribute to Faradic pseudocapacitance, and on the other hand adversely reduce the EDLC’s performances, including the initial reversibility, coulombic efficiency, and capacitance retention. It is found that the AC behaves significantly different in the Li/AC half cells and in the AC/AC full cells and that the SOF’s pseudocapacitance increases with widening the EDLC’s operating voltage. The latter is attributed to the large-voltage hysteresis of the redox of SOFs. In this paper, the AC’s unique behaviors in Li salt electrolyte are presented, and a possible mechanism for the observed behaviors is proposed.     

碳纳米管在室温熔盐中的电容特性

研究了碳纳米管在室温熔盐二(三氟甲基磺酸酰)亚胺锂(LiTFSI)-乙酰胺中的电容特性. 将碳纳米管制成薄膜电极, 以LiTFSI-乙酰胺为电解液, 装配成模拟电容器, 用循环伏安和恒流充放电法研究其电化学性能. 结果表明, 碳纳米管在室温熔盐中表现出典型的电容特性, 其比电容为22 F•g^-1, 模拟电容器的工作电压可达2.0 V, 具有非常好的循环性能, 循环充放电1000次后容量损失仅10%, 表明室温熔盐是超级电容器非常有前景的新型电解液.     

酚醛基活性炭纤维孔结构及其电化学性能研究

利用水蒸汽活化法制备了酚醛基活性炭纤维(ACF-H2O), 对其比表面积、孔结构与在LiClO4/PC(聚碳酸丙烯酯)有机电解液中的电容性能之间的关系进行了探讨. 用N2(77 K)吸附法测定活性炭纤维的孔结构和比表面积, 用恒流充放电法和交流阻抗技术测量双电层电容器(EDLC)的电容量及内部阻抗. 研究表明, 在LiClO4/PC有机电解液中, ACF-H2O电极的可用孔径(d)应在0.7 nm以上. 随着活化时间的延长, ACF-H2O的孔容和比表面不断增大, 但微孔(0.7 nm ＜ d ＜ 2.0 nm)和中孔(d ＞ 2.0 nm)率变化很小, 活化过程中孔的延伸和拓宽同步进行, 但过度活化则造成孔壁塌陷, 孔容和比表面迅速下降. 因此, 除活化过度的样品外, 电容量随比表面积呈线性增长, 最高达到109. 6 F•g-1. 但中孔和微孔的孔表面对电容的贡献不同, 其单位面积电容分别为8.44 μF•cm-2和4.29 μF•cm-2, 中孔具有更高的表面利用率. ACF-H2O电极的电容量、阻抗特性和孔结构密切相关. 随着孔径的增大, 时间常数减小, 电解液离子更易于向孔内快速迁移, 阻抗降低, 电极具有更好的充放电倍率特性. 因此, 提高孔径和比表面积, 减少超微孔(d ＜ 0.7 nm), 是提高 EDLC能量密度和功率密度的重要途径. 然而仅采用水蒸汽活化, 只能在小中孔以下的孔径范围内进行调孔, ACF-H2O电极电容性能的提高受限.     

A novel carbon electrode material for highly improved EDLC performance

Porous materials, developed by grafting functional groups through chemical surface modification with a surfactant, represent an innovative concept in energy storage. This work reports, in detail, the first practical realization of a novel carbon electrode based on grafting of vinyltrimethoxysilane (vtmos) functional group for energy storage in electric double layer capacitor (EDLC). Surface modification with surfactant vtmos enhances the hydrophobisation of activated carbon and the affinity toward propylene carbonate (PC) solvent, which improves the wettability of activated carbon in the electrolyte solution based on PC solvent, resulting in not only a lower resistance to the transport of electrolyte ions within micropores of activated carbon but also more usable surface area for the formation of electric double layer, and accordingly, higher specific capacitance, energy density, and power capability available from the capacitor based on modified carbon. Especially, the effects from surface modification become superior at higher discharge rate, at which much better EDLC performance (i.e., much higher energy density and power capability) has been achieved by the modified carbon, suggesting that the modified carbon is a novel and very promising electrode material of EDLC for large current applications where both high energy density and power capability are required.     

酚醛基活性碳纤维双电层电化学电容器的研究

利用KOH活化制得了酚醛基活性碳纤维(ACF).研磨后形成细颗粒酚醛基活性碳纤维材料(P-ACF).对比研究P-ACF与ACF在6 mol·L-1 KOH溶液中的电化学性能,结果表明:P-ACF电极表现出更佳的电容性质,比电容达200 F·g-1,大电流放电比电容衰减速率较慢,其微孔离子迁移电阻(Rp,2.96Ω)较ACF的(4.65Ω)小.研磨可增加ACF的断面暴露量,降低纤维间接触电阻和微孔内离子迁移电阻.     

一种新型有机硅离子液体电解液在超级电容中的应用

设计合成了一种新型有机硅室温离子液体(SiN1IL), 并对其化学结构和电化学窗口进行表征, 通过与具有高介电常数的丙烯碳酸酯(PC)/低粘度的乙腈(AN)匹配组成电解液, 其离子电导率达到商业实际应用的要求(19.6 mS·cm^-1). 对以活性炭(AC)为对称电极的超级电容器的电化学性能测试表明, SiN1IL 基电解液与活性炭有很好的界面相容性, 其高倍率充放电、阻抗性能优于商用四乙基四氟硼酸铵(Et₄NBF₄)/PC 电解液, 在电流密度为1000 mA·g^-1的条件下, 工作电压为2.7 V, 其比电容为108 F·g^-1.     

碳纳米管/五氧化二钒空心球的制备及其电化学性能研究

采用溶剂热法制备了碳纳米管穿插的分级结构五氧化二钒空心球（VOC_x）. 使用XRD、SEM、循环伏安曲线和充放电曲线研究了不同碳纳米管量对产物结构、形貌和电化学性能的影响. 结果表明,碳纳米管的加入明显改善了VOC的倍率特性. 碳纳米管含量为7.1%时,0.5 A·g^-1电流密度下,其比电容达到346 F·g^-1,8 A·g^-1电流密度时,其电容保持率可达75%. 与活性炭组装成混合电容器,在功率密度为700 W·kg^-1时,能量密度达12.6 Wh·kg^-1.     

Synthesis and electrochemical properties of activated carbons and Li4Ti5O12 as electrode materials for supercapacitors

New activated nanoporous carbons, produced by carbonization of mixtures of coal tar pitch and furfural with subsequent steam activation, as well as electrochemically active oxide Li₄Ti₅O₁₂, prepared by thermal co-decomposition of oxalates, were tested and characterized as electrode materials for electrochemical supercapacitors. The phase composition, microstructure, surface morphology and porous structure of the materials were studied. Pure carbon electrodes as well as composite electrodes based on these materials obtained were fabricated. Two types of supercapacitor (SC) cells were assembled and subjected to charge–discharge cycling study at different current rates: (1) symmetric sandwich-type SC cells with identical activated carbon electrodes and different organic electrolytes, and (2) asymmetric hybrid SC cell composed by activated graphitized carbon as a negative electrode and activated carbon–Li₄Ti₅O₁₂ oxide composite as a positive electrode, and an organic electrolyte (LiPF₆–dimethyl carbonate/ethylene carbonate (DMC/EC). Four types of carbons with different specific surface area (1,000–1,600 m² g^?1) and texture parameters, as well as three types of organic electrolytes: Et₄NBF₄–propylene carbonate (PC), LiBF₄–PC and LiPF₆–DMC/EC in the symmetric SC cell, were tested and compared with each other. Capacitance value up to 70 F g^?1 for the symmetric SC, depending on the electrolyte microstructure and conductivity of the carbon material used, and capacitance of about 150 F g^?1 for the asymmetric SC cell, with good cycleability for both supercapacitor systems, were obtained.     

聚3-(4-氟苯基)噻吩/碳化聚丙烯腈泡沫复合电极的电化学研究

噻吩衍生物是合成导电高分子材料的单体之一,在有机电致发光器件和电能存储等方面有着广泛的应用。聚3-(4-氟苯基)噻吩(PFPT)是一类既可进行p型掺杂又可进行n型掺杂的窄能带聚合物,在导电高分子型电化学电容器方面具有很好的应用前景,聚丙烯腈微孔膜已在锂离子电池方面有了很好的应用。若将它与碳纸复合后,再进行高温碳化和CO2活化,可制得导电性好、比表面积大的片状材料,作为电化学电容器的电极材料具有一定的双电层电容量．本文在三电极电解池中以这种材料的薄片为工作电极使3-(4-氟苯基)噻吩在乙腈溶液中进行电化学聚合,制备了聚3-(4-氟苯基)噻吩／碳化聚丙烯腈泡沫复合电极并研究了电极的电化学特性。     

电化学双电层电容器电极材料——豌豆荚基活性炭的制备与表征

以豌豆荚为碳源、ZnCl₂或KOH为活化剂制备了活性炭, 并用作双电层电容器的电极材料. 采用比表面及孔隙度分析仪表征了豌豆荚基活性炭的孔结构. 通过KOH或ZnCl₂活化后, 活性炭比表面积从1.69 m²·g^-1增大到2237或621 m²·g^-1. 采用循环伏安法和恒流充放电测试技术表征了豌豆荚基活性炭的电化学特性. 结果表明: 在6 mol·L^-1 KOH溶液中经KOH活化处理的活性炭的质量比电容高达297.5 F·g^-1, 并具有良好的充放电稳定性, 在5 A·g^-1的高电流密度下循环充放电500次后, 质量比电容仅衰减8.6%.     

Surface modification by graphene oxide:An efficient strategy to improve the performance of activated carbon based supercapacitors

An efficient and cost-effective strategy to modificate the surface of active carbon (AC), form a 3D-conductive network, and therefore improve the electrochemical performance of AC based supercapacitor was developed.     

A 3-V electrochemical capacitor study based on a magnesium polymer gel electrolyte by three different carbon materials

An organic medium with lithium and sodium salts is not so safe in some cases. Structural features of carbon electrodes play a vital role on the capacitor parameters. Based on that above said, we have studied three kinds of supercapacitors using a gel electrolyte from 0.5 M of magnesium imide salt–polyethylene oxide (PEO) in propylene carbonate (PC). The cell electrodes were carbide derived carbon (CDC), PICACTIF and YECA activated carbons. The gel component interactions were viewed by infrared spectroscopy. The cell reversibility and symmetric were analyzed using cyclic voltammetry (CV) technique. Linear sweep voltammetry (LSV) technique was taken to approximate the electrolyte stability. Electrochemical impedance spectroscopy (EIS) result reflects the resistance and capacitive behavior of the cells, i.e., The YECA carbon shows a good capacitive behavior over the CDC- and PICACTIF-based cells whereas the CDC cell has shown a low resistance. Galvanostatic charge-discharge study (CD) results have shown a stable and ideal 2.5-V capacitor behavior. The capacitors have also proven an obtainable good specific capacitance, real power, and real energy density of ~25 F g^?1, 0.7 kW kg^?1, and 25 W·h kg^?1, respectively. Moreover, the cells were tested for 3-V limit.     

An activated carbon supercapacitor analysis by using a gel electrolyte of sodium salt-polyethylene oxide in an organic mixture solvent

A gel electrolyte of sodium bis(trifluoromethanesulfonyl)imide (NaTFSI)-polyethylene oxide (PEO) in an organic solvent mixture has been prepared and examined for supercapacitor applications by using activated carbon electrodes. The solvent was a mixture of propylene carbonate, dimethyl carbonate, and ethylene carbonate at equal molar ratio, and also, a propylene carbonate-based gel was used for a comparison. The polymer-salt interaction was viewed by infrared spectral study. The cells have been characterized in a two-electrode type using linear sweep voltammetry, cyclic voltammetry, galvanostatic cycling, and impedance techniques at 22 °C. The voltammograms evidence symmetry and reversibility of the cells. The ternary gel has shown better electrochemical performances. Moreover, the cell operative potential window was found to be stable at 2.5 V with high specific capacitance and also a good efficiency at low charge rate. The typical obtained specific capacitance, real power, and energy density values are 24 F g^?1, 0.52 kW kg^?1, and 18.7 Wh kg^?1, respectively, which may be viewable for a compact capacitor.     

Preparation and performance of polyvinyl alcohol-based activated carbon as electrode material in both aqueous and organic electrolytes

Porous carbon materials with high surface area and different pore structure have been successfully prepared by phenolic resin combined with polyvinyl alcohol (PVA) and KOH as activation agents. The surface morphology, structure, and specific surface area of the carbon materials were studied by scanning electron microscopy, X-ray diffraction, and nitrogen sorption measurement, respectively. Furthermore, the effects of specific surface area, pore structure, and electrolyte on electrochemical properties were investigated by galvanostatic charge–discharge measurement. The results show that KOH–PVA-activated carbon materials display specific capacitance as high as 218 F?g^?1 in 30 wt.% KOH aqueous electrolyte, 147 F?g^?1 in 1 M LiPF₆/(ethylene carbonate (EC) + dimethyl carbonate) (1:1?v/v), and 115 F?g^?1 in 1 M Et₃MeNBF₄/propylene carbonate organic electrolyte, respectively. In addition, the carbon materials demonstrate long-term cycle stability, especially the AK3P-0.30 in aqueous electrolyte and the AK2P-0.30 with excellent rate capability in organic electrolyte. These reveal that the existence of a micro-mesoporous structure of activated carbon is beneficial to store energy in an aqueous supercapacitor and broad pore size distribution of activated carbon is favorable to energy storage in an organic supercapacitor. The carbon materials with pore size distribution in different ranges improve the electrochemical performance of supercapacitor in different electrolytes. A new pore-expand agent (PVA combining with KOH) was used to obtain porous carbons with enhanced properties for supercapacitor.     

1-乙基-3-甲基咪唑三氟乙酸盐作为电化学双电层电容器电解液的电化学性能

应用循环伏安法和直流恒流充放电研究了以离子液体1-乙基-3-甲基咪唑三氟乙酸盐([EMIm]CF3COO)和高比表面活性炭电极构成的电化学双电层电容器的电化学性能.实验表明,[EMIm]CF3COO具有高的比电容、良好的循环特性以及高的充放电效率.在离子液体稳定的电化学窗口内,比电容随电化学窗口的增加而增大.能量密度随电流和电化学窗口的增加逐渐提高,功率密度随电流的增加而减小、随电化学窗口的增加而增加,是一种优良的电化学双电层电解液.     

静电纺氧化锰复合碳纳米纤维柔性膜的电化学性能

采用一步法静电纺丝技术制备了具有超亲水特性的氧化锰/碳纳米纤维(MnO_x/CNFs)复合柔性膜电极材料,并通过X射线衍射、扫描电子显微镜和透射电子显微镜等对复合材料进行了表征.电化学性能测试结果表明,复合材料的电容性能优于单一材料,醋酸锰质量分数为40%时制得的复合纳米纤维电极(MC-4)在1 A/g电流密度下,于2 mol/L KOH电解液中的比电容高达1112.5 F/g,10 A/g电流密度下循环3000次比容量保持在93.4%,具有很好的稳定性.MnO_x/CNFs复合材料电化学性能增强一方面是由于三维超亲水纤维膜结构有利于电解液的快速浸润渗透,从而极大缩短了传输到材料基质的有效路径;另一方面是由于碳和MnO_x的协同效应,包裹在MnO_x粒子周围的碳层避免了MnO_x在充放电过程中的体积膨胀效应,这2种叠加机制促进了电化学性能的提升.     

Effects of activation conditions on the electrochemical capacitance of activated carbon nanotubes

The effects of different activation conditions (including KOH/CNTs ratio, activation temperature, activation time and nitrogen flow rate) on the electrochemical capacitance of activated carbon nanotubes (CNTs) have been investigated. All the four factors can affect the activated CNTs’ electrochemical capacitance. And the effects on the activated CNTs’ electrochemical capacitance carried out by virtue of their effects on activated CNTs’ BET specific surface area and graphitized degree.     

Silicon-containing anodes with high capacity loading for lithium-ion batteries

Comparative analysis of cycling performance of hybrid electrodes based on the MAG synthetic graphite mechanic mixtures with silicon nanopowder and “nano-Si/SiO₂/hard carbon” ceramic frame-ordered composite in 1 M LiPF₆ solution in a monofluoroethylene carbonate-ethyl methyl carbonate mixture (30: 70, v/v), added with 3 wt % vinylene carbonate and 2 wt % ethylene sulfite, is performed. The high capacity loading (up to 6.8 mA h cm^?2 at the electrode layer thickness of 37 μm) and acceptable accumulated irreversible capacity of the composite-containing electrodes are achieved, due to the electrodes’ high density and stable silicon-containing electrode/electrolyte interface formation.