Performance of a combined capacitor based on ultrafine nickel oxide／carbon nanotubes composite electrodes

A new sol-gel process for the preparation of ultrafine nickel hydroxide electrode materials was developed. The composite electrodes consisting of carbon nanotubes and Ni(OH)2 were developed by mixing the hydroxide and carbon nanotubes together in different mass ratios. In order to enhance energy density, a combined type pseudocapacitor/electric double layer capacitor was considered and its electrochemical properties were characterized by cyclic voltammetry and dc charge/discharge test. The combined capacitor shows excellent capacitor behavior with an operating voltage up to 1.6 V in KOH aqueous electrolyte. Stable charge/discharge behaviors were observed with much higher specific capacitance values of 24 F/g compared with that of EDLC (12 F/g) by introducing 60% Ni(OH)2 in the anode material. By using the modified anode of a Ni(OH)E/Carbon nanotubes composite electrode, the specific capacitance of the cell was less sensitive to discharge current density compared with that of the capacitor employing pure nickel hydroxide as anode. The combined capacitor in this study exhibits high energy density and stable power characteristics.     

Performance of a 60 F carbon nanotubes-based supercapacitor for hybrid power sources

A supercapacitor based on charge storage at the interface between a high surface area carbon nanotube electrode and a Li-ClO4/PC electrolyte was assembled. The performance of the capacitor depends on not only the material used in the cell but also the construction of the cell. From a constant charge-discharge test, the capacitance of 60 F was obtained. The performance of the power capacitor for pulse power sources was described. The specific energy (0.8 W·h·kg-1) and the specific power (0.75 kW·kg-1) of the power supercapacitor were demonstrated with a cell of the maximum operating voltage of 2.5 V. A hybrid power source consisting of a lithium ionic battery and the 60 F supercapacitor was demonstrated to power successfully a simulated power load encountered in GSM portable communication equipment. The addition of the supercapacitor to the power train of a cellular phone results in significantly more energy from the battery being used by the load. The experiments indicate that more than 33.8% energy i     

Nanosized Nickel Oxides Derived from the Citrate Gel Process and Performances for Electrochemical Capacitors

Nanosized nickel oxide powders were prepared by thermal decomposition of the nickel citrate gel precursors. The thermal decomposition and powder materials derived from calcination of these gel precursors with various ratios of citric acid （CA） to nickel at different temperatures and times were characterized by thermal analysis （TG/DTA）, scanning electron microscopy （SEM）, x-ray diffraction （XRD）, and measurement of specific surface area （BET） with porosity analyses. The optimized processing conditions of calcination temperature 400℃ for 1 hour with the CA/Ni ratio of 1.2, were determined to produce the nanosized nickel oxide pow- ders with a high specific surface area of 181 m^2/g, nanometer particle sizes of 15-25 nm, micro-pore diameter distribution between 4-10 nm. The capacitance characteristics of the nanosized nickel oxide electrode in various concentrations of KOH solutions were studied by the cyclic voltammetry （CV） exhibiting both a double-layer capacitance and a faradaic pseudocapacitance. The nanosized nickel oxide electrode shows a high cyclic stability and is promising for high performance electrochemical capacitors.     

Excellent supercapacitive performance of a reduced graphene oxide/Ni（OH）2 composite synthesized by a facile hydrothermal route

A reduced graphene oxide/Ni（OH）2 composite with excellent supercapacitive performance was synthesized by a facile hydrothermal route without organic solvents or templates used.XRD and SEM results reveal that the nickel hydroxide,which crystallizes into hexagonal β-Ni（OH）2 nanoflakes with a diameter less than 200 nm and a thickness of about 10 nm,is well combined with the reduced graphene oxide sheets.Electrochemical performance of the synthesized composite as an electrode material was investigated by cyclic voltammetry,electrochemical impedance spectroscopy and galvanostatic charge/discharge measurements.Its specific capacitance is determined to be 1672 F/g at a scan rate of 2 mV/s,and 696 F/g at a high scan rate of 50 mV/s.After 2000 cycles at a current density of 10 A/g,the composite exhibits a specific capacitance of 969 F/g,retaining about 86% of its initial capacitance.The composite delivers a high energy density of 83.6 W·h/kg at a power density of 1.0 kW/kg.The excellent supercapacitive performance along with the easy synthesis method allows the synthesized composite to be promising for supercapacitor applications.     

Development of supercapacitors based on carbon nanotubes

Block-type electrodes made of carbon nanotubes were fabricated by different processes. The volumetric specific capacitance based on such electrodes reached 107 F/cm3, which proves carbon nanotubes to be ideal candidate materials for supercapacitors. The composite electrodes consisting of carbon nanotubes and RuO2 ·xH2O were developed by the deposition of RuO2 on the surface of carbon nanotubes. Supercapacitors based on the composite electrodes show much higher specific capacitance than those based on pure carbon nanotube ones. A specific capacitance of 600 F/g can be achieved when the weight percent of RuO2· xH2O in the composite electrodes reaches 75% . In addition , supercapacitors based on the composite electrodes show both high energy density and high power density characteristics.     

Preparation of activated carbons from mesophase pitch and their electrochemical properties

The influences of molar ratio of KOH to C and activated temperature on the pore structure and electrochemical property of porous activated carbon from mesophase pitch activated by KOH were investigated. The surface areas and the pore structures of activated carbons were analyzed by nitrogen adsorption, and the electrochemical properties of the activated carbons were studied using two-electrode capacitors in organic electrolyte. The results indicate that the maximum surface area of 3 190 m2/g is obtained at molar ratio of KOH to C of 5:1, the maximum specific capacitance of 122 F/g is attained at molar ratio of KOH to C of 4:1, and 800 ℃ is the proper temperature to obtain the maximum surface area and capacitance.     

Electrochemical characterization of MnO_2 as the cathode material for a high voltage hybrid capacitor

Manganese dioxide(MnO2) was prepared using the ultrasonic method.Its electrochemical performance was evaluated as the cathode material for a high voltage hybrid capacitor.And the specific capacitance of the MnO2 electrode reached 240 F·g-1.The new hybrid capacitor was constructed,combining Al/Al2O3 as the anode and MnO2 as the cathode with electrolyte for the aluminum electrolytic capacitor to solve the problem of low working voltage of a supercapacitor unit.The results showed that the hybrid capacitor had ...     

Optimal electrochemical performances of CO2 activated carbon aerogels for supercapacitors

Activated carbon aerogels（ACAs） derived from sol-gel polycondensation of resorcinol （R） and formaldehyde （F） were pyrolyzed under Ar flow and activated in CO2 atmosphere. The morphology of ACAs was characterized by scanning electron microscopy （SEM） and the structural properties were determined by N2 adsorption at 77 K. The results show that ACAs have a typical three-dimensional nanonetwork structure composing of cross-linking of carbon nanoparticles. The specific surface area and the total pore volume remarkably increase with increasing activation time while the previous porous structure still remains. The specific capacitance of the 950-10-ACA electrode can reach up to 212.3 F/g in 6 mol/L KOH electrolyte. The results of constant-current charge-discharge testing indicate that the ACAs electrodes present fast charge- discharge rate and long cycle life （about 98% capacitance retained after 3000 charge-discharge cycles at 1.25 mA/cm2）. Lower internal resistances can be achieved for 950-10-ACA electrode in KOH electrolyte. Our investigations are very important to improve the wettability and electrochemical performance of electrode for supercapacitors.     

Comparison of capacitive behavior of activated carbons with different pore structures in aqueous and nonaqueous systems

The pore structures of two activated carbons from sawdust with KOH activation and coconut-shell with steam activation for supercapacitor were analyzed by N2 adsorption method. The electrochemical properties of both activated carbons in 6 mol/L KOH solution and 1 mol/L EtgNPF4/PC were compared, and the effect of pore structure on the capacitance was investigated by cyclic voltammetry, AC impedance and charge-discharge measurements. The results indicate that the capacitance mainly depends on effective surface area, but the power property mainly depends on mesoporosity. At low specific current （1 A/g）, the maximum specific Capacitances of 276.3 F/g in aqueous system and 123.9 F/g in nonaqueous system can be obtained from sawdust activated carbon with a larger surface area of 1 808 m^2/g, butat a high specific current, the specific capacitance of coconut-shell activated carbon with a higher mesoporosity of 75.1% is more excellent. Activated carbon by KOH activation is fitter for aqueous system and that by steam activation is fitter for nonaqueous system.     

Preparation and properties of pitch carbon based supercapacitor

Using the mesophase pitch as precursor, KOH and CO2 as activated agents, the activated carbon electrode material was fabricated by physical-chemical combined activated technique for supercapacitor. The influence of activated process on the pore structure of activated carbon was analyzed and 14 F supercapacitor with working voltage of 2.5 V was prepared. The charge and discharge behaviors, the properties of cyclic voltammetry, specific capacitance, equivalent serials resistance (ESR), cycle properties, and temperature properties of prepared supercapacitor were examined. The cyclic voltammetry curve results indicate that the carbon based supercapacitor using the self-made activated carbon as electrode materials shows the desired capacitance properties. In 1 mol/L Et4NBF4/AN electrolyte, the capacitance and ESR of the supercapacitor are 14.7 F and 60 m?, respectively. The specific capacitance of activated carbon electrode materials is 99.6 F/g; its energy density can reach 2.96 W·h/kg under the large current discharge condition. There is no obvious capacitance decay that can be observed after 5000 cycles. The leakage current is below 0.2 mA after keeping the voltage at 2.5 V for 1 h. Meanwhile, the supercapacitor shows desired temperature property; it can be operated normally in the temperature ranging from -40 ℃ to 70 ℃.     

载镍活性炭材料及复合型超级电容器

为提高碳基电化学电容器的比电容和和能量密度,采用化学沉积法将少量镍氧化物沉积在活性炭上,得到沉积镍氧化物的活性炭材料并以此材料做成复合电极用于混合型电化学电容器的正极.研究显示,沉积镍氧化物后,碳材料的比表面积略有减小,但孔径分布没有明显变化.复合电极作为混合型电容器的正极时,比电容达到194.01F/g,比纯活性炭正极的175F/g提高了10.84%;复合电极在6mol/L的电解液中析氧电势为0.296V,比纯活性炭电极的0.220V高出0.076V,因此,具有较高的能量密度.不同放电电流密度下的恒电流测试结果显示,沉积镍氧化物活性炭复合电极的比电容值没有明显变化,与纯活性炭电极一样表现出良好的功率特性.采用沉积镍氧化物活性炭作为正极材料的复合型电容器,在6mol/L的KOH水溶液作为电解液时,单体电容器的工作电压可以达到1.2V,高于纯活性炭制备的双层型电容器0.2V.充放电循环10000次时,复合型电容器的电容仅降低到初始电容的90%.上述结果表明,在活性炭上沉积少量镍氧化物颗粒可以提高碳基电化学电容器的比电容和能量密度.     

氧化镍/活性炭电极的超电容性能

在制作双电层电容器基础上,采用电化学沉积法,在活性炭电极表面负载氧化镍.XRD测定表明,镍氧化物以NiO形态负载于活性炭电极上.电化学性能研究表明,氧化镍/活性炭复合电极循环伏安曲线呈矩形特征,具有良好的电容特性;其交流阻抗谱由圆弧和直线组成,电化学过程受扩散和氧化镍的赝电容行为控制;其恒电流充电曲线呈直线,电容特性显著,大电流性能良好,比容量达104.7 F/g,是活性炭电极比容量的1.35倍.     

基于飞渡电容的超级电容组动态均衡控制算法

超级电容器具有充电速度快、比功率高、循环寿命长、低温特性好等优点,其缺点是能量密度比化学电池低.这种特点使得超级电容器用于城市短距离公交车比较适合.但是由于单体之间的差异,在经过多个循环的深度充/放电后,单体电容之间的电压差将会加大,这将加速性能较弱的单体电容器的老化.为了保护超级电容器,提高其有限容量的利用率,研究了基于飞渡电容的超级电容组动态均衡算法.首次将飞渡电容式动态均衡管理系统用于超级电容公交车,该系统可以工作于动态和静态两种模式下,给出了电容组处于充、放电和静置三种状态下的均衡控制算法及其实验结果.实际运行结果表明,系统的均衡精度满足超级电容组运行要求.     

纳米门炭结构及超级电容特性

以生石油焦为原料,采用KOH活化法制备纳米门炭。采用氮气吸附法、X射线衍射(XRD)和光电子能谱衍射(XPS)对其孔结构、微晶结构和表面性质进行分析,并以其为电极组装超级电容器,测试了电容特性。结果表明:纳米门炭可在3.5V电压下工作,通过首次充电过程中的电化学活化而获得较大的比电容。样品N900比表面积仅为61m2/g,但比电容确高达136.7F/g,能量密度高达58.1Wh/kg。     

Pseudo-capacitance of ruthenium oxide/carbon black composites for electrochemical capacitors

Hydrous ruthenium oxide was formed by a new process. The precursor was obtained by mixing the aqueous solutions of RuCl3·xH2O and NaHCO3. The addition of NaHCO3 led to the formation of an oxide with extremely fine RuO2 particles forming a porous network structure in the oxide electrode. Polyethylene glycol was added as a controller to partly inhibit the sol-gel reaction. The rate capacitance of 530 F·g-1 was measured for the powder formed at an optimal annealing temperature of 210°C. Several details concern...     

氢氧化镍掺杂活性炭复合电化学电容器的研究

在活性炭中掺入一定量的Ni（OH）2作为电化学电容器的上下极活性物质，通过恒流充放电测试考察了掺入Ni（OH）2的活性炭正极与纯活性炭负极组成的复合型电容器，在不同充放电条件下的电化学电容特性。实验发现，该复合电容器的稳定工作电压可提高至1．3V，并具有较高的比电容量，可以有效地提高了电化学电容器的能量密度。与纯活性炭型电容器相比，其能量密度可以增加70％～85％，同时，这种复合型的电化学电容器具有较长的循环寿命和较低的自放电率。     

水系和有机系活性炭超级电容器的性能研究

采用活性炭作为电极活性物质,以碳纳米管为导电剂,用聚四氟乙烯隔膜制备水系和有机系扣式超级电容器,考察并分析二者在容量特性、自放电性能、循环性能、功率密度、能量密度等方面的优劣。结果表明,实验制得的电容器样品表现出良好的电容行为和循环性能;水系电容器样品10h自放电率为28.7%,1h漏电流为0.32mA;有机系电容器样品在电流密度为1.04A/g时,能量密度为10.32Wh/kg,功率密度达到1.88kW/kg。     

NiO/AC非对称超级电容器的研究

通过热处理球形Ni（OH）2得到NiO粉末，将其作为正极与活性炭（AC）负极组装成非对称超级电容器，用恒流充放电测试分析了超级电容器的电容特性。讨论了正负极活性物质比例、充放电电流和热处理时间对超级电容器比电容量、内阻的影响。结果表明：正负极活性物质比为1：3，工作电流密度为200mA／g，当Ni（OH）2的热处理时间为2h，充电电压为1．3V时，超级电容器的双电极比电容量可达71．5F／g。     

纳米氧化镍的制备及其电化学电容

通过金属碳酸盐、硝酸(氧化剂)和柠檬酸(燃料)的凝胶-燃烧方法合成了纳米氧化镍粉体。在柠檬酸与Ni2+的摩尔比为1.3:1,热处理温度为400℃的条件下,以1mol/LKOH水溶液为电解液对纳米NiOx制备的电极进行了循环伏安、充放电及电化学阻抗谱分析。分析结果表明纳米NiOx电极在KOH水溶液电解液中具有良好的赝电容特性,其平均比容量最大为78.8F/g,并具有良好的循环寿命。