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.     

Electrochemical performance of nickel oxide／KOH／active carbon super-capacitor

The fabrication and characterization of new type Nickel oxide/KOH/Active carbon super-capacitor have been described. Porous nickel oxide was prepared by hydrolysis of nickel acetate and heated in air at 300℃. The resulting nickel oxide behaved as an electrochemical capacitor electrode with a specific capacitance (50-70 F/g) superior to most active carbon electrodes. This kind of nickel oxide maintained high utilization at high rate of discharge (i.e., high power density) and had excellent cycle life more than 1 000 times,while the capacitance of the cell composed of two identical nickel oxide electrodes was poor at high discharge current density and the maximum operational voltage of this type capacitor was limited to 0.5 V. A new type super-capacitor was designed in which the nickel oxide and the active carbon were applied to the positive and negative electrodes respectively. The breakdown voltage of this type super-capacitor was improved effectively to 0.8 V and excellent characteristic of high power discharge was attained in this way. The Nickel oxide/KOH/Active carbon super-capacitor has promising potentials in portable telecommunications, uninterruptable power supplies and battery load leveling applications.     

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 ℃.     

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.     

Effect of Ni-doping on electrochemical capacitance of MnO2 electrode materials

Mn/Ni composite oxides as active electrode materials for supercapacitors were prepared by solid-state reaction through the reduction of KMnO4 with manganese acetate and nickel acetate at low temperature. The products were characterized by X-ray diffractometry(XRD) and transmission electron microscopy(TEM). The electrochemical characterizations were performed by cyclic voltammetry (CV) and constant current charge-discharge in a three-electrode system. The effects of different potential windows, scan rates, and cycle numbers on the capacitance behavior of Mn0.8Ni0.2Ox composite oxide were also investigated. The results show that the composite oxides are of nano-size and amorphous structure. With increasing the molar ratio of Ni, the specific capacitance goes through a maximum at molar fraction of Ni of 20%. The specific capacitance of Mn0.8Ni0.2Ox composite oxide is 194.5 F/g at constant current discharge of 5 mA.     

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     

Structural characteristics of spherical Ni（OH）2 and its charge／discharge process mechanism

Spherical Ni(OH)2 particles were prepared by an aqueous solution precipitation route. The structure of spherical Ni(OH)2 was investigated by scanning electron microscopy and transmission electron microscopy and compared with that of traditional Ni(OH)2. The results show that the spherical nickel hydroxide consists of Ni(OH)2 spheres with a reticulate structure of platelet-like, which is almost arranged radially and the crystalline grains intervene and connect with each other to form a three-dimensional net. The spherical Ni(OH)2 particle is full of pores,crannies between cleave planes. It is supposed that this structure is beneficial to the structural stability for the spherical particles during the charge/discharge processes and can improve the cycle life of the electrode; the pores and the crannies in spherical particles can shorten the proton diffusion distance and speed its velocity, which may result in that the local polarization is lowered. The electrochemical performances of the spherical Ni(OH)2 are improved by enhancing the conducting properties of the crystalline lattice due to its quick proton diffusion.     

Synthesis and performance of carbon-modified LiFePO_4 using an in situ PVA pyrolysis procedure

LiFePO4/carbon composite cathode material was prepared by granulating and subsequent pyrolysis processing in N2 at- mosphere with polyvinyl alcohol (PVA) as the carbon source. The influences of carbon content on the microstructure and battery performance were investigated. Single LiFePO4 phase and amorphous carbon can be found in the products. A special mi- cro-morphology of the optimum sample was observed. The discharge capacity of the cell with the optimum cathode was 135 mAh·g?1, close to the charge capacity of 153 mAh·g?1 at 17 mA·g?1. The influence of ambient temperature on the cell capacity was investigated. The temperature dependence of its electrochemical characteristic was evaluated by using AC impedance spectroscopy. A new equivalent circuit based on the charge and mass transfer control process in an electrode was proposed to fit the obtained AC im- pedance spectra. The tendency of every element in the equivalent circuit was used to interpret the temperature dependence of the ca- pacity of the optimum cathode.     

Synthesis of mesoporous carbon as electrode material for supercapacitor by modified template method

The pore structures and electrochemical performances of mesoporous carbons prepared by silica sol template method as electrode material for supercapacitor were investigated. The mean pore size and mass specific capacitance of the mesoporous carbons increase with the increase of mass ratio of silica sol to carbon source （glucose）. A modified template method, combining silica sol template method and ZnCl2 chemical activation method, was proposed to improve the mass specific capacitance of the mesoporous carbon with an improved BET surface area. The correlation of rate capability and pore structure was studied by constant current discharge and electrochemical impedance spectroscopy. A commercially available microporous carbon was used for comparison. The result shows that mesoporous carbon with a larger pore size displays a higher rate capability. Mesoporous carbon synthesized by modified template method has both high mass specific capacitance and good rate capability.     

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.     

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.     

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。     

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。     

NiAl-LDHs 电极材料的水热合成及其超级电容器电化学性能

超级电容器具有大充放电速率、良好的循环稳定性及高功率密度等优点, 是一种新兴的绿色环保储能器件。采用简单的水热合成法制备镍铝层状双金属氢氧化物(NiAl-LDHs) 超级电容器电极材料, 探究不同镍铝比对其形貌组成及电化学性能的影响。所制备的Ni₁Al₁-LDHs 电极材料在电流密度为1 A/g 时表现出378 F/g 的高比电容。以活性炭(AC) 为负极组成的Ni₁Al₁-LDHs//AC 非对称超级电容器在能量密度为27.5 Wh/kg 时, 具有1.4 kW/kg 的高功率密度, 表现出优异的电化学性能。     

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 ...