热处理对线团状二氧化锰结构及其电化学性质的影响

Effects of Heat Treatment on the Physical and Electrochemical Properties of Clew-like Manganese Dioxide

以氯化锰与高锰酸钾为原料,在低浓度下大数量合成由无数片状纳米层组成的线团状二氧化锰粒子.采用X衍射,扫描电镜,液氮等温吸附脱附、循环伏安、交流阻抗及恒流充放电等方法研究了温度对产物结构及电化学性质的影响.结果表明处理温度升高,微孔减少,比表面积减小,孔径变大,在300℃以下二氧化锰粒子的结构保持无定型结构.交流阻抗测试显示随着处理温度的升高,样品的法拉第电荷传递能力和离子在电解液与活性材料界面的扩散能力均得到提高.比电容测试显示在200℃处理的二氧化锰具有最高的比电容,以1 mol·L-1Na2SO4为工作介质,扫速为2mV·s-1时,其比电容是210.6 F·g-1.该研究表明:材料的电化学性质可以通过热处理进行调整,适当的热处理能提高该材料作为超级电容器活性材料的性质.

The clew-like manganese dioxide nanostructures composed of interleaving nanoplates were successfully prepared by adding 8 L dilute potassium permanganate solution（0.015 mol·L-1） to 8 L dilute manganese chloride solution（0.01 mol·L-1） with the dropping rate of 20 mL·min-1under a stirring condition.The effects of heat treatments on the physical and electrochemical properties of the obtained manganese dioxide were studied using X-ray diffraction（XRD）,scanning electron microscopy（SEM）,Brunauer-Emmett-Teller（BET） surface area measurement,cyclic voltametry（CV）,electrochemical impedance spectroscopy（EIS） and constant current charge-discharge method.The pore size of the obtained clew-like manganese dioxide was ca.6.5 nm and its distribution was uniform.The results of physical characterization showed that heat treatment could adjust the microstructure of manganese dioxide.The increase of the treating temperature induced the decrease of the specific surface area and the amount of the micropores while the mean pore size increased with the increase of the treating temperature.The MnO2particles remained amorphous below 300 ℃.The cyclic voltametry measurements indicated that all the amorphous MnO2 samples have characteristic of the ideal pesudocapacitor.The impedance spectroscopy tests showed that a suitable treating temperature could promote the ability of faradic charger-transfer and the diffusion of ion on the interface between the active material particles and electrolyte.Though the MnO2 sample treated at 200 ℃ did not have the highest specific surface area,it had the lowest faradic charger-transfer resistance and the highest specific capacitance,which was 210.6 F·g-1 at the scan rate of 2 mV·s-1 in 1 mol·L-1 Na2SO4 solution.The constant charge-discharge curves of this sample are approximately symmetrical and linear for both charge and discharge portions,which indicated this sample had an ideal capacitive characterization.The cycling life test was conducted by the CV method.The first CV capacitance at 5 mV s-1was 178.1 F·g-1.93.5% of its initial capacitance was remained after 1000 cycles,showing an excellent cycling performance.The effects of heat treatment on physical and electrochemical of manganese dioxide indicated that a suitable heat treatment can promote the electrochemical performance of manganese dioxide through adjusting its microstructure.