合成路径对超级电容器用二氧化锰性质的影响

Effect of Synthesis Routes on the Performances of MnO_2 for Electrochemical Capacitors

研究了不同合成路径对二氧化锰结构及电化学性能的影响.路径1为将0.15mol/L醋酸锰溶液加入到0.1mol/L高锰酸钾溶液中;路径2中,物料的加料方式与路径1相反.X射线衍射和扫描电镜测试表明合成的产物均为无定型α-MnO2,晶粒尺寸为200～300nm.氮吸附曲线测试结果表明:路径1所得的二氧化锰具有较大的比表面积(329m2/g),其孔径分布比较均一,孔径6～12nm,孔体积较小(0.45cm3/g);路径2所得的二氧化锰比表面积较小(298m2/g),具有从微孔到大孔的连续分布孔,平均孔径11.4nm,孔体积较大(0.66cm3/g).交流阻抗和循环伏安电化学测试结果显示:路径2所得样品具有较大的法拉第阻抗,在较低扫描速度下(2mV·s-1),其比电容(203F·g-1)比路径1所得MnO2高(189F·g-1),路径1所得二氧化锰的比电容随扫描速度变化的趋势较小.恒流充放电测试显示路径1合成的二氧化锰具有较好的功率特性.在2A·g-1的电流密度下,其比容量为0.1A·g-1电流密度下的96.3%,而路径1的样品的容量保持率为92.5%.造成上述结果差异的原因是由于不同合成路径导致二氧化锰存在不同的孔结构特征所致.

The effect of synthesis routes on the performances of MnO2 used as an active material in electrochemical capacitors was studied by two different routes using 0.15 mol·L^-1 manganese acetate and 0.1 mol·L^-1 potassium permanganate as starting materials. Method 1 was addition of manganese acetate solution to potassium permanganate solution and in method 2, the solutions were swapped. The XRD diffractions and the SEM images of samples by two routes showed that the obtained MnO2 were both amorphous like and their particle sizes are ca. 200-300 nm. By BET method, MnO2 particles using method 1 have higher surface area value （329 m^2·g^-1）, uniform size distribution （in the range of 6-12 nm） and lower pore volume （0.45 cm^3·g^- 1）, while method 2 produced particles with wide continuous pore size distribution （from micropores to macropores, mean pore size 11.4 nm）, lower surface area （298 m^2/g） and higher pore volume （0.66 cm^3·g^- 1）. Impedance spectroscopy studies revealed that the charge transfer resistance of MnO2 by method 2 has higher value than that of MnO2 by method 1. The results of cyclic voltammograms showed that the specific capacity of MnO2 by method 2 at low scan rate （203 F·g^-1 at 2 mV·s^-1） was larger than that of MnO2 by method 1 （189 F·g^-1 at 2 mV·s^-1）. With the increase of the scan rate, the loss of the specific capacitance of MnO2 by method 1 is smaller than that of MnO2 by method 2. The charge-discharge measurements showed that MnO2 by method 1 exihibits better rate capability, for the specific capacity of MnO2 by method 1 at 2 A·g^-1 is 96.3% of its capacity at 0.1 A·g^-1, while the spcific capacity of MnO2 by method 2 at 2 A·g^-1 is 92.5% of its value at 0.1 A·g^-1. All the results indicated that the differences of the performances of MnO2 from the different synthesis routes arised from the different microstructure characteristics of MnO2.