基于离子尺寸与孔径关系的不对称电容行为

采用具有不同孔径分布的活性炭作为电极材料, 研究了离子尺寸与孔结构对电容性能的影响. 结果表明, 正负极表现出不对称的电容行为, 正负极的质量比电容分别为113和7 F·g^-1. 在负极电位区间，循环伏安曲线的响应电流明显减小. 材料表面最大电荷存储量的理论计算与实验结果有着很好的一致性, 这些结果表明用于阳离子电荷存储的电极孔隙空间不够发达, 导致电容器在充电过程中负极材料表面达到电荷饱和状态，进而表现出较差的电容行为. 然而, 四氟硼酸根阴离子可以进入到正极电极材料大多数孔道中, 电极未发生电荷饱和效应, 表现出优异的电容行为. 负极较低的比电容将会影响电容器的整体性能. 因此, 正负极应当根据离子尺寸与电极材料孔结构的构效关系进行匹配, 以使电容器的比电容最大化.

Asymmetric Capacitance Behavior Based on the Relationship between Ion Dimension and Pore Size

We reported on the capacitive behaviors regarding to the relationship between ion size and pore architecture,using activated carbons with an adjusted pore structure as electrode materials.The results revealed that an asymmetric capacitance response occurred in both electrodes.The gravimetric capacitances for the positive and negative electrodes were 113 and 7 F.g-1,respectively.A significant current decay was presented in the negative region of cyclic voltammetry curve.Experimental and calculated maximum storage charges had a good agreement.This results suggested that the insufficiently developed pore architecture for cation accommodation led to a saturation effect on the active surface,consequently,a deteriorated capacitive performance in the negative electrode.Contrarily,when pore size was larger than tetrafluoroborate dimension,the saturation effect was not found.However,this was at the expense of the lower specific area capacitance in the positive electrode.The poor capacitive behavior of the negative electrode would limit the usable voltage of the cell system and consequently the deliverable energy and power.As a result,an optimal match between the pores size and the ion dimension with respect to each electrode would be considered to obtain the maximum capacitance for the capacitor unit.