Rennie Anthony J R, Martins Vitor L, Smith Rachel M, Hall Peter J
Chemical and Biological Engineering, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, England, UK.
Instituto de Química, Universidade de São Paulo - C.P. 26077, CEP 05513-970, São Paulo, SP, Brazil.
Sci Rep. 2016 Feb 25;6:22062. doi: 10.1038/srep22062.
Electrochemical double layer capacitors (EDLCs) employing ionic liquid electrolytes are the subject of much research as they promise increased operating potentials, and hence energy densities, when compared with currently available devices. Herein we report on the influence of the particle size distribution of activated carbon material on the performance of ionic liquid based EDLCs. Mesoporous activated carbon was ball-milled for increasing durations and the resultant powders characterized physically (using laser diffraction, nitrogen sorption and SEM) and investigated electrochemically in the form of composite EDLC electrodes. A bi-modal particle size distribution was found for all materials demonstrating an increasing fraction of smaller particles with increased milling duration. In general, cell capacitance decreased with increased milling duration over a wide range of rates using CV and galvanostatic cycling. Reduced coulombic efficiency is observed at low rates (<25 mVs(-1)) and the efficiency decreases as the volume fraction of the smaller particles increases. Efficiency loss was attributed to side reactions, particularly electrolyte decomposition, arising from interactions with the smaller particles. The effect of reduced efficiency is confirmed by cycling for over 15,000 cycles, which has the important implication that diminished performance and reduced cycle life is caused by the presence of submicron-sized particles.
与目前可用的器件相比，采用离子液体电解质的电化学双层电容器（EDLC）因其有望提高工作电位，进而提高能量密度，而成为众多研究的主题。在此，我们报告了活性炭材料的粒度分布对基于离子液体的EDLC性能的影响。对介孔活性炭进行了不同时长的球磨，对所得粉末进行了物理表征（使用激光衍射、氮吸附和扫描电子显微镜），并以复合EDLC电极的形式进行了电化学研究。发现所有材料均呈现双峰粒度分布，且随着球磨时间的增加，较小颗粒的比例增加。一般来说，在使用循环伏安法（CV）和恒电流循环的广泛速率范围内，电池电容随着球磨时间的增加而降低。在低速率（<25 mV s⁻¹）下观察到库仑效率降低，且随着较小颗粒体积分数的增加，效率降低。效率损失归因于与较小颗粒相互作用产生的副反应，特别是电解质分解。通过超过15000次循环证实了效率降低的影响，这具有重要意义，即亚微米级颗粒的存在会导致性能下降和循环寿命缩短。
