期刊
ACS NANO
卷 6, 期 2, 页码 1732-1741出版社
AMER CHEMICAL SOC
DOI: 10.1021/nn204734t
关键词
supercapacitor; nanotube; network; percolation; transparent
类别
资金
- Science Foundation Ireland (SFI) [03/CE3/M406s1, 07/IN.1/11772]
- European Research Council
We have explored the effects of percolation on the properties of supercapacitors with thin nanotube networks as electrodes. We find the equivalent series resistance, R-ESR, and volumetric capacitance, C-V, to be thickness independent for relatively thick electrodes. However, once the electrode thickness falls below a threshold thickness (similar to 100 nm for R-ESR and similar to 20 nm for C-V), the properties of the electrode become thickness dependent. We show the thickness dependence of both R-ESR and C-V to be consistent with percolation theory. While this is expected for R-ESR, that the capacitance follows a percolation scaling law is not. This occurs because, for sparse networks, the capacitance is proportional to the fraction of nanotubes connected to the main network. This fraction, in turn, follows a percolation scaling law. This allows us to understand and quantify the limitations on the achievable capacitance for transparent supercapacitors. We find that supercapacitors with thickness independent R-ESR and C-V occupy a well-defined region of the Ragone plot. However, supercapacitors whose electrodes are limited by percolation occupy a long tail to lower values of energy and power density. For example, replacing electrodes with transparency of T = 80% with thinner networks displaying T = 97% will result in a 20-fold reduction of both power and energy density.
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