Abstract
Supercapacitors have exceptional power density and cyclability but smaller energy density than batteries. Their energy density can be increased using ionic liquids and electrodes with subnanometre pores, but this tends to reduce their power density and compromise the key advantage of supercapacitors. To help address this issue through material optimization, here we unravel the mechanisms of charging subnanometre pores with ionic liquids using molecular dynamics simulations, navigated by a phenomenological model. We show that charging of ionophilic pores is a diffusive process, often accompanied by overfilling followed by de-filling. In sharp contrast to conventional expectations, charging is fast because ion diffusion during charging can be an order of magnitude faster than in the bulk, and charging itself is accelerated by the onset of collective modes. Further acceleration can be achieved using ionophobic pores by eliminating overfilling/de-filling and thus leading to charging behaviour qualitatively different from that in conventional, ionophilic pores.
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Change history
25 March 2014
In the version of this Article originally published, the e-mail address of Svyatoslav Kondrat was misspelt; it should have read ‘s.kondrat@fz-juelich.de’. This error has now been corrected in the online versions of the Article.
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Acknowledgements
We thank the Clemson-CCIT office and E. Duffy for providing computer facilities. R.Q. acknowledges the support of the NSF (CBET-1264578). S.K. and A.K. were supported by the Engineering and Physical Science Research Council via Grant EP/H004319/1. We are grateful to Y. Gogotsi, P. Simon, C. Pérez, J. Griffin, G. Oshanin and F. Stoeckli for fruitful discussions, and X. Jiang for technical assistance.
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A.A.K., R.Q. and S.K. designed the research. P.W. performed MD simulations and S.K. performed MFT calculations. The results were analysed jointly by R.Q., S.K., A.A.K. and P.W., and all participated in writing the paper.
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Kondrat, S., Wu, P., Qiao, R. et al. Accelerating charging dynamics in subnanometre pores. Nature Mater 13, 387–393 (2014). https://doi.org/10.1038/nmat3916
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DOI: https://doi.org/10.1038/nmat3916
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