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Title: Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?

Abstract

The ionophobicity effect of nanoporous electrodes on the capacitance and the energy storage capacity of nonaqueous-electrolyte supercapacitors is studied by means of the classical density functional theory (DFT). It has been hypothesized that ionophobic nanopores may create obstacles in charging, but they store energy much more efficiently than ionophilic pores. In this paper, we find that, for both ionic liquids and organic electrolytes, an ionophobic pore exhibits a charging behavior different from that of an ionophilic pore, and that the capacitance–voltage curve changes from a bell shape to a two-hump camel shape when the pore ionophobicity increases. For electric-double-layer capacitors containing organic electrolytes, an increase in the ionophobicity of the nanopores leads to a higher capacity for energy storage. Without taking into account the effects of background screening, the DFT predicts that an ionophobic pore containing an ionic liquid does not enhance the supercapacitor performance within the practical voltage ranges. However, by using an effective dielectric constant to account for ion polarizability, the DFT predicts that, like an organic electrolyte, an ionophobic pore with an ionic liquid is also able to increase the energy stored when the electrode voltage is beyond a certain value. We find that the critical voltagemore » for an enhanced capacitance in an ionic liquid is larger than that in an organic electrolyte. Finally, our theoretical predictions provide further understanding of how chemical modification of porous electrodes affects the performance of supercapacitors.« less

Authors:
 [1];  [2];  [1];  [3];  [4]
  1. East China Univ. of Science and Technology, Shanghai (China). State Key Lab. of Chemical Engineering
  2. (United States). Dept. of Chemical and Environmental Engineering
  3. Brigham Young Univ., Provo, UT (United States). Dept. of Chemistry and Biochemistry
  4. Univ. of California, Riverside, CA (United States). Dept. of Chemical and Environmental Engineering
Publication Date:
Research Org.:
Brigham Young Univ., Provo, UT (United States); Univ. of California, Riverside, CA (United States); East China Univ. of Science and Technology, Shanghai (China)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Chinese Scholarship Council; National Natural Science Foundation of China (NNSFC)
OSTI Identifier:
1340472
Grant/Contract Number:
AC05-00OR22725; 91334203; B08021
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physics. Condensed Matter
Additional Journal Information:
Journal Volume: 28; Journal Issue: 41; Journal ID: ISSN 0953-8984
Publisher:
IOP Publishing
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; energy storage; nonaqueous electrolytes; ionophobic nanopore; electrical double layer; classical density functional theory

Citation Formats

Lian, Cheng, Univ. of California, Riverside, CA, Liu, Honglai, Henderson, Douglas, and Wu, Jianzhong. Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?. United States: N. p., 2016. Web. doi:10.1088/0953-8984/28/41/414005.
Lian, Cheng, Univ. of California, Riverside, CA, Liu, Honglai, Henderson, Douglas, & Wu, Jianzhong. Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?. United States. doi:10.1088/0953-8984/28/41/414005.
Lian, Cheng, Univ. of California, Riverside, CA, Liu, Honglai, Henderson, Douglas, and Wu, Jianzhong. 2016. "Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?". United States. doi:10.1088/0953-8984/28/41/414005. https://www.osti.gov/servlets/purl/1340472.
@article{osti_1340472,
title = {Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?},
author = {Lian, Cheng and Univ. of California, Riverside, CA and Liu, Honglai and Henderson, Douglas and Wu, Jianzhong},
abstractNote = {The ionophobicity effect of nanoporous electrodes on the capacitance and the energy storage capacity of nonaqueous-electrolyte supercapacitors is studied by means of the classical density functional theory (DFT). It has been hypothesized that ionophobic nanopores may create obstacles in charging, but they store energy much more efficiently than ionophilic pores. In this paper, we find that, for both ionic liquids and organic electrolytes, an ionophobic pore exhibits a charging behavior different from that of an ionophilic pore, and that the capacitance–voltage curve changes from a bell shape to a two-hump camel shape when the pore ionophobicity increases. For electric-double-layer capacitors containing organic electrolytes, an increase in the ionophobicity of the nanopores leads to a higher capacity for energy storage. Without taking into account the effects of background screening, the DFT predicts that an ionophobic pore containing an ionic liquid does not enhance the supercapacitor performance within the practical voltage ranges. However, by using an effective dielectric constant to account for ion polarizability, the DFT predicts that, like an organic electrolyte, an ionophobic pore with an ionic liquid is also able to increase the energy stored when the electrode voltage is beyond a certain value. We find that the critical voltage for an enhanced capacitance in an ionic liquid is larger than that in an organic electrolyte. Finally, our theoretical predictions provide further understanding of how chemical modification of porous electrodes affects the performance of supercapacitors.},
doi = {10.1088/0953-8984/28/41/414005},
journal = {Journal of Physics. Condensed Matter},
number = 41,
volume = 28,
place = {United States},
year = 2016,
month = 8
}

Journal Article:
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  • Electric double-layer capacitors (EDLCs) are electrical devices that store energy by adsorption of ionic species at the inner surface of porous electrodes. Compared with aqueous electrolytes, ionic liquid and organic electrolytes have the advantage of larger potential windows, making them attractive for the next generation of EDLCs with superior energy and power densities. The performance of both ionic liquid and organic electrolyte EDLCs hinges on the judicious selection of the electrode pore size and the electrolyte composition, which requires a comprehension of the charging behavior from a microscopic view. In this Perspective, we discuss predictions from the classical density functionalmore » theory (CDFT) on the dependence of the capacitance on the pore size for ionic liquid and organic electrolyte EDLCs. CDFT is applicable to electrodes with the pore size ranging from that below the ionic dimensionality to mesoscopic scales, thus unique for investigating the electrochemical behavior of the confined electrolytes for EDLC applications.« less
  • The comparative performance of the solid-state electrical double layer capacitors (EDLCs) based on the multiwalled carbon nanotube (MWCNT) electrodes and poly (vinaylidinefluoride-co-hexafluoropropyline) (PVdF-HFP) based gel polymer electrolytes (GPEs) containing potassium and lithium salts have been studied. The room temperature ionic conductivity of the GPEs have been found to be ∼3.8×10{sup −3} and 5.9×10{sup −3} S cm{sup −1} for lithium and potassium based systems. The performance of EDLC cells studied by impedance spectroscopy, cyclic voltammetry and constant current charge-discharge techniques, indicate that the EDLC with potassium salt containing GPE shows excellent performance almost equivalent to the EDLC with Li-salt-based GPE.
  • Polyethylene oxide (PEO), polymethyl methacrylate (PMMA), and polyacrylonitrile (PAN) based gel electrolytes with a mixture of ethylene carbonate and propylene carbonate as plasticizer and lithium perchlorate were used to fabricate an electric double-layer capacitor (EDLC). The performance of EDLCs with these gel electrolytes was investigated by using isotropic high-density graphite electrodes. The ion conductivities of various gel electrolytes were of the order of 10{sup {minus}4} to 10{sup {minus}3} S/cm, and they decreased in the order PAN > PEO > PMMA at ambient temperature. Capacitances approaching the value of EDLCs using organic liquid electrolyte, 20 mF/cm{sup 2}, with an isotropic high-densitymore » graphite electrode were obtained in PAN and PMMA gel electrolytes. The EDLC with PMMA-based gel electrolyte showed good charge-discharge behavior over 10{sup 4} cycles at a charge potential of 3.0 V. The rapid progress in the development of electric vehicles and electronic devices has placed increased demand on high-power capacitors. The EDLC is attractive as a rechargeable pulse power source or backup power supply for such applications.« less