Theory of volumetric capacitance of an electric double-layer supercapacitor

Abstract

Electric double layer supercapacitors are a fast-rising class of high-power energy storage devices based on porous electrodes immersed in a concentrated electrolyte or ionic liquid. As of yet there is no microscopic theory to describe their surprisingly large capacitance per unit volume (volumetric capacitance) of ~ 100 F/cm^3, nor is there a good understanding of the fundamental limits on volumetric capacitance. In this paper we present a non-mean-field theory of the volumetric capacitance of a supercapacitor that captures the discrete nature of the ions and the exponential screening of their repulsive interaction by the electrode. We consider analytically and via Monte-Carlo simulations the case of an electrode made from a good metal and show that in this case the volumetric capacitance can reach the record values. We also study how the capacitance is reduced when the electrode is an imperfect metal characterized by some finite screening radius. Finally, we argue that a carbon electrode, despite its relatively large linear screening radius, can be approximated as a perfect metal because of its strong nonlinear screening. In this way the experimentally-measured capacitance values of ~ 100 F/cm^3 may be understood.

11 pages, 9 figures; extra discussion added; published version

References in corpus (4)

• Superionic state in double-layer capacitors with nanoporous electrodes
• Charge distribution and screening in layered graphene systems
• Anomalously large capacitance of an ionic liquid described by the restricted primitive model
• Non-monotonic swelling of a macroion due to correlation-induced charge inversion

Cited by in corpus (9)

• Accelerating charging dynamics in sub-nanometer pores
• Charge fluctuations in nano-scale capacitors
• Generalization of Linearized Gouy-Chapman-Stern Model of Electric Double Layer for Nanostructured and Porous Electrodes: Deterministic and Stochastic Morphology
• Double layer in ionic liquids: capacitance vs. temperature from atomistic simulations
• Quantum Capacitance Modifies Interionic Interactions in Semiconducting Nanopores
• Wigner crystal in snaked nanochannels
• Critical gate distance for Wigner crystallization in the two-dimensional electron gas
• Classical theory of electron-ion correlations at electrochemical interfaces: Closing the circuit from double-layer charging to ion adsorption
• Replica RISM molecular solvation theory for electric double layer in nanoporous materials