Analysis of the electrolyte characteristics on the performance of electric double layer capacitor

Abstract

The characteristics of electrolyte have great impacts on the performance of electrical double layer capacitor (EDLC), in which the three electrolytes of binary fully ionized electrolyte, binary weak electrolyte and multi-species electrolyte are chosen in the current investigation. The generalized modified Poisson-Nernst-Planck (GMPNP) equations are employed to analyze the effects of ion valency and size as well as the valency and size difference between two ions on the ion concentration distribution and thickness of electric double layer (EDL) in electrolyte as well as the cell potential and specific energy in EDLC. More cell potential and specific energy occur in the capacitors with either lower ion valencies and valency sum of anion and cation, and the ion size and its difference between the anion and cation serve as the key factors in binary fully ionized electrolyte. The concentration distributions of ions in the diffuse layer and ionization reaction rate are closely related to the ionization degree in binary weak electrolyte. The ion size and valency difference among anions as well as the highest valency of anion in the multi-species electrolyte influence the performances of EDLC greatly.