Suppression of Self-Discharge in Aqueous Supercapacitor Devices Incorporating Highly Polar Nanofiber Separators

Abstract

One of the major problems limiting the applications of electric double-layer (EDLC) supercapacitor devices is their inability to maintain their cell voltage over a significant period. Self-discharge is a spontaneous decay in charged energy, often resulting in fully depleted devices in a matter of hours. Here, a new method for suppressing this self-discharge phenomenon is proposed by using directionally polarized piezoelectric electrospun nanofiber films as separator materials. Tailored engineering of polyvinylidene fluoride (PVDF) nanofiber films containing a small concentration of sodium dodecyl sulfate (SDS) results in a high proportion of polar β phases, reaching 38 ± 0.5% of the total material. Inducing polarity into the separator material provides a reverse-diode mechanism in the device, such that it drops from an initial voltage of 1.6 down to 1 V after 10 h, as opposed to 0.3 V with a nonpolarized, commercial separator material. Thus, the energy retained for the polarized separator is 37% and 4% for the nonpolarized separator, making supercapacitors a more attractive solution for long-term energy storage.