Research on the aging of micro-supercapacitor under the condition of longtime storage

Abstract

Given the phenomenon that the capacity retention rate, anti-surge voltage capability, and frequency characteristic of the micro-supercapacitors (MSCs) would become poor under the condition of long time storage, a study was carried on a long time natural aging of MSCs with (PPy/GO-RuO2) membrane electrode and (PVA-KOH-KSCN-EG) gel electrolyte, and it fell into two parts: one was to measure the self-discharge, breakdown voltage, and capacitance value diffusion of samples with various natural storage time, and the second to carry on a scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) test of the membrane electrode. The possible causes of a decrease of the capacity retention rate and the capacitance value diffusion threshold, an increase of the leakage current was found, based on the two test results. SEM analysis showed that the three-dimensional structure collapsed in the surface area of the membrane electrode with an increase of storage time, which made the pore and specific surface area of the active substance decreasing, resulting in capacity retention rate decrease, and the leakage current increases. XRD and XPS analysis showed that the amorphous RuO2•nH2O lost water gradually, which made RuO2 and Ru constantly appear, resulting in the polarization voltage of the membrane electrode and the breakdown voltage increase, and the specific capacity of MSCs reduce. Meanwhile, the amino group (- NH) protonation in PPy weakened the electron-donating ability, which increased faraday resistance RF, leading to the continuous decrease of capacitance diffusion threshold. The above research results were beneficial for improving the manufacturing process and service conditions of MSCs.