Real-time monitoring the formation of polymer double network for gel polymer electrolyte by means of dielectric spectroscopy

Abstract

A non-destructive method of detecting the internal information of the system is attempted in a polymer double network for gel polymer electrolyte in lithium-ion battery. The real-time monitoring for polymerization of 1,3-dioxolane (DOL) and cross-linking of cyanoethyl poly(vinyl alcohol) (PVA-CN) is carried out in a coin cell at 0–80 ℃ by means of dielectric spectrum. A widely distributed dielectric relaxation varying with monitoring time and temperature is observed in the frequency range of 3–103 kHz, and the relaxation parameters of the three sub-relaxations are obtained by fitting the dielectric spectrum with the HN equation. It is found that the relaxation intensity Δε and relaxation time τ are obviously dependent on the monitoring time and temperature: Δε and τ change obviously near the respective gel points of DOL and PVA-CN (DOL at 25 ℃, PVA-CN at 60 ℃), suggesting gelation at two gel points respectively. The different structural changes of the system before and after gelling temperature are speculated, and the possible microstructure of the system in each temperature range is proposed after analyzing the relaxation parameters. The applicability of the real-time dielectric monitoring in the study of the structure of gel polymer electrolytes is preliminarily concluded.