Lithium ion capacitor based on polyoxide-polythiol co-networks

Abstract

The present article emerges from our recent finding of supercapacitive behavior of polymer electrolyte membranes (PEM) via photo-crosslinking of polyethylene glycol diacrylate (PEGDA) with trimethylolpropane tris(3-mercaptopropionate) (TMPTMP) via thiol-ene click reaction in the presence of succinonitrile (SCN) plasticizer and lithium bis(trifluoromethane sulfonyl imide) (LiTFSI) salt. The photo-cured polymer electrolyte membrane (PEM) co-network revealed a superionic conductor level of 1.26 mS/cm at 23 °C and an elongation at break of around 23%, suggestive of a highly conductive and stretchable character. Upon deep discharging to the potential range of lithium metal anode at −0.5–0.5 V, lithium-ion stripping from the Li metal electrode (i.e, oxidation at 0–0.3 V) affords continuous supply of Li-ions, which not only afford the lithium-ion storage within the PEM through ion-dipole interaction (i.e., temporary holding of Li ions), but also facile ion transport once the complexation sites of Li-ion with ether oxygen and thiols are fully saturated with excess Li-ions. To elucidate a plausible energy storing mechanism of the PEM, the cyclic voltammetry (CV) investigation was performed in the full battery configuration as well as in the symmetric carbonaceous electrode configuration. A novel supercapacitor behavior was noticed in the PEM involving both pseudocapacitor and electric double-layer capacitor (EDLC) types. Last but not least, specific capacitance and specific energy densities from the CV curves were evaluated and discussed.