High-Ionic-Conductivity\nSodium-Based Ionic Gel Polymer\nElectrolyte for High-Performance and Ultrastable Microsupercapacitors

Abstract

Due to the lower cost and greater natural abundance of\nthe sodium\nelement on the earth than those of the lithium element, sodium-based\nionic gel polymer electrolytes (IGPEs) are becoming a more cost-effective\nand popular material choice for portable and stationary energy solutions.\nThe sodium-based IGPEs, however, appeared relatively inferior to their\nlithium-based counterparts for use in high-performance microsupercapacitors\nin terms of ionic conductivity and electrochemical stability. To tackle\nthese issues, poly(ethylene glycol) diacrylate (PEGDA) with fast polymerization\nto build a polymer matrix and sodium perchlorate (NaClO₄) with high chemical stability and high thermal stability are employed\nto generate free ions for an ionic conducting phase with the support\nof tetramethylene glycol ether (G4) and 1-ethyl-3-methylimidazolium\nbis(triflouromethylsulfonyl)imide (EMIM-TFSI). It was found that the\nionic conductivity (σ_dc) of this sodium-based IGPE\nreaches up to 0.54 mS/cm at room temperature. To manifest a high-conductivity\nsodium-based IGPE (SIGPE), a microsupercapacitor (MSC) with an area\nof 5 mm² is designed and fabricated on an interdigital\nreduced graphene oxide electrode. This MSC demonstrates prominent\nperformance with a high power density of ∼2500 W/kg and a maximum\nenergy density of ∼0.7 Wh/kg. Furthermore, after 20,000 cycles\nat an operating potential window from 0.0 to 1.0 V, it retains approximately\n98.9% capacitance. An MSC array in 3 series × 3 parallels (3S\n× 3P) was successfully designed as a power source for a basic\ncircuit with an LED. Therefore, we believe that our sodium-based IGPE\nmicrosupercapacitor holds its promising role as a solid-state energy\nsource for high-performance and high-stability energy solutions.