A star-shaped single lithium-ion conducting copolymer by grafting a POSS nanoparticle

Abstract

Single-ion conducting polymer electrolytes (SCPE) are attractive candidates for high-performance energy storage devices. A star-shaped single lithium-ion conducting polymer electrolyte was synthesized by combining the “grafting to” and “grafting from” strategy utilizing a polyhedral oligomeric silsesquioxane (POSS) nanoparticle as the core. Carboxylic acid terminated polyethylene oxide (PEO) and Reversible Addition Fragmentation Chain Transfer Agent (RAFT-CTA) were attached to the POSS nanoparticle to form a POSS-cored macro RAFT CTA (PMR-CTA). The PMR-CTA was used to mediate the polymerization of potassium (styrene-4-sulfonyltrifluoromethyl-sulfonyl)imide (STF-K+) and subsequent counter ion exchange resulted in a star-shaped single lithium-ion conducting copolymer (SSCP-Li+). The grafting ratio of poly(STF-Li+) and PEO per POSS nanoparticle can be tuned by modifying the feed ratio of the two polymer components. The synthesized star-shaped SCPE-Li+ are characterized by 1H NMR, FT-IR, UV-Vis, DLS, GPC and DSC, and their ionic conductivity is studied by broadband dielectric spectroscopy. The obtained results are compared to a conventional linear homopolymer poly(STF-Li+) and block copolymer PEO-b-poly(STF-Li+), and reveal a significant “decoupling” of ion conductivity from segmental dynamics for all of the studied SCPE-Li+. Blending extra PEOs with SCPE-Li+ was also performed to improve the ionic conductivity.