Perfluoroinated Ionomer as an Artificial SEI for Silicon Nano-Flake Anode in LiTFSI/Tetraglyme Solvate Ionic Liquid

Abstract

Cycle performance of silicon nano-flake powder (LeafPower® Si) anodes was improved by coating of perfluorosulfonic acid (PFSA) polymers (Nafion® and Aquivion®) as an artificial solid electrolyte interphase (SEI). The Si electrodes were coated with PFSA ionomer by addition of PFSA ionomer solution to aqueous slurry of the Si composite electrode. H+-type Nafion®-coated Si electrodes demonstrated improved capacity retentions and Coulombic efficiencies owing to the formation of a LiF-rich SEI composed of reductive decomposition products of Nafion®. The Nafion® coating suppressed the increase in polarization and the electrode swelling upon cycling because the LiF-rich SEI effectively suppressed electrolyte decomposition. Li+ and Cs+-type Nafion® and H+-type Aquivion®, which has a shorter side chain than Nafion®, provided similar positive effects on cycle performance of the Si electrodes. Furthermore, the Si electrodes achieved good cycleability up to 500 cycles owing to synergy effects of the Nafion® coating and an SEI-forming additive of fluoroethylene carbonate (FEC).