Perfluoroinated Ionomer as an Artificial SEI for Silicon Nano-Flake Anode in LiTFSI/Tetraglyme Solvate Ionic Liquid
Masakazu Haruta, Hiroto Konaga, Takayuki Doi, Minoru Inaba
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).