At the polymer electrolyte interfaces: the role of the polymer host in interphase layer formation in Li-batteries

Abstract

In this study, X-ray photoelectron spectroscopy was applied for compositional analysis of the interphase layers formed in graphite and LiFePO₄ Li-battery half cells containing solid polymer electrolytes (SPEs) consisting of poly(trimethylene carbonate) (PTMC) and LiTFSI salt. Decomposition of PTMC was observed at the anode/SPE interface, indicating different reaction products than those associated with the more conventional host material poly(ethylene oxide). Degradation mechanisms of the PTMC host material at low potentials are proposed. Compared to the LiFePO₄/PEO interface, the absence of LiOH – a result of water contamination – was generally seen when using hydrophobic PTMC as the polymer host. A clear correlation of moisture content with the constitution of interphase layers in Li polymer batteries could thus be concluded. At the SPE/LiFePO₄ interface, good stability was seen regardless of the polymer host materials.