Forming solid electrolyte interphase in situ in an ionic conductingLi_1.5Al_0.5Ge_1.5(PO₄)₃-polypropylene (PP) basedseparator for Li-ion batteries

A new concept of forming solid electrolyte interphases (SEI) in situ in an ionic conducting Li_1.5Al_0.5Ge_1.5(PO₄)₃-polypropylene (LAGP-PP) based separator during charging and discharging is proposed and demonstrated. This unique structure shows a high ionic conductivity, low interface resistance with electrode, and can suppress the growth of lithium dendrite. The features of forming the SEI in situ are investigated by scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). The results confirm that SEI films mainly consist of lithium fluoride and carbonates with various alkyl contents. The cell assembled by using the LAGP-coated separator demonstrates a good cycling performance even at high charging rates, and the lithium dendrites were not observed on the lithium metal electrode. Therefore, the SEI-LAGP-PP separator can be used as a promising flexible solid electrolyte for solid state lithium batteries.