Effect of Lithium Salt in Nanostructured Silica–Polyethylene Glycol Solid Electrolytes for Li-Ion Battery Applications

Abstract

Organic–inorganic hybrid solid electrolytes based on silica–polyethylene glycol PEG(200, 400) with bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) or lithium trifluoromethanesulfonate (LiOTf) were synthesized by a sol–gel process. The thermal and structural properties of the materials thus obtained were systematically investigated by a variety of techniques including SEM, TGA-DTA, DSC, FTIR, Raman, and multinuclear (1H, 13C, 7Li) solid-state NMR. Arrehenius behavior was observed for solid hybrid electrolyte membranes, implying that segmental motions of the organic network were involved in ionic conductivity. The Li-ion transfer number was determined and correlated with their ionic conductivities, and the interfacial stability against lithium was evaluated. Maximum ionic conductivities for the solid hybrid electrolyte membrane SiO2–PEG400 with LiTFSI and a [Li+]/[O] = 0.10 (class II hybrid) of 3.9 × 10–4 and 4.5 × 10–3 S/cm–1 were obtained at room temperature and 60 °C, respectively. The good value of electrochemical stability window (∼6 V) and stable interfacial impedances against lithium metal make these hybrid electrolytes a promising candidate for all-solid-state lithium battery applications.