Oxygen-vacancy-rich nanosized CeO2 for enhancing ionic transport and cycling stability in PEO-LiTFSI composite solid electrolytes

Low ionic conductivity and low Li⁺ transference numbers limit the practical application of polyethylene oxide (PEO)-based polymer solid electrolytes, arising from PEO semi-crystallinity and poor lithium salt dissociation at ambient conditions. Here, we systematically investigate the size-dependent role of CeO 2 fillers by incorporating nanosized (∼5 nm) and submicron particles into PEO-LiTFSI electrolytes. The nanosized CeO 2 , enriched with surface oxygen vacancies and high specific surface area, simultaneously suppresses PEO crystallinity and provides abundant Lewis acid sites that immobilize TFSI⁻ via Lewis acid-base interactions, increasing the mobile Li + carrier concentration. As a result, the nanosized CeO 2 -based composite electrolyte exhibits an ionic conductivity of 5.95 × 10 –5  S/cm at room temperature (2.4 × higher than pristine PEO) and a Li⁺ transference number of 0.30, nearly fourfold higher than the filler-free system (0.08). In addition, it delivers a widened electrochemical stability window of ∼4.9 V, a high critical current density of 0.8 mA/cm², and stable Li||Li symmetric cycling over 600 h, substantially outperforming both the submicron CeO 2 -based composite and the filler-free electrolytes. Download: Download high-res image (522KB) Download: Download full-size image