Surface-modified BaTiO₃ as a functional filler in poly(ethylene oxide)-based solid polymer electrolytes for lithium-metal batteries

Poly(ethylene oxide) (PEO)-based polymer electrolytes are regarded as promising candidates for solid-state lithium metal batteries due to their unique lithium conduction mechanism compared to inorganic solid-state electrolytes. However, the development of these electrolytes is hindered by their low ionic conductivity and poor mechanical strength. In this study, we enhance the mechanical stability and ionic conductivity of a PEO-based polymer electrolyte by incorporating barium titanate nanoparticles coated with 3-(triethoxysilyl)propionitrile (BTO@TESPN) as solid fillers. With 10 wt% of BTO@TESPN, ionic conductivity and critical current density at 60 °C are improved to 5.67 × 10⁻⁴ S cm⁻² and 1.6 mA cm⁻², respectively, compared to 2.69 × 10⁻⁴ S cm⁻² and 1.0 mA cm⁻² without the filler. Furthermore, the symmetric cell with Li utilizing this electrolyte demonstrates stable cycling at a rate of 0.1 mA cm⁻² for a minimum duration of 1000 h. Additionally, the lithium iron phosphate (LiFePO₄)-Li battery exhibits excellent stability up to 700 cycles at 60 °C at a current rate of 0.5C while maintaining a capacity retention of up to 93.0%. This research presents an innovative approach towards enhancing PEO-based solid polymer electrolytes, by regulating the interface between the filler and the polymer matrix. © The Royal Society of Chemistry 2025.