Composite solid-state electrolyte based on hybrid poly(ethylene glycol)-silica fillers enabling long-life lithium metal batteries

Hybrid silica-based nanofillers were synthesised by grafting short chains of poly(ethylene glycol) (PEG) with different molecular weight on the surface of SiO2 porous nanoparticles. Based on this approach, homogeneous poly(ethylene oxide) (PEO)-based ceramic-in-polymer solid-state electrolytes with SiO2 loadings up to 23 wt% were obtained, thanks to the high compatibility between the two phases endowed by the grafted PEG chains. These electrolytes showed satisfying ionic conductivity and excellent resistance against dendrite piercing that enabled long operation, for more than 350 h, under continuous stripping/plating of lithium in symmetric Li/electrolyte/Li cells. Additionally, the operating life of these devices was improved by the self-healing reaction between Li dendrites and silica fillers, being able to reinstate the cycling after short circuit. Finally, a lithium metal full cell, equipped with LiFePO4 positive material and the solid-state electrolyte containing 18 wt% of SiO2, demonstrated high stability against dendrite penetration and discharge capacity at 70 °C comparable to cells based on liquid analogues.