Enhancing the safety and stability of lithium metal batteries through the use of composite ionogels

Solid-state polymer electrolytes are a promising platform for safer lithium-metal batteries, but low ionic conductivity and high interfacial resistance with electrodes limit the room temperature applications. Herein, an ionogel (IG) composed of a crosslinked polymer matrix and an ionic liquid (PYR14TFSI), prepared through a one-pot thermal polymerization has been investigated. Alumina nanoparticles (Al2O3 NPs) were added into this IG to further increase ionic conductivity and cycling performances, by coordinating anionic species at the surface of the inorganic filler, promoting the Li+ motion. The alumina composite IG shows an ionic conductivity of 2.05·10–4 S cm−1 at 20 °C such as a wide electrochemical stability window (ESW) of 5.12 V vs. Li+/Li. The LiFePO4/Li batteries assembled with different IGs present good cycling performance at room temperature, interesting capacity retention after 500 cycles at 0.2 C and more importantly, improved capacity even at 1 C, compared to the ionic liquid alone soaked on a glass fiber separator. This work provides a simple approach to prepare safer composite IG with remarkable electrochemical performances at room temperature for lithium metal batteries.