Stable cycling of lithium metal electrode in nanocomposite solid polymer electrolytes with lithium bis(fluorosulfonyl)imide

Nanocomposite solid polymer electrolytes (NSPEs) comprising lithium salt based on two representative sulfonylimide anions (i.e., bis(fluorosulfonyl)imide ([N(SO2F)(2)](-), FSI-) and bis(trifluoromethanesulfonyl)imide ([N(SO2CF3)(2)](-), TFSI-)) have been prepared by simply dissolving the corresponding lithium salt in poly(ethylene oxide) matrix in the presence of inert nano-sized Al2O3 fillers. The physicochemical and electrochemical properties of the FSI- and TFSI-based NSPEs are investigated, in terms of phase transition, ion transport behavior, chemical and electrochemical compatibility with Li metal. With the addition of nano-sized Al2O3 fillers, a significant improvement in chemical and electrochemical compatibility with Li metal has been observed in both the FSI- and TFSI-based NSPEs. Particularly, the symmetric cell using the FSI-based NSPE can be continuously cycled for > 1000 h at 70 degrees C. The Li vertical bar LiFePO4 cell with the FSI-based NSPEs shows good cycling stability and capacity retention. These promising results make them attractive electrolytes for safe and stable rechargeable Li metal batteries.