Poly(ethylene oxide) (PEO, Mw 5,000,000, Sigma-Aldrich) was dried under vacuum at 50 °C for 24 h before use. N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide (C 3 mpyrFSI) (purity 99.5%) from Solvionic and lithium bis(fluorosulfonyl)imide (LiFSI) from Nippon Shokubai were dried under vacuum at 50 °C for 48 h before use. Lithium iron phosphate (LFP) powder was purchased from Custom Cells, lithium manganese oxide (LMO) was supplied from Calix Ltd and Super C65 carbon was purchased from Sigma. All materials were kept in an argon-filled glove box for further SPE preparation.