Tailoring the Solid Electrolyte Interphase Composition on Lithium Metal Anodes by the Choice of Ionic Liquid during Mechanochemical Modification

Lithium metal batteries (LMBs) have a great potential to become widely commercialized. However, an improved solid electrolyte interphase (SEI) is needed to enable safe long-term cycling. Here, further a mechanochemical modification method is developed, where lithium metal is roll-pressed in contact with ionic liquids (ILs). The choice of IL allows tailoring the composition and thickness of the SEI, examined via X-ray photoelectron spectroscopy and cryo transmission electronic microscopy, to tune its properties and enable low overvoltage, smooth deposit morphology, and cycling at high current densities. Among the examined ILs, N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (Pyr(14)FSI) provides the best results, facilitating stable cycling in a carbonate-based electrolyte at current densities up to 10 mA cm(-2), which results from the suppression of dendrite formation and electrolyte consumption presumably due to a better lithium ion conductivity and homogeneity of the SEI. Furthermore, the modified lithium metal anodes show a good compatibility with NMC cathodes, which is crucial for high-voltage LMB applications. Finally, modified lithium anodes are used in combination with a ternary solid polymer electrolyte, showing also in this context, a much-improved cycling performance.