Facile ex-situ formation of a LiF-polymer composite layer as an artificial SEI layer on Li metal by simple roll-press processing for carbonate electrolytes-based Li metal batteries

Lithium (Li) metal has been considered as an ideal anode for next-generation Li metal batteries (LMBs). However, Li dendrite formation and low Coulombic efficiency (CE) are major obstacles for the practical use in LMBs. The engineering of interface between Li metal and electrolytes is crucial for better Li ion kinetic and interface stability to overcome above problems. In this study, we report a thin LiF/defluorinated polymers (LiF@Po) composite as artificial SEI layer. The LiF@Po composite layer, formed by facile and scalable roll-pressing process using polytetrafluoroethylene (PTFE) and Li metal, is composed of inside (lithium side) LiF-rich layer and outside (electrolyte side) polymer rich (polyene/fluoropolymer) layer. The free space between LiF particles could be conformally filled with polymeric layer, improving the Li surface coverage property of the protection layer. This novel LiF@Po protection layer enables highly stable cyclability even in the carbonate-based electrolyte more than 1000 h at 1 mA cm-2 in the Li||Li symmetric cell and the cycle retention of 80% capacity for > 200 cycles with an extremely stable average CE of 99.7% in the Li||LiCoO2 full cell. Furthermore, this LiF@Po protection layer could significantly enhance the cyclability and reversible capacity in Li||LiNi0.8Co0.1Mn0.1O2 (NCM-811) full cell.