Versatile Zn-salt additive enabling superior solid polymer electrolyte for dendrite-free all-solid-state Li metal batteries

•A feasible and scalable method by introducing versatile zinc trifluoromethanesulfonimide enables superior solid polymer electrolyte.•The Zn2+ weakens the ion-dipolar effect between Li and O atoms and suppresses the activity of TFSI− anion.•Alloy-phase in-situ formed in the SEI improves the Young's modulus and causes close contact between electrolyte and Li metal.