A lithium-metal battery includes: a cathode; a garnet solid-state electrolyte disposed on the cathode; and a lithium anode disposed on the garnet solid-state electrolyte, such that a modification layer is disposed at an interface of the lithium anode and garnet solid-state electrolyte, the modification layer comprising an inorganic lithium salt. A method of forming a lithium-metal battery includes treating garnet solid-state electrolyte with an acid solution; and exposing the acid-treated garnet solid-state electrolyte to hydrogen fluoride to form a modification layer atop the garnet solid-state electrolyte.