Plating-stripping reversibility of lithium metal is improved by reinforcing the solid-electrolyte interphase layer by inorganic nanobeads. The outmost solid-electrolyte interphase shell is clearly identified, which is the passive layer formed on current collectors (or lithium metal) before the first lithium metal deposition. The outmost shell is intrinsically brittle and fragile so that it is easily broken by lithium metal dendrites growing along the progress of plating. Lithium metal deposit is not completely stripped back to lithium ions. On the other hand, lithium metal cells containing inorganic nanobeads in electrolyte show high reversibility between plating and stripping. The nanobeads are incorporated into the outmost shell during its formation. The nanobead-reinforced outmost shell having mechanically durable toughness suppresses dendritic growth of lithium metal, not allowing the dendrites to penetrate the shell. In addition to the mechanical effect of nanobeads, the LiF-rich solid-electrolyte interphase layer formation is triggered by HF generated by the reaction of the moisture adsorbed on oxide nanobeads with PF6-. The LiF-rich composition is responsible for facile lithium ion transfer through the passive layers.