Despite their widespread study, lithium metal anodes still face the bottleneck problem of low average Coulombic efficiency. Herein, we adopt an electroless plating method and introduce additive (vanillin) to develop nanoscale silver hosts. The uniform nanoscale silver layer is conducive to seamless Li/Ag alloying process, thereby enabling flat lithium deposition. Since the Li/Ag alloying process occurs after the formation of solid electrolyte interphase (SEI), the seamless alloying process stabilizes the SEI, which improves the reversibility of the lithium metal anode. On this basis, a 3D-printed copper host-coated dense nanoscale silver layer is constructed, which reduces the effective current density and hence lowers the polarization of lithium deposition or stripping. Moreover, the 3D structure induces the epitaxial growth of lithium and thus alleviates the volume change of lithium metal. As a result, an average Coulombic efficiency of 99.61% is achieved in the Li/3D Ag half-cell.