Solid-state Li-ion batteries with lithium anodes offer higher energy densities and are safer than conventional liquid electrolyte-based Li-ion batteries. However, the growth of lithium dendrites across the solid-state electrolyte layer leads to the premature shorting of cells and limits their practical viability. Here, using solid-state Li half-cells with metallic interlayers between a garnet-based lithium-ion conductor and lithium, we show that interfacial void growth precedes dendrite nucleation and growth. Specifically, void growth was observed at a current density of around two-thirds of the critical current density for dendrite growth. Computational calculations reveal that interlayer materials with higher critical current densities for dendrite growth also have the largest thermodynamic and kinetic barriers for lithium vacancy accumulation at their interfaces with lithium. Our results suggest that interfacial modification with suitable metallic interlayers decreases the tendency for void growth and improves dendrite growth tolerance in solid-state electrolytes, even in the absence of high stack pressures.