These results conclusively show it is the presence of the layer of Na-K liquid that mitigates impedance growth at the interface from which Li is being stripped. In the Li/NaK/LLZTO/NaK/Li cells, stripping of lithium from this interface can be carried out to ultra-high areal capacities (30 mAh cm -2 ) with minimal impedance growth. We interpret this behavior to indicate an absence of void formation in the Li metal, due to flow of the Na-K metal, which also acts as a mixed transport medium for electrons and Li atoms. In contrast, the sharp impedance rise and high overall impedance observed when Li is stripped from the solid Li metal electrode interface is consistent with void formation.