In the symmetric cells tested above, the same type of interface is being stripped of lithium and is depositing lithium at the same time, and does not allow the impact of the Na-K liquid on the two processes to be separated. We therefore constructed asymmetric Li/NaK/LLZTO/Li cells, in which the direction of current allows stripping to be performed at the Li or Li-NaK interface, while plating occurs at the opposing electrode (Fig. ). The behavior of the asymmetric cells was furthermore compared to that of symmetric Li/LLZTO/Li cells. The cells were subjected to a single cycle at fixed current densities of 0.25 or 0.5 mA cm - , to a fixed areal capacity of 6 mAh cm -2 . All cells had an applied stack pressure of 1.5 MPa with the Li metal pre-formed to the LLZTO electrolyte at 170°C under the same pressure. Comparing polarization curves with the Li/LLZTO/Li cell under the same testing conditions isolates the exact conditions that enable "ultrahigh" accessible areal capacity, as the hallmark of such behavior is extended stripping/plating with minimal increases in cell impedance (< 50 Ω cm 2 ). Such behavior indicates the absence of increasing cell impedance over time, which has been associated with stripping-induced voids. and the observed polarization in the bottom figure, as well as the ASR of the two interfaces combined, obtained after subtracting the resistance of the solid electrolyte. In all cases, stripping from the plain Li interface (Fig. and) resulted in a sharp rise in polarization and ASR. The rise in impedance was exacerbated at the higher stripping current density of 0.5 mA cm -2 (Fig. and), yielding cell ASR values of 1000-2000Ω cm 2 , while tests at 0.25 mA cm -2 stripping current (Fig. and) yielded cell ASR values of 150-300Ω cm 2 . In contrast, stripping from the NaK-Li electrode resulted in a lower ASR of ~50-100 Ω cm 2 for both stripping currents of 0.25 and 0.5 mA cm -2 (Fig. ), and stable polarization over the entire plated capacity of 6 mAh cm - regardless of the direction of current. The impedance of these cells is comparable in magnitude to that seen in the Li-NaK/LLZTO/Li asymmetric cells when stripping occurs at the plain Li electrode. Polarization curves analogous to a) -d) for Li/LLZTO/Li symmetric cells. Positive and negative current both correspond to stripping and plating from a plain Li electrode. Note that the vertical axis scale is different in each of the six subfigures. In each subplot, the interfacial ASR values provided are the total contribution from both interfaces within the cell. This value is obtained by subtracting the ASR due to the bulk electrolyte (100 Ω cm 2 ) from the total measured ASR. The cell polarization that corresponds to zero interfacial ASR in each current direction is indicated by the solid black bands. In all cases, rapid impedance rises are associated with stripping from a plain Li electrode.