Efficient plating/stripping of Na metal is critical to stable operation of any rechargeable Na metal battery.However,it is often overlooked or misunderstood in electrochemical measurements using thick Na electrodes with large excess of Na reserves.Herein,we report two crucial aspects,which have generally been ignored in previous studies,in the development of more practical capacity-controlled Na metal electrodes that can be efficiently cycled at 100％ depth.We find that common carbonate electrolytes induce severe side reaction and highly irreversible Na plating/stripping,whereas ether electrolytes without any additive support thick Na metal electrodes operating at a high average Coulombic efficiency of 99.6％ for over 300 cycles.We further show that to realize such high efficiency in thin Na metal electrodes,it is necessary to ensure strong adhesion between the thin Na layer and the Cu current collector,which we solve by introducing an Au interlayer.The resulting transferable thin Na metal electrodes enable high-energy-density,high-efficiency and reasonably stable-cycling Na||Na3V2(PO4)3 batteries.