The sulfate esters of 1,3,2-dioxathiolane 2,2-dioxide (DTD) and trimethylene sulfate (TMS) are evaluated as electrolyte additives for K-metal cells. A symmetric K∥K cell filled with 0.8 M KPF6/EC:DEC + 1 wt % of DTD electrolyte delivers plating-stripping polarization of ∼20 mV, i.e., ∼10 mV per K electrode, which is significantly lower than those for the additive-free and TMS-added electrolyte cells. Moreover, a K∥K2Mn[Fe(CN)6] cell filled with the DTD-added electrolyte exhibits a larger reversible capacity and suppressed irreversible capacity than the DTD-free cells. Electrochemical tests and gas chromatography-mass spectrometry (GC-MS) reveal that DTD addition is efficient in passivating the K-metal surface and inhibiting the formation of electrolyte-soluble oligocarbonates, which are formed in the DTD-free electrolyte. The oligocarbonates are oxidized on the positive electrode and cause irreversible capacity. Thus, the DTD additive enables the high reversibility and low polarization of K-metal cells.