Lithium metal is used to achieve high-energy-density batteries due to its large theoretical capacity and low negative electrochemical potential. The introduction of quasi-solid electrolytes simultaneously overcomes the safety problems induced by the liquid electrolytes and the high interfacial resistance issues confronted by all solid-state electrolytes. In-depth investigations involving interfacial behaviors in quasi-solid lithium metal batteries are inadequate. Herein an ultrathin Li3 OCl quasi-solid-state electrolyte layer (500 nm thickness) is used to cover a lithium anode. The polarization of the anode is remarkably reduced by introducing the Li3 OCl quasi-solid-state electrolyte. In contrast to the decomposition of solvents in a standard electrolyte (EC-DEC,1.0 m LiPF6 ), the established quasi-solid-state electrolyte interfaces can significantly inhibit the decomposition of solvents when the cut-off voltage is 4.5 V.