Realizing anode free lithium metal battery (AFLMB) is a promising approach to achieve higher energy density without complicated anode chemistry and processing cost. However, uneven lithium (Li) deposition on copper current collector results in dendrite growth and low reversibility. Herein, we report the effect of potassium nitrate (KNO3) additive to boost the cycling life and average coulombic efficiency (CE) of both full cell (Cu//LiNi1/3Mn1/3Co1/3O2 or Cu//NMC) and half cell (Cu–Li) configurations. The Cu//NMC cell possesses a capacity retention (CR) of ~40% after 50 cycles in the presence of KNO3 compared to ~40% after 15 cycles in the control electrolyte, 1 M LiPF6 in ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1 v/v). The average CE of Cu//NMC cell with additive for 50 cycles increases to 96.50%, whereas it is 91.32% after 35 cycles without KNO3. The average efficiencies of Cu–Li cells are 96.20% and 85.74% after 60 cycles with and without KNO3 respectively. Morphological investigations by Scanning Electron Microscope (SEM) reveal a relatively smooth Li deposition with KNO3. These achievements originate mainly from (1) new solid electrolyte interphase components from the enhanced reductive decompositions of PF6 − and NO3 − and (2) electrostatic shielding effect of K+.