There is no doubt that lithium-metal batteries (LMBs) are considered as attractive power sources owing to their extraordinarily high energy density. However, the formation of lithium dendrites during repeated plating/stripping processes hinders their practical application. Herein, we introduce phosphorous pentoxide (P2O5) as an additive to commercial carbonate-based electrolytes to effectively suppress the dendritic growth on the surface of a lithium-metal anode. Significant improvement of the lifespan and coulombic efficiency of the cell were observed with the addition of P2O5 to the electrolyte in Li || Li, Li || Type 316L SS, Li || Cu, and Li || graphite cells. According to surface analyses and microscopic studies, we found reduction mechanism of the P2O5-induced solid-electrolyte interphase (SEI) formation on Li metal. Namely, electrolytic decomposition product, LiF, reacts with P2O5 additive in electrolyte, so that LiPO2F2 is produced by following reaction: 6LiF + 2P2O5 → 3LiPO2F2 + Li3PO4, of which those products suppress dendritic growth of lithium as visualized by operando Synchrotron tomography. The compatibility and outstanding rate performance of the additive-based electrolyte were also demonstrated in Li || NCM full cells. As a result, this finding confirms an effective way to stabilize SEI layers in LMBs via a facile and inexpensive route.