The effect of sodium on the electrochemical behavior of lithium in alkaline electrolyte with additives was investigated via hydrogen evolution rate, discharge current density, anodic potential, XRD (X-ray diffraction) and SEM (scanning electron microscope) in this paper. The results show that minor addition of sodium to lithium slightly decreases the hydrogen evolution at the electrode. Addition of 0.057wt.% Na to lithium has a minor effect on discharge current and anodic potential of lithium anode. The scanning electron microscopy (SEM) result shows that the lithium–sodium alloy surface is less porous than the lithium surface. Theoretical analysis indicates that the water activity at the Li–Na anode/electrolyte interface is reduced by LiOH+NaOH solution formation. Hydrogen evolution decrease, prompted by the addition of sodium to lithium, is related to the water activity reduction at the metal/electrolyte interface and reduced porosity of the film.