In this work, the enrichment of commercially available separators with LiNO3 was investigated in ZELMBs using Cu || Li and NCM622 || Li cell configurations with carbonate-based electrolyte (LP57). The cells with LiNO3-modified separators show superior performance compared to those with unmodified separators. Furthermore, the approach of using LiNO3 precipitated in the separator rather than as an electrolyte additive in carbonate-based electrolytes positively affects the cycling stability. In Cu || Li cells, LiNO3-modified separator leads to an extended cycle life with lower overpotentials and increased CE compared to the cells with unmodified separators. Postmortem analysis indicates that the morphology of the lithium deposits is mossy and highly porous in the cells using the unmodified separator, while dense and well-packed lithium deposits are formed for the cells containing the LiNO3-modified separators. The investigations of NCM622 || Cu cells indicate a prolonged cycle life with better capacity retention when LiNO3 is added to the separator. With the help of IC measurements, we show that the concentration of LiNO3 remains almost constant in the electrolyte when LiNO3 is present in the separator rather than in the electrolyte. Based on the results presented here, we can conclude the following key points: a) the presence of LiNO3 in the electrolyte is beneficial for the morphology of the Li deposits, resulting in improved CEs, b) the addition of LiNO3 in the separator rather than in the carbonate-based electrolyte allows an increase of the duration over which the LiNO3 is present in the electrolyte, keeping in mind the sacrificial effect of LiNO3 as electrolyte additive, and c) the presence of LiNO3 in NMC || Cu cells (i.e., ZELMBs) indicates the importance of electrolyte additives in stabilizing the cycling performance of ZELMBs with liquid electrolytes. Although this work shows an elegant way to use LiNO3 with carbonate electrolytes for ZELMBs, there is still much improvement needed in order to further stabilize the capacity fading mechanism observed in ZELMBs with liquid electrolytes.