Lithium nitrate (LiNO₃) has been the most studied electrolyte additive in lithium-sulfur (Li-S) cells, due to its known function of suppressing the shuttle effect in Li-S cells, which provides a significant increase in the cell's coulombic efficiency and cycling stability. Previous studies indicated that LiNO₃ participated in the formation of a passive layer on the lithium electrode and thus suppressed the redox shuttle of the dissolved polysulfides. However, the effects of the LiNO₃ on the positive electrode materials have rarely been investigated. By combining scanning electron microscopy, element-selective X-ray absorption spectroscopy, and electrochemical characterizations, we performed a comprehensive study of how the LiNO₃ altered the properties of the sulfur electrode/electrolyte interface in Li-S cells and thus influenced the cell performance. We found that LiNO₃ is a double-edged sword in the Li-S cell: on one hand, it increased the consumption of the active sulfur; on the other hand, it promoted the survival of the carbon matrix constituent in the sulfur electrode. These two competitive effects indicated that a proper moderate concentration of LiNO₃ is required to achieve an optimized cell performance.