Lithium nitrate: A double-edged sword in the rechargeable lithium-sulfur cell

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.