Comprehensive elucidation of the multifunctional role of lithium nitrate in lithium–sulfur batteries: Expanding beyond shuttle suppression

Abstract

Lithium–sulfur (Li–S) batteries are promising candidates for next-generation energy storage systems, but practical use is limited by polysulfide (PS) shuttling and Li metal anode instability. Lithium nitrate (LiNO₃) is widely used to mitigate these issues; however, its interfacial effects across the anode, electrolyte, and cathode during operation are not fully understood. Here, operando optical microscopy with a custom side-by-side cell enables simultaneous monitoring of the Li anode, liquid electrolyte, and sulfur cathode in a single field of view under conditions with and without LiNO₃. In the absence of LiNO₃, the Li surface undergoes rough stripping and fragmented, non-coalescent deposition, accompanied by PS-induced corrosion and accumulation of parasitic byproducts at the anode-electrolyte interface. Redness Intensity (RI), introduced to quantify electrolyte-phase PS dynamics, indicates sustained transport toward the anode and delayed conversion to elemental sulfur. By contrast, LiNO₃ induces uniform Li stripping and the growth of aggregated, interconnected deposits, while mitigating PS crossover and promoting efficient sulfur crystallization at the cathode. Complementary SEM-EDS, UV–vis, XPS, TXM, and CT analyses corroborate these observations. By elucidating the multifunctional role of LiNO₃, this study clarifies the interfacial dynamics that govern Li–S battery performance.

Keywords

electrolyte additives / lithium nitrate / lithium–sulfur batteries / operando optical imaging

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