Dual Functional High Donor Electrolytes for Lithium–Sulfur Batteries under Lithium Nitrate Free and Lean Electrolyte Conditions

Electrolyte engineering is a highly promising strategy in lithium–sulfur batteries to increase the sulfur utilization and maintain a stable interface at the lithium metal anode for long-term cycling. Whereas high donor electrolytes can increase the solubility of polysulfides to promote the sulfur utilization and therefore operate under lean electrolyte conditions, their poor thermodynamic stability toward lithium metal anode causes uncontrolled decomposition at its interface and impair the cycle life severely. Here, we introduce a dual functional high donor electrolyte, 3-fluoropyridine (3-FPN), to simultaneously achieve high polysulfide solubility up to 1.5 M and compatibility with lithium metal. These features result in a high specific capacity of 1087.9 mAh g_sulfur^–1 and robust cycling under a lean electrolyte condition of 7 μLelectrolyte mg_sulfur^–1 in the absence of LiNO3. Remarkably, 3-FPN preserves stable cyclability even at a high areal sulfur loading of 8 mg_sulfur ^cm–2, which opens a new avenue in advancing the electrolytes for lithium–sulfur batteries toward their high volumetric energy density and long cycle life