Anion Regulation for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries, characterized by their high energy density and cost-effectiveness, are the primary candidates for lithium-ion batteries. Yet, critical challenges persist, largely owing to the polysulfide (PS) anion shuttle and the instability of the lithium metal anode (LMA). Salt anions are indispensable in batteries, which influence the basic properties of bulk electrolytes (e.g., solubility, stability, and ion conductivity) and the electrode-electrolyte interphases. Apart from those, the intrinsic characteristics of anions are of particular importance in Li-S batteries, as PS anions are major active intermediates that directly determine the sulfur redox kinetics and reversibility. However, the anion regulation needs further investigated, especially according to the Li-S chemistry. In this regard, fundamental considerations are provided on the anion engineering of Li-S batteries. Through a comprehensive analysis, the electrochemical behaviors of anions are reviewed. Then, the recent works on anion regulation for cathodes and anodes are summarized. For sulfur cathodes, the PSs dissolution, adsorption, conversion kinetics, and pathway are discussed in detail. For LMA, the influence of anion on lithium diffusion kinetic, the formation of SEI, and the anticorrosion are summarized. Finally, insights into the future development of anion studies are provided, aiming to identify more adequate anions for Li-S batteries.