Achieving high capacity retention for SnS2 anodes via the solvent-driven reversible conversion-alloying reactions

Despite their large theoretical capacity (typically > 1000 mAh g � 1), anode materials featuring Na storage via a combined mechanism of conversion and alloying reactions are practically limited in Na-ion batteries owing to their poor initial Coulombic efficiency (typically -50%). Using SnS2 as an example, we present a model that elucidates the physics underpinning its inferior Coulombic efficiency by incorporating an understanding of the thermodynamics and kinetics of conversion-alloying reactions. The developed model show that conversionalloying reactions and their reversibility can be engineered by modulating the solvation tendency of electrolyte solvents, resulting in an enhanced initial Coulombic efficiency of > 70% (corresponding to 817 mAh g � 1) even without expensive pretreatment and the use of nanoscale SnS2 particle anodes. Thus, this study that correlates the solvent properties and first-cycle reversibility offers a solution for selecting appropriate electrolytes for designing high-energy-density anodes based on various sodium storage mechanisms.