A Self-Assemble Micelle Electrolyte for Polysulfide Suppression and Li Stabilization in Li-S Battery

Abstract

Li-S battery, a promising next-generation technology, has received dramatic attention recently due to high theoretical energy density (2600Wh kg-1 ) and low materials cost. However, its application has been impeded by notorious polysulfide dissolution/shuttling which causes poor cycling stability and coulombic efficiency. Herein, I will introduce a novel strategy to suppress the polysulfide dissolution by using hydrofluoroethers (HFEs) electrolyte additive. A bi-functional, surfactant-like molecule structure with a polar lithiophilic “head” attached to a fluorinated lithiophobic “tail”, was designed for these HFE solvents whereby a unique solvation mechanism is proposed: dissociated lithium ions are readily coordinated with lithiophilic “head” to induce self-assembly into micelle-like complex structures. Complex formation is verified experimentally by small angle X-ray scattering (SAXS) and is studied as a function of additive structure and concentration. The modeling work is underway to further investigate coordination between molecules and micelle structure evolution under different conditions. These HFE-based electrolytes are found to prevent polysulfide dissolution and to have excellent chemical compatibility with lithium metal, which is evidenced by superior battery performance: Li-S cells are demonstrated with 1395 mAh g-1 initial capacity and 71.9% retention over 100 cycles at >99.5% efficiency; Li||Cu stripping/plating tests reveal high coulombic efficiency (>99.5%), modest polarization, and smooth surface morphology of the uniformly deposited lithium.