Journal
FRONTIERS IN CHEMISTRY
Volume 8, Issue -, Pages -Publisher
FRONTIERS MEDIA SA
DOI: 10.3389/fchem.2020.00484
Keywords
polysulfide suppression; Li metal stabilization; fluorinated ether electrolyte; micelle-like complex formation; solvation mechanism; high coulombic efficiency
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Funding
- Energy Efficiency, Vehicle Technologies Office of the U.S. Department of Energy, under the Advanced Battery Materials Research (BMR) Program
- Office of Science, Office of Basic Energy Sciences, of the US Department of Energy [DE-AC02-05CH11231]
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The Li-S battery is a promising next-generation technology due to its high theoretical energy density (2600 Wh kg(-1)) and low active material cost. However, poor cycling stability and coulombic efficiency caused by polysulfide dissolution have proven to be major obstacles for a practical Li-S battery implementation. In this work, we develop a novel strategy to suppress polysulfide dissolution using hydrofluoroethers (HFEs) with bi-functional, amphiphlic surfactant-like design: a polar lithiophilic head attached to a fluorinated lithiophobic tail. A unique solvation mechanism is proposed for these solvents whereby dissociated lithium ions are readily coordinated with lithiophilic head to induce self-assembly into micelle-like complex structures. Complex formation is verified experimentally by changing the additive structure and concentration using small angle X-ray scattering (SAXS). These HFE-based electrolytes are found to prevent polysulfide dissolution and to have excellent chemical compatibility with lithium metal: Li||Cu stripping/plating tests reveal high coulombic efficiency (>99.5%), modest polarization, and smooth surface morphology of the uniformly deposited lithium. Li-S cells are demonstrated with 1395 mAh g(-1)initial capacity and 71.9% retention over 100 cycles at >99.5% efficiency-evidence that the micelle structure of the amphiphilic additives in HFEs can prohibit polysulfide dissolution while enabling facile Li(+)transport and anode passivation.
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