A Micelle Electrolyte Enabled by Fluorinated Ether Additives for Polysulfide Suppression and Li Metal Stabilization in Li-S Battery

• Published in: Frontiers in chemistry Vol. 8; p. 484
• Main Authors: Zhao, Yangzhi, Fang, Chen, Zhang, Guangzhao, Hubble, Dion, Nallapaneni, Asritha, Zhu, Chenhui, Zhao, Zhuowen, Liu, Zhimeng, Lau, Jonathan, Fu, Yanbao, Liu, Gao
• Format: Journal Article
• Language: English
• Published: United States Frontiers Research Foundation 19.06.2020; Frontiers Media S.A
• Subjects: Chemistry; ENERGY STORAGE; fluorinated ether electrolyte; high coulombic efficiency; Li metal stabilization; micelle-like complex formation; polysulfide suppression; solvation mechanism
• ISSN: 2296-2646; 2296-2646
• DOI: 10.3389/fchem.2020.00484

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.