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

Zhao, Yangzhi; Fang, Chen; Zhang, Guangzhao; Hubble, Dion; Nallapaneni, Asritha; Zhu, Chenhui; Zhao, Zhuowen; Liu, Zhimeng; Lau, Jonathan; Fu, Yanbao; Liu, Gao

doi:10.3389/fchem.2020.00484

DOE OSTI · 1646843

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

Zhao, Yangzhi·Fang, Chen·Zhang, Guangzhao·Hubble, Dion·Nallapaneni, Asritha·Zhu, Chenhui·Zhao, Zhuowen·Liu, Zhimeng·Lau, Jonathan·Fu, Yanbao·Liu, Gao

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Abstract

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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Zhao, Yangzhi, Fang, Chen, Zhang, Guangzhao, Hubble, Dion, Nallapaneni, Asritha, Zhu, Chenhui, Zhao, Zhuowen, Liu, Zhimeng, Lau, Jonathan, Fu, Yanbao, Liu, Gao. 2020-06-19. A Micelle Electrolyte Enabled by Fluorinated Ether Additives for Polysulfide Suppression and Li Metal Stabilization in Li-S Battery. https://doi.org/10.3389/fchem.2020.00484

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