The emerging secondary battery system with room-temperature lithium-sulfur (Li-S) chemistry is gaining much attention as a promising next-generation energy storage technology for a broad range of applications.^{1, 2} However, this battery technology is currently facing a critical obstacle due to a so-called “polysulfide-shuttle” behavior during cell operation.^{3, 4} Although a lot of efforts have been attempted to address such a challenge since it has been recognized many year ago, there is still a lack of reliable approaches that can fully prevent the polysulfide-shuttle without bringing any other negative effects to the Li-S cell system. For instance, attempts in the development of the advanced cathode matrices or structural configurations can alleviate the polysulfide diffusion to certain extent, but these approaches are not able to absolutely encapsulate the polysulfides in the cathode.⁵ Use of the Li⁺-ion conductive solid electrolyte can effectively prevent the migration of the polysulfide species through. But these approaches usually bring new problems due to the relatively low room-temperature conductivity of the currently available solid electrolytes and the brittleness of the ceramic materials.⁶

Herein we present an alternative strategy to suppress the polysulfide-shuttle in the Li-S batteries with functionalized polymer electrolytes. One example is the use of a lithiated Nafion membrane (Li-Nafion) as both the Li⁺-ion selective electrolyte and the electrically insulating separator. Upon lithiation, the non-porous Li-Nafion offers both a reasonable Li⁺-ion conductivity and remarkably reduced polysulfide-shuttle, attesting to great advantages over the traditional Celgard membranes in terms of retention of polysulfide species and cyclability enhancement of the Li-S batteries.

Another example is the modification of a traditional polypropylene (PP) separator to form a desired carboxyl functional group at the PP back-bone. With the resulting carboxyl-PP as the separator, the Li || carboxyl-PP || S battery shows significantly enhanced capacity retention ability in comparison to the cell with the unmodified PP separator.

A series of mechanistic studies have also been performed towards the understanding of the cation/anion transport behavior at the functionalized polymer interface. Relevant mechanism regarding the polysulfide retention by the functionalized polymer electrolyte/separator will be presented.

References

 

1.    A. Manthiram, Y. Z. Fu, S. H. Chung, C. X. Zu and Y. S. Su, Chem Rev, 2014, 114, 11751-11787.

2.    Y. X. Yin, S. Xin, Y. G. Guo and L. J. Wan, Angew Chem Int Edit, 2013, 52, 13186-13200.

3.    A. Manthiram, S. H. Chung and C. X. Zu, Adv Mater, 2015, 27, 1980-2006.

4.    D. Bresser, S. Passerini and B. Scrosati, Chem Commun, 2013, 49, 10545-10562.

5.    C. J. Hart, M. Cuisinier, X. Liang, D. Kundu, A. Garsuch and L. F. Nazar, Chem Commun, 2015, 51, 2308-2311.

6.    X. W. Yu, Z. H. Bi, F. Zhao and A. Manthiram, Acs Appl Mater Inter, 2015, 7, 16625-16631.