Sommaire:

Use of polymer electrolytes instead of traditional liquid electrolytes offers elegant solutions to many problems in current battery technology. However, a major obstacle in use of polymer electrolytes is their low ionic conductivity. Classical theories suggest that structural (segmental) relaxation controls ionic conductivity in polymers. This is indeed observed in materials such as polyethylene oxide (PEO), the classical polymer electrolyte. However, the mechanism of ionic conductivity in polymers remains poorly understood. In this talk we present an overview of traditional mechanisms of ionic conductivity with emphasis on ‘superionic’ behavior in some materials. Based on this understanding we demonstrate that only strong decoupling of ionic conductivity from segmental dynamics can lead to a ‘superionic’ behavior of a polymer and might provide sufficiently high conductivity required for many applications at ambient temperature. Using the knowledge on diffusion and decoupling phenomena developed in the field of soft materials we suggest the way to design of polymeric structures with strongly decoupled ionic conductivity [1,2]. Our experimental studies demonstrate feasibility of the proposed approach and reveal ‘superionic’ behavior in several new polymers. The polymer specific decoupling of ionic conductivity is especially well illustrated by a comparison of ionic liquids with their polymerized analogs [3,4]. Our detailed studies of polymerized ionic liquids (PolyILs) helped to unravel mechanisms controlling ion diffusion in this promising class of polymer electrolytes [3-5]. We present a model that predicts the glass transition temperature and decoupling of ion conductivity from segmental dynamics in PolyILs based on knowledge of their chemical structure. Ways to further enhancement of ionic conductivity in PolyILs and their possible limitations are discussed at the end.

References
[1] Y. Wang, et al., Phys. Rev. Letters 108, 088303 (2012).
[2] Y. Wang, et al., Polymer 55, 4067 (2014).
[3] J. R. Sangoro, et al., Soft Matter 10, 3536 (2014).
[4] F. Fan, et al. Macromolecules 49, 4557 (2016)
[5] F. Fan, et al., Macromolecules 48, 4461 (2015).

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