Lithium iodide transport in double gyroid nanochannels formed by zwitterion-containing solid polymer electrolytes

Abstract

The fabrication of nanostructured block copolymer (BCP) films endowed with lithium ion-conducting gyroid (GYR) nanochannels is an appealing solution to build solid polymer electrolytes (SPEs) that combines high ionic conductivity (IC) with suitable mechanical properties. However, the formation of a well-developed GYR structure remains challenging to achieve from the self-assembly of polyelectrolyte BCP chains. To overcome this issue, large ion conducting gyroid grains were produced within freestanding polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO) films by combining a solvent vapor annealing (SVA) treatment with an infiltration process. Here, the SVA treatment enabled the manufacture of SPEs entirely composed of a GYR structure while the infiltration process allowed for the incorporation of an appropriate Li salt (i.e., lithium iodoacetate, LiIAc) within the 3D-interconected nanochannels via a Menshutkin reaction. By using this SVA-Infiltration strategy, it has been demonstrated that the creation of ion conducting GYR nanochannels enhances the ion transportation capacity of pyridine-containing SPEs since substantially lower ICs were measured from analog PS-b-P2VP-b-PEO/LiIAc films having a nominally disordered as-cast state. Remarkably, zwitterionic pyridinium-based moieties formed inside the interpenetrated nanochannels enable an efficient migration of Li⁺ and I₃⁻ species, leading to an IC as high as 10⁻⁴ S cm⁻¹ at 70°C.