Effect of Confinement\non the Structure–Conductivity\nRelationship in PEO/LiTFSI Electrolytes in 3D Microporous Scaffolds

Because 3D batteries comprise solid polymer electrolytes\n(SPEs)\nconfined to porous scaffolds with high surface areas, the interplay\nbetween polymer confinement and interfacial interactions on SPE total\nionic conductivity must be understood. This paper investigates contributions\nto the structure–conductivity relationship in poly(ethylene\noxide) (PEO)–lithium bis(trifluorosulfonylimide) (LiTFSI) complexes\nconfined to microporous nickel scaffolds. For bulk and confined conditions,\nPEO crystallinity decreases as the salt concentration (Li<sup>+</sup>:EO (<i>r</i>) = 0.0125, 0.0167, 0.025, 0.05) increases.\nFor pure PEO and all <i>r</i> values except 0.05, PEO crystallinity\nunder confinement is lower than in the bulk, whereas the glass transition\ntemperature remains statistically invariant. At 298 K (semicrystalline),\ntotal ionic conductivity under confinement is higher than in the bulk\nat <i>r</i> = 0.0167 but remains invariant at <i>r</i> = 0.05; however, at 350 K (amorphous), total ionic conductivity\nin confinement is lower than in the bulk for both salt concentrations.\nTime-of-flight secondary ion mass spectrometry indicates selective\nmigration of ions toward the polymer–scaffold interface. In\nsummary, for the 3D structure studied, polymer crystallinity, interfacial\nsegregation, and tortuosity play important roles in determining total\nionic conductivity and, ultimately, the emergence of 3D SPEs as energy\nstorage materials.