Ionic Conductivity Enhancement Through Directed Crystallization Polymer Electrolytes

Polymer electrolyte (PE) is promising for solid-state lithium metal batteries due to its flexibility, chemical stability, and processibility¹. However, common poly(ethylene oxide) (PEO) based PE suffers from low room temperature conductivity due to its crystallinity. The randomly oriented PEO crystals in unaligned samples increase the tortuosity of the conduction pathway and hinder ion transport efficiency². Our goal here is to improve the conductivity of PE through directed crystallization. PEO/lithium triflate salt is used as a model system. To achieve aligned crystallization, the polymer electrolyte film is hot drawn at 90 °C followed by crystallization at a lower temperature with the strain maintained. Wide-angle X-ray scattering experiments indicate that the (120) and (032) planes of PEO crystals are oriented and the degree of orientation increases with the stretching ratio. As a result, the through-plane conductivity increases by nearly a factor of 5. The effect of crystallization temperatures and different lithium salt on conductivity will also be discussed.
References
(1) Nat. Rev. Mater. 2020, 5 (3), 229–252.
(2) Macromolecules 2015, 48 (13), 4503–4510.