Improving Ion Conductivity in Polymer Blend Electrolytes by Tuning Microdynamics and Interfaces

Abstract

Solid polymer electrolytes (SPE) have attracted a great deal of interest; however, their poor room temperature ionic conductivities still impede their practical application in lithium-ion batteries. Although the polymer blend is considered to be an effective strategy to improve ionic conductivity of SPEs, no quantitative model describing the ion conduction mechanism in polymer blends has yet been identified, and the interplay between the components has not been well elucidated. In this work, we focus on poly­(ethylene oxide) (PEO)-based electrolytes blended with poly­(methyl methacrylate) (PMMA) or poly­(vinylidene fluoride) (PVDF) with systematically changed component ratios. A maximum ionic conductivity of 1.4 × 10–4 S/cm at 30 °C is achieved by accelerated interfacial and segmental dynamics, together with decreased charge-concentrated layers, which promote ion concentration. We demonstrate that both segmental motion and interfacial polarization quantitatively determine ion conduction in polymer blends. Flory–Huggins interaction parameters unveil the thermodynamic interaction between the components and are directly related to the ionic conductivity of polymer blend electrolytes. Furthermore, the polymer blend enables viable applications of the SPE with fairly good ionic conductivity and allows the LFP||Li cell to deliver a discharge-specific capacity of ∼113.5 mAh/g at 1 C and a capacity retention of ∼70% after 100 cycles.