(Invited) Design of Solid Polymer Electrolytes with Poly(Ethylene Oxide) Backbone for Lithium Batteries Operated at Room Temperature

Abstract

Replacing organic liquid electrolytes with all-solid polymer electrolytes (SPEs) remedies various safety problems related to lithium ion batteries (LIBs). This work focuses on the design of SPE membranes with a backbone of poly(ethylene oxide) (PEO), containing no solvent, ionic liquid, oligomer, or semisolid additives, for LIBs operated at room temperature. Despite their ability in dissociating the lithium salt and Li+-ion coordination, PEO-based SPEs exhibit poor ionic conductivity at room temperature because their polymer chains tend to crystallize. Instead of adding inert fillers to suppress the crystallization tendency, this work employs functional linkers, such as silsesquioxanes, isocyanates, and triglycerides, to crosslink the PEO-based chains and produce a three-dimensional polymer network. These crosslinkers serve as hubs to facilitate effective Li+-ion motion. A low glass transition temperature and a low activation energy for ion conduction confirm the high segmental mobility of the polymer chains. When incorporated with a porous PVDF membrane, the SPEs exhibit high mechanical, chemical, and electrochemical stability, showing an ionic conductivity of ~ 10−4 S cm−1 and a stable potential of >5 V (vs. Li/Li+) at room temperature. The resulting Li|SPE|LiFePO4 batteries deliver discharge capacities of >155 and >135 mAh g−1 (based on LiFePO4) at 0.1 and 1 C-rates, respectively, at room temperature with an excellent charge-discharge cycling stability (>300 cycles).