Solid Polymer Electrolytes Based on Poly(ethylene oxide)/Carbonated Soybean Oil Blends

Blends of poly(ethylene oxide) and carbonated soybean oil with lithium bis(trifluoromethane sulfonyl)imide salt are investigated here as free-standing solid polymer electrolyte (SPE) membranes. Carbonated soybean oil decreases the crystallinity of poly(ethylene oxide) and confers adhesive nature to the polymer blends, in addition to better interface with electrodes. An ionic conductivity of 3.3 × 10^–5 S cm^–1 at room temperature and a broad electrochemical stability window (>4.2 V versus Li/Li⁺) are observed for the membranes prepared from those blends, together with a high stability versus lithium metal electrodes as inferred from stripping and plating experiments (for cycling time > 300 h). Subsequently, LiFePO₄/polymer blend/lithium metal battery prototypes are assembled and deliver 108 mA h g^–1 of discharge capacity with high Coulombic efficiency at 0.1C and 60 °C in the first cycle. Here, the trade-offs in poly(ethylene oxide)-based SPEs are addressed with bioderived carbonate-containing molecules contributing toward sustainable materials development.