Multifunctional Polar Polymer Boosting PEO Electrolytes toward High Room Temperature Ionic Conductivity, High-Voltage Stability, and Excellent Elongation

Poly(ethylene oxide) (PEO) has been widely studied as an electrolyte owing to its excellent lithium compatibility and good film-forming properties. However, its electrochemical performance at room temperature remains a significant challenge due to its low ionic conductivity, narrow electrochemical window, and continuous decomposition. Herein, we prepare a multifunctional polar polymer to optimize PEO's electrochemical properties and cycling stability. PEO's crystallinity is disrupted with the addition of polar polymer, and the amorphous polymer segments create more transfer pathways for Li-ion. More importantly, the polar groups enhance PEO's Li-ion transference number by facilitating lithium salt dissociation through Lewis acid-base interactions and weaken the coordination between Li-ion and ether oxygen, thereby expediting Li-ion migration. In addition, the trifluoromethyl groups promote TFSI^- defluorination, forming LiF-rich solid electrolyte interphase layers that prevent continuous decomposition of PEO. The resulting composite electrolyte exhibits excellent room temperature ionic conductivity (2.06 × 10^-4 S cm^-1) and Li-ion transference number (0.30) and outstanding voltage (4.9 V). The assembled symmetric lithium battery could perform stably for 620 h at 0.1 mA cm^-2. Li||LiFePO₄ cells exhibit excellent capacity retention (87.81%) and Coulombic efficiency (100.0%) at 0.5 C over 700 cycles.