Competitive ion-dipole interaction of Li⁺ achieving eutectic PEO-based composite electrolytes for room-temperature all-solid-state lithium-metal batteries

Composite Solid electrolytes (CSEs) with superior ionic conductivity, mechanical strength and interface compatibility are in urgent development for safe all-solid-state lithium metal battery. However, limited content of inorganic fillers in CSEs caused by poor interface contact between inorganics and polymer restricts its improvement of mechanical stiffness as well as electrochemical property. Thus, a new type of polyethylene oxide (PEO)-based CSEs is developed with fast ion transfer and high adhesion on the basis of eutectic polymer adopting high-concentrated lithium-salt. The lithium ions are largely freed through the introduced competitive ion-dipole effects, and strong adhesion of the eutectic polymer derived from inter-molecular dual hydrogen bonds and dipole-dipole interaction eliminates incompatibility between PEO and inorganic fillers, thus the ionic conductivity reaches 3.9 × 10⁻⁴ S cm⁻¹ and the ionic transference number climbs to 0.42 at room temperature when the eutectic polymer is compounded with equivalent Al₂O₃. Moreover, the widely application potential to fabricate CSEs with high contend of inorganics is further proved by the superior performance of electrolyte prepared by compounding eutectic polymer with Li_1.5Al_0.5Ge_1.5(PO₄)₃. The room-temperature discharge specific capacity of LiFePO₄||Li battery reaches 141.2 mAh g⁻¹ at 1C, and holds capacity retention rate of 73 % after cycled for 300 cycles at 0.5C.