Multiple ionic conduction highways and good interfacial stability of ionic liquid-encapsulated cross-linked polymer electrolytes for lithium metal batteries

PEO-based electrolytes are promising for solid-state lithium metal batteries, but their low ionic conductivity and unstable interfacial compatibility with electrodes are the bottlenecks restricting their further applications. Herein, a unique ionic liquid (Pyr 14 TFSI)-encapsulated cross-linked polymer electrolyte with abundant ether–oxygen repeat units (C-SPE-IL) is proposed and prepared through an in-situ thermal polymerization process. The Pyr 14 + cations of ionic liquid present a stronger affinity towards ether–oxygen groups by means of tight coordinated interactions, which promotes ionic liquid encapsulated uniformly in the polymer matrix to release more mobile Li ions into ionic liquid and create multiple ionic conduction highways in both ionic liquid and polymer matrix. The C-SPE-IL shows a much higher ionic conductivity of 3.98 × 10 −4 S/cm at 30 °C. Moreover, tight interfaces with LiF– and Li 3 N– rich components between C-SPE-IL and Li anode are constructed to ensure effective suppression of lithium dendrites during cycling. The LiFePO 4 /Li batteries using C-SPE-IL present stable cycling performances at both 35 °C and 60 °C. This work provides a facile and accessible approach to design novel SPE with both ionic conduction highways and good interfacial stability for high-performance solid-state lithium metal batteries. • Ionic liquid-encapsulated cross-linked polymer electrolytes for Li metal battery. • Strong coordination between ionic liquid cation and polymer to release more Li + . • Creating multiple ion-conducting pathways to achieve high ionic conductivity. • Enhanced oxidation stability and stable interface with lithium anode. • Good rate capability and cyclability of LiFePO 4 /Li full cell at 35 °C and 60 °C.