Molecular-level Regulation of PEO-Based Electrolytes with CaF₂ Nanoparticles for Advanced Solid-State Lithium Metal Batteries

The poly(ethylene oxide) (PEO)-based electrolyte has caught much attention for its flexibility, interfacial compatibility, and low cost, but the low ionic conductivity and poor mechanical strength severely hinder its further application in solid-state batteries. Herein, a molecular level regulation through adding CaF2 nanoparticle fillers is proposed to enhance the electrochemical performance of the PEO-based electrolyte. The strong coordination effects of the Ca cation with a Li salt anion and ether-oxygen increase the dissociated Li ion concentration and accelerate Li ion migration, thus enhancing the ionic conductivity of the electrolyte when combined with their physical disruption in the PEO matrix (0.31 mS cm–1 at 55 °C). Moreover, the spontaneous reaction between Li and CaF2 generates a LiF-rich solid electrolyte interphase, which promotes homogeneous Li deposition. Consequently, the PEO-CaF2 electrolyte delivers symmetric cells over 6300 h and maintains full batteries over 1000 cycles with 80% capacity retention. The assembled pouch-cell displays robust performance, further demonstrating its potential practical application.