Fluorinated Functional Units for Li+ Flux Homogenization in Silica Framework-Based Zwitterionic Single Ion Conductors for Stable Lithium Metal Batteries

Abstract

Progress in commercializing solid polymer electrolytes (SPEs) for lithium metal batteries (LMBs) has been impeded by challenges, like concentration polarization, non-uniform Li⁺ flux, and an unstable solid electrolyte interface (SEI), which contribute to dendrite formation. To address these issues, silica framework (SF)-based single-ion conductors are proposed, featuring a unique solvation channel composed of a fluorinated segment, a high-dipole zwitterion, and a rotation-motion-driven ion-hopping medium. This design promotes low resistance at the cathode/electrode interface, suppresses dendrite growth at the anode/electrolyte interface, and maintains a uniform Li⁺ flux. This results show that continuous ion channels within a robust framework enhance Li-ion dissociation and transport, achieving high ionic conductivity (σ_DC =  8.8  × 10⁻⁴ S cm⁻¹), a modulus of 0.9 GPa, a high lithium transference number (≈0.83), and an extended electrochemical stability window (up to 5.2 V) at 25 °C. This design fosters the formation of a hybrid organic/inorganic SEI layer composed of Li₂CO₃, LiF, and Li₂O, enabling ultra-stable Li plating/stripping for over 4000 h at 0.1 mA cm⁻². Furthermore, the full cells demonstrate excellent rate performance and long-term cycling stability and capacity retention (81% for Li||LFP and 86% for Li||NCM811 after 400 cycles at 1 C) and high coulombic efficiency, offering a promising strategy to stable LMBs.