Advancing quasi-solid-state electrolytes with COF-confined solvate ionic liquids for stable lithium metal batteries over a wide temperature range

The quest for solid-state electrolytes (SSEs) that exhibit both elevated ionic conductivity and thermal stability is imperative for the progression of secure and high-energy-density lithium metal batteries (LMBs), a goal that presents considerable difficulties. Herein, we present an innovative approach to fabricate high-performance quasi-solid-state electrolytes (QSSEs) by confining solvate ionic liquids (SILs) within the nanochannels of a methoxy‑functionalized covalent organic framework (COF-OMe). This design leverages the synergistic interaction between the COF's ordered nanochannels and the SILs, resulting in QSSEs that exhibit exceptional Li⁺ conductivity (up to 1.65 × 10⁻⁴ S cm⁻¹, 25 °C) and excellent thermal stability (up to 150 °C). Experimental and theoretical calculations reveal that the confined SILs and methoxy groups synergistically enhance Li⁺ transport by lowering the dissociation energy of lithium salts and creating efficient pathways for ion migration. This results in a significant increase in the Li⁺ transference number (up to 0.80) and effectively suppresses lithium dendrite growth. At the molecular level, these interactions enhance ionic conductivity, transference number, and overall thermal stability. These QSSEs show exceptional cyclability and rate performance across an extensive temperature range (–10 °C to 80 °C) when implemented in Li|QSSE|LiFePO₄ batteries. This work not only provides a new avenue for designing advanced SSEs but also highlights the potential of COF-based materials in next-generation solid-state LMBs.