Multifunctional COF Colloid Regulates Anion Coordination in Solid Poly(Ionic Liquid)‐Based Electrolyte for Lithium Metal Batteries

The development of solid polymer electrolytes (SPEs) has been significantly impeded by two primary challenges: low ionic conductivity and the inhomogeneous deposition of lithium metal anode. Overcoming these limitations needs to reduce polymer crystallization and to design continuous, stable, fast ion transport pathways. In this study, the incorporation of covalent organic framework colloid (COF-C) as a multifunctional additive to SPEs is proposed, aiming to regulate lithium transport and construct stable electrolyte-electrode interphases. The interaction of COF-C with anions of poly(ionic liquid) (PIL) restricts the growth of PIL spherical crystals and reduces the crystallinity of the electrolyte. Acting as an anion receptor, COF-C promotes uniform Li⁺ distribution and enhances ion transport kinetics. Additionally, COF-C demonstrates to regulate the anions coordination and create stable solid-state electrolyte interphases between the lithium metal and SPEs. As a result, optimized SPE enables ionic conductivity of 2.70 × 10^-4 S cm^-1 at 25 °C. The solid-state Li/PIL-COF-C/LiFePO₄/ batteries demonstrate exceptional cycle stability, evidenced by a notable discharge specific capacity of 142.4 mAh g^-1 at 1 C, along with a commendable capacity retention of 93.1% following 500 cycles. In addition, the PIL-COF-C can be adapted to a higher mass loading of LiFePO₄.