Engineering Electronic Inductive Effect of Linker in Metal-Organic Framework Glass Toward Fast-Charging and Stable-Cycling Quasi-Solid-State Lithium Metal Batteries

Metal-organic frameworks (MOFs) have been corroborated as promising quasi-solid-state electrolytes (QSSEs) matrix relying on their structural and compositional traits, while low Li⁺ conductivity (σ_Li⁺) still afflicts their further advances due to intense constraints from anions and large ionic resistance from the grain boundary. Herein, a combination strategy of simultaneous electronic engineering of linker and vitrification is adopted to optimize σ_Li⁺ for MOF-based QSSEs. The introduction of an electrophilic ─Cl substituent in benzimidazole linker compels the electron to deviate from Zn²⁺ and modulates their charge distribution, which immobilizes bis(trifluoromethanesulfonyl)imide anions and thus boosts Li⁺ transference number. Meanwhile, the vitrification endows ZIF-62 with the elimination of boundary resistance for high ionic conductivity. Consequently, ─Cl-substituted glassy ZIF-62 containing Li salt (Cl-Li-G62) showcases a high σ_Li⁺ of 4.89 × 10⁻⁴ S cm⁻¹ at 25 °C. Impressively, Li metal batteries pair with LiFePO₄ cathode and Cl-Li-G62 present an initial capacity of 145.4 mAh g⁻¹ with a decay rate of 0.006% at 1C, and a superior rate performance of 79.5 mAh g⁻¹ at 5C. The work demonstrates the effectiveness of introducing electron-withdrawing groups into MOF glass for enhancing σ_Li⁺ and offers a strategy to boost fast-charging and stable cycling performance of MOF glass-based quasi-solid-state lithium metal batteries.