Significantly promoting the lithium-ion transport performances of MOFs-based electrolytes via a strategy of introducing fluoro groups in the crystal frameworks

Abstract

Metal–organic frameworks (MOFs) with well-ordered channels are considered ideal solid-state electrolytes (SSEs) for lithium ionic conductors and are expected to be utilized in all-solid-state Li-ion batteries. However, the outstanding Li⁺ conductivity of MOFs, especially the properties at low temperatures, has become a crucial problem to overcome. Herein, a breakthrough is first realized to cope with this challenge via a strategy of introducing fluoro-substituted bridging ligands in MOFs. Benefiting from the fluorinated strategy in MOFs (Cu-MOF-F₄), an outstanding Li⁺ conductivity of 1.16 × 10⁻³ S cm⁻¹ at room temperature, a low activation energy of 0.15 eV, and a high transference number of 0.84 are achieved. In particular, Cu-MOF-F₄ shows high conductivities of (0.15–2.99) × 10⁻³ S cm⁻¹ in the temperature range of −40 to 110 °C. The proposed novel fluoro-substituted strategy of bridging ligands in MOFs is of great significance for developing high-performance SSEs for solid-state lithium batteries.