Solvent molecule layer assisted rapid lithium ion transport in MOF pore for wide-temperature solid-state lithium battery

Two-dimensional metal-organic frameworks (2D MOFs), coupling the individual advantages of organic polymer with excellent flexibility and processability, as well as inorganic crystal with well-ordered and temperature-independent structure, are emerging solid-state electrolyte (SSE) materials for wide-temperature solid-state lithium batteries. However, present MOFs have seldom been directly utilized as SSEs, due to the insurmountable transport energy barrier and resultant low ionic conductivity. Here, we report a lamellar MOF electrolyte with high ionic conductivity over wide-temperature ranges through confining DMF (N, N-dimethylformamide, DMF) solvent into the ordered pore channel of 2D MOF lamellar framework. We demonstrate that, the fine-tuned microstructure of pore walls could induce the rearrangement of DMF solvent layer, forming long-range ordered and stable solvent layer along pore walls. The solvent layer then acts as low-energy-barrier lithium ion transport path, affording MOF SSE high ionic conductivity over wide-temperature ranges (2.87 × 10⁻⁴ – 1.58 × 10⁻³ S cm⁻¹ at −20 – 100 ^oC), surpassing most of the currently reported solid-state electrolytes. The MOF SSE also exhibits high <em>t_Li+</em> of 0.81 and low activation energy of 0.106 eV. Consequently, the assembled LiFePO₄|Li half-cell can stably cycle over wide-temperature ranges, retaining high discharge specific capacities of 158.4 mAh g⁻¹ at −20 ^oC and 171.2 mAh g⁻¹ at 60 ^oC, respectively, after 300 cycles. This work offers an innovative approach for the design of advanced ion conductors towards wide-temperature solid-state lithium batteries.