High-Voltage and Wide-Temperature Lithium Metal Batteries Enabled by Ultrathin MOF-Derived Solid Polymer Electrolytes with Modulated Ion Transport

Solid polymer electrolytes (SPEs) of superior ionic conductivity, long-term cycling stability, and good interface compatibility are regarded as promising candidates to enable the practical applications of solid lithium metal batteries (SLMBs). Here, a mixed-matrix SPE (MMSE) with incorporated metal–organic frameworks (MOFs) and ionic liquid is prepared. The dissociation of Li salt in MMSE can be promoted effectively due to the introduction of MOF via the Fourier-transform infrared spectroscopy (FT-IR) analysis, density functional theory calculation, and molecular dynamics simulation. The as-formed MMSE exhibits an ultralow thickness of 20 μm with a satisfactory ionic conductivity and lithium-ion transference number (1.1 mS cm^–1 at 30 °C, 0.72). The optimized SLMBs with high-voltage LiMn_0.75Fe_0.25PO₄ (LMFP) exhibit an excellent cyclability at 4.2 V under room temperature. Moreover, Li/MMSE/LiFePO₄ cells have desirable cycle performance from −20 to 100 °C, and their capacity remains 143.3 mA h g^–1 after being cycled 300 times at 10 C at 100 °C. The Li/LiFePO₄ pouch cells also show excellent safety under extreme conditions. The Li symmetric cells can work steadily even at a supreme current density of 4 mA cm^–2 at 100 °C. From the above analysis, these MMSEs present new opportunities for the development of SLMBs with good electrochemical properties.