Fe-MIL-101 metal organic framework integrated solid polymer electrolytes for high-performance solid-state lithium metal batteries

Abstract

Solid polymer electrolytes (SPEs) show tremendous potential for solid-state lithium metal batteries; however, challenges such as low ionic conductivity and poor mechanical strength hinder their progress. This study integrates Fe-MIL-101 metal organic framework into a poly(vinylidene fluoride-co-hexafluoro propylene) (PVdF-HFP)-based SPE system to address these limitations. The integration of Fe-MIL-101 offers two critical benefits: (1) interaction of inorganic Fe³⁺ metal centers with PVdF-HFP enables fast Li⁺ transport by increasing free Li⁺ availability in the system through Lewis acid–base interactions. (2) Fe-MIL-101 significantly improves the mechanical strength of the SPE, boosting its structural integrity. Fe-MIL-101-integrated SPE enables excellent room temperature cycling stability in solid-state Li‖LiFePO₄ (LFP) full cells, retaining ∼91% capacity after 300 cycles and ∼89% capacity after 400 cycles at 0.2 C. Advanced characteristic techniques such as synchrotron-based in situ X-ray diffraction and X-ray absorption spectroscopy were employed to explore structural evolutions in the LFP cathode and the Fe-MIL-101-integrated SPE during cycling. Furthermore, improved room temperature electrochemical performance is demonstrated in solid-state Li‖LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) batteries with Fe-MIL-101-integrated SPE, retaining 91.4% capacity after 175 cycles at 0.1 C. This work highlights the effectiveness of Fe-MIL-101 in enhancing the SPE properties, paving the way for the advancement of high-performance solid-state lithium metal batteries.