Bio-MOF Nanofillers in PEO-Based Polymer Electrolytes for Enhanced Solid-State Battery Performance

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) are promising for solid-state lithium batteries but remain hindered by high crystallinity and limited electrochemical stability. This study introduces a bio-derived metal−organic framework (MOF), MIP-202, as a functional nanofiller to engineer high-performance composite polymer electrolytes (CPEs). Unlike common hydrophobic or purely structural fillers, the amino-acid-based zirconium MOF utilizes abundant −NH2 and −COOH groups to coordinate with Li+ ions and immobilize TFSI− anions through hydrogen bonding. Consequently, MIP-202 suppresses PEO crystallinity from 68.4 to 33.4%, which is a significantly more effective reduction compared to traditional fillers like ZIF-8. These interactions enhance room-temperature ionic conductivity from 9.8 × 10−6 to 2.3 × 10−5 S cm−1 and improve the lithium-ion transference number from 0.22 to 0.35. Furthermore, the electrochemical stability window is expanded to 4.8 V, representing a substantial 1.1 V increase over pristine SPEs. The LiFePO4||Li full cells demonstrate the practical efficacy of this approach, maintaining 87.1% capacity retention after 100 cycles at 0.5 C. This work establishes bio-MOFs as superior, environmentally sustainable nanofillers for regulating ion transport in advanced solid-state batteries.