Electrospun polyimide/cellulose acetate propionate nanofiber membrane-based gel polymer electrolyte with fast lithium-ion transport and high interface stability for lithium metal batteries

Polyimide (PI)-based gel polymer electrolytes (GPEs) have been regarded as a hopeful alternative to liquid electrolytes to build safer lithium metal batteries due to their high thermal stability, chemical resistance, insulation properties, and self-extinguishing abilities. However, limited electrolyte affinity and low mechanical strength hindered their application in quasi-solid lithium metal batteries. In this work, a novel composite GPE matrix consisting of highly thermo-stable PI and eco-friendly cellulose acetate propionate (CAP) nanofibers was successfully fabricated by electrospinning. CAP was introduced for the first time to improve the electrolyte wettability by providing polar functional groups and to offer favorable thermal/mechanical properties via hydrogen bonding with the rigid PI chains. As a result, the obtained PI-CAP composite matrix showed ultra-flexibility, high mechanical strength (7.1 MPa), and excellent thermal stability (over 200 °C). The PI-CAP GPE exhibited high ionic conductivity (2.09 × 10 –3 S cm −1 ) and Li + transference number (0.89). The assembled LiFePO 4 /PI-CAP GPE/Li cell displayed a high capacity retention up to 95% after 300 cycles at 1 C and showed better rate capability than the LiFePO 4 /PI GPE/Li cell. The positive effects of CAP on inhibiting lithium dendrite growth and promoting the generation of stable SEI were also confirmed through SEM results of cycled lithium metals. The results indicate that the PI-CAP GPE has a good potential as a cellulose-based quasi-solid electrolyte for lithium metal batteries.