Electrospun gel composite electrolyte of solvent-free SiO2 nanofluids coupled polyacrylonitrile nanofibers for high-rate lithium-metal batteries

Composite polymer electrolytes (CPEs) are considered as one of the most promising electrolytes for the next generation of solid-state lithium metal batteries (LMBs) because of their good flexibility, favorable interface contact, easy large-scale processing and improved safety. To address the severe agglomeration of inorganic nanofillers at the high-level loading, a new gel polymer electrolyte (GPE) was fabricated by electrospun membranes adopting polyacrylonitrile (PAN) as the host matrix and solvent-free SiO2 nanofluids (NFs) as nanofillers, presenting low crystallinity, high electrolyte uptake, superior flexibility, and large porosity. The as-prepared PAN/SiO2 GPEs containing 20 % SiO2 NFs show the optimum mechanical and thermal properties, the maximum ionic conductivity (3.44 x 10−4 S cm−1) and Li+ transfer number (0.73), and the widest electrochemical stable window (4.99 V). Benefiting from multiple advantages, the percolated 3D Li+ transport networks are well-established to suppress the electrode polarization and Li dendrite growth. Further, the abundant ester groups on the SiO2 NFs shell and Lewis acid-based sites on SiO2 cores are favored to dissociate lithium salts and produce more free Li+. Accordingly, the assembled solid-state LiFePO4/Li cell exhibits superior cycling stability (132.7 mAh/g after 500 cycles at 3C with a retention of 90.8 %) and rate capability (80.4 mAh/g at 25C) at ambient temperature. This work provides a facile strategy to fabricate GPEs by incorporating solvent-free NFs containing inorganic cores for LMBs with high-rate capability, good cycling stability, and high safety.