Black Phosphorus Nanosheets as Efficient Ion Navigators at Room Temperature in Polyacrylonitrile‐Based Composite Solid Polymer Electrolyte for Li‐Ion Batteries

Solid polymer electrolytes (SPEs) have garnered significant interest lately for all‐solid‐state batteries (ASSBs) because of their easy processability and flexibility; however, their low ionic conductivity has to be enhanced by forming composite polymer electrolyte (CPE). Herein, a polyacrylonitrile (PAN)‐based triple‐composite solid polymer electrolyte with black phosphorus nanosheets (BPN) and SiO 2 nanoparticles (SO) is reported, which synergistically utilizes the efficient directed Li+ pathways (via BP) while reducing PAN crystallization (by SiO 2 ) and enhancing the dissociation of Li salts. Thus, an impressive ionic conductivity of 4.41 × 10 −4 S cm −1 is realised in PAN‐BPN‐SO‐LiClO4 CPE, which is 65 times higher than that of PAN‐LiClO 4 (6.8 × 10 −6 S cm −1 ). A wider electrochemical stability window (up to 4.68 V vs Li/Li + ) is also realized, enabling compatibility with high‐voltage cathodes. The BPN‐SO CPE exhibited good discharge capacities 146 mAh g −1 at 0.1C and 108 mAh g −1 at 1C rate, with 75% capacity retention after 100 cycles. The graphite/LiFePO 4 full‐cell with PAN‐BPN‐SO‐LIClO4 CPE showed a room‐temperature discharge capacity of 87 mAh g −1 at 0.1 C, which is significantly enhanced to 152 mAh g −1 at 40 °C. A CPE‐based pouch cell (12 cm 2 , 111.29 mAh g −1 at 0.1 C) performed well in folding, puncturing, and cutting performance tests. A computational modelling study is performed to elucidate the mechanism.