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 SiO₂ nanoparticles (SO) is reported, which synergistically utilizes the efficient directed Li+ pathways (via BP) while reducing PAN crystallization (by SiO₂) 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-LiClO₄ (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/LiFePO₄ 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 cm², 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.