Uniform Boron Nitride Nanospheres with Reactive Surface Defects for Composite Solid-State Electrolytes

Low ionic conductivity, oxidation potential, and poor lithium stability limit the applications of solid polymer electrolyte (SPE) in advanced energy storage systems. Combining functional inorganic materials and flexible polymers is crucial for achieving high ionic conductivity and exceptional rate performance in all-solid-state batteries (ASSBs). Herein, uniform boron nitride nanosphere (BNSPH) with reactive surface defects was prepared through an improved chemical vapor deposition method with high-temperature ammonia immobilization treatment and was introduced to the poly(ethylene oxide) (PEO)-based SPE. Homogeneously dispersed nanostructures reduce the polymer's crystallinity, facilitating the movement of polymer chain segments and significantly improving the composite electrolyte's ionic conductivity. The interaction between BNSPH and the PEO chain enhances the structural stability of the composite polymer electrolyte (CPE) under high voltage, and the oxygen vacancies on the BNSPH surface immobilize TFSI–, promoting the transfer of more dissociated Li+ through the PEO chain. In addition, the excellent thermal conductivity enhances the interface stability and effectively avoids the growth of lithium dendrites. The CPE-5% exhibits an ionic conductivity of 3.86 × 10–4 S cm–1 and high voltage stability at 60 °C. Therefore, the assembled Li|CPE-5%|Li cell exhibited stable plating/stripping for 2000 h with a small polarization voltage. Furthermore, Li/LFP batteries incorporating CPE-5% exhibit remarkable rate performance (87.8 mA h g–1 at 2.0 C) and outstanding cycle stability (157.4 mA h g–1 after 150 cycles at 0.5 C and 60 °C). Furthermore, the NCM622/Li assembled with CPE-5% could achieve an excellent lifespan. This study confirms the feasibility of this application and inspire the application of defect-rich BNSPH in SPEs.