Polydopamine Doped Hexagonal Boron Nitride Coating Separator With Excellent Heat Resistance and Wettability for High-Performance Lithium Metal Batteries

The uneven porous structure of commercial polypropylene (PP) separators leads to non-uniform lithium deposition in lithium metal batteries. This non-uniform deposition promotes the growth of lithium dendrites, which can penetrate the separator, causing internal short circuits and posing significant safety risks. In this work, polydopamine (PDA), which is capable of undergoing self-polymerization, was introduced into h-BN. The two components formed a conjugated molecular structure through π-π interactions, providing enhanced mechanical strength and thermal stability. Subsequently, the PDA-h-BN composite (PB) was coated onto the surface of commercial PP separators to fabricate a novel composite separator (PP-PB). The modified PP-PB separator exhibits excellent thermal stability, electrolyte wettability, and mechanical strength, ensuring uniform heat distribution and acting as a robust barrier against lithium dendrite penetration. Furthermore, the Li/PP-PB/Li cell demonstrated stable cycling for over 1000 h at 1 mA·cm⁻² and 0.5 mAh·cm⁻². Similarly, the Li/PP-PB/Cu cell maintained a coulombic efficiency (CE) of 98.5% after 200 cycles at 0.5 mA·cm⁻². The PP-PB separator ensures uniform lithium deposition and effectively suppresses the formation of lithium dendrites. Additionally, the Li/PP-PB/LFP battery retained a capacity of 158.6 mAh·g⁻¹ with a capacity retention rate of 98.75% after 900 cycles at 1 C, demonstrating superior cycling stability and (CE) compared to the PP-based battery (120 mAh·g⁻¹, 85.7%). This study provides valuable insights for advancing the development of lithium metal batteries.