Crystallization-templated high-performance PVDF separator used in lithium-ion batteries

In this work, high-performance PVDF separators have been successfully fabricated for lithium-ion batteries (LIBs) based on crystallization template in PVDF/PBSU blends. The crystallization of PVDF produces co-continuous structures of crystalline phase and amorphous phase. On one hand, the continuous state of PBSU enables its removal via selective solvent extraction, yielding 3D interpenetrated nanochannels which have been confirmed with the help of X-ray imaging technology. On the other hand, the continuous PVDF crystal framework contributes to superior mechanical performance and heat resistance of resultant separator, playing crucial roles in the inhibition of Li dendrite growth and improvement of LIBs safety. The optimal specimen of PVDF-30 (from PVDF/PBSU 30/70) exhibits higher discharge capacity (135.5 mA h g−1), higher coulombic efficiency (∼99.9% after 200 cycles) and enhanced cycle stability relative to the reference (commercial polypropylene separator). Such a significant improvement can be attributed to the combination of excellent connectivity of diffusion channels, outstanding mechanical performance and higher electrolyte uptake resulting from stronger polarity of PVDF. Our results provide a novel strategy for fabricating PVDF separators with superior performances used in lithium-ion batteries.