Aromatic Polyamide Porous Film Separator for Li-Ion Batteries

The patent changes the material parameter from polyolefin to aromatic polyamide, which fundamentally alters the thermal behavior. Aromatic polyamide maintains dimensional stability at high temperatures without melting, eliminating the shrinkage problem while preserving heat resistance. This parameter change resolves the contradiction by selecting a material whose intrinsic properties satisfy both heat resistance and short-circuiting prevention requirements.

The patent employs a porous film structure with controlled pore size distribution (predominantly 0.01-1 μm pores) and specific porosity (30-80%). This porous structure provides mechanical reinforcement while maintaining ion permeability. The porous network distributes stress evenly throughout the film, enabling thin films (≤50 μm) to achieve sufficient mechanical strength while retaining the heat resistance of aromatic polyamide material.

The patent extracts and removes fine particles (colloidal silica or metal oxide particles) from the casting solution before film formation. By removing these pore-forming agents in advance, the method creates uniform macropores without the problematic fine gaps and septa that result from particle decomposition during or after casting. This extraction approach enables precise control over pore structure while maintaining ease of manufacture.

The patent extracts fine particles from the casting solution before film formation, rather than forming the film with particles and then removing them. This prevents the creation of fine gap connection portions and bottle necks entirely. The resulting porous structure has open, unobstructed pores that maintain high ion permeability while achieving uniform pore distribution, resolving the contradiction between pore uniformity and ion transport speed.