Improving the wettability and thermal resistance of polypropylene separators with a thin inorganic-organic hybrid layer stabilized by polydopamine for lithium ion batteries

This study aims to improve the wettability and thermal resistance of polypropylene (PP) separators for lithium ion batteries. The PP separator was first coated with polydopamine (PDA) on the basis of mussel-inspired surface chemistry. Then a thin inorganic-organic hybrid layer was immobilized onto the PDA-coated separator via a sol-gel process using tetraethoxysilane (TEOS) solutions. This method does not need any commonly-used polymeric binders because of the unique adhesion behaviour of the PDA intermediate layer, which greatly reduces the thickness of the modification layer and avoids excessive pore blocking. Owing to the incorporation of the hybrid layer, the composite separators showed better affinity with the liquid electrolyte and obvious reduction in thermal shrinkage in comparison to the unmodified separator. And the battery performances, such as interfacial resistance, discharge capacity and C-capacity were all improved after modification. Considering the effective adhesion of PDA onto nearly all kinds of separator/membrane surfaces, this modification strategy can be widely used without causing any obvious damage to the mechanical strength of the unmodified separators/membranes.