Engineering High Transport Plastic Separators for Next-Generation Li-ion Batteries

Benefited from their tunable porosity, bondability, high voltage stability, fast transport properties, and good electrolyte retention, plastic separators have been an attractive technology option for separators in Li ion batteries. Despite their invention in 1994 at Bellcore, there has been little optimization and further understanding of this plastic separator comprised of PVDF-HFP copolymer resin, a plasticizer (dibutyl phthalate), and nano filler (SiO2). This paper explores the impact of formulation of the Bellcore plastic separator on transport and pore structure to identify the optimal pore architecture for fast ion transport. Each formulation was investigated for pore size distribution by gas adsorption analysis (BET) and He ion microscopy, ionic conductivity and tortuosity by electrochemical impedance spectroscopy (EIS), and mechanical properties by tensile testing to correlate pore size distribution to transport, mechanical properties, and formulation. Bondable, high voltage stable separator formulations were created with ~ 280% greater conductivity than the baseline formulation and an industry standard polyolefin separator.