Abstract:Polypropylene (PP) was blended with polypropylene grafted polyethylene glycol (PP-g-PEG), for preparation of hydrophilic PP microporous membranes by uniaxial stretching technology. The porous structures and properties of the microporous membranes were characterized by mercury porosimetry, SEM, Gurley value, and water vapor permeability. The performance of Li-ion batteries assembled with modified membranes was also evaluated. The effects of PP-g-PEG content, grafting degree of PEG, and PEG chain length on the porous structure, permeability of microporous membranes and battery performance were investigated. It is found that, by raising content of PP-g-PEG with 0.78% grafting degree, the porosity and pore size of the membranes drop, the porous tortuosity and thoat/pore ratio increase. The water vapor permeability (WVTR) comes to the maximum at 2.5% PP-g-PEG content, due to the compromising of porous structure and hydrophilic effect. Batteries assembled with modified membranes containing 2.5% and 5% PP-g-PEG demonstrate lower complex impedance and specific capacity, much better than the battery assembled with unmodified membrane. Increasing grafting degree of PEG has negative effect on porous structure, but bigger improvement to the hydrophilicity of the membranes, leading to higher WVTR and better battery performance. PP-g-PEG with long PEG chain length deteriorate the porous structure more seriously than PP-g-PEG with short PEG chain length, giving rise to poorer battery performance.