The study on methyl methacrylate graft-copolymerized composite separator prepared by pre-irradiation method for Li-ion batteries

The pre-irradiation method was introduced to prepare the methyl methacrylate (MMA) graft-copolymerized composite separators based on the commercial trilayer (PP/PE/PP) microporous separators. Through scanning electron microscopy (SEM), the morphologies of the grafted membranes (GMs) with different degree of grafting (DG) were investigated and the possible reasons for “accelerating activation” were also discussed. The results of electrochemical impedance spectra (EIS) measurements showed that the Li+ ionic conduction behaviors obey the Arrhenius equation for the activated GM and they could give favorable electrolyte/electrode interfacial properties due to the presence of gelled PMMA layer. Furthermore, compared with polyolefin separator, the coin cell containing the GM with 36.8% DG showed better charge–discharge performance with little capacity loss after 80 cycles. Fortunately, the grafting reaction based on the pre-irradiation technique did not destroy the crystallinity characteristics of original separators, the GMs could still retain thermal shutdown mechanism.