Polyimide hybrid membranes with graphene oxide for lithium–sulfur battery separator applications

Novel polyimide composite films containing graphene oxide are prepared for use in the lithium-sulfur (Li–S) battery. Poly(amic acid)s of biphenyl tetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA) are synthesized and mixed with graphene oxide, followed by chemical imidization and freeze-drying. The samples are in the form of xerogels, which have excellent thermal and chemical stability with negligible thermal shrinkage. They also adsorb polysulfide reversibly and allow lithium ions to pass through, thereby improving battery performance. The Li–S batteries are fabricated by inserting the PI composite xerogel films as the separator between electrodes. They show a high coulombic efficiency of above 99% and exhibit an initial discharge capacity of 1306.5 mAh/g at 0.2C, and are maintained at 730 mAh/g even after 100 cycles. In the repeated charge/discharge experiment, the electrolyte uptake and interfacial compatibility of the PI hybrid xerogel separator are improved significantly compared to those measured from the PI separator.