Graphene paper with controlled pore structure for high-performance cathodes in Li-O2 batteries

In non-aqueous Li-O2 batteries, relatively large amounts of discharge products are formed on air cathodes. As such, the expansion of air cathodes is a critical issue that remains to be solved. Here, we report the fabrication of highly porous free-standing graphene paper by introducing macropores within the paper using polystyrene colloidal particles as a sacrificial template. The as-prepared macroporous graphene paper (mp-GP) have a large Brunauer-Emmett-Teller (BET) surface area (ca. 373 m2 g−1), a large pore volume (ca. 10.9 cm3 g−1), and a high porosity (91.6%). Owing to the high surface area and large pore volume, the mp-GPs exhibit a high specific capacity of ca. 12,200 mAh g−1 at a current density of 200 mA g−1, as well as good rate capability, when used as an air cathode in a non-aqueous Li-O2 battery. Moreover, the mp-GP shows good stability up to 100 and 78 cycles at a current density of 500 mA g−1 and 2000 mA g−1 respectively, with a limiting capacity of 1000 mAh g−1. It is found that formation and decomposition of the discharge product, Li2O2, occur within the macropores, and thus, the mp-GP maintains its original structure without considerable expansion during cycling.