A graphene/PVDF/PP multilayer composite separator for long-life and high power lithium-ion batteries

The separator is an important part of lithium-ion batteries and its optimization from both material and structural considerations can improve the performance of the battery. We prepared multilayer separators by coating a slurry containing graphene and PVDF in N-methylpyrrolidone on one side of a commercial polypropylene (PP) separator, followed by water treatment at 60℃ for 6 h and vacuum drying at 60℃ for 12 h to manipulate the pore structure of the composite layer. Results indicate that the discharge capacities of batteries using PP and the composite separator were nearly the same at a low rate of 0.5 C. However, the capacity of the former at a high rate of 5 C fades quickly while that of the latter remains almost unchanged after 600 cycles. The composite separators have a high absorption and wettability of the electrolyte, resulting in an improved conductivity.