Graphene nanosheet supported bifunctional catalyst for high cycle life Li-air batteries

Abstract

Rechargeable lithium-air batteries offer great promise for transportation and stationary applications due to their high specific energy and energy density. Although their theoretical discharge capacity is extremely high, the practical capacity is much lower and is always cathode limited. A key for rechargeable systems is the development of an air electrode with a bifunctional catalyst on an electrochemically stable carbon matrix. The use of graphene as a catalyst matrix for the air cathode has been studied in this work. A Li-air cell using an air cathode consisting of nano-Pt on graphene nanosheets (GNS) has shown promising performance at 80% energy efficiency with an average capacity of 1200 mAh g−1 and more than 20 cycles without significant loss of total energy efficiency. Replacement of Pt with a bifunctional catalyst resulted in more than 100 cycles with an average capacity of 1200 mAh g−1 and total energy efficiency of about 70%. Electrochemical impedance spectroscopy data revealed increasing solution and charge transfer resistance during cycling, which hindered the cycle life. The increased solution resistance can be attributed to the evaporation and decomposition of electrolyte especially at high charge voltages. Further investigation on ionic liquid based electrolytes in Li-air systems is being conducted.