Role of Oxygen Functional Groups in Carbon Nanotube/Graphene Freestanding Electrodes for High Performance Lithium Batteries

Hierarchical functionalized multiwalled carbon nanotube (MWNT)/graphene structures with thicknesses up to tens of micrometers and relatively high density (>1 g cm3) are synthesized using vacuum filtration for the positive electrode of lithium batteries. These electrodes, which are self-standing and free of binder and current collectors, utilize oxygen functional groups for Faradaic reactions in addition to double-layer charging, which can impart high gravimetric (230 Wh kg1 at 2.6 kW kg1) and volumetric (450 Wh L1 at 5 kW L1) performance. It is demonstrated that the gravimetric and volumetric capacity, capacitance, and energy density can be tuned by selective removal of oxygen species from as-prepared functionalized MWNT/graphene structures with heat treatments in H2/Ar, potentially opening new pathways for the design of electrodes with controlled surface chemistry.