Mesoporous Reduced Graphene Oxide as a High Capacity Cathode for Aluminum Batteries

Research in the field of aluminum batteries has focused heavily on electrodes made of carbonaceous materials. Still, the capacities reported for these multivalent systems remain stubbornly low. It is believed that a high structural quality of graphitic carbons and/or specific surface areas of >1000 m² g^-1 are key factors to obtain optimal performance and cycling stability. Here an aluminum chloride battery is presented in which reduced graphene oxide (RGO) powder, dried under supercritical conditions, is used as the active cathode material and niobium foil as the current collector. With a specific surface area of just 364 m² g^-1, the RGO enables a gravimetric capacity of 171 mAh g^-1 at 100 mA g^-1 and remarkable stability over a wide range of current densities (<15% decrease over 100 cycles in the interval 100–20000 mA g^-1). These properties, up to now achieved only with much larger surface area materials, result from the cathode's tailored mesoporosity. The 20 nm wide mesopores facilitate the movement of the chloroaluminate ions through the RGO, effectively minimizing the inactive mass content of the electrode. This more than compensates for the ordinary micropore volume of the graphene powder.