Comparison of carbon materials as cathodes for the aluminium-ion battery

Aluminium-ion batteries are of increasing interest as alternatives to lithium-ion batteries, as they use more abundant materials and suffer from fewer safety risks. The limiting factor for battery performance is the capacity of the cathode towards [AlCl4]- intercalation. Although several cathode materials have been used recently, there have been few studies that directly compare the capacity of different cathodes. Graphitic carbon materials have many features that make them ideal for aluminium-ion intercalation: they are electrically conductive, low density and low-cost, and are available in a wide variety of morphologies. This work compares four common forms of graphitic carbon: pyrolytic graphite, carbon paper, carbon cloth and carbon felt as aluminium-ion cathodes. The materials differ in their porosity, average graphite crystallite size, and properties as aluminium-intercalating agents. It was found that of all the materials examined, carbon paper had the highest energy density at 122 Wh.kg−1, and had superior stability compared to pyrolytic graphite as the C-rate of cycling was increased. It also did not undergo crystallographic alteration even after cycling up to the 20C rate. Both carbon paper and pyrolytic graphite have capacities around 70 mAh.g−1 for aluminium intercalation, and carbon cloth and felt have lower capacities of 20–40 mAh.g−1. Schematic Diagram showing operation principle of aluminium-ion battery (top right), with microstructure of cathodes (a) carbon cloth, (b) carbon paper, (c) carbon felt and (d) pyrolytic graphite (bottom right). The discharge capacity of materials (b) and (d) at varying current densities is shown on the left. [Display omitted]