Advanced rechargeable aluminium ion battery with a high-quality natural graphite cathode

Recently, interest in aluminium ion batteries with aluminium anodes, graphite cathodes and ionic liquid electrolytes has increased; however, much remains to be done to increase the cathode capacity and to understand details of the anion-graphite intercalation mechanism. Here, an aluminium ion battery cell made using pristine natural graphite flakes achieves a specific capacity of similar to 110 mAh g(-1) with Coulombic efficiency similar to 98%, at a current density of 99mA g(-1) (0.9 C) with clear discharge voltage plateaus (2.25-2.0 V and 1.9-1.5 V). The cell has a capacity of 60 mAh g(-1) at 6 C, over 6,000 cycles with Coulombic efficiency similar to 99%. Raman spectroscopy shows two different intercalation processes involving chloroaluminate anions at the two discharging plateaus, while C-Cl bonding on the surface, or edges of natural graphite, is found using X-ray absorption spectroscopy. Finally, theoretical calculations are employed to investigate the intercalation behaviour of choloraluminate anions in the graphite electrode.