First investigations towards the feasibility of an Al/Br2 battery based on ionic liquids

We present first investigations towards the feasibility of an Al/Br2 battery based on ionic liquids (ILs). The charged battery consisted of an Al anode, a bromoaluminate IL as the anolyte, an ion‐exchange membrane, a polybromide IL as the catholyte, and an inert cathode. The open‐circuit voltage (OCV) of the battery was strongly dependent on the molar ratio of AlBr3 in the anolyte with values of 1.9 V when using a Lewis basic anolyte and 1.1 V when using a Lewis neutral anolyte. NMR studies with different organic cations in both electrolytes revealed the migration of organic cations as major charge‐balancing ions, which leads to a reduced theoretical energy density of 33 Wh L−1 (as opposed to 166 Wh L−1 for an anion mechanism). The battery could be discharged with high discharge resistance values of up to 3 kO cm2, and preliminary charging attempts revealed high overpotentials. Hitherto, an Al/Br2 cell with a Lewis basic anolyte could be used as primary battery with an OCV of 1.9 V.