Reversible phosphorus-based five-electron transfer reaction for aluminium–phosphorus batteries

Abstract

The use of multi-electron redox materials has been proved as an effective strategy to increase the energy density of batteries. Herein, we report a new reversible phosphorus-based five-electron transfer reaction (P(0) ⇆ P(+5)) in chloroaluminate ionic liquids (CAM-ILs), which represents a new reaction mechanism offering one of the theoretically highest specific capacities of 4325 mAh g−1 among all secondary batteries. Theoretical calculations further confirm the phosphorus electrochemical oxidation pathway with a potential oxidation voltage of ∼2.0 V. Detailed characterisation reveals fresh insight of the role of CAM-ILs, which can catalyze the electrochemical oxidation process of phosphorus by forming electron-enriched state of phosphorus. As a result, a conceptual aluminium-phosphorus battery was assembled, which deliver a high performance of 1512 mAh g−1 and 1176 Wh kg−1, outperforming many similar metal ion battery chemistry. This study sheds light on phosphorus oxidation process in CAM-ILs and presents a new pathway using non-metallic element based multi-electron oxidation to achieve high performance batteries.