Modulating aluminium solvation with ionic liquids for improved aqueous based Aluminium-ion batteries

Aqueous-based Al-ion batteries are attractive alternatives to Li-ion batteries due to their safety, high volumetric energy density, abundance and recyclability. Although aluminium-ion batteries are attractive, there are major challenges to overcome, which include understanding the nature of the passive layer of aluminium oxide on the aluminium anode, the narrow electrochemical window of aqueous electrolytes and lack of suitable cathodes. Here, we report using experiments in conjunction with DFT simulations to clarify the role of ionic liquids in altering the Al solvation dynamics, which in turn affects the aluminium electrochemistry and aqueous-based battery performance significantly. DFT calculations showed that the addition of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIMTfO) changes the aluminium solvation structure in aqueous (Al(TfO)3) electrolyte to lower coordinated solvation shells, thereby influencing and improving Al deposition/stripping on Zn/Al alloy anode. Furthermore, the addition of ionic liquid reduces the strain in manganese oxide during intercalation/deintercalation, thereby improving the Zn/Al-MnOx battery performance. By optimising the electrolyte composition, a battery potential of >1.7 V was achieved for Zn/AlMnOx system