Understanding Aluminium Electrochemistry in Aqueous and Aqueous-Ionic Liquid Mixtures for Aluminium-Ion Batteries

Abstract

Among various batteries, Aluminium ion batteries are potential low-cost alternatives to Li-ion batteries, which possess highest theoretical volumetric capacity of 8056 mAh cm-3 and a modest gravimetric capacity of 2981 mAh g-1. 1 However, due to passive layer formation of Aluminium and lack of suitable cathode materials, there are major challenges to overcome in order to accomplish a suitable Al-ion battery.Here, we have studied the Al electrochemistry on electrodeposited MnO2 cathode and Zn anode in aqueous and aqueous-ionic liquid mixtures. Both from experiment and DFT calculations, we show that the presence of ionic liquid (1-ethyl-3-methylimidazolium trifluoromethanesulfonate) changes the Al solvation chemistry, which leads to a change in Al electrochemistry both on Zn and MnO2 (figure below). A strain-induced intercalation/deintercalation process was identified in MnO2 cathode leading to crack formation and capacity fading during Zn/Al-MnO2 battery cycling. By developing a MnO2-polymer matrix, a relatively stable average capacity of 150 mAh g-1 could be achieved over 50 cycles at a current density of 0.1 A g-1. Acknowledgement: The financial support by Royal Society grant (RGS\\R2\\212184) is gratefully acknowledged. References Faegh et al, Nat. Energy, 2021, 6, 21-29 Figure 1