Enabling Al-metal anodes for aqueous electrochemical cells by using low-cost eutectic mixtures as artificial protective interphase

Elemental aluminum is an exciting battery anode material due to its high abundance and volumetric capacity (8040 mAh cm−3). However, it tends to form a stubborn surface oxide layer that blocks ion transport through the electrode–electrolyte interphase and stops battery cyclability. To circumvent this problem, here we engineer an artificial protective barrier layer on metallic Al by using AlCl3 + urea and AlCl3 + triethylamine hydrochloride eutectic coating formulations. We find both coatings provide significantly facile ion migration kinetics at the anode/electrolyte interface, enabling a drastic reduction in anodic electroplating/stripping overpotentials, but AlCl3 + urea is superior. Using depth-profiling XPS spectroscopy and impedance studies, we find that the AlCl3 + urea derived artificial interphase is also stable in ambient air, affording extended protection for metallic Al anodes from air-oxidation in the form of a battery electrode SEI. We demo the eutectic-treated Al anode (UTAl) based on a FeHCF | 2 m AlTFS | UTAl full cell chemistry and obtain a stable battery performance of ∼ 60 Wh kg−1 over 100 cycles. Our study promotes the strategic viability of using facile, inexpensive reagent treatments to enable the application of water-based electrolytes for rechargeable Al-ion batteries, and specifically encourages systematic exploration of analogue coating formulations using our anode enhancement protocol for similar high-capacity metal/alloy battery chemistries.