Protective Al₂O₃ Thin Film Coating by ALD to Enhance the Anodic Stability of Metallic Current Collectors in Ethereal Mg Electrolyte Solutions

Abstract

Organometallic complex-based magnesium electrolytes in ethereal solutions have been extensively studied in the context of rechargeable magnesium batteries (RMBs) due to their ability to facilitate highly reversible magnesium deposition while demonstrating wide enough electrochemical stability windows. However, these solutions containing a unique mixture of organo-halo aluminate complexes have a detrimental effect on the anodic stability of metallic current collectors for cathodes, like Ni and Al foils. We were able to synthesize and isolate Mg2Cl3(THF)6Ph2AlCl2/THF electrolyte as the sole electroactive species using simple precursors: Ph2AlCl and MgCl2 in THF, via atom efficient mono-chloro abstraction Schlenk technique. We characterized the anodic stability of Ni, Ni@C, Al, and Al@C current collectors by monitoring their electrochemical behavior. Additionally, we investigated the anodic stability enhancement of various current collectors by Al2O3 thin films coating using atomic layer deposition (ALD). Linear sweep voltametric studies showed that coating current collectors enhanced the oxidative stability of Al and Ni foils by 0.1-0.3 V vs Mg/Mg2+ compared to the uncoated foils. Our findings show that current collectors’ protection by ALD coating can help in long-term stability and improving RMBs’ energy density by using high-voltage cathode materials, a crucial step in developing practical rechargeable Mg batteries.