Benchmarking the Degradation Behavior of Aluminum Foil Anodes for Lithium‐Ion Batteries

Abstract

AbstractAluminum is an attractive candidate for replacing graphite anodes in lithium‐ion batteries because of its high specific capacity and the potential for direct use as foil. However, achieving reversible reaction of aluminum is challenging due to volume changes, SEI formation, and sluggish ion transport. Although prior work has investigated electrochemical transformation behavior of aluminum, the effects of key variables, including areal capacity per cycle and alloy composition, are not well understood. Here, we carry out comprehensive electrochemical testing to benchmark the performance of two different aluminum foils (99.999 % Al and Al 8111). We find that for constant thickness, both foil compositions exhibit a power‐law dependence of cycle life on the lithiated areal capacity per cycle, revealing that degradation is significantly more rapid at higher areal capacities. This behavior is interpreted as an “electrochemical fatigue” mechanism, in analogy to mechanical fatigue. Additionally, the alloy composition was found to strongly affect the Coulombic efficiency (CE), with high‐purity foils exhibiting higher initial CE but reduced long‐term stability. Finally, operando optical microscopy revealed different spatiotemporal reaction mechanisms amongst the different materials. This improved understanding of aluminum foil anodes paves the way for efforts to engineer aluminum‐based foils with enhanced stability.