Competitive Lithiation Mechanism of Silicon in Aluminum–Silicon Alloy Foil Anodes for Lithium-Ion Batteries

Alloying-type foil anodes have garnered interdisciplinary attention for the development of future high-energy-density lithium-ion batteries (LIBs). However, the relative research is still in the infant stage, with many unexplored mechanisms regarding uneven lithiation, sluggish lithiation kinetics, low Coulombic efficiency, severe stress concentration, and rapid mechanic-electrochemical failure. Herein, we investigate the electrochemical behavior, corresponding microstructure variation, and phase transition process of aluminum (Al)–silicon (Si) alloy foils to elucidate the intricate interplay between Al and Si during lithiation/delithiation processes, on the basis of which a mechanism of competing lithiation of Si in the anode of Al–Si alloy foils for LIBs is proposed. During partial lithiation/delithiation, Al primarily governs the process due to its high electrical conductivity and alloying plateau advantage, whereas precipitated crystalline Si provides phase boundaries (PBs) that effectively enhance lithiation kinetics without any capacity contribution. However, Si particles play diverse roles in the first full lithiation and the subsequent cycling, from providing PBs to directly participating in lithiation, influencing the overall performance of the Al–Si foils. This comprehensive understanding of the competitive lithiation mechanism sheds light on optimizing the design and engineering of Al–Si alloy foil anodes, potentially leading to enhanced performance and longevity in LIBs with high energy density.