Stacking-Sequence Engineering of Functional Metal Bilayers for Rapid Direct-Contact Prelithiation of SiOx Anodes

Silicon suboxide (SiOx) is a promising anode material for next-generation lithium-ion batteries because of its high capacity and structural stability. However, its practical application is severely limited by substantial irreversible lithium consumption during the first cycle, making effective prelithiation essential for improving the initial Coulombic efficiency (ICE). Although direct-contact prelithiation provides a simple approach for lithium compensation, controlling lithium transfer at the electrode/Li interface remains a major challenge. Herein, Ni/Ag bilayer thin films with identical nominal total metal thickness but different stacking sequences were introduced onto SiOx electrodes to regulate direct-contact prelithiation. Single-layer Ni and Ag coatings together with Ni/Ag bilayers of opposite stacking sequences were systematically investigated to examine the influence of the SiOx-facing and Li-facing metal layers. Among them, the SiOx/Ni/Ag electrode exhibited the most efficient prelithiation behavior, achieving an ICE of 96.9% after only 7 min of direct contact, whereas the SiOx/Ag/Ni electrode reached only 87.7% even after 10 min of prelithiation. Structural and depth-resolved chemical analyses revealed that the optimized stacking sequence promoted more complete conversion toward Li-rich silicate species while suppressing electrode expansion. Consequently, the SiOx/Ni/Ag electrode exhibited lower interfacial resistance and faster electrochemical stabilization while maintaining stable cycling performance. These findings demonstrate that the arrangement of functional metal layers, rather than metal composition alone, strongly influences lithium transfer during direct-contact prelithiation, establishing stacking-sequence engineering as a useful thin-film design strategy for efficient prelithiation of high-capacity Si-based anodes.