Mechanistic insights into self-limiting Si–F CEI formation via a molecularly designed sacrificial additive

High-nickel layered cathodes, such as NCM811, promise high energy density for next-generation lithium-ion batteries but suffer from interfacial degradation, irreversible capacity loss, and transition metal dissolution under high-voltage operation. Here, a sacrificial silyl ketone additive, bis(di‑tert-butylmethylsilyl) ketone, (MetBu₂Si)₂CO, is introduced to simultaneously modulate cathode–electrolyte interphase (CEI) formation and suppress parasitic reactions. (MetBu₂Si)₂CO undergoes preferential oxidation during the first cycle, forming a self-limiting, thin, and uniform protective layer while scavenging HF, as evidenced by Si 2p XPS and ¹⁹F NMR studies. Furthermore, in situ XRD reveals that (MetBu₂Si)₂CO mitigates lattice distortions during the first cycle. Because of these multifunctional roles, our new additive is shown to significantly improve capacity retention and perform better than previously reported organosilicon additives. These results establish (MetBu₂Si)₂CO as a sacrificial, self-limiting additive that leads to the formation of an interphase ensuring long-term cathode stabilization, thus offering a molecular-level strategy to enable durable high-voltage lithium-ion battery operation.