Architecting Phase-Selective Interlayers for Stable SiOx Lithium Storage via Dual-Function Design.

Silicon suboxide (SiOx) anode offer higher capacities than graphite; however, their practical use is hindered by unstable interfaces and poorly controlled formation of lithium silicates during initial lithiation. Insufficient or nonuniform lithiation results in oxygen-rich lithium silicates that block deep silicon (Si) alloying, while uncontrolled interfacial reaction consumes active lithium, lowers initial Coulombic efficiency, and destabilizes the solid-electrolyte interphase (SEI). In this study, we address a specific, falsifiable question: what factors dictate which lithium silicate phase forms in the subsurface, and can this process be manipulated to improve both deep Si alloying and SEI stability? We define the Phase-Selective Conductive Interfacial Interlayer (PSCII) as a Li4SiO4-rich and ion-accessible subsurface formed through coupled control of bulk oxygen stoichiometry and local electron supply. A stepwise control series from commercial SiO to layered SiOx (LS-SiOx), deoxygenated layered SiOx (DLS-SiOx), and single-walled carbon nanotubes (SWCNTs)-wired DLS-SiOx@CNT separates the contributions of layered buffering, bulk deoxygenation, and conductive wiring. As a result, DLS-SiOx@CNT delivers 1650 mAh g-1, retains >820 mAh g-1 after 700 cycles at 1 A g-1, and enables stable LCO full-cell cycling. These results identify subsurface lithium silicate phase selection as a practical design strategy for durable high-capacity SiOx anodes.