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

Silicon suboxide (SiO_x) 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 SiO_x (LS-SiO_x), deoxygenated layered SiO_x (DLS-SiO_x), and single-walled carbon nanotubes (SWCNTs)-wired DLS-SiO_x@CNT separates the contributions of layered buffering, bulk deoxygenation, and conductive wiring. As a result, DLS-SiO_x@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 SiO_x anodes.