Oxygen Content in SiO _x Impacts Chemical Prelithiation Kinetics, Swelling, and Lithium Partitioning

Silicon suboxide (SiO _x ) is attractive for lithium-ion (Li-ion) anodes but suffers from low initial Coulombic efficiency (ICE) due to solid-electrolyte interphase (SEI) and lithium-silicate formation. We examine how oxygen content (3.2-17.0 wt %) governs chemical prelithiation (CPL) of SiO _x using Li-biphenyl/2-methyltetrahydrofuran. By investigating CPL kinetics, electrode swelling, and Li partitioning, we found that oxygen in SiO _x mitigates volume expansion during CPL by buffering the swelling per unit of ICE improvement. Moderate oxygen levels accelerate early-stage CPL kinetics, while lower oxygen levels favor late-stage Li storage. Distribution of the CPL lithium reveals that increasing the oxygen content raises the fraction of irreversible Li (SEI/lithium silicates) at the expense of reversible Li-Si alloying. In full cells (LCO/SiO _x ), CPL improves ICE and capacity as a one-time lithium supplement to pristine anodes. These results provide design rules linking bulk oxygen content to CPL kinetics, swelling, and lithium partitioning, defining practical dosing windows for SiO _x prelithiation.