Oxygen Content in SiO _<i>x</i> Impacts Chemical Prelithiation Kinetics, Swelling, and Lithium Partitioning

Silicon suboxide (SiO _<i>x</i> ) 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 _<i>x</i> using Li-biphenyl/2-methyltetrahydrofuran. By investigating CPL kinetics, electrode swelling, and Li partitioning, we found that oxygen in SiO _<i>x</i> 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 _<i>x</i> ), 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 _<i>x</i> prelithiation.