Influence of Oxygen Content on the Structural Evolution of SiO_x Thin-Film Electrodes with Subsequent Lithiation/Delithiation Cycles

SiOx negative electrodes for Li-ion batteries enable high energy density while providing better structural integrity compared to pure Si electrodes. The oxygen content has a critical impact on structural changes that occur during electrochemical cycling. In this study, the near-surface structural evolution in SiOx thin films with different compositions (0.3 ≤ x ≤ 2) was probed by various electrochemical techniques and X-ray photoelectron spectroscopy. These results show that all of the SiOx films undergo significant chemical changes during cycling. Even the films with high oxygen content (x = 2) undergo significant restructuring after sufficiently long cycling times. The changes that occur in all films indicate that the near-surface regions of SiOx materials react in ways that effectively make them part of the solid electrolyte interphase (SEI). This also implies that tuning the surface oxygen content of Si-based electrodes can be used to control SEI performance. Hence, the structural changes in SiOx observed in this study may provide useful guidelines for designing passivating layers for improved cycle efficiency.