Enabling Li2O as an Effective Lithium Ion Source Material for In Situ Prelithiation of SiOx Anodes in Li-Ion Batteries

Abstract Li₂O is one of the most promising lithium ion source materials (LSM) for in-situ prelithiation of SiOx anodes in Li-ion batteries due to its high theoretical lithium-ion capacity (1794 mAh g⁻¹). However, its use faces two major challenges: (1) high Li⁺ extraction over-potential and (2) slight solubility in electrolytes along with high reactivity of oxygen and its oxidation intermediates toward carbonate solvents. To overcome these issues, this work proposes silicon nanoparticles (Si) as absorbents for oxygen and its oxidation intermediates through the reaction “2Li₂O + Si + 4e⁻ → SiO₂ + 4Li⁺”, where the produced SiO₂ is neither soluble in the electrolyte nor reactive with electrolyte solvents and active cathode materials. A 3:1 (wt) Li₂O-Si mixture is shown to reduce the Li⁺ extraction potential to below 4.4 V with a capacity of 1076 mAh g⁻¹, a significant improvement over the 4.8 V and 74 mAh g⁻¹ capacity of pure Li₂O. Additionally, incorporating 2 wt% of the Li₂O-Si additive into the cathode improves the long-term cycling stability of SiOx/NCM811 cells with minimal increases in polarization and capacity loss. These results demonstrate that the Li₂O-Si additive is a highly effective LSM for the in-situ prelithiation of SiOx anodes in Li-ion batteries.