Effect of surface oxidation on the performance of silicon nanoparticles

Reducing silicon particle size in lithium-ion battery anodes not only mitigates surface stress, prevents pulverization, and reduces SEI film cracking but also significantly enhances surface area, thereby amplifying the impact of particle surface chemistry on performance. In this study, the surface of silicon particles with 80-nm diameter were oxidized in air to prepare Si@SiO_x with a core–shell structure. We investigated the effect of different oxidation levels of the shell on the cycling performance of the nanosized silicon particles. The results showed that longer heating times decreased initial coulombic efficiency (ICE) but improved cycling performance. An interesting phenomenon was observed that, when the oxidation level was high, fast charging reduced battery capacity; while at lower oxidation levels, fast charging maintained or even slightly increased battery capacity. Based on electrochemical analysis, we proposed an explanation for this phenomenon: for small-sized nanoparticles with a large specific surface area, the effect of potential is particularly significant. The oxidation level of the particle surface affects the impedance of the SEI film, and high charge/discharge rates will also produce bias voltage, both of the two factors will limit the formation of crystallized Li₁₅Si₄ (c-Li₁₅Si₄). Reducing the amount of c-Li₁₅Si₄ can effectively improve the cycling performance of the electrode, but excessive bias voltage will sacrifice the lithium storage capacity of the electrode. For the designing of small size silicon particles, both factors should be considered.