Comparative Study of Irreversible Lithium Formation Mechanisms in Various Silicon Anode Materials for Li-Ion Secondary Batteries

Lithium-ion secondary batteries play a crucial role in mobile power storage systems, supplying energy for electronic devices and electric vehicles. However, compared to current carbon-based anode materials, they suffer from limitations in energy density and cycle stability . The application of silicon materials is emerging as a promising alternative to overcome these limitations due to its high theoretical capacity, approximately 10 times higher than that of graphite (4200mAh/g compared to 372mAh/g). However, the structural instability caused by volume changes during charging and discharging poses a challenge in the application of silicon materials. Various silicon anode materials that can be applied to lithium-ion secondary batteries include crystalline silicon, amorphous silicon, silicon alloys, and oxide-based silicon. These diverse silicon materials each possess different capacities and electrochemical properties. The composition of lithium-silicon compounds formed during charging varies with different silicon materials, leading to differences in electrochemical properties. Additionally, the crystal structures formed during charging differ, influencing their irreversible lithium formation and affecting the battery's cyclability and expansion characteristics. Therefore, it is essential to compare and analyze the irreversible lithium formation and charging/discharging mechanisms of silicon anode materials. In this study, we will observe the crystallographic structural changes occurring during charging and discharging of crystalline silicon, amorphous silicon, silicon alloys, and oxide-based silicon anode materials using ex-situ X-ray diffraction (XRD) and transmission electron microscopy (TEM). Furthermore, we will examine how these crystallographic changes affect the electrochemical properties and volume expansion.