Evolution of the volume expansion of SiO/C composite electrodes in lithium-ion batteries during aging cycles

As a negative electrode material for lithium-ion batteries, silicon monoxide (SiO) suffers from dramatic volume changes during cycling, causing excessive stress within the electrode and resulting in electrode deformation and fragmentation. This ultimately leads to a decrease in cell capacity. The trends of volume expansion and capacity change of the SiO/graphite (SiO/C) composite electrode during cycling were investigated via in situ expansion monitoring. First, a series of expansion test schemes were designed, and the linear relationship between negative electrode expansion and cell capacity degradation was quantitatively analyzed. Then, the effects of different initial pressures on the long-term cycling performance of the cell were evaluated. Finally, the mechanism of their effects was analyzed by scanning electron microscope. The results show that after 50 cycles, the cell capacity decreases from 2.556 mAh to 1.689 mAh, with a capacity retention ratio (CRR) of only 66.08%. A linear relationship between the capacity retention ratio and thickness expansion was found. Electrochemical measurements and scanning electron microscope images demonstrate that intense stress inhibits the lithiation of the negative electrode and that the electrode is more susceptible to irreversible damage during cycling. Overall, these results reveal the relationship between the cycling performance of SiO and the internal pressure of the electrode from a macroscopic point of view, which provides some reference for the application of SiO/C composite electrodes in lithium-ion batteries.