Capacity Fading Mechanism and Improvement of Cycling Stability of the SiO Anode for Lithium-Ion Batteries

In this study, we first investigate the major causes of capacity fading in silicon monoxide (SiO) anodes. Major capacity loss occurs in the early cycles followed by less capacity fading during the following cycles. Close examination of the electrochemical test results shows that similar to silicon, the major capacity loss of the SiO anode at the early cycles occurs at the earlier stages of lithiation (>0.27 V vs Li/Li⁺), suggesting the phenomenon of incomplete delithiation due to electrode volume expansion/contraction. Unlike silicon which shows continuous capacity loss toward lower voltages, the capacity retention of SiO stabilizes after the initial fast capacity loss, demonstrating the better cycling stability of SiO over Si. The capacity loss of SiO during long-term cycling has contribution from the whole voltage range, indicating loss of active material due to extensive cycling. The capacity loss can be mitigated with an optimized electrode composition. The long-term capacity retention of SiO is also found to be affected by the annealing treatment. The removal of the defects in the interphase region within the particle and the removal of the unfavorable surface groups from the surface are suggested as the possible reasons for the improved performance for annealed SiO.