Quantitative measurement of solid electrolyte interphase growth on Si-based anode materials

Symmetric cells have been developed to evaluate electrode degradation directly associated with solid electrolyte interphase (SEI) growth in Li-ion cells. This limits their applications to only certain anodes, such as graphite and Li4Ti5O12. In this work, symmetric cells have been applied to investigate the degradation of high energy density anodes, such as Si-alloys, which undergo multiple degradation mechanisms, including mechanical failure and SEI growth. A Li inventory model has been developed to correlate the symmetric cell capacity fade and the multiple anode degradation mechanisms. Using symmetric cells with a pseudo-reference electrode, it was found that irreversible capacity caused by anode degradation can be partially compensated by a positive shift in electrode upper endpoint potential, which is key to interpreting degradation mechanisms. Importantly, a feasible method to measure Li consumption due to SEI growth on Si-alloys has been established using symmetric cells. This method could help battery researchers develop technologies to lower the SEI growth rate on Si-alloys.