Evaluating the roles of electrolyte components on the passivation of silicon anodes

A protocol was recently developed to compare calendar life using a constant potential while monitoring the electrical current required to maintain the potential. Here, this calendar life protocol is used with electrolyte formulations containing various mole fractions of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and LiPF6 to elucidate the role each component plays in passivation for high silicon anodes. Together, EC and LiPF6 lead to higher currents, and thus poorer passivation, whereas EMC acts as a spectator. The variation of the components' mole fraction also changes the solid-electrolyte interphase (SEI) composition, as measured by x-ray photoelectron spectroscopy. Importantly, higher LiPF6 content leads to increased LiF as well as increased current, indicating that higher LiF content does not enhance the passivation of the silicon surface. Finding that EC did not yield a passivating SEI, instead ethylene sulfite, sulfolane, and propylene carbonate (PC) were used in place of EC. Using ethylene sulfite and sulfolane resulted in poorer passivation compared to EC, whereas PC resulted in superior passivation. The superior passivation may be related to more stable lithium-solvent complexes.

Automated summary

A new protocol was developed to compare battery life by using a constant potential and monitoring the current needed to maintain the potential. The results showed that EC and LiPF6 led to higher current and poorer passivation, while EMC had no effect on passivation. The mole fractions of the components also affected the composition of the solid-electrolyte interphase (SEI). Higher LiPF6 content resulted in increased LiF and current, but did not enhance passivation on the silicon surface. Comparing different compounds, it was found that EC did not generate a passivating SEI, while other compounds showed varying levels of passivation.