The chemical and mechanical stability of SEI layers are particularly important for high capacity anode materials such as silicon, which undergoes large volume changes (∼300%) during cycling. In this work, we present a novel approach for applying controlled strains to SEI films with patterned Si electrodes to systematically investigate the impact of large volume changes on SEI formation and evolution. Comparisons between patterned silicon islands and continuous silicon thin films make it possible to correlate the irreversible capacity losses due to expansion and contraction of underlying silicon. The current work demonstrates that strain in the SEI layer leads to more lithium consumption. The combination of in situ AFM and electrochemical lithium loss measurements provides further information on SEI layer growth. These experiments indicate that in-plane strains in the SEI layer lead to substantial increases in the amount of inorganic phase formation, without significantly affecting the overall SEI thickness. These observations are further supported with EIS and TOF-SIMS results. A map of irreversible capacity evolution with strain in the SEI is obtained from the experimental results.
Keywords: capacity loss; in situ atomic force microscope; lithium-ion battery; silicon anode; solid electrolyte interphase.