Tailoring Breathing Behavior of Solid Electrolyte Interphases Unraveled by Cryogenic Transmission Electron Microscopy

The cycling stability of batteries is closely related to the dynamic evolution of solid electrolyte interphases (SEIs) in response to the discharging/charging processes. Here, the state-of-the-art cryogenic transmission electron microscopy (cryo-TEM) and spectroscopy are utilized to probe the SEI breathing behavior induced by discharging/charging on the conversion-type anode made of Fe2O3 quasi-cubes. The incorporation of the identical-location strategy allows the tracking of the evolution of the same SEIs at different charge states. SEI breathing is shown to involve swelling (contracting) upon lithiation (de-lithiation) driven by the reversible compositional change. Bare Fe2O3 anodes develop an unstable SEI layer due to the intermixing with the lithiation product Li2O, which exhibits a large thickness variation upon breathing as well as excessive growth. A transition from organic to inorganic-type SEI is also identified upon cycling, which gives rise to significantly increased SEI resistance. To tailor the SEI behavior, N-doped carbon coating is applied on Fe2O3 (Fe2O3@CN), which can effectively separate the lithiation product from SEI. A thinner and chemically more stable SEI layer develops on Fe2O3@CN, resulting in remarkably enhanced cycling stability compared to bare Fe2O3. This work demonstrates the importance of understanding and optimizing the dynamic behavior of SEIs to achieve better battery performance.

Automated summary

This study investigates the breathing behavior of solid electrolyte interphases (SEIs) induced by discharging/charging on Fe2O3 conversion-type anodes using cryogenic transmission electron microscopy and spectroscopy. The SEI breathing involves swelling and contracting upon lithiation and de-lithiation due to reversible compositional changes. Bare Fe2O3 anodes develop unstable SEI layers with thickness variation and excessive growth. By applying N-doped carbon coating on Fe2O3, a thinner and chemically more stable SEI layer develops, resulting in significantly enhanced cycling stability.