High-performance conversion anode enabled by the stable solid electrolyte interphase (SEI) for Li-ion batteries Xuyun Guo 1 , Xiaoqiong Du 1 , Valeria Nicolosi 1 , Biao Zhang 2 and Ye Zhu 2 1 School of Chemistry, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) & Advanced Materials Bio-Engineering Research Centre (AMBER), Trinity College Dublin, Dublin D02PN40, Ireland, 2 Department of Applied Physics, Research Institute for Smart Energy, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 000000, P.R. China Solid electrolyte interphase (SEI) formed from electrolyte decomposition and deposited on the electrode surfaces is critical for battery life. The complex discharging/charging environment in a battery could cause the dynamic response of SEIs. However, these structure and chemistry changes of SEI at different charge states are rarely explored in conversion anodes, which usually suffer from an unstable SEI layer. Here we apply N-doped carbon coating on conversion-type anode Fe 2 O 3 (Fe 2 O 3 @CN) quasi-cubes to remarkably enhance the electrochemical cycling stability compared to bare Fe 2 O 3 . The reasons are unequivocally unravelled by state-of-the-art cryogenic transmission electron microscopy (cryo-TEM) and spectroscopy. It is found that the bare Fe 2 O 3 anode develops an unstable SEI layer due to the intermixing with the lithiation product Li 2 O, which exhibits a large thickness variation upon breathing as well as excessive growth, causing substantial capacity fading within 100 cycles. A transition from organic to inorganic-type SEI is also identified upon cycling, which gives rise to significantly increased SEI resistance. Nevertheless, the Fe 2 O 3 @CN with CN layer can effectively separate the lithiation product from SEI and develop a thinner and chemically more stable SEI layer on the surface, resulting in high performance for Li-ion batteries. This work demonstrates the importance of understanding and optimizing stable SEIs to achieve better battery performance. References 1. X.Guo, X.Du, V. Nicolosi, B. Zhang, Y. Zhu, Adv. Energy Mater. 2023 . Accepted.10.1002/aenm.202300240.
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