Cathode-Electrolyte Interphase of Ni-Rich Layered Oxides: Evolving Structure and Implication on Stability.

Li, Menghao; Yang, Xuming; Wei, Xianbin; Zhu, Yuanmin; Sun, Xueliang; Gu, M Danny · Nano Lett · 2025

basic_science · Level V

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Abstract

The cathode-electrolyte interphase (CEI) is recognized as a crucial component in battery systems; however, knowledge regarding its structure and function remains limited and often controversial. This study demonstrates the feasibility of revealing atomic-resolution CEI structures via cryogenic transmission electron microscopy (cryo-TEM). Using Ni-rich oxide (LiNi<sub>0.8</sub>Co<sub>0.1</sub>Mn<sub>0.1</sub>O<sub>2</sub>, NCM811) microparticles as the model cathode, ultrafine images of CEI were obtained, revealing its dynamic evolution over cycling and its impact on battery performance. In ethylene carbonate (EC)-based electrolytes, the CEI forms an amorphous organic-rich layer, while, in fluoroethylene carbonate (FEC)-based electrolytes, the CEI contains abundant LiF grains. Both CEIs thicken with cycling but exhibit different structural evolutions: the former adopts a mosaic structure, while the latter forms a dual-layer structure with a compact LiF inner layer. These unprecedented high-resolution images and comprehensive analysis advance the understanding of CEI dynamics, addressing existing controversies and providing insights for improving battery performance.