Single-Crystal α-FeO with Engineered Exposed (001) Facet for High-Rate, Long-Cycle-Life Lithium-Ion Battery Anode.

Designing electrode materials with engineered exposed facets provides a novel strategy to improve their electrochemical properties. However, the controllability of the exposed facet remains a daunting challenge, and a deep understanding of the correlation between exposed facet and Li-transfer behavior has been rarely reported. In this work, single-crystal α-FeO hexagonal nanosheets with an exposed (001) facet are prepared with the assistance of aluminum ions through a one-step hydrothermal process, and structural characterizations reveal an Al-concentration-dependent-growth mechanism for the α-FeO nanosheets. Furthermore, such α-FeO nanosheets, when used as lithium-ion battery anodes, exhibit high specific capacity (1261.3 mAh g at 200 mA g), high rate capability (with a reversible capacity of approximately 605 mAh g at 10 A g), and excellent cyclic stability (with a capacity of over 900 mAh g during 500 cycles). The superior electrochemical performance of α-FeO nanosheets is attributed to the pseudocapacitive behavior, Al-doping in the α-FeO structure, and improved Li-transfer property across the (001) facet, as elucidated by first-principles calculations based on density functional theory. These results reveal the underlying mechanism of Li transfer across different facets and thus provide insights into the understanding of the excellent electrochemical performance.