Morphology-Dependent Investigation of Li-ion Insertion into Single Crystal Hematite -Fe₂O₃ Nanostructures

Hematite iron oxide (alpha-Fe2O3) is one of the promising anode materials for Li, Na, and K-ion batteries with higher theoretical capacity than that of the commercially used graphite. Its utilization is hindered by the complex ion storage mechanisms which involve the insertion of Li-ion followed by a conversion reaction. The insertion process is less studied in the literature and is assumed to have minimal effect during the Li-ion storage process. In this work, Li-ion insertion behavior into single-crystal alpha-Fe2O3 nanostructures with determined facets and highlights of its role in the storage process were investigated. Three morphologies with mainly {104}, {012}, and {113} facets are electrochemically investigated in the Li-ion insertion voltage window. The contribution of the Li-ion insertion charge transfer process is studied at different facets. The formation and development of the solid electrolyte interface (SEI) are observed for each morphology. The reversibility of the insertion process is investigated by cycling and impedance measurements. The observed results suggest better Li-ion insertion toward the {113} facet. Capacity degradation and continuous SEI growth were observed as the cells were cycled, which calls for further consideration toward optimization of the Li-ion insertion process.