Crystal structure analysis of γ-Fe2O3 with chemical lithium insertion

Abstract

Abstract To better understand the lithium insertion mechanism on γ-Fe 2 O 3 , we investigated the crystal structure changes of γ-Fe 2 O 3 in the process of chemical lithium insertion by using the X-ray Rietveld analysis. We newly found that the lithium inserted sample was a mixture of two phases both belonging to the space group Fd - 3m , one is rich in lithium and the other is lean in lithium. It was revealed that the chemical lithium insertion process into γ-Fe 2 O 3 occurs via a two phase reaction, i.e. inserted lithium forms a Li-rich phase in which the quantity of lithium is constant, and the overall lithium concentration is controlled by the mole fraction changes between the Li-rich phase and Li-lean phase. The Li-rich phase is thought to be the same phase previously reported by Bonnet et al. and Pernet et al., in which the iron occupancy of the 16 c site was not equalized with that of the 16 d site indicating the space group not to be Fm - 3m but Fd - 3m . Fast lithium insertion could form the two phases, Li-lean and Li-rich, even for an electrochemical lithium insertion process.