Structural and electrochemical study of lithium insertion into γ-Fe2O3

Abstract Lithium insertion into the defect spinel γ-Fe 2 O 3 was investigated both chemically and electrochemically. A combination of slow potential-controlled insertion and in situ X-ray diffraction shows three successive reactions: (i) filling the octahedral vacancies up to x (Li) ≈ 0.25, (ii) a spinel→rocksalt-type first-order transition at increasing x (Li) (equilibrium potential 1.60 V versus Li + /Li), (iii) filling the remaining octahedral vacancies in the rocksalt phase. Structure refinements at x (Li)=0.86±0.01 from both X-ray and neutron diffraction data showed a remaining occupation of tetrahedral sites equal to ≈0.10.