Reaction mechanism of the olivine-type Li-x(Mn0.6Fe0.4)PO4 (0 <= x <= 1)

The charge-discharge reaction mechanism of the olivine-type Li-x(Mn0.6Fe0.4 )PO4 (0 less than or equal to x less than or equal to 1.0), a possible 4 V class cathode material for lithium batteries, was investigated using equili brium voltage measurements, X-ray diffraction, Mossbauer spectroscopy, and X-ray absorption spectroscopy. The Rat two-phase region with an open-circui t voltage (OCV) of ca. 4.1 V (region I: 0 less than or equal to x less than or equal to 0.6. Mn3+/Mn2+) and the S-curved single-phase region with OCV approximate to 3.5 V (region II: 0.6 less than or equal to x less than or e qual to 1.0, Fe3+/Fe2+) were clearly identified together with the correspon ding change in the unit cell dimensions of the orthorhombic lattice. These features show significant differences from the reaction mechanism of LixFeP O4 (0 less than or equal to x less than or equal to 1), in which the whole Fe3+/Fe2+ reaction proceeds in a two-phase manner (LiFePO4-FePO4) with a Ra t voltage profile at 3.4 V. (C) 2001 The Electrochemical Society.