Phase Diagram of Li[sub x](Mn[sub y]Fe[sub 1−y])PO[sub 4] (0≤x, y≤1)

Abstract

The room temperature x, y two-dimensional phase diagram of the olivine-type solid-solution, Li x (Mn y Fe 1y )PO 4 (0 x, y 1, orthorhombic, D 2h 16 : Pmnb), is determined. The x-dependent changes in the unit cell dimensions at various fixed Mn contents y are analyzed in detail. The manganese substitution for iron in the octahedral 4c sites induces 1, the two-phase Mn 3 /Mn 2 redox region with a potential of 4.1 V vs. Li/Li ; 2, a partial conversion of the form of the Fe 3 /Fe 2 redox reaction 3.4 V vs. Li/Li ) from two-phase to single-phase; and 3, phase instability at the composition region close to the point x, y 0, 1 caused by the Jahn-Teller effect of Mn 3 . The conversion, 2, is complete at around y 0.6. The phase instability, 3, makes the Mn-rich phase (y 0.8) unsuitable for battery applications. The local lattice deformation around Mn 3 is severe enough to induce significant selective damping in the extended X-ray absorption fine structure for Mn 3 .