Intermediate Phases in LixFePO4

Abstract

AbstractRietveld analysis for the time of flight powder neutron diffraction profile for LiFePO4 at room temperature was performed. Refined tensor elements of the unisotropic thermal factor under the elliptic approximation showed the principal axis of the lithium vibration is toward the face shared vacant tetrahedral space and is consistent with the theoretical prediction; lithium ions diffuse along curved one-dementional chain along b-axis. Impact of temperature on the phase diagram of LixFePO4 with > 200nm particle size was slight under the unmixing line around 200 C. While the reduction in particle size down to <100 nm seems to have significant effect to the room temperature miscibility gap. The thermodynamic concepts for the extended solution in smaller particles are discussed, followed by a demonstration of very high rate capability observed for the small spherical particles < 80 nm.