Comparative Kinetic Study of Olivine Li[sub x]MPO[sub 4] (M=Fe, Mn)

A huge kinetic difference in olivine is demonstrated in a quantitative manner. Galvanostatic discharge profiles and the current relaxation to the stepwise anodic overvoltage (chronoamperometry) are comparatively measured for the and under identical extrinsic conditions, which are carefully controlled and confirmed using Rietveld refinement for the X-ray diffraction profiles, direct texture observation by scanning electron microscope, Brunauer-Emmett-Teller surface area measurements, and tap density measurements. The current durability for is orders-of-magnitude inferior to that of the origin of which is clearly attributed to their intrinsic crystallographic and transport property differences. Heavy polaronic holes localized on the sites are suggested as an important rate-limiting factor. In spite of the higher open-circuit voltage of (4.05 V) compared to that of (3.45 V) in the olivine framework, the abnormally large polarization may eliminate pure as a practical lithium battery cathode due to much lower effective energy density than © 2004 The Electrochemical Society. All rights reserved.