Determination of the chemical diffusion coefficient of lithium in lifepo4

The lithium insertion in the ordered olivine-type structure of LiFePO4 was analyzed as an insertion process with a Frumkin type sorption isotherm. A minimum in the chemical diffusion coefficient of lithium (DLi) was predicted by the model for strong attractive interactions between the intercalation species and the host matrix. The DLi in the material was measured as a function of the lithium content by using the galvanostatic intermittent titration technique (GITT). The diffusion coefficient was found 1.8 x 10-14 and 2.2 x 10-16 cm2 sec-1 for LiFePO4 and FePO4, respectively with a minimum in correspondence of the peak of the differential capacity. The DLi has been also measured by AC impedance method for various lithium contents. The calculated values are in very good agreement with the previous calculated values.