Determination of the chemical diffusion coefficient of lithium in LiFePO4

Abstract The lithium insertion in the ordered olivine-type structure of LiFePO 4 was analyzed as an insertion process with a Frumkin-type sorption isotherm. A minimum in the chemical diffusion coefficient of lithium ( D Li ) was predicted by the model for strong attractive interactions between the intercalation species and the host matrix. The D Li 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 1.8×10 −14 and 2.2×10 −16 cm 2 s −1 for LiFePO 4 and FePO 4 , respectively, with a minimum in correspondence of the peak of the differential capacity. The D Li has also been measured by AC impedance method for various lithium contents. The calculated values are in very good agreement with the previous calculated ones.

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