The influence of the Li+ addition rate during the hydrothermal synthesis of LiFePO4 on the average and local structure

Abstract

A hydrothermal method was used to synthesize LiFePO₄ to explore the effect of the rate of addition of the Li⁺ precursor to a mixture of the Fe²⁺ and PO₄^3- precursors. Both the average and local structures were investigated using powder X-ray diffraction, Mössbauer spectroscopy and X-ray absorption spectroscopy. Slower addition rates led to increased oxidation of Fe²⁺ to Fe³⁺ despite purging all solutions constantly, as well as increased defects. The local structure as determined by extended X-ray absorption fine structure displayed far less variation between the samples. The formation of a Li₃PO₄ impurity appeared to be independent of the Li⁺ addition rate.