Facile synthesis of LiMnPO4 olivines with a plate-like morphology from a dittmarite-type KMnPO4·H2O precursor

Abstract

Dittmarite-type compound KMnPO₄·H₂O was used as a new precursor for the synthesis of nanostructured LiMnPO₄ phospho-olivines with a plate-like morphology at low temperature (about 200 °C) and a short reaction time (90–180 min). The dehydration of KMnPO₄·H₂O was studied by DTA and TG analysis. Structural and morphological characterization of both KMnPO₄·H₂O and LiMnPO₄ was performed by powder XRD, SEM and TEM analyses. The formation of nanostructured LiMnPO₄ was examined by electron paramagnetic resonance spectroscopy and TEM. It was found that the reaction between KMnPO₄·H₂O with the LiCl–LiNO₃ mixture includes a fast ionic exchange of K⁺ with Li⁺ in the framework of the dittmarite structure, followed by H₂O release and the formation of the olivine-type structure. The morphology and texture of the dittmarite-type precursor results in a plate-like morphology of LiMnPO₄ with a preferred orientation along the [100] direction. The plate-like morphology of LiMnPO₄ is stable after annealing at 500 °C. The plates are composed of nanocrystallites, with various sizes in the range 10–20 nm. The EPR signal of LiMnPO₄ is due to the exchange-coupled Mn²⁺ ions. It was demonstrated that the EPR line-width correlates with the Scherrer crystallite size.