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

Dittmarite-type compound KMnPO4 center dot 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 degrees C) and a short reaction time (90-180 min). The dehydration of KMnPO4 center dot H2O was studied by DTA and TG analysis. Structural and morphological characterization of both KMnPO4 center dot 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 center dot 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 degrees 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.