Dittmarite precursors for structure and morphology directed synthesis of lithium manganese phospho-olivine nanostructures†
We have demonstrated the capability of dittmarite-type precursors to act as structure and morphology directed agents for a facile synthesis of electrochemically active lithium manganese phospho-olivine nanostructures which are of interest as positive electrode materials for lithium ion batteries. Two types of compounds from the dittmarite series are considered: potassium and ammonium manganese phosphate monohydrates, M′MnPO4·H2O (M′ = K, NH4). Both KMnPO4·H2O and NH4MnPO4·H2O precursors interact with the eutectic LiCl–LiNO3 composition before its melting, leading to the formation of the target LiMnPO4. The reaction of KMnPO4·H2O with LiCl–LiNO3 takes place by a topotactic mechanism including a fast ion exchange of K+ for Li+ and H2O release, as a result of which nanostructured LiMnPO4 is formed. The NH4MnPO4·H2O precursor reacts with the lithium salts by massive evolution of H2O, NH3, NO and N2O gasses, resulting in fragmentation of the pristine plate-like aggregates into well-shaped and dispersed particles with nanosizes of about 20–50 nm.