Dittmarite precursors for structure and morphology directed synthesis of lithium manganese phospho-olivine nanostructures

Abstract

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.