Carbon-coated nano-sized LiFe1-xMnxPO4 solid solutions (0 ≤ x ≤ 1) obtained from phosphate-formate precursors

Abstract

LiFe1-xMnxPO4 solid solutions in the whole concentration range (0 ≤ ≤ B 1) are obtained at 500 °C by a phosphate-formate precursor method. The method is based on the formation of homogeneous lithium-iron-manganese phosphate-formate precursors by freeze-drying of aqueous solutions containing Li(I), Fe(II), Mn(II), phosphate, and formate ions. Thermal treatment of the phosphate-formate precursors at temperatures at 500 °C yields nano-sized LiFe1-xMnxPO4 coated with carbon. The structure and the morphology of the LiFe 1-xMnxPO4 compositions are studied by XRD, IR spectroscopy, and SEM analysis. The in situ formed carbon is analyzed by Raman spectroscopy. The electrochemical performance of LiFe1-xMn xPO4 is tested in model lithium cells using a galvanostatic mode. All LiFe1-xMnxPO4 compositions are characterized with an ordered olivine-type structure with a homogeneous Fe2+ and Mn2+ distribution in the 4c olivine sites. The morphology of LiFe1-xMnxPO4 consists of platelike aggregates which are covered by in situ formed carbon. Inside the aggregates nano-sized isometric particles with narrow particles size distribution (between 60 and 100 nm) are visible. The structure of the deposited carbon presents a considerable disordered graphitic phase and does not depend on the Fe-to-Mn ratio. The solid solutions LiFe1-xMn xPO4 deliver a good reversible capacity due to the Fe 2+/Fe3+ and Mn2+/Mn3+ redox-couples at 3.5 and 4.1 V, respectively. © 2011 Springer Science+Business Media, LLC.