LiFe(1-x) Mn (x) PO(4) solid solutions in the whole concentration range (0 a parts per thousand currency sign x a parts per thousand currency sign 1) are obtained at 500 A degrees 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 A degrees C yields nano-sized LiFe(1-x) Mn (x) PO(4) coated with carbon. The structure and the morphology of the LiFe(1-x) Mn (x) PO(4) compositions are studied by XRD, IR spectroscopy, and SEM analysis. The in situ formed carbon is analyzed by Raman spectroscopy. The electrochemical performance of LiFe(1-x) Mn (x) PO(4) is tested in model lithium cells using a galvanostatic mode. All LiFe(1-x) Mn (x) PO(4) compositions are characterized with an ordered olivine-type structure with a homogeneous Fe(2+) and Mn(2+) distribution in the 4c olivine sites. The morphology of LiFe(1-x) Mn (x) PO(4) consists of plate-like 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 LiFe(1-x) Mn (x) PO(4) deliver a good reversible capacity due to the Fe(2+)/Fe(3+) and Mn(2+)/Mn(3+) redox-couples at 3.5 and 4.1 V, respectively.