Synthesis of multicomponent olivine by a mixed metal oxalate coprecipitation method and electrochemical characterization

Abstract

The multicomponent olivine cathode material, $LiMn_{1/3}Fe_{1/3}Co_{1/3}PO_4$, was synthesized via a novel coprecipitation method of the mixed metal oxalate, $Mn_{1/3}Fe_{1/3}Co_{1/3}(C_2O_4)·2H_2O$. The stoichiometric ratio and distribution of transition metals in the oxalate precursor and the final olivine product was affected sensitively by the synthesis conditions of the coprecipitation process. Furthermore, they are the important factors in determining the electrochemical performance of the olivine cathode material with multiple transition metals. The effect of the pH, atmosphere, temperature, and aging time was investigated systematically with respect to the atomic ratio of transition metals, phase purity, and morphology of the mixed metal oxalate. The electrochemical activity of each transition metal in the olivine synthesized using the mixed metal oxalate precursor clearly was enhanced as shown in the cyclic voltammetry (CV) and galvanostatic charge/discharge measurement. Three distinctive contributions from Mn, Fe, and Co redox couples were detected reversibly in multiple charge and discharge processes. The first discharge capacity at the C/5 rate was 140.5 $mAh g^{-1}$ with good cycle life. The rate capability test showed that the high capacity is still retained even at the 4C and 6C rates with 102 and 81 $mAh g^{-1}$, respectively.