Synergistic effects of transition metal substitution in conversion electrodes for lithium-ion batteries

Abstract

Different solid solutions in the FexCo1−xC2O4·2H2O system have been prepared in the form of nanoribbons by a reverse micelles method. The orthorhombic crystallographic structure differs from the monoclinic massive products FeC2O4·2H2O and CoC2O4·2H2O. The dehydration process is studied by thermal analysis to prepare the anhydrous solid solution oxysalts, in which the nanoribbon-shaped particles are preserved and a porous system is developed. Anhydrous mixed oxalates are used for the first time as high-capacity lithium storage materials with improved rate performance, and display synergistic effects as compared with the end members. Fe0.75Co0.25C2O4 displays a reversible capacity ca. 600 mA h g−1 at 5C rate with a very good capacity retention after 75 cycles by a hybrid mechanism. The solids display faradaic capacities due to a novel conversion reaction that produces nanodispersed transition metals, which is responsible for the high energy density, and a capacitive response that leads to high power densities in Li-ion batteries. The low temperature synthesis of these materials makes them an inexpensive option for this purpose.