Li3MxV2−x(PO4)3/C (M=Fe, Co) composite cathodes with extended solubility limit and improved electrochemical behavior

Abstract

A first attempt has been made to prepare Li₃M_xV_2−x(PO₄)₃/C (M=Fe, Co) composite solutions by adopting a novel oxalic dihyrazide assisted combustion (ODHAC) method. The pillaring effect of Fe in Li₃Fe_xV_2−x(PO₄)₃/C and the possible electrochemical activity of the Co^3+/4+ redox couple of Li₃Co_xV_2−x(PO₄)₃/C at a 4.8 V limit increases the structural and cycling stability of the native Li₃V₂(PO₄)₃/C cathode respectively, thereby ultimately improving the electrochemical behaviour of Li₃M_xV_2−x(PO₄)₃/C solid solutions. An extended solubility limit of x = 0.10 for Fe dopant has been achieved for the first time through the present study against the reported value of x = 0.05 in Li₃Fe_xV_2−x(PO₄)₃/C compounds. The study demonstrates the suitability of the ODHAC synthesis approach in preparing a wide variety of phase pure Li₃M_xV_2−x(PO₄)₃/C cathodes. Further, the superiority of Li₃Co_0.10V_1.90(PO₄)₃/C in exhibiting the highest capacity (178 mAh g⁻¹) and negligible fade (4%) and the demonstrated cyclability under the influence of 10 C rate has been understood as a function of the synergistic effect of the ODHAC synthesis method and the optimum concentration of Co dopant chosen for the study.