Electrochemical Investigations of Mn and Al Co-doped Li2FeSiO4 /C Cathodes for Li-Ion Battery

Few studies on orthosilicate cathodes co-doped with two cations have been reported until now. Here, we report the synthesis of Mn and Al co-doped Li2Fe0 .8− x Mn0.2Al x SiO4 (x = 0.05 and 0.1) by a solid-state reaction route and characterized by X-ray diffraction (XRD), particle size analysis, scanning electron microscopy (SEM), galvanostatic charge/discharge tests, and capacity intermittent titration technique (CITT), as compared to the single-doped Li2Fe0.8Mn0.2SiO4. Though the co-doping leads to a slight decreased capacity owing to the increased impurity and Al3+ inertia, a better cycling performance is obtained as expected. Especially when x is 0.05, the modified sample (Li2Fe0.75Mn0.2Al0.05SiO4) shows an initial discharge capacity of 159.3 mAh/g and high capacity retention of 78% after 50 charge/discharge cycles. The present work indicates that a synergistic effect of Mn and Al co-substitution at the Fe site could partly make up the disadvantage of single Mn doping, and might provide an effective guide for the dopant incorporation to Li2FeSiO4 systems.