The effect of Ni or Pb substitution on the electrochemical performance of Li2FeSiO4/C cathode materials

Abstract

In this paper, Li2Fe1−xNixSiO4/C, Li2FeSi1−xNixO4/C, Li2Fe1−xPbxSiO4/C and Li2FeSi1−xPbxO4/C(x = 0.01, 0.02, 0.03, 0.05) were synthesized as cathode materials via the high temperature solid-phase method. After synthesizing, a comparative study of the electrochemical properties was conducted on these materials of which Fe site and Si site were doped with Ni or Pb respectively through a range of methods including constant current charge-discharge test, cyclic voltammetry and electrochemical impedance analysis. The study shows that the materials with doping Ni or Pb at Fe site present more stable electrochemical attribute. The initial discharge capacity of Li2Fe0.97Ni0.03SiO4/C is 146.0 mAh/g, and the capacity retention rate is 93.3% after 10 cycles at 0.1 C. The electrochemical performance of Li2Fe0.97Pb0.03SiO4/C is more stable than that of other materials doped with Pb in different doping ratio. Its capacity is 162.2 mAh/g after 10 cycles at 0.1 C, and the capacity retention rate is 95.2%. The initial discharge capacity of the material is improved by Ni or Pb doped at Si site. The initial discharge capacity of Li2FeSi0.98Ni0.02O4/C and Li2FeSi0.97Pb0.03O4/C is equivalent to 1.06 and 1.08 Li+ deintercalation respectively. Furthermore, Li2Fe0.97Ni0.03SiO4/C, Li2FeSi0.98Ni0.02O4/C, Li2Fe0.97Pb0.03SiO4/C and Li2FeSi0.97Pb0.03O4/C were selected for SEM and XRD tests. The graph of SEM shows that the particle size of Li2Fe0.97Ni0.03SiO4/C and Li2Fe0.97Pb0.03SiO4/C are uniform and no obvious agglomeration phenomenon could be observed. The XRD shows that there is no the peak characteristic of Fe, Li2SiO3 and Li2Fe3O4. The cell volume of Li2Fe0.97Ni0.03SiO4/C and Li2Fe0.97Pb0.03SiO4/C is increased and the electrochemical property of them is stable.