Synthesis and characterization of Li2Fe0.97M0.03SiO4 (M = Zn2+, Cu2+, Ni2+) cathode materials for lithium ion batteries

Attempts to dope Zn2+, Cu2+ or Ni2+ are made for Li2FeSiO4. The effects of dopant on the physical and electrochemical characteristics of Li2FeSiO4 were investigated. Zn2+ successfully entered into the lattice of Li2FeSiO4 and induced the change of lattice parameters. Compared with the undoped Li2FeSiO4, Li2Fe0.97Zn0.03SiO4 has higher discharge capacity, better electrochemical reversibility and lower electrode polarization. The improved electrochemical performance of Li2Fe0.97Zn0.03SiO4 can be attributed to the improved structural stability and the enhanced lithium ion diffusivity brought about by Zn2+ doping. However, Ni2+ and Cu2+ cannot be doped into the lattice of Li2FeSiO4. Cu and NiO are formed as impurities in the Cu- and Ni-containing samples, respectively. Compared with the undoped Li2FeSiO4, the Cu- and Ni-containing samples have lower capacities and higher electrochemical polarization.