Doping effects of zinc on LiFePO₄ cathode material for lithium ion batteries

Alien atom doping has been adopted to modify the electrochemical performance of olivine type LiFePO₄ for cathode material of the lithium ion batteries. Here, we first report that zinc-doping can improve the performance of LiFePO₄. The effects of zinc-doping have been studied by the measurements of X-ray diffraction pattern, scanning electronic microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The results indicate that the zinc atoms do not destroy the lattice structure of LiFePO₄, and enlarge the lattice volume. During de-intercalation and intercalation process of lithium ions, the doped zinc atoms protect the LiFePO₄ crystal from shrinking. This kind of "pillar" effect provides larger space for the movement of lithium ions. Consequently, the conductivity is enhanced and the lithium ion diffusion coefficient is boosted after doping. These favourable changes are beneficial to the improvement of the electrochemical performance of LiFePO₄ including discharge capacity and rate capability.