Electrode material designs for lithium rechargeable batteries

Abstract

In this study, the solid solution of spinel $(2/3)Li(Li_{1/3}Ti_{5/3})O_4 - (1/3)Li(Ni_{1/2}Ti_{3/2})O_4$ as an anode material and the olivine $Li(FeCo)_{0.05}Mn_{0.9}PO_4$ as a cathode material were investigated for the improved properties of lithium secondary batteries. In the anode material, the structural/electrochemical properties of solid solution of spinel $(2/3)Li(Li_{1/3}Ti_{5/3})O_4 - (1/3)Li(Ni_{1/2}Ti_{3/2})O_4$ were compared with $Li(Li_{1/3}Ti_{5/3})O_4$ to identify the effect of doping to the structural invariance of $(2/3)Li(Li_{1/3}Ti_{5/3})O_4$. The solid solution retained the zero strain characteristic of $(Li(Li_{1/3}Ti_{5/3})O_4$ during discharge/charge with an excellent cycle stability, while the rate capability was notably improved. However, a reversible broadening of the XRD peak was observed at the end of discharge, indicating some structural changes. XAS measurements showed that the oxidation state of Ti was +4 and that of Ni was +2 in the solid solution. In the cathode material, the structural/electrochemical properties of olivine $Li(FeCo)_{0.05}Mn_{0.9}PO_4$ were compared with $Li(FeCo)_{0.05}Mn_{0.9}PO_4$ and $LiMnPO_4$ to identify the effect of small amounts of co-doping of Fe and Co. The rate capability of $Li(FeCo)_{0.05}Mn_{0.9}PO_4$ was notably improved. Easier and more frequent nucleation by Fe and Co in Mn-based olivines significantly enhanced the rate capability as evidenced by the electrochemical results.