Surface Modification of LiCoO₂ by NASICON-Type Ceramic Materials for Lithium Ion Batteries

Three types of NASICON-type ceramic materials which are Li_1.3Al_0.3Ti_1.7(PO₄)₃, Li_1.3Sc_0.15Y_0.15 Ti_1.7(PO₄)₃ and Li_1.3Al_0.3Zr_1.7(PO₄)₃ are prepared by a solid-state reaction for surface modification of LiCoO₂ by mechano-chemical fusion coating. Ionic conductivity of the prepared ceramic electrolytes are evaluated as temperature changes, Li_1.3Al_0.3Ti_1.7(PO₄)₃, Li1.3Sc0.15Y0.15Ti1.7(PO₄)₃ and Li_1.3Al_0.3Zr_1.7(PO₄)₃ exhibit the high ionic conductivity of 6.49×10⁻⁴ S cm⁻¹, 5.61×10⁻⁴ S cm⁻¹ and 4.85 × 10⁻⁴ S cm⁻¹, respectively, at room temperature. Under the high cut-off potential for utilization large amount of lithium, the surface modification by ionic conducting coatings improves cycleability and rate capability of the lithium ion batteries. As ionic conductivity of coating materials increases, the coated LiCoO₂ exhibits the better electrochemical performances. With AC impedance analyses, it is elucidated that the NASICON surface-coatings greatly relieve the interfacial resistance between LiCoO₂ electrode and electrolyte.