Structural stability during charge-discharge cycles in Zr-doped LiCoO 2 powders

Abstract

Zirconium-doped Li1.1Co1-xZrxO2 (0≤x≤0.05) powders as cathode materials for lithium ion batteries were synthesized using an ultrasonic spray pyrolysis method. Cyclic voltammetry and cyclic stability tests were performed, and the changes of microstructure were observed. The solubility limit of zirconium into Li1.1CoO2 was less than 5 mol%, and monoclinic Li2ZrO3 phase was formed above the limit. The Zr-doping suppressed the grain growth and increased the lattice parameters of the hexagonal LiCoO2 phase. The Zr-dopiong of 1 mol% resulted in the best cyclic performance in the range of 3.0∼4.3 V at 1C rate (140mA/g); the initial discharge capacity decreased from 158mAh/g to 60mAh/g in the undoped powder, while from 154mAh/g to 135mAh/g in the Zr-doped powder of 1 mol% after 30 cycles. The excellent cycle stability of Zr-doped powder was due to the low polarization during charge-discharge processes which resulted from the delayed collapse of the crystal structure of the active materials with Zr-doping.