Electrochemical properties and thermal stability of LiaNi1-xCoxO2 cathode materials

Conductive and electrochemical properties as well as thermal stability of L iaNil-xCoxO2 where x = 0-0.3 and a = 1.0-0.4 have been studied using impeda nce spectroscopy, galvanostatic intermittent titration technique, cyclic vo ltammetry, electrochemical cycling, and differential scanning calorimetry ( DSC). The electronic conductivity of partially charged material (a less tha n or equal to 0.8) increases substantially when the cobalt content is incre ased to x = 0.3 from 0.2. The mobility, chemical diffusion coefficient, and Li+ ion diffusion coefficient in the partially charged material are in the neighborhood of 10(-6) cm(-2)/V s, 10(-8) cm(2)/s, and 5 x 10(-10) cm(2)/s , respectively, and are rather insensitive to the values of a and x. Result s of electrochemical and DSC studies show that LiNi0.7Co0.3O2 is the best c athode material for a Li cell of all materials studied here in view of the best cycle stability, the smallest irreversible capacity, and the greatest thermal stability with minimal reduction of specific capacity from that of LiNiO2. (C) 2000 The Electrochemical Society. S0013-4651(99)04-113-9. All r ights reserved.