Electrochemical investigation of the Li insertion-extraction reaction as a function of lithium deficiency in Li1-xNi1+xO2

The electrochemical characteristics of Li1 - xNi1 + xO2 samples have been extensively investigated as a function of the lithium deficiency x in the narrow composition range 0.008-0.065. In particular, the electrochemical and structural behaviours of the quasi-stoichiometric compound (x = 0.008) have been proved to be strongly different from those exhibited by a sample with x = 0.025. The faster kinetics for Li transport combined with structural changes which are minimized in the quasi-ideal compound explain the lack of notable polarization voltage and the good cycle life of the latter cathode material with a stable capacity of 140 A h/kg over 40 cycles at C/10 rate. In addition, interesting and useful correlations (i) between the cathode impedance and the lithium deficiency and (ii) between the evolution of the cathode impedance and the cycling performance have been established. (C) 2001 Elsevier Science Ltd. All rights reserved.