Effect of Cr dopant on the cathodic behavior of LiCoO2

Compounds of the formula LiCo1-yCryO2 (0.0 less than or equal to y less than or equal to 0.20 and y = 1.0) have been synthesized by high temperature solid-state reaction and were characterized by XRD and FT-IR. Hexagonal a and c lattice parameters increase with increasing y as expected from ionic size effects. Cyclic voltammograms reveal that the phase transformation occurring at x = 0.5 in Li1-x(Co1-yCry)O-2 is suppressed for y = 0.05 and 0.10. Low-current (0.01 C; 1 C = 140 mA g(-1)) galvanostatic charging curves show that the deintercalation voltage for y = 0.05 and 0.10 decrease for a given x as compared to LiCoO2. Galvanostatic charge-discharge cycling of the Li(Co1-yCry)O-2 cathodes at 0.14 C and 2.7-4.3 V (vs. Li) show that increasing amount of chromium content in the LiCoO2 lattice drastically reduces the amount of Li that can be reversibly cycled. Ex-situ XRD of the cycled cathodes show that slight cation-mixing occurs in the layered structure for y = 0.05 and 0.10 and could be the reason for their poor electrochemical performance. Reversible Li intercalation/deintercalation is not possible in LiCrO2 in the voltage range 2.7-4.3 V. (C) 2002 Published by Elsevier Science Ltd.