Influence of the Cr content on the electrochemical behavior of the LiCryMn2-yO4 (0 <= y <= 1) compounds - III. Galvanostatic study of bulk and superficial processes

Changing y in the LiCryMn2-yO4 materials enables the monitoring of the aver age discharge voltage between 4 and 4.5 V. The Cr substitution is beneficia l to the specific energy (and to the specific capacity) that increase,, by 16% compared to LiMn2O4, for 0.25 less than or equal to y less than or equa l to 0.62. The cycling behavior is all the more poor as y is high in the co mposition range 0.62 less than or equal to y less than or equal to 1. The b est cyclability is observed for y = 0.25. Its loss of the relative capacity after 280 cycles is about twice as small as that observed for LiMn2O4. The irreversible capacity, due to electrolyte oxidation, decreases rapidly wit h the cycle number and reaches a limit of about 2 to 6% of the cyclable cap acity, depending on the experimental conditions. This limit is lowered when the end-of-charge voltage is decreased and/or when the charge rate is incr eased. The capacity decrease is negligible for discharge rates slower than D/2 in the 5.4-3.4 V range, and remains smaller than 50% for discharge rate s slower than 8D. The power behavior of materials with y = 0.06, 0.25, and 0.5 has proved to be excellent, with very high powers of similar to 6000 mW g(-1) for energies of 100 mWh g(-1). (C) 2001 The Electrochemical Society.