Influence of the Cr content on the electrochemical behavior of the LiCryMn2-yO4 (0 ≤ y ≤ 1) compounds -: II.: Cyclovoltammetric study of bulk and superficial processes

In the 3.8-4.3 V range, deintercalation of Li from the title compounds, occurs in one or two well resolved steps (depending on y) which are single-phase phenomena for y > 0. For 0 < y 0.5, the first step capacity is constant, whereas the second decreases rapidly. For larger y values, the only remaining step is the first, whose capacity decreases linearly with y, down to zero for y = 1. An interpretation based on Li-Li repulsive interactions which play a role when y < 0.5 and disappear when y > 0.5, is proposed. In the 4.3-5.2 V range, deintercalation of Li occurs in two steps (at similar to4.55 and similar to4.92 V for 0 < y 0.12 and at similar to4.75 V and similar to4.92 V for 0.12 < y 0.75) which are single-phase phenomena. For y less than or equal to 0.75, the cyclable capacity increases with y while the irreversible capacity remains low. On the other hand, for y > 0.75 an important capacity loss is observed at the second cycle, and a catalytic effect of the Cr content on the electrolyte oxidation is observed. Above 5.5 V, the kinetics of electronic transfer, associated to the electrolyte oxidation, remains about three times slower than expected for a standard monoelectronic transfer. This oxidation begins similar to0.2 V below, and its kinetics is faster for y = 0.62 compared to y = 0.25. The onset voltage of this reaction is always higher than the end of deintercalation voltage. LiCryMn2-yO4 materials remain remarkably stable against oxidation when they are subjected to high end-of-charge voltages. (C) 2001 The Electrochemical Society.