THE CARBON LI1+XMN2O4 SYSTEM

In this paper, we review our studies of the rocking-chair cells based on carbon (coke or graphite) as the negative electrode, and the spinel LixMn2O4 as the positive electrode. A brief history of Li-ion batteries is first discussed to emphasize the advantages of the Li-based metal oxide/C system and the practical benefits of the Li1+xMn2O4/C system. The major findings that made possible the successful implementation of the spinel LixMn2O4 into practical Li-ion cells are presented with emphasis on the optimization of both electrode/electrolyte interfaces. These include (1) an improvement of the initial capacity and the capacity fading characteristics of the lithiated manganese oxide positive electrode upon cycling upon cycling through extensive studies of the thermal synthesis (annealing temperatures and cooling rates) of lithiated manganese oxide containing a varying lithium content, (2) understanding the mechanism of electrolyte oxidation at high voltage (up to 5 V versus Li) to minimize the irreversible capacity loss in order to both enhance the cycle life and diminish the self-discharge, and (3) enhancement of the carbon electrode capacity. We show that three-electrode cells are a powerful tool to understand and optimize the behavior of the carbon/LixMn2O4 rocking-chair cells and we propose a technique to quantify precisely the irreversible capacity due to electrolyte oxidation on LixMn2O4 at high voltage. These findings were reduced to practice through the construction of AA-size prototypes with enhanced safety characteristics and performance similar to that of similar laboratory tests cells.