Preparation and Electrochemical Characterization of Overlithiated Spinel LiMn2 O 4

Abstract

Parasitic reactions taking place at the carbon anode are primarily responsible for the capacity loss that occurs during the “formation cycles” of a carbon/ Li‐ion battery. The additional amount of cathode material required to supplement this irreversible capacity leads to a reduction in the specific energy of the battery. This can be overcome with the use of the overlithiated cathode material, , in which the excess Li, x, is used to compensate the irreversible apacity at the anode. This investigation highlights the usefulness of n‐BuLi reduction to synthesize from and demonstrates the long‐term rechargeability of these materials in Li cells. Reaction of cubic spinel with BuLi to form overlithiated cathode materials of the general formula (x = 0.1–1.0) was found to be quantitative under mild conditions at room temperature. The X‐ray diffraction of each appeared to represent a nominal composition of a two‐phase material consisting of and at a‐x:x mole ratio, where x represents the number of moles of reacted with BuLi. Electrochemical characterization of indicated that the chemically introduced Li(x in ) could be extracted nearly 100% in a voltage plateau around 3.0 V vs. . Furthermore, the rate capability and cycle life of these materials when cycled between 4.25 and 3.0 V were identical to those of the baseline . In balanced carbon/ full cells, the chemically inserted Li could be fully utilized to compensate for the irreversible capacity loss occurring in their formation cycles.