Structural Evolution of LiMn2O4 in Lithium-Ion Battery Cells Measured In Situ Using Synchrotron X-Ray Diffraction Techniques

We describe synchroton based X-ray diffraction techniques and issues related to in situ studies of intercalation processes in battery electrodes. We then demonstrate the utility of this technique, through a study of two batches of LiMn2O4 cathode materials. The structural evolution of these spinel materials was monitored in situ during the initial charge of these electrodes in actual battery cells. Significant differences were observed in the two batches, particularly in the intercalation range of x = 0.45 to 0.20. The first-order structural transitions in this region indicated coexistence of two cubic phases in the batch 2 material, whereas the batch 1 material showed suppressed two-phase coexistence. Batch 2 cells also indicated structural evolution in the low-potential region below 3.0 V in contrast to the batch 1 material. Differences in structural evolution between batches of LiMn2O, could have important ramifications in their cycle life and stability characteristics.