Changes in the stage structure of Li-intercalated graphite electrode at elevated temperatures

Abstract

To examine the phase transition upon deintercalation of Li from graphite at elevated temperatures, structural changes in C6Lix (x = 0.284, 0.532, 0.666, 0.739, 0.812) samples during heating were evaluated by in situ X-ray diffraction (XRD) analysis. The diffraction patterns of the sample, in which the stage-1 and the stage-2 structures coexist, drastically converted to the profile of a Li-defect stage-1 structure at temperatures above 200 °C without Li intercalation and/or deintercalation. Meanwhile, the reflection peak corresponding to the stage-1 structure in the XRD patterns of C6Li0.812 continuously shifted to higher angles at temperature above 330 °C, which implied deintercalation of Li through reaction with the binder and the formation of the Li-defect stage-1 structure. Li deintercalated from C6Lix while maintaining the same stage structure, likely via a solid-state reaction at temperatures above 330 °C. The lattice misfit calculated from the difference in interlayer spacing between stage-1 and stage-2 in C6Li0.666 drastically decreased from 4.58% at 50 °C to 1.43% at 350 °C. These kinetics for Li graphite intercalation compounds at elevated temperatures are formulated for the first time and should be helpful in understanding the Li intercalation/deintercalation mechanism of the graphite electrodes used in Li-ion batteries.