Analysis of Intercalation/De-Intercalation of Li Ions Into/From Graphite at 0 °C via Operando Synchrotron X-ray Diffraction

The charge/discharge reaction mechanisms of graphite negative electrodes in Li ion batteries were investigated via operando synchrotron X-ray diffraction at 0 degrees C and 25 degrees C. The intercalation of Li ions at 25 degrees C formed the stage 1 compound with an in-plane structure of LiC6; while intercalation at 0 degrees C only formed stage 2, with in-plane structures of LiC9 and LiC6. The degree of graphite expansion in the a, b-axes and c-axis directions by intercalation at 0 degrees C was less than that at 25 degrees C. Hence, it was difficult to form the stage 1 structure by further increases in the Li ion concentration, and the charging reaction at low temperature became difficult. De-intercalation at 0 degrees C did not follow the Daumas-Herold model and proceeded discretely in the order: stage 1 -> stage 2 -> stage 4 -> graphite, without going through stages 3, 5-8 and dilute stage 1.

Automated summary

The charge/discharge reaction mechanisms of graphite negative electrodes in Li ion batteries were studied using operando synchrotron X-ray diffraction at 0 degrees C and 25 degrees C. The intercalation of Li ions at different temperatures resulted in different stage compounds and varying degrees of graphite expansion. The de-intercalation process did not follow the expected pattern at low temperatures.