In-Plane Ordering of Li-Intercalated Turbostratic Graphite for the Negative Electrode of High-Power Long-Life Li-Ion Batteries

Abstract

Turbostratic carbon graphitized at ca. 2000 °C exhibits low discharge capacity but excellent pulse charge/discharge characteristics and long cycle performance. In this study, to clarify the charge/discharge mechanism, the intercalation process of Li into turbostratic graphite was investigated by operando synchrotron X-ray diffraction and 7Li-NMR spectroscopy. The dataset obtained from both methods was synchronously analyzed by treating it as a function of the LiC x composition estimated from the charge/discharge curves. It was found that both the synchrotron X-ray diffraction profile and 7Li-NMR spectrum dynamically changed in conjunction with the composition and the LiC9-type and LiC6-type in-plane structures formed in turbostratic graphite, as in the case of natural graphite when Li ions intercalate. The domain formed by these in-plane structures was a short-range ordered structure that changed depending on the misorientation angle between the two adjacent graphene sheets, and a stage structure with a periodic distance in the c-axis direction did not form, as in the case of natural graphite.