Understanding the Influence of Temperature on Phase Evolution during Lithium-Graphite (De-)Intercalation Processes: An Operando X-ray Diffraction Study

Abstract

Knowing the phase evolution behavior of battery materials is important for optimizing the operating conditions and understanding the aging behavior of the material. Phase changes of state-of-the-art battery materials at room temperature are well understood, but the influence of temperature on the phase evolution is barely investigated. In this study, operando X-ray diffraction (XRD) is applied for the observation of phase changes of graphite during cycling at different temperatures. The phase evolution is altered at lower temperatures (0 °C) compared to room temperature due to slower kinetics and diffusion rates even at low current rates of C/20. Differences in phase evolution between charge and discharge are more pronounced at 0 °C compared to higher temperatures. During delithiation at 43 °C, the formation of stage 2L is more distinct than at 25 °C whereas at 0 °C, no stage 2L formation is observed. However, at 0 °C, several phases co-exist, supporting the theory of the shrinking annuli mechanism for phase evolution during (de-)lithiation of graphite.