Thermal structural behavior of electrochemically lithiated graphite (LixC6) anodes in Li‐ion batteries

A full series of variously lithiated graphite anodes material LixC6 (0<x<1) corresponding to a different state‐of‐charge (SOC) between 0% and 100% was collected from 18650‐type cylinder Li‐ion batteries, and the thermal structural behavior of these electrodes was mapped using ex situ high‐resolution X‐ray and neutron diffraction. Their structural behavior was analyzed over a broad temperature range. At high temperatures, a non‐reversible decomposition of the lithiated graphite anodes takes place, accompanied by a loss of intercalated lithium ions, forming novel phases such as LiF and Li2O strongly coupled to the degradation of the solid electrolyte interface (SEI). Complementary calorimetric measurements showed the strongly exothermic chemical reactions during the decomposition matching well to the collected diffraction data. Post mortem analysis applying scanning electron microscopy revealed various morphological features supplementing the treatment of battery anodes and highlighted the importance of the SEI layer during the cycling of the cell and its thermal degradation.