Analytical study of dark spots on anode surface in high energy-density lithium-ion cells

There are three types of visible surface stains on the lithium-ion cell graphite anode. These are dark spots, bubble spots, and lithium plating. Dark spots are formed by a different mechanism from the other two types of stains, while bubble-spots and lithium-plating can be well demonstrated. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, nuclear magnetic resonance, and Raman spectroscopy used to analyze dark spots and normal anode regions. These analyses indicate that the dark spots are mainly caused by imperfect solid electrolyte interface formation, which affects the structural stability of the graphite resulting in cell capacity and safety.