During the first charge and discharge of the liquid lithium-ion battery, the electrode material reacts with the electrolyte at the solid-liquid interface to form a passivation layer covering the surface of the electrode material. The formed passivation film can effectively prevent the passage of solvent molecules, but Li can be freely embedded and exfoliated through the passivation layer, with the characteristics of a solid electrolyte, so this passivation film is called \"solid electrolyte interface\" (SEI).
SEM refers to the reaction of the negative electrode with the electrolyte to generate a dense film, which is attached to the surface of the negative electrode, and the SEM only allows Li ions to pass, which is equivalent to isolating the other components of the electrolyte and lithium ions