Solid electrolyte interphase (SEI)

The solid electrolyte interphase (SEI) is a thin, protective layer that forms on the surface of a battery’s anode (typically graphite) during initial charging. It results from chemical reactions between the electrode and the electrolyte. The SEI allows lithium ions to pass through while preventing further undesirable reactions, helping stabilize the battery’s performance and prolonging its lifespan. Think of it as a safety coating that forms to improve battery stability. Good SEI formation is essential for efficient, safe, and durable rechargeable batteries, such as those used in smartphones and electric vehicles.