The Solid-Electrolyte-Interphase (SEI) model, introduced by E. Peled in 1979, has revolutionized the understanding and development of lithium batteries. Prior to this model, researchers used the Butler-Volmer equation, which assumed direct electron transfer from the electrode to lithium cations in the solution. The SEI model demonstrated that this assumption was incorrect and that electron transfer from the electrode to the solution must be prevented to avoid fast self-discharge and poor battery performance. This model provided new equations for electrode kinetics, anode corrosion, SEI resistivity, growth rate, and irreversible capacity loss in lithium-ion batteries. The SEI layer, formed when an alkali metal comes into contact with the electrolyte, consists of insoluble and partially soluble reduction products of electrolyte components. It acts as a solid electrolyte interphase, preventing the transfer of electrons from the electrode to the solution. The SEI is crucial for the safety, power capability, morphology of lithium deposits, shelf life, and cycle life of batteries. Techniques such as X-ray Photoelectron Spectroscopy (XPS), SEM, X-ray Diffraction (XRD), and others have been used to study the SEI's chemical and physical properties. The SEI formation process involves multiple reduction reactions of salts, solvents, and impurities, leading to the precipitation of inorganic compounds like LiF, LiCl, and Li2O, as well as the formation of Li2CO3 and semi-carbonates. The SEI's structure is complex, with a compact core and a porous outer layer that enhances mechanical stability and flexibility. The SEI's thickness and composition depend on various factors, including the type of carbon, temperature, electrolyte components, and current density. The SEI's role in lithium-ion batteries is critical, affecting battery performance, safety, and longevity. The SEI's ability to minimize the risk of dendrite formation and thermal runaway under overcharge conditions is particularly important. The SEI's chemical composition and properties are temperature-sensitive, affecting battery performance at extreme temperatures. Efforts to detect polymers in the SEI have been made to prevent their detrimental effects on battery performance and safety. The SEI model has been extended to include lithium-metal and lithium-ion batteries, as well as future systems such as silicon-based anodes, lithium-sulfur, lithium-air, sodium, potassium, and calcium batteries. The SEI's formation, kinetics, and growth are influenced by various factors, and ongoing research aims to optimize its properties for improved battery performance and safety.The Solid-Electrolyte-Interphase (SEI) model, introduced by E. Peled in 1979, has revolutionized the understanding and development of lithium batteries. Prior to this model, researchers used the Butler-Volmer equation, which assumed direct electron transfer from the electrode to lithium cations in the solution. The SEI model demonstrated that this assumption was incorrect and that electron transfer from the electrode to the solution must be prevented to avoid fast self-discharge and poor battery performance. This model provided new equations for electrode kinetics, anode corrosion, SEI resistivity, growth rate, and irreversible capacity loss in lithium-ion batteries. The SEI layer, formed when an alkali metal comes into contact with the electrolyte, consists of insoluble and partially soluble reduction products of electrolyte components. It acts as a solid electrolyte interphase, preventing the transfer of electrons from the electrode to the solution. The SEI is crucial for the safety, power capability, morphology of lithium deposits, shelf life, and cycle life of batteries. Techniques such as X-ray Photoelectron Spectroscopy (XPS), SEM, X-ray Diffraction (XRD), and others have been used to study the SEI's chemical and physical properties. The SEI formation process involves multiple reduction reactions of salts, solvents, and impurities, leading to the precipitation of inorganic compounds like LiF, LiCl, and Li2O, as well as the formation of Li2CO3 and semi-carbonates. The SEI's structure is complex, with a compact core and a porous outer layer that enhances mechanical stability and flexibility. The SEI's thickness and composition depend on various factors, including the type of carbon, temperature, electrolyte components, and current density. The SEI's role in lithium-ion batteries is critical, affecting battery performance, safety, and longevity. The SEI's ability to minimize the risk of dendrite formation and thermal runaway under overcharge conditions is particularly important. The SEI's chemical composition and properties are temperature-sensitive, affecting battery performance at extreme temperatures. Efforts to detect polymers in the SEI have been made to prevent their detrimental effects on battery performance and safety. The SEI model has been extended to include lithium-metal and lithium-ion batteries, as well as future systems such as silicon-based anodes, lithium-sulfur, lithium-air, sodium, potassium, and calcium batteries. The SEI's formation, kinetics, and growth are influenced by various factors, and ongoing research aims to optimize its properties for improved battery performance and safety.