A review of solid electrolyte interphases (SEI) on lithium metal anodes is presented, highlighting the importance of SEI in inhibiting dendrite growth and enhancing the cycling performance of lithium metal batteries (LMBs). The SEI forms through the reduction and decomposition of electrolyte components, and its structure and composition are influenced by factors such as electrolyte components, temperature, and current density. The SEI layer is crucial for preventing direct contact between lithium and the solvent, ensuring dynamic stability in certain organic solvents, and facilitating the transport of lithium ions from the bulk electrolyte to the anode. The SEI is typically composed of inorganic and organic components, with a thickness of approximately 20 nm. The formation of the SEI involves several steps, including the shedding of solvent molecules by solvated lithium ions, their migration through the SEI, and their deposition on the anode surface. Various mechanisms have been proposed to explain the formation of the SEI, including the Peled model, the mosaic model, and the Coulombic interaction mechanism. The SEI's structure and composition can be analyzed using techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These techniques provide insights into the surface chemistry, morphology, and electrochemical properties of the SEI. However, each technique has limitations, and a combination of methods is often necessary for a comprehensive understanding of the SEI. The SEI's electrochemical properties can be studied using techniques such as electrochemical impedance spectroscopy (EIS), which provides information on the resistance of the SEI layer. The dynamic characteristics of the SEI can be investigated using in situ and in operando technologies, which allow for the observation of the SEI during the charging and discharging processes. Theoretical calculations, such as density functional theory (DFT), have also been used to gain insights into the atomic-level understanding of the SEI. The SEI can be modified through various strategies, including the use of electrolyte additives, ex situ-formed protective layers, and electrode design. The addition of electrolyte additives, such as fluorinated salts and halogenated salts, can enhance the stability of the SEI and improve the cycling performance of LMBs. The SEI can also be modified by introducing new electrolyte systems, such as dual-salt electrolytes, which can provide a more stable and robust SEI layer. Additionally, the use of ex situ-formed protective layers, such as artificial SEI structures, can enhance the stability and performance of LMBs. In conclusion, the SEI plays a critical role in the performance and safety of lithium metal batteries. Understanding the formation, structure, and properties of the SEI is essential for developing stable and efficient LMBs. The use of advanced characterization techniques and theoretical calculations is crucial for gaining a comprehensive understanding ofA review of solid electrolyte interphases (SEI) on lithium metal anodes is presented, highlighting the importance of SEI in inhibiting dendrite growth and enhancing the cycling performance of lithium metal batteries (LMBs). The SEI forms through the reduction and decomposition of electrolyte components, and its structure and composition are influenced by factors such as electrolyte components, temperature, and current density. The SEI layer is crucial for preventing direct contact between lithium and the solvent, ensuring dynamic stability in certain organic solvents, and facilitating the transport of lithium ions from the bulk electrolyte to the anode. The SEI is typically composed of inorganic and organic components, with a thickness of approximately 20 nm. The formation of the SEI involves several steps, including the shedding of solvent molecules by solvated lithium ions, their migration through the SEI, and their deposition on the anode surface. Various mechanisms have been proposed to explain the formation of the SEI, including the Peled model, the mosaic model, and the Coulombic interaction mechanism. The SEI's structure and composition can be analyzed using techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These techniques provide insights into the surface chemistry, morphology, and electrochemical properties of the SEI. However, each technique has limitations, and a combination of methods is often necessary for a comprehensive understanding of the SEI. The SEI's electrochemical properties can be studied using techniques such as electrochemical impedance spectroscopy (EIS), which provides information on the resistance of the SEI layer. The dynamic characteristics of the SEI can be investigated using in situ and in operando technologies, which allow for the observation of the SEI during the charging and discharging processes. Theoretical calculations, such as density functional theory (DFT), have also been used to gain insights into the atomic-level understanding of the SEI. The SEI can be modified through various strategies, including the use of electrolyte additives, ex situ-formed protective layers, and electrode design. The addition of electrolyte additives, such as fluorinated salts and halogenated salts, can enhance the stability of the SEI and improve the cycling performance of LMBs. The SEI can also be modified by introducing new electrolyte systems, such as dual-salt electrolytes, which can provide a more stable and robust SEI layer. Additionally, the use of ex situ-formed protective layers, such as artificial SEI structures, can enhance the stability and performance of LMBs. In conclusion, the SEI plays a critical role in the performance and safety of lithium metal batteries. Understanding the formation, structure, and properties of the SEI is essential for developing stable and efficient LMBs. The use of advanced characterization techniques and theoretical calculations is crucial for gaining a comprehensive understanding of