ISO/TR 20891:2020 is a technical report published by the international standards organization (ISO) on the on-orbit health assessment of lithium-ion batteries in space systems. The standard details the health assessment methods of lithium-ion batteries during flight, including the collection and analysis of battery performance data and the assessment process of health status (SoH). It emphasizes the importance of data mass and makes targeted recommendations for different orbital environments such as GEO and LEO. The standard also addresses the application of advanced detection technologies such as electrochemistry Impedance Spectroscopy (EIS), providing scientific assessment guidelines for spacecraft manufacturers, battery suppliers and operators to ensure the safety and Reliability of lithium-ion batteries in extreme space environments.