Because of their high specific and volumetric energy density, lithium-ion cells are popular in energy storage systems with strict mass and volume restrictions. Such applications include electric vehicles, power tools, consumer electronics, all-electric aircraft, as well as high-reliability military and crewed spacecraft. Next-generation rechargeable lithium cell designs are characterized by higher specific energy which further increases the severity of thermal runaway (TR) safety hazards. Even with carefully controlled high-quality manufacturing processes, TR can occur unpredictably due to latent defects inside the cells causing internal short circuits. This work elaborates on the lessons learned from cell and battery pack safety research for crewed spacecraft applications.