Evaluation of Lithium-Ion Battery Thermal Runaway Initiation and Propagation: A Cross-Standard, Multilevel Evidence-Chain and Equivalence-Assessment Framework

Thermal runaway (TR) initiation and propagation tests are essential for evaluating the safety of lithium-ion batteries (LIBs). However, differences among existing standards in application scenarios, test levels, initiation methods, boundary conditions, and acceptance criteria hinder direct comparison and cross-level transfer of safety evidence. This study reviews representative standards and experimental research concerning road vehicles, industrial batteries, stationary energy storage, and railway transportation. External heating, nail penetration, overcharge, built-in devices, and induction heating are compared in terms of target failures, energy input, structural disturbance, and source-term characterization. The analysis shows that TR initiation methods, together with cell chemistry, state of charge, capacity, and format, determine thermal, gaseous, and ejecta source terms. Cell spacing, electrical connections, thermal management, mechanical constraints, and enclosure ventilation and pressure relief further govern propagation pathways and system-level consequences. Accordingly, a multilevel evidence chain is proposed, encompassing target-failure definition, cell-level initiation-method qualification, module- or representative-propagation-unit validation, pack/system-level consequence assessment, and product-change review. A six-risk-domain equivalence-assessment method is also established to address source terms, topology, thermal pathways, protection, enclosure boundaries, and personnel exposure. The framework provides a traceable basis for interpreting cross-standard results, validating large-scale LIB systems hierarchically, and inheriting safety evidence following product changes.