Engineering Strategies to Suppress Thermal Runaway Propagation in Lithium-Ion Battery: Mechanisms, Metrics, Materials, and Evaluation Methods.

Thermal runaway propagation (TRP) in lithium-ion battery modules and packs represents a critical safety challenge, as failure of a single cell can rapidly escalate into system-level hazards. This review provides an engineering-oriented overview of TRP suppression strategies, focusing on propagation mechanisms, mitigation materials, and evaluation methodologies. First, the distinction between thermal runaway initiation and inter-cell propagation is clarified, emphasizing the roles of conductive, convective, and radiative heat transfers, gas venting, and combustion in driving cell-to-cell failure. The influences of system configuration, propagation modes, and key factors are systematically discussed, along with measurable metrics for TRP risk assessment. Second, materials for TRP suppression are reviewed from a pathway-oriented functional perspective, including thermal buffering, thermal insulation, flame and gas suppression, and multifunctional composite barriers. Particular attention is paid to how these materials are practically integrated into battery modules and packs to interrupt dominant propagation pathways. Finally, experimental and simulation approaches for TRP assessment are reviewed, highlighting propagation experiments performed under different abuse conditions, as well as physics-based and data-driven models. Current challenges and future research directions are outlined. Overall, this review bridges fundamental understanding and engineering practice related to TRP, providing guidance for safer lithium-ion battery systems with enhanced resistance to TRP.