Thermal runaway mechanisms and early-warning strategy determination of LiNi_0.8Co_0.1Mn_0.1O₂ batteries through material and cell levels analysis

Thermal runaway (TR) remains the most critical safety challenge limiting the large-scale application of lithium-ion batteries. A comprehensive understanding of the internal chain reaction mechanisms and their correlation with external early-warning signals is urgently required. This study establishes a stepwise analytical framework from single component and binary/ternary mixtures to full cells to bridge the gap between material-level reaction mechanisms and cell-level signal features. TG-DSC-MS experiments on designed component combinations revealed the underlying reaction mechanisms. These mechanisms were correlated with the synchronous evolution of multidimensional signals, including temperature, expansion force, voltage, and the concentrations of five characteristic gases (H₂, CO, CO₂, HF, and VOCs), during cell-level overheating tests. Through this cross-scale correlation, a three-stage “initiation-acceleration-runaway” chain-reaction pathway is identified for the first time at material level and subsequently validated against cell-level signal evolution, clarifying the transition from internal chemistry to observable failure. Specifically, the initiation stage is driven by cathode/electrolyte interfacial reactions, while the acceleration stage is governed by EC ring-opening polymerization occurring in the presence of lithiated graphite, and the runaway stage is triggered by the uncontrolled oxidative reactions initiated by cathode oxygen release. The TR process is further divided into five consecutive stages with distinct critical signal thresholds. Based on this mechanism-signal correspondence, a four-level hierarchical early-warning strategy is established, enabling early detection up to 698 seconds before TR. This work offers a viable pathway for translating mechanistic insights into quantifiable warning indicators, thereby bridging the gap between mechanistic understanding and engineering application.