Quantifying Gas‐Phase Crosstalk and SiO/Gr Reactivity Competition Governing Thermal Runaway in Composite‐Anode Batteries

Silicon-graphite composite anodes are pivotal for boosting the energy density of commercial lithium-ion batteries, yet this gain inevitably intensifies internal reactivity and aggravates safety risks. However, the thermal runaway mechanisms of these high-energy-density cells remain incompletely elucidated, hindering safety improvements. Herein, we combine systematic analyses of heat and gas generation, reaction kinetics, and mechanistic modeling to quantitatively unravel the contributions of gas-phase crosstalk and the competitive reactions between silicon and graphite in driving battery thermal runaway. We demonstrate that the heat released from reactions between anode-derived reductive gases and the cathode occurs prior to SEI decomposition and serves as the primary trigger for self-heating. Furthermore, the distinct reactivity of graphite and silicon dictates the sequence of lithium consumption: lithium in graphite is preferentially released to react with the electrolyte at lower temperatures, while the lithium-silicon alloy reacts predominantly with the cathode at elevated temperatures. Increasing silicon content reduces the onset temperature of self-heating while elevating the triggering temperature and peak temperature of thermal runaway. This study highlights the critical role of gas-phase crosstalk and competitive lithium reactions in dictating thermal runaway behavior, providing essential insights for the rational design of safer high-energy-density batteries with silicon-graphite composite anodes.