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

Abstract

ABSTRACT 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.