Mechanistic understanding of silicon-graphite composite anode thermal stability in lithium-ion batteries

Understanding the mechanistic evolution of thermal instability in silicon-graphite (Si-C) composite anodes is crucial for advancing the safety and reliability of lithium-ion (Li-ion) cells. This study investigates the coupled influence of silicon content and state-of-charge on the thermo-electrochemical stability and safety of Li-ion cells comprising composite Si-C anodes and LiNi_xCo_yMn_zAl_1-x-y-zO₂ (NCMA) cathodes. The pivotal role of Si-C composition in inducing mechanistic tradeoffs with respect to the electrochemical performance, impedance characteristics, and thermal stability is revealed. Achieving enhanced thermo-electrochemical stability requires an optimal Si-C composition, as Si-free formulations offer minimal improvements, while excessive silicon increases internal resistance and thermal instabilities. Through a comprehensive thermal stability analysis, combining accelerating rate calorimetry and mechanistic modeling, we identify the impact of silicon dopants in affecting the anode-silicon exothermic reactions and mitigating the solid electrolyte interphase decomposition and anode-binder interactions. Cognizant of the thermo-kinetic reaction mechanisms, a hierarchical modeling framework is established to predict the thermal runaway behavior of large-format Si-C based Li-ion cells. The proposed thermal analytics framework establishes a baseline for evaluating the thermal stability and safety of Si-based Li-ion chemistries, providing critical insights for designing next-generation batteries with high energy density.