Thermochemical Crosstalk in Si‐C Anodes: Mechanism and Stabilization via a Polymerizable Phosphorus‐Based Additive

ABSTRACT Silicon–carbon (Si─C) anodes enable high energy density but suffer from poor thermal safety due to their strong reactivity with electrolytes. In this work, we identify the thermochemical reaction mechanism between lithiated silicon and carbonate solvents, revealing the formation of Si─C bonds as direct evidence of electrolyte decomposition. Density functional theory calculations confirm the reaction's spontaneity, establishing that the deteriorated safety of Si─C cells originates from the intrinsic Si–electrolyte reaction that intensifies anode–cathode crosstalk during thermal runaway. To validate this mechanism, tripropargyl phosphate (TPP) is introduced as an electrolyte additive. Its alkyne groups effectively scavenge protons and suppress hydrogen generation, leading to reduced gas evolution and delayed exothermic onset. Compared with the FEC system, the TPP‐based electrolyte demonstrates lower H ₂ release and reduced thermal runaway peak temperature by 30 °C. Moreover, TPP facilitates the formation of a uniform and inorganic‐rich SEI, enhancing interfacial stability and cycling performance. This study provides new insights into the design of safer high‐energy Si‐based lithium‐ion batteries.