Recognizing the mandates in sustainability and material abundance, sodium-ion batteries hold great potential in being alternate chemistry for applications such as grid storage systems. Along with other performance matrices, the safety problem known as “thermal runaway” must be understood and overcome for the practical realization of sodium-ion batteries in countless applications. While the physiochemical properties of the model electrode materials play a major role in determining overall thermal stability, electrolyte-derived unstable solid electrolyte interphases (SEI) can also trigger early thermal instability. Since the sodium-ion battery has a highly soluble SEI layer, especially in carbonate electrolytes, it is essential to understand the thermal instability signatures of electrode-electrolyte interactions. So far, the interfacial driven thermal stability of sodium-ion battery electrodes remains largely unexplored. Herein, we aim to investigate the intrinsically stochastic and heterogeneous nature of the SEI layer, illustrating the role of carbonate and glyme solvents in determining the overall thermal stability of the cell. The fundamentals of the thermal failure issues explored in this work can pave the way toward building a safer sodium-ion battery.