Fire and explosion hazards represent a major barrier to the widespread adoption of lithium-ion batteries (LIBs) in electric transportation and energy storage systems. Although mitigating the flammability of linear organic carbonate electrolytes in LIBs is an obvious solution to the thermal safety issue, it often comes at the expense of battery performance and costs. Here, combining alkyl chain extension and alkoxy substitution that decreases solvent volatility and increases solvation power simultaneously, we demonstrate that molecular engineering of the linear carbonates presents a viable route to achieve thermally stable high-performance batteries. While the tailored molecule bis(2-methoxyethyl) carbonate (BMEC) exhibits a 90°C higher flash point than the conventional ones, it still maintains the electrolyte quality enabling long-lasting cycling of the flagship electrode combination of graphite and Ni-rich layered oxide over 400 cycles in practical pouch cells. As opposed to the commercial electrolyte, we prove that the BMEC electrolyte effectively alleviates heat and reactive gas release under thermal/mechanical/electrical abuse conditions in the presence of charged electrodes, thereby preventing the thermal explosion of a 4 Ah pouch cell upon nail penetration.