Li‐ion batteries (LIBs) that promise both safety and high energy density are critical for a new‐energy future. However, recent studies on battery thermal runaway (TR) suggest that the higher the energy is compressed in a battery, the thermal accidents with fires and explosions can occur in a more catastrophic way. This “trade‐off” between energy density and safety poses challenging obstacles toward the future applications of the developing high‐energy chemistries. Herein, the thermal studies on the most appealing high‐energy (HE)‐LIB chemistries are carefully reviewed. The TR characters of the HE‐LIBs, the material thermal failure behaviors as well as the underneath reaction mechanisms, and the most advanced TR mitigation technologies are comprehensively summarized. Moreover, the effectiveness of different TR mitigation routes is analyzed. Based on the analysis, the main challenges for TR mitigation in HE chemistries are further explained. Finally, opinions on the future TR mechanism studies and the promising safety design routes to overcome this intrinsic “trade‐off” between high energy and safety are presented.