Elucidating the Origin of Intensified Thermal Safety Concerns of Practical Next‐Generation High‐Energy‐Density Li‐Ion Batteries

High‐specific‐energy battery systems, crucial for powering heavy‐lift unmanned aerial vehicles (UAVs) and electric vertical take‐off and landing (eVTOL) aircraft, are regarded as key enablers for the development of the low‐altitude economy. However, their commercialization remains hindered by significant thermal safety concerns. In this work, using an ultrahigh Ni‐rich layered oxide cathode (Ni accounts for 96%) paired with a mixed Si@C anode as a model system, we systematically investigate real‐time gas evolution behavior and elucidate the underlying mechanisms of gas generation at both cathode/anode electrodes, along with their crosstalk reactions during thermal runaway. The results reveal severe gas emission from the Si@C anode, with H 2 constituting 71.12% (mass ratio) of the total gas released. Meanwhile, the Ni96 cathode releases active oxygen species (O n− /O 2 ) at elevated temperatures (e.g., 220°C), which react with reducing gases generated from the Si@C anode and electrolyte, thereby triggering the onset of thermal runaway. Furthermore, a specially tailored low‐hydrogen (low‐H) electrolyte is employed to effectively suppress H 2 evolution, thereby enhancing the safety of high specific energy battery systems. These insights into gas evolution mechanisms provide a foundation for the targeted design of battery materials and the formulation of practical safety strategies for the low‐altitude sector.