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 H2 constituting 71.12% (mass ratio) of the total gas released. Meanwhile, the Ni96 cathode releases active oxygen species (On-/O2) 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 H2 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.