Reductive gas manipulation at early self-heating stage enables controllable battery thermal failure

Li-ion batteries are regarded as unsafe due to the volatility and flammability of the organic liquid electrolytes. However, research on substitutes (solid, inorganic, etc.) still encounters tough obstacles toward commercialization. Here, we manage to control the thermal failure process of liquid batteries by manipulating the deleterious reactions at an earlier stage, where heat accumulates mildly before accelerating to catastrophes. We reveal that the reductive gases, specifically those with low bond dissociation energies (unsaturated hydrocarbons as alkenes and alkynes), can induce cathode crystal change with oxygen release and initiate and accelerate battery thermal failure from lower than 80°C. Four safety countermeasures to break this "reductive attack" pathway are designed and successfully prevent commercial Li-ion batteries from thermal runaway (capacity of 60 Ah and energy density of 280 Wh kg−1). We anticipate that our new safety insights and methodologies will overcome the limitations of liquid electrolytes for safe energy applications.