In situ TEM studies of the oxidation of Li dendrites at high temperatures

Although lithium (Li) is inert to dry oxygen at room temperature, it reacts with dry oxygen at elevated temperatures, causing thermal runaway and fire hazard in Li metal batteries (LMBs). However, the oxidation mechanism of Li at high temperatures is not explored. Here, real-time transmission electron microscopy studies of the effect of temperature on the oxidation mechanisms of Li dendrites are reported. The oxidation is controlled by the outward diffusion of Li${}^{+}$ through the oxide layer (the Wagner oxidation mechanism), forming thin films of Li${}_2$O comprising nanograins at temperatures between 100 and 140 °C. When the temperature is between 160 and 200 °C, the oxidation product is plate-like LiOH due to the presence of trace amount of water vapor in the atmosphere. When the temperature is above 300 °C, the oxidation product becomes single crystalline Li${}_2$O nanocubes. Density function theory calculations reveal the Li oxidation chemistry is controlled by the thermodynamics and kinetics of the interactions between O${}_2$ or H${}_2$O and Li${}_2$O at high temperatures. These results provide an important understanding of the microscopic oxidation mechanism of Li at elevated temperatures, which sheds lights on the thermal runaway of LMBs. (© 2022 Wiley‐VCH GmbH)