LAUSR

Thermal runaway is a major safety concern hindering the large‐scale application of Ni‐rich lithium ion batteries. In this paper, the thermal runaway behaviors of lithium ion batteries with LiNi0.6Co0.2Mn0.2O2 and LiNi0.8Co0.1Mn0.1O2 cathode materials are investigated using accelerating rate calorimetry. The onset temperature of thermal runaway for the battery with LiNi0.8Co0.1Mn0.1O2 cathode is 20°C lower than that with LiNi0.6Co0.2Mn0.2O2 cathode, demonstrating that battery thermal runaway is highly correlated with cathode chemistry. In situ X‐ray diffraction and thermogravimetry tests further reveal that the LiNi0.8Co0.1Mn0.1O2 exhibits more severe structural change and oxygen generation compared to LiNi0.6Co0.2Mn0.2O2, leading to worsen of battery thermal runaway behavior. Based on the correlation between cathode thermal stability and battery thermal runaway, an approach by changing cathode morphology from polycrystal to single crystal is proposed to mitigate the thermal runaway of battery with LiNi0.8Co0.1Mn0.1O2 cathode. The single crystal LiNi0.8Co0.1Mn0.1O2 can reduce cationic distribution and enhance cathode thermal stability, and thus improve the safety performance of large format Ni‐rich battery by postponing thermal runaway by 13°C and reducing temperature rate.