Study of Thermal Decomposition of Li1‐x(Ni1/3Mn1/3Co1/3)0.9O₂ Using In‐Situ High‐Energy X‐Ray Diffraction

Safety has been a major technological concern hindering the deployment of lithium‐ion batteries for automobile applications. We investigated the decomposition mechanism of delithiated cathode materials at thermal abuse conditions using Li 1.1 [Ni 1/3 Mn 1/3 Co 1/3 ] 0.9 O 2 as a model cathode material. An in‐situ high‐energy X‐ray diffraction technique was established as an alternative to conventional thermal analysis techniques like differential scanning calorimetry and accelerating rate calorimetry. The X‐ray diffraction data revealed that the thermal decomposition pathway of delithiated Li 1‐x [Ni 1/3 Mn 1/3 Co 1/3 ] 0.9 O 2 strongly depended on the exposed chemical environment, like solvents and lithium salts. A phase transformation of dry delithiated Li 1‐x [Ni 1/3 Mn 1/3 Co 1/3 ] 0.9 O 2 was observed at about 278 °C, and its onset temperature was reduced to about 197°C with the presence of the electrolyte. It is suggested that the reduction in thermal stability is possibly related to proton intercalation into the delithiated material.