Decisive Factors in the Sequential Thermal Decomposition Reactions of Ni-Based Layered Cathode Materials

Understanding thermal behaviors of energy storage materials according to the charged states is essential to uncover the key factors for improving thermal stability. Herein, we trace the crystallographic changes of Ni-based layered energy storage materials during an increase in external temperature for three different states-of-charges. The most remarkable aspect is that the onset temperature of the formation of disordered spinel structure is dominantly influenced by the intermediate tetrahedron size, the space through which the cations pass. However, the completion temperature is determined by the Li contents of the Li layer. Moreover, a highly charged state triggers the rapid reduction of Ni ions, resulting in a sudden lattice expansion during the thermally induced decomposition reaction, aggravating the danger of thermal runaway. These findings give a detailed comprehension of the crystallographic behaviors of Ni-based layered materials during the thermal decomposition reaction and contribute to designing rechargeable batteries with better thermal stability.