Thermal Safety Analysis of Disordered Li-Rich Rock salt Li_1.3Mn_0.4Nb_0.3O₂ Cathode

The improvement of Li-ion battery energy density greatly depends on the cathode composition/material. Recently, a Li-rich rock salt cathode, Li1.3Mn0.4Nb0.3O2, has gained significant attention as a promising cathode material because of its ability to extract more than one Li reversibly leading to a high theoretical capacity (>300 mA h g–1) and high operating potential (>4 V). However, rapid capacity decay, voltage fade, and increased voltage hysteresis with cycling still need to be addressed despite the intense effort to understand the electrochemical behavior and degradation mechanism. Furthermore, there is little understanding of the thermal properties and their implication on battery safety. Considering this important knowledge gap, we studied the thermal decomposition mechanism in a Li-rich rock salt cathode system under different charged and discharged conditions employing differential scanning calorimetry (DSC). The DSC results infer that Li1.3Mn0.4Nb0.3O2 under discharged conditions exhibited the least thermal stability as compared to both charged and pristine ones with an exothermic onset temperature of 118 °C. Moreover, the results show that Li1.3Mn0.4Nb0.3O2 is more likely to cause a thermal runaway as compared to the state-of-the-art of cathode materials. In addition, the temperature-dependent scanning transmission electron microscopy–energy-dispersive X-ray spectrometry mapping and ex situ X-ray diffraction measurements suggest that the thermal stability of Li1.3Mn0.4Nb0.3O2 is limited by the reaction of the transition metal with electrolyte.