Effects of electrolyte/cathode ratio on investigation of their thermal behaviors using differential scanning calorimetry

Battery materials with high-energy density and good safety performance have been regarded as the ultimate target for larger-scale applications of lithium-ion batteries in electric transportation and grid energy storage. Thermal safety of high energy density cathode materials has been a hot topic for battery safety research in recent years. Differential scanning calorimetry (DSC) is widely used to investigate thermal reaction characteristics of battery materials, but the results are always affected by multiple variables, e.g., sample pre-processing and testing conditions. The variety of DSC results reported in literature have been perplexing the research community. Herein, the cathode-electrolyte system is chosen to reveal the changes of reaction mechanisms with different electrolyte/cathode ratios, since this system has been widely adopted to characterize thermal stability of cathodes and electrolytes in previous studies. Lithium-rich manganese-based layered oxide cathode and ester-based electrolyte are selected as representative samples. Our results reveal that flooded, sufficient, insufficient, and lean electrolyte conditions may lead to distinct thermal behaviors from probably different reaction routines, which may hold different reference values for battery-level safety analysis. This study also suggests the importance of systematic investigations on test conditions in battery material thermal safety research.