Distinguishing the thermal behavior of Na- and Li-intercalated hard carbons via differential scanning calorimetry

The thermal stabilities of Na- and Li-intercalated hard carbons were examined by differential scanning calorimetry (DSC) to determine whether Na-ion batteries or Li-ion batteries exhibit superior thermal stability. The DSC profiles of both C6Na0.65 and C6Li0.65 displayed sharp exothermic peaks with enthalpy changes of ~1200 J·g−1, which could be attributed to the reaction between C6Na0.65 (or C6Li0.65) and PF5. Hence, the total amounts of heat generated in these Na- and Li-ion batteries were equal, regardless of the intercalants present. However, the temperatures corresponding to the maximum exothermic peaks differed between the two battery systems (i.e., 184 °C for C6Na0.65 and 264 °C for C6Li0.65), indicating that Na-ion batteries are less thermally stable. The DSC profile of C6Li0.25Na0.37 revealed that this difference is due to differences in the solid-electrolyte interphase films between C6Nax and C6Liy.