Thermal Stability of Graphite Electrode as Cathode for Dual-Ion Batteries

The increasing number of accidents relating to battery fire and explosion is raising people's attention towards safety of batteries. Abnormal battery operation can generate much heat and cause thermal runaway due to the exothermic reactions of the electrodes and electrolyte. Recently, dual-ion battery (DIB) has gained many interests because of its low cost and high working voltage compared with traditional lithium-ion battery (LIB). However, investigation on thermal stability of DIB is rare. In this paper, differential scanning calorimetry (DSC) was used to study the thermal stability of DIB using graphite as cathode with different states of charge (SOC) and with different amount of fluoroethylene carbonate as co-solvent in the electrolyte. Then, the thermal stability of graphite cathode for DIB was compared with those of LiCoO₂ and LiNi_0.5Mn_1.5O₄ at their fully charged states. Specifically, charged DIB using graphite as cathode in 3 M LiPF₆ EMC showed superior thermal stability with no exothermic peaks in DSC tests, in contrast to traditional lithium-containing cathodes for LIB, which gave out significant amount of heat at evaluated temperature. In addition, the thermal stability of graphite depended on the type of intercalation species in it. While PF₆⁻ intercalated graphite [C_n(PF₆)] showed an endothermic peak at about 320°C, Li⁺ intercalated graphite [C_n(Li)] showed an exothermic peak at about 300 °C. Moreover, the type of electrolyte also affected heat generation from the charged electrodes and should be properly designed to improve thermal stability in the future.