Experimental study on flame stability limits of lithium ion battery electrolyte solvents with organophosphorus compounds addition using a candle-like wick combustion system

Abstract

To evaluate the fire-retardant effectiveness of organophosphorus compounds (OPC) added to Li-ion battery electrolyte solvents, the limiting oxygen concentration (LOC) method is used in conjunction with a wick combustion system, called as wick-LOC method. With the wick-LOC method, two modes of stabilized flame are found, namely, wake flame and full flame. When OPC is added to the electrolyte, two distinct branches of extinction processes occur according to the different flame modes near extinction with no transition from the full flame to the wake flame in the case of higher OPC addition. The flame stability limits are measured as a function of OPC addition for both flame modes. The wake flame is shown to be consistently more stable at low levels of OPC addition. However, once the OPC addition exceeds a critical amount, the full flame shows higher stability with a lower LOC than the wake flame. These phenomena in the two regimes are also found in other cases of high OPC addition (different type of OPC and electrolyte solvent). In the most stable flame mode, the regime switches from the wake flame to the full flame with increasing OPC addition, and they are defined correspondingly as “blow-off regime” and “quenching regime”. To explain the presence of these two regimes, the thermal balance effect is considered in the discussion of flame extinction mechanisms. The difference in flame volume near the extinction limit shows that the quenching mechanism dominates flame extinction under higher OPC addition. The thermal balance effect on flame stabilization or extinction can be the additional impact on the fire retardation abilities of OPC itself.