# Investigation into the Fire Hazards of Lithium-Ion Batteries under Overcharging
## 4 Conclusions  
In order to have a better understanding of the fire hazards of overcharged LIB, two widely used commercial LIBs, NMC and LFP, with different cut-off voltage (4.2 V, 4.5 V, 4.8 V and 5.0 V), were tested in this work. The detailed analysis of the burning phenomena, the surface temperature, the flame temperature, voltage, and radiative heat flux offered here represents a comprehensive understanding of the fire hazards posed by burning LIB. The main conclusions are as follows:  
1. The initial discharging voltage increases with the growth of charge cut-off voltage. A battery with higher cut-off voltage possesses a higher initial discharging voltage. Moreover, the higher the cut-off voltage, the longer the discharging time to reach 2.5 V.
2. LIB has a significant temperature rise during charging and discharging under the effect of irreversible heat (\(Q_{irr}\)) and reversible heat (\(Q_{rev}\)). Compared with the NMC battery, the LFP battery exhibits a more obvious temperature rise during the process.
3. Compared to the normal LIB, the overcharged LIB experiences earlier safety vent cracks, ignition, and thermal runaway. This reveals that the overcharged LIB possesses a more serious combustion process and a lower stability than the normal LIB. Moreover, the severity will deteriorate with the increase of cut-off voltage. The higher the voltage, the more reactive the electroactive materials of  
Figure 12: The schematic of yir electrochemical model.  
Figure 13: The schematic of s battery catching fire.  
the battery will become. In addition, it is revealed that the NMC fails earlier than the LFP under the same conditions.
4. After thermal runaway, the temperature rise rate of LIB grows with the increase in the cut-off voltage. A battery with higher cut-off voltage will experience a more violent combustion if ignited. Moreover, it is interesting to note that the safety vent cracks temperature, the ignition temperature, and the thermal runaway temperature exhibit similar values for the same conditions, which demonstrates that LIB will fail at a certain temperature. The cut-off voltage has little influence on these parameters, which mainly depend on the incident heat.
5. For the NMC battery, the peak heat flux rises with the increase in voltage. The total radiative heat flux and total radiative heat also present the similar phenomenon. This indicates that the NMC with higher voltage will release more heat after catching fire. As for the LFP battery, it exhibits similar circumstances except for the 5.0 V LFP, whose peak heat flux and total radiative heat show an obvious drop compared to the others. This is attributed to the violent ejection of a highly overcharged battery, resulting in incomplete combustion and less heat being released.  
Finally, it is expected that these results could be a reference for use in assessing LIB safety problems, especially when they are in a state of overcharge. Much more work is needed to have a detailed understanding of the fire hazards of LIB.  
This work was supported by the National Nature Science Foundation of China (No. 51376172).  
[PERSON], [PERSON], [PERSON], and [PERSON] wrote this work together.  
The authors declare no conflicts of interest.