Influence of positive temperature coefficient and battery aging on external short circuit for 18,650-type battery

This work investigates the influence of positive temperature coefficient (PTC) and battery aging on external short circuit (ESC). The voltage, current and temperature changes for batteries after ESC are analyzed. Based on the results, the ESC characteristics are divided into four stages. At the first stage, the discharging current and voltage increases and decreases fast at the moment of ESC. Temperature of lithium-ion battery starts to increases. At the second stage, the discharging current decreases slowly. Voltage of battery increases and becomes stable slowly. These two stages are the same to other studies. At the third stage, the resistance of PTC increases after its temperature increase. The discharging current of battery decreases to the minimum. Joule heat in the “jelly roll” decreases to the minimum. However, the heat generation in PTC increases. The heat is transferred from the top of steel case to the bottom. Temperature of battery increases to the maximum and remains after that for a long time. At the fourth stage, resistance of PTC decreases owing to its temperature decrease. Battery voltage and discharging current increase with the decrease of PTC resistance. Although PTC can be used to prevent thermal runaway for 18,650-type lithium-ion battery caused by ESC, long high temperature interval is also an issue to be solved. Resistance and capacity of aged batteries increases and decreases. Discharging current is lower for aged batteries after ESC. Time interval for the second stage and third stage increases and decreases, as lower Joule heat rate in the second stage and faster discharging current decrease at the third stage. The maximum temperature of aged batteries increases owing to the occurrence of lithium plating. Compared to capacity, resistance has a bigger impact on ESC for 18,650-type lithium-ion battery.