Comprehensive analysis of gas production for commercial LiFePO4 batteries during overcharge-thermal runaway

The failure and fires have increasingly become puzzles that may not be ignored for Li-ion batteries (LIBs). Overcharging is notoriously difficult to detect in the early stage. To address this problem, eight types of commercial LiFePO4 batteries are used to evaluate overcharge-thermal runaway (TR) properties in a sealed chamber, including surface temperature, voltage, pressure, and vent gas. And a gas-based fault diagnosis method is proposed based on the gas results. The results show that the Tmax and Pmax of the cells are between 121-150 degrees C and 132-144 kPa except for the battery type 3. The primary gases measured by the gas chromatograph are CO, H2, CO2, and alkanes, and the total amount of gases ranges from 12 to 45 mmol. Moreover, the proportions of H2 and CO2 both exceeded 30 %. Furthermore, the overcharge-warning experiment showed that H2 was outperformed by CO and CH4, and the capture time was 271 s and 579 s earlier than smoke and TR. Once the gases are detected, TR may be completely suppressed, and the battery neither smokes nor fires. The gas-based TR method is significantly superior to the traditional method in terms of reliability and rapidity. This study can provide a reference for the fault diagnosis of LIBs.

Automated summary

This study investigates the problems of overcharging and thermal runaway in Li-ion batteries. By evaluating commercial LiFePO4 batteries and analyzing gas results, a gas-based fault diagnosis method is proposed. The results show that the temperature and pressure ranges of the cells are within certain limits, and the gas analysis indicates the proportions of CO2 and H2 exceed 30%. The overcharge-warning experiment demonstrates the effectiveness of gas detection in preventing thermal runaway and associated hazards.