Battery Safety: A systematic study of battery performance under extreme conditions
Open Access
- Author:
- Sawlsville, Julie A
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Chao Yang Wang, Thesis Advisor/Co-Advisor
- Keywords:
- Lithium Ion Battery
Safety
Short Circuit
Constant Voltage
Inrush Current
Limiting Current
Automotive
GATE Program
ECEC - Abstract:
- Safety has become a critical issue for Li-ion batteries, which are becoming more frequently used in new generation vehicles. In this study, commercial coin cells (2032, with capacity 40 mAh) and cylindrical cells (18650, with capacity of 2250 mAh) are studied systematically under extreme conditions to investigate the safety issue of Li-ion batteries. The cells were subjected to standard short circuit (constant resistance) tests and a novel constant voltage test. The constant voltage discharge test was used to determine how batteries perform under low voltages to calculate the limiting current. The cells were tested at their nominal voltage, 3.6 V, as well as 3 V, and 2 V. The coin cell was also tested at 1 V and 0.5 V. Upon the start of each discharge the cell current shows a sharp peak and then gradually decreases. This test was repeated at one higher and three lower ambient temperatures for coin cells with similar current and temperature trends observed for each test. Linear trends were observed for the coin cell with respect to inrush current and maximum temperature rise vs. discharge voltage. The 18650 cell test was performed at room temperature and also exhibited linear trends for inrush current and maximum temperature rise vs. discharge voltage. The results of the constant voltage tests are used to determine the limiting current of the cells using a linear regression of the data to extrapolate to 0V. The limiting current was 2.23 A (equivalent to 56 C) for the coin cell and 88.1 A (equivalent to 39 C) for the 18650 cell. The constant resistance tests were performed on the cell to determine how it behaves under short circuit conditions as well as to obtain limiting current data for comparison with the calculations from constant voltage tests. Both cell types showed very high inrush current at the start of discharge but rapidly decreased to lower values and then gradually decreased. The inrush currents increased with decreasing resistance for both cell types, however the 18650 cell experienced higher currents overall. The maximum temperature rise for the coin cell tests did not vary much with the external resistance, while that for the18650 cell increased with decreasing external resistance. The inrush current during short circuit test was 2.51 A for the coin cell (with constant resistance of 0.026 Ω) and 85 A for 18650 cell (with constant resistance of 0.050 Ω ). These inrush current values are very close to the limiting currents obtained from the constant voltage tests. The coin cells survived all the extreme condition tests with maximum temperature lower than 50 C, but 18650 cells failed during 2 V constant voltage test and 0.050 Ω short circuit test with surface temperature up to 122 C. The results clearly demonstrate that safety issue is much more serious for larger format Li-ion batteries and more efforts are warranted.