Li-ion cells are being developed for high-power applications in hybrid electric vehicles currently being designed for the FreedomCAR (Freedom Cooperative Automotive Research) program. These cells offer superior performance in terms of power and energy density over current cell chemistries. Cells using this chemistry are the basis of battery systems for both gasoline and fuel cell based hybrids. However, the safety of these cells needs to be understood and improved for eventual widespread commercial application in hybrid electric vehicles. The thermal behavior of commercial and prototype cells has been measured under varying conditions of cell composition, age and state-of-charge (SOC). The thermal runaway behavior of full cells has been measured along with the thermal properties of the cell components. We have also measured gas generation and gas composition over the temperature range corresponding to the thermal runaway regime. These studies have allowed characterization of cell thermal abuse tolerance and an understanding of the mechanisms that result in cell thermal runaway.
To address lithium-ion cell safety issues in demanding power applications, electrical and thermal abuse tests were performed on 18650 sized cells. Video and electrically monitored abuse tests in air included short circuit, forced overcharge, forced reversal, and controlled overheating (thermal) modes. Controlled overheating tests to 200 C were performed in a sealed chamber under a helium atmosphere and the gases released from the cell during thermal runaway were analyzed at regular intervals using gas chromatography and mass spectrometry. In addition to alkane and alkene solvent breakdown fragments, significant H{sub 2} was detected and evidence that HF was evolved was also found.
Abuse tests were conducted on the lead-acid batteries used to power electrical testers used at the Department of Energy's Pantex Plant. Batteries were subjected to short circuits, crushes, penetrations, and drops. None of the observed responses would be a threat to nuclear explosive safety in a bay or cell at Pantex. Temperatures, currents, and damage were measured and recorded during the tests.