(504d) Determination of Safety Parameters in Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have raised increasing interest due to high energy density and efficient energy storage. LIBs are used not only in portable electronics, such as cell phones and computers, but also for energy storage systems (UPS and Grid applications.), and electric vehicles. LIB’s offer; excellent performance, high energy density, high specific capacity & voltage, no memory loss, very little self-discharge, and a wide operating temperature range. This has made LIBs increasingly popular. However, safety is a major concern, and a large number of LIBs have been recalled due to explosion and fire accidents. Consequently, increasing attention is being paid to LIB safety issues and a large number of safety strategies are being developed.

The safety of a battery is determined by the battery chemistry, its operating environment, and its abuse tolerance. The internal failure of a LIB is caused by electrochemical system instability. Thus, understanding the material properties, electrochemical reactions, and side reactions occurring in LIBs is fundamental in assessing battery safety. Temperature and voltage are the two controlling factors of the battery reactions. Safety accidents are accompanied by continuous heat and gas generation, which causes battery rupture and ignition of the combustible materials. Cells are equipped with safety features such as separator shut down to stop the flow of current and opening of the vent to help prevent the cell from bursting and/or catching fire in addition to others.

In this study, a testing method was developed using accelerating rate calorimeter (ARC®) to determine thermal behavior of a cell under thermal abuse conditions. Onset temperature of self-heating of the cell, separator shutdown temperature, leak/vent temperature, and ignition temperature of the cell were all determined. The two types of cells that were tested were cylindrical 18650 cells and polymer pouch cells. All tests were run with 100% state of charge. Attached below is an ARC test result from a polymer pouch cell (4.2V, 1800 mAh). It was found that the separator shutdown temperature was 140°C, the primary self-heating onset temperature was 134°C, and ignition temperature was 160°C. Cell leak temperature was found to be in the range of 141°C to 147°C.