• PDF / 2,845,367 Bytes
• 24 Pages / 439.37 x 666.142 pts Page_size
• 29 Downloads / 226 Views

DOWNLOAD

REPORT

---

Characterization of Thermally Induced Runaway in Pouch Cells for Propagation Erik Archibald , Department of Civil Engineering, The University of Texas at Austin, Austin, TX, USA Robert Kennedy, Kevin Marr and Ofodike Ezekoye, Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA Judith Jeevarajan, Underwriters Laboratories, League City, TX, USA Received: 28 September 2019/Accepted: 17 March 2020

Abstract. Thermal runaway of lithium-ion batteries is particularly dangerous in systems where runaway can propagate through many cells. To understand thermal runaway propagation in these systems, it is important to understand the differences between failure characteristics of the initial cell that fails due to an abuse event and subsequent cells that fail due to thermal runaway propagation. This work compares thermal runaway events for single cells failed using a heater with cells failed due to propagation in an array. Most of the tests were conducted in an inert environment within a pressure vessel. Cell clamping stress, vessel gas pressure and temperature data show that runaway in cells within an array traverses the cells more slowly and releases gas at a slower rate than singly failed cells. For heater-initiated cell failure, post-experiment cell teardowns suggest that thermal runaway originates at a single point and creates a gas flow stream that causes heavy damage and exits from one side of the cell. Teardowns of cells which failed due to array propagation show more uniform damage and gas release from a larger area. Keywords: Lithium-ion safety, Thermal runaway, Failure propagation, Thermal runaway propagation

1. Introduction Lithium-ion batteries are becoming increasingly common in energy storage systems, electric vehicles, and consumer devices. Under some misuse conditions or because of defects, internal exothermic reactions can occur in cells causing a thermal runaway (TR) state. During thermal runaway, cells can release large amounts of hot flammable gas. When runaway propagates from cell to cell in a module comprised of cells, these systems can present a serious fire and explosion risk. Many previous studies have examined the thermal runaway behavior of single cylindrical cells, such as the 18650 cylindrical cell [1–6]. Others have examined thermal runaway of prismatic cells [7, 8]. Unlike cylindrical and prismatic cells where gases are typically released through a burst disc or safety vent, pouch cells are not designed with safety vents and may vent from any side of the cell. Since *Correspondence should be addressed to: Ofodike Ezekoye, E-mail: [email protected]

1

Fire Technology 2020 the location of venting is uncertain, this makes it more difficult for system designers to design modules that exhaust hot gases in a preferred direction. Additionally, mitigating TR propagation for arrays of pouch cells is more difficult than for cylindrical cells due to more intimate heat transfer contact between the cells (i.e., high contact area and minimal separation between cells). Vario