Impact of Battery Size and Charge on the Thermal Runaway of Lithium Ion Batteries

Abstract

Catastrophic battery failure is typically studied at or near full charge of the battery. This is generally assumed to be the worst-case scenario, and it is taken as conventional wisdom that the risk of thermal runaway is very low below 50% state of charge. Further, due to cost and safety issues, the bulk of laboratory scale battery abuse testing and careful calorimetry work is performed on relatively small cells (<5 AH). However, little has been reported on how data collected using these smaller cells scales to the large cells proposed for advanced energy storage applications, such as electric drive vehicles and grid scale energy storage. This work looks at how thermal failure of lithium ion batteries may scale as both the size of the battery and state of charge are changed. Different battery chemistries are observed using over temperature (thermal ramp) testing as well as large volume Accelerating Rate Calorimeters (ARC) to observe how the energy release and kinetics of thermal runaway scale as battery size increases, and through this discuss the benefits and limitations of smaller scale calorimetry. ARC is used as well to observe the nature of thermally induced battery failure as the state of charge changes. As part of these results we explore the difference between the total heat released during battery failure, which has been observed to scale relatively linearly with state of charge, and the kinetics of battery failure, which has been observed in this work to scale exponentially at high states of charge (>80% SOC). A large format battery at a low state of charge may still have the potential for a significant amount of energy release even if a rapid thermal runaway is unlikely. This is of particular concern in large battery systems where well insulated cells in close contact with one another may see a propagating failure due to the significant amount of energy available to heat surrounding cells even if the thermal runaway of a single cell is unlikely. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.