Modeling Li-Ion Battery Temperature and Expansion Force during the Early Stages of Thermal Runaway Triggered by Internal Shorts

Abstract

Thermal runaway of Li-ion batteries is a major safety issue. It is a complex process involving high heat generation, fast temperature rise and significant amounts of generated gas. Modeling thermal runaway will enable a better understanding and earlier detection of the phenomenon. Since the majority of the thermal runaway incidents are triggered by an internal short circuit, this paper presents a model describing lithium-ion battery thermal runaway triggered by an internal short. In this study, two internal short circuit experiments were conducted on two nickel manganese cobalt oxide pouch cells, one that was fully charged and one half charged. The fully charged cell went into a quick thermal runaway, while the half-charged cell evolved only into a slow, self-discharge process. Both of these experiments demonstrate that a huge battery swelling force signal can be detected prior to the surface temperature rise during an internal short circuit event. This thermal runaway model is the first attempt to connect gas generation with force signal, and successfully capture the early stages of thermal runaway, including the early rise of force signal, after parameter tuning. This model’s use of force measurement enables higher confidence in the early detection of thermal runaway induced by an internal short.