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.

Li-ion Battery Fault Detection in Large Packs Using Force and Gas Sensors

“…The internal short circuit region is a small area inside the cell. The localized heating Q ohmic due to the ISC, causes a rapid local temperature increase, while temperature for the rest of the cell remains relatively constant during the early stages of thermal runaway (see Cai et al (2019b)).…”

“…For hard internal short circuits, the battery internal temperature can be elevated in a few seconds, causing a large temperature gradient inside the cell. In Cai et al (2018Cai et al ( , 2019b, the authors divided the battery into three temperature sections and showed that at the early stage of ISC, the battery surface temperature rise is much slower than the voltage drop and the expansion force rise. In Lammer et al (2017), the authors showed that a large amount of CO 2 is released with the first venting during a thermal runaway event.…”

“…For internal short circuit events that evolve without going into thermal runaway, cell surface temperature increase is limited (Cai et al (2019b)) and the fault is even more difficult to detect by conventional methods using voltage and temperature measurements. If left undetected, the cell might develop into a thermal runaway after continuous use (Zhang et al (2017)).…”

“…This type of event features a fast drop and quick recovery of the voltage and is named as the "Fusing Phenomenon" in Zhang et al (2017). In this internal short, the high temperature in the ISC region will trigger battery side reactions, which produce a large amount of gas (Cai et al (2019b)). The generated gas leads to the swelling of the pouch cell that can be measured as a sudden increase in expansion force at the pack level.…”

An experimental study on the mechanical characteristics of Li‐ion battery during overcharge‐induced thermal runaway

“…It is also concluded that the expansion force can diagnose the ISC faster and with higher confidence levels than voltage and temperature alone. 23 An internal short detection methodology based on force measurement with high accuracy is proposed. 24 It has been confirmed that gas generated from SEI layer decomposition is the root cause of the huge expansion force.…”