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Thermal Runaway in Li-ion Batteries – Initiation & Safety Strategies

Sneha Lele

Technological advancements and rapidly increasing manufacturing capacities with reduced costs has resulted in a steep increase in popularity of Lithium-ion (Li-ion) batteries for grid storage applications. The current market for grid-scale battery storage both in the US and globally is dominated by Li-ion chemistries. Since the widespread adoption of Li-ion batteries for grid storage applications, several incidents have occurred raising safety concerns. For grid energy storage applications, owing to the large scale of batteries, system complexity and use conditions, battery safety is of utmost importance. Single cell field failures, particularly in large battery systems require consideration of how these failures can impact neighboring cells and subsequently the entire system. To prevent this cascading effect, battery systems must be well designed with redundant protection features. In the absence of a commonly accepted methodology to evaluate propagation resistance in a large battery system, a UL 1973 Internal Fire Task Group was set up in 2016. This has resulted in the induction of the ‘Tolerance to internal cell failure’ tests in Edition 2 of UL 1973-2018 (Standard for Batteries for Use in Stationary, Vehicle Auxiliary Power and Light Electric Rail (LER) Applications). The intent of this test is to evaluate system tolerance by simulating thermal runaway in a single cell using techniques that emulate real-life occurrences in the field as closely as possible.

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