Mapping safety transitions as batteries degrade: A model-based analysis towards full-lifespan battery safety management

TL;DR

This paper introduces a physics-based framework to dynamically model how battery failure risks evolve over time with degradation, highlighting the limitations of static safety limits and proposing a pathway for full-lifespan safety management.

Contribution

It presents the first comprehensive model capturing evolving safety zones in degrading batteries, integrating multiple failure mechanisms and analyzing their impact on safety boundaries.

Findings

Safety zones change significantly with degradation.

Capacity fade alone is insufficient to assess safety.

Degradation mechanisms influence failure pathways.

Abstract

Battery safety is important, yet safety limits are normally static and do not evolve as batteries degrade. Consequently, many battery systems are overengineered to meet increasingly stringent safety demands. In this work we show that failure behaviour evolves over time as batteries degrade, and discuss the challenges and opportunities to manage battery safety dynamically throughout its lifetime. We introduce the first framework for capturing how the likelihood and severity of battery failures change over time based upon the concepts of safety zones and their boundaries. Through the development of a comprehensive physics-based model that integrates multiple degradation and thermal runaway failure mechanisms, we then show how the safety zones and boundaries of a commercial 21700 battery change after varied use and how these changes may lead to false negatives with existing management strategies. Further analyses reveal that degradation mechanisms strongly affect safety characteristics, causing significant changes despite similar capacity fade, highlighting the limitations of using capacity fade alone to assess batteries' usability. By synthesising our results with literature, we map possible degradation-to-failure pathways and recommend future research needs to achieve full-lifespan battery safety management, with advanced diagnostic and modelling techniques to accurately define state-of-safety for real-world applications as key priorities.