Current and temperature imbalances in parallel-connected grid storage battery modules

TL;DR

This paper investigates current and temperature imbalances in large grid storage battery modules, quantifies their evolution through simulations and experiments, and proposes robustness metrics to mitigate failure risks.

Contribution

It provides a detailed analysis of imbalance causes, thresholds, and mitigation strategies for parallel-connected lithium iron phosphate battery modules.

Findings

Contact and cell resistances significantly influence temperature differences.

Safety thresholds depend on cell and module parameter variations.

Lower C-rates and narrower SOC ranges reduce failure risks.

Abstract

A key challenge with large battery systems is heterogeneous currents and temperatures in modules with parallel-connected cells. Although extreme currents and temperatures are detrimental to the performance and lifetime of battery cells, there is not a consensus on the scale of typical imbalances within grid storage modules. Here, we quantify these imbalances through simulations and experiments on an industrially representative grid storage battery module consisting of prismatic lithium iron phosphate cells, elucidating the evolution of current and temperature imbalances and their dependence on individual cell and module parameter variations. Using a sensitivity analysis, we find that varying contact resistances and cell resistances contribute strongly to temperature differences between cells, from which we define safety thresholds on cell-to-cell variability. Finally, we investigate how these thresholds change for different applications, to outline a set of robustness metrics that show how cycling at lower C-rates and narrower SOC ranges can mitigate failures.