A Fast Diagnostic to Inform Screening of Discarded or Retired Batteries

TL;DR

This paper proposes a rapid internal resistance measurement method for retired lithium-ion battery cells, enabling efficient screening of their capacity for secondary use without extensive testing.

Contribution

The study introduces a quick, SOC-independent resistance assessment technique validated against HPPC tests for retired batteries.

Findings

Resistance remains constant across mid to high voltages

Internal resistance correlates linearly with capacity

Resistance measurement can predict capacity without SOC knowledge

Abstract

With the increased pervasiveness of Lithium-ion batteries, there is growing concern for the amount of retired batteries that will be entering the waste stream. Although these batteries no longer meet the demands of their first application, many still have a significant portion of their initial capacity remaining for use in secondary applications. Yet, direct repurposing is generally not possible and each cell in a battery must be evaluated, increasing the cost of the repurposed packs due to the time intensive screening process. In this paper, a rapid assessment of the internal resistance of a cell is proposed. First, this method of measuring the resistance is completed on cells from twelve retired battery packs and one fresh pack using a hybrid pulse power characterization (HPPC) test as a benchmark for the analysis. Results from these tests show relatively constant resistance measurements across mid to high terminal voltages, allowing this metric to be independent of state of charge (SOC). Then, the relation between internal resistance and capacity across the various packs is discussed. Initial experimental results from this study show a correlation between internal resistance and capacity which can be approximated with a linear fit, suggesting internal resistance measurements taken above a threshold cell terminal voltage may be a suitable initial screening metric for the capacity of retired cells without knowledge of the SOC.