Abstract
State-of-Health (SoH) is a critical parameter for determining the safe operating area of a battery cell and battery packs to avoid abuse and prevent failure and accidents. Experiments were performed at the US Naval Research Laboratory (NRL) on a 4P1S cell array using pulsed discharge and electrochemical impedance spectra (EIS) to determine a single-point SoH frequency for the array as a whole. Individual cell EIS measurements were taken, as well as measurements of the array as a whole. This work will discuss experimental results to date.
Highlights
The US Naval Research Laboratory has initiated a series of experiments to evaluate the performance of a 4P1S battery array using electrochemical impedance spectroscopy to identify key frequencies that may describe battery state of health at any state of charge
When the fSOH is examined for a set of four cells discharged in parallel, the individual EIS response for each cell shows an accelerated rate of aging versus data from baseline batteries
The aggregate imaginary impedance at 158 Hz for all four cells in parallel appears to be very sensitive to battery SOH, with a sudden change to an oscillation pattern that correlates to a drop in energy delivered per cell to the load
Summary
The US Naval Research Laboratory has initiated a series of experiments to evaluate the performance of a 4P1S battery array using electrochemical impedance spectroscopy to identify key frequencies that may describe battery state of health at any state of charge. Using a large sample number of cells, the state of health frequency, fSOH, for these LiFePO4 26650 cells is found to be 158 Hz. When the fSOH is examined for a set of four cells discharged in parallel, the individual EIS response for each cell shows an accelerated rate of aging versus data from baseline batteries. The aggregate imaginary impedance at 158 Hz for all four cells in parallel appears to be very sensitive to battery SOH, with a sudden change to an oscillation pattern that correlates to a drop in energy delivered per cell to the load.
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