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Title A Single-Frequency Impedance Diagnostic for State of Health Determination in Li-ion 4P1S Battery Packs
Publication Date
Date Accessioned
Degree PhD
Discipline/Department Electrical Engineering
Degree Level doctoral
University/Publisher Virginia Tech
Abstract State-of-Health (SoH), a specified measure of stability, 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. A series of experiments were performed 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. Four experiments were performed to evaluate the lifetime in different configurations: single-cell at 1C (2.6A), single-cell at 10C (26A), four cells in parallel at 10C (ideal match), and four cells in parallel (manufacturer match). The lifetime for each experiment set degraded substantially, with the final parallel series reaching end of life at 400 cycles, a 75.32% reduction in life compared to operating solo. Analysis of the fSoH data for these cells revealed a change in imaginary impedance at the critical frequency that corresponded to changes in the capacity and current data, supporting the development of a single-frequency diagnostic tool. An electrochemical model of the battery was generated, and it indicated the anode material was aging faster than the SEI layer, the opposite of normal cell degradation. A post-mortem analysis of cells from three configurations (baseline, single-cell, and parallel-cell) supported the modeling, as physical damage to the copper current collector in the anode was visible in the parallel-connected cell.
Subjects/Keywords Pulsed Power; Electrochemical Impedance Spectroscopy; EIS; Computed Tomography; Battery; LiFePO4
Contributors Mili, Lamine M (committeechair); Odendaal, Willem G (committee member); Zaghloul, Amir I (committee member); Wetz, David Alan (committee member); Centeno, Virgilio A (committee member); Brown, Alan J (committee member)
Rights This item is protected by copyright and/or related rights. Some uses of this item may be deemed fair and permitted by law even without permission from the rights holder(s), or the rights holder(s) may have licensed the work for use under certain conditions. For other uses you need to obtain permission from the rights holder(s).
Country of Publication us
Record ID handle:10919/80573
Repository vt
Date Indexed 2019-01-08
Issued Date 2017-11-29 00:00:00
Note [degree] PHD;

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