Abstract
Prior work has shown that equivalent circuit models (ECM) fitted to match frequency data (EIS) do not necessarily match time data (HPPC). Depending on the fitting methodology, the quality of data, and the ECM order, the parameter mismatch is manageable and can be justified by the simplification of the physical phenomena in an ECM. An investigation of the fitting methods and the sensitivity to noise will be shown using synthetic data of an OCV-R2RC model.The investigation will be expanded in fitting EIS and HPPC synthetic data from an SPMe and an SPM model. The sensitivity of the SPM parameters to the measured EIS and HPPC will clarify long-standing confusion of the uniqueness and even the magnitude of physically-relevant parameters in SPM models.The learnings from the synthetic data will then be demonstrated with EIS and HPPC data obtained from several Graphite/NMC battery pouch cells at different states of charge (SOC) and states of health (SOH) after cycling at a variety of accelerated aging protocols that include c-rates, temperatures, SOC swing, and externally applied pressure.Figure: Voltage Profile of Characterization Protocols(HPPC and EIS) for a single cell at different SOC.Bottom right, Nyquist plot corresponding to first characterization scheme of a fresh and aged cell. Figure 1
Published Version
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