Float Current Analysis for Lithium-Ion Battery Aging: Insights into SEI Growth and Cathode Lithiation with EIS and ICP OES

Journal of The Electrochemical Society, vol. 172, pp. 070529

Abstract

This study investigates calendar-aging mechanisms in lithium-ion batteries, focusing on cathode lithiation due to decomposition of conductive salt and SEI growth, by correlating quantified float currents, capacity loss rates, and pulse resistances with changes in electrochemical impedance spectroscopy (EIS) spectra. Seven SamSung 25 R cells are aged at different float voltages with periodic EIS measurements at 30 °C. Using a pre-characterization cell, the internal processes via EIS are allocated across various states of charge and temperatures and GITT measurements are performed to derive scaling factors. GITT, float currents and capacity loss rate measurements at 30 °C enables the separation of SEI growth I SEI growth and cathode lithiation current I CL based on float current behavior across a temperature range of 5 °C to 50 °C. The distribution of relaxation times (DRT) method is employed to deconvolute overlapping electrochemical processes. EIS and DRT analyses showed significant changes in cathode charge transfer resistance and diffusion, confirming that cathode lithiation correlates substantially to elevated internal resistance at high cell voltages. The theory of I SEI growth and I CL is further supported using inductively coupled plasma atomic emission spectroscopy by quantifying elemental inventory changes and linking phosphorus release and lithium consumption to degradation mechanisms.

Authors 4

1. Mohamed Azzam corresponding Aachen Chair for Electrochemical Energy Conversion and Storage Systems Institute for Power Electronics and Electrical Drives (ISEA)

   RWTH Aachen University · Technische Hochschule Ingolstadt

   Affiliation as printed

   Chair for Electrochemical Energy Conversion and Storage Systems, Institute for Power Electronics and Electrical Drives (ISEA), RWTH Aachen University, 52074 Aachen, Germany

   Research Group Electromobility and Learning Systems, Technische Hochschule, Ingolstadt D-85049, Germany

2. Christian Endisch corresponding

   Technical University of Munich · Technische Hochschule Ingolstadt

   Affiliation as printed

   Research Group Electromobility and Learning Systems, Technische Hochschule, Ingolstadt D-85049, Germany

   Technical University of Munich (TUM), Institute for Electrical Drive Systems and Power Electronics, 80333 Munich, Germany

3. Dirk Uwe Sauer corresponding Aachen Institute for Power Generation and Storage Systems (PGS)

   RWTH Aachen University · Forschungszentrum Jülich · Jülich Aachen Research Alliance · Helmholtz-Institute Münster

   Affiliation as printed

   Helmholtz Institute Münster (HI MS), IEK 12, Forschungszentrum Jülich, 52425 Jülich, Germany

   Institute for Power Generation and Storage Systems (PGS), E.ON ERC, RWTH Aachen University, 52074 Aachen, Germany

   Jülich Aachen Research Alliance, JARA-Energy, 52056 Aachen, Germany

4. Meinert Lewerenz corresponding

   Technische Hochschule Ingolstadt

   Affiliation as printed

   Research Group Electromobility and Learning Systems, Technische Hochschule, Ingolstadt D-85049, Germany