An important step toward safer and more reliable lithium-ion battery systems is the development of better methods for detection and characterization of battery degradation. For a method to be suitable for online application (e.g., onboard an electric vehicle), it must be simple, explanatory, and non-invasive. In this work, we develop and track aging indicators over the life of 18650-format lithium-ion batteries with a blended NMC532-LMO positive electrode and graphite negative electrode. Cells are cycled until reaching 80 % of their original capacity under combinations of four different cycling conditions: ambient and sub-ambient temperatures (29 and 10 °C) and fast and mild rates (2.7 and 1.0C). Loss of lithium inventory dominates aging for all cases, with additional loss of NMC capacity under the combination of sub-ambient temperature and mild rate. A novel, easily acquired polarization factor (supported by electrochemical impedance spectroscopy) complements capacity fade analysis; it correlates well with ultimate cell lifetime and indicates changes in active aging processes. These processes are further revealed by differential voltage analysis (DVA) and incremental capacity analysis (ICA). New indicators and aging scenarios are evaluated for these techniques and supported by post mortem analysis. From in operando cycling data and a single, slow discharge curve, these four methods (capacity fade, polarization factor, DVA, and ICA) comprise a simple, explanatory, and non-invasive toolbox for evaluating aging online in lithium-ion battery systems.
Lithium-ion battery SoH estimation based on incremental capacity peak tracking at several current levels for online application