Expanded In Situ Aging Indicators for Lithium-Ion Batteries with a Blended NMC-LMO Electrode Cycled at Sub-Ambient Temperature
Alexander J. Smith, Pontus Svens, Maria Varini, Göran Lindbergh, Rakel Wreland Lindström
Abstract
An important step toward safer and more reliable lithium-ion battery systems is the improvement of methods for detection and characterization of battery degradation. 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 cycling conditions: ambient and sub-ambient temperatures (29 °C 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 complements capacity fade analysis; it correlates well with impedance and galvanostatic cycle life 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 in lithium-ion battery systems.