Dead, Slow, and Overworked Graphite: Operando X‐Ray Microdiffraction Mapping of Aged Electrodes
Gozde Oney, Federico Monaco, Saptarshee Mitra, Asma Medjahed, Manfred Burghammer, Dmitry Karpov, Marta Mirolo, Jakub Drnec, Isabelle Jolivet, Quentin Arnoux, Samuel Tardif, Quentin Jacquet, Sandrine Lyonnard
Abstract
Abstract Aging limits lithium‐ion battery lifetime and must be understood to improve durability and performance, requiring a detailed understanding of how aging alters the availability of cyclable lithium and the integrity of active particles. In this work, (de)lithiation mechanisms are examined and spatially‐resolved at the microscale in aged graphite electrodes dismounted from a large format graphite/LiFePO 4 ‐Li(NiCoAl)O 2 cell at 70% remaining capacity. A multitechnique workflow is employed, combining electrochemical methods with postmortem structural and morphological analyses, and introducing synchrotron micro X‐ray 2D diffraction imaging as a technique to probe aged graphite, applied at cycling rates from C/5 to C. In‐plane and through‐plane heterogeneities in graphite dynamics are evidenced, showing the presence of inactive regions localized in two dimensions. In these areas, particles are either disconnected (irreversibly lost) or kinetically limited (reactivated at a slow C‐rate), with dead or slow particles exhibiting a wide range of compositions, from x = 0 to x = 1 in Li x C 6 . These inactivated graphite particles are found to be heterogeneously distributed throughout the depth of the aged negative electrode. In particular, the most inactivated region localizes at the negative electrode‐separator interface, correlating to overworking graphite near the separator.