Due to complex degradation mechanisms, disparities between the theoretical and practical capacities of lithium-ion battery cathode materials persist. Specifically, Ni-rich chemistries such as LiNi0.8Mn0.1Co0.1O2 (or NMC811) are one of the most promising choices for automotive applications; however, they continue to suffer severe degradation during operation that is poorly understood, thus challenging to mitigate. Here we use operando Bragg coherent diffraction imaging for 4D analysis of these mechanisms by inspecting the individual crystals within primary particles at various states of charge (SoC). Although some crystals were relatively homogeneous, we consistently observed non-uniform distributions of inter-and intracrystal strain at all measured SoC. Pristine structures may already possess heterogeneities capable of triggering crystal splitting and subsequently particle cracking. During low-voltage charging (2.7-3.5 V), crystal splitting may still occur even during minimal bulk deintercalation activity; and during discharging, rotational effects within parallel domains appear to be the precursor for the nucleation of screw dislocations at the crystal core. Ultimately, this discovery of the central role of crystal grain splitting in the charge/discharge dynamics may have ramifications across length scales that affect macroscopic performance loss during real-world battery operation.
Bibliographical noteFunding Information:
This work was supported by an EPSRC Grant EP/I022562/1, “Phase modulation technology for X-ray imaging”, and funding from Faraday Institution, Grants EP/S003053/1 FIRG001 and FIRG013. We also acknowledge the Royal Academy of Engineering (Grant CiET1718\59) for financial support. Work at Brookhaven National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-SC0012704. Experiments were carried out at The Diamond Lightsource, beamline I13-1 under experiments MG25852, MG25440, MG24129, MG22373, MG22309, and MG21652.
Copyright 2021 Elsevier B.V., All rights reserved.
- electric vehicle
- Li ion
ASJC Scopus subject areas
- Materials Science(all)
- Physics and Astronomy(all)