Voltage fade prevents effective use of the excess capacity and represents the most crucial technical challenge faced by Li-and Mn-rich cathode materials (LMR) in modern batteries.Although oxygen release has been arguably considered as an initiator for the failure mechanism, its prerequisite driving force has yet to be fully understood. Herein, relying on the in-situ nanoscale sensitive coherent X-ray diffraction imaging (BCDI) technique, we are able to track the dynamic structure evolution of the LMR cathode. The results, surprisingly, reveal that continuous nanostrain accumulation arose from lattice displacement in nano-domain structures during cell operation is the original driving force for detrimental structure degradations together with oxygen loss that triggers the well-known rapid voltage decay in LMR. By further leveraging primary to multi-particle structure and electrode-level as well as atomic scale observations, we demonstrate that the heterogeneous nature of the LMR cathode inevitably causes pernicious phase displacement which cannot be eliminated by the previous trials. With these fundamental discoveries, we propose the structural design strategy to mitigate the lattice displacement and inhomogeneous electrochemical/structural evolutions, thereby achieving stable voltage and capacity profiles. These findings highlight the significance of lattice displacement in voltage decay mechanism and will inspire a wave of efforts to unlock the potential of the broad-scale commercialization of LMR cathode material.

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 (BCDI) 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 de-intercalation 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.

The worldwide energy demand in electric vehicles and the increasing global temperature have called for development of high‐energy and long‐life lithium‐ion batteries (LIBs) with improved high‐temperature operational resiliency. However, current attention has been mostly focused on cycling aging at elevated temperature, leaving considerable gaps of knowledge in the failure mechanism, and practical control of abusive calendar aging and thermal runaway that are highly related to the eventual operational lifetime and safety performance of LIBs. Herein, using a combination of various in situ synchrotron X‐ray and electron microscopy techniques, a multiscale understanding of surface structure effects involved in regulating the high‐temperature operational tolerance of polycrystalline Ni‐rich layered cathodes is reported. The results collectively show that an ultraconformal poly(3,4‐ethylenedioxythiophene) coating can effectively prevent a LiNi0.8Co0.1Mn0.1O2 cathode from undergoing undesired phase transformation and transition metal dissolution on the surface, atomic displacement, and dislocations within primary particles, intergranular cracking along the grain boundaries within secondary particles, and intensive bulk oxygen release during high state‐of‐charge and high‐temperature aging. The present work highlights the essential role of surface structure controls in overcoming the multiscale degradation pathways of high‐energy battery materials at extreme temperature.