Abstract
Surface lattice reconstruction is commonly observed in nickel-rich layered oxide battery cathode materials, causing unsatisfactory high-voltage cycling performance. However, the interplay of the surface chemistry and the bulk microstructure remains largely unexplored due to the intrinsic structural complexity and the lack of integrated diagnostic tools for a thorough investigation at complementary length scales. Herein, by combining nano-resolution X-ray probes in both soft and hard X-ray regimes, we demonstrate correlative surface chemical mapping and bulk microstructure imaging over a single charged LiNi0.8Mn0.1Co0.1O2 (NMC811) secondary particle. We reveal that the sub-particle regions with more micro cracks are associated with more severe surface degradation. A mechanism of mutual modulation between the surface chemistry and the bulk microstructure is formulated based on our experimental observations and finite element modeling. Such a surface-to-bulk reaction coupling effect is fundamentally important for the design of the next generation battery cathode materials.
Highlights
Surface lattice reconstruction is commonly observed in nickel-rich layered oxide battery cathode materials, causing unsatisfactory high-voltage cycling performance
It is observed that the degree of the lattice reconstruction effect is inhomogeneous over the particle surface
The regions with higher porosity are associated with more severe surface lattice reconstructions, which suggests a mutual modulation between the surface chemistry and the bulk microstructure
Summary
Surface lattice reconstruction is commonly observed in nickel-rich layered oxide battery cathode materials, causing unsatisfactory high-voltage cycling performance. The undesired surface reactions include, but are not limited to the, reconstruction of the surface lattice structure[5,6,7,8], the formation of a reaction passive interface[9], dissolution and precipitation of metal cations[10], growth of lithium dendrites from the particle surface etc[11] These surface chemical processes lead to the development of local impedance and effectively cause the lithium ions and the electrons to detour through geometrically less optimal pathways, result in unwanted phenomena like cell polarization and capacity/ voltage fade[12]. Through such mechanisms, they affect the participation level of the active particles in the cell scale chemistry. We would like to highlight that, the size of the Xray focal spot (i.e. the nominal spatial resolution) for the XRDCT technique may not be very fine, this technique is sensitive to the material’s lattice structure, which is directly related with the atomic-scale structural and chemical evolution of the cathode material upon electrochemical cycling
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