Soft X-ray Ptychography Chemical Imaging of Degradation in a Composite Surface-Reconstructed Li-Rich Cathode.

The capability in spatially resolving the interactions between components in lithium (Li)-ion battery cathodes, especially correlating chemistry and electronic structure, is challenging but critical for a better understanding of complex degradation mechanisms for rational developments. X-ray spectro-ptychography and conventional synchrotron-based scanning transmission X-ray microscopy image stacks are the most powerful probes for studying the distribution and chemical state of cations in degraded Li-rich cathodes. Herein, we propose a chemical approach with a spatial resolution of around 5.6 nm to imaging degradation heterogeneities and interplay among components in degraded Li-rich cathodes. Through the chemical imaging reconstruction of the degraded Li-rich cathodes, fluorine (F) ions incorporated into the lattice during charging/discharging processes are proved and strongly correlate with the manganese (Mn) dissolution and oxygen loss within the secondary particles and impact the electronic structure. Otherwise, the electrode-electrolyte interphase component, scattered LiF particles (100-500 nm) along with the MnF layer, is also visualized between the primary particles inside the secondary particles of the degraded cathodes. The results provide direct visual evidence for the Li-rich cathode degradation mechanisms and demonstrate that the low-energy ptychography technique offers a superior approach for high-resolution battery material characterization.