Cryogenic Correlative TEM and APT for Probing Lithium Redistribution, Damage Evolution, and Liquid–Solid Interfaces in Single-Crystal NMC

Understanding degradation in battery electrode materials requires resolving coupled structural and chemical evolution across multiple length scales. In high-energy lithium-ion (Li-ion) cathodes, failure often initiates at the electrolyte–electrode liquid–solid interface and propagates into the bulk through lithium redistribution, transition metal migration, and mechanical fracture. However, directly characterizing these processes remains challenging: lithium is a highly mobile, low-atomic-number element that is difficult to detect, and preserving reactive solid–liquid interfaces during preparation for high-vacuum analysis is non-trivial. Here, we present a fully cryogenic, correlative microscopy workflow to interrogate degradation in single-crystal nickel–manganese–cobalt oxide (NMC) cathodes, we developed for initially for just APT samples [1,2]. We first employ cryogenic focused ion beam (cryo-FIB) slice-and-view tomography to obtain a large field-of-view, three-dimensional map of morphological evolution within electrochemically cycled electrodes [3]. Using the cryogenic and vacuum transfer workflow, we preserve electrolyte-containing regions and minimize redistribution of mobile species. This approach enables volumetric reconstruction of crack networks, particle fracture, and mesoscale structural changes across extended electrode volumes, as shown in Figure 1. From the knowledge gained via the macroscale three-dimensional SEM dataset analysis, regions of interest are identified and site-specifically extracted under cryogenic conditions to prepare both scanning transmission electron microscopy (TEM) lamellae and atom probe tomography (APT) needle specimens. Cryogenic transfer is maintained throughout to preserve the liquid–solid interface and the electrochemical state of the material [4-6]. At the nanoscale, cryogenic STEM provides high-resolution structural and defect characterization, while electron energy loss spectroscopy (EELS) and four-dimensional STEM (4D-STEM) probe local bonding environments, oxidation states, and phase. Complementarily, cryogenic APT as shown in Figure 2, delivers three-dimensional compositional reconstructions with parts-per-million detection sensitivity and strong sensitivity to light elements, enabling direct mapping of lithium redistribution and interfacial compositional gradients [2]. By correlating cryogenic slice-and-view tomography, STEM structural analysis, EELS electronic structure measurements, and APT three-dimensional compositional mapping, we connect macroscale morphological degradation to atomic-scale lithium dynamics and liquid–solid interfacial chemistry. This integrated cryogenic approach establishes a pathway for resolving mobile light elements and solid–liquid interfaces in working battery materials, advancing mechanistic understanding of degradation in high-energy nickel–manganese–cobalt oxide cathodes [7]. SEM image of SC-NMC cathodes with electrolyte a) before cycling, and b) after cycling. The cathodes are composed of small single-crystalline particles, with some larger particles formed through amalgamation of smaller ones. These larger particles undergo cracking during the cycling process, indicating they may be polycrystalline. APT reconstructions of the Ni ions in a pristine NMC particle, and a particle after 20 cycles. The migration of Li in the electrolyte means that the structures are not directly comparable, but the particles also show significant compositional differences, with the cycled particle being comparatively richer in Ni