Sangsul Lee

This work elucidates the growth of lithium nickel cobalt manganese oxide (NCM)/lithium lanthanum zirconate (LLZO)/zinc ferrite (ZFO) films using X-ray diffraction (XRD), Rutherford backscattering (RBS), electron probe microanalysis (EPMA) and X-ray absorption spectroscopy (XAS). Prior to deposition of LLZO and NCM/LLZO, ZFO films (deposition times: 25 (NLZ25) and 100 min (NLZ100)) were deposited on silicon (100) substrates using radio frequency (RF) sputtering at a base pressure of 5.0 × 10⁻⁶ Torr. LLZO was deposited for 90 min at RF power of 40 W. Thereafter, an NCM layer was deposited on these bilayer structures for 100 min (RF power—35 W). Obtained trilayer structures were annealed at 900 °C for 1 h. XRD shows ZFO is able to attain crystalline phase of spinel structure for both NLZ25 and NLZ100. In the trilayer structures onsets of some impurity phases are observed. RBS analysis reveals that for NLZ25, NCM, LLZO, and ZFO layers have thicknesses of approximately 30, 60, and 70 nm. For NLZ100, the corresponding layer thicknesses are 40, 90, and 200 nm, respectively. The significant change in ZFO thickness is attributed to the longer deposition duration for later cases. The O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra of grown trilayer structures exhibit spectral features associated with ZFO, LLZO and NCM. The pre-edge region in the O K-edge NEXAFS spectra is strongly influenced by the interaction of ions from various layers in these structures. La M-edge NEXAFS spectra exhibit characteristic spectral features of La ions in LLZO and show the presence of La³⁺ in respective layers.

A physically consistent framework for precise emissivity design in multilayer nanomembranes via Å-scale prediction of thickness-dependent optical constants.

This study reports the deposition of garnet-structured lithium lanthanum zirconate (LLZO) thin films using radio frequency (RF) sputtering on glass substrates by varying the heating/cooling rate. Deposition was carried out at a sputtering power of 70 W for 30 min under Ar environment. As-deposited films were annealed at 500°C at different heating/cooling rates (1.5, 6 and [ ]C/min). It was observed that these films were amorphous in nature and no crystalline phase was reported despite the change in heating/cooling rates. Thickness and compositions of these films were estimated using Rutherford backscattering spectroscopy (RBS) measurements. Thicknesses of as-deposited films were 110[ ]nm and reduced to 90[ ]nm on annealing at different heating/cooling rates, suggesting intermixing at the interface. This intermixing phenomenon, observed at the interfaces of the LLZO thin film, suggests potential interactions or diffusion processes during the annealing process.

By quantitatively linking Ni charge heterogeneity to irreversible lithium loss, our study provides a mechanistic foundation for mitigating IRC loss and optimizing Ni-rich cathode performance.

X‐ray photoelectron spectroscopy (XPS) in ferrites (MFe ₂ O ₄ ; M is divalent transition metal (TM) ion) materials is capable to differentiate between chemical states with the help of intensive investigation of Fe 2p, and M 2p spectra, particularly through splitting into their components, detecting chemical shifts, and shake‐up satellites. Therefore, it could shed light on the behavior of Fe ²⁺ /Fe ³⁺ , M ²⁺ /M ³⁺ , and even partially filled site occupancies. The binding energy of ions is influenced by several factors, such as average ligand electronegativity, metal‐to‐charge transfer, initial state effect, screening effect and relaxation effect that elucidate the role of the surrounding of ions to be probed. Hence, identification of cations in different surroundings is another feature of XPS. Thus, detailed deconvolution of Fe and other metal core‐level spectra of ferrites can provide insights into the cation inversion, an important factor that directly governs the performance of ferrite‐based devices in spintronics, catalysis, and energy storage. Hence, XPS is not just an analytical tool that can bring the oxidation states into consideration, but a quantitative probe that can clarify cation‐inversion profiles and site occupancy. Thus, this review article summarizes the extensive XPS studies on ferrites, focusing mainly on spinel ferrite systems and doped ferrites.

Doping, coating, surface modification, formation of composites and control of crystalline orientation can control the capacity retention of Ni-rich cathodes. Furthermore, the design of Co-free Ni-rich cathodes may provide a cost-effective solution.

Nickel-rich layered cathode materials and their correlation with the electronic structure are crucial to understanding the functionality of Li-ion batteries in the commercial deployment of electric vehicles. In this study, we employ synchrotron X-ray diffraction and hard X-ray absorption spectroscopy measurements, along with the corresponding first-principles calculations, to provide atomic-level insights into the first cycle irreversible capacity (IRC) loss of a LiNi_0.90Mn_0.05Co_0.05O₂ (NCM900505) cathode. Our results identify that the first cycle IRC loss is strongly related to the irreversibility of the Ni charge state, which limits the capacity and energy density. We show that the shift to higher energies of the Ni K-edge X-ray absorption spectrum during charging is a result of a decreased number of Ni²⁺/Ni³⁺ ions, while the number of Ni⁴⁺ ions increases. Our findings also indicate that the increased number of Ni⁴⁺ ions shortens the averaged Ni–O bond length after the first charging, and these changes in the atomic structure are irreversible after discharging. We expect that these new insights of Ni-rich cathodes (Ni > 80%) provide a fundamental understanding of their cycling behavior and offer strategies to understand this first cycle IRC loss and suggest structural design routes of Li-ion batteries for electric vehicles.