Analyzing Nanometer-Thin Cathode Particle Coatings for Lithium-Ion Batteries—The Example of TiO₂ on NCM622

Abstract

Cathode active materials (CAMs) in state-of-the-art lithium-ion batteries are mostly lithium-transition-metal oxides such as Li(Ni x Co y Mn z )O 2 (x + y + z = 1). To achieve optimum cycling stability and performance of the cathode, the extent of degradation processes and side reactions between CAMs and liquid or solid electrolytes has to be minimized. For this purpose, various coating strategies for CAMs have been developed in recent years. The underlying mechanism of the protective function of nanoscale coatings and their role for the enhanced cycling performance are mostly unclear, which is often based on incomplete characterization of the coating. Only a few analytical methods, such as X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray analysis, or X-ray photoelectron spectroscopy, have frequently been used in recent years, which often cannot provide enough information for a reliable and consistent picture of the very thin coating. For this reason, we demonstrate a systematic study on the analytical characterization of coated CAM using additional analytical methods. NCM622 coated with TiO 2 by atomic layer deposition is used as a model system and analyzed with SEM/EDX, focused ion beam scanning electron microscopy, scanning transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, low-energy ion scattering, and time-of-flight secondary ion mass spectrometry. The results highlight the advantages and disadvantages of each analytical method for the analysis of typical CAM coatings. The results demonstrate that a combination of the different methods is essential to understand CAM coatings and their properties in full detail.

A Dry‐Processed Al2O3/LiAlO2 Coating for Stabilizing the Cathode/Electrolyte Interface in High‐Ni NCM‐Based All‐Solid‐State Batteries

“…For a more detailed surface analysis, the microstructure of the coating layer was characterized by transmission electron microscopy (TEM) in combination with EDS. [ 48 ] As shown in Figure a,c, for Alu‐NCM, the coating layer is highly porous as observed by Herzog et al. [ 34 ] Figure 3a shows that the gaps between the primary NCM particles are completely filled with Al 2 O 3 , leaving the surface uncovered.…”

Understanding surface chemical processes in perovskite oxide electrodes

“…The result contrasts with the Sr-enriched surface observed and discussed previously in this work. It is common to observe an AO-terminated surface layer on the surface of an annealed perovskite oxide, 18,30,33,42,43,48,70–74 however, a La-enriched surface is scarcely reported. An example of the La 3d spectra collected from the sample annealed in dry oxygen at 700 °C is illustrated in Fig.…”

“…1c and d, the atomic ratio of [Sr] total : [La] total was found to be markedly higher than the stochiometric ratio (conrmed on the as-polished sample with Table 1 Summary of the time-of-flight secondary ion mass spectrometry (ToF-SIMS), low energy ion scattering spectroscopy (LEIS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and energydispersive X-ray spectroscopy (EDX) techniques applied in this study. [41][42][43]…”

Effect of Annealing on the Structure, Composition, and Electrochemistry of NMC811 Coated with Al2O3 Using an Alkoxide Precursor

“…A plethora of coating materials have now been investigated. Some of the most common materials used to coat NMC cathode particles include metal oxides such as Al 2 O 3 , − TiO 2 , ZrO 2 , and SiO 2 but also metal phosphates and fluorides like AlPO 4 , FePO 4 , AlF 3 , CaF 2 , and LiAlF 4 . These coatings can be deposited using vapor-deposition techniques such as atomic layer deposition (ALD) ,, or solution-based methods which do not require sophisticated equipment and tend to be easier to scale up. − ,, …”