Thin Film NCM Cathodes as Model Systems to Assess the Influence of Coating Layers on the Electrochemical Performance of Lithium Ion Batteries

Abstract

A facile procedure is demonstrated to prepare lithium nickel cobalt manganese oxide (NCM) thin film cathodes. Via a sol‐gel approach and subsequent spin‐coating, a crystalline and phase‐pure cathode layer is prepared without any further additives or binders. It is shown that the thin film cathodes are ideal model systems to access the effect of coating layers on electrochemical performance in lithium ion batteries. For this purpose, the thin films are coated with an ultrathin alumina layer using atomic layer deposition. The samples are structurally and electrochemically characterized, exhibiting comparable properties as cathodes prepared from powder. After cycling, post‐mortem analysis is conducted to investigate structural changes inflicted by the electrochemical treatment. The characterization reveals that uncoated samples exhibit severe structural changes due to cycling, while coated samples show only minor changes under the same conditions. Post‐mortem surface analysis using X‐ray photoelectron spectroscopy confirms the corrosion of the uncoated cathode and proofs the scavenging effect of alumina. The presented results provide a simple and versatile method to prepare thin film NCM model systems, which enable an accurate analysis of the cathode–electrolyte interface and thus allow to obtain a deeper understanding of the beneficial effect of coatings for next‐generation lithium ion batteries.

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

“…The deconvolution confirms that the signal comprises two different peaks. One at a binding energy of 73.9 eV (corresponding to Al 2 O 3 or Al(OH) 3 ) [53] and a second one at 72.8 eV, which is attributed to LiAlO 2 as observed by Tang et al [54] The results confirm the conversion of an insulating Al 2 O 3 coating into an ion conducting Al 2 O 3 /LiAlO 2 coating during heat treatment, as discussed in detail in previous studies. [39,40] The diffusion of Li + from NCM into the Al 2 O 3 layer during the heat treatment is expected to result in the formation of conductive pathways for the Li + ions and thus an improvement of the ionic conductivity of the Al 2 O 3 /LiAlO 2 coating.…”

“…No peak shift is observed for the Ni 3p peak for all samples, which additionally confirms the structural stability of NCM during the coating and annealing processes. However, the presence of Ni implies that the coating is not completely covering the NCM surface or, alternatively, thinner than the typical probing depth of XPS of about 3–7 nm, [ 53 ] as already indicated by the TEM measurements shown in Figure 3f,g. Deconvolution of the Al 2p peak (Figure 4d) reveals that Alu‐NCM shows only one peak at a binding energy of 73.9 eV, which is distinctive for Al atoms in an oxygen environment, such as Al 2 O 3 or Al(OH) 3 .…”

Multi‐Element Surface Coating of Layered Ni‐Rich Oxide Cathode Materials and Their Long‐Term Cycling Performance in Lithium‐Ion Batteries

“…The TEM investigation of the interface between two primary particles in coated and uncoated LNO CAMs is detailed in Figure S7, Supporting Information, showing smooth edges and a clear gap for coated LNO, but rough edges and a gap diffusely filled with oxygen, fluorine, and nickel for uncoated LNO. The match in location of fluorine and nickel, also in Figure 7, suggests the presence of NiF 2 [ 34 ] as a degradation product from acid leaching, which is further evident from TEM results for cycled NCM851005 CAMs (see Figures S8 and S9, Supporting Information). For uncoated NCM851005, surface corrosion can be observed.…”

“…This increase in binding energy is indicative of a fluorine-scavenging effect of the coating, leading to a change from oxide to oxyfluoride environment for the aluminum ions, as also suggested by the fluorine-containing layer observed by TEM (Figure 7) and described in the literature. [34,40,41] Figure S11, Supporting Information, shows the Al 2p XP spectra of coated and uncoated CAM powder samples. Silicon (Si 2p) was probed via XPS too, but because of residual silicon in the particles and the low amount of coating, no clear effect could be observed.…”

Lithium-Ion Battery Operation, Degradation, and Aging Mechanism in Electric Vehicles: An Overview

“…Moreover, the battery operation at a high voltage (at high SOC level) or high environment temperature will accelerate the dissolution of the transition metal (TMD), especially for the Mn element, which dissolves in organic solvents, producing water and HF [76]. The produced HF continues to dissolve the transition metals and the Li + on the surface of the cathode, leading to significant capacity fade [77].…”