Electrografting of diazonium salts containing a protected alkyne moiety was used for the first functionalization of silicon and highly ordered pyrolytic graphite model surfaces. After deprotection with tetrabutylammonium fluoride, further layers were added by the thiol-yne click chemistry. The composition of each layer was characterized via X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. The same approach was then used to functionalize graphite powder electrodes, which are classically used as negative electrode in lithium-ion batteries. The effect of the coating on the formation of the solid electrolyte layer was investigated electrochemically by cyclovoltammetry and galvanostatic measurements. The modified graphite electrodes showed different reduction peaks in the first cycle, indicating reduced and altered decomposition processes of the components. Most importantly, the electrochemical investigations show a remarkable reduction of irreversible capacity loss of the battery.

Thin alumina coatings on Li-rich nickel cobalt manganese oxide (Li-rich NCM) particles used as cathode material in Li-ion batteries can improve the capacity retention during cycling. However, the underlying mechanisms are still not fully understood. It is crucial to determine the degree of coverage of the particle’s coating on various length scales from micrometer to nanometer and to link it to the electrochemical properties. Alumina coatings applied on Li-rich NCM by atomic layer deposition or by chemical solution deposition were examined. The degree of coverage and the morphology of the particle coatings were investigated by time-of-flight secondary-ion mass spectrometry (ToF-SIMS), scanning electron microscopy, elemental analysis using inductively coupled plasma optical emission spectrometry, and scanning/transmission electron microscopy. ToF-SIMS allows investigating the coverage of a coating on large length scales with high lateral resolution and a surface sensitivity of a few nanometers. Regardless of the chosen coating route, analytical investigations revealed that the powder particles were not covered by a fully closed and homogenous alumina film. This study shows that a fully dense coating layer is not necessary to achieve an improvement in capacity retention. The results indicate that rather the coating process itself likely causes the improvement of the capacity retention and increases the initial capacity.

Multilayer samples of alternating n-type ZnO and insulating ZnS layers were deposited by radiofrequency (RF) magnetron sputtering on glass substrates. The number of ZnO/ZnS periods was varied throughout the series to increase the number of interfaces, whilst keeping the ratio of total thicknesses of ZnO and ZnS constant. Scanning electron microscopy (SEM) revealed the individual layers, but also a columnar structure. The in-plane Seebeck coefficient S and electric conductivity r were measured between 50 K and 300 K. The dependence of S and r on thickness d of the individual ZnO layers can be modeled by introducing a narrow interface layer of high conductivity for d > 100 nm. At lower d, fluctuations of the interfaces lead to additional effects on S and r which arise due to percolation and can be explained qualitatively in the framework of a network model.