RESUMEN
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.
RESUMEN
Hybrid solar cells were fabricated using aluminum-doped zinc oxide (AZO) grown by electrochemical deposition from chloride electrolyte solutions with Al/Zn molar ratios of 0.5, 2.5, and 5.0%. The substrates were AZO- and ZnO-seeded ITO. Ordered nanorod structures with high optical transmittance were grown at 0.5% Al/Zn ratio while interconnected micron-sized flakes were grown at 2.5% and 5.0%. The estimated band gap energies increase for higher Al dopant content, showing Burstein-Moss effect. EDX analysis detected high aluminum content in the 5.0% samples suggesting that insulating aluminum oxide phases were formed thus causing reduced solar cell efficiencies. The highest power conversion efficiency of 1.71%, from the 0.5% sample grown on ZnO-seeded ITO, can be attributed to the presence of AZO nanorods which provide a large interfacial area and effective charge transport.