The cycle life of LiCoO 2 cathodes cycled at a high cutoff voltage can be largely improved by surface modification with ZnO coating. The bright-field transmission electron microscopy ͑TEM͒ images and selected area diffraction patterns of as-coated LiCoO 2 particles reveal the existence of continuous ZnO films with a 10-nm thickness deposited on LiCoO 2 surfaces, indicating a Li-Zn-O phase formed on the surface region. Besides high-voltage cycleability, cycle-life degradation caused by inappropriate conductive carbon can also be moderated by ZnO coating. Furthermore, the rate capability at high current density can also be notably improved. The role ZnO coating played in the charge-discharge process is discussed from the viewpoint of surface chemistry with the aid of data from scanning electron microscopy, TEM, energy-dispersive X-ray, and impedance spectra. Moreover, the correlation between electrochemical performance and surface properties of ZnO-coated LiCoO 2 is explored.

Effects of calcination treatment on samples of mono-metallic Pd and Pd77-Ag23 alloy with primary particles around 8 nm were studied with the temperature-programmed reduction technique. Temperature profiles of hydrogen consumption for calcined samples from a stream of 10% H2 in N2 were monitored by a thermal conductivity detector. Two distinct peaks, i.e., a consumption of hydrogen for PdO reduction and a subsequent desorption of hydrogen from bulk palladium hydride, were observed. The extent of palladium oxidation upon calcinations increased with the temperature of calcination (T o):  i.e., chemisorption of oxygen on particle surface upon calcination at T o < 373 K, reconstruction into a surface PdO structure at 473 K and incorporation into sublayers to form bulk PdO structure at high T o. Minimum temperature (T r) required for reduction of oxidized palladium by the hydrogen stream was generally low (150 K < T r < 320 K) and increased with the extent of oxidation. A quantitative measurement of hydrogen desorbed from reduced samples suggested a formation of alloy phase in freshly prepared Ag77−Pd23 primary particles. The freshly prepared alloy was inhomogeneous in composition but became homogeneous upon calcination at T o > 673 K.

Newly developed LiNi 0.75−x Co 0.25 Mn x O 2 ͑0.1 ഛ x ഛ 0.25͒ cathode materials were successfully synthesized by mixing Ni 0.75−x Co 0.25 Mn x ͑OH͒ 2 and Li 2 CO 3 via the solid-state reaction followed by heating to elevated temperatures. X-ray diffraction patterns showed that the samples calcined at 900°C exhibited a typical hexagonal ␣-NaFeO 2 structure without any other impurities present. The ratio of peak intensities of ͑003͒ to ͑104͒ decreased with the increasing Mn content. The scanning electron microscopy micrograph revealed uniform primary particle size, and the small primary particles agglomerated to form the secondary ones with size distribution in the range of 6-9 m. The X-ray photoelectron spectroscopy measurement indicated that the valence of Ni ions was a mixture of 2+ and 3+. The amount of Mn substituted for Ni increased proportional to the ratio of Ni 2+ /Ni 3+ in the samples was increased. Besides, for dynamic equilibrium ͑Ni 2+ + Mn 4+ ↔ Ni 3+ + Mn 3+ ͒, small amount Mn 4+ was reduced to Mn 3+ . After cycling, the cathode materials showed good electrochemical performance, with initial discharge capacity around 170 mAh/g at 0.1 C rate in the voltage range of 3-4.3 V. At a high rate of 1 C, 85% efficiency was still attainable in all samples.

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Point contact Andreev reflection (PCAR) spectroscopy is a common technique for determining the spin polarization of a ferromagnetic sample. The polarization is extracted by measuring the bias dependence of the conductance of a metallic/superconducting point contact. Under ideal conditions, the conductance is dominated by Andreev reflection and the Blonder-Tinkham-Klapwijk (BTK) model can be used to extract a value for the polarization. However, PCAR spectra often exhibit unwanted features in the conductance that cannot be appropriately modelled with the BTK theory. In this paper we isolate some of these unwanted features and show that any further extraction of the spin polarization from these non-ideal spectra proves unreliable. Understanding the origin of these features provides an objective criterion for rejection of PCAR spectra unsuitable for fitting with the modified BTK model.