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This paper describes an electrochemical technique for growing adhesive copper oxide films on copper with attractive colors ranging from gold-brown to pearl with intermediate colors from red violet to gold green. The technique consists of anodically dissolving copper at transpassive potentials in hot sodium hydroxide, and then depositing brilliant color films of Cu2O onto the surface of copper after the anodic potential has been turned off. The color of the copper oxide film depends on the temperature, the anodic potential, the time t1 of polarization, and the time t2, which is the time of immersion after potential has been turned off. (At potentials lower than the transpassive region, that is, in the passive region, the oxide film is a dark gray or dark green matte with a blue powder hydroxide on the surface and it is not attractive.) The brilliant colored films were characterized using glancing angle x-ray diffraction, and the film was found to be primarily Cu2O. Cyclic voltammetry, chronopotentiometry, scanning electron microscopy, and x-ray photoelectron spectroscopy were also used to characterize these films. These techniques show that the different colors were due to differences in porosity and thickness rather than changes in composition. [ABSTRACT FROM AUTHOR]

In this paper, the real geometries of cathode particles are reconstructed using atomic force microscopy (AFM). Finite element analysis of intercalation-induced stress is applied to the reconstructed realistic geometries of single and aggregated particles. The reconstructed particle geometry shows rugged surfaces at the boundary for Li-ion flux, which cause larger surface areas than smooth particles. The finite element model of a LiMn2O4 system is simulated under galvanostatic and potentiodynamic control. To investigate the realistic level of boundary flux at particle scale, macroscale simulation results are also applied to intercalation-induced stress analysis of real cathode particles. The numerical results of intercalation-induced stress show that the von Mises stress is concentrated at sharply dented boundaries due to curvature effects when Li ions intercalate or deintercalate and is an order-of-magnitude higher in realistic particle geometries than the stress in ideal smooth particles. It has also been shown that the stress under potentiodynamic control is higher than the stress under galvanostatic control because the high Li-ion flux at two plateaus in the open-circuit potential of a LiMn2O4 system results from linear voltage sweep. We also present results showing that some mesh architectures are preferred for handling these potentially singular regions. [ABSTRACT FROM AUTHOR]