In situ and ex situ studies of materials with relevance to electrochemical energy storage and energy generation

Surface analytical techniques have been employed for the preparation and characterization of modified surfaces of relevance to electrochemical energy storage and generation in ultrahigh vacuum environments. Complementary in situ spectroscopic studies were also performed using Raman microscopy for monitoring static and dynamic aspects of Li intercalation and deintercalation into transition metal oxides and graphitic materials. The most important conclusions emerging from this investigation can be summarized as follows: (i) Ruthenium-modified Pt(100) surfaces of very high purity and controlled stoichiometry were prepared in ultrahigh vacuum (UHV) by irradiating Ru₃(CO)₁₂ films condensed on cold Pt substrates at 150 K with X-rays, and subsequent annealing at ca. 620 K. Exposure of non-annealed Ru(&thetas;_Ru ≥0.22)/Pt(100) to large exposures of CO at ca. 200 K, yielded smaller &thetas; _CO, and temperature programmed desorption peaks ca. 50 K lower than those observed for bare Pt(100). (ii) Raman spectra of isolated single particles of technical grade LiMn₂O₄ embedded in Au foils were recorded in situ in 1M LiPF₆ in EC/DMC solutions in real time during a voltammetric scan using a Raman microscope. Similar experiments involving single KS-44 carbon particles (8–50 μm in diameter) embedded into thermally annealed Ni foils in 1M LiClO₄, ethylene carbonate (EC) diethyl carbonate (DEC) solutions allowed the average concentration of Li+ within the volume of the particle probed by the laser beam following application of a potential step to be monitored spectroscopically in real time. Analysis of these transient data yielded deintercalation time constants for Li+ for dilute stage 1 phase consistent with reported values of Li+ diffusion coefficients within graphitic materials. A new Raman band ascribed to bounding graphite layers was found upon continuous cycling of single KS-44 particles deep into the Li+-intercalation region. This feature was attributed to chemical modifications of carbon that may be at least partially responsible for irreversible capacity losses. (iii) Optically smooth Zn films (rms roughness ca.0.3 nm) supported on Cu-coated glass and quartz substrates were prepared by physical vapor deposition of Zn in metallic form at Ar pressures of about 3∼5 mtorr, yielding smooth features of dimensions ca. 200 nm.