Ethylene, carbon layers surface

Most of the ethylene that interacts with Ru(001) at 323 K produces a nondesorbable carbon layer. This result is similar to that for the interaction of C2H4 with Ni, which produces a surface carbide at temperatures between about 300-600 K (14). SIMS results suggest, however, the presence of small amounts of molecularly adsorbed ethylene, acetylenic and other hydrocarbon complexes in addition to the nondesorbable carbon layer. 

Most of the ethylene that interacts with an Ru(OOl) surface at 323 K produces a nondesorbable carbon layer. 

Thermal desorption of CO, Auger electron spectroscopy, and temperature programmed oxidation all show that the carbon layer 1) is Immobile below 550 K 2) forms a more densely packed surface phase at temperatures of 550-1150 K and 3) dissolves into the bulk at 1350 K. SIMS measurements of isotope mixing in the ions confirm formation of dense-phase (graphitic) islands after heating the carbon layer to 923 K. SIMS spectra also demonstrate that at 520 K, CO dissociates on Ru(OOl). The oxygen-free carbon layer that forms behaves similarly to the carbon from ethylene. Both SIMS and thermal desorption results show no positive interaction between adsorbed CO and D but significant attraction between and C formed by CO dissociation. 

CO Thermal Desorption. On a clean Ru(OOl) surface, 9 L of CO induces saturation coverage by molecular CO. When this dose of CO is applied to a surface preexposed to C H at 323 K, the CO uptake is diminished but not completely blocked by the carbon layer. The CO uptake is still 90% of the saturation value when the carbon coverage is 1/4 M.L. and falls to 1/4 of the saturation value after 15 L preexposure to ethylene. 

Because of a high barrier for the reaction leading to oligo(ethylene carbonate) formation, this reaction is expected to be slnggish with a low yield. It is consistent with the formation of a thin passivation layer on the cathode surface. Poly(ethylene carbonate) formation on cathode surfaces as a result of the oxidation-induced decomposition of an EC-based electrolyte was also recently suggested from experimental studies [46]. 

It is well known that graphite is unstable in some aprotic electrolytes. For instance, when propylene carbonate (PC) is used as a solvent, the cointercalation of solvent molecules and the Li ions will lead to the exfoliation of graphite layers Only in some selected electrolyte systems such as LiPF in EC/DEC (EC for ethylene carbonate and DEC for diethyl carbonate), can graphite show better cycling behavior. Solvent decomposition on the surface of conductive carbon or lithium electrodes will lead to the formation of a passivating layer. Peled named this layer as solid electrolyte interphase (SEI). ° It is an ionic conductor but electron insulator, mainly composed of LijCOj and various lithium alkylcarbonates (ROCO Li) as well as small amounts of LiE, LijO, and nonconductive polymers. These compounds have been detected on carbon and Li electrodes in various electrolyte systems. Therefore, it would be an interesting question whether semiconductive nano-SnO anode is also sensitive to electrolyte and electrolyte decomposition takes place on it. This section will characterize the structures and compositions of the... 

We have here exploited photoelectron spectroscopy using synchrotron radiation (PES-SR) to characterise the interface formed on carbon-coated LiFePO particles in the cathode of a lithium-ion battery after storage and electrochemical cycling at 23°C and 40 in a IM LiPF, mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The PES-SR technique facilitates non-destructive depth-profile analysis of the surface layer. An example is given in Figure 14. 

It is reported that the surface of LiCo02 in used LIBs is covered with floccules, which inhibits the efficiency of LIBs [78]. And, these floccules mainly consist of PVDF and Ethylene carbonate (EC) [78]. The LiCo02 in LIBs enjoyed layered crystal structure, and the organic matter stuck to the crystal s surface, being agglomerate. Hydrothermal reaction with ultrasonic-assisted can eliminate the EC and PVDF which was in pores. 

For the chemically delithiated Lio49Co02, exothermic reactions start at 190°C (Figure 2.4a), which corresponds to the transition from the layered R3m structure to the spinel Fd3m instead of oxygen evolution. Its reactions with the nonaqueous electrolyte (1 M LiPF solution in a mixture of ethylene carbonate [EC]/dimethyl carbonate [DMC]) produce two clear exothermic peaks (Figure 2.4b). The peak at 190°C corresponds to the decomposition of the solvents at the active surface of LiCo02, and the peak starting at 230°C... 

Stability region. Electrochemical reduction of both the solvent and salt of the electrolyte can cause the formation of a film on the surface of the anode. This film is composed of insoluble reduction products of the electrolyte. The presence of this film, the SEl, has been known to be an important feature of graphite anodes that allows for reversible cycling and long-term stability due to surface passivation. " The components of the SEl on graphite electrodes have been well studied and have shown that the decomposition products of the ethylene carbonate solvent, namely Li allg l carbonates and Li carbonate, dominate the SEl layer. -... 

With the advent of sophisticated experimental techniques for studying surfaces, it is becoming apparent that the structure of chemisorbed species may be very different from our intuitive expectations.10 For example, ethylene (ethene, H2C=CH-2) chemisorbs on platinum, palladium, or rhodium as the ethylidyne radical, CH3—C= (Fig. 6.2). The carbon with no hydrogens is bound symmetrically to a triangle of three metal atoms of a close-packed layer [known as the (111) plane of the metal crystal] the three carbon-metal bonds form angles close to the tetrahedral value that is typical of aliphatic hydrocarbons. The missing H atom is chemisorbed separately. Further H atoms can be provided by chemisorption of H2, and facile reaction of the metal-bound C atom with three chemisorbed H atoms dif-... 

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