| 1. |
- Lindström, Rakel, et al.
(författare)
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Thin films of vanadium oxide grown on vanadium metal : oxidation conditions to produce V2O5 films for Li-intercalation applications and characterisation by XPS, AFM, RBS/NRA
- 2006
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Ingår i: Surface and Interface Analysis. - : Wiley. - 0142-2421 .- 1096-9918. ; 38:1, s. 6-18
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of vanadium oxide were grown on vanadium metal surfaces W in air at ambient conditions, (ii) in 5 mm H2SO4 (aq), pH 3, (iii) by thermal oxidation at low oxygen pressure (10(-5) mbar) at temperatures between 350 and 550 degrees C and (iv) at near-atmospheric oxygen pressure (750 mbar) at 500 degrees C. The oxide films were investigated by atomic force microscopy (AIM), X-ray photoelectron spectroscopy (XPS), X-Ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). The lithium intercalation properties were studied by cyclic voltammetry (CV). The results show that the oxide films formed in air at room temperature (RT), in acidic aqueous solution, and at low oxygen pressure at elevated temperatures are composed Of V2O3. In air and in aqueous solution at RT, the oxide films are ultra-thin and hydroxylated. At 500 degrees C, nearly atmospheric oxygen pressure is required to form crystalline V2O5 films. The oxide films grown at pO(2) = 750 mbar for 5 min are about 260-nm thick, and consist of a 115-nm outer layer of crystalline V2O5. The inner oxide is mainly composed Of VO2. For all high temperature oxidations, the oxygen diffusion from the oxide film into the metal matrix was considerable. The oxygen saturation of the metal at 450 degrees C was found, by XPS, to be 27 at.% at the oxide/metal interface. The well-crystallized V2O5 film, formed by oxidation for 5 min at 500 degrees C and 750 mbar O-2, was shown to have good lithium intercalation properties and is a promising candidate as electrode material in lithium batteries.
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| 2. |
- Le Van, K., et al.
(författare)
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Amorphous vanadium oxide films synthesised by ALCVD for lithium rechargeable batteries
- 2006
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 160:1, s. 592-601
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Tidskriftsartikel (refereegranskat)abstract
- This study addresses the lithium insertion performances of amorphous vanadium oxide films, synthesized by atomic layer chemical vapour deposition (ALCVD). AFM and SEM investigations showed that the as-deposited films are amorphous, compact and homogeneous. As revealed by XPS and Raman spectroscopy, the ALCVD oxide films after deposition are mainly composed of V2O5, with V4+ surface content (about 10%). The insertion of Li+ into the lattice was investigated in 1 M LiClO4-PC. The results show that the electrochemical performances obtained with amorphous vanadium oxide films, with an optimal thickness of 200 nm (455 mAh g(-1), i.e. composition of Li2.9V2O5), were superior to crystalline V2O5 films. The amorphous films exhibit higher capacity and better cycle ability even for deep lithium insertion ratio compared to crystalline V2O5 films. The chemical diffusion coefficients, deduced from numerical simulation of chronopotentiograms, were comprised between 3 x 10(-12) and 10(-12) cm(2) s(-1) for a lithium insertion ratio comprised between 0 and 2.9. AFM and Raman spectroscopy performed before and after lithiation showed that neither the morphology nor the local order of the amorphous films were significantly affected by the insertion/extraction of lithium. Raman measurements also revealed that a very small amount of lithium are locally trapped in the oxide lattice.
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| 3. |
- Lindström, Rakel, et al.
(författare)
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Li-intercalation behaviour of vanadium oxide thin film prepared by thermal oxidation of vanadium metal
- 2006
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 51:23, s. 5001-5011
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Tidskriftsartikel (refereegranskat)abstract
- In order to produce thin films of crystalline V2O5, vanadium metal was thermally oxidised at 500 degrees C under oxygen pressures between 250 and 1000 mbar for 1-5 min. The oxide films were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). The lithium intercalation performance of the oxide films was investigated by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS). It was shown that the composition, the crystallinity and the related lithium intercalation properties of the thin oxide films were critically dependent on the oxidation conditions. The formation of crystalline V2O5 films was stimulated by higher oxygen pressure and longer oxidation time. Exposure for 5 min at 750 mbar 02 at 500 degrees C resulted in a surface oxide film composed of V2O5, and consisting of crystallites up to 200 nm in lateral size. The thickness of the layer was about 100 nm. This V2O5 oxide film was found to have good cycling performance in a potential window between 3.8 and 2.8 V, with a stable capacity of 117 +/- 10 mAh/g at an applied current density of 3.4 mu A/cm(2). The diffusion coefficients corresponding to the two plateaus at 3.4 and 3.2V were determined from the impedance measurements to (5.2 and 3.0) x 10(-13) cm(2) s(-1), respectively. Beneath the V2O5 layer, lower oxides (mainly VO2) were found close to the metal. At lower oxygen pressure and shorter exposure times, the oxide films were less crystalline and the amount of V4+ increased in the surface oxide film, as revealed by XPS. At intermediate oxygen pressures and exposure times a mixture of crystalline V2O5 and V6O13 was found in the oxide film.
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