Surface evolution of Ni–V transparent oxide films upon Li insertion reactions

Abstract

A detailed picture is reported of the nature of an Li insertion Ni-V mixed-oxide electrode and of its evolution upon prolonged intercalation/deintercalation cycles. A combination of bulk and surface-sensitive techniques is used, including electrochemical analysis (cyclic voltammetry, impedance spectroscopy), atomic force microscopy (AFM) and XPS. The Ni-V oxide film, obtained by r.f. sputtering as a thin film on conductive glass for use as a transparent electrode in electrochromic windows, is an Li insertion material with high charge capacity, very good reversibility and a surface morphology characterized by a low initial roughness. Its surface composition shows an initial Ni enrichment. The nominal Ni-V stoichiometry is recovered already after ten cycles. Extended Li charge-discharge cycles induce progressive changes in the electrode reversibility (capacity fading) and in the reaction kinetics (increase of impedance). The surface evolution consists of the progressive accumulation of an Li carbonate layer, with thickness and roughness increasing with the number of cycles. The constancy of the core level and Auger peaks of Ni and V after 100 cycles excludes major changes in the electronic structure of the host oxide. However, electrochemical and AFM experiments performed after 1000 cycles indicate that the carbonate deposition on the electrode progresses further, therefore the surface layer is unable to yield a permanent electrode passivation and stabilization.

XPS and IR studies of transparent InVO4 films upon Li charge–discharge reactions

“…As to the O 1s and C 1s regions, the lithiation is responsible for the appearance of new peaks at higher BEs, which are still of sizeable intensity after delithiation. The appearance of such peaks, corroborated by the analysis of the valence band region (as previously shown for the mixed Ni -V oxide film electrodes [15]), can be explained by the presence of a carbonate surface layer, mainly deposited during the cathodic reaction. The new peaks in the C 1s, Li 1s and O 1s core levels and the structures at 13 eV (valence band spectrum in Fig.…”

“…6) support an assignment of the surface carbonate to Li 2 CO 3 , by comparison with the data from the relevant literature [16]. Such layer is in large part removed by delithiation, as deduced from XPS relative quantitative data, but is expected to grow thicker on the electrode surface after hundreds (thousands) charge -discharge cycles, as already observed for other oxide film electrodes [15]. Other features of the photoemission spectrum from the valence band region (Fig.…”

Ni/SBA-15 catalysts for CO methanation: effects of V, Ce, and Zr promoters

“…It is observed that the 10Ni-5V/SBA-15 reduced catalyst has higher V 2p 3/2 binding energy (Table 2 and Fig. 6(b)) relative to the 5V/SBA-15 sample, implying the occurrence of electron transfer from V species to Ni, 44 and which further enhances the Ni electron cloud density. As the V 4+ peaks are broader than those of V 5+ and V 3+ (Fig.…”

Electrochromics for smart windows: thin films of tungsten oxide and nickel oxide, and devices based on these

“…[208][209][210][211] The optical properties of these novel materials will be treated from a device perspective in more detail in section IV. Intercalation of Li + into Ni-oxidecontaining films has been researched several times, [352][353][354][355][356] but it seems that the optical properties are not modulated to any large extent. 357,358 This means that electrochromic Ni oxide films only can be used in devices where the optical modulation depends on proton/electron transport.…”