Li diffusion and electrochromism in amorphous and crystalline vanadium oxide thin film electrodes

Abstract

Filmes amorfos de óxido de vanádio foram depositados sobre substratos de vidro recobertos com ITO, pela técnica de deposição de filmes de óxidos metálicos por filamento aquecido. Os espectros de difração de raios-X mostraram que os filmes como-depositados tratados termicamente em atmosfera de argônio em 200 e 300 o C continuaram amorfos e os tratados a 400 e 500 o C tornaram-se policristalinos, com a estrutura do V 2 O 5 . Os eletrodos foram eletroquimicamente reversíveis sob intercalação de Li + , exibindo o efeito eletrocrômico, observado por medidas da transmitância ótica em 632,8 nm. O coeficiente de difusão do Li, DC, foi medido pela técnica de titulação galvanostática intermitente (GITT) em função da carga inserida. Para os filmes cristalinos, a absorbância ótica e o DC aumentam com a quantidade de Li inserido, nas regiões de fase única de Li x V 2 O 5 cristalino e decrescem nas regiões de duas fases. Para essas, um DC efetivo foi considerado. Nos filmes cristalinos foi inferida a presença de outros óxidos de vanádio misturados à matriz de V 2 O 5 , através das medidas de cronopotenciometria e de DC.Amorphous vanadium oxide films were synthesized onto ITO-coated glass substrates by the hot filament metal oxide deposition technique. The as-deposited samples were heat-treated in an argon atmosphere. X-ray diffraction analysis revealed that the films treated at 200 and 300 o C were still amorphous, while those treated at 400 and 500 o C were crystalline, with a V 2 O 5 structure. All electrodes were electrochemically reversible for Li + intercalation, exhibiting the electrochromic effect, observed from optical transmittance measurements at 632.8 nm. The Li-diffusion coefficient, DC, was measured by the galvanostatic intermittent titration technique (GITT) as function of the inserted charge. For the crystalline films it was observed that the optical absorbance and the DC increase with increasing Li insertion in the single-phase regions of crystalline Li x V 2 O 5 and decrease in the two-phase regions. For the latter, an effective DC was considered. The presence of other vanadium oxides mixed to the V 2 O 5 matrix was inferred for the crystalline films from the chronopotentiometric and DC measurements. Keywords: vanadium oxide film, chronopotentiometric, DC measurements IntroductionThin films of vanadium oxides have been extensively studied as electrodes for lithium electrochemical insertion. Owing to the usually high charge intercalation capacity of these films, they are highly promising as cathodes for secondary microbatteries 1 and electrochromic devices. 2 The interest in these oxides lies on their performance as high Li intercalation capacity, high potential, high energy density, good cycling performance and on the unusual double electrochromic effect. The latter is the appearance of an anodic coloration in the near-ultraviolet region and a cathodic coloration in the near-infrared region as Li is intercalated. 3 Amorphous and crystalline vanadium oxide thin film electrodes have been prepared using chemical...

In situ SEM study of lithium intercalation in individual V2O5 nanowires

“…The integral charge for intercalation (Q Cε + Q Cδ = (1.13±0.06)·10 -9 C) is almost equal to that for deintecalation (Q Aε + Q Aδ = (1.17±0.05) ·10 -9 C), which confirms that the process was completely reversed and no lithium remained in the distorted NB. These values are comparable or higher than the average effective radius of the NB, which implies that the diffusion of Li + in the NB was slower than in the films reported in [ 35 ]. 1, the volume of intercalation was about 0.7 µm 3 .…”

“…The integral charge was calculated by integrating the corresponding current segments shown in Figure 4g over time (which was recorded during cycling, but is not shown here). Li + diffusivity in thin V 2 O 5 films grown by thermal evaporation in a vacuum and annealed at 500 °C (in Ar) was reported 35 to increase from 0.3·10 -12 cm 2 /s for V 2 O 5 to 100·10 -12 cm 2 /s for δ-LiV 2 O 5 . Thus, according to Eq.…”

Characteristics of mechanochemically prepared host–guest hybrid nanocomposites of vanadium oxide and conducting polymers

“…The character of the obtained quasiequilibrium discharge curves corresponds to the form of the CVA: the potential monotonically decreased and was formed of smoothed, weakly expressed plateaus. Such plateaus could be due to the presence of a variety of intercalation centers for Li + ions with different energy, a manifestation of the rather disordered state of the structure of the materials [84]. Thus it is more convenient to consider the intercalation process using differential capacity curves: as can be seen from Fig.…”

Amorphous Vanadium Oxide Thin Films as Stable Performing Cathodes of Lithium and Sodium-Ion Batteries

“…Such a study was initiated by Julien et al in 1999 to get amorphous V 2 O 5 thin films by PLD at pO 2 ~ 13.33 and 19.995 Pa and at a substrate temperature of 300 °C that is too high to get the amorphous phase [15]. At this temperature, amorphous V 2 O 5 phase formation is not likely possible as it is well above 200 °C which is widely agreed minimum temperature limit to get the crystalline phase [16–21]. The detailed elemental and chemical (XPS) composition analysis of the so claimed amorphous V 2 O 5 phase needs to be studied.…”