XPS and TOF‐SIMS study of the distribution of Li ions in thin films of vanadium pentoxide after electrochemical intercalation

Abstract

The intercalation of vanadium pentoxide by lithium ions leads to a change in optical properties, a process that is of value in thin-film electrochromic devices. The extent of intercalation can be measured, electrochemically, from the charge capacity of the film and, is in good agreement with that determined in the outermost layers by X-ray photoelectron spectroscopy (XPS), when intercalation occurs homogeneously through the film thickness. SIMS profiles of V 2 O 5 -deposited on ITO-glass coupons have allowed examination of the interface between these layers and in prior work showed a marked build up of Li in this interphase. Investigation of the distribution of lithium within the interphase showed it to be present in parts of the testpiece that were not immersed in the electrolyte used for Li insertion. In this work we have tested the suggestion that the lithium found in the interface can be introduced, during intercalation, via the exposed edge of the V 2 O 5 /ITO interface at the periphery of the sample. A series of intercalation cycles using modified cells to expose either: a) the periphery; or b) the centre; of the thin film have been carried out. The distribution of lithium after intercalation has been examined using a combination of ToF-SIMS and XPS. XPS showed lithium in the film to be related only to the immersed regions of the testpiece whilst SIMS profiles confirmed the widespread distribution of Li through the interface, only when an edge was exposed. We work confirms an important influence of an unsealed edge when samples are produced by cutting from larger glass plates.

Life-cycling and uncovering cation-trapping evidence of a monolithic inorganic electrochromic device: glass/ITO/WO3/LiTaO3/NiO/ITO

“…The study of electrochromism-driven lithium ion chemistry in a buried EC layer is made difficult by its lack of an Auger electron emission and its weak signal in other techniques. 15 In the case of a laminated EC system, the analysis of the reaction mechanism is somewhat easier because it can be decomposed. 16 In contrast to this, the analysis of monolithic all-thin-film devices is too difficult to deduce a definite conclusion.…”

Exploring Lithium-Ion Intensity and Distribution via a Time-of-Flight Secondary Ion Mass Spectroscopy

“…The result of ToF-SIMS positive ion mass spectrum integrated from the surface to crater bottom is shown in Figure 5, where two peaks of isotopes of lithium ( 6 Li : 7 Li = 7.59% : 92.41% in nature) are identified. Based on the intensity, 6 Li is used in the current study because the intensity of 7 Li exceeds the limit of the detector. Fe + or P + are also observed in the positive ion mass spectrum (not shown).…”

“…The intensity of lithium-ion is very high compared to other atoms such as Fe + or P + in the LiFePO 4 material sample due to much higher secondary ion yield of Li. 6 Li + and 7 Li + . The intensity of 6 Li + is chosen in this study due to the saturation of 7 Li + .…”

“…To better detect lithium-ion intensity from surface to bulk for several electrode materials [7][8][9][10][11][12][13], Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) has been used, specifically to investigate the formation of Solid Electrolyte Interphase (SEI) layers. ToF-SIMS is a highly sensitive surface analytical technique that can be used to detect atoms and molecules even at low concentration down to ppm level [6].…”

In Situ Imaging of Lithium-Ion Batteries Via the Secondary Ion Mass Spectrometry

“…To better detect the lithium-ion intensity from the surface to bulk materials, a ToF-SIMS is used [12][13][14][15][16][17][18]. ToF-SIMS is a highly sensitive surface analytical technique that can be used to detect atoms and molecules even at low concentrations down to the ppm level [12,19].…”