Abstract
Prussian Blue analogues (PBAs) are a promising class of electrode active materials for batteries. Among them, copper nitroprusside, Cu[Fe(CN)5NO], has recently been investigated for its peculiar redox system, which also involves the nitrosyl ligand as a non-innocent ligand, in addition to the electroactivity of the metal sites, Cu and Fe. This paper studies the dynamics of the electrode, employing surface sensitive X-ray Photoelectron spectroscopy (XPS) and bulk sensitive X-ray absorption spectroscopy (XAS) techniques. XPS provided chemical information on the layers formed on electrode surfaces following the self-discharge process of the cathode material in the presence of the electrolyte. These layers consist mainly of electrolyte degradation products, such as LiF, LixPOyFz and LixPFy. Moreover, as evidenced by XAS and XPS, reduction at both metal sites takes place in the bulk and in the surface of the material, clearly evidencing that a self-discharge process is occurring. We observed faster processes and higher amounts of reduced species and decomposition products in the case of samples with a higher amount of coordination water.
Highlights
In the last century, global energy demand has grown remarkably, and all the indicators suggest it will keep on increasing in the few decades [1]
We report a study aimed at the understanding of the self-discharge process occurring at two copper nitroprusside electrodes employing a surface sensitive technique—X-ray Photoelectron spectroscopy (XPS)—and a bulk sensitive one—X-ray absorption spectroscopy (XAS)—in order to gain complementary information
The –N 1s of (NO) group and water are expected to be present in the material, while we can address the third signal as an impurity—probably some carbonate species from the adsorption of CO2
Summary
Global energy demand has grown remarkably, and all the indicators suggest it will keep on increasing in the few decades [1]. One of the focuses for further development is to find new solutions in terms of energy storage devices [2]. The lithium ion technology is the most mature technology [3,4]. Li-ion batteries are key components in portable devices and the computing and telecommunication tools required daily by society [5]. The principal challenges that these devices have faced in real-life application are cost, safety and service life. The points that need to be considered to lower costs are automation of manufacturing, material density, rate capabilities and service life. To guarantee long service life, avoiding undesired chemical reactions between the electrolyte and the electrodes could be one of the keys [2]
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