In situ Raman and UV-Vis spectroscopic analysis of lithium-ion batteries
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In situ Raman and UV-Vis spectroscopic analysis of lithium-ion batteries Marcel Heber, Christian Schilling, Toni Gross and Christian Hess Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, 64287 Darmstadt, Germany ABSTRACT The potential of Raman and UV-Vis diagnostics for spatially-resolved and in situ diagnostics of lithium-ion batteries is demonstrated. Regarding the use of in situ Raman diagnostics focus is put on LiCoO2 electrode materials, which were investigated in detail as composites of LiCoO2 with binder and conductive additives. The potential of in situ UV-Vis analysis is illustrated for carbon-based materials showing significant absorption changes during electrochemical cycling due to lithium de-/intercalation. INTRODUCTION Lithium-ion batteries are commonly used for electrical energy storage in portable devices and are promising systems for large-scale energy storage. However, their application is still limited due to electrode degradation and stability issues [1]. Despite a large number of studies a fundamental understanding of electrode degradation is still missing [2]. A strategy to elucidate the origin of degradation is to employ in situ diagnostics to study the electrodes directly even under working conditions of the battery (operando approach). In the past, a variety of techniques has been applied to the in situ characterization of battery electrodes such as Raman, FTIR, XAS and XRD [2]. It turns out to be a particular challenge to develop and apply in situ techniques that provide information on the electrolyte/electrode interfaces and/or offer sufficient spatial (~μm) resolution to monitor single electrode particles. While recent applications of X-ray absorption spectroscopy (XAS) [3] and sum-frequency generation (SFG) [4] have highlighted their use for studies on LiCoO2 electrode/electrolyte interfaces, Raman micro-spectrometry has been shown to be a powerful tool to access spatially-resolved information of electrode materials of lithiumion batteries [5-8]. Despite its potential to provide insight into the electronic structure of electrode materials and its excellent in situ capabilities UV-Vis spectroscopy has been barely applied to electrode materials for Li-ion batteries [9]. A previous UV-Vis study focused on the de-intercalation (discharge) of a lithiated petroleum coke electrode [9]. Spectroscopic changes occurred mainly at wavelengths above 400 nm and were attributed to changes in the number of free charge carrier electrons. In this contribution, we describe recent results from in situ Raman and UV-Vis analysis of electrode materials for Li-Ion batteries. We demonstrate that in situ spectroscopy provides crucial information on the local electrode dynamics and mechanistic insight into Li-ion battery operation. Possible future directions in the development of in situ diagnostics for battery research are outlined.
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EXPERIMENT The active material LiCoO2 was prepared via a modified Pechini process using high purity nitra
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