In situ Raman and XRD studies of ion insertion from supercapacitor-type electrolyte into graphitic materials

摘要

Increase of energy density is one of the main research and development topics in order to bring electrochemical double layer capacitors (EDLC) to the market. Two main routes are envisaged to achieve this goal, (i) increase of cell voltage beyond 2.7 V and (ii) utilization of charge storage processes other than double layer charging. As has been demonstrated before by Hahn et al. ion insertion is at least one process to be considered when extending the working voltage of the EDLC to above 2.7 V. Also, ion insertion can be considered as an additional charge storage process in novel EDLC electrode materials such as the "electric field activated" carbon suggested by Okamura et al. utilized in the so called Nanogate Capacitor. Ion insertion processes are typical for lithium ion batteries and have been studied extensively in situ using Raman microscopy and X-ray diffraction (XRD). In the current contribution we present in situ Raman and XRD investigations of different graphitic carbon materials in supercapacitor type systems utilizing Et{sub}4NBF{sub}4 in acetonitrile (AN) and propylene carbonate (PC). The results show that these methods not only give valuable information about ion insertion processes but also about possible ageing phenomena.