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Structural and electrochemical characterization of graphite materials for Li ion batteries
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Materials Science and Engineering.
2012 (English)MasteroppgaveStudent thesis
Abstract [en]

The purpose of this study is to find a correlation between the crystallite sizes in the basal plane direction of graphite materials, used in carbon anodes in Lithium-ion batteries. Carbon anodes are the most common type of anode used in rechargeable Lithium-ion batteries today. The two major causes of capacity fading in graphite anodes is structural disordering during cycling and SEI (solid electrolyte interface) formation, which causes a loss of active graphite material and loss of active lithium-ion respectively. On this basis, the crystallite size in the basal plane direction La of graphite are measured by structural characterization methods for later comparison with the performance of the graphite powder when used as a carbon anode. In this work, three characterization methods have been utilized to characterize four different types of graphite powders. These three characterization methods are Raman spectroscopy, X-ray powder diffraction and SEM analysis, with special emphasis on Raman spectroscopy due to its flexibility when it comes to sample preparation methods. Three different sample preparation methods have been carried out on the graphite powders before doing Raman measurements. A comparison of the results from the Raman measurements shows a clear trend in which the calculated R-ratio is dependent on the sample preparation method, where the R-ratio is largest for samples prepared as carbon anodes. It is very likely that this trend is attributed to the increase in R-ratio due to mechanical milling of the graphite powders as a part of the processing steps of the carbon anode sample. Determining the La value with X-ray powder diffraction is usually a difficult task due to poor resolution of the diffraction peaks necessary to derive the La value. This is due to preferred orientation of non-spherical shaped graphite powders when the powder is applied directly on a Si-sample holder for X-ray diffraction measurements. However, by air spraying the graphite powders mixed with ethanol, the particle are more random oriented, giving visible diffraction peaks needed to derive the La value. It has been shown that Raman spectroscopy is an unreliable method for determining the La value by comparing the results from X-ray with the results from Raman measurements. However, if Raman spectroscopic measurements are used together with X-ray measurements, a new linear relationship between the X-ray measured La value and the Raman R-ratio can be derived. 3

Place, publisher, year, edition, pages
Institutt for materialteknologi , 2012. , 76 p.
URN: urn:nbn:no:ntnu:diva-21147Local ID: ntnudaim:6874OAI: diva2:631284
Available from: 2013-06-20 Created: 2013-06-20 Last updated: 2013-06-20Bibliographically approved

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