Lithium ion batteries are used extensively in electronic devices as well as hybrid and electric vehicles. The anode electrode layer in the battery can be fabricated by coating an aqueous dispersion of carbon, binder, and additives, and then drying. During manufacturing, the distribution of the binder through the coating thickness can become nonuniform, which compromises the properties and performance of the battery. In this study, a quantitative method to analyze the binder distribution in the electrode during drying was established. A drying apparatus with an integrated analytic balance and surface-temperature measurement was used to prepare specimens. At specific time points during drying, specimens were removed from the apparatus, quickly frozen, and then freeze-dried. Raman spectroscopy was then used to measure the binder concentration at different points through the cross section of the freeze-dried electrode coating. Scanning electron microscopy was also used to explore the changing microstructure qualitatively. Using a model electrode formulation, the method demonstrated different binder distributions for electrodes dried at 150 C under airflow and room temperature, 20 C, with no airflow. The results also showed continued changes in distribution in the interior of the coating as drying continued.
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Acknowledgments The authors thank Toyota Motor Company for their support of the Industrial Partnership for Interfacial and Materials Engineering (IPRIME) at the University of Minnesota, and Chris Fretham, Bing Luo, and Kyle Price for their assistance. Portions of this study were carried out at the University of Minnesota Characterization Facility, which receives partial support from the National Science Foundation (NSF) through the MRSEC program. LFF also thanks the NSF for support under Award No. CBET 0967348.
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- Raman spectroscopy