An ex-situ fluorescence spectroscopy system was set up and utilized to study the interaction of fluorescent dyes with an oxygen quencher. The... Show moreAn ex-situ fluorescence spectroscopy system was set up and utilized to study the interaction of fluorescent dyes with an oxygen quencher. The Stern-Volmer relationship was obtained and fitted to correlate the partial pressure of oxygen to the dye fluorescence intensity. The oxygen quenching constant α for 30 μM 9,10-dimethylanthracene_(DMA) dissolved in the mixture of ethylene carbonate_(EC) and dimethyl carbonate_(DMC) (1:1 volume ratio) were 0.69/0.62 at high/low partial pressure of oxygen. Operation of the self-made pouch cells with LiCoO2 as the cathode material was examined by charging/discharging at C/10. The discharge capacities were 107 and 104 mAh/g for the pouch cell both with and without the optical probe, which indicates that the optical probe did not significantly affect the performance and capacity of the cell. The optical probe was inserted into the pouch cell to measure the fluorescence intensity of the dye that was dissolved in the electrolyte. Time series experiments before charging demonstrated that the fluorescence intensity was stable for at least 24 hours. However, the fluorescence intensity decreased abruptly as the voltage of the pouch cell increased during the initial stages of charging, which means that the dye (DMA) could not be employed to detect the oxygen generated in the cell. Both the real-time fluorescence spectroscopy and the cyclic voltammetry illustrated that this dye was not suitable for the in-situ fluorescence tests. The electrochemical stability at room temperature of different dyes such as anthracene, Palladium (II) meso-tetrakis (pentafluorophenyl porphyrin)_(PTTFPP) and Platinum octaethylporphyrin_(PtOEP) were examined in the organic solvents used in the electrolytes in Li-ion cells. Cyclic voltammograms of anthracene and PTTFPP showed oxidation peaks at 2V and reduction peaks at around 1V, with the possible formation of the radical anion causing spectral changes. The chemical compound 1-hexyl-3- methylimidazolium bis (trifluormethylsulfonyl)imide_(HMIM BTI) was electrochemically stable, but the fluorescence intensity was too low (5% of dye DMA) to be used in the in-situ detection of oxygen. As a result, more work must be performed in the future to find a suitable dye. Keywords: fluorescence spectroscopy, in-situ Li-ion cell operation, quencheroxygen, the Stern-Volmer relationship M.S. in Chemical Engineeering, July 2016 Show less
