Development of an evaluation tool for characterization of electrodes using Lasermicroscope imaging

Consulta en la Biblioteca ETSI Industriales (Riunet)

[EN] A series of graphite / lithiumironphosphate (LFP) commercial cells, aged under different conditions are disassembled and analyzed in order to identify ageing phenomena. The cells were aged under varying DOD and current rates for cycle ageing and varying temperatures and SOC for calendar ageing. The extracted positive and negative electrodes are studied using laser microscope images and Fourier Transform Infrared (FTIR) spectra in different parts of the disassembled cell. The results of the analysis exhibit uneven ageing of the graphite electrodes, showing differences over the electrode height between middle parts of the electrode compared to the upper or lower parts. The ageing optically detected by laser microscope is related to capacity fade and increase of internal resistance measured at life cycle test of the full cells. Evaluation of the images according to surface layer and dendritic formation show that there is a good correlation between them. Calendar aged cells show no evidence of ageing in laser microscope images even in the hardest measured conditions of 60 °C and 100% SOC. FTIR spectrometer provides information about the possible ageing compounds in the electrodes. Some SEI components could be detected and other ones derived from electrolyte decomposition. Cathode and separator measurements show good signal spectra but anode spectra shows low peak signal and some variability between the measurements. Only one cell has been evaluated by FTIR spectrometer to show the proof of concept of this techniques.