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Quasi-In-Situ Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy during Cycling and Calendar Aging of Silicon Nanoparticle Anodes
Poster Exhibition
Cell characterization
Characterization methods

Obtaining a detailed understanding of cycle and calendar aging is essential for confronting the challenges of silicon anodes. Recent developments in in-situ and in-operando scanning electron microscopy (SEM) techniques showed the kinetics of the Li in Si distribution and the volume expansion during electrochemical de-/lithiation of silicon. Due to the high vacuum in the SEM in-situ batteries require complex cell designs and uncommon electrolytes such as ionic liquid and polymer electrolytes or cooling of the cell to prevent electrolyte evaporation. This leads to an unrealistic and restricted cell set-up. Furthermore, the in-situ SEM set-up limits the resolution of the images to the micrometer scale and the measurement is often limited to only a few charge-/discharge-cycles due to beam damage. In addition, an in-situ energy dispersive X-ray spectroscopy (EDX) observation of the electrode surface composition is not possible due to the presence of the electrolyte. On the contrary, ex-situ SEM and EDX measurements compare different electrodes leading to possible misinterpretation due to artefacts and minor differences in the electrode structure. To overcome the challenges of in- and ex-situ SEM measurements we combined aspects of ex- and in-situ techniques allowing comparable images and realistic cycling conditions. SEM images and EDX spectra of the same spot of the nanoscale silicon were obtained at the same state of charge in the pristine state, after formation and after a set number of cycles by disassembling a standard coin cell under argon and transferring the anode in vacuum in and out of the SEM, which ensured a quasi-in-situ environment. This quasi-in-situ SEM/EDX study contributes to a more detailed understanding of degradation mechanisms of silicon nanoparticle anodes during charge-/discharge cycling at different c-rates such as pulverization, permanent volume change and composition of surface decomposition products. Beside the aging during cycling, we examined the calendar aging at different state of charges and at different temperatures comparing SEM images and EDX spectra of the same spot of the silicon-based anode.

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Markus Börner, Martin Winter