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Cycling. All cycling experiments start with an initial slower activation cycle followed by the regular cycling, which consists of an initial rest time, a constant-current (CC) discharge to 1.5 V, a variable rest time, a CC charge to 2.8 V, and finally a constant voltage (CV) charge which ends once the current drops below a certain threshold, typically 5 % of the CC charging current. 2.5 Dead ends More materials, techniques and procedures were tested and applied, but not found to be particularly helpful or constructive. For completeness, this information is also included here, but the corresponding results are not presented or discussed. These “dead ends” include: • Thermogravimetric analysis (TGA): The measurements did not work out very well because of the high reactivity of Li2S which decomposes rapidly in ambient air. TGA samples need to be sealed in aluminum containers in the glovebox, which are then opened by the TGA machine right before the heating starts. Still, the drift is quite high and there is considerable weight loss even before the tem- perature starts to rise. • Impedance of symmetrical cells (both Li/Li and S/S): The former turned out to be highly dependent on the Li pretreatment, an effect which is deemed to be irrelevant for real cells after completing the first cycle. For the latter it was very difficult to obtain reproducible results, especially for SoC ̸= 0 %. The most promising method is to remove a positive electrode from a cell cycled to the de- sired SoC, cut it into half, and build a new cell using the two halves as electrodes. However, it is tricky to cut and align the two parts perfectly symmetrically. Also, most of the original electrolyte is lost (even if the separator is reused) and has to be replaced, which causes a significant loss of polysulfides and thus a change in SoC. • Baking electrodes after fabrication: In addition to drying, electrodes were baked for 2–4 h at 70–100 °C. While the electrodes look rather similar in SEM images (except for some cracks), their electrochemical performance and lifetime was always significantly worse than that of non-baked electrodes. • Atomic Force Microscopy (AFM) was used as an analysis method complemen- tary to SEM. An environmentally protected holder including the AFM tip can be loaded with the sample in the glovebox, and directly installed in the instrument (MFP-3D, Asylum Research, Santa Barbara, CA, USA). While the resolution is 32PDF Image | Lithium-Sulfur Battery: Design, Characterization, and Physically-based Modeling
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