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cyclability and stable capacity retention. After 100 cycles, a capacity of ~600 mAh g-1 was preserved, when applying C/5 rate. He et al.111 reported on improved cyclability and cycle life when CMC/SBR binder was used, as compared with PVdF-based electrodes. According to their results, final S/carbon/binder electrodes displayed better dispersion, higher homogeneity, together with better electrochemical performances, when using CMC/SBR binder. Apart from galvanostatic cycling evaluation of the binder effect on prolonged cycling and capacity value, electrochemical impedance spectroscopy (EIS) was also applied for evaluation of the binder effect. Lacey et al.120 performed systematic investigation of the electrode compositions with different binders, by comparing the voltage profiles obtained at higher rates (1C; equivalent to i = 0.84 mA cm-2) and resulting hysteresis. They further correlated GCPL results to EIS findings, with the main focus on the evaluation of the electron transfer kinetics of the polysulfides reaction. For that purposes, EIS was measured on standard two-electrode cells at the end of charge/discharge at different cycles, and the major semicircles were compared in terms of resistance value, together with relaxation time constant. This semicircle was attributed to the reactions of polysulfides at the positive electrode side (Figure 1-8). (a) (b) Figure 1-8. Nyquist plots of Li/S two-electrode cells recorded at the end of charge and discharge of 10th, 100th and 200th cycles. Positive electrode is composed of different binder compositions: PEO:PVP 4:1 (a) and PVP solely (b)120. The EIS studies were in correlation with the overpotential observation, i.e. PVP-based electrode showed the slowest kinetics among all compositions (the lower relaxation time constant and the highest resistance of the semicircle) through EIS tests, together with the highest overpotential recorded on the voltage profile curves. Urbonaite et al.109 reported that the influence of binder can actually be visible, resulting in better cycling performances between the electrodes based on different polymers. However, they also pointed out that sometimes such differences are relatively small and in the global view, electrodes with different binders behave similarly in terms of capacity value and retention. In the same manner, effects of the initial sulfur particle size and of the type of carbon used do not lead to drastically improved performances. On the contrary, this work highlights the influence of electrolyte parameters, (i.e. amount, solvent, additives, etc.), which are the key Chapter 1: Literature review 26PDF Image | Accumulateur Lithium Soufre
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Sulfur Deposition on Carbon Nanofibers using Supercritical CO2 Sulfur Deposition on Carbon Nanofibers using Supercritical CO2. Gamma sulfur also known as mother of pearl sulfur and nacreous sulfur... More Info
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