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Conclusions & Perspectives In this work, two main axes were systematically followed. The first one was mainly devoted to improvements of already existing solutions for both systems: Li/S and ‘negative electrode’/Li2S batteries, understanding the way they perform, along with carrying out developments and tests of new and innovative solutions. Another aspect was dedicated to deeper understanding of the phenomena occurring inside the Li/S batteries, the complexity of the working mechanisms and of the limiting parameters. For this purpose, two main experimental techniques were used: electrochemical impedance spectroscopy and in situ and operando X-ray diffraction. Aiming to develop Li/S batteries, we purely focused on preparation positive electrodes on both aluminum and NwC-current collectors. Our work was based on very simple positive electrodes, i.e. fabricated in a facile way with the use of cheap and commercially available products along with practical electrode loadings of at least 2.0 mgsulfur cm-2, keeping in mind the future application. Several parameters were investigated, but no significant difference in cyclability was found when using different carbon additives (SuperP®, Ketjenblack®, VGCF®) or binders (PVdF, CMC/NBR). Quite similar overall capacity retention (with slightly better performances of CMC composition) was obtained for both types of binder. In order to find eventual correlation between the electrodes’ morphology, their electric properties and cycling performances, symmetric coin cells composed of two identical sulfur electrodes were prepared and intensively studied with EIS. It was found out that the main response in the Nyquist plot is associated with the bulk response of the electrode. The large resistance values (even ~ 20 Ω) may be related to a weak homogeneity of the electrode morphology with not efficient electronic pathways, which strongly depend on the electrode ink preparation method. Well-dispersed and homogenous inks, made with Dispermat®, resulted in significantly decreased resistance response, whatever the binder used. With well-dispersed ink, the response of bulk electrode is very small, of 1 or 2 Ω only. Moreover, no correlation was obtained between EIS response at the initial state and capacity retention, contrarily to what is claimed in literature. A main semicircle in the Nyquist plot (in the MF range) of the sulfur electrode is not associated with the charge transfer reaction, but with the electrode morphology and its structural modifications after cycling (an example: problems of adhesion were also detected by increased impedance). An efficient way to increase the electrode loading and to improve the mechanical integrity of the electrode is to use a 3D type porous current collector. Utilization of such non-woven carbon felt (NwC) was adapted from the previous work of a former PhD student in our research groups. The use of 3D carbon-based current collector allowed to obtain highly loaded electrodes, 229 Conclusions & PerspectivesPDF Image | Accumulateur Lithium Soufre
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