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need to be done in order to understand this phenomenon better, minimalize it or even avoid for the future. 3.6. Conclusions The use of carbon based porous current collector allowed to obtain highly loaded electrodes, without sacrificing the practical discharge capacities. Relatively high discharge capacities of ~ 1200 mAh g-1 can be obtained at moderate C-rates (up to C/5). This architecture, however, is not optimized yet for power rate applications. The benefit of NwC over Al collector is mostly visible, when comparing highly loaded electrodes. It is then obvious that much higher capacity values can be obtained with NwC- based electrodes, with lower polarization. The reason for such improved capacity values when using NwC sheet, is not directly related with the fact, that it offers an additional conductive surface area for solid products precipitation (Li2S) at the end of discharge, as cleared out by the calculations of surface area. Thus, a more important factor is linked to its high porosity (~ 80 %) and 3D conductive network, which improve both efficient ionic and electronic conductive pathways. It also provides a rigid and stable carbon matrix for the electrode, which is beneficial from the point of view of dissolution/precipitation cycles that occur in Li/S batteries and capacity retention. One should also keep in mind that NwC used in this work was a commercial product, not optimized in terms of thickness and weight. Thus, development of on-demand NwC papers with optimized parameters (in terms of thickness, porosity, specific surface, etc.) should be consider in the future as it may result in better performances. Last but not least, one of the main obstacle systematically observed was the appearance of micro short circuits during charge, since we were working with relatively highly loaded electrodes (profound depth of lithium stripping/plating). This phenomenon, when occurring, was progressively becoming more severe, leading in the worst case to the cell death. This problem points out the requirement to investigate and focus on the lithium metal problematics. It also allows to evidence the motivation to develop alternative anode materials for Li/S cells, and the next chapter is dedicated to Li-ion/sulfur cells development and studies. 108 Chapter 3: S8 electrode on NwCPDF Image | Accumulateur Lithium Soufre
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