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It is worth noticing that different sulfur loadings also imply different sulfur/electrolyte ratio (for the same electrolyte amount, which is quite often the case when aiming for comparing solely different sulfur electrodes). This is another parameter that should be carefully considered and reported in every experimental section, which, unfortunately, is not often the case. 1.3.1.d) Carbon based current collectors Among other proposed solutions in terms of application as a porous current collectors (i.e. metal foams126,127), carbon-based current collectors are definitely attracting the highest attention128,104,129-133, as an alternative solution to the classical 2D aluminum foil. The macroporous structure of such collector allows for high loads of sulfur per geometric cathode area, reaching dramatically improved loadings (even ~ 7 mgSulfur cm-2), as compared with classical aluminum based electrodes. As reported in the literature, utilization of such collectors improves significantly the electronic conductivity of the electrode, by providing better connection of sulfur particles to the 3D conductive network. Electrode resistance is decreased thanks to facilitated electrons propagation along the 3D continuous conductive network8,124. The porous structure also offers much easier electrolyte penetration throughout the whole cathode structure124. Carbon porous collectors can be applied in a different manners into the Li/S cell. Depending on the way how it is incorporated, we can distinguish between following architectures, as illustrated on Figure 1-12: • ‘catholyte’ all liquid cells (Figure 1-12a), where active material is dissolved directly in the electrolyte in the form of soluble lithium polysulfide species126,134, and pure carbon collector is used as a positive electrode. Different ways of ‘catholyte’ preparation are presented in the literature (i.e. reaction of solid S8 with Li in ether solvents, reaction of Li2S and S8 powders). Nevertheless, what matters is the equivalent amount of sulfur introduced into the system, which reflects the active material loading. • ‘binder-free cells’ (Figure 1-12d) with sulfur impregnated directly into the pores of carbon collector124,133, or simply elemental sulfur melted on the surface of carbon-based current collector104,131,132,135. • ‘composite electrodes’ supported by a carbon collectors (Figure 1-12c), where a standard electrode ink is coated on the porous carbon sheet, instead of Al foil128,136. • ‘inter-layer’ structure (Figure 1-12b), where porous carbon electrode is placed between the positive electrode and the separator129,137,138. Carbon collector used in such configuration is aimed for increasing the obtained capacity and mitigating polysulfides diffusion to the negative side In most of the cases, carbon collectors are available commercial products of different suppliers, initially providing this kind of materials for fuel cells industry (gas diffusion layers, GDL). Several different types of substrates, varying in thickness and mass were used. Some literature Chapter 1: Literature review 29PDF 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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