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limitations are as well. Therefore, the following description of the main problems with attribution to the positive electrode, electrolyte and the negative one, is more ‘virtual’. 1.2.2.a) Positive electrode issues One of the main limitations associated with the positive electrode is the electronic property of sulfur, which is commonly known as a poor electronic conductor (σ = 5·10-30 S cm-1)28, and which requires addition of conductive carbon additive, very often in high weight fractions (even up to 50 wt%)29,30. However, such high carbon content may reduce the final volumetric and gravimetric energy densities due to the presence of inactive mass, and the practical density values may not be better than the Li-ion cells31. Sulfur is easily soluble in most of the organic solvents used in the electrolyte, thus self- discharge32-34 can occur, visible in the OCV potential decrease and lowered discharge capacity obtained after storage. Significant morphology change of the positive electrode upon cycling is another detrimental factor. Once the battery starts to operate, the active material leaves the carbon/binder matrix, and dissolves in the electrolyte in the form of soluble polysulfides. This affects the global porosity of the electrode and may give the rise to strong electrode pulverization or even collapse. It can also be imagined that some parts of the carbon/binder agglomerates may get disconnected from the current collector, resulting in the active surface area losses. As a matter of fact, a characteristic feature of Li/S cells capacity retention shows drastic capacity fading right after the initial cycle35. The aforementioned morphology changes are strongly responsible for that behavior (but are not the only reason for that). During discharge, the final solid Li2S product is also of insulating nature, and gets formed on any available electronic conductive area of the positive electrode. Therefore, strong polarization increases upon discharge due to the passivation layer formed on the electrode surface. There is also a risk that such insulating layer may not be completely consumed (oxidized) in the following charge, giving a rise to an inactive material losses since unable to participate in the further reactions. This may result in progressive capacity fading, and such insulating leftovers decrease the effective active surface to perform the redox reactions36,37. Furthermore, the difference in the densities of two solid products, 2.07 g cm-3 for α-S8 and 1.66 g cm-3 for Li2S38,39, results in a large volumetric changes of the global electrode upon cycling (expansion up to ~ 79 %)40 . Chapter 1: Literature review 20PDF 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
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
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