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Electrochem 2020, 1 237 improved charge-discharge capacity and stability. After 100 cycles (0.5 C), a capacity of 820 mAhg−1 was observed, while a capacity of 640 mAh g−1 was still observed even after 500 cycles. A Li-S battery has also been achieved in which a Li2S6 catholyte is hosted by a carboxyl-modified graphene oxide sponge having the highest specific pore volume reported to date (6.4 cm3 g−1) [47]. The highly porous structure of this material successfully sequesters lithium polysulfides while displaying high electron and electrolyte transportation with commensurately improved charge storage capacity. A discharge capacity of 1607 mAh g−1 (0.1 C) and areal capacity of 3.53 mAh cm−2 were observed. Importantly, a high sulfur loading (6.6 mg cm−2) can be used and the devices still achieve nearly 80% active material utilization (0.1 C). After 200 cycles (1 C), a capacity fading rate of 0.065% per cycle was observed. This study especially emphasizes that the physical form taken by the material can be just as important as the chemical identity of the material used. More studies of this nature are needed to evaluate how different surface areas, porosities, etc. influence device performance of materials otherwise comprising the same molecular elements. A sulfur host that is imbued with Lewis acidic sites to serve as potential trapping sites for polysulfides is another cathode material that is actively pursued. One study, for example, employed as the cathode support what the authors described as a “necklace-like structure” comprising interwoven carbon-nanotubes and Prussian blue ([Fe(CN)6]3−) nanocrystals [48]. This setup relied on the carbon nanotube aErlercatroychteom 2p0r20o, v2,iFdOeR cPoEEnRdRuEVcItEiWvity and ion/electron channels, while the Prussian blue p1r3ovided the necessary Lewis acidic sites to interact with polysulfides. Li-S batteries using the Prussian blue/carbon interwoven carbon-nanotubes and Prussian blue ([Fe(CN)6]3–) nanocrystals [48]. This setup relied on nanotube-supported cathode exhibit initial capacities of 1200 to 1457 mAh g−1. Capacity retention of the carbon nanotube array to provide conductivity and ion/electron channels, while the Prussian blue up to 74% (0.2 C) after 200 cycles and 61% (0.5 C) after 500 cycles were obtained. Some dependence provided the necessary Lewis acidic sites to interact with polysulfides. Li-S batteries using the −1 Prussianblue/carbonnanotube-supportedcathodeexhibitinitialcapacitiesof1200to1457mAhg . on the amount of Prussian blue was observed, with more of the Lewis basic sites leading to better Capacity retention of up to 74% (0.2 C) after 200 cycles and 61% (0.5 C) after 500 cycles were obtained. performance in general, but if Prussian blue is used alone without the carbon nanotubes, the initial Some dependence on the amount of Prussian blue was observed, with more of the Lewis basic sites capacity is only around 500 mAh g−1 due to the low conductivity of Prussian blue. leading to better performance in general, but if Prussian blue is used alone without the carbon Another study employing iron salts showed that Fe O nanoparticles that are anchored in nanotubes, the initial capacity is only around 500 mA h g du2e t3o the low conductivity of Prussian multi-walled carbon nanotubes (MWCNTs) were effective cathode components of Li-S batteries Another study employing iron salts sh−o1wed that Fe2O3 nanoparticles that are anchored in multi- blue. (Figure 9) [49]. Rates as high as 340 mAh g at 7 C-rate were achievable and stability over at least walled carbon nanotubes (MWCNTs) were effective cathode components of Li-S batteries (Figure 9) 500 cycles was demonstrated (over 545 mAh g−1, at 1 C-rate). The authors attributed the impressive [49]. Rates as high as 340 mA h g−1 at 7 C-rate were achievable and stability over at least 500 cycles − performanwceasodfemthoensetrabtaedtt(eorviers5t4o5 mthAehagbi the shuttling issue. − 1 1,liaty1Cof-rtahtee).FTheeOauthnoarsnaottpriabruttiecdlethneoimdpersestsoivaetpternfouramtaenaceggregation 23 of these batteries to the ability of the Fe2O3 nanoparticle nodes to attenuate aggregation and and dimensional swelling or to MWCNTs adsorbing polysulfides during operation, thus mitigating dimensional swelling or to MWCNTs adsorbing polysulfides during operation, thus mitigating the shuttling issue. Figure 9. Schematic Demonstrating the interaction of iron oxide particles with sulfur and polysulfides Figure 9. Schematic Demonstrating the interaction of iron oxide particles with sulfur and polysulfides during charging and discharging processes. Reprinted with permission from reference [49]. during charging and discharging processes. Reprinted with permission from reference [49]. Copyright Copyright 2020 Elsevier. 2020 Elsevier. Nanoparticles in graphene have also attracted significant attention. When spray-drying NanofpaabritciactlieosnimnegtrhaopdsheanreeuhsaedvetoalcsomabtitnreacMteodS2sniganoifitucbaenstwaitthen-tdionpe.dWghraepnhesnperashye-edtrs,yfiancgilefabrication formation of a three-dimensional porous material was accomplished [50]. This architecture was methods are used to combine MoS2 nanotubes with n-doped graphene sheets, facile formation of a hypothesized to facilitate conductivity due to the high surface area and the ability of electrolyte to three-dimensional porous material was accomplished [50]. This architecture was hypothesized to pervade the hollow tubes in the structure. Indeed, high reversible capacity of 1219 mAh g−1 was facilitate conductivity due to the high surface area and the ability of electrolyte to pervade the hollow observed even after 200 cycles at 0.2 C. The low long-term cycling capacity decay of 0.039% per cycle over 500 cycles at 1 C and improvements in rate were also attributed to the benefits endowed by the architecture. Although tremendous effort has been put into developing cathode materials and in devising separator layers, comparably less effort has been extended into devising porous interlayers to be placed between the cathode and the separator. This is another approach to minimize shuttle effects. In one effort in this vein, a porous interlayer was rapidly fabricated of carbon microfibers using centrifugal spinning [51]. A remarkable impact on the cell resistance was observed as a result of thePDF Image | Lithium-Sulfur Batteries: Advances and Trends
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