The lithium–sulfur (Li–S) battery is regarded as the most promising rechargeable energy storage technology for the increasing applications of clean energy transportation systems due to its remarkable high theoretical energy density of 2.6 kWh kg−1, considerably outperforming today's lithium‐ion batteries. Additionally, the use of sulfur as active cathode material has the advantages of being inexpensive, environmentally benign, and naturally abundant. However, the insulating nature of sulfur, the fast capacity fading, and the short lifespan of Li–S batteries have been hampered their commercialization. In this paper, a functional mesoporous carbon‐coated separator is presented for improving the overall performance of Li–S batteries. A straightforward coating modification of the commercial polypropylene separator allows the integration of a conductive mesoporous carbon layer which offers a physical place to localize dissolved polysulfide intermediates and retain them as active material within the cathode side. Despite the use of a simple sulfur–carbon black mixture as cathode, the Li–S cell with a mesoporous carbon‐coated separator offers outstanding performance with an initial capacity of 1378 mAh g−1 at 0.2 C, and high reversible capacity of 723 mAh g−1, and degradation rate of only 0.081% per cycle, after 500 cycles at 0.5 C.

Silicon is a promising negative electrode for secondary lithium-based batteries, but the electrochemical reversibility of particularly nanostructured silicon electrodes drastically depends on their interfacial characteristics, commonly known as the solid electrolyte interface (SEI). The beneficial origin of certain electrolyte additives or different binders is still discussed controversially owing to the challenging peculiarities of interfacial post-mortem investigations of electrodes. In this work, we address the common difficulties of SEI investigations of porous silicon/carbon nanostructures and study the addition of a fluoroethylene carbonate (FEC) as a stabilizing additive as well as the use of two different binders, carboxymethyl cellulose/styrene-butadiene rubber (CMC/SBR) and polyacrylic acid (PAA), for the SEI formation. The electrode is composed of silicon nanocrystallites below 5 nm diameter allowing a detailed investigation of interfacial characteristics of silicon owing to the high surface area. We first performed galvanostatic long-term cycling (400 times) and carried out comprehensive ex situ characterization of the cycled nanocrystalline silicon electrodes with XRD, EDXS, TEM and XPS. We modified the preparation of the electrode for post-mortem characterization to distinguish between electrolyte components and the actual SEI. The impact of the FEC additive and two different binders on the interfacial layer is studied and the occurrence of diverse compounds, in particular LiF, Li2O and phosphates, is discussed. These results help to understand general issues in SEI formation and to pave the way for the development of advanced electrolytes allowing for a long-term performance of nanostructured Si-based electrodes.

Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are the most frequently used electrolyte additives to enhance the lifetime of anode materials in Li-ion batteries, but for silicon it is still ambiguous when FEC or VC is more beneficial. Herein, a low-cost nanostructured silicon/carbon anode derived from HSiCl3 is tailored by the rational choice of the additive, to obtain an anode material outperforming current complex silicon structures. We demonstrate highly reversible areal capacities of up to 5 mAh/cm2 at 4.4 mg/cm2 mass loading, a specific capacity of 1280 mAh/gAnode, a capacity retention of 81 % after 500 deep-discharge cycles versus lithium metal and successful full-cell tests with high-voltage cathodes meeting the requirements for real application. Electrochemical impedance spectroscopy and post-mortem investigation provide new insights in tailoring the interfacial properties of silicon-based anodes for high performance anode materials based on an alloying mechanism with large volume changes. The role of fluorine in the FEC-derived interfacial layer is discussed in comparison with the VC-derived layer and possible degradation mechanisms are proposed. We believe that this study gives a valuable understanding and provides new strategies on the facile use of additives for highly reversible silicon anodes in Li-ion batteries

The lithium−sulfur (Li−S) battery is one of the most promising candidates for the next generation of rechargeable batteries owing to its high theoretical energy density, which is 4-to 5-fold greater than those of state-of-theart Li−ion batteries. However, its commercial applications have been hampered due to the insulating nature of sulfur and the poor cycling stability caused by the polysulfide shuttle phenomenon. In this work, we show that Li−S batteries with a mesoporous carbon interlayer placed between the separator and the sulfur cathode not only reduces the internal resistance of the cells but also that its intrinsic mesoporosity provides a physical place for trapping soluble polysulfides as well as to alleviate the negative impact of the large volume change of sulfur. This improvement of the active material reutilization allows one to obtain a stable capacity of 1015 mAh g −1 at 0.2 C after 200 cycles despite the use of a conventional sulfur−carbon black mixture as cathode. Furthermore, we observe an excellent capacity retention (∼0.1% loss per cycle, after the second cycle), thus making one step closer toward feasible Li−S battery technology for applications in electric vehicles and grid-scale stationary energy storage systems.

Since the resurgence of interest in lithium-sulfur (Li-S) batteries at the end of the 2000s, research in the field has grown rapidly. Li-S batteries hold great promise as the upcoming post-lithium-ion batteries owing to their notably high theoretical specific energy density of 2600 W h kg À1 , nearly five-fold larger than that of current lithium-ion batteries. However, one of their major technical problems is found in the shuttling of soluble polysulfides between the electrodes, resulting in rapid capacity fading and poor cycling stability. This review spotlights the foremost findings and the recent progress in enhancing the electrochemical performance of Li-S batteries by using nanoscaled metal compounds and metals. Based on an overview of reported functional metal-based materials and their specific employment in certain parts of Li-S batteries, the underlying mechanisms of enhanced adsorption and improved reaction kinetics are critically discussed involving both experimental and computational research findings. Thus, material design principles and possible interdisciplinary research approaches providing the chance to jointly advance with related fields such as electrocatalysis are identified. Particularly, we elucidate additives, sulfur hosts, current collectors and functional interlayers/hybrid separators containing metal oxides, hydroxides and sulfides as well as metalorganic frameworks, bare metal and further metal nitrides, metal carbides and MXenes. Throughout this review article, we emphasize the close relationship between the intrinsic properties of metal-based nanostructured materials, the (electro)chemical interaction with lithium (poly)sulfides and the subsequent effect on the battery performance. Concluding the review, prospects for the future development of practical Li-S batteries with metal-based nanomaterials are discussed. Fig. 2 (a) Stepwise reduction pathway of octet sulfur (S 8 ) to solid Li 2 S 2 and Li 2 S products, including intermediate LiPSs (Li 2 S n ; 3 # n # 8). 17 (b) Representative Li-S cell configuration and the characteristic charging/ discharging voltage profile based on the stoichiometric redox chemistry between lithium and sulfur. 22 (a) Reproduced with permission from ref. 17. View Article OnlineMass percentage of sulfur on the whole cathode excluding the Al or Ni substrate. c Capacity degradation rate is estimated from the gure since authors did not provide the specic value in the reference. d GO ¼ graphene oxide. e CNTs ¼ carbon nanotubes. f LiNO 3 -free electrolyte was used for the tested battery. g RFC ¼ resorcinol-formaldehyde carbon.This journal is Fig. 9 Some chosen studies dealing with cobalt sulfides in sulfur cathodes: (a) Galvanostatic cycling of a Co 9 S 8 /S (75 wt% S) composite. 200 (b) Galvanostatic cycling at 0.5C (within the 56 wt% S cathode) and (c) the capability to adsorb LiPSs of different carbon host materials with and w/o CoS 2 . 203 (d) SEM and TEM pictures of carbon/Co 3 S 4 polyhedra as a host material for sulfur and their electrochemical performanc...

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In order to utilize silicon as alternative anode for unfavorable lithium metal in lithium -sulfur (Li-S) batteries, a profound understanding of the interfacial characteristics in ether-based electrolytes is required. Herein, the solid electrolyte interface (SEI) of a nanostructured silicon/carbon anode after long-term cycling in an ether-based electrolyte for Li-S batteries is investigated. The role of LiNO 3 and 1,3-dioxolane (DOL) in dimethoxy ethane (DME) solutions as typically used electrolyte components on the electrochemical performance and interfacial characteristics on silicon are evaluated. Because of the high surface area of our nanostructured electrode owing to the silicon particle size of around 5 nm and the porous carbon scaffold, the interfacial characteristics dominate the overall electrochemical reversibility opening a detailed analysis. We show that the use of DME/DOL solutions under ambient temperature causes higher degradation of electrolyte components compared to carbonate-based electrolytes used for Li-ion batteries (LIB). This behavior of DME/DOL mixtures is associated with different SEI component formation and it is demonstrated that LiNO 3 addition can significantly stabilize the cycle performance of nanostructured silicon/carbon anodes. A careful postmortem analysis and a discussion in context to carbonate-based electrolyte solutions helps to understand the degradation mechanism of silicon-based anodes in rechargeable lithium-based batteries. Silicon is a highly attractive anode material for rechargeable Liion batteries (LIB) and post LIB systems owing to its high capacity and comparable discharge potential to lithium metal. Considerable progress has been achieved in recent years to tackle the peculiarities of silicon during de-/lithiation.1-2 The enormous volume expansion which causes fracture of individual particles and a low reversibility could be addressed by hierarchically designed nano-sized and amorphous silicon structures.3-6 However, it was shown that among other parameters the electrochemical performance of particularly nanostructured silicon significantly depends on the chosen electrolyte. [7][8][9] This observation is mainly caused by the characteristics of the interfacial layer strongly related to the surface area of the electrode material which is especially high on nanostructures. The interfacial layer, commonly known as solid-electrolyte-interface (SEI), is a surface film typically formed in the initial cycles by decomposition of electrolyte components. Because of the large volume expansion of silicon during lithiation, the SEI likely cracks and is regenerated causing continuous electrolyte consumption and high degradation. In order to reduce degradation and apply silicon as high-performance anode in rechargeable Li-based batteries, a profound knowledge of the interfacial characteristics is necessary. The SEI on silicon is typically studied in carbonate-based electrolytes since silicon is majorly considered as alternative anode for graphite in LIB. [10][11][12][13] Howeve...

Because of the outstanding high theoretical specific energy density of 2600 Wh kg(-1), the lithium-sulfur (Li-S) battery is regarded as a promising candidate for post lithium-ion battery systems eligible to meet the forthcoming market requirements. However, its commercialization on large scale is thwarted by fast capacity fading caused by the Achilles' heel of Li-S systems: the polysulfide shuttle. Here, we merge the physical features of carbon-coated separators and the unique chemical properties of N and S codoped mesoporous carbon to create a functional hybrid separator with superior polysulfide affinity and electrochemical benefits. DFT calculations revealed that carbon materials with N and S codoping possess a strong binding energy to high-order polysulfide species, which is essential to keep the active material in the cathode side. As a result of the synergistic effect of N, S dual-doping, an advanced Li-S cell with high specific capacity and ultralow capacity degradation of 0.041% per cycle is achieved. Pushing our simple-designed and scalable cathode to a highly increased sulfur loading of 5.4 mg cm(-2), the Li-S cell with the functional hybrid separator can deliver a remarkable areal capacity of 5.9 mAh cm(-2), which is highly favorable for practical applications.