Review—The Importance of Chemical Interactions between Sulfur Host Materials and Lithium Polysulfides for Advanced Lithium-Sulfur Batteries

Abstract

This overview details the recently recognized importance of strong chemical interactions between sulfur host materials and lithium polysulfides/sulfide to improve the performance of Li-S batteries, especially with respect to cycle life. Sulfur hosts consisting of: functionally modified surfaces, metal oxides and carbides that rely on either polar interactions or the thiosulfate mechanism for sulfide binding, metal-organic frameworks that exhibit Lewis-acid behavior, and functional polymers are reviewed. We summarize a variety of studies that explore the nature and strength of the interaction of these materials with polysulfides and its effect on cycle life, showing that capacity fading is reduced to as low as 0.03% per cycle with effective functional cathode host surfaces. The ever-growing demand and consumption of energy as well as the depletion of fossil fuels and its associated environmental pollution have driven scientists to pursue renewable energy alternatives. Photovoltaic panels and wind farms are being installed worldwide. However, to fully utilize the electricity generated by these inherently intermittent sources, rechargeable battery systems are a vital part of the system, enabling grid-scale electric storage and benefitting electric and hybrid-electric vehicular transport. 1Amongst all the rechargeable battery systems that have serviced mankind for decades, lithium-ion batteries (LIBs) have dominated the commercial battery market, owing to their high cell voltage, low self-discharge rate, and stable cycling performance.2-4 However, the applications of these batteries have been somewhat limited due to their low energy density (100-220 W·h·kg −1 ) and high cost. 5,6 These battery systems -which consist of a graphite anode and a lithium metal oxide cathode and rely on a Li-ion intercalation mechanismare very attractive for the electric vehicle market. Nonetheless, they do not enable a long driving range unless very large battery packs are utilized, which comes at very high cost and weight. Thus the goal of traveling 500 km per charge is still unattainable. Electrochemical systems that offer a higher capacity and energy density as well as a longer life-time at a lower cost are becoming promising options, but are definitely challenging to bring into practice.Lithium-sulfur (Li-S) batteries are considered as one of the most promising candidates for the next-generation energy storage systems, because of their high theoretical energy density and the natural abundance of sulfur.7-10 A conventional Li-S cell consists of a lithium metal anode and an elemental sulfur cathode in an ether-based electrolyte. The coupling of the high-capacity electrodes of lithium (3840 mA·h·g −1 ) and sulfur (1675 mA·h·g −1 ) affords an average cell voltage of 2.2 V and a theoretical energy density of 2570 W·h·kg −1 . The reversible conversion reaction between sulfur and lithium sulfide (Li 2 S) is accompanied by a series of intermediate lithium polysulfides (LiPSs, Li 2 S n , 2 ≤ n ≤ 8). The electrochemical reactions of Li-S batte...

A sulfur host based on titanium monoxide@carbon hollow spheres for advanced lithium–sulfur batteries

“…Among these methods, the most popular strategy is composing sulfur with carbonaceous materials671819, since their intrinsic good conductivity and diversity in nanostructures make the carbon materials very attractive19202122. However, the carbon/sulfur composite cathodes still generally suffer from rapid capacity fading over long-term cycling, because the nonpolar carbon can only provide weak physical adsorption to the polar LiPSs23. Once LiPSs are solvated, they can easily dissolve into the organic electrolyte from the electrode surface and diffuse away.…”

New Separators in Lithium/Sulfur Cells with High-Capacity Cathodes

“…Common E/S ratios are currently around 9 ml/g, but will need to be reduced to 4-5 ml/g to achieve competitive high-energy Several interesting strategies have been described in the literature to sequester sulfur and its reduction products within the cathode, either by modifying the cathode structure and/or electrolyte, or by fortifying the Li anode with a protective coating. Among these approaches, the improvements from cathode modifications are noteworthy as pioneered by the studies of Nazar et al 12 with sulfurencapsulated porous carbon scaffolds which led to several novel carbonaceous nanostructures that confine the sulfur products and also restrict electron transport distances. [13][14][15][16][17][18][19][20][21][22][23] Sulfur is incorporated into such nanoporous carbon scaffolds (e.g., Hierarchical Porous Carbon (HPC) containing both micro-and mesopores), often by melt-infusion, to form carbon−sulfur composite cathodes.…”

Structural Design of Lithium–Sulfur Batteries: From Fundamental Research to Practical Application

“…3). There have been several reviews that expand on these topics and can be found in the references [106][107][108][109][110][111][112][113][114][115][116][117][118] (Fig. 5).…”