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Lithium-sulfur (Li-S) batteries have shown great application prospects as next-generation energy storage systems due to their high theoretical capacity and high energy density. However, the practical application of Li-S batteries is still hindered by several challenges, such as their sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs). To date, significant research has been focused on the confinement adsorption and catalytic conversion of LiPSs using theoretical or/and experimental methods. Among them, theoretical calculations are highly attractive to observe complex LiPS conversion reactions, which facilitate the rational design of S mediators for high-performance Li-S batteries. In this review, we summarize and discuss the recent advances in the adsorption and conversion of LiPSs from the viewpoint of theoretical calculations. Moreover, a set of theoretical principles to guide the screening of suitable host materials for Li-S batteries is presented and discussed. Finally, some personal insights about the future challenges and the focus of research in this field are presented, which will push a milestone step toward high-efficiency and long-life Li-S batteries.

Ultrathin and flexible layers containing BaTiO3 (BTO) nanoparticles, graphene oxide (GO) sheets, and carbon nanotube (CNT) films (BTO/GO@CNT) are used to trap solvated polysulfides and alleviate the shuttle effect in lithium-sulfur (Li-S) batteries. In the functional layers, the CNT films build a conductive framework, and the GO sheets form a support membrane for the uniform dispersion of BTO nanoparticles. BTO nanoparticles without ferroelectricity (nfBTO) can trap polysulfides more effectively by chemical interaction compared to BTO nanoparticles with ferroelectricity (fBTO). A Li-S cell with the nfBTO/GO@CNT functional layer exhibits a reversible capacity of 824.5 mA h g-1 over 100 cycles at 0.2 C. At a high sulfur loading of 5.49 mg cm-2, an electrode with the functional layer shows an areal capacity of 5.15 mA h cm-2 at 0.1 C, demonstrating the nfBTO/GO@CNT functional layer's potential in developing high-performance Li-S batteries.

Lithium-sulfur (Li-S) batteries, as the next generation of energy storage systems, are currently limited by insufficient capture ability and sluggish catalytic reaction kinetics, thus leading to serve the shuttle effect of lithium polysulfides (LiPSs). Realizing the accelerated conversion of polysulfides in the cathode host of Li-S batteries is an effective way to improve its coulombic efficiency. The essence of fast conversion relies on enhanced oxidation reaction kinetics by virtue of the metal catalyst, but the generation of various intermediates exacerbate the complexity of the system and perplex the perfect operation of batteries relying on only one catalyst. In this work, the xMoO2:yCo2Mo3O8 heterostructures were designed, in which controlling the content of cobalt could balance the capture capability towards LiPSs by MoO2 and catalytic ability of liquid-solid conversion by Co2Mo3O8 catalytic sites. Therefore, utilizing synergy effect of MoO2-Co2Mo3O8 heterostructure enhances capture and catalytic ability toward polysulfides in Li-S batteries. As a result, the 9MoO2:2Co2Mo3O8-based cathode delivers excellent reversibility of 880 mA h g-1 after 100 cycles at 0.2C and 509 mA h g-1 after 1000 cycles at 1C with 0.056% capacity decay each cycle. This work provides a new method for synthesizing heterostructures by doping metals. Moreover, it promotes the understanding of balancing and promoting the capture capacity and catalytic conversion ability toward LiPSs.

Lithium–sulfur (Li–S) batteries with high energy density, which show great application potential in flexible electronic products, have attracted a lot of research enthusiasm. However, the low utilization of sulfur and shuttle effect limit the application of Li–S batteries. Materials with a void structure and high conductivity can be used as a sulfur host to overcome these issues. Herein, a flexible MXene-coated textile fabric electrode (MF@Ti3C2Tx/S) is designed by integrating the MXene-coated textile fabric (MF) with in situ sulfur loaded MXene nanosheets (Ti3C2Tx/S). The MF provides a flexible 3D conductive framework, which is covered with Ti3C2Tx/S nanosheets to form the layer-by-layer structure. This unique structure not only provides enough space for volume expansion to maintain the structural stability in the electrochemical process, but also promotes the physical encapsulation and chemical adsorption of lithium polysulfides (LiPSs). Consequently, the MF@Ti3C2Tx/S50 electrode exhibits a high initial capacity of 916 mA h g−1 at 1C and an ultralong-term cycling stability of 674 mA h g−1 at 1C after 1000 cycles. Furthermore, this electrode also exhibits excellent rate performance at a high energy density (290 mA h g−1 at 5C after 800 cycles). A pouch cell is prepared by using the MF@Ti3C2Tx/S50 electrode and shows excellent cycle performances at different bending angles, which indicates that this study is valuable in the field of flexible energy storage. This work provides a new concept design for flexible Li–S batteries, which have great application potential as wearable and portable electronic devices.

To overcome the shuttle effect in lithium-sulfur (Li-S) batteries, an sp/sp2 hybridized all-carbon interlayer by coating graphene (Gra) and hydrogen-substituted graphdiyne (HsGDY) with a specific surface area as high as 2184 m2 g-1 on a cathode is designed and prepared. The two-dimensional network and rich pore structure of HsGDY can enable the fast physical adsorption of lithium polysulfides (LiPSs). In situ Raman spectroscopy and ex situ X-ray photoelectron spectroscopy (XPS) combined with density functional theory (DFT) computations confirm that the acetylenic bonds in HsGDY can trap the Li+ of LiPSs owing to the strong adsorption of Li+ by acetylenic active sites. The strong physical adsorption and chemical anchoring of LiPSs by the HsGDY materials promote the conversion reaction of LiPSs to further mitigate the shuttling problem. As a result, Li-S batteries integrated with the all-carbon interlayers exhibit excellent cycling stability during long-term cycling with an attenuation rate of 0.089% per cycle at 1 C over 500 cycles.