problems such as non-conductivity of sulfur, growth of lithium dendrites and the shuttle effect, impeding the process of commercialization. [7][8][9][10] In principle, people generally regard shuttle effect is the core problem that results in the poor cycle performance. For the shuttle effect, the soluble polysulfides from the sulfur cathode dissolve into the electrolyte, shuttle to the anode, and react with the lithium metal, which leads to the rapid capacity fading, low Coulombic efficiency, and a short cycle life. In addition, the polysulfides hinder the electron transport during the electrochemistry process, which brings about sluggish conversion of polysulfides and low sulfur utilization. [11][12][13][14][15] Consequently, it is highly desired to explore an effective strategy to prevent the shuttle effect and facilitate the redox kinetics. Separators play an important role in batteries that facilitates ion transportation, blocks electron and avoids short circuit. Nevertheless, unmodified separators are not able to retard the diffusion of the polysulfides. In recent years, numerous researches have been conducted to investigate functional separators to confine polysulfides and promote kinetics process of the transformation from the immobilized polysulfides to Li 2 S (kinetics conversion of the immobilized lithium polysulfides). It is generally believed that the commercial separator modification by coating functional materials is the most effective approach to design functional separator, which is more convenient and cost-effective than the fabrication of the composite sulfur cathodes. [4,[16][17][18] In the past decades, a series of materials and strategies have been explored to modify separators. Initially, carbon materials were widely used as coating materials to physically adsorb polysulfides due to their high porosity and surface area. Nevertheless, physical adsorption is so weak to some extent that the separation effect is limited. Then chemical adsorption as a more efficient method was developed to adsorb polysulfides because the chemical bonds are stronger to anchor the polysulfides and suppress the shuttle effect. The polar materials such as transition metal oxides, sulfides and nitrides usually possess chemical active sites to adsorb polysulfides. However, these materials possess weak catalytic performance so that the sluggish redox kinetics of polysulfides confined on the active coating has an adverse effect on the cycle performance of the Li-S batteries. Taking metal sulfides as an example, theThe practical application of Li-S batteries is seriously hindered due to its shuttle effect and sluggish redox reaction, which requires a better functional separator to solve the problems. Herein, polypropylene separators modified by MoS 2 nanosheets with atomically dispersed nickel (Ni-MoS 2 ) are prepared to prevent the shuttle effect and facilitate the redox kinetics for Li-S batteries. Compared with pristine MoS 2 nanosheets, Ni-MoS 2 nanosheets exhibit both excellent adsorption and catalysis performance f...

The severe shuttle effect of polysulfides and sluggish redox kinetics are the main problems that hinder the practical applications of lithium–sulfur (Li–S) batteries. In this study, dual metallic single atom pairs are implanted into carbon nanospheres to address the shuttle effect and facilitate the bi‐directional redox kinetics of sulfur. Fe sites are found to be favorable for the reduction reaction of polysulfides, while Co sites facilitate the dissolution of Li2S experimentally and theoretically, promoting the overall electrochemical performance of Li−S batteries due to the synergetic effect. The sulfur cathode with the dual metallic single atom pairs exhibits an ultrahigh capacity retention of 96.4% after 100 cycles at 0.5 C. More importantly, it demonstrates excellent rate performance (618 mAh g−1 at current density of 10 C) and outstanding cycle performance at 2 C after 2800 cycles with only 0.01% decay per cycle. Impressively, the assembled pouch cell delivers a high discharge capacity of 1385 mAh g−1 and retains 869 mAh g−1 after 100 cycles at 0.2 C. These results demonstrate the potential of dual single atom catalysts for the favorable bi‐directional redox kinetics in Li−S batteries.

Lithium–sulfur battery is the most promising candidate for the next generation of rechargeable batteries because of the high energy density. However, the severe shuttle effect of lithium polysulfides (LiPSs) and degradation of the lithium anode during cycling are significant issues that hinder the practical application of lithium–sulfur batteries. Herein, monodispersed metal–organic framework (MOF)-modified nanofibers are prepared as building blocks to construct both a separator and a composite polymer electrolyte in lithium–sulfur systems. This building block possesses the intrinsic advantages of good mechanical properties, thermal stability, and good electrolyte affinity. MOFs, grown continuously on the monodispersed nanofibers, can effectively adsorb LiPSs and play a key role in regulating the nucleation and stripping/plating process of the lithium anode. When assembled into the separator, the symmetric battery remains stable for 2500 h at a current density of 1 mA cm–2, and the lithium–sulfur full cell shows improved electrochemical performance. In order to improve the safety property, the composite polymer electrolyte is prepared with the MOF-modified nanofiber as the filler. The quasi-solid-state symmetric battery remains stable for 3000 h at a current density of 0.1 mA cm–2, and the corresponding lithium–sulfur cell can cycle 800 times at 1 C with a capacity decay rate of only 0.038% per cycle.

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