Urchin-shaped NiCo 2 Se 4 (u-NCSe) nanostructures as efficient sulfur hosts are synthesized to overcome the limitations of lithium-sulfur batteries (LSBs). u-NCSe provides a beneficial hollow structure to relieve volumetric expansion, a superior electrical conductivity to improve electron transfer, a high polarity to promote absorption of lithium polysulfides (LiPS), and outstanding electrocatalytic activity to accelerate LiPS conversion kinetics. Owing to these excellent qualities as cathode for LSBs, S@u-NCSe delivers outstanding initial capacities up to 1403 mAh g −1 at 0.1 C and retains 626 mAh g −1 at 5 C with exceptional rate performance. More significantly, a very low capacity decay rate of only 0.016% per cycle is obtained after 2000 cycles at 3 C. Even at high sulfur loading (3.2 mg cm −2 ), a reversible capacity of 557 mAh g −1 is delivered after 600 cycles at 1 C. Density functional theory calculations further confirm the strong interaction between NCSe and LiPS, and cytotoxicity measurements prove the biocompatibility of NCSe. This work not only demonstrates that transition metal selenides can be promising candidates as sulfur host materials, but also provides a strategy for the rational design and the development of LSBs with long-life and high-rate electrochemical performance.

Original measurement data are available upon reasonable request.

The inhibition of this polysulfide shuttle effect and the promotion of the redox reaction kinetics remains as the key material challenges of lithium-sulfur batteries (LSBs) to be urgently solved.Here we report a new architecture for the cathode material based on nanoreactor of ZnSe/Ndoped hollow carbon (ZnSe/NHC). This material combination and the hollow geometry provide three key benefits to the LSBs cathode: i) The combination of lithiophilic sites of NHC and sulfiphilic sites of ZnSe effectively trap LiPS as demonstrated by experimental results and density functional theory (DFT) calculations; ii) In part related to this promoted adsorption, the ZnSe/NHC material combination is able to facilitate the Li + diffusion, thus promoting the redox reaction kinetics; iii) The hollow nanoreactor design traps LiPS and accommodates volumetric expansion preventing the cathode material decomposition. As a result, LSBs cathodes based on this hybrid material, S@ZnSe/NHC, are characterized by high initial capacities, 1475 mAh g −1 at 0.1 C and 542 mAh g −1 at 3 C, and excellent rate capability. Besides, these cathodes deliver stable operation with only 0.022% capacity decay per cycle after 800 cycles at 3 C. Even at high sulfur loading of 3.2 mg cm −2 , a reversible capacity of 540.5 mAh g −1 is delivered after 600 cycles at 1 C. Overall, this work not only further demonstrates the large potential of transitionmetal selenides as cathode materials in LSBs, but also demonstrates the nanoreactor design to be a highly suitable architecture to enhance cycle stability.

The shuttle effect and sluggish conversion kinetics of lithium polysulfides (LiPS) hamper the practical application of lithium–sulfur batteries (LSBs). Toward overcoming these limitations, herein an in situ grown C2N@NbSe2 heterostructure is presented with remarkable specific surface area, as a Li–S catalyst and LiPS absorber. Density functional theory (DFT) calculations and experimental results comprehensively demonstrate that C2N@NbSe2 is characterized by a suitable electronic structure and charge rearrangement that strongly accelerates the LiPS electrocatalytic conversion. In addition, heterostructured C2N@NbSe2 strongly interacts with LiPS species, confining them at the cathode. As a result, LSBs cathodes based on C2N@NbSe2/S exhibit a high initial capacity of 1545 mAh g−1 at 0.1 C. Even more excitingly, C2N@NbSe2/S cathodes are characterized by impressive cycling stability with only 0.012% capacity decay per cycle after 2000 cycles at 3 C. Even at a sulfur loading of 5.6 mg cm−2, a high areal capacity of 5.65 mAh cm−2 is delivered. These results demonstrate that C2N@NbSe2 heterostructures can act as multifunctional polysulfide mediators to chemically adsorb LiPS, accelerate Li‐ion diffusion, chemically catalyze LiPS conversion, and lower the energy barrier for Li2S precipitation/decomposition, realizing the “adsorption‐diffusion‐conversion” of polysulfides.

Lithium–sulfur batteries (LSBs) are considered to be one of the most promising next generation energy storage systems due to their high energy density and low material cost. However, there are still some challenges for the commercialization of LSBs, such as the sluggish redox reaction kinetics and the shuttle effect of lithium polysulfides (LiPS). Here a 2D layered organic material, C2N, loaded with atomically dispersed iron as an effective sulfur host in LSBs is reported. X‐ray absorption fine spectroscopy and density functional theory calculations prove the structure of the atomically dispersed Fe/C2N catalyst. As a result, Fe/C2N‐based cathodes demonstrate significantly improved rate performance and long‐term cycling stability. Fe/C2N‐based cathodes display initial capacities up to 1540 mAh g−1 at 0.1 C and 678.7 mAh g−1 at 5 C, while retaining 496.5 mAh g−1 after 2600 cycles at 3 C with a decay rate as low as 0.013% per cycle. Even at a high sulfur loading of 3 mg cm−2, they deliver remarkable specific capacity retention of 587 mAh g−1 after 500 cycles at 1 C. This work provides a rational structural design strategy for the development of high‐performance cathodes based on atomically dispersed catalysts for LSBs.

The shuttling behavior and sluggish conversion kinetics of the intermediate lithium polysulfides (LiPS) represent the main obstructions to the practical application of lithium–sulfur batteries (LSBs). Herein, a 1D π–d conjugated metal–organic framework (MOF), Ni‐MOF‐1D, is presented as an efficient sulfur host to overcome these limitations. Experimental results and density functional theory calculations demonstrate that Ni‐MOF‐1D is characterized by a remarkable binding strength for trapping soluble LiPS species. Ni‐MOF‐1D also acts as an effective catalyst for S reduction during the discharge process and Li2S oxidation during the charging process. In addition, the delocalization of electrons in the π–d system of Ni‐MOF‐1D provides a superior electrical conductivity to improve electron transfer. Thus, cathodes based on Ni‐MOF‐1D enable LSBs with excellent performance, for example, impressive cycling stability with over 82% capacity retention over 1000 cycles at 3 C, superior rate performance of 575 mAh g−1 at 8 C, and a high areal capacity of 6.63 mAh cm−2 under raised sulfur loading of 6.7 mg cm−2. The strategies and advantages here demonstrated can be extended to a broader range of π–d conjugated MOFs materials, which the authors believe have a high potential as sulfur hosts in LSBs.

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