A Highly Efficient Sulfur Host Enabled by Nitrogen/Oxygen Dual-Doped Honeycomb-Like Carbon for Advanced Lithium-Sulfur Batteries

High energy density and long cycle life of lithium-sulfur (Li-S) batteries suffer from the shuttle/expansion effect. Sufficient sulfur storage space, local fixation of polysulfides, and outstanding electrical conductivity are crucial for a robust cathode host. Herein, a modified template method is proposed to synthesize a highly regular and uniform nitrogen/oxygen dual-doped honeycomb-like carbon as sulfur host (N/O-HC-S). The unique structure not only offers physical entrapment for polysulfides (LiPSs) but also provides chemical adsorption and catalytic conversion sites of polysulfides. In addition, this structure offers enough space for loading sulfur, and a regular space of nanometer size can effectively prevent sulfur particles from accumulating. As expected, the as-prepared N/O-HC900-S with high areal sulfur loading (7.4 mg cm^-2 ) shows a high areal specific capacity of 7.35 mAh cm^-2 at 0.2 C. Theoretical calculations also reveal that the strong chemical immobilization and catalytic conversion of LiPSs attributed to the spin density and charge distribution of carbon atoms will be influenced by the neighbor nitrogen/oxygen dopants. This structure that provides cooperative chemical adsorption, high lithium ions flux, and catalytic conversion for LiPSs can offer a new strategy for constructing a polysulfide confinement structure to achieve robust Li-S batteries.

Self-Template-Directed Metal-Organic Frameworks Network and the Derived Honeycomb-Like Carbon Flakes via Confinement Pyrolysis

Metal-organic frameworks (MOFs) have become a research hotspot since they have been explored as convenient precursors for preparing various multifunctional nanomaterials. However, the preparation of MOF networks with controllable flake morphology in large scale is not realized yet. Herein, a self-template strategy is developed to prepare MOF networks. In this work, layered double-metal hydroxide (LDH) and other layered metal hydroxides are used not only as a scaffold but also as a self-sacrificed metal source. After capturing the abundant metal cations identically from the LDH by the organic linkers, MOF networks are in situ formed. It is interesting that the MOF network-derived carbon materials retain the flake morphology and exhibit a unique honeycomb-like macroporous structure due to the confined shrinkage of the polyhedral facets. The overall properties of the carbon networks are adjustable according to the tailored metal compositions in LDH and the derived MOFs, which are desirable for target-oriented applications as exemplified by the electrochemical application in supercapacitors.

Fabrication of Fe3 O4 Dots Embedded in 3D Honeycomb-Like Carbon Based on Metallo-Organic Molecule with Superior Lithium Storage Performance

A novel metallo-organic molecule, ferrocene, is selected as building block to construct Fe₃ O₄ dots embedded in 3D honeycomb-like carbon (Fe₃ O₄ dots/3DHC) by using SiO₂ nanospheres as template. Unlike previously used inorganic Fe₃ O₄ sources, ferrocene simultaneously contains organic cyclopentadienyl groups and inorganic Fe atoms, which can be converted to carbon and Fe₃ O₄ , respectively. Atomic-scale Fe distribution in started building block leads to the formation of ultrasmall Fe₃ O₄ dots (≈3 nm). In addition, by well controlling the feed amount of ferrocene, Fe₃ O₄ dots/3DHC with well-defined honeycomb-like meso/macropore structure and ultrathin carbon wall can be obtained. Owing to unique structural features, Fe₃ O₄ dots/3DHC presents impressive lithium storage performance. The initial discharge and reversible capacities can reach 2047 and 1280 mAh g^-1 at 0.05 A g^-1 . With increasing the current density to 1 and 3 A g^-1 , remarkable capacities of 963 and 731 mAh g^-1 remain. Moreover, Fe₃ O₄ dots/3DHC also has superior cycling stability, after a long-term charge/discharge for 200 times, a high capacity of 1082 mAh g^-1 can be maintained (80% against the capacity of the 2nd cycle).