Co–Zn/N–C polyhedral nanocages: porous bimetallic Co/Zn embedded N-doped carbon (Co–Zn/N–C) polyhedral nanocages have been synthesized through annealing a ZIF-8@ZIF-67 precursor for the first time. The excellent lithium-storage ability is attributed to the unique structure of Co–Zn/N–C.

used as a cathode material. However, there are many shortcomings to hinder the development of Li-S batteries. First, insulating nature of sulfur and its discharge products (Li 2 S) lead to the poor electrochemical activity and low utilization of sulfur. On the other hand, during the charge/discharge process, the long-chain lithium polysulfides (Li 2 S x , 4 ≤ x ≤ 8) are very easily dissolved in the organic electrolyte [4,5] and diffuse toward the anode conductive bone, which results in undesired shuttle reactions, a rapid fading of capacity and lower Coulombic efficiency. [6] In order to promote the development of Li-S batteries, many researchers have tried attempts to solve these problems. For example, a variety of carbon materials have been designed as the host of sulfur with good electrical conductivity such as graphite or graphene, [7][8][9][10] meso-/ microporous carbon, [11,12] carbon nanotubes (CNTs)/nanofibers, [13][14][15] hollow carbon nanospheres, [16,17] and so on. Furthermore, porous carbon materials could effectively alleviate the dissolution and shuttle reactions of intermediate polysulfides by physical absorbability of pores. [11] By means of combination with chemical functionality, N-rich porous carbon materials have extensively attracted researchers' attention. For instance, Zhang and co-workers have presented a facile integration of high-quality aligned CNTs and graphene (ACNT/G hybrids) without barrier layers, followed by the process of nitrogen doping (N-ACNT/G hybrids). After combination with sulfur, electrochemical tests fully verify the superior cathode performance of N-ACNT/G hybrids to pristine ACNT/G. [18] According to the documents, pyridinic and pyrrolic nitrogen atoms can well provide abundant active sites and relieve "sulfur shuttling" by strong Li-N chemical interactions with soluble polysulfides. [19,20] Our group has reported dual N/O-doped carbon materials and explored it as carbon hosts. Because of the surficial chemical absorption function of heteroatoms for long-chain polysulfides, the related cells achieve a stable cyclic performance, even though the carbon matrix exhibits a low surface area. [19] More recently, Zheng and co-workers have proposed the derivation from metal-organic frameworks (MOFs), i.e., a synergistic composite containing cobalt and N-doped graphitic carbon (Co-N-GC), which demonstrates doped carbon facilitating S redox process and a remarkable enhancement of performance. [20] As we all known, nitrogen atoms doped in carbon matrix are beneficial for Herein, a flexible method is designed to engineer nitrogen-doped carbon materials (NC) with different functional and structural specialties involving N-doping level, graphitization, and surface area via tuning the carbonization temperature of the pre-prepared zeolitic imidazolate framework-8 (ZIF-8 ) crystals. With the aim to unveil the effect of these features on the electrochemical performance of sulfur cathode, these samples are evaluated as sulfur host and comprehensively investigated. NC-800 (800 °C, 10.45%N...

Well-distributed graphene sheets doped with nitrogen (NGS) were prepared via a thermal annealing strategy with the existence of cyanamide. The cyanamide can efficiently restrain the conglomeration of the resultant graphene sheets and synchronously make sure the doping of nitrogen. Followed by the next-step of low-temperature solvothermal route, uniform ultrasmall tin sulfide (SnS 2 ) nanocrystals were readily grown on the preformed NGS (denoted as SnS 2 -NGS).Benefiting from the synergistic function between NGS and SnS 2 , the resultant composites exhibit excellent electrochemical performance. In case of estimation as anode materials for lithium-ion batteries (LIBs), SnS 2 -NGS with moderate weight ratio of SnS 2 deliver outstanding electrochemical outcomes giving the high reversible capacity of 1407 mA h g -1 at 200 mA g -1 after 120 cycles. The composites can also maintain a reversible capacity of about 200 mA h g -1 at a high current density of 10 A g -1 . The lithium-ion storage ability of prepared SnS 2 -NGS electrode is at the top rank in comparison with the other works. The obtained composites also achieve good sodium storage ability.

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