| Rechargeable lithium–sulfur?Li-S?batteries have attracted extensive attention due to their high theoretical specific energy density(2600 Wh kg-1),environmental friendliness and low cost of sulfur.However,the practical progress of Li-S batteries is greatly restricted by the insulation of active sulfur and solid discharge-end products,rapid capacity decay,poor rate performance and Coulombic efficiency,and slow electrochemical redox kinetics of polysulfide conversion reactions.Based on the core issues such as notorious shuttle effect derived from dissolution/diffusion of soluble polysulfide intermediates and severe volumetric expansion effect of sulfur cathodes during charge/discharge cycling,the novel sulfur cathode materials were constructed from the idea of structure design and chemical regulation to synthetically improve the electrochemical performances of Li-S batteries.First,Mn CO3microcube templates were prepared,and then a template-assisted strategy was adopted to prepare the hollow porous Mo S2microboxes.After in-situ growth of Sn O2nanoparticles on the Mo S2microboxes,a sulfur host of Sn O2-decorated Mo S2microboxes?Mo S2@Sn O2?was developed.The specific research contents are as follows:?1?The Mn CO3microcube templates were successfully prepared by the co-precipitation method,and the reaction temperature and reaction time in the process conditions were optimized.The crystallinity and purity of Mn CO3products were investigated by X-ray diffraction?XRD?,Raman and so on.The size distribution and dispersion of the Mn CO3microcube templates were observed by scanning electron microscope?SEM?.It was determined that the Mn CO3microcube templates synthesized at the reaction temperature of 50oC and the reaction time of 6 h has good dispersibility,no obvious agglomeration phenomenon,highly uniform size,and very smooth surface.Through this experiment,the high-quality Mn CO3templates with good crystallinity,high purity,uniform size and good dispersibility were obtained,which can be well used as a template for template-assisted strategy preparation of hollow Mo S2materials.?2?With the cubic Mn CO3prepared with the optimal process conditions as the template,the uniform coating of Mo S2nanosheets was achieved through hydrothermal treatment.After etching and denucleation in dilute hydrochloric acid and further annealing treatment,the hollow porous Mo S2microboxes were successfully synthesized and used as the novel sulfur host.The electrochemical performance of Mo S2microboxes cathode matrix was compared with that of Mo S2microparticles.The results show that the Mo S2microboxes exhibit a well-defined hollow porous structure,enlarged interlayer distance,increased specific surface area(30.55 m2g-1)and pore volume(0.168 cm3g-1).The Mo S2microboxes/S cathode shows a significantly improved electrochemical performance:an initial discharge specific capacity of 992.8 m Ah g-1is obtained at 0.2 C;its reversible capacity remains at 381.6 m Ah g-1at 1 C after 717 cycles,and the capacity decay is approximately 0.068%per cycle,which are much better than that of Mo S2microparticles/S cathode.These confirm the effectiveness of the hollow structure for polysulfides confinement and performance improvement.?3?The Sn O2-decorated Mo S2microboxes?Mo S2@Sn O2?sulfur host was developed through in-situ growth of Sn O2nanoparticles on Mo S2microboxes via hydrothermal reaction.First,the optimal Mo/Sn molar ratio?1:2?of Mo S2@Sn O2composites was determined.Subsequently,the Mo S2@Sn O2-1:2 was used as the novel sulfur host,and the electrochemical performance of Mo S2@Sn O2-1:2 cathode matrix was compared with those of Mo S2microboxes and Mo S2microparticles.The results show that Mo S2@Sn O2-1:2 exhibits a well-defined hollow porous structure,enlarged interlayer distance?about 0.67 nm?,larger specific surface area(112.97 m2g-1)and pore volume(0.204 cm3g-1)than that of Mo S2microboxes,rich electroactive sites and high binding energy,which remarkably improve physical/chemical dual-confined capability for polysulfides.Combined with outstanding structural stability and excellent electrolyte wettability,Mo S2@Sn O2-1:2/S cathode achieves a better electrochemical performance than those of Mo S2microboxes/S and Mo S2microparticles/S cathodes:an initial discharge specific capacity of 1280.6 m Ah g-1is obtained at 0.2 C;a high specific capacity of 701.3 m Ah g-1is obtained at 1 C after1000 cycles,and the capacity decay is only about 0.033%per cycle.This work may provide a powerful strategy for designing a multifaceted cathode by rationally integrating the relationships of structure,composition and property for Li-S batteries. |
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