| In recent years,high-energy density and low-cost lithium sulfur batteries（LSBs）technology has received great attention.However,the energy density of LSBs can actually achieve is far lower than its theoretical value.The main reasons can be summarized in the“shuttle effect”of polysulfides（Li PSs）,the poor conductivity of sulfur（S8）and lithium sulfide（Li2S2/Li2S）and uncontrollable growth of lithium dendrites.To tackle these problems,researchers have proposed many strategies:such as designing novel cathode materials,electrolytes,interlayers,separators,artificial solid electrolyte interphase,etc.Based on the idea of separators modification,sea urchin-like carbon-based interlayers and metal of framework（MOFs）doped multi-level structure gel polyvinylidene fluoride（PVDF）nanofiber membranes were prepared,and systematically testing and analyzing their electrochemical performance.The specific research contents are as follows:（1）The graphite phase carbon nitride（g-C3N4）was prepared by thermal condensation reaction,and then dispersed in a methanol solution to in situ grow ZIF-67 nanoparticles.After low-temperature carbonization,the sea urchin-like carbon material with zero-dimensional cobalt（Co）nanoparticles,one-dimensional carbon nanotubes（CNTs）and two-dimensional defect CxNy nanosheets（DCNS）was prepared,and then applied as an interlayer material coating on the cathode side of the separator.The results show that:Co and N atoms can chemically adsorb Li PSs by forming Li-N and Co-S bonds,long-range ordered CNTs provide abundant paths for the transport of electrons,and the porous sea urchin-like structure can physically limit Li PSs and accommodate the volume expansion during cycling.Therefore,the cells with the prepared interlayer exhibited stable performances with an initial capacity of 1348.3m Ah g-1 at 0.2 C and an extended cycling stability of 0.04%per cycle during the 1000cycles at 1 C.Even at a high sulfur loading of 3.1 mg cm-2,a specific capacity of 691.7m Ah g-1 can be maintained after 500 cycles at 0.5 C.（2）The uniform sized ZIF-8 nanoparticles were synthesized through solvent reaction,and dispersed into the prepared PVDF spinning solution to prepare multi-level structure nanofiber membranes by electrospinning,and then applied as a separator for LSB.The prepared nanofibers were yielded multi-level structure with gel fibers,small pore size,high porosity and uniformly exposed ZIF-8 nanoparticles on the surface,thus can provide more Li PSs absorption sites and suppress the shuttle effect.In particular,the uniform distribution of lithium ions above the lithium anode with the limitation of the multi-level structure reduced the generation of lithium dendrites and improve the cell safety performance.Moreover,the LSBs with the prepared membranes exhibited outstanding electrochemical performance:the first-cycle discharge capacity reached1324.2 m Ah g-1 with extended cycling stability of 0.05%per cycle after the 700 cycles at 2 C. |
