| Nowadays,with the growing severe energy source issues and the fast global-warming trend,it is vital and urgent to develope energy storage and conversion devices with high energy density,high-capacity,and environmental friendliness.Under this premise,due to the outstanding characteristics of high specific capacity,high energy density,abundant resources,green and environmental friendliness,lithium sulfur battery has been widely studied by researchers.Unfortunately,lithium-sulfur batteries still face many obstacles,such as poor conductivity of active substances,serious shuttle effect,slow dynamics,large volume change,etc.,which make lithium-sulfur batteries fail to enter the stage of commercialization.To tackle these problems,in this paper,the interlayer material of lithium-sulfur battery is taken as the research object to improve the overall conductivity of lithium-sulfur battery,enhance the limiting effect on the shuttle effect of polysulfide,and accelerate the redox kinetics of polysulfides.The following research works are carried out.（1）Through a simple electrospinning process and subsequent pre-oxidation and carbonization,we synthesized a self-supporting tin modification and nitrogen-doped carbon skeleton intermediate layer（TCS）to effectively alleviate these problems and maintain a long cycle life of lithium-sulfur batteries.In TCS,the carbon-skeleton builds a high-effective conductive network for the whole interface,while the uniformly distributed metallic tin nanoparticles act as an absorbent of polysulfides and a catalyst to promote the conversion of sulfur species.As a result,both the charge-discharge capacity and cyclic stability of Li-S battery are significantly improved with the assistance of the TCS interlayer.With a high sulfur content of 72.6wt%,Li-S battery used TCS as interlayer shows an ultrahigh initial capacity of 1123.1m A h g-1 at 0.2 C and a high capacity retention of 92.8%after 100 cycles.Besides,even under the sulfur loading of 3.67 mg cm-2,it still keeps a high areal capacity of3.15 m A h cm-2 under a current density of 0.2C,and the decay rate in the first 50cycles is only 0.0043%.As such,this work will provide a facile and practical strategy to the development of a long cycling Li-S battery.（2）Ni-MOF nanofibers were synthesized by electrospinning and in-situ growth method.And then,through subsequent pre-oxidation and carbonization,we present a tentacles-like metallic nickel-modified and nitrogen-doped carbon skeleton（NCS）to serve as adsorbent and catalyst in LSBs.The carbonized skeleton and derived carbon tubes jointly construct conductive networks and adequate ion pathways.Meanwhile,abundant metallic nickel nanoparticles synergistically build a multifunctional interface with polar networks for the fixation and conversion of polysulfides,giving rise to significant improvement of cyclic-stability and reaction kinetics of LSBs.As a result,the Li-S batteries using NCS as interlayer could possess superior electrochemical performance including cyclic stability,high specific capacity(1204.8m Ah g-1 at 0.2 C,998.7 m Ah g-1 at 1 C)and good coulombic efficiency.More importantly,even with the areal sulfur loading up to 6.1 and 7.5 mg cm-2,it still demonstrates superior electrochemical performance with the areal capacity of 4.2 and5.9 m Ah cm-2 with a steady cycling,respectively.In conclusion,we confirm this work provides a promising way to explore and expand the application of metal nanoparticles in interlayer for advanced Li-S batteries.（3）In order to enhance the adsorption of polysulfides,we designed nitrogenous carbon skeleton interlayers（CPNCS）co-doped with metal cobalt and phosphorus from the perspective of bidirectional adsorption of polysulfides.In this interlayer,cobalt interacts with the polysulfide anion by virtue of Lewis acid-base interaction,and phosphorus and nitrogen interact with the solvated lithium cation in the polysulfide by virtue of polarity,so the shut-back effect of polysulfide is significantly limited under multiple adsorptions.Secondly,the metal cobalt has excellent catalytic activity,in the intermediate layer,the metal cobalt sites can act as catalytic sites to expedite the conversion of polysulfides and enhance the utilization of active materials.Furthermore,as an excellent conductive network,carbon skeleton provides a strong support for lithium-ion diffusion and electron transfer,and improves the overall conductivity.Therefore,the lithium-sulfur battery using CPNCS can deliver a high initial specific discharge capacity of 1224.2 m Ah g-1 at 0.2 C,and has excellent rate performance.It can still obtain a high reversible specific discharge capacity of 750.3m Ah g-1 at a high current density of 2 C.In addition,after 300 cycles at 1 C,it still has a considerable capacity retention rate,with a low decay rate per cycle.Even at high sulfur loading of 4.0 mg cm-2,the surface capacity of nearly 1000 m Ah g-1(4.0m Ah cm-2)was maintained at 0.2 C for 50 cycles with a negligible decay.The design of the CPNCS provides a valuable method from the multi-adsorption angle for producing high sulfur-loading lithium-sulfur batteries. |
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