Controllable Preparation Of Two-dimensional Carbon-loaded Ⅳ-Ⅴ Family Transition Metal Nitride Nanocrystals And Applications In Lithium-sulfur Batteries

With lithium metal as the anode,sulfur as cathode,lithium sulfur battery has super high theoretical capacity and energy density.The abundant sulfur reserves in the crust directly reduce the cost-effectiveness of the battery.Environmental-friendly sulfur promotes low-carbon energy and green energy,which is considered as the most potential representative of emerging energy storage systems and the first choice for the next generation of commercial energy storage systems.However,the unsatisfactory sulfur cathode performance and the uncontrollable growth of lithium anode dendrite are the two core problems restricting the practical application of lithium-sulfur batteries.To date,the researchers have proposed various strategies based on material synthesis and structure optimization to address the problems of lithium polysulfide shuttling and lithium dendrite.In this paper,VN ultrafine nanocrystals and WN nanocrysts loaded on nitrogen-doped carbon hybrid nanoparticles are designed to enhance sulfur cathode performance and promote uniform lithium deposition by using the unique catalytic effects of polar materials and the rich active sites exposed by small particles.The main work is as follows:(1)Herein,we design and fabricate monodisperse VN ultrafine nanocrystals immobilized on nitrogen-doped carbon hybrid nanosheets(VN@NCSs)via an one-step in-situ selftemplate and self-reduction strategy,which simultaneously promotes the interaction with polysulfides and the kinetics of the sulfur conversion reactions demonstrated by experimental and theoretical results.By virtue of the multifunctional structural features of VN@NCSs,the cell with ultrathin VN@NCSs(only 5 μm thickness)modified separator indicates improved electrochemical performances with long cycling stability and excellent rate capability.(2)Here,a multifunctional separator coating with monodisperse WN ultrafine nanocrystals is proposed to realize synchronous regulation on both electrodes.The functional modified layer takes into account the transformation of sulfur and lithium plating behavior,and realizes the synchronous regulation of double electrodes.It is worth mentioning that we design WN nanocrystals on nitrogen-doped carbon hybrid nanosheets via an in-situ structure-oriented method and self-reduction strategy,and single-atom W were synthesized in this reaction,which partly increased the exposed active site.On the one hand,The formation of tiny nanocrystalline cells(<3 nm)and a small number of single atoms increases the chance of the WN surface to interact with the polysulfide,thus they play an effective role in catalyzing the sulfur-containing reaction.On the other hand,the performance of the Li//Li symmetric battery suggests that the WN@NCSs modification layer can well induce uniform lithium deposition.