Regulating Sulfur Cathode By Vanadium-Based Materials For Lithium-Sulfur Batteries

With the growing prominent energy crisis and environment pollution,as well as the rapid development of electric and electronic devices,the traditional energy systems have been unable to satisfy the increasing requirements.As one of the emerging systems,Lithium-sulfur(Li-S)battery has become a research hotspot due to its remarkable theoretical capacity(1672 mAh·g-1)and outstanding energy density(2600 Wh·kg-1).However,the practical application of Li-S battery is handicapped by a multitude of obstacles,mainly including the lithium polysulfide(LiPS)shuttle,the insulting nature of sulfur and discharge product Li2S,and noticeable volume change effect.These technical challenges result in the sluggish sulfur redox kinetics,limited sulfur utilization and inferior electrochemical performances of Li-S battery.To address the above issues,we herein mainly focus on the design of vanadium-based materials for host and interlayer construction.The aim of this dissertation is to promote the reaction kinetics and enhance the electrochemical performance of Li-S battery by building a high-efficiency mechanism for LiPS regulation.First,we demonstrate VO2(B)nanobelts serve as an effective host additive for sulfur cathode.The VO2 nanobelts show an ultrafast anchoring behavior of LiPSs.Such an outstanding anchoring ability of VO2 can attributed to:(i)the high binding energy between VO2 and LiPSs;(ii)the distinctive anchoring modes due to its redox potentials within a targeted range.Additionally,VO2 displays remarkable catalytic effect on the reaction kinetics.With these advantages,the incorporation of VO2 into cathode enhances the rate and cycling performances of battery.We also present an in situ constructed VO2-VN heterostructure which combines the merits of ultrafast anchoring(VO2)with conducting(VN).The cooperative interface between VO2 and VN is favorable for the smooth immobilization-diffusion-conversion of LiPSs.Along this line,to synergize the functions of VO2 and VN aiming to achieve superior performances of the binary host,two different compositions of heterostructures(denoted as1 VO2-3 VN and 3VO2-1VN)are also synthesized.The result shows that 3VO2-1 VN exhibits more balanced management of adsorption,diffusion and conversion in contrast to 1VO2-3VN,accelerating the reaction kinetics and hence improving the rate and cycling performances of battery.Impressively,even in the scenarios of high sulfur loading(13.2 mg·cm-2),high temperature(50?)and wearability,the batteries incorporated with 3VO2-1 VN still maintain stable electrochemical performances.A cooperative interface bridging adsorptive V2O3 and conducting graphene is also built in-situ by virtue of direct plasma-enhanced chemical vapor deposition(Direct PECVD),leading to a highly efficient immobilization-diffusion-conversion of LiPSs.The reaction kinetics and electrochemical performances of the battery are accordingly improved due to the effective LiPS regulation.Impressively,the battery realizes a low capacity decay of 0.046%per cycle at 2.0 C after 1000 cycles.Our devised PECVD route offers an efficient strategy with respect to high-efficiency LiPS management and promoted sulfur redox kinetics.In order to optimize the sulfur cathode,we propose a VN interlayer as an effective promoter to regulate LiPSs and propel the reaction kinetics of the battery.Owing to the dense packing structure and polar surface of VN,the VN interlayer presents the bifunctionality of physical blocking and chemical anchoring the migration of LiPSs while affording smooth Li+diffusion.Additionally,the conducting surface of VN offers abundant sites for LiPS conversion.Benefiting from these advantages,the battery integrated with VN interlayer displays a low capacity decay of 0.077 per cycle at 1.0 C after 800 cycles.The design of VN interlayer provides not only in-depth insight of understanding the relationship of structure and properties of materials,and reaction process bur also paves a new way for efficient LiPS regulation toward advanced Li-S battery design.We develop a N-doped hierarchical graphene(NHG)interlayer to achieve an efficient LiPS scavenger for Li-S battery.The NHG architectures are realized by our designed bio-templating CVD approach.Due to the perfect inheritance from the diatomite template,NHG presents devious inner-channel structure.In addition,the nitrogen doping concentration of NHG is up to 5.3 atom%with a pyridine and pyrrolic N ratio of 35.8%.Benefiting from the textural structure and ample nitrogen doping of NHG frameworks,the NHG interlayer propels the reaction kinetics and thereby enhances the electrochemical performances of battery.The NHG interlayer design offers not only a route for constructing advanced electrode materials but also a new strategy toward high-efficiency LiPS regulation.