Study On Novel Interlayer Structure Inhibiting Shuttle Effect Of Lithium-Sulfur Batteries

The depletion of oil resources and environmental issues are imminent,leading to an increasing demand for green energy.S is a cathode material for a promising high energy density lithium ion battery,the expansion and application of Li-S batteries have attracted wide attention from researchers.Nowadays,commercial mainstream cathode materials include lithium cobaltate（LiCoO₂）and lithium manganate（LiMn₂O₄）,energy density remains insufficient to meet need.S is inexpensive and represent one of the most abundant elements worldwide,and the theoretical specific capacity of Li-S batteries is as high as 1675mAh/g.Despite Li-S batteries have good development prospects,there are still some problems that need to be solved in practical applications,such as volume expansion during charging and discharging and shuttle effect.Herein,we start the study with the interlayer structure between the positive electrode and the separator,synthesized and prepared different interlayers for Li-S batteries to improve the cycle performance.3Dporous carbon/MWCNTs/aramid fiber flexible interlayer prepared by multi-walled carbon nanotubes（MWCNTs）or3D carbon materials and various types of fibers by vacuum filtration.Use it as a substrate and coating with hydroxyl functional groups（hydroxyapatite nanowires）,oxides（SnO₂）,and lithium fluoride（LiF）for surface modification,which is regarded as a novel embedded interlayer structure placed between the cathode and the separator,thus inhibit the shuttle effect and improve the electrochemical performance of Li-S batteries.（1）After pretreatment,the material is carbonized in a high-temperature tube furnace to prepare a novel 3D porous carbon material.The 3D porous CNT interlayer can significantly increase the capture rate of polysulfides due to its unique porous structure and large specific surface area.3D honeycomb porous carbon（Co-PC）was prepared by simple chemical and physical methods and used as a high-performance interlayer material for Li-S batteries,which significantly improved the specific capacity retention capacity and long-term cycle stability of Li-S batteries.The 3D honeycomb porous carbon formed by the etching of Conanoparticles at high temperature can prevent the dissolution and diffusion of polysulfides,and effectively suppress the shuttle effect.Furthermore,compared with the ordinary Li-S batteries,the primary discharge specific capacity of Co-PC interlayer Li-S battery increased by82.2%.The specific capacity maintained at 637 mAh/g and 445 mAh/g at 1 C and 3 C rates respectively.（2）Nano-SnO₂was used as absorbent and prepared by hydrothermal synthesis,and nano-SnO₂was embeded into a porous paper fabricated by mixing MWCNTs and aramid paper（AP）to form the porous paper（SMAP）.Electrochemical tests shown that the primary discharge capacity of electrode with SMAP interlayer reached1526mAh/g at a rate of 0.05 C,showing good rate and cycle performance.The chemical adsorption principle of embedded metal oxide is used to improve the electrochemical performance of Li-S batteries,and it also provides an effective and feasible path for achieving high energy density and long life cycle.（3）Hydroxyapatite nanowires（HN）were prepared as a polysulfide absorbent by hydrothermal synthesis,and are combined with AP interlayer to form a hierarchically cross-linked new type of hydroxyphosphate nanowire composite interlayer（HNAP）.The electrochemical test results showed that the primary discharge capacity of electrode with HNAP interlayer reached 1456mAh/g at a rate of0.05 C,and the first discharge specific capacity is still as high as 599 mAh/g at 5 C.HN is not only the main mineral component of bones and teeth in living organisms,but also has excellent biocompatibility.Furthermore,HN has strong adsorption capacity and binding affinity for polysulfides,which is due to the chemical bonds in HN such as-OH and P=O cause coordination bond adsorption on polysulfides.（4）Lithium fluoride（LiF）as a coating to form a crosslinked network structure with AP.The Li-S battery assembled with LiF/AP interlayer displayed a high discharge capacity of 885 mAh/g at 1 C after 200 cycles,with a low attenuation rate of 0.0302%per-cycle,and the specific capacity of the Li-S battery using the LiF/AP interlayer at 4 C is 693 mAh/g.LiF interacts with the electrolyte to form an artificial solid electrolyte interface（SEI）membrane that hinders the transport of polysulfides.Simultaneously,the addition of LiF can enhance the stability of the SEI film and improve the electrochemical performance of the Li-S battery.