Investigation Of Sulfur-Based Composite Cathode Materials And Functional Separators For Lithium-sulfur Batteries

With the rapid development of hand-held electronic devices and electric vehicles,high-energy-density energy storage systems have been capturing extensive witnesses and ever-increasing research enthusiasm.Lithium-sulfur?Li-S?batteries are considered as a promising candidate for next-generation rechargeable batteries due to its high theoretical energy density(2600 Wh kg^-1).In addition,sulfur possesses distinct advantages,such as cost effectiveness,nontoxicity,and abundant natural resource.Nevertheless,the problems,including the poor conductivity of sulfur,the volumetric expansion,and the shuttle effect cause by the long-chain polysulfides are hinder the Li-S batteries practical application.To solve above-mentioned challenges,N,O,and S codoped mesoporous carbon nanospheres?NOS-MCS?were successfully designed by a simultaneous method of polymerization of aniline and assembly of colloidal SiO₂ nanoparticles,and serves as the sulfur host.The large surface area of NOS-MCS provides abundant active sites for anchoring polysulfides,the large pore volume and uniform pore structure improves the sulfur amount and active materials utilization in cathodes.Combining the synthetic of physical structure confinement and chemical adsorption of polysulfides,when the sulfur loading of NOS-MCS@S cathode is 75.9%,after 500 cycles,the capacity decay only 0.062%per cycle.Though heteroatom doped carbon materials great improve the chemical adsorption polysulfides capability and thus prolong the cycle performance of Li-S batteries.The active sites are limited to the amounts of heteroatoms.Therefore,mesoporous MnO₂nanospheres with uniform pore structure were prepared using a facile self-assembly and room-temperature reaction method,and employing as the sulfur host,the pore size of the mesoporous MnO₂ nanospheres can be precisely controlled by tuning the particle diameter of the SiO₂ templates.The versatile architecture of MnO₂ not only provides a powerful chemical adsorption to anchor polysulfide intermediates on the large polar surface area but also restrains them within the nanopores by physical confinement.As a result,the mesoporous MnO₂ stabilized sulfur cathode demonstrates a high reversible capacity of 1349.3 mAh g^-1 and a low capacity fading rate of 0.073%over 500 cycles,when the sulfur loading is 80%,the cathode also exhibits a 2.5 mAh cm^-2 reversible areal capacity.Although design the structure and composition of the sulfur host greatly improve the electrochemical performance of Li-S batteries,the shuttle effect still exists in a working cell.Therefore,gum arabic?GA?,a natural and widely used polymer,is introduced to conductive carbon nanofiber?CNF?networks to build free-standing CNF-GA composite films as the polysulfides shield layer via a solution-coating method.The strong chemical adsorption between GA and polysulfides were confirmed by the DFT calculation and visual experiment,meanwhile the action mechanism was clarified by the XPS and found the exists of the lithium bond,coupling with the high conductivity of the CNF.The sulfur cathode with the CNF-GA interlayer demonstrated possesses excellent cycle performance,superior rate performance,great anti-self-discharge capability,and high energy density.