Rational Design And Electrochemical Performance Of MoS₂ Based Functional Interlayer Mateterials For Lithium-Sulfur Batteries

The growing demand for high-energy-storage technologies has led to an enormous growth of research interest in battery systems with high energy densities and prolonged cycle lives.As traditional lithium-ion batteries are approaching their theoretical energy density limits,lithium-sulfur（Li-S）battery is considered as a promising candidate for the next-generation energy-storage system due to its high theoretical specific capacity(1675mAh g^-1)and theoretical energy density(2600 Wh kg^-1),and the low cost,nontoxic,and naturally abundant sulfur cathode.However,the commercialization of Li-S battery has been limited by multiple obstacles,and the most severe ones are the shuttle effect from the sulfur redox intermediates polysulfides and serious safety concerns caused by the uncontrollable lithium（Li）dendrite growth on Li anode.Aiming to address the above issues,four novel functional interlayers based on MoS₂ nanosheets have been designed and prepared in this dissertation,their effects on suppressing the polysulfide shuttle,accelerating Li⁺diffusion and suprressing Li dendrite growth have been investigated.The obtained research results are as following:（1）Radially oriented MoS₂ nanospheres（3D MoS₂）was assembled by ultrathin MoS₂nanosheets via a one-step hydrothermal reaction,and used as cathode interlayer in Li-S battery.Assembling MoS₂ nanosheets into a 3D framework prevents the restacking of MoS₂nanosheets and improves the polysulfide adsorption capacity.Meanwhile,the MoS₂nanosheets have expanded interlayer spacing allowing for easy Li⁺diffusion and the well-organized channels for fast electrolyte filling,synergistically facilitating Li⁺diffusion.Li-S batteries assembled with the 3D MoS₂ interlayers exhibit the improved electrochemical performances with a 0.06%capacity decay over 600 cycles.（2）Polydopamine（PDA）was self-polymerized and subsequently encapsulated on the surface of 3D MoS₂ via an aqueous reaction.After calcination,a newly synthesized multi-functional interlayer material with core-shell structure,N-doped porous carbon encapsulated 3D MoS₂（MoS₂@NC）,was prepared and employed as cathode interlayer in Li-S batteries.The integration of the polysulfide-catalyst MoS₂ and the electrically conductive carbon offers a smooth flow of electrons to the captured polysulfides for accelerating polysulfide conversion and consequently suppressing polysulfide shuttle,thus significantly improves the Li-S battery performance.Li-S batteries assembled with MoS₂@NC interlayers achieve prolonged cycle lifes of 1500 cycles,with a capacity decay of only 0.033%.（3）MoS₂ nanosheets encapsulated mesoporous SiO₂ microspheres with core-shell structure（SiO₂@MoS₂）were designed by a facile one-step assembly.SiO₂@MoS₂microspheres take full advantage of the great polysufilde affinity from MoS₂ nanosheets and the easy electrolyte wettability from mesoporous SiO₂,therefore simultaneously suppress polysulfide migration and enable fast Li⁺diffusion.As a result,the SiO₂@MoS₂ interlayer significantly improves the electrochemical performance of Li-S batteries with a negligible capacity decay of 0.028%per cycle over 2500 cycles,which is superior to the Li-S batteries with a MoS₂ interlayer or a mesoporous SiO₂ interlayer.This study provides a new strategy of the rational design for cathode interlayer in Li-S battery.（4）A double-sided modified separator with laminated structure was constructed by layer-by-layer self-assembly（LbL）of poly（diallyl dimethyl ammonium chloride）-nano MoS₂hybrids and poly（acrylic acid）（PAA）on the pretreated commercial separator.PAA provides a physical shield against polysufides as well as the chemical dual adsorption of such species.At the same time,the mechanically robust and Li⁺conductive MoS₂ layer in the modified separator effectively suppresses Li dendrite growth.As a result,the ultralight coating(0.10mg cm^-2)simultaneously protects sulfur cathode and Li anode,achieving an outstanding cycle stability with a negligible 0.029%capacity decay over 2000 cycles.The proposed LbL approach opens the door to the simple,scalable,and economic fabrication of advanced separator interlayer in Li-S battery.