Modification Of Molybdenum Disulfide And Its Application In Lithium-sulfur Batteries

The growing demand for mobile devices and electric vehicles has significantly promoted the development of advanced energy storage technologies in recent years.Up to the present,lithium-sulfur（Li-S）batteries have become one of the most promising candidates for energy storage batteries due to the high theoretical capacity(1673 m Ah g^-1)and low cost of sulfur.However,there are still several significant technological challenges including the low sulfur utilization,“shuttle effect”of soluble polysulfides,and the irreversible,large volume expansion of cathode structure,which hinders the commercialization of Li-S batteries.MoS₂ has attracted great attention in the field of Li-S batteries owing to its tunable structures,good catalytic activity,high ionic conductivity and low cost.It can effectively catalyze the conversion of dissolved polysulfides to inhibit the shuttle effect.Nevertheless,MoS₂,especially in two-dimensional morphology,exhibits significant edge adsorption and catalytic effects,i.e.,the large amount of inert sites on the basal plane greatly limits its adsorption and catalytic ability toward polysulfides.To solve above problems,the electrochemical catalysis and adsorption capacity of MoS₂ inert substrate were further activated by heterostructure design and hetero-atom doping,and further use it for separator modification to suppress the shuttle effect.The research contents are as follows:（1）Heterostructured MoS₂-MoO₃ coupled with carbon shell as a catalytic material for lithium-sulfur batteries.A MoS₂-MoO₃/carbon shells（MoS₂-MoO₃/CS）composite was synthesized by a H₂O₂-enabled oxidizing process under mild conditions,which is further used for separator modification.The MoS₂-MoO₃heterostructures can conform to the carbon shell morphology,forming two-dimensional nanosheets,and thus shorten the transport path of lithium ion and electrons.Based on our experiments and theoretical calculations,the heterostructures show strong surface affinity toward polysulfides,and good catalytic activity to accelerate polysulfides conversion.The Li-S battery with the MoS₂-MoO₃/CS modified separator can retain 78.0%of its capacity after 100 cycles at 0.2 C with a high sulfur loading of5.9 mg cm^-2,showing good cycling stability.（2）Oxygen-doped MoS₂ supported on carbon nanosheets as a catalytic material for lithium-sulfur batteries.The Moprecursor was partially sulfurized by the ethylene glycol-thiourea competitive reduction system to form O-MoS₂.The uniform distribution of O dopants can generate abundant adsorption/catalytic sites on the MoS₂ basal plane and enlarge the MoS₂ interlayer spacing to facilitate ion transport,thereby accelerating the catalytic conversion of polysulfides.The oxygen doped MoS₂ is supported on carbon nanosheets and the composite is employed to modify the separator.Even under a raising sulfur loading of 8.2 mg cm^-2,the assembled Li-S battery also delivers a high discharge capacity(554 m Ah g^-1)with an outstanding cycle stability（84.6%capacity retention）after 100 cycles at 0.5 C.In summary,heterostructure design and heteroatom doping can activate MoS₂ inert basal plane to promote the adsorption and catalytic ability for polysulfides.Using the modified MoS₂as a Li-S battery separator modifier can accelerate the catalytic polysulfides conversion and inhibit the shuttle effect,which greatly improves the battery cycle performance and sulfur utilization.This provides a new avenue for the design of efficient polysulfides catalysts.