Research On The Design And Development Of Graphene-based Multifunctional Composite Interlayer And Its Application In Lithium-sulfur Batterie

Lithium-sulfur(Li-S)batteries with high theoretical specific capacity and energy density are considered to be the most potential candidate for the next generation secondary batteries.However,they still suffer from many difficult problems in their practical applications,that mainly include the low conductivity of elemental sulfur,the volume expansion from sulfur to lithium sulfides,and the shuttle effect of lithium polysulfides(Li PSs).To tackle these issues,this thesis proposes to design a new interlayer between the cathode and traditional separator in the Li-S batteries to accelerate the conversion of sulfur species and inhibit the shuttle effect of Li PSs.The main research contents are as follows:(1)The hydrogen-substituted graphdiyne(Hs GDY)with a specific surface area of up to 2184 m²g^-1was prepared by a copper ion-catalyzed coupling reaction.After that a Hs GDY/Gra interlayer was designed by employing he synergistic effect of Hs GDY and graphene(Gra).The CNTs-S cathode materials together with this interlayer was used to construct new cathode(CNTs-S@Gra-Hs GDY)for high-performance Li-S batteries.The experimental demonstrated that the battery present a mean decay rate of 0.089%per cycle after 500 cycles at a current density of 1.0 C,showing good cycle stability.Furthermore the in-situ Raman spectroscopy and ex-situ X-ray photoelectron spectroscopy(XPS)combined with density functional theory(DFT)calculations were carried out to study the their working mechanisms.The results show that the strong adsorption capacity of the active sites(acetylenic bond)in Hs GDY for Li⁺contribute to the chemical anchoring of Li PSs and promotes the conversion of sulfur species during the charge and discharge process.This new type of all-carbon interlayer provides an extremely attractive solution for promoting the actualization of Li-S batteries performance.(2)Previous reports indicated that the introduction of Fe-N₄structure into Li-S batteries could accelerate the conversion of Li PSs.The analogous Sn-N structurewith similar single-atom catalytic function may be also a good sulfur conversion catalyst.Therefore,based on the first job,we studied the design of Sn Cl₂Pc for interlayer to further improve the catalysis of Li PSs.The introduced Sn Cl₂Pc into Gra can in situ form a(Sn Cl₂Pc)_npolymer on the surface of Gra after a heat treatment of?200^oC.The(Sn Cl₂Pc)_npolymer together with the Gra was used as the interlayer of Li-S batteries to construct a new cathode(CNTs-S@Sn Cl₂Pc-Gra-200).At the current density of 0.2 C,the cathode can deliver a high initial discharge capacity of 1351 m Ah g^-1,and a relatively low decay rate of 0.085%per cycle under the current of 1.0 C,which shows excellent rate performance and cycle stability.The ex-situ XPS tests result proved that the phthalocyanine polymer loaded on Gra can accelerate the sulfur conversion and play a significant effect on inhibiting the shuttle effect.The polymers of organic molecules as the interlayer of Li-S batteries pave the way for further developing of high performance Li-S batteries.