Synthesis Of Transition Metal Nitride(Selenide)for Their Applications In Lithium-Sulfur Batteries

Lithium-sulfur batteries have the advantages of high theoretical specific capacity,low cost and environmental friendliness,and are considered as the next generation of rechargeable energy storage batteries with development prospects.However,the polysulfide"shuttle effect"leads to the loss of active sulfur,the formation of"dead lithium"in the metal lithium negative electrode,the specific capacity of the battery,the coulomb efficiency is reduced,and the cycle life is declinated.The diaphragm is one of the core parts of the battery,but the commercial diaphragm can not inhibit the diffusion and shuttle of polysulfide due to its large aperture.Therefore,the introduction of a multifunctional intermediate layer with adsorption and catalytic conversion of polysulfides between the membrane and the positive electrode is an effective strategy to inhibit the shuttle effect.In this paper,from the perspective of membrane modification and the introduction of independent intermediate layer,functional materials are designed to play the function of limiting polysulfide shuttle and catalyzing polysulfide transformation,and improve the performance of lithium-sulfur batteries.Specific research contents are as follows:1.Ti N flexible nanofiber film was prepared by electrospinning technology and used as a functional intermediate layer to accelerate polysulfide conversion in lithium-sulfur batteries.The catalytic activity on polysulfide was verified by electrochemical CV technology,and the initial specific discharge capacity of lithium-sulfur battery was improved to 709 m Ah g^-1 at 5C,the capacity retention rate was 95%after 200 cycles,the coulomb efficiency was always maintained at 97%,and the average capacity decay rate per cycle was 0.025%.Ti N flexible nanofiber interlayer realizes high rate charge and discharge lithium-sulfur battery.2.The Oxygen-Nitrogen co-doped Carbon substrate（OCN）supported Zn Se-Sn Se₂（Zn Se-Sn Se₂@OCN）functionalized composite was synthesized by high temperature solid phase method and in situ selenization method to inhibit shuttle effect of functional membranes of Li-sulfur batteries.For the lithium-sulfur battery with Zn Se-Sn Se₂@OCN separator,the initial specific discharge capacity can reach 1078 m Ah g^-1 at 1C,and after 200 cycles,the specific discharge capacity remains at 714 m Ah g^-1,the average capacity attenuation rate per cycle is0.16%,and the coulomb efficiency is maintained at 93.4%.Zn Se-Sn Se₂@OCN The functionalized diaphragm enables a high-capacity lithium-sulfur battery.3.The mechanism of adsorption of polysulfide by Zn Se,Sn Se₂ and Zn Se-Sn Se₂ at atomic and molecular scales was revealed by first principles density functional theory.Zn,Sn,Se sites at the Zn Se-Sn Se₂ heterointerface can anchor polylithium sulfide,showing greater adsorption energy and stronger adsorption inhibition of shuttle effect.In theory,the mechanism of atomic-molecular-scale bonding that the heterostructure inhibits shuttle in lithium-sulfur batteries is described.