Study On The Application Of Multi-Configuration Metallic Oxygen Group Compounds In Separator Modification Of High-Performance Lithium-Sulfur Batteries

Lithium-sulfur battery is considered as the next generation of energy system with great commercial application prospects due to its high theoretical specific capacity(1675 m Ah g^-1)and high theoretical energy density(2600 Wh kg^-1),abundant reserves of cathode material sulfur（S）,low cost and environmental friendliness.However,many defects restrict its further development:the poor conductivities of cathode material S and its reduction product lithium sulfide（Li₂S）are not conducive to the rapid progress of REDOX reaction;the densities of S and Li₂S differ greatly,leading to an 80%volume expansion;besides,the notorious“shuttle effect”of soluble polar polysulfide lithium（LPS）can not only reduce the utilization rate of S,but also induce the disproportionation reaction with lithium metal,resulting in disorderly growth of lithium dendrites,and even series of safety issues.In this study,based on the strong chemical adsorption effect of polar metallic oxygen group compounds on LPS,hydrothermal method,chemical vapor deposition method and low temperature combustion method are further applied to construct the multi-configuration of the polar compounds to improve their specific surface area and electrical conductivity.Furthermore,the difference of inhibition mechanism of“shuttle effect”are investigated.By applying the multi-configuration metallic oxygen group compounds as separator modifier of Li-S batteries,the battery performance can be effectively enhanced.The specific research content and results are as follows:1.Co/N co-doped multi-configuration carbon（C）coated vanadium trioxide（V₂O₃）core-shell spheres（Co,N@V₂O₃-C）have been prepared.The three-dimensional（3D）core-shell sphere is self-assembled by 0D hexagonal structure V₂O₃,and 2D layers of V₂O₃ are in situ grown on the surface of the shell.The whole multi-configuration sphere is uniformly coated with N-doped C layers.The construction of multi-configuration increases the specific surface area and provides more LPS adsorption sites.N-doped C layer improves the conductivity.Co,N elements can catalyze the reversible conversion between LPS.Based on the synergistic inhibition of“shuttle effect”,Li-S battery performance can be effectively improved by applying the multi-configuration Co,N@V₂O₃-C as separator modifier:an initial discharge capacity of 1485.3m Ah g^-1can be obtained at 0.1C;an initial discharge capacity of 1322.2m Ah g^-1 can be obtained at 1C and remained at 360.5m Ah g^-1 after 1100 cycles,with a capacity loss rate of0.064%per cycle;an initial discharge capacity of 973.9m Ah g^-1can be obtained at 3C and remained at 399.1m Ah g^-1 after 1000 cycles,with a capacity loss rate of 0.059%per cycle.2.Multi-configuration carbon coated zinc vanadate/zinc oxide（Zn V₂O₄/Zn O）heterojunction porous lamellar spheres（Co Ni@Zn V₂O₄/Zn O-N,C）rich of oxygen vacancies have been prepared.The 3D multi-configuration is self-assembled from 2D heterojunction porous layers,on which 0D Co Ni alloy particles are in situ grown.The entire 3D multistage structure is uniformly coated by N-doped C layers.The multi-configuration can provide more LPS adsorption sites.The formation of heterogeneous structure can adjust the interfacial energy level and enhance the ion transport and conductivity.Abundant oxygen vacancies in heterogeneous structure can replace lattice oxygen to adsorb LPS and maintain the lattice stability.Co Ni alloy and doped N can promote the reversible conversion of LPS.Based on the synergistic inhibition of“shuttle effect”,the battery performance can be improved when applying the multi-configuration as separator modifier:an initial discharge capacity of 1468.9 m Ah g^-1can be obtained at 0.1C;an initial discharge capacity of 1394.9 m Ah g^-1 can be obtained at1C and remained at 533 m Ah g^-1after 900 cycles,with a capacity loss rate of 0.054%per cycle;an initial discharge capacity of 921.2 m Ah g^-1 can be obtained at 3C and maintained at 467.9 m Ah g^-1 after 1000 cycles,with a capacity loss rate of 0.049%per cycle.3.Multi-configuration cadmium sulfide（CdS）quantum dots（QDs）composite（CdS@C）with abundant trap centers have been prepared,in which CdS are in the form of 0D QDs and embedded in 3D carbon skeleton,and 2D layers are in situ grown on the 3D carbon skeleton.The strain test of a single CdS@C composite device shows that the external strain and bias can effectively regulate the Fermi level and barrier height on the surface of QDs,and then control the injection and ejection of central electrons in the trap centers.When the CdS@C composite material is applied as the separator modifier after ball milling,the trap centers can be rapidly injected with electrons during the charging and discharging process.Hence,the Fermi level of CdS QDs increases,the surface barrier decreases,and the electron transition between traps and quantum tunneling effect are more significant.Based on the trap center effect of multi-configuration composite and its synergistic effect on LPS polar adsorption,the“shuttle effect”can be effectively inhibited,and the battery performance can be improved:the initial discharge capacity of 1325.5 and 988 m Ah g^-1 can be obtained at 0.1 and 1C,respectively,and remained at 599 m Ah g^-1after 400 cycles at 1C;an initial discharge capacity of 752 m Ah g^-1 can be obtained at 3C.In this study,simple preparation methods have been applied to construct multi-configuration of polar metal oxides,metal-oxide heterojunctions which are rich of oxygen vacancies and metal-sulfide QDs which are rich of trap centers.The mechanisms of polar adsorption,oxygen vacancy effect and trap center effect in inhibiting LPS“shuttle effect”have been explored.This study provides an innovative idea for the application of multi-configuration polar metallic oxygen group compounds in the separator modification of Li-S batteries.