Study On Separator Modification Of Lithium-sulfur Batteries Based On CNT/N-Co@TiO₂ And Ni-N-C Materials Derived From Metal Organic Frameworks

With the rapid development of modern society,the demand for energy is increasing day by day.However,due to the limitation of theoretical specific capacity of the existing commercial lithium-ion batteries,it is difficult for energy density to be further greatly improved,thus restricting the rapid development of the energy industry to a certain extent.Lithium-sulfur battery has attracted extensive attention due to their high theoretical specific capacity of 1675 m Ah g^-1 and high energy density of 2600 Wh kg^-1,and therefore it is considered to be one of the most suitable secondary batteries to meet energy needs.However,the poor conductivity of elemental sulfur（S）,the formation of lithium dendrite,and the shuttle effect of lithium polysulfide seriously affect its performance,thus restricting its commercial application in lithium-sulfur battery.To improve the shuttle effect of lithium polysulfide,in this paper,the materials derived from metal organic frameworks（MOFs）are used to modify the separator of lithium-sulfur battery,and finally it is expected to enhance the electrochemical performance of battery.Specific work contents are as follows:（1）With a catalytic source of ZIF-67,cobalt and nitrogen codoped one-dimensional（1D）carbon nanotubes（CNT/N-Co）were prepared by chemical vapor deposition,in which some of cobalts were precipitated to form zero-dimensional（0D）nanoparticles embedded in 1D CNT,and then 0D titanium dioxide nanoparticles were loaded onto CNT by solvothermal method to obtain CNT/N-Co@TiO₂ three-dimensional（3D）composites integrated with multiple nanostructures.Then,the composite materials are used to modify the separator of lithium-sulfur battery.Not only lithium polysulfides can be effectively intercepted and captured,but also the conversion between lithium polysulfides can be rapidly accelerated under the catalysis of highly active TiO₂ and Co nanoparticles.Therefore,the“shuttle effect”of lithium polysulfides can be effectively inhibitd,thus improving the performance of lithium-sulfur battery.Under the current density of 0.2 C,the initial discharge capacity can reach 1320 m Ah g^-1.After 500 cycles,the capacity attenuation per cycle is only 0.071%at 1 C.At a relatively high current density of 3 C,an initial specific discharge capacity of 653 m Ah g^-1 can be produced.Under a high sulfur loading of 5.1 mg cm^-1,it can still maintain 640 m Ah g^-1 at 0.1 C after 60 cycles.（2）Zn-Ni@MOFs was prepared from 2-methylimidazole,nickel acetate（Ni（CH₃COO）₂）and zinc nitrate by solvothermal method.Then,nickel-nitrogen-carbon（Ni-N-C）materials were obtained by removing zinc particles through high-temperature annealing and sacrificial template method.After that,the materials were modified on the separator of lithium sulfur battery.Not only lithium polysulfides can be effectively intercepted and captured,but also the conversion between different lithium polysulfides can be rapidly accelerated by using the active sites of Ni-N-C.As a consequence,the“shuttle effect”of lithium polysulfides can be effectively inhibited,thus improving the performance of lithium-sulfur battery.At 0.1 C,an initial discharge capacity of 1534 m Ah g^-1 can be obataned.At 0.5 C,it can show an initial discharge capacity of 1209 m Ah g^-1,and moreover the attenuation per cycle is only 0.06%after300 cycles.At 2 C,its initial discharge capacity can reach 778 m Ah g^-1.Under a high sulfur loading of 4.5 mg cm^-2,its initial specific capacity is 827.1 m Ah g^-1 at 0.1 C,and moreover it can still deliver 634.4 m Ah g^-1 after 162 cycles.