Synthesis Of Transition Metal LDHs-Based Materials Derived From MOFs And Their Application In Lithium-Sulfur Batteries

Lithium-sulfur（Li-S）batteries are a new type of secondary battery with a high theoretical specific energy of 2600 Wh/kg,and are considered an ideal storage device for the most promising next-generation energy storage batteries.The sulfur is used as the active material in the cathode of the Li-S battery,with a specific capacity of up to1675 m Ah/g,which is 3-5 times higher than the commercialized cathode materials of Li Fe PO₄（170 m Ah/g）and Li Co O₂（274 m Ah/g）.Additionally,sulfur is one of the most abundant elements on Earth,with low cost and environmentally friendly characteristics.However,the commercialization of Li-S batteries is limited by issues such as the electronic insulation of sulfur and its discharge product lithium polysulfide,the shuttle of soluble polysulfides between the cathode and anode,and the volume expansion of sulfur during charging and discharging.In this article,based on the triple design of sulfur storage,solidification,and limitation,we designed,prepared,and studied two different structures of cathode materials.Through preparation strategies,structural regulation,and catalytic conversion,we optimized the performance of the sulfur cathode,achieving the goal of improving conductivity,accelerating reaction kinetics,and suppressing shuttle effects.The details of the study and the main findings are as follows:In this study,Ni Co-LDH and Fe Ni Co-LDH materials were prepared using the sacrificial template method,with metal-organic framework（MOF）material ZIF-67 as the template and cobalt,nickel,and iron metal ions as etching agents.A hollow-structured Ni Co-LDH/Co₉S₈ composite was synthesized by in-situ sulfidation of Ni Co-LDH using SEM,XRD,TEM,EDS and other characterization methods.The resulting material exhibited a diamond-shaped dodecahedral hollow nano-cage structure.The sulfur loading capacity of the prepared positive electrode materials was above 76 wt%,and the materials were assembled into batteries for electrochemical performance testing.The S@Ni Co-LDH/Co₉S₈ positive electrode material maintained a discharge-specific capacity of 987.2 m Ah/g with a capacity retention rate of 76.5%after 300 cycles at a current density of 0.2 C.Under the same discharge conditions,the reversible discharge specific capacities of the S@Ni Co-LDH and S@Fe Ni Co-LDH electrodes were 826m Ah/g and 716.4 m Ah/g,respectively,with capacity retention rates of 74.5%and67.4%.Compared with single LDHs,Co₉S₈ significantly improved the conductivity of LDHs,increased the storage space for active sulfur,and enhanced the efficiency of active sulfur conversion in the positive electrode.A polymeric electrolyte-modified sulfur/carbon/metal hydroxide self-supported film（S@C/PDDA/L）was obtained by vacuum filtration.This strategy utilized the structural characteristics of MWCNT and GO to construct a 3D conductive carbon network and composite it with Ni Co-LDH/Co₉S₈.Simultaneously,cationic polyelectrolyte PDDA was used to modify the composite material,enhancing the adsorption of anionic lithium polysulfides.The S@C/PDDA/L self-supported thin film has the characteristics of a 3D porous structure,self-supporting,no binder,and no current collector,and can be directly used as a positive electrode material for lithium-sulfur batteries.Characterization by SEM,EDS,and TEM showed that the active material sulfur was uniformly loaded into the 3D conductive network formed by graphene and carbon nanotubes.The electrochemical test results showed that at a current density of 0.2 C,the initial discharge-specific capacity of the S@C/PDDA/L positive electrode was 862.6 m Ah/g,and after 300 cycles,the discharge-specific capacity of the S@C/PDDA/L positive electrode still remained at 684.3 m Ah/g,with a Coulombic efficiency of 96.2%.