MOFs Derived Carbon-based Cobalt Nickel Metal Compounds Preparation And Electrochemical Properties Of Composite Materials

Lithium-ion batteries are widely used in cell phones,notebook computers,new energy vehicles and other fields due to their stable service life and high energy density.The actual mass energy density of lithium-ion battery（Li Co O₂/C）is about 250 Wh kg^-1at this stage,and it is close to the theoretical specific capacity,which cannot meet the current demand of high energy density battery.Lithium-sulfur batteries are gradually becoming a key area of focus due to their high theoretical specific capacity（about 8 times that of commercial lithium-ion batteries）,green environment and low cost.In order to improve the cycle life and multiplier performance of lithium-sulfur batteries,a simple hydrothermal-carbonation method is used to derive a high specific surface composite from the perspective of cathode modification,with the aim of suppressing the shuttle effect,accelerating the conversion of polysulfides,and improving the reaction kinetics.The main work is as follows.Hollow Co₉S₈dodecahedra（Co₉S₈@C-QQT）were prepared by hydrothermal method using thioacetamide（CH₃CSNH₂）as the sulfur source,and N-doped carbon-based metal sulfides（N-Co₉S₈@HPC）were prepared by low-temperature carbonization as the carrier of the cathode active material to assemble lithium-sulfur batteries.The experiments showed that the prepared N-Co₉S₈@HPC has an overall dodecahedral polygon shape with a rough surface and a hollow structure inside.The first-turn discharge capacity is as high as 1564.5 m Ah g^-1at 0.1 C,and the reversible capacity is 361.3 m Ah g^-1at a current density of 1.0 C for 500 times(only 192.6 m Ah g^-1using general carbon sulfur composite as the cathode),and the Coulomb efficiency is close to 100%,with excellent cycling performance even under high sulfur loading.By introducing a Ni²⁺source on the surface of ZIF-67,the hydrothermally derived flower-like Ni and Co bimetallic MOFs material BM was obtained and as a cathode active material carrier the carbon-based bimetallic oxide BM@C was prepared by carbonization.It is shown that the bimetallic catalyst using this composite accelerated the conversion of polysulfides and improved the electrochemical performance of the cell.The process conditions were optimized by comparative experiments,and the assembled lithium-sulfur battery has an initial discharge capacity of 1625.1 m Ah g^-1at 0.1 C,which is close to the theoretical capacity of lithium-sulfur batteries(1675 m Ah g^-1),and still provides a high reversible discharge capacity of 547.2 m Ah g^-1and stable long-cycle（500 turns at 1.0 C）performance even at 2.0 C.