Preparation And Electrochemical Performance Of Zn/Ni-MOF-derived Porous Carbon-based Composite Electrodes

With the rapid development of the global economy,the depletion of non-renewable resources and the increasingly serious environmental problems,the development of clean energy is the key to solving energy and environmental crises.Lithium-sulfur battery has become a promising energy storage technology for the next generation of new energy electric vehicles and consumer mobile electronic products due to its high theoretical specific capacity and high specific energy,abundant sulfur reserves and low price.However,lithium-sulfur batteries themselves have many problems such as:their sulfur itself does not conduct electricity,the dissolution of the intermediate product polysulfide produces a serious"shuttle effect",and the insulation of sulfur and discharge products(Li₂S₂/Li₂S)hinders electron transfer.The reaction kinetics of sulfur conversion is limited and its electrochemical performance is seriously hindered.Therefore,in order to solve the above-mentioned problems of lithium-sulfur batteries,researches based on MOF-derived porous carbon-based composite materials as lithium-sulfur battery electrodes have been carried out.The prepared core-shell structure material has shown excellent performance in lithium-sulfur battery research.The main work of the thesis is as follows:1?A core-shell nanocomposite with a carbon core derived from ZIF-8 and a carbon shell doped with graded Mn₃O₄/N as the main sulfur was prepared.It is used as a cathode material for lithium-sulfur batteries and exhibits good electrochemical performance.The adsorption experiment and XPS test show that Mn₃O₄can have a strong bond with the intermediate product polysulfide,thereby slowing down the shuttle effect and improving its cycle stability.The results show that the initial capacity of ZPC@Mn₃O₄-NPC/S composite material at 0.1 C discharge is 1236 mAh·g^-1,and the specific capacity at 8 C high rate discharge is 430 mAh·g^-1,and cycle 1000 The theoretical specific capacity after the second time is 301 mAh·g^-1at 5 C,and ZPC@HMn₃O₄/NC has good electrochemical performance as a sulfur carrier.2?Three-dimensional porous Ni₂P@NC composite materials were prepared by using a one-step calcination method to form a 3D conductive framework with Ni-MOF.It was applied to lithium-sulfur battery cathode materials,and the Ni₂P@NC composite material with the best temperature was determined through electrochemical performance characterization,and the strong adsorption effect of Ni₂P on lithium polysulfide was determined.The results show that,based on Ni₂P@NC-800/S cathode,it has excellent rate performance and good cycle stability(The discharge capacity of Ni₂P@NC-800/S is as high as 830 mAh·g^-1at the initial stage,and after 300 cycles After cycling,it remains at 522 mAh·g^-1,which is equivalent to a retention rate of 63%.3?Using CMK-3 as the conductive skeleton,the CMK-3@ZIF-8 composites with different concentrations of 3D network series structure were prepared by one-step hydrothermal method.As a conductive skeleton,CMK-3 can not only provide a fast conductive path for electrons,but also provide additional space for sulfur loading;ZIF-8-C can produce strong bonding with polysulfides,and thus greatly The suppression of the shuttle effect.It is used as a cathode material for lithium-sulfur batteries and exhibits good electrochemical performance.The results show that the specific capacity of CMK-3-6M@C-ZIF-8-10/S is as high as 1457.96 mAh·g^-1at a current density of 0.1C.At a high current density of 1C,The discharge capacity of CMK-3-6M@C-ZIF-8-10/S is as high as 707 mAh·g^-1at the initial stage,and remains at 400 mAh·g^-1after 350 cycles,which is equivalent to a retention rate of 56.6%.This provides a promising method for the design of sulfur host materials for lithium-sulfur batteries.