Preparation And Lithium Storage Properties Of MOFs Derived Polymetallic Chalcogenides@carbon Composites

Since Sony introduced the first commercial lithium-ion battery in the 1990s,lithium-ion batteries（Li Bs）have been widely accepted for their many advantages,and are now widely used in a variety of applications,including personal terminal powered vehicles and energy storage power stations.However,with the continuous increase of energy demand,the traditional LIBs system has been difficult to meet people’s actual needs.Therefore,the development and design of new electrode materials with higher energy density and longer service life have become the top priority of research.Among the new electrode materials,metallic chalcogenides have the advantages of a wide range of sources,low price and high theoretical capacity,but their inherent volume expansion problem affects the performance and safety of the battery,and limits their practical application.In order to overcome the above defects,we used metal-organic frameworks（MOFs）as the precursor to derive a series of metal-sulfur compounds@carbon composite electrodes with stable structure and good lithium storage performance.The main ideas and work are as follows:（1）Polymetallic chalcogenides have better electronic conductivity and more electrochemical reaction sites.Zn S/Co S-NCNTs were prepared as anode materials for lithium-ion batteries using Zn Co-ZIF as precursor,in which the Zn S/Co S heterojunction was uniformly embedded in the in-situ generated three-dimensional N-doped carbon nanotube framework.Zn S/Co S-NCNTs were prepared as anode materials for lithium-ion batteries using Zn Co-ZIF as precursor,in which the Zn S/Co S heterojunction was uniformly embedded in the in-situ generated three-dimensional N-doped carbon nanotube framework.As anode materials for lithium-ion batteries,the electrode maintains high specific capacities of 1007 and 803 m Ah g^-1after 1000 cycles at 1.0 A g^-1and 2000 cycles at 5.0 A g^-1,respectively.Even at a high current density of 13 A g^-1,a high specific capacity of 652 m Ah g^-1is maintained.（2）The morphology and structure have a great influence on the performance of electrode materials.New negative materials such as hollow core-shell or yolk core-shell structure have significant advantages such as high specific surface area and volume expansion resistance.Bimetallic Co-5-Zn-ZIF precursor with core-shell structure was prepared by using the difference of reaction kinetics between cobalt-based zeolite imidazole skeleton（Co-ZIF）and zinc-based zeolite imidazole skeleton（Zn-ZIF）.The yolk-shell polyhedron structure material Co-5-Zn-700 was synthesized by one-step selenization.The yolk and inner shell were formed by Co_0.85Se@NC nanoparticles,and the outer shell was formed by Co_0.85Se@NC and Zn Se@NC nanoparticles.At a current density of 5.0 A g^-1,the electrode exhibits a long cycle performance of more than 3000cycles without capacity fading.At the current densities of 0.1 and 5.0 A g^-1,the high reversible capacities of 1047 and 468 m Ah g^-1were demonstrated,respectively.